Conformations of Carnosine in Aqueous Solutions by All-Atom Molecular Dynamics Simulations and 2D-NOSEY Spectrum

All-atom molecular simulations and two-dimensional nuclear overhauser effect spectrum have been used to study the conformations of carnosine in aqueous solution. Intramolecular distances, root-mean-square deviation, radius of gyration, and solvent-accessible surface are used to characterize the properties of the carnosine. Carnosine can shift between extended and folded states, but exists mostly in extended state in water. Its preference for extension in pure water has been proven by the 2D nuclear magnetic resonance (NMR) experiment. The NMR experimental results are consistent with the molecular dynamics simulations.     

Symmetry-based 29Si dipolar recoupling magic angle spinning NMR spectroscopy: a new method for investigating three-dimensional structures of zeolite frameworks

A new 29Si solid-state MAS NMR experiment is described for investigating the framework structures of pure silica zeolites. The symmetry-based homonuclear dipolar recoupling sequence SR26411 has been incorporated into a two-dimensional NMR experiment to probe the Si-O-Si bonding connectivities and long-range Si-Si distances in zeolite frameworks. This dipolar recoupling sequence is shown to have a number of advantages over the J-coupling-based INADEQUATE experiment. For the clathrasil Sigma-2, it is demonstrated that there is excellent agreement between experimental double-quantum build-up curves obtained from a series of two-dimensional double-quantum correlation spectra and simulated curves which consider all Si-Si distances out to 8 A. This result suggests that this experiment could be used to solve zeolite frameworks with unknown structures.     

Hydrogen bond directed self-assembly of core-substituted naphthalene bisimides with melamines in solution and at the graphite interface

A series of red and blue highly fluorescent core-substituted naphthalene bisimide dyes has been synthesized and they have been investigated as supramolecular building blocks. NMR and UV-Vis titration experiments of these dyes with complementary melamines revealed the formation of triple hydrogen bonds (DAD-ADA arrays) in solution. At stoichiometric ratios, ditopic melamine receptors could dissolve otherwise insoluble bisimides by means of hydrogen bonding, even in aliphatic solvents. At the solution/graphite interface, one-dimensional chains of hydrogen bonded naphthalene bisimides and two-dimensional adlayers of ditopic melamines are formed for the pure compounds but little evidence for heterocomplexes between the two complementary building blocks could be obtained.     

Chiral palladacycle promoted asymmetric synthesis of functionalized bis-phosphine monoxide ligand

An organopalladium complex containing orthometalated (R)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary has been used to promote the asymmetric hydroalkoxylation reactions between weak nucleophile methanol and 1,1-bis(diphenylphosphino)ethylene or 1,1-bis(diphenylphosphino)ethylene monoxide in good regio- and stereo-selectivities in the presence of an external base. The major addition product obtained from methanol and 1,1-bis(diphenylphosphino)ethylene monoxide was subsequently isolated in a quantitative yield in its configurationally pure form and characterized by means of two-dimensional rotating-frame nuclear Overhauser enhancement (ROESY) NMR spectroscopy as well as single crystal X-ray diffraction analysis. The enantiomerically pure bis-phosphine monoxide ligand was subsequently liberated in high yield.     

NMR spectroscopic elucidation of the structure and stereochemistry of tricyclic 3-styrylpyrazolines

Diastereomeric mixtures of tricyclic 3-styrylpyrazolines have been prepared by the reaction of 3-cynnamylidenechroman-4-ones and their 1-thio analogs with hydrazine in hot acetic acid or propionic acid solutions. The diastereomeric mixtures were separated by column chromatography to obtain the pure diastereomers. The elucidation of their structure and stereochemistry and complete (1)H and (13)C assignments have been performed by a combination of various one- and two-dimensional NMR experiments.     

The composition and structure of polyvinyl butyral furfural: NMR study

With the use of ¹H NMR, ¹³C NMR and two-dimensional NMR spectroscopy, the composition and structure of polyvinyl butyral furfural samples obtained at different stages of poly(vinyl alcohol) acetalization have been determined. The structure of low-molecular-mass and oligomer admixtures that may be formed in the course of synthesis of the copolymer or during its dissolution in alcohol has been estimated via one-dimensional and two-dimensional diffusion NMR spectroscopy.     

Generalised 2D-correlation NMR analysis of a wine fermentation

A wine fermentation has been monitored on a daily basis by (1)H NMR spectroscopy. Following data pre-processing that includes synthesis of the spectra to ensure all peaks are of constant half-width, the series of spectra were examined using generalised two-dimensional correlation techniques. Synchronous and asynchronous data maps have been generated and employed to interpret the changes in the fermentation process as a function of time. The results illustrate the potential of high resolution NMR with multivariate data analysis as a tool for process monitoring and the manner in which two-dimensional correlation mapping can aid in data interpretation.     

