用^3HNMR波谱法分析微波激发催化交换制备的^3H标记颠茄类生物碱

用~3H NMR波谱法测定了微波激发催化交换制备的四种~3H标记颠茄类生物碱示踪剂的氚标记位置及其相对百分含量。并在用~1H NMK归属原料纯度及标记物分子各基因化学位移时采用了水峰抑制技术(简称WEFT),既能同时消除溶剂氘代甲醇及水峰的影响;又能提高灵敏度(近10倍),从而计算出所得标记产物的化学纯度值与放化纯度值。为快速、准确寻找制备标记生物碱的最佳实验条件和控制标记物质量提供了唯一的物理无损分析方法。     

Unambiguous structural characterization of hydantoin reaction products using 2D HMBC NMR spectroscopy

Data from two-dimensional (2D) NMR experiments were used to identify the reaction products resulting from the opening of pyroglutamates with isocyanates or thioisocyanates. The reaction has the potential to produce compounds that would have very similar one-dimensional proton ((1)H) or carbon-13 ((13)C) NMR spectra. Careful analysis of (1)H--(1)H COSY, (1)H--(1)H NOESY, and HMBC data, including chemical shifts and coupling constants, were used to distinguish correctly between carbamoyl-2-pyrrolidinone, hydantoin, and perhydro-1,3-diazepine-2,4-dione type structures that could result from this reaction. This work describes their preparation and subsequent identification using 2D NMR spectroscopy, and includes complete (13)C assignments of the reaction products. The 2D NMR techniques and analysis described here can be applied successfully to other synthetic reactions with the potential to produce isomeric products.     

Synthesis and spectroscopic studies of some new ortho functionalized triazene compounds and their reactivity with mercury (II) ion

In this work, a series of triazene derivatives in which the substituents have a wide range of electronic characters were synthesized to understand the effect of the substituent identity in controlling the changes in their electronic absorption spectra and NMR chemical shifts, as well as their tendency for interaction with some heavy metals. Elemental analysis and ¹H NMR, ¹³C NMR, and FT-IR spectroscopies were used to elucidate the chemical structures of the new compounds. Thermal analysis and protolysis of these triazenes were evaluated. The thermodynamic parameters were calculated from thermal data using Coats-Redfern method. Complexation of these compounds with mercury (II) ion in acetonitrile and deuterated dimethylsulfoxide (DMSO-d₆) solution were studied by UV–vis and ¹H NMR spectroscopy, respectively. Stoichiometry and formation constants of the complexes were calculated by the mole ratio titration method. The effects of the nature of the substituents on the formation constants were discussed.     

How reliable are GIAO calculations of 1H and 13C NMR chemical shifts? A statistical analysis and empirical corrections at DFT (PBE/3z) level

Reliability of calculated (1)H and (13)C NMR chemical shifts for various classes of organic compounds obtained with gauge-invariant atomic orbital (GIAO) approach has been studied at the PBE/3ζ level (as implemented in PRIRODA code) using linear regression analysis with experimental data. Empirical corrections for the calculated chemical shifts δ(H,calc) = δ(PBE/3ζ) - 0.08 ppm (RMS 0.18 ppm, MAD 0.66 ppm) and δ(C,calc) = δ(PBE/) (3) (ζ) - 6.35 ppm (RMS 3.09 ppm, MAD 9.42 ppm) have been developed using the sets of 263 and 308 experimental values for (1)H and (13)C chemical shifts, respectively. The confidence intervals of NMR chemical shifts at 95% confidence probability are δ(H,calc) ± 0.35 ppm for (1)H and δC,calc) ± 6.05 ppm for (13)C.     

Structure elucidation and NMR spectral assignment of five new xanthones from the bark of Garcinia xanthochymus

Five new xanthones, namely Garcinexanthones A-E (1-5), were isolated from the barks of Garcinia xanthochymus. Their structures were elucidated by spectral analysis, primarily NMR, MS, and UV. The complete assignments of the (1)H NMR and (13)C NMR chemical shifts for the compounds were achieved by using 1D and 2D NMR techniques, including DEPT, HSQC, and HMBC NMR experiments.     

