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Retinal degeneration 3 (RD3) protein, a retinal guanylyl cyclase regulator, forms a monomeric and elongated four helix bundle
摘要： Retinal degeneration 3 (RD3) protein promotes accumulation of retinal membrane guanylyl cyclase (RetGC) in photoreceptor outer segment and suppresses RetGC activation by guanylyl cyclase activating proteins (GCAPs). Mutations truncating RD3 cause severe congenital blindness by preventing the inhibitory binding of RD3 to the cyclase. The high propensity of RD3 to aggregate in solution has prevented structural analysis. Here, we produced a highly soluble variant of human RD3 (residues 18–160) that is monomeric and can still bind and negatively regulate RetGC. The NMR solution structure of RD3 revealed an elongated backbone structure (70? long and 30? wide), consisting of a four helix bundle with a long unstructured loop between helices 1 and 2. The structure reveals that RD3 residues previously implicated in RetGC binding map to a localized and contiguous area on the structure, involving a loop between helices 2 and 3 and adjacent parts of helices 3 and 4. The NMR structure of RD3 was validated by mutagenesis. Introducing Trp85 or Phe29 to replace Cys or Leu, respectively, disrupts packing in the hydrophobic core and lowers RD3’s apparent affinity for RetGC1. Introducing a positive charge at the interface (Glu32 to Lys), also lowered the affinity. Conversely, introducing Val in place of Cys93 stabilized the hydrophobic core and increased the RD3 affinity for the cyclase. The NMR structure of RD3 presented here provides a structural basis for elucidating RD3/RetGC interactions relevant for normal vision or blindness.
关键词： phototransduction,retina,NMR spectroscopy,guanylate cyclase (guanylyl cyclase),retinal degeneration 3 (RD3),photoreceptor,blindness
更新于2025-09-23 15:22:29
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Dynamic Nuclear Polarization of Metal–Organic Frameworks Using Photoexcited Triplet Electrons
摘要： While dynamic nuclear polarization based on photoexcited triplet electrons (triplet-DNP) has the potential to hyperpolarize nuclear spins of target substrates in the low magnetic field at room temperature, there has been no triplet-DNP system offering structural rigidity and substrate accessibility. Here, we report the first example of triplet-DNP of nanoporous metal?organic frameworks. Accommodation of a carboxylate-modified pentacene derivative in a partially deuterated ZIF-8 (D-ZIF-8) results in a clear 1H NMR signal enhancement over thermal equilibrium.
关键词： dynamic nuclear polarization,photoexcited triplet electrons,metal?organic frameworks,NMR signal enhancement
更新于2025-09-23 15:21:21
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Structural, vibrational, spectroscopic, NMR and quantum chemical studies on fullerene and bromofullerenes
摘要： The most stable, optimized structures of fullerene (C60) and bromofullerenes (C60Br6) molecules were predicted by the density functional theory calculations using B3LYP method with 6311G(d,p) basis set. The obtained parameters were estimated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Bromofullerene (C60Br6) was architectured by directly bonding with bromine atom at C60 reactive sites. Theoretically calculated vibrational wavenumbers were assigned and compared. Ultraviolet-visible spectrum was mimicked by Polarizable Continuum model. The 13C NMR spectra were simulated by nuclear magnetic tensor GIAO for C60 and C60Br6 relative to tetramethyl silane. The molecular electrostatic potential surface was simulated. The transition between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) revealed different charge transfer possibilities which occur for the molecule and other related molecular properties were computed and tabulated. Natural bond orbital (NBO) analysis was carried out to image the charge transfer between the localized bonds and lone pairs of the electrons. The enhanced reactivity and peculiar energy gap by the substitution of bromine in fullerene pave way for designing the optoelectronic devices and bioactive molecules which will be useful in the field of sensors and carbon nano medicine.
