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.     

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.     

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。     

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.     

The magnetic properties of myoglobin as studied by NMR spectroscopy

Deoxymyoglobin has been investigated by NMR spectroscopy to determine the magnetic anisotropy through pseudocontact shifts and the total magnetic susceptibility through Evans measurements. The magnetic anisotropy values were found to be Deltachi(ax)=-2.03+/-0.08 x 10(-32) m(3) and Deltachi(rh)=-1.02+/-0.09 x 10(-32) m(3). The negative value of the axial susceptibility anisotropy originates from the z tensor axis lying in the heme plane, unlike all other heme systems investigated so far. This magnetic axis is almost exactly orthogonal to the axial histidine plane. The other two axes lie essentially in the histidine plane, the closest to the heme normal being tilted by about 36 degrees from it, towards pyrrole A on the side of the proximal histidine. From the comparison with cytochrome c' it clearly appears that the position of the one axis lying in the heme plane is related to the axial histidine orientation. Irrespective of the directions, the magnetic anisotropy is smaller than that of the analogous reduced cytochrome c' and of the order of that of low-spin iron(III). The magnetic anisotropy of the system permits the measurement of residual dipolar couplings, which, together with pseudocontact shifts, prove that the solution structure is very similar to that in the crystalline state. Magnetic measurements, at variance with previous data, demonstrate that there is an orbital contribution to the magnetic moment, micro(eff)=5.5 micro(B). Finally, from the magnetic anisotropy data, the hyperfine shifts of iron ligands could be separated in pseudocontact and contact components, and hints are provided to understand the spin-delocalisation mechanism in S=2 systems by keeping in mind the delocalisation patterns in low-spin S=1/2 and high-spin S= 5/2 iron(III) systems.     

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.     

Weak molecular complexes as studied by NMR spectroscopy of oriented molecules

Weak molecular interactions such as those in pyridine—iodine, benzene—iodine and benzene—chloroform systems oriented in thermotropic liquid crystals have been studied from the changes of the order parameters as a result of complex formation. The results indicate the formation of at least two types of charge transfer complexes in pyridine—iodine solutions. The pi-complexes in benzene—chloroform and benzene—iodine mixtures have also been detected. No detectable changes in the inter-proton distances in these systems were observed.     

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.     

Self-diffusion of water-ethanol mixture in chitosan membranes obtained by pulsed-field gradient nuclear magnetic resonance technique

The self-diffusion of water and ethanol for crosslinked and uncrosslinked chitosan membranes have been investigated by pulsed-field gradient nuclear magnetic resonance (NMR) spectroscopy. It has been shown that during diffusion processes, water and ethanol are localized in different parts of the chitosan membrane. In the crosslinked membrane, the self-diffusion coefficient for water is higher, but that for ethanol is essentially lower, than those for the uncrosslinked membrane. For this reason, the mobility selectivity is essentially higher in crosslinked membrane as compared to the uncrosslinked. The sorption selectivity are the same for these two types of membranes.     

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.