scholarly journals Solubility, Rheology, and Coagulation Kinetics of Poly-(O-Aminophenylene)Naphthoylenimide Solutions

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2454
Author(s):  
Ivan. Y. Skvortsov ◽  
Valery G. Kulichikhin ◽  
Igor I. Ponomarev ◽  
Lydia A. Varfolomeeva ◽  
Mikhail S. Kuzin ◽  
...  
Keyword(s):  
Rheological Properties ◽  
Time Window ◽  
Polymer Concentration ◽  
Effect Of Temperature ◽  
Coagulation Bath ◽  
Continuous Polymerization ◽  
Coagulation Kinetics ◽  
The Stability ◽  
First Time ◽  
Kinetics Of

The effect of temperature and storage time at a constant temperature on the stability of poly-(o-aminophenylene)naphthoylenimide solutions in N-methylpyrrolidone has been analyzed using rotational rheometry. A temperature–time window beyond which an irreversible change in the viscoelastic properties of solutions due to cumulative reactions of continuous polymerization and possible intramolecular cyclization has been detected. The influence of polymer concentration and its molecular weight on the rheological properties of solutions determining the choice of methods for their processing into fibers and films has been investigated. The effect of non-solvents (water and ethanol) additives on the rheological properties of solutions and the kinetics of their coagulation has been studied. Dosed addition of non-solvent into the solution promotes a significant increase in the viscoelasticity up to gelation and phase separation. Non-solvent presence in the polymer solutions reduces the activity of the solvent, accelerates the movement of the diffusion front at coagulation, and minimizes the number of macro defects. The combination of parameters under investigation renders it possible for the first time to develop new principles modifying dopes for wet spinning into aqueous or ethanol coagulation bath and finally to obtain a heat- and fire-resistant polynaphthoylenebenzimidazole fibers.

Dissolution kinetics of meta-torbernite under circum-neutral to alkaline conditions

2009 ◽  
Vol 6 (6) ◽  
pp. 551 ◽  
Author(s):  
Dawn M. Wellman ◽  
Bruce K. McNamara ◽  
Diana H. Bacon ◽  
Elsa A. Cordova ◽  
Ruby M. Ermi ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Coupled Processes ◽  
Effect Of Temperature ◽  
Subsurface Environments ◽  
Alkaline Conditions ◽  
Flow Through ◽  
Uranium Phosphate ◽  
The Stability ◽  
Kinetics Of

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].

scholarly journals THE EFFECT OF PLANT PROTEINS ON THE FORMATION OF STRUCTURAL AND RHEOLOGICAL PROPERTIES OF NOUGAT

2020 ◽  
Vol 14 (4) ◽  
Author(s):  
L. Gordiienko ◽  
V. Tolstykh ◽  
K Avetisian
Keyword(s):  
Rheological Properties ◽  
Nutritional Value ◽  
Unsaturated Fatty Acids ◽  
Foam Stability ◽  
Soya Protein ◽  
Plant Proteins ◽  
Plastic Strength ◽  
Calcium Magnesium ◽  
The Stability ◽  
Kinetics Of

This paper considers the problem of increasing  the nutritional value of whipped confectionery such as nougat by using hemp- based and soya-based protein-containing ingredients. The  main  tendencies of obtaining new types of food based on plant proteins with complete amino acid composition are described. The paper presents information on cultivating and using hemp and soya both in Ukraine and in the world, and suggests how products of their processing can be applied to improve the quality and increase the biological value of confectionery. It has been investigated what effect protein-containing ingredients obtained from hemp and soya have on the structural properties of foam in the technology of whipped confectionery such as nougat. It has been  established  that increasing the amount of plant protein additives leads to a decrease in the foaming ability, but the stability of protein foams increases. Adding 10% of protein-containing hemp additives increases the foam stability by 6%, while protein-containing soya additives increase it by 5%. The paper presents the results of studying the structural and rheological properties of nougat mass with protein-containing plant additives in the amount 2.5–10% of the weight of sugar. It has been determined that adding protein-containing hemp and soya ingredients increases the viscosity and plastic strength of the products and stabilises their structure. The effect of different amounts of nuts on the kinetics of nougat crystallisation has been studied. It is recommended to add 5% of hemp and 7.5% of soya protein-containing additives instead of sugar during the whipping of nougat mass, because it reduces the whipping time and has a positive effect on structure formation. The recommended  amount of roasted pistachio kernels in the samples suggested is 25–35% of the total weight of nougat, with the resting time 30–60 minutes and the moulding temperature 50–55°C. The nutritional value of the new products with protein-containing hemp and soya  ingredients and nuts has been calculated. It has been noted that nougat has been enriched with protein, unsaturated  fatty acids, and minerals (potassium, calcium, magnesium, phosphorus).

