Isotropic Shifts Research Articles

Mononuclear/Binuclear [VIVO]/[VVO2] Complexes Derived from 1,3-Diaminoguanidine and Their Catalytic Application for the Oxidation of Benzoin via Oxygen Atom Transfer.

Ligands H4sal-dag (I) and H4Brsal-dag (II) derived from 1,3-diaminoguanidine and salicylaldehyde or 5-bromosalicylaldehyde react with one or 2 mol equivalent of vanadium precursor to give two different series of vanadium complexes. Thus, complexes [VIVO(H2sal-dag) (H2O)] (1) and [VIVO(H2Brsal-dag) (H2O)] (2) were isolated by the reaction of an equimolar ratio of these ligands with [VIVO(acac)2] in MeOH. In the presence of K+/Cs+ ion and using aerially oxidized [VIVO(acac)2], the above reaction gave complexes [K(H2O){VVO2(H2sal-dag)}]2 (3), [Cs(H2O){VVO2(H2sal-dag)}]2 (4), [K(H2O){VO2(H2Brsal-dag)}]2 (5), and [Cs(H2O){VVO2(H2Brsal-dag)}]2 (6), which could also be isolated by direct aerial oxidation of complexes 1 and 2 in MeOH in the presence of K+/Cs+ ion. Complexes [(H2O)VIVO(Hsal-dag)VVO2] (7) and [(H2O)VIVO(HBrsal-dag)VVO2] (8) were isolated upon increasing the ligand-to-vanadium precursor molar ratio to 1:2 under an air atmosphere. When I and II were reacted with aerially oxidized [VIVO(acac)2] in a 1:2 molar ratio in MeOH in the presence of K+/Cs+ ion, they formed [K(H2O)5{(VVO2)2(Hsal-dag)}]2 (9), [Cs(H2O)2{(VVO2)2(Hsal-dag)}]2 (10), [K2(H2O)4{(VVO2)2(Brsal-dag)}]2 (11), and [Cs2(H2O)4{(VVO2)2(Brsal-dag)}]2 (12). The structures of complexes 3, 4, 5, and 9 determined by single-crystal X-ray diffraction study confirm the mono-, bi-, tri-, and tetra-anionic behaviors of the ligands. All complexes were found to be an effective catalyst for the oxidation of benzoin to benzil via oxygen atom transfer (OAT) between DMSO and benzoin. Under aerobic condition, this oxidation also proceeds effectively in the absence of DMSO. Electron paramagnetic resonance and 51V NMR studies demonstrated the active role of a stable V(IV) intermediate during OAT between DMSO and benzoin.

Quantum chemical study of effect on adsorption properties of antituberculosis drug N-Cyclopentylidenepyridine-4-carbohydrazide interaction with CNT(C56H16)

Tuberculosis is the most common disease that affects the lungs in humans. The electronic structural and chemical properties of the antituberculosis drug N-Cyclopentylidenepyridine-4-carbohydrazide have already been investigated. The adsorption properties of the antituberculosis drug N-Cyclopentylidenepyridine-4-carbohydrazide (CPPC) with single-wall carbon nanotube CNT(C56H16) are investigated using a combination of DFT/B3LYP method and 6-31G(d,p) basis set in both gaseous and water solvent, and calculated results are compared. By comparing CNT's corresponding optimized bond lengths with CNT@CPPC, the effect of CPPC adsorption on optimized drug delivery system parameters has been discussed. Based on topological parameters, the nonbonding interaction between CNT and CPPC drug is discussed using QTAIM analysis at BCP in both gas and water solvent. The thermodynamical stability of the CPPC@CNT adsorption process is also calculated, showing the adsorption of CPPC with CNT favors in both media. Natural bond analysis (NBO) was used to investigate the IR spectra, and the effect of charge transfer from CPPC to CNT in CNT@CPPC in both media provides information about how polarity changes from gas to water solvent. Because drug delivery action is done in blood plasma, the UV–Vis spectra of CNT are compared to CNT@CPPC in water solvent, providing insight into the adsorption of CPPC drug by CNT. We have compared the chemical shift isotropic (CS1) and chemical shift anisotropic (CSA) of CNT, CPPC, and CNT@CPPC to determine the change in electron density.

