Publications

Abstract In the current work, the complexes formed between triplet vinyl nitrene ((CH2CHN)-C-3) and some Lewis acids YA (LiH, LiF, BeH2, BeF2, BH3, BF3, ClH, ClF, HCl, HF) have been investigated through calculations of the electronic structure. These calculations have been carried out in order to determine the energetic stability of the N center dot center dot center dot Y (with Y = Li, Be, B, Cl, H) interactions and also to understand their chemical nature. Quantum chemical calculations predict that the molecular complexes (CH2CHN)-C-3 center dot center dot center dot Y-A are always more stable than the separated (CH2CHN)-C-3 and Y-A species. The interaction energies range from -0.98 kcal mol(-1) (in CH2=CHN center dot center dot center dot ClH) to -39.03 kcal mol(-1) (in CH2=CHN center dot center dot center dot BH3) at the CCSD(T)/6-311++G(2d,2p) level of theory. Accordingly, some of these complexes may serve to experimentally detect and characterize the elusive triplet vinyl nitrene species. Moreover, AIM theory, in particular the L(r) = -A1/4a double dagger(2) rho(r) function, reveals that the N center dot center dot center dot Y interactions established between the electron lone pair of the nitrogen atom and the charge density depletion region of the Y atom are mainly of electrostatic character.

Abstract Complex self-assembled structures can be built up in aqueous media by making use of non-covalent interactions between small organic molecules and conventional amphiphiles. The macrocycle p-sulfonatocalix[4]arene (SC4) is a known receptor for organic ammonium cations in aqueous solution, showing strong binding ability for those guests and selectivity for several amino acids. Previous studies have shown that this type of water-soluble calixarenes are able to modify the aggregation behavior of surfactants. Here, we explore the interactions and morphologies present in mixtures of SC4 and a cationic serine-based surfactant, resorting to surface tension, light microscopy, cryo-scanning electron microscopy and nuclear magnetic resonance studies. Complexation of the amino acid-based surfactant by the calixarene leads initially to mixed micelle formation and a significant lowering of the critical micelle concentration with respect to the neat surfactant even for very low content of SC4 (up to 1.4 mol%). Interestingly, as the SC4 fraction in the system is gradually increased (about 2-6 mol%), highly flexible tubular structures and vesicles are assembled. The observed self-assembly is rationalized in terms of electrostatic complexation between the two co-solutes and the preferred packing of the supramolecular complexes formed.

Abstract A theoretical analysis of the enol-based photoacidity of oxyluciferin in water is presented. The basis for this phenomenon is found to be the hydrogen-bonding network that involves the conjugated photobase of oxyluciferin. The hydrogen-bonding network involving the enolate thiazole moiety is stronger than that of the benzothiazole phenolate moiety. Therefore, enolate oxyluciferin should be stabilized versus the phenolate anion. This difference in strength is attributed to the fact that the thiazole moiety has more potential hydrogen-bond acceptors near the proton donor atom than the benzothiazole moiety. Moreover, the phenol-based excited-state proton transfer leads to a decrease in the hydrogen-bond acceptor potential of the thiazole atoms. The ground-state enol-based acidity of oxyluciferin is also studied. This phenomenon can be explained by stabilization of the enolate anion through strengthening of a bond between water and the nitrogen atom of the thiazole ring, in an enol-based proton-transfer-dependent way.

Abstract Fluorescent water soluble carbon nanoparticles, in short carbon dots (CDs), was synthesized from lactose by microwave assisted hydrochloric acid method. Characterized by TEM and DLS to obtain the morphology shape (average 10 nm in size), with a higher negative surface charge supported by the composition was obtained by XPS spectroscopy. The maximum of the emission was centered at 450 nm with a lifetime of 2.1 ns. Without further functionalization of the CDs a nanosensor was obtained that responded exponentially to HAAs in the 0.35-0.45 mg L-1 concentration range by fluorescence static quenching, demonstrated by the lifetime analysis of the CDs in presence of HAAs. Some amino compounds were selected as model for interferences to evaluate the selectivity of this method, showing a notorious added value, with recoveries around 98%. The accuracy of the method was in terms of RSD about 2.5%. The results suggest their promising applications in chemical sensing.

Abstract We investigated the reductive intramolecular cyclization of bromopropargyl ethers derivatives, catalyzed by electrogenerated (1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane)nickel(I), [Ni(tmc)]+ as the catalysts in N,N,N-trimethyl-N-(2- hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide,[N<inf>1112</inf>(OH)][NTf<inf>2</inf>] and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C<inf>2</inf>mim][NTf<inf>2</inf>] by cyclic voltammetry and controlled-potential electrolysis. The results show that the reaction leads to the formation of the expected cyclic compounds, which are important intermediates in the synthesis of natural products with possible biological activities. © The Electrochemical Society.

Abstract This report presents a comprehensive experimental and computational study of the thermodynamic properties of two bromine fluorene derivatives: 2-bromofluorene and 2,7-dibromofluorene. The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the crystalline phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapour pressures of the crystalline phase of the two compounds were measured using the Knudsen effusion method and a static method that has also been used to measure the liquid vapour pressures of 2-bromofluorene. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation of the two compounds studied and of vapourisation of 2-bromofluorene were derived. The enthalpies and temperatures of fusion were determined from DSC experiments. Derived results of standard enthalpies and Gibbs energies of formation, in both gaseous and crystalline phases, were compared with the ones reported in the literature for fluorene. The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates based on density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with the 6-311++ G(d,p) basis set.

Abstract Two new synthetic strategies have been developed for the synthesis of a new class of cyclophthalazine derivatives. 6-BenzyL-2,3-dihydroimidazo[2,1-a]phthalazine and 2H-7-benzyl-3,4-dihydropyrimido[2,1-a]phthalazine were obtained (i) by intramolecular cyclization of the 2-(aminoalkyl)-4-benzyl-2H-phthalazin-1-one or (ii) by intramolecular cyclization of the corresponding 2-(4-benzylphthalazin-1(2H)-ylide-neamino)alcohols previously prepared. The second of the described routes afforded the desired derivatives in high yields.

Abstract This work addresses an energetic and structural study regarding hydroxy and methoxy naphthaldehyde derivatives, based both on experimental and computational research. The massic energy of combustion and vapor pressures at different temperatures were measured by static-bomb combustion calorimetry and Knudsen mass-loss effusion techniques, respectively. The computational studies were performed using the G3(MP2)//B3LYP method, an appropriate theoretical procedure for these kinds of compounds. The combination of experimental and computational data enabled the determination of the enthalpies, entropies, and Gibbs energies of sublimation and formation of these compounds both in the crystal and gas phase. Complementing the experimental studies, the intramolecular hydrogen bonding energetics of all three o-hydroxynaphthaldehydes and their corresponding tautomeric structures were evaluated. Additionally, the gasphase Gibbs free energy and enthalpy of formation of the radical and anion as well as the O-H homolytic bond dissociation enthalpy and gas-phase acidity were studied.