Vedrana Marin

Photooxidation processes for an azo dye in aqueous media: modeling of degradation kinetic and ecological parameters evaluation.

Three photooxidation processes, UV/H(2)O(2), UV/S(2)O(8)(2-) and UV/O(3) were applied to the treatment of model wastewater containing non-biodegradable organic pollutant, azo dye Acid Orange 7 (AO7). Dye degradation was monitored using UV/VIS and total organic carbon (TOC) analysis, determining decolorization, the degradation/formation of naphthalene and benzene structured AO7 by-products, and the mineralization of model wastewater. The water quality during the treatment was evaluated on the bases of ecological parameters: chemical (COD) and biochemical (BOD(5)) oxygen demand and toxicity on Vibrio fischeri determining the EC(50) value. The main goals of the study were to develop an appropriate mathematic model (MM) predicting the behavior of the systems under investigation, and to evaluate the toxicity and biodegradability of the model wastewater during treatments. MM developed showed a high accuracy in predicting the degradation of AO7 when considering the following observed parameters: decolorization, formation/degradation of by-products and mineralization. Good agreement of the data predicted and the empirically obtained was confirmed by calculated standard deviations. The biodegradability of model wastewater was significantly improved by three processes after mineralizing a half of the initially present organic content. The toxicity AO7 model wastewater was decreased as well. The differences in monitored ecological parameters during the treatment indicated the formation of different by-products of dye degradation regarding the oxidant type applied.

The comparison of photooxidation processes for the minimization of organic load of colored wastewater applying the response surface methodology

In this comparative study, the effectiveness of three photooxidation processes (UV/H(2)O(2), UV/S(2)O(8)(2-) and UV/O(3)) for degradation of an azo dye model pollutant was investigated using several process parameters. The process parameters such as initial pH, the concentrations of oxidant in the reactor inlet stream and the type of oxidant were considered. In order to investigate the influence of cross-factor effects of process parameters, the full factorial design was applied with three factors (two numeric and one categorical) at three levels combined with response surface modeling. The ANOVA results (R(2), F, p) showed high accuracy of developed quadratic model for the zero-order mineralization rate constants of AO7 model wastewater. Among process parameters studied, the type of oxidant and the concentration of oxidant were shown to be the most influential parameters of studied photooxidation processes. The highest rate of mineralization of AO7 model wastewater, k(obs)=7.507×10(-7) M s(-1), was obtained for UV/O(3) process at the initial pH 10 and oxidant reactor input rate of 0.6 mM min(-1). However, when comparing the operating costs for each process studied, it was evident that UV/H(2)O(2) process is 1.6 times less expensive than UV/O(3) process considering the mineralization of organic content of AO7 model wastewater.

Roles of the SH2 and SH3 domains in the regulation of neuronal Src kinase functions.

Previous studies demonstrated that intra‐domain interactions between Src family kinases (SFKs), stabilized by binding of the phosphorylated C‐terminus to the SH2 domain and/or binding of the SH2 kinase linker to the SH3 domain, lock the molecules in a closed conformation, disrupt the kinase active site, and inactivate SFKs. Here we report that the up‐regulation of N‐methyl‐d‐aspartate receptors (NMDARs) induced by expression of constitutively active neuronal Src (n‐Src), in which the C‐terminus tyrosine is mutated to phenylalanine (n‐Src/Y535F), is significantly reduced by dysfunctions of the SH2 and/or SH3 domains of the protein. Furthermore, we found that dysfunctions of SH2 and/or SH3 domains reduce auto‐phosphorylation of the kinase activation loop, depress kinase activity, and decrease NMDAR phosphorylation. The SH2 domain plays a greater regulatory role than the SH3 domain. Our data also show that n‐Src binds directly to the C‐terminus of the NMDAR NR2A subunit in vitro, with a KD of 108.2 ± 13.3 nm. This binding is not Src kinase activity‐dependent, and dysfunctions of the SH2 and/or SH3 domains do not significantly affect the binding. These data indicate that the SH2 and SH3 domains may function to promote the catalytic activity of active n‐Src, which is important in the regulation of NMDAR functions.

UV-assisted persulfate oxidation: the influence of cation type in the persulfate salt on the degradation kinetics of an azo dye pollutant

With the aim to investigate the influence of UV-assisted persulfate oxidation operating parameters (cation type in persulfate salt, persulfate concentration and initial pH), the empirical/modeling approach applying full factorial experimental design (FFD) combined with response surface methodology (RSM) and mechanistic modeling (MM) was used. The efficiency of UV-assisted persulfate oxidation as a wastewater treatment method and the dependence on the aforementioned process parameters was evaluated in the case study where an azo dye (C.I. Acid Orange 7—AO7) was used as a model pollutant in water matrix. The FFD matrix with three independent variables representing the studied process parameters established experimental combinations, on which the UV-assisted persulfate oxidation process response, the AO7 decolorization rate was determined and correlated using RSM over quadratic polynomial equations, i.e. RSM model. The significance and accuracy of the developed RSM model was evaluated on the basis of analysis of variance and obtained statistical parameters (R2, F, p), used also to examine the influence of studied process parameters. It was determined that the persulfate salt is the most influential process parameter, followed by rather high combined influence of initial pH and cation type, indicating the practical implications regarding the cation type. The MM used to describe the UV-assisted persulfate oxidation system showed high accuracy in predicting the AO7 degradation monitored over several parameters (decolorization, degradation of naphthalene and benzene structures, as well as overall mineralization) as well as high flexibility covering the broad pH range of application set by different cation type ion the persulfate salt.

