Antibacterial Effects of Flavonoids and Their Structure-Activity Relationship Study: A Comparative Interpretation

According to the latest report released by the World Health Organization, bacterial resistance to well-known and widely available antibacterial drugs has become a significant and severe global health concern and a grim challenge to tackle in order to cure infections associated with multidrug-resistant pathogenic microorganisms efficiently. Consequently, various strategies have been orchestrated to cure the severe complications related to multidrug-resistant bacteria effectively. Some approaches involved the retardation of biofilm formation and multidrug-resistance pumps in bacteria as well as the discovery of new antimicrobial agents demonstrating different mechanisms of action. In this regard, natural products namely alkaloids, terpenoids, steroids, anthraquinone, flavonoids, saponins, tannins, etc., have been suggested to tackle the multidrug-resistant bacterial strains owing to their versatile pharmacological effects. Amongst these, flavonoids, also known as polyphenolic compounds, have been widely evaluated for their antibacterial property due to their tendency to retard the growth of a wide range of pathogenic microorganisms, including multidrug-resistant bacteria. The hydroxylation of C5, C7, C3′, and C4′; and geranylation or prenylation at C6 have been extensively studied to increase bacterial inhibition of flavonoids. On the other hand, methoxylation at C3′ and C5 has been reported to decrease flavonoids’ antibacterial action. Hence, the latest information on the antibacterial activity of flavonoids is summarized in this review, with particular attention to the structure–activity relationship of this broad class of natural compounds to discover safe and potent antibacterial agents as natural products.     

Effect of styrene–acrylonitrile content on 0.5?M NaI/0.05?M I2 liquid electrolyte encapsulation for dye-sensitized solar cells

The effect of a gel polymer electrolyte (GPE) as the redox electrolyte used in dye-sensitized solar cells was studied. A GPE solution consisting of 0.5?M sodium iodide, 0.05?M iodine, and ethylene carbonate/propylene carbonate (1:1 w/w) binary solvents was mixed with increasing amounts of styrene–acrylonitrile (SAN). Bulk conductivity measurements show a decreasing trend from 4.54 to 0.83×10^?3?S?cm^?1 with increasing SAN content. The GPE exhibits Newtonian-like behavior and its viscosity increases from 0.041 to 1.093?Pa?s with increasing SAN content. A balance between conductivity (1.3?×?10^?3?S?cm^?1) and viscosity (1.4?Pa?s) is observed at 19?wt.% SAN. Fourier transform infrared spectroscopy detects elevated ring torsion at 706?cm^?1 upon the addition of SAN into the liquid electrolyte. This indicates that SAN does not bond with the liquid electrolyte. Finally, the potential stability window of 19?wt.% SAN, which ranges from ?1.68 to 1.38?V, proves its applicability in solar cells.     

Studies on coordination chemistry of a nitrogen–sulfur donor ligand with lighter and heavier metal ions and biological activities of its complexes

Complexes of S-benzyldithiocarbazate (SBDTC) with lighter and heavier metals, viz., Cr^III, Fe^III, Sb^III, Zr^IV, Th^IV and U^VI have been prepared and characterized by elemental analyses, conductivity measurements, and spectral studies. The complexes: [Cr(SBDTCA)₃],^** [Fe(SBDTCA)₃], [Sb(SBDTCA)₃], [Sb(SBDTCA)₂Cl · H₂O], [Zr(O)(SBDTCA)₂ · H₂O], [Th(SBDTCA)(NO₃)₃ · H₂O)], and [U(O)₂(SBDTCA)₂] were all prepared in alkaline media. They were all hexa-coordinated with bidentate, uninegative chelation of the ligand. [Fe(SBDTCA)₃], [Sb(SBDTCA)₃] and [Sb(SBDTCA)₂Cl · H₂O] were strongly effective against bacteria giving clear inhibition zones with Pseudomonas aeruginosa and Bacillus cereus. The compounds showed poor antifungal activity. The antimony complexes were strongly cytotoxic against leukemic cells with CD₅₀ values of 3.2–6.7 g cm^–3 as compared to the CD₅₀ value of 14.5 g cm^–3 of the free SbCl₃ molecule.     

Electrochemical impedance study of lithium-ion insertion into rice husk carbon

Electrochemical impedance spectroscopy (EIS) was employed to study electrochemical behaviors during Li-ion insertion into rice husk carbon. The impedance spectra consist of two depressed semicircles in the high and middle range frequency and an incline line at low frequency. The impedance spectra, obtained in the potential range 2.0 to 0.005 V were analyzed with an equivalent circuit model. Kinetic parameters such as the charge-transfer resistance and surface film resistance were evaluated and discussed. Paper presented at the International Conference on Solid State Science and Technology 2006, Kuala Terengganu, Malaysia, September 4–6, 2006.     

Enhancement of catalytic activity of titanosilicalite-1 - sulfated zirconia combination towards epoxidation of 1-octene with aqueous hydrogen peroxide

Summary Titanosilicalite-1 (TS-1) in combination with sulfated zirconia efficiently catalyzes the epoxidation of 1-octene with aqueous hydrogen peroxide. The presence of both octahedral zirconium and sulfate species in the catalysts enhances the epoxidation rates.     

EFFECT OF VERTICAL BAFFLES ON PARTICLE MIXING AND DRYING IN FLUIDIZED BEDS OF GROUP D PARTICLES

This study reports the effect of vertical baffles on the group D powder mixing and drying characteristics in a batch fluidized bed dryer. Results obtained in this study showed that operating the fluidized bed dryer with vertical baffles gave better particle mixing. This is due to the fact that the vertical baffles acted to limit the growth of small bubbles into large bubbles and the small bubbles caused more vigorous mixing in the bed of particles before finally erupting at the bed surface. Thus, insertion of vertical baffles is a useful way to process group D particles in a fluidized bed, especially when the fluidized bed is large.     

Theoretical and experimental studies of ion imprinted polymer for nitrate detection

Molecular imprinting is an approach to synthesize receptors with specific molecular recognition properties. A computational method was carried out to study interaction between template and monomer in prepolymerization mixture. The functional monomer and template complexes were optimized, at the minimum energy confirmation using Austin Model 1 semi empirical method within Restricted Hartree Fock formalism. The theoretical results showed that allylthiourea (functional monomer) has the largest interaction energy towards template (sodium nitrate) with the mole ratio of 4 : 1; functional monomer : template. The resulting polymers were characterized using Fourier Transform infrared spectroscopy, thermogravimetry analysis and field emission scanning electron microscopy. Rebinding experiments were carried out to evaluate binding capacity of the polymer. The adsorption data of ion imprinted polymer (IIP) were fitted with Langmuir-Freundlich isotherm model. Pseudo-second order kinetic model was used to describe the kinetic adsorption behavior of IIP. The experimental binding result showed good agreement with theoretical computation and the IIP was further used for nitrate ion detection. The results of membrane optimization indicated that the sensor, which composed of 30% polyvinylchloride, 60% nitrophenyl octyl ether as a plasticizer, 2% sodium tetraphenyl borate, and 10% IIP as ionophore exhibited an almost Nernstian slope with the limit of detection 3.9 × 10^-6 M. The fabricated sensor had shown good potential in nitrate detection with wide linear range, low limit of detection and found to have good selectivity towards nitrate ion over other anion.