Photodegradation study of sodium usnate solution: influence of pH

Photodegradation of 2.6 × 10^-5 M aqueous solutions of sodium usnate at various pH was studied. Photodegradation appeared to follow first-order kinetics and was found to be pH dependent. The degradation rate constant was calculated to be 9.20 × 10^-4 min^-1, 5.93 × 10^-4 min^-1, 9.69 × 10^-4 min^-1, and 9.88 × 10^-4 min^-1 at pH 6, pH 7, pH 8, and pH 9, respectively.     

New Ultraviolet spectrophotometric method for the estimation of nimesulide

Two simple and accurate ultraviolet (UV) spectrophotometric methods with better detection range for estimation of nimesulide in pure form and in solid dosage form were developed in the present studies using 50% v/v and 100% v/v acetonitrile as the solvent system. The linearity range of nimesulide in both the methods was found to be 10-50 μg/ml at a λ_max of 300 nm. The linear regression equations obtained by the least-square regression method are Abs = 1.33 × 10^-1. Conc + 1.89 × 10^-1 in 50% v/v acetonitrile and Abs = 1.05 × 10^-1. Conc + 1.14 × 10^-1 in 100% v/v acetonitrile. The detection limit as per the error propagation theory was found to be 0.46 μg/ml and 1.04 μg/ml, respectively, in 50% v/v and 100% v/v acetonitrile. The developed methods were employed with high degree of precision and accuracy for the estimation of total drug content in three commercial tablet formulations of nimesulide. The results of the analysis were validated statistically and by recovery studies.     

An electron diffraction study of the ZnIn2Se4 crystal structure: A novel phase

A novel layered-structure ZnIn₂Se₄ phase has been obtained. Texture electron diffraction patterns aid in the identification of a crystal structure with lattice parameters a = 4.045 Å and c = 52.29 Å, space group R m, and z = 4.5. Crystal electron diffraction patterns displayed superstructural reflection, thus indicating a √3-fold increase in the a parameter. The similirity of reflection locations and intensities both on the crystal rotation electron diffraction pattern and on texture electron diffraction patterns showed that no phase transition occurred on specimen pounding. Electrophysical and optical parameters (E_g = 1.68 eV; N = 8 × 10²² m^-3; = 0.1Ωm) are studied at 300 K. The Hall coefficient is constant (R_H = 7.2 × 10^-5m³C^-1, mobility μ = 8 × 10^-3m²V^-1s^-1 at 200–300 K.     

Determination of the Acidic Degradation Products, Acetic, Propionic, Butyric, and Phthalic Acid in Aqueous Pseudolatexes of Cellulosic Esters by High Performance Liquid Chromatography

An isocratic, reversed-phase HPLC method was developed to quantify the organic acids, acetic, propionic, butyric, and phthalic acid, formed as a result of ester hydrolysis, in pseudolatexes of cellulosic esters. Colloidal dispersions of cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate were prepared by a microfluidization-solvent evaporation method. Dispersions of cellulose acetate phthalate were prepared by redispersion of a spraydried commercial pseudolatex. The acids were detected at 210 nm, the mobile phase being 0.025 M phosphate buffer: methanol (80:20 v/v%, pH 3.0). The peak height response was linear over the studied concentration range of 2 - 10 mM/L for the aliphatic acids and 20-100 μM/L for phthalic acid. The minimum detectable quantities for acetic, propionic, butyric, and phthalic acid were 0.02 mM/L, 0.05 mM/L, 0.1 mM/L, and 0.0005 mM/L, corresponding to a % change in acetyl, propionyl, butyryl, and phthalyl content of 4.0 × 10⁴, 1.2 × 10³, 2.9 × 10³, and 2.8 × 10^-5 for a 30% w/v pseudolatex. The colloidal polymer particles were separated by ultracentrifugation, filtration, or flocculation with aluminum chloride solution before analysis of the aqueous phase. Similar acid concentrations were obtained for the three separation methods. The recovery from spiked samples was almost complete for acetic, approximately 90% for propionic acid, and less than 80% for butyric acid.     

Transport of insulin in modified Valia-Chien chambers and Caco-2 cell monolayers

The transport characteristics of insulin were investigated using two different absorption models. Using the modified Valia-Chien chambers, permeability coefficients of insulin in the duodenum, jejunum, and ileum were 0.71 × 10^-7, 7.11 × 10^-7 and 9.45 × 10^-7 cm/s, respectively. In the Caco-2 cell monolayers, the bidirectional transepithelial fluxes of insulin across Caco-2 cell line showed symmetry. Confocal laser scanning microscopy visualized that FD-4 and FITC-insulin were mainly located in the paracellular route. It is evident that the lower intestine might be an advantageous region, and absorption enhancer that helps open tight junctions between cells should be used for oral delivery of insulin.     

