Prediction of the ^(13)C NMR Chemical Shifts of Stilbene Analogues by GIAO Method

After the geometry optimization at B3LYP/6-31＋G（d,p） level,the calculations of the NMR chemical shifts of a series of stilbene analogues were carried out by means of Gauge Including Atomic Orbitals（GIAO） method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at both HF/6-31＋G（d） and B3LYP/6-31＋G（d,p） levels are in agreement with the observed values.By virtue of a series of linear correction equations（δpred.=a＋bδcalcd.） of the 13C chemical shifts,accurate prediction of 13C chemical shifts was achieved for the new stilbene compounds.For the 13C NMR chemical shifts calculated at HF/6-31＋G（d） level,the linear correlation of δpred.with δexptl.is excellent,and the square of correlation coefficient,r2,is 0.9985.The maximum absolute difference between δpred.and δexptl.,Δδ,is 2.3,and the root-mean-square error between δpred.and δexptl.is 0.98.In the meantime,for those obtained at B3LYP/6-31＋G（d,p） level,the linear correlation of δpred.with δexptl.is also excellent,and the square of correlation coefficient,r2,is up to 0.9987.The maximum absolute difference between δpred.and δexptl.,Δδ,is 2.2,and the root-mean-square error between δpred.and δexptl.is only 0.88.

Prediction of the ^(13)C NMR Chemical Shifts of Fluorenone Analogues by the GIAO Method

After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at HF/6-31＋G（d） level show better agreement with the observed values.By a series of linear correction equations （δpred=a ＋ bδcalc）,accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound.The linear correlation of δpred with δexptl is excellent,and the square of correlation coefficient,r2,is up to 0.994.The maximum absolute difference between δpred and δexptl,Δδ,is 4.6 ppm,and the root-mean-square error between δpred and δexptl is only 2.6 ppm.

DFT Studies on Thermal Stabilities,Electronic Structures,and ^(13)C Chemical Shifts of C_(24)O_2 Based on Fullerene C_(24)(D_6)

Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G（d） level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.

Correlation of ^1H NMR Chemical Shift for Aqueous Solutions by Statistical Associating Fluid Theory Association Model

^1H NMR chemical shifts of binary aqueous mixtures of acylamide, alcohol, dimethyl sulphoxide (DMSO), and acetone are correlated by statistical associating fluid theory (SAFT) association model. The comparison between SAFT association model and Wilson equation shows that the former is better for dealing with aqueous solutions. Finally, the specialties of both models are discussed.

Simulation of ^(13)C NMR chemical shifts of carbinol carbon atoms using quantitative structure-spectrum relationships

A quantitative structure-spectrum relationship (QSSR) model was developed to simulate 13C nuclear magnetic resonance (NMR) spectra of carbinol carbon atoms for 55 alcohols. The proposed model,using multiple linear regression,contained four descriptors solely extracted from the molecular structure of compounds. The statistical results of the final model show that R2= 0.982 4 and S=0.869 8 (where R is the correlation coefficient and S is the standard deviation). To test its predictive ability,the model was further used to predict the 13C NMR spectra of the carbinol carbon atoms of other nine compounds which were not included in the developed model. The average relative errors are 0.94% and 1.70%,respectively,for the training set and the predictive set. The model is statistically significant and shows good stability for data variation as tested by the leave-one-out (LOO) cross-validation. The comparison with other approaches also reveals good performance of this method.

Substituent Effect on Mercury-199 Chemical Shifts in Some Bisarylmercurials and Aryl(2-benzothiazolylthio) mercurials

The present paper covers the 199 Hg NMR chemical shifts of 24 substituted diphenylmercurials and phenyl(2-benzothiazolylthio)mercurials. There is a good linear relationship between the chemical shift and the Hammett constant of the substituents for both series of compounds, and electron donating substituents cause the chemical shift towards downfield.

