bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR and NMR Studies on the Effects of Magnesium Ion on Chloroplast Manganese
Authors: Khanna Rita , Rajan S. , Steinback K. E. , Bose S. , Govindjee  , Gutowsky H. S.
Published: November 2013

The addition of 1–50 mM MgCl, to “low salt” thylakoid membranes causes a monotonic decrease in the transverse, aqueous proton relaxation rate (R2 = 1/T2) and an increase in the 6‐line ESR spectrum characteristic of free Mn(II) but does not affect the oxygen evolution rate. These results suggest that magnesium ion at low concentrations replaces Mn(II) from a very loosely bound pool which is not involved in oxygen evolution. The decrease of R2 is probably due mainly to the smaller molar relaxivity of free compared with bound Mn(II). R2 can be affected by conformational and structural changes involving the Mn(II) as well as by the amount of Mn(II) and the nature of its binding. However, MgCl2 causes the same decrease in R2 for trypsin treated thylakoids, which do not undergo the gross structural changes, e.g. grana stacking, that it produces in untreated membranes. R2 measurements of isolated light harvesting complex preparations indicate the presence of bound Mn in it; neutron activation analysis of these samples shows that they have about one‐third of the functional manganese bound in thylakoid membranes—this may be the tightly bound pool of Mn, but the results are not conclusive.
Circular Dichroism and Other Optical Properties of Antenna Chlorophyll Proteins from Higher Plants
Authors: Shepanski John F. , Knox Robert S.
Published: November 2013

We report the measurement of the room‐temperature optical properties of antenna chlorophyll proteins (prepared with sodium dodecyl sulfate membrane solubilization) from six plant species of five different orders: pea (Pisum sativum), soy (Glycine max), barley (Hordeum vulgare), spinach (Spinacea oleracea), yew (Taxus canadensis), and fern (Onoclea sensibilis). All six species' antenna protein preparations exhibit optical spectra which are similar in great detail, implying similar internal chromophore arrangements from species to species. Features of the spectra thought due to chromophore interactions disappear upon heat denaturation. A model proposed by Van Metter for spinach chlorophyll protein has been revised and is consistent with all the data presented here.
The Reaction Center and Antenna Pigments of Green Photosynthetic Bacteria
Authors: Swarthoff T. , Amesz J. , Kramer H. J. M. , Rugersberg C. P.
Published: November 2013

Experiments are reported on the optical properties and orientation of reaction center pigments of the green photosynthetic bacterium Prosthecochloris aestuarii. Analysis of the light‐induced absorption difference spectra of P840, the primary electron donor, and of reaction center triplet formation indicates that the bleaching of the P840 band at 836 nm is accompanied by band shifts of bacteriochlorophylls absorbing at 797, 816 and 833 nm at 80 K. The Qy transitions of the long‐wave bacteriochlorophylls were found to be oriented more or less parallel to the membrane, the Qx transitions were more or less perpendicularly oriented. Fluorescence emission spectra of bacteriochlorophyll a in intact cells and isolated pigment‐protein complexes are presented for the temperature range 295‐4 K. Experiments with different wavelengths of excitation indicate that in the PP and RCPP complexes light absorbed by bacteriochlorophyll a produces mainly emission by light‐harvesting bacteriochlorophyll, whereas light absorbed by pigments absorbing at 670 nm (bacteriopheophytin c or a possibly related pigment) predominantly excites long‐wave fluorescence, which appears to be emitted by pigments more closely associated with the photochemical reaction center. The emission spectra of the light‐harvesting bacteriochlorophyll a complex at various temperatures indicated temperature equilibrium between the emitting species. In intact cells, an increase in bacteriochlorophyll c fluorescence upon cooling indicates a decrease in the efficiency of energy transfer between the chlorosome and bacteriochlorophyll a.
Oxidation‐Reduction Physical Chemistry of the Acceptor Quinone Complex in Bacterial Photosynthetic Reaction Centers: Evidence for a New Model of Herbicide Activity
Authors: Wraight C. A.
Published: November 2013

The oxidation‐reduction midpoint potential (Em) of the primary quinone (QA) of the acceptor quinone complex of bacterial photosynthetic reaction centers has been measured as a function of pH in the presence and absence of ubiquinone and o‐phenanthroline (o‐Phen). Reaction centers, isolated from Rhodopseudomonas sphaeroides, were incorporated into egg phosphatidylcholine vesicles. Contrary to earlier reports, the Em was found to exhibit a pH‐dependence very similar to that observed in chromatophores, with a slope of ‐ 60 mV/pH up to a p K for Q−A/Q−A(H+) at pH 9.5–10.0. In the presence of ubiquinone to reconstitute the secondary quinone (QB), the Em/pH curve of QA was shifted to lower potentials, indicating that the binding of Qn (actually QBH2) was suppressed by reduction of QA. o‐Phen, an inhibitor of electron transport from QA to QB, raised the pK of Q−A/Q−A(H+) and, at pH‐values below but not above this pK, reversed the effects of QB. In the absence of QB, o‐Phen lowered the Em of QA above the pK but had no effect below it. These results are discussed in terms of interactions between the binding sites for QA and QB (A‐ and B‐sites). It is suggested that ubiquinone and o‐Phen compete for the B‐site in a mutually exclusive fashion, and that their relative binding strengths are modulated by the redox and protonation state of QA. In preparations with low quinone content, o‐Phen inhibits photochemistry suggesting that it can also compete with ubiquinone at the A‐site. Competitive displacement of quinone from the B‐site by o‐Phen and other inhibitors is suggested as the primary mode of action of a broad class of herbicides active in Photosystem II of plants. The relative binding affinities of the various redox states of QB are also discussed and it is concluded that the order of binding strength is: Q−B → QB → QBH2. This accounts for the atypical stability of the semiquinone and the lower average Em for reduction to the quinol, compared to free ubiquinone in the quinone pool. It may also be significant in the functioning of quinones in communicating reducing equivalents from the reaction center to other electron transport complexes in the intact membrane.
Rearrangements of Methyl Substituted N‐Neopentylmethyleneaziridines in Methanol
Authors: Wiering Petrus G. , Steinberg Herbert
Published: November 2013

