Studies of lithium and sodium complexation by silicon podand solvents

The complex formation of lithium and sodium ions with silicon podand solvents: phenyl-tris(1,4-dioxapentyl) silane (PhSi23) and ethyl-tris(1,4-dioxapentyl) silane (EtSi23) has been studied by FTIR, ¹H-, ¹³C-, ⁷Li- and ²³Na NMR. The far FTIR spectra show that the Li⁺ cations fluctuate very fast whereas Na⁺ cations are still localised between the oxygen atoms of the oxaalkyl chains. The ⁷Li NMR spectra prove that one Li⁺ cation can be coordinated not only by one but also two silicon podand molecules. The concentration dependence of the molar conductivity of LiClO₄ in the podand solvents indicates charge transfer between ion clusters.     

A comparative study of NMR chemical shifts of sparteine thiolactams and lactams

The ¹³C and ¹H NMR spectra of the four possible thiolactams of sparteine (1) were recorded and the thiolactam group effects were determined. Most of the effects are greater than those of the lactam group in the oxo analogs. A good linear correlation between the ¹³C chemical shifts of CS and those of CO was found. The effects could help in assignment of the spectra and determination of conformation of thiolactams and related thiocarbonyl compounds.     

Simulation of 2D H homo- and H-C heteronuclear NMR spectra of organic molecules by DFT calculations of spin-spin coupling constants and H and C-chemical shifts

Simulation of 2D ¹H homo- and ¹H-¹³C heteronuclear NMR spectra of organic molecules are here suggested as a tool in the structure elucidation of organic compounds. DFT calculations of ¹H and ¹³C chemical shifts are performed on a sample compound, the ethyl ester of the exo-2-norbornanecarbamic acid, with the mPW1PW91 method using the 6-31G(d) basis set, following a full optimization of the geometry. Homo and heteronuclear spin-spin coupling constants are also calculated, providing full prediction of the common 2D ¹H-¹H COSY, 2D ¹H-¹³C HSQC, and 2D ¹H-¹³C HMBC.     

Beryllium(II) Complexes with Bis(dimethylamino)phosphorylfluoride: A Multinuclear NMR (31P, 19F,and 9Be) Characterization in Solution

Complexes of beryllium chloride and nitrate with (Me₂N)₂P(O)F were characterized in solution by multinuclear NMR spectroscopy and in some cases by IR spectroscopy and conductimetry. ³¹P and ¹⁹F NMR spectra were informative of changes associated with complex formation revealing resonances consistent with different species in solution and suggest an equilibrium between these species in both beryllium derivatives. These compounds show narrow lines in the solution ⁹Be NMR spectra, indicative of a highly symmetric environment for beryllium. The presence of the different species was more pronounced in beryllium chloride complexes. The results are compared to those reported in the literature for hexamethylphosphoramide (HMPA).     

Automatic identification of terpenoid skeletons by feed-forward neural networks

Feed-forward neural networks (FFNNs) were used to predict the skeletal type of molecules belonging to six classes of terpenoids. A database that contains the ¹³C NMR spectra of about 5000 compounds was used to train the FFNNs. An efficient representation of the spectra was designed and the constitution of the best FFNN input vector format resorted from an heuristic approach. The latter was derived from general considerations on terpenoid structures.     

Microstructure evolution in Stöber-type silica nanoparticles and their in vitro apatite deposition

Prepared via Stöber-type sol–gel routes were three types of silica particles of <1 μm in size: pure silica, Ca-involving silica, and chitosan/alginate-coated silica with a polymershell-silica core structure. Calcium ions were impregnated in the organic layers of the polymer-coated silica particle. The sol–gel procedure was applied to tetraethoxysilane dissolved in an ethanol/water mixture, while Ca–silica was derived from CaCl₂-containing ethanol/water solutions. Scanning and transmission electron micrograph analyses indicated that those silica particles consisted of ~10 nm primary particles, the Ca–silica particles (~500 nm) were larger than the Ca-free ones (~200 nm) and that their size increased with the Ca concentration in the precursor solutions. From ¹H- and ²⁹Si- magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra and ²⁹Si cross-polarization NMR spectra, the mechanism of primary particle agglomeration and degradation of the secondary particles in saline were discussed in terms of the content of H₂O molecules and >Si–OH as well as hydrogen bonding interactions among them. In addition, the Ca–silica and core-shell silica deposited apatite in Kokubo’s simulated body fluid. Thus, the present Ca–silica and polymer-coated silica particles were suggested to be applicable to injectable bone fillers for bone generation.     

