Nanosecond-Flash 15N Photo-CIDNP MAS NMR on Reaction Centers of Rhodobacter sphaeroides R26

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is observed with time-resolved ¹⁵N magic-angle spinning (MAS) nuclear magnetic resonance (NMR) in uniformly ¹⁵N-labeled reaction centers (RCs) of the purple bacterium Rhodobacter (Rb.) sphaeroides R26 under illumination with nanosecond laser flashes. The ¹⁵N NMR signals enhanced by the solid-state photo-CIDNP effect are related to electron spin densities in the primary radical pair and allow for reconstruction of the electronic structure at atomic scale. New assignments for the photochemically active nitrogens are proposed based on simulations of the intensities. The ratio of electron spin densities between cofactors P _L and P _M is observed to be about 4:1. The origin of the high asymmetry is discussed.     

13C qNMR结合DFSS方法测定油品芳碳率

利用六西格玛设计（design for six Sigma,DFSS）方法,通过定量核磁共振碳谱（quantitative carbon nuclearmagnetic resonance spectroscopy,¹³C qNMR）对由11种已知烃类化合物组成的模型油品进行了芳香碳摩尔百分比C（ar）%,简称芳碳率]测定的系统研究,建立了C（ar）%与样品浓度Conc.、弛豫试剂浓度[Cr（acac）₃]和循环延迟D13个参数之间的数学模型,据此模型得到了优化的参数设置：Conc.为180 mg/mL,[Cr（acac）₃]为12 mg/mL,D1为10.5 s.按此设置进行了8组验证实验,其结果重现性较好,相对标准偏差（relative standard deviation,RSD）为0.61%;准确性较高,达到99.0%~100.6%.该方法也可用于其它分析测试方法的系统研究,且实验结果对现行油品芳碳率测定标准中相关参数,如[Cr（acac）₃]和D1的设置能够提出补充性建议.     

Magnetic susceptibility effects on 13C MAS NMR spectra of carbon materials and graphite

13C high-resolution solid-state nuclear magnetic resonance (NMR) was employed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut, peat, and PVC). For heat treatment temperatures (HTTs) above about 600 C, all materials presented 13C NMR spectra composed of a unique resonance line associated with carbon atoms in aromatic planes. With increasing HTT a continuous broadening of this resonance and a diamagnetic shift in its central frequency were verified for all samples. The evolution of the magnitude and anisotropy of the magnetic susceptibility of the heat-treated carbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite, for which the magnetic susceptibility effect is also present and is much more pronounced.     

Magnetic field dependence of13C photo-CIDNP MAS NMR in plant photosystems I and II

Photochemically induced dynamic nuclear polarization is observed in the two photosynthetic reaction centers of plants, photosystem I (PSI) and photosystem II (PSII) by¹³C magic-angle spinning nuclear magnetic resonance (NMR) at three different magnetic fields 17.6, 9.4, and 4.7 T. There is a significant difference in field dependence detected in the light-induced signal pattern of the two photosystems. For PSII the optimal NMR enhancement factor of about 5000 is observed at 4.7 T. On the other hand, the maximal light-induced signals of PSI are observed at 9.4 T.     

甲烷水合物的固体核磁共振碳谱与激光拉曼光谱研究

甲烷水合物（CH₄·nH₂O）是主要由甲烷和水分子构成的冰状笼型化合物,在自然界储量巨大．固体核磁共振（NMR）波谱和激光拉曼光谱是在分子水平分析甲烷水合物的重要手段．该文利用低温固体核磁共振碳谱（¹³C NMR）对合成的甲烷水合物结构进行了研究,分别使用¹³C交叉极化（¹³C CP）和高功率质子去偶（¹H HPDEC）2种脉冲程序采集甲烷水合物的¹³C NMR谱图,结合实验结果分析及理论推导可知,使用¹H HPDEC方法得到的¹³C NMR谱图信号更强,更利于定量分析;甲烷气体与冰粉合成的甲烷水合物为I型,其大笼和小笼占有率分别为0.988和0.824,水合数为6.07;甲烷气体与SH2站位沉积物和冰粉合成的甲烷水合物也为I型,其大笼和小笼占有率分别为0.987和0.887,水合数为5.98;SH2站位沉积物使合成的甲烷水合物的小笼占有率提高、水合数降低、水合物饱和度提高．激光拉曼光谱结果证实了上述结果的准确性．该文为甲烷水合物测试提供了重要的方法参考．     