scholarly journals Thermokinetics and rheology of agarose gel applied to bioprinting technology

2020 ◽  
Vol 24 (1 Part A) ◽  
pp. 347-353
Author(s):  
Boris Pokusaev ◽  
Andrey Vyazmin ◽  
Nikolay Zakharov ◽  
Sergey Karlov ◽  
Dmitry Nekrasov ◽  
...  
Keyword(s):  
Rheological Properties ◽  
Point Of View ◽  
Gel Formation ◽  
Operating Modes ◽  
Preliminary Preparation ◽  
Immobilized Microorganisms ◽  
The Stability ◽  
And Storage ◽  
Kinetics Of ◽  
Selection Of

The paper presents new results on the study of thermokinetics of gel system based on agarose in the process of transition from solution to gel and opposite. This issue is extremely relevant, since the stability and predictability of thermophysical and rheological properties in such transformations, especially in the presence of components of the nutrient medium and immobilized microorganisms, come to the fore in terms of design and selection of modes of operation of the printing device promising 3-D bioprinters, as well as the system of preparation and storage of the presence of the hysteresis effect, both from the point of view of the kinetics of gel formation and from the point of view of the dependence of rheological properties on temperature, at different concentrations of modifying components, is shown. The obtained results allow to draw a conclusion about the possibility of using the scheme with preliminary preparation of the initial biogel for the implementation of bioprinting technology based on agarose, and to recommend the obtained values for modeling the operating modes of devices of this type.

scholarly journals Progestogens Are Metabolized by the Gut Microbiota: Implications for Colonic Drug Delivery

Pharmaceutics ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 760
Author(s):  
Zoe Coombes ◽  
Vipul Yadav ◽  
Laura McCoubrey ◽  
Cristina Freire ◽  
Abdul Basit ◽  
...  
Keyword(s):  
Cytochrome P450 ◽  
Oral Delivery ◽  
Cytochrome P450 Enzymes ◽  
Colonic Delivery ◽  
Delivery Methods ◽  
Colonic Drug Delivery ◽  
Colonic Flora ◽  
The Stability ◽  
First Time ◽  
Kinetics Of

Following oral administration, the bioavailability of progestogens is very low and highly variable, in part due to metabolism by cytochrome P450 enzymes found in the mucosa of the small intestine. Conversely, the mucosa in the colon contains much lower levels of cytochrome P450 enzymes, thus, colonic delivery of progestogens may be beneficial. Microbiota in the colon are known to metabolize a great number of drugs, therefore, it is important to understand the stability of these hormones in the presence of colonic flora before developing formulations. The aim of this study was to investigate the stability of three progestogens: progesterone, and its two synthetic analogues, medroxyprogesterone acetate (MPA) and levonorgestrel (LNG), in the presence of human colonic microbiota. Progesterone, MPA, and LNG were incubated in mixed fecal inoculum (simulated human colonic fluid) under anerobic conditions. Progesterone was completely degraded after 2 h, whereas levels of MPA and LNG were still detectable after 24 h. The half-lives of progesterone, MPA, and LNG in fecal inoculum were 28, 644, and 240 min, respectively. This study describes the kinetics of colonic microbial metabolism of these hormones for the first time. MPA and LNG show promise for delivery to the colon, potentially improving pharmacokinetics over current oral delivery methods.

scholarly journals Effect of temperature on the association step in thrombin-fibrinogen interaction

