Search

One of the greatest current challenges in structural biology is to study protein dynamics over a wide range of timescales in complex environments, such as the cell. Among magnetic resonances suitable for this approach, electron paramagnetic resonance spectroscopy coupled to site-directed spin labeling (SDSL-EPR) has emerged as a promising tool to study protein local dynamics and conformational ensembles. In this work, we exploit the sensitivity of nitroxide labels to report protein local dynamics at room temperature. We demonstrate that such studies can be performed while preserving both the integrity of the cells and the activity of the protein under investigation. Using this approach, we studied the structural dynamics of the chaperone NarJ in its natural host, Escherichia coli. We established that spin-labeled NarJ is active inside the cell. We showed that the cellular medium affects NarJ structural dynamics in a site-specific way, while the structural flexibility of the protein is maintained. Finally, we present and discuss data on the time-resolved dynamics of NarJ in cellular context., (© 2022 Wiley-VCH GmbH.)

Background: The assessment of patients' medication literacy skills (i.e., abilities to access, comprehend and interact with medication-related information) is an important step in assisting clinicians to plan for appropriate care. Despite several attempts by researchers to develop measures of medication literacy, an instrument tailored to the specific needs of older adults remains a significant shortfall. Therefore, an interprofessional team that included a citizen co-researcher conceptualized a new standardised measure of medication literacy-the MEDedication Literacy Assessment of Geriatric patients and informal caregivers (MED-fLAG). MED-fLAG was designed as a three-dimensional self-reported measure of functional, interactive and critical skills. This study describes the conceptualization process and provides the results of an evaluation of MED-fLAG's content validity, acceptability, and feasibility during a hospital stay., Methods: MED-fLAG was developed in accordance with the guidance on scale development and standards for good content validity, by using the following steps: (I) conceptualization of a provisional version of MED-fLAG; (II) iterative qualitative evaluation of its content validity by older adults, informal caregivers and healthcare professionals., Results: The qualitative assessment of the initial 54-item MED-fLAG was conducted in 36 participants, namely 13 home-dwelling older adults and/or informal caregivers and 23 healthcare professionals. Six rounds of revisions were performed to achieve content validity and to propose a 56-item revised MED-fLAG. Participants reported benefits of using a standardized assessment of medication literacy during a hospital stay but warned about certain limitations and prerequisites. The extent to which MED-fLAG could be integrated into discharge planning needs to be further investigated., Conclusions: MED-fLAG is the first medication literacy measure tailored to the specific needs of older patients and informal caregivers. A unique feature of this measure is that it includes prescribed and non-prescribed medications, irrespective of the galenic form. Additional studies are required to evaluate the other measurement properties of MED-fLAG, and to reduce the number of items before considering its clinical application., (© 2022. The Author(s).)

The quinol oxidation site Q D in E. coli respiratory nitrate reductase A (EcNarGHI) reacts with the three isoprenoid quinones naturally synthesized by the bacterium, i.e. ubiquinones (UQ), menaquinones (MK) and demethylmenaquinones (DMK). The binding mode of the demethylmenasemiquinone (DMSK) intermediate to the EcNarGHI Q D quinol oxidation site is analyzed in detail using 1,2 H hyperfine (hf) spectroscopy in combination with H 2 O/D 2 O exchange experiments and DFT modeling, and compared to the menasemiquinone one bound to the Q D site (MSK D ) previously studied by us. DMSK D and MSK D are shown to bind in a similar and strongly asymmetric manner through a short (~1.7 Å) H-bond. The origin of the specific hf pattern resolved on the DMSK D field-swept EPR spectrum is unambiguously ascribed to slightly inequivalent contributions from two β-methylene protons of the isoprenoid side chain. DFT calculations show that their large isotropic hf coupling constants (A iso ~12 and 15 MHz) are consistent with both (i) a specific highly asymmetric binding mode of DMSK D and (ii) a near in-plane orientation of its isoprenyl chain at Cβ relative to the aromatic ring, which differs by ~90° to that predicted for free or NarGHI-bound MSK. Our results provide new insights into how the conformation and the redox properties of different natural quinones are selectively fine-tuned by the protein environment at a single Q site. Such a fine-tuning most likely contributes to render NarGHI as an efficient and flexible respiratory enzyme to be used upon rapid variations of the Q-pool content., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In vivo specific isotope labeling at the residue or substituent level is used to probe menasemiquinone (MSK) binding to the quinol oxidation site of respiratory nitrate reductase A (NarGHI) from E. coli. 15 N selective labeling of His 15 Nδ or Lys 15 Nζ in combination with hyperfine sublevel correlation (HYSCORE) spectroscopy unambiguously identified His 15 Nδ as the direct hydrogen-bond donor to the radical. In contrast, an essentially anisotropic coupling to Lys 15 Nζ consistent with a through-space magnetic interaction was resolved. This suggests that MSK does not form a hydrogen bond with the side chain of the nearby Lys86 residue. In addition, selective 2 H labeling of the menaquinone methyl ring substituent allows unambiguous characterization of the 2 H-and hence of the 1 H-methyl isotropic hyperfine coupling by 2 H HYSCORE. DFT calculations show that a simple molecular model consisting of an imidazole Nδ atom in a hydrogen-bond interaction with a MSK radical anion satisfactorily accounts for the available spectroscopic data. These results support our previously proposed one-sided binding model for MSK to NarGHI through a single short hydrogen bond to the Nδ of His66, one of the distal heme axial ligands. This work establishes the basis for future investigations aimed at determining the functional relevance of this peculiar binding mode., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Quinones are essential building blocks of respiration, a universal process dedicated to efficient harvesting of environmental energy and its conversion into a transmembrane chemiosmotic potential. Quinones differentiate mostly by their midpoint redox potential. As such, γ-proteobacteria such as Escherichia coli are characterized by the presence of demethylmenaquinone (DMK) with an intermediate redox potential between low-potential (menaquinone) and high-potential (ubiquinone) quinones. In this study, we show that demethylmenaquinol (DMKH2) is a good substrate for nitrate reductase A (NarGHI) in nitrate respiration in E. coli. Kinetic studies performed with quinol analogs on NarGHI show that removal of the methyl group on the naphthoquinol ring impacts modestly the catalytic constant but not the KM. EPR-monitored redox titrations of NarGHI-enriched membrane vesicles reveal that endogeneous demethylmenasemiquinone (DMSK) intermediates are stabilized in the enzyme. The measured midpoint potential of the DMK/DMKH2 redox couple in NarGHI (E'm,7.5 (DMK/DMKH2) ~-70mV) is significantly lower than that previously measured for unbound species. High resolution pulsed EPR experiments demonstrate that DMSK are formed within the NarGHI quinol oxidation site. Overall, our results provide the first characterization of a protein-bound DMSK and allows for comparison for distinct use of three quinones at a single Q-site in NarGHI., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The biological denitrification process is crucial for removing nitrogen and reducing nitrous oxide (N2O) emissions. To investigate the mechanism of action of key enzymes in the denitrification process, it is necessary to analyze the protein structure, active site, and conformational changes of denitrifying enzymes. X-ray crystallography, nuclear magnetic resonance (NMR), and cryogenic electron microscopy (Cryo-EM), as well as spectroscopic analyses such as Raman resonance and UV-vis, have been used to study the structure of denitrifying enzymes. However, practical application is limited by protein folding and assembly, as well as issues of purity, concentration, and homogeneity. This review summarizes the biochemical properties of the four denitrifying enzymes and typical purification methods. Additionally, this review emphasizes important factors to consider during protein expression, crude extract, and chromatographic purification. It also provides insight into the future development of protein purification methods for denitrifying enzymes. This review aims to bridge the gap between the complex biochemical process of denitrifying enzymes and the technical intricacies of protein purification, with the ultimate goal of reducing N2O emissions in ecosystems. [ABSTRACT FROM AUTHOR]

