scholarly journals Modelling pH-Optimized Degradation of Microgel-Functionalized Polyesters

2016 ◽  
Vol 2016 ◽  
pp. 1-8
Author(s):  
Lisa Bürgermeister ◽  
Marcus Hermann ◽  
Katalin Fehér ◽  
Catalina Molano Lopez ◽  
Andrij Pich ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Degradation Products ◽  
Degradation Process ◽  
Diffusion Reaction ◽  
Rate Equations ◽  
Algebraic Equations ◽  
Aliphatic Polyesters ◽  
Acidic Degradation ◽  
Ph Level ◽  
Polymer Foils

We establish a novel mathematical model to describe and analyze pH levels in the vicinity of poly(N-vinylcaprolactam-co-acetoacetoxyethyl methacrylate-co-N-vinylimidazole) (VCL/AAEM/VIm) microgel-functionalized polymers during biodegradation. Biodegradable polymers, especially aliphatic polyesters (polylactide/polyglycolide/polycaprolactone homo- and copolymers), have a large range of medical applications including delivery systems, scaffolds, or stents for the treatment of cardiovascular diseases. Most of those applications are limited by the inherent drop of pH level during the degradation process. The combination of polymers with VCL/AAEM/VIm-microgels, which aims at stabilizing pH levels, is innovative and requires new mathematical models for the prediction of pH level evaluation. The mathematical model consists of a diffusion-reaction PDE system for the degradation including reaction rate equations and diffusion of acidic degradation products into the vicinity. A system of algebraic equations is coupled to the degradation model in order to describe the buffering action of the microgel. The model is validated against the experimental pH-monitored biodegradation of microgel-functionalized polymer foils and is available for the design of microgel-functionalized polymer components.

scholarly journals Stability Indicating HPTLC Method for Analysis of Rifaximin in Pharmaceutical Formulations and an Application to Acidic Degradation Kinetic Study

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Kalpana G. Patel ◽  
Nitesh R. Jain ◽  
Purvi A. Shah
Keyword(s):  
High Performance ◽  
Degradation Products ◽  
Pharmaceutical Formulations ◽  
Degradation Process ◽  
Order Rate Constant ◽  
Forced Degradation ◽  
Phase System ◽  
Degradation Kinetic ◽  
Stability Indicating ◽  
Acidic Degradation

A specific stability indicating high-performance thin-layer chromatographic method for analysis of rifaximin both as a bulk drug and in formulations was developed and validated. The method employed HPTLC aluminium plates precoated with silica gel 60 F254 as the stationary phase. The optimized mobile phase system consisted of n-hexane : 2-propanol : acetone : ammonia (5 : 4.1 : 1, v/v/v/v), which gave compact spots for rifaximin at of 0.59 ± 0.03. Rifaximin was subjected to forced degradation studies in order to check the specificity of the method. Densitometric analysis of rifaximin was carried out in the absorbance reflectance mode at 443 nm. The calibration plots showed linear relationship in the concentration range of 400–3200 ng per band. Moreover, linearity was also confirmed by verification of homoscedasticity of variance. According to validation studies, the developed method was repeatable and specific as revealed by % RSD less than 2 and hence can be used for routine analysis of pharmaceutical formulation. Moreover, the method could effectively separate the drug from its degradation products; hence it can be employed as a stability indicating one. The kinetics of acid degradation process at various temperatures was also investigated and first-order rate constant, half-life, shelf life, and activation energy were computed.

A Numerical Study of Unsteady Natural Convection in a Rectangular Enclosure: The Effect of Compressibility

2004 ◽  
Author(s):  
K. M. Akyuzlu ◽  
Y. Pavri ◽  
A. Antoniou
Keyword(s):  
Mathematical Model ◽  
Stokes Equations ◽  
Numerical Study ◽  
Vertical Wall ◽  
Ideal Gas ◽  
Working Fluid ◽  
Two Dimensional ◽  
Algebraic Equations ◽  
Rectangular Enclosure ◽  
Circulation Patterns

