Riparin-B as a Potential Inhibitor of AdeABC Efflux System from Acinetobacter baumannii

Acinetobacter baumannii is an important opportunistic pathogen that causes serious health-related infections, especially in intensive care units. The present study aimed to investigate the antimicrobial activity of Riparin-B (Rip-B) alone and in association with norfloxacin against multidrug-resistant clinical isolates of A. baumannii. For this, the minimum inhibitory concentrations were determined by the microdilution method. For the evaluation of resistance-modulating activity, MIC values for antibiotics were determined in the presence or absence of subinhibitory concentrations of Rip-B or chlorpromazine (CPZ). The AdeABC-AdeRS efflux system genes from these isolates were detected by PCR. Docking studies were also carried out to evaluate the interaction of Riparin-B and the AdeABC-AdeRS efflux system. The study was conducted from 2017 to 2019. The results showed that Rip-B showed weak intrinsic activity against the strains tested. On the other hand, Rip-B was able to modulate norfloxacin's response against A. baumannii strains that express efflux pump-mediated resistance. Docking studies provided projections of the interaction between Rip-B and EtBr with the AdeB protein, suggesting that Rip-B acts by competitive inhibition with the drug. Results found by in vitro and in silico assays suggest that Rip-B, in combination with norfloxacin, has the potential to treat infections caused by multidrug-resistant A. baumanni with efflux pump resistance.

Phase changes of tris(glycinato)chromium(III) monohydrate crystal systematically studied by thermal analyses, XRPD, FTIR, and Raman combined with ab initio calculations

Tris(glycinato)chromium(III) monohydrate [Cr(C₂H₄NO₂)₃·H₂O] crystals were grown through the slow solvent evaporation method. The crystals were studied by Fourier transform infrared (FTIR) and Raman spectroscopy at room temperature. The assignments of vibration modes were performed using the Density Functional Theory (DFT). Thermal analyses (TGA, DTA, and DSC), X-ray diffraction (XRD), and Raman were used to study the phase changes on the crystals under high- and low-temperature conditions. Temperature-dependent XRPD measurements were carried out in the interval of 473-12 K. Several changes were observed in the patterns, like the appearance of new peaks and the disappearance of peaks occurring within 373-393 K due to water loss. In addition, the Raman measurements were performed in the 423-10 K interval. Several changes on the inter and intramolecular vibration bands during the cooling, such as decreasing bands' intensities, the appearance of vibration modes, and discontinuities on the modes' behavior, were observed. These spectral modifications occurred at about 370 K and within 120-220 K, thus, confirming that the crystals undergo two phase changes, one being structural and the other one conformational, respectively, at high- temperature and low-temperature conditions. Finally, thermal investigations corroborated the structural and vibrational results under high temperatures.

Antibacterial and antibiotic modifying activity, ADMET study and molecular docking of synthetic chalcone (E)-1-(2-hydroxyphenyl)-3-(2,4-dimethoxy-3-methylphenyl)prop-2-en-1-one in strains of Staphylococcus aureus carrying NorA and MepA efflux pumps

A large number of infections are caused by multi-resistant bacteria worldwide, adding up to a figure of around 700,000 deaths per year. Because of that many strategies are being developed in order to combat the resistance of microorganisms to drugs, in recent times, chalcones have been studied for this purpose. Chalcones are known as α, β-unsaturated ketones, characterized by having the presence of two aromatic rings that are joined by a three-carbon chain, they are a class of compounds considered an exceptional model due to chemical simplicity and a wide variety of biological activities, which include anticancer, anti-inflammatory, antioxidants, antimicrobials, anti-tuberculosis, anti-HIV, antimalarial, anti-allergic, antifungal, antibacterial, and antileishmanial. The objective of this work was evaluate the antibacterial and antibiotic modifying activity of chalcone (E)-1-(2-hydroxyphenyl)-3-(2,4-dimethoxy-3-methylphenyl)prop-2-en-1-one against the bacteria Staphylococcus aureus carrying a NorA and MepA efflux pump. The results showed that chalcone was able to synergistically modulate the action of Norfloxacin and Ethidium Bromide against the bacteria Staphylococcus aureus 1199B and K2068, respectively. The theoretical physicochemical and pharmacokinetic properties of chalcone showed that the chalcone did not present a severe risk of toxicity such as genetic mutation or cardiotoxicity, constituting a good pharmacological active ingredient.

