Theoretical description of aggregation of cationic gemini surfactants in the bulk solution and on the silica surface

A theory of cationic dimeric (gemini) surfactant adsorption onto negatively charged surface is presented. In the proposed model it is assumed that the adsorbed phase is a mixture of singly dispersed molecules of surfactant and spherical, globular and cylindrical aggregates of different dimensions. Only the “excluded area” interactions between the adsorbed species are considered and the effects of surface heterogeneity on monomer adsorption are taken into account. The aggregation behavior of gemini surfactants is based on the additive free energy model proposed by Camesano and Nagarajan (2000). The calculated surfactant adsorption isotherms and the differential molar enthalpies of micellisation and adsorption are compared with the experimental results obtained for a series of gemini surfactants depending on the length of a spacer, temperature or the presence of electrolyte. On the basis of theoretical results the evolution of adsorbed phase of gemini surfactants with the increasing adsorption is discussed. It is shown that the evaluated cmc values and the dimensions of surfactant aggregates are in a good agreement with experiment. Unfortunately, the theoretical model does not describe properly the temperature dependence of micellisation process.     

Titanium and zirconium benzofuranoxides. Crystal structures and catalytic properties

Reactions of Ti(OiPr)4 or Zr(OEt)4 with 4 equivalents of 2,3-dihydro-2,2-dimethyl-7-benzofuranol (ddbfoH) in toluene gave neutral complexes that in the solid state are dimers of [Ti(micro-ddbfo)2(ddbfo)6] and [Zr(ddbfo)3(EtOH)(micro-EtO)]2 composition. The former could also be conveniently synthesized in a direct reaction of TiCl4 with ddbfoH. This air-stable aryloxo compound was found to initiate living ring-opening polymerization of lactides affording polyesters with narrow molecular weight distribution. It also catalyzed addition of terminal acetylenes to aryl aldehydes.     

The unusual binding abilities of the His-analogue of Arg-vasopressin towards Cu2+

A new vasopressin analogue, [His(1,6)]AVP, was synthesized and characterized by potentiometric measurements as well as by UV-Vis, CD and EPR spectroscopy. At the physiological pH the peptide forms a stable complex with Cu(2+) ions which is characterized by the {NH(2), N(Im), N(Im(macrochelate))} binding mode. The replacement of both Cys by His residues in the vasopressin sequence results in a very significant increase in the efficiency of Cu(2+) binding.     

The electrodeposition and properties of Zn-Ni + Ni composite coatings

The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm^?2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15?C18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40?C50 mA cm^?2.     

Mechanisms of reaction in cytochrome P450: Hydroxylation of camphor in P450cam

The fundamental nature of reactivity in cytochrome P450 enzymes is currently controversial. Modelling of bacterial P450cam has suggested an important role for the haem propionates in the catalysis, though this finding has been questioned. Understanding the mechanisms of this enzyme family is important both in terms of basic biochemistry and potentially in the prediction of drug metabolism. We have modelled the hydroxylation of camphor by P450cam, using combined quantum mechanics/molecular mechanics (QM/MM) methods. A set of reaction pathways in the enzyme was determined. We were able to pinpoint the source of the discrepancies in the previous results. We show that when a correct ionization state is assigned to Asp297, no spin density appears on the haem propionates and the protein structure in this region remains preserved. These results indicate that the haem propionates are not involved in catalysis.     

A Mechanism of Efficient G6PD Inhibition by a Molecular Clip

Triple duty : A synthetic molecular clip traps nicotinamide adenine dinucleotide phosphate (NADP⁺; see picture) as well as occupying both the cofactor‐ and the substrate‐binding site in glucose‐6‐phosphate (G6P) dehydrogenase. This combination of two inhibition mechanisms makes the clip highly effective and selective for this enzyme over other dehydrogenases.

     

Antiviral Potential of Plants against Noroviruses

Human noroviruses, which belong to the enterovirus family, are one of the most common etiological agents of food-borne diseases. In recent years, intensive research has been carried out regarding the antiviral activity of plant metabolites that could be used for the preservation of fresh food, because they are safer for consumption when compared to synthetic chemicals. Plant preparations with proven antimicrobial activity differ in their chemical compositions, which significantly affects their biological activity. Our review aimed to present the results of research related to the characteristics, applicability, and mechanisms of the action of various plant-based preparations and metabolites against norovirus. New strategies to combat intestinal viruses are necessary, not only to ensure food safety and reduce infections in humans but also to lower the direct health costs associated with them.     

Self‐assembled monolayers of mercaptosuccinic acid monolayers on silver and gold surfaces designed for protein binding. Part II: vibrational spectroscopy studies on cytochrome c immobilization

An attempt has been made for using MSA‐modified electrodes as linkage monolayers for electrostatic and covalent binding of cytochrome c (Cc). For MSA monolayers grown from an aqueous solution on Ag, attachment of Cc in its native state is proved in the case of covalent bonding. Electrostatic immobilization of Cc at pH 7 results in presence of at least some amount of Fe²⁺ high‐spin configuration and/or Fe³⁺ oxidation state. Native protein Fe²⁺ low‐spin state of Cc is observed after applying a negative potential to the Ag electrode. The influence of the solvent used for the preparation of the MSA monolayer and thiol surface coverage of the Ag surface was studied. It was shown that the key factor to obtain the native structure of Cc is the successful blocking of the metal surface by the MSA linking layer. IRRAS measurements of MSA on monocrystalline gold (111) at neutral pH confirm the successful electrostatic Cc immobilization, which preserves the Fe²⁺ oxidation state of the chromophore on this substrate. Copyright © 2007 John Wiley & Sons, Ltd.