In the crayfish Astacus leptodactylus, as in several crustacean species, the crustacean hyperglycemic hormone is present as two isoforms differing by the chirality of the third residue, a phenylalanine. In the present work, isoforms synthesized full length by solid-phase peptide synthesis have been purified, refolded, the location of the disulfide bridges has been checked, their immunoreactivity against different antibodies have been analyzed and their hyperglycemic activity tested, to ensure the identity of the synthetic peptides with their natural homologs. Different parameters of the hyperglycemic activity of both isoforms were studied. In addition to a difference in the kinetics of hyperglycemia, already known from other studies, it was observed that the dose-response was different depending on the season where experiments were performed, the response being stronger in spring than in autumn, especially for the d-Phe containing isoform. A dosage method based on sandwich enzyme linked immunosorbent assay (ELISA) has been developed to measure hemolymphatic levels of the isoforms after spiking of the animals with one isoform or the other. It was found that hemolymphatic clearance was identical for both isoforms, indicating that their differential effect is not linked to their different lifetime in the hemolymph but may rather rely on other mechanisms such as their binding to different target tissues., (Copyright © 2012 Elsevier Inc. All rights reserved.)

[FeFe]-hydrogenases catalyze the protons/hydrogen interconversion through a unique di-iron active site consisting of three CO and two CN ligands, and a non-protein SCH(2)XCH(2)S (X=N or O) dithiolate bridge. Site assembly requires two "Radical-S-adenosylmethionine (SAM or AdoMet)" iron-sulfur enzymes, HydE and HydG, and one GTPase, HydF. The sequence homology between HydG and ThiH, a Radical-SAM enzyme which cleaves tyrosine into p-cresol and dehydroglycine, and the finding of a similar cleavage reaction catalyzed by HydG suggests a mechanism for hydrogenase maturation. Here we propose that HydG is specifically involved in the synthesis of the dithiolate ligand, with two tyrosine-derived dehydroglycines as precursors along with an [FeS] cluster of HydG functioning both as electron shuttle and source of the sulfur atoms.

A survey is presented of picosecond kinetics of heme-residue bond formation after photolysis of histidine, methionine, or cysteine, in a broad range of ferrous six-coordinate heme proteins. These include human neuroglobin, a bacterial heme-binding superoxide dismutase (SOD), plant cytochrome b 559, the insect nuclear receptor E75, horse heart cytochrome c and the heme domain of the bacterial sensor protein Dos. We demonstrate that the fastest and dominant phase of binding of amino acid residues to domed heme invariably takes place with a time constant in the narrow range of 5-7 ps. Remarkably, this is also the case in the heme-binding SOD, where the heme is solvent-exposed. We reason that this fast phase corresponds to barrierless formation of the heme-residue bond from a configuration close to the bound state. Only in proteins where functional ligand exchange occurs, additional slower rebinding takes place on the time scale of tens of picoseconds after residue dissociation. We propose that the presence of these slower phases reflects flexibility in the heme environment that allows external ligands (O2, CO, NO, . . .) to functionally replace the internal residue after thermal dissociation of the heme-residue bond.

