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The controlled switching of fluorophores between non-fluorescent and fluorescent states is central to every superresolution fluorescence microscopy (nanoscopy) technique, and the exploration of radically new switching mechanisms remains critical to boosting the performance of established, as well as emerging superresolution methods. Photoactivatable dyes offer significant improvements to many of these techniques, but often rely on photolabile protecting groups that limit their applications. Here we describe a general method to transform 3,6-diaminoxanthones into caging-group free photoactivatable fluorophores. These photoactivatable xanthones (PaX) assemble rapidly and cleanly into highly fluorescent, photo- and chemically stable pyronine dyes upon irradiation with light. The strategy is extendable to carbon- and silicon-bridged xanthone analogs, yielding a new family of photoactivatable labels spanning much of the visible spectrum. Our results demonstrate the versatility and utility of PaX dyes in fixed and live-cell fluorescence microscopy, and both coordinate-targeted stimulated emission depletion (STED) and coordinate-stochastic single-molecule localization superresolution microscopy (SMLM).

The introduction of MINFLUX nanoscopy allows single molecules to be localized with one nanometer precision in as little as one millisecond. However, current applications have so far focused on increasing this precision by optimizing photon collection, rather than minimizing the localization time. Concurrently, commonly used fluorescent switches are specifically designed for stochastic methods (e.g., STORM), optimized for a high photon yield and rather long on-times (tens of milliseconds). Here, accelerated MINFLUX nanoscopy with up to a 30-fold gain in localization speed is presented. The improvement is attained by designing spontaneously blinking fluorescent markers with remarkably fast on-times, down to 1–3 ms, matching the iterative localization process used in a MINFLUX microscope. This design utilizes a silicon rhodamine amide core, shifting the spirocyclization equilibrium toward an uncharged closed form at physiological conditions and imparting intact live cell permeability, modified with a fused (benzo)thiophene spirolactam fragment. The best candidate for MINFLUX microscopy (also suitable for STORM imaging) is selected through detailed characterization of the blinking behavior of single fluorophores, bound to different protein tags. Finally, optimization of the localization routines, customized to the fast blinking times, renders a significant speed improvement on a commercial MINFLUX microscope.

Asymmetric diarylethenes with benzo[b]thiophen-3-yl and 2-thienyl residues having variable oxidation degrees (S and/or SO2) remained unexplored. These photochromes provide reversibly photoswitchable absorbance and multicolor emission modulation. Here we report 18 photochromic 1,2-diarylperfluorocyclopentenes with oxidized and non-oxidized 2-methylbenzo[b]thiophen-3-yl, as well as 5-aryl-3-methylthiophen-2-yl groups. The structure–property relationships were studied for three groups of compounds: non-oxidized, mono-oxidized (to SO2 in the benzothiophene part), and fully-oxidized (to 2 × SO2). The quantum chemistry calculations helped to interpret the substituents’ effects in each group and predict the photophysical properties of yet unavailable photochromes. The photochromic systems with absorbance modulation introduced in this work were designed for the use in diffraction-unlimited writing and reading with light, nanopattering and optical lithography.

Fluorescein and its analogues have found only limited use in biological imaging because of the poor photostability and cell membrane impermeability of their O-unprotected forms. Herein, we report rationally designed N-cyanorhodamines as orange- to red-emitting, photostable and cell-permeant fluorescent labels negatively charged at physiological pH values and thus devoid of off-targeting artifacts often observed for cationic fluorophores. In combination with well-established fluorescent labels, self-labelling protein (HaloTag, SNAP-tag) ligands derived from N-cyanorhodamines permit up to four-colour confocal and super-resolution STED imaging in living cells.

We designed caging-group-free photoactivatable live-cell permeant dyes with red fluorescence emission and ∼100 nm Stokes shifts based on a 1-vinyl-10-silaxanthone imine core structure. The proposed fluorophores undergo byproduct-free one- and two-photon activation, are suitable for multicolor fluorescence microscopy in fixed and living cells and are compatible with super-resolution techniques such as STED (stimulated emission depletion) and PALM (photoactivated localization microscopy). Use of photoactivatable labels for strain-promoted azide-alkyne cycloaddition and self-labeling protein tags (HaloTag, SNAP-tag), and duplexing of imaging channel with another large Stokes shift dye have been demonstrated.

Searching for photoconvertible or photoactivatable dyes, we considered trimethine (Cy3) and pentamethine (Cy5) fluorophores with a 4-amino-1-diazo-2-butanone fragment (H2N(CH2)2COCH=N2) attached to the meso (γ) position of the polymethine chain via the amino group. The Cy3 derivative was prepared. All Cy5 derivatives with the basic amino group at this position decomposed with breaking the polymethine chain. However, amino-squaraine based Cy5 dyes were found to be stable and accessible. Photolysis of Cy3 and squaraine-based Cy5 dyes with a 4-amino-1-diazo-2-butanone fragment was accompanied with Wolff rearrangement and led to pyrrolidones (in methanol and aprotic solvents) formed via intramolecular cyclization of the intermediate ketenes. In aqueous acetonitrile, ketenes reacted with water and gave carboxylic acids. Both products were non-fluorescent, though the model Cy5 dyes (without the squaraine fragment) with acylated amino and N-methylamino groups were found to be fluorescent.

A bright and photostable fluorescent dye with a disulfide (S S) linker and maleimide group (Rho594-S2-mal), as cleavable and reactive sites, was synthesized and conjugated with anti-GFP nanobodies (NB). The binding of EGFP (FRET donor) with anti- GFP NB labeled with one or two Rho594-S2-mal residues was studied in vitro and in cellulo. The linker was cleaved with dithiothreitol recovering the donor (FP) signal. The bioconju- gates (FP-NB-dye) were applied in FRET-FLIM assays, confocal imaging, and superresolution STED microscopy.

