Lysozyme binding to poly(4-vinyl-N-alkylpyridinium bromide)

The adsorption behavior of polycations at ionic strengths (1) ranging from 0.001 to 0.1 onto silicon wafers was studied by means of ellipsometry, contact angle measurements and atomic force microscopy (AFM). Polycations chosen were bromide salts of poly(4-vinylpyridine) N-alkyl quaternized with linear aliphatic chains of 2 and 5 carbon atoms, QPVP-C2 and QPVP-C5, respectively. Under 1 0.001 the reduction of screening effects led to low adsorbed amounts of QPVP-C2 or QPVP-C5 (1.0 +/- 0.1 mg/m(2)), arising from the adsorption of extended chains. Upon increasing l to 0.1, screening effects led to conformational changes of polyelectrolyte chains ill Solution and to higher adsorbed amount values (1.9 +/- 0.2 mg/m(2)). Advancing contact angle theta(a) measurements performed with water drops onto QPVP-C2 and QPVP-C5 adsorbed layers varied from (45 +/- 2)degrees to (50 +/- 5)degrees, evidencing the exposure of both hydrophobic alkyl groups and charged moieties. The adsorption of lysozyme (LYZ) molecules to QPVP-C5 layers was more pronounced than to QPVP-C2 films. Antimicrobial effect of LYZ bound to QPVP-C2 or QPVP-C5 layers or to Si wafers was evaluated with enzymatic assays using Micrococcus luteus as Substrates. The adsorption behavior of QPVP-C2 and QPVP-C5 at the water-air interface was studied by means Of surface tension measurements. Only QPVP-C5 was able to reduce water Surface tension. Mixtures of LYZ and QPVP-C5 were more efficient in reducing Surface tension than pure LYZ solution, evidencing co-adsorption at liquid-air interface. Moreover, antimicrobial action observed for mixtures of LYZ and QPVP-C5 was more pronounced than that measured for pure LYZ. Hydrophobic interaction between LYZ and QPVP-C5 ill Solution seems to drive the binding and to preserve LYZ secondary structure. (c) 2008 Elsevier Inc. All rights reserved.

Direct detection of underivatized chitooligosaccharides produced through chitinase action using capillary zone electrophoresis

Capillary electrophoresis with capacitively coupled contactless conductivity detection was successfully used to quantify N-acetylglucosamine and five N-acetyl-chitooligosaccharides (C2-C6) produced after reaction with a purified chitinase (TmChi) from Tenebrio molitor (Coleoptera). No derivatization process was necessary. The separation was developed using 10 mM NaOH with 10% (v/v) acetonitrile as background electrolyte and homemade equipment with a system that avoids the harmful effect of electrolysis. The limit of detection for all oligosaccharides was ca. 3 mu M, and the results indicated that the larger the oligosaccharide, the higher the sensitivity. Analysis of the chitooligosaccharides produced revealed that TmChi has an endolytic cleavage pattern with C5 as the best substrate (higher catalytic efficiency k(cat)/K-M) releasing C2 and C3. (c) 2007 Elsevier Inc. All rights reserved.

Spectroscopic and theoretical studies of some 2-ethylsulfinyl-(4 `-substituted)-phenylthioacetates

The analysis of the IR nu(co) bands of the 2-ethylsulfinyl-(4`-substituted)-phenylthioacetates 4`-Y-C(6)H(4)SC(O)CH(2)S(O)Et (Y = NO(2) 1, Cl 2, Br 3, H 4, Me 5, OMe 6) supported by B3LY/6-31G(d,p) calculations along with the NBO analysis for 1.4 and 6 and X-ray analysis for 3, indicated the existence of four gauche (q-g-syn, g(3)-syn. g(1)-atin and q-g(2)-syn) conformers for 1-6 The calculations reproduce quite well the experimental results, i e the computed q-g-syn and g3-syn conformers correspond in the IR spectrum (in solution), to the nu(co) doublet higher frequency component of larger intensity, while the computed grant, conformer correspond to the nu(co) doublet lower frequency component (in solution) NBO analysis showed that the n(s) -> pi(center dot)(c1=o2), no(co) -> sigma(c1-s3), no(co) -> sigma(c1-c4) orbital interactions are the main factors which stabilize the q-g-syn, g(3)-syn, g(1)-anti and q-g(2)-syn conformers for 1, 4 and 6 The no(co) -> sigma(c1-s3) interaction which stabilizes the q-g-syn, g(3)-syn and q-g(2)-syn conformers into a larger extent than the granti conformer, is responsible for the larger tto frequencies of the former conformers relative to the latter one. The q-g-syn, g(3)-syn and q-g(2)-syn conformers are further stabilized sigma(c4-s5) -> pi(co)center dot (strong). pi(co)/sigma(c1-c4,) no(co) -> sigma(c6-H17[Et]) (weak) and pi(co)/sigma(c4-c5) pi(co) (strong) orbital interactions. The q-g-syn conformer is also stabilized by sigma(c4-s5) -> pi(center dot)(co) (strong), pi(co)/sigma(c4-c5).no(co) -> sigma(c6-H17[Et]), pi(C9=C11[ph]) -> sigma(c4-H6x-CH2]) (weak). no((SO)) -> sigma(C11-H23[ph]) (medium) pi(co)/sigma(c4-c5)(strong) orbital interactions. The q-g-syn conformei is further stabilized by the n(S5) O((C))(8-) S((SO))(8+) attractive Coulornbic interaction while the q-g(2)-syn conformer is destabilized by the n55 0,8c-0) repulsive Coulombic interaction. This analysis indicates the following conformer stabilization order. q-g-syn, g(3)-syn > g(1)-anti >> q-g(2)-syn X-ray single crystal analysis of 3 indicates that it assumes in the solid a distorted q-g(2)-syn geometry which is stabilized through almost the same orbital and Coulombic interaction which takes place for the q-g(2)-syn conformer, in the gas, along with dipole moment coupling and a series intermolecular C-HO0 interactions. (C) 2010 Elsevier B V All rights reserved

Studies on chemo- and diastereo-selectivity of the Diels-Alder reactions of sulfinyltoluquinones with cyclopentadiene

Sulfinyltoluquinones (2a-2c) were submitted to thermal or catalyzed [4+2] cycloaddition reactions with cyclopentadiene. For p-tolylsulfinyltoluquinones (2b) and (2c), almost complete C2-C3-chemo- and unlike-diastereoselectivity was achieved by catalysis with ZnBr(2), yielding adducts 6. Under thermal conditions, Diels-Alder reaction took place at the C5-C6 double bonds of quinones 2a-2c, generating mixtures of diastereoisomeric like- and unlike-adducts 4.