Crystal structure and 13C CP/MAS NMR of the p-xylene clathrate of Dianin's compound

Single-crystal X-ray diffraction and ¹³C solid state NMR spectroscopy were used to characterize the structure and dynamics of the p-xylene clathrate of Dianin's compound. In contrast to conclusions obtained from single-crystal ²H NMR and modelling, the diffraction results suggest there is a single (symmetry disordered) guest site without any significant distortion of the host framework. A single xylene guest statistically disordered over six overlapping equivalent positions can account for the ¹³C NMR spectrum at room temperature. The high crystal-lographic symmetry arises from space averaging. At high temperatures the ¹³C spectrum is consistent with the onset of dynamic processes that result in higher effective symmetry.     

Quantification of Hydroxyacetaldehyde in a Biomass Pyrolysis Liquid Using 13C NMR Spectroscopy

We report on a method that allows direct identification and quantitative determination of hydroxyacetaldehyde using ¹³C NMR spectroscopy. The quantitative procedure was checked and validated with commercially available hydroxyacetaldehyde and then applied to the carbohydrate fraction of a biomass pyrolysis liquid (bio‐oil).     

13C NMR Studies on 3-Aryl-4-Cyanosydnones (II). NMR Spectroscopy and the Chain-Conjugated Structure of Sydnones

Carbon-13 NMR spectra of 3-aryl-4-cyanosydnones have been analyzed to serve as an electronic structure probe of sydnones. 2-Dimensional INADEQUATE experiments and spin-lattice relaxation time measurements were employed to ascertain exact assignments. Deshielding of the phenyl carbon para to the sydnone ring manifests that N(3) bears positive charge. The electronic-rich property of C(4) is confirmed by shift data of cyano carbons, which have been found by far the most shielded cyano carbons in nitrile-containing compounds yet reported. Shift variations of C(5) resulting from the substitution at C(4) and supplementary oxygen-17 chemical shift data provide evidence in favor of the chain-conjugated structure.     

1H MAS, 13C CP/MAS, and 2H NMR spectra studies of piperidinium {\emph{p}}-chlorobenzoate

Anomalous H/D isotope effects were detected in the ¹H MAS NMR spectra of piperidinium p-chlorobenzoate (C₅H₁₀NH $_{2}{^{+}}\cdot $ ClC₆H₄COO^???) upon deuterium substitution of hydrogen atoms which form two kinds of N-H?O H-bonds in the crystal; in contrast to these spectra, only slight chemical shifts were recorded in ¹³C CP/MAS NMR spectra. ²H NMR spectrum of the deuterated sample show quadrupole coupling constants of 148 and 108 kHz, and reveal that there are a few motions contributing to the electric-field modulation of the ²H nucleus. The ¹H MAS NMR spectra of piperidinium p-chlrobenzoate-d ₁₆ (C₅D₁₀ND $_{2}{^{+}}\cdot $ ClC₆D₄COO^???) and -d ₁₄ (C₅D₁₀NH $_{2}{^{+}}\cdot $ ClC₆D₄COO^???) revealed that the change in the envelope is caused by chemical shifts of each signal upon deuteration. Calculations based on the density-functional-theory showed that the N-H distance along the crystallographic a-axis mainly contributes to the anomalous isotope effects on ¹H MAS NMR envelopes.     

H-SSZ-13分子筛催化乙醇脱水制乙烯反应的原位固体核磁共振研究

本文采用原位连续流动条件和间歇条件下的固体核磁共振技术,以及二维¹³C-¹³C基于偶极耦合的结合R2（COmbined R2 Driven,CORD）自旋扩散序列的核磁共振实验捕获了H-SSZ-13分子筛催化乙醇脱水过程中多种中间物种,并揭示了各种中间物种的动态演变过程.结果发现H-SSZ-13分子筛催化乙醇脱水过程中,存在两种不同吸附构型的乙醇、活化态的乙醚、乙氧基以及三乙基氧鎓离子,并首次通过原位固体核磁共振技术观测到乙烯的生成.这些结果加深了相关研究者对乙醇脱水反应的认识.     