On heating the N‐neopentylalkylideneaziridine1or4, a mixture of1, 4and N‐neopentyl‐2,2‐dimethylcyclopropanimine3is obtained. The imine3does not rearrange, but breaks down into the fragments isobutene and neopentylisocyanide. The reaction between1(or4) and methanol gives the ring‐opened products5and6and the cyclopropylamino ether7. Addition of acid gives rise to only ring‐opened products5, 6and8. It is believed that the reactions proceed via the common intermediate 2‐N‐neopentylaminoallyl cation2, followed by a rapid ring closure to the protonated isomeric aziridines1and4and 2,2‐dimethylcyclopropanimine3.
Circular Dichroism. LXXVI. CD of Chiral Vinyl—Cyclopropanes
Authors: Itô Shô , Kuriyama Kaoru , Norin Torbjörn , Snatzke Günther
Published: November 2013

The sign of the CD within the first absorption band (200–220 nm) of optically active vinyl‐cyclopropanes has been correlated with the absolute conformation of the chromophore in a non‐empirical way. A positive torsional angle between the C=C and the bisectrix of the cyclopropane ring between 0° and ≃ + 70° gives a positive Cotton effect; between ≃ + 110° and 180° it gives a negative one. The rule has been tested mainly on models of terpenoid origin.
Reactions of Photoexcited Triplet States of Zinc Porphyrin with Transient Radicals in Aqueous Solutions
Authors: Neta P. , Levanon Haim
Published: November 2013

The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPST in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 1010 M−1 s−1. The CH2C(CH3)2OH radical from t‐BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 109 M−1 s−1) with ZnTPPST to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH3)2COH radical reduces both ZnTPPS (k = 1 × 108 M−1 s−1) and ZnTPPST (k = 3 × 109 M−1 s−1) to the anion radical (ZnTPPS)−. The radical Br−2 oxidizes both states to the cation radical (ZnTPPS)+ with k = 8 × 108 M−1 s−1 for the ground state and 5 × 109 M−1 s−1 for the triplet. The transient cation Cd+ reduces both states with a diffusion‐controlled rate (k = 1 × 1010 M−1 s−1) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra.
Photoinduced Charge Separation and Recombination in Exciplex Systems in Lipid Bilayer Vesicles
Authors: Neumann S. , Korenstein R. , Barenholz Y. , Ottolenghi M.
Published: November 2013

Pulsed laser photolysis experiments are carried out in lipid bilayer vesicles in which the fluorescence of excited pyrene (P), pyrene‐ethanol (P‐CH2OH) and pyrene‐monosulphonate (P‐SO−3) are quenched by N.N‐diethylaniline (DEA). The observed photochemical patterns are basically different from those encountered in homogeneous solutions: No detectable exciplex emission is observed, and the yield of the separated ions P− + DEA+ is small. Two alternative explanations are given for the complete lack of an exciplex fluorescence in the vesicles. One involves the requirement of a highly polar environment around the reacting species in the membrane interior. More plausibly, serious limitations imposed by the “liquid crystal” membrane microenvironment on the relative orientation of the 1P* acceptor and the DEA donor, must be assumed. The quenching process leads to the formation of the P− + DEA+ radical ion pair and of the pyrene triplet state 3P*. An analysis of the submicrosecond ions decay process, including its behaviour around the phase transition point of the lipids, indicates that the ions do not escape the vesicle and recombine by an intravesicle diffusion process. The relatively small yield of P− and DEA+ is attributed to a microviscosity effect, inhibiting the primary separation of the solvent‐shared ion pair {P− … DEA+}. An analysis of temperature (phase transition) and external magnetic field effects indicates that the pyrene triplet state, 3P*, is generated by geminate recombination in a geometrically correlated radical pair [P− … DEA+]. The results bear on the general problem of photoinduced charge separation in nonisotropic media and on the structure of biomembranes.
Semiconductor‐Oxide Heterojunctions as Electrodes in Photoelectrochemical Cells
Authors: Decker F. , Melsheimer J. , Gerischer H.
Published: November 2013

The use of semiconductor‐oxide Schottky barriers as electrodes in photoelectrochemical cells has been investigated. The conducting oxide has the function of protecting the semiconductor surface from corrosion and of driving the electrochemical reaction. Since the oxide layer is only a few hundred Å thick, the ohmic resistance of this layer is low and nearly 90% of the incoming light is transmitted through it. Regenerative photoelectrochemical cells based on n‐Si‐SnO2junctions have shown solar efficiencies around 4%. Further improvements will require the addition of a catalyst to the oxide surface in order to increase the speed of the electrochemical reaction.
The Application of the Method of Pseudopotentials to Hydrides of Silicon and their Methyl Analogs
Authors: Janoschek Rudolf , Sax Alexander , Halevi E. Amitai
Published: November 2013

