bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Size Effects in the Kinetics of the Electroreduction of Nitroalkanes on Mercury
Authors: Kashti S. , Kirowa‐Eisner E. , Gileadi E.
Published: November 2013

The reduction of nitroalkanes at the dropping mercury electrode in neutral solutions (pH 5.4–7.4) was studied. Careful measurements at the foot of the polarographic wave allow accurate determination of the Tafel slopes to within ± 1 mV, thus the effect of molecular size on the Tafel slope could be determined. The analysis of the results indicates that the adsorbed intermediate, which is a charged species, is situated about halfway between the metal surface and the outer Helmholtz plane. It is also shown that the intermediate is adsorbed with the functional nitro group lying flat on the surface. Only the carbon atoms in the position α and β to the nitrogen atom seem to occupy space on the surface. The importance of employing several members of a homologous series having a common functional group to evaluate the mechanism of electrode reactions is emphasized and the importance of employing the combined isotherm in such analysis is pointed out.
Chemical Approach to Genetics
Authors: Lavie David , Kirson Issac , Abraham Arieh
Published: November 2013

The modifications taking place in the substitution pattern of organic molecules during cross breeding by pollination has been investigated. Through the process of hybridisation of different “chemotypes” of Withania somnifera (Solanaceae), changes have been observed among the substituents present in the steroidal lactones of the withanolide type which are characteristic for this and related species. Several reciprocal cross‐pollinations were performed between the types and the structures of the withanolides produced in the leaves were analysed and determined. These studies led to an understanding of the biogenetic processes leading to specific substitution patterns, and in certain cases enabled a genetic control over the compounds produced in the plant. Compounds not present in natural types could be anticipated to be formed, and indeed were present in the hybrids. Through these studies an insight on the reactions governed by the genetic background of the types taking part in the hybridisation was achieved. Groupings, when found in specific locations of the skeleton could be described as present there due to dominant or recessive genetic characters. These conclusions were reached following analysis of a large number of offsprings for several generations. This method enabled the study of the genetic characters of a plant on the chemical level.
Vibrational Photochemistry
Authors: Bergmann K. , Leone S. R. , Macdonald R. G. , Bradley Moore C.
Published: November 2013

The increase in the rate of chemical reactions with vibrational excitation opens the possibility for selective photochemical processes and isotope enrichment. Recent measurements of chemical reaction rates for vibrationally excited molecules are discussed. A simple kinetic model is used to illustrate some limits on possible process parameters.
Vibrational Electronic Coupling and a Close Look at a Severe Case
Authors: Ross I. G.
Published: November 2013

Electronic spectroscopy, at once the oldest and most intricate branch of spectroscopy, has seen intense activity over the past decade. The difference between small‐molecule and large‐molecule spectroscopy is pointed out. The emphasis here is on larger polyatomics. Certain developments of note, especially of the interpretation of unresolved rotational fine structure, are mentioned. No point of principle has remained more tantalizing than the issue of the integrity of an electronic state: to what extent are electronic and nuclear motions really separable, in the Born‐Oppenheimer sense? There is much new theory, yet quantitative applications of theory to real cases are few, especially in polyatomic molecules. A straightforward computational approach to vibronic (= vibrational‐electronic) coupling in molecules such as naphthalene has proved to be quantitatively successful. Physical insight is harder to obtain, however, but a fairly straightforward explanation (based on a polyatomic version of Walsh's rules) can be offered for the presence of exceptionally strong vibronic coupling between two excited electronic states of azulene (C10H8). The effects of this coupling are so profound that the electronic spectrum is highly sensitive to such minor influences as partial deuteration or changes of solvent. These effects can be modelled rather successfully.
Chiral Organotin Compounds
Authors: Gielen Marcel , Simon Serge , Tondeur Yves , van De Steen Michel , Hoogzand Cornelis , van Den Eynde Ivan
Published: November 2013

Several classes of organotin compounds are configurationally stable within the NMR time‐scale and are even optically stable for weeks. Optically active tetraorganotin compounds, triorganotin hydrides and an optically active (triorganogermyl)triorganotin compound have been synthesized. Two reactions transforming optically active triorganotin hydrides into optically active tetraorganotin compounds are described.
Optical Activity and Lifetime Measurements of Tris‐(2,2′‐Bipyridine) Ruthenium (II) Bromide: Evidence for some Singlet‐Singlet Emission
Authors: Gafni Ari , Steinberg Izchak Z.
Published: November 2013

