On the interpretation of inflated correlation path weights in concentration graphs

Statistical models associated with graphs, called graphical models, have become a popular tool for representing network structures in many modern applications. Relevant features of the model are represented by vertices, edges and other higher order structures. A fundamental structural component of the network is represented by paths, which are a sequence of distinct vertices joined by a sequence of edges. The collection of all the paths joining two vertices provides a full description of the association structure between the corresponding variables. In this context, it has been shown that certain pairwise association measures can be decomposed into a sum of weights associated with each of the paths connecting the two variables. We consider a pairwise measure called an inflated correlation coefficient and investigate the properties of the corresponding path weights. We show that every inflated correlation weight can be factorized into terms, each of which is associated either to a vertex or to an edge of the path. This factorization allows one to gain insight into the role played by a path in the network by highlighting the contribution to the weight of each of the elementary units forming the path. This is of theoretical interest because, by establishing a similarity between the weights and the association measure they decompose, it provides a justification for the use of these weights. Furthermore we show how this factorization can be exploited in the computation of centrality measures and describe their use with an application to the analysis of a dietary pattern.

Antibiotics as Inhibitor of Glutathione S-transferase: Biological Evaluation and Molecular Structure Studies

Background: The glutathione S-transferases (GSTs) are family of enzymes that are notable for their role in phase II detoxification reactions. Antibiotics have been reported to have several adverse effects on the activity of the enzymes in mammals. Aim: The aim of this study was structural and biochemical characterization of rat erythrocyte GST and understanding the effects of gentamicin, clindamycin, cefazolin, ampicillin and scopolamine butylbromide on the activity of human erythrocyte GST using rat as a model. Methods: The enzyme was purified by GSH-agarose affinity chromatography. In vitro GST enzyme activity was measured at 25°C using CDNB as a model substrate. IC50 of drugs were measured by activity %–vs compound concentration graphs. Lineweaver–Burk graphs were drawn to determine the inhibition type and Ki constants for the drugs. The structure of the enzyme was predicted via Protein Homology/analogY Recognition Engine. Results: In this study, GST was purified from rat erythrocyte with a specific activity of 6.3 EU/mg protein, 44 % yield and 115 fold. Gentamicin and clindamycin inhibited the enzymatic activity with IC50 of 1.69 and 6.9 mM and Ki of 1.70 and 2.36 mM, respectively. Ampicillin and scopolamine butylbromide were activator of the enzyme while the activity of the enzyme was insensitive to cefazolin. The enzyme was further characterized by homology modeling and sequence alignment revealing similarities with human GST. Conclusion: Collectively, it could be concluded that gentamicin and clindamycin are the inhibitors of erythrocyte GST.

DEVELOPMENT OF ELECTROCHEMICAL SENSORS FOR QUANTITATIVE ANALYSIS OF METHYLDOPA AT MODIFIED-GCE AND PGE ELECTRODES BY VOLTAMMETRY

Methyldopa is one of the important drugs used in the treatment of high blood pressure (hypertension). In addition to various methods such as chromatographic and spectrophotometric methods, electrochemical methods are used for the determination of methyldopa. However, poly (p-aminobenzene sulfonic acid), pen-tip graphite electrode (PGE) study was not found in the literature search. Modified electrodes are important because they increase the sensitivity of the analysis. Furthermore, electrochemical methods have advantages such as being faster and cheaper than other instrumental analysis methods, being more sensitive, not requiring long pretreatments in the preparation of samples. In this study, the glassy carbon electrode (GCE) was modified with poly(p-aminobenzene sulfonic acid) to prepare poly (p-aminobenzene sulfonic acid) -modified glassy carbon electrodes. Cyclic voltammetry (CV) technique was used for the electropolymerization process. Methyldopa was selected in various concentrations of phosphate pH 7.40 buffer, anodic and cathodic voltamograms were taken and oxidation and reduction properties were investigated. Measurements were taken at different scanning rates by CV technique and the current type of methyldopa was determined. Peak flow-concentration graphs were drawn from the measurements taken by Differential Pulse Voltammetry (DPV) technique and the linearity range was 0.020- 2.500 µM for modified-GCE and 0.020-2.820 µM for PGE. The limit of detection (LOD) was calculated as 0.006 µM for modified-GCE, 0.012 µM for PGE. The limit of quantification (LOQ) was calculated as 0.020 µM for modified-GCE and 0.040 µM for PGE.

Path weights in concentration graphs

Summary A graphical model provides a compact and efficient representation of the association structure in a multivariate distribution by means of a graph. Relevant features of the distribution are represented by vertices, edges and higher-order graphical structures such as cliques or paths. Typically, paths play a central role in these models because they determine the dependence relationships between variables. However, while a theory of path coefficients is available for directed graph models, little research exists on the strength of the association represented by a path in an undirected graph. Essentially, it has been shown that the covariance between two variables can be decomposed into a sum of weights associated with each of the paths connecting the two variables in the corresponding concentration graph. In this context, we consider concentration graph models and provide an extensive analysis of the properties of path weights and their interpretation. Specifically, we give an interpretation of covariance weights through their factorization into a partial covariance and an inflation factor. We then extend the covariance decomposition over the paths of an undirected graph to other measures of association, such as the marginal correlation coefficient and a quantity that we call the inflated correlation. Application of these results is illustrated with an analysis of dietary intake networks.

Anodisation of Aluminium in Aqueous Sodium Oxalate and Sodium Sulphate Media

An investigation was conducted on the anodisation of commercial grade aluminium in aqueous sodium sulphate and sodium oxalate solutions. The parameters investigated were anodisation potential and electrolyte composition. Degree of anodisation was evaluated by visual observation of the anodised surface, analyses of current-concentration graphs at constant potential and current-potential characteristics, and measurement of corrosion rate of the anodised surface. Anodisation potential played an important role on the degree of anodisation. The optimum potential was 400 mV and 800 mV wrt saturated Ag/AgCl (SSE) reference electrode for sodium sulphate and sodium oxalate solutions respectively. Below and above the optimum potential poor anodisation was due to insufficient production of Al3+ to form anodic film and surface breakdown respectively. Anodisation increased with the increase of oxalate concentration. Sulphate concentration was less effective on the degree of anodisation. Between the two electrolytes sodium oxalate was more suitable than sodium sulphate for aluminium anodisation. DOI: http://dx.doi.org/10.3329/rujs.v38i0.16544 Rajshahi University J. of Sci. 38, 09-16 (2010)