C-13 NMR Spectra of N-Aminopyridinium Perchlorates

C-13 NMR spectra of fifteen N-aminopyridinium perchlorates show the effect of amination of the ring nitrogen atom to be similar to that observed in the pyridine N-oxide spectra, particularly for the 2(6) and 3(5) positions. Benzene and pyridine increments predict well the carbon chemical shifts for the title compounds unless both positions 2 and 6 are occupied. The chemical shifts of some carbon atoms in the compounds studied are linearly dependent on those in the respective benzene derivatives as well as on the Hammett σ constants.     

Inverse polarization transfer for detecting in vivo 13C magnetization transfer effect of specific enzyme reactions in 1H spectra

The wide chemical shift dispersion and long T(1) of (13)C have allowed determination of in vivo magnetization transfer effects caused by aspartate aminotransferase and lactate dehydrogenase reactions using (13)C magnetic resonance spectroscopy. In this report, we demonstrate that these effects can be observed in the proton spectra by transferring the equilibrium magnetization of (13)C via the one-bond scalar coupling between (13)C and (1)H using an inverse insensitive nuclei enhanced by polarization transfer-based heteronuclear polarization transfer method. This inverse method allows a combination of the advantages of the long (13)C T(1) for maximum magnetization transfer and the high sensitivity of proton detection. The feasibility of this in vivo inverse polarization transfer approach was evaluated for detecting the (13)C magnetization transfer effect of aspartate aminotransferase and lactate dehydrogenase reactions from a 72.5-microl voxel in the rat brain at 11.7 T.     

13C NMR Chemical Shifts and CH Coupling Constants of Substituted 4-Ylidenebutenolides

The ¹³C chemical shifts and CH coupling constants for 6 substituted 4-ylidenebutenolides are reported. The CH coupling constants are useful in helping to determine the stereochemistry of the substituted exocyclic double bond.     

Carbon-13 Nuclear Magnetic Resonance Studies of Aspergillomarasmine A,Anhydroaspergillomarasmine B and of Aspergillomarasmine A Ca+2 Chelate

Carbon-13 NMR determinations have been carried out on aspergillomarasmine A, anhydroaspergillomarasmine B, isolated from different species of fungi and comparisons allow the attribution of the signals to all carbon atoms. Changes observed in the spectrum by forming the 1:1 che-late of aspergillomarasmine A and the fact that aspergillomarasmine B cannot give chelates, lead to a proposal for the structure of this complex.     

The Use of Protonation Induced Changes in Carbon-13 NMR Chemical Shifts to Investigate the Solution Microscopic Structure of Partially Protonated Polybasic Molecules

Abstract

Changes in the NMR chemical shift of carbon-13 nuclei upon protonation of a nearby basic center are shown to be a useful method of probing the microscopic site of protonation of molecules containing multiple basic centers, such as diethylenetriaminepenta-acetic acid (DTPA). This approach is also shown to support the predominance of the pyridine amine protonated tautomer in the 4-pyridone ? 4-hydroxypyridine equilibrium.     

Lanthanide Shift Reagents XIII the Influence of Phenyl, 1-Adamantyl and Tert-Butyl Substituents on Equilibrium Constants

We have recently extended our Infrared studies of the binding of anilines with lanthanide shift reagents¹ to an NMR examination of hindered phenyl-carbinols² and a series of aldehydes and ketones related to benzaldehyde and acetophenone³.     

Sensitive, quantitative carbon-13 NMR spectra by mechanical sample translation

Collecting a truly quantitative carbon-13 spectrum is a time-consuming chore. Very long relaxation delays, required between transients to allow the z-magnetization, M_z, of the spin with the longest T₁ to return to the equilibrium value, M₀, must precede each transient. These long delays also reduce sensitivity, as fewer transients per unit time can be acquired. In addition, sometimes T₁ is not known to within even a factor of two: a conservative guess for the relaxation delay then leads to very low sensitivity. We demonstrate a fresh method to bypass these problems and collect quantitative carbon-13 spectra by swapping the sample volume after each acquisition with a different portion where the magnetization is already equilibrated to M₀. Loading larger sample volumes of 10–20 mL into an unusually long (1520 mm) 5 mm OD. NMR tube and vertically sliding the tube between acquisitions accomplishes the swap. The relaxation delay can then be skipped altogether. The spectra are thus both quantitative, and far more sensitive. We demonstrate the moving tube technique on two small molecules (thymol and butylhydroxytoluene) and show good carbon-13 quantification. The gain in sensitivity can be as much as 10-fold for slowly-relaxing ¹³C resonances. These experiments show that quantitative, sensitive carbon-13 spectra are possible whenever sufficient sample volumes are available. The method is applicable to any slow-relaxing nuclear spin species, such as ²⁹Si, ¹⁵N and other low-γ nuclei.     

