Biosorbents for heavy metals removal and their future

"Natively unfolded" proteins occupy a unique niche within the protein kingdom in that they lack ordered structure under conditions of neutral pH in vitro. Analysis of amino acid sequences, based on the normalized net charge and mean hydrophobicity, has been applied to two sets of proteins: small globular folded proteins and "natively unfolded" ones. The results show that "natively unfolded" proteins are specifically localized within a unique region of charge-hydrophobicity phase space and indicate that a combination of low overall hydrophobicity and large net charge represent a unique structural feature of "natively unfolded" proteins.

Why are "natively unfolded" proteins unstructured under physiologic conditions?

Heavy metal removal from water/wastewater by nanosized metal oxides: a review.

The experimental material accumulated in the literature on the conformational behavior of intrinsically unstructured (natively unfolded) proteins was analyzed. Results of this analysis showed that these proteins do not possess uniform structural properties, as expected for members of a single thermodynamic entity. Rather, these proteins may be divided into two structurally different groups: intrinsic coils, and premolten globules. Proteins from the first group have hydrodynamic dimensions typical of random coils in poor solvent and do not possess any (or almost any) ordered secondary structure. Proteins from the second group are essentially more compact, exhibiting some amount of residual secondary structure, although they are still less dense than native or molten globule proteins. An important feature of the intrinsically unstructured proteins is that they undergo disorder–order transition during or prior to their biological function. In this respect, the Protein Quartet model, with function arising from four specific conformations (ordered forms, molten globules, premolten globules, and random coils) and transitions between any two of the states, is discussed.

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Natively unfolded proteins: a point where biology waits for physics.

Adsorption of dyes and heavy metal ions by chitosan composites: A review

Heavy metal adsorbents prepared from the modification of cellulose : A review

Summary: Three new genes encoding the serine-aspartate (SD) repeat-containing proteins SdrC, SdrD and SdrE were found in Staphylococcus aureus strain Newman. The SD repeats had earlier been found in the S. aureus fibrinogen-binding clumping factors ClfA and ClfB. The clfA and clfB genes encode high-molecular-mass fibrinogen-binding proteins that are anchored to the cell surface of S. aureus. The sdr genes now reported are closely linked and tandemly arrayed. The putative Sdr proteins have both organizational and sequence similarity to ClfA and ClfB. At the N-terminus, putative secretory signal sequences precede approximately 500 residue A regions. The A regions of the Sdr and Clf proteins exhibit only 20–30% residue identity when aligned with any other member of the family. The only conserved sequence is the consensus motif TYTFTDYVD. The Sdr proteins differ from ClfA and ClfB by having two to five additional 110–113 residue repeated sequences (b-motifs) located between region A and the r-region. Each b-motif contains a consensus Ca2+-binding ef-hand loop normally found in eukaryotic proteins. The structural integrity of recombinant Sdrd(B1-B5) protein comprising the five b-repeats of SdrD was shown by bisANS fluorescence analysis to be Ca2+-dependent, suggesting that the ef-hands are functional. When Ca2+was removed the structure collapsed to an unfolded conformation. The original structure was restored by addition of Ca2+. The C-terminal r-domains of the Sdr proteins contain 132–170 sd residues. These are followed by conserved wall-anchoring regions characteristic of many surface proteins of Gram-positive bacteria. The Sdr locus was present in all 31 S. aureus strains from human and bovine sources tested by Southern hybridization, although in a few strains it contained two rather than three genes.

Three new members of the serine-aspartate repeat protein multigene family of Staphylococcus aureus.

The legacy of surface mining: Remediation, restoration, reclamation and rehabilitation

Regenerated cellulose wood pulp was grafted with the vinyl monomer glycidyl methacrylate (GMA) using ceric ammonium nitrate as initiator and was further fuctionalised with imidazole to produce a novel adsorbent material, cellulose-g-GMA-imidazole. All cellulose, grafted cellulose and functionalized cellulose grafts were physically and chemically characterized using a number of analytical techniques, including elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis, and scanning electron microscopy. The cellulose-g-GMA material was found to contain 1.75 mmol g−1 epoxy groups. These epoxy groups permitted introduction of metal binding functionality to produce the cellulose-g-GMA-imidazole final product. Following characterization, a series of adsorption studies were carried out on the cellulose-g-GMA-imidazole to assess its capacity in the removal of Cu2+ ions from solution. Cellulose-g-GMA-imidazole sorbent showed an uptake of ∼70 mg g−1 of copper from aqueous solution. The adsorption process is best described by the Langmuir model of adsorption, and the thermodynamics of the process suggest that the binding process is mildly exothermic. The kinetics of the adsorption process indicated that copper uptake occurred within 30 min and that pseudo-second-order kinetics best describe the overall process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 2006

A chelating cellulose adsorbent for the removal of Cu(II) from aqueous solutions

A series of adsorption studies was carried out on a glycidyl methacrylate- modified cellulose material functionalised with imidazole (Cellulose-g-GMA-Imidazole) to assess its capacity in the removal of Ni(II) ions from aqueous solution. The study sought to establish the effect of a number of parameters on the removal of Ni(II) from solution by the Cellulose-g-GMA-Imidazole. In particular, the influence of initial metal concentration, contact time, solution temperature and pH were assessed. The studies indicated a Ni(II) uptake on the Cellulose-g-GMA-Imidazole sorbent of approximately 48 mg g−1 of nickel from aqueous solution. The adsorption process fitted the Langmuir model of adsorption and the binding process was mildly endothermic. The kinetics of the adsorption process indicated that nickel uptake occurred within 400 min and that pseudo-second order kinetics best describe the overall adsorption process. Nickel(II) adsorption, recovery and re-adsorption studies indicated that at highly acidic pH values the adsorbent material becomes unstable, but in the range pH 3–6, the adsorbent is stable and shows limited but significant Ni(II) recovery and re-adsorption capability. Copyright © 2006 Society of Chemical Industry

David W. O'Connell

Papers

Heavy metal adsorbents prepared from the modification of cellulose : A review

Three new members of the serine-aspartate repeat protein multigene family of Staphylococcus aureus.

The legacy of surface mining: Remediation, restoration, reclamation and rehabilitation

A chelating cellulose adsorbent for the removal of Cu(II) from aqueous solutions

A modified cellulose adsorbent for the removal of nickel(II) from aqueous solutions