With monovalent cation

Quantitative calculations of the IMECs of the C=C stretching and C-H bending bands confirmed this trend (Table 1). Furthermore, for Ca2+ and Mg2+ cations the IMEC values exceed those for the free molecules, while for the Na+ ions there is little effect. This indicates a stronger polarization of the C=C bond in ji-complexes of propene with bivalent than with monovalent cations. As follows from Table 1 the IMECs of the C-H stretching vibrations of propene adsorbed by different cations are strongly decreased in comparison with the free molecule. The ratio of the IMECs for C=C and C-H stretching bands is increased for propene adsorbed by Mg2+ cations in comparison with the ratio obtained for the free molecule. 

They form relatively stable complexes with monovalent cations, especially with alkali metal cations, where the complex stability has ion-selective character [88, 100, 193, 202, 213]. 

There is only little information available for orthovanadates with monovalent cations, as seen in Table 2. The IR spectra for Li3V04 and Li3V04 show clearly the bands associated with the VOl" polyhedron. The high value of vi for TI3VO4 is certainly an error. 

Table 2. IR data (in cm l) for orthovanadates with monovalent cations...

Cardiolipin Monolayers. Among various phospholipids studied by monolayer techniques, only cardiolipin (41) and phosphatidylserine (36) monolayers show significant condensation of their surface pressure-area curves in the presence of divalent as compared with monovalent cations in the subsolution. The condensation of cardiolipin is explained by the decrease in molecular area caused by the attraction between a divalent cation and the two phosphate groups in the molecule. This condensation is eliminated when the ratio of monovalent to divalent cations is greater than 5 to 1. At high surface pressures, the difference in the compressibility of cardiolipin monolayers correlates with the ionic radii of the metal ions (Mg2+ < Ca2+ < Sr2+ < Ba2+). 

The ability of water molecules to promote a reaction depends on many factors. In most cases, zeolites with monovalent cations have low activity. However, the addition of water molecules to X and Y zeolites with monovalent ions increased the isomerization of cyclopropane (63). De-cationized zeolites can be promoted readily with water, and the process is reversible (2, 60, 64). It was shown (2) that the promoting ability of water molecules in faujasites is less when the Si02/Al203 increases. Dealu-minated faujasites are even more difficult to promote. For erionite and mordenite the maximum effect of water was observed only after treatment with liquid water and subsequent heating (2). The effect of water on zeolites saturated with polyvalent cations is less pronounced (65, 66, 67). However, the presence of multivalent cations stabilizes the catalytic activity. Water and alcohols were reported to promote ion exchanged zeolites for n-pentane isomerization (68) and n-hexadecane hydrocracking (69). 

It is also of interest to use MAS NMR for the study of the thermal treatment of zeolites which are not in the ammonium-exchanged form. In an X-ray study, Pluth and Smith (179) found electron density at the center of the sodalite cages in dehydrated zeolites Ca-A and Sr-A and attributed this to a partial occupancy of these sites by a four-coordinated aluminous species. No such effect was found in zeolite A exchanged with monovalent cations. Corbin et al. (180) used 27A1 MAS NMR to examine commercial samples of K-A, Na-A and (Ca,Na)-A, as received (see Fig. 41). For K-A and Na-A, only framework tetrahedral Al species were observed, with chemical shifts of 57 and 52 ppm respectively. However, in (Ca,Na)-A an additional intense resonance at 78 ppm, typical of AlfOH) but definitely not due to framework aluminum, was also found (see Fig. 41). A much weaker signal, also at 78 ppm, was detected in zeolite Sr-A its intensity increased greatly on heating the sample to 550°C. Freude et al. (183) came to very similar conclusions in their NMR study of heat-treated zeolite Ca-A. They found that maximum framework dealumination occurs at 500°C and corresponds to ac. 17% of total Al. 

Amino-2,4,6-trioxo-l,3-perhydrodiazine-A,iV-diacetic acid (uramil-A,A-diacetic acid) also forms quite stable complexes with monovalent cations such as lithium (log AT, 5).2,3... 

In contrast to the previously discussed carbon-carbon bond rearrangements, these results clearly show that Lewis acid sites can also act as catalytically active sites for nucleophilic substitutions. Note that if catalysts without Bronsted acid sites are used (i.e., with zeolites exchanged with monovalent cations) the competitive side reaction leading to (i)-hydroxybutryonitrile via protonation of the acid amide can be completely suppressed (Scheme 6). 