Theoretical and Experimental Study on Molecular Docking, Spectral and Electronic Properties of N,N-Bis (Salysylaldehyde-2,3-Diamino-1-Propanol) Nanostructure

In this study, theoretical and experimental properties (Structural, Spectral and Electronic Properties) and molecular docking of N,N- bis (salysylaldehyde-2,3- Diamino-1-propanol) molecule were studied. Timedependent density functional theory (TDDFT) and density functional theory (DFT) are employed for the theoritcal calculation. The composite's spectroscopic surveys were conducted using Proton nuclear magnetic resonance, FT-IR and UV/Vis spectroscopy techniques. The 1H NMR spectra for proton nuclear magnetic resonance have been examined with DMSO4 solvent. The FT-IR spectrum in rigid situation has been calculated to be between 4000-400 cm-1. The absorption spectra intensity of the composite with ethanol has been calculated to be between 200 and 800 nm. Scanning electron microscope (SEM) image has been study. Results demonstrated that the compound scanning electron microscopy image resembled a sphericals with particle size of 50 nm. The data structure, vibrational central modes, UV/V spectrum with 1H NMR isotropic chemical shifts of this molecule in the ground state were assessed utilizing the theory of functional density (thus DFT) and the B3LYP/6- 311G(d,p) basis group. The energies of reorganization for the hole and the electron have also been calculated. Finally, the assessment between the data of experiment and the results that have been calculated showed a good agreement. The inhibitory potential of the investigated compound was assessed against the protein PBP1 bacteria in a molecular docking. The chemical's carbonyl group was demonstrated to show a substantial role in antibacterial application; out of seven contacts, the carbonyl group made five bonds with the bacteria's main protein (Van der Waals bond and four good hydrogen bonds). This high bind energy was computed (-6.9 kcal/mol) indicating considerable antibacterial action.

Glycan Conformation in the Heavily Glycosylated Protein, CEACAM1.

Glycans attached to glycoproteins can contribute to stability, mediate interactions with other proteins, and initiate signal transduction. Glycan conformation, which is critical to these processes, is highly variable and often depicted as sampling a multitude of conformers. These conformers can be generated by molecular dynamics simulations, and more inclusively by accelerated molecular dynamics, as well as other extended sampling methods. However, experimental assessments of the contribution that various conformers make to a native ensemble are rare. Here, we use long-range pseudo-contact shifts (PCSs) of NMR resonances from an isotopically labeled glycoprotein to identify preferred conformations of its glycans. The N-terminal domain from human Carcinoembryonic Antigen Cell Adhesion Molecule 1, hCEACAM1-Ig1, was used as the model glycoprotein in this study. It has been engineered to include a lanthanide-ion-binding loop that generates PCSs, as well as a homogeneous set of three 13C-labeled N-glycans. Analysis of the PCSs indicates that preferred glycan conformers have extensive contacts with the protein surface. Factors leading to this preference appear to include interactions between N-acetyl methyls of GlcNAc residues and hydrophobic surface pockets on the protein surface.

Quantum chemical, spectroscopic and molecular docking investigations of potential pulmonary fibrosis drug methyl 2-chloro 4-iodonicotinate.

In this work, the methyl 2-chloro 4-iodonicotinate (MCIN) was investigated to study the structural, spectroscopic and electronic properties using density functional theory (DFT) quantum chemical calculations. The most stable structure of MCIN was optimized by DFT/B3LYP method with a LanLD2Z basis set. The optimized parameters and vibrational wavenumbers were determined. The vibrational task of the molecule was done by potential energy distribution calculations. The 13 C NMR spectrum of the MCIN molecule was simulated by the Gauge-Invariant-Atomic Orbital method using a dimethyl sulfoxide solution and the isotropic chemical shift values of the molecule were calculated and observed. Ultraviolet-visible spectra were simulated and observed. The pharmaceutical activity was predicted using frontier molecular orbital and natural bond orbital analysis. The reactive sites of the MCIN molecule were determined using Mulliken atomic charge distribution, molecular electrostatic potential surface and the local reactivity analysis. The molecular docking analysis confirms that the title molecule can be used in drug design for the treatment of pulmonary fibrosis.

