Lamellar lyomesophases under shear as studied by deuterium nuclear magnetic resonance

The lamellar phases of two aqueous ethylene oxide surfactants, tetra(ethylene oxide) dodecyl ether and hexa(ethylene oxide) dodecyl ether, have been investigated by deuterium nuclear magnetic resonance spectroscopy during shear. The evolution of the shear-induced NMR line shapes and their dependence on surfactant concentration, shear geometry and shear history is analyzed. Two of three previously described shear-induced states (Diat O, Roux D, Nallet F (1993) J Phys II France 3: 1427–1452), namely the state of aligned lamellae with the layer normal parallel to the velocity gradient, which occurs at low shear rates, and the vesicular state at intermediate shear rates are found and identified by their characteristics NMR line shapes.     

利用27Al NMR研究茶多酚与铝形成配合物的形态

采用27Al NMR技术,研究了不同茶叶中茶多酚与铝形成配合物的形态。考察了在不同pH值和配体/金属(L/M)下铝的存在形态,系统地研究了焦性没食子酸、儿茶酚等官能团模拟化合物与铝的配位体系中铝的形态,探讨了配体取代基的个数与焦性没食子酸-铝配合物的δ27Al的关系,获得了非常有意义的规律,并确定了茶多酚与铝配合物的结构。     

Inhibition and enhancement of resonance as studied by 13C nuclear magnetic resonance spectroscopy

¹³C chemical shifts are reported for a series of 2-substituted 1,3-dimethylbenzenes: comparisons of these values with those for the corresponding monosubstituted benzenes reveal, in some cases, large differences in the para-carbon substituent chemical shifts, which are attributable to steric hindrance of resonance. The questions of steric enhancement of resonance, and methoxy group conformation in certain anisoles are also studied by the ¹³C NMR technique. Studies of selected 2-substituted fluorenes are also reported, and substituent chemical shifts at carbon-7 (traversing eight bonds) of greater than 2ppm are observed. These effects are consistently greater than those reported for the corresponding biphenyl compounds, and are associated with planarity-enforced enhancement of resonance.     

Evaluation of conditional stability constants of dissolved aluminum/humic substance complexes by means of 27Al nuclear magnetic resonance

An analytical procedure for evaluating the conditional stability constants K′ of aluminum/humic substance complexes, based on ²⁷Al nuclear magnetic resonance spectroscopy, is described. It is well suited for the determination of Al(III) dissociated from dissolved humic substances at slightly acidic pH values. The new procedure offers a good sensitivity and requires neither special preparation of the sample nor the evaluation of complex coupled chemical equilibria. The pK′ values range from 2.0 to 4.3 depending on the ratio [Al_complex] to dissolved organic carbon and the pH.     

Conformational preferences of some substituted methyl groups in cyclohexanes as studied by carbon-13 nuclear magnetic resonance

Low temperature ¹³C NMR spectra of 80:20 mixtures of cis and trans-4? CH₃? CH₃? C₆H₁₀CH₂X, where ? C₆H₁₀-is 1, 4-disubtituted cyclohexyl and X=Br, CN, OH, OCH₃, Si(CH₃)₃, Sn(CH₃)₃, Pb(CH₃)₃ and HgOCOCH₃ have been recorded. The signals of the trans (e, e) components were assigned from the ambient temperature spectra of C₆H₁₁CH₂X and the established substituent effects of an equatorial methyl group in cyclohexane. Conformational equilibria of the cis (e, a?a, e) components were then computed from the intensities of the (remaining) signals (～180 K) of the two conformational isomers. From these equilibria A values of CH₂X were calculated, assuming additivity of conformational energies of CH₃ and CH₂X (the counter-poise approach). In general, these values are very similar to the value of the CH₃, although some trends do emerge. This study provides α, β, γ, and δ effects for a wide range of axial and equatorial ? CH₂X groups.     

Proton nuclear magnetic resonance spectra ofOrtho-metalated alkyne-carbonyltriosmium complexes

Summary The¹H nuclear magnetic resonance spectra of Os₃(CO)₈(Ph₂C₂)₂ and Os₃(CO)₈[(p-ClC₆H₄)₂C₂]₂ are described. In these metal cluster complexes theortho-metalation involves phenyl groups linked to a cyclopentadiene ring.     

Silver nitrate-acetonitrile and iodine-benzene complexes as studied by NMR in thermotropic liquid crystals

Silver nitrate-acetonitrile and π iodine-benzene complexes in thermotropic liquid crystals have been studied by ¹H, ²H, and ¹³C NMR spectroscopy and by optical microscopy. Evidence for at least two silver complexes in each liquid crystal is presented.     

Ontogenetic changes of the water status in the heated quail's egg as studied by nuclear magnetic resonance imaging.

The 1H-magnetic resonance imaging technique was applied for monitoring the extent of the heat coagulation in the shell egg. It is demonstrated that spin-spin relaxation time (T2) is an effective marker to observe the extent of coagulation in egg white and yolk and that the T2 value image is quite useful to recognize non-destructively the extent and status of coagulation of the heated eggs. This technique can also be applied to the material science as well as food science for observation of the inner status of the objects.     

Conformation and orientation of tetraalanine in a lyotropic liquid crystal studied by nuclear magnetic resonance

The (1)H NMR spectra of two isotopomers of tetraalanine deuterated on the two external methyl groups and on the two internal ones, respectively, were recorded in the lyotropic solvent cesium pentadecafluorooctanoate (CsPFO)/water. Eight dipolar couplings could be estimated from the spectra. The set of dipolar couplings was fitted assuming that one rigid conformer is present. Of the four major conformers considered, selected on the basis of theoretical calculations, the one characterized by the two couples of internal dihedral angles in the Ramachandran region of PPII resulted to be the only one to fit the set of couplings within experimental error. The data indicate that the molecule is oriented with the long molecular axis tilted with respect to the surface of the micelles formed by CsPFO.     

