Antonio Cipiciani

Structural properties of water-ethanol mixtures: A correlation with the formation of micellar aggregates

Abstract The effect of ethanol on the critical micelle concentration (CMC) of several surfactant aqueous solutions has been studied by surface tension methods. The results show that with increasing alcohol concentration the CMC values first reach a minimum at an intermediate ethanol mole fraction x2* ≈ 0.055 and then increase with increasing x2. The value of x2* is close to that at which structural changes in the mixture occur as inferred from compressibility and optical absorption measurements. The present experiments support the assumption that the dominant mechanism by which ethanol affects the micellization process is through its effect on the structure of water.

Structure and catalytic behavior of myoglobin adsorbed onto nanosized hydrotalcites.

The adsorption of myoglobin (Mb) onto nanosized nickel aluminum hydrotalcite (NiAl-HTlc) surface was studied, and the structural properties of the resulting protein layer were analyzed by using FT-IR, Raman, and fluorescence spectroscopies. Upon adsorption onto the nanoparticle surface, the protein molecules maintained their secondary structure, while the tertiary structure was altered. The fluorescence spectra and anisotropy values of adsorbed Mb revealed that the emitting amino acid residues are affected by different microenvironments when compared to the native protein behavior. Moreover, the decrease of fluorescence decay times of tryptophan indicated the occurrence of interactions among the fluorophores and the constituents of the nanoparticles, such as the metal cations, which can take place when conformational changes of Mb occur. Raman spectra indicated that the interaction of Mb molecules with NiAl-HTlc nanoparticles modified the porphyrin core, changing the spin state of the heme iron from high spin (HS) to low spin (LS). The enzymatic activity of the nanostructured biocomposite was evaluated in the oxidation of 2-methoxyphenol by hydrogen peroxide and discussed on the basis of structural properties of adsorbed myoglobin.

Enzymatic kinetic resolution of (±)-4-acetoxy[2.2]paracyclophane by Candida cylindracea lipase. An efficient route for the preparation of (+)-R-4-hydroxy- and (+)-S-4-acetoxy[2.2]paracyclophane

Abstract The enzymatic kinetic resolution of (±)-4-acetoxy[2.2]paracyclophane by Candida cylindracea lipase was investigated in water and in a two-phase aqueous organic system. The (+)-(R)-4-hydroxy- and (+)-(S)-4-acetoxy[2.2]-paracyclophanes were isolated in excellent yields and high enantiomeric excesses. The resolution was carried out on multi-gram scale in hexane-water at 40° C.

Mechanisms of inhibition of phenylalanine ammonia-lyase by phenol inhibitors and phenol/glycine synergistic inhibitors

Phenylalanine ammonia-lyase (PAL) catalyzes the beta-elimination of ammonia from L-phenylalanine to trans-cinnamic acid. A study of inhibition of PAL by phenol, ortho-cresol, and meta-cresol gave mixed inhibition; para-cresol is not an inhibitor. The calculated values of K(i) and alphaK(i) are phenol, K(i)=2.1+/-0.5 mM and alphaK(i)=3.45+/-0.95 mM; ortho-cresol, K(i)=0.8+/-0.2 mM and alphaK(i)=3.4+/-0.2 mM; meta-cresol, K(i)=2.85+/-0.15 mM and alphaK(i)=18.5+/-1.5 mM. The synergistic inhibition of the same inhibitors with glycine showed a lack of inhibition with the para-cresol/glycine pair, while mixed inhibition was observed with the ortho-cresol/glycine pair (K(i)=0.038+/-0.008 mM, alphaK(i)=0.13+/-0.04 mM) and phenol/glycine pair (K(i)=0.014+/-0.003 mM, alphaK(i)=0.058+/-0.01 M). The meta-cresol/glycine pair gave competitive inhibition (K(i)=0.36+/-0.076 mM). The strong synergistic inhibition observed implies that the inhibitors bind at the active site: in fact, the inhibitors used imitate the structure of the substrate. The order of synergistic inhibition is the same for the sites related to K(i) and alphaK(i). These results are in agreement with the inhibitors entering two active sites located in two different subunits.

Synthesis of colloidal dispersions of NiAl, ZnAl, NiCr, ZnCr, NiFe, and MgFe hydrotalcite-like nanoparticles

Colloidal aqueous dispersions of nanometric NiAl, ZnAl, NiCr, ZnCr, NiFe, and MgFe hydrotalcite-like compounds were prepared in a water/cetyltrimethylammonium bromide/n-butanol/isooctane microemulsion. Particle sizes were analyzed with different techniques, and the results confirm dimensions between 10 and 30 nm, except for ZnAl-HTlc (150-200 nm). A good colloidal stability of HTlc-NPs aqueous dispersions, investigated with DLS and Pz measurements, was obtained without the need for any stabilizing agent. SEM images clearly showed that the obtained HTlc posses a high tendency to spontaneously form homogeneous and dense stacking of plate-like HTlc crystals directly from aqueous solution, giving rise to the developing of functional materials in optical, electrical and magnetic fields.

