最高量子相关谱技术在同核偶合常数测定中的应用(英文)

偶合常数是一个重要的NMR参数,其数值与分子中化学键的二面角有关,可以为分子结构研究提供很重要的信息.多维NMR谱由于具有较大的化学位移分辨率,因此常常被用来测定同核或异核自旋-自旋偶合常数.本文介绍了利用最高量子相关技术(MAXY)测定同核偶合常数的方法.MAXY是最近发展的一种多维NMR谱编辑技术,可以使不同官能团(CH,CH₂,CH₃)的相关峰分布于不同的图谱区域,因此比常规的二维谱具有更高的化学位移分辨率.而且被分离开来的NMR相关峰呈吸收性线型,能清楚地展示各自的偶合分裂特征,可以直接用于测定偶合常数.     

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.     

用于测量J偶合常数的同时多层选择性恒时J分解谱的方法(英文)

标量偶合是核磁共振(NMR)波谱的一个重要参数.其中氢-氢偶合能提供关于分子结构的有用信息.但是,在复杂的偶合网络中解析出氢-氢偶合常数(J_(H-H))较为困难.本文提出了一种基于空间编码选择性恒时演化的测量J_(H-H)的方法,利用一次实验就能解析分子中所有氢核的偶合网络,并测量J_(H-H).该方法被称为同时多层选择性恒时J分解谱(SMS-SECTJRES).它结合空间编码梯度和选择性恒时演化,并利用平面回波谱成像(EPSI)采样模块,从不同的空间位置提取出对应不同氢核偶合网络的J分解谱,促进了NMR技术在分子结构解析中的进一步应用.     

新生育酚氧模型自由基的ESR研究

对新生育酚(维生素E)模型化合物(生育酚1:2,2-二甲基-4-异丙基-7-特丁基-6-色满酚),在甲苯溶剂里以过氧化二叔丁基引发产生生育酚氧自由基进行电子自旋共振(ESR)波谱测试,获得质子超精细分裂(hfs)偶合常数和g_iso因子值.以获得的质子超精细分裂偶合常数进行了计算机图谱模拟.     

采用BP神经网络研究C-F键核自旋偶合常数

通常理论研究核自旋偶合常数的方法是基于线性模型进行拟合和预测，该方法在拟合和预测中仍有较大误差. 本文在前面工作的基础上，提出了基于非线性模型对C-F键核自旋偶合常数进行研究的观点，采用BP神经网络方法对C-F键核自旋偶合常数的函数关系式进行拟合，并用拟合结果对4种化合物的偶合常数进行预测. 结果表明，采用非线性的BP神经网络方法其训练效果与预测效果均优于线性模型方法；其预测误差对文中的4种化合物不超过0.40%.     

基于纯化学位移的同核二维正交相敏J分解核磁共振波谱

二维J分解(2D J_RES)核磁共振(NMR)波谱是一种简单且用户友好的谱图表达形式,其将J偶合常数和化学位移信息分离到两个正交的频率维度上.自40年前首次被提出以来,2D J_RES技术在脉冲序列和方法的改进,以及实际应用的进展方面一直备受关注.本文回顾了新型2D J_RES脉冲序列,以及用于精确测量同核J偶合常数的2D J编辑谱的最近进展,特别是基于纯化学位移演化机制的正交相敏2D J_RES谱方法及其应用,并阐述其在克服强偶合效应和磁场不均匀性等方面的能力.     

应用E.COSY型的13C-1H相关谱准确测定果糖-1,6-二磷酸根离子中异核31P-1H和31P-13C偶合常数

建议了一种E .COSY型的1 3C 1 H相关实验 .在相应的1 3C 1 H相关谱中 ,31 P核对1 3C ,1 H核的被动偶合给出E .COSY型的谱峰裂分 ,可用于准确测定含磷化合物中的31 P 1 H和31 P 1 3C偶合常数及其相对符号 .测定了果糖 1 ,6 二磷酸根离子的31 P 1 H和31 P 1 3C偶合常数     