The method of local pseudopotentials is applied to the calculation of several ground‐ and excited‐state properties of selected silicon compounds. The calculated ground‐state geometries and ionization potentials of the silicon hydrides: SiH, SiH2, SiH3 and SiH4 and of the ions SiH+, SiH−, SiH+3 and SiH−3 are in good agreement with the best theoretical and experimental results — whenever these are available. All the singly excited states of SiH2 originating from a given occupied orbital are evaluated in a single calculation. For those few valence states for which reliable experimental and theoretical data exist, agreement is good. The conceptual and computational advantages of transforming the basis set of silicon into a set of atomic pseudoorbitals are demonstrated by repeating the latter computations with increasingly large sets of atomic orbitals, ranging from [3s, 3p] to [3s, 3p, 3d, 4s, 4p]. The utility of this procedure for reliable and economical calculations on organosilicon compounds is illustrated with a similar set of computations on the ground‐state properties and vertical excitation energies of Si(CH3)2. The effect of methyl substitution on the ground‐state properties of silylene and on the energetic ordering of its excited states is discussed.
On the Chemistry of Pyrrole Pigments. 461 Phytochrome Model Studies: The Tautomerism at N22—N23 of Unsymmetrically Substituted Bilatrienes‐abc and 2,3‐Dihydrobilatrienes‐abc
Authors: Falk Heinz , Grubmayr Karl , Magauer Karl , Müller Norbert , Zrunek Ulrich
Published: November 2013

A set of model compounds substituted with methyl groups in positions 7,8,12 and 13 were prepared to elucidate the tautomerism within the pyrromethene moiety of unsymmetrical bilatrienes and of 2,3‐dihydrobilatrienes‐abc. Configurational and 1H‐NMR signal assignments were achieved using NOE difference spectra, coupling phenomena and comparison to the spectra of compounds substituted with ethyl groups in strategic positions. By application of resolution enhancement and the COSY‐technique a characteristic coupling pattern between the methyl groups of a pyrrole ring which is different from the one observed for the pyrrolenin ring could be documented using derivatives with fixed tautomeric structure (N‐methylation). All unsymmetrical bilatrienes and 2,3‐dihydrobilatrienes‐abc investigated are shown to be single tautomers — the position of the proton (N22, N23) obviously is governed by an optimisation of intramolecular hydrogen bonding.
Picosecond Kinetics of Excited State Relaxation in Biliverdin Dimethyl Ester
Authors: Holzwarth Alfre D. , Wendler Joachim , Schaffner Kurt , Sundström Villy , Sandström Ake , Gillbro Tomas
Published: November 2013

The relaxation processes of biliverdin IXα dimethyl ester have been studied by time‐resolved absorption and fluorescence detection, using pump‐probe and single‐photon timing techniques, respectively. The results complement and extend those of earlier investigations.1,3–5In 2‐methyltetrahydrofuran, chloroform, ethanol, and ethyl lactate, four emitting species, two short‐lived (picosecond) and two long‐lived ones (nanosecond), have been detected. In methanol, the number of emitters is possibly reduced to three. In the cases of four emitters, these can be attributed to either three or four ground state forms. We conclude that the radiationless relaxation of the short‐lived excited states is simultaneously induced both by proton transfer processes and by conformational changes, as previously discussed.3The spectroscopic properties of the long‐lived species point to the presence of relatively rigid conformations of the bilatriene in liquid solutions at room temperature. The possible relevance of this observation with regard to the influence of protein interactions on the conformational equilibrium of tetrapyrroles in phycobiliproteins is discussed.
Determination of Bilirubin in Serum by Fast Scan Square Wave Voltammetry
Authors: Saar Jacob , Yarnitzky Chaim
Published: November 2013

The use of fast scan square wave voltammetry for the determination of bilirubin in serum is described. The reduction of bilirubin in alkaline solutions with or without serum albumin results in three current peaks. The peak potential and current are related to bilirubin and albumin concentrations and allow the determination of the bilirubin concentrations after the addition of KOH to the sample. The effect of light and time on peak current was also checked. Comparison of results achieved by electroanalytical and spectrophotometric methods prove the feasibility of measuring total bilirubin in serum by electrochemical methods.
NMR Studies of Sodium Cholate–Lecithin Mixed Micelles
Authors: Eriksson Per‐Olof , Arvidson Gösta , Lindblom Göran
Published: November 2013

T1 and T2 2H‐NMR relaxation times have been measured for 2H‐labelled phosphatidylcholine in the aqueous solution phase of the ternary system lecithin–sodium cholate–water. In this phase aggregates are formed by a mixture of cholate and lecithin. Information about the dimension of these micellar aggregates has been obtained from a simple model of the relaxation times in which two modes of molecular motion are considered. The results obtained accord well with recent investigations using laser‐light scattering techniques.
Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR
Authors: Boeffel Ch. , Hisgen B. , Pschorn U. , Ringsdorf H. , Spiess H. W.
Published: November 2013

The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the mesogenic group and at the spacer. The temperature dependence of the order parameter of the mesogenic group indicates significant differences between the intermolecular potential in polymeric liquid crystals and their low molecular weight analogues. The order parameter of the spacer (methylene group adjacent to the polymer chain) is reduced to 50% of the value of the mesogenic group, whereas the equivalent methylene group in the low molecular weight system exhibits a reduction by only 25%. This indicates a substantially higher fraction of gauche‐conformers in the spacer of the polymeric liquid crystal than in the alkyl chains of low molecular weight liquid crystals. In the glassy state the order parameter of the mesogenic group is high, 0.85 and 0.65 for a frozen smectic‐A and a frozen nematic system, respectively. In the glassy state rapid rotational jumps by 180° are observed. This process can be followed by 2H NMR line‐shape analysis down to temperatures 100K below the glass transition.
Oxidation of Diphenyl Sulfide by Singlet Oxygen Generated Carbonyl Oxides
Authors: Agarwal Sudhir K. , Murray Robert W.
Published: November 2013

