Role Of Metal Cations Research Articles

Role of metal cations in colour transition and hydrolysis of the chromophores of retinal-binding photoreceptor proteins

Rates of hydrolysis of a model retinylidene Schiff base chromophore, namely all- trans-N-retinylidene-β-naphthylamine ( 1), have been determined in tetrahydrofuran, CHCl 3, and CH 3CN, in the presence and absence of metal cations (Li +, Mg 2+) and trichloroacetic acid as the protonating agent. A mechanism for the hydrolysis of the Schiff base chromophore in visual pigments and a representation of the role of metal ions in maintaining the structure functions of bacteriorhodopsin have been proposed.

Role of metal cations in the regulation of NADP-linked isocitrate dehydrogenase from porcine heart.

The regulatory role of divalent metal cations in the NADP-linked isocitrate dehydrogenase (EC 1.1.1.42) from porcine heart was analysed. Saturation curves with respect to the substrate threo-DS-isocitrate complexed with the metals including manganous, cadmium, cobaltous and zinc ions showed sigmoid relationships characteristic of allosteric enzymes. The Hill's interaction coefficients were 1.90, 1.75, 1.28 and 1.12, respectively. Saturation kinetics of the substrate-metal complexes including magnesium, ferrous and nickel ions exhibited normal hyperbolic curves with Hill's coefficients of 1. The ionic radii of metal cations were closely correlated with the maximal velocity, the enzyme affinity and the Hill's n11 values for the substrate-metal complexes. Cooperative interactions of metal-substrate complexes with NADP-isocitrate dehydrogenase are discussed in relation to the sites of the enzyme for the binding of the metal-substrate complex.

Metal cation assisted protonation of retinylidene Schiff base in aqueous acetonitrile and in reverse micelles

Metal cations (Ca2+, Mg2+, Zn2+) cause water to protonate all-trans-N-retinylidenebutylamine when solubilised in (i) acetonitrile containing aqueous MgBr2 and (ii) CaA2, MgA2 and ZnA2[where A = bis(2-ethylhexyl) sulfosuccinate anion] solubilised water pools in heptane. The results are discussed in terms of the role of metal cations and water in wavelength regulation in the opsin family of proteins.

The role of metal cations in improving the inhibitive performance of hexamine on the corrosion of steel in hydrochloric acid solution

Hexamethylenetetramine (HA) or hexamine (or urotropin) have a moderate inhibitive effect on the corrosion of mild steel in concentrated acid solution (3N) but have a negligible effect in very dilute solutions (N/200) of the acid. Incorporation of Cu 2+, As 3+, Sb 3+ and Sn 2+ with HA improves its performance, which is synergistic in nature. These additives (except As 3+), however, exhibit an antagonistic effect when tested in dilute acid solutions. Cu 2+ and As 3+ have the most pronounced effect in 3N acid solution. In N/200 HCl solution, the antagonistic effect is a maximum in the case of Sb 3+ followed by Sn 2+ and Cu 2+ cations. Weight-loss, electrochemical polarization and zeta potential measurements are performed to understand the mechanism of action of these inhibitors. The positive role played by the cations on the inhibitive performance of HA is due to the formation of anionic complexes with the chloride ions of the acid solution. These anions replace the adsorbed chloride ion from the metal-electrolyte interface owing to their higher affinity toward the interface and help the protonized molecule of HA to be adsorbed more strongly at the interface. Accumulation of FeCl 3 in concentrated acid solution lowers the performance of HA to a greater extent (about 100 times) than HA blended with Cu 2+. The latter composition also has a substantially stronger inhibitive role on hydrogen absorption by the steel than the former one.

