High-resolution solid-state 13C14N and 13C15N heteronuclear correlation spectroscopy

Two-dimensional heteronuclear correlation spectroscopy is applied to coupled carbon and nitrogen nuclei in single crystals of amino acids and peptides. High resolution is available because the spectra have the carbon chemical shift along one frequency axis and the nitrogen chemical shift (and the second-order quadrupole shift in the case of ¹⁴N) along the second frequency axis. These two-dimensional spectra enable direct measurements of resonance frequencies and dipole-dipole couplings that are useful in providing information about the structure, dynamics, and spectral characteristics of molecules.     

3D 13C–13C–13C correlation NMR for de novo distance determination of solid proteins and application to a human α-defensin

The de novo structure of an antimicrobial protein, human α-defensin 1 (HNP-1), is determined by combining a 3D ¹³C–¹³C–¹³C (CCC) magic-angle spinning (MAS) correlation experiment with standard resonance assignment experiments. Using a short spin diffusion mixing time to assign intra-residue cross peaks and a long mixing time to detect inter-residue correlation peaks, we show that the 3D CCC experiment not only reduces the ambiguity of resonance assignment, but more importantly yields two orders of magnitude more long-range distances without recourse to existing crystal structures. Most of these distance constraints could not be obtained in a de novo fashion from 2D correlation spectra due to significant resonance overlap. Combining the distance constraints from the 3D CCC experiment and the chemical-shift-derived torsion angles, we obtained a de novo high-resolution NMR structure of HNP-1, with a heavy-atom RMSD of 3.4 Å from the crystal structure of the analogous HNP-3. The average energy of the minimum-energy ensemble is less than of 40 kcal/mol. Thus, the 3D CCC experiment provides a reliable means of restraining the three-dimensional structure of insoluble proteins with unknown conformations.     

13C NMR Module-13C化学位移经验预测软件

¹³C NMR Module软件是瑞士联邦高等工学院(ETH)有机化学系A.Fuerst编写的可附中于Windows3.1以后版本中ChemWindow软件中用以计算¹³C NMR化学位移的子程序.目前由Soft Shel International公司发售,单价为149美元,研究单位为99美元,研究生用为29美元.     

Tri-bimaximal neutrino mixing from A4 and θ13∼θC

It is a common believe that, if the tri-bimaximal mixing (TBM) pattern is explained by vacuum alignment in an $A_4$ model, only a very small reactor angle, say ${\theta }_{13}～O({\lambda }_C^2)$ being ${\lambda }_C\equiv {\theta }_C$ the Cabibbo angle, can be accommodated. This statement is based on the assumption that all the flavon fields acquire VEVs at a very similar scale and the departures from exact TBM arise at the same perturbation level. From the experimental point of view, however, a relatively large value ${\theta }_{13}～O({\lambda }_C)$ is not yet excluded by present data. In this paper, we propose a seesaw $A_4$ model in which the previous assumption can naturally be evaded. The aim is to describe a ${\theta }_{13}～O({\lambda }_C)$ without conflicting with the TBM prediction for ${\theta }_{12}$ which is rather close to the observed value (at ${\lambda }_C^2$ level). In our model the deviation of the atmospherical angle from maximal is subject to the sum-rule: ${\sin }^2{\theta }_{23}\approx 1/2+\sqrt{2}/2\cos \delta \sin {\theta }_{13}$ which is a next-to-leading order prediction of our model.     

13C NMR and Fukui function analysis on C82 hydroxylated fullerene through density functional theory

Density functional theory calculations were performed on C₈₂ hydroxylated fullerene. B3LYP and PBE0 functionals with 6-31G** basis set were utilised to get chemical shieldings, chemical shifts and the isotropic Fermi contact coupling on each atomic site. A relation between nuclear magnetic resonance (NMR) properties and reactivity of the molecule, obtained through the electronic Fukui function, was observed. Interestingly, the most stable configurations of OH groups adsorbed on C₈₂ surface were obtained when the hydroxyl groups are adsorbed on deshielded (isotropically and anisotropically) sites. For open-shell systems, a relation between isotropic Fermi contact, spin density and average Fukui function was found, that is, sites with a great amount of Fukui function (analytical and the one obtained through finite difference) and spin density have the largest isotropic Fermi contact coupling data. With the adsorption of the first hydroxyl molecules, spin densities and Fukui functions show preferential sites to adsorb the following OH groups close to previously adsorbed. Additionally, theoretical spectra of chemical shifts of C₈₂(OH)_n (n = 1, 2, 3 and 4) were obtained and they were compared with experimental reports, getting a reasonable comparison. For example, regarding ¹³C NMR chemical shifts obtained in C₈₂OH molecule, 80 ppm (B3LYP) and 79 ppm (PBE0) were calculated on hydroxylated carbon, which is in good agreement with experimental results in C₆₀ fullerols.     