A two-dimensional, mathematical model is adopted to investigate the development of buoyancy driven circulation patterns and temperature contours inside a rectangular enclosure filled with a compressible fluid (Pr=1.0). One of the vertical walls of the enclosure is kept at a higher temperature then the opposing vertical wall. The top and the bottom of the enclosure are assumed insulated. The physics based mathematical model for this problem consists of conservation of mass, momentum (two-dimensional Navier-Stokes equations) and energy equations for the enclosed fluid subjected to appropriate boundary conditions. The working fluid is assumed to be compressible through a simple ideal gas relation. The governing equations are discretized using second order accurate central differencing for spatial derivatives and first order forward finite differencing for time derivatives where the computation domain is represented by a uniform orthogonal mesh. The resulting nonlinear equations are then linearized using Newton’s linearization method. The set of algebraic equations that result from this process are then put into a matrix form and solved using a Coupled Modified Strongly Implicit Procedure (CMSIP) for the unknowns (primitive variables) of the problem. A numerical experiment is carried out for a benchmark case (driven cavity flow) to verify the accuracy of the proposed solution procedure. Numerical experiments are then carried out using the proposed compressible flow model to simulate the development of the buoyancy driven circulation patterns for Rayleigh numbers between 103 and 105. Finally, an attempt is made to determine the effect of compressibility of the working fluid by comparing the results of the proposed model to that of models that use incompressible flow assumptions together with Boussinesq approximation.

A mathematical model of the carbon metabolism in photosynthesis. Difficulties in explaining oscillations by fructose 2, 6-bisphosphate regulation

1989 ◽  
Vol 237 (1289) ◽  
pp. 389-415 ◽  
Keyword(s):  
Mathematical Model ◽  
Active Sites ◽  
Starch Synthesis ◽  
Standard Free Energy ◽  
Atp Synthesis ◽  
Rate Equations ◽  
Standard Free Energy Change ◽  
Sucrose Synthesis ◽  
Carbon Reduction ◽  
Fructose 2

A mathematical model of the pentosephosphate carbon reduction (PCR) cycle is presented. The internal structure of the model is consistent with and complements the known biochemical pathways in the PCR cycle, together with starch and sucrose synthesis. Individual enzymes are described by maximum rate ( V m ), standard free energy change (Δ G´ 0 ) and Michaelis constant ( K m ) values as parameters and rate-equations, sym­metrical for the direct and reverse reactions. Enzymic control is included in the starch synthesis pathway (activation by phosphoglycerate (PGA)), inhibition by inorganic phosphate) and in the reactions of sucrose synthesis based on fructose 2, 6-bisphosphate (F2, 6BP) as a metabolite con­trolling the cytosolic fructose bisphosphatase (FBPase) activity. The phosphate translocator carries out the exchange of triose phosphates, orthophosphate and PGA. Ionic forms of metabolites are calculated in relation to pH and assumed to be the actual reacting substances. The significant concentration of the active sites of ribulose 1, 5-bisphosphate (RuBP) carboxylase is taken into account. Light reactions are included only in the form of an ATPase the Δ G´ 0 of which is shifted towards ATP synthesis by the existing proton gradient. The behaviour of the model was studied with the aim of reproducing oscillations in photosynthesis. It is concluded that oscillations in photosynthesis cannot be caused by the fructose 2, 6-bisphosphate control of sucrose synthesis alone, but that an additional control of photosynthetic rate must also be involved.

Kinetic modelling of microalgal growth and fucoxanthin synthesis in photobioreactor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xiaojuan Zhang ◽  
Junru Zhao ◽  
Jie Zhang ◽  
Shijing Su ◽  
Luqiang Huang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Kinetic Parameters ◽  
Kinetic Modelling ◽  
Inhibitory Effect ◽  
Rate Equations ◽  
Phosphorus Concentration ◽  
Model Output ◽  
Nitrogen And Phosphorus ◽  
Nitrogen Phosphorus

