Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at the reference temperature of 298.15 K, of 2-amino-4-methylpyrimidine ((98.1 +/- 1.6) kJ . mol(-1)), 2-amino-4,6-dimethylpyrimidine ((55.9 +/- 1.8) kJ . mol(-1)) and 4-amino-2,6-dimethylpyrimidine ((60.1 +/- 1.8) kJ . mol(-1)) were calculated from the enthalpies of formation, in the crystalline phase, and enthalpies of sublimation, derived, respectively, from static bomb combustion calorimetry and Knudsen effusion technique results. In order to quantify the resonance effects arising from the substitution on the pyrimidine ring, hypothetical isodesmic reactions were used to analyze the experimental gaseous-phase enthalpies of formation. The aromaticity of benzene, pyridine, pyrimidine and the substituted pyrimidines was investigated in terms of magnetic (NICS), geometric (HOMA), electronic (Shannon aromaticity, QTAIMs ring critical point properties and HOMO-LUMO gap), reactive (hardness), vibrational (Kekule mode) and spectroscopic (UV-Vis) properties.

Abstract Testing impulsive behavior in rodents is challenging and labor-intensive. We developed a new behavioral paradigm-the Variable Delay-to-Signal (VDS) test-that provides rapid and simultaneous assessment of response and decision impulsivity in rodents. Presentation of a light at variable delays signals the permission for action (nose poke) contingent with a reward. 2 blocks of 25 trials at 3 s delay flank a block of 70 trials in which light is presented with randomly selected 6 or 12 s delays. Exposure to such large delays boosts the rate of premature responses when the delay drops to 3 s in the final block, an effect that is blunted by an acute methamphetamine challenge and that correlates with the delay-discounting (DD) paradigm (choice impulsivity). Finally, as expected, treatment with the NMDA antagonist MK-801 caused a generalized response increase in all VDS blocks. The pharmacological validation, particularly with methamphetamine which has a well established dual effect on response and decision impulsivity, and the correlations between the impulsive behavior in the DD and VDS paradigms, suggests that the later is able to provide, in a single session, a multi-dimensional assessment of impulsive behavior.

Abstract Objectives With the aim of finding new adenosine receptor (AR) ligands based on the chalcone scaffold, we report the synthesis of a new series of coumarinchalcone hybrids and the pharmacological characterization of their actions at four subtypes of AR. Methods The synthesized compounds 510 were characterized in radioligand binding (A1, A2A and A3) and adenylyl cyclase activity assays (A2B) to determine the affinity of the compounds for the four human AR (hAR) subtypes. Key findings Coumarinchalcone hybrids were found to be ligands with a novel structure, not reported thus far, that showed varying affinity and selectivity for AR subtypes. Conclusions The coumarinchalcone hybrids in which ring B of the chalcone scaffold was a thiophene (compounds 5 and 9) were found to be the most potent compounds of the series. Compound 9, in which ring A of the chalcone moiety was the phenyl ring of the coumarin, showed similar activity against hA1, hA2A and hA3 ARs, while compound 5, in which ring A of the chalcone was substituted by the benzopyrone ring of the coumarin moiety, showed similar activity only at the hA3 AR and, therefore, was deemed to be selective (Ki (dissociation constant)=5160nm).

Abstract The thermochemistry of alpha-D-xylose(cr) was studied by means of oxygen bomb calorimetry and a Physical Property Measurement System (PPMS) in zero magnetic field. The sample of alpha-D-xylose(cr) used in this study was one well-characterized by HPLC, Karl Fischer analysis, NMR, and by carbon dioxide analysis. The standard molar enthalpy of combustion was found to be Delta H-c(m)o = -(2342.2 +/- 0.8) kJ.mol(-1) at T = 298.15 K and at the standard pressure p degrees = 0.1 MPa. The standard molar heat capacity for alpha-D-xylose(cr) was measured with the PPMS over the temperature range 1.9001 <= T/K <= 303.66. At T = 298.15 K, C-p,m(o) = (178.1 +/- 1.8) J.K-1.mol(-1). The values of C-p,m(o) were fit as a function of T by using theoretical and empirical models for appropriate temperature ranges. The results of these fits were used to calculate values of C-p,m(o), the entropy increment Delta S-T(0)m(o), Delta H-T(0)m(o), and Phi(o)(m) = (Delta S-T(0)m(o) - Delta H-T(0)m(o)/T) from T = 0.5 K to T = 300 K. Derived quantities for alpha-D-xylose(cr) are the standard molar enthalpy of formation Delta H-f(m)o = -(1054.5 +/- 1.1) kJ.mol(-1), the third law standard molar entropy S-m(o) = (175.3 +/- 1.9) J.K-1.mol(-1), and the standard molar Gibbs energy of formation Delta(f)G(m)(o) = -(750.5 +/- 1.0) kJ.mol(-1). A comparison of values of Delta H-c(m)o and S-m(o) for the five-carbon aldoses demonstrated a striking similarity in the values of these respective properties for alpha-D-xylose(cr), D-ribose(cr), and D-arabinose(cr). Thermochemical network calculations were performed that led to values of the standard formation properties at T = 298.15 K for a variety of biochemical substances: D-xylose(aq), D-xylose(aq), D-xylose(2) (aq), D-lyxose(cr and aq), D-lyxose (aq), D-xylulose(aq), xylitol(aq), 1,4-beta-D-xylobiose(am and aq), and 1,4-beta-D-xylotriose(am and aq).

