RESUMEN
Quorum sensing (QS) is a major controller of virulence and biofilm formation in pathogenic bacteria. The aim of the research was to screen novel synthetic compounds (18) from 2 series (Pyrazole and Diene dione) for quorum sensing and biofilm inhibitory potential against resistant pathogens isolated from patients with chronic sinusitis. Most of the compounds have documented zone of inhibition against Gram positive strains Staphylococcus aureus, Enterococcus faecalis and moderate activity against Gram negative Klebseilla pneumoniae and Proteus mirabilis in comparison with standard antibiotic. Compounds Q1 and Q7 have given the maximum zone of inhibition 18 and 20 mm with MICs 0.312 mg/mL and .156 mg/mL against S aureus and E faecalis, respectively. Some compounds were equally potent at inhibiting the formation of biofilm which later established by phase contrast microscopy. Regarding quorum sensing inhibition, the tested concentration of synthetic compound UA3 0.313 mg/mL inhibited violacein production without decreasing Chromobacterium pseudoviolaceum count which was significantly lower than determined MIC's. It was depicted from the results that selected compounds exhibited low level of cytotoxicity toward human red blood cells. Hence, these findings revealed that most novel compounds were effective antibacterial, whereas compound UA3 has shared significant anti-quorum sensing potential against Chromobacterium pseudoviolaceum.
RESUMEN
Sinusitis or rhinosinusitis is inflammation of the paranasal sinuses which can be due to autoimmune, allergy, and infection problems. Current study was aimed to evaluate the antibiofilm and antibacterial potential of different varieties of A sativum. Four different varieties (China white, China pink, Desi white, and Desi pink) were used and extracted with methanol and water. Results of antioxidant analysis of A sativum extracts showed that all varieties of garlic have considerable quantity of flavonoids with significant DPPH inhibition and reductive potential. Antibacterial activity of A sativum extracts was tested against different Gram negative and Gram-positive sinusitis isolates. All the sinusitis isolates were susceptible to both methanolic and aqueous extracts of different varieties of A sativum with least MIC values. Antibiofilm potential of extracts against sinusitis isolates was evaluated through crystal violet assay, and all extracts of A sativum were significantly effective against destruction of microbial biofilm. In summary, A sativum extracts possess effective antibacterial and antibiofilm activity against sinusitis isolates and can be utilized for prevention of drug resistance against sinusitis infections and further evaluation is necessary.
RESUMEN
The aurivillius family of compounds SrBi4Ti4O15 (SBTi) and SrBi4Ti3.8Nb0.2O15 has been prepared using solid state reaction techniques. The niobium doping enhances the value of the dielectric constant, but decreases the phase transition temperature and grain size of SBTi. Grain conductivity evaluated from the impedance data reveals that Nb doping increases the resistance of grains which indicates the decrease in oxygen vacancies. The negative temperature coefficient of resistance shown by the grain boundary conductivity is explained using the Heywang-Jonker model. The variation of ac conductivity with frequency is found to obey Jonscher's universal power law. The frequency exponent (n), pre-exponential factor (A), and bulk dc conductivity (σ dc) are determined from the fitting curves of Jonscher's universal power law. From the frequency exponent (n) versus temperature curve, we conclude that the conduction mechanism of SBTi changes from large-polaron tunneling (300-475 °C) to small-polaron tunneling (475-550 °C), and in that of the niobium doped it is small-polaron tunneling (300-375 °C) to correlated band hopping (375-550 °C). Activation energies have been calculated from different functions such as loss tangent, relaxation time, grain and grain boundary conductivities, and ac and dc conductivity. The activation energies reveal that conductivity in the sample has contributions from migrations of oxygen vacancies, bismuth ion vacancies, electrons ionized from strontium vacancies, strontium ion vacancies and valence fluctuations of Ti4+/Ti3+ ions.
RESUMEN
The largest piezoelectric properties, d33 = 416 pC/N and 490 pC/N, in KxNa1-xNbO3 ceramics have been reported for compositions close to polymorphic phase transition (PPT); however, they also have Curie temperatures, TC, of around 217-304 °C, considerably lower than those of undoped KNN ceramics (420 °C). High d33 along with high TC remains the ideal choice for applications but, unfortunately, not attained up to now. Here, we show that using KNN single crystals as seeds for template grain growth (TGG) of KNN ceramics enables dramatic improvements in the electromechanical properties while maintaining a high TC. The (001)-oriented (K0.5Na0.5)0.98Li0.02NbO3 ceramics engineered by TGG using (K0.5Na0.5)NbO3 crystals as templates exhibit a high d33 of 280 pC/N while maintaining the high TC of 430 °C. Enhanced piezoelectricity is attributed to long-range ordered ferroelectric domain patterns consisting of 90° and 180° domains, similar to single crystals. It is the first time that pairing high d33 and high TC in KNN, keeping a high PPT temperature, is achieved. This study is an unequivocal proof that it is possible to maximize d33, keeping a high TC in KNN without resorting to heavily doped compositions. This work opens the door to high-performance, rare-earth free, compositionally simple lead-free and low-cost electromechanical compounds, which can largely expand lead-free piezoelectrics applications.
RESUMEN
The relationship between charge transport, defects and ferroelectric response is established for K0.5Na0.5NbO3 (KNN) and Mn-doped KNN ceramics. At room temperature the conduction in KNN is associated with hole transport and can be suppressed by Mn doping. Because of that a less leaky ferroelectric hysteresis loop is obtained for Mn-doped KNN. At high temperatures the conduction is dominated by the motion of ionized oxygen vacancies, the concentration of which increases with Mn doping. This work adds relevant information on KNN and leverages its potential application.