We have implemented the recently demonstrated technique of chirped-pulse upconversion of midinfrared femtosecond pulses into the visible in a visible pump-midinfrared probe experiment for high-resolution, high-sensitivity measurements over a broad spectral range. We have succeeded in time-resolving the CO ligand transfer process from the heme Fe to the neighboring Cu(B) atom in the bimetallic active site of mammalian cytochrome c oxidase, which was known to proceed in <1 ps, using the full CO vibrational signature of Fe-CO bond breaking and Cu(B)-CO bond formation. Our differential transmission results show a delayed onset of the appearance of the Cu(B)-bound species (200 fs), followed by a 450-fs exponential rise. Trajectories calculated by using molecular-dynamics simulations with a Morse potential for the Cu(B)-C interaction display a similar behavior. Both experimental and calculated data strongly suggest a ballistic contribution to the transfer process.

Following different reports on the stoichiometry and configuration of NO binding to mammalian and bacterial reduced cytochrome c oxidase aa(3) (CcO), we investigated NO binding and dynamics in the active site of beef heart CcO as a function of NO concentration, using ultrafast transient absorption and EPR spectroscopy. We find that in the physiological range only one NO molecule binds to heme a(3), and time-resolved experiments indicate that even transient binding to Cu(B) does not occur. Only at very high (approximately 2 mM) concentrations a second NO is accommodated in the active site, although in a different configuration than previously observed for CcO from Paracoccus denitrificans [E. Pilet, W. Nitschke, F. Rappaport, T. Soulimane, J.-C. Lambry, U. Liebl and M.H. Vos. Biochemistry 43 (2004) 14118-14127], where we proposed that a second NO does bind to Cu(B). In addition, in the bacterial enzyme two NO molecules can bind already at NO concentrations of approximately 1 microM. The unexpected differences highlighted in this study may relate to differences in the physiological relevance of the CcO-NO interactions in both species.

Electron transfer (ET) within proteins occurs by means of chains of redox intermediates that favor directional and efficient electron delivery to an acceptor. Individual ET steps are energetically characterized by the electronic coupling V, driving force DeltaG, and reorganization energy lambda. lambda reflects the nuclear rearrangement of the redox partners and their environment associated with the reactions; lambda approximately 700-1,100 meV (1 eV = 1.602 x 10(-19) J) has been considered as a typical value for intraprotein ET. In nonphotosynthetic systems, functional ET is difficult to assess directly. However, using femtosecond flash photolysis of the CO-poised membrane protein cytochrome c oxidase, the intrinsic rate constant of the low-DeltaG electron injection from heme a into the heme a(3)-Cu(B) active site was recently established at (1.4 ns)(-1). Here, we determine the temperature dependence of both the rate constant and DeltaG of this reaction and establish that this reaction is activationless. Using a quantum mechanical form of nonadiabatic ET theory and common assumptions for the coupled vibrational modes, we deduce that lambda is <200 meV. It is demonstrated that the previously accepted value of 760 meV actually originates from the temperature dependence of Cu(B)-CO bond breaking. We discuss that low-DeltaG, low-lambda reactions are common for efficiently channeling electrons through chains that are buried inside membrane proteins.

Fast intraprotein electron transfer reactions associated with enzymatic catalysis are often difficult to synchronize and therefore to monitor directly in non-light-driven systems. However, in the mitochondrial respiratory enzyme cytochrome oxidase aa(3), the kinetics of the final electron transfer step into the active site can be determined: reverse electron flow between the close-lying and chemically identical hemes a(3) and a can be initiated by flash photolysis of CO from reduced heme a(3) under conditions where heme a is initially oxidized. To follow this reaction, we used transient absorption spectroscopy, with femtosecond time resolution and a time window extending to 4 ns. Comparison of the picosecond heme a(3)-CO photodissociation spectra under different redox states of heme a shows significant spectral interaction between both hemes, a phenomenon complicating the interpretation of spectral studies with low time resolution. Most importantly, we show that the intrinsic electron equilibration, corresponding to a DeltaG(0) of 45-55 meV, occurs in 1.2 +/- 0.1 ns. This is 3 orders of magnitude faster than the previously established equilibration phase of approximately 3 mus, which we suggest to reflect a change in redox equilibrium closely following CO migration out of the active site. Our results allow testing a number of conflicting predictions regarding this reaction between both experimental and theoretical studies. We discuss the potential physiological relevance of fast equilibration associated with this low-driving-force redox reaction.

Cytochrome c oxidase (CcO) has a high affinity for nitric oxide (NO), a property involved in the regulation of respiration. It has been shown that the recombination kinetics of photolyzed NO with reduced CcO from Paracoccus denitrificans on the picosecond time scale depend strongly on the NO/enzyme stoichiometry and inferred that more than one NO can be accommodated by the active site, already at mildly suprastoichiometric NO concentrations. We have largely extended these studies by monitoring rebinding dynamics from the picosecond to the microsecond time scale, by performing parallel steady-state low-temperature electron paramagnetic resonance (EPR) characterizations on samples prepared similarly as for the optical experiments and comparing them with molecular-modeling results. A comparative study was performed on CcO ba(3) from Thermus thermophilus, where two NO molecules cannot be copresent in the active site in the steady state because of its NO reductase activity. The kinetic results allow discrimination between different models of NO-dependent recombination and show that the overall NO escape probability out of the protein is high when only one NO is bound to CcO aa(3), whereas strong rebinding on the 15-ns time scale was observed for CcO ba(3). The EPR characterizations show similar results for aa(3) at substoichiometric NO/enzyme ratios and for ba(3), indicating formation of a 6-coordinate heme-NO complex. The presence of a second NO molecule in the aa(3) active site strongly modifies the heme-NO EPR spectrum and can be rationalized by a rotation of the Fe-N-O plane with respect to the histidine that coordinates the heme iron. This proposal is supported by molecular-modeling studies that indicate a approximately 63 degrees rotation of heme-bound NO upon binding of a second NO to the close-lying copper center CuB. It is argued that the second NO binds to CuB.