Abstract This paper presented a mathematical model to describe the production of fucoxanthin by alga Thalassiosira weissflogi ND-8 in photobioreactor. Our interest was focused on characterizing the effects of nitrogen and phosphorus on the growth of microalgae and on the synthesis of fucoxanthin. The rate equations of microalgal growth, fucoxanthin synthesis and substrate consumptions were formulated. Kinetic parameters of the model and their sensitivities with respect to model output were estimated. The predicted results were compared with experimental data, which showed that this model closely agrees with actual experiment and is able to reflect the growth and metabolism characteristics of microalgae. Our results also indicated that nitrogen plays a major role in the synthesis of fucoxanthin, and the synthesis of fucoxanthin is partially linearly related to the consumption of nitrogen. Phosphorus is primarily consumed in the growth and metabolism of microalgal cells, while excessive phosphorus concentration has an inhibitory effect on the growth of microalgae.

scholarly journals Isolation and Structure Determination of Echinochrome A Oxidative Degradation Products

Molecules ◽  
2020 ◽  
Vol 25 (20) ◽  
pp. 4778
Author(s):  
Natalia P. Mishchenko ◽  
Elena A. Vasileva ◽  
Andrey V. Gerasimenko ◽  
Valeriya P. Grigorchuk ◽  
Pavel S. Dmitrenok ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Degradation Products ◽  
Lethal Dose ◽  
Oxidative Degradation ◽  
Degradation Process ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Ionization Mass ◽  
Echinochrome A ◽  
Esi Ms

Echinochrome A (Ech A, 1) is one of the main pigments of several sea urchin species and is registered in the Russian pharmacopeia as an active drug substance (Histochrome®), used in the fields of cardiology and ophthalmology. In this study, Ech A degradation products formed during oxidation by O2 in air-equilibrated aqueous solutions were identified, isolated, and structurally characterized. An HPLC method coupled with diode-array detection (DAD) and mass spectrometry (MS) was developed and validated to monitor the Ech A degradation process and identify the appearing compounds. Five primary oxidation products were detected and their structures were proposed on the basis of high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) as 7-ethyl-2,2,3,3,5,7,8-heptahydroxy-2,3-dihydro-1,4-naphthoquinone (2), 6-ethyl-5,7,8-trihydroxy-1,2,3,4-tetrahydronaphthalene-1,2,3,4-tetraone (3), 2,3-epoxy-7-ethyl-2,3-dihydro-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (4), 2,3,4,5,7-pentahydroxy-6-ethylinden-1-one (5), and 2,2,4,5,7-pentahydroxy-6-ethylindane-1,3-dione (6). Three novel oxidation products were isolated, and NMR and HR-ESI-MS methods were used to establish their structures as 4-ethyl-3,5,6-trihydroxy-2-oxalobenzoic acid (7), 4-ethyl-2-formyl-3,5,6-trihydroxybenzoic acid (8), and 4-ethyl-2,3,5-trihydroxybenzoic acid (9). The known compound 3-ethyl-2,5-dihydroxy-1,4-benzoquinone (10) was isolated along with products 7–9. Compound 7 turned out to be unstable; its anhydro derivative 11 was obtained in two crystal forms, the structure of which was elucidated using X-ray crystallography as 7-ethyl-5,6-dihydroxy-2,3-dioxo-2,3-dihydrobenzofuran-4-carboxylic acid and named echinolactone. The chemical mechanism of Ech A oxidative degradation is proposed. The in silico toxicity of Ech A and its degradation products 2 and 7–10 were predicted using the ProTox-II webserver. The predicted median lethal dose (LD50) value for product 2 was 221 mg/kg, and, for products 7–10, it appeared to be much lower (≥2000 mg/kg). For Ech A, the predicted toxicity and mutagenicity differed from our experimental data.

