Size effects in the alkali metal ion-templated formation of oligo(ethylene glycol)-containing [2]catenanes

2016 ◽  
Vol 14 (3) ◽  
pp. 1153-1160 ◽  
Author(s):  
Yong-Jay Lee ◽  
Tsung-Hsien Ho ◽  
Chien-Chen Lai ◽  
Sheng-Hsien Chiu
Keyword(s):  
Alkali Metal ◽  
Ethylene Glycol ◽  
Metal Ions ◽  
Size Effects ◽  
Metal Ion ◽  
Alkali Metal Ions ◽  
Alkali Metal Ion

The most suitable alkali metal ions for templating the assembly of various homo- and hetero-[2]catenanes from the diamines containing central di-, tri-, and tetra(ethylene glycol) motifs, and isophthalaldehyde are investigated.

Alkali metal ion catalysis in nucleophilic displacement by ethoxide ion on p-nitrophenyl phenylphosphonate: Evidence for multiple metal ion catalysis

2003 ◽  
Vol 81 (1) ◽  
pp. 53-63 ◽  
Author(s):  
Erwin Buncel ◽  
Ruby Nagelkerke ◽  
Gregory RJ Thatcher
Keyword(s):  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Metal Ion ◽  
Alkali Metal Ions ◽  
Phosphoryl Transfer ◽  
Alkali Metal Ion ◽  
Nucleophilic Displacement ◽  
Displacement Reactions ◽  
Metal Ion Catalysis

In continuation of our studies of alkali metal ion catalysis and inhibition at carbon, phosphorus, and sulfur centers, the role of alkali metal ions in nucleophilic displacement reactions of p-nitrophenyl phenylphosphonate (PNPP) has been examined. All alkali metal ions studied acted as catalysts. Alkali metal ions added as inert salts increased the rate while decreased rate resulted on M+ complexation with 18-crown-6 ether. Kinetic analysis indicated the interaction of possibly three potassium ions, four sodium ions, and five lithium ions in the transition state of the reactions of ethoxide with PNPP. Pre-association of the anionic substrate with two metals ions in the ground state gave the best fit to the experimental data of the sodium system. Thus, the study gives evidence of the role of several metal ions in nucleophilic displacement reactions of ethoxide with anionic PNPP, both in the ground state and in the transition state. Molecular modeling of the anionic transition state implies that the size of the monovalent cation and the steric requirement of the pentacoordinate transition state are the primary limitations on the number of cations that can be brought to bear to stabilize the transition state and catalyze nucleophilic substitution at phosphorus. The bearing of the present work on metal ion catalysis in enzyme systems is discussed, in particular enzymes that catalyze phosphoryl transfer, which often employ multiple metal ions. Our results, both kinetic and modeling, reveal the importance of electrostatic stabilization of the transition state for phosphoryl transfer that may be effected by multiple cations, either monovalent metal ions or amino acid residues. The more such cations can be brought into contact with the anionic transition state, the greater the catalysis observed.Key words: alkali metal ion catalysis, nucleophilic displacement at phosphorus, multiple metal ion catalysis, phosphoryl transfer.

Confined alkali metal ion in two-dimensional aluminum phosphate promoted activity for condensation of lactic acid to 2,3-pentanedione

2021 ◽  
Author(s):  
Xinli Li ◽  
Ju Zhang ◽  
Yunsheng Dai ◽  
Congming Tang ◽  
Chenglong Yang
Keyword(s):  
Lactic Acid ◽  
Alkali Metal ◽  
Metal Ions ◽  
Metal Ion ◽  
Aluminum Phosphate ◽  
Sustainable Production ◽  
Alkali Metal Ions ◽  
Two Dimensional ◽  
Alkali Metal Ion

The sustainable production of 2,3-pentanedione from bio-lactic acid was investigated over the alkali metal ion intercalated laminar aluminum phosphate. The confined alkali metal ions by the adjacent layers of aluminum...

scholarly journals N-Alkyl pyrrolidone ether podands as versatile alkali metal ion chelants

2014 ◽  
Vol 43 (8) ◽  
pp. 3153-3161 ◽  
Author(s):  
Andrea Perrin ◽  
Dominic Myers ◽  
Katharina Fucke ◽  
Osama M. Musa ◽  
Jonathan W. Steed
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Metal Ion ◽  
Alkali Metal Ions ◽  
Carbonyl Groups ◽  
Alkali Metal Ion ◽  
Lactam Carbonyl

The highly polar nature of lactam carbonyl groups makes them potent chelators of alkali metal ions as part of a flexible podand ligand.

scholarly journals Alkali-metal-ion- and H+-dependent activation and/or inhibition of intestinal brush-border sucrase. A model involving three functionally distinct key prototropic groups

1988 ◽  
Vol 251 (3) ◽  
pp. 667-675 ◽  
Author(s):  
M Vasseur ◽  
G Van Melle ◽  
R Frangne ◽  
F Alvarado
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Brush Border ◽  
Metal Ion ◽  
Molecular Mechanisms ◽  
Competitive Inhibitor ◽  
Ionization Constants ◽  
Alkali Metal Ions ◽  
Alkali Metal Ion ◽  
Intestinal Brush Border

