Application of a modified z-cosy experiment for the analysis of spectra of oriented molecules - the spectrum of cis,cis-mucanonitrile

NMR spectra of cis,cis-mucanonitrile oriented in a liquid crystal have been analysed using the connectivity information obtained from a modified Z-COSY experiment which provided crucial clues for the starting parameters for the iterative analysis. The proton spectra with and without C-13 satellites and the C-13 spectra have thus been interpreted. The indirect spin-spin couplings required for the analyses have been obtained from the corresponding isotropic spectra. The H-1-H-1 and C-13-H-1 dipolar couplings so obtained have been utilized to determine the relative internuclear distances. The results indicate that the molecule is planar. (C) 1994 Academic Press, Inc.

Organometallics of diphosphazanes. Part 10. Dinuclear group 6 metal carbonyl complexes bridged by a cyclodiphosphazane in its cis or trans form

Mononuclear Group 6 metal tetracarbonyl complexes containing a cyclodiphosphazane ligand, [PhNP(OC(6)H(4)Me-p)](2) (L), have been used as synthons to prepare homo- and hetero-bimetallic complexes in which the cyclodiphosphazane bridges the two metal centres in its cis or trans isomeric forms. The dimolybdenum complex [Mo-2(eta(5)-C5H5)(2)(CO)(4)(mu-L)] has also been synthesized. The trends in P-31 NMR chemical shifts and the structural features as revealed by X-ray crystallography are discussed.

C-13 MAS NMR spectra of cis,cis-mucononitrile in liquid-crystalline media and in the solid state. Orientation of the carbon chemical-shift tensors

The spinning sidebands observed in the C-13 MAS NMR spectra of cis,cis-mucononitrile oriented in liquid-crystalline media and of the neat sample in the solid state are studied. There are differences in the sideband intensity patterns in the two cases. These differences arise because the order parameters which characterize the orientation of the solute in the liquid-crystalline media differ for different axes. It is shown that, in general, the relative intensities of the sidebands contain information on the sign and magnitude of an effective chemical-shift parameter which is a function of the sum of the products of the principal components of the chemical-shift tensor and the corresponding order parameters with respect to the director. A method for obtaining the orientation of the carbon chemical-shift tensor is proposed. The carbon chemical-shift tensors obtained from gauge-including atomic orbital calculations are also presented for comparison. (C) 1996 Academic Press, Inc.

(+/-)-cis-Dichloro[P-(isopropylamino)-dinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine](triethylphosphine)platinum(II) dichloromethane solvate

In the racemic title compound, [PtCl2(C23H20NO2P)-(C6H15P)].CH2Cl2, the platinum(II) ion, which has approximately square-planar coordination geometry, is coordinated to two different monophosphorus ligands in a cis arrangement along with two chloride ions. A significant shortening of the P-N bond [1.604(7) Angstrom] relative to that in phosphinoamines and their complexes was observed.

Characterization of a Negative cis-Acting DNA Element Regulating the Transcription of CYP2B1/B2 Gene in Rat Liver

The region -160 to -127 nt of the upstream of CYP-2B1/B2 gene has been found to function as a negative cis-acting element on the basis of DNase-I footprint and gel mobility shift assays as well as cell-free transcriptional assays using Bal-31 mutants. A reciprocal relationship in the interaction of the negative and the recently characterized positive elements with their respective protein factors has been found under repressed and induced conditions of the gene. The negative element also harbors the core glucocorticoid responsive sequence, TGTCCT. It is concluded that the negative element mediates the repressed state of the gene under the uninduced condition and also mediates the repressive effect of dexamethasone, when given along with the inducer phenobarbitone in rats. Dexamethasone is able to antagonize the effects of phenobarbitone at as low a concentration as 100 mu g/kg body wt in these animals. (C) 1995 Academic Press,Inc.