Repeatability of two-dimensional chemical shift imaging multivoxel proton magnetic resonance spectroscopy for measuring human cerebral choline-containing compounds

AIM To investigate the repeatability of proton magnetic resonance spectroscopy in the in vivo measurement of human cerebral levels of choline-containing compounds(Cho).METHODS Two consecutive scans were carried out in six healthy resting subjects at a magnetic field strength of 1.5 T. On each occasion, neurospectroscopy data were collected from 64 voxels using the same 2 D chemical shift imaging(CSI) sequence. The data were analyzed in the same way, using the same software, to obtain the values for each voxel of the ratio of Cho to creatine. The Wilcoxon related-samples signed-rank test, coefficient of variation(CV), repeatability coefficient(RC), and intraclass correlation coefficient(ICC) were used to assess the repeatability. RESULTS The CV ranged from 2.75% to 33.99%, while the minimum RC was 5.68%. There was excellent reproducibility, as judged by significant ICC values, in 26 voxels. Just three voxels showed significant differences according to the Wilcoxon related-samples signed-rank test. CONCLUSION It is therefore concluded that when CSI multivoxel proton neurospectroscopy is used to measure cerebral choline-containing compounds at 1.5 T, the reproducibility is highly acceptable.

SUBSTITUENT CHEMICAL SHIFT (SCS) AND THE SEQUENCE STRUCTURE OF ETHYLENE-VINYL ALCOHOL COPOLYMERS

Three ethylene-vinyl alcohol copolymers were studied by means of the substituent chemical shift (SCS) method. The SCS parameters of hydroxy (-OH) in two different solvents were obtained: in deuterium oxide/phenol (20/80 W/W ) the parameters are S_1 = 42.77±0.08ppm, S_2 = 7.15±0.06 ppm, S_3 (s)= -4.08±0.02ppm, S_3 (t) =-3.09±0.20ppm,S_4 = 0.48±0.03ppm, S_5 = 0.26±0.05ppm. In o-dichloro-benzen-d_4 S_1(s)=44.79±0.61ppm, S_2=7.40±0.00ppm, S_3(s)=-4.51±0.17ppm, S_3(t)=-3.13 ±0.00 ppm, S_4 =0.63±0.04ppm, S_5=0.36±0.00ppm.Simultaneously the ^(13)CNMR spectra of EVA copolymers were assigned by using the SCS parameters obtained.

Prediction of the ^(13)C NMR Chemical Shifts of 9,10-Dihydrophenanthrene Analogues by the GIAO Method

After the geometry optimizations at the B3LYP/6-31＋G（d,p） level, the NMR calculations of a series of 9,10-dihydrophenanthrene analogues have been carried out by GIAO method at the HF/6-31＋G（d） level. The calculated ^13C NMR chemical shifts are in agreement with the observed values. By a series of linear correlation equations （δpred = a ＋ bδcal.c） of the ^13C chemical shifts, accurate prediction of ^13C chemical shifts was achieved for the new 9,10- dihydrophenanthrene compound, for which the predicted ^13C NMR chemical shifts are in quite good agreement with the experimental values. The linear correlation between δpred and δexptl is excellent, and the square of correlation coefficient, r^2, is up to 0.9973. The maximum absolute difference between δpred and δexptl, △δ, is 4.5 ppm, and the rms error between δpred and δexpt is 2.55 ppm. In the meantime, according to the theoretical predicted result, we could confirm that the new 9,10-dihydrophenanthrene analogue is erianthridin （2,7-dihydroxy-3,4-dimethoxy-9,10-dihydro- phenanthrene）.

ACCEPT-NMR: A New Tool for the Analysis of Crystal Contacts and Their Links to NMR Chemical Shift Perturbations

We have developed an open-source cross-platform software toolkit entitled ACCEPT-NMR (Automated Crystal Contact Extrapolation/Prediction Toolkit for NMR) as a helpful tool to automate many of the complex tasks required to find and visualize crystal contacts in structures of biomolecules and biomolecular assemblies. This toolkit provides many powerful features geared toward NMR spectroscopy and related disciplines, such as isotopic labeling, advanced visualization options, and reporting tools. Using this software, we have undertaken a survey of available chemical shift data in the literature and deposited in the BMRB, and show that the mere presence of one or more crystal contacts to a residue confers an approximately 65% likelihood of significant chemical shift perturbations (relative to solution NMR chemical shifts). The presence of each additional crystal contact subsequently increases this probability, resulting in predictive accuracies in excess of 80% in many cases. Conversely, the presence of a significant experimental chemical shift perturbation indicates a >60% likelihood of finding one or more crystal contacts to a particular residue. Pinpointing sites likely to experience large CSPs is critical to mapping solution NMR chemical shifts onto solid-state NMR data as a basis for preliminary assignments, and can thus simplify the assignment process for complex biomolecules. Mapping observed CSPs onto the molecular structure, on the other hand, can indicate the presence of crystal interfaces where no crystal structure is available. Finally, by detecting sites critical to intermolecular interfaces, ACCEPT-NMR can help guide experimental approaches (e.g. isotopic labeling schemes) to detect and probe specific inter-subunit interactions.