1993 ◽  
Vol 294 (2) ◽  
pp. 563-567 ◽  
Author(s):  
M Picozzi ◽  
R De Cristofaro
Keyword(s):  
Order Rate Constant ◽  
Effect Of Temperature ◽  
Fibrinogen Concentration ◽  
Human Fibrinogen ◽  
Fibrinogen Binding ◽  
Specificity Constant ◽  
Entropy Of Activation ◽  
Equilibrium Dissociation ◽  
First Time ◽  
Kinetics Of

Kinetics of fibrinopeptide A release by human alpha-thrombin at low fibrinogen concentration allowed us to measure the specificity constant, i.e. kcat/Km, for the interaction between the enzyme and human fibrinogen. A study of the dependence of the ratio kcat/Km upon the viscosity of the medium revealed that fibrinogen acts as a ‘sticky’ substrate, or, in other words, as a substrate that dissociates from the Michaelis complex with a rate comparable with that for acylation of the active site. These experiments allowed us also to compute for the first time the second-order rate constant for thrombin-fibrinogen association. A study of the temperature-dependence of the association rate, carried out over the temperature range spanning from 10 degrees C to 37 degrees C (pH 7.50; I0.15) permitted the estimation of the enthalpy and entropy of activation, delta H++ and delta S++, which were found to be equal to 5.69 +/- 0.77 kJ.mol-1 and -80.25 +/- 1.79 kJ.K-1.mol-1 respectively. In addition, the values of Km for thrombin-fibrinogen reaction were measured at different solution viscosities in order to derive the equilibrium dissociation constant, Ks, of this interaction. These experiments showed that the Ks values for thrombin-fibrinogen binding was equal to 1.8 microM at 25 degrees C. Altogether these results indicated that fibrinogen, though interacting with both the catalytic pocket and the fibrinogen recognition site on the thrombin molecule, dissociates from Michaelis complex with a rate comparable with that shown by amide substrates, which interact only with the catalytic site.

scholarly journals Evaluation of mesostructured silica materials with different structures and morphologies as carriers for quercetin and naringin encapsulation

2021 ◽  
Author(s):  
Sonia Morante-Zarcero ◽  
Alba Endrino ◽  
Natalia Casado ◽  
Damián Pérez-Quintanilla ◽  
Isabel Sierra
Keyword(s):  
Biomedical Applications ◽  
Textural Properties ◽  
Molecular Size ◽  
Release Process ◽  
Mesostructured Silica ◽  
Before And After ◽  
The Stability ◽  
First Time ◽  
Kinetics Of ◽  
Potential Use

AbstractTwo mesostructured silicas with wormhole-like pore arrangement (HMS and MSU-2) were synthesized and evaluated for the first time as carriers for the encapsulation of two bioactive flavonoids (quercetin and naringin). For comparative purposes, a hexagonal mesostructured SBA-15 silica type frequently used as encapsulating support was also prepared and tested. All the materials were characterized before and after the loading with the analytes. Different silica/analyte ratios were evaluated to determine the loading and encapsulation kinetics of the different materials. Both flavonoids were successfully loaded inside the pores of the three silicas. The quercetin loading capacity of HMS was higher than SBA-15 and MSU-2 silicas, whereas for naringin SBA-15 and MSU-2 were slightly more effective. These differences could be attributed to the molecular size of the analytes and the textural properties of the different materials. Nevertheless, HMS was the silica that enabled to release the highest amount of both analytes. Thus, it could be considered a suitable carrier of these flavonoids and an alternative to other materials such as SBA-15. Moreover, the release process was performed under controlled conditions (pH 2.0 and 7.4) to simulate digestive conditions. Quercetin was delivered faster and more efficiently from the encapsulated at pH 2.0, whereas no differences were observed for naringin at both pHs. Finally, the antioxidant activity of the resulting encapsulates was determined. The results obtained suggested the potential use of wormhole-like mesostructured silicas as carriers to enhance the stability and bioavailability of flavonoids, so they can be used in future food and biomedical applications.