Mechanism of the lethal effect of Riparin E against bacterial and yeast strains

Riparins are alkamides naturally found in the fruits of Aniba riparia (Nees) Mez, but currently synthetic molecules as Riparin E (Rip-E) can be obtained. Potential biological of Rip-E as schistosomicidal agent against Schistosoma mansoni worms, as well as against Staphylococcus aureus strains has already been described. However, the mechanism of action related to antimicrobial activity of Rip-E against bacterial or fungi species has not yet been reported. This study had as objective to evaluate the Rip-E antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as against yeast species of clinical importance. Minimal inhibitory concentrations of the compound against bacterial and yeast strains were determined by microdilution method. To verify if a possible lethal effect caused by Rip-E were related to plasma membrane damage, microbial cells treated with Rip-E were stained with 7-aminoactinomycin D (7-AAD) and analyzed by flow cytometry. Rip-E showed a bactericide effect against Gram-positive species S. aureus and S. epidermidis, as well as, against Gram-negative species Escherichia coli and Salmonella enterica Typhimurium, but was inactive against Pseudomonas aeruginosa. Moreover, Rip-E showed activity against fungi species Candida albicans and C. tropicalis. S. aureus, E. coli and C. albicans cells treated with Rip-E were marked with 7-aminoactinomycin D (7-AAD) indicating that Rip-E can cause plasma membrane damage, acting as a potential microbicide agent for prevention or treatment of infectious diseases.

Chalcones Isolated from Arrabidaea brachypoda Flowers as Inhibitors of NorA and MepA Multidrug Efflux Pumps of Staphylococcus aureus

Bacterial resistance to antibiotics has become a public health issue around the world. The present study aimed to evaluate the antibacterial activity of chalcones isolated from flowers of Arrabidaea brachypoda, and their potential as efflux pump inhibitors of Staphylococcus aureus efflux pumps. Microdilution assays were performed with natural products from A. brachypoda. Chalcones 1, 3, 4, and 5 did not show intrinsic antimicrobial activity against all S. aureus strains tested, but they were able to potentiate the Norfloxacin action against the SA1199-B (norA) strain, with a better modulating action for the 4 trimethoxylated chalcone. All chalcones were also able to potentiate the action of EtBr against SA1199-B strain, suggesting a potential NorA inhibition. Moreover, chalcone 4 was able to interfere in the activity of MepA, and interfered weakly in the QacA/B activity. Molecular docking analyzes showed that tested chalcones are capable of binding in the hydrophobic cavity of NorA and MepA, in the same Norfloxacin binding site, indicating that chalcone 4 compete with the antibiotic for the same NorA and MepA binding sites. Association of chalcone 4 with Norfloxacin could be an alternative against multidrug resistant S. aureus over-productive of NorA or MepA.

High pressure Raman scattering of DL‑isoleucine crystals and DFT calculations

DL‑isoleucine single crystals were grown by the slow evaporation method at ambient temperature. Their vibrational properties were studied at ambient temperature as a function of pressure by Raman scattering. At ambient conditions the mode assignment was done in terms of the Potential Energy Distribution (PED) through density functional theory calculations. Both nitrogen and neon were used as pressure transmitting media. The pressure-dependent investigation shows modifications in the Raman spectra recorded between 30 and 3200 cm^-1 that were interpreted as phase transitions undergone by the crystal between 1.3 and 1.9 GPa and between 3.6 and 5.1 GPa. Finally, stress was simulated on the unit cell of the crystal from ambient up to 5.0 GPa.

Structural, vibrational and thermal studies on bis(l-glutaminato)copper(II)

Copper(II) complexes of amino acids have been widely studied as potentials medicines and dietary supplementation, so the knowledge about the metal-ligand sites, thermal stability and behavior of these complexes is an important subject of study. Although the Raman spectroscopy could help to elucidate the nature of the interactions into crystal there are only few information about vibrational study of this compound in the literature and no data depending on the temperature. In addition, there is no temperature-dependent X-ray diffraction study of this material. We report here Raman Spectroscopy and Powder X-ray Diffraction measurements, both as a function of temperature and as a way of studying the thermal stability of the material. After the synthesis of the sample and confirmation of its crystal structure by Powder X-ray Diffraction, Raman measurements were performed in the 70-3600 cm^-1 spectral region as a function of temperature from 10 up to 300 K. Some peaks become more evident during the cooling, due to a decrease in width and an increase in intensity. There is a discontinuity in the wavenumbers evolution around 110 K, that should be associated with a conformation of the structure. Optimized geometry and vibrational frequencies were obtained by means of Density Functional Theory and for the first time the analysis of the vibrational modes was done in terms of the Potential Energy Distribution. X-ray diffraction measurements as a function of temperature and Rietveld refinement showed discontinuities in the lattice parameters and degradation around 493 K (at air atmosphere) and 513 K (under vacuum). These results were corroborated by the thermal analysis which indicates that the compound is stable up to 493 K.