Anomeric Proton and Carbon (H1-C1) NMR Chemical Shifts of Antigenic Mannans Obtained from Pathogenic Yeast <i>Candida tropicalis</i>

On two dimensional maps of 1H-13C correlation spectroscopy (H-C COSY) analysis for the mannan of Candida tropicalis, nine cross peaks of anomeric proton and carbon were useful for the purpose of obtaining information on the chemical structure of this molecule. Namely, the mannans was comb-like structure constructed with the linear α-1,6-linked polymannnosyl backbone and several oligomannnosyl side chains composed of α-1,2-, α-1,3-, and β-1,2-linkages. Therefore, in the structural investigation of comb-like mannan, two-dimensional H-C COSY analysis is as useful as two-dimensional nuclear Hartmann-Hahn (HOHAHA) analysis.

Structures and Hydrogen Bonding Interactions in Urea-water System Studied by All-atom MD Simulation and Chemical Shifts in NMR Spectrum

脲水系统的相互作用和结构被一个所有原子学习分子的动力学(MD ) 模拟。结合氢的网络和光线的分发函数在 MD 模拟被采用。脲水混合物的结构能从结合氢的网络的分析被分类进不同区域。脲分子与脲增加的鼹鼠部分显示出某些趋势到自我总数。而且，模拟也是的 MD 的结果在模拟与象氢原子和粘性的化学移动那样的实验数据一致的 MD 把水的答案，和平均数字氢契约的统计结果与脲的化学移动和粘性作比较。

Ab Initio Prediction of ^(29)Si-NMR Chemical Shifts

The ability of several ab initio models to predict experimental 29Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allyltrimethylsilane (C) are calculated by GIAO , CSGT and IGAIM methods, using HF/6-31G*, B3LYP/6-31G*, HF/6-311+G **, B3LYP/6-311+G ** and MPW1PW91/6-311+G ** models respectively. The 29Si chemical shifts calculated by GIAO method using HF/6-311+G ** model are highly in agreement with those obtained experimentally. All of the models above reproduce the trends of chemical shifts in all cases studied, suggesting that the models are of practical value.

不同MR设备CSE MR序列定量骨髓质子密度脂肪分数的一致性分析

目的探讨以单体素氢质子磁共振波谱成像(MRS)为参照,验证不同厂家3T化学位移编码水/脂分离MR序列(CSE-MRI)定量腰椎骨髓质子密度脂肪分数(PDFF)的可重复性与一致性。方法选取38例受试者进行腰椎MRS(PDFF_(MRS))、联影CSE-MRI(PDFF_(FACT))与西门子CSE-MRI(PDFF_(Dixion))扫描。以均方根误差(RMSE)和均方根变异系数(RMS-CV)评价CSE-MRI定量PDFF的精密度及可重复性。使用组内相关系数(ICC)评估不同观察者及观察者内测定PDFF值的一致性。采用Linear regression及Bland-Altman分析评价不同CSE-MRI序列与MRS定量PDFF的可代替性及不同公司间CSE-MRI序列定量PDFF的一致性。结果PDFF_(MRS)、PDFF_(FACT)及PDFF_(Dixion)定量骨髓PDFF值分别为58.2%(38.7%,67.0%)、56.7%(37.2%,66.6%)、56.3%(36.8%,65.4%)。PDFF_(FACT)与PDFF_(Dixion)RMSE分别为1.48%、1.57%,RMS-CV分别为2.37%、2.25%,可重复性良好。观察者内及观察者间测定PDFF具有实质性的一致性,ICC均大于0.99。MRS、FACT及Dixon VIBE序列定量骨髓PDFF之间的线性回归分析,R^(2)=0.985~0.989,差异有统计学意义(P<0.001)。Bland-Altman分析PDFF_(FACT)与PDFF_(MRS)差值97.4%的点落在95%可信区间内,PDFFDixon与PDFF_(MRS)差值92.1%的点落在95%可信区间内,PDFF_(FACT)与PDFFDixon差值92.1%的点落在95%可信区间内,显示了良好的一致性。结论联影与西门子CSE MR序列定量腰椎PDFF可重复性良好,其准确性可等同于MRS。