Solid state13C NMR spectra of metal carbonyl clusters

The solid state¹³C NMR spectra of four¹³CO enriched carbonyl clusters having a tri-iron metallic core have been analyzed to provide structural and dynamic information. In Fe₃(CO)₁₂ (1), the high temperature spectra suggest the occurrence of large amplitude motions of the CO groups around their position at the vertexes of the coordination polyhedron in addition to the motion involving the Fe₃-triangle previously detected in the VT-¹³C MAS spectra.¹³C and³¹P NMR data of Fe₃(CO)₁₁PPh₃ (2) indicates the presence of one molecule in the asymmetric unit in apparent disagreement with the previously reported X-ray data. Furthermore, we show that structural information can be obtained from the chemical shift tensor components readily available from the analysis of the spinning sideband manifold.     

H and C NMR spectroscopy of 9-acridinones

The ¹H and ¹³C NMR spectra of 9-acridinone and its five derivatives dissolved in CDCl₃, CD₃CN and DMSO-d₆ were measured in order to reveal the influence of the constitution of the compounds and features of the solvents on chemical shifts and ¹H-¹H coupling constants. Experimental data were compared with theoretically predicted chemical shifts, on the GIAO/DFT level of theory, for DFT (B3LYP)/6-31G^∗∗ optimized geometries of molecules—also for four other 9-acridinones. This comparison helped to ascribe resonance signals in the spectra to relevant atoms and enabled revelation of relations between chemical shifts and physicochemical features of the compounds. It was found that experimentally or theoretically determined ¹H and ¹³C chemical shifts of selected atoms correlate with theoretically predicted values of dipole moments of the molecules, as well as bond lengths, atomic partial charges and energies of HOMO.     

微量热法研究丹皮酚及其两种同分异构体与γ-环糊精在水溶液中的相互作用

在298.15 K下利用纳瓦级等温滴定微量热法研究了γ-环糊精与丹皮酚(Pae)及其两种同分异构体(2'-羟基-5'-甲氧基苯乙酮, Hma; 4'-羟基-3'-甲氧基苯乙酮, Ace)在水溶液中的相互作用, 并结合核磁共振对其相互作用的微观结构进行了表征. 试验表明, γ-环糊精与三种药物分子都是1∶1结合, 其中 Pae, Hma与γ-环糊精相互作用过程是焓驱动, 而Ace与γ-环糊精相互作用却是焓-熵共驱动; ¹H NMR 谱表明 Pae, Ace 与γ-环糊精形成典型的包结物, 其中 Pae 分子从 g-环糊精空穴的小口端进入, Ace分子从 g-环糊精空穴的大口端进入, 而 Hma 与γ-环糊精之间只是以弱相互作用结合而非包结作用. 结果显示γ-环糊精对三种同分异构体具有明显的分子识别功能.     

Solid-state C NMR and molecular modeling studies of acetyl aleuritolic acid obtained from Croton cajucara Benth

Solid-state ¹³C nuclear magnetic resonance (¹³C NMR) with magic-angle spinning (MAS) and with cross-polarization and magic-angle spinning (CP/MAS) spectra, and differential scanning calorimetry (DSC) techniques were used to obtain structural data from a sample of acetyl aleuritolic acid (AAA) extracted from the stem bark of Croton cajucara Benth. (Euphorbiaceae) and recrystallized from acetone. Since solid-state ¹³C NMR results suggested the presence of more than one molecule in the unitary cell for the AAA, DSC analysis and molecular modeling calculations were used to access this possibility. The absence of phase transition peaks in the DSC spectra and the dimeric models of AAA simulated using the semi-empirical PM3 method are in agreement with that proposal.     

