Absence Of Various Metal Ions Research Articles

Manipulating Assemblies in Metallosupramolecular Gels, Driven by Isomeric Ligands, Metal Coordination, and Adaptive Binary Gelator Systems.

Metallosupramolecular gel (MSG) is a unique combination of metal-ligand coordination chemistry and supramolecular gel chemistry with extraordinary adaptivity and softness. Such materials find broad uses in industry, pharmaceutical and biomedical sectors, and in technology generation among many others. Pyridyl-appended bis(urea) gelator systems have been extensively studied as potential MSG-forming materials in the presence of various metal ions. The previous molecular engineering approaches depicted competitive intermolecular and intramolecular binding modes involving urea and pyridyl groups and further fine-tuned by the presence of various molecular spacers. In those studies, formation of intermolecular hydrogen bonding among urea moieties to form urea tape was found to be the key factor in one-dimensional assembly and gel formation. In the present study, we show how two isomeric pyridyl-appended bis(urea) ligands can be designed appropriately to essentially eliminate the interference of competitive factors, leaving the intermolecular urea assembly practically unaffected even in the presence of metal ions. We found that one of the two ligands (L2) and the mixed ligand (L1 + L2) assemblies formed gel in the presence and absence of various metal ions. A metal ion with a linear coordination geometry significantly strengthened the gels. Moreover, an inherently weak L1 + L2 assembly appears to be more adaptive in accommodating larger metal ions especially with nonlinear coordination geometry preferences. Small-angle neutron scattering and rheological, spectroscopic, and morphological characterizations, collectively, capture a detailed interplay among ligand assembly, metal-ligand coordination, and adaptivity, driven by the pure versus mixed ligand assemblies. The knowledge gathered from the present study would be highly beneficial in engineering the metallosupramolecular polymeric assemblies toward their functional applications.

Removal of triphenylmethane dyes in single-dye and dye-metal mixtures by live and dead cells of metal-tolerant Penicillium simplicissimum

ABSTRACT In the absence of various metal ions, live cells of Penicillium simplicissimum decolorized Crystal Violet (CV), Methyl Violet (MV), Malachite Green (MG) and Cotton Blue (CB) (75.6–90.8%, 0.5–2 h) more efficiently than dead cells (43.9–75.2%, 4 h). Cu(II) enhanced CB removal by live and dead cells (64.1–82.0%) but with Cd(II), Zn(II) and Cr(III), removal of CV, MV and MG were inhibited. Pb(II) inhibited dye removal by live cells (63.1–78.1%), while dead cells remained unaffected (40.6–74.0%). Dye removal was attributed to binding to hydroxyl, carbonyl, amino, phosphoryl and nitro groups based on FTIR analyses. Dye-metal-fungi interactions revealed new binding sites and non-involvement of specific functional groups that previously interacted with single dyes. Hence, this study indicated that isolate 10 (especially live cells) is capable of removing dyes from dye-metal solutions.

Synthesis of N-Hydroxy Isopeptide Containing Proteins

Chemical synthesis of a peptide-ubiquitin conjugate linked by an N-hydroxy isopeptide bond to determine what effect the N-hydroxy group has on the enzymatic hydrolysis of the isopeptide linkage by deubiquitinases is reported. This conjugate was subjected to proteolysis by UCH-L3 in the presence and absence of various metal ions, and no substantive difference in hydrolysis was seen compared to a control lacking the N-hydroxy group. The accessibility of N-hydroxy ubiquitinated substrates may find uses to study other deubiquitinases in particular those which use a zinc ion as a part of their catalytic mechanism.

Kinetics and Mechanism of Facile and Selective Dephosphorylation of 2'-Phosphorylated and 2'-Thiophosphorylated Dinucleotides: Neighboring 3'-5' Phosphodiester Promotes 2'-Dephosphorylation.

2'-Phosphorylated and 2'-thiophosphorylated dinucleotides U(2'-p)pU (1) and U(2'-ps)pU (2) were found to undergo facile 2'-specific dephosphorylation at 90 degrees C in neutral aqueous solution to give UpU, and the first-order rate constants of these reactions were determined by HPLC. Particularly, U(2'-ps)pU (2, k = 1.38 +/- 0.4 x 10(-)(3) s(-)(1), t(comp) = 1 h) was cleanly dephosphorylated ca. 100 times more rapidly than U(2'-p)pU (1, k = 1.41 +/- 0.05 x 10(-)(5) s(-)(1), t(comp) = 72 h). Dephosphorylations of 1 and 2 were faster than those of thymidine 3'-phosphate (8) and thymidine 3'-thiophosphate (9), respectively. The kinetic data observed were independent of the 2'- or 3'-position of the phosphate group and the kind of base moiety. The neighboring 3'-5' phosphodiester function most probably promotes the 2'-dephosphorylation efficiently. A branched trimer, U(2'-pU)pU (3), and related compounds having a substituent on the 2'-phosphoryl group, such as U(2'-pp-biotin)pU (4) and U(2'-ps-bimane)pU (5), were rather resistant to hydrolysis. The addition of divalent metal ions (Mg(2+), Mn(2+), Zn(2+), Ca(2+), Co(2+), and Cd(2+)) remarkably decreased the rate of 2'-de(thio)phosphorylation of 1 or 2. Among these metal ions, Zn(2+) most significantly inhibited the dephosphorylation. On the contrary, trivalent metal ions considerably accelerated the 2'-de(thio)phosphorylation of 1 or 2. The mechanism of 2'-dephosphorylation in the presence and absence of various metal ions is also discussed.

Electrokinetics of oxidized coal

Electrokinetic measurements were carried out in order to determine the properties of oxidized coal surfaces over a wide pH range both in the presence and absence of various metal ions and flotation collectors. It was found that polyvalent cations, such as Fe ++, Fe +++ and Al +++ decreased the zeta potential to zero and then reversed the charge. In the presence of cationic collectors, the negative value of zeta potential of oxidized coal was driven positive, below 9.3 to 10.9 depending on the type and concentration of collector used. The infrared spectra of oxidized coal did not indicate any characteristic bands for amine at any pH. These studies demonstrated that amines are not chemically adborbed on oxidized coal surfaces.

Limited digestion of calmodulin with trypsin in the presence or absence of various metal ions.

The limited proteolysis of bovine brain calmodulin with trypsin in the presence or absence of various metal ions was reinvestigated in detail by HPLC. With metal ion-free calmodulin, limited proteolysis occurred at Arg 37 and Arg 106 with a cleavage ratio of 1 to 5, resulting in fragments consisting of residues 1-37, 38-148, 1-106 and 107-148. Fragments 1-37 and 107-148 accumulated under metal ion-free conditions. In the presence of calcium ions, the susceptibility of these sites to trypsin decreased and limited proteolysis occurred at Lys 77 as already reported by other workers. Fragment 78-148 accumulated, whereas fragment 1-77 was unstable under calcium-bound conditions, giving smaller peptides. Upon binding of manganese ions, calmodulin underwent a change of susceptibility to trypsin, resulting in cleavage at Lys 77, as observed for calcium-bound calmodulin. In the presence of zinc or magnesium ions, calmodulin was cleaved at the same sites as metal ion-free calmodulin under conditions where calmodulin would be expected to bind the respective ions.

The titration curve of insulin in the presence of various bivalent metal ions.

1. Titration curves of insulin in the presence and absence of various metal ions are reported. 2. The difference in base consumption with and without the metal ions is compared with calculated curves. 3. These experiments suggest that in dilute solutions Zn(2+) and Cu(2+) ions are bound to alpha-amino groups.