Nuno Ribeiro

A Comparative Study of Naproxen – Beta Cyclodextrin Complexes Prepared by Conventional Methods and Using Supercritical Carbon Dioxide

Naproxen is a poorly soluble anti-inflammatorydrug, the solubility of which canbe enhanced by complexation withbeta-cyclodextrin. Besides that, the inclusioncomplex reduces the incidence of gastrointestinal side effects of the drug. The aim of this work was to compare the physicochemical characteristics of the solid complexes prepared by traditional methods (kneading, freeze-drying and spray-drying) and using a supercritical fluid technology. The unusual solvent properties of carbon dioxide above their critical temperature and pressure were exploited in order to prepare inclusion compounds. Complexes prepared using supercritical fluid technology showed similar properties to those of freeze-drying andspray-drying complexes as proved by DSC, FT-IRand UV.

Optimisation of Supercritical Carbon Dioxide Systems for Complexation of Naproxen : Beta-Cyclodextrin

Supercritical carbon dioxide (scCO2)offers several attractive scenarios for thepharmaceutical processing as an alternativeto aqueous and organic solvents. In thiswork naproxen, a widely used non steroidalanti-inflammatory drug with analgesic andanti-inflammatory properties, was chosenas a model drug. Its complexation with cyclodextrinsimproves the rate and extent of dissolutionof the drug, increase its rate of absorption and mayreduce the unpleasant side-effects of the drug.The interest in using this supercritical technologyled us to develop an experimental unit for the useof supercritical CO2 as a processing medium forthe complexation of naproxen with beta cyclodextrin (CD).

Correlation of Vapor–Liquid Equilibrium for Carbon Dioxide + Ethanol + Water at Temperatures from 35 to 70°C

A simple mathematical model, based on polynomial functions, was used to correlate experimental vapor–liquid equilibrium (VLE) data for the CO2 + ethanol + water system. The data were collected from the literature for temperatures 35, 40, 50, 60, and 70°C and pressures from 10 MPa to 18.5 MPa. This model is able to reproduce the equilibrium compositions of the two phases within the experimental error given in the group of selected publications.

Acoustic determination of the critical surface of {x1CO2+x2C2H6+ (1 −x1−x2)CHF3}

A simple acoustic method was used to investigate the ternary mixture CO2 + C2H6 + CHF3 and the corresponding binary sub-systems. Critical data obtained on the binary mixtures of CO2 + CHF3 were used for comparison with values given in the literature using the traditional methods. The acoustic results are in agreement with those obtained by the conventional methods, within the combined experimental errors. The binary critical line of C2H6 + CHF3 was determined over the whole composition range showing that this system deviates from ideality since the critical line exhibits a large temperature and a pressure minimum. The ternary system CO2 + C2H6 + CHF3 was investigated by a “ quasibinary” approach. Two different ratios of CO2 to CHF3 with four mixtures each were investigated. The “quasibinary” lines also show a distinctive temperature minimum. The course of the whole ternary critical surface was extrapolated. The Peng–Robinson equation of state, with conventional mixing and combining rules, was used to correlate the binary and ternary experimental data.

A simple acoustic probe for fluid phase equilibria: application to the CO2 + N(C2H5)3 system

Abstract An acoustic technique was applied to investigate the critical behaviour of CO2+N(C2H5)3. This study is part of a major programme on the determination of the critical behaviour of a series of tertiary amines in supercritical CO2. Measurements of the critical temperature Tc and pressure pc of the binary mixture of xCO2+(1−x)N(C2H5)3 were performed restricted to the region richer in carbon dioxide, in the CO2 mole fraction range 1–0.911. The Peng–Robinson equation of state with conventional mixing and combining rules, was used to correlate the binary experimental data. The course of the whole binary critical line was extrapolated. Additionally, this paper briefly reviews the experimental methods for determining critical properties. The theoretical basis of our acoustic method and the systems studied are discussed.

A visual acoustic high-pressure cell for the study of critical behavior of nonsimple mixtures

A visual acoustic high-pressure cell was constructed for the determination of critical data of multicomponent mixtures. The cell was specially designed to include two piezoelectric transducers and two sapphire windows that make this cell well suited to investigate the critical behavior of mixtures, simultaneously using the acoustic technique and the direct visual inspection of the critical opalescence. Critical data obtained on the binary mixtures of CO2+CHF3 were used for comparison with values given in literature using the traditional methods. The acoustic results are in agreement with those obtained by the conventional methods, within the combined experimental errors. Comparison of visual and acoustic data enabled the evaluation of the applicability of the acoustic technique to study the critical behavior of multicomponent mixtures.

Towards a Systemic Risk Indicator Based on Contingent Claim Analysis

Traditionally, the literature in systemic risk focuses on financial institutions and on their relations. The financial crisis that began in the United States in 2007 and, particularly, the subsequent European sovereign debt crisis have shown that there are many more channels of contagion apart from the ones that link risks within the banking system. As these channels propagate shocks, understanding them better can help to defect the mechanics behind systemic risk. This type of analysis is, nevertheless, confronted with several data gaps and limitations, which flow-of-funds statistics tries to overcome.

Incorporating Risk in the Efficiency and Productivity Analysis of Banking Systems

Among the many impacts of the credit crunch will be the necessity for economists to find a reformulation of models for performance measurement in banks. One of the most important issues to address is how to include risk in the measurement of the performance of banking systems. In this contribution, we review three different approaches to the incorporation of risk in measuring the efficiency and productivity performance of banking systems: the use of equity capital as an explanatory variable, the role of scale efficiency change as an indicator of risky behaviour and, finally, the use of second moment statistics to measure risk. The first two approaches can be regarded as indirect measures of risk in contrast to the third, which is a direct measure of it. We illustrate this with empirical work from Boucinha et al. (2009); Kenjegalieva and Weyman-Jones (2009) and Shen et al. (2009). We argue that while the direct approach is theoretically superior it faces very challenging and possibly insurmountable empirical problems.