Walter J. Peláez

TD-DFT calculations of UV absorption bands and their intensities in the spectra of some tetrahydroquinolines

A detailed analysis of the MOs involved in electronic transitions in UV spectra as well as a conformational study of 1-benzenesulfonyl-1,2,3,4-tetrahydroquinoline (BSTHQs) derivatives have been carried out using the TD-DFT (B3LYP/6-31+G(d,p)) method. Based on experimental solvent effects and theoretical investigations the long-wavelength bands have been assigned to π → π* transitions caused by HOMO–LUMO intramolecular charge transfer from the tetrahydroquinoline fragment (THQ) to the benzenesulfonyl moiety (BS). Nevertheless, for the NO2 derivative the HOMO–LUMO transition was found to be forbidden. In this case the long-wavelength band has been associated to an n → π* transition. Good correlation of theoretical and experimental data for the energy transitions and the molar extinction coefficients of the compounds studied has been obtained and is presented for the first time.

Cyclohexene-fused 1,3-oxazines with selective antibacterial and antiparasitic action and low cytotoxic effects

Oxazine derivatives, a class of heterocyclic compounds, exhibit a variety of biological properties, such as anticonvulsant and antitumor activities. In this study, we evaluated the effect of two cyclohexene-fused 1,3-oxazines (cis‑1-benzyl-N-phenyl-1,4,4a,5,8,8a-hexahydro-3,1-benzoxazin-2-imine (1) and trans‑N-phenyl-1,4,4a,5,8,8a-hexahydro-3,1-benzoxazin-2-imine (2)) in cultures of Bacillus cereus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Salmonella enterica, Serratia marcescens, Shigella flexneri and Staphylococcus aureus by the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). Additionally, the ex vivo antiparasitic activity of oxazines was assessed against Schistosoma mansoni, a helminth that is one of the major agents of the disease schistosomiasis Also, oxazines were evaluated on three tumor cell lines, NCI-H292 (human lung carcinoma), MCF-7 (human breast adenocarcinoma) and HEp-2 (human cervix carcinoma), and two normal cell lines (Vero and red blood cells). Bioassays revealed that oxazine 2 is more effective against bacteria than oxazine 1, with the lowest MIC and MBC values of 3.91 and 32.5μg/mL, respectively. Similarly, compound 2 demonstrated higher antiparasitic activity than 1, and scanning electron microscopy analysis showed several morphological alterations in the tegument of worms in a concentration-dependent manner. In contrast, both oxazines exhibited low cytotoxic effects on cancer and normal cell lines. These results indicated that oxazines exerted direct effects on bacteria and parasite schistosomes. More importantly, since schistosomiasis control programs rely on one drug, praziquantel, oxazines may have the potential to become new antischistosomal agents.

Flash vacuum pyrolysis (F.V.P.) of 1,2,4-benzotriazine derivatives

Flash vacuum pyrolysis of 3-methylsulfanyl-1,2,4-benzotriazine N-oxide, 3-methylsulfanyl-1,2,4-benzotriazine, and 3-phenyl-1,2,4-benzotriazine are described. The N-oxide derivative underwent deoxygenation between 500 and 600°C, whereas at higher temperatures both methylsulfanyl compounds, besides yielding the same products, also gave benzimidazole formed by an independent mechanism. Transformation of these derivatives between 600 and 750°C led to formation of a complex reaction mixture indicating the radical nature of the processes. The phenyl substituted derivative was studied between 575 and 650°C and afforded benzonitrile and traces of biphenylene.

Inhibition of the NorA efflux pump of Staphylococcus aureus by synthetic riparins

The goal of this study was to increase knowledge about the antimicrobial activity of some synthetic Riparin‐derived compounds, alone or in combination with fluoroquinolone antibiotics, against a strain of Staphylococcus aureus resistant to fluoroquinolone by way of overexpression of the NorA efflux pump.

UV characterization and photodegradation mechanism of the fungicide chlorothalonil in the presence and absence of oxygen

An experimental and theoretical study of the UV spectrum of chlorothalonil (CT) was carried out and the vibrationally resolved HOMO→LUMO transition is presented for the first time. The fluorescence spectrum has also been recorded. Furthermore, preparative photolysis allowed a detailed study of the photoproducts formed with recognition of different isomers. In the presence of oxygen only the first reductive dechlorination-decyanation occurred, while in its absence a successive dechlorination-decyanation takes place.