磺胺-N-苯基J酸分光光度法测定亚硝酸盐研究

筛选了重氮组分和偶合组分。研究了重氮偶合显色反应的条件和方法,提出了借助于磺胺-J酸系列染料中间体(N-苯基J酸、J酸、双J酸)重氮偶合技术分光光度法测定亚硝酸盐。在常温溴化钾共存下,亚硝酸盐在稀盐酸溶液中与磺胺发生重氮化反应,在碳酸钠水溶液中重氮盐与J酸系列染料中间体偶合生成有色偶氮化合物。磺胺-N-苯基J酸偶氮化合物的表观摩尔吸光系数为4.63×104 L·mol-1·cm-1,线性范围为0.003～0.7 mg·L-1,回收率为99.5%～101.6%。相对标准偏差为2.10%。该本方法可用于环境水体中痕量亚硝酸盐的测定。     

直接键连原子间的NMR偶合常数的自然杂化轨道研究Ⅲ、α-C-H键核自旋偶合常数1JCH

报道了一种计算直接键连原子间的核自旋-自旋偶合常数的通用关系式,结合CNDO/2分子轨道方法和自然杂化轨道方法,具体计算了一些极性α-C-H键的核自旋偶合常数。结果表明,本文方法适合于多种类型的直接键连原子间的偶合常数的计算,且与已有实验值吻合一致.     

核自旋偶合常数的计算(Ⅲ)烃类分子H-H偶合常数3J、4J、5J…的计算

本文把计算隔两个化学键的偶合常数²J的原理和方法,推广到烃类分子中的隔三个化学键的偶合常数³J和远程偶合常数⁴J、⁵J……的计算。对20个化合物的57个偶合常数的计算结果表明,除了个别与实验值相差较大外,一般都能较好地符合。     

The application of maximum entropy processing to the deconvolution of coupling patterns in NMR

The deconvolution of J-coupling patterns in NMR by iterative maximum entropy processing is demonstrated. Both the in-phase and the antiphase coupling patterns are considered. The deconvolution of the coupling pattern, either for one value of the coupling constant (1D J deconvolution) or for a range of coupling constants (2D J deconvolution) is shown. It is demonstrated that the method can be used for improving the signal-to-noise ratio for known coupling patterns by removing the coupling structure, as well as for extracting coupling constants from an unknown spectrum. Examples are shown both in 1D NMR and in slicewise processing of 2D spectra.     

Analyses, extensions and comparison of three experimental schemes for measuring ((n)J(CH)+D(CH))-couplings at natural abundance

Three types of experiments for measuring (n)J(CH) heteronuclear long-range coupling constants are examined and extended with state-of-the-art pulse sequence building-blocks: The use of a HMBC with corresponding reference-HSQC for accurate coupling determination is combined with the constant time technique and the conversion of antiphase magnetization into ZQ/DQ-coherences; CPMG-based LR-CAHSQC and BIRD(r,X)-HSQMBC experiments are examined in detail with respect to their coherence transfer properties; finally, the HSQC-TOCSY-IPAP experiment is introduced, a sequence derived from previously published alpha and beta selective HSQC-TOCSYs using a different spin state selection technique and a recently developed ZQ-suppression method. The experiments are characterized with their advantages and disadvantages and compared using strychnine and menthol as standard molecules.     

Measurement of small spin-spin splittings in the presence of chemical exchange: case of deuteriated water

A new implementation of a described data processing for measuring small scalar coupling constant J is proposed. It is applied particularly to situations where the coupling constant is around the linewidth at half-height, and in the presence of chemical exchange. This modified data processing uses only a simple "one-pulse" experiment instead of a series of spin echoes experiments required by the previous processing. The FID recorded in the one pulse experiment is used by a reconstitution program to generate a set of signals, which are analyzed in the time domain to obtain a spectrum where the scalar coupling constant is apparently multiplied by n+1, where n is positive. The new processing is tested with simulated spectra. The coupling constant between proton and deuterium is measured in the proton spectrum of a solution of 80% of D(2)O and 20% of H(2)O. It was found to be J=1.54+/-0.01 Hz.     

