Showing papers in "Israel Journal of Chemistry in 1970"
TL;DR: In this article, the rate constants of 60 typical electron donor-acceptor systems have been measured in de-oxygenated acetonitrile and are shown to be correlated with the free enthalpy change, ΔG23, involved in the actual electron transfer process.
Abstract: Fluorescence quenching rate constants, kq, ranging from 106 to 2 × 1010 M−1 sec−1, of more than 60 typical electron donor-acceptor systems have been measured in de-oxygenated acetonitrile and are shown to be correlated with the free enthalpy change, ΔG23, involved in the actual electron transfer process
in the encounter complex and varying between + 5 and −60 kcal/mole. The correlation which is based on the mechanism of adiabatic outer-sphere electron transfer requires ΔG≠23, the activation free enthalpy of this process to be a monotonous function of ΔG23 and allows the calculation of rate constants of electron transfer quenching from spectroscopic and electrochemical data.
A detailed study of some systems where the calculated quenching constants differ from the experimental ones by several orders of magnitude revealed that the quenching mechanism operative in these cases was hydrogen-atom rather than electron transfer.
The conditions under which these different mechanisms apply and their consequences are discussed.
3,485 citations
TL;DR: In this article, the dominant organisms in the surface water were found to be two red halophilic bacteria, followed in abundance by a green flagellated alga, Dunaliella virdis.
Abstract: Studies were performed to determine the distribution of microbiota in the Dead Sea during 1963 to 1965. The dominant organisms in the surface water were found to be two red halophilic bacteria, followed in abundance by a green flagellated alga, Dunaliella virdis. Cultures inoculated with Dead Sea water produced growth of the red bacteria as well as unidentified non-pigmented halo-tolerant bacteria, capable of growing in 25% salt solution, and bacteria that grew only in dilute salt media. The latter are mainly spore-forming aerobes, probably introduced by rain-wash of the soil, as well as from the Jordan River and fresh water springs. Sulfate reducing bacteria were also cultured from the water and from the sediment. Pigment studies on extracts from laboratory cultures of the red bacteria, from centrifuged suspensions of Dead Sea water and, by comparison, from a pure culture of Halobacterium salinarium, showed that the dominant pigment in all cases was the carotene α-bacteriorubrin. The total number of organisms decreased with depth of the water column, especially below the thermocline. The interpretations given for the decrease are: lack of dissolved oxygen, decrease in incident light, and lack of dissolved phosphate. The last factor is probably due to rapid precipitation of phosphate by divalent ions.
62 citations
TL;DR: In this article, the surface area of montmorillonites was determined from observations of the amount of methylene blue absorbed on the clay required to produce optimum flocculation; this condition corresponds to an effective coverage of the surfaces with methylENE blue ions.
Abstract: Absorption isotherms have been determined for methylene blue absorbed from aqueous solutions on montmorillonites saturated with various cations. Surface areas are determined from observations of the amount of methylene blue absorbed on the clay required to produce optimum flocculation; this condition corresponds to an effective coverage of the surfaces with methylene blue ions. Cation exchange capacities are determined from saturation absorptions. With Li- and Na-saturated clays, the surface areas are approximately 750 m2/g and the exchange capacities agree with values obtained by titration techniques. With K-montmorillonites, values about 15% smaller are obtained and this is probably due to a small fraction of the clay not expanding beyond about 15A in water. With M2+-montmorillonites, a marked difference in behavior is observed between a clay from Wyoming and one from Texas. The Wyoming clay gives much smaller effective flocculation areas and clearly defined saturation absorptions are not obtained. These results are attributed to relatively large particle sizes, so that external surfaces are covered when internal surfaces are only partially covered, and ultimate saturation is hindered by the large particles. With finer particles, the Texas clay gives flocculation areas nearer to those obtained with Li- and Na-clays and the apparent exchange capacities also are nearer to those obtained for the monovalent ion clays. A limitation on surface area measurements for montmorillonites with exchange capacities less than about 100 meq/100 g is discussed.
56 citations
TL;DR: In this paper, the phytanyldiether is probably derived from the phosphatidyl glycerophosphate lipid, which has been demonstrated by Kates and co-workers to be the dominant lipid present in red halophilic bacteria.