Pressure induced transformations in sorbic acid

This research reports a pressure dependent Raman study of the sorbic acid between 0.0 and 10.0GPa. The unpolarized Raman spectra were measured in the spectral range of 20-3000cm^-1. The high-pressure Raman scattering study of the sorbic acid showed that it underwent a gradual, disordering process. At the room temperature and at the ambient pressure conditions, the crystal structure of the sorbic acid belongs to the monoclinic system with a C2/c (C_2h⁶) space group. The pressure increase induced a higher disorder in the monoclinic unit cell, since a single bending mode, and only very broad stretching Raman modes are present at pressure of ~10GPa. Upon pressure release the high-pressure phase transforms directly into the ambient-pressure phase. The presence of the internal vibrational modes is a guarantee that the molecular structure is maintained. Beyond this, the presence of external modes shows that the crystal has a memory to reverse the process and suggest that the crystal, which was in high disorder (broad Raman bands), does not suffer decomposition in the crystalline structure. The DFT calculations for the sorbic acid were performed in order to understand the vibrational properties. The theoretical study showed that the volume of the unit cell and beta angle decrease significatively when passing from the 0.0GPa to 8.0GPa. The decreases in the volume and beta angle of this particular unit cell were supposed to induce the larger increase in the bandwidths of the observed bands, pointing to some disorder in the monoclinic phase.

Low-temperature Raman spectra of the 2-(α-methylbenzylamino)-5-nitropyridine crystal

The polar organic 2-(α-methylbenzylamino)-5-nitropyridine crystal (MBANP) has been studied by Raman spectroscopy at low temperatures (from 300 to 10K). The effect of temperature change on the vibrational spectrum is discussed with the aid of DFT calculations. The behavior of the Raman spectra indicates that MBANP molecules present a different conformation at low temperatures associated with the rotation of the phenyl and pyridine rings. Temperature-dependent X-ray measurements and differential scanning calorimetry (DSC) analysis were utilized as complementary techniques to investigate the structural stability of MBANP crystal.

Conformational change in the C form of palmitic acid investigated by Raman spectroscopy and X-ray diffraction

Fatty acids are substances found in most living beings in nature. Here we report the effect of the low temperature in the vibrational and structural properties of the C form of palmitic acid, a fatty acid with 16 carbon atoms. The Raman spectra were obtained in the temperature interval from 300 to 18K in the spectral range between 30 and 3100 cm(-1). The assignment of the duly observed bands was done based on the density functional theory. On cooling, the main changes observed in the lattice mode region of the Raman spectra were interpreted as a conformational modification undergone by the palmitic acid molecules in the unit cell. The X-ray diffraction measurements were obtained from 290 to 80K showing a slight modification in the lattice parameters at about 210K. Differential scanning calorimetry (DSC) measurements were recorded between 150 and 300K and no enthalpic anomaly in the DSC thermogram was observed. These techniques provided strong evidence of the conformational change in the molecules of palmitic acid at low temperatures.

Vibrational spectroscopy, ab initio calculations and Frontier Orbital analysis of 4,5,6,8,9-pentachloropyrimido-[1,2-a][1,8]naphthyridin-10-one

In this work we present a study of the vibrational spectra of 4,5,6,8,9-pentachloropyrimido-[1,2-a][1,8]naphthyridin-10-one, C11H2Cl5N3O, a substance belonging to the important pharmacological class of 1,8-naphthyridine derivatives. The Fourier transform infrared and the Fourier transform Raman spectra of the crystal were recorded at room temperature in the regions 400-4000 and 50-4000 cm(-1), respectively. Vibrational wavenumbers were predicted using Density Functional Theory calculations with the B3LYP functional on 6-31G(d,p) and 6-311++G(d,p) basis sets. The descriptions of the normal modes were made after calculating the potential energy distribution. Additionally, potential reaction sites were evaluated through Mulliken population and Frontier Orbital analysis.

Temperature-dependent vibrational spectroscopic study and DFT calculations of the sorbic acid

This work reports a temperature-dependent vibrational spectroscopic study of the sorbic acid (C6H8O2), as well as the mode assignment at ambient conditions, based on the density functional theory. Temperature-dependent vibrational properties have been performed in polycrystalline sorbic acid through both Raman and infrared spectroscopy in the 20-300 K and 80-300 K temperature ranges, respectively. These studies present the occurrence of some modifications in the Raman spectra that could be interpreted as a low temperature phase transition undergone by sorbic acid from the monoclinic phase to an unknown phase with conformational change of the molecules in the unit cell.