关键词： HOMO,Fullerene,LUMO,NMR,Bromofullerene
更新于2025-09-23 15:21:21
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Multimodal Approach for Rationalization and Quantification of Structural Disorder in Transition Al 2 O 3
摘要： Transition aluminas form a basis of important catalytic and catalytic support materials due to their unique surface acidity, high temperature structural stability, and their viability for synthesis as high surface area materials. The origin of transition aluminas attractive properties has been extensively studied in the past 50+ years, but despite this effort, there are number of structural, electronic and surface properties that remain poorly understood. The poor understanding stems mostly from the inadequate crystallographic description of transition alumina polymorphs of γ-Al2O3, δ-Al2O3, θ-Al2O3 that evolve as a continuum of metastable structures. This work focuses on rationalization and quantification of structural disorder in Boehmite derived transition aluminas by using a suite of complementary imaging, spectroscopy and quantum calculation techniques. Based on aberration corrected STEM HAADF imaging, it will be shown that the individual polymorphs of δ?Al2O3 and θ-Al2O3 accommodate a significant degree of structural disorder, which leads to loss of crystallographic periodicity. The complexity of this disorder can be rationalized as an atomic scale intergrowth of closely related crystallographic variants. As a part of this work, we present a crystallographic approach based on real space interpretation of projected atomic potential that enabled us to unambiguously derive Al3+ coordination in δ-Al2O3 and θ-Al2O3 from a series of low-index STEM HAADF images. This work lead to a full crystallographic description of the crystallographic variants belonging to δ-Al2O3 and θ-Al2O3 family. To quantify the heterogeneous microstructure of transition aluminas on statistically relevant bases, we employed novel approaches for characterization of structural disorder using XRD and NMR techniques. XRD is one of the most employed methods for crystallographic bulk characterization, but historically it has not been successfully used on transition alumina. It will be shown that the crystallographic polymorphs and their structural disorder can be quantified with the use of recursive algorithms as implemented in DIFFAX and TOPAS XRD simulation packages. To further validate the quantification of structural disordered in transition Al2O3, we also employed complementary NMR spectroscopy, combined with DFT NMR simulation methods. As a part of this talk, we also discuss results from DFT energetic calculations explaining how energetic degeneracy between the number of crystallographic variants leads to structural disorder in transition aluminas.
关键词： DFT,transition aluminas,structural disorder,NMR,XRD,STEM HAADF imaging
更新于2025-09-23 15:21:21
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The role of ionic liquid breakdown in the electrochemical metallization of VO <sub/>2</sub> : An NMR study of gating mechanisms and VO <sub/>2</sub> reduction
摘要： Metallization of initially insulating VO2 via ionic liquid electrolytes, otherwise known as electrolyte gating, has recently been a topic of much interest for possible applications such as Mott transistors and memory devices. It is clear that the metallization takes place electrochemically and, in particular, there has previously been extensive evidence for the removal of small amounts of oxygen during ionic liquid gating. Hydrogen intercalation has also been proposed, but the source of the hydrogen has remained unclear. In this work, solid-state magic angle spinning NMR spectroscopy (1H, 2H, 17O and 51V) is used to investigate the thermal metal-insulator transition in VO2, before progressing to catalytically hydrogenated VO2 and electrochemically metallized VO2. In these experiments electrochemical metallization of bulk VO2 particles is shown to be associated with intercalation of hydrogen, the degree of which can be measured with quantitative 1H NMR spectroscopy. Possible sources of the hydrogen are explored, and by using a selectively deuterated ionic liquid, it is revealed that the hydrogenation is due to deprotonation of the ionic liquid; specifically, for the commonly used dialkyl-imidazolium based ionic liquids, it is the “carbene” proton which is responsible. Increasing the temperature of the electrochemistry is shown to increase the degree of hydrogenation, forming first a less hydrogenated metallic orthorhombic phase then a more hydrogenated insulating Curie-Weiss paramagnetic orthorhombic phase, both of which were also observed for catalytically hydrogenated VO2. The NMR results are supported by magnetic susceptibility measurements, which corroborate the degree of Pauli and Curie-Weiss paramagnetism. Finally, NMR spectroscopy is used to identify the presence of hydrogen in an electrolyte gated thin film of VO2, suggesting that electrolyte breakdown, proton intercalation and reactions with decomposition products within the electrolyte should not be ignored when interpreting the electronic and structural changes observed in electrochemical gating experiments.