On the molecular mechanisms of the rapid and slow solar-to-electric energy storage processes by the other natural photosynthetic system, bacteriorhodopsin

Abstract

ChemInform Abstract: The Role of Metal Cations on the Corrosion Behavior of 8090‐T851 Alloy in a pH 2.0 Solution.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The role of metal cations on the corrosion behaviour of 8090-T851 alloy in a pH 2.0 solution

The influence of cations such as Cu 2+, Al 3+ and Li + on the corrosion behaviour of 8090-T851(Al-Li) alloy in a pH 2.0 HCl solution was investigated by weight loss and polarisation techniques. Weight loss experiments showed that the effect of cation is a strong function of its nature and concentration and the effect became significant only above a critical concentration. Of the cations studied, Cu 2+ ions were found to be the most aggressive corrosion activators followed by Al 3+ ions while Li + ions showed little effect. Polarisation experiments inferred that Cu 2+ ions influence the corrosion process mainly by accelerating the cathodic reaction. While a decrease in both cathodic and anodic reactions was evident in the presence of Al 3+ ions at higher concentration, Li + ions showed no remarkable affect either on cathodic or anodic reactions. Critical analyses of results of the two experiments indicated that the corrosion activation by Al 3+ ions is due to their chemical reactivity with the corroding substrate. Little enhancement in corrosion by Li + ions is attributed to the increase in solution conductivity in their presence.

Effect of medium composition on the ultrastructure of Lactobacillus strains

The growth of some locally isolated Lactobacillus strains forming D(-) or L(+) lactic acid, Lactobacillus helveticus ATCC 15009 and Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 was examined in different media. L. helveticus and Lactobacillus LBL strains formed atypical protoplast-like cells in LAPT medium, sensitive to SDS and proteinase. Specific morphological changes in the cell wall structure of these variants were revealed by transmission and scanning electron microscopy. The effect of glucose and various salts on their appearance was investigated. The prevalent role of metal cations, especially of Mg2+, was established.

ChemInform Abstract: Role of Metal Cations in the Corrosion and Corrosion Inhibition of Aluminum in Aqueous Solutions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The role of metal cations in the corrosion and corrosion inhibition of aluminium in aqueous solutions

The influence of K +, Mg 2+, Ba 2+, Cu 2+, Zn 2+, Hg 2+, Cd 2+, Co 2+, Ni 2+ or Fe 3+ on the general and pitting corrosion of aluminium in neutral and acid media has been determined by gravimetric, potentiodynamic polarization and thermometric measurements together with surface analysis by XPS, Auger profile depth analysis and examination by SEM. Alkali and alkaline earth cations showed practically no effect. Transition and heavy metal cations caused initial inhibition at low concentrations. Above minimum concentrations strong acceleration of corrosion took place. This behaviour is interpreted on the basis of deposition of the metals by displacement which is not homogeneous on the surface of aluminium. Cd 2+ ions showed efficient inhibition over a particularly wide concentration range which suggested its application as an inhibitor of aluminium corrosion. It inhibited the accelerating effect of Cu 2+ and Fe 3+ through hindering their deposition by displacement. Cadmium is incorporated into the oxide film that develops on the aluminium surface to form a mixed oxide with aluminium. This film would suppress the kinetics of the partial cathodic reaction leading to the observed corrosion inhibition.

Regulation of mammalian melanogenesis II: the role of metal cations

Melanogenesis can be divided into two phases. The first one involves two tyrosinase-catalyzed oxidations from tyrosine to dopaquinone and a very fast chemical step leading to dopachrome. The second phase, from dopachrome to melanin, can proceed spontaneously through several incompletely known reactions. However, some metal transition ions and protein factors different from tyrosinase might regulate the reaction rate and determine the structure and relative concentrations of the intermediates. The study of the effects of some divalent metal ions (Zn, Cu, Ni and Co) on some steps of melanogenesis pathway has been approached using different radiolabeled substrates. Zn(II) inhibited tyrosine hydroxylation whereas Ni(II) and Co(II) were activators. Ni(II), CU(II) and Co(II) accelerated chemical reactions from dopachrome but inhibited its decarboxylation. Dopachrome tautomerase also decreased decarboxylation. When metal ions and this enzyme act together, the inhibition of decarboxylation was greater than that produced by each agent separately, but amound of carboxylated units incorporated to the melanin was not higher than the amount incorporated in the presence of only cations. The amount of total melanin formed from tyrosine was increased by the presence of both agents. The action of Zn(II) was different from other ions also in the second phase of melanogenesis, and its effect on decarboxylation was less pronounced. Since tyrosine hydroxylation is the rate-limiting step in melagonesis, Zn(II) inhibited the pathway. This ion seems to be the most abundant cation in mammalian melanocytes. Therefore, under physiological conditions, the regulatory role of metal ions and dopachrome tautomerase does not seem to be mutually exclusive, but rather complementary.