Solid State NMR Studies of the Bromocyclohexane/Thiourea Inclusion Compound

Solid state ¹³C-MAS and ²H-NMR investigationshave been performed on the bromo-cyclohexane/thiourea inclusion compound.The main objective of this study was the evaluation of the molecularfeatures of the guest molecules and their changes over a large temperaturerange (100 K < T < 350 K). Particular emphasis was placed on themolecular behaviour in the vicinity of a solid–solid phase transitionat T = 237 K and in the low temperature phase, which was hitherto unknown.The ²H-NMR lineshape and relaxation studies reveal that, inthe low temperature phase, restricted but fast overall motions (MHz to GHzregion) of the guest molecules are dominant and reflect the distortedsymmetry of the thiourea channels. On heating above the solid–solidphase transition almost unrestricted overall motions appear, together with alarge degree of orientational disorder at higher temperature. Furthermore,the ring interconversion process presents a major relaxation process in theMHz region. The conformational order is unusual in the sense that the axialconformational state of the guest molecules is stabilized in the thioureachannels. It turns out that this unique property is also preserved in thelow temperature phase.     

Substitution clustering in a non-stoichiometric celsian synthesized by the thermal transformation of barium exchanged zeolite X

The thermal transformation of Ba exchanged zeolite X to celsian has been studied by ²⁷Al and ²⁹Si MAS NMR spectroscopy. Evidence for the degradation of the zeolite framework is present in the ²⁹Si NMR spectra after thermal treatment at 850 °C. Confirmation is provided by the ²⁹Si NMR data that synthesis of celsian via the decomposition of Ba exchanged zeolite leads to a single defect phase. Clustering of the isomorphous replacement of aluminium by silicon must occur to explain the observed ²⁹Si chemical shifts. The ²⁷Al NMR data show distorted aluminium co-ordination sites upon the thermal transformation of Ba exchanged zeolite X. The distortions present in the amorphous matrix are greater than those present in the monoclinic and hexagonal crystalline phases of celsian.     

Molecular structure and spectroscopic properties of N-methylmorpholine betaine complex with 4-hydroxybenzoic acid

Crystal structure of the 1:1 complex of N-methylmorpholine betaine (MMB) with 4-hydroxybenzoic acid (4-HBA) has been determined by X-ray diffraction. Crystals are orthorhombic, space group Pna2₁ with a=7.933(2), b=15.336(3), and Z=4, R=0.033. The acid molecule forms two O-H?O hydrogen bonds with two betaine molecules. The COOH group of the acid forms shorter hydrogen bond with betaine (2.587(2) Å), than the hydroxyl group (2.677(2) Å). The carbonyl oxygen atom of the acid also interacts with the methylene hydrogen atom of the betaine through C-H?O hydrogen bond (3.256(2) Å). Thus formed infinite chains parallel to the z axis are connected by other C-H?O hydrogen bonds into layers perpendicular to the x axis. The morpholine ring has a chair conformation with the methyl group in the equatorial position and CH₂COO⁻ group in the axial one. The powder FTIR and Raman spectra and semiempirical calculations of the isolated molecule confirm the structure of the complex investigated. The ¹H and ¹³C spectra indicate that in DMSO-d₆ solution, protons are not transferred from the acid to the betaine molecules.     

NMR studies of molecular motion in tetramethylammonium hydroxide pentahydrate

Polycrystalline (CH₃)₄NOH·5 H₂O (I) and (CH₃)₄NOD·5D₂O (II) have been studied by¹H NMR lineshapes, second moments and spin-lattice relaxation times and by²H NMR lineshapes as a function of temperature. From low temperatures the first motion to occur is reorientation of the internally rigid (CH₃)₄N⁺ ion about a uniqueC ₃ axis (E _ta = 8.37 kJ/mol forI,E _a = 9.00 kJ/mole forII), followed closely by pseudo isotropic reorientation of the whole ion (E _a = 18.10 kJ/mol). Motion of the cage molecules (water and hydroxide ion) occurs at higher temperatures with an apparentE _a = 11.30 kJ/mol. There is some evidence of a phase transition inII but notI in the 220–230 K region.²H NMR lineshapes ofII below 220 K indicate static cage molecules. Some of the²H quadrupole coupling constants derived from these spectra correspond to O·O hydrogen-bond distances which are incompatible with the known room temperature structure ofI. Above the possible transition inII the anisotropic²H lineshapes indicate rapid motion of²H among all possible hydrogen-bond sites via transfer along the bonds and molecular reorientation. This motion persists in the high temperature phase but the lineshape becomes isotropic due to the cubic symmetry of this phase. It is possible that¹H or²H tunnelling plays an important part in the motion of the cage molecules and the different phase behaviour ofI andII.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Analysis of lipoproteins using 2D diffusion-edited NMR spectroscopy and multi-way chemometrics