Abstract Recommended vapor pressure data for ferrocene (CAS Registry Number: 102-54-5) in the temperature range from 242 K to 447 K were developed by the simultaneous correlation of critically assessed vapor pressures, heat capacities of the crystalline phase and the ideal gas, and calorimetrically determined enthalpies of sublimation. All of the properties needed for the correlation were newly determined in this work. The value for the enthalpy of sublimation, Delta(g)(cr) H-m(298.15 K) = (74.38 +/- 0.38) kJ.mol(-1), is recommended. Comparisons with literature values are shown for all measured and derived properties.

Abstract Has been noticed a decline in students' interest in learning science. It is necessary, therefore, an implementation of teaching strategies that enable students to understand the usefulness of learning science and relevance of scientific knowledge. Given the unquestionable importance of pedagogical integration of technology, the design of digital learning resources can be relevant to motivate and encourage the involvement of young people in the construction of learning. It is this philosophy that fits PROFILES European project, and its predecessor PARSEL. This paper will present the basic principles of these projects, also referring to the potential of inquiry in the teaching and learning of science. In close connection with the inquiry and educational technology this paper also presents two examples of digital educational resources, developed by us, to enhance the learning of science, more effective and meaningful for students.

Abstract In this work an analysis of the effect of ortho, meta and para isomerization and the number of phenyl rings on the heat capacity and phase behavior of oligophenyls, n(Ph), from 3 up to 5 is presented. The phase behavior from 298.15 K to the melting temperature was analysed by differential scanning calorimetry (DSC) and the temperature, enthalpies and entropies of fusion along the oligophenyls series were determined. With the exception of terphenyl isomers, the meta oligophenyls series show lower melting temperatures and higher entropies of fusion. Heat capacities, at T = 298.15 K, were determined for the ortho and meta quaterphenyl and p-quinquephenyl oligomers by means of high precision drop calorimetry. The heat capacities of the ortho and meta isomers are systematically lower than those of the corresponding para isomers. It was found that the subtle isomerization effect on the heat capacity is partially related to the ring rotation restrictions in their supramolecular structure and increases with the increase of the number of phenyl rings.

Abstract Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 2-coumaranone and 3-coumaranone were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by mini-bomb combustion calorimetry. Standard molar enthalpies of sublimation of both isomers were determined by Calvet microcalorimetry. These results were combined to derive the standard molar enthalpies of formation of the compounds, in gas phase, at T = 298.15 K. Additionally, accurate quantum chemical calculations have been performed using DFT methods and high level composite ab initio calculations. Theoretical estimates of the enthalpies of formation of the compounds are in good agreement with the experimental values thus supporting the predictions of the same parameters for isobenzofuranone, an isomer which has not been experimentally studied. The relative stability of these isomers has been evaluated by experimental and computational results. The importance of some stabilizing electronic intramolecular interactions has been studied and quantitatively evaluated through Natural Bonding Orbital (NBO) analysis of the wave functions and the nucleus independent chemical shift (NICS) of the studied systems have been calculated in order to study and establish the effect of electronic delocalization upon the relative stability of the isomers.

Abstract A new water-soluble porphyrin, 5,10,15,20-tetrakis(4-piperidyl)porphyrin (T(4-Pip)P), has been synthesized. T(4-Pip)P is related to the extensively studied water-soluble porphyrin 5,10,15,20-tetrakis(4-pyridyl)porphyrin (T(4-Py)P) but has substituents with different electronic and hydrogen-bonding properties and is soluble over a much larger pH range due to the higher pK(a) of its conjugate acid T(4-H-Pip)P4+. Investigations of the ionic self-assembly reactions of T(4-H-Pip)P4+ with anionic water-soluble porphyrins reveal that it forms nanoscale materials.

Abstract Thermotropic liquid crystal formation by salt-free catanionic surfactants (alkyltrimethylammonium alkylsulfonates, herein designated as TA(m)So(n)) has been investigated as a function of chain length mismatch (asymmetry). Previous studies on these compounds have revealed an unusual and rich asymmetry-dependent lyotropic phase behavior. Herein, phase transition temperatures and transition enthalpies/entropies were determined by differential scanning calorimetry, while mesophases were assigned by polarized light microscopy. Three series of compounds were investigated, namely: the TA(16)So(n) series, where n = 6-10; the TA(m)So(8) series, where m = 12-16; and a constant m + n series, TA(m)So(n) where m + n = 22. Typically, several solid phases and two smectic mesophases are found prior to isotropization to the liquid phase. As asymmetry decreases, two somewhat counterintuitive tendencies emerge: a general decrease in enthalpy/entropy for solid-solid and solid-first mesophase transitions, and an increase in solid-first mesophase transition temperatures. Yet, solid phases are seen to be more stable for the most asymmetric compounds, while the second mesophase is more stable for the least asymmetric ones, in what appears to be a more complex behavior than expected. The results are globally interpreted in terms of subtle differences in chain interdigitation and packing, and odd-even chain effects.