Application of quantum chemistry to biology: Some new currents.

Some novel quantum chemical approaches to biological problems are reviewed. First, molecular orbital calculations for carcinogenic and mutagenic compounds were presented with their molecular structural characteristics. Next, approaches to ion channels were described indicating usefulness of molecular orbital calculations of transition state theory. Finally attempts were introduced by using molecular orbitals to clarify mechanism of evolution with roles of metal cations.

The role of metal cations in the homogeneous phase redox reaction of a NADH model compound

The catalytic activity of magnesium cations in the charge transfer between 1-benzyl-1,4-dihydronicotinamide (BNAH) and several aromatic compounds has been studied in acetonitrile by electrochemical techniques. Magnesium cations form complex compounds with both BNAH and the organic substrates studied. At the same time, magnesium forms ion-associates with negatively charged substrate molecules. Energetically, the effect of ion-pairing is much greater than the negative effect of complex formation. The rate of homogeneous phase reaction was also studied to show that the Michaelis-Menten type mechanism is operating.

The role of metal cations in the homogeneous phase redox reaction of a NADH model compound

The catalytic activity of magnesium cations in the charge transfer between 1-benzyl-1,4-dihydronicotinamide (BNAH) and several aromatic compounds has been studied in acetonitrile by electrochemical techniques. Magnesium cations form complex compounds with both BNAH and the organic substrates studied. At the same time, magnesium forms ion-associates with negatively charged substrate molecules. Energetically, the effect of ion-pairing is much greater than the negative effect of complex formation. The rate of homogeneous phase reaction was also studied to show that the Michaelis-Menten type mechanism is operating.

Ring transformation of γ-butyrolactone into 2-pyrrolidinone over synthetic zeolites

Catalytic activities of synthetic zeolites for the ring transformation of γ-butyrolactone into 2-pyrrolidinone were compared in a flow reactor and CuY, HY, LiY, and NaY were found to have high activity. Alkaline earth forms of Y-zeolites lose their activity rapidly though their initial activities are high. For CuY, effects of the reaction temperature and the partial pressures of the reactants on the catalytic activity and the selectivity for 2-pyrrolidinone were examined. At 230 °–260 °C, selectivity of 80–90% is easily attained. The product, 2-pyrrolidinone, works as a strong poison for the catalysis. The role of metal cations in zeolites is discussed and the reaction mechanism is proposed.

Transformations of rat skin collagen; with special reference to the ageing process.