The supramolecular interaction between lanthanide complexes and proteins is at the heart of numerous chemical and biological studies. Some of these complexes have demonstrated remarkable interaction properties with proteins or peptides in solution and in the crystalline state. Here we have used the paramagnetism of lanthanide ions to characterize the affinity of two lanthanide complexes for ubiquitin. As the interaction process is dynamic, the acquired NMR data only reflect the time average of the different steps. We have used molecular dynamics (MD) simulations to get a deeper insight into the detailed interaction scenario at the microsecond scale. This NMR/MD approach enabled us to establish that the tris-dipicolinate complex interacts specifically with arginines and lysines, while the crystallophore explores the protein surface through weak interactions with carboxylates. These observations shed new light on the dynamic interaction properties of these complexes, which will ultimately enable us to propose a crystallization mechanism. [ABSTRACT FROM AUTHOR]

Semiconductor materials with layered structures usually have excellent thermoelectric properties and exhibit pronounced anisotropy such as Bi2Te3, SnSe, etc. The layered-like nature of GeTe has been studied by theoretical calculations, but it lacks sufficient experimental evidence. Herein, we study the crystal structure of GeTe single crystals by synchrotron radiation and atomic resolution scanning transmission electron microscopy. Lattice distortion along the [111]PC direction is found to be the main reason for the layered-like structure exhibited by r-GeTe. Meanwhile, the structure-related anisotropy for thermal expansion coefficients and thermal conductivities of r-GeTe single crystals is reported. Since the layered-like structure induces noticeable scattering of phonons, GeTe single crystals exhibit an intrinsic low lattice thermal conductivity in the [111]PC direction compared with the ⊥[111]PC direction and polycrystals. All of these are based on chemical bonding and the crystal structure, which emphasizes the key role they play in material properties. Our work led to a deeper understanding of the relationships between the crystal structure and thermal/electrical transport properties of GeTe families, which also provides a guide for the further investigation of GeTe-based materials. [ABSTRACT FROM AUTHOR]

The direct impact of structural quality on the ferroelectric properties of hexagonal Al1–xScxN with an Sc-content of x = 0.3 was investigated using dynamic hysteresis measurements, high-resolution x-ray diffraction (HRXRD), and atomic force microscopy. The films investigated were deposited on p-doped (001)-Si substrates by reactive pulsed DC magnetron sputtering under different gas mixtures to vary the structural quality and surface morphology between samples. Misoriented grains were identified as ferroelectrically inactive, as these grains resulted in an underestimation and distortion of the ferroelectric quantities. In fact, a high amount of misoriented volume was found to have a significant effect on the coercive electric field, as this is mainly determined by the crystal strain in the ferroelectric [0001]-oriented regions, independent of its origin. Furthermore, it was concluded that the crystal quality does not have a pronounced effect on the coercive field strength. Conversely, the polarization in the film is mainly determined by the crystal quality, as a difference of 1° in the HRXRD FWHM of the ω-scan resulted in a 60% loss of polarization. The amount of polarization was influenced to a lesser extent by the misoriented grains since the ferroelectric volume of the layers was only slightly overestimated. This reveals that optimizing reproducible and transferable properties, such as crystal quality and surface morphology, is more reasonable, as the film with the lowest misoriented volume and the highest degree of c-axis orientation showed the highest polarization. [ABSTRACT FROM AUTHOR]

Background: Low medication literacy is prevalent among older adults and is associated with adverse drug events. The Medication Literacy Test for Older Adults (TELUMI) was developed and content validated in a previously published study., Aim: To evaluate the psychometric properties and provide norms for TELUMI scores., Method: This was a cross-sectional methodological study with older adults selected from the community and from two outpatient services. Descriptive item-analysis, exploratory factor analysis (EFA), item response theory (IRT), reliability, and validity analysis with schooling and health literacy were performed to test the psychometric properties of the TELUMI. The classification of the TELUMI scores was performed using percentile norms., Results: A total of 344 participants, with a mean age of 68.7 years (standard deviation = 6.7), were included; most were female (66.6%), black/brown (61.8%), had low schooling level (60.2%) and low income (55.2%). The EFA pointed to the one-dimensional structure of TELUMI. A three-parameter logistic model was adopted for IRT. All items had an adequate difficulty index. One item had discrimination < 0.65, and three items had an unacceptable guessing index (< 0.35) and were excluded. The 29-item version of TELUMI had excellent internal consistency (KR20 = 0.89). There was a positive and strong association between TELUMI scores and health literacy and education level. The scores were classified as inadequate medication literacy (≤ 10.0 points), medium medication literacy (11-20 points), and adequate medication literacy (≥ 21 points)., Conclusion: The results suggest that the 29-item version of TELUMI is psychometrically adequate for measuring medication literacy in older adults., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Copyright of Swiss Political Science Review is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Does federalism fuel tensions in divided states? This paper addresses this question from a power-sharing angle. It provides a longitudinal analysis of the evolution of ethno-territorial conflict during five waves of federalization in a least-likely case: Belgium (1979–2018). Two original datasets on all cabinet conflicts (N = 1013; N = 328) provide an unprecedented picture of ethno-territorial conflict's intensity, nature, and frequency (absolute/relative). All indicators forcefully contradict the paradox thesis. Conflict did not increase. If anything, there is a tentative decline. Exposing intra-segmental and segmentally mixed conflicts, this study also challenges conventional views on factors like bipolarity and the repercussions of split party systems. [ABSTRACT FROM AUTHOR]

