Search

Two coumarin-based boron complexes (HBN and MBN) with aggregation-induced emission were designed and synthesized. The photophysical properties of the complexes were investigated in different solvents and in the solid state. Results showed that the inhibited CN isomerization by N,O-chelated BF2 caused the significant enhancement of fluorescence in THF. In particular, the complexes displayed red-shifted emissions (>60 nm) in mixed solvents of CH3CN and water because of the aggregation-induced charge-transfer enhancement. In the solid state, the bright red emission appeared at 650 nm (620 nm), with a Stokes shift of 170 nm. Cell-imaging experiments indicated that the complexes have good membrane permeability and can be used as lysosome trackers. [ABSTRACT FROM AUTHOR]

Tounderstand chemical reactivity of molecules in condensed phasein real time, a structural dynamics technique capable of monitoringmolecular conformational motions on their intrinsic time scales, typicallyon femtoseconds to picoseconds, is needed. We have studied a strongphotoacid pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, HPTS,pKa* ≈ 0) in pure methanol andobserved that excited-state proton transfer (ESPT) is absent, in sharpcontrast with our previous work on HPTS in aqueous solutions whereinESPT prevails following photoexcitation. Two transient vibrationalmarker bands at ∼1477 (1454) and 1532 (1528) cm–1appear in CH3OH (CD3OD), respectively, risingwithin the instrument response time of ∼140 fs and decayingwith 390–470 (490–1400) fs and ∼200 ps time constantsin CH3OH (CD3OD). We attribute the mode onsetto small-scale coherent proton motion along the pre-existing H-bondingchain between HPTS and methanol, and the two decay stages to the low-frequencyskeletal motion-modulated Franck–Condon relaxation within ∼1ps and subsequent rotational diffusion of H-bonding partners in solutionbefore fluorescence. The early time kinetic isotope effect (KIE) of∼3 upon methanol deuteration argues active proton motions particularlywithin the first few picoseconds when coherent skeletal motions areunderdamped. Pronounced quantum beats are observed for high-frequencymodes consisting of strong phenolic COH rocking (1532 cm–1) or H-out-of-plane wagging motions (952 cm–1)due to anharmonic coupling to coherent low-frequency modes impulsivelyexcited at ca. 96, 120, and 168 cm–1. The vividillustration of atomic motions of HPTS in varying H-bonding geometrywith neighboring methanol molecules unravels the multidimensionalenergy relaxation pathways immediately following photoexcitation,and provides compelling evidence that, in lieu of ESPT, the photoacidityof HPTS promptly activates characteristic low-frequency skeletal motionsto search phase space mainly concerning the phenolic end and to efficientlydissipate vibrational energy via skeletal deformation and proton shuttlingmotions within the intermediate, relatively confined excited-stateHPTS–methanol complex on a solvent-dependent dynamic potentialenergy surface. [ABSTRACT FROM AUTHOR]

Proton transfer reaction plays an essential role in amyriad ofchemical and biological processes, and to reveal the choreographyof the proton motion intra- and intermolecularly, a spectroscopictechnique capable of capturing molecular structural snapshots on theintrinsic time scale of proton transfer motions is needed. The photoacidpyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, HPTS) serves asa paradigm case to dissect excited state proton transfer (ESPT) eventsin aqueous solution, triggered precisely by photoexcitation. We haveused femtosecond stimulated Raman spectroscopy (FSRS) to yield novelinsights into the ultrafast conformational dynamics of photoexcitedHPTS in complex with water and acetate molecules. Marker bands attributedto the deprotonated form of HPTS (1139 cm–1, ∼220fs rise) appear earlier and faster than the monomer acetic acid peak(864 cm–1, ∼530 fs rise), indicating thatwater molecules actively participate in the ESPT chain. Several keylow-frequency modes at 106, 150, 195, and 321 cm–1have been identified to facilitate ESPT at different stages from300 fs, 1 ps, to 6 ps and beyond, having distinctive dynamics contributingthrough hydrogen bonds with 0, 1, and more intervening water molecules.The time-resolved FSRS spectroscopy renders a direct approach to observethe reactive coupling between the vibrational degrees of freedom ofphotoexcited HPTS in action, therefore revealing the anharmonicitymatrix both within HPTS and between HPTS and the neighboring acceptormolecules. The observed excited state conformational dynamics arealong the ESPT multidimensional reaction coordinate and are responsiblefor the photoacidity of HPTS in aqueous solution. [ABSTRACT FROM AUTHOR]

Vesicles of surfactants in aqueous solution have received considerable attention because of their use as simple model systems for biological membranes and their applications in various fields including colloids, pharmaceuticals, and materials. Because of their architecture, vesicles could prove useful as “soft” templates for the synthesis of “hard materials”. The vesicle phase, however, has been challenging and difficult to work with in the construction of hard materials. [ABSTRACT FROM AUTHOR]

Studies the synthesis of pyrazine C-nucleosides using sequential dilithiation-addition method. Dilithiopyrazine and electrophile reaction; Aromatic peaks of the O-benzyl groups on the sugar moiety; Result of the nucleophilic substitution by phenylthiolithium; Ortho relationship between the methyl peaks.

