ChemInform Abstract: CONCENTRATION AND SUBSTRATE DEPENDENT REACTION MECHANISMS IN THE METAL KETYL-ALKYL HALIDE SYSTEM, MAGNETOCHEMICAL ZERO-ORDER KINETICS AS EVIDENCE FOR A DIAMAGNETIC REACTIVE SPECIES AT HIGH KETYL CONCENTRATIONS, CATALYSIS BY TRANSITION

AbstractThe kinetics of copper deposition by the hydrogen-assisted reduction of bis(2,2,7- trimethyloctane-3,5-dionato)copper in supercritical carbon dioxide was studied as a function of temperature and precursor concentration. The growth rate was found to be as high as 31.5 nm/min. Experiments between 220 °C and 270 °C indicated an apparent activation energy of 51.9 kJ/mol. The deposition kinetics were zero order with respect to precursor at 250 °C and 134 bar and precursor concentrations between 0.016 and 0.38 wt.% in CO2. Zero order kinetics over this large concentration interval likely contributes to the exceptional step coverage obtained from Cu depositions from supercritical fluids.

Download Full-text

Spectroscopic Study of Photosensitized Oxidation of Polyisoprene

Rubber Chemistry and Technology ◽

10.5254/1.3535167 ◽

1977 ◽

Vol 50 (4) ◽

pp. 704-713 ◽

Cited By ~ 25

Author(s):

M. A. Golub ◽

M. L. Rosenberg ◽

R. V. Gemmer

Keyword(s):

Zero Order ◽

Double Bonds ◽

Photosensitized Oxidation ◽

The Third ◽

Type Process ◽

Zero Order Kinetics ◽

Hydroperoxide Formation ◽

Cis And Trans ◽

In Cis ◽

Suitable Measure

Abstract The microstructural changes which occur in cis- and trans-1,4-polyisoprenes and in squalene during photosensitized oxidation were investigated with the aid of infrared and proton and carbon-13 NMR spectroscopy. The singlet oxygenation of these isoprenic compounds resulted in allylic hydroperoxides with shifted double bonds, according to the expected “ene”-type process. In contrast to trans-1,4-polyisoprene and squalene, which displayed the three possible double bond shifts, cis-1,4-polyisoprene showed essentially two of the shifts (to di- and trisubstituted double bonds) and very little of the third (to exomethylene groups). A suitable measure of the extent of hydroperoxidation was afforded by the absorbance ratio, A3400/A1440≡A′. Similar correlations of A′ with oxygen uptake were obtained for the three isoprenic compounds, using chlorophyll or methylene blue as sensitizer. The use of rose bengal gave erratic results indicative of some autoxidation accompanying the hydroperoxide formation. The singlet oxygenation followed zero-order kinetics, the relative rates for cis- and trans-1,4-polyisoprenes being approximately 1.0:1.5.

Download Full-text

The catalytic decomposition of ethers on evaporated tungsten films

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1968.0024 ◽

1968 ◽

Vol 302 (1470) ◽

pp. 385-398 ◽

Cited By ~ 3

Keyword(s):

High Activity ◽

Water Vapour ◽

Metal Surface ◽

Initial Period ◽

Catalytic Decomposition ◽

Zero Order ◽

Transitional Period ◽

Zero Order Kinetics ◽

Rate Of Reaction ◽

Combined Action

The reactions of diethyl and di- n -propyl ethers have been studied in the presence of hydrogen on evaporated films of tungsten. In the temperature range from 200 to 260°C ethane and ethylene were formed from diethyl ether and small amounts of butenes were also produced. Each film had an initial high activity, especially for the formation of ethane, but the activity declined to a steady value during a transitional period. Subsequently, the decomposition of the ether occurred with zero order kinetics. A similar transitional period was observed during the decomposition of di- n -propyl ether but the change in the character of the reactions was more marked. Propane and propylene were formed initially, but very little further propane was produced after the initial period. If the surface of the tungsten was oxidized before exposure to ether, a high activity for the dehydration of the propyl ether was observed. Evidence from a number of experiments showed that irreversible changes were occurring to the catalyst during the transitional periods in which the metal surface was being converted to a different type of surface under the combined action of the ether and water vapour which was either added or formed by reaction. Most of the results could be interpreted on the assumption that two types of surface were formed—an oxidized surface of high activity for dehydration and an inactive surface covered by strongly adsorbed hydrocarbon residues. Subsidiary experiments were carried out with n -propanol on oxidized tungsten and evidence was found that the dehydration of the alcohol which was strongly adsorbed probably controlled the rate of reaction of the ether.

