T.P. Iglesias

Estimation of parameters of Nitta–Chao model for ester+1-alkanol mixtures

Abstract An updated database with experimental values on vapor–liquid equilibria, activity coefficient at infinite dilution, enthalpies of mixing and excess molar volumes of alkyl alkanoate+1-alkanol binary systems was used to redetermine structure and interaction parameters of the Nitta–Chao model. We have compared the theoretical results obtained with the Nitta–Chao model and our parameters with the experimental data. The percentual mean deviations with the parameters calculated in this work are quite good for all properties studied. We have used the same database to analyse the quality of the predictions of three versions of UNIFAC model for this type of mixtures.

Temperature dependence of thermophysical properties of octane+1-butanol system

The aim of this work is to complete our studies on physical properties of binary mixtures of alkane+1-alkanols. This work reports densities, refractive indices, speeds of sound and isentropic compressibilities of the mixture octane + 1-butanol at different temperatures, from 288.15 to 308.15 K. From the experimental values, the corresponding excess and deviation values were computed (excess molar volumes, changes of refractive index on mixing, changes of speed of sound on mixing and changes of isentropic compressibilities on mixing). The results were fitted to variable-degree polynomials. Excess molar volumes were compared with the predictions of Nitta-Chao Group Contribution Model.

Estimation of parameters of Nitta-Chao model for linear monoether + 1-alkanol mixtures

We have estimated the interaction parameters for ether and hydroxyl groups using an extensive experimental database of vapour-liquid equilibria, activity coefficients at infinite dilution, enthalpies of mixing and volumes of mixing of linear monoether + 1-alkanol binary systems. The theoretical results obtained with the parameters proposed are significantly closer to the experimental values than those determined with the parameters of Eckart et al. In addition, the values of thermodynamic properties obtained by the Nitta-Chao model with both set of parameters have been compared with the predictions resulting from other models, such as the DISQUAC model and the UNIFAC model, in its original version and those of Dang and Tassios, Larsen et al. (UNIFAC-Lingby) and Gmehling et al. (UNIFAC-Dortmund).

Relative permittivities of binary mixtures of 1-butanol + n-alkane AT 298.15 k

A previous study on the physical properties of 1-alkanol + n-alkane has establised a correlation between dielectric permittivity at 1 GHz and excess molar volumes for all binary systems that were studied. In order to determine whether this behaviour is similar at lower frequencies, relative permittivity was measured at 100 kHz. The refractive index was measured to explore the effects at higher frequencies. Mixtures under study are in particular the systems (1-butanol + n-hexane, or n-octane, or n-decane) at the temperature of 298.15 K and atmospheric pressure, over the entire composition range.

Caledonin, a natural peptide bolaphile with ZnII and CuI complexing properties from the tunicate Didemnun rodriguesi

Abstract Caledonin (1) is a modified peptide isolated from the marine tunicate Didemnun rodriguesi . Caledonin comprises a central L-phenylalanine residue connected via its amino group to ( S )-3-amino-5-mercaptopentanoic acid (a new sulfur-containing β-amino acid), and by its carboxyl group to a six membered cycloguanidine moiety, bearing an n -octyl chain. Caledonin is a natural bolaphile which strongly binds Zn II and Cu I ions.

Estimation of the Nitta-Chao Parameters for the ether-group. Ether + n-alkane mixtures

Abstract In this work we have estimated the structural and interactional parameters of the ether- group for the group-contribution model of Nitta-Chao using a extensive experimental database of thermodynamic properties of ethers (monoethers, polyethers and acetals) and ether + n-alkane and ether + ether mixtures. The results obtained by Nitta-Chao model with this parameters get closer to the experimental values than those obtained with parameters of Eckart et al. (1986). The thermodynamic properties obtained by the Nitta-Chao model with old and new parameters were compared to predictions by other models such as Flory (1965) theory, DISQUAC (Kehiaian, 1977) model and UNIFAC model (versions of Dang and Tassios, 1986, and Larsen et al., 1987).

Excess permittivity behaviour of some mixtures n-alcohol + alkane : an interpretation of the underlying molecular mechanism

A molecular mechanism is proposed that underlies the macroscopic behaviour of excess dielectric permittivity of some mixtures {n-alcohol + alkane} at low (100 kHz) and microwave frequencies (1 GHz). This behaviour has been determined experimentally at 298 K, as a function of molar fraction, for the mixtures {n-hexane + (pentan-1-ol, hexan-1-ol or heptan-1-ol)} and {cyclohexane + (pentan-1-ol, hexan-1-ol or heptan-1-ol)}. From the magnitudes inherent to the process of dielectric relaxation the results obtained have been explained in terms of the behaviour of thermodynamic magnitudes such as the excess molar enthalpy and the excess molar volume, as well as the consideration that the total dipole moment of a multimere is greater than the sum of all dipole moments of the monomeres in which it can be decomposed (when hydrogen bonds are broken), in agreement with the linear association model of Malecki (LAM). Measurements of the relaxation times for the mixtures under study at various molar fractions using time-domain reflectometry (TDR) (DC–5 GHz) at ambient temperature confirm the considerations that support the proposed interpretation.

Refractive Indices and Speeds of Sound of Binary Mixtures of N-Octane with 1-Alkanol at the Temperature 298.15 K

Abstract This paper reports experimental values for the refractive index, speed of sound, and isentropic compressibility of binary mixtures of n-octane with (1-butanol, 1-hexanol and 1-octanol) at the temperature of 298.15 K and atmospheric pressure, as a function of mole fraction. From the experimental values, the corresponding derived values were computed (changes of refractive index, changes of speed of sound and changes of isentropic compressibilities) using variable-degree polynomials to fit the data. Also, an attempt was made to correlate the behaviour of these magnitudes to the number of carbon atoms in the 1-alkanol chain.

Minalemines A-F: Sulfamic acid peptide guanidine derivatives isolated from the marine tunicate Didemnun rodriguesi

Abstract Six new guanidine compounds, named minalemines A-F 2 , were isolated from the marine tunicate Didemnun rodriguesi by careful HPLC separation. Their structures were elucidated by MS, 1D- and 2D-NMR spectral analysis, and chemical degradation. These compounds incorporate one agmatine (Agma) and one homoagmatine (Hagma) terminal unit with their guanidine groups free and the primary amino groups linked through a peptidic bond to L-Leu and a very rare β - N -carboxymethyl amino acid (Ncma) bearing a saturated long chain. The saturated chains of minalemines A-C are homologs (C7, C8, and C9 respectively). Minalemines D-F are the sulfamic acid derivatives of minalemines A-C and constitute the first examples of such a functional group in a marine organism.

Surface charge density model for predicting the permittivity of liquid mixtures and composites materials

The case “cube inside cube” for the recent predictive equivalent capacitance model (ECM) is resolved into three different analytic equations expressing the relative permittivity of a composite in terms of constituent relative permittivities and inclusion volume fraction, and they are averaged analytically (ECM-average). Although ECM represents an advance, it requires a specific calculation for each inclusion shape. Sharing the same assumptions and basic physics with ECM an alternative numerical model, named surface charge density model (SCDM), is developed. Using this model it is shown that ECM is an approximation in any of the three solutions mentioned above. Since the approach “cube inside cube” leads to isotropic systems where the volume fraction of the inclusion can be varied from zero to one, an attempt is made to apply SCDM and ECM to binary liquid mixtures. Literature values for relative permittivities of some organic–organic liquid systems are used to test values predicted by SCDM and ECM, as well...