scholarly journals Kinetics and mechanisms of catalyzed dual-E (antithetic) controllers

2021 ◽  
Author(s):  
Qaiser Waheed ◽  
Huimin Zhou ◽  
Peter Ruoff
Keyword(s):  
Ternary Complex ◽  
Reaction Kinetic ◽  
Zero Order ◽  
Control Engineering ◽  
Environmental Disturbances ◽  
Integral Control ◽  
Analysis And Design ◽  
Zero Order Kinetics ◽  
Ping Pong ◽  
Kinetic Mechanisms

Homeostasis plays a central role in our understanding how cells and organisms are able to oppose environmental disturbances and thereby maintain an internal stability. During the last two decades there has been an increased interest in using control engineering methods, especially integral control, in the analysis and design of homeostatic networks. Several reaction kinetic mechanisms have been discovered which lead to integral control. In two of them integral control is achieved, either by the removal of a single control species E by zero-order  kinetics ("single-E controllers"), or by the removal of two control species  by second-order kinetics ("antithetic or dual-E control"). In this paper we show results when the control species E 1  and E 2  in antithetic control are removed enzymatically by ping-pong or ternary-complex mechanisms. Our findings show that enzyme-catalyzed dual-E controllers can work in two control modes. In one mode, one of the two control species is active, but requires zero-order kinetics in its removal. In the other mode, both controller species are active and both are removed enzymatically. Conditions for the two control modes are put forward and biochemical examples with the structure of enzyme-catalyzed dual-E controllers are discussed.

The Influence of Temperature and Concentration on Copper Deposition Kinetics in Supercritical Carbon Dioxide

2004 ◽  
Vol 812 ◽  
Author(s):  
Yinfeng Zong ◽  
James J. Watkins
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Supercritical Fluids ◽  
Zero Order ◽  
Copper Deposition ◽  
Deposition Kinetics ◽  
Zero Order Kinetics ◽  
Concentration Interval ◽  
Kinetics Of ◽  
Supercritical Carbon

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.

Spectroscopic Study of Photosensitized Oxidation of Polyisoprene

1977 ◽  
Vol 50 (4) ◽  
pp. 704-713 ◽  
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.

The catalytic decomposition of ethers on evaporated tungsten films

1968 ◽  
Vol 302 (1470) ◽  
pp. 385-398 ◽  
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.

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

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.

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

INDIAN DRUGS ◽  
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.

Ontogenic expression of acetylcholinesterase activity in trachealis of young swine

1991 ◽  
Vol 261 (4) ◽  
pp. L322-L326 ◽  
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.

scholarly journals Ranitidine Loaded Biopolymer Floats: Designing, Characterization, and Evaluation

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.

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