129Xe nuclear magnetic resonance studies of supported platinum-alumina catalysts

¹²⁹Xe nuclear magnetic resonance spectra of xenon adsorbed on supported platinum-alumina catalysts have been examined. The state of metallic platinum particles (Pt^o) was shown to be different for Pt/Al₂O₃ and Pt/Al₂O₃(Cl) samples. Some assumptions about the mutual arrangement of supported metallic particles have been made.

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¹²⁹Xe , , Pt⁰ Pt(II). , (Pt⁰) , . Pt⁰ Pt(II).

     

129Xe NMR: Porous-structure of silica gels

¹²⁹Xe NMR has been used to study the pore structure of several commercial silicas. They have been shown to possess micropores of 5–10 Å size. Micropores of different type appear not to be connected directly. A model is suggested explaining the experimental dependences of chemical shifts on temperature and pressure.     

129Xe NMR法研究醇二元混合溶液

129Xe NMR可以作为研究液体结构状态的探针．甲醇是一个与水结构差别最小的有机溶剂．本文研究了129Xe在甲醇-丁醇,甲醇-戊醇,甲醇-辛醇,甲醇-癸醇混合溶剂中化学位移随组成的变化,并测定了混合溶剂的密度和折射率．129Xe化学位移随混合溶剂的摩尔分数的变化为四条曲率很近的曲线,而化学位移随混合溶剂的体积分数的变化为斜率随多碳醇碳原子数增加的直线．这表明甲醇-多碳醇二元混合溶剂中不存在疏溶剂作用,而构成分子均匀分布的体系．129Xe在甲醇-丁醇,甲醇-癸醇中的化学位移与混合溶剂折射率的一种函数的关系为两条斜率很接近的直线,表明Xe在溶液中主要受范德华力作用．     

MCM-41分子筛的合成及129Xe核磁共振的研究

Purely siliceous MCM-41 with a narrow pore-size distribution, different pore size, high surface area was synthesized . As prepared, calcined and catalytically tested MCM-41 materials have been comprehensively characterized by N₂ adsorption/desorption at 77K and ¹²⁹Xe NMR. By adding mesitylene during the synthesis, the pore size of MCM-41 was enlarged to 5.2nm. The chemical shift in ¹²⁹Xe NMR spectroscopy of adsorbed xenon indicates that the MCM-41 is one dimensional pore channels .     

129Xe NMR study of the localization of PdCl2 supported on carbon nanotubes

Localization of PdCl₂ clusters supported on multi-wall carbon nanotubes (MWCNT) has been investigated using ¹²⁹Xe NMR of adsorbed xenon. As-made MWCNTs with channels initially inaccessible for adsorption and ball-milled MWCNTs with the totally accessible internal surface were used as supports. The observed ¹²⁹Xe NMR spectra were determined by the dynamics of xenon exchange between the aggregate pores and nanotube channels. No considerable changes of the ¹²⁹Xe NMR spectrum with the concentration of supported PdCl₂ were observed for the as-made MWCNT, while an additional resonance appeared for the ball-milled nanotubes. The ¹²⁹Xe NMR experiments evidenced the supported species to be localized on the internal surface of the ball-milled MWCNT.     

NMR study of 129Xe adsorbed on L,Z and ZSM zeolites

¹²⁹Xe can be used as a probe for determining zeolite properties. For example the chemical shift of xenon adsorbed in a zeolite is related to the st     

13C nuclear magnetic resonance spectra of ethers and glycols

The ¹³C NMR spectra of 21 linear and branched ethers together with the corresponding alcohols have been determined in an attempt to correlate the shieldings in both series. It has been found that the shielding of a carbon in an acyclic ether can be given by the summation of additive shift parameters for substituents and correction parameters for the substitution patterns based on the shielding of the parent alcohol. On examination of solvent-induced shifts for α- and β-carbons in ethers and alcohols, significant ones have been noted in carbon tetrachloride→dimethylsulfoxide and carbon tetrachloride→trifluoroacetic acid. No appreciable concentration-dependent shifts of the shieldings have been observed in both ethers and alcohols. For the shieldings of α-carbons in acyclic glycols, it has been noticed that the observed and predicted values are in accord in 1,3-, 1,4- and 1,5-glycols but deviate in 1,2-glycols. The latter has been examined in a polycyclic system, where the deviations ( > 3·5ppm) in a cis (gauche) 1,2-glycol are larger than those (<2·5 ppm) in a trans (anti-parallel) 1,2-glycol.     

