José M. Leal

On the properties of 1-butyl-3-methylimidazolium octylsulfate ionic liquid

This work reports on a theoretical and experimental study on the ionic liquid 1-butyl-3-methylimidazolium octylsulfate ([BMIM]OS). The halogen-free ionic liquid [BMIM]OS is a stable solvent regarding hydrolysis, whose availability, toxicologically favourable features and well documented biodegradability turns it into a suitable candidate for different multiton-scale industrial applications. The pressure–volume–temperature behaviour of this fluid has been evaluated accurately over wide ranges of temperature and pressure, and correlated successfully with the empirical TRIDEN equation. From the measured data the relevant derived coefficients, isothermal compressibility, isobaric expansibility and internal pressure have been calculated. Other valuable properties such as isobaric heat capacity, speed of sound and refractive index were measured at several temperatures and atmospheric pressure. The molecular structure was looked into by quantum computations at the B3LYP/6-31 + g(d) level and classical molecular dynamics simulations in the NPT ensemble with the OPLS–AA forcefield. Both macroscopic and microscopic studies concur in a complex structure involving microheterogenous polar and non-polar domains, brought about by the aggregation of the non-polar anionic chains.

Formamide–(C1–C5) alkan-1-ols solvent systems

Excess volumes, excess viscosities, and exess Gibbs energies of activation for viscous flow of binary liquid mixtures of formamide with (C1–C5) alkan-1-ols have been calculated from the densities and viscosities measured at 298.15 K over the whole composition range. The viscosity–mole fraction data of the five systems were used to test various empirical laws proposed to describe the viscosity of mixtures: the one-parameter models by Nissan–Grunberg, Hind–McLaughlin–Ubbelohde and Teja–Rice, and the two-parameter models by McAllister, Heric, Lobe, and Cao–Fredenslund–Rasmussen were tested. All correlations were in good agreement except that of Teja–Rice. Deviations with respect to ideal behaviour were interpreted in terms of specific interactions between unlike molecules.

New Insights into the Mechanism of the DNA/Doxorubicin Interaction

Doxorubicin (DOX) is an important anthracycline antibiotic whose intricate features of binding to DNAs, not yet fully understood, have been the object of intense debate. The dimerization equilibrium has been studied at pH = 7.0, I = 2.5 mM, and T = 25 °C. A thermodynamic and kinetic study of the binding of doxorubicin to DNA, carried out by circular dichroism, viscometry, differential scanning calorimetry, fluorescence, isothermal titration calorimetry, and T-jump relaxation measurements, has enabled us to characterize for the first time two different types of calf thymus DNA (ctDNA)/DOX complexes: PD1 for C(DOX)/C(DNA) < 0.3, and PD2 for higher drug content. The nature of the PD1 complex is described better in light of the affinity of DOX with the synthetic copolymers [poly(dA-dT)]2 and [poly(dG-dC)]2. The formation of PD1 has been categorized kinetically as a two-step mechanism in which the fast step is the groove binding in the AT region, and the slow step is the intercalation into the GC region. This bifunctional nature provides a plausible explanation for the high PD1 constant obtained (K1 = 2.3 × 10(8) M(-1)). Moreover, the formation of an external aggregate complex ctDNA/DOX (PD2) at the expense of PD1, with K2 = 9.3 × 10(5) M(-1), has been evinced.

Shear viscosities of the N-methylformamide–andN,N-dimethylformamide–(C1–C10) alkan-1-ol solvent systems

Viscosities of some N-methylformamide– and N,N-dimethylformamide–(C 1 –C 10 ) alkan-1-ol binary mixtures have been measured at 298.15 K over the whole composition range. The excess viscosities and excess Gibbs energies of activation for viscous flow, compared with values for other amide–alcohol mixed solvents, suggest that the alcohol size does not play a significant role in the mixture behaviour. The alcohol mixtures with aliphatic amides gave heteroaggregates to a greater extent, the lower the self-association of the pure amides. An analysis in terms of solvent solubility parameters gave good agreement with experimental results.

High-Pressure Study of the Methylsulfate and Tosylate Imidazolium Ionic Liquids

The considerable interest aroused in recent years by the unique properties and industrial applications of ionic liquids has given rise to the need for a detailed statement of the linkage between their molecular features and the observed macroscopic behavior. A combined experimental/computational approach to the study of ionic liquids is submitted here and applied to the relevant, nonhalogenated ionic liquids 1,3-dimethylimidazolium methylsulfate and 1-ethyl-3-methylimidazolium tosylate. To establish a reliable equation of state pertinent to these fluids, density data over wide pressure (0.1-60 MPa) and temperature (318.15-428.15 K) ranges, along with high pressure (1-70 MPa) viscosities and other selected ambient pressure properties were measured to assemble sufficient experimental information for the seek of predictive models for process design. A computational method based on ab initio and classical molecular dynamics yielded a deal of structural information, borne out by the experimental readings. Likewise, the predictive ability of the force field applied in molecular dynamics simulations was faced with the measured properties. The pictorial description of the selected ionic liquids reached this way may become widespread to other relevant examples in order to infer valuable structure/property relationships.

