Hiroshi Kawazura

A second-order asymmetric transformation of racemic 2-hydroxymethyl[5]thiaheterohelicene into a single enantiomer upon uptake by bovine serum albumin

Abstract Racemic 2-hydroxymethylthieno[3,2-e:4,5-e′]di[1]benzothiophene (2-HT) with a labile helical structure was converted into a P enantiomer upon uptake by bovine serum albumin (BSA) in 1 % ethanol-water. The effect of the alteration of the molar ratio [2-HT]: [BSA] on UV and CD spectra of the 2-HT-BSA complex solution revealed that BSA possesses two different substratebinding sites with a distinct ability to recognize chirality of enantiomers of 2-HT. The stability of the 2-HT-BSA complex and the chirality recognition at the two sites of BSA were evaluated by the equilibrium constants and the thermodynamic parameters which were obtained from the temperature-dependence of CD-absorptional intensities. BSA pretreated at 50 ∼ 70 °C in an aqueous solution exhibited a great depression of ability in diseriminating chirality between enantiomers of 2-HT, though it possessed slightly altered ability for uptake of 2-HT, in comparison with untreated BSA.

Use of VO2+ as a spin probe for dynamics of polar headgroups in phosphatidylcholine bilayers

Abstract VO 2+ was used as a probe of polar headgroup dynamics in fully hydrated dipalmitoylphosphatidylcholine membranes. The ESR spectrum exhibited an anisotropic pattern consisting of g zz and g xx (= g yy ) components, which is characteristic of VO 2+ in a slow motion regime. The VO 2+ probe was capable of detecting the main transition from gel to liquid crystalline phase through a change in spectral characteristics. Liouville lineshape analysis revealed that the rotational diffusion of VO 2+ in the liquid crystalline phase is two orders slower than that of the choline terminal methyls, indicating that VO 2+ experiences the motion of the headgroup back-bone due to a tight binding to the phosphate group. The probe also detected the lack of phase transition in the membrane containing 40 mol% cholesterol, which agrees with the depiction of recent phase diagrams. As viewed using the probe, incorporation of cholesterol enhanced the rotational diffusion of DPPC headgroups in the gel phase by a factor of approximately 6, but produced no significant effect in the liquid crystalline phase. The VO 2+ -probing method is applicable for investigating motion with diffusion rates larger than 1×10 6 s −1 in phosphatidylcholine membranes.

The conformations and 1H nuclear magnetic resonance parameters of dibenzylideneacetone

Dibenzylideneacetone, (C6H5CHCH)2CO, with two degrees of rotational freedom imparted by the two single bonds between the olefin and the carbonyl group was studied to determine its stable conformers by 1H n.m.r. spectroscopy and by an INDO molecular orbital method. A solvent effect induced by benzene on the trans-olefinic protons and a least squares analysis of the temperature dependence of the internal chemical shift (δAB) between the olefinic protons have revealed support of the theoretical calculations of δAB that the major conformation is s-cis,cis and the minor one is s-cis,trans. An INDO calculation of the conformers concerned confirmed this deduction together with the absence of the s-trans,trans form. δAB is a characteristic parameter of the conformation with the values 0.5 and 1.5 p.p.m. for the s-cis and s-trans forms, respectively, in the olefinic portions of dibenzylideneaċetone.