Influence of pH and temperature on the enantioselectivity of propan-2-ol-treated Candida rugosa lipase in the kinetic resolution of (±)-4-acetoxy-[2,2]-paracyclophane

Abstract The reaction temperature, pH of the aqueous medium and use of an aqueous- n -hexane reaction medium markedly influenced the hydrolysis rate and enantioselectivity of (±)-4-acetoxy-[2,2]-paracyclophane with propan-2-ol-treated Candida rugosa lipase. The results have been justified on the basis of a possible conformational change in the enzyme as a consequence of the displacement of its polypeptide lid.

Improving the enantioselectivity of Candida rugosa lipase in the kinetic resolution of racemic methyl 2-(2,4-dichlorophenoxy)propionate

Abstract Racemic methyl 2-(2,4-dichlorophenoxy)propionate (±)-1, was subjected to hydrolysis in water and in a series of two-phase aqueous organic media in the presence of Candida rugosa lipase (CRL). The biocatalytic material used was the commercial preparation and enzyme purified by using different procedures. The (+)-R- and (−)-S-2-(2,4-dichlorophenoxy)propionic acids (3) were obtained in excellent yield and high enantiomeric excess when the hydrolysis of (±)-1 was performed in water/benzene in the presence of 2-propanol treated CRL. The kinetic resolution of (±)-1 was scaled-up.

Enantioselectivity of alcohol-treated Candida rugosa lipase in the kinetic resolution of racemic methyl 2-aryloxypropionates in water and aqueous organic media

Abstract Racemic methyl 2-aryloxypropionates (±)-1 were subjected to hydrolysis in water and in a series of two-phase aqueous organic media in the presence of Candida rugosa lipase (CRL). The biocatalytic material used was the enzyme of commercial CRL purified by treatment with different alcohols. The purification of CRL and the reaction medium play an important role in the enantioselection of racemates (±)-1. While it is not possible to use the same protocol for all substrates, by combining the different ways of purifying the enzyme with the various reaction media, it is possible to achieve high enantioselectivities of racemic esters.

Protein interactions with nanosized hydrotalcites of different composition

Nanosized hydrotalcite-like compounds (HTlc) with different chemical composition were prepared and used to study protein adsorption. Two soft proteins, myoglobin (Mb) and bovine serum albumin (BSA), were chosen to investigate the nature of the forces controlling the adsorption and how these depend on the chemical composition of the support. Both proteins strongly interact with HTlc exhibiting in most cases a Langmuir-type adsorption. Mb showed a higher affinity for Nickel Chromium (NiCr-HTlc) than for Nickel Aluminum (NiAl-HTlc), while for BSA no significant differences between supports were found. Adsorption experiments in the presence of additives showed that proteins exhibited different types of interactions onto the same HTlc surface and that the adsorption was strongly suppressed by the addition of disodium hydrogen phosphate (Na(2)HPO(4)). Atomic force microscopy images showed that the adsorption of both proteins onto nanoparticles was followed by the aggregation of biocomposites, with a more disordered structure for BSA. Fluorescence measurements for adsorbed Mb showed that the inorganic nanoparticles induced conformational changes in the biomolecules; in particular, the interactions with HTlc surface quenched the tryptophan fluorescence and this process was particularly efficient for NiCr-HTlc. The adsorption of BSA onto the HTlc nanoparticles induced a selective quenching of the exposed fluorescent residues, as indicated by the blue-shift of the emission spectra of tryptophan residues and by the shortening of the fluorescence decay times.

Hydration of p-Alkyloxy-α-α-α-trifluoroacetophenone and water activity at a micellar surface

Abstract Equilibrium hydration of p-methoxy-α-α-α-trifluoroacetophenone (MTFA) in water and anionic micelles of sodium dodecyl sulfate (SDS) has been followed by 19F NMR and UV spectrometry, and is strongly disfavored by the micelles. The effects can be separated into those due to the different transfer equilibria of the carbonyl and hydrate forms and to a decrease in water activity in the micelles. The transfer equilibria of the carbonyl and hydrate forms of MTFA between water and micelles have been followed by NMR spectrometry and an activity of water at the micellar surface of 0.6 has been determined. Attainment of hydration equilibrium in water, aqueous acetonitrile, and micelles has been followed by UV spectrometry and rate constants for forward and reverse reactions have been calculated. The overall equilibrium of the p-octyloxy derivative has been examined in aqueous acetonitrile and SDS micelles. The hydrophobic octyl group reduces the rate and equilibrium constants of hydration.