Nanobody GPS by PCS: An Efficient New NMR Analysis Method for G Protein Coupled Receptors and Other Large Proteins.

NMR chemical shift changes can report on the functional dynamics of biomacromolecules in solution with sizes >1 MDa. However, their interpretation requires chemical shift assignments to individual nuclei, which for large molecules often can only be obtained by tedious point mutations that may interfere with function. We present here an efficient pseudocontact shift NMR method to assign biomacromolecules using bound antibodies tagged with lanthanoid DOTA chelators. The stability of the antibody allows positioning the DOTA tag at many surface sites, providing triangulation of the macromolecule nuclei at distances >60 Å. The method provides complete assignments of valine and tyrosine 1H-15N resonances of the β1-adrenergic receptor in various functional forms. The detected chemical shift changes reveal strong forces exerted onto the backbone of transmembrane helix 3 during signal transmission, which are absorbed by its electronic structure. The assignment method is applicable to any soluble biomacromolecule for which suitable complementary binders exist.

A flow electrochemistry-enabled synthesis of 2-substituted N-(methyl-d)piperidines.

A synthesis of N-monodeuteriomethyl-2-substituted piperidines is described. An efficient and readily scalable anodic methoxylation of N-formylpiperidine in an undivided microfluidic electrolysis cell delivers methoxylated piperidine 3, which is a precursor to a N-formyliminium ion and enables C-nucleophiles to be introduced at the 2-position. The isotopically labelled N-deuteriomethyl group is installed using the Eschweiler-Clarke reaction with formic acid-d2 and unlabelled formaldehyde. Monodeuterated N-methyl groups in these molecular systems possess small isotropic proton chemical shift differences important in the investigation of molecules that are able to support long-lived nuclear spin states in solution nuclear magnetic resonance.

Rational Design of Iron Spin-Crossover Complexes Using Heteroscorpionate Chelates.

The optical, structural, and magnetic properties of iron(II,III) sandwich complexes, Fe(Tp')2n+ (Tp' = bis(3,5-dimethylpyrazolyl)benzotriazolylborate), are described. The intensely colored FeII(Tp')2 (orange) and FeIII(Tp')2+ (purple) show strong MLCT bands. Geometric isomerism for M(Tp')2 is established crystallographically in the racemate of chiral cis-Fe(Tp')2. For the first time, paramagnetic 11B NMR describes solution-phase low-spin (LS, S = 0) to high-spin (HS, S = 2) crossover behavior in Fe(Tp')2. Thermochemical parameters for solution-phase SCO of Fe(Tp')2 demonstrate the endothermic LS to HS conversion and entropic preference of the HS state. Entropy changes for both Fe(Tp')2 isomers are significantly larger than for the majority of iron scorpionate SCO systems. Solid-state magnetic and thermochemical measurements show cis-Fe(Tp')2 to be thermally stable up to 520 K, allowing experimental investigation of a solid-state SCO magnetic hysteresis of over 45 K. A large solution vs solid-state SCO difference was observed: cis-Fe(Tp')2 shows Tc ≈ 270 K (solution) and Tc ≈ 385 K (solid), with the remarkably wide ΔTc ≈ 115 K; trans-Fe(Tp')2 shows Tc ≈ 278 K (solution) and Tc ≈ 372 K (solid). Solid-state Tc values are among the highest seen for iron(II) molecular systems. The large solution/solid ΔTc difference is explained by "anchoring" intermolecular interactions in the solid state that prevent thermal expansion of the LS iron(II) coordination sphere in its transition to the HS state. DFT calculations, validated against LS cis-Fe(Tp')2 crystallography and LS to HS SCO thermochemical parameters, demonstrate the role the benzotriazole rings play in its structural and optical properties. The Lewis basicity of M(Tp')2 is shown with the structural characterization of the air-stable tin(II) adduct [cis-Fe(Tp')2-SnCl2]; tin(II) coordination does not alter the iron(II) spin state. The Tp' chelate adds functionality (asymmetry, chirality, chemical reactivity) to the array of iron SCO materials for potential incorporation into nanoscale magnetic switches and spintronic devices.

Structure Determination of Binuclear Triple-Decker Phthalocyaninato Complexes by NMR via Paramagnetic Shifts Analysis Using Symmetry Peculiarities.