嗜热链球菌grx02化学限定增殖培养基及变温培养策略的研究

文章研究了能够促进嗜热链球菌grx02生长的化学限定培养基成分、浓度及其变温培养方法。通过单一成分扣除实验确定化学限定培养基的碳源、氨基酸、维生素矿物质等营养成分的组成,进一步通过单因素实验,对化学限定培养基组分浓度、变温培养方法进行优化,以提高嗜热链球菌grx02的活菌数。结果表明,嗜热链球菌grx02化学限定增殖培养基由1种碳水化合物、16种氨基酸、6种维生素、3种矿物质、4种无机盐、2种有机盐组成;培养初始温度、延滞末期及对数末期温度分别为39、37、39℃。最终嗜热链球菌grx02生物量达到1.40,较优化前提高了1.63倍,活菌数达到9.04 log CFU/mL。可为嗜热链球菌生产及其代谢与功能研究提供参考。

骨髓脂肪对骨转移的影响及磁共振成像定量评估

背景:早期骨转移的准确诊断对治疗方案和预后有着至关重要的作用。骨活检是骨转移诊断的金标准,但由于有创且标本尺寸小等缺点,在实际临床工作中难以落实。近年来,随着MRI技术的不断发展,磁共振定量成像技术如磁共振波谱成像、基于化学移位编码的水脂肪成像等被广泛应用于骨转移的诊断,衍生的标志物包括表信号脂肪分数和质子密度脂肪分数,均能反映骨髓脂肪含量。目前,对于骨髓脂肪在骨转移瘤发生中的作用已经成为了人们关注的新焦点。目的:现就骨髓脂肪对骨转移的影响及磁共振成像定量评估技术进行综述,归纳比较不同磁共振脂肪定量技术评估骨转移的优劣势以及临床应用情况。方法:应用计算机在PubMed和中国知网数据库检索相关文献,英文检索词为“bone metastases,bone marrow adipocytes,magnetic resonance imaging,quantitative MRI,fat fraction,magnetic resonance spectrum,chemical shift encoding-based water–fat imaging”,中文检索词为“骨转移,骨髓脂肪,磁共振成像,定量磁共振成像,脂肪分数,磁共振波谱成像,基于化学移位编码的水脂肪成像”,根据纳入和排除标准共获得相关文献67篇。结果与结论:(1)骨髓脂肪细胞能通过分泌多种相关激素及细胞因子、为肿瘤细胞提供能量、诱导破骨细胞分化等多种途径协助骨转移的发生;(2)磁共振定量技术能够精确地定量脂肪组织,测量骨髓中脂肪含量的变化有助于骨转移的诊断;(3)磁共振波谱成像能够通过不同质子的进动频率反映不同的代谢产物,因此可用于脂肪定量,是目前用于评估转移性骨折的一种辅助检查手段;(4)基于化学移位编码的水脂肪成像可以使水和脂肪信号得以在正相位和反相位相分离,从而测量脂肪组织的信号,在鉴别椎体良恶性骨折方面具有较高的敏感性、特异性和准确性。

Study on the relationships between Raman shifts and temperature range for α-plane GaN using temperature-dependent Raman scattering

In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K.The temperature-dependences of GaN phonon modes（A1（TO）,E2（high）,and E1（TO）） and the linewidths of E2（high） phonon peak are studied.The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range,and the relationship can be fitted to the pseudo-Voigt function.From analytic results we find a critical temperature existing in the relationship,which can characterize the anharmonic effects of a-plane GaN in different temperature ranges.In the range of higher temperature,the relationship exhibits an approximately linear behavior,which is consistent with the analyzed results theoretically.

Bonding and Mssbauer Isomer Shifts in(Tl,Pb)-1223 Cuprate

By using the chemical bond theory of dielectric description, the chemical bond parameters of (Tl, Pb) - 1223 was calculated. The results show that the Sr-O, Tl-O, and Ca-O types of bond have higher ionic character and the Cu-O types of bond have more covalent character. Mssbauer isomer shifts of 57Fe and 119Sn doped in (Tl, Pb) -1223 were calculated by using the chemical environmental factor, he, defined by covalency and electronic polarizability. Four valence state tin and three valence iron sites were identified in 57Fe, and 119Sn doped (Tl, Pb) -1223 superconductor. We conclude that all of the Fe atoms substitute the Cu at square planar Cu (1) site, whereas Sn prefers to substitute the square pyramidal Cu (2) site.