Evidence for some emission from the first excited singlet state of tris‐(2,2′‐bipyridine) ruthenium (II) bromide is presented based on circular dichroism, circular polarization of luminescence and fluorescence decay measurements. The anisotropy factors in absorption and emission assume very similar values in the wavelength region where these two spectra overlap. Moreover, the two anisotropy factors change markedly in this wavelength range indicating the existence of a second emission band at the short wavelength edge of the main phosphorescence band of the chelate. This observation is further supported by fluorescence decay measurements which reveal biexponential decay kinetics with a fast decaying component at the short wavelength edge of the emission.
Steric Demands of Tertiary Phosphine Ligands
Authors: Clark Howard C.
Published: November 2013

The concept of Cone Angle as defined by Tolman provides a useful measure of relative sizes of phosphine ligands. In attempting to arrive at better descriptions of absolute sizes, the importance of ligand intermeshing is illustrated, and recent calculations of the steric demands of phosphine ligands are reviewed. The effect of steric compression of the ligand, and the effect of possible variations in the metal‐phosphorus distance are also considered.
The Isolation of Stable Platinum(II) σ‐Allylic Derivatives
Authors: Pearson Ralph G. , Laurent Michel
Published: November 2013

The isolation of some stable platinum(II)‐σ‐allylic complexes is reported. The complexes, trans‐Pt(σ‐all)X(PEt3)2:(X = CI, all = allyl, crotyl; X = Br, all = allyl) are synthesized by the oxidative addition of allylic halide to Pt(PEt3)4 in hexane at room temperature. They were characterized by infrared, 1H NMR and 13C NMR spectroscopy.
A Biomimetic Synthesis of Benzo[c]Phenanthridine Alkaloid Nitidine
Authors: Kametani Tetsuji , Takemura Makoto , Ihara Masataka , Fukumoto Keiichiro , Takahashi Keiichi
Published: November 2013

Oxidation of 1,2,3,4‐tetrahydro‐7‐hydroxy‐6‐methoxy‐3‐(4,5‐dimethoxy‐2‐vinylphenyl)‐2‐methylisoquinoline (10), derived from the corresponding berbine methiodide (8), with lead tetraacetate, followed by acidic treatments, gave 5,6‐dihydro‐8‐hydroxy‐2,3,9‐trimethoxy‐5‐methylbenzo[c]phenenthridine (20). By a similar procedure, 1,2,3,4‐tetrahydro‐7‐hydroxy‐6‐methoxy‐3‐(4,5‐methylenedioxy‐2‐vinylphenyl)‐2‐methylisoquinoline (11) was converted to cis‐8‐acetoxy‐4b,5,6,10b‐tetrahydro‐9‐methoxy‐5‐methyl‐2,3‐methylenedioxybenzo[c]phenanthridine (17), whose hydrolysis with hydrochloric acid followed by methylation with diazomethane furnished dihydronitidine (22).
Synthesis of a Steroidal Dicarbamate Related to Meprobamate from 3‐Ketobisnorcholenal
Authors: Golander Yechiel , Breuer Eli , Sarel Shalom
Published: November 2013

Condensation of 3‐ketobisnorcholenal (1) with malononitrile could be directed selectively to the aldehyde group to afford dicyanomethylene ketone 3. Ketalization of 3 with ethylene glycol followed by alkaline hydrolysis gave the aldehydo dioxolane 5, which served as starting material for the syntheses of 1,3‐propanediol derivatives 7 and 10 and their respective dicarbamates 9 and 11.
The Varied and Fascinating Chemistry of Marine Mollusks
Authors: Scheuer Paul J.
Published: November 2013

With illustrations from a single phylum of marine invertebrates, the mollusks, this review presents a cross section of recent marine natural product research. The origins of this research, biological, biomedical, chemical, or serendipitous, are presented as well as the results.
III. Total X‐ray Scattering and Two‐Electron Density Functions
Authors: Stewart Robert F.
Published: November 2013

Within the Waller–Hartree theory it is possible to map out the interelectron density function (the diagonal elements of the intracule matrix) from an analysis of total X‐ray scattering intensities. Theoretical studies of He and H2 show that electron correlation effects substantially influence total X‐ray scattering intensities, but do not appreciably alter the elastic X‐ray scattering intensity. On the other hand, theoretical studies of Be(1S), Ne(1S) and CO(1Σ*) indicate that electron correlation influences both total and elastic X‐ray scattering intensities by comparable amounts (∼ 1–2%), but at differing regions of the scattering vector variable.
XVIII. On the Relation Between the Spatial Electron Density and the Conformational Properties of Molecular Systems
Authors: Hagler A. T.
Published: November 2013

The increasing power of computer simulation experiments for molecular systems is discussed. These include such apparently disparate calculations as Monte Carlo simulation of solvent structure in biological systems, conformational analysis and folding of oligopeptide chains, and lattice‐energy calculations and the effect of lattice forces on molecular geometry. All such calculations have in common the requirement of an analytic expression of the energy of the system as a function of the inter‐ and intramolecular coordinates of interest.