Spontaneously blinking fluorophores, a class of molecules switching rapidly between a dark and a brightly emitting state, have emerged as a popular core to build fluorescent markers for super-resolution microscopy. With typical on-times in the order of tens of milliseconds, they are most suitable for STORM and related nanoscopy methods. Recent MINFLUX nanoscopy, however, can localize molecules even within a millisecond and achieve an up to ten times higher localization precision. Here, we present a series of spontaneous blinkers with short on-times (1-3 ms) matching MINFLUX recording time-scales. Our design builds upon a silicon rhodamine fluorescent core with a modified thiophene- or a benzothiophene-fused spirolactam fragment, which shifts the spirocyclization equilibrium toward the dark closed form at physiological conditions, imparting cell permeability. Concurrently, we obtain a highly photostable, short-lived open form with bright red emission. Characterizing the blinking behavior of single fluorophores bound to three different protein tags (antibodies, nanobodies, and HaloTag self-labeling enzyme) allowed us to select the best candidate for MINFLUX microscopy. The short on-times speed up MINFLUX localization by up to 30-fold.

Reversibly switchable fluorescent proteins (RSFPs) can be repeatedly transferred between a fluorescent on- and a nonfluorescent off-state by illumination with light of different wavelengths. Negative switching RSFPs are switched from the on- to the off-state with the same wavelength that also excites fluorescence. Positive switching RSFPs have a reversed light response, where the fluorescence excitation wavelength induces the transition from the off- to the on-state. Reversible saturable optical linear (fluorescence) transitions (RESOLFT) nanoscopy utilizes these switching states to achieve diffraction-unlimited resolution but so far has primarily relied on negative switching RSFPs by using time sequential switching schemes. On the basis of the green fluorescent RSFP Padron, we engineered the positive switching RSFP Padron2. Compared to its predecessor, it can undergo 50-fold more switching cycles while displaying a contrast ratio between the on- and the off-states of more than 100:1. Because of its robust switching behavior, Padron2 supports a RESOLFT imaging scheme that entirely refrains from sequential switching as it only requires beam scanning of two spatially overlaid light distributions. Using Padron2, we demonstrate live-cell RESOLFT nanoscopy without sequential illumination steps.

The use of photoactivatable dyes in STED microscopy has so far been limited by two‐photon activation through the STED beam and by the fact that photoactivatable dyes are poorly solvable in water. Herein, we report ONB‐2SiR, a fluorophore that can be both photoactivated in the UV and specifically de‐excited by STED at 775 nm. Likewise, we introduce a conjugation and purification protocol to effectively label primary and secondary antibodies with moderately water‐soluble dyes. Greatly reducing dye aggregation, our technique provides a defined and tunable degree of labeling, and improves the imaging performance of dye conjugates in general., ONB‐2SIR, a photoactivatable dye resistant against two‐photon uncaging by 775 nm STED light is synthesized and used to perform STED microscopy before and after photoactivation without undesired activation by the STED light. The effects of the low water‐solubility of ONB‐2SIR on antibody conjugation was overcome by glycan labelling with defined degree of labelling (DOL) and a phase separation purification method.

Two fluorophores bound with a short photoreactive bridge are fascinating structures and remained unexplored. To investigate the synthesis and photolysis of such dyes, we linked two rhodamine dyes via a diazoketone bridge (−COCN2−) attached to position 5′ or 6′ of the pendant phenyl rings. For that, the mixture of 5′- or 6′-bromo derivatives of the parent dye was prepared, transformed into 1,2-diarylacetylenes, hydrated to 1,2-diarylethanones, and converted to diazoketones Ar1COCN2Ar2. The high performance liquid chromatography (HPLC) separation gave four individual regioisomers of Ar1COCN2Ar2. Photolysis of the model compound─C6H5COCN2C6H5─in aqueous acetonitrile at pH 7.3 and under irradiation with 365 nm light provided diphenylacetic acid amide (Wolff rearrangement). However, under the same conditions, Ar1COCN2Ar2 gave mainly α-diketones Ar1COCOAr2. The migration ability of the very bulky dye residues was low, and the Wolff rearrangement did not occur. We observed only moderate fluorescence increase, which may be explained by the insufficient quenching ability of diazoketone bridge (−COCN2−) and its transformation into another (weaker) quencher, 1,2-diarylethane-1,2-dione.

Photoswitchable fluorophores─proteins and synthetic dyes─whose emission is reversibly switched on and off upon illumination, are powerful probes for bioimaging, protein tracking, and super-resolution microscopy. Compared to proteins, synthetic dyes are smaller and brighter, but their photostability and the number of achievable switching cycles in aqueous solutions are lower. Inspired by the robust photoswitching system of natural proteins, we designed a supramolecular system based on a fluorescent diarylethene (DAE) and cucurbit[7]uril (CB7) (denoted as DAE@CB7). In this assembly, the photoswitchable DAE molecule is encapsulated by CB7 according to the host–guest principle, so that DAE is protected from the environment and its fluorescence brightness and fatigue resistance in pure water improved. The fluorescence quantum yield (Φfl) increased from 0.40 to 0.63 upon CB7 complexation. The photoswitching of the DAE@CB7 complex, upon alternating UV and visible light irradiations, can be repeated 2560 times in aqueous solution before half-bleaching occurs (comparable to fatigue resistance of the reversibly photoswitchable proteins), while free DAE can be switched on and off only 80 times. By incorporation of reactive groups [maleimide and N-hydroxysuccinimidyl (NHS) ester], we prepared bioconjugates of DAE@CB7 with antibodies and demonstrated both specific labeling of intracellular proteins in cells and the reversible on/off switching of the probes in cellular environments under irradiations with 355 nm/485 nm light. The bright emission and robust photoswitching of DAE-Male3@CB7 and DAE-NHS@CB7 complexes (without exclusion of air oxygen and addition of any stabilizing/antifading reagents) enabled confocal and super-resolution RESOLFT (reversible saturable optical fluorescence transitions) imaging with apparent 70–90 nm optical resolution.

The controlled switching of fluorophores between non-fluorescent and fluorescent states is central to every superresolution fluorescence microscopy (nanoscopy) technique, and the exploration of radically new switching mechanisms remains critical to boosting the performance of established, as well as emerging superresolution methods. Photoactivatable dyes offer significant improvements to many of these techniques, but often rely on photolabile protecting groups that limit their applications. Here we describe a general method to transform 3,6-diaminoxanthones into caging-group free photoactivatable fluorophores. These photoactivatable xanthones (PaX) assemble rapidly and cleanly into highly fluorescent, photo- and chemically stable pyronine dyes upon irradiation with light. The strategy is extendable to carbon- and silicon-bridged xanthone analogs, yielding a new family of photoactivatable labels spanning much of the visible spectrum. Our results demonstrate the versatility and utility of PaX dyes in fixed and live-cell fluorescence microscopy, and both coordinate-targeted stimulated emission depletion (STED) and coordinate-stochastic single-molecule localization superresolution microscopy (SMLM).

