DFT Simulations as Valuable Tool to Support NMR Characterization of Halide Perovskites: the Case of Pure and Mixed Halide Perovskites

Solid state NMR spectroscopy is swiftly emerging as useful tool to characterize the structure, composition and dynamic properties of lead halide perovskites. On the other hand, interpretation of solid state NMR signatures is often challenging, because of the potential presence of many overlapping signals in small range of chemical shifts, hence complicating the extraction of detailed structural features. Here, we demonstrate the reliability of periodic Density Functional Theory in providing theoretical support for the NMR characterization of halide perovskite compounds, considering nuclei with spin I=1/2. For light ¹H and ¹³C nuclei, we predict NMR chemical shifts in good agreement with experiment, further highlighting the effects of motional narrowing. Accurate prediction of the NMR response of ²⁰⁷Pb nuclei is comparably more challenging, but we successfully reproduce the downshift in frequency when changing the halide composition from pure iodine to pure bromine. Furthermore, we confirm NMR as ideal tool to study mixed halide perovskite compounds, currently at the limelight for tandem solar cells and color-tunable light emission.     

NMR properties of sedimented solutes

This perspective paper is intended to give some insights into the recently proposed technique of NMR of solutes sedimented by ultracentrifugation in a rotor used for solid state NMR experiments. Sedimented "states" correspond to molecules with very little reorientational capability in extremely concentrated solutions. They provide solid state NMR spectra comparable in quality with those of the best microcrystalline samples. Here we report some experiments to look for chemicals which affect the properties of the sediment, and we show that it is possible to fill the rotor in a true ultracentrifuge and then record the spectra. The latter possibility opens new horizons for NMR of sedimented systems.     

DETERMINATION OF THREE-DIMENSIONAL STRUCTURE OF CODEINE BY NMR MOLECULAR GRAPHICS TECHNIQUES

In this paper, we describe a method for calculating the three-dimensional structure ofantagonist drug codeine by means of one- and two-dimensional NMR and computer tech-niques. The calculation of molecular mechanics is based on NMR data, so we call it NMRmolecular graphics (NMRMG). With codeine as a demonstration. we find that the molecularstructure data from NMRMG are in quite good agreement with those by X-ray diffractionmeasurement. NMRMG can be utilized to study configuration and conformation of naturalproducts, especially rigid structure compounds in solution.     

Hydrogen bonds of RNA are stronger than those of DNA, but NMR monitors only presence of methyl substituent in uracil/thymine

Recently, Vakonakis and LiWang (J. Am. Chem. Soc. 2004, 126, 5688) reported experimental evidence for stronger hydrogen bonds in RNA A:U than in DNA A:T base pairs, which was based on differences in NMR shielding for adenine C2. We have analyzed the proposed correlation between NMR shielding and hydrogen-bond strength using density functional theory. Although we agree with the conclusion that A:U is more strongly bound, we find no correlation between the hydrogen-bond strength and the NMR shielding of C2. Our study shows that NMR merely probes the presence/absence of the methyl group in thymine/uracil, without any relation to the strength of the hydrogen bonds involved. In other words, one cannot infer the Watson-Crick hydrogen-bond strength from the NMR shielding constant of adenine C2.     

µ-NMR at the point of care testing

NMR shows strong analytical capability for obtaining molecular information on materials and is used in a variety of fields. Micro-NMR (µNMR) is mainly based on low-field NMR (LF-NMR), which makes NMR detection portable and inexpensive. Point-of-care testing (POCT) has gradually become an area of major concern, and scientists have made much progress in applying µNMR systems for POCT. To the best of our knowledge, this is the first review of the latest development in miniaturization of µNMR systems. Then, we discuss cutting-edge µNMR-based applications in POCT and the outlook for future developments.     

