Thirumalachari Ramasami

Removal of diazo and triphenylmethane dyes from aqueous solutions through an adsorption process

Direct Red 31, Acid Black 1 and Acid Green 16 belonging to diazo and triphenylmethane classification of dye chemicals are widely used during the manufacture of leather. The spent dyestuffs in wastewater escape biological treatment owing to their poor biodegradability. An adsorption procedure was used in this study for the removal of dyes from aqueous solution using Rice Bran-based Activated Carbon (RBAC). The molecular weight of the dye chemicals, the mass of RBAC and the diameter of RBAC particle had positive effects on the rate of adsorption. Initial concentration of dye chemicals, pH of the dye solution and temperature of adsorption showed a negative impact on adsorption. The enthalpies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were -32.1, -23.4 and -21.7 KJ mol -1 respectively, indicating the adsorption was an exothermic physical process. The entropies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were -96.94, -59.92 and -26.96 J K -1 mol -1 respectively, suggesting that RBAC favours the adsorption process.

Recent Trends in Leather Making: Processes, Problems, and Pathways

Leather processing has emerged as an important economic activity in several developing countries. Awareness of environmental problems has increased considerably and during recent years protecting environment has become a global issue. Currently the leather processing industry is going through a phase change due to global environmental regulations. The article summarizes the current leather processing methods with their rationale and environmental problems. It has been revealed that pretanning and tanning processes contribute 80–90% of the total pollution load (BOD, COD, TS, TDS, Cr, S2−, sludge, etc.). Further, toxic gases like ammonia and hydrogen sulfide are also emitted. Volatile organic compounds, heavy metals, and carcinogenic arylamines from posttanning and finishing operations are also creating severe concern. Apart from this, a great deal of solid wastes like lime sludge from tannery and chrome sludge from effluent treatment plants are being generated. Advanced processing techniques as well as effluent treatment strategies for combating environmental and human health risks are reviewed in detail. The leather processing industry in various countries, however, is facing a serious challenge from the public and government. This is in spite of the implementation of several advanced processing techniques and treatment systems. Hence, there is a need to revamp leather processing methods anew for the sustainability of leather industry. Some of the novel concepts in leather processing are briefly mentioned and discussed.

Apoptosis of lymphocytes induced by chromium(VI/V) is through ROS-mediated activation of Src-family kinases and caspase-3

Mechanistic insights into Cr(VI)-induced carcinogenicity and possible implication of Cr(V) species formed by the redox reactions of chromium-bearing species have attracted interest. We have previously demonstrated that when human peripheral blood lymphocytes are exposed to the Cr(V) complexes, viz., sodium bis(2-ethyl-2-hydroxybutyrato)oxochromate(V), Na[Cr(V)O(ehba)(2)] and sodium bis(2-hydroxy-2-methylbutyrato)oxochromate(V), Na[Cr(V)O(hmba)(2)], apoptosis and formation of reactive oxygen species (ROS) are observed. The molecular mechanisms involving cellular signaling pathways leading to apoptosis are addressed in the present study. Treatment of lymphocytes with Na[Cr(V)O(ehba)(2)] and K(2)Cr(2)O(7) leads to the activation of the Src-family protein tyrosine kinases namely, p56(lck), p59(fyn), and p56/53(lyn), which then activates caspase-3, both of which are under the partial influence of ROS. Inhibition of the Src-family tyrosine kinases activity by PP2 and of caspase-3 by Z-DEVD-FMK reverses apoptosis, thereby suggesting their importance. Antioxidants only partially reverse the apoptosis induced by Cr(VI/V), suggesting that pathways other than those induced by ROS cannot be ruled out. Although the complex, Na[Cr(V)O(ehba)(2)] is known to be relatively stable in aqueous solutions, previous studies have shown that the Cr(V) complex, Na[Cr(V)O(ehba)(2)] disproportionates to Cr(VI) and Cr(III) forms at pH 7.4 through complex mechanistic processes. Dynamics studies employing EPR data show that the Cr(V) state in Na[Cr(V)O(ehba)(2)] is relatively more stable in RPMI-1640 medium containing plasma. Formation of ROS during the reaction of redox partners with Na[Cr(V)O(ehba)(2)] is an early event and compares favorably in kinetic terms with the reported rate processes for disproportionation. This investigation presents evidence for the direct implication of Cr(V) in Cr(VI)-induced apoptosis of lymphocytes.