The detailed knowledge about the structure of multinuclear paramagnetic lanthanide complexes for the targeted design of these compounds with special magnetic, sensory, optical and electronic properties is a very important task. At the same time, establishing the structure of such multinuclear paramagnetic lanthanide complexes in solution, using NMR is a difficult task, since several paramagnetic centers act simultaneously on the resulting chemical shift of a particular nucleus. In this paper, we have demonstrated the possibility of molecular structure determination in solution on the example of binuclear triple-decker lanthanide(III) complexes with tetra-15-crown-5-phthalocyanine Ln2[(15C5)4Pc]3 {where Ln = Tb (1) and Dy (2)} by quantitative analysis of the pseudo-contact lanthanide-induced shifts (LIS). The symmetry of complexes was used for the simplification of the calculation of pseudo-contact shifts on the base of the expression for the magnetic susceptibility tensor in the arbitrary oriented magnetic axis system. Good agreement between the calculated and experimental shifts in the 1H NMR spectra indicates the similarity of the structure for the complexes 1 and 2 in solution of CDCl3 and the structure in the crystalline phase, found from the data of the X-ray structural study of the similar complex Lu2[(15C5)4Pc]3. The described approach can be useful for LIS analysis of other polynuclear symmetric lanthanide complexes.

Molecular Structure of Cu(II)-Bound Amyloid-β Monomer Implicated in Inhibition of Peptide Self-Assembly in Alzheimer’s Disease

Metal ions, such as copper and zinc ions, have been shown to strongly modulate the self-assembly of the amyloid-β (Aβ) peptide into insoluble fibrils, and elevated concentrations of metal ions have been found in amyloid plaques of Alzheimer's patients. Among the physiological transition metal ions, Cu(II) ions play an outstanding role since they can trigger production of neurotoxic reactive oxygen species. In contrast, structural insights into Cu(II) coordination of Aβ have been challenging due to the paramagnetic nature of Cu(II). Here, we employed specifically tailored paramagnetic NMR experiments to determine NMR structures of Cu(II) bound to monomeric Aβ. We found that monomeric Aβ binds Cu(II) in the N-terminus and combined with molecular dynamics simulations, we could identify two prevalent coordination modes of Cu(II). For these, we report here the NMR structures of the Cu(II)-bound Aβ complex, exhibiting heavy backbone RMSD values of 1.9 and 2.1 Å, respectively. Further, applying aggregation kinetics assays, we identified the specific effect of Cu(II) binding on the Aβ nucleation process. Our results show that Cu(II) efficiently retards Aβ fibrillization by predominately reducing the rate of fibril-end elongation at substoichiometric ratios. A detailed kinetic analysis suggests that this specific effect results in enhanced Aβ oligomer generation promoted by Cu(II). These results can quantitatively be understood by Cu(II) interaction with the Aβ monomer, forming an aggregation inert complex. In fact, this mechanism is strikingly similar to other transition metal ions, suggesting a common mechanism of action of retarding Aβ self-assembly, where the metal ion binding to monomeric Aβ is a key determinant.

Sensitization Pathways in NIR-Emitting Yb(III) Complexes Bearing 0, +1, +2, or +3 Charges.

Yb(III) complexes of macrocyclic ligands based on 1,4,7,10-tetraazacyclododecane were synthesized. The ligands carried a carbostyril chromophore for Yb(III) sensitization, and carboxylate or carbamide donors for metal binding, forming complexes of 0, +1, +2, or +3 overall charge. The coordination geometry was little affected by the replacement of carboxylates with amides, as shown by paramagnetic 1H NMR spectroscopy. The Yb(III)/Yb(II) reduction potentials were dependent on the nature of the metal binding site, and the more positively charged complexes were easier to reduce. Carbostyril excitation resulted in Yb(III) luminescence in every complex. The residual carbostyril fluorescence quantum yields were smaller in complexes containing more reducible Yb(III) centers decreasing from 5.9% for uncharged complexes to 3.1-4.4% in +3 charged species, suggesting photoinduced electron transfer (PeT) from the antenna to the Yb(III). The relative Yb(III) luminescence quantum yields were identical within the experimental error, except for the +3 charged complex with fully methylated coordinating amides, which was the most intense Yb(III) emitter of the series in water. Quenching of the Yb(III) excited state by NH vibrations proved to limit Yb(III) emission. No clear improvement of the Yb(III) sensitization efficiency was shown upon faster PeT. This result can be explained by the concomitant sensitization of Yb(III) by phonon-assisted energy transfer (PAEnT) from the antenna triplet excited state, which was completely quenched in all of the Yb complexes. Depopulation of the triplet by PeT quenching of the donor singlet excited state would be compensated by the sensitizing nature of the PeT pathway, thus resulting in a constant overall sensitization efficiency across the series.