In prokaryotes, the role of Mo/W enzymes in physiology and bioenergetics is widely recognized. It is worth noting that the most diverse family of Mo/W enzymes is exclusive to prokaryotes, with the probable existence of several of them from the earliest forms of life on Earth. The structural organization of these enzymes, which often include additional redox centers, is as diverse as ever, as is their cellular localization. The most notable observation is the involvement of dedicated chaperones assisting with the assembly and acquisition of the metal centers, including Mo/W-bisPGD, one of the largest organic cofactors in nature. This review seeks to provide a new understanding and a unified model of Mo/W enzyme maturation. [ABSTRACT FROM AUTHOR]

Antiferroelectric (AFE) has emerged as a promising branch of electroactive materials, due to intriguing physical attributes stemming from the electric field-induced antipolar-to-polar phase transformation. However, the requirement of extremely high electric field strength to switch adjacent sublattice polarization poses great challenges for exploiting new molecular AFE system. Although photoirradiation is striking as a noncontact and nondestructive manipulation tool to optimize physical properties, optical control of antiferroelectricity still remains unexplored. Here, by adopting light-sensitive I 3 - anion into 2D perovskite family, we design a new I 3 - -intercalated molecular AFE of (t-ACH) 2 EA 2 Pb 3 I 10 (I 3 ) 0.5  ⋅ ((H 3 O)(H 2 O)) 0.5 (1, t-ACH=trans-4-aminomethyl-1-cyclohexanecarboxylate, EA=ethylammonium). The I 3 - -intercalating gives an ultra-narrow band gap of 1.65 eV with strong absorption. In term of AFE structure, the anti-parallel alignment of electric dipoles results in a large spontaneous polarization of 4.3 μC/cm 2 . Strikingly, 1 merely shows AFE behaviour in the dark even under ultrahigh voltage, while the field-induced ferroelectric state can be facilely obtained upon visible illumination. Such unprecedented visible-photo-assisted phase switching ascribes to the incorporation of photoactive I 3 - anions that reduces AFE-to-ferroelectric switching barrier. This pioneering work on the photo-assisting transformation of ferroic orders paves a way to develop future photoactive materials with potential applications., (© 2024 Wiley-VCH GmbH.)

In this work, four saddled Pd(II) porphyrins were developed as photocatalyst for N-dealkylation of triethyl Rhodamine (TER) under visible light, and their catalytic ability was found to be negatively related to the out-of-plane of their macrocycles. Two important relationships involving the metalloporphyrins as catalyst were revealed: (1) a photoexcitative semiconductor effect between the 4d x 2 - γ 2 (Pd) and a 2u (π) orbitals of Pd(II) porphyrin on the dealkylation. (2) a domino process from strap length, ring geometry, core deformation, d-π gap variation, to photocatalytic activity. Two revelations imply a unidirectional electron transfer route from axial ligand, to central metal, to porphyrin ring based on photoexcitation and guide the design and development of complex photocatalysts, and their revelation is attributed to the acquisition of a series of Pd(II) porphyrins with continuous ring distortion. The findings help to understand the photocatalytic single electron transfer (SET)-first mechanism based on metallic complex., (© 2024 Wiley-VCH GmbH.)

A versatile and efficient chemo selective synthesis of 4-aryl-3-formyl-2H-chromenes (AFC) was undertaken using Pd-catalyzed cross-coupling conditions. The key oxidative transmetalation was successfully applied to a significant range of substitutions on the chromene moiety and aryl ring in Ar(BOH) 3 , accommodating both electron-rich and electron-deficient groups. These π-extended scaffolds exhibited green-yellow fluorescence with a large Stokes shift and high quantum yield. Measurement of photophysical properties revealed that the compound with methoxy substitution in the chromene ring, 3t, caused a significant bathochromic shift. The AFCs obtained from this method can be transformed into biologically active 4-aryl-3-iminoantipyrine-2H-chromenes (AAC) through functionalization of the formyl chromenes. The AFCs and AACs with methoxy substitutions (3t and 4e) were docked against AChE inhibition, and compound 4e had the lowest binding energy of -11.20 kcal/mol. DFT calculations performed on representative compounds revealed that compound 4e is more reactive than 3t, which is in accordance with the docking studies., (© 2024 Wiley-VHCA AG, Zurich, Switzerland.)

