G. A. Nagana Gowda

Spatial distribution of oil in groundnut and sunflower seeds by nuclear magnetic resonance imaging

Abstract. The nuclear magnetic resonance imaging technique has been used to obtain images of different transverse and vertical sections in groundnut and sunflower seeds. Separate images have been obtained for oil and water components in the seeds. The spatial distribution of oil and water inside the seed has been obtained from the detailed analysis of the images. In the immature groundnut seeds obtained commercially, complementary oil and water distributions have been observed. Attempts have been made to explain these results.

Synthetic and physicochemical studies of uranium complexes with semicarbazone and hydrazone

Uranyl complexes of two Schiff bases, semicarbazone and hydrazone containing OON donor atoms have been synthesized and characterized on the basis of NMR, IR and electronic spectral studies, conductance, magnetic susceptibility and thermogravimetric data. The 1H NMR spectrum of the semicarbazone complex shows low field signals due to OH, NH and ---CH=N groups at 10.23, 9.31 and 8.17 ppm, respectively. The aromatic protons appear in the range 7.74–7.40 ppm. On complexation with U(VI) the signals due to OH and NH disappear evidently due to their participation in coordination. The coordination number of the o-vanillin semicarbazone (oVSC) complex is 6 whereas, that of the o-vanillin isonicotinic acid hydrazone (oVINAH) complex is 8, in addition to the two oxygen atoms already bonded to U(VI) in each species. The thermograms show the presence of 3 and 2 water molecules in these complexes, respectively and the IR spectral data also support the above conclusion. Suitable structures have been assigned.

Diastereomerism in palladium(II) allyl complexes of P,P-, P,S- and S,S-donor ligands, Ph2P(E)N(R)P(E′)Ph2 [R=CHMe2 or (S)-*CHMePh; E=E′=lone pair or S]: solution behaviour, X-ray crystal structure and catalytic allylic alkylation reactions

The reactions of achiral homodonor diphosphazane ligands, Ph2P(E)N(CHMe2)P(E)Ph-2[E = E = lone pair (1) or S (2)] with the chloro bridged palladium dimers, [Pd(eta(3)-1,3m R-R-C3H3)(mu-Cl)](2) (R, R = H, Me or Ph) in the presence of NH4PF6 give cationic eta(3)-allyl palladium complexes, [Pd(eta(3)-1 3-R-R-C3H3)(L-L)]. Each of these complexes exists as single species in solution except the 1,3-dimethyl allyl complex, which exists as two isomers (syn/syn- and syn/anti-) in solution. Analogous allyl palladium complexes derived from the chiral homodonor diphosphazane ligand, Ph2PN((S)-*CHMePh)PPh2 (3) exist as a single species when the allyl moiety is symmetrical (R = R = H or Ph) but a 1:1 mixture of two different face-coordinated diastereomers if the allyl moiety is unsymmetrically substituted (R not equal R). The 1,3-dimethyl-allyl complex, [Pd(eta(3)-1,3-Me-2-C3H3 {Ph2PN((S)-*CHMePh)PPh2-k(2)P,P}]PF6 (20) exists as a mixture of two isomers. The major isomer (20a) has the syn/syn-allylic arrangement while the minor isomer (20b) has the syn/anti configuration. These isomers (20a and 20b) equilibrate in solution via a syn-anti isomerisation pathway. Achiral and chiral heterodonor monosulphide ligands, Ph2P(S)N(R)PPh2 [R = CHMe2 (4), (S)-*CHMePh(5)] give rise to allyl palladium complexes which exist as several isomers in solution. The presence of a chiral centre in the ligand 5 enables the observation of two NMR distinguishable face-coordinated diastereomers for its allyl complexes. However, the solid state structure of [Pd(eta(3)-C3H5){Ph2P(S)N((S)-*CHMePh)PPh2-k(2)P,S}]PF6 (27) shows the presence of only one diastereomer. Two-dimensional (2D) phase sensitive H-1-H-1 NOESY and ROESY measurements indicate that the monosulphide complexes undergo exchange by the opening of the eta(3)-allyl group selectively at the trans position with respect to the greater pi-acceptor phosphorus centre to generate a eta(1)-bonded intermediate. Preliminary studies on the use of the ligands 1-5 for catalytic allylic alkylation reactions of an unsymmetrically substituted substrate, (E)-1-phenyl-2-propenyl-acetate are reported.

Room-temperature and low-ordered, amphotropic-lyotropic ionic liquid crystal phases induced by alcohols in phosphonium halides.

Tri- n-decylmethylphosphonium chloride and bromide ( 1P10X) salts are not liquid crystalline. However, mesophases are induced by adding very small amounts of an alcohol or water. The temperature ranges of the induced smectic A 2 (SmA 2) liquid-crystalline phases can be very broad and the onset temperatures can be below room temperature depending upon the concentration of the alcohol or water and the structure of the alcohol. At least one molar equivalent of hydroxyl groups is necessary to convert the 1P10X completely into a liquid crystal. Strong association between the hydroxyl groups of an alcohol or water and the head groups of the 1P10X is indicated by spectroscopic, diffraction, and thermochemical data. Unlike many other smectic phases, those of the 1P10X/alcohol complexes are easily aligned in strong magnetic fields and the order parameters of selectively deuterated alcohols as measured by (2)H NMR spectroscopy, approximately 10 (-2), are much lower than the values found when the host is a commonly employed thermotropic liquid crystal. The dependence of the specific values of the order parameters on temperature, the nature of the halide anion, and the structure and concentration of the alcohol are reported. In sum, a detailed picture is presented to explain how and why an alcohol or water induces liquid crystallinity in the 1P10X salts. The data also provide a blueprint for designing media with even lower order parameters that can be hosts to determine the conformations and shapes of guest molecules.

