Ionic complexes of biosynthetic poly(malic acid) and poly(glutamic acid) as prospective drug-delivery systems

The hydrolytic degradability and erythromycin release from stoichiometric ionic complexes of biotechnological poly(beta,L-malic acid)s and poly(gamma,D-glutamic acid)s with alkyltrimethylammonium surfactants were investigated. The influence of pH, temperature and antibiotic load on hydrolysis rate was examined. It was found that poly(malic acid) complexes degraded by a surface erosion mechanism at a higher rate than poly(glutamic acid) complexes, which eroded in bulk. Erythromycin was lodged in the paraffinic subphase of the complexes and upon aging it was delivered according to a sigmoidal profile that appeared to be independent on the antibiotic load.     

Absolute rate calculations. Proton transfers in solution

The reaction path of the intersecting-state model is used in transition-state theory with the semiclassical correction for tunneling (ISM/scTST) to calculate the rates of proton-transfer reactions from hydrogen-bond energies, reaction energies, electrophilicity indices, bond lengths, and vibration frequencies of the reactive bonds. ISM/scTST calculations do not involve adjustable parameters. The calculated proton-transfer rates are within 1 order of magnitude of the experimental ones at room temperature, and cover very diverse systems, such as deprotonations of nitroalkanes, ketones, HCN, carboxylic acids, and excited naphthols. The calculated temperature dependencies and kinetic isotope effects are also in good agreement with the experimental data. These calculations elucidate the roles of the reaction energy, electrophilicity, structural parameters, hydrogen bonds, tunneling, and solvent in the reactivity of acids and bases. The efficiency of the method makes it possible to run absolute rate calculations through the Internet.     

Comparative study of the nucleophilic attack step in the proteases catalytic activity: A theoretical study

ABSTRACT

The nucleophilic attack step of the hydrolysis reaction mechanism of the glycine-glycine peptide bond mediated by the enzymatic action of various proteases was elucidated by means of DFT calculations. Five different protease models were considered; namely: cysteine (Cys), threonine (Thr), serine (Ser), aspartyl (Asp) proteases, and a metalloprotease containing zinc (Zn). The model was simplified in order to gain information about the nucleophilic attack in this type of reaction. As a comparative study, this work is focused on the trend in the reactivity of the models. According to the computed activation energies, the reactivity order was determined as follows Cys?<?Thr?<?Ser?<?Zn?<?Asp, being in all cases faster than the uncatalysed spontaneous hydrolysis. A further analysis of the reactions by means of the reaction force approach showed that the structural changes accounts for 65–90% of the total activation energy. Moreover, a natural bond orbital analysis allows the reactions to be classified as synchronous with a late transition state for all cases. Systems analogous to the Cys-protease can be proposed as a promising candidate for the design of mimetic systems capable to cleavage amide bonds.     

Extension of Fermat’s last theorem in Minkowski natural spaces

Journal of Mathematical Chemistry - Minkowski natural (N?+?1)-dimensional spaces constitute the framework where the extension of Fermat’s last theorem is discussed. Based on...     

Rapid methods for radiostrontium determination in aerosol filters and vegetation in emergency situations using PS resin

Journal of Radioanalytical and Nuclear Chemistry - This study describes a rapid and novelty method for radiostrontium determination in aerosol filters and vegetation based on the use of plastic...     

Direct assembly of polyarenes via C-C coupling Using PIFA/BF3·Et2O

Direct oxidative Kita-type coupling between naphthalene and substituted benzenes was found to proceed via four-component coupling, leading to a linear tetraarene with a binaphthalene core. The methodology was extendable to the coupling of unfunctionalized 1,1'-binaphthalene with mesitylene to give a linear hexaarene product in a remarkably chemoselective manner in 87% yield. The method represents an attractive alternative to the traditional syntheses of related oligonaphthalene products via a sequence of metal-catalyzed cross-coupling steps.     

Positive periodic solutions for impulsive differential equations with infinite delay and applications to integro-differential equations

Sufficient conditions for the existence of at least one positive periodic solution are established for a family of scalar periodic differential equations with infinite delay and nonlinear impulses. Our criteria, obtained by applying a fixed-point argument to an original operator constructed here, allow to treat equations incorporating a rather general nonlinearity and impulses whose signs may vary. Applications to some classes of Volterra integro-differential equations with unbounded or periodic delay and nonlinear impulses are given, extending and improving results in the literature.     

Quantitative multiple recurrence for two and three transformations

We observe a subadditivity property for the noise sensitivity of subsets of Gaussian space. For subsets of volume 1/2, this leads to an almost trivial proof of Borell’s Isoperimetric Inequality for ρ = cos( π/2?), ? ∈ N. Rotational sensitivity also easily gives the Gaussian Isoperimetric Inequality for volume-1/2 sets and a.8787-factor UG-hardness for Max-Cut (within 10^?4 of the optimum). As another corollary we show the Hermite tail bound \(||{f^{ > k}}||_2^2 \geqslant \Omega (Var[f]).\frac{1}{{\sqrt k }}for:{R^n} \to \{ - 1,1\} \). Combining this with the Invariance Principle shows the same Fourier tail bound for any Boolean f: {?1, 1} ⁿ → {?1, 1} with all its noisy-influences small, or more strongly, that a Boolean function with tail weight smaller than this bound must be close to a junta. This improves on a result of Bourgain, where the bound on the tail weight was only \(\frac{1}{{{k^{1/2 + o(1)}}}}\). We also show a simplification of Bourgain’s proof that does not use Invariance and obtains the bound \(\frac{1}{{\sqrt k {{\log }^{1.5}}k}}\).