We prepared water soluble, biocompatible fluorescent turn-on pH nanosensors and characterized their behavior as a function of changes in pH. The response relies on a halochromic reaction of a spirorhodamineamide derived from the bright and highly chemically and photo-stable rhodamine 6G, encapsulated in core/nanoporous shell silica nanoparticles. The fluorescent sensors displayed a fast response in the pH range of intracellular compartments. The encapsulation conferred solubility in aqueous environments and biocompatibility. We assessed the two main properties of the sensor, namely the useful pH range and the kinetics of the response, and compared them to those of the free probe. We found that such properties are strongly dependent on the functionalization and position in the silica matrix relative to the core/shell structure. Finally, we demonstrated the cellular uptake of the nanosensors, and their localization in lysosomes of living cells, by fluorescence confocal microscopy. Fil: Di Paolo, Matias Andres. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Roberti, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bordoni, Andrea Veronica. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Constituyentes | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Constituyentes.; Argentina Fil: Aramendia, Pedro Francisco. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; Argentina Fil: Wolosiuk, Alejandro. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Constituyentes | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Constituyentes.; Argentina Fil: Bossi, Mariano Luis. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

Spectral stability of small-molecule fluorescent probes is required for correct interpretation and reproducibility of multicolor fluorescence imaging data, in particular under high (de)excitation light intensities of super-resolution imaging or in single-molecule applications. We propose a synthetic approach to a series of spectrally stable rhodamine fluorophores based on sequential Ru- and Cu-catalyzed transformations, evaluate their stability against photobleaching and photoconversion in the context of other fluorophores using chemometric analysis, and demonstrate chemical reactivity of fluorophore photoproducts. The substitution patterns providing the photoconversion-resistant triarylmethane fluorophores have been identified, and the applicability of nonbluing labels in live-cell STED nanoscopy is demonstrated.

Significance In superresolution fluorescence microscopy, employing synthetic dyes that can be reversibly photoswitched between a nonfluorescent (“dark”) and a fluorescent (“bright”) state has been an attractive alternative to using photoswitchable fluorescent proteins. However, employing such synthetic dyes has been elusive because they have defied reliable attachment to proteins and required UV light for photoswitching. Here we prepared “turn-on mode” fluorescent diarylethenes (fDAEs) that are switchable with visible rather than UV light and blink between a bright fluorescent and a dark state in aqueous buffers. Moreover, our thienyl-substituted fDAEs effectively labeled two thiol groups on nanobodies bearing a single maleimide tag. With these small-sized probes, we acquired superresolution images of vimentin filaments in cells by applying just yellow (561 nm) light., The use of photoswitchable fluorescent diarylethenes (fDAEs) as protein labels in fluorescence microscopy and nanoscopy has been limited by labeling inhomogeneity and the need for ultraviolet light for fluorescence activation (on-switching). To overcome these drawbacks, we prepared “turn-on mode” fDAEs featuring thienyl substituents, multiple polar residues, and a reactive maleimide group in the core structure. Conjugates with antibodies and nanobodies displayed complete on-switching and excitation with violet (405 nm) and yellow-green (

Compact “push–pull” photochromic diaryethenes (DAEs) with unsymmetric oxidation pattern of the benzothiophene core display multicolour fluorescence switching, as a result of dual emission from both “open” and “closed” forms. These DAEs also present an unprecedented photo-fatigue resistance.

A modular assembly of water-soluble diarylethenes (DAEs), applicable as biomarkers for optical nanoscopy, is reported. Reversibly photoswitchable 1,2-bis(2-alkyl-6-phenyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentenes possessing a fluorescent "closed" form were decorated with one or two methoxy group(s) attached to the para-position(s) of phenyl ring(s) and two, four, or eight carboxylic acid groups. Antibody conjugates of these DAEs feature low aggregation, efficient photoswitching in aqueous buffers, specific staining of cellular structures, and photophysical properties (high emission efficiencies and low cycloreversion quantum yields) enabling their application in superresolution microscopy. Images of tubulin, vimentin, and nuclear pore complexes are presented. The superresolution images can also be acquired by using solely 488 nm light without additional photoactivation with UV light. These DAEs exhibit reversible photoswitching without requiring any additives to the imaging media and open new paths toward the modular design of fluorescent dyes for bioimaging with optical superresolution.

Electronic energy transfer (EET) between chromophores is of fundamental importance for many biological processes and optoelectronic devices. However, common models fall short in fully describing the process, especially in bichromophoric model systems with a donor and acceptor connected by a rigid linker providing perpendicular geometries. Herein, we report a novel strategy for preparing bichromophores containing adamantane or 2-(2-adamantylidene)adamantane as rigid spacers, providing a fixed distance between chromophores, and their parallel or perpendicular arrangement without chromophore rotation. New fluorophores were developed and linked via spiroatoms. Bichromophores with identical (blue-blue) or different (blue-red) chromophores were synthesized, either in orthogonal or parallel geometry. These were characterized by absorption/fluorescence spectroscopy, time-resolved fluorescence anisotropy, and fluorescence antibunching measurements. Based on the Förster point-dipole approximation, EET efficiencies were estimated by using geometrical parameters from (time-dependent) density functional calculations. For bichromophores with parallel geometry, the predicted EET efficiencies were near unity and fit the measurements. In spite of estimated values around 0.4 and 0.5, 100 % efficiency was observed also for bichromophores with orthogonal geometry. The new rigid scaffolds presented here open new possibilities for the synthesis of bichormophores with well-defined parallel or perpendicular geometry.