Abstract: Reducing surface sediment from a depth of 300 m in the Dead Sea was found to contain phytanic acid (520 μg/Kg), dihydrogen phytol (800 μg/Kg) and phytane (17 μg/Kg). An investigation revealed that glycerol phytanyldiether could be isolated from the sediment by hydrolysis of a lipid soluble fraction. The phytanyldiether is probably derived from the phosphatidyl glycerophosphate lipid, which has been demonstrated by Kates and co-workers to be the dominant lipid present in red halophilic bacteria. Comparison of results by analysis of Halobacterium cutirubrum, using the same analytical procedure as was used for the sediment investigation, confirmed the authenticity of the lipid characterization. In view of this finding, it is suggested that phytane in the Dead Sea sediment has been derived from this lipid and that long-chain isoprenoid hydrocarbons in some ancient environments may have had a similar origin.
51 citations
TL;DR: In this article, the fluorescence quantum yields of tryptophan, 3-methylindole and 3-β-hydroxyethylindole were investigated as a function of temperature in a variety of polar and non polar solvents.
Abstract: The fluorescence quantum yields of tryptophan, 3-methylindole and 3-β-hydroxyethylindole were investigated as a function of temperature in a variety of polar and non polar solvents. Similar quantum yields and “activation energies” were found for the different systems. It was concluded that the same collisional solvent deactivation is responsible for the decrease in quantum yield with temperature irrespective of solvent system used. A notable exception is water where a different mechanism is indicated. The quenching of the indole chromophore fluorescence by a variety of specific agents both attached to the ring by an ethylene bridge and in homogeneous solution was also studied. It was found that potential proton donating groups were good quenching agents, the effect being much greater for groups carrying a positive charge. Polarization by a neighboring group also enhanced the quenching ability of any specific group. It was concluded that an excited state charge transfer complex is probably involved as a first step in the quenching process.
49 citations
TL;DR: In this paper, the application of a low energy pulsed nitrogen laser as a fast excitation source in photochemistry is described and the experimental problems concerning detection of transients by absorption spectroscopy are discussed.
Abstract: The application of a low energy pulsed nitrogen laser as a fast excitation source in photochemistry is described. The experimental problems concerning detection of transients by absorption spectroscopy are discussed. The instrument is applied to the measurement of the absorption spectrum curve of coronene in its lowest excited singlet state.
48 citations
TL;DR: In this paper, a 14-day period of extraction from quartz particles, 10 to 2 microns in diameter, was studied and it was found that the dissolution rate of SiO2 increased with decrease in particle size, from 1 to 3 ppm for quartz particles 50 to 20 microns and 30 to 44 ppm for particles 2 to 0.2 microns.
Abstract: Quartz particles (10 to 2 microns in diameter, produced by grinding) released 45 ppm of SiO2 to a buffer solution of pH 7 during a 48 hr period. The grinding of quartz particles produced a disturbed surface layer with solubility properties intermediate between crystalline quartz (6 ppm SiO2) and amorphous silica (120 ppm SiO2). Removal of the disturbed layer by treatment with 1N HF lowered the SiO2 dissolution from 45 to 3 ppm. Use of 12N HF decreased the amount of SiO2 dissolved to 2 ppm, a result found to coincide with a preferential dissolution of the finer quartz particles in addition to the removal of the disturbed surface layer. The rate of dissolution of SiO2 from quartz particles, subsequent to treatment with 1N HF, increased with decrease in particle size, from 1 to 3 ppm for quartz particles 50 to 20 microns in diameter to 30 to 44 ppm for particles 2 to 0.2 microns in diameter, during each of three consecutive 14-day extractions with pH 7 buffer solution. The amount of SiO2 dissolved from quartz in buffer solutions increased in the pH range of 4 to 10, from 0.6 ppm of SiO2 at pH 4 to 19 ppm at pH 10 during a 14-day period of extraction from quartz particles, 10 to 2 microns in diameter. Quartz particles, subsequent to the removal of the disturbed surface layer, removed SiO2 from pH 4 and pH 8 buffer solutions prepared with more SiO2 in solution than would be released from quartz in the respective solution.
41 citations
TL;DR: In this paper, it was shown that cyclohexylamine sorbed by montmorillonite depends upon the interlayer cations and the origin of the lattice charge.
