Showing papers in "Israel Journal of Chemistry in 1968"
TL;DR: In this paper, the light absorption spectra of monoionic montmorillonite suspensions with Li, Na, K, Rb, NH4, Cs, Mg, Ca and Ba as adsorbed ions were studied in the wavelength range 200-800 mμ.
Abstract: The light absorption spectra of monoionic montmorillonite suspensions with Li, Na, K, Rb, NH4, Cs, Mg, Ca and Ba as adsorbed ions were studied in the wavelength range 200–800 mμ. Theoretical analysis of the spectra showed that in the visible range, only scattering is responsible for light intensity attenuation. The scattering was found to depend on the type of adsorbed ion and to increase systematically along the series from Li to Ba. This was attributed to increased particle size of the clay caused by parallel plate condensation to form tactoids. A geometrical model of a montmorillonite tactoid was assumed. The general dependence of the properties of such tactoids, and of their suspensions, on the number of plates per tactoid was formulated. Using the measured values of light absorbance index, and the theoretical model, the relative sizes, measured by the number of plates per tactoid, in the different ionic forms were calculated. The relative sizes thus estimated were found to agree favorably with relative sizes calculated from negative adsorption surface area measurements.
A typical peak of specific light absorption was observed at 240–245 mμ, for both the suspensions and their clay-free supernatant solutions. Though the compound responsible for this peak is unidentified yet, its quantity in the various suspensions could be roughly estimated. The quantity was found to be negatively correlated with the relative size of the tactoid.
It was concluded that the average particle size of montmorillonite in suspension markedly and systematically depends on the type of adsorbed ion. The implications of this finding are discussed.
91 citations
TL;DR: In this article, the viscosity and light transmittance of montmorillonite suspensions saturated with Na+, Ca++ and known mixtures of these ions in the adsorbed phase were investigated.
Abstract: The viscosity and light transmittance of montmorillonite suspensions saturated with Na+, Ca++ and known mixtures of these ions in the adsorbed phase were investigated. Introduction of a small fraction of Na+ (10% – 15%) into the exchange complex of Ca—clay, does not result in the breakdown of the tactoids. The breakdown of the tactoids occurred when the equivalent fraction of Na increased from 0.2 to 0.5. Montmorillonite clay saturated with 50% calcium (and less) exists as single platelets. Combining the structural data with an equilibrium equation based on the diffuse double layer theory indicates that when tactoids are formed, demixing occurred by which Na+ ions are concentrated on the external surfaces of the tactoids and Ca++ ions on the internal surfaces.
87 citations
TL;DR: In this paper, the pulsed magnetic resonance technique was applied to the measurement of the longitudinal (T1) and transversal (T2) relaxation time of water molecules adsorbed by Na- and Ca-Montmorillonite.
Abstract: The pulsed magnetic resonance technique was applied to the measurement of the longitudinal (T1) and transversal (T2) relaxation time of water molecules adsorbed by Na- and Ca-Montmorillonite, In the Na-clay the water was adsorbed as a monomolecular layer whilst in the Ca-clay, the bimolecular layer was formed under specified water vapor pressures. The effect of paramagnetic centers (Fe3+) was corrected and the samples were studied between + 30°C and −80°C. The main contribution to T1 was the “inter” contribution of protons diffusing from one water molecule to another whilst T2 results from simultaneous rotational (intramolecular) and diffusional (intermolecular) contributions. The proton diffusion coefficient and the life-time of a proton on one specified water molecule is derived from T1 inter. The calculated value at 298°C is equal to 10−7 times the life-time in liquid water, suggesting a dissociation degree 107 times higher in the adsorbed state than in liquid water. This increase in the dissociation degree as well as the reported activation energies are in good agreement with experimental data obtained from conductimetric and dielectric measurements performed previously.
82 citations
TL;DR: In this paper, it was shown that diffuse double theory is completely inadequate for describing swelling of calcium saturated clays and for predicting the pore solution composition, and the use of chloride exclusion measurements to provide information on the nature of particle interaction was discussed.
Abstract: Particle interaction discussed in this paper may be limited, in which contiguous interacting plate shaped particles are within 10 A of each other, or extensive, in which surface separations exceed 40 A. Extensive swelling is caused by the interaction of Gouy-Chapman diffuse double layers and the conditions under which diffuse double layer theory can be used to describe extensive swelling are re-viewed. The essential feature of extensive swelling is its dependence on electrolyte concentration.
X-ray studies of the variation of d(001) spacings for montmorillonite and vermiculite when saturated with divalent and large monovalent ions have been discussed as examples of limited swelling. This behaviour is contrasted with sodium montmorillonite which exhibits extensive crystalline swelling for concentrations less than 0.3 M NaCl.