^13C NMR Module—^13C化学位移经验预测软件

13CNMRModule软件是瑞士联邦高等工学院（ETH）有机化学系A．Fuerst编写的可附加于Windows3．1以后版本中ChemWindow软件中用以计算‘’CNMR化学位移的子程序．目前由SoftShellInternational公司发售，单价为149美元，研究单位为腴美元，研究生用为29美元.(e-mail:info@softshell.com)它适用于用6－PC机，有4兆内存以上，ChelnWilldow3．0．2版本以后的程序中·除‘’C化学位移预测外，尚可提供计算分子量等一般功能问．其原理见门．众所周知，自从Paul，Grant间1964年提出可用取代基作用的加和定律预测“CNMR化学位移值以来，…     

(e,e′), (γ, π+ and (π−, γ) on12C and13C

A detailed theoretical analysis of spin degrees of freedom in carbon isotopes is performed, probing them by electron scattering, pion photoproduction and radiative pion capture from the mesoatomic orbits.Dedicated by the co-authors to the memory of J. Gmitro.The present paper is one of the last works made together with our colleague Marian Gmitro. We had to complete it without him. We mourn for his sudden death and we will always keep alive the memory of his bright personality.     

小型13C NMR谱图数据库

本文着重介绍用当前微机系统上流行的DBASEⅡ建立谱图数据库以及用BASIC语言进行结构检索的方法。检索系统能方便地提供用户收集、修正、查询、显示和打印谱图数据和分子结构图的功能。这种系统对建立专用的小型谱图数据库有实用价值。     

High-resolution infrared spectroscopy of H12C13CD and H13C12CD in the 470–5200 cm−1 spectral region

The fundamental ro-vibrational bands and the 2ν₄?←?GS, 2ν₅?←?GS, 2ν₃?←?GS, ν₄?+?ν₅?←?GS, ν₃?+?ν₄?←?GS, ν₃?+?ν₄?←?ν?₄, ν₃?+?ν₅?←?ν₅, overtone, combination and hot bands of the two rare isotopologues of acetylene H¹²C¹³CD and H¹³C¹²CD have been detected by Fourier transform infrared spectroscopy (FTIR). The analysis of the data has provided very accurate rotational and vibrational parameters for the ground and for the vibrationally excited states.     

High resolution infrared and Raman spectroscopy of ν 2 and associated combination and hot bands of 13C12CD2

Infrared and Raman spectra of dideuterated acetylene containing one ¹³C atom, ¹³C¹²CD₂, have been recorded and analysed to obtain detailed information on the fundamental ν ₂ band and associated combination and hot bands. Infrared spectra were recorded at 4?×?10^?3?cm^?1 resolution in the region 1150?2900^?cm^?1, which contains combination and hot bands from the ground and the bending v ₄?=?1 and v ₅?=?1 states. The Q-branches of the ν ₂ fundamental and associated hot bands (ν ₂?+?ν ₄???ν ₄, ν ₂?+?ν ₅???ν ₅, ν ₂?+?2ν ₄???2ν ₄, ν ₂?+?2ν ₅???2ν ₅ and ν ₂?+?ν ₄?+?ν ₅???(ν ₄?+?ν ₅)) were recorded using inverse Raman spectroscopy, with an instrumental resolution of about 3?×?10^?3?cm^?1. In addition, the observation of the 2ν ₂???ν ₂ Raman band was carried out populating the v ₂?=?1 state by stimulated Raman pumping. In total, 11 Raman and 9 infrared bands were analysed, involving all the l-vibrational components of the excited stretching?bending manifolds up to v _t ?=?v ₄?+?v ₅?=?2.

A simultaneous analysis of all infrared and Raman assigned transitions has been performed on the basis of a theoretical model which takes into account the rotation and vibration l-type resonances within each vibrational manifold and the Darling?Dennison anharmonic resonance between the ν ₂?+?2ν ₄ and ν ₂?+?2ν ₅ states. The parameters obtained reproduce the assigned transition wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.     

