In vitro and in silico studies of terpenes, terpenoids and related compounds with larvicidal and pupaecidal activity against Culex quinquefasciatus Say (Diptera: Culicidae).

BACKGROUND: In order to develop new larvicidal agents derived from phytochemicals, the larvicidal activity of fifty molecules that are constituent of essential oils was evaluated against Culex quinquefasciatus Say. Terpenes, terpenoids and phenylpropanoids molecules were included in the in vitro evaluation, and QSAR models using genetic algorithms were built to identify molecular and structural properties of biological interest. Further, to obtain structural details on the possible mechanism of action, selected compounds were submitted to docking studies on sterol carrier protein-2 (SCP-2) as possible target. RESULTS: Results showed high larvicidal activity of carvacrol and thymol on the third and fourth larval stage with a median lethal concentration (LC50) of 5.5 and 11.1 µg/mL respectively. Myrcene and carvacrol were highly toxic for pupae, with LC50 values of 31.8 and 53.2 µg/mL. Structure-activity models showed that the structural property π-bonds is the largest contributor of larvicidal activity while ketone groups should be avoided. Similarly, property-activity models attributed to the molecular descriptor LogP the most contribution to larvicidal activity, followed by the absolute total charge (Qtot) and molar refractivity (AMR). The models were statistically significant; thus the information contributes to the design of new larvicidal agents. Docking studies show that all molecules tested have the ability to interact with the SCP-2 protein, wherein α-humulene and ß-caryophyllene were the compounds with higher binding energy. CONCLUSIONS: The description of the molecular properties and the structural characteristics responsible for larvicidal activity of the tested compounds were used for the development of mathematical models of structure-activity relationship. The identification of molecular and structural descriptors, as well as studies of molecular docking on the SCP-2 protein, provide insight on the mechanism of action of the active molecules, and the information can be used for the design of new structures for synthesis as potential new larvicidal agents.

Synthesis, electronic, and spectral properties of novel geranylated chalcone derivatives: a theoretical and experimental study.

Novel chalcone derivatives with different substituents attached to A and B-rings: hydroxyl, methoxyl, geranyl, and prenyl groups were synthesized. The obtained compounds were characterized by NMR, HRMS, UV-Vis, IR, and MS. The theoretical analysis was carried out in all the compounds using density functional theory (DFT) with the B3LYP, PBE0, and M06-2X functionals in combination with the 6-311G(d,p) Pople-type basis set. The excited state properties were calculated by time dependent density functional theory (TD-DFT) using the same methodology applied for the ground state properties. The calculated vertical absorption wavelengths (λmax) in gas phase and in ethanol as a solvent are consistent with the experimental ones, being the TD-DFT:B3LYP/6-311G(d,p) and PCM-TD-DFT:PBE0/6-311G(d,p) the best methodologies for these calculations with good approximation to the experimental values. The calculated reorganization energies indicated that, the four chalcone derivatives present an electron transfer character due to the smaller registered values. From these parameters it is proposed that these show an n-type semiconductor character. The localization of the frontier orbitals (HOMO and LUMO) shows that only the compound containing a hydroxyl group on the A-ring displays a marked delocalization favoring the charge-transfer process in this system. The HOMO-LUMO gap energies indicate that the inclusion of different donor groups in the rings does not improve the obtained values for this property. Graphical Abstract Relationship between spectroscopic and geometrical properties of chalcones were carried out using quantum-chemical calculations and compared with experimental values.

Use of essential oils and extracts from spices in meat protection.

The hydro distillation method was used in this study to get essential oils (EOs) from cumin (Cuminum cyminum L.), clove (Eugenia caryohyllata) and Elecampane (Inula helenium L.) and the co-hydro distillation method (addition of fatty acid ethyl esters as extraction cosolvents) to get functional extracts (EFs). The MIC (Minimum Inhibitory Concentration) and the MBC (Minimum Bactericidal Concentration) were determined on five pathogenic strains (Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, Yersinia enterocolitica, Campylobacter jejuni, Clostridium perfringens, Staphylococcus aureus and Toxoplasma Gondi). The results showed that essential oils of cumin and clove and their functional extracts are effective on concentrations from 500 mg/L to 750 mg/L. The essential oils with functional extracts were used on meat samples at three different concentrations: 750, 1,500 and 2,250 µL. The cumin essential oil produced a reduction of 3.78 log UFC/g with the application of 750 µL, the clove essential oil produced a reduction of 3.78 log UFC/g with the application of 2,250 µL and the cumin and clove functional extracts got a reduction of 3.6 log UFC/g. By chromatography, eugenol was identified in the clove oil, cuminaldehyde in the cumin oil and the isoalactolactones and alactolactones in the elecampane oil as main compounds on the chemical composition of the essential oils and functional extracts obtained.

Hexavalent chromium reduction by bacterial consortia and pure strains from an alkaline industrial effluent.