GLC and Radiometric Determination of Hydrolysis Rate Constants of [[2-[4-(Methoxycarbonyl) 1) Benzamido]Diethyl]Triamino] Methylated Polystyrene

The rate constants of the hydrolysis of the methyl ester in 3N HC1 as function of temperature was determined and found to be in the range of 1.3 × 10^-2 to 1.2 × 10^-1 h^-1 at 40 and 60 C respectively. The rate constants were determined by GLC on Pola-pack-Q and by a radiotracer technique.     

Degradation of tobramycin in aqueous solution

The kinetics of degradation of tobramycin (Ne-De-Ka) in aqueous solution was studied as a function of pH. Tobramycin hydrolyzes in acidic solution to yield kanosamine (Ka-OH) and nebramine (Ne-De-OH) with a pseudo first-order rate constant of 2.7 × 10^-6 s^-1 in 1 N HCl at 80°C. The activation energy for the acid catalyzed hydrolysis is 32 kcal mol^-1. In basic solution, the hydrolysis products are deoxystreptamine (De-OH), nebramine (Ne-De-OH) and deoxystreptamine-kanosaminide (HO-De-Ka). The pseudo first-order rate constant for the hydrolysis in 1 N KOH is 1 × 10^-8 s^-1 at 80°C. The activation energy for the base catalyzed hydrolysis is 15 kcal mol^-1. Tobramycin is very stable towards hydrolysis at neutral pH; however, it rapidly oxidizes giving several products including De-OH, Ne-De-OH, and HO-De-Ka. In pH 7 phosphate buffer (0.01 M), the t₉₀ value is 70 hr at 80°C.     

Characteristics of the radiation damage seen in the silicon microstrip detector of Fermilab experiment E771

The central region of the silicon microstrip detector used in Fermilab experiment E771 was subjected to a peak fluence of 9.5 × 10¹³ p/cm² induced by 800 GeV protons over a two-month period. Fourteen 300 μm thick planes manufactured by Micron Semiconductor were operated at bias voltages ranging from 84 to 109 V. Analysis of data from low intensity beam triggers taken near the end of the run shows that the mean pulse height from our amplifiers began to decline at a fluence of approximately 2 × 10¹³ p/cm² and fell to near zero by 6 × 10¹³ p/cm². We show that the use of fast amplifiers contributed to this early loss of signal.     

Determinatiom of the Rydrolysis of Quinolinium-I-Methyliocide-6-Carboxt-Methyl Ester by Glc

A CLC method for the determination of the hydrolysis of quiolinlues I-methyliodide-6-carboxy-mathylester is dascribed. GLC is parforsud on porous polymer composed of ethylvinylbenzena crose-linked with divinyl-bensen (Polapak-Q). The retention times of methyl alcohol and the internal standare (tertiary butanol) are 2.8 and 6.3 min., respectively. The- apparent pseudo-first order rate constants as a function of taparature (37.C and 50°C) in the presence of 6N HCl were calculated and found to be 2.6 × 10^-2 min^-1 and 2.7 × 10^-2 win-1 respactively.     

Gel Materials from Fullerene-Silane Compounds and their Optical Nonlinearities

Two fullerene-silane compounds and their corresponding gels were synthesized. The maximum molar ratio of C₆₀Si in the gel can reach a value of 1.6 × 10^-3. The optical nonlinearity of the obtained gel under picosecond excitation at 1.06μm has been studied primarily by the Z-scan technique.     

Investigation of the nucleation mechanism in bias-enhanced diamond deposition on silicon and molybdenum

Polycrystalline diamond films were deposited on Si and Mo substrates in a microwave plasma-enhanced chemical vapour deposition reactor employing bias-enhanced nucleation. The deposition process was subdivided into two consecutive steps: the pretreatment (bias-enhanced nucleation) and the diamond growth step. To investigate the nucleation process we kept the deposition parameters during the diamond growth step constant and only changed the parameters during the pretreatment. The methods employed to analyze the deposited films after the pretreatment step were electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy.

The nucleation density (N_D) on Si following the complete deposition cycle (pretreatment and diamond growth step) increases considerably from 5 × 10⁸ cm⁻² to 5 × 10¹⁰ cm⁻² with an increase in the substrate temperature during the pretreatment (T_p) in the temperature range from 680 to 750 °C. For T_p ≥ 770 °C continuous films are formed. The structure of the pretreatment deposit undergoes likewise considerable changes: if T_p exceeds 770 °C the appearance of an intense diamond plasmon at 34 eV is observed, indicative of an increase in the concentration of diamond crystallites embedded in an otherwise amorphous carbon matrix. Our experiments suggest that diamond crystallites formed during the pretreatment serve as nucleation centres for the subsequent diamond growth.