Diphenyl sulfide has been oxidized to the sulfoxide by a series of 4,4′‐disubstituted benzophenone oxides. The carbonyl oxides were produced by photosensitized oxidation of the corresponding diazo compounds. Treatment of the data by a Hammett ρΣ approach indicates that the oxygen atom transfer is electrophilic in nature with ρ = +0.90. The results are discussed in terms of analogous reactions which are mediated by flavin‐dependent monooxygenase and particularly those oxidations believed to be involved in producing hepatotoxins.
Mechanisms and Products of Photosensitized Degradation of Nucleic Acids and Related Model Compounds
Authors: Cadet J. , Decarroz C. , Wang S. Y. , Midden W. R.
Published: November 2013

The mechanisms and products of photosensitized and singlet oxygen oxidation of nucleic acid model compounds have been investigated using kinetics analysis and product isolation and identification. A competitive kinetics analysis is presented as a simple yet quantitative method for the determination of the role of singlet oxygen in homogeneous chemical reactions. This method is compared to other techniques that have been used in the past including determination of the solvent isotope effect and the effect of singlet oxygen quenchers and variations in oxygen and substrate concentration. The results of competitive kinetics experiments indicate that the photooxidation of dGuo (2′‐deoxyguanosine) at pH 7–10 in buffered aqueous solution sensitized by Rose Bengal, Methylene Blue, Thionine or several other dyes proceeds predominantly by a pathway requiring intermediate formation of singlet oxygen. In contrast, dGuo photooxidation under the same conditions sensitized by flavin or pterin derivatives proceeds predominantly by pathways that do not involve singlet oxygen. Most of the primary products of dGuo photooxidation are very unstable and consequently are difficult, if not impossible, to isolate and characterize. However, two compounds have now been isolated that correspond to the addition of a single molecule of oxygen to the purine ring of guanine with the purine ring system still intact. Some of the products formed in the singlet oxygen oxidation of 2′‐deoxyguanosine appear to be different than some of the products formed in flavin photosensitized reactions in agreement with kinetic results that indicate that the flavin sensitized reactions proceed by mechanisms that do not involve intermediacy of singlet oxygen. If the unique nature of the products of 2′‐deoxyguanosine oxidation by singlet oxygen can be firmly established it may be possible to detect singlet oxygen reactions in vivo by product analysis.
Microwave Discharge of O2 and CO2 as a Synthetic Tool for Oxidations of Unsaturated Compounds Adsorbed on Solid Supports
Authors: Zadok Elazar , Rubinraut Sara , Mazur Yehuda
Published: November 2013

Cis and trans stilbene, styrene, 1‐decene and 6‐dodecene adsorbed on silica gel were reacted with oxygen atoms produced by microwave discharge of O2 and CO2. At 0°C these compounds gave mainly epoxides and carbonyl compounds as in neat liquid reactions. Below — 60°C ozonolysis products were formed; cis and trans stilbene and styrene gave benzaldehyde while 1‐decene and 6‐dodecene resulted mainly in ozonides.
Synthetic Utility of (Propargyl)dicobalt Hexacarbonyl Cations. A New Cyclopentenone Annelation
Authors: Saha Manasi , Nicholas Kenneth M.
Published: November 2013

The regiospecific alkylation of cyclic ketones and TMS enol ethers by the cobalt‐stabilized propargyl cations 1 followed by demetalation and regiospecific acetylene hydration proceeds in good overall yield to produce 1,4‐diketones. The latter are efficiently cyclized in the presence of base to annelated cyclopentenones.
Alkenyl Copper Derivatives 251: Synthesis of E or Z Enol Ethers by Carbocupration of Alkoxy‐Allenes
Authors: Alexakis A. , Normant J. F.
Published: November 2013

Alkoxy‐allenes react smoothly with organocopper and cuprate derivatives to afford almost pure E or Z substituted enol ethers according to the reaction conditions. Lithium diorganocuprate reagents in diethyl ether show the greatest E selectivity, while lithium organocopper reagents in THF are completely Z selective. The obtained alkenyl copper or cuprate derivatives may react further with various electrophiles leading to polysubstituted enol ethers of known configuration.
Organoselenium Chemistry. Preparation of Allyl and Homoallyl Amines by Aminomethylation of Phenylseleno‐Substituted Allyl Tin Reagents
Authors: Reich Hans J. , Schroeder Mel C. , Reich Ieva L.
Published: November 2013

Metalation of methallyl phenyl selenide, allyl phenyl selenide, and methallyl phenyl sulfide followed by tri‐n‐butylstannylation gave exclusively the γ‐stannylated sulfide or selenide (e.g., 1‐phenylseleno‐2‐methyl‐3‐tri‐n‐butylstannyl‐1‐propene (5)). Compound 5 reacts with a series of immonium electrophiles to give products of aminomethylation α‐ to selenium. Electrophiles have included N‐(bromomethyl)phthalimide/ZnBr2, Eschenmoser salt (dimethylmethyleneammonium iodide), and Mannich reagents generated in situ from diethylamine, piperidine, isopropyl sarcosinate and benzylmethylamine. The selenide from the last of these amines (N, 3‐dimethyl‐N‐benzyl‐2‐phenylseleno‐3‐butenamine, 10) has been subjected to further transformations as follows: (1) treatment of 10 with trimethylstannyllithium results in replacement of phenylseleno by stannyl; this allyltin (11) can then again be aminomethylated giving compound 12 or 13; (2) oxidation of 10 gives amino alcohol 14 by [2, 3] sigmatropic rearrangement of the allyl selenoxide; (3) photolysis of 10 results in 1,3‐rearrangement of the phenylseleno group; oxidative rearrangement of this allyl selenide gives amino alcohol 16. The phthalimidomethylation product (6) is converted to a precursor for the side chain of the cytokinin zeatin by oxidation and [2, 3] sigmatropic rearrangement.
Metal Enolate Mediated Aldol Reactions
Authors: Mukaiyama Teruaki
Published: November 2013

Three types of metal enolate mediated aldol reactions developed in our laboratory are discussed.
Temperature Jump Measurements in Gas Kinetics
Authors: Gozel P. , Calpini B. , van Den Bergh H.
Published: November 2013

The temperature jump relaxation method is applied to kinetic measurements in the gas phase. The system N2O4⇄2NO2is studied. Fast T‐jumps are induced by IR absorption from a TEA CO2laser. Temperature jumps of less than 1 K lead to readily detectable concentration changes which are monitored by UV absorption in a simple single shot experiment.krec(Ar) is found to be 1.05 × 1010cm3mol−1s−1atPAr= 1 bar andT= 258 K, in agreement with recent experimental data.
Photoresponsive Crown Ethers. Part 11. Azobenzene‐Pillared Cylindrical Macrocycle As a Photoresponsive Receptor
Authors: Shinkai Seiji , Honda Yoshihiro , Ueda Kaori , Manabe Osamu
Published: November 2013

A cylindrical ionophore (1) in which two diaza‐crown ethers are linked by two azobenzene pillars serves as a photoresponsive host molecule. In alkaline solution containing K+, (1) forms a cascade complex with dianionic guest molecules, but photoirradiated (1) which has a shortened cylinder cannot bind the guest molecules so effectively as (1). (1) solubilised in acidic aqueous solution by protonation of four tertiary nitrogens provides a hydrophobic cavity to bind several anionic azo dyes. The association is also suppressed by photoirradiation. The results indicate that parallel array of the azobenzene segments in (1) provides a host cavity and the photoinduced structural change is readily reflected by the association tendency. This is the first example for the photoresponsive inclusion complex.
Polymerized Surfactant Vesicles
Authors: Endler Janos H.
Published: November 2013

Irradiation of surfactant vesicles prepared from (C18H37)2 N+(CH3)C6H4‐CHCH2p,CT−, 1, [C15H31CO2(CH2)2]2N+(CH3)CH2C6H4CHCH2,CL− 2, and (C18‐H37)2N+(CH3)CH2CH2OCOC6H4CHCH2p,Br−, 3, by ultraviolet light or by bursts of 266 nm laser pulses have resulted in the loss of styrene absorbances. This process has been accounted for in terms of a model which considers intravesicular surface reactions to give polymers with average chainlength of 22. Degreees of photopolymerization have been determined in vesicles prepared from 3 subsequent to separating the polystryrene, formed in the photolysis, from the surfactants. Vesicle surface photopolymerizations result in aqueous cleft formation and in enhanced stabilities. Polymerized vesicles provide media for in situ generation of colloidal catalysts and semiconductors.
Second‐sphere Coordination of [Pt(bipy)(NH3)2]2+ by Dibenzo‐crown Ethers. Solution Spectroscopic Studies and the Crystal and Molecular Structures of [Pt(bipy)(NH3)2.dibenzo‐30‐crown‐10] [PF6]2.0.6 H2O and [Pt(bipy)(NH3)2.dibenzo‐24‐crown‐8] [PF6]2
Authors: Colquhoun Howard M. , Doughty Simon M. , Maud John M. , Fraser Stoddart J. , Wllliams David J. , Wolstenholme John B.
Published: November 2013

In addition to hydrogen bonding and Coulombic forces, charge transfer interactions stabilise the 1:1 adducts formed between [Pt(bipy)(NH3)2] 2+ and a series of dibenzo‐3n‐crown‐n (n = 6–12) ethers as evidenced by 1H NMR and UV‐visible spectra in solution and by X‐ray crystal structures (for n = 8 and 10) in the solid state. Mutual diamagnetic (ring current) shielding by the aromatic systems of host and guest results in dramatic upfield shifts of certain aromatic proton resonances on adduct formation, especially when n = 10 or 11. A broad charge‐transfer absorption band at 350 nm attains its maximum intensity at n = 11 though stability constant measurements indicate optimum binding when n = 10. X‐ray diffraction studies reveal that, when n = 8, only one of the crown ether benzo‐rings interacts with the bipyridyl ligand in a charge‐transfer sense. However, when n = 10, the macrocycle is sufficiently large and flexible to allow both benzo‐rings to enter into stabilising interactions with the bipyridyl ligand such that the platinum complex is encapsulated by the host in a U‐shaped cavity.
Nature and Size of Included Guest Molecule Determines Architecture of Crystalline Cyclodextrin Host Matrix
Authors: Saenger Wolfram
Published: November 2013

Owing to its annular shape, the cyclic hexasaccharide α‐cyclodextrin (α‐CD) can form inclusion complexes in aqueous solution. If these are crystallized, the guest molecules are invariably accommodated in the cavities of the host. Depending on size and molecular or ionic character of the guest, different crystal modifications are formed belonging to the herringbone or brick‐type cage structures or to the channel structures. Small molecular guests lead to herringbone cages, small aromatic guests crystallize in brick‐type cages whereas ionic and long molecular guests are enclosed in infinite channels. Thus, there is a clear dependence of crystal packing on the physical properties of the guest molecule. Polyiodide cocrystallizes with α‐CD in different channel forms with iodine atoms arranged linearly in the channels. The packing of the channels is in tetragonal, hexagonal or sheet‐like arrays, depending on counterions which are located in voids between the channels. If a α‐CD is replaced by the larger β‐CD (channel diameters 5 and 6.2 Å resp.), polyiodide now adopts a zigzag structure — a clear case of an influence of host matrix geometry on guest configuration.
Design and Synthesis ofα‐Diketones. The Cyclobutane‐1,2‐dione Chromophore: Synthesis, Dienophilic Reactivity and Electronic Properties of Cyclobutenedione and Polycyclic Cyclobutanediones [1]
Authors: Albert Bernhard , Heller Constanze , Iden Rudiger , Martin Georg , Martin Hans‐Dieter , Mayer Bernhard , Oftring Alfred
Published: November 2013

A new synthesis of cyclobutenedione(1)is described. It is found that the tricyclic cyclobutanedione3splits into1and cyclopentadiene if subjected to flash pyrolysis conditions. The dienophilic reactivity of 1 allows the construction of various polycyclic cyclobutanediones, such as3–5and12–14.Other new polycyclic diones, like9–11, 15and16are prepared by means of the acyloin condensation. The low stereoselectivity of1with cyclopentadiene is compared with the selectivity of other cyclobutenes, and the results are placed in the context of secondary interactions and steric hindrance. The unusual colour properties of these diones, from colourless1to blue6are investigated by means of photoelectron spectroscopic measurements and semi‐empirical calculations (MNDO, HAM/3, CNDO/S‐CI).
Characterization of Several Metalloporphyrins in Unusual Oxidation States. The Effect of Axial and Equatorial Ligands
Authors: Cocolios P. , Kadish K.M.
Published: November 2013

The effect of axial and equatorial ligands on the generation of unusual oxidation states in metalloporphyrins is discussed. Selected examples have been taken from the literature. These include the generation of Ni(III) and Ru(III) porphyrins from Ni(II) and Ru(II) complexes containing specific axial and equatorial ligands as well as the generatoin of a Cu(I) metalloporphyrin dianion which is produced upon the overall three‐electron reduction of Cu(II) tetracyanoporphyrin. Special emphasis is placed on the oxidation and reduction of σ bonded iron phenyl porphyrins. These complexes, which are stable as Fe(III), may be oxidized by a single electron to yield unstable compounds characterized as containing a great deal of Fe(IV) character, or reduced by a single electron to produce stable species which resemble, in part, radical anions of Fe(III). This singly deduced species may be described by a resonance equilibria between an Fe(III) porphyrin anion radical and an Fe(II) porphyrin anion. Likewise, the singly oxidized complex may be described by a resonance equilibria between an Fe(IV) porphyrin cation and an Fe(III) cation radical.
Metal—Metal Triple Bonds Possessing the Electron‐Rich σ2π4δ2δ*2 Electronic Configuration
Authors: Walton Richard A.
Published: November 2013

The structural and reaction chemistry of dimetal complexes containing metal—metal triple bonds of the electron‐rich type (σ2π4δ2δ*2 configuration) is reviewed. Metal cores possessing this unit are Mo2+2, Re4+2, Ru6+2, and Os6+2, of which only Re4+2 has yet been subject to a detailed study. Emphasis is placed upon the more recent developments in this field.
Synthesis and Properties of Conducting Bridged Macrocyclic Metal Complexes
Authors: Hanack Michael
Published: November 2013

Stacked bridged macrocyclic metal complexes of the type shown in Fig. 1A, with pyrazine and 1,4‐diisocyanobenzene as the bridging ligands L, phthalocyanine (Pc) and tetrabenzoporphyrine (TBP) as the macrocycle (Mac), and Fe and Ru as the central metal atoms M, are doped with iodine. The properties and conductivities of the doped compounds [MacML]n are reported. The synthesis and properties of type‐B polymers (Fig. 1B) ([PcMCN]n, M = Co, Rh, Fe, Mn, Cr) with CN as the bridging ligand are described. With Co and Fe these polymers show room temperature conductivities around 10−1 S/cm without doping, which are in the same range as the iodine doped [PcML]n‐compounds. [PcCo(SCN)]n and [TBPCoCN]n are additional examples of type B polymers.
Cyclophanes, XXIII [1] [2.2] Indenophanes — Building Blocks for Novel Multilayered Organoiron Complexes
Authors: Hopf Henning , Raulfs Friedrich‐Wilhelm
Published: November 2013

A general approach for the synthesis of [2.2] indenophanes is described employing readily available mono‐(8, 13) and bis‐formyl[2.2]paracyclophanes (20, 21) as substrates. The anellated five‐membered ring is introduced by a multistep sequence involving Wittig‐Horner chain elongation of the different aldehydes, saponification, catalytic hydrogenation, acid‐catalyzed ring closure, and dehydration. In this manner the novel indenophanes 11, 16, 17, 26, and 27 have been synthesized in good yields. The first representatives of a novel class of extended metallophanes, the multilayered ferrocenophanes 32 and 34, have been prepared from 11 and 28, respectively, via their sodium salts 29 and 33. The effect of an anellated [2.2] paracyclophane unit on the proton chemical shifts of the model compounds 30, 31, and 35 is discussed.
Molecular Design of Specific Uranophiles
Authors: Tabushi Iwao , Kobuke Yoshiaki
Published: November 2013

Molecular design of uranyl specific ligands is reviewed. Basic principles to characterise the unique nature of uranyl complexes are scrutinized from ligand field caluclations, crystallographic analyses and stability constants of various complexes. The most typical characteristic of uranyl coordination is a planar hexacoordiantion by anionic ligands giving rise to the formation of the “ate‐complex.” Several macrocycles were synthesized by the appropriate combination of these principles. Approaches to recovery of uranium from sea water are briefly reviewed. Organic chelating resins are the most promising candidates for the practical adsorbent.
Structure‐Conductivity Relationship of a Novel Semiconducting Diacetylene Polymer
Authors: Thakur M. , Lando J.B.
Published: November 2013