Di- and tri-metallic complexes containing two bridging cyclodiphosphazane ligands: the crystal structure of [MO2(CO)8{µ-cis-[PhNP(OC6H4Me-p)]2}2]

The reactions of the mononuclear cyclodiphosphazane complexes, cis-[Mo(CO)(4){cis-[PhNP(OR)](2)}(2)] with [Mo(CO)(4)(nbd)] (nbd = norbornadiene). [Mo(CO)(4)(NHC5H10)(2)] or [MCl(2)(cod)] (cod = cycloocta-1,5-diene) afforded the homobimetallic complexes; [Mo-2(CO)(8){mu-cis-[PhNP(OR)](2)}(2)] (R = C(5)H(4)Me-p 5 or CH2CF3 6) or the heterobimetallic complexes. [Mo-2(CO)(8){mu-cis-[PhNP(OE)](2)}(2)MCl(2)] (R = C(6)H(4)Me-p; M = Pd 7 or Pt 8). In all the above complexes, the two metal moieties are bridged by two cyclodiphosphazane ligands. The reactions of the mononuclear complexes, cis-[M(CO)(4)(A){cis-[PhNP(OC(6)H(4)Me-p)](2)}] with (M'Cl-2(cod)] afforded the trinuclear complexes, cis-[M'Cl-2[M(CO)(4)(A){cis-[PhNP(OC(6)H(4)Me-p)](2)}](2)] (M' = Pd, M = Mo, A = P(OMe)(3) 10; M' = Pt, M = Mo. A = P(OMe)(3) 11; M' = Pd. M = W. A = NHC5H10 12; M' = Pt, M = W. A = NHC5H10 13). The structure of the complex 5 has been determined by single-crystal X-ray crystallography.

A stereospecific approach to cis-anti-cis triquinanes

A methodology for the synthesis of compounds containing the cis-anti-cis fused triquinane system has been developed starting from tricyclo[5.2. 1.0(2.6)]deca-4,8-dien-3-(exo)ol 6 involving Ireland ester Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions as key steps.

Trans -> Cis isomerization of trans-[(dPPM)(2)Ru(H)(L)][BF4] (L = P(OR)(3)) Complexes: Preparation of cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2)

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2) (dppm = Ph2PCH2PPh2; L = P(OMe)(3), P(OEt)(3), PF((OPr)-Pr-i)(2)) have been prepared by protonating the precursor hydride complexes cis-[(dppm)(2)Ru(H)(L)][BF4] (L = P(OMe)(3), P(OEt)(3), P((OPr)-Pr-i)(3)) using HBF4.Et2O. The cis-[(dppm)(2)Ru(H)(L)][BF4] complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The eta(2)-H-2 ligand in the dihydrogen complexes is labile, and the loss of H-2 was found to be reversible. The protonation reactions of the starting hydrides with trans PMe3 or PMe2Ph yield mixtures of the cis and the trans hydride complexes; further addition of the acid, however, give trans-[(dPPM)(2)Ru(BF4)Cl]. The roles of the bite angles of the dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this series of complexes are discussed. X-ray crystal structures of trans-[(dppm)(2)Ru(H)(P(OMe)(3))][BF4], cis-[(dppm)(2)Ru-(H)(P(OMe)(3))][BF4], and cis-[(dppm)(2)Ru(H)(P((OPr)-Pr-i)(3))][BF4] complexes have been determined.

An Enantiospecific Approach to Irregular Ligusticum grayi Sesquiterpenes: Synthesis of cis-Preisothapsa-2,8(12)-diene

Enantiospecific syntheses of 1-epi- (or cis-)-preisothapsa-2,8(12)-diene and 1-epi- and 1,8-diepipreisothapsa-2-en-12-ols, starting from the readily available monoterpene (R)-carvone, have been accomplished.