The same deposition parameters which result in the formation of a continuous diamond film on Si, yield only low nucleation densities on Mo. An increase in N_D from 6 × 10⁶ cm⁻² to 2 × 10⁸ cm⁻² can be achieved by raising the methane concentration [CH₄] in the gas phase during the pretreatment from 5 to 50% (T_p = 820 °C). The carbon concentration at the surface for the pretreatment deposit, determined by XPS analysis, increases likewise with [CH₄]. According to the EELS analysis the structure of the pretreatment deposit is comparable with disordered graphite or a-C and no diamond plasmon is observed. The high [CH₄] is required to form the Mo-carbide interface and balance the diffusion of carbon into the metal before the a-C layer can be formed.

The formation of nucleation centres during the bias-enhanced nucleation seems under these deposition conditions to proceed via different pathways on Si and Mo. While the nucleation on Si appears to be linked to the formation of diamond nanocrystals during the pretreatment, this is not the case for Mo.     

Stability of Mixtoxantrone Hydrochloride in Solution

A stability-indicating reversed-phase high performance liquid chromatographic method was developed for the detection of mitoxantrone HC1 and its degradation products under accelerated degradation conditions. The degradation kinetics of mitoxantrone HC1 in aqueous solution over a pH range of 1.18 to 7.20 and its stability in propylene glycol-or polyethylene glycol 400-based solutions were investigated. The observed rate constants were shown to follow apparent first-order kinetics in all cases. The pH-rate profile shows that maximum stability of mitoxantrone HC1 was obtained at pH 4.01. No general acid or base catalysis from acetate or phosphate buffer species was observed. The catalysis rate constants on the protonated mitoxantrone imposed by hydrogen ion water and hydroxy ion were determined to be 3.72 × 10 min^-1 5.64 × 10-min^-1 and 1.108 × 10^-2min^-1, respectively. The degradation rate constants of mitoxantrone affected by different ionic strength systems. Irradiation with 254 nm UV light at 25±0.5°C was found when canpared with the light-protected controls. Incorporation of nonaqueous propylene glycol or polyethylene glycol in the pH 4.01 mitoxantrone solution shows an increase in its stability at 502±0.5°C.     

Correlation Between Physico-Chemical Properties and Cohesive Behavior of Furosemide Crystal Modifications

Abstract

This study reports the influence of changes in crystal form, with subsequent changes in physicochemical properties, on the cohesive properties of furosemide powders. Two known polymorphs and three crystal habits were prepared by changing the crystallisation solvent and velocity. Crystallised products were characterised by their XRD profiles. Powder properties including solid-state photochemical reactivity, particle size and distribution, density, wettability and dissolution were measured. Fine particles of form I, mean size 3 μm, were extremely cohesive, mean size of agglomerates 108 μm, and poorly wettable, contact angle > 90°. Changes in the crystal habit of form I led to the crystallisation of large (mean size > 50 μm) tabular and rod shape, less cohesive but also poorly wettable (contact angle > 90°) particles. These large particles although not cohesive had poor dissolution properties. Milled particles with a mean size of smaller than 10 μm, obtained from the large crystals were again cohesive. The method of preparation of form II produced small plate like crystals, mean size 8 μm, fractionally more wettable, contact angle 75°, and not as cohesive, mean size agglomerates 25 μm. Milling to a mean size of 4 μm increased the cohesive properties because the mean size of agglomerates was then 53 μm. Different crystal habits of form I did not show a difference in degradation during the nucleation period, mean rate constant 1.4×10^?2 h^?1, and the growth period, mean rate constant 2.4×10^?2h^?1. In summary crystal modification improved the wettabillity and cohesive properties of furosemide particles without changing the solid-state stability of the drug. The dissolution properties of larger less cohesive particles were however poor and milling, to increase the surface area available for dissolution, increased the cohesive properties of particles.     