Download Full-text

Xanthan and Poly(vinyl alcohol) - Based Composite Films, as Supports for Chloramphenicol Immobilization

Eurasian Chemico-Technological Journal ◽

10.18321/ectj566 ◽

2017 ◽

Vol 3 (3) ◽

pp. 195

Author(s):

Alupei Iulian Corneliu ◽

Popa Marcel ◽

Hamcerencu Mihaela ◽

Savin Alexandru ◽

Abadie Marc Jean

Keyword(s):

Vinyl Alcohol ◽

Composite Films ◽

Three Dimensional ◽

Biological Action ◽

Zero Order ◽

Experimental Program ◽

Poly Vinyl Alcohol ◽

Knowing That ◽

Zero Order Kinetics ◽

Dimensional Network

The paper discusses a method for the realization of some polymer - drug systems in which the macromolecular support is represented by a three-dimensional network based on xanthan and poly(vinyl alcohol). Knowing that the drug (chloramphenicol) was to be inserted through a diffusion process, the support – selected according to an experimental program – had the highest degree of swelling. Several variants of chloramphenicol inclusion into the synthesized support are analyzed by studying the process kinetics. The study of chloramphenicol release from the inclusion products, in the form of films, indicated the installation of a “zero order” kinetics. The tests devoted to the system’s antimicrobial activity evidenced their biological action.

Download Full-text

SUSTAINED RELEASE MATRIX TABLETS OF DICLOFENAC SODIUM EMPLOYING KOLLIDON SR, PEG 6000, LACTOSE MONO HYDRATE AND EUDRAGIT S100 IN COLON TARGET

INDIAN DRUGS ◽

10.53879/id.54.10.10814 ◽

2017 ◽

Vol 54 (10) ◽

pp. 38-43

Author(s):

Ch. Taraka Ramarao ◽

◽

B. Srinivasa Rao ◽

J. Vijayaratana

Keyword(s):

Drug Release ◽

Diffusion Mechanism ◽

Diclofenac Sodium ◽

Zero Order ◽

Matrix Tablets ◽

Fickian Diffusion ◽

Colon Targeting ◽

Zero Order Kinetics ◽

Eudragit S100 ◽

Lag Period

Matrix Tablets, each containing 50 mg of diclofenac sodium, are prepared employing Kollidon SR by direct compression method. All the tablets were found to be non-disintegrating in acidic (pH1.2) and alkaline (pH 7.4) fluids. As such, the prepared tablets were of good quality with respect to drug content, hardness and friability. As the tablets formulated were non- disintegrating in acidic fluids, they are considered suitable for colon targeting. From the drug release study, it may be concluded that the (DK2) E2 formula of diclofenac sodium matrix tablets gives the desired release profile by showing a minimal release during the lag period of 5 h and complete release at the end of 12 h. The tablets having the optimised formula (DK2)E2, having 25% Kollidon SR with 5% of channelling agent (Eudragit S100 to that of Kollidon SR) showed minimal release of 27. 4% in the lag period of 5 hours and 99.3 % of the drug was released y the end of 12 h. The diclofenac sodium matrix tablets formulated by employing Kollidon SR and various channelling agents showed non-Fickian diffusion mechanism and followed zero order kinetics. The optimized formula (DK2) E2 follows Supercase II transport as mechanism for drug release and it follows zero order kinetics. Matrix tablets (DK2) E2 formulated employing 25% Kollidon SR and 5% Eudragit S100 are best suited to be used for colon targeting of diclofenac sodium.

Download Full-text

Ontogenic expression of acetylcholinesterase activity in trachealis of young swine

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1991.261.4.l322 ◽

1991 ◽

Vol 261 (4) ◽

pp. L322-L326 ◽

Cited By ~ 3

Author(s):

T. M. Murphy ◽

R. W. Mitchell ◽

I. J. Phillips ◽

A. R. Leff

Keyword(s):

Contractile Response ◽

Age Groups ◽

Acetylcholinesterase Activity ◽

Zero Order ◽

Maximal Inhibition ◽

Zero Order Kinetics ◽

Contractile Forces ◽

Ontogenic Expression ◽

Cholinergic Contraction

Previous investigations have demonstrated that cholinergic contraction of porcine tracheal smooth muscle (TSM) decreases between the second and tenth weeks of life. In this investigation, we hypothesized that the greater contractile response to acetylcholine (ACh) in TSM of 2-wk-old swine (2ws) vs. 10-wk-old swine (10ws) was the result of a relative decrease in activity of acetylcholinesterase (AChase). To examine this hypothesis, we assessed AChase activity directly in homogenates of TSM from eight 2ws and seven 10ws using a newly adapted method that measures the rate of cleavage of acetylthiocholine; enzyme activity was expressed as absorbance units per minute per milligram protein. The AChase from tissues of both age groups saturated at approximately 3 mM substrate. However, maximal AChase activity (Vmax) was significantly greater in 10ws than 2ws. Eadie-Hofstee analysis of enzyme kinetics revealed similar Michaelis-Menten constants for 2ws and 10ws. The concentration of physostigmine (PS), an inhibitor of cholinesterase, that elicited half-maximal inhibition of AChase activity also was similar for 2ws and 10ws. In separate studies, contraction of TSM strips was assessed in vitro at optimal resting length and expressed as a function of maximal force generation to potassium chloride. Strips of TSM from 2ws contracted with greater force than those of 10ws. After pretreatment with 10(-8) M PS, contractile forces were similar in 2ws and 10ws. We conclude that AChase activity measured directly in muscle homogenates is significantly reduced in TSM of 2ws vs. 10ws and that this may result in augmented contraction to ACh under conditions of zero-order kinetics.

