A method for disrupting conidia of Neurospora

Method for disrupting conidi

Catabolite effects on enzymes

Catabolite effects on enzyme

Purification of glutomine synthetase

Purification of glutomine synthetas

Selecting RNA aptamers for synthetic biology: investigating magnesium dependence and predicting binding affinity.

The ability to generate RNA aptamers for synthetic biology using in vitro selection depends on the informational complexity (IC) needed to specify functional structures that bind target ligands with desired affinities in physiological concentrations of magnesium. We investigate how selection for high-affinity aptamers is constrained by chemical properties of the ligand and the need to bind in low magnesium. We select two sets of RNA aptamers that bind planar ligands with dissociation constants (K(d)s) ranging from 65 nM to 100 microM in physiological buffer conditions. Aptamers selected to bind the non-proteinogenic amino acid, p-amino phenylalanine (pAF), are larger and more informationally complex (i.e., rarer in a pool of random sequences) than aptamers selected to bind a larger fluorescent dye, tetramethylrhodamine (TMR). Interestingly, tighter binding aptamers show less dependence on magnesium than weaker-binding aptamers. Thus, selection for high-affinity binding may automatically lead to structures that are functional in physiological conditions (1-2.5 mM Mg(2+)). We hypothesize that selection for high-affinity binding in physiological conditions is primarily constrained by ligand characteristics such as molecular weight (MW) and the number of rotatable bonds. We suggest that it may be possible to estimate aptamer-ligand affinities and predict whether a particular aptamer-based design goal is achievable before performing the selection

OPTIMIZATION AND CHARACTERIZATION OF ION ACTIVATED OCULAR IN-SITU GEL FORMULATION FOR BACTERIAL CONJUNCTIVITIS

Objective: The present research work aims at describing the formulation, optimization and evaluation of ion activated ocular in-situ gel of gatifloxacin for treatment of bacterial conjunctivitis so as to overcome patient inconvenience, precorneal drug elimination, variation in efficacy, vision blurring and frequent instillation associated with conventional eye drops and ointments. Methods: In-situ gel was prepared using gellan gum as an ion activated phase transition polymer and HPMC K100M as release retardant. Gatifloxacin was characterized by spectrophotometry. Crystalline state of the drug was determined using X Ray Diffraction study. The developed formulation exhibited instantaneous gel formation in simulated lacrimal fluid (pH 7.4), which was further evaluated for its rheology, irritancy parameters, in vitro release, trans-corneal permeation and antimicrobial activity. Results: Gatifloxacin exhibited λmax 286 nm obeying Beer Lambert’s law and pH-dependent solubility at a pH range of 2 to 4. 0.6% gellan gum and 0.4% HPMC K100M were optimized in the formulation which exhibited a viscosity of 55 cps in sol form and 325 cps in gel form with pseudoplastic behavior and prolonged in vitro release. Permeation of formulation was 75.8% in 7 h with log P of drug 0.59. Developed isotonic and non-irritant formulation had a lower apparent permeability coefficient of 8.15 x 10-5 cm/sec as compared to marketed formulation. Conclusion: A Formulation can be viewed as an efficacious medicine by virtue of its higher zone of inhibition, ability to enhance precorneal residence time and consequently ocular bioavailability with lesser frequency of administration attributed to slow and prolonged diffusion of the drug from the polymeric solutions

The Band Gap in Silicon Nanocrystallites

The gap in semiconductor nanocrystallites has been extensively studied both theoretically and experimentally over the last two decades. We have compared a recent ``state-of-the-art'' theoretical calculation with a recent ``state-of-the-art'' experimental observation of the gap in Si nanocrystallite. We find that the two are in substantial disagreement, with the disagreement being more pronounced at smaller sizes. Theoretical calculations appear to over-estimate the gap. Recognizing that the experimental observations are for a distribution of crystallite sizes, we proffer a phenomenological model to reconcile the theory with the experiment. We suggest that similar considerations must dictate comparisons between the theory and experiment vis-a-vis other properties such as radiative rate, decay constant, absorption coefficient, etc.Comment: 5 pages, latex, 2 figures. (Submitted Physical Review B

Submicron gate InP power MISFET's with improved output power density at 18 and 20 GHz

The microwave characteristics are presented at 18 and 20 GHz of submicron gate indium phosphide (InP) metal-insulator-semiconductor field-effect transistors (MISFET's) for high output power density applications. InP power MISFET's were fabricated and the output power density was investigated as a function of drain-source spacing. The best output power density and gain were obtained for drain-source spacing of 3 microns. The output power density is 2.7 times greater than was previously measured for InP MISFET's at 18 and 20 GHz, and the power-added efficiency also increased

Electron beam induced damage in PECVD Si3N4 and SiO2 films on InP

Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectic. The electron beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage