天然丰度的N-磷酰化氨基酸的15N NMR 研究

采用¹⁵N-¹H的2D HSQC、HMBC实验方法,测定了天然丰度的N-磷酰化氨基酸样品在溶液中的¹⁵N化学位移δ_N及偶合常数J_N-P,J_N-H. 实验表明：对于¹⁵N天然丰度样品,这是一种快速有效的实验方法. 研究发现：N-酰化后的氨基酸,其δ_N以及与氮原子直接相连的质子¹H的化学位移均发生十分明显的高场位移,而偶合常数¹J_N-P,¹J_N-H的变化与化合物构型相关联 .     

甲醛缩氨基脲及其有关化合物的15N和13C核磁共振研究

本文测定了12个甲醛缩氨基脲类化合物的¹⁵N和¹³C NMR谱,研究并对比了不同取代基对¹⁵N和¹³C化学位移的影响,结果表明:¹⁵N化学位移对分子结构和取代基的电子效应更加敏感,变化范围更大.对N-苯甲醛缩氨基脲¹⁵N化学位移与Hammatt取代常数σ的相关性进行了研究,并与苯胺的取代效应作了对比.     

脂肪胺类化合物氨基15N NMR化学位移规律的研究

提出了计算脂肪胺类化合物的¹⁵N NMR化学位移的经验公式：δ_cal（¹⁵N）=-380.2+ΣΔα+ΣΔβ+ΣΔγ+ΣΔδ+ΣC,结合最小二乘法通过线性回归得到了11种取代基参数,计算结果以133种化合物的133个¹⁵N NMR化学位移数据为样本点进行回归检验,置信度为99.5 %,约有94.7 %的¹⁵N NMR化学位移计算值的计算误差小于5.0（相对误差小于0.5 %）.     

有机磷化合物的NMR研究——Ⅱ0,0-二烷基膦酸酯的1H、13C和31PNMR谱

本文报道了21个0,0一二烷基膦酸酯类化合物的¹H、¹³C和³¹P NMR参数。研究和讨论了不等价的二烷基¹H、¹³C化学位移和磷碳偶合常数与立体化学的关系。测定了(CH₃CH₂O)₂P(O)CH(CH₂NO₂)(p-OCH₃C₆H₄)的¹³C自旋一晶格弛豫时间T₁,二乙基¹³C T₁间的差别,说明在类似化合物中,含有化学位移各向异性对弛豫的贡献。     

阿尔茨海默氏症致病蛋白－Aβ(12-28) 肽段的NMR研究

Aβ肽的多聚化和纤维化在阿尔茨海默氏症(Alzheimer's diseas)的发生中起关键作用, 其中以Aβ_(1-42) 的致病作用为最强,因此阻断其聚集成为阿尔茨海默氏症一种潜在的治疗方式. 作者在研究中发现某些化合物可以结合于Aβ_(12-28) 肽段. 该文采用¹H-¹H COSY、TOCSY、ROESY和¹⁵N-HSQC多种核磁分析方法, 对此肽段的¹H和¹⁵N NMR谱信号进行了归属和详细分析,为进一步研究其与小分子抑制剂的相互作用提供了基础.     

新药硫酸头孢匹罗的NMR研究

应用1D NMR、2D NMR （COSY、HMQC、HMBC、NOESY）及脉冲梯度场2D NMR技术[gHSQC（¹H-¹⁵N）、gHMBC（¹H-¹⁵N）]深入研究了第四代新型超广谱头孢菌素类抗生素硫酸头孢匹罗的结构,并首次对其¹H NMR、¹³C NMR谱和¹⁵N NMR谱的信号进行了全归属,通过NOESY实验对其立体结构提供有力依据.     

卤代苯和卤代萘磺化产物的1H NMR研究

研究了卤代苯和卤代萘磺化产物的¹H NMR分析方法.结合各产物有关质子的化学位移,偶合常数,分裂形式,积分高度可得到各种磺化产物的比例.讨论了双共振去偶合实验的具体应用,化学位移理论值的计算及其在质子谱峰归属中所起的作用,磺化产物¹H和¹⁹F的偶合分裂现象.首次报道了卤代芳香化合物多磺酸取代产物的¹H NMR数值.     

几种N-取代马来酰胺酸辅酶模型的核磁共振研究

我们对8种N-取代马来酰胺酸辅酶模型与不同类型的亲核试剂反应后生成的产物进行了¹H、¹³C NMR的研究, 测得¹H、¹³C谱化学位移,研 究探讨其规律性, 并测试了IR谱和元素分析.     

同核RELAY相干传递技术在复杂天然有机化合物1H谱解析中的应用

用同核化学位移相关谱和同核RELAY谱等二维NMR方法完全归属了复杂天然有机化合物人参皂甙Rb₁的¹H NMR谱线,并用积算符方法证实一级和二级RELAY实验中观察到的意外交叉峰是通过远程偶合传递的RELAY信号。     

高转速下采用S-RESIDOR方法测量1H-27Al偶极偶合常数

提出利用S-RESIDOR(Symmetry-based Resonance Echo Saturation Irradiation DOuble Resonance)方法测量¹H-²⁷Al偶极偶合常数. 通过理论模拟,讨论了四极作用常数、饱和照射脉冲功率、照射时间对¹H/²7Al S-RESIDOR实验的影响. 发现四极作用常数对¹H/²⁷Al S-RESIDOR偶极去相曲线影响较小,中等强度的饱和照射功率即能满足实验要求. 高转速下,在氢型丝光沸石上进行了¹H/²⁷Al S-RESIDOR实验,测量得到Br-nsted酸位上的 ¹H与骨架上²⁷Al的偶极偶合常数为874 Hz.     

A 15N NMR Study of Some Imidazolidine-2,4-Dichalcogen Derivatives

The ¹⁵N NMR chemical shifts and ¹(¹⁵N-¹H) coupling constants of a series of imidazolidine-2,4-dichalcogen (O, S) derivatives are reported.The ¹⁵N NMR chemical shifts show a linear correlatlon wlth the vNH stretchlng vlbratlons. The influence of the substitution of the oxygen at C₂ and/or C₄ with the sulphur, and of the hydrogen at C₅ wlth the methyls and phenyls has been considered. The ¹J(¹⁵N-¹H)'s found In thls serles of molecules agrees well with the expected values.     

The Influence on NMR Parameters of Silicon Penta Coordination in Silatranes

¹H, ¹³C, ¹⁹F and ²⁹Si NMR chemical shifts and coupling constants for Si-substituted silatranes, XSi(OCH₂CH₂)₃N, and triethoxysilanes, XSi(OCH₂CH₃)₃, where X = H, CH₃, and F have been studied. Expansion of the coordination numbers of silicon and tin leads to similar changes in the NMR parameters.     

A15N-1H dipolar CSA solid-state NMR study of polymorphous polyglycine (-CO-CD2-15NH-)n

The solid-state¹H MAS (magic-angle spinning),²H static,¹⁵N CP (cross polarization)-MAS and¹⁵N-¹H dipolar CSA (chemical shielding anisotropy) NMR (nuclear magnetic resonance) spectra of two different modifications of C_α-deuterated^l5N-polyglycine, namely PG I and PG II (-CO-CD₂-^l5NH-)_n are measured. The data from these spectra are compared to previous NMR, infrared, Raman and inelastic neutron scattering work. The deuteration of C_α eliminates the largest intramolecular¹H-¹H dipolar coupling. The effect of the remaining (N)H-(N)H interaction (～5 kHz) is not negligible compared to the¹⁵N-¹H coupling (about 10 kHz). Its effect on the dipolar CSA spectra, described as a two-spin system, is analyzed analytically and numerically and it is shown that those parts of the powder spectrum, which correspond to orientations with a strong dipolar¹⁵N-¹H interaction, can be described as an effective two-spin system, permitting the measurement of the strength of the¹⁵N-¹H dipolar interaction and the orientation of the dipolar vector with respect to the¹⁵N CSA frame. While in the PG II system the¹⁵N CSA tensor is collinear with the amide plane, in the PG I system the CSA tensor is tilted ca. 16° with respect to the (δ₁₁δ₂₂) CSA plane.     

Structural Assignment of Stilbenethiols and Chalconethiols and Differentiation of Their Isomeric Derivatives by Means of 1H‐ and 13C‐NMR Spectroscopy

Abstract

The ¹H‐ and ¹³C‐NMR spectra of some substituted stilbenes and chalcones were assigned unambiguously on the basis of a combination of homo‐ (COSY) and heteronuclear (HETCOR) two‐dimensional methods, the chemical shifts, as well as spin‐coupling constants. The A_ik empirical parameters of the –O–C(S)–N(CH₃)₂, –S–C(O)–N(CH₃)₂, and –SH group were calculated to help predict the chemical shifts of substituted stilbenes, 4′‐nitrostilbenes, and chalcones. The ¹H‐ and ¹³C‐NMR spectra have been shown to be able to differentiate between the isomers of O‐stilbenyl (4, 5) and S‐stilbenyl N,N‐dimethylthiocarbamates (7, 8) as well as O‐chalconyl (6) and S‐chalconyl N,N‐dimethylthiocarbamates (9).     