Crystallophores are lanthanide complexes that have demonstrated outstanding induction of crystallization for various proteins. This article explores the effect of tailored modifications of the crystallophore first generation and their impact on the nucleating properties and protein crystal structures. Through high-throughput crystallization experiments and dataset analysis, we evaluated the effectiveness of these variants, in comparison to the first crystallophore generation G 1 . In particular, the V 1 variant, featuring a propanol pendant arm, demonstrated the ability to produce new crystallization conditions for the proteins tested (hen-egg white lysozyme, proteinase K and thaumatin). Structural analysis performed in the case of hen egg-white lysozyme along with Molecular Dynamics simulations, highlights V 1 's unique behavior, taking advantage of the flexibility of its propanol arm to explore different protein surfaces and form versatile supramolecular interactions., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Molybdenum-containing enzymes of the xanthine oxidase (XO) family are well known to catalyse oxygen atom transfer reactions, with the great majority of the characterised enzymes catalysing the insertion of an oxygen atom into the substrate. Although some family members are known to catalyse the "reverse" reaction, the capability to abstract an oxygen atom from the substrate molecule is not generally recognised for these enzymes. Hence, it was with surprise and scepticism that the "molybdenum community" noticed the reports on the mammalian XO capability to catalyse the oxygen atom abstraction of nitrite to form nitric oxide (NO). The lack of precedent for a molybdenum- (or tungsten) containing nitrite reductase on the nitrogen biogeochemical cycle contributed also to the scepticism. It took several kinetic, spectroscopic and mechanistic studies on enzymes of the XO family and also of sulfite oxidase and DMSO reductase families to finally have wide recognition of the molybdoenzymes' ability to form NO from nitrite. Herein, integrated in a collection of "personal views" edited by Professor Ralf Mendel, is an overview of my personal journey on the XO and aldehyde oxidase-catalysed nitrite reduction to NO. The main research findings and the path followed to establish XO and AO as competent nitrite reductases are reviewed. The evidence suggesting that these enzymes are probable players of the mammalian NO metabolism is also discussed. [ABSTRACT FROM AUTHOR]

Calixarenes are hallmark molecules in supramolecular chemistry as hosts for small ligands. They have also conversely proved their interest as ligands toward assisted co-crystallization of proteins. These functionalized macrocycles target positively-charged residues, and notably surface-exposed lysines, with a site-selectivity finely characterized experimentally, but that remains to be assessed. Relying on a tailored molecular dynamics simulations protocol, we explore the association of para-sulfonato-calix[4]arenes with an antifungal protein, as a small yet most competitive system with 13 surface-exposed lysines. Our computational approach probes de novo the electrostatically-driven interaction, ruled out by a competition with salt bridges, corroborating the presence of two main binding sites probed by X-ray. The attach-pull-release (APR) method provides a very good assessment of the overall binding free energy measured experimentally (−6.42 ± 0.5 vs. −5.45 kcal mol−1 by isothermal titration calorimetry). This work also probes dynamic modifications upon ligand binding, and our computational protocol could be generalized to situate the supramolecular forces ruling out the calixarene-assisted co-crystallization of proteins. [ABSTRACT FROM AUTHOR]

Depicting how biomolecules move and interact within their physiological environment is one of the hottest topics of structural biology. This Feature Article gives an overview of the most recent advances in Site-directed Spin Labeling coupled to Electron Paramagnetic Resonance spectroscopy (SDSL–EPR) to study biomolecules in living cells. The high sensitivity, the virtual absence of background, and the versatility of spin-labeling strategies make this approach one of the most promising techniques for the study of biomolecules in physiologically relevant environments. After presenting the milestones achieved in this field, we present a summary of the future goals and ambitions of this community. [ABSTRACT FROM AUTHOR]

Site-directed spin labeling (SDSL) combined with continuous wave electron paramagnetic resonance (cw EPR) spectroscopy is a powerful technique to reveal, at the local level, the dynamics of structural transitions in proteins. Here, we consider SDSL-EPR based on the selective grafting of a nitroxide on the protein under study, followed by X-band cw EPR analysis. To extract valuable quantitative information from SDSL-EPR spectra and thus give a reliable interpretation on biological system dynamics, a numerical simulation of the spectra is required. However, regardless of the numerical tool chosen to perform such simulations, the number of parameters is often too high to provide unambiguous results. In this study, we have chosen SimLabel to perform such simulations. SimLabel is a graphical user interface (GUI) of Matlab, using some functions of Easyspin. An exhaustive review of the parameters used in this GUI has enabled to define the adjustable parameters during the simulation fitting and to fix the others prior to the simulation fitting. Among them, some are set once and for all (gy, gz) and others are determined (Az, gx) thanks to a supplementary X-band spectrum recorded on a frozen solution. Finally, we propose guidelines to perform the simulation of X-band cw-EPR spectra of nitroxide labeled proteins at room temperature, with no need of uncommon higher frequency spectrometry and with the minimal number of variable parameters. [ABSTRACT FROM AUTHOR]

Lipoquinones are the topic of this review and are a class of hydrophobic lipid molecules with key biological functions that are linked to their structure, properties, and location within a biological membrane. Ubiquinones, plastoquinones, and menaquinones vary regarding their quinone headgroup, isoprenoid sidechain, properties, and biological functions, including the shuttling of electrons between membrane-bound protein complexes within the electron transport chain. Lipoquinones are highly hydrophobic molecules that are soluble in organic solvents and insoluble in aqueous solution, causing obstacles in water-based assays that measure their chemical properties, enzyme activities and effects on cell growth. Little is known about the location and ultimately movement of lipoquinones in the membrane, and these properties are topics described in this review. Computational studies are particularly abundant in the recent years in this area, and there is far less experimental evidence to verify the often conflicting interpretations and conclusions that result from computational studies of very different membrane model systems. Some recent experimental studies have described using truncated lipoquinone derivatives, such as ubiquinone-2 (UQ-2) and menaquinone-2 (MK-2), to investigate their conformation, their location in the membrane, and their biological function. Truncated lipoquinone derivatives are soluble in water-based assays, and hence can serve as excellent analogs for study even though they are more mobile in the membrane than the longer chain counterparts. In this review, we will discuss the properties, location in the membrane, and syntheses of three main classes of lipoquinones including truncated derivatives. Our goal is to highlight the importance of bridging the gap between experimental and computational methods and to incorporate properties-focused considerations when proposing future studies relating to the function of lipoquinones in membranes. [ABSTRACT FROM AUTHOR]

