Biomedical subjects

R Weerasooriya

Publications and source records attributed to R Weerasooriya.

7 recordsLinked to original sources

PubMed2005

Thermodynamics of monochlorophenol isomers and pyrite interfacial interactions in the activation state.

Thermodynamic parameters of the activation state for phenol and three monochlorophenol (MCP) isomer-pyrite complexes, i.e., MCP isomers used were 2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), have been derived from the temperature-dependent kinetic data. Both the initial rate and adsorption density values increased in the order phenol < 2-CP < 3-CP < 4-CP. This suggests that the presence of chlorine substituent on the aromatic ring results in enhanced CP adsorption on pyrite. The activation energy (E(a)), Gibbs free energy (deltaG#), entropy (deltaS#), and enthalpy (deltaH#) of the activation stage for MCP adsorption on pyrite were calculated by Arrhenius and Eyring models. Always deltaS# values approximate to zero and -TdeltaS# values are positive, which indicates that the activation state of MCP adsorption process is entropy-controlled, and the observed linear dependence of deltaH# on -TdeltaS# signals an entropy-enthalpy compensation effect of the MCP adsorption process. The gammaMCP data were quantified well both by 1 - pK diffused double layer (1 - pK DLM) and Langmuir models.

Journal Article↗

PubMed2004

Modeling interactions at the tributyltin-kaolinite interface.

Tributyltin (TBT) is a common pollutant in natural environments and the interaction with mineral surfaces largely determine its solubility, speciation, bioavailability, and transport in aqueous systems. The present work aimed at quantifying the TBT adsorption using kaolinite and a kaolinite-rich sediment as sorbent materials. Experiments were conducted under conditions that are important from an environmental perspective. Proton adsorption data were determined for kaolinite as a function of pH and electrolyte concentrations to ascertain intrinsic acidity constants and site density values. The pH(zpc) of kaolinite sample KGa was determined at 4.9 by surface titration. The generalized diffused double layer model (DLM) was used to quantify both, proton and TBT adsorption. Following intrinsic acidity and TBT binding constants resulting from the TBT/kaolinite system were used: >SOH ==> >SO- + H+, logK = -5.4; >SOH + H+ ==> SOH2+, logK = 4.6; >XNa + H ==> XH + Na+, logK(X/H+) = -1.1; >SO- + TBT+ ==> >SOTBT, logK = 3.5; >XNa + TBT+ ==> Na+, logK(X/TBT) = 1.0. All surface-active variable charge sites on kaolinite, namely >AlOH and >SiOH are grouped and collectively refer to as >SOH in this paper. >XNa refers to ion exchange sites. Modeling of TBT adsorption onto kaolinite was conducted distinguishing selective (high affinity) sites (>S(S)OH) in addition to non-selective sites (>SOH). The inclusion of >S(S)OH was essential in order to quantify TBT adsorption successfully, while the inclusion of >XNa was optional. The reduction of surface coverage values by a 10-fold TBT adsorption modeling is in agreement with the results of molecular model calculations of the system. Parameters calculated for the monophase kaolinite were subsequently used to quantify the TBT adsorption onto kaolinite-rich sediment.

Adsorption↗

PubMed2004

Macroscopic and vibration spectroscopic evidence for specific bonding of arsenate on gibbsite.

The As(V) adsorption onto gibbsite under different experimental conditions was examined. Macroscopic data suggests strong As(V) bonding on gibbsite possibly via a bidendate binuclear complexation mechanism. The As(V) adsorption was quantified with the charge distribution multi-site ions complexation (CD-MUSIC) model distributing the anion charge over 0- and 1-planes according to the modified Pauling's bond valence theory. In the dual-adsorbates system of As(III) and As(V), the As(III) adsorption was predicted up to pH 8 utilizing the binding constants derived for single-adsorbate data. However, with pH > 8, the modeled As(III) adsorption data is overestimating the experimental values.

Adsorption↗

PubMed2003

On the mechanistic modeling of As(III) adsorption on gibbsite.

Arsenite adsorption on gibbsite was examined as a function of pH, ionic strength (I) and contact time (t(C)). As(III) showed a weak affinity for gibbsite surface. The trends of pH=f(Gamma(ads)) curves have showed a marked deviation from a typical anion adsorption edge showing a maximum Gamma(ads) around pH approximately 8.2. The experimentally derived proton exchange ratio has always converged to zero when 0.26< summation operator [As(III)]<7 microM and 6.2<pH<8.2. The isosteric heat of adsorption, DeltaH(r), exhibited invariant behavior with respect to Gamma(ads). The As(III) adsorption data was quantified by charge distribution multi-site complexation (CD MUSIC) model using the surface complex postulated below:

Adsorption↗

PubMed2001

Pyrite-assisted degradation of trichloroethene (TCE).

Chemical kinetics of trichloroethene (TCE) degradation by pyrite was investigated at different experimental conditions. The TCE was transformed into C2H2, 1,1-dichloroethene (DCE) and C2H4 by a slow process (240 h required to convert TCE by 80%). Thereafter, the degradation rate showed a monotonous increase with the pH. A simple kinetic model was proposed to quantify the TCE degradation by pyrite.

Iron↗

PubMed1999

Modeling Anion Adsorption on Kaolinite.

Anion adsorption onto kaolinite was quantified using the triple layer surface complexation model. Fluoride adsorption data were described by both anion exchange and H-bonded complexation mechanisms. The outer-sphere complexation mechanism was used to describe the weak adsorption of Cl-, Br-, and I- on kaolinite. The F- adsorption in the presence of Br- or I- was decreased over a range of pH 4-5 whereas Cl- showed a negligible effect. Competition for binding sites appeared to be an important factor in determining the adsorptive behavior of F- in Br- or I- mediated systems. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Effects of chelation with EDTA and vitamin B therapy on nitric oxide-related endothelial vasodilator function.

1. 'Chelation therapy' with EDTA is being frequently used in patients with cardiovascular disease, despite limited objective evidence of effectiveness. Depressed nitric oxide (.NO)-related endothelial function accompanies atherosclerosis, and even the vascular risk factors alone, and is improved by numerous interventions that also improve prognosis in vascular disease. 2. The aim of the present study was to determine the influence of chelation therapy with EDTA alone and EDTA in combination with B vitamins on endothelial function. 3. After a control series of saline infusions, we examined the effects of a series of EDTA infusions (1.5 g, 10 times over 6 weeks) in eight subjects with coronary artery disease. In addition, because EDTA is commonly supplemented by other components, particularly B group vitamins, we subsequently examined the effect of a similar series of vitamin-supplemented EDTA infusions. 4. Forearm blood flow (FBF) was assessed by plethysmography and graded intrabrachial infusions of the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent dilator sodium nitroprusside (SNP). 5. There was no difference in vasodilation to either drug after EDTA alone compared with the control periods, but the response to ACh was augmented after combined therapy (P < 0.03, ANOVA). The latter was accompanied by a small but consistent mean (+/- SEM) fall in plasma homocysteine of 1.6 +/- 0.5 mumol/L (P < 0.05). 6. The selective increase in the vasodilator response to ACh after therapy with EDTA and several B group vitamins indicates that NO-related endothelial function was improved. The absence of response to EDTA alone suggests that the supplementary vitamins were necessary for this benefit, which may have been related to the accompanying decrease in plasma homocysteine. These results, along with the current interest in the possible cardioprotective effects of vitamins and the increasing administration of 'chelation therapy', call for more definitive studies on these aspects of 'alternative medicine'.

Acetylcholine↗