Complete Analysis of the 1H and 13C NMR Spectra of 5-Isopropylsulfonyl-2-Norbornenes Through the Application of Two-Dimensional NMR Techniques

Total assignment of ¹³C and ¹H NMR spectra of the 5-isopropylsulfonyl-2-norbornenes 2 was achieved using the concerted application of two-dimensional homonuclear and heteronuclear chemical shift correlations. The stereochemistry of both the diastereoisomers endo 2a and exo 2b have been established using the magnitude of the proton coupling constants.     

14N NMR relaxation times of several protein amino acids in aqueous solution--comparison with 17O NMR data and estimation of the relative hydration numbers in the cationic and zwitterionic forms

The 14N nuclear magnetic resonance (NMR) linewidths of the alpha-amino groups of several protein amino acids were measured in aqueous solution, with and without composite proton decoupling, to estimate the effect of proton exchange and molecular weight on the linewidths. It is shown that, contrary to earlier claims, the increase in the linewidth at low pH is not exclusively due to the effect of proton exchange broadening. The 14N linewidths, under composite proton decoupling, increase with the bulk of the amino acid, and increase at low pH. Statistical treatment of the experimental 14N and literature 17O NMR data was performed assuming two models: (i) an isotropic molecular reorientation of a rigid sphere in a medium of viscosity eta, (ii) a stochastic diffusion of the amino and carboxyl groups comprising contributions from internal (tauint) and overall (taumol) motions. Assuming a single correlation time from overall molecular reorientation (taumol), then, a linear correlation was found between the linewidths and the molecular weights of the protein amino acids at the pH values 0.5 and 6.0, which are characteristic of the cationic and zwitterionic forms, respectively. The slopes of the straight-lines were found to be dependent of pH for 14N, contrary to the 17O linear correlations whose slopes were found to be independent of pH. Assuming effective correlation times of the amino and carboxyl groups, which comprise contributions from the internal (tauint) and overall (taumol) motions, then, a significant improvement of the statistics of the regression analysis was observed. The 14N relaxation data, in conjunction with 17O NMR linewidths, can be interpreted by assuming that the 14N quadrupole coupling constants (NQCCs) are influenced by the protonation state of the carboxyl group, the 17O NQCCs remain constant, and the cationic form of the amino acids is hydrated by an excess of 1-3 molecules of water relative to the zwitterionic state.     

C-13 and H-1 NMR Assignments of the Chamigrenes Prepacifenol and Dehydroxyprepacifenol Epoxioes

A complete assignment of the signals in the ¹H and ¹³C NMR spectra and the stereostructural analysis of the compounds prepacifenol epoxide and the new dehydroxyprepacifenol epoxide are presented. These compounds were extracted from the marine mollusc Aplysia dactylomela and represent the first occurrence of chamigrenes found in Brazilian waters. The NMR analyses are supported by NOE difference and COSY experiments and also by gradient selected HMBC, HSQC-TOCSY and HSQC-DE. ¹H spectra simulations were done for the final fitting of the chemical shifts and coupling constants.     

13C Nuclear Magnetic Resonance Studies of the Conformations of Serine‐3′‐ and 5′‐Thymidine Monophosphate Conjugates

The differences in the backbone conformation between O‐thymidine‐3′‐(1) and 5′‐yl O‐alkyl N‐phosphoryl serine methyl esters (2) have been investigated by solution ¹³C NMR spectroscopy. The stereo‐sensitive vicinal ³¹P–¹³C coupling constants were measured and used in the conformational analysis for the P–O5′–C5′, P–O3′–C3′, and P–N–C_α bonds. Three‐dimensional structural characteristics of dephosphorylation reactions of Compounds are also discussed.     

Determination of Internucleotide JHN Couplings by the Modified 2D JNN-Correlated [N, H] TROSY

Recent developments in the direct observation of J couplings across hydrogen bonds in proteins and nucleic acids provide additional information for structure and function studies of these molecules by NMR spectroscopy. A J_NN-correlated [¹⁵N, ¹H] TROSY experiment proposed by Pervushin et al. (Proc. Natl. Acad. Sci. USA 95, 14147–14151, 1998) can be applied to measure ^hJ_HN in smaller nucleic acids in an E.COSY manner. However, it cannot be effectively applied to large nucleic acids, such as tRNA^Trp, since one of the peaks corresponding to a fast relaxing component will be too weak to be observed in the spectra of large molecules. In this Communication, we proposed a modified J_NN-correlated [¹⁵N, ¹H] TROSY experiment which enables direct measurement of ^hJ_HN in large nucleic acids.