We present a new series of photochromic 1,2-bis(2-ethylbenzo[b]thiophen-3-yl)perfluorocyclopentenes with an oxidized benzothiophene core (O) or a nonoxidized one, decorated with mono- (Th1) and bithiophene (Th2) units attached to positions 6 and 6′ (Sy = symmetric) or only to position 6 (As = asymmetric). “Oxidized” compounds have highly fluorescent closed forms emitting in the visible region (yellow to red). The dyes with nonoxidized benzothiophenes possess fluorescent open forms with rather low emission efficiency. The photoswitching kinetics was studied at several wavelengths with UV and visible light. New diarylethenes underwent ring-closure reactions by irradiation with UV light (365 nm, 405 nm), and the reversible ring-opening by irradiation with visible light (470 nm, 530 nm). The on-switching of fluorescence due to the ring-closure reaction was observed also with visible light of 470 nm (to an extent of 10% for compound SyOTh1) and attributed to the Urbach tail effect. Due to a high degree of fluorescence modulation (>270), good fatigue resistance and large fluorescence quantum yield, compound SyOTh1 emerged as a candidate for single-molecule based super-resolution fluorescence microscopy.

Low photostability in aqueous solutions is the main drawback of synthetic photochromic dyes, which limits their switching performance and utility in biology, medicine, and life sciences. Even the most promising photochromes—reversibly photoswitchable diarylethenes (DAEs) with fluorescent “closed” forms—are known to undergo only several tens (typically 20–30) of switching cycles in aqueous solutions. In this work, we introduce water-soluble and highly photostable 1,2-[bis(2-ethyl/2-isobutyl-1-benzothiophene-1,1-dioxide-6-phenyl-3-yl)]perfluorocyclopentenes decorated with four −CONHC(CH2R)3 residues capped with 12 carboxylic acid groups (R = CH2CO2H, O(CH2)2CO2H). Under irradiation with UV (365 nm) and visible light (470 nm), they provide several hundred (for the “rapid” DAEs with isobutyl groups, up to 1000) full switching cycles in aqueous solutions without exclusion of air oxygen (outperforming the photoswitchable and fluorescent protein Dreiklang). The new branching approach based on secondary carboxamides with N-tert-alkyl residues decorated with polar groups may serve as a blueprint for the design of highly fatigue resistant and reversibly photoswitchable fluorescent probes applicable in life sciences as aqueous solutions.

Reversibly photoswitchable 1,2‐bis(2‐ethyl‐6‐phenyl‐1‐benzothiophene‐1,1‐dioxide‐3‐yl)perfluorocyclopentenes (EBT) having fluorescent “closed” forms were decorated with four or eight carboxylic groups and attached to antibodies. Low aggregation, efficient photoswitching in aqueous buffers, specific staining of cellular structures, and good photophysical properties were demonstrated. Alternating light pulses of UV and blue light induce numerous reversible photochemical transformations between two stables states with distinct structures. Using relatively low light intensities, EBTs were applied in biology‐related super‐resolution microscopy based on the reversible saturable (switchable) optical linear fluorescence transitions (RESOLFT) and demonstrated optical resolution of 75 nm.

We report synthesis and photophysical studies of spirorhodamines (SRA) with amide N-aliphatic substituents, including measurements of single-crystal X-ray structures, fluorescence emission, and quantum mechanical calculations. Variations in the equilibrium position between closed and open states, a transition that is catalysed under acidic conditions, of several SRAs sharing the same central chromophore (Rhodamine 6G) were measured. For the different substituents in the lactam position, the pH-dependent lactam ring opening reaction displays a strong correlation with the volume of the functional group. The open form shows similar absorption and emission spectrum, fluorescence efficiency and emission lifetime, regardless of the nature of the substituents. The molecular volume of the substituent is a simple and straightforward molecular design feature to control the equilibrium between the dark and bright states of the probe, without any further changes in the emission properties of the fluorescent form. These results allow rational design of pH-sensitive aliphatic SRAs fluorescent probes. Fil: Di Paolo, Matias Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Boubeta, Fernando Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Alday, Julieta Ruth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Michel Torino, Mateo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Aramendia, Pedro Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; Argentina Fil: Suarez, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

Spectral stability of small-molecule fluorescent probes is required for correct interpretation and reproducibility of multicolor fluorescence imaging data, in particular under high (de)excitation light intensities of super-resolution imaging or in single-molecule applications. We propose a synthetic approach to a series of spectrally stable rhodamine fluorophores based on sequential Ru- and Cu-catalyzed transformations, evaluate their stability against photobleaching and photoconversion in the context of other fluorophores using chemometric analysis, and demonstrate chemical reactivity of fluorophore photoproducts. The substitution patterns providing the photoconversion-resistant triarylmethane fluorophores have been identified, and the applicability of nonbluing labels in live-cell STED nanoscopy is demonstrated.

Photoactivatable rhodamine spiroamides and spirocyclic diazoketones emerged recently as synthetic markers applicable in multicolor super-resolution microscopy. However, their applicability in single molecule localization microscopy (SMLM) is often limited by aggregation, unspecific adhesion, and low reactivity caused by insufficient solubility and precipitation from aqueous solutions. We report here two synthetic modifications increasing the polarity of compact polycyclic and hydrophobic labels decorated with a reactive group: attachment of 3-sulfo-l-alanyl-beta-alanine dipeptide (a "universal hydrophilizer") or allylic hydroxylation in photosensitive rhodamine diazoketones (and spiroamides). The super-resolution images of tubulin and keratin filaments in fixed and living cells exemplify the performance of "blinking" spiroamides derived from N, N, N', N'-tetramethyl rhodamine.