The similarity of the swelling behaviour of a montmorillonite crystal and of a parallel assemblage of crystals constituting a domain has been noted and presented as an argument for domains being regarded as particulate entities in calcium saturated clay materials.
The limited crystalline swelling of calcium montmorillonite and domain swelling of calcium saturated clays is little affected by electrolyte concentrations less than molar. The inter-crystalline swelling which occurs in soils and clay materials is triggered off by the adsorption of two layers of water; the adsorption of the two layers of water at areas of crystal overlap release mechanical energy stored as a result of crystal bending and packing on the drying cycle. This release of mechanical energy creates pores in which liquid is held by surface tension forces as distinct from water held at the clay solution interface by hydration and osmotic forces.
The use of chloride exclusion measurements to provide information on the nature of particle interaction is discussed. The information presented on domain structure and ion distribution at interfaces, as deduced from chloride exclusion measurements, reveals that diffuse double theory is completely inadequate for describing swelling of calcium clay systems and for predicting the pore solution composition.
72 citations
TL;DR: The isolation of aristolochic acid-I from Pachlioptera aristolchiae (Fabr.) is described and the larvae feed exlusively on plants of the family Aristolochiaceae and presumably ingest the acid which is stored and carried through the pupal stage to the adult insect.
Abstract: The isolation of aristolochic acid-I from Pachlioptera aristolochiae (Fabr.) is described. About 0.1 mg is present in each butterfly. The larvae feed exlusively on plants of the family Aristolochiaceae and presumably ingest the acid which is stored and carried through the pupal stage to the adult insect.
60 citations
TL;DR: Sorption of aniline by montmorillonite was studied by infra-red, X-ray diffraction and differential thermal analysis methods in this paper, where the interlayer cations: anilinium, H+- and Al3+- gave anilina anilines, NH44-ammonium anilinea ions, alkalis and alkaline earths except Cs are bonded to anilini through water bridges and transition metal cations are coordinated to aninium partly directly and partly through water bridge.
Abstract: Sorption of aniline by montmorillonite was studied by infra-red, X-ray diffraction and differential thermal analysis methods. The amount of aniline sorbed and the type of bonding depend upon the interlayer cations: anilinium, H+- and Al3+- give anilinium aniline ions, NH44-ammonium aniline ions, alkalis and alkaline earths except Cs are bonded to aniline through water bridges and transition metal cations are coordinated to aniline partly directly and partly through water bridges. Sorption does not occur in the complete absence of water.
54 citations
TL;DR: Withanolide D, the major component of the leaves of Withania somnifera chemotype II, is a steroidal lactone of the withanolide type, isomeric with withaferin A.
Abstract: Withanolide D, the major component of the leaves of Withania somnifera chemotype II, is a steroidal lactone of the withanolide type, isomeric with withaferin A. It has been identified as 5, 6β-epoxy-4β, 20α-dihydroxy-1-oxo-(5β)witha-2, 24-dienolide. The structure has been elucidated by NMR measurements and by chemical degradation to 4β-acetoxy-5,6β-epoxy (5β) pregnan-1, 20-dione.
44 citations
TL;DR: In heat denatured DNA photosensitized dimerization of thymine occurs in a higher proportion of the TT dinucleotide sequences than in native DNA and the trans-syn thymine dimer isomer is formed as a minor photoproduct.
Abstract: Thymine and cytosine homo- and heterodimers ate produced when E. coli DNA is irradiated at wavelength > 300 mμ in the presence of acetone as photosensitizer. Employing acetophenone as sensitizer only thymine containing dimers are obtained. In heat denatured DNA photosensitized dimerization of thymine occurs in a higher proportion of the TT dinucleotide sequences than in native DNA and the trans-syn thymine dimer isomer is formed as a minor photoproduct.
41 citations
TL;DR: In this article, a dihydrobenzopyran ring system is formed by cyclization of one of the phenolic groups of a cannabinoid with the C1 carbon in the terpene moiety of the molecule.
Abstract: Synthetic routes are described which lead to iso-tetrahydrocannabinols, a new series of structural isomers of the natural Δ1-tetrahydrocannabinol. In this group of compounds a dihydrobenzopyran ring system is formed by cyclization of one of the phenolic groups of a cannabinoid with the C1 carbon in the terpene moiety of the molecule.
35 citations
TL;DR: In this article, the results indicate that Gred, which is the sum of Geaq + GH = 3.3, is pH-independent in the range 11 − 14.