Abstract: Infrared spectra indicate that protonation of cyclohexylamine sorbed by montmorillonite depends upon the interlayer cations and the origin of the lattice charge. No protonation occurs with Cs and very little with Na, but with all the other interlayer cations studied cyclohexylammonium ions are formed. Protonation occurs more readily if the lattice charge originates in the octahedral layer. Various associations are inferred between interlayer hydroxides, hydrated cations, ionic and molecular cyclohexylamine and water. The sorption of cyclohexylamine is compared with that of aniline and the validity of the concept “surface acidity” is questioned.
34 citations
TL;DR: In this paper, it has been shown that a small amount of perpendicular stacking occurs, resulting in the development of particles four layers thick, while the original sodium montmorillonite suspension remains unchanged.
Abstract: Electron microscope studies have shown that calcium montmorillonite, originally dispersed into separate platelets, flocculates with time to form large flat sheet-like particles which exhibit pronounced flow birefringence. Although kinetic studies indicate for rapid salt flocculation face to face condensation is unlikely to occur, it has been shown that with long times in electrolyte free systems a small amount of perpendicular stacking occurs, resulting in the development of particles four layers thick. During the same period the sodium montmorillonite suspension remains unchanged. Lateral growth of the particles is most likely brought about by an intermediate orientation of the particles with overlapping of the edges of the particles, so that they link together to form a flat sheet. These results prove that in suspension calcium montmorillonite quasi crystals definitely have different dimensions from the original sodium montmorillonite. Kinetic and electron microscope studies of salt flocculated calcium montmorillonite systems indicate that the salt floccules consist of particles randomly oriented relative to one another. However electron microscope studies show that salt floccules may undergo rearrangements, depending on their treatment, resulting in a greater ordering of individual particles. Dialysis of the salt flocculated system leads to birefringent units similar to those formed in the absence of salt. Further stacking and lateral growth is induced by drying. These results explain the very different surface areas of calcium montmorillonite determined by chloride exclusion measurements.
32 citations
TL;DR: In this article, the gelling and flocculation of aqueous dispersions of a synthetic hectorite-like clay, Laponite CP, on the addition of electrolytes or water miscible organic solvents was studied.
Abstract: Optical and Theological methods have been used to study the gelling and flocculation of aqueous dispersions of a synthetic hectorite-like clay, Laponite CP, on the addition of electrolytes or water miscible organic solvents. There is a positive correlation between the yield value and turbidity when the dispersions are flocculated with electrolyte. Addition of polar solvent, however, shows no such correlation, only a sudden change from very clear to very cloudy dispersion, while the yield value increases gradually until gross flocculation takes place. It is suggested that two different flocculation mechanisms are being observed.
28 citations
TL;DR: In this article, a simple chemical method was used for the estimation of allophane (amorphous alumina, silica, and iron oxide with water) and kaolinite plus halloysite.
Abstract: Clay mineralogical analyses were made of red soils and black soils developed from southern Victoria, Australia. The clays of the black soils are dominantly montmorillonite (39%) and vermiculite (16%) but have an average siliceous allophane content of 17%. The clays of the red soils are dominantly kaolinite and halloysite (26%) and chlorite (30%) but have an average halloysitic allophane content of 21%. Two to eight per cent of mica and quartz occur in both. A longer period of eolian dust accumulation and concurrent weathering and soil development have occurred in the red soils than in the black soils since the last cycle of geological erosion. A simple chemical method was used for the estimation of allophane (amorphous alumina, silica, and iron oxide with water) and kaolinite plus halloysite. After selective dissolution of allophane, free Al(OH)3, and amorphous SiO2 during 2.5 min of boiling in 0.5N KOH solution, the residue is subjected to heat treatment at 550°C to dehydroxylate the kaolinite and halloysite. This is followed by another 2.5 min dissolution treatment in 0.5N KOH and a further deferration with dithionite. Some iron-rich montmorillonitesaponite (smectite) and vermiculite are also dehydroxylated on heating and subsequently are partially dissolved in the KOH. The kaolinite and halloysite constituents were then calculated.
TL;DR: The role of clay minerals in influencing the polymerization of organic monomers can be ascribed to a charge transfer between the clay and the adsorbed species as mentioned in this paper, which may be either initiated or inhibited by the clays.
Abstract: The role of clay minerals in influencing the polymerization of organic monomers can be ascribed to a charge transfer between the clay and the adsorbed species. Polymerization may be either initiated or inhibited by the clays.