Identification and Quantitative Determination of Dipropylene Glycol in Terpene Mixtures Using 13C NMR Spectroscopy

A method that allows direct identification and quantitative determination of dipropylene glycol (DPG) using ¹³C NMR spectroscopy was developed. The quantitative procedure was checked and validated with commercially available DPG, controlled with two DPG-added essential oils, and then applied to commercial “Extraits de parfum” (perfume extracts).     

Rh基催化剂上氢甲酰化反应过程的原位高压NMR研究

制备了用于丙烯氢甲酰化反应的Rh/SBA-15 和PPh₃修饰的PPh₃-Rh/SBA-15催化剂. 应用原位变温高压核磁共振技术,对比研究了丙烯在Rh/SBA-15 和PPh₃修饰的多相催化剂PPh₃ Rh/SBA-15上的氢甲酰化反应,实现了高压条件下催化反应的原位固体核磁共振表征. ¹³C MAS NMR研究结果表明：在1.0 MPa的反应压力下,随着反应温度升高丙烯与合成气在Rh/SBA-15催化剂上可转化生成丁醛,而PPh₃配体修饰的PPh₃-Rh/SBA-15催化剂上丁醛产物的正异比显著提高.     

Amino-acid selective experiments on uniformly 13C and 15N labeled proteins by MAS NMR: Filtering of lysines and arginines

Amino-acid selective magic-angle spinning (MAS) NMR experiments can aid the assignment of ambiguous cross-peaks in crowded spectra of solid proteins. In particular for larger proteins, data analysis can be hindered by severe resonance overlap. In such cases, filtering techniques may provide a good alternative to site-specific spin-labeling to obtain unambiguous assignments that can serve as starting points in the assignment procedure. In this paper we present a simple pulse sequence that allows selective excitation of arginine and lysine residues. To achieve this, we make use of a combination of specific cross-polarization for selective excitation [M. Baldus, A.T. Petkova, J. Herzfeld, R.G. Griffin, Cross polarization in the tilted frame: assignment and spectral simplification in heteronuclear spin systems, Mol. Phys. 95 (1998) 1197-1207.] and spin diffusion for transfer along the amino-acid side-chain. The selectivity of the filter is demonstrated with the excitation of lysine and arginine side-chain resonances in a uniformly 13C and 15N labeled protein preparation of the alpha-spectrin SH3 domain. It is shown that the filter can be applied as a building block in a 13C-13C lysine-only correlation experiment.     

1H and 13C MAS NMR studies of light alkanes activation over MFI zeolite modified by Zn vapour

The early stages of methane, ethane and propane conversion were studied by in situ ¹H and ¹³C MAS NMR techniques over fully exchanged Zn²⁺/MFI catalyst obtained by the reaction with zinc vapour. The in situ techniques revealed strong interaction of alkanes with Zn²⁺ cations evidenced by significant shift of the corresponding NMR lines. Besides that, the formation of methyl zinc, ethyl zinc and n-propyl zinc species along with bridging and silanol surface OH-groups was detected already at the ambient temperature. These results pointed to dissociative adsorption of alkanes over (ZO)–Zn²⁺–(OZ) and (ZO)–Zn²⁺–(OSi) active sites of the catalyst. The dissociative adsorption was shown to be a dead-end surface reaction in the case of methane starting reactant, while in the case of ethane and propane, it appeared to be responsible for the initiation of the catalytic cycle leading to alkenes and dihydrogen formation and regeneration of zinc containing catalytic sites.     

