Alkaline degradation of model compounds related to beech xylan

Holzforschung ◽  
2004 ◽  
Vol 58 (6) ◽  
pp. 588-596 ◽  
Author(s):  
Jürgen Sartori ◽  
Antje Potthast ◽  
Thomas Rosenau ◽  
Andreas Hofinger ◽  
Herbert Sixta ◽  
...  
Keyword(s):  
Capillary Electrophoresis ◽  
Industrial Production ◽  
Degradation Products ◽  
Isotopic Labeling ◽  
Alkaline Degradation ◽  
Chemical Behavior ◽  
Model Compounds ◽  
Degradation Reactions ◽  
Alkaline Conditions ◽  
Kinetics Of

Abstract To address the chemical behavior of beech xylan (O-acetyl-4-O-methyl-glucuronoxylan) under alkaline conditions, three model compounds, 2-O-methylxylobiose (1), aldobiouronic acid (4-O-methyl-α-D-glucopyranosyluronic acid-(1→2)-xylose, 2), and aldotriouronic acid (4-Omethyl-α-D-glucopyranosyluronic acid-(1→2)-β-D-xylopyranosyl-(1→4)-D-xylose, 3), were subjected to strong alkaline conditions equal to those used for the industrial production of viscose (18% NaOH, 43°C). Kinetics of the degradation of the model compounds were monitored by capillary electrophoresis in combination with pre-column derivatization. It was demonstrated that substitution at O-2 of the reducing xylose unit strongly retarded the alkaline degradation reactions (1 and 2). By isotopic labeling experiments and isolation of degradation products it was shown that under the pertinent conditions deprotonation at C-2 occurs, followed by epimerization to the respective lyxo derivative. Aldotriouronic acid 3 was degraded to 2 as an intermediate according to classical peeling pathways. Genuine degradation reactions and epimerization processes were distinguished.

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.

scholarly journals New insights into wood and cement interaction

Holzforschung ◽  
2005 ◽  
Vol 59 (3) ◽  
pp. 330-335 ◽  
Author(s):  
Alexandre Govin ◽  
Arnaud Peschard ◽  
Emmanuel Fredon ◽  
René Guyonnet
Keyword(s):  
Electrical Conductivity ◽  
Chemical Composition ◽  
Carboxylic Acids ◽  
Degradation Products ◽  
Wood Fiber ◽  
Alkaline Degradation ◽  
Wood Extractives ◽  
Alkaline Conditions ◽  
Wood Chemical Composition ◽  
The Impact

Abstract This work deals with the influence of poplar extractives and poplar alkaline degradation products on the hydration of cement. The wood chemical composition was characterized to determine the impact of soft alkaline conditions on wood fiber. Some of the constituents were hydrolyzed and converted into carboxylic acids, which were identified and quantified. Monitoring by electrical conductivity clearly showed that wood extractives are less effective than wood alkaline degradation products in inhibiting the hydration of cement.

Study of kinetics of reaction of lignin model compounds with propylene oxide

Holzforschung ◽  
2008 ◽  
Vol 62 (2) ◽  
pp. 169-175 ◽  
Author(s):  
Krishna K. Pandey ◽  
Tapani Vuorinen
Keyword(s):  
Chemical Reaction ◽  
Propylene Oxide ◽  
Aqueous Media ◽  
Reaction Products ◽  
Model Compounds ◽  
Rapid Reduction ◽  
Visible Absorption ◽  
Lignin Model Compounds ◽  
Lignin Model ◽  
Kinetics Of

Abstract The etherification of phenolic groups has been found to inhibit photodegradation in wood and lignin rich pulps. The precise understanding of kinetics of chemical reaction between lignins or their model compounds and the etherifying agent is the first step for developing a viable modification procedure. In this study, we have investigated the reaction of lignin model compounds (namely, phenol and guaiacol) with propylene oxide in aqueous media. The kinetics of etherification reaction was studied under varying pH conditions in the temperature range 30–60°C. The etherified reaction products were characterized by gas chromatogram-mass spectrum (GC-MS). The extent of etherification of phenols and the rate of chemical reaction was followed by UV-Visible absorption spectroscopy. The reaction between lignin model compounds and propylene oxide was indicated by a rapid reduction in the absorbance accompanied by the development of a new band corresponding to etherified products. The reaction kinetics was investigated at pH ∼12 under the condition of excess concentration of propylene oxide. The reaction followed first order kinetics and rate constants increased linearly with an increase in the temperature and concentration of propylene oxide. The MS fragment data of reaction product support the proposed reaction scheme. The activation energy of the reaction of propylene oxide with phenol and guaiacol, calculated with the Arrhenius equation, was 56.2 kJ mol-1 and 45.4 kJ mol-1, respectively.

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.

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