Outer-sphere hexacyanoferrate(III) oxidation of organic substrates

Abstract This review surveys the kinetics of the oxidation of organic substrates by hexacyanoferrate(III). Although a relatively poor oxidant, hexacyanoferrate(III) is a selective outer-sphere reactant applicable to the most easily oxidizable substrates, and frequently it is used as an interceptor of free radicals; this converts this species into an efficient one-electron oxidant particularly interesting in the comparative study of octahedral complexes. The major developments for each family of substrates are emphasized, comparing the mechanistic details for the various reaction types.

Alkali-metal ion catalysis of the oxidation of L-ascorbic acid by hexacyanoferrate(III) in strongly acidic media

The kinetics of the oxidation of L-ascorbic acid by hexacyanoferrate(III) ions have been investigated in strongly acidic media over a wide range of acidity. Two different mechanisms involving the monoascorbate anion, AH–, the neutral molecule of ascorbic acid AH2, and the protonated species AH+3, as well as the hexacyanoferrate(III) ion Fe(CN)3–6, and the monoprotonated form HFe(CN)2–6 are suggested. Kinetic evidence for a specific catalytic effct by binding of alkali-metal ions to oxidant is reported. The derived rate equations are in good agreement with the experimental observations.

Derivation of structure-activity relationships from the anticancer properties of ruthenium(II) arene complexes with 2-aryldiazole ligands.

The ligands 2-pyridin-2-yl-1H-benzimidazole (HL(1)), 1-methyl-2-pyridin-2-ylbenzimidazole (HL(2)), and 2-(1H-imidazol-2-yl)pyridine (HL(3)) and the proligand 2-phenyl-1H-benzimidazole (HL(4)) have been used to prepare five different types of new ruthenium(II) arene compounds: (i) monocationic complexes with the general formula [(η(6)-arene)RuCl(κ(2)-N,N-HL)]Y [HL = HL(1), HL(2), or HL(3); Y = Cl or BF4; arene = 2-phenoxyethanol (phoxet), benzene (bz), or p-cymene (p-cym)]; (ii) dicationic aqua complexes of the formula [(η(6)-arene)Ru(OH2)(κ(2)-N,N-HL(1))](Y)2 (Y = Cl or TfO; arene = phoxet, bz, or p-cym); (iii) the nucleobase derivative [(η(6)-arene)Ru(9-MeG)(κ(2)-N,N-HL(1))](PF6)2 (9-MeG = 9-methylguanine); (iv) neutral complexes consistent with the formulation [(η(6)-arene)RuCl(κ(2)-N,N-L(1))] (arene = bz or p-cym); (v) the neutral cyclometalated complex [(η(6)-p-cym)RuCl(κ(2)-N,C-L(4))]. The cytototoxic activity of the new ruthenium(II) arene compounds has been evaluated in several cell lines (MCR-5, MCF-7, A2780, and A2780cis) in order to establish structure-activity relationships. Three of the compounds with the general formula [(η(6)-arene)RuCl(κ(2)-N,N-HL(1))]Cl differing in the arene moiety have been studied in depth in terms of thermodynamic dissociation constants, aquation kinetic constants, and DNA binding measurements. The biologically most active compound is the p-cym derivative, which strongly destabilizes the DNA double helix, whereas those with bz and phoxet have only a small effect on the stability of the DNA double helix. Moreover, the inhibitory activity of several compounds toward CDK1 has also been evaluated. The DNA binding ability of some of the studied compounds and their CDK1 inhibitory effect suggest a multitarget mechanism for their biological activity.

Volumetric properties, viscosities and refractive indices of binary mixed solvents containing methyl benzoate

Densities, dynamic viscosities, and refractive indices of the binary mixed solvents of methylbenzoate with a set of eleven organic solvents provided with six carbon atoms but different structure and functional groups were measured over the whole composition range. Thermodynamic, transport, solubility, and electrical properties were analyzed for all systems; from the experimental quantities, excess and mixing properties were deduced and interpreted in terms of intermolecular interactions and structural changes upon mixing. Mixing viscosities and excess Gibbs energies of activation for viscous flow support the role played by the size of the cosolvent on the mixture behaviour. Analysis in terms of solvent solubility parameters was in convincing good agreement with experimental results. The Soave and Peng–Robinson equations of state and the Wong–Sandler mixing rule are used to correlate volumetric properties. The predictive ability of several one-parameter and two-parameter viscosity models was also tested.

Ag2 and Ag3 clusters: synthesis, characterization, and interaction with DNA.

Subnanometric samples, containing exclusively Ag2 and Ag3 clusters, were synthesized for the first time by kinetic control using an electrochemical technique without the use of surfactants or capping agents. By combination of thermodynamic and kinetic measurements and theoretical calculations, we show herein that Ag3 clusters interact with DNA through intercalation, inducing significant structural distortion to the DNA. The lifetime of Ag3 clusters in the intercalated position is two to three orders of magnitude longer than for classical organic intercalators, such as ethidium bromide or proflavine.