NMR Studies in the Heterocyclic Series. XXIII. - 13C Spectra of Indazole and 3-Azido-Indazole in Acidified Dimethylsulfoxid Solutions

We reported previously the ¹³C NMR spectra of indazole 1 ² and 3-azido-indazole 2 ³.     

化合物SADTLER标准13C图谱编号检索系统

本文介绍一个建立了包括常用检索和智能检索SADTLER标准¹³C图谱系统,其中还具有设定谱峰数峰和谱化学位移误差之功能。系统中的程序用高级BASIC语言编写并由编译BASIC变为机器语言。系统运行于16位的IBM-PC兼容微机。     

CYCLCROP indirect 13C mapping for long-time and chemical-shift selective diffusion measurements in complex hydrocarbon systems

Cyclic cross-polarization from a proton magnetization to ¹³C and from there back to proton coherences permits the indirect, ¹³C chemical shift selective detection of hydrocarbon compounds in the proton NMR channel. This excitation technique can be combined with elements of one-, two- or three-dimensional magnetic resonance imaging permitting the measurement of time-resolved spatial distributions of hydrocarbon components. Beginning this sort of CYCLCROP mapping experiment with a non-equilibrium distribution of the constituents in the system allows one to study the time evolution of the concentrations of all components that can be identified by characteristic ¹³C resonance lines. As applications, studies of ingress, mixing, gel formation, transport and metabolism in living plants, long-time inter- and self-diffusion in complex hydrocarbon systems are suggested. As a test experiment, the diffusion of methanol in swollen polymethylmethacrylate was examined.     

Fourier Transform 13C NMR Analysis of Some Methaqualone Metabolites

The natural abundance carbon-13 nuclear magnetic resonance spectra of some methaqualone metabolites were recorded using the pulse fourier transform technique. The chemical shift of various carbon resonances have been assigned on the basis of the chemical shift theory, multiplicities observed in SFORD spectrum and comparison with the chemical shifts of the corresponding carbons of methaqualone.     

Use of the optogalvanic effect (OGE) for isotope ratio spectrometry of 13CO2 and 14CO2

The use of isotopic carbon dioxide lasers for determination of carbon (and oxygen) isotope ratios was first demonstrated in 1994. Since then a commercial device called LARA^?, has been manufactured and used for Helicobacter pylori breath tests using ¹³C-labelled urea. The major advantages of the optogalvanic effect compared with other infrared absorption isotope ratio measurement techniques are its lack of optical background and its high sensitivity resulting from a signal gain proportional to laser power. Continuous normalisation using two cells, a standard and sample, lead to high accuracy as well as precision. Recent advances in continuous flow measurement of ¹³C/¹²C ratios of CO₂ in air and extensions of the technique to ¹⁴C, which can be analysed as a stable isotope, are described.     

Preparation of aminofunctionalized TiO2 surfaces by binding of organophosphates

Titanium dioxide (TiO₂) powder was chemically modified with 2-aminoethyl dihydrogen phosphate (AEPH₂) and with 2-aminoethyl hydrogen ammonium phosphate (AEPHNH₄) in order to achieve an aminofunctionalized high-surface-area TiO₂ carrier suitable for more complex functionalizing. AEPH₂ was found to form the monoammonium salt AEPHNH₄ with ammonium ion rather than the diammonium salt AEP(NH₄)₂. The AEPHNH₄ was thoroughly characterized by various techniques and compared with AEPH₂. Bonding of AEPH₂ and AEPHNH₄ with TiO₂ powder was studied. According to the ³¹P NMR and elemental analysis results, AEPH₂ and AEPHNH₄ form covalent chelate bidentate bonds between the phosphate group and the TiO₂, while the amino groups remain accessible, creating uniform aminofunctionalized TiO₂ surface fully occupied by AEP groups. Amount of AEP groups on TiO₂ was limited to 1.5 wt-%.     

直接键连原子间的NMR偶合常数的自然杂化轨道研究V.13C-13C和13C-31P核自旋偶合常数1JCC和1JCP

在前文工作的基础上,结合MNDO/EHMO分子轨道方法和自然杂化轨道方法,具体计算了C-C键和C-P键的核自旋偶合常数.计算结果表明,¹J_CC和¹J_CP主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定.为从简单价键理论角度解释和计算¹J_CC和¹J_CP值提供了简便直观的方法.     

