The N quadrupole coupling tensor of pyridine and pyrimidine in solution, assigned by NMR in an electric field

The principal components of the ¹⁴N quadrupole coupling tensor in liquid pyridine and pyrimidine are determined from the ²H and ¹⁴N NMR spe     

The dynamics of the CH3CN molecule in the isotropic phase and in a nematic solution

NMR lineshape studies of acelonitrile in the isotropic and the liquid-crystalline nematic phase of PCH have been performed. The scalar relaxation of the second kind due to the presence of the ¹⁴N quadrupolar nucleus has been confirmed as the most important relaxation mechanism for this molecule in both the isotropic and the anisotropic phase. It has been found largely responsible for the selective broadening on ¹³C and ¹H transitions. A minor contribution arising from intramolecular dipolar relaxation mechanism has also been investigated. Linewidth analysis of the NMR spectra allowed us to determine the quadrupolar relaxation time T_IN of the ¹⁴N nucleus. This is connected to the correlation time for rotational diffusion perpendicular to the molecular symmetry axis. A possible explanation of a residual selective broadeining which effects the ¹³C and ¹H NMR transitions and is not taken into account by this mechanism, is also given.     

H NMR relaxation in urea

Proton NMR spin–lattice relaxation times T₁ were measured for urea as a function of temperature. An activation energy of 46.3 ± 4.7 kJ/mol was extracted and compared with the range of 38–65 kJ/mol previously reported in the literature as measured by different magnetic resonance techniques. In addition, proton NMR spin–lattice relaxation times in the rotating frame T_1ρ were measured as a function of temperature. These measurements provide acquisition conditions for the ¹³C and ¹⁵N CP/MAS spectra of pure urea in the crystalline phase.     

自然丰度氮-15核磁共振的研究(Ⅰ)——哌啶衍生物中4-位取代基对15N化学位移的远程相互作用及其与13C化学位移的关系

测定了8个4-位取代的2,2,6,6-四甲基哌啶的自然丰度¹⁵N核磁共振谱及¹³C谱,发现4-位取代基对¹⁵N化学位移有一定的远程相互作用,¹³C化学位移与4-位卤素取代基的原子电负性有近似的线性关系。     

The N and C solid state NMR study of intramolecular hydrogen bond in some Schiff bases

In present work set of eight Schiff bases derived from substituted salicylaldehydes and aliphatic and aromatic amines has been studied in the solid state by ¹⁵N and ¹³C CPMAS NMR methods. ¹⁵N CPMAS NMR measurement is especially useful for investigation of the tautomerism in the compounds considered, owing to the large difference in the nitrogen chemical shifts of OH and NH tautomers. In the solid state, four of the compounds examined were shown by ¹⁵N CPMAS NMR to exist as OH tautomeric forms, and the remaining four as the corresponding NH forms with different stage of proton transfer process, from oxygen to nitrogen site.

This was confirmed by ¹³C CPMAS. The results reported were compared with those obtained for only two compounds in CDCl₃ solutions (solubility problems).     

C, N and Sn NMR spectral evidence for tin five-coordination in triorganotin(IV) oxinates

The ¹³C and ¹¹⁹Sn NMR spectra of tri(1-butyl)tin(IV) and triphenyltin(IV) oxinates and 1-naphthoxides in neat liquid and deuteriochloroform, pentadeuteriopyridine and hexamethylphosphortriamide solutions, and the ¹⁵N NMR spectra of both the oxinates and 8-methoxyquinoline in deuteriochloroform have been recorded. From the comparison of chemical shifts δ(¹³C), δ(¹⁵N) and δ(¹¹⁹Sn) and coupling constants ⁿJ(¹¹⁹Sn¹³C) of the compounds it is concluded that the triorganotin(IV) oxinates, both as the neat liquid and in solution, form complexes containing five-coordinate tin atoms. In the neat liquid and in deuteriochloroform (a non-coordinating solvent) oxinates form chelate complexes with a cis-trigonal bipyramid arrangement. In coordinating solvents (pentadeuteriopyridine, hexamethylphosphortriamide) these are equilibria involving the formation of small amounts of oxinate complexes with one solvent molecule. These complexes have trans-trigonal bipyramid geometry with butyl or phenyl groups in equatorial plane and the monodentate oxinate group and a solvent molecule in axial positions.     