AIMS: To characterize the bacterial consortia and isolates selected for their role in hexavalent chromium removal by adsorption and reduction. METHODS AND RESULTS: Bacterial consortia from industrial wastes revealed significant Cr(VI) removal after 15 days when incubated in medium M9 at pH 6·5 and 8·0. The results suggested chromium reduction. The bacterial consortia diversity (T-RFLP based on 16S rRNA gene) indicated a highest number of operational taxonomic units in an alkaline carbonate medium mimicking in situ conditions. However, incubations under such conditions revealed low Cr(VI) removal. Genomic libraries were obtained for the consortia exhibiting optimal Cr(VI) removal (M9 medium at pH 6·5 and 8·0). They revealed the dominance of 16S rRNA gene sequences related to the genera Pseudomonas/Stenotrophomonas or Enterobacter/Halomonas, respectively. Isolates related to Pseudomonas fluorescens and Enterobacter aerogenes were efficient in Cr(VI) reduction and adsorption to the biomass. CONCLUSIONS: Cr(VI) reduction was better at neutral pH rather than under in situ conditions (alkaline pH with carbonate). Isolated strains exhibited significant capacity for Cr(VI) reduction and adsorption. SIGNIFICANCE AND IMPACT OF STUDY: Bacterial communities from chromium-contaminated industrial wastes as well as isolates were able to remove Cr(VI). The results suggest a good potential for bioremediation of industrial wastes when optimal conditions are applied.

Evaluation of aroma generation of Lactococcus lactis with an electronic nose and sensory analysis.

There is an increased interest in exploring the potential of new Lactococcus lactis strains isolated from different natural ecosystems for the production of aroma compounds. Thus, the objective of this study was to screen the aroma generation of Lactococcus lactis strains isolated from different sources by an electronic nose and sensory evaluation for their potential use in starter cheese cultures. Twenty-three strains of Lactococcus lactis were isolated from dairy sources such as artisanal raw-milk cheeses, nondairy sources, and commercial starter cultures (industrial). All the strains were assessed for their ability to produce aromas by an electronic nose and sensory analysis after their incubation in milk. Some phenotypic characteristics of technological importance such as lactose fermentation, proteolytic activity, and citrate utilization were also evaluated. Lactococcus lactis strains showed clear phenotypic differences related to their isolation source. Strains isolated from raw-milk dairy products or commercial starter cultures presented faster lactose fermentation and proteolytic activity than those presented by strains isolated from nondairy sources. Additionally, strains isolated from dairy and nondairy sources presented better citrate utilization than strains isolated from commercial dairy starters. On the other hand, there was not a clear relationship between the source of isolation and the ability of lactococci strains to produce aroma. Principal components analysis of electronic nose data revealed 4 distinctive groups based on aroma profiles. Additionally, odor intensity scores (yogurt-like and Fresco cheese-like) for these 4 groups revealed the nature of their differences. In general, strains from dairy products presented intense yogurt-like and Fresco cheese-like aromas, with the latter being the most intense for one specific strain. On the other hand, the majority of wild strains from nondairy sources presented a stronger yogurt-like aroma, whereas industrial strains presented low intensity for both aroma descriptors. Additionally, an aroma potentiation effect was observed when mixtures of 2 lactococci strains isolated from different sources acted together.

TEM evidence of ultrastructural alteration on Pseudomonas aeruginosa by photocatalytic TiO2 thin films.

The antibacterial efficiency of longwave UV-irradiated TiO(2) thin films as well as the ultrastructural damage on bacterial cells was evaluated using Pseudomonas aeruginosa as a model. The quantitative antibacterial efficiency assays showed a bacterial inhibition in the range of 32-72% at different times of irradiation. Transmission electron microscopy (TEM) was used to detect the effect of irradiation of TiO(2) thin films on the ultrastructure of the bacterial cell in order to reveal possible cellular damage. After 40 min irradiation, an abnormal cellular division was observed: instead of a normal septum, an 'elongated bridge' was formed. At a longer irradiation time, wavy structures all around the outer cell membrane were observed, and also some bubble-like protuberances, which expelled inner material. The mechanism of irreversible bacterial cell damage caused by the photocatalytic effect of TiO(2) could be related to abnormal cell division, aside from the reported physicochemical alteration of the cell membrane.

Photoinduced bactericidal activity against Pseudomonas aeruginosa by TiO(2) based thin films.

The photoinduced bactericidal capacity of TiO(2) based films was evaluated, using as model organism Pseudomonas aeruginosa. Thin films were obtained by spray pyrolysis; they included undoped, Cu doped, and Al doped TiO(2). Scanning electron microscopy was used to observe the final effect of the irradiated films upon the bacteria. Depending on the composition and characteristics of the films, quantitative experiments show that bacterial inhibition varies between 28 and 96%. The order of magnitude of the average quantum yield of the films was determined between 10(-9) and 10(-11) inhibited bacterial per photon.