Sequential adsorption of PdCl42- within weak polyelectrolyte layer-by-layer (LbL) self-assembled multilayer films with further electrochemical reduction to yield Pd0 nanoparticles (Pd-NPs) has been demonstrated. The electrocatalytic hydrogenation (ECH) of model molecules such as acetophenone and benzophenone on Pd-NPs of different sizes (6 to 35 nm) and bulk Pd crystal surface in hydroalcoholic acid solution has been investigated. Distribution of reaction products (secondary alcohols and alkanes) and faradaic yield was systematically investigated. While the polyelectrolyte multilayers act as nanoreactors by confining PdCl42- ions and preventing the formation of large crystals, their presence also alters the hydrogenation reaction and therefore heat treated surfaces showed only the effect of nanocrystal size on the reaction selectivity and faradaic yield. This journal is Fil: Villalba, Matias Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Calvo, Ernesto Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as “hidden” markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2-diazo-1-indanone group can be irreversibly photoactivated, either by irradiation with UV- or violet light (one-photon process), or by exposure to intense red light (λ∼750 nm; two-photon mode). All dyes possess a very small 2-diazoketone caging group incorporated into the 2-diazo-1-indanone residue with a quaternary carbon atom (C-3) and a spiro-9H-xanthene fragment. Initially they are non-colored (pale yellow), non-fluorescent, and absorb at λ=330–350 nm (molar extinction coefficient (ε)≈104 M−1 cm−1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range (λ=511–633 and 525–653 nm, respectively). The unmasked dyes are highly colored and fluorescent (ε= 3–8×104 M−1 cm−1 and fluorescence quantum yields (ϕ)=40–85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water-soluble caged red-emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino-reactive N-hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375–420 nm light or intense red light (λ=775 nm). Protein conjugates with optimal degrees of labeling (3–6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions (ϕ=20–38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10–40 % of the non-fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a “dark” non-emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super-resolution optical microscopy is exemplified. Fil: Belov, Vladimir N.. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Mitronova, Gyuzel Yu.. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Boyarskiy, Vadim P.. St. Petersburg State University; Rusia Fil: Hebisch, Elke. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Geisler, Claudia. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Kolmakov, Kirill. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Wurm, Christian A.. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Willig, Katrin I.. Max Planck Institute for Biophysical Chemistry ; Alemania Fil: Hell, Stefan W.. Max Planck Institute for Biophysical Chemistry ; Alemania

Reversibel photoschaltbares 1,2-Bis(2-ethyl-6-phenyl-1-benzothiophen-1,1-dioxid-3-yl)perfluorcyclopenten (EBT) mit fluoreszierender “geschlossener” Form wurde mit vier oder acht Carboxygruppen versehen und an Antikorper gebunden. Die carboxylierten Derivate wiesen geringe Aggregation, effizientes Photoschalten in wassrigen Puffern, gezieltes Farben von zellularen Strukturen und gute photophysikalische Eigenschaften auf. Abwechselnde Bestrahlung mit UV und blauem Licht relativ geringer Intensitat fuhrte zu reversibler photochemischer Isomerisierung zwischen zwei stabilen Strukturen uber mehrere dutzend Schaltzyklen. Dies ermoglichte die Verwendung der Farbstoffe fur hochauflosende RESOLFT-Mikroskopie (“reversible switchable optical linear fluorescence transitions”). Hierbei konnte eine optische Auflosung von 75 nm an zellularen Tubulin-Filamenten erzielt werden.

The spatial resolution of fluorescence microscopes is limited by diffraction to about half of the light wavelength, hampering the observation of many important intracellular processes. Recent emerging techniques have overcome that diffraction barrier using the temporal discrimination of close objects that are otherwise unresolved or blurred within the spatial resolution of the microscope. The key of these techniques is to switch the signal of fluorescence markers on and off exploiting their distinct molecular states, and detect and localize these markers at the single-molecule level. This underlying principle highlights the critical role of the photophysical properties of the probes, and the importance of finding adequate switching mechanisms. Here, we present strategies to achieve fluorescence modulation based on novel molecular assemblies containing a [1,3]oxazine as the two states, building block responsible for the transformation. Two different triggering events, based on the photochromic and halochromic properties of the oxazine, induce a large absorption and emission bathochromic shift of a pendant fluorophore, as the ultimate fluorescence switching event. The implementation of these approaches to achieve spatial resolution beyond the diffraction limit is also discussed.

Nanoparticle-based temperature imaging is an emerging field of advanced applications. Herein, the sensitivity of the phosphorescence of tris(bipyridine)ruthenium(II)-doped silica nanoparticles towards temperature is studied. 130 nm size particles were prepared by a modification of Stöber’s method, that allows the incorporation of Ru[(bpy)3]2+ into the outer particle shell. The entrapped Ru[(bpy)3]2+ retains its photophysical properties, yet the emission of the particles is not affected by the presence of O2, neither by anionic quenchers; quenching by MV2+, on the other hand, is strongly dependent on pH. Between 20 and 60 °C, the steady-state emission of the particles decreases linearly with increasing temperature. The slope of the straight line diminishes slightly on thermal cycling, but soon stabilizes. Fluorescence measurements by scanning confocal microscopy indicate that the silica nanoparticles doped with Ru[(bpy)3]2+ can indeed be employed to probe thermal processes in micro-environments. Fil: Mirenda, Martin. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Levi, Valeria. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bossi, Mariano Luis. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bruno, Luciana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bordoni, Andrea Veronica. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Regazzoni, Alberto Ernesto. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Wolosiuk, Alejandro. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The synthesis, characterization, structural analysis and fluorescence properties of two rhodamine 6G derivatives are described, namely a propargylamine derivative, 3′,6′-bis(ethylamino)-2′,7′-dimethyl-2-(methylcyanide)spiro[isoindole-1,9′-xanthen]-3(2H)-one (I), and a γ-aminobutyric acid (GABA) derivative, 3′,6′-bis(ethylamino)-2′,7′-dimethyl-3-oxospiro[isoindole-1,9′-xanthen]-2(3H)-yl)butyricacid (II). Both structures are compared with four similar ones from the Cambridge Structural Database (CSD), and the interactions involved in the stabilization are analyzed using the atoms in molecules (AIM) theory. Finally, a single-crystal in-situ reaction study is presented, carried out by fluorescence methods, which enabled the 'opening' of the spirolactam ring in the solid phase. Fil: Di Paolo, Matias Andres. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Baggio, Ricardo Fortunato. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Suarez, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina

During the last decade far-field fluorescence microscopy methodshave evolved that have resolution far below the wavelength oflight. To outperform the limiting role of diffraction, all thesemethods, in one way or another, switch the ability of a moleculeto emit fluorescence. Here we present a novel rhodamine amidethat can be photoswitched from a nonfluorescent to a fluorescentstate by absorption of one or two photons from a continuous-wave laser beam. This bright marker enables strict control of on/off switching and provides single-molecule localization precisiondown to 15 nm in the focal plane. Two-photon induced nonlinearphotoswitching of this marker with continuous-wave illuminationoffers optical sectioning with simple laser equipment.Future synthesis of similar compounds holds great promise forcost-effective fluorescence nanoscopy with noninvasive optical sectioning. Fil: Fölling, Jonas. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Belov, Vladimir. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Riedel, Jennifer Denise. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Schönle, Andreas. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Egner, Alexander. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Eggeling, Christian. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Hell, Stefan W.. Max Planck Institute for Biophysical Chemistry; Alemania

