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D Zanette

Publications and source records attributed to D Zanette.

9 recordsLinked to original sources
PubMed2005

pH at the micellar interface: synthesis of pH probes derived from salicylic acid, acid-base dissociation in sodium dodecyl sulfate micelles, and Poisson-Boltzmann simulation.

The study of the H+ concentration at the micellar interface is a convenient system for modeling the distribution of H+ at interfaces. We have synthesized salicylic acid derivatives to analyze the proton dissociation of both the carboxylic and phenol groups of the probes, determining spectrophotometrically the apparent pK(a)'s (pK(ap)) in sodium dodecyl sulfate, SDS, micelles with and without added salt. The synthesized probes were 2-hydroxy-5-(2-trimethylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumhexanoyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumundecanoyl)benzoate; 2-hydroxy-5-acetylbenzoic acid; and 2-hydroxy-5-dodecanoylbenzoic acid. Upon incorporation into SDS micelles the pK(ap)'s of both carboxylic and phenol groups increased by ca. 3 pH units and NaCl addition caused a decrease in the probe-incorporated pK(ap). The experimental results were fitted with a cell model Poisson-Boltzmann (P-B) equation taking in consideration the effect of salt on the aggregation number of SDS and using the distance of the dissociating group as a parameter. The conformations of the probes were analyzed theoretically using two dielectric constants, e.g., 2 and 78. Both the P-B analysis and conformation calculations can be interpreted by assuming that the acid groups dissociate very close to, or at, the interface. Our results are consistent with the assumption that the intrinsic pK(a)'s of both carboxylic and phenol groups of the salicylic acid probes used here can be taken as those in water. Using this assumption the micellar and salt effects on the pK(ap)'s of the (trialkylammonium)benzoate probes were described accurately using a cell model P-B analysis.

Carboxylic Acids↗
PubMed1999

Self-organizing molecular networks.

Strong diffusional mixing and short delivery times typical for micrometer and sub-micrometer reaction volumes lead to a special situation where the turnover times of individual enzyme molecules become the largest characteristic time scale of the chemical kinetics. Under these conditions, populations of cross-regulating allosteric enzymes form molecular networks that exhibit various kinds of self-organized coherent collective dynamics.

Allosteric Regulation↗
PubMed1999

Ideal Mixing of Polymer-Surfactant Complexes of Polyethylene Oxide and Sodium Dodecyl Sulfate Plus Sodium Dodecanoate.

Mixtures of the anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecanoate (SDoD) were investigated regarding their ability to bind to a hydrophilic nonionic polymer, polyethylene oxide (PEO). By electrical conductivity measurements, the parameters with respect to the onsets of surfactant aggregation were determined in the presence of 0.06 M PEO (critical aggregation concentration) and in its absence (critical micelle concentration). It was found that both plots of these parameters for the multicomponent mixtures against molar fraction of SDoD showed an ideal mixing behavior. The same technique was used to estimate the degree of ionization as a fundamental parameter relating to the interfacial composition of mixed aggregates. In addition, in order to monitor changes in polymer-surfactant structures, we used steady-state quenching fluorescence measurements to characterize the sizes of PEO-SDS/SDoD complexes at different compositions of the complex mixture. Copyright 1999 Academic Press.

Journal Article↗
PubMed1998

Human IL-1 receptor antagonist from Escherichia coli: large-scale microbial growth and protein purification.

Interleukin-1 receptor antagonist (IL-1ra) is a recently discovered cytokine which specifically inhibits IL-1 pro-inflammatory activities in various experimental conditions. In this work, the growth conditions of a recombinant E. coli strain which in laboratory studies expressed human IL-1ra mostly in insoluble form, have been optimized at the level of 6-1 bioreactors and then scaled up to a 50-1 process. As a result, a high amount (0.43 g l-1 of microbial culture) of soluble, active IL-1ra has been directly obtained in the large-scale cell lysate with no need for protein solubilization. Also, an efficient purification procedure has been developed for the soluble protein, based on cation exchange expanded bed adsorption directly followed by anion exchange chromatography. This process, which does not include any intermediate dialysis step or gradient elutions, can be easily scaled up to larger production volumes and is therefore well-suited for manufacturing. As a result of the overall optimization study, more than 12 g of pure IL-1ra have been obtained from a single 50-1 fermentation run, without any denaturation/renaturation process. The final product, whose identity and purity have been checked also by MALDI-TOF and ESI-MS, shows full biological activity both in cellular assays and in in vivo experiments with Cynomolgus monkeys.