2-iminoacetate synthase ThiH is a radical S-adenosyl-L-methionine (SAM) L-tyrosine lyase and catalyzes the L-tyrosine Cα–Cβ bond break to produce dehydroglycine and p-cresol while the radical SAM L-tryptophan lyase NosL cleaves the L-tryptophan Cα–C bond to produce 3-methylindole-2-carboxylic acid. It has been difficult to understand the features that condition one C–C bond break over the other one because the two enzymes display significant primary structure similarities and presumably similar substrate-binding modes. Here, we report the crystal structure of L-tyrosine bound ThiH from Thermosinus carboxydivorans revealing an unusual protonation state of L-tyrosine upon binding. Structural comparison of ThiH with NosL and computational studies of the respective reactions they catalyze show that substrate activation is eased by tunneling effect and that subtle structural changes between the two enzymes affect, in particular, the hydrogen-atom abstraction by the 5´-deoxyadenosyl radical species, driving the difference in reaction specificity. ThiH is a radical SAM L-tyrosine lyase involved in the biosynthesis of the thiazole ring of vitamin B1. Here, the authors report the crystal structure of ThiH in complex with its L-tyrosine substrate, revealing an unexpected protonation state and tunneling effect that lowers the reaction energy barrier. [ABSTRACT FROM AUTHOR]

Time-resolved infrared (IR) spectroscopy is a widely used technique in the investigation of photoinduced reactions, given its capabilities of providing structural information about the presence of intermediates and the reaction mechanism. Despite the fact that it is used in several fields since the '80s, the communication between the different scientific communities (photochemists, photobiologists, etc.) has been to date quite limited. In some cases, this lack of communication happened—and still happens—even inside the same scientific community (for instance between specialists in ultrafast ps/fs IR and those in "fast" ns/µs/ms IR). Even more surprising is the difficulty of non-specialists to understand the potential of time-resolved IR spectroscopy, despite the fact that IR spectroscopy is normally taught to all chemistry and material science students, and to several biology and physics students. This tutorial review aims at helping to solve these issues, first by providing a comprehensive but reader-friendly overview of the different techniques, and second, by focusing on five "case studies" (from photobiology, gas-phase photocatalysis, photochemistry, semiconductors and metal-carbonyl complexes). We are confident that this approach can help the reader—whichever is its background—to understand the capabilities of time-resolved IR spectroscopy to study the mechanism of photoinduced reactions. [ABSTRACT FROM AUTHOR]

We herein report a general and efficient enantioselective C-H arylation of aryl bromides based on the use of BozPhos as the bisphosphine ligand and SP-NHC-Pd II as recoverable heterogeneous catalyst. By exploiting the "release and catch" mechanism of action of the catalytic system, we used BozPhos as a broadly applicable chiral ligand, furnishing high enantioselectivities across all types of examined substrates containing methyl, cyclopropyl and aryl C-H bonds. For each reaction, the reaction scope was investigated, giving rise to 30 enantioenriched products, obtained with high yields and enantioselectivities, and minimal palladium leaching. The developed catalytic system provides a more sustainable solution compared to homogeneous systems for the synthesis of high added-value chiral products through recycling of the precious metal., (© 2023 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

We highlight the reported developments of the palladium-catalyzed C–H activation and functionalization of the inactive/unreactive prochiral C(sp3)–H bonds of aliphatic and alicyclic compounds. There exist numerous classical methods for generating contiguous stereogenic centers in a compound with a high degree of stereocontrol. Along similar lines, the Pd(II)-catalyzed, directing group-aided functionalization of inactive prochiral/diastereotopic C(sp3)–H bonds have been exploited to accomplish the stereoselective construction of stereo-arrays in organic compounds. We present a concise discussion on how specific strategies consisting of Pd(II)-catalyzed, directing group-aided C(sp3)–H functionalization have been utilized to generate two or more stereogenic centers in aliphatic and alicyclic compounds. [ABSTRACT FROM AUTHOR]

Background: Gastric microbiota may be involved in gastric cancer. The relationship between gastrointestinal microbes and the risk of gastric cancer is unclear. This study aimed to explore the gastric and intestinal bacteria associated with gastritis and gastric precancerous lesions. We conducted a case-control study by performing 16S rRNA gene analysis of gastric biopsies, juices, and stool samples from 148 cases with gastritis or gastric precancerous lesions from Anhui and neighboring provinces, China. And we validated our findings in public datasets. Results: Analysis of microbial sequences revealed decreased bacterial alpha diversity in gastric bacteria during the progression of gastritis. Helicobacter pylori was the main contributor to the decreased microbial composition and diversity in the gastric mucosa and had little influence on the microbiota of gastric juice and feces. The gastric mucosal genera Gemella , Veillonella, Streptococcus, Actinobacillus , and Hemophilus had the higher degree of centrality across the progression of gastric precancerous lesions. And Acinetobacter may contribute to the occurrence of intraepithelial neoplasia. In addition, the microbial model of H. pylori -positive gastric biopsies and feces showed value in the prediction of gastric precancerous lesions. Conclusions: This study identified associations between gastric precancerous lesions and gastric microbiota, as well as the changes in intestinal microbiota, and explored their values in the prediction of gastric precancerous lesions. [ABSTRACT FROM AUTHOR]