Characterization of the Binary Nitrides VN and ScN by Solid‐State NMR Spectroscopy

AbstractNMR spectra of polycrystalline samples of the binary nitrides ScN and VN were acquired under magic‐angle spinning. The observed nuclides 45Sc, 51V and 14N are all quadrupolar nuclei with a spin . However, due to the high symmetry of their rock‐salt type structures, the spectra of the nitrides do not exhibit effects of quadrupolar or other anisotropic interactions of significant magnitude. This allows a relatively straightforward evaluation of the acquired spectra, leading to isotropic chemical shift values (δiso) of −213 ppm (51VN), 378 ppm (V14N), 290 ppm (45ScN) and 442 ppm (Sc14N) against commonly used reference standards. In the wider context of 14N‐NMR of binary nitrides, it is shown that the distance of nitrogen to the nearest neighbour cation can be correlated to the observed chemical shift.

Al27 NMR insight into the phase transition in BaFe2Al9

We have applied $^{27}\mathrm{Al}$ nuclear magnetic resonance (NMR) spectroscopy to investigate the iron-based aluminide of $\mathrm{Ba}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{9}$. This material has been a subject of current interest due to indications of charge density wave behavior below the transition temperature ${T}_{C}\ensuremath{\simeq}100$ K. Two sets of the $^{27}\mathrm{Al}$ NMR resonance lines that are associated with two nonequivalent crystallographic aluminum sites have been well resolved. We have discussed the obtained electric field gradient and anisotropic Knight shift for each individual aluminum site, revealing the strong $ab$ plane bonding configuration for the structural properties of $\mathrm{Ba}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{9}$. Pronounced features in the isotropic Knight shift and nuclear spin-lattice relaxation rate have been observed in the vicinity of ${T}_{C}$. Furthermore, the detailed $^{27}\mathrm{Al}$ NMR analyses have provided evidence for the decrease of the electronic density of states upon lowering temperature below ${T}_{C}$.

Measuring Local Electrostatic Potentials Around Nucleic Acids by Paramagnetic NMR Spectroscopy.

Electrostatic potentials around macromolecules in the presence of mobile charges are difficult to assess especially for highly charged systems. Here, we report measurements of local electrostatic potentials around DNA by paramagnetic NMR. Through quantitative analysis of NMR paramagnetic relaxation enhancement arising from positively charged or neutral paramagnetic cosolutes, we were able to determine local electrostatic potentials around 1H nuclei at >100 sites in major and minor grooves of 13C,15N-labeled 15-bp DNA at 100 mM NaCl. Our experimental electrostatic potential data directly confirmed the Coulombic end effects of DNA. The effective near-surface electrostatic potentials from the NMR data were in good agreement with the theoretical predictions with the Poisson-Boltzmann equation. This NMR method allows for unprecedented experimental investigations into the electrostatic properties of nucleic acids.

Supramolecular architecture and SHG activity of organic crystals formed between the amidinothiourea and nicotinic acid