Quantitative analysis of tungsten, oxygen and carbon concentrations in the microcrystalline silicon films deposited by hot-wire CVD

In order for hot-wire chemical vapor deposition to compete with the conventional plasma-enhanced chemical vapor deposition technique for the deposition of microcrystalline silicon, a number of key scientific problems should be cleared up. Among these points, the concentration of tungsten (nature of the filament), as well as the concentration of oxygen and carbon (elements issued when vacuum is broken between two runs), should not exceed threshold values, beyond which electronic properties of the films could be degraded, as in the case of monocrystalline silicon. Quantitative chemical analysis of these elements has been carried out using the secondary ion mass spectrometry technique through depth profiles. It has been shown that for a high effective filament surface area (S_f=27 cm²), the W content increases steadily from 5×10¹⁴ to 2×10¹⁸ atoms cm⁻³ when the filament temperature T_f increases from 1500 to 1800 °C. For a fixed T_f, the W content increases with the effective surface area S_f. Thus, considering our reactor geometry, the W content does not exceed the detection limit (5×10¹⁴ atoms cm⁻³) when T_f and S_f are limited to 1600 °C and 4 cm², respectively. For O and C elements, under deposition conditions of high dilution of silane in hydrogen (96%), O and C concentrations approaching 10²⁰ atoms cm⁻³ have been obtained. The introduction of an inner vessel inside the reactor, the addition of a load-lock chamber and a decrease in substrate temperature to 300 °C have led to a drastic decrease in these contents down to 3×10¹⁸ atoms cm⁻³, compatible with the realization of 6% efficiency HWCVD μc-Si:H solar cells.     

Piroxicam benzoate--synthesis,HPLC determination,and hydrolysis

An improved method of piroxicam benzoate synthesis was described, and an isocratic reversed-phase high-performance liquid chromatography method for its determination was developed and fully validated. The method was found to be specific, precise (relative standard deviation 0.3%), accurate (mean recovery 99.9%), and robust. Limit of detection was estimated at 0.055 µg mL^-1 and limit of quantification at 0.185 µg mL^-1. The kinetics of piroxicam benzoate hydrolysis in aqueous buffer solutions (pH 1.1 and 10), simulated gastric and intestinal fluids was studied. The hydrolysis followed first-order kinetics. The following rate constants were obtained at pH 10: k = 1.8 × 10^-3 hr^-1 at 37°C and k = 3.4 × 10^-2 hr^-1 at 60°C. In acidic media, no significant hydrolysis was observed after 24 hr. During the 24-hr period in simulated intestinal fluid, only 10.9% of the starting ester was hydrolyzed.     

Excited-state absorption at 1.57 μm in U:CaF2 and Co:ZnSe saturable absorbers

Appreciable excited-state absorption (ESA) in U²⁺:CaF₂ and Co²⁺:ZnSe saturable absorbers was measured at λ=1.573 μm by optical transmission versus light fluence curves of 30–40 ns long pulses. The ground- and excited-state absorption cross-sections obtained were (9.15±0.3)×10⁻²⁰ and (3.6±0.2)×10⁻²⁰ cm², respectively, for U²⁺:CaF₂, and (57±4)×10⁻²⁰ and (12.5±1)×10⁻²⁰ cm² for Co²⁺:ZnSe. Thus, ESA is not negligible in U²⁺:CaF₂ and Co²⁺:ZnSe, as previously estimated.     

Storage Stability of Polyynes and Cyanopolyynes in Solution and the Effect of Ammonia or Hydrochloric Acid

The storage stability of an acetonitrile solution of polyynes and monocyanopolyynes was studied by liquid chromatographic analysis for about 50 days at room temperature in a closed Pyrex flask. Monocyanopolyynes decomposition starts immediately after their synthesis; the decomposition can be approximated by a pseudo-first-order kinetic law and the rate constant is dependent from the length of the monocyanopolyyne chains, being faster for longer chains. For instance, for HC₇N the decomposition rate is k=-3.4×10^-7 s^-1 but becomes -7.0×10^-5 s^-1 for HC₁₃N decay, 204 times faster than the decay of the former compound. Polyynes mixed with monocyanopolyynes in the same CH₃CN show an induction time before starting to decompose. The induction time appears linked to the decomposition of monocyanopolyynes, which seems to protect the polyynes from the decomposition. Once the monocyanopolyynes are vanished also the decomposition of polyynes starts with a slower kinetics than monocyanopolyynes and following the rule that longer chains disappear at higher speed than shorter chains. For example, the pseudo-first-order rate constant for C₈H₂ is k=-1.31×10^-8 s^-1. Ammonia exerts a deleterious effect on monocyanopolyynes. In fact, ammonia addition to an acetonitrile solution of monocyanopolyynes causes their immediate decomposition due to a nucleophilic addition of ammonia to the polyyne chains. Instead, hydrogen-teminated polyynes are much more resistant toward the nucleophilic addition of ammonia. Hydrochloric acid does not influence the stability of polyynes and monocyanopolyynes.     