Caspase-3: Its potential involvement in Cr(III)-induced apoptosis of lymphocytes

In this study, we have examined the role of caspase-3 in apoptosis of lymphocytes induced by the chromium(III) complexes viz. tris-(1,10-phenanthroline)chromium(III) chloride (Cr(III)-phen) and trans-diaqua[1,3-bis(salicylideneamino)propane-chromium(III)] perchlorate (Cr(III)-salprn). Evidence for caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage in lymphocytes exposed to Cr(III) complexes is revealed through Western blotting analysis. Blocking the activity of caspase-3 with z-DEVD-fmk, prevents apoptosis as evidenced through [3H]-thymidine incorporation, DNA fragmentation assay and measurement of sub-G1 cells by flow cytometry. Pretreatment of lymphocytes with free radical scavengers completely attenuates the activity of caspase-3 suggesting that reactive oxygen species (ROS) are upstream activators of caspase-3. Preincubation of lymphocytes with PP2, a selective Src-family tyrosine kinase inhibitor, abolishes the activation of caspase-3 indicating that Src-family tyrosine kinases viz. p56lck, p59fyn and p53/56lyn are mediators of caspase-3 activation during Cr(III) exposure. Collectively, our findings support a plausible mechanism in which Cr(III) mediates ROS generation that precedes the up-regulation of p56lck, p59fyn and p53/56lyn which eventually activates caspase-3 to promote apoptotic cell death of lymphocytes. To our knowledge, this is the first report suggesting the importance of Src-family tyrosine kinases for the activation of caspase-3 in metal-induced apoptotic cell death.

Speciation and recovery of chromium from chromite ore processing residues

The processing of chromite ore is associated with the generation of large quantities of solid wastes containing chromium, which have been disposed of as landfill for many years. The mobilization and operational speciation of chromium contained in soils contaminated with metal salts are important in terms of the environment. Several methods have been employed for the extraction and recovery of solid wastes. Chromium contained in contaminated soils and solid wastes can be categorized as exchangeable, oxidizable, carbonate-bound, reducible and residual. The results from this study indicate a need for efficient leaching methodologies in chromite ore processing plants to decrease the non-detrital fractions of chromium in the residue. Aggressive methodologies are required to recover chromium from the detrital fractions. The potential benefits of employing sodium peroxide for the complete recovery of chromium from chromite residue have been demonstrated, and the need to ensure the safety of the process has been emphasized.

Inhibition of collagenase by Cr(III): its relevance to stabilization of collagen

Bacterial collagenase has now been reacted with a select series of Cr(III) complexes and modifications in the activity of chromium-modified collagenase has been deduced from the extent of hydrolysis of (2-furanacryloyl-L-leucyl-glycyl-L-prolyl-L-alanine), FALGPA. A homologous series of Cr(III) complexes with dimeric, trimeric and tetrameric structures as in 1, 2 and 3 respectively has been investigated for their ability to inhibit the action of collagenase against FALGPA. Whereas competitive and non-competitive modes of inhibition of collagenase are expressed by 1, (dimer) and 2, (trimer) respectively, the tetramer, 3, exhibits poor affinity to collagenase and the inhibition of the enzyme activity is uncompetitive. Evidence for different modes of inhibition of collagenase depending on the nature of Cr(III) species has been presented in this work. Circular dichroism and gel electrophoresis data on Cr(III) modified collagenase corroborate the hypothesis that the inhibition of collagenase by the heavy metal ion arises from secondary and quaternary structural changes in the enzyme. The implications of the observed Cr(III) species specific inhibition of collagenase in gaining new insight into the mechanism of stabilization of collagen by Cr(III) are discussed.

Molecular dynamic simulation studies on the effect of one residue chain staggering on the structure and stability of heterotrimeric collagen-like peptides with interruption†

A systematic molecular dynamics (MD) simulation has been carried out on collagen-like peptides with different combinations of interruptions in the Gly-X(AA) -Y(AA) repeats. Although experimental studies have been carried out to elucidate the structural consequences of homotrimeric collagen-like peptides, this is the first report on the structural effect on the heterotrimeric models with G4G and G1G breaks present simultaneously in the constituent chains with difference in one residue chain staggering. The results reveal that the axial registry of the interrupted region changes significantly from that of conventional triple helical peptide without interruption. Further, results from MD simulations show the formation of a kink in the interrupted region of the triple-helical peptides. The conformational analysis reveals that the interruption in the Gly-X(AA) -Y(AA) pattern in these peptides induces β-strand conformation in triple helical peptides. The conventional hydrogen bonds in the interrupted triad are affected and new nonconventional H-bonds are formed in the triple helical structure, and as a result interrupted region becomes locally fragile. MM-PBSA calculations on the different systems clearly suggest that the binding affinity varies marginally due to one residue staggering. However, it is found from the structural parameters that hydrogen-bonding pattern differs significantly due to the difference in the staggering of chains.