The development of near-infrared fluorescent probes with low pKa, high selectivity, high photostability, and high sensitivity for lysosomal pH detection is of great importance. In the present work, we developed a novel near-infrared lysosomal pH probe (Lyso-hNR) based on a rhodamine derivative. Lyso-hNR showed fast, highly sensitive, and highly selective fluorescence response to acidic pH caused by the H+-induced structure changes from the nonfluorescent spirolactam form to the highly emissive open-ring form. Lyso-hNR displays a significant fluorescence enhancement at 650 nm (over 280-fold) from pH 7.0 to 4.0 with a pKa value of 5.04. Live cell imaging data revealed that Lyso-hNR can selectively monitor lysosomal pH changes with excellent photostability and low cytotoxicity. In addition, Lyso-hNR can be successfully used in tracking lysosomal pH changes induced by chloroquine and those during apoptosis. All these features render Lyso-hNR a promising candidate to investigate lysosome-associated physiological and pathological processes. [ABSTRACT FROM AUTHOR]

Fluorescentproteins (FPs) are luminescent biomolecules that emitcharacteristic hues upon irradiation. A group of calmodulin (CaM)-greenFP (GFP) chimeras have been previously engineered to enable the opticaldetection of calcium ions (Ca2+). We investigate one ofthese genetically encoded Ca2+biosensors for optical imaging(GECOs), GEM-GECO1, which fluoresces green without Ca2+but blue with Ca2+, using femtosecond stimulated Ramanspectroscopy (FSRS). The time-resolved FSRS data (<800 cm–1) reveal that initial structural evolution following 400 nm photoexcitationinvolves small-scale coherent proton motions on both ends of the chromophoretwo-ring system with a <250 fs time constant. Upon Ca2+binding, the chromophore adopts a more twisted conformation in theprotein pocket with increased hydrophobicity, which inhibits excited-stateproton transfer (ESPT) by effectively trapping the protonated chromophorein S1. Both the chromophore photoacidity and local environmentform the ultrafast structural dynamics basis for the dual-emissionproperties of GEM-GECO1. Its photochemical transformations along multidimensionalreaction coordinates are evinced by distinct stages of FSRS spectralevolution, particularly related to the ∼460 and 504 cm–1modes. The direct observation of lower frequencymodes provides crucial information about the nuclear motions precedingESPT, which enriches our understanding of photochemistry and enablesthe rational design of new biosensors. [ABSTRACT FROM AUTHOR]

A coumarin-derived complex, Hg2L2, was reported as a highly sensitive and selective probe for the detection of mercapto biomolecules in aqueous solution. The addition of Cys to a 99% aqueous solution of Hg2L2 resulted in rapid and remarkable fluorescence OFF--ON (emission at 525 nm) due to the ligand-exchange reaction of Cys with L coordinated to Hg2+. The increased fluorescence can be completely quenched by Hg2+ and recovered again by the subsequent addition of Cys. Such a fluorescence OFF--ON circle can be repeated at least 10 times by the alterative addition of Cys and Hg2+ to the solution of Hg2L2, indicating that it can be used as a convertible and reversible probe for the detection of Cys. The interconversion of Hg2L2 and L via the decomplexation/complexation by the modulation of Cys/Hg2+ was definitely verified from their crystal structures. Other competitive amino acids without a thiol group cannot induce any fluorescence changes, implying that Hg2L2 can selectively determine mercapto biomolecules. Using confocal fluorescence imaging, L/Hg2L2 as a pair of reversible probes can be further applied to track and monitor the self-detoxification process of Hg2+ ions in SYS5 cells. [ABSTRACT FROM AUTHOR]

A salt-free cationic and anionic (catanionic) surfactant system was formed by mixing a double-tailed di-(2-ethylhexyl) phosphoric acid (DEHPA, commercial name P204), which is an excellent extractant of rare earth metal ions, with a single-tailed cationic trimethyltetradecylammonium hydroxide (TTAOH) in water. With the mole ratio (r) of DEHPA to TTAOH varying from 0.9 to 1, the phase transition occurred from a densely stacked vesicle phase (Lαv) to a lamellar phase (Lαl). Macroscopic properties, such as polarization and rheology, were measured and changed greatly during the course of the phase transition. When rwas 0.96 or 0.98, the steady state shear curves exhibited two yield stress values, indicating the coexistence of the Lαvphase and the Lαlphase. The Lαlphase formed in the salt-free and zero-charged system (r= 1.0) is defective and undulating, which was confirmed by cryogenic transmission electron microscopy (cryo-TEM). The deuterium nuclear magnetic resonance spectra (2H NMR) showed that a single peak (singlet) split into two symmetric peaks (doublet) gradually, indicating the phase transition from the Lαvphase to the Lαlphase. Correspondingly, phosphorus nuclear magnetic resonance spectra (31P NMR) presented changes in both the chemical shift and the peak width, indicating that these two types of bilayer structures are of different anisotropy degrees and different viscosities. When the Lαlphase is subjected to a certain shear force, it can be reversed to a Lαvphase again, which was proved by rheological, 2H NMR, and 31P NMR measurements. Furthermore, a theoretical consideration about the formation of the defective and undulating Lαlphase was taken into account from a viewpoint of energy. [ABSTRACT FROM AUTHOR]