The single crystals of [1-(diaminomethylene)thiouron-1-ium] pyridine-3-carboxylate were grown using a solution growth technique. Depending on the concentration of the 1: 1 amidinothiourea: nicotinic acid solution, two different forms of 1: 1 crystal (orthorhombic non-centrosymmetric, P212121,(1), and monoclinic centrosymmetric, C2/c, (2)) were obtained. These phases differ in ordering, the orthorhombic phase is ordered, and in the monoclinic phase the 1-(diamino-methylene)-thiouron-1-ium cation is disordered and has two non-equivalent orientations with occupations of around 0.80 and 0.20. This ordering/disordering is due to the rate of crystallization: slow crystallization from a dilute solution leads to an ordered orthorhombic phase and quick crystallization from a saturated solution leads to a disordered monoclinic phase. Multiple recrystallizations of 1 and 2 from heavy water gives deuterated analogs 1d and 2d The conformation of the 1-(diaminomethylene)thiouron-1-ium cation in both phases is very similar and slightly non-planar. In the orthorhombic phase the plane of the carboxylate group is more twisted in relation to the plane of the pyridine ring than in the monoclinic phase. The oppositely charged components of the crystals, i.e., 1-(diaminomethylene)thiouron-1-ium cations and pyridine-3-carboxylate anions interact each other forming three-dimensional supramolecular architecture. Both compounds were also characterized by IR and Raman spectroscopy. Assignment of the vibrational bands were supported by the DFT calculations and the isotropic frequency shift. The SHG efficiency of the powdered orthorhombic phase relative to potassium dihydrogen phosphate (KDP) was found to be 1.70.

Ligand Elucidation of Dissolved Transition Metal Ions in Pristine and Degraded Electrolytes in Li-Ion Batteries

During operation of a Li-ion battery, layered transition metal oxides release metal ions into the electrolyte. In addition to capacity loss, dissolved metal ions are mobile in the electrolyte and can deposit at the anode, enhancing Faradaic losses and posing the risk of dendrite formation.[1] In the electrolyte solution, transition metal ions are characterized mainly by their oxidation state and complexation behavior, which dictate the transport through the electrolyte. Additionally, mechanistic insights, indirect information about electrolyte degradation, and design of counter-measures might be extracted thereof. However, particularly the coordination sphere is difficult to access, due to inherently low concentrations and scarcity of suitable analytics.In this work, the coordination sphere of dissolved transition metal ions is selectively probed by pulse Electron Paramagnetic Resonance (pEPR). pEPR selectively addresses isolated paramagnetic ions, masking analytical interference from other species in the battery. Because of its known impact on capacity fade, firstly Mn2+ is analyzed in premixed pristine and degraded electrolyte solutions. Carbonates with high dielectric constants such as ethylene carbonate (EC) are the dominant ligands, accompanied by electrolyte salt anions for charge compensation. If present, trace amounts of electrolyte degradation products such as fluorophosphates selectively form the first coordination sphere. The results from pEPR measurements, that have to be performed on frozen solutions at cryogenic temperatures, agree with paramagnetic NMR results at ambient temperatures. Furthermore, samples from batteries operating with vanadium-based cathodes were investigated. Depending on the storage conditions, V4+ ligands predominantly consist of decomposition products from the electrolyte solvent ethylene carbonate (e.g. ethylene glycol anions) or electrolyte salt LiPF6 (fluorophosphates).[2,3] [1] C. Zhan, T. Wu, J. Lu, K. Amine, Energy Environ. Sci. 2018, 11, 243–257.[2] C. Szczuka, R.-A. Eichel, J. Granwehr, ACS Appl. Energy Mater. 2022, 5, 449–460.[3] C. Szczuka, P. Jakes, R.-A. Eichel, J. Granwehr, Adv. Energy Sustain. Res. 2021, 2, 2100121.

Solution Structure of a Lanthanide-binding DNA Aptamer Determined Using High Quality pseudocontact shift restraints.

In this contribution we report the high-resolution NMR structure of a recently identified lanthanide-binding aptamer (LnA). We demonstrate that the rigid lanthanide binding by LnA allows for the measurement of anisotropic paramagnetic NMR restraints which to date remain largely inaccessible for nucleic acids. One type of such restraints - pseudocontact shifts (PCS) induced by four different paramagnetic lanthanides - was extensively used throughout the current structure determination study and the measured PCS turned out to be exceptionally well reproduced by the final aptamer structure. This finding opens the perspective for a broader application of paramagnetic effects in NMR studies of nucleic acids through the transplantation of the binding site found in LnA into other DNA/RNA systems.