The enantioselective functionalization of nonactivated enantiotopic secondary C−H bonds is one of the greatest challenges in transition‐metal‐catalyzed C−H activation proceeding by an inner‐sphere mechanism. Such reactions have remained elusive within the realm of Pd0 catalysis. Reported here is the unique reactivity profile of the IBiox ligand family in the Pd0‐catalyzed intramolecular arylation of such nonactivated secondary C−H bonds. Chiral C2‐symmetric IBiox ligands led to high enantioselectivities for a broad range of valuable indane products containing a tertiary stereocenter, as well as the arylation of secondary C−H bonds adjacent to amides. Depending on the amide substituents and upon control of reaction time, indanes containing labile tertiary stereocenters were also obtained with high enantioselectivities. Analysis of the steric maps of the IBiox ligands indicated that the level of enantioselectivity correlates with the difference between the two most occupied and the two less occupied space quadrants, and provided a blueprint for the design of even more efficient ligands. [ABSTRACT FROM AUTHOR]

Homogeneous catalytic reactions are typically controlled by the stereoelectronic nature of the ligand(s) that bind to the metal(s). The advantages of the so-called first coordination sphere effects have been used for the efficient synthesis of fine chemicals relevant for industrial and academic laboratories since more than half a century. Such level of catalyst control has significantly upgraded in the last few decades by mastering additional interactions beyond the first coordination sphere. These so-called second coordination sphere effects are mainly inspired by the action mode of nature's catalysts, enzymes, and, in general, rely on subtle hydrogen bonding for the exquisite control of activity and selectivity. In order to span the scope of this powerful strategy to challenges that cannot be solved purely by hydrogen bonding, a variety of less common interactions have been successfully introduced in the last few years for a fine chemical synthesis. This review covers the latest and most exciting developments of this newly flourishing area with a particular focus on highlighting how these types of interactions can be rationally implemented to control the reactivity in a remote fashion, which is far away from the active site similar to what enzymes also do. [ABSTRACT FROM AUTHOR]

We herein report amide directed enantioselective β‐C(sp3)−H borylation of unbiased methylene C−H bonds of acyclic amides enabled by iridium catalysis for the first time. The key to the success of this transformation relies on the careful selection of the combination of iridium precursor and chiral bidentate boryl ligands. A variety of functional groups are well‐tolerated, affording chiral β‐functionalized amides in good to excellent enantioselectivities. We also demonstrate the application of the current method by stereospecific conversion of C−B bond into other functionalities. [ABSTRACT FROM AUTHOR]

The stereoelectronic properties of a series of trifluoromethylated aromatic phosphines have been studied using different approaches. The σ‐donating capability has been evaluated by nuclear magnetic resonance (NMR) spectroscopy of the selenide derivatives and the protonated form of the different trifluoromethylated phosphines. The coupling constants between phosphorous and selenium (1JSeP) and phosphorous and hydrogen (1JHP) can be predicted by empirical equations and correlate the basicity of the phosphines with the number and relative position of trifluoromethyl groups. In contrast, the π‐acceptor character of the ligands has been evaluated by measuring the frequency of the CO vibration in the infrared (IR) spectra of the corresponding Vaska type iridium complexes ([IrCl(CO)(PAr3)2], PAr3=triarylphosphine). Moreover, the correlation between the electronic properties and the performance of these phosphines as ligands in the rhodium‐catalysed hydroformylation of 1‐octene has been established. Phosphines with the lowest basicity, that are those with the highest number of trifluoromethyl groups, gave rise to more active catalytic systems. [ABSTRACT FROM AUTHOR]

In the past few decades, processes that involve transition‐metal catalysis have represented a major part of the synthetic chemist′s toolbox. Recently, the interest has shifted from the well‐established cross‐coupling reactions to C−H bond functionalization, thus making it a current frontier of transition‐metal‐catalyzed reactions. Constant progress in this field has led to the discovery of enantioselective methods to generate and control various types of stereogenic elements, thereby demonstrating its high value to generate scalemic chiral molecules. The present review is dedicated to enantioselective Pd0‐catalyzed C−H activation, which may be considered as an evolution of Pd0‐catalyzed cross‐couplings, with a focus on the different chiral ligands and catalysts that enable these transformations. [ABSTRACT FROM AUTHOR]

The enantioselective desymmetrizing C−H activation of α‐gem‐dialkyl acyclic amides remains challenging because the availability of four chemically identical unbiased methylene C(sp3)−H bonds and increased rotational freedoms of the acyclic systems add tremendous difficulties for chemo‐ and stereocontrol. We have developed a method for the synthesis of acyclic aliphatic amides with α,β‐contiguous stereogenic centers via PdII‐catalyzed asymmetric arylation of unbiased methylene C(sp3)−H, in good yields and with high levels of enantio‐, chemo‐ and diastereoselectivity (up to >99 % ee and >20:1 d.r.). Successive application of this method enables the sequential arylation of the gem‐dialkyl groups with two different aryl iodides, giving a range of β‐Ar1‐β′‐Ar2‐aliphatic acyclic amides containing three contiguous stereogenic centers with excellent diastereoselectivity. [ABSTRACT FROM AUTHOR]

Enantioselective synthesis of tetrahydroisoquinolines bearing an all-carbon quaternary stereogenic center, was achieved via asymmetric C–H activation with high enantioselectivities (up to 93% ee). Fair substrate tolerance was indicated throughout the scope investigation and no evident loss of enantioselectivity was exhibited in late-stage derivatization. This study provides incentives for the construction of diverse chiral isoquinoline derivatives, which are prevalent among pharmaceuticals, natural products, etc. [ABSTRACT FROM AUTHOR]