DOSS–(dioctyl sulfosuccinate) based quaternaryammonium ionic liquids (QAILs) were synthesized and used as both neatlubricants and lubricant additives. The influence of structure ontheir miscibility, thermal stability, and tribological property wasdiscussed. These QAILs are low cost as compared with conventionalhalogen-containing ionic liquids (ILs). They are noncorrosive andhydrolysis stable because of their halogen-free characteristics. Thetribological properties of these QAILs as neat lubricants for steel/steeland steel/copper contacts are found to be better than conventionalhalogen-containing ILs 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(L-F104) and far better than traditional synthetic lubricant poly-α-olefin(PAO). Moreover, oil-soluble ILs were obtained by properly adjustingthe chain length and cation asymmetry of these QAILs, which can beeasily dissolved in nonpolar synthetic-oil PAO. They are found tobe effective lubricant additives for improving the friction-reducingand antiwear properties of PAO. It is a great advantage as comparedwith conventional ILs, which have extremely low solubility in PAOand are difficult to be used as lubricant additives for this kindof base oil. Furthermore, the coking test results indicated that thesynthesized QAILs have high deterging ability when used as lubricantadditives for PAO. Thus, they can restrain carbonaceous depositionas well as oil sludge and varnish formation on the metal contactsduring the sliding process. They can also disperse, loosen, and removethe already formed harmful substances and keep the metal contactsclean. The present work may make obvious progress toward preparinglow cost, noncorrosive, and environmentally benign IL lubricants inlubrication engineering. [ABSTRACT FROM AUTHOR]

Thefabrication of core/shell charged polymer brushes-grafted hollowsilica nanoparticles (PSPMA-g-HSNPs) is reported.Because of the excellent hydration capability of the shells consistingof charged polymer brushes, the functional nanoparticles can achievea good lubricating effect in aqueous media via hydration lubricationmechanism. The mesoporous hollow silica cores endow the nanoparticleswith drug loading–release capability. Aspirin, as a usefuldrug for treating arthritis, was employed to carry out in vitro drugloading and release studies. It is clear that brushes-modified hollowsilica exhibited long-term drug release performance. The combinationof lubrication and drug loading capabilities results in the greatclinical potential of new multifunctional nanoparticles as injectablejoint lubricant fluid in arthritis treatment. [ABSTRACT FROM AUTHOR]

We present a paradigm that dramaticallytunes friction from superior lubrication (μ ∼ 10–3) to ultrahigh friction (μ > 1) using responsivepolyelectrolyte brushes. The tunable friction is based on counterion-driveninteractions in polyelectrolyte brushes that can be simply achievedby exchanging the counterions. We systematically investigated theeffects of opposite counterions of different types on the frictionproperties of polyanionic, polycationic, and polyzwitterionic brushes.For cationic brushes with quaternary ammonium groups, the frictioncoefficient was progressively tuned from ∼10–3to ∼100according to the counterions series Cl–< ClO4–< PF6–< TFSI–. The frictionof anionic brushes can be tuned by oppositely charged surfactants(tetraalkylammonium) with different length of hydrophobic tails, multivalentmetal ions, and protons. The friction increase of cationic brushesis due to the dehydration and the collapse of polyelectrolyte chainsinduced by ion-pairing interactions. For anionic brushes, the frictionincreased with the length of hydrophobic tails of surfactants, whichresulted from hydrophobicity induced electrostatic interaction amongsurfactants and polymer chains. The anionic brushes with the carboxylateand the sulfonate side groups revealed different friction responses,which is owing to the carboxylate groups getting stronger specificinteraction with the quaternary ammonium and thus with the multivalentmetal ions as well. The mechanism of tuning friction was finally concluded;that is, highly hydrated and swelling polymer brushes show superiorlubrication, partially collapsed polymer chains have moderate lubrication,and completely dehydrated and collapsed conformation loses lubricatingcapability. [ABSTRACT FROM AUTHOR]

N,N-Dimethyl-N-(pyrenyl-1-methyl) dodecan-1-ammonium has been designed and applied as a fluorescent probe for sensing bacterial endotoxin. Upon assembly with bacterial endotoxin (lipopolysaccharide) in aqueous solution, the probe exhibits a ratiometric and sensitive fluorescence response with a low detection limit (100 nM). Moreover, the probe shows high selectivity for bacterial endotoxin over other related biological species. [ABSTRACT FROM AUTHOR]