Molecular theory of piezoelectricity of α-helical polypeptide

A molecular theory of the piezoelectric constant of the α-helical backbone of polypeptide is developed on the basis of fluctuation formalism. The piezoelectric constant, electric susceptibility, and elastic compliance of the α-helix are calculated through the method of molecular lattice dynamics by use of normal-coordinate analysis. Displacements of each atom due to the external stress exerted upon the backbone are also calculated. The piezoelectricity of the α-helix is concluded to arise mainly from rotation of the CO? NH bond. The value of the piezoelectric constant of poly(γ-benzyl-L-glutamate) film calculated from the above theoretical constants along with a composite theory is found to agree reasonably with experiment.     

Compatibility and mesophase separation in blends of α-helical polyglutamates

Blends composed of the α-helical polymers, poly-L-glutamates [(? NHC^αHRC′O? )_n, R = ? CH₂CH₂COO? (CH₂)_m(C₆H₅] (Lm) and the corresponding D enantiomers (Dm), have been studied by x-ray diffraction and viscoelastic measurements. Binary blends of L2, D2, L3, and D3 are compatible and form isomorphous mixed crystals at all compositions, whereas other pairs, with the exception of L1/D1, are incompatible. The demixing process is described for a ternary system consisting of L1, D3, and a diluent chloroform at 40°C. The phase diagram comprises four regions, I, IA, A, and AA, with increasing polymer concentration; I: isotropic, A: anisotropic, IA: I–A biphasic, and AA: A–A biphasic. The IA biphasic gap is greater in the ternary system than in the binary ones. The high-molecular-weight component (D3) is partitioned into the A phase in the IA region. The AA separation originates from incompatibility of the polymers. The phase behavior is discussed on the basis of the Abe-Flory theory by incorporating the polymer-polymer interaction parameter.     

High-resolution mass spectra of two α,β-unssaturated γ-dilactones

The fragmentations of two α,β-unsaturated γ-dilactones in a mass spectrometer are studied. The main feature is conecutive carbon monoxide expulsions. Strong indication of ejection of a fragment C₂O₂ is presented, however. Masses were determined by the high resolution rechnique and metastable transitions were detected by defocusing. Corresponding deuterated dilactones were also studied to verify the fragmentation mechanism.     

Comparison of Methionine α,γ‐Lyase and Homocysteine α,γ‐Lyase for Electrochemical Determination of Homocysteine

Recently, a novel enzymatic method was developed for determination of homocysteine. This method utilizes the electrochemical hydrogen sulfide sensor along with methionine α,γ‐lyase to accomplish the fast, accurate, sensitive and selective measurements. As a continuation of this work, another enzyme, homocysteine α,γ‐lyase, was used and the parallel experiments of using both enzymes were carried out against the effect of pH, sensitivity, linearity, and interferences, in an intended comparison between these two enzymes. The excellent linearity of amperometric currents against homocysteine concentrations, high sensitivities and low detection limits for both enzymes reconfirmed that the electrochemical method is superior over other analytical means. The high enzymatic activity of methionine α,γ‐lyase surpassing homocysteine α,γ‐lyase endowed the former higher sensitivity, lower detection limit and faster response than the latter, suggesting methionine α,γ‐lyase a better candidate for homocysteine measurement by electrochemical method. The differences between these two enzymes on the trends of response time and sensitivity at different pH environments, reactivity toward several forms of homocysteine as well as on the interference from several agents were also addressed and discussed.     

Polymers of α- and β-substituted acrylates with controlled structures

Isotactic and syndiotactic living polymerizations of methacrylates with t-C₄H₉MgBr and t-C₄H₉Li-R₃Al (Al/Li≥2), respectively, were utilized to prepare highly stereoregular block and random copolymers, stereoblock PMMAs, highly branched star polymers with stereoregular arms, stereoregular PMMA macromonomers with methacryloyl functions and stereoregular comblike and graft polymers derived therefrom. A combination of t-C₄H₉Li and bis(2,6-di-t-butylphenoxy) methylaluminum was found to be an efficient initiator for heterotactic living polymerization of methacrylates in toluene at −78°C; e.g. ethyl methacrylate gave a polymer with mr content of 87%. Polymerization of triphenylmefhyl crotonate (TrC) with fluorenyllithium (FILi)/N,N,N′,N′-tetramethylethylenediamine in toluene at −78°C gave a threodiisotactic polymer with narrow MWD, whose stereochemistry was confirmed from the x-ray analysis of the pentamer of methyl crotonate (MeC) derived from the TrC pentamer and ¹H NMR spectral comparison of the pentamer and the poly(MeC). The poly(TrC) prepared with FILi/(S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino) butane also gave a threodiisotactic polymer which showed optical activity due to the one-handed helix. Polymerization of t-butyl crotonate was also discussed in some detail.     

A novel synthesis of α-hydroxy- and α,α′-dihydroxyketone from α-iodo and α,α′-diiodo ketone using photoirradiation

A novel reaction of α-iodo ketone (α-iodocycloalkanone, α-iodo-β-alkoxy ester, and α-iodoacyclicketone) with irradiation under a high-pressure mercury lamp gave the corresponding α-hydroxyketone in good yields. In the case of α,α′-diiodo ketone, α,α′-dihydroxyketone which little has been reported until now was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxy- and α,α′-dihydroxyketone.     

Scalable synthesis and coupling of quaternary α-arylated amino acids: α-aryl substituents are tolerated in α-helical peptides

Quaternary amino acids are important tools for the modification and stabilisation of peptide secondary structures. Here we describe a practical and scalable synthesis applicable to quaternary alpha-arylated amino acids (Q4As), and the development of solid-phase synthesis conditions for their incorporation into peptides. Monomeric and dimeric α-helical peptides are synthesised with varying degrees of Q4A substitution and their structures examined using biophysical methods. Both enantiomers of the Q4As are tolerated in folded monomeric and oligomeric α-helical peptides, with the (R)-enantiomer slightly more so than the (S).

Both R and S enantiomers of Fmoc-protected amino acids bearing α-aryl substituents may be made on gram scale. Solid-phase synthesis leads to helical peptides unperturbed by the presence of these additional α-aryl groups.     

Microwave-assisted synthesis of α-hydroxy ketone and α-diketone and pyrazine derivatives from α-halo and α,α′-dibromo ketone

A novel reaction of α-halo ketone (α-bromo and α-chloro ketone) with irradiation under microwave gave the corresponding α-hydroxyketone and pyrazine derivative in good yields. In the case of α,α′-dibromo ketone, α-diketone was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxyketone, α-diketone, α-chloro ketone and pyrazine derivative.