氢原子光谱实验研究

氢原子的结构简单，其光谱具有明显的规律，各种原子光谱线规律性的研究首先是在氢原子上得到突破。通过测量氢光谱可见谱线的波长，能较准确测定氢的里德伯常数，可使学生对近代物理测量有初步了解。     

The new HMQC-based technique for the quantitative determination of heteronuclear coupling constants. Application for the measurement of 3J(H'(i),P(i+1)) in DNA oligomers

A new general J-HMQC-based technique is presented, which allows an accurate determination of heteronuclear coupling constants. The most important feature of this new approach includes acquisition of the two data sets with and without the additional pi(S)-pulse at the end of coupling evolution period. This enables preservation and separation of the two orthogonal terms of coupling evolution, which are manifested by in- and antiphase cross-peaks, respectively. The coupling magnitudes are evaluated by the nonlinear least-squares fitting of the ratios of integrated signal volumes for both kinds of signals. The effectiveness of the new sequence is demonstrated by determination of the 3J(H3'(i),P(i+1)) couplings in DNA octamer duplex d(GCGTACGC)(2) sample. Additionally, the ability of the new method for the measurement at the natural abundance level of 13C nuclei is presented for the beta-cyclodextrin.     

J＇K耦合的Zeeman效应

在分析光谱数据基础上，本文以Ｎｅ原子６３２８谱线为Ｊ’Ｋ耦合Ｚｅｅｍａｎ效应实例计算了谱线在较弱磁场中的分裂情况；从而廓清了有关教材中不正确的论述。     

HAT HMBC: a hybrid of H2BC and HMBC overcoming shortcomings of both

A new 2D NMR experiment, HAT HMBC, that is a hybrid of H2BC and HMBC aims at establishing two-bond correlations absent in H2BC spectra because of vanishing (3)J(HH) coupling constants. The basic idea is to create an additional pi phase difference in the multiplet structure in HMBC peaks with respect to the (n+1)J(HH) coupling constant between the proton(s) attached to a (13)C and a (1)H separated by n bonds. Thus HMBC peaks associated with small J(HH) will be the most attenuated in a HAT HMBC spectrum in comparison to a regular HMBC spectrum, i.e. peaks associated with (n+1)J(HH) and (n)J(CH) will for n>2 usually be strongly attenuated. The HAT HMBC pulse sequences contain the same number of pulses as regular HMBC and are only a few milliseconds longer.     

Novel methods for characterizing a decoupler channel using "undetectable" quantum coherences.

Exact solutions for the effect of time-independent RF pulses on any initial configuration of an IS J-coupled system demonstrate that on-resonance CW decoupling yields signals whose frequency depends on RF field strength and homogeneity. These signals are enhanced starting with "undetectable" antiphase and multiple quantum coherences, which can also produce centerband intensity to mimic the signal from decoupled Sx. Conversely, these coherences can be generated from Sx using a low-power pulse, B1 = J/2, of length (2J)-1, dubbed a "90J pulse" since it is the selective equivalent of {(2J)-1-90[I]}. Utilizing 90J pulses, new characterization-of-decoupler (COD) pulse sequences can determine the performance of an insensitive I-spin channel by observing large signals from either antiphase or multiple quantum coherences with the S-spin channel, allowing, in minutes rather than hours: (i) frequency calibration to an accuracy of 0.1 Hz; (ii) measurement of RF amplitudes over a 500-fold variation; and (iii) mapping of RF homogeneity along the sample axis with a single 1D B1 spectrum. These 90J coherence transfer pulses are of potential general use for selective spectroscopy.     

Antiphase States in Coupled Oscillator Systems

Coupled identical oscillators with resistive couplings are investigated. Various antiphase states are observed. The bifurcation threshojds for the antiphase states of coupled van der Pol oscillators and the unstable modes of these systems at the bifurcation points are explicitly compu ted. The dependence of antiphase states on system size and coupling length is investigated in detail. General coupled limit cycle models are also investigated. The realizations of antiphase states can be explained, based on the global potential analysis.     

Pattern formation in arrays of chemical oscillators

We describe a simple model mimicking diffusively coupled chemical micro-oscillators. We characterize the rich variety of dynamical states emerging from the model under variation of time delay in coupling, coupling strength and boundary conditions. The spatiotemporal patterns obtained include clustering, mixed dynamics, inhomogeneous steady states and amplitude death. Further, under delay in coupling, the model yields transitions from phase to antiphase oscillations, reminiscent of that observed in experiments [M Toiya et al, J. Chem. Lett. 1, 1241 (2010)].