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Determining the binding capacity of concrete to chloride ions has always been the focus of the durability study of reinforced concrete structures. In many cases, concrete interior is in the electric field environment, such as railway track affected by stray current, component under electrical chloride removal (ECR), and concrete in corrosion electric field. However, the influence of electric field intensity on the chloride binding ability of concrete has not been determined clearly and quantitatively. In this paper, an experimental study is conducted to investigate the evolution of chloride binding capacity under various electrical current densities. The results indicate that the binding capacity of concrete is degraded by the electrical field, and the amount of physical adsorption for chloride is far less than the that of chemical binding. Based on experimental data, the modified Langmuir isotherm is given, and the evolution of key coefficients is measured quantitatively. The research findings are of great significance to the accurate evaluation of subsequent transmission of chloride ions after the initiation of steel corrosion and corrosion protection effect by ECR technique.

Owing to their surface active properties, surfactants have numerous applications in different fields of life. In the present research work, the solubilization of reactive red 2 (RR2) has been studied in single and mixed micellar systems (MMS) using UV-visible spectroscopy and electrical conductivity measurements. The interaction of RR2 with ionic micelles of cetylpyridinium chloride (CPC) was investigated. In order to probe the interaction of RR2 in MMS, mixtures of CPC and TX-114 (Triton X-114, a nonionic surfactant) were used. UV-visible spectroscopy has been used to obtain the degree of solubilization of RR2 in terms of the partition coefficient (Kc) and Gibbs free energy of partitioning (ΔG°p). Electrical conductivity data have been employed to detect the critical micelle concentration (CMC) of the surfactant systems in the presence of RR2 and, accordingly, to calculate the thermodynamic parameters of the micellization. From the obtained data, it is concluded that the micellization is spontaneous at all studied temperatures. Moreover, the micellization was observed to be driven by both enthalpy and entropy. The results also indicated that MMS have better solubilizing power than single micellar solutions. [ABSTRACT FROM AUTHOR]

Owing to their surface active properties, surfactants have numerous applications in different fields of life. In the present research work, the solubilization of reactive red 2 (RR2) has been studied in single and mixed micellar systems (MMS) using UV-visible spectroscopy and electrical conductivity measurements. The interaction of RR2 with ionic micelles of cetylpyridinium chloride (CPC) was investigated. In order to probe the interaction of RR2 in MMS, mixtures of CPC and TX-114 (Triton X-114, a nonionic surfactant) were used. UV-visible spectroscopy has been used to obtain the degree of solubilization of RR2 in terms of the partition coefficient (Kc) and Gibbs free energy of partitioning (ΔG°p). Electrical conductivity data have been employed to detect the critical micelle concentration (CMC) of the surfactant systems in the presence of RR2 and, accordingly, to calculate the thermodynamic parameters of the micellization. From the obtained data, it is concluded that the micellization is spontaneous at all studied temperatures. Moreover, the micellization was observed to be driven by both enthalpy and entropy. The results also indicated that MMS have better solubilizing power than single micellar solutions.

Abstract In this study, we utilized a size exclusion chromatography (SEC) system that was equipped with a fluorescence emission scanning mode to explore the heterogeneous distribution of the humification index (HIX) values within bulk dissolved organic matter (DOM). The HIX-based SEC chromatograms showed that the molecular weight (MW)-dependent distribution of aromatic condensation was heavily affected by the DOM sources and the progress of biodegradation. The HIX heterogeneity across different MW was more pronounced for terrestrial versus aquatic DOM sources. Microbial incubation of leaf litter DOM led to the initial enhancement of the HIX at a relatively low MW, followed by a gradual increase at larger MW values. The dynamic changes of the HIX can be attributed to (1) the preferential removal of non-aromatic or less-aromatic molecules by microorganisms, (2) the production of microbial metabolites, (3) microbial humification, and (4) self-assemblage of humic-like molecules. From the SEC chromatograms, the HIX-based average molecular weight (or MW HIX) was proposed as a unifying surrogate to represent an MW that was highly associated with aromatic condensation. The MW HIX discriminated four different DOM sources and described well the biodegradation-induced changes. The MW HIX also presented a good positive correlation with pyrene organic carbon-normalized binding coefficients (K oc). The prediction capability of the MW HIX for pyrene K oc was higher than those based on the single descriptors of bulk DOM, such as HIX and MW, which revealed its superior linkage with the DOM reactivity related to both MW and HIX. Graphical abstract Unlabelled Image Highlights • A SEC system with multi emission scan was applied to propose a new DOM descriptor. • The new index, MW HIX , represents a MW value associated with aromatic condensation. • MW HIX was useful to describe the structural changes of DOM upon biodegradation. • MW HIX proved its effectiveness for the prediction of pyrene binding affinity. [ABSTRACT FROM AUTHOR]