The crystal structure and electrical conductivity of the polymerized dimer of 1,11‐dodecadiyne has been recently reported. In this article we will present the temperature dependence of the electrical conductivity of this conducting polymer in the undoped state and will probe the structure‐conductivity relationship via a band theoretical approach.
Crystalline‐State Reaction of Cobaloxime Complexes by X‐ray Exposure. XII. A New Type of Racemization with a Negligibly Small Change of the Cell Dimensions [1]
Authors: Tomotake Yasuko , Uchida Akira , Ohashi Yuji , Sasada Yoshio , Ohgo Yoshiaki , Baba ShōE
Published: November 2013

Crystals of [(R)‐1‐cyanoethyl] bis(dimethylglyoximato)(diphenylmethyl‐phosphine)cobalt(III), [Co(C3H4N)(C4H7N2O2)2(C13H13P)], on exposure to X‐rays undergo crystalline‐state racemization with a negligibly small change of the cell dimensions. At the initial stage the two crystallographically independent molecules are related by pseudo inversion symmetry in the A2 cell. On X‐ray irradiation to the crystal, the pseudo inversion center becomes a true crystallographic one and the space group becomes A2/a. Both the chiral cyanoethyl groups are converted to the disordered racemates. The rate of the racemization was measured by the intensity variation of the reflections that should disappear after the racemization. The rate constants at 293 and 343 K are calculated to be 4.81 and 5.07 × 10−6 s−1, respectively, assuming first‐order kinetics. The cavities for the two cyanoethyl groups in the initial structure have the largest volumes known in this and related crystals. The positive correlation between the reaction rate and the volume of the cavity for the reactive group holds good for the present crystal.
Effect of the Structure of Some New Weak‐Base Ion‐Exchange Resins on Anion Selectivity
Authors: Bolto B.A. , Jackson M.B. , Siudak R.V.
Published: November 2013

The selectivity of some poly(N‐substituted diallylamine) ion‐exchange resins and some polyamine ion‐exchange resins prepared from crosslinked polyepichlorohydrin toward the systems SO=4/Cl−, NO−3/Cl− and HCO−3/Cl− was measured. The polyallylamine resins show the usual selectivity behaviour towards SO=4 over Cl− with the affinity of SO=4 increasing with dilution of the solution and decreasing with reducing ionization of the resin, providing equilibrium has been reached. The size of the nitrogen substituent on the resin, the resin capacity (which affects the overall charge density) and the base strength of the resin all influence the resin selectivity. The resin type and the nature of the two ions being exchanged determine the relative importance of each factor. In the systems considered in this paper, apart from the normal factors which affect selectivity, the most noteworthy parameter appeared to be the size of the nitrogen substituent. The selectivity behaviour toward the HCO−3/Cl− system of a polyamine prepared from crosslinked polyepichlorohydrin and aminated with homopiperidine compared favourably with Amberlite IRA 68 in a DESAL‐type process.
Soluble Polychelatogenes for Separation of Actinide Ions by Membrane Filtration
Authors: Bayer Ernst , Eberhardt Hans , Grathwohl Paul‐Anton , Geckeler Kurt
Published: November 2013

Separation of metal ions by functionalized soluble polymers using membrane filtration has been investigated. Actinide elements and members from the transition groups and rare earth elements have been bound to polymeric chelatogenes as a function of pH. Sixteen different polymers and derivatives based on poly(ethylenimine), poly(vinylalcohol), poly(urethane), and poly(acrylic acid) have been studied in terms of their capacity and selectivity. Binding studies and cleavage experiments have been carried out by application of membrane filtration for several metals and polychetatogenes. Finally, the stability of polymers and membranes has been studied and found to be sufficient for selective separation of actinide ions.
Solvent‐Polymeric Membranes for Separation of Li+ From Other Alkali Metal and Alkaline Earth Ions
Authors: Jagur‐Grodzinski Joseph , Schori Ehud
Published: November 2013

Lithium may be recovered from the Dead Sea brines by a process which combines membrane separation with ion‐exchange. Solvent‐polymeric membranes based on alkyl‐arylphosphates cause selective permeation of lithium ions with Br−3 as counter ions. Addition of the derivatives of neutral “crown” ethers did not improve their performance and an adverse effect, due to the decrease in the fluidity of the membrane system, was observed. Incorporation of ionizable “crown” ethers compatible with the system may, however, be advantageous; pH gradients could act as a driving force for transport of lithium in such systems. Membranes prepared with (2‐ethylhexyl)‐diphenyl phosphate (Santicizer 141) gave the best results from the point of view of selectivity of Li+ transport vs. Mg2+ and Ca2+. Maintenance of ca. 10−3 M concentrations of Br2 in the end‐brine solutions gives optimal membrane performance. No significant change in membrane permeability and selectivity occurred during six months of their operation. Lithium ions in the product solution of the membrane separation process may be further separated from the residual Mg2+ and Ca2+ ions and concentrated up to 1 M by ion exchange processes. Lithium may be precipitated from such solutions, free from alkaline earth ions, as Li2CO3.
The Thermal Rearrangement of 1,2,7‐Trienes
Authors: Huntsman William D. , Li Yong‐Jing , Giannamore Vincent P.
Published: November 2013

The thermal rearrangement of 1,6,7‐nonatriene and 1,2,7‐octatriene at 400°C has been studied. Besides intramolecular [2 + 2] cycloaddition reactions, these hydrocarbons undergo intramolecular ene reactions, furnishing cis‐1‐methyl‐2‐(1‐propynyl)cyclopentane and cis‐1‐ethynyl‐2‐methylcyclopentane, respectively.
A New Multi‐Step Thermal Rearrangement of a Terminal Allene
Authors: Mazur Mark R. , Berson Jerome A.
Published: November 2013