Territorial origin of olive oil: representing georeferenced maps of olive oils by NMR profiling

ABSTRACT Proton NMR profiling is nowadays a consolidated technique for the identification of geographical origin of food samples. The common approach consists in correlating NMR spectra of food samples to their territorial origin by multivariate classification statistical algorithms. In the present work, we illustrate an alternative perspective to exploit territorial information, contained in the NMR spectra, which is based on the implementation of a geographic information system (GIS). Nuclear magnetic resonance spectra are used to build a GIS map permitting the identification of territorial regions having strong similarities in the chemical content of the produced food (terroir units). These terroir units can, in turn, be used as input for labeling samples to be analyzed by traditional classification methods. In this work, we describe the methods and the algorithms that permit to produce GIS maps from NMR profiles and apply the described method to the analysis of the geographical distribution of olive oils in an Italian region. In particular, we analyzed by ¹H NMR up to 98 georeferenced olive oil samples produced in the Abruzzo Italian region. By using the first principal component of the NMR variables selected according to the Moran test, we produced a GIS map, in which we identified two regions incidentally corresponding to the provinces of Teramo and Pescara. We then labeled the samples according to the province of provenience and built an LDA model that provides a classification ability up to 99% . A comparison between the variables selected in the geostatistics and classification steps is finally performed. Copyright © 2016 John Wiley & Sons, Ltd.     

Resolving NMR signals of short‐chain fatty acid mixtures using unsupervised component analysis

Nuclear magnetic resonance (NMR) is a very powerful instrumental technique suited to identify and characterize organic compounds. NMR has been successfully used in the analysis of complex biological and environmental samples; however, these applications are still rather limited. In this work, we describe unsupervised component analysis as a multivariate unsupervised method suited to identify the number of relevant NMR signal contributions and to deconvolve mixed signals into signal individual sources and respective contributions. Using this approach, we were able to advance further in the field of quantification of NMR spectra, and this methodology will help in the characterization of complex biological samples. Copyright © 2017 John Wiley & Sons, Ltd.     

Critical investigation of coupled liquid chromatography–NMR spectroscopy in pharmaceutical impurity identification

In this paper, we investigate the application of coupled LC–NMR to the identification of low‐level impurities. We consider the absolute sensitivity of the technique with our instrumentation, and how this is degraded by peak broadening on and after column, and we compare the sensitivity and other aspects of LC–NMR with a more classical approach of impurity isolation and tube NMR. We show that despite the undoubted advantages of LC–NMR in many situations, for the identification of very low‐level impurities it may not always be the most efficient overall approach when all factors are considered. Copyright © 2003 John Wiley & Sons, Ltd.     

A Novel Conformation Investigation on Newly Synthesized Compound of Diethyl Puerarin-7-yl Phosphate

1INTRODUCTION Puerarin(4?,7-dihydroxy-8-β-D-glucosylisoflavo ne),whose chemical structure is shown in Fig.1,is a C-glycoside compound.It is present in a large amount of active components of Puerariae radix,a com-monly used Chinese herb,which exerts sedative and antipyretic actions and is often used to treat influ-enza,wrist stiffness and headache[1].A number of investigations were carried out internationally to iden-tify the physiological activities of puerarin such as antiproliferative…     

13C固体核磁共振测定气体水合物结构实验研究

采用高功率1H去偶结合魔角旋转13C固体核磁共振技术,在低温常压条件下对合成的乙烷和丙烷气体水合物进行了测试,获得了两种纯气体水合物的13C核磁共振谱图,初步建立了固体核磁共振波谱法测定天然气水合物的实验方法.实验表明:乙烷水合物的13C核磁共振谱图中仅有一条谱线(δ7.7),结构类型为sI,且乙烷分子仅填充在大笼中(...     

Reconstructing Reliable Powder Patterns from Spikelets (Q)CPMG NMR Spectra: Simplification of UWNMR Crystallography Analysis

Spikelets NMR spectra are very popular as they enable the shortening of experimental time and give the possibility to obtain required NMR parameters for nuclei with ultrawide NMR patterns. Unfortunately, these resulted ssNMR spectra cannot be fitted directly in common software. For this reason, we developed UWNMRSpectralShape (USS) software which transforms spikelets NMR patterns into single continuous lines. Subsequently, these reconstructed spectral envelopes of the (Q)CPMG spikelets patterns can be loaded into common NMR software and automatically fitted, independently of experimental settings. This allows the quadrupole and chemical shift parameters to be accurately determined. Moreover, it makes fitting of spikelets NMR spectra exact, fast and straightforward.     