High resolution magic angle spinning NMR for analyzing small molecules attached to solid support

Solid phase synthesis has become a routine technique in combinatorial chemistry. The need in analytical methods to characterize nondestructively resin bound molecules has been fulfilled by the introduction of High Resolution Magic Angle Spinning (HR MAS) NMR of solvent swollen beads. HR MAS NMR can give solution like proton NMR spectra and one- and two-dimensional NMR techniques are amenable, allowing detailed structure analysis. Recent developments are the application of a diffusion filter to suppress solvent signals and dipolar recoupling techniques to gain spatial information. HR MAS NMR has been applied to monitor reactions and elucidate reaction products.     

Assessment of techniques for DOSY NMR data processing

Diffusion-ordered spectroscopy (DOSY) NMR is based on a pulse-field gradient spin-echo NMR experiment, in which components experience diffusion. Consequently, the signal of each component decays with different diffusion rates as the gradient strength increases, constructing a bilinear NMR data set of a mixture. By calculating the diffusion coefficient for each component, it is possible to obtain a two-dimensional NMR spectrum: one dimension is for the conventional chemical shift and the other for the diffusion coefficient. The most interesting point is that this two-dimensional NMR allows non-invasive “chromatography” to obtain the pure spectrum for each component, providing a possible alternative for LC-NMR that is more expensive and time-consuming. Potential applications of DOSY NMR include identification of the components and impurities in complex mixtures, such as body fluids, or reaction mixtures, and technical or commercial products, e.g. comprising polymers or surfactants.

Data processing is the most important step to interpret DOSY NMR. Single channel methods and multivariate methods have been proposed for the data processing but all of them have difficulties when applied to real-world cases. The big challenge appears when dealing with more complex samples, e.g. components with small differences in diffusion coefficients, or severely overlapping in the chemical shift dimension. Two single channel methods, including SPLMOD and continuous diffusion coefficient (CONTIN), and two multivariate methods, called direct exponential curve resolution algorithm (DECRA) and multivariate curve resolution (MCR), are critically evaluated by simulated and real DOSY data sets. The assessments in this paper indicate the possible improvement of the DOSY data processing by applying iterative principal component analysis (IPCA) followed by MCR-alternating least square (MCR-ALS).     

原位制备8-氘代奥美拉唑钠

奥美拉唑分子中的氮原子质子化,对邻近的碳核产生有效的电四极矩驰豫,使邻近碳核信号加宽或消失,以致奥美拉唑在DMSO-d6或DMSO-d6/D2O溶液中的碳谱(13CNMR、DEPT-90、DEPT-135)及碳-氢相关谱(HMQC、HMBC)具有非典型的特征,即部分碳原子不出峰且峰形很差,以致无法确定具体的碳数,延长脉冲重复时间无改观。本实验通过将奥美拉唑与NaOH的D2O溶液反应原位制备8-氘代奥美拉唑钠,使吡啶氮原子去质子化,从而使部分不出峰的碳核信号变窄或重又出现,顺利地完成了8-氘代奥美拉唑钠上述谱图的采集,间接地解决了奥美拉唑的碳谱分析,因而提供了一种可通用的测试苯骈咪唑类质子泵抑制剂碳谱及其二维相关谱的方法。     

Spectra and structure of binary azeotropes VI-benzene-methanol

Benzene and methanol make a minimum boiling point homogeneous binary azeotrope with the mole ratio 2:3. Some characteristic vibrational modes, as well as ¹H NMR signals change due to the azeotrope formation. The extend of interaction of these molecules causes significant changes on some vibrational modes involved, and ¹H NMR signals show some changes on their position. No IR, Raman, and NMR spectra have been reported for this constant boiling mixture, also there has not been any attempt to investigate the unit-structure of this azeotrope. In this work the FTIR, FT-Raman, and ¹H NMR spectra of pure benzene, pure methanol, and corresponding azeotrope were recorded, mutual influences resulting from azeotrope formation have been analyzed, and spectral changes has been discussed. The unit-structure of cluster has been deduced based on mole ratio, boiling point depression of constituents, and comparison among the spectra obtained by FTIR, FT-Raman, and ¹H NMR techniques.     

Pure Isotropic Proton NMR Spectra in Solids using Deep Learning

The resolution of proton solid-state NMR spectra is usually limited by broadening arising from dipolar interactions between spins. Magic-angle spinning alleviates this broadening by inducing coherent averaging. However, even the highest spinning rates experimentally accessible today are not able to completely remove dipolar interactions. Here, we introduce a deep learning approach to determine pure isotropic proton spectra from a two-dimensional set of magic-angle spinning spectra acquired at different spinning rates. Applying the model to 8 organic solids yields high-resolution ¹H solid-state NMR spectra with isotropic linewidths in the 50–400 Hz range.     

Spectra and structure of binary azeotropes V-acetone-cyclopentane

Acetone and cyclopentane make a minimum boiling homogeneous binary azeotrope with mole ratio 2:3. Some characteristic vibrational modes, as well as (1)H NMR signals change due to the azeotrope formation. The extend of interaction of these molecules causes significant changes on some vibrational modes involved and (1)H NMR signals show some changes on their position. In this work the FTIR and (1)H NMR spectra of pure acetone, pure cyclopentane and corresponding azeotrope were recorded, mutual influences resulting from azeotrope formation have been analyzed, and spectral changes has been discussed. The unit-structure of cluster have been deduced, based on mole ratio, boiling point depression of constituents, and comparison between the spectra obtained by FTIR and (1)H NMR techniques.     