The nature and derivation of these force fields and their relation to the spatial electron densities in relevant molecular systems is reviewed. The method of the derivation of intermolecular force fields from crystal data of amides is outlined. It is shown that information which may be obtained from ab‐initio molecular orbital or X‐ray diffraction studies, population analysis, and total and difference electron density maps, may be used in conjunction with the crystal data both to verify (or test) assumptions made in the derivation and to help in the formulation of the models on which the analytical expressions for the energy are based. Finally, the relation between intramolecular forces and the electron distribution as represented in difference electron density maps is discussed. Several examples involving carbonyl compounds are presented, in which changes in the molecular geometry, intramolecular forces and vibrational frequencies on protonation and substitution are discussed both in terms of “valence or Urey—Bradley” type interactions and the changes which occur in the difference electron density maps.
Resonant and Near‐Resonant Rayleigh and Raman Scattering for a Diatomic Molecule
Authors: Berg J. O. , Robinson G. W.
Published: November 2013

Using the results of a unified theory of scattering in the time‐independent (narrow exciting line) limit, excitation profiles for Rayleigh and Raman cross sections have been calculated for an actual diatomic molecule from over 8000 cm−1 off resonance into the resonance region. Three interference effects, a “vibrational level interference”, an “on‐resonance Franck—Cordon interference”, and “off‐resonance interference,” are discussed.
Application of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) to Spin‐Forbidden Processes
Authors: Halevi E. A. , Trindle Carl
Published: November 2013

Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) is extended to deal with thermal reactions in which spin multiplicity changes. Only minor revisions are required in the theoretical foundation previously established for OCAMS. For reactions in which triplets may be interconverted with singlets, the use of geminals rather than one‐electron wave functions allows us to provide a symmetry criterion for determining whether spin‐orbit coupling can induce the interconversion and—if so—which component of the triplet state would participate in it.

A number of examples illustrate the analysis, including: intersystem crossing between 1A1 and 3B1 CH2; the direct production of 3CH2 by thermolysis of singlet diazomethane; and the stereospecific trapping of 3CH2 by ethylene. We also analyze the intriguing reactions of Dewar‐benzene and 1,2‐dioxetanes, described as “photochemistry without light”, and clarify the complex manifold of thermolysis reactions of methylenepyrazoline.
Mass Spectral Studies of Amaryllidaceae Alkaloids
Authors: Onyiriuka O. S. , Jackson A. H.
Published: November 2013

Amaryllidaceae alkaloids have been isolated from the bulbs of Crinum ornatum and Crinum natans and studied by a combination of mass spectral techniques including EI, CI, FD and GLC/EI mass spectrometry. In addition to the abundant lycorine present in both species three new alkaloids have been obtained in crystalline form from C. ornatum and one new crystalline alkaloid from C. natans. Several other new alkaloids were also shown to be present by GLC/MS and FD/MS. Tentative structures are proposed for the new alkaloids from C. ornatum based on mass and NMR spectral evidence.
Ionization Potential, Oxidation Potential Comparisons for Compounds Containing Amino Nitrogen
Authors: Nelsen Stephen F.
Published: November 2013

Plots of solution oxidation potential (Eo′, V vs sce in acetonitrile) versus vapor phase vertical ionization potential (IPv, eV) are discussed for several types of compounds containing amino nitrogen, including tetraalkylhydrazines, tetraalkyl‐2‐tetrazenes, bicyclic diamines, and ortho and para‐substituted phenylenediamines. All amino compounds fall considerably below the polycyclic aromatic hydrocarbon line in an Eo′ vs IPv plot, and there is not a linear correlation of Eo′ vs IPv for amino compounds. Reasons for the non‐linearity, and the information that can be gained by comparison of the ease of electron removal in the vapor and solution phases are discussed.
Electrode Kinetics of Solvated Electrons in Liquid Ammonia
Authors: Harima Y. , Aoyagui S.
Published: November 2013