CHARACTERIZATION OF NEURONAL SRC KINASE PURIFIED FROM A BACTERIAL EXPRESSION SYSTEM

Neuronal Src (n-Src) is an alternative isoform of Src kinase containing a 6-amino acid insert in the SH3 domain that is highly expressed in neurons of the central nervous system (CNS). To investigate the function of n-Src, wild-type n-Src, constitutively active n-Src in which the C-tail tyrosine 535 was mutated to phenylalanine (n-Src/Y535F) and inactive n-Src in which the lysine 303 was mutated to arginine in addition to the mutation of Y535F (n-Src/K303R/Y535F), were expressed and purified from Escherichia coli BL21(DE3) cells. We found that all three types of n-Src constructs expressed at very high yields (∼500 mg/L) at 37°C, but formed inclusion bodies. In the presence of 8M urea these proteins could be solubilized, purified under denaturing conditions, and subsequently refolded in the presence of arginine (0.5M). These Src proteins were enzymatically active except for the n-Src/K303R/Y535F mutant. n-Src proteins expressed at 18°C were soluble, albeit at lower yields (∼10-20 mg/L). The lowest yields were for n-Src/Y535F (∼10 mg/L) and the highest for n-Src/K303R/Y535F (∼20 mg/L). We characterized the purified n-Src proteins expressed at 18°C. We found that altering n-Src enzyme activity either pharmacologically (e.g., application of ATP or a Src inhibitor) or genetically (mutation of Y535 or K303) was consistently associated with changes in n-Src stability: an increase in n-Src activity was coupled with a decrease in n-Src stability and vice versa. These findings, therefore, indicate that n-Src activity and stability are interdependent. Finally, the successful production of functionally active n-Src in this study indicates that the bacterial expression system may be a useful protein source in future investigations of n-Src regulation and function.

Prediction of biodegradability of aromatics in water using QSAR modeling

The study was aimed at developing models for predicting the biodegradability of aromatic water pollutants. For that purpose, 36 single-benzene ring compounds, with different type, number and position of substituents, were used. The biodegradability was estimated according to the ratio of the biochemical (BOD5) and chemical (COD) oxygen demand values determined for parent compounds ((BOD5/COD)0), as well as for their reaction mixtures in half-life achieved by UV-C/H2O2 process ((BOD5/COD)t1/2). The models correlating biodegradability and molecular structure characteristics of studied pollutants were derived using quantitative structure-activity relationship (QSAR) principles and tools. Upon derivation of the models and calibration on the training and subsequent testing on the test set, 3- and 5-variable models were selected as the most predictive for (BOD5/COD)0 and (BOD5/COD)t1/2, respectively, according to the values of statistical parameters R2 and Q2. Hence, 3-variable model predicting (BOD5/COD)0 possessed R2=0.863 and Q2=0.799 for training set, and R2=0.710 for test set, while 5-variable model predicting (BOD5/COD)1/2 possessed R2=0.886 and Q2=0.788 for training set, and R2=0.564 for test set. The selected models are interpretable and transparent, reflecting key structural features that influence targeted biodegradability and can be correlated with the degradation mechanisms of studied compounds by UV-C/H2O2.

Comparative analysis of UV-C/H2O2 and UV-A/TiO2 processes for the degradation of diclofenac in water

The study investigates the treatment of diclofenac (DCF), a pharmaceutical included in the first watch list of the European Water Framework Directive as a new potential priority substance in water. Since the conventional wastewater treatment technologies do not efficiently remove DCF, advanced treatment technologies capable of its complete removal or destruction of its biological activity, need to be evaluated and eventually employed. For that purpose, typical representatives of photooxidative and photocatalytic advanced oxidation processes were applied. The effectiveness of UV-C/H2O2 and UV-A/TiO2 were compared regarding DCF conversion and mineralization kinetics, water quality parameters for assessing biodegradability and toxicity. In spite of similar biodegradability profiles, the obtained results indicate different DCF degradation pathways, which are reflected in different profiles of toxicity towards Vibrio fischeri. The observed DCF conversion and mineralization kinetics revealed the benefits of UV-C/H2O2 process. However, lower toxicity favored the application of photocatalytic over photooxidative treatment for DCF removal.

Structural Influence on Photooxidative Degradation of Halogenated Phenols

The influence of structure on degradation of five halogenated phenols (XPs) by UV/H2O2 process was investigated. The combined influence of type or number of substituents and UV/H2O2 process parameters (pH and [H2O2]) on the degradation kinetics of 2-fluorophenol (2-FP), 2-chlorophenol (2-CP), 2-bromophenol (2-BP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) was studied using modified miscellaneous 33 full factorial design and response surface modeling (RSM). Studied XPs obey first-order degradation kinetics within the investigated range of process parameters. Determined degradation rate constants (kobs) were correlated with process and structural parameters by the quadratic polynomial models. Analysis of variance (ANOVA) demonstrated RSM models’ accuracy and showed that, in addition to pH and [H2O2], model terms related with the pollutant structure are highly influential. kobs of mono-XPs follow the decreasing order 2-FP, 2-CP, and 2-BP, while CPs follow the decreasing order 2-CP, 2,4-DCP, and 2,4,6-TCP. Biodegradability (biochemical oxygen demand (BOD)5/chemical oxygen demand (COD)) and toxicity (TU) were evaluated prior to the treatment and at the reference time intervals. The observed differences are correlated with the structural characteristics of studied XPs.