For rabbit intestinal brush-border sucrase, a model based on classical Michaelis-Dixon theory cannot fully explain the peculiar antagonistic relationship existing between the substrate and one key proton, Hx, which at acid pH values behaves as a fully competitive inhibitor. In the same pH range, a second proton, Hy, is responsible for changes in catalytic activity and behaves as a mixed-type partially non-competitive inhibitor [Vasseur, Tellier & Alvarado (1982) Arch. Biochem. Biophys. 218, 263-274]. Although involved in the same ionization reaction, these two protons have different kinetic functions, since they are responsible for affinity-type and capacity-type effects respectively. Depending on whether Hx is bound or not, we postulate the enzyme to alternate between two distinct forms differing in their binding properties. The alkali-metal ions Na+ and Li+ have a concentration-dependent biphasic effect on this equilibrium. At low concentrations they facilitate the release of Hx, resulting in K-type activation. At higher concentrations they favour enzyme reprotonation, causing K-type inhibition. On the basic side of the pH spectrum, our results confirm the existence of separate non-competitive effects of the alkali-metal ions, particularly Li+ [Alvarado & Mahmood (1979) J. Biol. Chem. 254, 9534-9541]. To explain the molecular mechanisms underlying the alkali-metal-ion- and H+-dependent effects, we formulate a sucrase model, the three-protons model, in which the acid and basic ionization constants involve respectively two and one key prototropic groups that are functionally distinguishable. A global iterative fit of the relevant general equation to our whole set of data has permitted us to estimate the numerical value of each of the constants constituting the model.

Impact Electrical Property of Alkali Metal Doped ZnO

2012 ◽  
Vol 468-471 ◽  
pp. 1501-1507 ◽  
Author(s):  
Hong Ling Tan ◽  
Cong Ying Jia ◽  
Chao Xiang ◽  
Ying Xiang Yang
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Metal Ion ◽  
Density Functional ◽  
Alkali Metal Ions ◽  
Acceptor Level ◽  
Electronic Density ◽  
Alkali Metal Ion ◽  
Doped Zno ◽  
P Type

Calculate the electronic structure of alkali metal ion-doped Zn crystal, based on density functional theory (DFT) first-principles plane-wave ultra-soft pseudo-potential method. Analyze the band structure of alkali metal ion-doped ZnO crystal, and the electronic density of states. The results indicated that in theory, the doping of alkali metal ions are able to form a p-type ZnO semiconductor, and introduce in the deep acceptor levels. In the actual substitution process, the dopant ions may enter the interstitial site. Thus the alkali metal ions are tending to become donor interstitial impurities. In addition, since the ionic radius of K is larger than the ionic radiuses of Li and Na. And K+ formed the minimum acceptor level (0.078eV), which is a shallow acceptor level. K+ is better than Li+ and Na+ as a dopant. In short, they are not good p-type dopants.

scholarly journals Alkali-metal ions in the metabolism of Bact. lactis aerogenes . I. Experiments on the uptake of radioactive potassium, rubidium and phosphorus

1951 ◽  
Vol 207 (1090) ◽  
pp. 424-424
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Metal Ion ◽  
Alkali Metal Ions ◽  
Carbon Substrate ◽  
Resting Cells ◽  
Alkali Cations ◽  
Alkali Metal Ion ◽  
Stages Of Growth ◽  
Hydrion Concentration

(This paper has been printed in full in Proceedings B, 138, 219) By the use as tracers of 42 K, 86 Rb and 32 P it has been shown that in the metabolism of Bact. lactis aerogenes ladis aerogenes ( a ) the alkali-metal ion enters the cell during oxidation of the carbon substrate (glucose, succinic acid, acetic acid) whether or not a nitrogen source is provided so that growth occurs; in either event the alkali-metal ion subsequently leaves the cell again; ( b ) if the pH is lowered the maximum uptake of the cation by the functioning cell is raised, although increased hydrion concentration first causes displacement of alkali-metal ions from resting cells. ( c ) in the early stages of growth, or of glucose oxidation without growth, the flow into the cell of alkali cations and of phosphate anions takes place in a parallel way.

Membrane transport systems. II. Transport of alkali metal ions against their concentration gradients

1981 ◽  
Vol 59 (12) ◽  
pp. 1734-1744 ◽  
Author(s):  
Thomas M. Fyles ◽  
Virginia A. Malik-Diemer ◽  
Dennis M. Whitfield
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Metal Ion ◽  
Complex Function ◽  
Membrane System ◽  
Ion Concentration ◽  
Transport Systems ◽  
Alkali Metal Ions ◽  
Concentration Gradients ◽  
Membrane Transport Systems

An artificial membrane system based on a series of macrocyclic polyether carriers (crown ethers) is described. Under the influence of a proton gradient the carriers move alkali metal ions from basic to acidic solution through a chloroform membrane phase. Transport occurs against the concentration gradient of the transported ion as a result of a coupled counterflow of protons. Different transport behaviors are observed depending upon the metal ion concentration. At high metal ion concentration the amount transported is a linear function of time; at lower metal ion concentration the amount transported is a complex function of time which may be described as the result of a pair of consecutive first order processes. Effects of metal ion, carrier, and proton concentration on transport rate are considered. The rate increases with increasing metal ion or carrier concentration but is essentially independent of the pH of either aqueous phase. Increased lipophilicity of the carrier also results in a rate increase. Carriers derived from 18-crown-6 transport potassium selectively and all ions more rapidly than 15-crown-5 derivatives which are, however, selective for sodium. The overall efficiency of the system is discussed in terms of competing "leak" reactions, either of cations from the basic phase or of anions from the acidic phase.

scholarly journals Interaction of Cu+ with cytosine and formation of i-motif-like C–M+–C complexes: alkali versus coinage metals

2016 ◽  
Vol 18 (10) ◽  
pp. 7269-7277 ◽  
Author(s):  
Juehan Gao ◽  
Giel Berden ◽  
M. T. Rodgers ◽  
Jos Oomens
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Metal Ion ◽  
Alkali Metal Ions ◽  
Metal Ion Complexes ◽  
Coinage Metals

Dimeric metal ion complexes of cytosine C–M+–C display divergent coordination motifs for coinage versus alkali metal ions.

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