Biomedical subjects

Enrico Prenesti

Publications and source records attributed to Enrico Prenesti.

7 recordsLinked to original sources

PubMed2005

Role of the activity coefficient in the dissemination of pH: comparison of primary (Harned cell) and secondary (glass electrode) measurements on phosphate buffer considering activity and concentration scales.

Despite recent efforts devoted to assessing both the theoretical rationale and the experimental strategy for assignment of primary pH values, these have not yet been accomplished satisfactorily. Traceability and comparability of pH values are achieved only within the constraints of internationally accepted conventions and predefined conditions that cannot account for all possible situations when pH is measured. Critical parameters to be defined are, in particular, the activity coefficients (gamma (i)) of the ionic species involved in the equilibrium with the hydrogen ions in the solution, which are usually estimated with the approximation typical of the Debye-Hückel theoretical model. For this paper, primary (Harned cell) measurements (traceable to the SI system) of the pH of a phosphate buffer have been considered and the results have been compared with secondary (glass electrode) measurements obtained by considering either the activity (paH) or concentration (pcH) scale of the hydrogen ions. With conventional approaches based on measurements related to activity or concentration scale, discrepancies emerge which have been assigned to incomplete inferences of gamma (i) arising from chemical features of the solution. It is shown that fitting and comparable paH and pcH results are attainable if evaluation of gamma (i) is performed using better estimates of the ionic strength, according to an enhanced application of the Debye-Hückel theory.

Journal Article↗

PubMed2005

Redox chemistry of red wine. Quantification by an oscillating reaction of the overall antioxidant power as a function of the temperature.

The redox and acid-base reactivity of red wines was studied from both the analytical and kinetic standpoint. Four homemade wines, made from Italian red grape varieties of two different vintages, were tested to study the effect of temperature (25 and 37 degrees C) on the overall antioxidant power, through the Briggs-Rauscher oscillating reaction. The reaction was monitored by potentiometry (platinum electrode) and by direct chronometric detection. A reference scale based on the response of gallic acid was also employed, so as to achieve a quantitative evaluation: the novel Briggs-Rauscher antioxidant index (BRAI) was developed to express the overall antioxidant power quantitatively versus the chosen standard molecule. Overall antioxidant power was found to be related to total polyphenol content measured using the Folin-Ciocalteu method: the older wines had a lower antioxidant ability. Total acidity was also estimated indirectly by means of coupled pH-metric/photometric titrations and visible spectrophotometric measurements; it revealed an overlap between acid-base and redox chemistry of red wine.

Antioxidants↗

PubMed2004

Complexes of copper(II) with adenosine or guanosine nucleosides, nucleotides 5'-monophosphate, 2'-deoxynucleosides or 2'-deoxynucleotides 5'-monophosphate in aqueous solution.

In this paper copper(II) complex formation in aqueous solution with a series of nucleosides (adenosine or guanosine) or nucleotides 5'-monophosphate is studied by means of potentiometry, visible spectrophotometry and ultraviolet circular dichroism. A chemical model has been formulated for each binary system (at T= 25 degrees C and I = 0.1 M), with particular attention to the interaction in the basic field. A spectrum (both visible absorption and ultraviolet circular dichroism) for each complex with a significant percentage of formation (in the adopted experimental conditions) has been calculated, allowing structural details to be hypothesised. The interaction with deprotonated alcoholic group(s) of the ribose moiety has been found to be fundamental in determining the co-ordination chemistry of each ligand considered while cases of co-operation between the purine and ribose donor(s) were also considered. Confirmations were also obtained by an investigation on the corresponding 2'-deoxy compounds as ligands.

Adenosine↗

PubMed2003

Ultraviolet spectrophotometric characterization of copper(II) complexes with imidazole N-methyl derivatives of L-histidine in aqueous solution.

