bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Stability of Apatites Containing Zinc Ions
Authors: Ben‐Dor Lina , Diab Hussam
Published: November 2013

Fluor‐carbonate‐apatites were prepared by a heterogeneous reaction from calcium carbonate, alkaline phosphate and fluoride and were doped with Zn2+ ions. The thermal stability of the doped apatites was studied by measuring the fluoride content before and after heat‐treatment using a selective electrode. It was shown that the doped apatites are thermally more stable than the pure material. The degree of stability is dependent on the amount of doping.
Iron‐Bearing Kaolinite in Venezuelan Laterites. II. DTA and Thermal Weight Losses of KCl and CsCl Mixtures of Laterites
Authors: Mendelovici E. , Villalba R. , Yariv S.
Published: November 2013

KCl and CsCl mixtures of Venezuelan laterite samples were examined by DTA. These laterites contain iron‐bearing kaolinite. The first endothermic peak at ∼300°C is characteristic of goethite and gibbsite. A second endothermic peak at 470–512°C characterizes kaolinite. In KCl mixtures, the maximum of this peak decreases with increasing iron content of the kaolinite crystal. In CsCl mixtures, such a relationship is obtained only after the removal of the gibbsite from the lateritic sample. A third endothermic peak at 650–760°C is characteristic of the melting of the salt. The intensity of this peak may be used as a reference. KCl may thus serve as an internal standard for the determination of kaolinite in a series of laterite samples. CsCl, which forms a complex with kaolinite, cannot be used as an internal standard. The fourth endothermic peak results largely from the evaporation of the salt. The location of this peak in the CsCl mixtures depends on the iron content of the kaolinite. The laterite—alkali halide mixtures were subjected to weight losses at temperatures between 105 and 1000°C. In addition to the dehydroxylation processes, hydrolysis of the salts on the surfaces of kaolinite, and the evaporation of HCl take place in the CsCl mixtures and to a lesser extent in the KCl mixtures. In the CsCl mixtures, when the dehydroxylation stage of the kaolinite was studied in stages, it was found that kaolinites with a high iron content tend to lose weight mainly at a high temperature (550°C) whereas those with a low iron content tend to lose weight even at 450°C.
Interaction of NO2 with a Pt(111) Surface
Authors: Segner J. , Vielhaber W. , Ertl G.
Published: November 2013

The interaction of NO2 with a Pt(111) surface was studied by molecular beam and thermal desorption techniques. At 300 K NO2 adsorbs dissociatively into NOad + Oad with an initial sticking coefficient so = 0.97. so decreases slightly with increasing surface temperature; the variation of the sticking coefficient with coverage exhibits a marked “precursor” state behavior. The rate of formation of gaseous NO is limited by desorption of this molecule, i.e. there is no evidence for a direct process NO2 ŕ NOg + Oad. At ≈ 400 K NO desorption is complete and only Oad is building up on the surface. The maximum coverage Θo,max ≈ 0.77 is much higher than that so far reported for exposure to O2 (0.25), which is ascribed to kinetic effects, i.e. a much higher sticking coefficient in the case of NO2. Two additional states with desorption energies of about 32 and 38 kcal/mol characterize the high oxygen coverage situation. Desorption of O2 starts above 450 K.
Multielectron Transfer Across the Metal Electrolyte Interface in Electrochemical Systems
Authors: Efrima S.
Published: November 2013

The theory for the rate of multielectron transfer across the metal electrolyte interface in electrochemical systems is developed. The two‐electron case is specifically considered and compared to the one‐electron case. It is found that the two‐electron path may become more important than the parallel one‐electron channel under certain well‐specified circumstances.
Theoretical Study on the Origin of the Behavior of Ketones and Thiones in Hydrogen Photoabstraction Reactions
Authors: Bigot B.
Published: November 2013

Natural correlation diagrams have been established to describe hydrogen photoabstraction in ketones and thiones for three different reaction paths (nx, πx and πc approaches). Their conclusions have been confirmed by ab initio SCF‐CI calculations. This procedure leads to the following conclusions: Energy barriers exist on the potential energy surfaces of all the potentially reactive excited states. The height of these barriers is strongly dependent on the distance separating the hydrogen acceptor and hydrogen donor atoms in the transition state. For the n approach, the reactive channel only involves nπ* excited states while, for the π approach, nπ* (hydrogen capture by the carbon atom) and ππ* (hydrogen capture by the oxygen or the carbon atom) excited states must also be taken into consideration. A proposal for resolving the ketone‐thione dichotomy is presented on the basis of these results.
Torsional Barriers Resulting from Two‐electron and Four‐electron Interactions. The Hydrazyl Cation and Anion Models
Authors: Kost D. , Aviram K. , Raban M.
Published: November 2013

The spectrum of rotations about single bonds has been divided into two different groups of processes, termed TA and TC. These describe interconversion of planar ground state conformations (as in amides), and interconversion of enantiomers (as in sulfenamides and hydroxylamines), respectively. A frontier molecular orbital analysis of the hydrazyl cation and anion reveals that a change in electron occupancy alone can bring about a change from one torsional process to the other. Thus, the four‐electron hydrazyl anion undergoes a TC process, while the corresponding two‐electron cation undergoes a TA rotation. Nonempirical SCF‐MO calculations of the model cation and anion with geometry optimization at the 4‐31G level confirm the results of the PMO analysis. The calculations also reveal a preference for an inversion (IA) mechanism for the topomerization of the cation system over a torsional process.
On the Electronic Origins of a Novel Transoid Structure of 1,3‐Diene‐zirconocene Complexes
Authors: Tatsumi Kazuyuki , Yasuda Hajime , Nakamura Akira
Published: November 2013

Coordinations of conjugated 1,3‐dienes to a transition metal had been considered to occur only in a s‐cis geometry, until the recent discovery of Cp2Zr(s‐trans‐diene), diene = butadiene and trans, trans‐1,4‐diphenylbutadiene. A molecular orbital analysis of metal‐butadiene interactions is carried out, for the specific cases of Fe(CO)3 (butadiene) and Cp2Zr(butadiene), to discern the electronic origin of the novel transoid geometry. Stability of the s‐cis and s‐trans structures of Cp2Zr(butadiene) is found to be well balanced and we show how the geometrical choice is affected by substitution on butadiene.
Pyrrole Exchange Reactions in the Bilirubin Series
Authors: Bonnett Raymond , Buckley Dennis G. , Hamzetash Dariush , McDonagh Antony F.
Published: November 2013

Acid treatment of a mixture of bilirubin IXα (1) and octaethyl‐10,23‐dihydro‐21H,24H‐bilin‐1,19‐dione (7), followed by dehydrogenation and esterification gives biliverdin IXα, biliverdin XIIIα and biliverdin IIIα (as the dimethyl esters, 2, 3, 4, respectively), and octaethylbilindione (8), together with two minor verdins of intermediate polarity. These are identified as the products of the crossed pyrrole exchange reaction, which are 8‐carboxyethyl‐12,13,17,18‐tetraethyl‐2, 7‐dimethyl‐3‐vinyl‐21H,24H‐bilin‐1,19‐dione methyl ester (9) and 8‐carboxyethyl‐12,13,17,18‐tetra‐ethyl‐3,7‐dimethyl‐2‐vinyl‐21H,24H‐bilin‐1,19‐dione methyl ester (10). An improved preparation of bilirubin XIIIα (5) and bilirubin IIIα (6) is described and the products are crystallised and characterised. The NMR spectra of bilirubin XIIIα and IIIα are recorded in a polar aprotic solvent (DMSO‐d6) at 400 MHz, and certain unusual features are discussed.
Hydrogen Bonding of Bilirubins and Pyrromethenones in Solution
Authors: Trull Francesc R. , Ma Jin‐Shi , Landen George L. , Lightner David A.
Published: November 2013

Analysis of bilirubin and pyrromethenone N—H 1H‐NMR chemical shifts indicates that in CDCl3 solvent, where intermolecularly H‐bonded dimers or intramolecularly H‐bonded conformations are involved, the lactam N—H groups are more deshielded than the broader pyrrole N—H groups. In d6‐DMSO, disaggregation and unfolding occurs with H‐bonding to the solvent and the sharper lactam N—H resonances becoming more shielded than the pyrrole N—H signals.
Isophorcarubin — A Conformationally Restricted and Highly Fluorescent Bilirubin
Authors: Kufer W. , Scheer H. , Holzwarth A. R.
Published: November 2013

The biliverdins 2b, 5 and 1 have been reduced with NaBH4 to the bilirubins 8, 7 and 6, respectively. The conformation of these pigments is increasingly extended and the flexibility is increasingly restricted in the sequence given above, which does not influence the ease of reduction. The fluorescence of 6 and 7 has been studied at ambient temperature and 77 K in ethanol and 2‐methyltetrahydrofuran. 6 has an unusually high fluorescence yield which has been related to the conformational rigidity of its ring C, D chromophore. Both 6 and 7 show evidence of solvent and temperature dependent inhomogeneities in their fluorescence spectra.
Potassium‐39 Nuclear Magnetic Resonance Studies of Counterion Binding in Lyotropic Liquid Crystals
Authors: Boden N. , Jones S. A.
Published: November 2013

The binding of K+ at the lamella bilayer surface in the lamellar phase of the potassium oleate–water system has been studied by 39K NMR. The effects of temperature, water content and solubilizate (octanol, benzyl alcohol, benzene and cyclohexane) are investigated. A simple two‐site equilibrium model is used to interpret the measurements. The manner in which the solubilizate interacts with and perturbs the structure of the lamella bilayer surface is implicit in the results.
Proton Spin Relaxation Dispersion for Some Nematic Homologues of the Liquid Crystal PAA
Authors: Nagel G. , Wölfel W. , Noack F.
Published: November 2013

In order to elucidate the nature of spin relaxation in nematic liquid crystals in the vicinity of the nematic–isotropic phase transition temperature, we present extensive measurements and a quantitative analysis of the proton spin, T1, relaxation dispersion for some homologues of the PAA series (PAA, PAB, HAB). The studies were made for the nematic state over a broad range of Larmor frequencies. By a detailed inspection of the frequency, temperature and chain length dependences we conclude that in all cases at least three kinds of molecular reorientations with rather different relaxation dispersion contribute to the total T1, i.e., order fluctuations of the director (OFN), self‐diffusion (SD) and an additional mechanism, which we attribute to order parameter fluctuations (OFS). The combined OFN–SD–OFS model extends existing interpretations and allows a quantitative description of the observed phase transition effects. The effects of both OFN and OFS on T1 clearly increase with the molecular length and we deduce from this that not only the ring protons, but also some chain protons undergo these types of fluctuation. Due to the rather high temperature of the mesophases, the diffusional contribution is hard to evaluate exactly and hence there are no significant variations between the homologues within the limits of experimental error. However, a small systematic discrepancy with respect to independent diffusion measurements, available for PAA, indicates that this relaxation model is still incomplete and that a fourth mechanism should be included in the analysis. Possibly, this could be some kind of rotation as previously reported for low‐temperature nematics.
The Ozonolysis of Haloalkenes in Solution
Authors: Gillies Charles W. , Kuczkowski Robert L.
Published: November 2013

A review of the ozonolysis of low molecular weight haloalkenes in solution is presented. The reaction products from the fluoroethylene series are discussed in detail. Secondary ozonides can be obtained from these alkenes although the yields decrease markedly with increased fluorination and diminish to negligible quantities with C2F4. Compared to alkylethylenes, a greater variety of products are obtained including some epoxides and fluorocyclopropanes. Yield data are supplemented by isotopic labeling results to elucidate the ozonolysis mechanism. The evidence indicates that the final ozonides are formed by the three step Criegee reaction mechanism although the stereoselectivity of the reaction differs from nonhaloalkenes.
Oxy‐Radicals and the Radiobiological Oxygen Effect
Authors: Greenstock Clive L.
Published: November 2013

The radiobiological oxygen effect can be separated into its biological and chemical components, using time‐resolved or kinetic studies. Rapid mix techniques show that the full oxygen enhancement ratio (OER) for radiation‐induced cell killing is expressed when oxygen is present or admitted 40 ms prior to irradiation. This predominant chemical action of oxygen, including direct and indirect action, is too fast to implicate processes other than those involving free radical species. The two principal hypotheses, “oxygen fixation” and “active oxygen”, are discussed. Pulse radiolysis studies of model systems provide kinetic data to indicate the principal damaging species and radiation targets, the kinetics and sequence of damaging events, and the role of redox processes involving oxygen, oxy‐radicals and radiation modifiers. Complementary steady‐state radiolysis studies enable the nature and extent of the physico‐chemical damage to be quantified. Mechanistic aspects of the radiobiological oxygen effect are inferred from in vitro studies of irradiated mammalian cells, comparing the different biological end‐points with specific forms of chemical damage, under a variety of physical, chemical and biological conditions.

While this review stresses the role of oxygen in sensitizing the critical cellular target DNA, responsible for the acute biological effect of cell killing, it must be remembered that for cancer and other chronic effects, having a long latent period between radiation exposure and the biological expression of deleterious damage, there may not be an oxygen effect or if there is, it may be quite different in terms of the damaging species, principal radiation targets, and the sequence and kinetics of the damaging events. Although oxygen and oxy‐radicals may be involved in the initiation and development of cancer, their overall roles in influencing the chronic effects of radiation may be complex and dependent upon cellular and multicellular factors, making it difficult to unambiguously elucidate possible mechanisms.
Conjugate Addition of Phosphine‐Complexed Organocopper Reagents to α,β‐Unsaturated Ketones
Authors: Suzuki M. , Suzuki T. , Kawagishi T. , Morita Y. , Noyori R.
Published: November 2013

Organocopper reagents formed from equimolar amounts of copper(I) iodide and organolithiums and 2 to 3 equiv of tri‐n‐butylphosphine undergo smooth reaction with α,β‐unsaturated ketones, and after aqueous quenching afford β‐substituted ketones in high yields. This method is economical (enone/organolithium=1:1.05 to 1:1.25) and applicable to a wide variety of entering groups and enone substrates, and compares well with the existing procedures.
Infrared Multiphoton Induced Isomerization of cis‐3,4‐Dichlorocyclobutene. III. Pressure Dependence of the Yield
Authors: Ringwelski Andrzej Z. , Presser Nathan , Gordon Robert J.
Published: November 2013

The multiphoton induced isomerization of cis‐3,4‐dichlorocyclobutene (DCCB) was studied as a function of pressure. Three experiments indicated the existence of a nonthermal mechanism at neat pressures below 60 mtorr. These were: (i) the leveling off of the fractional yield of isomerization products at low pressures; (ii) the absence of dissociation products from 2‐iodo‐2‐methyl propane, which served as a chemical thermometer in the presence of a large excess of DCCB; and (iii) a break in the power‐law dependence of the optoacoustic signal produced by neat DCCB. The increased yield at higher DCCB pressures is believed to be due partly to a thermal reaction and partly to increased absorption caused by rotational or vibrational hole filling. Optoacoustic measurements also showed that at constant fluence the absorbed energy was greater for long, low intensity pulses, as might be expected for inhomogeneous excitation. However, the present experiments did not reveal an intensity dependence of the reaction yield. Addition of argon as a buffer gas monotonically decreased the yield, indicating that vibrational quenching more than offsets any hole‐filling effects.
The Preparation and Kinetic Properties of Fully‐Functionalized Imidazole Vesicles
Authors: Moss Robert A. , Kim Kwang Yoo
Published: November 2013

The 4‐imidazolecarboxylic acid ester of N,N‐dihexadecyl‐N‐methyl‐N‐(β‐hydroxyethyl)ammonium chloride (1) and an analogous monohexadecyldi‐methylammonium ion surfactant (2) were prepared from readily available starting materials. Surfactant (1) formed fully‐functionalized imidazole vesicles which are powerful catalysts for the cleavage of p‐nitrophenyl acetate, p‐nitrophenyl hexanoate and 4‐acetoxy‐3‐nitrobenzenesulfonate. Maximum observed rate constants ([1] = 3.4 × 10−3 M, pH 8.0, 0.01 Tris buffer, μ = 0.01, 25°C) are 2.82, 16.3 and 14.3 s−1, respectively, for the three substrates. These and related kinetic parameters are compared with those of imidazole‐functionalized micellar surfactants, such as 2.
The Borane Adventure — Past, Present and Future
Authors: Brown Herbert C.
Published: November 2013

Forty‐eight years ago, diborane was a chemical rarity, available only in two laboratories in the world. The requirements of research during World War II led to the discovery of practical synthetic methods of diborane and to the discovery of sodium borohydride. These turned out to be excellent reducing agents in organic chemistry. Exploration of these reducing characteristics led to the discovery of hydroboration. Hydroboration made organoboranes readily available. These organoboranes have proven to be the most versatile intermediates now available for organic synthesis. A recent development makes possible the synthesis of essentially any compound containing a chiral center in both optical isomers in essentially 100% optical purity. Thus this research program has taken boranes from a material available only in trace quantities to a reagent widely used in organic synthesis, greatly assisting the chemist in overcoming synthetic difficulties.
Trivalent and Tetravalent Nickel in Oxime‐Imine‐Amine Coordination
Authors: Chakravorty Animesh
Published: November 2013

Model complexes of nickel(III) and nickel(IV) are furnished by hexadentate and tridentate oxime‐imine‐amine ligands derived by the condensation of biacetyl monoxime with amines. The synthesis, characterisation, structure, redox equilibria and reactivity of these complexes are critically reviewed. Correlations and generalisations pertaining to oxidation state stability, electroprotic equilibria and reaction mechanisms are examined. The possible significance of the present complexes in the context of the nickel‐containing methanogenic enzymes is noted.
Kinetic Aspects of Redox Reactions of Nickel(III) Complexes
Authors: Mcauley Alexander , Norman Paul R.
Published: November 2013

The synthesis and characterisation of nickel(III) complexes are reviewed. Kinetic aspects of redox reactions including oxidation by Co(OH2)3+6 and Fe(phen)3+3 are described, as are the reactions involving oxidation of non‐metallic substrates. Reference is made to the evaluation of self‐exchange rates for the Ni(III)L/Ni(II)L couples, especially for systems where both oxidant and reductant retain an octahedral geometry. Using the reversible reaction between Ni(9‐aneN3)3+2 and Ni(10‐aneN3)3+2 (9‐ane = 1,3,7‐triazanonane, 10‐ane = 1,3,7‐triazadecane), data are presented for evaluation of the self‐exchange rate constant for the Ni(10‐aneN3)3+/2+2 couple [(7.5 ± 1) X 103 M−1s−1]. This value is compared with that for similar systems where changes in bond lengths on oxidation have been determined by X‐ray techniques.
Nickel(III) and Copper(III) Complexes with 13‐ and 14‐membered Tetra‐aza Macrocycles. Ring‐size and Medium Effects on the MIII/MII Redox Couple Potentials
Authors: Fabbrizzi Luigi , Licchelli Maurizio , Perotti Angelo , Poggi Antonio , Soresi Silvia
Published: November 2013

The one‐electron oxidation of the NiII and CuII complexes with 13‐ and 14‐membered macrocycles 1 and 2 to produce authentic NiIII and CuIII species has been electrochemically investigated and the E1/2 values associated to the reversible MIII/MII redox couple have been determined by means of the Differential Pulse Voltammetry technique. The 13‐membered ring favours the attainment of the CuIII state, whereas the 14‐membered ring favours the formation of the NiIII complex. This opposite behaviour is satisfactorily interpreted in terms of size of the metal ions and aperture of the macrocyclic cave. Moreover the effect of the concentration of the inert electrolyte (NaClO4, 0.1–7.0 M) on the E1/2(MIII/MII) values has been investigated: the increase of the NaClO4 concentration favours the formation of the CuIII complexes and disfavours the formation of the NiIII species. This behaviour is ascribed to the destabilization of NiIII and CuII complexes induced by perchlorate ion through the formation of hydrogen bonds with water molecules axially coordinated to the metal ions.
Reactivity of Intermediates in the Photochemistry of Copper(II) Macrocyclic Complexes
Authors: Ferraudi G.
Published: November 2013

The reactivity of unstable copper macrocycles which act as intermediates in photochemical transformations of copper(II) complexes with synthetic macrocyclic ligands has been reviewed. Although most of these species were investigated by flash photolysis, a number of pulse radiolytic investigations of related species were also incorporated in this review.
Structural Parameters of Photochromic Dihydroindolizines. X‐ray Analysis and MINDO/3‐Calculations
Authors: Dorweiler C. , Spang P. , Dürr H. , Peters K. , Schnering H.G.V.
Published: November 2013

To elucidate the detailed geometry as well as the bonding situation in the new photochromic spirodihydroindolizines 3 an X‐ray structure analysis of 3a, an analogue of 3, as well as MINDO/3‐calculations for 4, a model for 3, were carried out. There is good agreement between the geometric data obtained by these two methods. The spiro bonds are long, due to spiro linking. The lengths of these bonds cannot be explained by spiro interactions, according to MINDO/3. They result, rather, from an increase of strain due to spiro linking. The longest of these bonds is the C(1)‐C(4) one, which is about 0.01‐0.20 Å longer than a normal C‐C single bond. This is due also to the neighbouring sp3‐hybridized N‐atom. The C(1)‐C(4) bond is therefore the weakest bond in the molecule, and can be broken very easily by UV or visible light, thus explaining the photochromic behaviour of this type of system.
Solid‐State Chemistry of Cyanine‐Type Dyes and the Effect of Two Novel Counterions on Their Crystal Properties
Authors: Etter Margaret C. , Holmes Brian N. , Kress Ruth B. , Filipoich George
Published: November 2013

Organic dyes undergo a variety of solid‐state chemical processes, including intra‐ and intermolecular reactions, gas‐solid reactions, and polymorphic transformations. The properties of dye solids are markedly affected by this chemistry. This paper reviews solid state dye chemistry from the literature and reports in detail the chemistry of two novel cyanine dye salts whose properties are controlled by the nature of their counterions. In cyanine‐oxonol salts, the oxonol counterion is a large planar dye which forms crystalline dye aggregates with cyanine ions. There is a multiplicity of polymorphic forms of these mixed dyes reflecting multiple favorable dye aggregate geometries. The cyanine‐borate salts undergo intermolecular solid‐state reactions. In either large single crystals or dispersions of the latter salts in polymer binders, alkyl transfer from the anion to the chromophore can be induced thermally or photochemically.
Solid State Hydrolysis of 2‐Methyl‐4H‐benzoxazin‐4‐one. Mode of Propagation of the Reaction Process During the Hydrolysis
Authors: Vicens Jacques , Decoret Claude , Royer Jean , Etter Margaret C.
Published: November 2013

Kinetic studies of hydrolysis and deuteriolysis of microcrystalline 2‐methyl‐4H‐benzoaxazin‐4‐one 1 into N‐acetylanthranilic acid 2 are presented. Hydrolysis of mixtures of microcyrstalline 1 and 2 are given. The results are interpreted and a mechanism is proposed for the solid gas reaction. A theoretical approach of the crystal packing of 1 permits an evaluation of the mode of diffusion of water molecules in the crystal. Both experimental and theoretical results lead to a proposal of the mechanism of water propagation and the hydrolysis process in the solid phase.
Stereochemical Discrimination at Organic Crystal Surfaces 1: The Systems Serine/Threonine and Serine/Allothreonine
Authors: Weissbuch I. , Shimon L.J.W. , Addadi L. , Berkovitch‐Yellin Z. , Weinstein S. , Lahav M. , Leiserowitz L.
Published: November 2013

The stereoselective interactions in aqueous solution between the crystal faces of centrosymmetric (R,S) serine 1 and additives resolved and racemic threonine 2 and allothreonine 3 were studied by four independent techniques: change in crystal habit on growth, anisotropic distribution of occluded additive during the crystal growth, etch pit formation on partial dissolution and atom‐atom potential energy calculations. The effects of the two diastereomers 2 and 3 are radically different due to differences in adsorption: threonine is adsorbed on the {011} crystal faces; the (R) enantiomer is adsorbed at, and eventually occluded through the (011) and (011) crystal faces replacing an (R) serine molecule. By symmetry, (S) threonine is adsorbed and occluded through the enantiotopic (011) and (011) faces replacing (S) serine. In contrast, (R) and (S) allothreonine are both adsorbed primarily at the (100) and (100) faces. The results indicate that the serine moiety of adsorbed threonine and allothreonine assume the same conformation and position as the substrate molecule. The additive is adsorbed only at specific sites such that the Cβ‐CH3 groups emerge from the crystal surface. The observed effects lead in the case of threonine, but not allothreonine, to the assignment of its absolute configuration.
Adsorption Behavior of Vanadium on Macroreticular Chelating Resins Containing Amidoxime Groups
Authors: Egawa Hiroaki , Nonaka Takamasa , Matsumoto Setsuo , Nakayama Morio
Published: November 2013

The macroreticular chelating resins containing amidoxime groups (RNH) showed high affinity for V(V), and were a high capacity of 2.30 mmol/g‐R at pH 5. In particular, it was found that RNH, which were prepared by using 10–16 mol% of DVB in the presence of toluene (80–100 vol%), exhibited the highest adsorption ability for V(V) in a dilute solution. When RNH exhibited the sufficient adsorption ability for V(V), the average pore radius, specific surface area, and pore volume were found to be 140–160 Å, 40–91 m2/g, and 0.26–0.36 ml/g, respectively. Vanadium adsorbed on RNH could be eluted by the treatment with 1 M sodium hydroxide solution.
Cation Transport Through Liquid Membranes Mediated by Photoreactive Crown Ethers. Effects of Alkali Metal Cations on Their Photoreactivities and Transporting Properties
Authors: Anzai Jun‐Ichi , Suzuki Yasuhiro , Ueno Akihiko , Osa Tetsuo
Published: November 2013

Photoreactivities and cation transporting properties of monomeric, dimeric, and polymeric crown ethers which contain cinnamoyl residues were investigated. Photochemical cycloaddition reaction of the cinnamoyl moieties was accelerated by NaCl or KCl for the dimeric and polymeric derivatives but not for the monomeric one. The dimeric and polymeric crown ethers after irradiation in the presence of KCl showed a significant enhancement in the transport rates for Rb+ cation.
On the Stereochemistry of Organocopper Mediated Conversion of Propargylic Esters to Allenes
Authors: Haces Alberto , van Kruchten Eugène M.G.A. , Okamura William H.
Published: November 2013

Using a vitamin D‐related steroidal CD fragment as a stereochemical probe, the effect of various factors on the stereochemical course of the organocopper induced conversion of propargylic esters to allenes has been studied. In all cases, an anti mode of attack by the organocopper species was found to be preferred. The effectiveness of Gilman‐type reagents (R2CuLi) versus that of the Lipshutz‐type higher‐order mixed cuprate systems (R2CuCNLi2) in promoting the reaction was also studied.
Nitrous Deamination of β‐Allenic Amines
Authors: Dulcere Jean‐Pierre , Santelli Maurice
Published: November 2013

Deamination of seven allenic amines 1Ad to 1Dd and 14, 15, 16 was performed in protic and aprotic media. Homoallenic participation has been shown to be the major process in deamination of acyclic amines 1Cd and 1Dd. In the latter case, intramolecular retentive substitution was observed.
Optical Rotations of Open‐Chain Allenes Revisited
Authors: Elsevier Cornelis J. , Vermeer Peter , Runge Wolfgang
Published: November 2013

A semiempirical theory for the calculation of optical rotations of allenes in the transparent region is presented. The significance of the suggested model is demonstrated by comparison between calculated and observed rotations of 75 open‐chain allenes with various chemically relevant (carbon and hetero‐) substituents. The physical interpretation of the model reveals that the substituent effect on the optical rotation is exerted via the substituent's polarity (field effect through space) and its polarizability.
“Push‐Pull” Substituted Allenes
Authors: Saalfrank Rolf W.
Published: November 2013

The synthesis, physical and chemical properties of donor/acceptor substitued allenes are reviewed.
Carbonium Ion and Hydridocobalt Intermediates in the Acidic Phase Transfer Catalyzed Reactions of Olefins and Dienes with Cobalt Carbonyl
Authors: Galamb Vilmos , Shim Sang Chul , Sibtain Fazle , Alper Howard
Published: November 2013

The intermediates mentioned in the title are probably involved in the hydrogenation of olefins and dienes; bidentate phosphine and arsine cobalt complexes are useful reagents for these reactions.
Phase Transfer Catalyzed Hypochlorite Oxidations Yielding Carbodiimides and Certain Heterocycles (Applications of Phase Transfer Catalysis, Part 27 [1])
Authors: Broda Witold , Dehmlow Eckehard V.
Published: November 2013

The known hypochlorite oxidation of thioureas to the corresponding carbodiimides becomes faster and more convenient by the use of PTC. Aromatic thioamides are transformed into 3,5‐substituted 1,2,4‐thiadiazoles by the same technique, and substituted 2,5‐diamino‐1,3,4‐thiadiazoles as well as 2‐phenylamino‐benzimidazoles and ‐benzoxazoles can be prepared similarly.
Onium Salt Catalyzed Preparation of Isocyanurates (Applications of Phase Transfer Catalysis, Part 28 [1])
Authors: Broda Witold , Dehmlow Eckehard V. , Schulz Hans‐Joachim
Published: November 2013

Trimerizations of isocyanates give isocyanurates (N.N.N‐trisubstituted 1,3,5‐triazinetriones) in an exothermic, high yield PTC process. Catalysis by various inorganic salts combined with onium salts or crown ethers is effective, Aliquat 336 being the best catalyst.
Halogenation by Phase Transfer Catalysis
Authors: Preston Reeves W. , Creswell Mark W. , Glass Dale S. , Scheide Gary M.
Published: November 2013

Several ketones have been halogenated with carbon tetrachloride employing basic phase transfer catalytic conditions. Acetophenone and phenylace‐tone yield halogenated epoxides while several other aromatic compounds underwent α‐oxidation.
Phase Transfer Oxidations with Hypochlorite: Scope and Mechanism
Authors: Lee George A. , Freedman H.H.
Published: November 2013

The use of phase transfer catalysis (PTC), with catalytic amounts of lipophilic quaternary ammonium salts for the transfer of hypochlorite ion from aqueous to organic media, has been found to be an extremely effective and convenient method for the oxidation of many alcohols and amines. An interesting and unexpected specific solvent effect has also been discovered with the use of ethyl acetate which greatly expands the synthetic utility of this method. Both the synthetic scope and mechanistic aspects of these reactions are reported.
Metal Carbonyls in Phase Transfer Catalysis
Authors: Abbayes Herve Des
Published: November 2013

This review is limited to phase transfer systems (solid—liquid and liquid—liquid) involving metal carbonyls. The principles of phase transfer catalysis, related to metal carbonyl properties which play a key role in these two‐phase systems, are first briefly recalled. Then, in the light of these principles, applications to inorganic chemistry (ligand exchange, preparation of metal carbonyl anions), organometallic chemistry (synthesis of π allyl complexes, clusters, orthometalated compounds, acylmetal carbonyls, complexed ylids), and finally to organic chemistry are comprehensively reviewed. In this last part, both stoichiometric and catalytic systems (with respect to the metal carbonyl) are reviewed essentially in the fields of functional reduction and carbonylation.
Phase Transfer Catalysis and Selectivity in Organic Synthesis
Authors: D'Incan E. , Viout P. , Gallo R.
Published: November 2013

Besides practical advantages and high versatility, phase transfer catalysis (PTC) gives important improvements in selectivity of organic reactions. This paper presents a discussion of selectivity changes induced under phase transfer conditions. Three main aspects are considered: chemoselectivity, regioselectivity and stereoselectivity.
Methyl Transfer Reaction IX. Linear Free Energy Relations and the Reactivity—Selectivity Principle
Authors: Lewis Edward S. , Douglas Thomas A. , Mclaughlin Mark L.
Published: November 2013

Methyl transfers between nucleophiles are representative and uncomplicated examples of group transfer reactions. Data are shown for rates and equilibria sufficient to allow a nearly rigorous application of the Marcus equation. Selectivities with a series of nucleophiles do not vary significantly with reactivity over a wide range of reactivities, except for diffusion controlled reactions. The Marcus equation, for which the necessary data are now available to calculate the rate, fits very well in cases to which it has been applied. It is shown that the (quadratic) Marcus equation is expected to be compatible with experimental linear free energy relations for most reactions; generally only very fast reactions will reveal the curvature, thus the Hammond postulate, the reactivity—selectivity principle, the variable transition state and the Marcus equation are not incompatible with linear free energy relations.
Nitrogen‐15 Kinetic Isotope Effects in the Menschutkin‐Type Reaction of Benzyl Benzenesulfonates with N,N‐Dimethylanilines
Authors: Ando Takashi , Yamataka Hiroshi , Wada Eitaro
Published: November 2013

Nitrogen‐15 kinetic isotope effects were measured for the Menschutkin‐type reaction of Z‐substituted benzyl X‐substituted benzenesulfonates with Y‐substituted N,N‐dimethylanilines (Eq. 1) in acetone at 35°C. The values of 14k/15k for six combinations of X, Y, and Z fell in the range of 1.002–1.004. These small and almost constant nitrogen isotope effects are in contrast to the large and extensively varying carbon‐14 and small but distinctly changing α‐tritium isotope effects observed for this reaction series. The results are discussed in connection with the reactivity–selectivity relationships.
Identity SN2 Reactions. The Relationship Between Transition State Geometry, Selectivity and the Mechanism of Solvent Action
Authors: Shaik Sason S.
Published: November 2013

Reactivity trends in the identity SN2 reaction (X−+ CH3X → XCH3+ X−) are discussed using the state correlation diagram model. The model projects that the activation process can be defined as adistortion effortto transfer asingle electronfrom the nucleophile to the leaving group across the alkyl group (CH3). Three domains of reactivity are discussed (a) the geometry of the transition state (looseness and tightness), (b) the intrinsic selectivity of substrates, and (c) the mechanism of solvent action. A link is drawn between these three domains, and a physical insight is provided.
Extensions of the Melander–Westheimer Postulate: Isotope Effects in Reactions with Equilibrium Values Far from Unity
Authors: Agmon Noam
Published: November 2013