A 13C nuclear magnetic resonance study of cyclobutadieneirontricarbonyl-substituted carbonium ions

The ¹³C NMR spectra of (hydroxymethyl)-, (α-hydroxyethyl)- and (α-hydroxybenzyl)cyclobutadieneiron tricarbonyl (in CDCl₃) and of their derived carbonium ions (in concentrated H₂SO₄) are reported. The data suggest extensive donation of electron density from the metal, via the cyclobutadiene unit, to the exocyclic, electron-deficient carbon atom, thus giving highly stabilized carbonium ions.     

The 1H and 13C nuclear magnetic resonance and IR adsorption spectra of substituted polymethylferrocenes

The NMR and IR spectra of sym-polymethylferrocenes have been studied. The abnormal shifts observed of the ¹³C signals from the adjacent methyl groups are discussed in terms of spatial interactions between these groups, which cause charge redistribution in the vicinity of the ¹³C nuclei.     

13C nuclear magnetic resonance spectra of aflatoxin B1 derived from acetate

The labeling distribution of the fungal metabolite, aflatoxin B₁, produced from [1- or 2- ¹³C] acetate was determined by ¹³C FT NMR. The results support the polyketide hypothesis for aflatoxin biogenesis.     

Studies on the structure of olivomycin a and mithramycin by 1H and 13C nuclear magnetic resonance spectroscopy

Extensive ¹H and ¹³CNMR studies confirmed the gross structure of olivomycin A except for a revision with respect to a saccharide linkage. The structure of mithramycin was elucidated similarly, resulting in a substantial revision of structure for its carbohydrate moiety including interglycosidic bonds.     

Effects of chemical shift anisotropy and 14N coupling on the 1H and 195Pt nuclear magnetic resonance spectra of platinum complexes

Broadening of the ¹⁹⁵Pt satellites in the ¹H NMR spectrum of trans-Pt(ethene)(2-carboxy-pyridine)Cl₂ at high field arises from relaxation of ¹⁹⁵Pt via the chemical shift anisotropy mechanism. We also demonstrate that well-resolved ¹⁴N-¹⁹⁵Pt couplings can be observed in ¹⁹⁵Pt NMR spectra of Pt(II) and Pt(IV) amine complexes, including anti-tumour agents, at elevated temperature where scalar coupling contributions to ¹⁹⁵Pt relaxation are much reduced.     

Biosynthesis of malonomicin-III advanced precursor studies using 2H nuclear magnetic resonance spectroscopy

²H-labelled precursors and high-field ²H- NMR spectroscopy have been used to demonstrate that the first tetramic acid derived intermediate in the biosynthesis of malonomicin is 5-aminomethyl-4-hydroxy-3-succinoyl-3-pyrrolin-2-one, formed by condensation of L-2,3-diaminopropanoic acid and 3-oxoadipic acid.     

The nuclear magnetic resonance line shapes of Xe in the cages of clathrate hydrates

We report, for the first time, a prediction of the line shapes that would be observed in the (129)Xe nuclear magnetic resonance (NMR) spectrum of xenon in the cages of clathrate hydrates. We use the dimer tensor model to represent pairwise contributions to the intermolecular magnetic shielding tensor for Xe at a specific location in a clathrate cage. The individual tensor components from quantum mechanical calculations in clathrate hydrate structure I are represented by contributions from parallel and perpendicular tensor components of Xe-O and Xe-H dimers. Subsequently these dimer tensor components are used to reconstruct the full magnetic shielding tensor for Xe at an arbitrary location in a clathrate cage. The reconstructed tensors are employed in canonical Monte Carlo simulations to find the Xe shielding tensor component along a particular magnetic field direction. The shielding tensor component weighted according to the probability of finding a crystal fragment oriented along this direction in a polycrystalline sample leads to a predicted line shape. Using the same set of Xe-O and Xe-H shielding functions and the same Xe-O and Xe-H potential functions we calculate the Xe NMR spectra of Xe atom in 12 distinct cage types in clathrate hydrates structures I, II, H, and bromine hydrate. Agreement with experimental spectra in terms of the number of unique tensor components and their relative magnitudes is excellent. Agreement with absolute magnitudes of chemical shifts relative to free Xe atom is very good. We predict the Xe line shapes in two cages in which Xe has not yet been observed.     

Nuclear magnetic resonance studies of 13 C-enriched acetylene

Analysis of ¹H and ¹³C spectra of 1-¹³ C-acetylene gives the same relative sign for ^J_CH and ^J'_CH. Precise chemical     

Nuclear magnetic resonance study of 19F motion in CsPbF3

The ¹⁹F nuclear magnetic relaxation times and line-widths have been measured in polycrystalline CsPbF₃ in the temperature range from ?150 to +300°C. The observed motional narrowing of the NMR line-width at low temperatures and the temperature dependences of the relaxation times are analysed in terms of a high vacancy diffusion of the F^? ions. A phase transition is found at ?93°C from measurements of the NMR line shapes.