Luigi Marrelli

Transport and consumption rate of O2 in alginate gel beads entrapping hepatocytes

Experiments carried out with hepatocytes entrapped in alginate gel particles with a cell density of about 107 cells ml−1 showed an oxygen consumption rate of about 2.2×10−16 mol cell−1 s−1. Under these conditions, no inner anoxic core is present in 1.8 mm diameter beads. From these data, the maximum bead size consistent with non-critical O2 concentration at the bead center has been evaluated for different cell densities and O2 concentrations in the medium.

Net proton charge of β- and κ-casein in concentrated aqueous electrolyte solutions

Abstract Titration experiments have been carried out in order to measure the net proton charge of β- and κ-casein in NaCl solutions at 0.1 M and 1 M salt concentrations, at 4 °C, in the pH range between 5.5 and 10.5. Experimental data are compared with model values calculated through pKas of titrable groups neglecting the electrostatic perturbation term (ΔpKa) in order to evaluate the magnitude of the error caused by this approximation and to delimit its effectiveness. At both ionic strengths, the agreement is good for κ-casein in the pH range [5.5, 9.5], while errors of up to 2 charges are observed for β-casein in the same range. These deviations are likely to be caused by strong electrostatic effects induced by the high density of negative charges of β-casein 1–21 peptide. In order to account for these electrostatic effects, the net proton charge on this peptide is evaluated through a model based on the counterion condensation theory developed for the titration of polyelectrolytes with different types of ionizable groups.

Effect of surface tension on the conformational stability of erythrocyte carbonic anhydrase

An experimental investigation was carried out on the influence of some hydroxylic additives (up to 30% by weight) on the thermal stability of erythrocyte carbonic anhydrase. The melting temperatures of the protein in the different media were determined by spectroscopic measurements. Xylitol and maltose stabilized the enzyme, whereas ethanol, 1-propanol, ethanediol and 1,2-propanediol caused a destabilization of the protein. In all the systems examined, the transition temperature was found to be strictly related to the surface tension of the medium. A molecular thermodynamic model was developed, based on the chemical equilibrium between the native and denatured protein forms, which enabled to interpret the observed behaviour.

PERTURBATION OF SURFACE TENSION OF WATER BY POLYHYDRIC ADDITIVES: EFFECT ON GLUCOSE OXIDASE STABILITY

An experimental investigation is reported on the influence of some polyhydric additives (ethanediol, 1,2-propanediol and glycerol) on the thermal behaviour of Aspergillus niger glucose oxidase. Spectroscopic measurements performed to follow protein unfolding showed that all the cosolvents destabilize the enzyme and caused an increase in the standard enthalpy and entropy of transition. Furthermore the melting temperature was found to be intimately related to the surface tension of the medium. The obtained results were interpreted as the consequence of preferential protein-cosolvent interactions determined by the perturbation of the surface tension of water.

Phase equilibria of binary systems containing ethylene carbonate and an aromatic compound

Abstract Boiling temperature data for binary systems of ethylene carbonate with benzene, toluene and p-xylene were measured at 500 mmHg. At lower temperatures (T Phase equilibria data were used to obtain the activity coefficients. Solubility of solid ethylene carbonate in p-xylene was also measured at temperatures lower than the melting point of ethylene carbonate. These data were correlated by using an experimental value of enthalpy of fusion and activity coefficients obtained from liquid-liquid data.

Influence of pore-network topology on the reaction-diffusion kinetics in porous pellets

Abstract The applications of fractal model to reaction diffusion problems in porous catalysts are discussed. The importance of scaling laws is stressed and the asymptotic scaling behaviour for first order reaction is discussed both theoretically and from extensive Monte-Carlo computer simulation.

Integration of Selective Membranes in Chemical Processes: Benefits and Examples

Integration of reaction and separation in a single unit is a powerful tool to increase efficiency and economic advantages of many chemical processes. Reactive distillation, extraction, and adsorption are well-known examples of this technological resource. Recently, a very promising solution is offered by membrane reactors (MRs).

Blood Oxygenators and Artificial Lungs

This chapter is aimed at discussing the main engineering aspects involved in the design of artificial lungs, defining the limits of the currently available devices and understanding the challenges for further developments. To that end, the first part of the chapter provides a short overview of the functions of the respiratory system, that allows defining the medical requirements for the artificial devices and the goals that must be achieved in their design; information on the historical development of the artificial lungs is also included. Subsequently, the physical and chemical fundamentals of gas solubility in blood and gas transport through the membranes widely used in artificial lungs are presented. These fundamentals provide the basis for the engineering analysis of the artificial lung and assessment of its performance. The chapter is concluded with a survey of the state of the art of the clinically used devices with indications for possible further improvements.

Multifractal analysis of frequency spectra

Abstract Relations between the power spectra of dynamical systems and chaotic behavior are discussed. The scaling structure of power spectra is studied on the basis of the multifractal analysis. This approach allows different chaotic behaviors to be recognized. Further, the multifractral analysis gives a useful method in order to distinguish between deterministic chaotic dynamics and a stochastic evolution. The problem of the noise in the time series is also discussed.

Artificial and Bio-Artificial Liver

This chapter is focused on the design of artificial liver support devices (LSD). After a short overview of liver functions and pathologies, aimed at defining the minimum requirements for artificial devices, a survey of the different artificial liver support devices developed and used in clinical practice is reported. Subsequently, starting from a description of the physicochemical phenomena that characterize each unit operation used in the detoxification process (albumin dialysis and toxin adsorption), mathematical models of dialysis and adsorption units are developed and combined into an LSD model. A proposal for a first approach to a patient-device model is also considered to predict the evolution in time of toxin levels in patient blood and to evaluate the effectiveness of the treatment. The chapter ends with a survey on the bio-artificial liver devices.