The gas‐phase pyrolysis of 2‐methylhept‐2‐ene‐6‐yne proceeds by two pathways, one of which leads via an acetylene → vinylidene rearrangement to a hypothetical bicyclo[3.1.0]hex‐1‐ene intermediate and subsequently to products derived from the 2‐isopropylidenecyclopentane‐1,3‐diyl biradical. The second pathway leads to 1,2‐dimethyl‐4‐methylenecyclopent‐1‐ene by a multi‐step process involving Cope rearrangement, two successive 1,5‐sigmatropic hydrogen shifts, and the equivalent of intramolecular ene reaction. This mechanism is supported by two separate isotopic labeling experiments.
From Allenes to Cyclic Compounds by Hetero‐Ene Synthesis
Authors: Bertrand M. , Cavallin B. , Roumestant M‐L. , Sylvestre‐Panthet P.
Published: November 2013

γ‐ and δ‐allenic carbonyl compounds have been synthesized and submitted to thermolysis. A variety of substituted ring systems are thus easily accessible by intramolecular hetero‐ene synthesis.
Cycloaddition Reactions of Substituted Allenes with Triplet Excited Aromatic Thiones: Product Formation and Reaction Mechanism
Authors: Kamphuis J. , Grootenhuis P.D.J. , Ruijter A.P. , Visser R.G. , Bos H.J.T.
Published: November 2013

The reactivity of substituted allenes H2CCC(R)X towards three triplet aromatic thiones has been investigated. Product analysis reveal the formation of two (2+2)‐cycloaddition products the thietanes3, 4(E + Z) and occasionally of one (4+2)‐cycloaddition product, thiopyran derivative (Z)‐5, generally in high overall yields. Steady state measurements show that electron donating substituents in the allenic system enhance the overall reaction rate. There is little effect of solvent polarity on the reaction rate. The correlation between the relative reaction rates and the first adiabatic ionization energy of the substituted allenes is in accordance with the formation of an exciplex between the excited thione and that π‐bond of the allenic system which is conjugated with the substituent X. From this exciplex two isomeric allylic 1,4‐biradicals (Z)‐8 and (E)‐8 are probably formed. After inter‐system crossing, ring closure gives the thietanes3, (E)‐4, (Z)‐4and/or thiopyran derivative (Z)‐5. The ratio in which3, (E)‐4, (Z)‐4and (Z)‐5are formed is explained by considering electronic and steric factors in the proposed reaction mechanism. Experiments with an optically active allene (+)‐PhC(H)CC(H)Me support the intermediacy of a non‐chiral relatively stable allylic 1,4‐biradical. At infinite allene concentration the quantum yield approaches 1, indicating no energy loss during the reaction. Thus no measurable disproportionation of the allylic biradicals (Z)‐8and (E)‐8occurs.
A Horner‐Emmons Approach to Cumulatrienes
Authors: Macomber Roger S. , Hemling Thomas C.
Published: November 2013

Reaction of allenic phosphonates of structure (R'O)2P(O)CH′CCR2 with LDA led to ylid‐like carbanions (2) by removal of H′. Intermediate 2 reacted with a variety of ketones (R′2′CO) to give adducts (3) which fragmented to cumulatrienes of structure R′2CCCCR2. The cumulatrienes prepared and their yields were: 4a (RCH3, R′Ph, 43%); 4b (R+RR′+R′(CH2)5, 64%); 4c (R+R(CH2)5, R′Ph, 28%); 4d (RR′CH3, 23%). In two cases, 4a and 4d, the cumulatrienes were complexed with chlorotris (triphenylphosphine)‐rhodium.
Electrophilic Additions to Allenes. VIII. The Kinetics and Mechanism of the Addition of Benzenesulphenyl Chloride to Allenes
Authors: Beaulieu Pierre L. , Morrisset Veronique M. , Garratt Dennis G.
Published: November 2013

The rates of addition of benzenefulphenyl chloride to 62 alkyl substituted allenes have been determined in methylene chloride solution at 24.5°C. The rates of addition span a range of 3.4 × 103 in reactivity. No correlation with the extended Taft equation or variations thereof was found when the rates of all 62 compounds were considered. Partitioned rate constants, wherein each term reflects the relative propensity for attack upon a given π orbital‐lobe of the allenic system, allows one to demonstrate the specific effect of placing an alkyl group in each of three stereochemically distinct positions. Of note is the observation that while the magnitude of the polar effect of an alkyl group changes with the stereochemical location, this magnitude is a constant for methyl, ethyl and isopropyl. The rates reported herein are interpreted in terms of rate‐limiting formation of alkylidenethiiranium ions.
Applications of Phase Transfer Catalysis to Arenediazonium Cation Chemistry
Authors: Gokel George W. , Ahern Michael F. , Beadle James R. , Blum Lorna , Korzeniowski Stephen H. , Leopold Ahuva , Rosenberg David E.
Published: November 2013

Arenediazonium cations have been known for many years but the synthetic utility has been diminished by their lack of stability and by their proclivity for undergoing sundry side reactions. Arenediazonium BF4 and PF6 salts are generally stable solids, but are relatively insoluble in nonpolar organic media. Crown complexation and other forms of phase transfer catalysis increase solubility and allow numerous synthetic transformations to be conducted in good yield. The yield improvements result from a reduction in competing side reactions rather than any fundamental change in mechanism. The reactions to which the phase transfer technique is successfully applied are diazo coupling, reduction, halogenation, arylation and cyclization. In the latter case, the use of potassium superoxide is sometimes a more efficacious reagent than potassium acetate. The phase transfer approach can be used in the high yield synthesis of arenediazosulfones and arenediazocyanides. The latter undergo cycloaddition with many dienes to yield pyridazine derivatives.