Characterisation of spatial variability and patterns in tree and soil δ13C at forested sites in eastern Canada

Wholistic isotopic studies provide a necessary foundation on which to build conceptual understanding of ecosystem development processes and provide the basis for further isotopic studies at a site or within an ecophysiological region. This study seeks to broadly characterise δ¹³C spatial variability and spatial patterns within soils and canopy tissues at five forest research sites in eastern Canada. We observe consistent and predictable patterns of leaf δ¹³C variation within trees and a consistent offset between woody and leafy tree tissues. Patterns are similar for both hardwoods and softwoods, but overall hardwoods had canopies that were more depleted in ¹³C. Soil carbon δ¹³C enrichment occurred with depth and appeared to vary according to site soil texture. Upper soil δ¹³C was intermediate between leaves and woody tissues, whereas deeper soil values suggested important contributions from more enriched tree tissues, such as persistent woody debris and possibly roots. The relationship between aboveground and belowground signatures suggests functional or developmental differences between study sites.     

Selective homonuclear Hartmann–Hahn for 13C→13C polarization transfer in solution state NMR

Polarization transfer has become a commonplace technique for the enhancement of a variety of nuclei in high field nuclear magnetic resonance (NMR). In this paper the homonuclear Hartmann-Hahn method for polarization transfer is revisited and it is shown that a 90% transfer of polarization can be achieved experimentally between a pair of scalar coupled ¹³C nuclei in a sample of isotopically enriched glycine. This may show particular utility in the field of dynamic nuclear polarization (DNP) and could be used as an addendum to already established DNP techniques allowing the favourable enhancement to be ‘stored’ on long-lived nuclei and subsequently transferred to shorter-lived nuclei prior to observation.     

取代喹啉的13C NMR研究

报道了14种新的取代喹啉的¹³C NMR谱.应用¹³C NMR等谱确定了这14种新化合物的分子结构,并对全部谱峰进行了归属,初步探讨了分子结构对¹³C NMR化学位移的影响.     

乙丙共聚物的13C NMR研究

研究用化学反应法制备的镁钛系载体高效催化剂合成的乙丙共聚物的¹³C NMR谱图,提出了无需进行分峰处理,通过将谱图直接分为八个独立的区域,并选取其中受仪器测试条件等影响较小的五个谱区的强度,直接计算此类共聚物序列分布的方法,并分别采用伯努利模型和马尔科夫模型对共聚物的三单元组序列分布进行处理,指出在化学反应法制备的载体催化剂催化的乙丙共聚合扫次末端基效应机理进行,且催化剂活性中心有利于乙丙各自的均聚合.     

13C 呼气实验与心脏病检查

13C 脂肪酸的呼气实验,被认为是检查和预测心脏疾病或心肌不良功能的诊断工具。本文概略地介绍了用呼气实验检查心脏病的原理和方法;用具体的实例说明了此法在临床上的应用;通过数据分析介绍了影响实验准确性的关键因素,即心脏负荷对呼气实验的影响;为说明呼气实验的发展过程,本文对稳定同位素在医学上的应用作了文献小结。     

Field-deployable measurements of free-living individuals to determine energy balance: fuel substrate usage through δ13C in breath CO2 and diet through hair δ13C and δ15N values

Carbon isotopes of breath CO₂ vary depending on diet and fuel substrate used. This study examined if exercise-induced δ¹³C-CO₂ changes in substrate utilization were distinguishable from baseline δ¹³C-CO₂ variations in a population with uncontrolled diet, and compared hair isotope values and food logs to develop an isotope model of diet. Study participants included nine women with diverse Body Mass Index (BMI), age, ancestry, exercise history, and diet. Breath samples were collected prior to and up to 12?h after a 5- or 10?K walk/run. Indirect calorimetry was measured with a smartphone-enabled mobile colorimetric device, and a field-deployable isotope analyzer measured breath δ¹³C-CO₂ values. Diet was assessed by food logs and δ¹³C, δ¹⁵N of hair samples. Post-exercise δ¹³C-CO₂ values increased by 0.54?±?1.09‰ (1 sd, n?=?9), implying enhanced carbohydrate burning, while early morning δ¹³C-CO₂ values were lower than daily averages (p?=?0.0043), indicating lipid burning during overnight fasting. Although diurnal δ¹³C-CO₂ variation (1.90?±?0.77‰) and participant baseline range (3.06‰) exceeded exercise-induced variation, temporal patterns distinguished exercise from dietary isotope effects. Hair δ¹³C and δ¹⁵N values were consistent with a new dietary isotope model. Notwithstanding the small number of participants, this study introduces a novel combination of techniques to directly monitor energy balance in free-living individuals.