Publications

Abstract In this work, rearrangement reactions subsequent to the oxidation of tertiary amines were studied in 2-(cyanoethyl)-2-azanorbornane/ene systems. [1,2]- and [2,3]-Meisenheimer rearrangements, as well as the Cope elimination reaction, were observed with virtually complete selectivity. It was found that 2-(cyanoethyl)-2-azanorbornanes afford N-hydroxylamines through Cope elimination reactions and 2-(cyanoethyl)-2-azanorbornenes are prone to Meisenheimer rearrangements. In addition, the endo/exo configuration of 2-azanorbornenes plays a key role in the Meisenheimer rearrangement outcome. All the synthesized compounds were fully characterized by NMR spectroscopy and HRMS.

Abstract Imidazopyrazinone dioxetanone is a central molecule in bioluminescence, as it is the scaffold responsible for light emission in many marine species. Herein, we have theoretically studied the thermolysis of its neutral and anionic forms. Our results allowed us to explain imidazopyrazinone bioluminescence with the Interstate Crossing-Induced Chemiexcitation (ICIC) mechanism, and explain why neutral forms emit light efficiently to the contrary of anionic ones. Both forms decompose via a step-wise-biradical pathway, but the biradical is formed either via an electron transfer (anion) or due to homolytic bond cleavage (neutral species). Absence of electron transfer leads to an entropic trap, a flat region where infinite possibilities for chemiexcitation exist. However, the resulting products can be in either triplet or singlet excited states. The triplet to singlet ratio is determined by the electron spin density distribution, which controls the rates of intersystem crossing.

Abstract We have performed a study of structural, thermochemical and thermophysical properties of the (Z)-cinnamic acid neutral molecule and its corresponding oxyanion (formed by deprotonation of the carboxylic group). The thermophysical study (heat capacities, temperature and enthalpy of fusion) was made by DSC. The following intrinsic (gas-phase) thermochemical magnitudes have been experimentally determined: (i) standard enthalpy of formation, at T = 298.15 K, of the neutral molecule, Delta H-f(m)0 (g) = (-215.5 +/- 3.2) kJ.mol(-1), by combustion calorimetry and by the Knudsen effusion technique, (ii) deprotonation enthalpy, Delta H-acid(0)(g) = (1416.4 +/- 8.8) kJ.mol(-1) and acidity, GA = (1386.7 +/- 8.8) kJ.mol(-1), by the EKM method using ESI-TQ Mass Spectrometry. From these results we have also derived the enthalpy of formation of the oxyanion, Delta H-f(m)0 (oxyanion, g) = (-303.5 +/- 9.4) kJ.mol(-1). A computational study, through density functional calculations at the B3LYP/6-311++ G(d, p) level of theory, was used to check the good consistency of the experimental results. The global results show that (Z)-cinnamic acid is significantly less stable than the corresponding (E)-isomer, which can be related to the greater acidity of the (Z)-form found in both the gas and aqueous solution phases.

Abstract In order to evaluate the impact of the alkyl side chain length and symmetry of the cation on the thermophysical properties of water-saturated ionic liquids (ILs), densities and viscosities as a function of temperature were measured at atmospheric pressure and in the (298.15-363.15) K temperature range, for systems containing two series of bis(trifluoromethylsulfonyl)imide-based compounds: the symmetric [C(n)C(n)im][NTf2] (with n = 1-8 and 10) and asymmetric [C(n)C(1)im][NTf2] (with n= 2-5, 7, 9 and 11) ILs. For water-saturated ILs, the density decreases with the increase of the alkyl side chain length while the viscosity increases with the size of the aliphatic tails. The saturation water solubility in each IL was further estimated with a reasonable agreement based on the densities of water-saturated ILs, further confirming that, for the ILs investigated, the volumetric mixing properties of ILs and water follow a near ideal behavior. The water-saturated symmetric ILs generally present lower densities and viscosities than their asymmetric counterparts. From the experimental data, the isobaric thermal expansion coefficient and energy barrier were also estimated. A close correlation between the difference in the energy barrier values between the water-saturated and pure ILs and the water content in each IL was found, supporting that the decrease in the viscosity of ILs in presence of water is directly related with the decrease of the energy barrier.

Abstract Ohmic heating offers a very efficient way to perform organic reactions in aqueous media. Potentially bioactive (E)-3-styrylquinolin-4(1H)-ones were synthesized by the Heck reaction of 3-iodo-1-methylquinolin-4(1H)-one with styrenes in water and with ohmic heating. Pd(OAc)(2) was used as catalyst, and tetrabutylammonium bromide was used as phase-transfer catalyst in the presence of an inorganic base. Comparison with other established procedures highlight the benefits of this new methodology.