The autochthonous dissolved organic matter (DOM) released by Microcystis aeruginosa ( M. aeruginosa -DOM) during its growth period was characterized by spectroscopy. Furthermore, the relationships between the M. aeruginosa -DOM spectroscopic descriptors and the pyrene binding coefficient ( K DOC ) values were explored. The results showed that the spectroscopic characteristics of the M. aeruginosa -DOM and the binding properties of pyrene were dynamically changed along with the algae growth. Pearson correlation analysis demonstrated that a higher pyrene K DOC value was observed for the M. aeruginosa -DOM that has a higher humification index (HIX) value, a lower biological index (BIX) value and a lower absorption ratio (E2/E3). The presence of protein-like and long-wavelength-excited humic-like components may impose negative and positive effects on binding of pyrene by the M. aeruginosa -DOM, respectively. Principal component analysis (PCA) further supported that the binding affinity of pyrene may be primarily influenced by the humification degree of the M. aeruginosa -DOM. [ABSTRACT FROM AUTHOR]

The complexation flocculation (CF) method was successfully employed to identify binding coefficients (K doc ) of specific organic contaminants to dissolved organic matter (DOM, often indicated by dissolved organic carbon, DOC) in a multi-contaminant hydrophobic organic contaminant (HOC) system. K doc values were obtained for most of the evaluated 33 HOCs, indicating the feasibility and applicability of the CF method in a multi-contaminant system. Significant positive correlations were observed between binding coefficients and octanol–water partition coefficients (K ow ) for organic halogen compounds, such as polybrominated diphenyl ethers (PBDEs) ( R 2 = 0.95, p < 0.05) and organic chlorine pesticides (OCPs) (methoxychlor excluded, R 2 = 0.82, p < 0.05). The positive correlations identified between the lgK doc and lgBCF (bioconcentration factor) for PBDEs and OCPs, as well as the negative correlation observed for polycyclic aromatic hydrocarbons (PAHs), indicated that different binding or partition mechanisms between PAHs and organic halogen compounds exist. These differences further result in discriminative competition partitions of HOCs between DOM and organisms. Assuming that only freely dissolved HOCs are bioconcentrative, the results of DOM-influenced bioconcentration factor (BCF DOM ) and DOM-influenced lowest observed effect level (LOEL DOM ) indicate that the ecological risk of HOCs is decreased by DOM. [ABSTRACT FROM AUTHOR]

We have performed single-molecule studies of GFP-Lacl repressor proteins bound to bacteriophage χ DNA containing a 256 tandem lac operator insertion confined in nanochannels. An integrated photon molecular counting method was developed to determine the number of proteins bound to DNA. By using this method, we determined the saturated mean occupancy of the 256 tandem lac operators to be 13, which constitutes only 2.5% of the available sites. This low occupancy level suggests that the repressors influence each other even when they are widely separated, at distances on the order of 200 nm, or several DNA persistence lengths. [ABSTRACT FROM AUTHOR]

The diffusion-limited binding kinetics of antigen (analyte), in solution with antibody (receptor) immobilized on a biosensor surface, is analyzed within a fractal framework. Most of the data presented is adequately described by a single-fractal analysis. This was indicated by the regression analysis provided by Sigmaplot. A single example of a dual-fractal analysis is also presented. It is of interest to note that the binding-rate coefficient ( k) and the fractal dimension (Df) both exhibit changes in the same and in the reverse direction for the antigen-antibody systems analyzed. Binding-rate coefficient expressions, as a function of the Df developed for the antigen-antibody binding systems, indicate the high sensitivity of the k on the Df when both a single- and a dual-fractal analysis are used. For example, for a single-fractal analysis, and for the binding of antibody Mab 0.5β in solution to gpl20 peptide immobilized on a BIAcore biosensor, the order of dependence on the Df was 4.0926. For a dual-fractal analysis, and for the binding of 25-100 ng/mL TRITC-LPS (lipopolysaccharide) in solution with polymyxin B immobilized on a fiberoptic biosensor, the order of dependence of the binding-rate coefficients, k1 and k2 on the fractal dimensions, Df1 and Df2, were 7.6335 and-11.55, respectively. The fractional order of dependence of the k(s) on the Df(s) further reinforces the fractal nature of the system. The k(s) expressions developed as a function of the Df(s) are of particular value, since they provide a means to better control biosensor performance, by linking it to the heterogeneity on the surface, and further emphasize, in a quantitative sense, the importance of the nature of the surface in biosensor performance. [ABSTRACT FROM AUTHOR]