Destruction of carbon disulfide in aqueous solutions by sonochemical oxidation

Carbon disulfide (CS₂) is toxic to animals and aquatic organisms, and can also decompose to carbonyl sulfide (OCS) and hydrogen sulfide (H₂S) in aqueous environment. The kinetics of the sonochemical degradation of aqueous CS₂ was studied in a batch reactor at 20 kHz and 20 °C, and the effects of process parameters (e.g. concentration, ultrasonic intensity, irradiating gas) investigated. The concentrations of unbuffered CS₂ solutions used were (6.4–7.0)×10⁻⁴, 10.5×10⁻⁴ and (13.2–13.6)×10⁻⁴ M and the intensities were varied from 14 to 50 W. The reaction rate was found to be zero-order and the rate constant for the degradation at 20 °C and 14W in air was 21.1 μM/min using the largest initial concentration range studied. At the same initial concentration range but at 50 W (39.47 W/m²) the degradation rate of CS₂ was 46.7 μM/min, more than two times that at 14 W (11.04 W/m²). The rate of CS₂ sonochemical degradation in the presence of the different gases was in the order of He>air≥N₂O>Ar; the rate with helium was found to be about three times that of argon. The formation of sulfate (SO₄²⁻) as reaction product with air as the irradiating gas was enhanced in the presence of hydrogen peroxide (H₂O₂) and inhibited in the presence of 1-butanol. The sonochemical oxidation of CS₂ may prove to be an efficient and environmentally benign way for the removal of this hazardous pollutant from natural water and wastewater.     

RADIATION CHEMICAL AND PHOTOPHYSICAL PROPERTIES OF C60(C4H8SO3Na)n IN AQUEOUS SOLUTION: A LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS STUDY

Optical absorption studies on aqueous solutions of C₆₀(C₄H₈SO₃Na)_n (n = 4-6) revealed deviation from the Beer-Lambert law in the 250-350 nm region, which is assigned to the formation of solute aggregates at concentrations higher than 1 × 10^-3 mol dm^-3. Dynamic light scattering experiments showed aggregates with an average size of ∼100 nm. The solute has a broad weak fluorescence emission (ϕ_f = 1.8 × 10^-3) in the 450-650 nm region, which remained independent of solute concentration. The broad transient absorption band in the 450-900 nm region (ε₆₆₀ = 2170 dm³ mol^-1 cm^-1), which formed immediately on laser flash photolysis (λ_ex = 355 nm, 35 ps), is assigned to singlet-singlet transition. It decays to a triplet excited state whose absorption is observed to depend strongly on solute concentration. In dilute solutions, an absorption band with λ_max = 590 nm is seen, and at high solute concentration a broad absorption in the 500-900 nm region is observed. The e_aq^- reacts with the solute with a bimolecular rate constant of 1.7 × 10⁸ dm³ mol^-1 s^-1 and forms weak broad absorption bands at 440, 540, 620, 870, 940, and 1020 nm. Isopropanol radicals also react with the solute with a bimolecular rate constant of 2.3 × 10⁸ dm³ mol^-1 s^-1 with the formation of a transient optical absorption spectrum similar to that observed on reaction with e_aq^- and assigned to a solute radical anion. The ^•H and ^-OH radicals react with bimolecular rate constants of 3.2 × 10⁹ and 4.4 × 10⁹ dm³ mol^-1 s^-1, respectively, and form transient absorption bands at 440, 510, and 660 nm. Based on electron transfer studies with suitable electron donor/acceptor substrates, the ranges of the reduction and oxidation potentials of the solute an estimated.     

INHIBITORY EFFECTS OF FULLERENE C60 DERIVATIVES ON ENDOTHELIUM-DERIVED RELAXATION IN RABBIT THORACIC AORTA

Inhibitory effects of newly synthesized fullerene C₆₀ derivatives 1 (C₆₀-bis(N,N-dimethylpyrrolidinium iodide)), 2 (C₆₀-proline-N-acetic acid) and 3 (C₆₀-ethylenediamine-N, N'-diacetic acid) on acetylcholine-induced relaxation in endothelium-intact rabbit thoracic aorta precontracted by phenylephrine (10^-6 M) were studied. Fullerene C₆₀ derivative 1 (3 × 10^-6 M), 2 (10^-5 M) and 3 (10^-5 M) reduced the maximum amplitude of the acetylcholine-induced relaxation without significantly changing the pD₂ values obtained from the concentration - response curves. In the presence of fullerene C₆₀ derivative 1 (10^-5 M) the acetylcholine-induced relaxation was eliminated and an acetylcholine-induced contraction was observed. These results suggest that fullerene C₆₀ derivative 1 strongly inhibits endothelium (nitric oxide)-dependent acetylcholine-induced relaxation in thoracic aorta of rabbit.