In this study we considered pi-methyl-L-histidine (pi-methis) and tau-methyl-L-histidine (tau-methis) as ligands for copper(II) ion, in order to clarify, by means of ultraviolet (UV) spectroscopy in aqueous solution (T = 25 degrees C, I = 0.1 M), some aspects of the co-ordination mode with respect to other ligands of a previous study in which copper(II) complexes of L-histidine, N-acetyl-L-histidine, histamine, L-histidine methyl ester or carnosine were investigated. Particularly, UV spectra (300-400 nm) were recorded on solutions at various pH values, containing each binary system Cu-L; afterwards, an UV absorption spectrum for single complexes was calculated, taking into account the chemical model previously assessed, in order to fulfil a correct spectrum-structure correlation. The problem related to the eventual superimposition of the CT shoulder (approximately 330 nm) to copper(II) of OH- and imidazole pyridine nitrogen groups were now solved by means of a comparison of the UV spectra of dimer species formed by both pi-methis or tau-methis. Finally, copper(II) complex formation with 2,2'-bipyridine was taken into account to compare the behaviour of pyridine (from 2,2'-bipyridine) and pyridine imidazole nitrogens (from pi-methis or tau-methis) with respect to the UV charge transfer process to copper(II) ion.

Copper↗

PubMed2002

Interaction of copper(II) with imidazole pyridine nitrogen-containing ligands in aqueous medium: a spectroscopic study.

UV (300-400 nm) and FT/IR (4000-850 cm(-1)) spectra were considered for a structural discussion of the copper(II) complexes formed with a series of imidazole-containing ligands (namely L-histidine, N-acetyl-L-histidine, histamine, L-histidine methyl ester and carnosine) in aqueous solution (T=25 degrees C, I=0.1 M). A shoulder at 330 nm was recorded for the main copper(II) complexes with all the ligands considered with the exception of carnosine: this singularity is discussed and a spectrum-structure correlation is proposed. epsilon(330) values were evaluated for CuL (59 M(-1) cm(-1)) and Cu(2)L(2)H(-2) (577 M(-1) cm(-1)) complexes with histamine and for CuL(2) (49 M(-1) cm(-1)) and CuL(3) (163 M(-1) cm(-1)) with N-acetyl-L-histidine, thus indicating the usefulness of UV spectra in the explored region for the purpose of structural definition. FT/IR spectra (recorded both in aqueous solution and on the residue of evaporated solutions of carnosine and N-acetyl-L-histidine only) help to reveal a significant conformational rearrangement of the ligand, corresponding to complex formation in solution: in fact, modifications in the fingerprint region of the FT/IR spectrum for the dimer of carnosine are observed. Indications of a copper(II)-imidazole nitrogen interaction are also obtained from FT/IR data in the 1000-1100 cm(-1) range.

Copper↗

PubMedDate not supplied

Metal ion distribution between water and river sediment: speciation model and spectroscopic validation.

Natural sediments show sequestering properties that can lead to a process of self-purification of aquatic environment from metal pollution. The study of the interaction between metal ions and sediment particles enhances what is known about the distribution and bioavailability of heavy metals in natural systems. Our contribution concerns the characterisation of the sequestering ability of a River Po sediment with regard to calcium(II), magnesium(II), cadmium(II), nickel(II) and copper(II), in fixed experimental conditions, through pH-metric and spectrometric measurements. A batch titration procedure was adopted and, in each solution, after equilibration, both pH and pM (M = Ca(II), Mg(II), Cd(II), Ni(II), Cu(II)) (via Inductively Coupled Plasma - Optical Emission Spectroscopy, ICP-OES) values were measured. The experimental data were first processed with a specific software to evaluate the concentration and protonation constants of the sediment ligand site(s). The speciation model was then assessed, together with the values of complexation constants, for the different sediment/metal cation systems. In order to better characterise the copper(II)-sediment interaction and to obtain more information about the nature of ligand site(s) involved, EPR (Electronic Paramagnetic Resonance) measurements were also made on the dry sediment before and after reaction with copper(II) ions.

Biological Availability↗

PubMedDate not supplied

Dioxouranium(VI)--carboxylate complexes. Interaction with dicarboxylic acids in aqueous solution: speciation and structure.

In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.

Dicarboxylic Acids↗