Download Full-text

Ranitidine Loaded Biopolymer Floats: Designing, Characterization, and Evaluation

Journal of Chemistry ◽

10.1155/2017/6924601 ◽

2017 ◽

Vol 2017 ◽

pp. 1-12

Author(s):

Abdul Karim ◽

Muhammad Ashraf Shaheen ◽

Tahir Mehmood ◽

Abdul Rauf Raza ◽

Musadiq Aziz ◽

...

Keyword(s):

Drug Delivery ◽

Drug Release ◽

Lag Time ◽

Zero Order ◽

Release Profile ◽

Drug Release Profile ◽

Independent Variables ◽

Zero Order Kinetics ◽

Model Drug ◽

Predicted Values

The float formulation is a strategy to improve the bioavailability of drugs by gastroretentive drug delivery system (GRDDS). A drug delivery model based on swellable and reswellable low density biopolymers has been designed to evaluate its drug release profile using ranitidine (RNT) as a model drug and formulations have been prepared utilizing 32factorial designs. The drug release (DR) data has been subjected to various kinetic models to investigate the DR mechanism. A reduction in rate has been observed by expanding the amounts of PSG and LSG parts, while an expansion has been noted by increasing the concentration of tragacanth (TG) and citric acid (CA) with an increment in floating time. The stearic acid (SA) has been used to decrease the lag time because a decrease in density of system was observed. The kinetic analysis showed that the optimized formulation (S4F3) followed zero-order kinetics and power law was found to be best fitted due to its minimum lag time and maximum floating ability. The resemblance of observed and predicted values indicated the validity of derived equations for evaluating the effect of independent variables while kinetic study demonstrated that the applied models are feasible for evaluating and developing float for RNT.

Download Full-text

Oxidation of Benzyl Alcohols by the Laccase-Mediator System (LMS) a Comprehensive Kinetic Description

Holzforschung ◽

10.1515/hf.2001.008 ◽

2001 ◽

Vol 55 (1) ◽

pp. 47-56 ◽

Cited By ~ 1

Author(s):

A. Potthast ◽

T. Rosenau ◽

K. Fischer

Keyword(s):

Benzyl Alcohol ◽

Cation Radical ◽

Product Formation ◽

Zero Order ◽

Enzymatic Oxidation ◽

Second Phase ◽

Rate Law ◽

Zero Order Kinetics ◽

Mediator System ◽

Laccase Mediator System

SummaryInvestigations into the reaction kinetics of the laccase-mediator system (LMS) have been carried out. Two widely used mediators, 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS,3) and 1-hydroxybenzotriazole (HOBT,4), were compared by means of a model reaction, the oxidation of 2,4-dimethoxybenzyl alcohol (DMBA,1) to 2,4-dimethoxybenzaldehyde (DMA,2). The consumption of dioxygen was recorded electrochemically, substrate consumption and product formation were monitored by GLC.With ABTS as the mediator, the LMS reaction proceeded in two clearly distinguishable stages. The first phase is characterized by a fast decrease in oxygen with zero-order kinetics and no detectable formation of 2,4-dimethoxybenzaldehyde (2). ABTS is converted into oxidized species, the cation radical6and the dication7, respectively. In the second phase, oxygen consumption was considerably slower and followed a second-order kinetics, while the benzaldehyde was produced according to a zero-order rate law. According to the kinetic studies, the ABTS dication, but not the enzyme itself, is acting as the actual oxidant. The rate of oxidation product formation increased with increasing mediator / benzyl alcohol ratio. Less oxygen than the equivalent amount was consumed in the second reaction stage indicating that the oxidized ABTS formed in the first stage acts as an oxidant reservoir, being reduced to ABTS in turn.The LMS reaction with HOBT (4) as the mediator did not exhibit distinguishable phases, and was characterized by a comparatively slow oxygen uptake with zero-order kinetics throughout. Enzymatic oxidation of HOBT to the HOBT radical (5), which acts as the actual oxidant towards the benzyl alcohol, was the rate-determining step. The production of 2,4-dimethoxybenzaldehyde thus followed a zeroorder rate law as well. The reaction rate increased with increasing HOBT / benzyl alcohol ratios. Increasing concentrations of4caused less oxygen to be consumed per equivalent of benzaldehyde formed, indicating the occurrence of another reaction pathway at high mediator charges. At low HOBT / benzyl alcohol ratios the HOBT radical (5) acts as one-electron oxidant and is reduced to HOBT in a reversible process. In contrast, at higher HOBT / benzyl alcohol ratios5acts as a three-electron oxidant, being irreversibly reduced to benzotriazole. At commonly employed mediator concentrations, a superposition of both mechanisms results. The pure borderline cases can only be observed at HOBT / benzyl alcohol ratios below 1 and above 6, respectively.

Download Full-text