15 documents found, page 1 of 2
How does dilution affect the conductivity, the propensity to aggregate and the ...
Roque, Cecília; Andrade, Érica; Duarte, Luís; Costa, Margarida; Tavares, Ana Paula M.; Madeira, Pedro P.The current theories do not provide a convincing explanation for many of the protein' manifestations in solution. Therefore, to shed some light on this critical question, the present work analyzed the effect of dilution on the ability of proteins to catalyze chemical reactions, the so-called biological activity. As models enzymes, laccase from Trametes versicolor and chicken egg white lysozyme were used. The re...
On the 1H NMR spectra of weak electrolytes under the influence of strong electr...
Madeira, Pedro P.Physical chemistry has yet to provide a convincing explanation for the many distinct ways the cosolute's properties are perturbed when under the field of action of salt ions. For that reason, a systematic and gradual approach to the problem was sought, with the present work being a step in that direction. Thus, acetic acid and n-butylamine were selected as simple models for the charged carboxyl and amine groups...
On the aggregation of bovine serum albumin
Madeira, Pedro P.; Rocha, Inês L. D.; Rosa, Marguerita E.; Freire, Mara G.; Coutinho, João A. P.In an attempt to elucidate the aggregation behaviour of bovine serum albumin and its modulation by salt ions, size-exclusion high-performance liquid chromatography was used and complemented by dynamic light scattering. The influence of the protein concentration, and type and concentration of inorganic salt on the aggregation of albumin in solution have been analyzed. Based on the observations herein reported an...
Effects of different solutes on the physical chemical properties of aqueous sol...
Silva, Nuno Miguel Sampaio Ribeiro Magalhães; Ferreira, Luisa A.; Belgovskiy, Alexander I.; Madeira, Pedro P.; Teixeira, J. A.; Mann, Elizabeth K.The Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectra of the OH-stretch band in aqueous solutions of inorganic salts and organic materials; Na2SO4, NaCl, NaClO4, NaSCN, trimethylamine N-oxide, urea, poly(ethylene glycol), polyvinylpyrrolidone, and copolymer of ethylene glycol and propylene glycol (Ucon) were studied at various concentrations. The decomposition of the band into four Gauss...
Hydrogen bond arrangement is shown to differ in coexisting phases of aqueous tw...
Madeira, Pedro P.; Titus, Amber R.; Ferreira, Luisa A.; Belgovskiy, Alexander I.; Mann, Elizabeth K.; Mann Jr., Jay Adin; Meyer, William V.Analysis by attenuated total reflection-Fourier transform infrared spectroscopy shows that each coexisting phase in aqueous two-phase systems has a different arrangement of hydrogen bonds. Specific arrangements vary for systems formed by different solutes. The hydrogen bond arrangement is shown to correlate with differences in hydrophobic and electrostatic properties of the different phases of five specific sys...
Linear relationships between partition coefficients of different organic compou...
Silva, Nuno R. da; Ferreira, Luisa A.; Madeira, Pedro P.; Teixeira, J. A.; Uversky, Vladimir N.; Zaslavsky, Boris Y.Analysis of the partition coefficients of small organic compounds and proteins in different aqueous two-phase systems under widely varied ionic compositions shows that logarithms of partition coefficients for any three compounds or proteins or two organic compounds and one protein are linearly interrelated, although for protein(s) there are ionic compositions when the linear fit does not hold. It is suggested t...
The role of carboxyl groups upon the precipitation of albumin at low pH
Madeira, Pedro P.; Freire, Mara G.; Coutinho, João A. P.Proteins play a major role in the organization of the living matter. Underlying this fact are their unique properties in aqueous solution, for which the available theories provide only a partial explanation. In order to throw some light into the behavior of proteins in aqueous solution, experiments on the precipitation of electropositive albumin by means of the sodium salts of sulfate, thiocyanate, nitrate, bro...
Distinct roles of salt cations and anions upon the salting-out of electro-posit...
Madeira, Pedro P.; Freire, Mara G.; Coutinho, João A. P.Precipitation experiments of electro-positive albumin by the action of a wide number of salts, and at differentconcentrations, were performed at a constant temperature (25 °C). The pH range studied covered extreme acidicconditions up to hydronium concentrations where the dissociation of the protein carboxyl groups becomes no-ticeable. The time required for the clouding phenomenon to occur and the quantity of sa...
Solvatochromism as a new tool to distinguish structurally similar compounds
Madeira, Pedro P.; Loureiro, Joana A.; Freire, Mara G.; Coutinho, João A. P.It is here reported a new concept based on solvatochromism to distinguish structurally similar compounds in aqueous solutions by the analysis of the stabilization of electronic excited states. The sensitivity of this approach to differentiate similar organic compounds, such as structural isomers or compound differing in the number of methylene groups, or proteins with conformational changes induced by being or ...
Mechanisms ruling the partition of solutes in ionic-liquid-based aqueous biphas...
Passos, Helena; Dinis, Teresa B. V.; Capela, Emanuel V.; Quental, Maria V.; Gomes, Joana; Resende, Judite; Madeira, Pedro P.; Freire, Mara G.In the past decade, the remarkable potential of ionic-liquid-based aqueous biphasic systems (IL-based ABSs) to extract and purify a large range of valued-added biocompounds has been demonstrated. However, the translation of lab-scale experiments to an industrial scale has been precluded by a poor understanding of the molecular-level mechanisms ruling the separation or partition of target compounds between the c...