We introduce far-field fluorescence nanoscopy with ordinaryfluorophores based on switching the majority of them to ametastable dark state, such as the triplet, and calculating theposition of those left or those that spontaneously returned to theground state. Continuous widefield illumination by a single laserand a continuously operating camera yielded dual-color imagesof rhodamine- and fluorescent protein–labeled (living) samples,proving a simple yet powerful super-resolution approach. Fil: Fölling, Jonas. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Bock, Hannes. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Medda, Rebecca. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Wurm, Christian A. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Hein, Birka. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Jakobs, Stefan. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Eggeling, Christian. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Hell, Stefan W. Max Planck Institute for Biophysical Chemistry; Alemania

Palladium nanoparticles (Pd NPs) were formed by electrochemical reduction of Pd(NH3)43+ ions entrapped by ion exchange in poly(acrylic acid) (PAA) multilayer films grown by the Sharpless "click reaction." The alkyne (PAAalk) and azide (PAAaz) groups were covalently bound to the PAA, and the catalyzed buildup of the multilayer film was performed by electrochemical reduction of Cu2+ to Cu+. The size of the Pd NPs formed in Au/(PAAalk)3(PAAaz)2 multilayer films by the click reaction, that is, 50 nm, is larger than that of similar Pd NPs formed in electrostatically bound Au/(PAA)3(PAH)2 nanoreactors, that is, 6-9 nm, under similar conditions. A combination of electrochemical methods and electrochemical quartz crystal microbalance, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), ellipsometry, and scanning electron microscopy has been used to follow these processes. Cyclic voltammetry of the resulting Pd NPs in a 0.1 M H2SO4 solution at 0.1 V·s-1 shows the PdO reduction peak at the same potential as that on the clean Pd surface unlike the NPs formed in electrostatically self-assembled Au/(PAA)3(PAH)2 nanoreactors with a 0.2 V shift in the cathodic direction most probably because of the strong adsorption of amino groups on the Pd NP surfaces. Fil: Villalba, Matias Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: del Pozo, Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Calvo, Ernesto Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

A coumarin fluorophore and an oxazine photochrome can be integrated within the same molecular skeleton and connected covalently to a secondary antibody. Illumination of the antibody-dyad conjugate at an appropriate activation wavelength opens the oxazine ring reversibly and shifts bathochromically the ground-state absorption of the coumarin component. Selective excitation of the photochemical product then produces significant fluorescence and allows the detection of activated bioconjugates at the single-molecule level. Such fluorescence activation events can be exploited to resolve temporally individual emitters and reconstruct images of immunolabeled cells with subdiffraction resolution. Relying on a similar conjugation protocol, a model compound, incorporating the same chromophore of the photochemical product, can also be connected covalently to a secondary antibody. Stimulated emission can be exploited to deplete the excited state of the bioconjugated chromophores and switch their fluorescence off. These operating principles for fluorescence switching also permit the imaging of immunolabeled cells with subdiffraction resolution. Thus, these photoswitchable molecules, in combination with the labeling ability of antibodies, can evolve into valuable probes for bioimaging with superresolution. Fil: Cusido, Janet. University of Miami; Estados Unidos Fil: Ragab, Sherif Shaban. University of Miami; Estados Unidos. National Research Centre; Estados Unidos Fil: Thapaliya, Ek Raj. University of Miami; Estados Unidos Fil: Swaminathan, Subramani. University of Miami; Estados Unidos Fil: Garcia-Amorós, Jaume. University of Miami; Estados Unidos Fil: Roberti, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Araoz, Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Mazza, Mercedes M. A.. University of Miami; Estados Unidos Fil: Yamazaki, Shiori. University of Miami; Estados Unidos Fil: Scott, Amy M.. University of Miami; Estados Unidos Fil: Raymo, Françisco M.. University of Miami; Estados Unidos Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

Trypanosoma cruzi, the flagellate protozoan agent of Chagas disease or American trypanosomiasis, is unable to synthesize sialic acids de novo. Mucins and trans-sialidase (TS) are substrate and enzyme, respectively, of the glycobiological system that scavenges sialic acid from the host in a crucial interplay for T. cruzi life cycle. The acquisition of the sialyl residue allows the parasite to avoid lysis by serum factors and to interact with the host cell. A major drawback to studying the sialylation kinetics and turnover of the trypomastigote glycoconjugates is the difficulty to identify and follow the recently acquired sialyl residues. To tackle this issue, we followed an unnatural sugar approach as bioorthogonal chemical reporters, where the use of azidosialyl residues allowed identifying the acquired sugar. Advanced microscopy techniques, together with biochemical methods, were used to study the trypomastigote membrane from its glycobiological perspective. Main sialyl acceptors were identified as mucins by biochemical procedures and protein markers. Together with determining their shedding and turnover rates, we also report that several membrane proteins, including TS and its substrates, both glycosylphosphatidylinositol-anchored proteins, are separately distributed on parasite surface and contained in different and highly stable membrane microdomains. Notably, labeling for α(1,3)Galactosyl residues only partially colocalize with sialylated mucins, indicating that two species of glycosylated mucins do exist, which are segregated at the parasite surface. Moreover, sialylated mucins were included in lipid-raft-domains, whereas TS molecules are not. The location of the surface-anchored TS resulted too far off as to be capable to sialylate mucins, a role played by the shed TS instead. Phosphatidylinositol-phospholipase-C activity is actually not present in trypomastigotes. Therefore, shedding of TS occurs via microvesicles instead of as a fully soluble form., Author Summary Trypanosoma cruzi is a flagellated protozoan parasite whose life cycle includes stages alternating between insect and mammal hosts. The membrane of the infective trypomastigote is equipped to allow survival in blood and to invade cells where it proliferates. Here we provide a novel description of the localization in separate microdomains of the trans-sialidase and mucins, enzyme and substrate, respectively, that play the main role in the crucial scavenging of sialic acids from the host, which allows parasite survival and infection. Even though these proteins, key in the parasite biology, share similar anchoring to the membrane, their puzzling segregation evidences the complexity of the trypanosome virulence mechanisms and protein trafficking. Instead of as soluble proteins, they are shed in microvesicles, a finding relevant to their known role in the pathogenesis of T. cruzi infection. This work provides an integrated view that explores these phenomena at the nanoscale and allows to build a model for the trypomastigote membrane physiology.

