Biomedical subjects

Giorgio Cerichelli

Publications and source records attributed to Giorgio Cerichelli.

5 recordsLinked to original sources

PubMed2005

An effective simulation of aqueous micellar aggregates by computational models.

We have computationally studied the interaction modes, localization and orientation of a benzene (Bz) molecule on the surface of micelles formed by cetyltrimethylammonium salts CTAX. Experimental 1H-NMR data on complexation shifts induced by Bz on the polar head hydrogens and on the adjacent methylene hydrogens of CTAX have been interpreted using a computational approach that combines an automatic molecular docking procedure with a calculation module that accounts for NMR complexation shifts due to ring current diamagnetic anisotropy. Three different models were used to reduce the complexity of the micellar system. Computational results, in good agreement with available experimental data, point to a preferential localization of the Bz molecule along the CTAX alkyl tail, about 3.9 angstroms away from the charged nitrogen. The Bz molecular plane is predicted perpendicular to the C-H bonds of the alkyl tail. The good results obtained with the simplest model suggest that it could be used to study more complex systems involving surfactants endowed with molecular recognition or catalytic abilities.

Catalysis↗

PubMed2004

Reverse micellar aggregates: effect on ketone reduction. 2. Surfactant role.

Kinetics of the reduction of 3-chloroacetophenone (CAF) with sodium borohydride (NaBH(4)) were followed by UV-vis spectroscopy at 27.0 degrees C in different reverse micellar media, toluene/BHDC/water and toluene/AOT/water, and compared with results in an isooctane/AOT/water reverse micellar system. AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate, and BHDC is benzyl-n-hexadecyl dimethylammonium chloride. The kinetic profiles were investigated as a function of variables such as surfactant and NaBH(4) concentration and the amount of water dispersed in the reverse micelles, W(0) = [H(2)O]/[surfactant]. In all cases, the first-order rate constant, k(obs), increases with the concentration of surfactant as a consequence of incorporating the substrate into the interface of the reverse micelles where the reaction takes place. The reaction is faster at the cationic interface than at the anionic one probably because the negative ion BH(4)(-) is part of the cationic interface. The effect of the external solvent on the reaction shows that reduction is favored in the isooctane/AOT/water reverse micellar system than that with an aromatic solvent. This is probably due to BH(4)(-) being more in the water pool of the toluene/AOT/water reverse micellar system. The kinetic profile upon water addition depends largely on the type of interface. In the BHDC system, k(obs) increases with W(0) in the whole range studied while in AOT the kinetic profile has a maximum at W(0) approximately 5, probably reflecting the fact that BH(4)(-) is part of the cationic interface while, in the anionic one, there is a strong interaction between water and the polar headgroup of AOT below W(0) = 5 and, above that, BH(4)(-) is repelled from the interface once the water pool has formed. Application of a kinetic model based on the pseudophase formalism, which considers the distribution of the ketone between the continuous medium and the interface and assumes that reaction takes place only at the interface, has enabled us to estimate rate constants at the interface of the reverse micellar systems. At W(0) < 10, it was considered that NaBH(4) is wholly at the interface and, at W(0) >/= 10, where there are free water molecules, also the partitioning between the interface and the water pool was taken into account. The results were used to evaluate CAF and NaBH(4) distribution constants between the different pseudophases as well as the second-order reaction rate constant of the reduction reaction in the micellar interface.

Journal Article↗

PubMed2004

Reverse micellar aggregates: effect on ketone reduction. 1. Substrate role.

The reduction of three aromatic ketones, acetophenone (AF), 4-methoxyacetophenone (MAF), and 3-chloroacetophenone (CAF), by NaBH(4) was followed by UV-vis spectroscopy in reverse micellar systems of water/AOT/isooctane at 25.0 degrees C (AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate). The first-order rate constants, k(obs), increase with the concentration of surfactant due to the substrate incorporation at the reverse micelle interface, where the reaction occurs. For all the ketones the reactivity is lower at the micellar interface than in water, probably reflecting the low affinity of the anionic interface for BH(4)(-). Kinetic profiles upon water addition show maxima in k(obs) at W(0) approximately 5 probably reflecting a strong interaction between water and the ionic headgroup of AOT; at W(0) < 5 by increasing W(0) BH(4)(-) is repelled from the anionic interface once the water pool forms. The order of reactivity was CAF >> AF > MAF. Application of a kinetic model based on the pseudophase formalism, which considers distribution of the ketones between the continuous medium and the interface, and assumes that reaction take place only at the interface, gives values of the rate constants at the interface of the reverse micellar system. At W(0) = 5, we conclude that NaBH(4) is wholly at the interface, and at W(0) = 10 and 15, where there are free water molecules, the partitioning between the interface and the water pool has to be considered. The results were used to estimate the ketone and borohydride distribution constants between the different pseudophases as well as the second-order reaction rate constant at the micellar interface.

Journal Article↗

PubMed2004

Oxidation of thioanisole by peroxomolybdate in assemblies of cetylpyridinium chloride and methyltri-n-octylammonium chloride.

Methyltri-n-octylammonium chloride (Aliquat 336) is sparingly soluble in water but is readily soluble with a 2-fold excess of micellized cetylpyridinium chloride (CPyCl), and the mixtures show breaks in plots of surface tension or electrolytic conductance against concentration indicative of a critical micelle concentration slightly lower than that of CPyCl. Micellization markedly increases 35Cl and 14N NMR line widths of CPyCl, but addition of NaCl reduces the 35Cl line width and addition of Aliquat increases it. Mixing Aliquat and CPyCl has little effect on their 14N line widths. Ion pairing in alcohol mixtures also increases 35Cl line widths. In water these mixed assemblies behave similarly to micelles of CPyCl as regards effects on rates and equilibria of interconversion of tri- and tetraperoxomolybdate ions, and oxidation of thioanisole by the latter, although it is slightly slower than in micelles of CPyCl. Despite differences in the hydrophobic regions, and relationships between amphiphilic structures and morphologies of association colloids, assemblies of CPyCl and Aliquat behave very much like CPyCl micelles in their physical properties and effects upon reactivity. Geometrical optimization indicates that Aliquat can adopt conformations that allow intercalation with CPyCl micelles.

Journal Article↗

PubMed2002

Alkylation of carbonyl compounds in water: formation of C-C and C-O bonds in the presence of surfactants.

The formation of C-C and C-O bonds by the reaction of enolate intermediates with electrophilic substrates commonly requires strong bases, aprotic solvents and very low temperatures. A way of performing the same reactions with sodium hydroxide at moderate temperatures in aqueous surfactant solutions is presented. Different halides, ketones and surfactants (cationic, zwitterionic and anionic) have been used. The results obtained show that the amount of ketone alkylation is much higher and that the reactions are faster in the presence than in the absence of surfactant aggregates. The hydrolysis of the halide is minimised in the presence of cationic or zwitterionic surfactants.

Journal Article↗