关键词： metal-insulator transition,hydrogen intercalation,VO2,NMR spectroscopy,electrolyte gating,ionic liquid
更新于2025-09-23 15:21:21
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Unlocking a diazirine long-lived nuclear singlet state via photochemistry: NMR detection and lifetime of an unstabilized diazo-compound
摘要： Diazirines are important for photoaffinity labelling and their photoisomerization is relatively well known. This work shows how hyperpolarized NMR spectroscopy can be used to characterise an unstable diazo-compound formed via photoisomerization of a 15N2-labelled silyl-ether substituted diazirine. This diazirine is prepared in a nuclear spin singlet state via catalytic transfer of spin order from para-hydrogen. The active hyperpolarization catalyst is characterised to provide insight into the mechanism. The photochemical isomerisation of the diazirine into the diazo-analogue allows the NMR invisible nuclear singlet state of the parent compound to be probed. The identity of the diazo-species is confirmed by trapping with N-phenyl maleimide via a cycloaddition reaction to afford bicyclic pyrazolines that also show singlet state character. The presence of singlet states in the diazirine and the diazo-compound are validated by comparison of experimental nutation behaviour with theoretical simulation. The magnetic state lifetime of the diazo-compound is determined as 12 ± 1 s in CD3OD solution at room temperature whereas its chemical lifetime is measured as 100 ± 5 s by related hyperpolarized NMR studies. Indirect evidence for the generation of the photoproduct para-N2 is presented.
关键词： SABRE-SHEATH,photochemistry,para-hydrogen,diazirine,photoisomerization,nuclear spin singlet state,diazo-compound,hyperpolarized NMR spectroscopy
更新于2025-09-23 15:21:21
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Effect on Local Structure and Phase Transition of Perovskite-Type [N(CH3)4]2Zn1-xCuxBr4 (x?=?0, 0.5, 0.7, and 1) Crystals with the Various Doping of Cu2+ Ions
摘要： This study focused on how the local structures in pure [N(CH3)4]2ZnBr4 crystal are affected by the partial replacement of Zn2+ ions with Cu2+ ions. The structures and phase transition temperatures TC of perovskite-type [N(CH3)4]2Zn1-xCuxBr4 (x = 0, 0.5, 0.7, and 1) mixed crystals were almost unchanged by the partial doping of Cu2+ ions. The environments for the local structures of [N(CH3)4]2Zn1-xCuxBr4 mixed systems were studied according to differences in the chemical shifts of the 1H magic angle spinning (MAS) NMR, 13C cross-polarization (CP)/MAS NMR, and 14N NMR spectra. The 1H and 13C NMR results showed that the local environments of 1H and 13C nuclei near TC are not affected by substituting Zn2+ ions with Cu2+ ions, whereas the 14N NMR results showed that the local environment is affected near TC. Consequently, the main indicators of the phase transition in [N(CH3)4]2Zn1-xCuxBr4 are related to the ferroelastic characteristics with different orientations.
关键词： phase transition,ferroelastic characteristics,NMR spectroscopy,perovskite structures,Metal-organic hybrids
更新于2025-09-23 15:21:01
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Understanding the Microscopic Behavior of Binary Mixtures of Ionic Liquids Through Various Spectroscopic Techniques
摘要： In recent times it has been shown that certain binary mixture of pure ionic liquids having appropriate chemical composition can behave like a new chemical entity. However, current knowledge about the microscopic behavior of these interesting systems is rather limited. The present study is undertaken with an objective to understand the microscopic behavior in terms of intermolecular interaction, structure and dynamics of these systems. In the present study, few (IL+IL) mixtures are chosen with a common cation and a variation of anion. The investigations are also carried out by taking individual pure ILs so that the difference in behavior between pure IL and (IL+IL) mixtures are understood. Initially the systems have been investigated by studying the thermophysical properties of the concerned mixtures. Synergistic effect between combining pure ILs through photochromism has also been studied. These mixtures have been investigated further through steady state and time resolved fluorescence spectroscopy, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and fluorescence correlation spectroscopy (FCS). Interestingly, time-resolved fluorescence data also pointed out that (IL+IL) mixtures are not only spatially heterogeneous but they are dynamically heterogeneous too. EPR measurements have suggested that the micro-polarity (ET(30)) of (IL+IL) mixture is close to aliphatic polyalcohol. Measurements of translational diffusion coefficients of the diffusing species through NMR and FCS studies have provided idea about the nano-structural organization within (IL+IL) binary mixtures. The analysis of data essentially reveals that the mixtures of ILs that are used in the current study do not behave like a non-ideal solution. The behavior of the IL mixtures is observed to be more like quasi-ideal type.