1H NMR analysis of O‐methyl‐inositol isomers: a joint experimental and theoretical study

Density functional theory (DFT) calculations of ¹H NMR chemical shifts for l ‐quebrachitol isomers were performed using the B3LYP functional employing the 6‐31G(d,p) and 6‐311 + G(2d,p) basis sets. The effect of the solvent on the B3LYP‐calculated NMR spectrum was accounted for using the polarizable continuum model. Comparison is made with experimental ¹H NMR spectroscopic data, which shed light on the average uncertainty present in DFT calculations of chemical shifts and showed that the best match between experimental and theoretical B3LYP ¹H NMR profiles is a good strategy to assign the molecular structure present in the sample handled in the experimental measurements. Among four plausible O‐methyl‐inositol isomers, the l ‐quebrachitol 2a structure was unambiguously assigned based only on the comparative analysis of experimental and theoretical ¹H NMR chemical shift data. The B3LYP infrared (IR) spectrum was also calculated for the four isomers and compared with the experimental data, with analysis of the theoretical IR profiles corroborating assignment of the 2a structure. Therefore, it is confirmed in this study that a combined experimental/DFT spectroscopic investigation is a powerful tool in structural/conformational analysis studies. Copyright © 2012 John Wiley & Sons, Ltd.     

一种金属洗涤剂的NMR分析

由于精细化工行业的迅速发展,作为“工业味精”的表面活性剂,已广泛进入日化、轻工、纺织、建筑、石化、金属加工等生产领域,对其的分析也显得日益重要。表面活性剂的分析历来是比较困难的课题之一,而通过核磁共振(NMR)进行定性和定量的文献则更少[1]。本文利用NMR为多种表面活     

Characterization of a new hexasodium diphosphopentamolybdate hydrate, Na6[P2Mo5O23]x7H2O, by 23Na MQMAS NMR spectroscopy and X-ray powder diffraction

A novel hexasodium disphosphopentamolybdate hydrate, Na6[P2Mo5O23]x7H2O, has been identified using X-ray powder diffraction, 1H, 23Na, and 31P magic-angle spinning (MAS) NMR, and 23Na multiple-quantum (MQ) MAS NMR. Powder XRD reveals that the hydrate belongs to the triclinic spacegroup P1 with cell dimensions a = 10.090(3) A, b = 15.448(5) A, c = 8.460(4) A, alpha = 101.45(6) degrees, beta = 104.09(2) degrees, gamma = 90.71(5) degrees, and Z = 2. The number of water molecules of crystallization has been determined on the basis of a quantitative evaluation of the 1H MAS NMR spectrum, the crystallographic unit cell volume, and a hydrogen content analysis. The 23Na MQMAS NMR spectra of Na6[P2Mo5O23]x7H2O, obtained at three different magnetic fields, clearly resolve resonances from six different sodium sites and allow a determination of the second-order quadrupolar effect parameters and isotropic chemical shifts for the individual resonances. These data are used to determine the quadrupole coupling parameters (CQ and eta Q) from simulations of the complex line shapes of the central transitions, observed in 23Na MAS NMR spectra at the three magnetic fields. This analysis illustrates the advantages of combining MQMAS and MAS NMR at moderate and high magnetic fields for a precise determination of quadrupole coupling parameters and isotropic chemical shifts for multiple sodium sites in inorganic systems. 31P MAS NMR demonstrates the presence of two distinct P sites in the asymmetric unit of Na6[P2Mo5O23].7H2O while the 31P chemical shielding anisotropy parameters, determined for this hydrate and for Na6[P2Mo5O23]x13H2O, show that these two hydrates can easily be distinguished using 31P MAS NMR.     

A Senior-level Experiment in Structural Elucidation Using 2-D NMR

One-dimensional (¹H, ¹³C, DEPT), and two-dimensional (COSY, HETCOR) NMR experiments are used to assemble the chemical structures of monoterpene unknowns assigned to senior instrumental analysis students. Students were asked to use their knowledge of NMR to deduce the structure of their assigned compound.     