Electrode reaction of ammoniated electrons was investigated with voltammetry, potentiometry and chronoamperometry. Experiments were conducted on Pt, Au and W electrodes in 0.5 M LiI, NaI, KI, CsI and KBr solutions of liq. NH3. The results in dilute solutions (< 10<−4 M) do not reflect the differences in alkali metal, electrode metal and supporting electrolyte and are explained by a simple one‐electron transfer process whose transferring species is a free solvated electron and its ion‐pair with a metal cation in a rapid equilibrium. The formal standard potential is −2.155 ± 0.005 V vs. Pb/Pb(NO3)2 (0.05 M) at −40°C in liq. NH3 involving 0.5 M alkali metal iodide. The lower limit of the averaged diffusion coefficient is 0.7 × 10−4 cm2 s−1. At higher metal concentrations (> 10−2 M), a two‐electron transfer process tends to prevail, which is explained by considering the dimer of ion‐pairs as the diffusing species.
Effect of Crystal and Molecular Structure on the Thermochromism and Photochromism of some Salicylidene‐2‐Aminopyridines
Authors: Hadjoudis E. , Moustakali‐Mavridis I. , Xexakis J.
Published: November 2013

Crystalline salicylidene‐2‐aminopyridine and its derivatives exhibit thermochromic phenomena, i.e. they show a reversible colour change as a result of variation in temperature. Photochromism, reversible colour change on ultraviolet irradiation, is not observed in this class of compounds. The appearance of the thermochromic phenomen and its generality depend upon the crystal structure and the molecular orientation of the compounds. In fluid solution, where the orientation of the molecules is random, the compounds exhibit photochromic phenomena. The process is so fast that it can be followed only by flash photolysis techniques or at liquid nitrogen temperature. The results and mechanisms of thermochromism and photochromism are compared with findings on salicylideneanilines.
Low Energy Electron Diffraction Studies of Organic Monolayers on Metal Surfaces
Authors: Firment L. E. , Somorjai G. A.
Published: November 2013

The structures of monolayers of organic molecules adsorbed at metal single crystal surfaces are conveniently studied using Low Energy Electron Diffraction (LEED). Analysis of LEED intensity data determined the structures formed on adsorption of acetylene on Pt(1 1 1). Structures within monolayers can be reliably inferred from LEED data without extensive analysis of the diffracted beam intensities if supplementary information, i.e. spectroscopic data, is available. Structures obtained in this way are discussed and several general features of the adsorption of organic molecules are presented. Weakly adsorbed molecules form close‐packed monolayers. Strongly adsorbed molecules adsorb in specific sites on the metal surface. The nature of the adsorption can be determined from observation of the monolayer registry with the metal lattice. The structure and bonding of organic molecules at metal surfaces depends strongly on temperature.
Circular Fluorescence Polarization of Achiral Molecules in Cholesteric Liquid Crystals
Authors: Stegemeyer H. , Stille W. , Pollmann P.
Published: November 2013

In liquid crystalline matrices the molecular axes of solute molecules adopt an orientation which is given by the director of the liquid crystal. Consequently, the physical properties of the solute become anisotropic, governed by the director distribution within the matrix. An example of this general effect is the circularly polarized fluorescence emission of achiral molecules dissolved in cholesteric liquid crystals. The degree of circular polarization (CPF), given by a dissymmetry factor ge = (IL ‐ IR)/1/2(IL + IR), is rather high (IL, IR intensity of left or right circularly polarized fluorescence, respectively). The sign of ge was found to depend (i) on the screw sense of the cholesteric helical structure, and (ii) on the direction of the electric transition moment within the emitting molecule. The absolute value of ge is a function of the helical pitch p. The CPF can be understood as an ensemble effect of helically orientated emitting chromophores (e.g. perylene, pyrene, azulene, diphenylhexatriene). Based on the theory of Mauguin and de Vries relations have been derived describing quantitatively the dependence of CPF on the structure of the emitting molecules as well as on the helix structure of the cholesteric solvent.
Polymerization of Mono‐ and Bi‐functional Diacetylene Derivatives in Monolayers at the Gas–Water Interface
Authors: Day D. , Hub H. H. , Ringsdorf H.
Published: November 2013

The spreading and polymerization behaviour of long chain acids and phospholipid analogues containing diacetylene groups is described. Especially the polymerization in monolayers is followed spectroscopically with a new device used in connection with a commercial UV spectrometer. The polymerization is topochemically controlled. Sonification of the phospholipid analogues in water results in the formation of liposomes with multilayered membranes. Polymerization of the liposomes in water forms aqueous solutions of polymer vesicles.
Hydrogen and Oxygen Production via Redox Catalysis in Colloidal Systems
Authors: Kiwi J.
Published: November 2013