关键词： thermophysical properties,binary mixtures,EPR,FCS,fluorescence spectroscopy,NMR,Ionic liquids,photochromism,spectroscopic techniques
更新于2025-09-23 15:21:01
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Investigating the Photochemistry of Spiropyran Metal Complexes with Online LED-NMR
摘要： As one of the best studied photoswitches, spiropyrans (SPs) have attracted significant interest in the scientific community. Among the many stimuli to alter the isomerization into the merocyanine (MC) isomer, such as temperature, pH, solvent polarity, redox potential, or mechanical force, the ability of the MC form to act as a ligand site for metal complexation has recently raised new attention. We herein synthesize hitherto undescribed coordination compounds of 8-methoxy-1′,3′,3′-trimethyl-6-nitrospiro-[chromene-2,2′-indoline] with s-block ([Ca(MC)4](ClO4)2), d-block ([Zn(MC)2(MeCN)2](ClO4)2, [Ni(MC)2(MeCN)2](ClO4)2), as well as f-block ([La(NO3)3(MC)2]) metals. All complexes are structurally described by X-ray crystallography and systematically investigated in solution via Job’s method of continuous variations (Job plots), as well as online NMR spectroscopic kinetic experiments with in situ irradiation of the analyte solution inside the NMR spectrometer (LED-NMR). We can unambiguously identify the photoresponsive nature of the complexes in solution, which is a crucial step toward the application of these promising molecules in material science.
关键词： photochemistry,LED-NMR,metal complexes,X-ray crystallography,spiropyrans
更新于2025-09-23 15:19:57
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Structural, spectral and nonlinear optical analysis of Bis(2-methyllactato)borate tetrahydrate: a new nonlinear optical crystal for laser applications
摘要： A new nonlinear optical crystal, ‘Bis(2-methyllactato)borate tetrahydrate’ (BMBT) has been crystallized by slowly evaporating the solvent. It crystallizes in the space group P21212. Sharp peaks present in powder XRD profile reveals the good crystallinity. Its transmission bandwidth (220 nm – 1100 nm) suggest that it can be used to generate UV radiation upto 220 nm and also in optoelectronic applications. Vibrations of functional groups (B-O, CH3, CO) associated with the crystal structure have been identified through FTIR and FT-Raman spectral studies. OH stretching vibrations have been observed near 3000 cm-1 clearly endorses the existence of water molecule in the BMBT structure. The chemical shifts observed in 1H and 13C NMR spectral results establishes the molecular structure of BMBT crystal. Second harmonic generation (SHG) efficiency is obtained as 0.9 times of KDP. The third order nonlinear susceptibility (χ3), nonlinear refractive index (n2) and nonlinear absorption co-efficient (β) were found using Z-scan technique. χ3 of title crystal is found to be 4.16 X10-5 esu. The existence of SHG efficiency and the enhanced χ3 value are due to the hydrogen bonded intermolecular interactions present in the BMBT crystal structure. The observed results suggest that BMBT can be used in Q-switching, mode locking and optical sensors like night vision devices.
关键词： Crystal structure,Z-scan analysis,crystal growth,NMR spectroscopy,second harmonic generation
更新于2025-09-23 15:19:57