Abstract: Alkaline N2O-saturated solutions of 2-D-2-propanol and ferri-ferrocyanide mixtures were irradiated. The results indicate that Gred, which is the sum of Geaq + GH = 3.3, is pH-independent in the range 11 – 14. The results do not indicate that Geaq and GH are pH-dependent.
34 citations
TL;DR: Ferrous iron in the layers increased 2-fold or more on deferration of coarser fractions of micaceous vermiculite naturally weathered from biotite (Colorado and Transvaal sources) as discussed by the authors.
Abstract: Ferrous iron in the layers increased 2-fold or more on deferration of coarser fractions of micaceous vermiculite naturally weathered from biotite (Colorado and Transvaal sources) The ferric iron content of the layers was decreased by the deferration treatment but the original content was restored by subsequent H2O2 treatment Sesquioxide coatings on micaceous vermiculite from Colorado, examined electron microscopically, were composed predominantly of Fe2O3 (80 to 85 percent), along with Al2O2 and SiO2 The CEC increased from 64 to 95 meq per 100 g in the fraction coarser than 1000 microns and 50 to 64 meq per 100 g in the fraction 2–02, microns in diameter, as a result of removal by deferration of positively charged sesquioxide coating which had originally blocked a portion of the CEC Although treatment with H2O2 after deferration restored the Fe3+ content to approximately the original value, the CEC was not affected probably because of deprotonation OH− O2− + H+ occurring simultaneous with Fe2+ Fe3+
TL;DR: In this article, it was shown that dissociation of adsorbed water on the clay surface plays a major role in protonation and hydrolysis of s-triazine herbicides.
Abstract: Adsorption of s-triazines on montmorillonite surfaces results in hydrolysis and protonation of the s-triazine compounds. Infrared studies suggest that dissociation of adsorbed water on the clay surface plays a major role in protonation and hydrolysis of the s-triazine herbicides.
TL;DR: In this paper, the effect of the degree of dispersion of the clay and the interlayer cations initially present on the amount of dye sorbed and the nature of the reaction products is investigated.
Abstract: Sorption of methylene blue by montmorillonite is a cation exchange reaction, but the replacement is not stoichiometric. The degree of dispersion of the clay and the interlayer cations initially present influence the amount of dye sorbed and the nature of the reaction products.
TL;DR: In this paper, it is suggested that ice nucleation occurs in the undercooled interfacial water layer at some distance removed from the particle surfaces and that heterogeneous nucleation (nucleation of ice due to the influence of a substrate) in all its essential aspects may be only a special case of homogeneous nucleations of water.
Abstract: Certain aspects of the phenomena of undercooling and ice nucleation in soils are discussed with respect to recently established properties of phase boundary water in soils. Nucleation temperature as a function of water content is given for representative clays. In view of the fact that silicate surfaces seem always to be separated from ice by an interfacial layer of unfrozen, liquid like water a new concept of heterogeneous nucleation is outlined. It is proposed that ice nucleation occurs in the undercooled interfacial water layer at some distance removed from the particle surfaces. This concept, in effect, suggests that heterogeneous nucleation (nucleation of ice due to the influence of a substrate) in all its essential aspects may be only a special case of homogeneous nucleation (no substrate present) of water.
TL;DR: A number of compounds related to these isomers and their ribosides have been synthesized, including 6-(3, 4-dihydroxy-3-methylbutylamino)-9-β-D-ribofuranosylpurine, and the cytokinin activities have been compared in the tobacco bioassay as mentioned in this paper.
Abstract: Chemical conversions of 6-(3-methyl-2-butenylamino)purine, 2iP, and 6-(3-methyl-3-butenylamino)purine, 3iP, to common products have been effected. A number of compounds related to these isomers and their ribosides have been synthesized, including 6-(3-hydroxy-3-methylbutylamino)-9-β-D-ribofuranosylpurine, 6-(3-chloro-3-methylbutylamino)purine, 6-(3, 4-dihydroxy-3-methylbutylamino) purine, and 6-(3,4-dihydroxy-3-methylbutylamino)-9-β-D-ribofuranosylpurine, and the cytokinin activities have been compared in the tobacco bioassay. The effect of 4-hydroxyl substitution on the side chain has been noted. Diagnostic fragmentations of the side chains have been observed in the mass spectra.
TL;DR: In this article, the light absorption spectra of Na, K, Ca and Ba-montmorillonite suspensions were studied in relation to the procedure of sample preparation, indicating hysteresis effects in the transformation process.
Abstract: The light absorption spectra of Na, K, Ca and Ba-montmorillonite suspensions were studied in relation to the procedure of sample preparation. These procedures included different sequences of transformations from one homoionic form into another, as well as a drying stage during the preparation.