Kinetics of Various 99mTc-Sn-Pyrophosphate Compounds in the Rat

1977 ◽  
Vol 16 (04) ◽  
pp. 157-162 ◽  
Author(s):  
C. Schümichen ◽  
B. Mackenbrock ◽  
G. Hoffmann
Keyword(s):  
Normal Saline ◽  
Half Life ◽  
Compound A ◽  
Short Half Life ◽  
Low Concentrations ◽  
The Stability ◽  
Kinetics Of ◽  
In Vitro Stability

SummaryThe bone-seeking 99mTc-Sn-pyrophosphate compound (compound A) was diluted both in vitro and in vivo and proved to be unstable both in vitro and in vivo. However, stability was much better in vivo than in vitro and thus the in vitro stability of compound A after dilution in various mediums could be followed up by a consecutive evaluation of the in vivo distribution in the rat. After dilution in neutral normal saline compound A is metastable and after a short half-life it is transformed into the other 99mTc-Sn-pyrophosphate compound A is metastable and after a short half-life in bone but in the kidneys. After dilution in normal saline of low pH and in buffering solutions the stability of compound A is increased. In human plasma compound A is relatively stable but not in plasma water. When compound B is formed in a buffering solution, uptake in the kidneys and excretion in urine is lowered and blood concentration increased.It is assumed that the association of protons to compound A will increase its stability at low concentrations while that to compound B will lead to a strong protein bond in plasma. It is concluded that compound A will not be stable in vivo because of a lack of stability in the extravascular space, and that the protein bond in plasma will be a measure of its in vivo stability.

Zeolites Fit For A Crown: Probing Host-Guest Interactions with Thermogravimetric Methods

2018 ◽  
Author(s):  
Asel Sartbaeva ◽  
Paul R. Raithby ◽  
Remi Castaing ◽  
Antony Nearchou
Keyword(s):  
Mass Spectrometry ◽  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Petrochemical Industry ◽  
Rational Use ◽  
New Methodologies ◽  
First Time ◽  
Kinetics Of

Through a combination of thermogravimetry, mass spectrometry and differential thermal analysis, we demonstrate for the first time that all four zeolites show experimental differences in their host-guest interactions with 18C6. In addition, we have estimated the kinetics of 18C6 decomposition, which is a technique that has not been applied to zeolites previously. Using these findings as a toolkit, a more rational use of OSDAs can be utilised to prepare designer zeolites. Furthermore, the new methodologies presented herein can be applied to current zeolites, such as MFI-type zeolites used in the petrochemical industry.

Applicability of Instability Index for In vitro Protein Stability Prediction

2019 ◽  
Vol 26 (5) ◽  
pp. 339-347 ◽  
Author(s):  
Dilani G. Gamage ◽  
Ajith Gunaratne ◽  
Gopal R. Periyannan ◽  
Timothy G. Russell
Keyword(s):  
Protein Stability ◽  
Caulobacter Crescentus ◽  
Effect Of Temperature ◽  
Instability Index ◽  
Dipeptide Composition ◽  
Experimental Conditions ◽  
The Stability ◽  
Vitro Protein

Background: The dipeptide composition-based Instability Index (II) is one of the protein primary structure-dependent methods available for in vivo protein stability predictions. As per this method, proteins with II value below 40 are stable proteins. Intracellular protein stability principles guided the original development of the II method. However, the use of the II method for in vitro protein stability predictions raises questions about the validity of applying the II method under experimental conditions that are different from the in vivo setting. Objective: The aim of this study is to experimentally test the validity of the use of II as an in vitro protein stability predictor. Methods: A representative protein CCM (CCM - Caulobacter crescentus metalloprotein) that rapidly degrades under in vitro conditions was used to probe the dipeptide sequence-dependent degradation properties of CCM by generating CCM mutants to represent stable and unstable II values. A comparative degradation analysis was carried out under in vitro conditions using wildtype CCM, CCM mutants and two other candidate proteins: metallo-β-lactamase L1 and α -S1- casein representing stable, borderline stable/unstable, and unstable proteins as per the II predictions. The effect of temperature and a protein stabilizing agent on CCM degradation was also tested. Results: Data support the dipeptide composition-dependent protein stability/instability in wt-CCM and mutants as predicted by the II method under in vitro conditions. However, the II failed to accurately represent the stability of other tested proteins. Data indicate the influence of protein environmental factors on the autoproteolysis of proteins. Conclusion: Broader application of the II method for the prediction of protein stability under in vitro conditions is questionable as the stability of the protein may be dependent not only on the intrinsic nature of the protein but also on the conditions of the protein milieu.

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