羟基聚合铝溶液的27Al 核磁(NMR)研究进展

结合国内外各课题组研究,从27Al NMR实验参数和铝形态研究两方面综合评述了液体27Al NMR的发展研究现况。首次明确提出27Al NMR测定中设置合适的预采集延迟时间的作用。将为进一步开展的27Al NMR测定研究提供有价值的参考。     

Rotamers or diastereomers? An overlooked NMR solution

The existence of rotamers in a solution of analyte complicates (1)H NMR analysis, especially when the presence of diastereomers is also possible. Organic chemists have often responded to this problem by conducting variable-temperature (VT) NMR experiments, changing NMR solvents, or adding complexing agents. Here, with specific examples, we illustrate the use of simple yet widely overlooked chemical-exchange NMR experiments which allow the nonintrusive rapid distinguishment of rapidly equilibrating small molecules such as rotamers from nonequilibrating diastereomers.     

Exploring experimental sources of multiple protein conformations in structure-based drug design

Receptor flexibility must be incorporated into structure-based drug design in order to portray a more accurate representation of a protein in solution. Our approach is to generate pharmacophore models based on multiple conformations of a protein and is very similar to solvent mapping of hot spots. Previously, we had success using computer-generated conformations of apo human immunodeficiency virus-1 protease (HIV-1p). Here, we examine the use of an NMR ensemble versus a collection of crystal structures, and we compare back to our previous study based on computer-generated conformations. To our knowledge, this is the first direct comparison of an NMR ensemble and a collection of crystal structures to incorporate protein flexibility in structure-based drug design. To provide an accurate comparison between the experimental sources, we used bound structures for our multiple protein structure (MPS) pharmacophore models. The models from an NMR ensemble and a collection of crystal structures were both able to discriminate known HIV-1p inhibitors from decoy molecules and displayed superior performance over models created from single conformations of the protein. Although the active-site conformations were already predefined by bound ligands, the use of MPS allows us to overcome the cross-docking problem and generate a model that does not simply reproduce the chemical characteristics of a specific ligand class. We show that there is more structural variation between 28 structures in an NMR ensemble than 90 crystal structures bound to a variety of ligands. MPS models from both sources performed well, but the model determined using the NMR ensemble appeared to be the most general yet accurate representation of the active site. This work encourages the use of NMR models in structure-based design.     

CABS‐NMR—De novo tool for rapid global fold determination from chemical shifts,residual dipolar couplings and sparse methyl‐methyl noes

Recent development of nuclear magnetic resonance (NMR) techniques provided new types of structural restraints that can be successfully used in fast and low‐cost global protein fold determination. Here, we present CABS‐NMR, an efficient protein modeling tool, which takes advantage of such structural restraints. The restraints are converted from original NMR data to fit the coarse grained protein representation of the C‐Alpha‐Beta‐Side‐group (CABS) algorithm. CABS is a Monte Carlo search algorithm that uses a knowledge‐based force field. Its versatile structure enables a variety of protein‐modeling protocols, including purely de novo folding, folding guided by restraints derived from template structures or, structure assembly based on experimental data. In particular, CABS‐NMR uses the distance and angular restraints set derived from various NMR experiments. This new modeling technique was successfully tested in structure determination of 10 globular proteins of size up to 216 residues, for which sparse NMR data were available. Additional detailed analysis was performed for a S100A1 protein. Namely, we successfully predicted Nuclear Overhauser Effect signals on the basis of low‐energy structures obtained from chemical shifts by CABS‐NMR. It has been observed that utility of chemical shifts and other types of experimental data (i.e. residual dipolar couplings and methyl‐methyl Nuclear Overhauser Effect signals) in the presented modeling pipeline depends mainly on size of a protein and complexity of its topology. In this work, we have provided tools for either post‐experiment processing of various kinds of NMR data or fast and low‐cost structural analysis in the still challenging field of new fold predictions. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