Large Stokes-shift coumarin dyes with an O-phosphorylated 4-(hydroxymethyl)-2,2-dimethyl-1,2,3,4-tetrahydroquinoline fragment emitting in the blue, green, and red regions of the visible spectrum were synthesized. For this purpose, N-substituted and O-protected 1,2-dihydro-7-hydroxy-2,2,4-trimethylquinoline was oxidized with SeO2 to the corresponding α,β-unsaturated aldehyde and then reduced with NaBH4 in a "one-pot" fashion to yield N-substituted and 7-O-protected 4-(hydroxymethyl)-7-hydroxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoline as a common precursor to all the coumarin dyes reported here. The photophysical properties of the new dyes ("reduced coumarins") and 1,2-dihydroquinoline analogues (formal precursors) with a trisubstituted C=C bond were compared. The "reduced coumarins" were found to be more photoresistant and brighter than their 1,2-dihydroquinoline counterparts. Free carboxylate analogues, as well as their antibody conjugates (obtained from N-hydroxysuccinimidyl esters) were also prepared. All studied conjugates with secondary antibodies afforded high specificity and were suitable for fluorescence microscopy. The red-emitting coumarin dye bearing a betaine fragment at the C-3-position showed excellent performance in stimulation emission depletion (STED) microscopy.

We designed a strategy to activate fluorescence under the influence of optical stimulations based on the intermolecular transfer of protons. Specifically, the illumination of a 2-nitrobenzyl derivative at an activating wavelength is accompanied by the release of hydrogen bromide. In turn, the photogenerated acid encourages the opening of an oxazine ring embedded within a halochromic compound. This structural transformation extends the conjugation of an adjacent coumarin fluorophore and enables its absorption at an appropriate excitation wavelength. Indeed, this bimolecular system offers the opportunity to activate fluorescence in liquid solutions, within rigid matrixes and inside micellar assemblies, relying on the interplay of activating and exciting beams. Furthermore, this strategy permits the permanent imprinting of fluorescent patterns on polymer films, the monitoring of proton diffusion within such materials in real time on a millisecond time scale, and the acquisition of images with spatial resolution at the nanometer level. Thus, our operating principles for fluorescence activation can eventually lead to the development of valuable photoswitchable probes for imaging applications and versatile mechanisms for the investigation of proton transport. © 2012 American Chemical Society. Fil: Swaminathan, Subramani. University of Miami; Estados Unidos Fil: Petriella, Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Deniz, Erhan. University of Miami; Estados Unidos Fil: Cusido, Janet. University of Miami; Estados Unidos Fil: Baker, James D.. University of Miami; Estados Unidos Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Raymo, Françisco M.. University of Miami; Estados Unidos

We investigate the equilibrium, kinetics, and mechanism of the photochromic transformation of a series of amido spirorhodamine compounds-differing in the nature of the substituents of the amido group and in the rhodamine chromophore-in ethanol at room temperature in the presence of trifluoroacetic acid. A proton participates in the equilibrium between the spiro form and the open rhodamine form. The relaxation times in the dark or under continuous irradiation show a linear dependence on the proton concentration. The slopes of these plots show a linear free energy relation with the equilibrium constant of the transformation. A mechanism involving reversible reaction steps between four states: the two thermodynamically stable isomers, a protonated spiro form, and a deprotonated open form, can account for the kinetic observations in the dark and under irradiation.

The morphological features of alpha-synuclein (AS) amyloid aggregation in vitro and in cells were elucidated at the nanoscale by far-field subdiffraction fluorescence localization microscopy. Labeling AS with rhodamine spiroamide probes allowed us to image AS fibrillar structures by fluorescence stochastic nanoscopy with an enhanced resolution at least 10-fold higher than that achieved with conventional, diffraction-limited techniques. The implementation of dual-color detection, combined with atomic force microscopy, revealed the propagation of individual fibrils in vitro. In cells, labeled protein appeared as amyloid aggregates of spheroidal morphology and subdiffraction sizes compatible with in vitro supramolecular intermediates perceived independently by atomic force microscopy and cryo-electron tomography. We estimated the number of monomeric protein units present in these minute structures. This approach is ideally suited for the investigation of the molecular mechanisms of amyloid formation both in vitro and in the cellular milieu. Fil: Roberti, Maria Julia. Max Planck Institute For Biophysical Chemistry (karl Friedrich Bonhoeffer Institute); . Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Fölling, Jonas. Institut Max Planck Fuer Gesellschaft; Alemania Fil: Celej, Maria Soledad. Institut Max Planck Fuer Gesellschaft; Alemania Fil: Bossi, Mariano Luis. Institut Max Planck Fuer Gesellschaft; Alemania Fil: Jovin, Thomas M.. Institut Max Planck Fuer Gesellschaft; Alemania Fil: Jares, Elizabeth Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina

Caged near-IR emitting fluorescent dyes are in high demand in optical microscopy but up to now were unavailable. We discovered that the combination of a carbopyronine dye core and a photosensitive 2-diazo-1-indanone residue leads to masked near-IR emitting fluorescent dyes. Illumination of these caged dyes with either UV or visible light (λ < 420 nm) efficiently generates fluorescent compounds with absorption and emission at 635 nm and 660 nm, respectively. A high-yielding synthetic route with attractive possibilities for further dye design is described in detail. Good photostability, high contrast, and a large fluorescence quantum yield after uncaging are the most important features of the new compounds for non-invasive imaging in high-resolution optical microscopy. For use in immunolabelling the caged dyes were decorated with a (hydrophilic) linker and an (activated) carboxyl group. Fil: Kolmakov, Kirill. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Wurm, Christian. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Sednev, Maksim V.. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Belov, Vladimir N.. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Hell, Stefan W.. Max Planck Institute for Biophysical Chemistry; Alemania