Diffusion ordered spectroscopy for resolution of double bonded cis, trans-isomers

NMR spectroscopic separation of double bonded cis- and trans-isomers, that have different molecular shapes but identical mass have been carried out using Diffusion Ordered Spectroscopy (DOSY). The mixtures of fumaric acid and maleic acid, that have similar hydrodynamic radii, have resolved been on the basis of their diffusion coefficients arising due to their different tendencies to associate with micelles or reverse micelles. Sodium dodecyl sulfate (SDS) and Dioctyl sulfosuccinate sodium salt (AOT) have been used as the media to mimic the chromatographic conditions, modify the average mobility and to achieve differential diffusion rates. The best separation of the components has been achieved by Dioctyl sulfosuccinate sodium salt (AOT) in D2O solution. (C) 2012 Elsevier B.V. All rights reserved.

Cis-trans peptide variations in structurally similar proteins

The presence of energetically less favourable cis peptides in protein structures has been observed to be strongly associated with its structural integrity and function. Inter-conversion between the cis and trans conformations also has an important role in the folding process. In this study, we analyse the extent of conservation of cis peptides among similar folds. We look at both the amino acid preferences and local structural changes associated with such variations. Nearly 34% of the Xaa-Proline cis bonds are not conserved in structural relatives; Proline also has a high tendency to get replaced by another amino acid in the trans conformer. At both positions bounding the peptide bond, Glycine has a higher tendency to lose the cis conformation. The cis conformation of more than 30% of beta turns of type VIb and IV are not found to be conserved in similar structures. A different view using Protein Block-based description of backbone conformation, suggests that many of the local conformational changes are highly different from the general local structural variations observed among structurally similar proteins. Changes between cis and trans conformations are found to be associated with the evolution of new functions facilitated by local structural changes. This is most frequent in enzymes where new catalytic activity emerges with local changes in the active site. Cis-trans changes are also seen to facilitate inter-domain and inter-protein interactions. As in the case of folding, cis-trans conversions have been used as an important driving factor in evolution.

A method for stabilizing the cis prolyl peptide bond: influence of an unusual n -> pi* interaction in 1,3-oxazine and 1,3-thiazine containing peptidomimetics

The cis/trans isomer ratios of the Xaa-Pyr (Pyr = pyrrolidine) 3 degrees amide bonds are significantly high (similar to 90% cis) in the novel peptidomimetics where Pyr contains 1,3-oxazine (Oxa) or 1,3-thiazine (Thi) at its 2 position. We find that an unusual n -> pi(i-1)* interaction, selectively stabilizes the cis conformer and the n X n repulsion destabilizes the trans conformer of these molecules. Both these electronic effects oppose the steric effects in the 3 degrees amide bond. The structural requirements for manifestation of these electronic effects are determined. (c) 2012 Elsevier Ltd. All rights reserved.

Computational interrogation of cis-regulatory elements of genes that are common targets of luteotropin and luteolysin in the primate corpus luteum

The rapid recent increase in microarray-based gene expression studies in the corpus luteum (CL) utilizing macaque models gathered increasing volume of data in publically accessible microarray expression databases. Examining gene pathways in different functional states of CL may help to understand the factors that control luteal function and hence human fertility. Co-regulation of genes in microarray experiments may imply common transcriptional regulation by sequence-specific DNA-binding transcriptional factors. We have computationally analyzed the transcription factor binding sites (TFBS) in a previously reported macaque luteal microarray gene set (n = 15) that are common targets of luteotropin (luteinizing hormone (LH) and human chorionic gonadotropin (hCG)) and luteolysin (prostaglandin (PG) F-2 alpha). This in silico approach can reveal transcriptional networks that control these important genes which are representative of the interplay between luteotropic and luteolytic factors in the control of luteal function. Our computational analyses revealed 6 matrix families whose binding sites are significantly over-represented in promoters of these genes. The roles of these factors are discussed, which might help to understand the transcriptional regulatory network in the control of luteal function. These factors might be promising experimental targets for investigation of human luteal insufficiency. (C) 2012 Elsevier B.V. All rights reserved.