SummaryThe formation of insoluble collagen in rat skin was studied both in vivo and in vitro in order to clarify the mechanism by which tropocollagen units are transformed into supermolecular structures, especially in relation to the ageing process.I. Suitable methods were developed for the fractionation and purification of soluble collagens (Fig. l), for the determination of the specific radioactivity of hydroxyproline in starch‐gel electrophoretic collagen fractions (Table IV, Fig. 2) and for the production of insoluble collagen in vitro (Fig. 12).II. The proportion of insoluble collagen was maximal in the skin of a newborn rat. The rapid growth period of the rat was characterized by an accumulation of collagen soluble in 0.5 M acetic acid at 4° (Fig. 3). The insoluble collagen was separated into two subfractions (designated ISC40 and ISCr). The proportion of collagen soluble in 0.5 M acetic acid upon heating at 40° (ISC40) increased with age (Figs. 4–5). ISCR could be brought into solution only after degradation of the collagen at temperatures above 60° (Fig. 5). Also the proportion of ISCR was maximal in the skin of a newborn rat (Fig. 4).The subfractions of insoluble collagen extracted by 0.5 M acetic acid at 40° from skins of 5‐day‐old rats consisted mainly of α‐ and β‐components. The proportions of β‐ and γ‐components were higher in corresponding fractions from skins of adult rats (Fig. 7). The ratio of hexmamine to hydroxyproline decreased rapidly in the insoluble collagen with advancing age (Table V).The content of free aldehyde groups was lower in the collagen of a lathyritic rat than in the collagen of a normal rat. The difference was largest in the a‐components (Table VII). The subfractions of insoluble collagen had different contents of aldehyde groups: ISC60°‐80° contained one acetaldehyde equivalent/TC less than ISC20°‐50° (Table VI).Incorporation studies indicated that insoluble collagen is formed faster in young than in adult rats (Table IX, Fig. 9). The half‐lives of 0.5 M NaC1‐soluble collagens from 6‐day‐old and 3‐month‐old rats were 27 and 73 hours, respectively (Fig. 10). The turnover of the α2‐component in 0.1 M acetic acid‐soluble collagen from a 6‐day‐old rat was faster than that of the α1‐component (Fig. 11).III. When skin slices labelled in vivo were incubated in vitro, the total and specific radioactivities of the hydroxyproline of the insoluble collagen increased during 8 hours (Table X, Fig. 12). The formation of insoluble collagen during incubation was augmented by (1) a rise in temperature of the incubation medium up to 37° (Fig. 13); (2) a decrease in the thickness of the slices to 0.3 mm (Table XI); and (3) the presence of calcium ions up to 3.0 mM concentration (Fig. 15). The 45Ca‐activity increased in the insoluble residue of skin when skin slices labelled in vivo were incubated in vitro (Table XIII).Metal cations influenced the formation of insoluble collagen in the following order of decreasing effectiveness (Table XIV and XV): Co2+ > Cu2+ > Cu+ > Au3+ = Ni2+ > Fe3+ > Hg2+ > Cr3+ > Ca2+ > Fe2+ > AI3+ > Bb4+ > Sn4+ > Sr2+ = Ba2+ > Mn2+ = Mg2+.The addition of EDTA and substances reacting with aldehyde groups (phenylhydrazine and semicarbazide) to the incubation medium (Figs. 16 ‐17) inhibited the formation of insoluble collagen.The rate of formation of insoluble collagen was lowest near pH 6.4 and increased in both alkaline and acid directions (Fig. 14).Attempts to influence the formation of insoluble collagen in vitro by employing anaerobic conditions and by adding sodium fluoride, sodium iodoacetate, αα‐dipyridyl and puromycin failed.The aldehyde groups in the 0.45 M NaC1‐soluble collagen increased when skin slices were incubated in the presence of glucose in vitro (Table XX).Insoluble collagen was formed also when skin homogenates were incubated in vitro (Table XVII).Two possible age‐dependent mechanisms leading to the formation of insoluble collagen are suggested. The roles of metal cations and aldehyde groups in the stabilization of collagenous structures are discussed.

On the role of metal cations in ceullular adhesion: cation specificity.

AbstractOf the four common alkaline earth cations, only Ca++ is able to protect Rana pipiens embryos from dissociation of the epidermis into isolated cells by EDTA. Presumably this is because only Ca++ is able to satisfy the divalent cation requirement for cellular adhesion in this tissue. Although early stage embryos are completely dissociable by EDTA, the axial musculature, brain and spinal cord become resistant to dissociation by stage 17. Tetraphenyl boron is also effective in disaggregating amphibian embryo tissues.

On the role of metal cations in cellular adhesion: effect on cell surface charge.

AbstractAn examination has been made of the hypothesis that the role of divalent cations in promoting reaggregation of dissociated cells is principally to reduce the negative electrostatic charge at the cell surface. This hypothesis would suggest that cells in the presence of different divalent cations would reaggregate at identical rates if the concentrations of the different cations were so adjusted that in all cases the cells possess the same charge. This expectation has not been fulfilled. Magnesium ion was most effective in promoting reaggregation, calcium somewhat less so, and strontium and barium had little or no effect.