Allylpalladium Complexes of Mixed-Donor Diphosphazane Ligands Bearing a Stereogenic Phosphorus Centre: Structure and Stereodynamics

( 3-Allyl)palladium complexes of general formula [Pd( 3-R C3H4){ 2-Ph2PN(R)PPh(N2C3HMe2-3,5)}](PF6) (3-6) and [Pd( 3-R C3H4){ 2-Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5)}](PF6) (7-8), containing pyrazolyl-substituted diphosphazane ligands bearing a stereogenic phosphorus centre, have been synthesised. NMR spectroscopic and X-ray diffraction studies showed that the diphosphazane ligand in [Pd( 3-R C3H4){ 2-Ph2PN(R)PPh(N2C3HMe2-3,5)}](PF6) [R = Me or Ph; R = CHMe2 (3 and 5) or (S)-*CHMePh (4 and 6)] displayed unprecedented P,N-coordination instead of the hitherto observed P,P-coordination. These complexes existed in solution as mixtures of endo,syn,trans, exo,syn,trans, and endo,syn,cis diastereomers. In the solid state, only the endo,syn,trans isomer was observed for complex 5. Phase-sensitive 2-D NOESY and ROESY spectra showed that the complexes 3-5 underwent syn,anti isomerisation; the NMR spectroscopic data were consistent with a mechanism involving the opening of the 3-allyl group at the trans position with respect to the phosphorus centre. The isomerisation thus appeared to be electronically controlled. The complexes [Pd( 3-MeC3H4){ 2-Ph2P(S)N(CHMe2)PPh(N2C3HMe23,5)}](PF6) (7) and [Pd( 3-PhC3H4){ 2-Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5)}](PF6) (8), bearing the diphosphazane monosulfide Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5) (1c), displayed P,S-coordination and existed in solution as six and four isomers, respectively. Exchange was observed among four of the six isomers of 7 and among all the four isomers of 8 at 298 K, through the opening of the 3-allyl moiety, which appeared to be subject to both electronic and steric control.

Metal-ion-ligand interactions in thermotropic liquid crystals

The interactions of lithium perchlorate with ligands such as dimethyl sulphoxide, acetonitrile, pyridine and the Schiff base liquid crystals are investigated. The experiments open a new field for the study of metal-ion-ligand interactions in thermotropic liquid crystals.

NMR spectra of mixed liquid crystals of opposite diamagnetic susceptibility anisotropies near critical point under variable angle sample spinning

The deuterium NMR spectra of molecules oriented in mixtures of nematic liquid crystalline phases for which the macroscopic diamagnetic susceptibility anisotropy (Δχ) is nearly zero reveal the dynamics of the director for different angles the spinning axis makes with the magnetic field and for different spinning speeds. It is observed that a switch over of the director orientation occurs as a function of the spinning speed and the angle the spinning axis makes with the magnetic field. The farther the angle between the spinning axis and the magnetic field from the magic angle, the higher the spinning speed required to effect such a switch over of the director orientation. The switch over takes place gradually as indicated by the appearance of the ‘powder pattern’ in the 2H NMR spectra.

Half-sandwich (η 6-arene)ruthenium(II) chiral Schiff base complexes: Analysis of the diastereomeric mixtures in solution by 2D-NMR spectroscopy

Abstract2D NMR spectroscopy has been used to determine the metal configuration in solution of three complexes, viz. [(η6-p-cymene)Ru(L*)Cl] (1) and [(η6-p-cymene)Ru(L*)(L′)] (C1O4) (L′ = H2O,2; PPh3,3), where L* is the anion of (S)-(l-phenylethyl)salicylaldimine. The complexes exist in two diastereomeric forms in solution. Both the (RRu,Sc)- and (SRu,Sc)-diastereomers display the presence of attractive CH/π interaction involving the phenyl group attached to the chiral carbon and the cymene ring hydrogens. This interaction restricts the rotation of the C*-N single bond and, as a result, two structural types with either the hydrogen atom attached to the chiral carbon (C*) or the methyl group attached to C* in close proximity of the cymene ring protons get stabilized. Using 2D NMR spectroscopy as a tool, the spatial interaction involving these protons are studied in order to obtain the metal configuration(s) of the diastereomeric complexes in solution. This technique has enabled us to determine the metal configuration as (RRu,Sc) for the major isomers of 1–3 in solution.

Solute induced liquid crystalline behaviour of a quaternary ammonium salt and its application to structure determination

A new liquid crystalline phase, induced by the addition of small amounts of a non-mesogenic solute (such as dimethyl sulphoxide or methyl iodide) to a quaternary ammonium salt, N-methyl-N,N,N-trioctadecylammonium iodide (MTAI), has been detected by NMR and optical microscopic studies. In some cases, there is a coexistence of nematic and smectic phases. Information on the ordering of the phases in the magnetic field of the spectrometer has been derived from NMR spectra of a dissolved molecule, C-13-enriched methyl iodide. The low order parameter of the pure thermotropic nematic phase of the salt provides first-order spectra of the dissolved oriented molecules. Analyses of spectra of cis,cis-mucononitrile exemplifies the utility of the MTAI nematic phase in the determination of structural parameters of the solute.

An NMR study of the coexistence of nematic and “induced” smectic phases in mixtures of nematics

Deuteron NMR studies of mixtures of nematic liquid crystals such as N-(p-ethoxybenzylidene)-p-n-butylaniline and trans-4-pentyl-4-(4-cyanophenyl)cyclohexane and the molecules dissolved therein show the coexistence of up to three different spectra at certain concentrations and temperatures. This is attributed to the coexistence of nematic and “induced” smectic phases.