Rommel B. Viana

Infrared Spectroscopy of Anionic, Cationic, and Zwitterionic Surfactants

This paper describes the ordering degree of anionic, cationic, and zwitterionic surfactants with the increase of their packing density on Ge substrate by using Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy. This work shows new insights on the conformational order of sodium dodecyl sulfate (SDS), N-hexadecyl-N-N-dimethyl-3-ammonio-1-propane-sulfonate (HPS), hexadecyl-trimethylammonium bromide (CTAB), and dodecyl trimethylammonium bromide (DTAB). DFT and semiempirical calculations are also performed in order to evaluate the effect of headgroup hydration and counterion. The CH2 asymmetric and symmetric stretching bands for the SDS molecule show a shift of 1.7 and 0.9 cm−1 to higher frequencies as the packing density increases, while it is observed a shift of 2.6 and 2.7 cm−1 for the HPS molecule, respectively. The DTAB molecule shows a shift of 4.5 cm−1 to lower frequencies for both CH2 asymmetric and symmetric stretching bands as the packing density increases, indicating the decrease of gauche conformations and the increase of all-trans conformations over the aliphatic chain.

Técnicas de extrações e procedimentos de clean-up para a determinação de hidrocarbonetos policílicos aromáticos (HPA) em sedimentos da costa do Ceará

Extraction and clean-up are essential points in polycyclic aromatic hydrocarbon (PAHs) analysis in a solid matrix. This work compares extraction techniques and clean-up procedures for PAH analysis. PAH levels, their toxicological significance and source were also evaluated in the waters of the Coco and Ceara rivers. The efficiency of PAH recovery was higher for the soxhlet and ultrasonic techniques. PAH recovery varied from 69.3 to 99.3%. Total PAH concentration (ΣHPA) varied from 720.73 to 2234.76 µg kg-1 (Coco river) and 96.4 to 1859.21 µg kg-1 (Ceara river). The main PAH sources are pyrolytic processes and the levels were classified as medium so that adverse effects are possible.

Adsorption of Sodium Dodecyl Sulfate on Ge Substrate: The Effect of a Low-Polarity Solvent

This paper describes the adsorption of sodium dodecyl sulfate (SDS) molecules in a low polar solvent on Ge substrate by using Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy and atomic force microscopy (AFM). The maximum SDS amount adsorbed is (5.0 ± 0.3) × 1014 molecules cm−2 in CHCl3, while with the use of CCl4 as subphase the ability of SDS adsorbed is 48% lower. AFM images show that depositions are highly disordered over the interface, and it was possible to establish that the size of the SDS deposition is around 30–40 nm over the Ge surface. A complete description of the infrared spectroscopic bands for the head and tail groups in the SDS molecule is also provided.

New insights in the formation of thioxophosphine: A quantum chemical study

The investigation of the thioxophosphine (PS) formation from different reaction paths is successfully performed and presented in this paper. The PH(3)+SH(1) reaction is likely to yield the intermediates PH(2) (2)+H(2)S through an energy barrier of 2.8 kcal mol(-1). However, the next step is the H(2)PS(2) formation, which has a too high energy barrier, 52.6 kcal mol(-1). The PH(3)+S(1) reaction path is the likely source of the HPS(1) molecule. The other possibilities are the PH(1)+H(2)S, PH(2) (2)+SH(1), and PH(3)+H(2)S reactions, but they are spin forbidden and energetically unfavorable for the HPS(1) and PSH(1) formations. On the other hand, the PS(2) formation is more likely to happen by the PH(1)+SH(1) reaction. The PH(2) (2)+S(1), PH(3)+SH(1), P(2)+H(2)S, and P(4)+H(2)S reactions are also favorable in terms of energetics; however, these reactions are spin forbidden. The chemical mechanism for the PS(2) formation is now presented in more details, which is of great importance in the atmosphere of Jupiter and Saturn, and in interstellar medium.

Manganese(II) complexes with thiosemicarbazones as potential anti-Mycobacterium tuberculosis agents

Through a systematic variation on the structure of a series of manganese complexes derived from 2-acetylpyridine-N(4)-R-thiosemicarbazones (Hatc-R), structural features have been investigated with the aim of obtaining complexes with potent anti-Mycobacterium tuberculosis activity. The analytical methods used for characterization included FTIR, EPR, UV-visible, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. Density functional theory (DFT) calculations were performed in order to evaluate the contribution of the thiosemicarbazonate ligands on the charge distribution of the complexes by changing the peripheral groups as well as to verify the Mn-donor atoms bond dissociation predisposition. The results obtained are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral complexes of the type [Mn(atc-R)2], paramagnetic in the extension of 5 unpaired electrons, whose EPR spectra are consistent for manganese(II). The electrochemical analyses show two nearly reversible processes, which are influenced by the peripheral substituent groups at the N4 position of the atc-R(1-) ligands. The minimal inhibitory concentration (MIC) of these compounds against M. tuberculosis as well as their in vitro cytotoxicity on VERO and J774A.1 cells (IC50) was determined in order to find their selectivity index (SI) (SI=IC50/MIC). The results evidenced that the compounds described here can be considered as promising anti-M. tuberculosis agents, with SI values comparable or better than some commercial drugs available for the tuberculosis treatment.