Quantitative determination of aluminium in tea by means of aluminium-27 nuclear magnetic resonance spectroscopy

A method for determining the Al levels in tea leaf digests and tea infusions by means of 27Al nuclear magnetic resonance (NMR) spectroscopy is described. Quantitative results down to 2.0 micrograms cm-3 of Al in 0.5-cm-3 acidified samples are readily obtainable in standard 5-mm NMR tubes. An acceptable quantitative determination is achieved by using an internal Al standard in a 1-mm capillary in conjunction with europium nitrate as a shift reagent.     

Quantification of organic acids in beer by nuclear magnetic resonance (NMR)-based methods

The organic acids present in beer provide important information on the product's quality and history, determining organoleptic properties and being useful indicators of fermentation performance. NMR spectroscopy may be used for rapid quantification of organic acids in beer and different NMR-based methodologies are hereby compared for the six main acids found in beer (acetic, citric, lactic, malic, pyruvic and succinic). The use of partial least squares (PLS) regression enables faster quantification, compared to traditional integration methods, and the performance of PLS models built using different reference methods (capillary electrophoresis (CE), both with direct and indirect UV detection, and enzymatic essays) was investigated. The best multivariate models were obtained using CE/indirect detection and enzymatic essays as reference and their response was compared with NMR integration, either using an internal reference or an electrical reference signal (Electronic REference To access In vivo Concentrations, ERETIC). NMR integration results generally agree with those obtained by PLS, with some overestimation for malic and pyruvic acids, probably due to peak overlap and subsequent integral errors, and an apparent relative underestimation for citric acid. Overall, these results make the PLS-NMR method an interesting choice for organic acid quantification in beer.     

Polymer-solvent complexes in thermoreversible gels and in solids as studied by NMR and other methods

The existence of polymer-solvent complexes, very probably of the inclusion type, was proved in gels and solids of syndiotactic poly(methyl methacrylate) (PMMA), in gels of isotactic PMMA, and in poly(vinyl chloride) gels by NMR spectroscopy combined with DSC and infrared measurements. For PMMA-solvent complexes, the stoichiometry was estimated. NMR was also used to characterize the dynamic structure of the crystalline intercalate complexes of poly(ethylene oxide) with p-nitrophenol and other hydroxybenzenes.     

Spins as qubits: quantum information processing by nuclear magnetic resonance

Storing information in quantum mechanical degrees of freedom and processing it by unitary transformation promises a new class of computers that can efficiently solve problems for which no efficient classical algorithms are known. The most straightforward implementation of this type of information processing uses nuclear spins to store the information and nuclear magnetic resonance for processing it. We discuss the basics of quantum information processing by NMR, with an emphasis on two fields of research: the design and implementation of robust logical gate operations and the loss of quantum information, which is known as decoherence.     

Anionic-nonionic surfactant interaction by nuclear magnetic resonance

Summary The interaction between anionic (sodium dodecyl benzene sulfonate) surfactant and nonionic (Tri and Tetra propylene glycol monomethyl ether) surfactant was studied using nuclear magnetic resonance measurement. It was observed that the addition of sodium dodecyl benzene sulfonate to the solution of nonionic surfactant (Tri and Tetra propylene glycol mono methyl ether) caused an upfield shift of the central protons of the nonionic surfactants. The aromatic protons of sodium-dodecyl benzene sulfonate undergo a very small, almost negligible, downfield shift. The changes in the chemical shift values and the integration values of the polypropylene protons and benzene protons was interpreted in terms of mixed micelle formation with the simultaneous presence of highly fluid mixed micelles of varying compositions.With 2 figures and 2 tables     

Cation distribution in co-doped ZnAl2O4 nanoparticles studied by X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy

Co(x)Zn(1-x)Al(2)O(4) (x = 0.01-0.6) nanoparticles were synthesized by the citrate sol-gel method and were characterized by X-ray powder diffraction and transmission electron microscopy to identify the crystalline phase and determine the particle size. X-ray photoelectron spectroscopy and (27)Al solid-state NMR spectroscopy were used to study the distribution of the cations in the tetrahedral and octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles as a function of particle size and composition. The results show that all of the as-synthesized samples exhibit spinel-type single phase; the crystallite size of the samples is about 20-50 nm and increases with increasing annealing temperature and decreases with Co-enrichment. Zn(2+) ions are located in large proportions in the tetrahedral sites and in small proportions in the octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles. The fraction of octahedral Zn(2+) increases with increasing Co concentration and decreases with increasing particle size. Besides the tetrahedral and octahedral coordinations, the presence of the second octahedrally coordinated Al(3+) ions is observed in the nanoparticles. The change of the inversion parameter (2 times the fraction of Al(3+) ions in tetrahedral sites) with Co concentration and particle size is consistent with that of the Zn fraction in octahedral sites. Analysis of the absorption properties indicates that Co(2+) ions are located in the tetrahedral sites as well as in the octahedral sites in the nanoparticles. The inversion degree of Co(2+) decreases with increasing particle size.     

ZrEDTA配合物的动态核磁共振1H NMR研究

研究了不同pH值下ZrEDTA配合物^1HNMR谱的温度依赖性，结果显示：pH=1．5和pH=6．8时配合物乙羧基质子都为1组AB谱，温度升高谱图无融合现象；而pH=5．0时配合物乙羧基质子呈现2组AB谱，且随温度升高出现融合现象．AB谱融合现象由△=∧迁移过程引起，通过全线型分析求得了速率常数及相关热力学参数。