13C N.M.R. and 14N N.Q.R. in ferroelectric liquid crystals Polar versus quadrupolar ordering

¹³C nuclear magnetic resonance and ¹⁴N nuclear quadrupole resonance spectra of ferroelectric smectic C*liquid crystals and their non-chiral analogues allow for a microscopic determination of the polar and quadrupolar (or bipolar) biasing of rotation around the long molecular axis as well as for a determination of the anisotropy in the fluctuations of this axis. The results show that the microscopic origin of the biquadratic coupling between the polarization and the tilt, which has been recently introduced into the extended Landau model of the S_A-S*_C transition, is the quadrupolar (or bipolar) rotational bias induced by the anisotropy in the fluctuations of the long molecular axis. The tilt induced anisotropy in the fluctuations is practically identical in chiral and non-chiral smectic C phases.     

Calculation of some N and C nuclear shielding parameters for some ureas and thioureas

Molecular orbital calculations using CNDO/S parameters are employed to determine bond-orders, charge-densities and the shielding of the ¹⁵N and ¹³C nuclei of a series of ureas and thioureas. For the sterically uncrowded molecules a linear relationship is noticed between the ¹⁵N chemical shifts and C---N bond-orders. When steric crowding occurs this simple relationship is no longer applicable.     

基于固体核磁共振方法的蛋白质组装体三维结构解析

蛋白质组装体广泛存在于生物体内,具有相关生物学功能或与人类的重要疾病密切相关。蛋白质组装体分子量大,通常难以溶解和结晶,限制了常用的结构研究手段如X射线晶体学和液体NMR等在其高分辨三维结构解析中的应用。固体核磁共振技术(ssNMR)在难溶、非结晶样品的三维结构解析中具有独特的优势,尤其随着固体NMR硬件包括高场磁体和高性能的探头、固体NMR多维脉冲实验技术和样品制备技术特别是同位素标记技术的快速发展,固体NMR已经成为了蛋白组装体三维结构解析的重要手段。在样品制备方法方面,强调了样品制备条件的优化对得到构象均一样品的重要性,以及丰富的同位素标记方法的使用对固体NMR谱图分辨率提高的重要作用。同时多种脉冲序列如质子驱动自旋扩散技术(PDSD),偶极辅助旋转共振技术(DARR),质子辅助重偶技术(PAR)或转移回波双共振技术(TEDOR)等的建立和发展为结构约束条件收集提供了基本的技术方法。此外,固体NMR与其它实验技术如扫描透射电镜(STEM),冷冻电镜(Cryo-EM)等和理论模拟方法的联用能显著地提高固体NMR的能力,从而能解析分子量更大、结构更复杂的蛋白质组装体的三维结构。本文以Aβ纤维和T3SS针状体的三维结构解析为例介绍固体NMR在蛋白质组装体结构研究的最新实验方法,重点介绍最新的距离约束条件获取的实验方法进展,以及固体NMR与其它实验和理论模拟研究手段的联用在蛋白质组装体结构解析上的最新进展,期望有助于读者对固体NMR技术在蛋白质组装体的三维结构解析方面的研究进展有所了解。     

Muon—nuclear quadrupolar level crossing resonance in solid nitrogen. Evidence for N2μ ion formation

Both integral and time-differential muon level crossing resonance techniques were used to identify the source of the diamagnetic μ⁺ SR signal in crystalline nitrogen. When the muon Zeeman splitting and the ¹⁴N nuclear quadrupole splitting are equal, the longitudinal field μ⁺ spin relaxation rate is increased due to dipolar ¹⁴N—μ⁺ coupling. At T = 37 K the resonance occurs at a magnetic field of 172 ± 2 G with a fwhm of 10 ± 2 G. The resonance parameters unambiguously confirm the formation of the N₂μ⁺ ion in solid nitrogen.     

