ISSN:0899-0042    

DOI:10.1002/chir.530030402

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractFischer demonstrated (1890–1919) that functional biomolecules are composed specifically of the D‐sugars and the L‐amino acids, and that in the laboratory synthetic reactions of such molecules propagate with chiral stereoselectivity. Given a primordial enantiomer, biomolecular homochirality followed without the intervention of the chiral natural force conjectured by Pasteur (1860), except prebiotically. Polarized solar radiation and other classical chiral forces were proposed as agencies generating a prebiotic enantiomeric excess, but the forces then known were found to be evenhanded on a time and space average, exemplifying parity conservation (1927). The weak nuclear force, shown to violate parity (1956), was unified with electromagnetism in the electroweak force (1970). Ab initio estimations including the chiral electroweak force indicate that the L‐amino acids and the D‐sugars are more stable than the corresponding enantiomers. The small energy difference between these enantiomer pairs, with Darwinian reaction kinetics in a flow reactor, account for the choice of biomolecular handedness made when l

ISSN:0899-0042    

DOI:10.1002/chir.530030403

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe influence of the intercalation of ethidium bromide (EB) on the characteristics of the DNA cholesteric and hexagonal mesophases is studied by optical microscopy, circular dichroism, and X‐ray diffraction. The distance between DNA rods in the hexagonal phase is not modified by the presence of EB whereas the pitch of the cholesteric mesophase is considerably shortened by the dye. This seems to be related to the stereochemical effect of the intercalation rather than to the presence of a random distribution of the positive charge of the dy

ISSN:0899-0042    

DOI:10.1002/chir.530030404

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractFour chiral analogues of the surfactant Aerosol‐OT (AOT) have been synthesized and characterized. All of them form reverse micelles in apolar solvents in thew0range 0–30 (w0= [water]/[tenside]). Reverse micellar solutions have been investigated by UV absorption and circular dichroism spectroscopies with the aim of clarifying whether the formation of the macromolecular micellar structure induces the appearance of new chromophoric bands or perturbs the existing ones. Methanolic solutions of the surfactants, in which no micellar aggregates are formed, were taken as references. One of the products 1(S),1′(S)‐dimethylbisheptylsulphosuccinate sodium salt (MH‐AOT) was capable of forming reverse micelles of relatively high water content (w0up to 40) and this process was accompanied by a specific increase in the intensity of the circular dichroism band associated with the ester absorbance of the molecule. As no concomitant changes were seen in the UV absorbance spectrum, it was concluded that this observation reflected conformational events occurring within the surfactant rather than chromophoric perturbation. These results are qualitatively similar to those found recently for lecithin reverse micelles which, however, form gels at sufficiently high water contents. The chiroptical properties of these supramolecular aggregates are compared with those of covalent macromolecular systems such as pol

ISSN:0899-0042    

DOI:10.1002/chir.530030405

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractWith the early aim of quantifying steric consequences of chirality, efforts to define a nonempirical steric parameter of chemical groups are reported. Steric hindrance of a reacting center by any acyclic saturated R group has been characterized by a geometric “axial steric parameter”: the solid angle of R. When the group is a “symmetric top substituent” (i.e., when all the terminal atoms are equivalent), the solid angle matches the solid angle of a cone envelope of R. The definition of this cone is compared with Tolman's definition of a ligand cone in organometallic complexes. The chemical significance of this parameter is shown by an excellent correlation with the Dubois' experimental steric parameterE′s. Modeling steric repulsion by the cone of R, and correcting solid angles for conformational effects, only 3 empirical coefficients are needed to calculate 33 values ofE′swith less than 10% error. The cone model is suggested to be relevant within the limits of random and independent free rotations about all the bonds in the C–R group. A separation between “axial cone steric hindrance” and other steric effects is proposed. The basic model and the corrections proposed allow the conformational features of ester

ISSN:0899-0042    

DOI:10.1002/chir.530030406

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe circular dichroism (CD) spectrum of tumor necrosis factor‐α has been measured into the vacuum UV to 168 nm. Analysis of the CD for secondary structure is in good agreement with X‐ray diffraction results, but the analysis is somewhat unstable. Adding the CD of this protein together with its X‐ray determined secondary structure to the basis set should improve subsequent analyses of CD spectra for other all‐β

ISSN:0899-0042    

DOI:10.1002/chir.530030407

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe physics involved in photochemistry with circularly polarized light, the warnings on its inherent limitations, as well as some examples of application on organic molecules are briefly reviewed.

ISSN:0899-0042    

DOI:10.1002/chir.530030408

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe configuration of carbon‐8 in feroxidin (1) was proven to be (S) by chemical correlation with (S)‐methylsuccinic acid. Previous demonstration that 6‐hydroxy and 8‐methyl groups are equatorial and pseudoaxial, respectively, in a half‐chair conformation of the cyclohexene ring (relative configuration) allowed the absolute stereochemistry of the whole molecule to be established (Fig. 3). The CD spectrum of feroxidin represents the first experimental test confirming the applicability of Snatzke's helicity rules to tetralinsm‐disubstituted on the ar

ISSN:0899-0042    

DOI:10.1002/chir.530030409

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA modern method is reported for the assignment of absolute configuration for peptidomimetics in bioactive peptides by use of1H‐NMR parameters in solution. Four peptide systems incorporating either retro‐inverso modifications or 2‐aminocyclopentanecarboxylic acid (2‐Ac5c) as a peptidomimetic for proline are discussed. (1) Two 14‐membered cyclic dermorphin analogs Tyr‐c[D‐A2bu‐Phe‐gPhe‐(S and R)‐mLeu] with a reverse amide bond between gPhe and mLeu residues where gPhe denotes agem‐diamino analog of Phe and mLeu refers to a malonyl analog of Leu. (2) Two cyclic hexapeptides related to somatostatin, c[gSar6‐(S and R)‐mPhe7‐D‐Trp8‐Lys9‐Thr10‐Phe11], with a reverse amide bond between the gSar and mPhe residues where the gSar and mPhe denote thegem‐diamino and malonyl analogs of the Sar and Phe residues, respectively. The superscript numbers refer to positions in native somatostatin. (3) Cyclic hexapeptide somatostatin analogs containing 2‐Ac5c [trans‐(1S,2S)‐2‐Ac5c,trans‐(1R,2R)‐2‐Ac5c,cis‐(1R,2S)‐2‐Ac5c, andcis‐(1S,2R)‐2‐Ac5c] in place of proline c[(2‐Ac5c)6‐Phe7‐D‐Trp8‐Lys9‐Thr10‐Phe11]. (4) Morphiceptin related analogs incorporating acis‐2‐Ac5c residue as shown in Tyr‐cis‐2‐Ac5c‐Phe‐Val‐NH2. The me

ISSN:0899-0042    

DOI:10.1002/chir.530030410

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractPolymerization of diphenyl‐2‐pyridylmethyl methacrylate was carried out with the complexes of organolithium compounds with 22 chiral ligands. Helix‐sense‐selectivity of the polymerization was largely affected by a slight structural difference of chiral ligands. (+)‐(S)‐2‐(1‐Pyrrolidinylmethyl)pyrrolidine was the most effective ligand in producing a one‐handed helical polymer with narrow molecular we

ISSN:0899-0042    

DOI:10.1002/chir.530030411

出版商:Alan R. Liss, Inc.    

年代:1991

数据来源: WILEY