FTIR study of degradation products of aliphatic polyesters–carbon fibres composites

2001 ◽  
Vol 596 (1-3) ◽  
pp. 69-75 ◽  
Author(s):  
Elżbieta Pamuła ◽  
Marta Błażewicz ◽  
Czesława Paluszkiewicz ◽  
Piotr Dobrzyński
Keyword(s):  
Degradation Products ◽  
Carbon Fibres ◽  
Aliphatic Polyesters ◽  
Ftir Study

scholarly journals Mathematical Modeling and Analysis of Multirobot Cooperative Hunting Behaviors

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Yong Song ◽  
Yibin Li ◽  
Caihong Li ◽  
Xin Ma
Keyword(s):  
Mathematical Modeling ◽  
Mathematical Model ◽  
Numerical Solutions ◽  
Rate Equations ◽  
Ratio Analysis ◽  
Hunting Behavior ◽  
Modeling And Analysis ◽  
Cooperative Hunting ◽  
Model Equations ◽  
The Mathematical Model

This paper presents a mathematical model of multirobot cooperative hunting behavior. Multiple robots try to search for and surround a prey. When a robot detects a prey it forms a following team. When another “searching” robot detects the same prey, the robots form a new following team. Until four robots have detected the same prey, the prey disappears from the simulation and the robots return to searching for other prey. If a following team fails to be joined by another robot within a certain time limit the team is disbanded and the robots return to searching state. The mathematical model is formulated by a set of rate equations. The evolution of robot collective hunting behaviors represents the transition between different states of robots. The complex collective hunting behavior emerges through local interaction. The paper presents numerical solutions to normalized versions of the model equations and provides both a steady state and a collaboration ratio analysis. The value of the delay time is shown through mathematical modeling to be a strong factor in the performance of the system as well as the relative numbers of the searching robots and the prey.

Solid supported in situ derivatization extraction of acidic degradation products of nerve agents from aqueous samples

2014 ◽  
Vol 1359 ◽  
pp. 325-329 ◽  
Author(s):  
Sridhar Chinthakindi ◽  
Ajay Purohit ◽  
Varoon singh ◽  
Vijay Tak ◽  
D.K. Dubey ◽  
...  
Keyword(s):  
Degradation Products ◽  
Nerve Agents ◽  
Aqueous Samples ◽  
Acidic Degradation ◽  
In Situ Derivatization

scholarly journals An NMR Study of the Bortezomib Degradation under Clinical Use Conditions

2009 ◽  
Vol 2009 ◽  
pp. 1-5 ◽  
Author(s):  
Adele Bolognese ◽  
Anna Esposito ◽  
Michele Manfra ◽  
Lucio Catalano ◽  
Fara Petruzziello ◽  
...  
Keyword(s):  
Boronic Acid ◽  
High Field ◽  
Degradation Products ◽  
Degradation Process ◽  
Spectroscopic Properties ◽  
Resonance Spectroscopy ◽  
Clinical Use ◽  
Common Condition ◽  
Nmr Study ◽  
The Common

The (R)-3-methyl-1-((S)-3-phenyl-2-(pyrazine-2-carboxamido)propanamido)butyl-boronic acid, bortezomib (BTZ), which binds the 20S proteasome subunit and causes a large inhibition of its activity, is a peptidomimetic boronic drug mainly used for the treatment of multiple myeloma. CommercialBTZ, stabilized as mannitol derivative, has been investigated under the common conditions of the clinical use because it is suspected to be easily degradable in the region of its boronic moiety. CommercialBTZsamples, reconstituted according to the reported commercial instructions and stored at , were analyzed by high-field nuclear magnetic resonance spectroscopy in comparison with identical samples bubbled with air and argon, respectively. All the samples remained unchanged for a week. After a month, the air filled samples showed the presence of two main degradation products (6% of starting material), the N-(1-(1-hydroxy-3-methylbutylamino)-1-oxo-3-phenylpropan-2-yl) pyrazine-2-carboxamide (BTZ1; 5%, determined from NMR integration) and the (S)-N-(1-(3-methylbutanamido)-1-oxo-3-phenylpropan-2-yl)pyrazine-2-carboxamide (BTZ2; 1%, determined from NMR integration), identified on the basis of their chemical and spectroscopic properties. TheBTZ1andBTZ2finding suggests that, under the common condition of use and at , commercial BTZ-mannitol is stable for a week, and that, in time, it undergoes slow oxidative deboronation which partially inactivates the product. Low temperature and scarce contact with air decrease the degradation process.

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