High-resolution ODMR- and ODNQR spectroscopy of acridine-d9 in its lowest excited triplet state

High-resolution ODMR- and ODNQR spectroscopy have been performed on acridine-d₉ in its photoexcited triplet state. The nuclear quadrupole constants e²qQ/h = −4.36(3) MHz and η = 0.22(1) have been measured for the ¹⁴N nucleus, where the sign of e²qQ/h is determined relative to the signs of the fine structure parameters, D and E. The ¹⁴N ODNQR spectrum, with linewidths as low as 60 kHz, exhibits a satellite structure attributable to the ²D nucleus located at the meso-position in the molecule. For this nucleus |e²qQ/h| = 180(30) kHz may be estimated. The intensity behaviour of the ODNQR transitions as a function of the NMR rf power level leads to a coarse determination of the in-plane components of the ¹⁴N hyperfine tensor with |A_yy^N| 0.2 MHz and |A _yy^N| 4.7 MHz. Owing to accidental overlap of two transitions in the 2E-ODMR spectrum of acridine, the ODNQR technique had to be extended to a five-pulse sequence.     

N, C and Sn NMR and other spectroscopic studies of 8-quinolinol, its O- and N-methyl derivatives, and chelate di- and tri-organotin(IV) complexes

The nature of the 8-quinolinato ligand in various forms has been examined by ¹⁵N, ¹³C and ¹¹⁹Sn NMR spectroscopy, with evidence also from electronic spectroscopy. These forms include 8-quinolinol (HQ), 8-quinolinate, the 8-hydroxyquinolinium ion, O- and N-methyl derivatives, 8-methoxyquinoline (MeQ), the zwitterionic N-methylquinolinium-8-olate and the N-methylquinolinium ion, and the chelating ligand in organotin(IV) complexes. The ¹⁵N shift from MeQ to HQ affords a measure of the intramolecular hydrogen bonding in HQ. The ¹⁵N shifts and ²J(¹⁵N¹H) couplings afford criteria of chelation, and the O- and N-methyl compounds provide useful reference points for its assessment. Evidence for chelation is demonstrated in three groups of compounds, [SnR₂Q₂] (R = Me, Et, Buⁿ, Octⁿ or Ph), [SnR₃Q] (R = Me, Et, Buⁿ or Ph) and [SnR₂ClQ] (R = Me, Et, Buⁿ or Octⁿ), the ¹⁵N and ¹¹⁹Sn shielding increasing from the [SnR₃Q] to the [SnR₂Q₂] compounds.     

2D-NMR研究中国生漆漆酚结构

用离心旋转薄层层析法在涂渍AgNO₃的硅胶板上成功地分离了乙酰化漆酚。对其主要组分(64.6%),用¹H、¹³C常规谱,DEPT编辑谱,同核、异核化学位移相关二维谱,二维J谱,异核中继相干传递二维谱及弛豫时间T₁等,确定了此化合物的结构与构型和¹H、¹³C谱线归属。实验证明漆酚中此组分是3-十五碳烯烃(8′Z、11′E、13′Z)邻苯二酚,异核中继相干传递二维谱新技术能有效地应用于复杂未知化合物的结构测定。     

Studies on adducts of rhodium(II) tetraacetate and rhodium(II) tetratrifluoroacetate with some amines in CDCl3 solution using H, C and N NMR

¹H, ¹³C and ¹⁵N NMR spectroscopy has been applied for investigation of amine adducts with rhodium(II) tetraacetate dimer and rhodium(II) tetratrifluoroacetate dimer in CDCl₃ solution. Subsequent formation of two adducts, 1:1 and 2:1, was proved by NMR and VIS titration experiments, and by NMR measurements at reduced temperatures, from 233 to 273 K. The adduct formation shift, defined as Δδ=δ_adduct−δ_ligand and characterizing complexation reaction, varies from ca. 0 to +1.6 ppm for ¹H, from ca. −10 to +6 ppm for ¹³C and from −4.4 to −39 ppm for ¹⁵N NMR. Formation of N–Rh bond slows the inversiof on the nitrogen atom and generates, in the case of N-methyl-(1-phenylethyl)-amine, a nitrogenous chiral center in the molecule. VIS spectra of amine-dirhodium salt mixture contain two bands in the 532–597 nm spectral range, assigned to 1:1- and 2:1-adducts.     

