Sante Capasso

Kinetics of the chemical degradation of diuron.

The influence of pH and buffer concentration on the chemical degradation of diuron in water has been analysed over a wide temperature range. The process irreversibly gives 3,4-dichloroaniline as the only product containing the phenyl ring. H+, OH- and phosphate buffer are efficient catalysts of the reaction. The rate constant first increases rapidly at low buffer concentrations and then gradually levels off at higher ones. At 40 degrees C and high phosphate concentration (>0.01 M), or in the extreme pH regions, the half-life is approximately 4 months and the activation energy is 127 +/- 2 kJmol(-1).

Kinetics and mechanism of succinimide ring formation in the deamidation process of asparagine residues

The cyclization of Ac–Gly–Asn–Gly–Gly–NHMe to the succinimide derivative has been studied in the pH range 5.5–10.4 at 37° and µ= 1 mol dm–3. Kinetic evidence indicates that the reaction is a multistep process with a change in the rate-determining step at pH 6.5–7.0.The suggested mechanism involves the pre-equilibrium deprotonation of the NH group next to the Asn residue, followed by nucleophilic attack of the nitrogen atom on the carbonyl carbon of the Asn side chain giving a cyclic tetrahedral intermediate. At acidic pH the cyclization step is rate determining, whereas, the removal of the leaving group by apparent general-base catalysis is the rate-determining step at neutral and basic pH. The literature data on the deamidation rate are discussed in light of the proposed mechanism.

Sorption of non-ionic organic pollutants onto a humic acids-zeolitic tuff adduct: Thermodynamic aspects

Sorption isotherms from water solutions for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol and cyclohexanol onto a humic acid-zeolite adduct were determined at 4, 14, 24 and 34 °C and utilized to calculate the isosteric enthalpy (ΔadsHi) and isosteric entropy (ΔadsSi) of the process. For hydrocarbon compounds, toluene, cyclohexane and o-xylene, both ΔadsHi and ΔadsSi were negative, the process was exothermic. In contrast, for hydroxyl compounds, benzyl alcohol, phenol and cyclohexanol, ΔadsHi and ΔadsSi were positive, the increase in entropy possibly reflecting the release of water molecules during sorption. The results suggest that sorption/desorption of either class of compounds could be controlled by operating on the temperature.

A novel organo-zeolite adduct for environmental applications: Sorption of phenol

A novel organo-zeolite adduct has been synthesized by sorbing humic acids (HA) onto zeolitic tuff and then heating the resulting complex at 330°C for 1.5h. Desorption tests showed that this procedure effectively immobilized HA on the tuff. The crystal structure of the zeolitic tuff and the chemical structure of HA were not altered during the preparation. Phenol sorption analysis demonstrated that the HA-zeolite adduct had good sorbing properties; moreover, the sorbed amount markedly decreased with increased ionic strength. These results point to prospective application of the HA-zeolite adduct as a low-cost and environmentally friendly sorbent for water purification from phenol and possibly other neutral organic pollutants.

Comment on “Removal of anionic dye Congo red from aqueous solution by raw pine and acid-treated pine cone powder as adsorbent: Equilibrium, thermodynamic, kinetics, mechanism and process design”

* Corresponding author. Tel.: þ39 0 823 2746 E-mail address: sante.capasso@unina2.it 0043-1354/

First evidence of spontaneous deamidation of glutamine residue via cyclic imide to α- and γ-glutamic residue under physiological conditions

e see front matter a 2012 Publi doi:10.1016/j.watres.2012.05.040 Recently, Dawood and Sen (2012) published a paper reporting a kinetic analysis of Congo red adsorption by natural material. In section 2.4.4. Thermodynamic study, they describe the determination of the thermodynamic parameters DH e DS by means of the van’t Hoff equation as follows:

Thermodynamic parameters of the reversible isomerization of aspartic residues via a succinimide derivative

At 37 °C and pH 7.4 the spontaneous deamidation of Gln-peptide proceeds prevalently via a glutarimide intermediate and gives a mixture of α-Glu- and γ-Glu-peptide.

Mitochondrial bovine aspartate aminotransferase: Preliminary sequence and crystallographic data

Abstract Values of the thermodynamic quantities ΔH ° and ΔS ° for the reactions “Asp-peptide ⇆ Asupeptide ⇆ β-Asp-peptide” in aqueous solution have been obtained for the model peptides AcGlyXGlyGlyNHMe and AcXGlyNHMe (X  Asp, β-Asp, Asu; Asu = aminosuccinyl residue) from the temperature-dependence of equilibrium constants. The ΔH ° and ΔS ° values for the cyclization reactions of the carboxylic-acid form of the Asp and β-Asp side chains of the dipeptides and tetrapeptides are positive and coincident within experimental error. Medium values are 34 kJ mol −1 and 127 J K −1 mol −1 for ΔH ° and ΔS °, respectively. The molar enthalpies and molar entropies of the Asp-dipeptide and β-Asp-dipeptide, and of the Asp-tetrapeptide and β-Asp-tetrapeptide, did not exhibit significant differences.

Kinetics and mechanism of the cleavage of the peptide bond next to asparagine

Cytosolic aspartate aminotransferase (EC 2.6.1.1) from ox heart has been fully characterized [ 1,2]; the most significant results have been reviewed [3]. An investigation is now in progress to establish structural and evolutionary relationships between this enzyme [4] and the homologous one from pig heart, whose complete primary structure has been reported [5,61. A more complete picture from an evolutionary point of view should also arise from a comparison of the mitochondrial enzymes. In fact the primary structure of the mitochondrial porcine enzyme has been reported [7,8]. Structural investigations on cytosolic and mitochondrial chicken aspartate aminotransferases are being pursued [9,10]. Therefore we have undertaken the purification and characterization of mitochondrial bovine aspartate aminotransferase. Preliminary sequence and crystallographic data are reported here.

Kinetics and mechanism of hydrolysis of phenylureas

The spontaneous cleavage reaction of the tetra-peptide Piv-Gly Asn-Sar-Gly-NHtBu to the C-terminal dipeptide and N-terminal succinimide dipeptide proceeds through pre-equilibrium deprotonation of the amide group of the asparagine side chain, followed by intramolecular nucleophilic attack of nitrogen on the peptide carbonyl carbonyl carbon atom. General acid-catalyzed breakdown of the intermediate then gives the products. According to this mechanism, the reaction rate strongly increases with pH and buffer concentration.