噻唑硫磷的结构研究

噻唑硫磷(fosthiazate)是一种新型、高效的有机磷农药。它是由2-氧化噻唑烷与S-仲丁基-O-乙基硫代磷酰氯通过取代反应制得,其化学名为O-乙基-S-仲丁基-2-氧代-1,3-噻唑烷-3-基硫代膦酸酯,结构式如下：     

NMR structure of the peptidyl transferase RNA inhibitor antibiotic amicetin

In this communication, we report the solution state NMR structure determination of the peptidyl transferase RNA inhibitor antibiotic amicetin. We have successfully characterised the NMR spectrum of amicetin using a range of homo- and heteronuclear NMR techniques. Using experimental ROE-based distance and 1H--1H scalar coupling derived dihedral angle geometrical constraints as input into the three-dimensional structure determination protocol, we have generated an energy-minimised average structure of the antibiotic. Amicetin adopts a stable well-folded conformation in solution, mediated by a network of hydrogen bonds caused by proton donor and acceptor groups at either end of the molecule. The NMR structure of amicetin shows that the cytosine moiety occupies the critical turn position within the fold, which may be structurally significant for interaction with peptidyl transferase ribosomal RNA. The structure is distinctly different from the published X-ray crystal structure of amicetin in which it adopts a linear, extended chain-like conformation with a number of intermolecular hydrogen bonds. In addition to structure, we have probed the dynamics of amicetin in solution and have observed retarded exchange of the amide proton involved in folding. We have also characterised the ionisation properties of amicetin by carrying out NMR pH titration and measuring the pKa of the primary and tertiary amino groups, 7.27 and 7.52, respectively, which are in agreement with the reported values in literature. Solving the NMR structure of amicetin provides a valuable opportunity to determine the structure of its complex with RNA in solution state.     

High-resolution magic-angle spinning NMR for the identification of reaction products directly from thin-layer chromatography spots

We have investigated the prospect of identifying organic reaction products directly from separated thin-layer chromatography (TLC) spots with high-resolution magic-angle spinning (HRMAS) NMR. The concept is to use the TLC spots for NMR analysis so that spectra can be obtained before the reaction is worked up, but without having to elute the product from the TLC stationary phase. Thus, the separated spot is scraped from the plate, transferred to an HRMAS sample rotor, and suspended with a deuterated solvent. Herein, we describe the effects of having the stationary phase present during NMR acquisition. Using a Varian 4 mm gHX Nanoprobe and rotenone as a test compound, we found that the presence of the stationary phase during NMR acquisition resulted in (i) a large, broad 'background' signal near 4.6 ppm and (ii) a decrease in the signal-to-noise ratio due to the adsorption of the product molecules to the adsorbent. However, both effects could be adequately and conveniently eliminated. The background signal was removed by using either a CPMG pulse sequence or chemical exchange. The adsorption was avoided by using a more polar solvent system. Finally, we found that spectra with good signal-to-noise ratio and resolution could be acquired in a matter of minutes even for cases of limited product concentration. Therefore, we believe the technique has value and provides the organic chemist with another option to obtain NMR data critical for structural elucidation or verification.     

锂/钠离子电池材料的固体核磁共振研究进展

固体核磁共振技术是一种定量分析固体材料结构与组成的强有力手段,结合固体核磁共振和常规x-射线衍射(XRD)、 x-射线吸收谱(XAS)等表征方法可对锂/钠离子电池材料在电化学反应中的结构演化过程进行全面的分析. 例如通过固体核磁共振研究, 可获得不同合成与修饰条件下, 锂/钠离子电池电极和电解质材料体相以及电极/电解质界面层的化学组成、局域结构和离子扩散动力学等信息,为高性能电池材料的设计和研发提供重要的基础数据. 本文结合本课题组的研究工作,综述了近三年来国内外固体核磁共振技术在锂/钠离子电池电极、电解质材料以及固体电解质界面膜（SEI）研究中的应用和进展.