纤维素13C同位素示踪法研究纤维素与木素连接方式

为了阐明裸子植物中纤维素与木素之间的连接方式,从多糖的角度分析糖单元与木素苯丙烷结构单元之间的共价键连接方式,合成了带6-13C标记的纤维素前驱物尿苷二磷酸葡萄糖,并将其与PAL酶的抑制剂AOPP及外源性木素前驱物松柏醇-β-D-葡萄糖苷一起投入生长中的银杏植物体内。碳13丰度检测得知纤维素在细胞壁的沉积主要是从在初生壁开始,高分辨率固体核磁13C NMR分析证实了纤维素6位碳与木素以苯甲醚键等方式连接。     

GC-R-CF-MS method to determine the 13C abundance of gaseous combustion products in cigarette smoke

To determine the ¹³C abundance of combustion and break down products formed in cigarette smoke, especially CO and CO₂, a simple and fast analytical method is needed. Taking into account the knowledge about the determination of the natural ¹³C abundance in air, an online method—based on gas chromatography-reaction-continuous flow mass spectrometry (GC-R-CF-MS)—has been developed, which enables the determination of the ¹³C abundance of CO and CO₂ in the vapour phase of cigarette smoke with a relative standard deviation of≤0.5% in one analytical run. Additionally, in a second step, the ¹³C abundance of total volatile carbon can be determined.     

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).     

Analysis of 1H and 13C{1H} NMR Spectral Parameters and Geometries of Three Isomeric Diphenylbicyclo[2.2.1]Hept-5-Ene-2,3-Dicarboxylic Anhydrides

Diels-Alder adducts of 1,4-diphenyl-1,3-cyclopentadiene and maleic anhydride were investigated by recording the ¹H and ¹³C{¹H} NMR spectra of three isomeric diphenylbicyclo[2.2.1]hept-5-ene endo and exo 2,3-dianhydrides. the spectra were recorded in CD₂Cl₂ and analysed completely. the effect of the endo and exo configuration of the anhydride ring on the chemical shifts of the bridgehead phenyl protons is discussed. the ortho protons of the exo isomers resonate at higher field than those of the endo isomer, and the resonance pattern of the aromatic protons is narrower in the exo than the endo anhydride. the aromatic regions of the spectra are compared with the same regions of the ¹H NMR spectra of the earlier investigated addition products of 1,4-di-p-tolyl-1,3-cyclopentadiene and 1-phenyl-4-p-tolyl-1,3-cyclopentadiene with maleic anhydride. Chemical shifts of the bridge protons are explained on the basis of X-ray data of the compounds and MacroModel calculations on the minimum energy conformations.     

Relayed (13)C magnetization transfer: detection of malate dehydrogenase reaction in vivo

Malate dehydrogenase catalyzes rapid interconversion between dilute metabolites oxaloacetate and malate. Both oxaloacetate and malate are below the detection threshold of in vivo MRS. Oxaloacetate is also in rapid exchange with aspartate catalyzed by aspartate aminotransferase, the latter metabolite is observable in vivo using (13)C MRS. We hypothesized that the rapid turnover of oxaloacetate can effectively relay perturbation of magnetization between malate and aspartate. Here, we report indirect observation of the malate dehydrogenase reaction by saturating malate C2 resonance at 71.2 ppm and detecting a reduced aspartate C2 signal at 53.2 ppm due to relayed magnetization transfer via oxaloacetate C2 at 201.3 ppm. Using this strategy the rate of the cerebral malate dehydrogenase reaction was determined to be 9+/-2 micromol/g wet weight/min (means+/-SD, n=5) at 11.7 Tesla in anesthetized adult rats infused with [1,6-(13)C(2)]glucose.     

1—(3—吡啶甲酰)—4—芳基氨基硫脲类和3—(3—吡啶基)—4—芳基—1,2,4—三唑啉—5—硫酮类化合物~(13)C—NMR谱研究

本文测定了1-(3—吡啶甲酰)—4—苯基氨基硫脲、3—(3—吡啶基)—4—苯基—1,2,4—三唑啉—5—硫酮等8个新化合物的~(13)C NMR谱,运用质子宽带去偶、偏共振去偶,结合信号强度对比、苯基取代基效应的计算,同时与模型化合物对照,一一归属了其谱峰。本文对这两类化合物之间的~(13)C NMR谱差异进行了探讨,并得到了在吡啶环3位取代的甲酰肼基对吡啶环各碳取代基效应的数据。