R. Spezia, C. Nicolas, F.-X. Coudert, P. Archirel, R. Vuilleumier, and A. Boutin (2004) Reactivity of an excess electron with monovalent cations in bulk water by mixed quantum classical molecular dynamics simulations. Mol. Sim. 30, p. 749... 

Figure 3.6. Calculated isotherms for divalent cation (B ) adsorption on a smectite initially saturated with monovalent cations at three electrolyte concentrations in solution.

In recent studies, antibiotic A23187 was found to form complexes of the type AM1 and A2HM1 with monovalent cations, and of the type A 2 M1 with divalent cations in solution63 232 The solution conformation of the (A23187)2-Ca complex and of the free antibiotic were deduced from NMR spectroscopic data63l... 

Metal oxygen cluster compounds with keggin structure have received attention as acid catalysts for several acid catalysed reactions in the liquid as well as in vapour phase conditions [1-6]. Studies on a series of salts with monovalent cations and various heteropolyanions have revealed that certain of these solids in particular those containing potassium, cesium,ammonium and thallium cations possess microporous structure [7-11]. Photoacoustic FTIR investigations and the studies on the chemisorption of ammonia and pyridine have shown that residual protons remain and these protons are responsible for the catalytic activity[12,13]. 

The more complicated G-quadruplex stabilizing properties of divalent cations may result from the ability for some divalent cations e.g., Mg ) to only screen electrostatic repulsions between the backbones of a G-quadruplex that coordinates other cations, whereas other divalent cations e.g., Sr ) can stabilize a G-quadruplex both by screening backbone repulsions and by coordination with G-quartets. Qualitatively different behavior may be seen with monovalent cations, as the ability for monovalent cations to screen backbone repulsions is significantly less than that of divalent cations, and monovalent cation stabilization of G-quartets may be less sensitive to G-quadruplex topology and nucleotide sequence. 

Many thorium hypophosphites, phosphites, their hydrates and related compounds with monovalent cations (usually K ) have been mentioned in the literature (see the Gmelin review by Bickel [1993BIC]), but the information available is essentially limited to preparation procedures, analysis, vibrational spectra and some DTA studies. X-ray structures have not been reported and, in fact, many of these compounds are amorphous to X-rays. Since no thermodynamic data relevant to this review have been reported, these compounds are not considered further. 

Considerably less information is available concerning the D structure of water molecules hydrating vermiculites that form surface complexes with monovalent cations. It appears that both Li- and Na-vermiculite can form mono- and bilayer hydrates, whereas K-, Rb-, and Cs-vermiculite cannot. For the latter, inner-sphere surface complexes are stable against solvation of the cations because of Lewis acid character and stereochemistry. These factors are especially notable when comparing with which have almost identical ionic radii. Barium-vermiculitc contains a monolayer of... 

First, we consider the liquid-phase exchange of bridging hydroxyls in zeolites with monovalent cations. This reaction is simple, because one proton is exchanged with one metal cation. It has been found by many authors that the bands of the bridging hydroxyls of various zeolites are consumed or strongly reduced in intensity during ion exchange (193,215,221,545,546). The reverse reaction is also used to prepare the H-forms of zeolites (547,548). 

Monensin, Na salt [5. cinnamonensis] 692.86 methanol, ethanol, ethyl acetate, chloroform, dmso forms stable complexes with monovalent cations Na-">K >Rb" >Cs-">Li >NH ... 

C42H70O11, Mr 751.01, cryst., mp. 112.5-113.5 °C, [a]o -63 (C2H5OH), an ionophoric polyether antibiotic with a dispiroketal structure produced by Strep-tomyces albus it preferentially forms complexes with monovalent cations (Na ). S. is formed biosyntheti-cally on the polyketide pathway, cyclization in the linear carboxylic acid proceeds on the diene/diepox-ide pathway. The 20-deoxy derivative is also formed. S. is used against coccidiosis in poultry breeding and also has antiviral activity (HIV). LD50 (mouse p.o.) 50 mg/kg. 

The peak to peak line width (At p) of pristine trans- polyacetylene, 1. IG, increases on n-doping with the divalent cations. This broadening of the EPR signal has been observed in polyacetylene n-doped with monovalent cations such as Na (26,27). Sodium-ammonia samples also exhibit line broadening. This line broadening for the divalent doped polyacetylenes is indicative of localization of charge within the soliton and/or bipolaron... 

Thus, alginic acids form water-soluble salts with monovalent cations but are precipitated in the presence of polyvalent cations, such as Ca ", Sr ", and Ba , among others. pH of the medium has also an important role in the solubility of... 

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