The optical density was usually influenced by the method of preparation, indicating hysteresis effects in the transformation process. The data were interpreted in terms of tactoid formation and size.
Transformation of monovalent into divalent clay suspensions resulted in small tactoids. Air drying of the clay before the transformation resulted in larger tactoids in both mono- and divalent clays. Negative adsorption of chloride in Ca-bentonite from two different preparations (which differed in their tactoid size) were in agreement with the light absorption measurements: the higher surface area was found in the suspension with the smaller tactoids.
The data available in the literature on negative absorption of chloride on montmorillonite are discussed. It is suggested that the discrepancies in the experimental results of different investigators could be, at least partially, explained by the differences in the preparation procedure of the clay suspensions.
TL;DR: In this article, the exchange isotherms of the ion pairs Ca-Na, Ca-K, Na-K and Na-H on the clay mineral montmorillonite were determined.
Abstract: The exchange isotherms of the ion pairs Ca-Na, Ca-K, Na-K, Ca-H and Na-H on the clay mineral montmorillonite were determined.
It was found that the selectivity coefficient is not constant along a given isotherm but changes with the relative fractions of the adsorbed ions. This variation is attributed to the structural properties of the mineral, namely, tactoid formation in the Ca state, and the presence of different exchange sites affecting the energy of exchange.
TL;DR: In this article, the authors proposed a model for the structure of the occlusion compound Na22[(AlO2)12(SiO2), 12(NO3)10], in terms of four NaI+ ions and four [NaI - NO3 - Na]+ groups at the apexes of the cubic unit cell and four NaII - NO 3 - Na]-1/3 groups coordinated with two [NaNO3]−2/3 group at the faces, to explain the properties of occluded zeolites.
Abstract: The occlusion of lithium, sodium, potassium and silver nitrates from the anhydrous melts in the respective zeolites has been studied by measuring the gain in weight and by direct analysis. The results in moles of occluded nitrate per formula weight of zeolite M12I[(AlO2)12(SiO2)12] are 11.7 for LiNO3, 10 for NaNO3 and 10 for AgNO3 and essentially zero for KNO3. A model is proposed for the structure of the occlusion compound Na22[(AlO2)12(SiO2)12(NO3)10], in terms of four NaI+ ions and four [NaI - NO3 - Na]+ groups at the apexes of the cubic unit cell and four [NaII - NO3 - Na]+1/3 groups coordinated with two [NaNO3]−2/3 groups at the faces, to explain the properties of the occluded zeolites.
TL;DR: Rats and chicks responded differently to toxic action of the two poisons, which may be related to the different metabolism of the poisons in the two species.
Abstract: The following biochemical parameters were determined in the livers of rats and chicks which had been previously treated with ethylene dibromide (EDB) and carbon tetrachloride: sulfhydryl groups, ascorbic acid, nicotinamid-adenine-dinucleotides (NAD and NADP) and alkaline phosphatase. Ascorbic acid levels were also determined in adrenals and alkaline phosphatase activity in blood. A marked depression in the level of free sulfhydryl groups was observed in the livers of the two species during the first hours after poisoning. The initial drop in the SH level was followed by a subsequent rise, the rate of which differed with species, sex, and poison. Carbon tetrachloride treatment resulted in a very marked depression of ascorbic acid content in rat liver while EDB caused only a slight depression. The ascorbic acid content of chick liver was less affected by the two poisons as was the liver NAD (P) content of both species. A rise of alkaline phosphatase was found with both poisons in rat liver in contrast to depression of the enzyme activity in chick liver. Rats and chicks responded differently to toxic action of the two poisons. This may be related to the different metabolism of the poisons in the two species.
TL;DR: The synthesis of 6-mono and 5-6 dihalogeno-uracils is described in this paper, and it is shown by ultraviolet absorption spectral comparisons in aqueous solutions that the neutral species of all synthesized compounds exist in the dilactam form.
Abstract: The synthesis of various 6-mono- and 5,6 dihalogeno-uracils is described It is shown by ultraviolet absorption spectral comparisons in aqueous solutions that the neutral species of all synthesized compounds exist in the dilactam form The monoanions are formed by loss of a proton from N-1 pKa values and ultraviolet absorption spectra are reported and the influence of the different halogen substituents are on these properties discussed
TL;DR: An 11-step process for total synthesis of dl-PGB1 (prostaglandin B1) is described and the chemical structure of each interim step in the process is presented.