Complete assignments of (1)H and (13)C NMR spectroscopic data for two new triterpenoid saponins from Ilex pernyi

Ilexpernoside A and ilexpernoside B, two new pentacyclic C(4)-nortriterpenoid saponins, were isolated from the leaves of Ilex pernyi Franch. Their chemical structures were determined by MS, NMR spectroscopy and chemical analysis. Complete assignments of the (1)H and (13)C NMR spectroscopic data were achieved by 1D and 2D NMR experiments (HSQC, HMBC, (1)H-(1)H COSY and NOESY).     

Application of the multi-standard methodology for calculating 1H NMR chemical shifts

Gauge including atomic orbitals (GIAO) (1)H NMR chemical shift calculations have been performed for 66 organic compounds at 72 different levels of theory using the multi-standard approach (MSTD) previously developed for (13)C NMR. This straightforward computational technique involves the combination of methanol and benzene as standards. The studied methodology has been shown to predict (1)H NMR chemical shifts efficiently at different levels of theory.     

Tacticity of poly(butyl-α-cyanoacrylate) chains in nanoparticles: NMR spectroscopy and DFT calculations

NMR spectroscopy and quantum chemical calculations were applied for structural characterization and determination of the preferred stereochemical sequence distribution of the monomer units in the homopolymer chains of poly(butyl-α-cyanoacrylate) nanoparticles. The stereochemical sequence distribution of the monomer units was defined by analysis of their high-resolution 1D ¹H and ¹³C NMR and 2D J-resolved, ¹H/¹³C HSQC and ¹H/¹³C HMBC NMR spectra. The results were verified by employment of B3LYP/6-31G(d) calculations and are consistent with the preferred tendency of polymer chains of PBCN to adopt syndiotactic placements. The proton and carbon chemical shielding were calculated at BPW91/6-31+G(2d,p) level using the GIAO approach and B3LYP/6-31G(d) optimized geometry.     

Lithium thiazolidine-4-carboxylate: synthesis, spectroscopic characterization and preliminary in vitro cytotoxic studies in human HeLa cells

A new water-soluble lithium salt of thiazolidine-4-carboxylic acid was synthesized and characterized by chemical and spectroscopic techniques. Elemental and mass spectrometric (ESI-MS) analyses of the solid compound fit to the composition LiC(4)H(6)NSO(2). (1)H, (13)C nuclear magnetic resonance (NMR), [(1)H-(15)N] NMR and infrared (IR) analyses permitted to elucidate the structure of the compound. Biological activity was evaluated by cytotoxic analysis using HeLa cells. Determination of cell death was assessed using a tetrazolium salt colorimetric assay, which reflects the cells viability.     

Structural assignment of Diels-Alder adducts: an experimental and theoretical approach

A detailed NMR analysis with total assignment of (1)H and (13)C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by (1)H and (13)C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311 + g(2d, p) from optimized structures at the B3LYP/6-31g(d) level.     

A new flavonoid glucoside from Cassia angustifolia

A new flavonoid glucoside with a known one was isolated from the leaves of Cassia angustifolia.Based on the spectral analysis, including MS,~1H NMR,~(13)C NMR,DEPT,~1H-~1HCOSY,HMQC,HMBC and NOSEY,their chemical structures were determined as kaempferol-3-O-[(6′′′-O-trans-sinnapoyl)-β-D-glucopyranosyl(1→)]-β-D-glucopyranoside 1 and apigenin-6,8-di-C-glycoside 2.     

Intramolecular hydrogen-bonding interactions in 2-nitrosophenol and nitrosonaphthols: ab initio, density functional, and nuclear magnetic resonance theoretical study

Intramolecular hydrogen bonding (IHB) interactions and molecular structures of 2-nitrosophenol, nitrosonaphthols, and their quinone-monooxime tautomers were investigated at ab initio and density functional theory (DFT) levels. The geometry optimization of the structures studied was performed without any geometrical restrictions. Possible conformations with different types of the IHB of the tautomers were considered to understand the nature of the HB among these conformers. The effect of solvent on hydrogen bond energies, conformational equilibria, and tautomerism in aqueous solution were studied. Natural bond orbital analysis was performed to study the IHB in the gaseous phase and in aqueous medium. The NMR 1H, 13C, 15N, and 17O chemical shifts in the gaseous phase and in solution for the studied compounds were calculated using the gauge-including atomic orbitals approach implemented in the Gaussian 03 program package. The optimized geometrical parameters and 1H NMR chemical shifts are in good agreement with previous theoretical and experimental data.     