Photooxidation of Di-tert-butyl Malonate in the Presence and Absence of Nitrogen Dioxide

The rate constant for the reaction of di-tert-butyl malonate (DTBM) with chlorine atoms in the gas phase was measured using cyclohexane and pentane as references. The measurements lead to a value of (1.5 ± 0.1) × 10-10 cm3 molecule-1 s-1. The subsequent photo-oxidation mechanism of DTBM in the absence and presence of nitrogen dioxide was investigated. The main carbonated products identified in the first case were acetone, formic acid, carbon monoxide, and carbon dioxide. The addition of nitrogen dioxide lead besides to the formation of (CH3)3CC(O)OONO2 and (CH3)3CONO2. The proposed photo-oxidation mechanism was supported both experimentally and computationally. The results reveal that the (CH3)3COC(O)CH2C(O)OC(CH3)2O• radical formed reacts according to two competitive reactions: decomposition to yield acetone and (CH3)3COC(O)CH2C(O)O• radical 55 ± 2%, and migration of the H atom of the methylene group to the terminal oxygen atom 40 ± 3%.

Photo-oxidation of Dimethyl Malonate Initiated by Chlorine Atoms in Gas Phase: Kinetics and Mechanism

The rate coefficient for the gas-phase reaction of chlorine atoms with dimethyl malonate (DMM, CH3OC(O)CH2C(O)OCH3) was determined at 298 K using relative methods giving a value of (3.8 ± 0.4) × 10-12, cm3 molecule-1 s-1). The photo-oxidation mechanism of DMM was also investigated. The main products were identified by infrared spectroscopy, and computational calculations were performed in order to support the experimental data. The results reveal that the photo-oxidation occurs mainly by the abstraction of an H atom from the methyl groups. The CH3OC(O)CH2C(O)OCH2O• radical formed subsequently reacts according to three competitive paths: reaction with molecular oxygen to yield CH3OC(O)CH2C(O)OC(O)H, isomerization-unimolecular decomposition to lead finally to CH3OC(O)C(O)H, CO2, and HC(O)OH, and α-ester rearrangement to form monomethyl malonate and carbon monoxide. The yield of products as a function of oxygen pressure was also determined.

(S)-5-Benzyl- and 5-benzylidene-imidazo-4-one derivatives synthesized and studied for an understanding of their thermal reactivity

Flash vacuum as well as static pyrolysis were used to gain insight into the mechanisms of decomposition of the title compounds. They were synthesized by the use of microwave techniques that allowed better yields than the established methods. Since the benzyl compounds always open a radical channel in the thermal processes, consequently lowering the yields of other important intramolecular processes, we also started the pyrolysis with benzylidene derivatives. Detection and quantification of products accompanied by kinetic analyses were carried out for both types of compounds. The activation energies as well as the entropy contributions have been determined. Moreover, DFT calculations provided support for and corroborating of the proposed thermal pathways.

Vibrational spectra of solid cis- and trans-2- thioxohexahydroquinazolin-4(1H)-one and theoretical calculations towards the interpretation of its thermal reactivity†

FT-Raman and FT-IR spectra of solid cis- and trans-2-thioxohexahydroquinazolin-4(1H)-one are reported from 4000 to 200 cm−1. The molecular geometry, Wiberg Index, NBO analysis and vibrational wavenumbers in the ground state have been calculated using a density functional method (B3LYP) with 6-31+G** and 6-311+G** basis set. Both compounds are stable as dimers in the solid phase, possessing C2 symmetry. The scaled theoretical wavenumbers showed very good agreement with the experimental values. This work contributes to the knowledge of important data which are rather scarce for quinazolinones.

Fast synthesis of a tris(N,N-diimine)chromium(III) complex by a microwave-assisted approach

Background: in the last ten years, Photodynamic Antimicrobial Chemotherapy (PACT) has emerged as a reliable option to treat several bacterial and fungal infections. Tris(N,N-diimine)chromium(III) complexes are known for their potential as photosensitizers; however, synthesis is usually a very time consuming procedure. Results: with our novel methodology, [Cr(biim)3](NO3)3 was prepared in a few seconds as a powder and the yield of the reaction was improved compared with previously described syntheses, where obtaining crystals is complicated due to the acidity of the media. The precursors for the synthesis are also synthesized through fast and simple methods. Identification of intermediates and the final product was performed by melting point, infrared, UV-vis and NMR spectroscopy. Conclusions: this article describes a quick, easy and eco-friendly procedure to synthesize [Cr(biim)3](NO3)3 by employing microwave irradiation.