J. Oyebamiji Babalola

Kinetic, equilibrium, and thermodynamic studies of the biosorption of cadmium (II) from solution by Stereophyllum radiculosum.

Biosorption of heavy metal ions can be an effective process for the removal of Cd(II) from wastewater. In this study, the batch removal of Cd(II) from dilute aqueous solution using Stereophyllum radiculosum as the biosorbent has been investigated. The Cd(II) uptake was dependent on the initial pH, contact time, initial metal ion concentration, and temperature. The residual Cd(II) in the solution was determined using Atomic Absorption Spectrophotometer. The optimum pH for the biosorption was pH 6. Maximum biosorption was obtained after 60 min of the process. Kinetic study showed that the pseudo-second-order rate equation best described the biosorption process. The adsorption isotherms obtained fitted well into the Freundlich and Langmuir isotherm. The Freundlich equation obtained was log Ⲅ = 2.6924 logC e + 0.1131, while the Langmuir equation obtained was 1/Ⲅ = 0.0008/C e + 17.41. The correlation factors obtained were 0.0995 and 0.9904, respectively. The free energy change obtained for the biosorption of Cd(II) at 300 K, initial Cd(II) concentration of 100 mg L-1 and pH 6 was -20.894 kJ mol-1. The thermodynamic study showed that the increase in temperature led to increase in the amount of the metal ion biosorbed. These results indicate that S. radiculosum has potential for the uptake of Cd(II) from industrial effluents.

Biosorption of Ni(II), Cr(III), and Co(II) from Solutions Using Acalypha hispida Leaf: Kinetics, Equilibrium, and Thermodynamics

Biosorption studies were conducted to study the removal of Ni(II), Cr(III), and Co(II) from aqueous solution of Acalypha hispida leaf. The FTIR spectral characteristics of Acalypha hispida leaf revealed the presence of ioniazable groups that could participate in the binding of metal ions in solution. The kinetic, equilibrium, and thermodynamic studies of the biosorption of the metal ions were investigated using various physicochemical parameters; each parameter was found to affect the biosorption process. The kinetic studies showed that the biosorption process was best represented by pseudo-second-order kinetics among four kinetic models tested. Equilibrium data were better represented by Freundlich isotherm among Langmuir and Freundlich adsorption isotherms. The study on the effect of dosage showed that the dosage of the biomass significantly affected the uptake of the metal ions from solution. Thermodynamic parameters such as standard Gibbs-free energy (), standard enthalpy (), standard entropy (), and the activation energy were calculated. The order of spontaneity of the biosorption process was found to be Cr(III) > Ni(II) > Co(II). The activation energy for the biosorption of each of the metal ions was less than 42 kJmol−1 at 323 K indicating that each was a diffusion-controlled process.

Kinetic, equilibrium and thermodynamic studies of the biosorption of Ni(II), Cr(III) and Co(II) from aqueous solutions using banana (Musa acuminata) leaf

The biosorption of Ni(II), Cr(III) and Co(II) by banana (Musa acuminata) leaf is reported in this work. The effects of solution pH, contact time, initial metal ion concentration and temperature on the biosorption of the metal ions were investigated. Optimum pH for each metal ion was obtained because the biosorption of each of the metal ions was found to be pH-dependent. Kinetic study shows that the pseudo-second-order kinetic model best represents the biosorption of the metal ions. The sorption of each metal ion was analysed with Freundlich and Langmuir isotherm models, and in each case, the Langmuir model appears to have better regression coefficients than the Freundlich model. Study on the effect of dosage, shows that the dosage of the biomass significantly affects the uptake of the metal ions from solution. Thermodynamically, the biosorption of each of the metal ions is endothermic and the order of spontaneity of the biosorption process being Ni(II)>Cr(III)>Co(II). Similarly, positive change in entropy was observed for each and the order of disorder is Co(II)>Ni(II)>Cr(III).

Effect of A3[6]βGlu → Val mutation on reactivity of the CysF9[93]β sulfhydryl group of human haemoglobin S

The pH dependence profiles of the apparent second-order rate constant, kapp, for the reaction of the oxy, carbon monoxy and aquomet derivatives of human haemoglobin S with 5,5′-dithiobis(2-nitrobenzoate)(DTNB) in buffers of ionic strength 50 mmol dm–3 are complex. The pKas of the ionizable organic phosphate binding groups which influence the reactivity of the CysF9[93]β sulfhydryl group have been determined from quantitative analyses of the complex profiles. These pKa values were not significantly different from those of haemoglobin A. In the presence of inositol hexakisphosphate (inositol-P6) each profile assumes a simple form resembling the titration curve of a diprotic acid. The pKas of HisHC3[146]β and CysF9[93]β were determined from quantitative analyses of the simple profiles. The mean values obtained, 6.6 ± 0.2 and 8.84 ± 0.04, respectively, were the same as those of haemoglobin A. Comparison of the kapp data for haemoglobin S with those of haemoglobin A shows that, irrespective of the presence or absence of inositol-P6 presence, the carbon monoxy and aquomet derivatives of haemoglobin A react more rapidly than the corresponding haemoglobin S derivatives. In contrast, in the absence of inositol-P6, oxyhaemoglobin A reacts faster than oxyhaemoglobin S; in the presence of the organic phosphate both haemoglobins react at about the same rate. At an ionic strength of 200 mmol dm–3 in the absence of inositol-P6, the pH dependence profiles of kapp for the oxy, carbon monoxy and aquomet derivatives of haemoglobins A and S are simple. Quantitative analyses of these profiles give mean pKa values of 5.4 ± 0.1 and 8.9 ± 0.2 for HisHC3[146]β and CysF[93]β, respectively. The oxy and carbon monoxy derivatives of both haemo-globins react at about the same rate, but aquomethaemoglobin A reacts significantly more rapidly than aquomethaemoglobin S.

Organic phosphate-binding groups electrostatically linked to the reactivity of the Cys F9 [93]β sulfhydryl group of haemoglobin

At an ionic strength of 0.05 mol dm–3 the pH-dependence profile for the reaction of the Cys F9 [93]β 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-P6) 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 pKa values around 6.6 and 8.7. These pKas are assigned to His HC3 [146]β and Cys F9 [93]β, respectively.Since inositol-P6 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 pKa 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]β sulfhydryl group. The pKa of 6.4 is assigned to His NA2 [2]β and HisH21 [143]β; the pKa of 7.5 is assigned to Val NA1 [1]β; and the pKa of 9.5 is assigned to Cys F9 [93]β. 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.

Tertiary conformational transition in sheep hemoglobins induced by reaction with 5,5´-dithiobis(2-nitrobenzoate) and by binding of inositol hexakisphosphate

We have determined the second-order reverse rate constant, k(R), for the reaction of 5,5 -dithiobis(2-nitrobenzoate) - DTNB - with sheep hemoglobins as a function of pH from values of the second-order forward rate constant, k(F), and the equilibrium constant, K(equ), at 25 degrees C: k(R)=k(F)K(equ). We demonstrate that (i) inositol hexakisphosphate (inositol-P(6)) decreases k(F) and k(R) by increasing K(rt), the rright harpoon over left harpoont tertiary conformation transition constant; (ii) the conformation favored for both the forward and reverse reactions is the r conformation. For stripped hemoglobin we obtain from the k(F) data a t isomer population of 34.6% (+/-14) prior to reaction with DTNB; from the k(R) data we calculate a t isomer population of 44.8% (+/-4) following reaction with DTNB. In the presence of inositol-P(6) the latter value is increased to 79.5% (+/-2). These results demonstrate that an allosteric transition occurs on reaction with DTNB and on inositol-P(6) binding.