Relation between Surface Area and Surface Potential Change during (co)Polyesters Degradation as Langmuir Monolayer

MRS Advances ◽  
2019 ◽  
Vol 5 (12-13) ◽  
pp. 667-677
Author(s):  
Natalia A. Tarazona ◽  
Rainhard Machatschek ◽  
Andreas Lendlein
Keyword(s):  
Surface Area ◽  
Surface Potential ◽  
Degradation Products ◽  
Degradation Mechanism ◽  
Langmuir Monolayers ◽  
Langmuir Monolayer ◽  
Potential Change ◽  
Alkaline Conditions ◽  
Hydrolysis Of ◽  
Random Scission

ABSTRACTPolyhydroxyalkanoates (PHAs) are degradable (co)polyesters synthesized by microorganisms with a variety of side-chains and co-monomer ratios. PHAs can be efficiently hydrolyzed under alkaline conditions and by PHA depolymerase enzymes, altering their physicochemical properties. Using 2D Langmuir monolayers as model system to study the degradation behavior of macromolecules, we aim to describe the the interdependency between the degradation of two PHAs and the surface potential, which influences material-proteins interaction and cell response. We hypothesize that the mechanism of hydrolysis of the labile ester bonds in (co)polyesters defines the evolution of the surface potential, owing to the rate of accumulation of charged insoluble degradation products. The alkaline hydrolysis and the enzymatically catalyzed hydrolysis of PHAs were previously defined as chain-end scission and random-scission mechanisms, respectively. In this study, these two distinct scenarios are used to validate our model. The surface potential change during the chain-end scission of poly(3-R-hydroxybutyrate) (PHB) under alkaline conditions was compared to that of the enzymatically catalyzed hydrolysis (random-scission) of poly[(3-R-hydroxyoctanoate)-co-(3-R-hydroxyhexanoate)] (PHOHHx), using the Langmuir monolayer technique. In the random-scission mechanism the dissolution of degradation products, measured as a decrease in the area per molecule, was preceded by a substantial change of the surface potential, provoked by the negative charge of the broken ester bonds accumulated in the air-water interface. In contrast, when chains degraded via the chain-ends, the surface potential changed in line with the dissolution of the material, presenting a kinetic dependent on the surface area of the monolayers. These results provide a basis for understanding PHAs degradation mechanism. Future research on (co)polymers with different main-chain lengths might extend the elucidation of the surface potential development of (co)polyesters as Langmuir monolayer.

Effect of acidity on the properties of silica-aluminas synthesized by sol-gel method

2020 ◽  
Vol 63 (7) ◽  
pp. 126-132
Author(s):  
Lyubov V. Furda ◽  
◽  
Evgenia A. Tarasenko ◽  
Sofya N. Dudina ◽  
Olga E. Lebedeva ◽  
...  
Keyword(s):  
Surface Area ◽  
Sol Gel ◽  
Molar Ratio ◽  
Active Centers ◽  
Indicator Method ◽  
Synthesis Conditions ◽  
Alkaline Conditions ◽  
Acidic Conditions ◽  
Amphoteric Properties ◽  
Hydrolysis Of

In the present work amorphous silica-aluminas were synthesized by the coprecipitation method during the hydrolysis of an alcohol solution of tetraethoxysilane (with a tetraethoxysilane: alcohol mass ratio of 1: 1) and 6% aqueous solution of aluminum nitrate at pH values of 1, 3, and 10. The Si/Al molar ratio for all synthesized samples were 4.72 (± 0.29). The amorphous character of the investigated materials was confirmed by X-ray phase analysis. According to the results of scanning electron microscopy, it was found that the resulting powders have particles with a size of 1-20 μm. It was shown that the conditions of synthesis affected the specific surface area and porosity of the materials under study. By the method of low-temperature adsorption-thermodesorption of nitrogen it was established that silica-aluminas obtained under acidic conditions were microporous materials. For the sample obtained under alkaline conditions (pH = 10), the contribution of macropores is very significant. A decrease in surface area is observed as the pH of the synthesis increases. The Hammett indicator method was used to identify and quantify surface centers of different acidity. All studied silica-aluminas are characterized by the presence of both Brønsted basic (pKax from 7 to 12.8) and acidic (pKax from 0 to 7) centers, and Lewis basic (pKax from -4.4 to 0) with a pronounced maximum at pKax = 1.02. It was found that the synthesis conditions had a significant effect on the concentration of active centers. The values of the Hammett function are practically the same for the 3 studied silica-aluminas and describe the studied samples as materials of medium acidity. The variety of Lewis and Brønsted centers on the surface indicates the amphoteric properties of the materials under study. This gives the samples the properties of polyfunctional sorbents and catalysts.

The influence of pH on the molecular degradation mechanism of PLGA

MRS Advances ◽  
2018 ◽  
Vol 3 (63) ◽  
pp. 3883-3889 ◽  
Author(s):  
Rainhard Machatschek ◽  
Burkhard Schulz ◽  
Andreas Lendlein
Keyword(s):  
Degradation Products ◽  
Bulk Material ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Controlled Drug Release ◽  
Interfacial Rheology ◽  
Alkaline Conditions ◽  
A Chain ◽  
The Impact ◽  
Kinetics Of

ABSTRACTPoly[(rac-lactide)-co-glycolide] (PLGA) is used in medicine to provide mechanical support for healing tissue or as matrix for controlled drug release. The properties of this copolymer depend on the evolution of the molecular weight of the material during degradation, which is determined by the kinetics of the cleavage of hydrolysable bonds. The generally accepted description of the degradation of PLGA is a random fragmentation that is autocatalyzed by the accumulation of acidic fragments inside the bulk material. Since mechanistic studies with lactide oligomers have concluded a chain-end scission mechanism and monolayer degradation experiments with polylactide found no accelerated degradation at lower pH, we hypothesize that the impact of acidic fragments on the molecular degradation kinetics of PLGA is overestimated. By means of the Langmuir monolayer degradation technique, the molecular degradation kinetics of PLGA at different pH could be determined. Protons did not catalyze the degradation of PLGA. The molecular mechanism at neutral pH and low pH is a combination of random and chainend-cut events, while the degradation under strongly alkaline conditions is determined by rapid chainend cuts. We suggest that the degradation of bulk PLGA is not catalyzed by the acidic degradation products. Instead, increased concentration of small fragments leads to accelerated mass loss via fast chain-end cut events. In the future, we aim to substantiate the proposed molecular degradation mechanism of PLGA with interfacial rheology.

Selective acid hydrolysis of 2,4,6-trimethylbenzyl esters and its application in peptide synthesis

1966 ◽  
Vol 19 (8) ◽  
pp. 1511 ◽  
Author(s):  
FHC Stewart
Keyword(s):  
Acid Hydrolysis ◽  
Peptide Synthesis ◽  
Trifluoroacetic Acid ◽  
Ester Group ◽  
Protecting Groups ◽  
Alkaline Conditions ◽  
Hydrolysis Of

Experiments with various N-acylamino acid 2,4,6-trimethylbenzyl esters have shown that the ester group is cleaved selectively by cold trifluoroacetic acid without affecting benzyloxycarbonyl, formyl, or phthaloyl amino-protecting groups present. The possible value of this selective behaviour in peptide syntheses where the use of alkaline conditions would be detrimental is illustrated by the synthesis of certain dipeptide derivatives.

Origin of surface potential change during ferroelectric switching in epitaxial PbTiO3 thin films studied by scanning force microscopy

2009 ◽  
Vol 94 (3) ◽  
pp. 032907 ◽  
Author(s):  
Yunseok Kim ◽  
Changdeuck Bae ◽  
Kyunghee Ryu ◽  
Hyoungsoo Ko ◽  
Yong Kwan Kim ◽  
...  
Keyword(s):  
Thin Films ◽  
Surface Potential ◽  
Scanning Force Microscopy ◽  
Potential Change ◽  
Force Microscopy ◽  
Scanning Force ◽  
Ferroelectric Switching

Investigation of acid hydrolysis for carbohydrate analysis in kraft black liquor

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Silvia Maitz ◽  
Marlene Kienberger
Keyword(s):  
Acid Hydrolysis ◽  
High Performance ◽  
Degradation Products ◽  
Black Liquor ◽  
Amperometric Detection ◽  
Kraft Process ◽  
Kraft Black Liquor ◽  
Carbohydrate Degradation ◽  
Reliable Detection ◽  
Hydrolysis Of

Abstract Black liquor (BL) from the kraft process is considered a promising feedstock for several biorefinery scenarios. Besides lignin and carboxylic acids, this liquor also contains hemicelluloses and their degradation products. A simple and reliable detection of those is of importance for further processing of the liquor. The present paper presents a thorough investigation of quantitative analysis of carbohydrates, by performing acid hydrolysis experiments with a concentrated BL sample of 44% total dry solids. The hydrolysates were then analysed for the four monosaccharides arabinose, xylose, galactose and glucose, by high performance ion chromatography (HPIC) with pulsed amperometric detection. The amount of sulphuric acid needed for complete hydrolysis of the carbohydrates was determined in the range of 3.5–5 mol kg−1 of BL. A lower acid concentration led to insufficient liberation of galactose and glucose, while higher acid concentrations led to degradation of arabinose and xylose. The carbohydrate degradation was also investigated over time for different dilutions and hydrolysis temperatures. These experiments confirmed that the hexoses require considerably harsher conditions for complete liberation compared to xylose and arabinose. The use of internal recovery standards (RSs) was tested; the highest recoveries were obtained by direct spiking of the samples with the RS prior to hydrolysis.

Validation of Analytical Methods for Tacrolimus Determination in Poly(ε-caprolactone) Nanocapsules and Identification of Drug Degradation Products

2021 ◽  
Vol 21 (12) ◽  
pp. 5920-5928
Author(s):  
Guilherme A. Camargo ◽  
Amanda M. Lyra ◽  
Fernanda M. Barboza ◽  
Barbara C. Fiorin ◽  
Flávio L. Beltrame ◽  
...  
Keyword(s):  
Liquid Chromatography ◽  
High Performance ◽  
Degradation Products ◽  
Multiple Reaction Monitoring ◽  
Forced Degradation ◽  
Alkaline Stress ◽  
Drug Degradation ◽  
Relative Standard ◽  
Polymeric Nanocapsules ◽  
Alkaline Conditions

The aim of this paper was to use chromatographic tools for validating an analytical method for the tacrolimus (TAC) determination in polymeric nanocapsules and for identifying the drug degradation products after alkaline stress. A rapid Ultra-High-Performance Liquid Chromatography coupled with photo-diode array (UHPLC-PDA) method was successfully performed using the following chromatographic conditions: the Shimadzu Shim-pack XR-ODS III C18 column (100 mm×2.00 mm, 2.2 μm), the mobile phase consisting of methanol and acidified ultrapure water (89:11 v/v), the flow rate of 0.55 mL·min−1, and the ultraviolet (UV) detection at 235 nm. This method was validated as per International Council for Harmonisation (ICH) guidelines. In addition, a TAC forced degradation assay was carried out after alkaline stress and its degradation products were investigated using Liquid Chromatography coupled tandem mass spectroscopy (LC-MS/MS). The calibration curve was linear in the range of 100.0–300.0 μg·mL−1 (r >0.9999). Accuracy was confirmed by the TAC recovery of 96.55 to 98.19%. Precision (intraday and interday) were demonstrated by relative standard deviation lower than 0.89% and 3.25%, respectively. Selectivity and robustness were also proved. The method developed it was successfully applied to quantify TAC from polymeric nanocapsules, showing a high loading efficiency rate (>96.47%). The main drug degradation product observed in a multiple reaction monitoring (MRM) experiment was m/z 844, confirming the susceptibility of TAC under alkaline conditions; this finding was first time described.

scholarly journals Complexing power of hydro-soluble degradation products from γirradiated polyvinylchloride: influence on Eu(OH)3(s) solubility and Eu(III) speciation in neutral to alkaline environment

2017 ◽  
Vol 105 (8) ◽  
Author(s):  
Pascal E. Reiller ◽  
Elodie Fromentin ◽  
Muriel Ferry ◽  
Adeline Dannoux-Papin ◽  
Hawa Badji ◽  
...  
Keyword(s):  
Oxidation State ◽  
Alkaline Hydrolysis ◽  
Degradation Products ◽  
Alkaline Environment ◽  
Hydrolysis Of

AbstractThe complexing power of hydrosoluble degradation products (HDPs) from an alkaline hydrolysis of a 10 MGy γ-irradiated polyvinylchloride is studied. The complexation of Eu(III), as an analogue of lanthanide and actinide radionuclides at their +III oxidation state for oxygen containing functions, is evidenced both from the increasing of Eu(OH)

scholarly journals Interactions of Na+ Cations with a Highly Charged Fatty Acid Langmuir Monolayer: Molecular Description of the Phase Transition

2019 ◽  
Author(s):  
Adrien Sthoer ◽  
Eric Tyrode
Keyword(s):  
Phase Transition ◽  
Surface Charge ◽  
Surface Potential ◽  
Arachidic Acid ◽  
Ion Pairs ◽  
Theoretical Models ◽  
Langmuir Monolayer ◽  
Vibrational Sum Frequency Spectroscopy ◽  
Ion Size ◽  
Contact Ion Pairs

Vibrational sum frequency spectroscopy has been used to study the molecular properties upon compression of a highly charged arachidic acid Langmuir monolayer, which displays a first order phase transition plateau in the surface pressure - molecular area (p-A) isotherm. By targeting vibrational modes from the carboxylic acid headgroup, alkyl chain, and interfacial water molecules, information regarding the surface charge, surface potential, type of ion pair formed, and conformational order of the monolayer could be extracted. The monolayer in the liquid expanded phase is found to be fully charged until reaching the 2D-phase transition plateau, where partial reprotonation, as well as the formation of COO⎺ Na<sup>+ </sup>contact-ion pairs, start to take place. In the condensed phase after the transition, three headgroup species, mainly hydrated COO⎺, COOH, and COO⎺ Na<sup>+ </sup>contact-ion pairs could be identified and their proportions quantified. Comparison with theoretical models shows that despite the low ionic strengths used (i.e. 10 mM), the predictions from the Gouy Chapman model are only adequate for the lowest surface densities, when the surface charge does not exceed -0.1 C/m<sup>2</sup>. In contrast, a modified Poisson-Boltzmann (MPB) model that accounts for the steric effects associated with the finite ion-size, captures many of the experimental observables, including the partial reprotonation, and surface potential changes upon compression. The agreement highlights the importance of hydronium ion – carboxylate interactions, as well as the layer of sodium ions packed at the steric limit, for explaining the phase transition behavior. The MPB model, however, does not explicitly consider the formation of contact ion pairs with the sodium counterion. The experimental results provide a quantitative molecular insight that could be used to test potential extensions to the theory.

Σύνθεση, χαρακτηρισμός και καταλυτική δραστικότητα μικτών πορώδων οξειδίων με βάση το μαγγάνιο

2001 ◽  
Author(s):  
Βασίλειος Σταθόπουλος
Keyword(s):  
Surface Area ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area ◽  
Deionized Water ◽  
X Rays ◽  
Thermal Gravimetry ◽  
Reaction Proceeds ◽  
Heating Treatment ◽  
Hydrolysis Of

The subject of investigation of the present study has been the synthesis and characterization of porous manganese based mixed oxides as well as their catalytic properties in heterogeneous reactions of environmental interest. A group of mesoporous materials was prepared by hydrolysis of the trinuclear complex [Mn3 0 (CH3C0 0 )6(pyr>3]C1 0 4, by adding drop wise deionized water oraqueous solutions of nitrate salts of the elements: Mg, Al, Fe, La, La/Sr, La/Ce and La/Sr/Ce. The precursors of the materials were studied by thermal analysis (Thermal gravimetry TG, Differential thermal analysis DTA, Differential thermal gravimetry DTG). After calcination at 300 400 and 500 °C the materials were tested by N2 adsorption at 77K and powder X-rays diffraction. The same materials after heating at 500 °C were examined in catalytic tests and their surface composition was also investigated by X-rays photoelectron spectroscopy (XPS). The following three catalytic reactions were studied: I) CH4 combustion in a mixture of 4.84% CH4 , 9.68% O2 in He with a GHSV=74000h‘\ Π) interconversion of 2% NO and 2% CO in a mixture in He with a GHSV=54000h'' and finally III) a lean de-NOx reaction in the gas mixture CH4/NO/O2 = 0.67%/0.2%/5% in He with a GHSV=20000h'1. The latter reaction was studied for four materials. In this reaction the influence of 4% H2O in the gas mixture was also investigated. Experiments of NO and O2 temperature programmed desorption were carried out in order to illuminate the factors controllingthe activity of these catalysts. The main remarks of the whole study are summarized as following:□ A new method involving the hydrolysis of the [Mn3 0 (CH3C0 0 )6 (pyr)3 ]C1 0 4 complex for preparing mesoporous and/or microporous mangenese based mixed oxides was applied successfully. The composition and the heating treatment influence the specific surface area and the mean pore size of the materials. Correspondingly, as determined by the vplots, the percentage of microporosity varies. □ The XRD studies showed that after heating treatment at 300 °C - 500 °C, the majority of materials are amorphous with high surface area. In some cases Mn0 2 was apparent after heating at 300°C while Mn20 3 is found after heating at 500 °C. The presence of Mn(III) at 500°C was proved of the XPS studies. α The gradual dropwise hydrolysis of the complex [MnjO(CHjCOO)6 (pyr)3 ]C1 0 4 by deionized water results in mesoporous mangenese oxides with MnC>2 crystal structure and low thermal stability. The presence of nitrates salts of Al, La, La/Sr,L$/Ce and/or La/Sr/Ce increases the specific surface area and improves the thermal stability of the materials. The material prepared in the presence of AIJ+ (Al-ΜηΟχ) possessed a very high surface area 711 m2/g. a The hydrolysis temperature "did'not influence significantly the surface features ofthe materials but the best results obtained at SO °C. Changes in the pH also did not influence significantly the surface features of the materials. As soon as the hydrolysis takes place the solution is buffered by the stoichiometric presence of pyridine and acetic acid that coexist as ligands in the complex coordination sphere. These compounds are readily formed with the addition of H2O. a The surface compositions of the materials, as investigated by XPS, proved the presence of Mn3* but also the presence of the rest of the added elements in lower surface concentration. In all cases except those of the hydrolysis in the presence of iron and cerium nitrate salts where the surface was enriched. Also in all materials the surface was enriched in oxygen. □ All the materials proved very reactive for the catalytic combustion of CH 4 and best case was the La-MnO* catalyst. This fact was attributed to the increased surface area and the surface presence of Mn(III) compared to the rest of the materials. A correlation of the surface presence of Μη(ΠΙ) and catalytic activitywas observed. For this same reaction a comparison between the present materials and catalysts reported in the literature showed that the materials are very active with CH« combustion in very low temperature (e.g. Temperature for the 50% of conversion is 366 °C). 0 For the reaction NO+CO, the conversion of the reactants appears even from room temperature. At low temperatures (<280 °C) the reaction proceeds through the route 2NO + CO -> N2O + CO2 . In higher temperatures the reaction proceeds through the route 2NO + 2CO -» N2 + 2 CO2 . The shift of thereaction path occurs within the same temperature region for all the materials. □ For the NO reduction by CH« in the presence of excess O2. the materials proved active in the temperature region of the diesel engines exhaust gases. The mixed oxide La-Sr-Ce-MnOx in particular found very reactive and efficient to convert NO to N2 . This behaviour was even better when H2O was added to the reaction mixture with selectivity towards N2 up to 96%. This stability was proved even after 20h test on stream. This excellent catalytic behavior was attributed to the interaction of surface with NO and the possible synergistic effect among the crystal phases of Μη2θ 3 and Ce0 2 .□ The catalytic superiority o f the La-Sr-Ce-MnOx, especially in cohiparison with 1% ' wt. RI1-A I2O 3 for the same reaction mixture using data from literature, provides further proof for the excellent catalytic activity of these solids.

Differences between in vitro and in vivo degradation of LHRH by rat brain and other organs

1987 ◽  
Vol 253 (3) ◽  
pp. E317-E321 ◽  
Author(s):  
F. A. Carone ◽  
M. A. Stetler-Stevenson ◽  
V. May ◽  
A. LaBarbera ◽  
G. Flouret
Keyword(s):  
Degradation Products ◽  
Venous Blood ◽  
Simultaneous Action ◽  
Pituitary Cells ◽  
Time Intervals ◽  
Luteinizing Hormone Releasing Hormone ◽  
Hydrolysis Of ◽  
The Brain

Homogenates of brain, pituitary, liver, lung, ovary, and testes were incubated with [pyro Glu1-3,4-3H]luteinizing hormone-releasing hormone ([3H]LHRH), and the profiles of metabolites generated as a function of time were determined. After 5 min of incubation, 5 was the predominant metabolite in most homogenates. Although the profiles of metabolites varied at different time intervals, metabolites 2, 3, 4, and 5, and in some instances 7 and 9, appeared to form simultaneously and were detectable at 10 min. Neither metabolite 6 nor other larger metabolites formed initially as dominant degradation products. The findings suggest cleavage of LHRH by the simultaneous action of several endopeptidases. After a single vascular transit of [3H]LHRH, metabolites were determined in the venous blood of liver, lung, and brain of rats in vivo. There were no metabolites of [3H]LHRH in venous blood of liver and lung; however, metabolites 2-4 were present in venous blood of the brain. Incubation of rat anterior pituitary cells with [3H]LHRH yielded metabolites 1-4 but not metabolites 5 or 9 as in homogenates. Incubation of [3H]LHRH with porcine follicular granulosa cells resulted in the generation of metabolites 2-7 and 9, similar to the profile in homogenates. Thus, since homogenates contain enzymes of disrupted cells, they do not always reflect mechanisms for in vivo hydrolysis of circulating LHRH. Brain degraded 12.1% of LHRH during a single vascular transit and may account for substantial degradation of the circulating hormone.

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