Synthesis, crystal structure and reactivity of trans-diaquo N,N′-ethylenebis-(3-methoxysalicylideneiminato)chromium(III)

A new chromium(III) Schiff base complex, [Cr(3-methoxysalen)(H2O)2]ClO4, where salen = N,N′-ethylenebis- (salicylideneimine), has been synthesized and characterized by spectroscopic techniques. Single crystal X-ray data reveals that the complex assumes a trans-diaquo structure with formulation [Cr(C18H22N2O6)]ClO4 but, unlike in Cr (salen)(H2O)2+, the two trans-water molecules are equidistant from CrIII. The effect of the substituent on the phenyl ring in respect of redox reactivity has been investigated. The kinetics of the oxidation of [Cr(Schiff base)- (H2O)2]ClO4, where Schiff base = salen, (1) and 3-OMe-salen, (2) by PhOI has been studied. The bimolecular rate constant for the formation of the O=Crv Schiff base in case of (2) was four times faster than that of (1). The introduction of the OMe group substituent on the phenyl ring influences not only the structure and crystal packing, but also the reactivity of the complex and the electronic environment around the metal ion.

Role of Secondary Structure on the Stress Relaxation Processes in Rat Tail Tendon (RTT) Collagen Fibre

One of the important physical properties of collagen is viscoelasticity. The molecular and the matrix stability of collagen arises from the interplay of wide range of forces, namely covalent and hydrogen bonding, ionic interactions, hydrophobic interactions, van der Waals forces and weak interactions. Therefore, the stress relaxation behaviour of native rat tail tendon (RTT) collagen fibre has been studied in water, saline media, 1, 3 and 6 M urea solutions, 0.02 M tris(maleate) buffer at pH 4–8 and 7 mol-% of methanol, ethanol and propanol at various temperatures. Experimental values of fractional stress change σ/σ0 as a function of time have been fitted to one-, two- and three-term models. The results show that the two-term model is the best fit for the experimental data. Two different rates of relaxation (fast and slow) have been computed using a non-linear least-squares fit. Arrhenius plots of the temperature dependence of the rates constant are non-linear. The activation energy values at absolute zero have been computed using the rates of relaxation under different experimental conditions. Thermodynamic parameters have also been calculated using the rates of relaxation.

Non-enzymatic phosphorylation of bovine serum albumin by Cr(V) complexes: Role in Cr(VI)-induced phosphorylation and toxicity

Evidence for the non-enzymatic phosphorylation of bovine serum albumin (BSA) by sodium bis(2-ethyl-2-hydroxybutyrato)oxochromate(V), Na[CrVO(ehba)2], 1, sodium bis(2-hydroxy-2-methylbutyrato)oxochromate(V), Na[CrVO(hmba)2], 2 and potassium dichromate, K2Cr2O7, 3 in the presence of labeled adenosine-5′-triphosphate (ATP) under conditions of physiological pH is presented. Aggregation and extent of phosphorylation of BSA mediated by 1, 2 or 3 seems to increase with the concentration and time of incubation of the reaction mixture containing all the reactants. The [γ-32P] label in ATP is incorporated into aggregates of BSA in the in vitro reaction of the protein with ATP in the presence of 1, 2 or 3. Phosphorylation of BSA by ATP in the absence of 1, 2 or 3 is negligible. Addition of EDTA reverses aggregation of protein and liberates partially the incorporated phosphate label. The stoichiometry of phosphorylation is found to be the highest and is equal to 12.25 mol PO43−/mol BSA in the presence of 500 μM of 1, which decreases to 10.56 mol PO43−/mol BSA after EDTA treatment. Resistance to the removal of phosphate label by EDTA increases with increase in time of incubation. Dialysis of phosphorylated BSA reverses the incorporated [γ-32P] label only partially, indicating the formation of covalent links of phosphate groups to BSA. Evidence for the site of phosphorylation in the reaction mediated by 1, 2 or 3 being hydroxyl side groups of tyrosine and serine/threonine residues has been gained. Based on the results, a possibility that 1, 2 and 3 mimic the function of tyrosine and serine/threonine kinases has been invoked.