Probing membrane surfaces and the location of membrane-embedded peptides by (13)C MAS NMR using lanthanide ions

A simple but efficient (13)C MAS NMR method is presented for the determination of the location of embedded molecules such as peptides relative to biological membrane surfaces by exploiting the interaction with paramagnetic lanthanide ions. Using various aqueous Dy(3+) concentrations a distance-dependent differential paramagnetic quenching of NMR lipid resonance intensities for specific carbon sites was observed, with residues at the bilayer surface quenched effectively and hydrophobic sites unaffected by Dy(3+). Tested on the membrane-embedded 50 residue long M13 coat protein, (13)C labeled at its Val-29 and Val-31 residues, no paramagnetic quenching was observed for the peptide resonances by Dy(3+), suggesting that Val-29 and Val-31 are not in close proximity to the bilayer interface, but buried deeply inside the hydrophobic region of the lipid bilayer.     

Time-resolved observation of the decomposition process of N,N,N-Trimethylanilinium cations on zeolite H-Y by in situ stopped-flow 13C MAS NMR spectroscopy

N,N,N-Trimethylanilinium cations were synthesized on acidic zeolite H-Y by direct reaction of N,N-dimethylaniline and methanol. Time-resolved observation of the detailed decomposition process of N,N,N-trimethylanilinium cations was achieved by in situ 13C stopped-flow (SF) MAS NMR spectroscopy at reaction temperatures of 498 K to 573 K.     

取代基效应对脂肪醇^13C NMR化学位移的影响

用原子电负性、静电作用、极化度作为基本参数, 并结合表征原子空间连接方式的立体效应参数, 对醇分子中不同环境碳原子的化学位移进行关联, 将120个模型化合物(91个脂肪一元醇, 29个二元醇)中747个碳原子相关参数值和化学位移值带入模型中得到如下估算方程:δC=42.947 9 + 63.064 0Qi-3.628 6F+5.121 3Σαx-6.584 8QiΣαx-4.842 7NαH-0.585 5NγH-4.104 6NγOH(R=0.998 1 R2=0.996 1 S=1.14 F=27 125.2 n=747)方程中各参数物理意义比较明确. 通过用"留一法"(LOO)检验(Rcv=0.998 0, R2cv=0.996 0, Scv=1.16)及对样本外5个化合物69个碳原子化学位移的预测值和实验值比较, 结果表明模型方程具有很好的稳定性和预测精度, 该模型的提出为以后计算更加复杂化合物的13C NMR化学位移奠定了良好的基础.     

Effect of ortho substituents on carbonyl carbon 13C NMR chemical shifts in substituted phenyl benzoates

¹³C NMR spectra of 37 ortho‐, meta‐, and para‐substituted phenyl benzoates, containing substituents in benzoyl and phenyl moiety, 4 ortho‐substituted methyl and 5 ethyl benzoates as well as 9 R‐substituted alkyl benzoates have been recorded. The influence of the ortho substituents on the carbonyl carbon ¹³C NMR chemical shift, δ_CO, was found to be described by a linear multiple regression equation containing the inductive, σ_I, resonance, σ°_R, and steric, E, or υ substituent constants. For all the ortho‐substituted esters containing substituents in the acyl part as well as the phenyl part, the substituent‐induced reverse inductive effect (ρ_I < 0), the normal resonance effect (ρ_R > 0), and the negative steric effect (δ_ortho < 0) with the E were observed. In the case of ortho substituents in the phenyl part, the resonance effect was negligible. Due to inductive effect, the ortho electron‐withdrawing substituents showed an upfield shift or shielding of the carbonyl carbon, while the electron‐donating substituents had an opposite effect. Because of the sterical consequences, ortho substituents revealed a deshielding effect on the ¹³C NMR chemical shift of the carbonyl carbon. For all the meta‐ and para‐substituted esters, the reverse substituent‐induced inductive and resonance effects (ρ_I < 0, ρ_R < 0) were found to be significant. In alkyl benzoates, the alkyl substituents showed the reverse inductive and steric effects. The log k values for the alkaline hydrolysis in water, aqueous 0.5 M Bu₄NBr and 2.25 M Bu₄NBr, and the IR frequencies, ν_CO, for the ortho‐, meta‐, and para‐substituted phenyl benzoates and alkyl benzoates were correlated nicely with the corresponding ¹³C NMR substituent chemical shifts, Δδ_CO. Copyright © 2009 John Wiley & Sons, Ltd.