An investigation about the solid state thermal degradation of acetylsalicylic acid: polymer formation

An investigation about the thermal degradation of acetylsalicylic acid (ASA) is performed. It is verified that the thermal degradation of ASA produces not only salicylic acid (SA) and acetic acid (AA) as products but also an ASA polymer, which is transparent and solid. And also verified that the temperature in which the polymer is obtained influences its physical consistence (solid or semi-solid). Furthermore, the ASA polymer is very stable from a thermic point of view, as verified by TG and DSC analysis. X-ray diffraction patterns obtained for the ASA polymer show that it exhibits a low crystallinity.     

Characterization of two dissimilatory sulfite reductases from sulfate-reducing bacteria

Mössbauer, EPR, and biochemical techniques were used to characterize two dissimilatory sulfite reductases: desulforubidin fromDesulfovibrio baculatus strain DSM 1743 and desulfoviridin fromDesulfovibrio gigas. For each molecule of desulforubidin, there are two sirohemes and four [4Fe?4S] clusters. The [4Fe?4S] clusters are in the diamagnetic 2+ oxidation state. The sirohemes are high-spin ferric (S=5/2) and each siroheme is exchanged-coupled to a [4Fe?4S]²⁺ cluster. Such an exchange-coupled siroheme-[4Fe?4S] unit has also been found in the assimilatory sulfite reductase fromEscherichia coli/1/ and in a low-molecular weight sulfite reductase fromDesulfovibrio vulgaris/2/. For each molecule of defulfoviridin, there are two tetrahydroporphyrin groups and four [4Fe?4S]²⁺ clusters. To our surprise, we discovered that about 80% of the tetrahydroporphyrin groups, however, do not bind iron.     

119Sn-Mössbauer spectroscopic studies on organoheterobimetallic half sandwich ruthenium–tin containing derivatives

A series of heterobimetallic complexes containing Ru–Sn bonds, of general formula [RuCp(L)₂SnX₂Y] [L = PPh₃, 1/2 dppe = 1,2-bis(diphenylphosphino)ethane; X, Y = F, Cl and Br], was prepared and studied by elemental analysis, ¹¹⁹Sn-Mössbauer spectroscopy, i.r. and ¹H-, ¹³C-, ¹⁹F-, ³¹P- and ¹¹⁹Sn-n.m.r. spectroscopy. ¹¹⁹Sn-Mössbauer studies allowed determination of the coordination number of the Sn^II center as well as the group electronegativity of the organometallic fragment [RuCp(L)₂]⁺. These results, supported by multinuclear n.m.r. data suggested that the electronic charge distribution between the Ru^II and Sn^II centers are strongly dependant upon the nature of L and the electronegativity of X and Y.     

Ligand K-edge X-ray absorption spectroscopy and DFT calculations on [Fe3S4]0,+ clusters: delocalization, redox, and effect of the protein environment

Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the mu(2)S(sulfide), mu(3)S(sulfide), and S(thiolate) ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe(3+) and Fe(2.5+) components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38% vs 61%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm(-1) vs -360 cm(-1), respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter lambda2/k(-), leads to an S = 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe(3+) center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite.     

Bioactive Natural Products for Chemical Control of Microorganisms: Scientific Prospecting (2001–2021) and Systematic Review

The inappropriate use of synthetic antibiotics has become a global public health problem. Therefore, the study of new alternatives for the treatment of infectious diseases is relevant and natural bioactive products are on the rise. This study conducted a scientific prospection of bioactive natural products with promising applications in the chemical control of microorganisms. A systematic review of the most recent articles was performed according to the following three steps: (i) eligibility assessment, (ii) screening, and (iii) inclusion of articles and information extraction. There has been an increase in the number of scientific publications on bioactive natural products for microbial control in the CAPES and SciELO databases (2001–2021). Seventeen relevant articles were included, most of which focused on extracts. Ascorbic acid, chlorogenic acid, chrysin, and quercetin were the most cited compounds. Natural products were shown to be effective in inhibiting more than 30 microorganisms. A discussion was presented on the research trends.     