NMR Crystallographic Approach to Study the Variation of the Dynamics of Quinine and Its Quasienantiomer Quinidine

The structure and dynamics of quinine and its quasienantiomer quinidine were studied at the atomic resolution by measuring the chemical shift anisotropy (CSA) tensor and site-specific spin–lattice relaxation time. For quinine, there are three crystallographically independent molecules “a”, “b”, and “c” in an asymmetric unit since its 13C CP-MAS SSNMR spectrum features three distinct resonance peaks for certain carbon nuclei. The 13C assignments are fulfilled by DFT calculations. The experimental 13C isotropic chemical shifts well match the calculated values. These variations of isotropic chemical shift for three independent molecules are also observed by two-dimensional 13C–1H heteronuclear correlation spectroscopy (HETCOR) of quinine. The spin–lattice relaxation time, and the principal components of CSA parameters are also varied substantially for certain carbon nuclei of “a”, “b”, and “c” molecules. For quinidine, its 13C CP-MAS SSNMR spectrum is remarkably different from that of quinine despite, their almost identical solution NMR spectra. Furthermore, the remarkable change in the structure and dynamics of quasienantiomers are also observed including the steric effect of the substituent vinyl group, the variation of helical motifs, and the variation of the strength of the intermolecular hydrogen bonds. The variation of the structure and dynamics of quasienantiomers are thoroughly studied by solid-state NMR measurements. These types of studies will enrich the field of NMR crystallography.

Combined Effect of Platelet-Rich Fibrin Matrix (PRFM) and Demineralized Freeze-Dried Bone Allograft (DFDBA) in Immediate Implant Placement: A Single-Arm Clinical Trial

Introduction Placement of immediate implants in contrast to delayed implant placement may be favorable. The factors contributing to this are shortened overall treatment time, aid in ideal orientation andfixture placement, bone preservation following extraction, and achieving optimal aesthetics involving soft tissue. However,the gap distance between the surface of the implant and the buccal bony wall during implant placement is critical for subsequent bone healing in a fresh extraction socket. Considering that as the gap broadens, the amount of bone-to-implant contact (BIC) decreases, causing an apical shift of the highest bone-implant contact. Incorporating a bone substitute material (BSM) within the fixture-socket gap preserves alveolar ridge volume by minimizing socket remodeling and encouraging de-novo bone formation. Aim and objectives To evaluate the efficacy of platelet-rich fibrin matrix (PRFM) and demineralized freeze-dried bone allograft (DFDBA) in fresh extraction socket with simultaneous implant placement. Methods Implants were immediately placed in 12 patients following a two-stage submerged protocol. The combination of PRFM and DFDBA was used to fill the gap between the implant body and the surrounding socket wall. The final restoration was placed after 3 months following implant placement. The full mouth plaque, gingival bleeding index, and gingival esthetics scores were assessed at baseline, 3, and 6 months. The crestal changes were evaluated using intraoral periapical radiographs (IOPA) at baseline, 3, and 6 months. Cone beam computed tomography (CBCT) images were obtained at baseline and 6 months after implant loading to analyze the buccolingual changes. Results At 6 months follow-up, the coronal bone remodeling detected on CBCT revealed a minimal (0.1 mm) narrowing of the alveolar ridge in a buccolingual direction, with a mean bone loss of 0.10+0.09, which was statistically non-significant (p > 0.05). Implant success was 100% at 6 months after loading as determined by Akbrektsson's criteria for implant success. Conclusions The adjunctive use of PRFM with DFDBA following immediate implant placement yielded a significant reduction in bone resorption and maintenance of buccolingual dimensions.

Identification of the Allosteric Binding Site for Thiazolopyrimidine on the C-Type Lectin Langerin.

Langerin is a mammalian C-type lectin expressed on Langerhans cells in the skin. As an innate immune cell receptor, Langerin is involved in coordinating innate and adaptive immune responses against various incoming threats. We have previously reported a series of thiazolopyrimidines as murine Langerin ligands. Prompted by the observation that its human homologue exhibits different binding specificities for these small molecules, we report here our investigations to define their exact binding site. By using structural comparison and molecular dynamics simulations, we showed that the nonconserved short loops have a high degree of conformational flexibility between the human and murine homologues. Sequence analysis and mutational studies indicated that a pair of residues are essential for the recognition of the thiazolopyrimidines. Taking solvent paramagnetic relaxation enhancement NMR studies together with a series of peptides occupying the same site, we could define the cleft between the short and long loops as the allosteric binding site for these aromatic heterocycles.