Preparation and study on the novel solid inclusion complex of ciprofloxacin with HP-beta-cyclodextrin

The interaction of ciprofloxacin with HP-beta-cyclodextrin (HP-beta-CD) has been studied by several analytical techniques, including 1H nuclear magnetic resonance (NMR), 13C NMR, fluorescence spectra, infrared spectroscopy, thermal analyzer and scanning electron microscope. In this paper, solid inclusion complex of ciprofloxacin with HP-beta-CD was synthesized by the coprecipitation method. In addition, the characterization of the inclusion complex has been proved by fluorimetry, infrared, differential scanning calorimetry and one-dimensional (1D), 2D NMR. The experimental results confirmed the existence of 1:1 inclusion complex of ciprofloxacin with HP-beta-CD. The formation constant of complex was determined by fluorescence method and 1H NMR. Spacial configuration of complex has been proposed on two-dimensional NMR technique.     

l-Lactide homopolymerization and l-lactide-ε-caprolactone block copolymerization by lanthanide tris(2,4,6-trimethylphenolate)s

The l-lactide (LLA) homopolymerization and copolymerization with ε-caprolactone (CL) in solution initiated by lanthanide tris(2,4,6-trimethylphenolate)s (Ln(OTMP)₃) are systematically investigated. The results indicate that La(OTMP)₃ is quite effective for the LLA polymerization. The ¹H NMR spectrum suggests the homopolymerization proceeds through an acyl-oxygen bond cleavage. Thermal analysis of homopolymers by DSC shows typical features of optically pure PLLA. The copolymerization of LLA with CL can only be achieved when CL is first polymerized followed by LLA. Feeding the two monomers simultaneously, however, only results in the formation of LLA homopolymers. The structure of the copolymers has been characterized by ¹H NMR and ¹³C NMR and the thermal behavior has also been evaluated. All these measurements demonstrate the pure diblock copolymer has been synthesized successfully.     

Electronic structure and solvatochromism of merocyanines NMR spectroscopic point of view

(1)H and (13)C NMR spectra of two series of malononitrile-based merocyanines, which possess positive and negative solvatochromism have been in detail investigated in low polar chloroform and polar dimethyl sulfoxide (DMSO). Careful attribution of signals in spectra has been made with the help of two-dimensional NMR experiments (COSY, NOESY, HMBC, and HMQC). Hence, the dependence of merocyanines electronic structure on their chemical structure and solvent nature has been studied by this powerful method. It has been shown that there exists a good correlation between the calculated charges on carbon atoms of a polymethine chain and their chemical shifts in (13)C NMR spectra. The influence of solvent polarity on bond orders for dyes with positive and negative solvatochromism is also observed. The comparison of (13)C NMR spectra of merocyanines and corresponding parent ionic dyes allows to determine their sign of solvatochromism irrespectively of electronic spectra, and also to find the key atoms of chromophore whose signals in (13)C NMR spectra are most informative.     

A new azorellane diterpenoid from Azorella madreporica

A new azorellane diterpenoid has been isolated and identified from the aerial parts of Azorella madreporica Clos. The structure of 1 was established by one- and two-dimensional NMR techniques.     

Isolation and structure determination of a lignan from the bark of Salix alba

A lignan, sisymbrifolin (1) found in the fruits of Solanum sisymbriflolium has been isolated from the bark extract of Salix alba (Salicaceae). Its structure was elucidated by its direct spectrum data of ESI-MS and one- and two-dimensional NMR spectroscopy for the first time.     

High-sensitivity visualisation of contaminants in heparin samples by spectral filtering of 1H NMR spectra

A novel application of two-dimensional correlation analysis has been employed to filter (1)H NMR heparin spectra distinguishing acceptable natural variation and the presence of foreign species. Analysis of contaminated heparin samples, compared to a dataset of accepted heparin samples using two-dimensional correlation spectroscopic analysis of their 1-dimensional (1)H NMR spectra, allowed the spectral features of contaminants to be recovered with high sensitivity, without having to resort to more complicated NMR experiments. Contaminants, which exhibited features distinct from those of heparin and those with features normally hidden within the spectral mass of heparin could be distinguished readily. A heparin sample which had been pre-mixed with a known contaminant, oversulfated chondroitin sulfate (OSCS), was tested against the heparin reference library. It was possible to recover the (1)H NMR spectrum of the OSCS component through difference 2D-COS power spectrum analysis of as little as 0.25% (w/w) with ease, and of 2% (w/w) for more challenging contaminants, whose NMR signals fell under those of heparin. The approach shows great promise for the quality control of heparin and provides the basis for greatly improved regulatory control for the analysis of heparin, as well as other intrinsically heterogeneous and varied products.