Influence of urban activities on polycyclic aromatic hydrocarbons in precipitation: Distribution, sources and depositional flux in a developing metropolis, Fortaleza, Brazil

We measured polycyclic aromatic hydrocarbons (PAHs) in bulk precipitation in the Fortaleza metropolitan area, Ceará, Brazil, for the first time. Because little information is available concerning PAHs in tropical climatic regions, we assessed their spatial distribution and possible sources and the influence of urban activities on the depositional fluxes of PAHs in bulk precipitation. The concentrations of individual and total PAHs (Σ(PAHs)) in bulk precipitation ranged from undetectable to 133.9 ng.L(-1) and from 202.6 to 674.8 ng.L(-1), respectively. The plume of highest concentrations was most intense in a zone with heavy automobile traffic and favorable topography for the concentration of emitted pollutants. The depositional fluxes of PAHs in bulk precipitation calculated in this study (undetectable to 0.87 μg.m(-2).month(-1)) are 4 to 27 times smaller than those reported from tourist sites and industrial and urban areas in the Northern Hemisphere. Diagnostic ratio analyses of PAH samples showed that the major source of emissions is gasoline exhaust, with a small percentage originating from diesel fuel. Contributions from coal and wood combustion were also found. Major economic activities appear to contribute to pollutant emissions.

4-Hydroxy-2,5-dimethylphenyl-benzophenone: Conformational stability, FT-IR and Raman investigation

In this paper we have studied the 4-hydroxyl-2,5 dimethylphenyl-benzophenone. Also, it was analyzed the vibrational assignment (FT-IR and Raman) in conjunction with computational results. The conformational analysis showed three barrier heights where two are due to the dihedral rotation and the other one is attributed to hydroxyl rotation. While the high dihedral rotational barrier (TS1) is 6.06-7.22 kcal mol(-1), the lower one (TS2) is almost three times smaller. The variations with the change of basis set is 5-8% to TS1, and 3-15% in the values predicted to TS2. In the case of OH rotational barrier, the values range from 3.70 to 4.86 kcal mol(-1), and it is also observed that this transition state is less sensitive to the change of basis set and to the method. Two isomers was detected due to the changes in the OH rotation with the gap energy lower than 0.7 kcal mol(-1), and at this point is seen that semi-empirical methods fail into describe the most stable conformation which may be due to the small energy gap. The enthalpy formation at 0 K and 298 K was 111.71 and 102.20 kcal mol(-1), respectively.

Understanding the Molecular Aspects of Tetrahydrocannabinol and Cannabidiol as Antioxidants

An antioxidant mechanism of tetrahydrocannabinol (THC) and cannabidiol (CBD) were compared with a simplified model of α-tocopherol, butylhydroxytoluene and hydroxytoluene in order to understand the antioxidant nature of THC and CBD molecules using DFT. The following electronic properties were evaluated: frontier orbitals nature, ionization potential, O-H bond dissociation energy (BDEOH), stabilization energy, and spin density distribution. An important factor that shows an influence in the antioxidant property of THC is the electron abstraction at the phenol position. Our data indicate that the decrease of the HOMO values and the highest ionization potential values are related to phenol, ether, and alkyl moieties. On the other hand, BDEOH in molecules with the cyclohexenyl group at ortho position of phenol are formed from lower energies than the molecules with an ether group at the meta position. In the light of our results, the properties calculated here predict that THC has a sightly higher antioxidant potential than CBD.

Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach

The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11 kcal·mol(-1)), with barrier heights ranging from 16 to 19 kcal·mol(-1). In contrast, the barrier energies on the keto/enol isomerization are almost 10 kcal·mol(-1) higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed.

Enzymatic Resolution of Racemic Sulcatol by Lipase from Candida Antarctica in a Large Scale

Large scale enzymatic resolution of racemic sulcatol 2 has been useful for stereoselective biocatalysis. This reaction was fast and selective, using vinyl acetate as donor of acyl group and lipase from Candida antarctica (CALB) as catalyst. The large scale reaction (5.0 g, 39 mmol) afforded high optical purities for S-(+)-sulcatol 2 and R-(+)-sulcatyl acetate 3, i.e., ee > 99 per cent and good yields (45 per cent) within a short time (40 min). Thermodynamic parameters for the chemoesterification of sulcatol 2 by vinyl acetate were evaluated. The enthalpy and Gibbs free energy values of this reaction were negative, indicating that this process is exothermic and spontaneous which is in agreement with the reaction obtained enzymatically.