Animals↗
PubMed1998

Self-organizing molecular networks.

Strong diffusional mixing and short delivery times typical for micrometer and sub-micrometer reaction volumes lead to a special situation where the turnover times of individual enzyme molecules become the largest characteristic time scale of the chemical kinetics. Under these conditions, populations of cross-regulating allosteric enzymes form molecular networks that exhibit various kinds of self-organized coherent collective dynamics.

Cell Physiological Phenomena↗
PubMed1997

The Absence of Conventional Polymer-Surfactant Interaction between Sodium Monodecyl Phosphate and Poly(ethylene Oxide): Conductivity and Kinetic Evidence

Mixtures of sodium monodecyl phosphate (NaDeP) and poly(ethylene oxide) (PEO) have been investigated conductimetrically in 0.05 M succinate buffer, pH 5.20. The conductivity vs NaDeP concentration profiles do not show the classical behavior of PEO-sodium dodecyl sulfate (SDS) mixtures. In the presence of different concentrations of PEO, the profiles exhibit only one discontinued point, whose SDS concentration values are similar to the NaDeP critical aggregation concentration. It was observed also that this conductivity breakpoint is not sensitive to variation in the polymer concentration and that it is independent of polymer molecular weight. However, the conductivity profiles of mixtures of NaDeP and SDS demonstrate behavior similar to that of SDS alone. For these mixtures, the evidence of binding, absent in the presence of NaDeP alone, is interpreted by assuming that it is solely driven by the SDS.

Journal Article↗
PubMed1995

Preliminary investigation of glycosylated proteins by capillary electrophoresis and capillary electrophoresis/mass spectrometry using electrospray ionization and by matrix-assisted laser desorption ionization/time-to-flight mass spectrometry.

In recent years, the biotechnological industry has emerged as the major source of new human therapeutic proteins. Although the great majority of these occur naturally as glycoproteins, it has been observed that glycosylation of the recombinantly produced proteins could be fundamental for their in vivo activity (e.g. tissue plasminogen activator, erythropoietin) or, on the contrary, insignificant (e.g. interleukin-1 receptor antagonist, gamma-interferon, granulocyte macrophage-colony-stimulating factor). The inherent heterogeneity of these complex biomolecules presents an exciting challenge in the analytical field for both their structural analysis and the development of suitable analytical methods to guarantee consistency of their production. Owing to this ever increasing therapeutic interest in proteins and glycoproteins, this paper compares the information provided by different analytical techniques (i.e. high-performance liquid chromatography, sodium dodecyl sulphate polyacrylamide gel electrophoresis, capillary electrophoresis, capillary electrophoresis/electrospray ionization mass spectrometry, matrix-assisted laser desorption/ionization time-of flight mass spectrometry and high-performance liquid chromatography/matrix-assisted laser desorption/ionization time-of flight mass spectrometry when used for the analysis of proteins and glycoproteins. For the sake of simplicity, reference standard proteins and glycoproteins were used as samples.

Chromatography, High Pressure Liquid↗
PubMed1984

Crystallization of hen eggwhite riboflavin-binding protein.

Crystals of hen eggwhite riboflavin-binding protein have been grown by equilibrium dialysis in solutions buffered with 0.05 M-Tris X HCl (pH 8.5) using ammonium sulphate as the precipitant. The crystals belong to the space group P3121 (or enantiomorph) with a = b = 112.5 A and c = 72.0 A, and diffract to a resolution of 2.8 A.

Animals↗