Manganese-doped CdS/ZnS quantum dots have been used as energy donors in a Förster-like resonance energy transfer (FRET) process to enhance the effective lifetime of organic fluorophores. It was possible to tune the effective lifetime of the fluorophores by about six orders of magnitude from the nanosecond (ns) up to the millisecond (ms) region. Undoped and Mn-doped CdS/ZnS quantum dots functionalized with different dye molecules were selected as a model system for investigating the multiple energy transfer process and the specific interaction between Mn ions and the attached dye molecules. While the lifetime of the free dye molecules was about 5 ns, their linking to undoped CdS/ZnS quantum dots led to a long effective lifetime of about 150 ns, following a non-exponential transient. Manganese-doped core-shell quantum dots further enhanced the long-lasting decay time of the dye to several ms. This opens up a pathway to analyse different fluorophores in the time domain with equal spectral emissions. Such lifetime multiplexing would be an interesting alternative to the commonly used spectral multiplexing in fluorescence detection schemes. Fil: Kaiser, Uwe. Philipps-University Marburg, ; Alemania Fil: Sabir, Nadeem. Philipps-University Marburg, ; Alemania Fil: Carrillo-Carrion, Carolina. Philipps-University Marburg, ; Alemania Fil: Del Pino, Pablo. CIC biomaGUNE; España Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Heimbrodt, Wolfram. Philipps-University Marburg, ; Alemania Fil: Parak, Wolfgang J.. Philipps-University Marburg, ; Alemania. CIC biomaGUNE; España

New photostable rhodamine dyes represented by the compounds 1a-r and 3-5 are proposed as efficient fluorescent markers with unique combination of structural features. Unlike rhodamines with monoalkylated nitrogen atoms, N′,N-bis(2,2,2-trifluoroethyl) derivatives 1e, 1i, 1j, 3-H and 5 were found to undergo sulfonation of the xanthene fragment at the positions 4′ and 5′. Two fluorine atoms were introduced into the positions 2′ and 7′ of the 3′,6′-diaminoxanthene fragment in compounds 1a-d, 1i-l and 1m-r. The new rhodamine dyes may be excited with λ= 488 or 514 nm light; most of them emit light at λ = 512-554 nm (compounds 1q and 1r at λ=576 and 589 nm in methanol, respectively) and have high fluorescence quantum yields in solution (up to 98%), relatively long excited-state lifetimes (>3ns) and are resistant against photobleaching, especially at high laser intensities, as is usually applied in confocal microscopy. Sulfonation of the xanthene fragment with 30% SO3 in H2SO4 is compatible with the secondary amide bond (rhodamine-CON(Me)CH2CH 2COOH) formed with MeNHCH2CH2COOCH3 to providing the sterically unhindered carboxylic group required for further (bio)conjugation reactions. After creating the amino reactive sites, the modified derivatives may be used as fluorescent markers and labels for (bio)molecules in optical microscopy and nanoscopy with very-high light intensities. Further, the new rhodamine dyes are able to pass the plasma membrane of living cells, introducing them as potential labels for recent live-cell-tag approaches. We exemplify the excellent performance of the fluorinated rhodamines in optical microscopy by fluorescence correlation spectroscopy (FCS) and stimulated emission depletion (STED) nanoscopy experiments. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. Fil: Mitronova, Gyuzel Yu. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Belov, Vladimir N.. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Wurm, Christian A.. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Meyer, Lars. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Medda, Rebecca. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Moneron, Gael. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Bretschneider, Stefan. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Eggeling, Christian. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Jakobs, Stefan. Max Planck Institute for Biophysical Chemistry; Alemania Fil: Hell, Stefan W.. Max Planck Institute for Biophysical Chemistry; Alemania

The spectroscopy and photochromic properties of transferred monolayers of the amphiphilic styryl-pyridinium dye 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate (DMPOP) were studied at different conditions during their transfer. The emission maxima of the monolayers transferred from the air-water interface in the liquid-expanded phase are strongly dependent on the surface pressure applied during the transfer process, even at values when the area per molecule is 2-3 times larger than the area occupied by a chromophore. In monolayers transferred from the liquid-condensed phase, the presence of a different kind of aggregates was observed. The fluorescence emission properties of the monolayers can be reversibly modulated by photoinduced E-Z isomerization. A blue shift up to 72 nm in the emission maximum, depending on the transfer conditions of the films, can be obtained by irradiation with blue light, and partially recovered (a red shift of up to 26 nm) with UV radiation. The rate at which the first process (E--Z) takes place is drastically reduced in monolayers transferred from the liquid-condensed phase as compared to those transferred from the liquid-expanded one. However, the rate of the reverse reaction (Z--E) is not significantly altered. These properties make DMPOP a promising material for the preparation of Langmuir-Blodgett films, whose properties can be effectively controlled by the transfer conditions and subsequently optically modulated, for potential applications as photonics devices for data storage.

Samples of a nematic mixture of ZLI1132 and of a twisted nematic mixture composed of ZLI1132 and chiral inductor S811, including 1%-10% (w/w) 4-N,N-dimethylaminoazobenzene (DAB), (4′-nitro)-4-N,Ndimethylaminoazobenzene (NDAB), spiropyran (SP), or spirooxazine (SO) were irradiated to produce the photochromic transformation of the dopant. The changes in the system were monitored by time-resolved transmission spectroscopy, time-resolved birefringence, or polarized Raman scattering. The medium sensitivity of the kinetics and spectroscopy of some of the probes was used to derive information on polarity of the medium. In the systems studied, apart from the changes in absorption spectrum, great changes in birefringence can be photoinduced and the order of the nematic phase can be changed in either direction, depending on the dopant. The open form of SP can discriminate orientation polarity. Although the polarity parallel to the mesogenic director is similar to that for acetone, the perpendicular orientation has a polarity similar to acetonitrile. In agreement with this observation, the kinetics of the Z f E isomerization of NDAB, oriented parallel to the mesogenic director, also experiences a polarity similar to that for acetone. The decay rate constant of the open form of SP displays a linear relationship between its Arrhenius parameters, which is universal in a great variety of homogeneous solvents, solvent mixtures, and liquid crystals, therefore validating the hypothesis that the same type of transformation is observed in all these cases, namely, the decay of the open form monomer. The dopants used have been proven to be adequate probes of bulklike properties in locally heterogeneous systems as liquid crystals. Fil: Bossi, Mariano Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Murgida, Daniel Horacio. Universität zu Berlin; Alemania Fil: Aramendia, Pedro Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina