A kinetic model for predicting biodegradation

Biodegradation plays a key role in the environmental risk assessment of organic chemicals. The need to assess biodegradability of a chemical for regulatory purposes supports the development of a model for predicting the extent of biodegradation at different time frames, in particular the extent of ultimate biodegradation within a '10 day window' criterion as well as estimating biodegradation half-lives. Conceptually this implies expressing the rate of catabolic transformations as a function of time. An attempt to correlate the kinetics of biodegradation with molecular structure of chemicals is presented. A simplified biodegradation kinetic model was formulated by combining the probabilistic approach of the original formulation of the CATABOL model with the assumption of first order kinetics of catabolic transformations. Nonlinear regression analysis was used to fit the model parameters to OECD 301F biodegradation kinetic data for a set of 208 chemicals. The new model allows the prediction of biodegradation multi-pathways, primary and ultimate half-lives and simulation of related kinetic biodegradation parameters such as biological oxygen demand (BOD), carbon dioxide production, and the nature and amount of metabolites as a function of time. The model may also be used for evaluating the OECD ready biodegradability potential of a chemical within the '10-day window' criterion.     

A kinetic model for predicting oxidative degradation rates in combined radiation-thermal environments

The complex degradation behavior of a poly(vinyl chloride) (PVC) cable jacketing material in combined radiation/temperature/air aging environments is experimentally separated into two dominant radiation dose-rate effect mechanisms. The first, operative at high dose rates, involves diffusion-limited oxidation, which leads to heterogeneously oxidized samples. The second, important at low dose rates, involves thermally-induced breakdown of intermediate peroxides. In the homogeneous degradation regime, a theoretical kinetic model is derived which, based on experimental evidence, assumes unimolecular termination kinetics and rate-determining, hydroperoxide-mediated branching reactions. Dependent upon the ratio of particular rate constants, the model predicts that dose-rate effects will either continue to increase or eventually disappear as the dose rate is lowered. Theoretical analysis of sequential (radiation followed by temperature exposures) aging experiments allows a time–temperature–dose rate shifting procedure to be developed. Using this procedure, higher temperature combined environment results can be shifted to a lower reference temperature, thereby extending the lower temperature results to lower (and experimentally inaccessible) dose rates. By applying this procedure to experimental PVC data, evidence in support of the theoretical model is obtained. In addition, model predictions are shown to agree with 12-year real-time aging results.     

Sustainable approach on the biodegradation of azo dyes: A short review

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A kinetic model for limonene oxidation

The kinetic regularities of the autooxidation of R(+)−limonene (LH) were experimentally studied at various temperatures. A kinetic model including the main elementary reactions and the corresponding rate constants was developed. The degenerate chain branching during limonene oxidation proceeds via bimolecular reactions and involves hydroperoxide LOOH + LH → L· + LO· + H₂O and LOOH + LOOH → LO· + LO₂ · + H₂O. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 80–86, January, 2008.     

Analysis of intermediates from polycyclic aromatic hydrocarbon biodegradation

A major difficulty in assessing bioremediation in hydrocarbon impacted field sites is the determination of the extent and products of contaminant biodegradation. Previously, various analytical techniques, including mass spectrometry and chromatography, have been used to characterize components in mixtures resulting from biodegradation. In this work, the applicability of capillary electrophoresis (CE) to this area of research is demonstrated. CE methods were optimized for analysis of compounds that are known metabolites of polycyclic aromatic hydrocarbon (PAH) biodegradation.     

Composting and biodegradation of thermally processed feather keratin polymer

Proteins obtained from agricultural sources represent a unique feedstock from which to prepare thermally processable polymers. In this study, thermally processed feather keratin films were composted with three-month-old compost inoculum in self-heating laboratory composters for 30 days and temperature and carbon dioxide development monitored. About 24% of the available carbon in the feather keratin polymer (FKP) was metabolized in this time and this may not be high enough for some applications. Degradation of the feather keratin polymers was observed within 10 days with concurrent molecular weight reduction measured using FT-IR. Visual inspection of the polymers also showed destruction of the films. A change in crystallinity was observed in DSC analysis and some degradation processes could be inferred from this as well.     

Environmental biodegradation of synthetic polymers I. Test methodologies and procedures

Biodegradation of synthetic polymers is an important property that is used in many applications. Evaluation of the extent of biodegradation has used different methods in recent years. For each environmental compartment, different approaches have to be made in order to obtain valuable data on biodegradability.This review describes validated and accepted methods based on standardized biodegradation tests, analytical tests, enzymatic tests or tests of physical properties to evaluate the biodegradability of synthetic polymers for different types of environmental compartments (e.g., soil, compost or aqueous media).Part II of this review will subsequently report on the environmental biodegradation of different groups of synthetic polymers.     

Biodegradabilities of some chain oils in groundwater as determined by the respirometric BOD OxiTop method

The respirometric BOD OxiTop method was used to monitor the biodegradation of different chain oils (mineral, rapeseed and tall oils) over 28 days in groundwater, as well as in standard conditions described by OECD 301 F. The aim of the study was to gather more information about the biodegradability of forestry oils in groundwater, as well as about the suitability of the automatic OxiTop method for biodegradation measurements. The BOD OxiTop method proved to be a precise and reliable technique for determining the biodegradations of different oils. Some comparative studies were also made using a traditional IR method in order to clarify the total oil concentrations. The results show that if biodegradation only is to be monitored, the OxiTop method is preferable. This is due to the influence of other reactions aside from biodegradation on total hydrocarbon concentrations when using the IR method.     

Characterization and biodegradation of chitosan-alginate polyelectrolyte complexes

Polyelectrolyte complexes (PECs) have been the focus of an expanding number of studies for their wide use. This study investigated the characteristics and biodegradation of chitosan-alginate PECs prepared by freeze-drying a precipitate from sufficient mixtures of the two polymers. The analyses of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) suggested that the partial protonated amine groups of chitosan reacted with the carboxylate groups of alginate and thus strong PECs were formed. After incubating in lysozyme solution, the PECs showed high ability of enzyme adsorption, and low degradation rate in spite of different degrees of deacetylation of chitosan, due to the strong interaction between chitosan and alginate and the hindrance of closely adsorbed lysozyme.     

A kinetic model for nonisothermic homogeneous nucleation

A model for isothermal homogeneous nucleation is proposed that improves the classical model. A quasiequilibrium distribution of clusters was calculated on a basis of the Frenkel’-Lothe-Pound theory. The dependence of the free energy of clusters on their size was represented by an interpolation formula relating the free energy of dimers and large clusters to which a notion of macroscopic surface tension is applicable. The nucleation rate and the dependence of the cluster temperature on their size were calculated by balance equations describing the heating of from a cluster due to the condensation of monomers and its cooling due to collisions with an ambient gas. It is shown that the nucleation rate in excess buffer gas is higher than for the pure condensing gas by approximately two orders of magnitude. The model adequately describes the experimental data for the nucleation of methanol supersaturated vapor.     

Thermal stability and biodegradation of novel D-mannose based glycopolymers

This paper presents the thermal stability and biodegradability testing of new glycopolymers obtained by copolymerization of a novel D-mannose based oligomer with 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate. The thermal analysis of these glycopolymers was investigated by thermogravimetry and the glass transition temperature was determined by DSC. While the acrylate derived glycopolymer has values of the glass transition temperature below 0 °C, the methacrylate derivative has positive values, above 50 °C. The biodegradation studies of the glycopolymers were carried out in a liquid medium, using pure cultures of two microorganisms, Zymomonasmobilis and Trichodermareesei. The weight losses of the new plastic materials were significant (almost 40%) and the best results were assessed for the 2-hydroxypropyl acrylate glycopolymer in the presence of both Z. mobilis and T. reesei. Microscopy showed that both microorganisms were present on the surface of the new glycopolymers and developed small colonies while modifying their surface. The changes inside the morphology of the polymeric materials structure were drastic and were studied via SEM analysis.     

Isotachophoretic determination of carboxylic acids in biodegradation samples

In the current study a method of isotachophoretic separation of selected carboxylic acids was developed. The method was used for the determination of carboxylated oligo(ethylene glycol)s and their degradation products in biodegradation tests of PEG 250 DA [a mixture of dicarboxylated oligo(ethylene glycol)s]. Two tests were performed in the studies: the Organization for Economic Cooperation and Development (OECD) screening test and the river water die-away test. Both the biodegradation tests proved relatively fast biodegradation of the studied compounds. In the OECD screening test the biodegradation was faster than in the river water die-away test which can be ascribed to a higher concentration of bacteria in the biodegradation liquor. The minimal sample pretreatment and relatively low cost of analysis by the isotachophoretic method used here make it a good alternative to existing methods of carboxylic acids analysis.     

Preparation, characterization and biodegradation of biopolymer nanocomposites based on fumed silica

PLA and PCL based nanocomposites prepared by adding three different types of fumed silica were obtained by melt blending. Materials were characterized by means of Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic–Mechanical Thermal Analysis (DMTA).A good distribution of the fumed silica into both polymer matrices was observed. The highest thermo-mechanical improvements were reached by addition of the fumed silica with higher surface area. PLA and its nanocomposites were degraded in compost at 58 °C; at this temperature all samples presented a significant level of polymer degradation, but a certain protection action of silica towards PLA degradation was observed, whereas the addition of fumed silica did not show considerable influence on the degradation trend of PCL. These dissimilarities were attributed to the different degradation mechanism of the two polymers.     

A kinetic model for nanocrystal morphology evolution.

A kinetic model is developed with the goal of understanding and predicting the morphology evolution of nanocrystals in nonequilibrium growth conditions. The model is based on the assumption that under such conditions, different crystal planes have different kinetic parameters. This model focuses on the morphology-developing stage and is successfully related to the nucleation process and other crystal evolution mechanisms. It is believed to be a universal model and is applied to discuss the morphology evolution of CdSe nanocrystals, including the aspect ratio, injection schemes, ligands effect and morphology distribution.     

A generalized kinetic model for heterogeneous gas-solid reactions

We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.     

A simplified kinetic model for isothermal catalytic ignition

The ignition of catalytic combustion of the stoichiometric propane/air mixture on an isothermally heated platinum wire in different experimental conditions of total pressure and wire temperature is studied and discussed on the basis of a simplified kinetic model. The platinum wire is heated electrically with a specially designed power supply, which ensures a quasi-rectangular profile of its temperature. The ignition process is monitored by measuring the input power required to maintain a constant temperature of the wire during an exothermic catalytic reaction. The difference between the input powers recorded in air and in a fuel/air mixture, for the same wire temperature and gas total pressure, allows the elimination of the heat transferred to surroundings and conversion of the results into the catalytic reaction rate r _R versus time curves of S-shaped form, illustrating the transition from kinetic to diffusion regime. The curve can be used to evaluate the ignition delay, as reported previously and also to fit different models to the data. The quasi-exponential increase of the isothermal reaction rate during the early stages of the process can be rationalized on the basis of a simplified kinetic model implying the multiplication of the adsorbed active intermediates. The adopted hypotheses allow the derivation of an analytical solution for the catalytic reaction rate before and during the ignition process, without diffusion limitations.     

A kinetic model for an atomic absorption signal

A kinetic model is proposed for describing the shape of an atomic absorption signal in the case of first-order kinetics. The formation energy of free copper ions (87 x 7 kJ/mol) and other kinetic parameters of an atomic absorption signal of copper at 2273–3073 K were determined from the experimental data.     

Effect of starch content on the biodegradation of polycaprolactone/starch composite for fabricating in situ pore-forming scaffolds

Bone tissue engineering is an efficient approach to regenerating bone-related defects. The optimal scaffold used for bone tissue engineering must possess adequate porosity and suitable mechanical properties. This work described the development of a biodegradable polymeric composite based on polycaprolactone (PCL) and starch that can form a porous structure in situ. The scaffold exhibited the required mechanical properties at the initial stage of implantation by controlling in situ degradation and subsequent pore formation. PCL/starch (SPCL) scaffolds with 100/0, 70/30, and 50/50 ratios were developed. Degradation studies were performed in phosphate buffer saline (PBS) containing α-amylase or lipase at 37 °C for 4 weeks. Fourier-transform infrared spectroscopy was used to analyze chemical bonds and their changes after degradation. Differential scanning calorimetry was applied to determine the crystallinity and recrystallization of samples before and after degradation. Mass loss and starch release were observed during degradation, and the porosity of samples was measured by the ethanol replacement method. Morphology was further determined using scanning electron microscopy. Finally, variations in compressive strength and modulus during degradation and pore formation were also measured. The porosity of samples reached 45% after 1 month of degradation, and mechanical properties were still appropriate for human bone tissue. Reduction in mechanical property after mass loss, starch release and pore formation was controlled by the hydrogen bonding and recrystallization effect of PCL after degradation. Results suggested that SPCL composite had potential to form porous scaffold with adequate mechanical properties in situ and is promising for bone tissue engineering applications.     

A method of predicting the site of alkylation of heterocyclic polyazines from kinetic data on model compounds

A method is presented which enables calculation of isomer ratios resulting from the N-methylation of polyazines in dimethyl sulfoxide. The method assumes that substituent and annular nitrogen atom effects on reactivity are additive in the absence of steric factors. Kinetic studies on model azines provide rate factors which are employed in the calculations. Observed and calculated isomer ratios are compared for a number of polyazines. An extension to N-oxidation is suggested.