The symmetric dependence of experimental primary kinetic isotope effects on the free energy change, obtained for reaction series with zero equilibrium isotope effects, can be inverted to obtain the free energy profile along the reaction coordinate. Trends in the kinetic isotope effects for the general case of non‐vanishing equilibrium effects can be understood by an extension of the same theory. Comparison is made with experiments for reactions of halogen atoms with hydrogen/deuterium molecules.
Electrophilic Additions to Highly Reactive Enol Ethers. The Particular Role of Resonance in Determining the Kinetic Selectivity Evidenced by Extensive Comparison of Olefin Bromination and Hydration
Authors: Ruasse Marie‐FrançOise
Published: November 2013

The kinetic selectivity of aliphatic enol ethers, EtOCR = CHR' (R and R′ = H or Me), towards electrophiles, I2, Br2 and H3O+, is expressed by the kinetic effect of a methyl substituent in the α position with respect to the ethoxy group, kα‐Me/kH. As expected from the reactivity–selectivity principle, RSP, these selectivities are small, 16, 18 and 330, respectively, as compared to those observed for less reactive olefins. However, a more general comparison of the selectivities of various XCH = CH2 olefins (X = Br, Me, Ph, OAc, OEt) reveals anomalies in their behavior with respect to the RSP: (i) enol ether iodination and bromination exhibit the same selectivity although their rates differ by 4 powers of ten, (ii) enol acetate and enol ether show similar selectivities in bromination but the rate of acetate is 3 × 105 times smaller than that of ether and (iii) in hydration the selectivities of these two olefins are similar to that of styrene although rates range over 7 powers of ten from styrene to enol ether. In contrast with what was previously observed for homogeneous series of R‐substituted styrenes (Ph(R)C = CH2), there is no reactivity–selectivity relationship for electrophilic additions to XCH = CH2 olefins. There is a parallelism, however, between the selectivities and the transition‐state position estimated by the Brønsted exponents for hydration and by the Winstein–Grunwald coefficients for solvent effects on halogenations. These results are discussed in terms of different resonance effects on transition states and on reactivities which could arise from differences in the relative contributions of thermodynamic and intrinsic kinetic (Hammond effects) factors on the selectivities.
On the Ring‐Opening of Some 3‐Lithiobithienyls and 3′‐Lithio‐α‐terthienyls
Authors: Gronowitz Salo , Svensson Arne
Published: November 2013

3‐Halobithienyls have been prepared through the Pd(PPh3)4‐catalyzed coupling of thiopheneboronic acids with 2,4‐dihalothiophenes. The ring‐opening of the corresponding 3‐lithiobithienyls obtained upon halogen‐metal exchange with phenyllithium has been investigated. Compound 12, 3′‐iodo‐2,2′,2″‐terthienyl, was prepared in one step through the Pd(PPh3)4‐catalyzed coupling of two equivalents of 2‐thiopheneboronic acid with 2,3,5‐triiodothiophene. Treatment of 12 with phenyllithium and methyl iodide gave a mixture of compounds 10 and 11 occurring in Berkheya and Cullumia species.
Regiocontrolled Synthesis of 4‐Halo‐5,6‐Dihydro‐4H‐1,2‐Oxazines; A Novel Route for α‐Fluorovinyl Ketones
Authors: Shatzmiller Shimon , Lidor Ramy , Shalom Eytan
Published: November 2013

Regiocontrolled deprotonation (e.g. lithiation) of 3‐methyl‐4‐H‐5,6‐dihydro‐1,2‐oxazine 1 is achieved at −65°C. The lithiated compound reacts cleanly with the halogens Cl2, Br2 and I2 at low temperatures (−65°C) to give the corresponding 4‐halo derivatives. Reaction of the 4‐iodo compound 2a with KF in diethyleneglycol gives the elimination product 4 whereas the bromo compound 2b reacts under substitution to the 4‐fluoro derivatives 5. The fluorooxazine derivatives 8a‐c were converted to the αfluoroenones 11 a‐c via the oxoiminium salts 10a‐c. The U.V. and 1HNMR of the novel series of halides 2a‐c and 5 were studied.
Stereoselectivity in the Wittig‐Horner‐Emmons Synthesis of Vinylphosphonates by the Reaction of Acylphosphonates with Acyclic or Heterocyclic Phosphonoacetates
Authors: Breuer Eli , Moshe Ruth
Published: November 2013

A new synthetic approach to vinylphosphonates is presented. The reaction of diethyl benzoylphosphonate (1) with diethyl methoxycarbonyl‐methyl‐phosphonate (2) gives diethyl 2‐methoxycarbonyl‐l‐styrylphosphonate (3) as a mixture of geometrical isomers (Z‐3) and (E‐3) in the ratio of 83:17. In contrast, reaction of 1 with the heterocyclic phosphonate reagent, 2‐methoxycarbonyl‐methyl‐2‐oxo‐4,5‐dimethyl [1,3,2] dioxaphospholane (4) leads to a mixture of the isomers (Z‐3) and (E‐3) in the ratio of 20:80.
A New Indole Synthesis Promoted by Metal Triflates
Authors: Kozikowski Alan P. , Cheng Xue‐Min , Li Chun‐Sing , Scripko James G.
Published: November 2013

A new synthesis of 4‐ and 7‐carbon‐substituted indoles is described. The overall sequence involves the addition of a nitrile oxide to 1 carboethoxy‐2‐(or 3‐) allylpyrrole, hydrogenation of the intermediate isoxazoline to β‐hydroxy ketone and cyclization of the ketol using magnesium or zinc triflate to the substituted indole. This new indole‐forming strategy can also accommodate the introduction of oxygen functionality into the indole 6‐position. Possible mechanistic aspects of the reaction are detailed.
Synthetic Studies on Mitomycins: The Synthesis of Mitosene
Authors: Ohnuma Takeshi , Sekine Yasuo , Ban Yoshio
Published: November 2013

The crisscross annulation, developed towards synthesis of diverse nitrogen‐containing heterocycles via a one‐pot reaction, is remarkably effective in the construction of pyrrolo[1,2‐α] indole derivatives (7 and 22) as the possible intermediates for syntheses of mitomycins. These were converted to mitosene derivatives (34 and 40) through the various repeated oxidation processes.
Pteridines, LXXVI [1]. Synthesis and Properties of New Condensed Pyrazolo‐, Thieno‐ and Pyrrolo‐Pteridines
Authors: Baur Ralph H. , Pfleiderer Wolfgang
Published: November 2013