Abstract In this work, the effect of the alkyl chain size in 1-ethylpyridinium cation-based ionic liquids are used to explore the nanostructuration effect. Densities and viscosities and their dependence on temperature were measured for the 2-alkyl-l-ethylpyridinium bis(trifluoromethanesulfonyl)imide, [(CN-2C2Py)-C-2-C-1] [NTf2] (N = 4,5, 6, 7, 8, 9, 10, 11,12) ionic liquid series. Molar volume, thermal expansion coefficients, VET parameters, as well as, the energy barrier related to the fluid shear at T= 298.15 K, were derived. Highly precise measurements of the heat capacities, at T = 298.15 K, were performed using a drop calorimeter. In agreement with the previously studies based on the alkylimidazolium ionic liquids series, the studied thermophysical and transport properties of the series presents an indication that in the pyridinium based ionic liquids the nanostructuration is intensified after a critical alkyl length, [(C5C2Py)-C-2-C-1][NTf2]. The observed trend shift in the viscosity and heat capacities of the pyridinium ionic liquids is more pronounced in the pyridinium than in the imidazolium ionic liquids series.

Abstract Photodynamic therapy (PDT) of cancer is known for its limited number of side effects, and requires light, oxygen and photosensitizer. However, PDT is limited by poor penetration of light into deeply localized tissues, and the use of external light sources is required. Thus, researchers have been studying ways to improve the effectiveness of this phototherapy and expand it for the treatment of the deepest cancers, by using chemiluminescent or bioluminescent formulations to excite the photosensitizer by intracellular generation of light. The aim of this Minireview is to give a precis of the most important general chemi-/bioluminescence mechanisms and to analyze several studies that apply them for PDT. These studies have demonstrated the potential of utilizing chemi-/bioluminescence as excitation source in the PDT of cancer, besides combining new approaches to overcome the limitations of this mode of treatment.

Abstract In the original article[1] there is an error in the structure of compound 3j (the methyl group should be attached to the β-position and not to the α-position) and in some NMR resonances; also the name of compound 3g and two of its NMR assignments are erroneous. Correct versions are given below in Scheme 1, Figure 2, and the two related paragraphs of the Exp. Sect. An amended file of the Supporting Information is also available. (Figure presented.) © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Abstract Gas-phase electronic and structural properties of the room temperature ionic liquid 1-ethyl-3-methylimidazolium tris(perfluoroethyl) trifluorophosphate ([EMIM][FAP]) were studied using density functional theory, and confirmed with results from infrared spectroscopy. A conformational analysis allowed the identification of several plausible conformers of the ion pairs. For the detected conformers, the infrared spectra were predicted and their thermodynamic properties were evaluated. The topology of the electronic density of the most stable conformers of [EMIM][FAP] ion pairs were characterised using the quantum theory of atoms in molecules. A number of possible hydrogen bonds between the cations and anions of the ionic liquid were identified. Excellent correspondence was found between the predicted spectra of gas-phase [EMIM][FAP] conformers and the experimental infrared spectrum, which in turn allowed a clear attribution of the vibration modes of [EMIM][FAP]. Finally, the contribution of the various conformers of both isomers of the [FAP](-) anion to the ionic liquid macro-properties is shown.

Abstract Highly and stable fluorescent carbon dots (CQDs), with lambda(ex)/lambda(em) = 350/465 nm were obtained using a strong acid oxidation of activated carbon in aqueous suspension. The nanoparticles had a mean size of 12 nm and quantum yield of 3.94%. After functionalization with amine groups by PAMAM-NH2 dendrimer (CQDs@PAMAM-NH2), the size of particles increased and aggregates of 65 nm were formed. Quantum yield also increased to 6.33%. CQDs were characterized by various analytical techniques including ATR-FTIR, Raman, XPS and fluorescence spectroscopies. The prepared CQDs@PAMAM-NH2 were used as fluorescent ratiometric nanosensor of 4-chloro-2,6-dinitroaniline, which is a constituent of explosives. As a result of interactions, the fluorescence at 465 nm was quenched. Moreover, a new band at 507 nm emerged and it is linked to a charge transfer and the formation of a Meisenheimer complex. A ratio of fluorescence intensities at 465 and 507 nm (I-465/I-507) is used for a ratiometric fluorescence sensing. A linear detection ranges from 1.0 x 10(-5) to 6.0 x 10(-4) M with a detection limit of 2 mu M and accuracy of 0.85% as standard relative deviation (RSD, n = 10). The detection accuracy in the presence of other nitrocompounds was 2.80% as RSD.