The influence of exchangeable aluminium ion concentration and of layer charge on the catalytic activity of montmorillonite clays

1989 ◽  
Vol 2 (3) ◽  
pp. 125-128 ◽  
Author(s):  
J. H. Purnell ◽  
J. M. Thomas ◽  
P. Diddams ◽  
J. A. Ballantine ◽  
W. Jones
Keyword(s):  
Catalytic Activity ◽  
Ion Concentration ◽  
Layer Charge ◽  
Aluminium Ion ◽  
Montmorillonite Clays

scholarly journals Intramolecular phenotypic capacitance in a modular RNA molecule

2015 ◽  
Vol 112 (40) ◽  
pp. 12444-12449 ◽  
Author(s):  
Eric J. Hayden ◽  
Devin P. Bendixsen ◽  
Andreas Wagner
Keyword(s):  
Catalytic Activity ◽  
In Vitro Selection ◽  
Ion Concentration ◽  
Magnesium Ion ◽  
Interacting Protein ◽  
Genetic Changes ◽  
Low Magnesium ◽  
Naturally Occurring ◽  
A Genome

Phenotypic capacitance refers to the ability of a genome to accumulate mutations that are conditionally hidden and only reveal phenotype-altering effects after certain environmental or genetic changes. Capacitance has important implications for the evolution of novel forms and functions, but experimentally studied mechanisms behind capacitance are mostly limited to complex, multicomponent systems often involving several interacting protein molecules. Here we demonstrate phenotypic capacitance within a much simpler system, an individual RNA molecule with catalytic activity (ribozyme). This naturally occurring RNA molecule has a modular structure, where a scaffold module acts as an intramolecular chaperone that facilitates folding of a second catalytic module. Previous studies have shown that the scaffold module is not absolutely required for activity, but dramatically decreases the concentration of magnesium ions required for the formation of an active site. Here, we use an experimental perturbation of magnesium ion concentration that disrupts the folding of certain genetic variants of this ribozyme and use in vitro selection followed by deep sequencing to identify genotypes with altered phenotypes (catalytic activity). We identify multiple conditional mutations that alter the wild-type ribozyme phenotype under a stressful environmental condition of low magnesium ion concentration, but preserve the phenotype under more relaxed conditions. This conditional buffering is confined to the scaffold module, but controls the catalytic phenotype, demonstrating how modularity can enable phenotypic capacitance within a single macromolecule. RNA’s ancient role in life suggests that phenotypic capacitance may have influenced evolution since life’s origins.

Solubility of simple aluminium compounds expected in soils. I. Hydroxides and oxyhydroxides

Soil Research ◽  
1963 ◽  
Vol 1 (1) ◽  
pp. 28 ◽  
Author(s):  
MR Raupach
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Aluminium Hydroxide ◽  
Ion Concentration ◽  
Aluminium Ion ◽  
Ph Range

Results from dissolution equilibria with four aluminium hydroxide and oxyhydroxide compounds in M/100 K2SO4 over pH range 3.5-10, when examined by plotting the negative logarithm of the aluminium ion concentration against the pH, showed that AlOH2+, Al(OH)2+, and Al(OH)4-, hydrated and possibly polymeric, were formed. For pH>7, precipitated aluminium hydroxide (containing mostly boehmite) gave bayerite equilibria while gibbsite, diaspore, and bauxite gave gibbsite equilibria. For p H t 7 amorphous A1(OH)3 and corundum equilibria were observed. Using accepted free energy values, the following were estimated at 2.5�: KS1 = log [(AlOH2+)(OH-)2] = -23.31 and KS2 = log [(Al(OH)2+)(OH-)] = - 14.04 for amorphous Al(OH), and KS1 = -24.41 and KS2 = -15.14 for corundum and also �F� values of 164.9, -215.1, and -313.9 kcal for A10H2+, Al(OH)2+, and Al(0H)-4 respectively in aqueous solution.

Influence of exchange cation and layer charge on the isomerization of α-pinene over SWy-2, SAz-1 and Sap-Ca

Clay Minerals ◽  
2001 ◽  
Vol 36 (4) ◽  
pp. 467-472 ◽  
Author(s):  
C. Breen ◽  
A. J. Moronta
Keyword(s):  
Catalytic Activity ◽  
Layer Charge ◽  
Exchange Cation

AbstractSWy-2 (Wyoming), Sap-Ca saponite (California) and SAz-1 (Cheto, Arizona) were exchanged with different cations (Al, Ni, Mg, Ca and Na). The catalytic activity of these ionexchanged clays was measured directly using the isomerization of α-pinene at 80°C for 2 h to yield camphene, limonene and other minor products. The order of activity for the different cationexchanged forms was Al > Ni > Mg > Ca > Na, which correlated well with the known polarizing power of these cations and the resulting interlayer acidity. Catalysts derived from Sap-Ca were the most active followed by SWy-2, with SAz-1 the least active by a considerable margin. The greater activity of Sap-Ca over SWy-2 was attributed to the high tetrahedral charge in the former. Reduction of the layer charge of SAz-1 using Li fixation caused a significant improvement in the catalytic activity of the Al-exchanged reduced-charge SAz-1.

K10 montmorillonite clays as environmentally benign catalysts for organic reactions

2014 ◽  
Vol 4 (8) ◽  
pp. 2378-2396 ◽  
Author(s):  
Basuvaraj Suresh Kumar ◽  
Amarajothi Dhakshinamoorthy ◽  
Kasi Pitchumani
Keyword(s):  
Catalytic Activity ◽  
Organic Reactions ◽  
Environmentally Benign ◽  
Montmorillonite Clays ◽  
Multifunctional Catalyst

This perspective summarizes the catalytic activity of K10 montmorillonite as a multifunctional catalyst for organic reactions.

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