The lumazines 1,3 dimethyl‐7‐methylthio‐6‐propionyl‐ (1) and 6‐chloro‐1,3‐dimethyl‐7‐propionyllumazine (7) provide an easy entry into the pyrazolo [4,5‐g] and ‐[5,4‐g] lumazine system by reaction with hydrazine and methylhydrazine to give 3–6. Thieno [2,3‐g] ‐ (22) and ‐ [3,2‐g] lumazines (21) can be synthesized from 6‐ (19) and 7‐carbomethoxymethylthio‐1,3‐dimethyllumazine (16) by homolytic acylation at the adjacent ring ‐ C ‐ atoms, followed by base‐catalyzed cyclization. A pyrrolo [3,2‐g] lumazine (28) is achieved in an analogous manner from 7‐(N‐carboethoxymethyl‐N‐methyl)amino‐1,3‐dimethyllumazine (25) by radical propionylation and subsequent ring closure. The newly synthesized compounds have been characterized by UV‐ and NMR spectra as well as pKa determinations.
The Structural Elucidation of Oligomeric Blue Dyes Derived from 9‐Alkylcarbazoles
Authors: Katritzky Alan R. , Saczewski Franciszek , Marson Charles M.
Published: November 2013

Carbazoles react with a variety of one‐carbon fragments at the 3‐ or 3,6‐positions to give di‐ and trimeric products with CH2: links. These precursors react by losing hydride ion to give blue oligomeric dyes. Carbazoles substituted in the 9‐position by CH2SPh, CH2SOPh, and CH2SO2Ph rearrange to give carbazole oligomers linked at the 3,6‐positions. Products are characterised spectrally, and their mechanism of formation is discussed.
Supercomputers for Quantum Chemistry, Statistical Mechanics and Fluid Dynamics of Biological Systems
Authors: Clementi E. , Chin S. , Logan D.
Published: November 2013

An experimental parallel computer system which is expected to achieve supercomputing performance is described. This system allows the execution of single large jobs on multiple processors. The system hardwares and softwares will be briefly described. The validity of this approach to performing large scale simulations of biological systems is verified by analyzing the performance results of a variety of application programs. Among the applications to be discussed are programs in quantum chemistry, statistical mechanics and fluid dynamics. Specific examples of large biological systems which have been studied shall also be discussed.
A Comparison of the Binding of the Ligand Trimethoprim to Bacterial and Vertebrate Dihydrofolate Reductases
Authors: Roberts Victoria A. , Dauber‐Osguthorpe Pnina , Osguthorpe David J. , Levin Eugene , Hagler Arnold T.
Published: November 2013

In this paper, we report on studies of ligand binding to the enzyme dihydrofolate reductase (DHFR). Energy minimizations of four complexes of DHFR with the inhibitor trimethoprim, an antibiotic, and the cofactor NADPH have been carried out in order to investigate the energetics responsible for the 100,000‐fold increase in binding affinity of trimethoprim to E. coli DHFR compared with chicken liver DHFR. Several factors suggested to be responsible for the enhanced binding in bacterial DHFR's were investigated in terms of intermolecular and intramolecular energetics. The strain energies of trimethoprim in the four complexes were calculated and found to be about 6 kcal mol−1 in all complexes of the two species. In the binary complex of chicken liver DHFR, where the largest variation was observed, 2 kcal mol−1 higher than in the other complexes, it was found that this increase was compensated for by the slightly more favorable intermolecular interaction of the trimethoxyphenyl moiety with the protein.

Comparison of the minimized binary and ternary complexes of E. coli allowed us to investigate the cooperativity in the binding of trimethoprim and NADPH in the bacterial enzyme in terms of the underlying intermolecular forces. This cooperativity was found to be due to a direct trimethoprim ‐ NADPH interaction in the E. coli enzyme rather than enhanced protein‐inhibitor interactions induced upon binding of the cofactor. These interactions are not as favorable in the vertebrate enzyme, consistent with the significantly diminished cooperativity observed in this enzyme.
Homogeneous Catalytic Cleavage of Saturated Carbon‐Nitrogen Bonds
Authors: Shvo Y. , Abed M. , Blum Y. , Laine R.M.
Published: November 2013

An evaluation of the catalytic reactivity of [CPD (CO)2RuH]2 (1) and (CPD)(CO)3Ru (2) (where CPD = tetraphenylcyclopentadienone) with amines suggests that these complexes catalyze C‐N bond cleavage by activating C‐H bonds alpha to the nitrogen atom of tertiary, secondary and primary amines at ca. 140° C. When two different amines are used, transalkylation takes place. With secondary and primary amines, ammonia and tertiary amines are formed. A series of amine complexes (CPD)(CO)2Ru.NR3 (R = alkyl/H) was isolated from stoichiometric reactions of 1 or 2 with primary and secondary amines. It was found that tertiary amines do not generate complexes of the above type but rather unexpectedly give secondary amine complexes by cleavage of an alkyl group. The only isolatable tertiary amine complex is the moderately stable (CPD)(CO)2RuNMe3. All amine complexes were characterized by spectral and elemental analyses. Catalytic aspects of C‐N bond cleavage were studied. Complexes (1) and (2) were found to react with primary, secondary and tertiary amines to generate imminium or eneamine species which subsequently undergo hydrolysis with water. This is in contrast to the Ru carbene mechanism previously proposed for cluster catalyzed C‐N bond activation and cleavage. The two reactions are compared with respect to D for H exchange (with D2O), water requirement and production of trace products during catalysis. A primary alcohol was found to substitute alkyl groups of a tertiary amine under the catalytic action of 1. A catalytic reaction cycle is proposed.