TL;DR: In this paper, a critical review of the most important recent achievements in the area of thermal and photochemical autoxidation is presented, focusing on the concept of critical antioxidant concentration, the multiple effects of heavy metals (including catalyst-inhibitor conversion), the development of new synergistic antioxidant combinations composed of free radical acceptor and peroxide decomposer and, finally, Denisov's direct experimental evidence for the reaction of heavy metal with molecular oxygen in organic media in support of Uri's trace metal hypothesis.
Abstract: Following an outline of the pioneering work of Haber's School, emphasis is placed on a critical review of the most important recent achievements These embrace, in the area of thermal autoxidation: the concept of critical antioxidant concentration, the multiple effects of heavy metals (including catalyst-inhibitor conversion), the development of new synergistic antioxidant combinations composed of free radical acceptor and peroxide decomposer and, finally, Denisov's direct experimental evidence for the reaction of heavy metals with molecular oxygen in organic media in support of Uri's trace metal hypothesis of the general mechanism of the initiation of autoxidation The following recent advances in the field of photochemical autoxidation are described: photosensitized initiation by trace metals and its inhibition, the singlet oxygen hypothesis, the inadequacy of phenolic antioxidants and the reliance on UV absorbers, the importance of energy transfer in photochemical protection leading to new stabilizers A very recent innovation which is relevant to both thermal and photochemical autoxidation is highlighted, ie, the development of new α-dithidiketone chelates, particularly bis (stilbenedithiolate) nickel (= NiS4C4Ph4or, abbreviated, NiSDT) as antioxidants which combine in a unique way the properties of free radical acceptors, peroxide decomposers and UV stabilizers They were then found to be the most powerful antioxidants for polyethylene and polypropylene
TL;DR: In this paper, the IR spectra, X-ray patterns and DTA curves of various aryl ammonium montmorillonites are characterized, and it is inferred that interlayer alkyl al ammonium ions also show protons with excess amine through water bridges.
Abstract: The IR spectra, X-ray patterns and DTA curves of various aryl ammonium montmorillonites, are characterized. Depending upon the particular amine, the aryl ammonium ions react with excess base by (1) showing a proton equally between two amine molecules through a water bridge, (2) by retaining the proton identified with one molecule, or (3) by polymerization liberating protons. It is inferred that interlayer alkyl ammonium ions also show protons with excess amine through water bridges but the stability of the aryl and alkyl compounds differs greatly.
TL;DR: In this paper, normal fatty acids ranging from C14 to C36 were found to account for a maximal 0.10% of the dry ash-free weight of a water soluble soil fulvic acid.
Abstract: Normal fatty acids ranging from C14 to C36 were found to account for a maximal 0.10% of the dry ash-free weight of a water soluble soil fulvic acid. Only 10.0% of the total fatty acids could be extracted by organic solvents from untreated fulvic acid. The remaining 90.0% was extractable only after methylation of the fulvic acid and adsorption on neutral aluminum oxide. While the nature of the molecular forces that hold the fatty acids to the fulvic acid is still a matter of conjecture, evidence was obtained that reduction of hydrogen bonding by methylation was related to the release of fatty acids by the fulvic acid.
Ninety-five percent of the acids that were isolated were saturated, the remaining 5.0% were unsaturated and branched-cyclic. The C24 acid was the major component. The overall C-even to C-odd carbon atom ratio for all acids was 2.3. The results suggested two different origins for the fatty acids: the C14 to C26 acids may be of microbiological origin, whereas the C27 to C36 acids may have arisen from plants.
Weight distribution plots of fatty acids and n-alkanes extracted from the fulvic acid showed an inverse concentration relationship between the two components with identical carbon numbers.
The data reported herein suggest that fulvic acid may act as a vehicle for the mobilization, transport and immobilization of water-insoluble organic compounds—some of which may be serious pollutants—in an aquatic environment.
TL;DR: In this paper, the various primary processes in excited oxyanions are discussed and the most common processes appear to involve one-unit change of oxidation number (one electron processes): the generation of e−aq and O−aq (or OHaq).
