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The hard fibrovascular network of the fruit of Luffa cylindrica, loofah, was used in a batch sorption system to remove methylene blue (MB) from aqueous solution. The effects of pH on the sorption of MB by loofah were studied using equilibrium isotherm experiment. The Langmuir sorption capacity (q m, mg/g) of the loofah increased with increase in pH. The Freundlich isotherm models favored the prediction of the theoretical sorption capacity more than the Langmuir isotherm models. The kinetics of the sorption process was studied at varying initial MB concentrations using pseudo-first-order and pseudo-second-order kinetic models. The pseudo-second-order kinetic model was found to fit the experimental data for the entire sorption period with high coefficient of determination (r 2). The prospects of regenerating the loofah was studied using four different eluting solvents in batch desorption studies. The results of the batch desorption studies showed that both chemisorption and ion-exchange played prominent role in the sorption process. The elution curve obtained from the continuous desorption studies showed that the elution rate was very fast and high elution efficiency could be obtained with 0.1 M HCl as an eluting solvent. The IR analysis confirmed the presence of polar functional groups and established interactions between the MB molecules and these functional groups.

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The sponge of Luffa cylindrical (LFC), a fibrous material, was employed as adsorbent for the removal of Brilliant Green (BGD) from aqueous effluent via batch studies. The optimum removal of BGD was found at pH 8.2 and the equilibrium was attained within 3 hours. The kinetic data are analyzed using several models including pseudo-first-order, pseudo-second-order, power function, simple elovich, intraparticle diffusion, and liquid film diffusion. The fitting of the different kinetics models to the experimental data, tested by error analysis, using the linear correlation coefficient ( 2 ) and chi-square analysis ( 2 ), showed that the mechanism of adsorption process was better described by pseudo-second-order and power function kinetic models. The equilibrium isotherm data were analyzed using Langmuir, Freundlich, and Temkin models and the sorption process was described by the Langmuir isotherm with maximum monolayer adsorption capacity of 18.2 mg/g at 303 K. The thermodynamic properties Δ 0 , Δ 0 , and Δ 0 showed that adsorption of BGD onto LFC was spontaneous, endothermic, and feasible within the temperature range of 303-313 K.

At an ionic strength of 0.05 mol dm-3 the pH-dependence profile for the reaction of the Cys F9 [93] /? sulfhydryl group of human haemoglobin (stripped of organic phosphates) with 5,5'-dithiobis(2-nitrobenzoate) (DTNB) is complex. In the presence of a four-fold molar excess of inositol hexakisphosphate (inositol-P,) over haemoglobin tetramers, the pH-dependence profile changes dramatically from a complex to a simple form resembling the titration curve of a diprotic acid. Values of the apparent second-order rate constant, kapp , are also drastically reduced. Quantitative analyses of the simple profiles indicate that the reactivity of the sulfhydryl is linked to the ionization of two amino acid residues on the protein, with pK, values around 6.6 and 8.7. These pK,s are assigned to His HC3 [146] /? and Cys F9 [93] /?, respectively.Since inositol-P, simplifies the complex pH-dependence profile obtained for stripped haemoglobin by binding to the cationic groups at the organic phosphate binding site, we have analysed the complex pH-dependence profile of stripped haemoglobin quantitatively by assuming that there is an electrostatic interaction between the sulfhydryl and the cationic groups. From the analyses of the complex profiles for the oxy, carbon monoxy, azidomet and cyanomet derivatives, mean pK, values of 6.4 & 0.1, 7.5 & 0.2 and 9.5 & 0.02 are obtained for the groups that are electrostatically linked to the Cys F9 [93] /? sulfhydryl group. The pK, of 6.4 is assigned to His NA2 [2] /? and HisH21 [143] /?; the pK, of 7.5 is assigned to Val NA1 [l] /?; and the pK, of 9.5 is assigned to Cys F9 [93] /?. For aquomethaemoglobin, analysis shows that, in addition to these groups, the water molecule attached to the sixth coordination position of the iron(iii) atom is also electrostatically linked to the sulfhydryl.