Abstract: An 11-step process for total synthesis of dl-PGB1 (prostaglandin B1) is described. The chemical structure of each interim step in the process is presented. The following analytical data were obtained for each new compound in the process: 1) ultraviolet absorption spectra in methanol; 2) infrared absorption spectra in chloroform; and 3) NMR spectra in deuterochloroform.
TL;DR: Ionization efficiency curves obtained by the RPD (retarding potential difference) method are presented for Cycl. C4F8−, Hg+, C2 H2+ and C2 F4+.
Abstract: Ionization efficiency curves obtained by the RPD (retarding potential difference) method are presented for Cycl. C4F8−, Hg+, C2 H2+ and C2 F4+. The C4 F8− resonance capture curve is given for a variety of experimental conditions. The curves for the positive ions are compared with similar curves obtained previously by the technique of photoionization combined with mass analysis. The results are discussed in terms of possible relaxation effects and other artefacts in the RPD method and in terms of threshold laws of ionization by electron and photon impact. Special emphasis is placed on autoionization processes. Experimental conditions, under which the RPD ion source may be reliably used, are specified.
TL;DR: In this paper, the mechanism of interference was investigated by means of a synthetic system, consisting of suspensions of reference clay with humic and fulvic acid added to increase the colloidal stability of the suspension.
Abstract: Surface waters which contain suspended clay and organic matter, differ strongly in response to flocculation from suspensions of “pure” reference clays in controlled systems. The mechanism of interference was investigated by means of a synthetic system, consisting of suspensions of reference clay with humic and fulvic acid added. These organic soil acids increase the colloidal stability of the suspension. Due to chemical reaction taking place between the organic acids and the cationic flocculant, higher flocculant doses were required in systems where interaction of clay and organic matter occurred.
TL;DR: In this article, it was shown that the observed dependence of the quantum yield on scavenger concentrations is due to homogeneous competition between the scavenger and a product or rational intermediates, rather than to cage scavenging competing with geminate recombination.
Abstract: Geminate recombination has been previously suggested in the photochemistry of several ions in solution, namely, the halides, phenolate ferrocyanide and thiocyanate It is demonstrated that in the concentration range studied, the observed dependence of the quantum yield on scavenger concentrations is due to homogeneous competition between the scavenger and a product or rational intermediates, rather than to cage scavenging competing with geminate recombination
TL;DR: In this paper, a mechanism with a six membered transition state involving a concerted proton transfer from the least substituted carbon in β position of the oxirane oxygen is suggested.
Abstract: The rearrangement of epoxides catalyzed by aluminum alkoxides affords a selective way of preparing allylic alcohols in high yields. It takes place in the presence of catalytic amounts of aluminum isopropoxide (AIP) which leads to cleavage of the ether linkage at the site of the more substituted α-carbon of the oxirane. A mechanism with a six membered transition state involving a concerted proton transfer from the least substituted carbon in β position of the oxirane oxygen is suggested. Mild conditions are sufficient to promote this rearrangement to allylic alcohols with epoxides having a tertiary carbon in α-position of the oxirane oxygen. However, alkoxide transfer to the cleaved α-carbon may take place when primary or secondary carbons are the only ones present in the α-positions of the oxirane oxygen with more drastic conditions and equimolar amounts of AIP. The major product is a mixture of α-glycol monoethers.
TL;DR: Substituted phenoxaphosphines were obtained from di-p-tolyl ether and alkyl- or arylphosphonous dichlorides, and, by alkylation, followed by reduction, from either 2,8-dimethylphenoxaphophosphinyl chloride or 2, 8-dimmethylphenoxophosphine 10-oxide as mentioned in this paper.
Abstract: Substituted phenoxaphosphines were obtained from di-p-tolyl ether and alkyl- or arylphosphonous dichlorides, and, by alkylation, followed by reduction, from either 2,8-dimethylphenoxaphosphinyl chloride or 2,8-dimethylphenoxaphosphine 10-oxide. Some reactions of the new heterocyclic compounds are described.
TL;DR: The in vivo activity of a number of pyrazolo(3,4-d) pyrimidines and purines, which are xanthine oxidase inhibitors in vitro, to inhibit purine catabolism in the mouse often did not correlate with the inhibitory activity in vitro.
Abstract: A method is described for the determination of the ability of a number of pyrazolo(3,4-d) pyrimidines and purines, which are xanthine oxidase inhibitors in vitro, to inhibit purine catabolism in the mouse. This method is based on the amount of oxypurines (hypoxanthine + xanthine) excreted in the urine during the first 5 hours after drug administration. The in vivo activity often did nut correlate with the inhibitory activity in vitro. The most active inhibitor in vivo was 4-hydroxypyrazolo(3,4-d)-pyrimidine (allopurinol).