Abstract: The various primary processes in excited oxyanions are discussed. The most common processes appear to involve one-unit change of oxidation number (one electron processes): the generation of e−aq and O−aq (or OHaq). The production of oxygen atoms (a two-electron process) occurs only with central atoms having high electron-affinities. There is no convincing evidence for one-step evolution of O2. Some major secondary processes are also discussed.
TL;DR: In this paper, the thermal decomposition of four different cellulose samples (untreated cellulose, powdered or ball-milled Whatman 544 filter paper, and micro-crystalline cellulose) was studied at 250°.
Abstract: The thermal decomposition of four different cellulose samples (untreated cellulose, powdered or ball-milled Whatman 544 filter paper, and micro-crystalline cellulose) was studied at 250°. In samples heated either alone or in the presence of NaHSO4, Na2SO4, Na3PO4, or NaCl for 2 or 4 hr, weight loss, total organic volatiles, levoglucosan, water, acids, average degree of polymerization, and crystallinity index were determined. The results obtained are tabulated and compared. Whereas pretreatment and crystallinity considerably affect the pyrolytic behavior of the different samples, the presence of additives tends to mask the observable differences.
TL;DR: The role of charge transfer to solvent (CTTS) intermediates in this process is demonstrated by Photoaquation according to as mentioned in this paper, who found very low, possibly zero quantum yield in this region.
Abstract: Light absorption by the Fe(CN−)4−6 ion in aqueous solution at selected wavelengths between 214 and 313 nm results in the formation of excited states which yield the reaction sequence:
with φe, the quantum yield, decreasing from 09 at the lowest to 01 at the highest wavelength At and above 3371 nm φe = 0 The role of charge transfer to solvent (CTTS) intermediates in this process is demonstrated Photoaquation according to
is found to have very low, possibly zero quantum yield in this region The role of acid-base equilibria, e g
and of the protonated species, in the photochemistry of cyanoferrate (II) species is discussed
TL;DR: In this paper, the photodynamic effects of molecular oxygen were simulated on molecules of biological interest including enzymes including enzymes using the excited species of the molecular oxygen in a separate vessel and carried into the sample by a stream of gaseous nitrogen.
Abstract: It was attempted to recreate on molecules of biological interest including enzymes some of the photodynamic effects using the excited species of molecular oxygen. Such a species is produced by a chemical reaction in a separate vessel and is carried into the sample by a stream of gaseous nitrogen.
TL;DR: The use of (1,1,2-trifluoro-2-chloroethyl)-diethylamine for the replacement of a hydroxyl group by a fluorine atom has been investigated as mentioned in this paper.
Abstract: The use of (1,1,2-trifluoro-2-chloroethyl)-diethylamine for the replacement of a hydroxyl group by a fluorine atom has been investigated. Particular attention has been paid to hydroxy-compounds carrying other functional groups, e. g. carbonyl, ester and amino-groups and combinations of them.
TL;DR: In this article, cobalt (II) ions were sorbed from various solutions onto the chelating ion exchanger Dowex A-1 and compared to the spectra of cation and anion exchangers loaded with cobalt species under the same equilibrating conditions and to the complexes formed with the monomeric iminodiacetate.
Abstract: Cobalt (II) ions were sorbed from various solutions onto the chelating ion exchanger Dowex A-1. The infrared, near infrared and visible spectra of the various sorbed species were measured and compared to the spectra of cation and anion exchangers loaded with cobalt species under the same equilibrating conditions and to the complexes formed with the monomeric iminodiacetate. The structure and bonding of the different species sorbed were discussed.
TL;DR: In this paper, LiNaphthalene reacts with acetic acid to give α-anion of lithium acetate, and the reaction of this anion with various ketones gives β-hydroxy-acids in good yield.
Abstract: Lithium naphthalene reacts with acetic acid to give α-anion of lithium acetate. The reaction of this anion with various ketones gives the corresponding β-hydroxy-acids in good yield.
TL;DR: In this paper, the interaction between montmorillonite and kaolinite clay minerals and humic acid (HA) was studied by absorbance measurements, which were interpreted as an indication of changes in the size of clay tactoids.
Abstract: The interaction between montmorillonite and kaolinite clay minerals and humic acid (HA) was studied in suspensions by absorbance measurements. Changes in absorbance as a result of the interaction were interpreted as an indication of changes in the size of clay tactoids. Na-humate caused dissociation of montmorillonite tactoids in suspension. Drying-wetting cycles increased the effect of Na-humate and resulted in tactoids similar in their size to those of the Li-saturated montmorillonite. Na-humate had no effect on the absorbance of kaolinite suspensions.