几种咔唑衍生物(有机光导材料)的13C核磁共振谱的研究

我们测定了3-溴咔唑,3,6二溴咔唑,9-(2',3'-环氧丙基)咔唑,9-(2',3'-环氧丙基)-3-溴咔唑和9-(2',3'-环氧丙基)-3,6-二溴咔唑(后分别简称化合物1,2,3,4,5)的宽带去偶谱、偏共振谱和非去偶谱。通过对它们的¹³C核磁共振谱的数据分析比较,就以下几方面进行了归纳总结:①信号的归属方法;②环氧丙基的¹³C化学位移范围;③偶合常数的范围,这些归纳总结有助于确定此类化合物的价键特征和结构。     

H, C, N NMR, ESI mass spectral and single crystal X-ray structural characterization of three spiro[pyrrolidine-2,3′-oxindoles]

Three spiro[pyrrolidine-2,3′-oxindoles], 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-phenyl-spiro[3H-indole-3,3′-[3H]-pyrrolizine]-2′-carboxylic acid methyl ester (1), 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-phenyl-spiro[3H-indole-3, 3′-[3H]-pyrrolizine] (2) and 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-(4″-chlorophenyl)-spiro[3H-indole-3,3′-[3H]-pyrrolizine] (3) have been synthesized and their ¹H, ¹³C and ¹⁵N spectra assigned. The chemical shift assignments are based on Pulsed Field Gradient (PFG) Double Quantum Filter (DQF) ¹H, ¹H correlation spectroscopy (COSY), PFG ¹H, ¹³C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG ¹H,X (X = ¹³C and ¹⁵N) Heteronuclear Multiple Bond Correlation (HMBC) experiments. The single crystal X-ray structures of 1–3 have been determined. Compounds 1 and 2 crystallized in monoclinic space group C2/c and compound 3 in monoclinic space group P2₁/c, respectively. Also the ESI-TOF MS data of 1–3 are given.     

Internal motion in 1-methylnaphthalene. A variable temperature NMR study using C and H spin—lattice relaxation time measurements

¹³C nuclear spin—lattice relaxation times of 1-methylnaphthalene and ²H nuclear spin—lattice relaxation times of the perdeuterated species, both in deuterochloroform solutions, were measured at several different temperatures. The effects of isotopic substitution on the effective correlation times are discussed. The Woessner approach to extracting the internal jump rates of the CH₃ and CD₃ groups from these relaxation times was used. Activation energies for the internal motions were calculated by fitting the temperature dependent jump rates to an Arrhenius type expression. The differences between the activation energies of the two isotopic species are discussed.     

基于稳定同位素的5种蔬菜产地真实性判别

为保护蔬菜产地真实性,以上海市场5种常见蔬菜(生菜、茼蒿、辣椒、番茄和黄瓜)为研究对象,应用单因素方差分析上海和其他产地蔬菜的 δ13 C、δ15 N、δ2 H和 δ18 O值差异,并通过主成分分析(PCA)和偏最小二乘判别分析(PLS-DA)建立上海地产蔬菜真实性判别模型.结果表明,上海地产5种蔬菜总的δ15 N、δ...     

Stemmosides C and D, two novel unusual pregnane glycosides from Solenostemma argel: structural elucidation and configurational study by a combined NMR-quantum mechanical strategy

Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17 side chain were isolated from the pericarps of Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto, cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of ¹H, ¹³C, and J coupling NMR parameters. DFT calculations of ¹H and ¹³C chemical shifts, and of the ¹H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers.     

The complete assignment of the h and C nmr spectra of the alkali metal salts of salinomycin and narasin

The preparation of the alkali metal salts of salinomycin and narasin, apart from lithium narasin, is described. The complete assignment of their ¹H spectra based on two dimensional COSY and NOESY spectra is reported. These asignments are then used in two dimensional ¹³C/¹H correlations via direct and long range couplings to assign the ¹³C spectra. Assignments in the ¹³C spectrum of sodium salinomycin differ in important details from those in a previous report.