Antifungal Effect and Inhibition of the Virulence Mechanism of D-Limonene against Candida parapsilosis

Yeasts from the Candida parapsilosis complex are clinically relevant due to their high virulence and pathogenicity potential, such as adherence to epithelial cells and emission of filamentous structures, as well as their low susceptibility to antifungals. D-limonene, a natural compound, emerges as a promising alternative with previously described antibacterial, antiparasitic, and antifungal activity; however, its mechanisms of action and antivirulence activity against C. parapsilosis complex species have not been elucidated. Therefore, in the present study, we aimed to evaluate the antifungal and antivirulence action, as well as the mechanism of action of D-limonene against isolates from this complex. D-limonene exhibited relevant antifungal activity against C. parapsilosis complex yeasts, as well as excellent antivirulence activity by inhibiting yeast morphogenesis and adherence to the human epithelium. Furthermore, the apoptotic mechanism induced by this compound, which is not induced by oxidative stress, represents an important target for the development of new antifungal drugs.     

The determination of the glass transition temperature by thermally stimulated depolarization currents. Comparison with the performance of other techniques

Several experimental techniques are currently used for the determination of the glass transition temperature, T_g. Thermally stimulated depolarization currents (TSDC) is a thermal analysis technique whose experimental results display a very clean glass transition signature and that, nevertheless, is seldom used as a technique for T_g determination. In the present work we explain how to get the glass transition temperature from TSDC data, and we compare the values obtained for a vast number of glass forming systems (with T_gs in a wide range between ?145 and +180 °C and fragilities between m = 15 and m = 100), with the values obtained by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). We conclude that the T_g determination by TSDC is direct, accurate and reproducible and that the obtained values correlate very well with those obtained by DSC and DRS. This general survey thus suggests TSDC as a valuable alternative technique for determining T_g.     

Synthesis of fluorescent water-soluble functionalised benzo[a]phenoxazinium salts

In order to develop long-wavelength functionalised oxazine dyes with good water solubility and high photostability for biological applications, a series of novel side-chain functionalised benzo[a]phenoxazinium salts were synthesised and characterised. These polycyclic cationic compounds showed strong fluorescence in ethanol and water (pH 7.4), with an emission wavelengths higher than 637 nm, as well as high quantum yields and moderate Stokes’ shifts. The photostability of the fluorophores synthesised, under irradiation at 419 nm, was good to excellent in ethanol and moderate in water at physiological pH.     

Counterion Nature and Alkylammonium Halide Adsorption Thermodynamics

Two surfactants were synthesized by reacting hydrogen halides (hydrogen chloride and hydrogen bromide) with 1-dodecylamine. The resultant cationic surfactants, 1-dodecylammonium chloride (DDAC) and 1-dodecylammonium bromide (DDAB), were characterized by NMR spectrometry and FTIR spectroscopy and data related to their adsorption at the fluid liquid/gas interface were obtained employing bubble surface tensiometry, in pure water and in HCl 0.1 M. Data did not fit well to Langmuir isotherm but Frumkin isotherm did adequately describe to process of adsorption. Adsorption isotherms, as well as data related to critical micelle concentration, CMC, indicated that in HCl 0.1 M, the presence of electrolytes and a common ion to DDAC decreased chloride solvation, changing surface packing and adsorption profile for this surfactant.     

Compatibility studies of trioxsalen with excipients by DSC,DTA, and FTIR

Psoralens are widely used for the treatment of psoriasis. Trioxsalen is a drug prescribed low-dose, belonging to the group of substituted psoralen. The aim of this study was to evaluate the compatibility of trioxsalen with pharmaceutical excipients used in the solid forms by analytical techniques. Binary mixtures between the trioxsalen and pharmaceutical excipients (namely, magnesium stearate, α-lactose, microcrystalline cellulose 102, pregelatinized starch, mannitol, sodium lauryl sulfate, sodium starch glycolate, and croscarmellose sodium) were examined. The trioxsalen–sodium lauryl sulfate mixture displayed some physical interaction based on the DTA and DSC results, but the FTIR study ruled out any chemical change.