Ab initio/GIAO-CCSD(T) study of structures, energies, and 13C NMR chemical shifts of C4H7(+) and C5H9(+) ions: relative stability and dynamic aspects of the cyclopropylcarbinyl vs bicyclobutonium ions

The structures and energies of the carbocations C 4H 7 (+) and C 5H 9 (+) were calculated using the ab initio method. The (13)C NMR chemical shifts of the carbocations were calculated using the GIAO-CCSD(T) method. The pisigma-delocalized bisected cyclopropylcarbinyl cation, 1 and nonclassical bicyclobutonium ion, 2 were found to be the minima for C 4H 7 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level the structure 2 is 0.4 kcal/mol more stable than the structure 1. The (13)C NMR chemical shifts of 1 and 2 were calculated by the GIAO-CCSD(T) method. Based on relative energies and (13)C NMR chemical shift calculations, an equilibrium involving the 1 and 2 in superacid solutions is most likely responsible for the experimentally observed (13)C NMR chemical shifts, with the latter as the predominant equilibrating species. The alpha-methylcyclopropylcarbinyl cation, 4, and nonclassical bicyclobutonium ion, 5, were found to be the minima for C 5H 9 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level ion 5 is 5.9 kcal/mol more stable than the structure 4. The calculated (13)C NMR chemical shifts of 5 agree rather well with the experimental values of C 5H 9 (+).     

Molecular structure, IR and NMR spectra of 2,6 distyrylpyridine by density functional theory and ab initio Hartree-Fock calculations

Vibrational frequencies and gauge including atomic orbital (GIAO) 13C NMR and 1H NMR chemical shift values of 2,6 distyrylpyridine (C21H17N) in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. These methods are proposed as a tool to be applied in the structural characterization of 2,6 distyrylpyridine (C21H17N). The title compound has C2v point group, thus providing useful support in the interpretation of experimental IR data. In addition, obtained results were related to the linear correlation plot of experimental 13C NMR, 1H NMR chemical shifts values and IR data.     

手性镧系位移试剂核磁共振法测定芳氧丙酸酯类除草剂对映体纯度

以Eu(hfc)3和Pr(hfc)3为手性镧系位移试剂(CLSR),比较了两种CLSR对2,4-滴丙酸甲酯的1HNMR和13C NMR谱手性分离效果,结果表明:Pr(hfc)3比Eu(hfc)3对手性中心相连的甲基具有更好的手性分离效果。首次应用Pr(hfc)3测定了盖草能、稳杀得和喹禾灵3种手性芳氧丙酸酯类除草剂的1HNMR和13CNMR谱,其1HNMR谱分离度R约为1,盖草能和喹禾灵的13C NMR谱分离度R大于1.5,说明1H NMR和13CNMR谱手性分离效果适用于对映体纯度测定。与手性色谱法相比,CLSR-NMR法测定对映体纯度具有操作简便、分析速度快的显著优势。     

1H and 13C NMR chemical shift assignments of spiro-cycloalkylidenehomo- and methanofullerenes by the DFT-GIAO method

The (1)H and (13)C NMR chemical shifts of spiro-cycloalkylidene[60]fullerenes were assigned using experimental NMR data and the Density Functional Theory (DFT)-Gauge Independence Of Atomic Orbitals method (GAIO) calculation method in the Perdew Burke Ernzerhof (PBE)/3z approach. The calculated values of the (13)C NMR chemical shifts adequately reproduce the experimental values at this quantum chemistry approach. Similar assignments will be helpful for (13)C NMR spectral analysis of homo- and methano[60]fullerene derivatives for structure elucidation and to determine the influence of fullerene frames on substituents and the influence of substituents on fullerene cores.