TL;DR: The first analysis of Dead Sea water was done in 1778 by Macquer, Lavoisier and Sage as discussed by the authors, who noted most of the unusual chemical properties of the lake, and the earliest search for life in the Dead Sea was made by Gay Lussac in 1817 while trace element analysis goes back to 1827.
Abstract: The first analysis of Dead Sea water was done in 1778. The progress in the science of analytical chemistry is reflected in the improved procedures used for analysis of Dead Sea water. The first analysis by Macquer, Lavoisier and Sage (1781) noted most of the unusual chemical properties of the lake. The earliest search for life in the Dead Sea was made by Gay Lussac in 1817 while trace element analysis goes back to 1827. Some of the early investigators suggested that most of the salt content is contributed by the Jordan River, accompanied by precipitation of CaCO3 and CaSO4. This hypothesis is now accepted by many investigators.
TL;DR: In this article, the cation exchange of N-nalkylpyridinium ions against inorganic ions in mica type layer silicates is dealt with and the arrangements of these ions in the interlayer space is derived from basal spacing measurements.
Abstract: This paper deals with the cation exchange of N-n-alkylpyridinium ions
against inorganic ions in mica type layer silicates. The arrangements of these ions in the interlayer space is derived from basal spacing measurements.
TL;DR: The compounds TlMnCl3, TlFeCl3 and TlNiCl3 were prepared by heating T1C1 with the corresponding transition metal dichloride in an evacuated ampoule as mentioned in this paper.
Abstract: The compounds TlMnCl3, TlFeCl3, TlCoCl3 and TlNiCl3 were prepared by heating T1C1 with the corresponding transition metal dichloride in an evacuated ampoule. Atomic positions were determined from powder photographs. All four compounds were found to be related to the perovskite type structure. TlMnCl3 has a cubic structure, space group Pm3m, with ao = 5.025 A. The other three compounds are hexagonal, probable space group P63mc, with cell dimensions (in A) a0 = 6.976 and c0 = 6.008 for the Fe compound, a0 = 6.907 and c0 = 5.981 for the Co compound and a0 = 6.863 and c0 = 5.881 for the Ni compound. The three hexagonal compounds are isomorphous. A measureable concentration of basal plane stacking faults was found to occur in TlFeCl3 and also, to a lesser degree, in TlCoCl3.
TL;DR: In this article, the ratio of cis:trans adducts varied considerably with solvent, temperature, and olefin concentration in steroid reactions but not in reactions with cyclohexenone.
Abstract: Photoadditions of ethylene and of cyclopentene to Δ4 - and Δ4,6-3-ketosteroids gave mixtures of cis-4α,5α and trans-4α. 5β adducts. In the case of cyclopentene and Δ4,6-androstadiene-3-one-17β-ol propionate, only the trans adduct was observed. Cis-4β,5β adducts were obtained by base-catalyzed isomerization of the trans adducts. The ratio of cis:trans adducts varied considerably with solvent, temperature, and olefin concentration in steroid reactions but not in reactions with cyclohexenone. The different types of adducts exhibited markedly different ORD curves in agreement with the structures assigned. Carbonyl maxima of trans adducts appeared at shorter wavelengths than maxima of cis adducts in both infrared and ultraviolet spectra. The infrared shifts provide a convenient method for differentiating between cis and trans fused isomers.
TL;DR: In this article, HO2 radicals were generated in a flow system by the reaction: Ce4+ + H2O2 Ce3+ +HO2 + H+ +H+ + HO2+H+ with V -H 2O2 solutions and ESR spectroscopy was used to follow the reaction.
Abstract: HO2 radicals were generated in a flow system by the reaction: Ce4+ + H2O2 Ce3+ +HO2 + H+. The HO2 radicals were mixed with V - H2O2 solutions and ESR spectroscopy was used to follow the reaction. It was shown that HO2 reacts with both VO(O2)+ and VO(O2)−2 complexes. The ESR signal of the complexed radical consists of eight lines, indicating that the unpaired electron interacts with the Vanadium nucleus. The kinetics of the formation and decay reactions of the complexed radical were studied.