Publications

Abstract Magnesium is an essential mineral in human metabolism, and is the second most abundant intracellular cation and the fourth most abundant in the human body. Magnesium has a large variety of biological functions, including being a cofactor for over 300 enzymes, mainly involving phosphorylation of proteins and nucleic acids. Low levels of magnesium in the body can develop during different illnesses, such as diabetes (type 2), metabolic syndrome, cardiac arrhythmias, and muscular constriction. The present review shows the advances in analytical chemistry based on sensor systems to quantify the concentration of magnesium in different biological samples, plasma, serum, or urine, that are relevant to human health.

Abstract BACKGROUNDStimuli responsive imprinted hydrogel micro-particles were prepared using reversible addition-fragmentation chain transfer polymerization for targeting genotoxic impurity aminopyridine in aqueous environment using a continuous flow micro-reactor. RESULTSThe feasibility of operation with a continuous flow micro-reactor for particles production was demonstrated. A comparative evaluation was carried out between batch and micro-reactor produced imprinted and non-imprinted hydrogels. Experimental results proved that molecular imprints generated by free radical polymerization and controlled radical polymerization showed outstanding performance in adsorption behavior: the q value estimate was about 1000 times higher than the value presented by other researchers. Solid phase extraction results further evidenced the promising imprinting with hydrogels using free radical polymerization and controlled radical polymerization by retaining c. 100% of 3-aminopyridine. The imprinting factor of 4.3 presented in this research appears to be the best value shown so far. CONCLUSIONThe imprinted materials were successfully prepared both in batch and with a continuous flow micro-reactor. The inclusion of a reversible addition-fragmentation chain transfer agent in controlled radical polymerization was important in optimizing the experimental conditions in the continuous microfluidic approach. Though the reversible addition-fragmentation chain transfer agent was very useful in controlling the reaction kinetics, imprinted micro-particles showed the existence of both non-specific and imprinted sites. It is worth extending this work to demonstrate the impact of reversible addition-fragmentation chain transfer agents in molecular imprinting, considering also operation in a continuous flow micro-reactor to obtain tailored smart hydrogel particles. (c) 2015 Society of Chemical Industry

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.