This study represents the first application of multi-way calibration by N-PLS and multi-way curve resolution by PARAFAC to 2D diffusion-edited ¹H NMR spectra. The aim of the analysis was to evaluate the potential for quantification of lipoprotein main- and subfractions in human plasma samples. Multi-way N-PLS calibrations relating the methyl and methylene peaks of lipoprotein lipids to concentrations of the four main lipoprotein fractions as well as 11 subfractions were developed with high correlations (R = 0.75-0.98). Furthermore, a PARAFAC model with four chemically meaningful components was calculated from the 2D diffusion-edited spectra of the methylene peak of lipids. Although the four extracted PARAFAC components represent molecules of sizes that correspond to the four main fractions of lipoproteins, the corresponding concentrations of the four PARAFAC components proved not to be correlated to the reference concentrations of these four fractions in the plasma samples as determined by ultracentrifugation. These results indicate that NMR provides complementary information on the classification of lipoprotein fractions compared to ultracentrifugation.     

Reactions of (E)-4-Stilbenethiole with Dibromoalkanes

New substituted stilbenes have been prepared by reactions of (E)-4-stilbenethiole with dibromoalkanes. ¹H and ¹³C NMR spectra of new compounds have been assigned unambiguously on the basis of a combination of homo- (¹H?¹H COSY) and heteronuclear (¹ H?¹³C COSY-HETCOR) two-dimensional methods, chemical shifts, and spin-coupling constants.     

Nonconventional lecithin gels in hydrocarbon oils

Nonconventional gels formed by lecithin in hydrocarbon oils containing a small amount of water have been studied with the help of temperature- and water-content-dependent phase transitions,³¹P NMR and FT-IR techniques. Gels are obtained in cyclohexane,n-octane, andn-dodecane. Addition of cholesterol in lecithin/water/oil ternary system either eliminates the gelation or shifts the transition temperature to higher values. The gels are thermoreversible, optically clear and are not birefringent. The composition of these gels indicates that the gelation takes place even at 15 weight % of lecithin and water. The lateral motion of the phosphate part of lecithin head group along surfactant monolayer, as well as the tumbling motion of the entangled assemblies of the rodshaped aggregates are fast enough to average out the chemical shift anisotropy of³¹P NMR spectra. From the FT-IR studies, it has been concluded that the gel formation involves the conformational changes in the polar head part of lecithin molecules in such a way that further hydration of phosphate group is drastically hindered.This paper is respectfully dedicated to the sixtieth birthday of Professor Hans F. Eicke, University of Basel, Switzerland     

Precursor structure and hydrolysis-gelation process of Al(O-sec-Bu)3 modified with ethylacetoacetate

The precursor structure and hydrolysis-gelation process of aluminum-sec-butoxide, Al(O-sec-Bu)₃, modified with ethylacetoacetate (EAcAc) were investigated using IR, UV and high magnetic field (11.7 T) ²⁷Al NMR spectra. ²⁷Al NMR showed that the reaction of EAcAc with Al(O-sec-Bu)₃ led to the formation of six-coordinated structural units and most of the precursors were assumed to be present as linear trimer containing a four- and two six-coordinated Al atoms. It was found that EAcAc formed the strong chelating bonds with Al(O-sec-Bu)₃, which were hardly hydrolyzed by the attack of water molecules in the gelation process.     

Study of the vibrational spectra of SO2, H2O and D2O using the U(4) algebraic model

Using the U(4) algebraic model, in this work we report a study of the vibrational spectra of SO₂, H₂0¹⁸ and D₂O¹⁶. The inclusion of intermode couplings in algebraic models has been stated to give a deep insight into detailed spectroscopy for these bent XY₂ molecules. Improved set of algebraic parameters has been reported to provide improved RMS deviations for these molecules.