Recent progress in the use of redox catalysts to break down water into H2 and O2 is reviewed. Special Lemphasis is given to the increased efficiency of the reactions when the catalyst is present in a colloidal form.
The Valence Bond Orbital Model as an Interpretive Framework for Understanding Electronic Structure
Authors: Kirtman Bernard , Palke William E. , Chipman Daniel M.
Published: November 2013

For purposes of interpretation and understanding, the valence bond orbital model of electronic structure provides a number of advantages over the more common molecular orbital model. This derives primarily from the unique description of valence bond orbitals in terms of highly localized bond pairs, lone pairs, etc. Optimization of the orbitals by a self‐consistent‐field procedure brings out features which were not evident from the semi‐empirical treatments of earlier workers. Calculations on CH4, NH3, H2O and H2S show that optimized valence bond orbitals are often bent even at the equilibrium nuclear configuration and generally do not follow the nuclei when bond angles are varied. Analysis of a large basis set calculation on H2O shows that the valence bond wavefunction can be fitted well with a minimal basis, making it possible to interpret more clearly the connection between hybridization and interorbital angles. It is shown how the valence bond method provides a rigorous basis for factorization even of difficult second order physical properties, such as polarizability, into separated bond and lone pair contributions. These contributions can be further decomposed into sums of atomic valence state values plus corrections due to bond polarization effects. Finally, the advantages of using the valence bond model as a starting point for the perturbation treatment of electron correlation are pointed out. Calculations on H2 and LiH indicate that valence bond theory need only be carried through second order to obtain results comparable in accuracy to a third order treatment based on molecular orbitals.
Intramolecular Interactions Through Triple Bonds. Internal Rotation in Aminoborylpolyynes, NH2(C≡C)n BH2
Authors: Radom Leo , Vincent Mark A.
Published: November 2013

Ab initio molecular orbital theory has been used to examine interactions through triple bonds in polyynes [H‐(C≡C)n‐H], aminopolyynes [NH2‐(C≡C)n‐H], borylpolyynes [H‐(C≡C)n‐BH2], and aminoborylpolyynes [NH2‐(C≡C)n‐BH2], with n = 1,2,3 and 4. The rotational barrier in aminoborylpolyynes is a particularly effective probe of interactions transmitted through the triple bond network. The barrier for NH2‐C≡C‐BH2 is substantial (25.1 kJ mol−1) but is reduced by a factor of approximately 3 by the interposition of each additional C≡C linkage. There is a residual barrier (of 1.0 kJ mol−1) in NH2‐C≡C‐C≡C‐C≡C‐BH2 despite the fact that the interacting groups are separated by a distance of greater than 11 Å.
Empirical Correlations Between Conformational Parameters in β‐D‐Furanoside Fragments Derived from a Statistical Survey of Crystal Structures of Nucleic Acid Constituents Full Description of Nucleoside Molecular Geometries in Terms of Four Parameters
Authors: De Leeuw Harry P. M. , Haasnoot Cornelis A. G. , Altona Cornelis
Published: November 2013

A data file was created containing internal coordinates and derived parameters for 178 β‐D‐furanoside fragments, occurring in X‐ray structures of ribo‐, 2′‐deoxyribo‐ and arabinonucleoside derivatives. The variability in bond angles and torsion angles can be described by four conformational parameters; the kind and degree of ring puckering as expressed in phase angle of pseudorotation P and puckering amplitude vm, the conformation of the side‐chain δ and the glycosidic torsion angle χ. Comparison between out‐of‐plane and torsion angle methods for calculation of pseudorotation parameters revealed that the latter method is better suited to describe the internal coordinates of the non‐equilateral five‐membered ring. Inspection of the distribution of phase angles and puckering amplitudes lends additional support to the hypothesis that conformational interconversion of the familiar N and S type ring conformers is a process of hindered pseudorotation, proceeding through the O4′endo conformation (P = 90°) and maintaining a constant puckering amplitude. Both syn‐anti distribution and preferred ranges of χ are correlated with furanose conformation in ribonucleosides; the distribution is also affected by the type of base, purines showing higher syn/anti ratios than pyrimidines. Three modes are observed for the backbone torsion angle δ(C4′–C5′); the most abundant rotamer is δ+, followed by δa. The δ− rotamer has so far been found only in S‐type furanosides. Regressions based on existing or modified equations were used to express variations in internal coordinates in terms of the four parameters involved. As a consequence of its anomeric character, the glycosidic bond length can be described by a cyclic function of χ. Endocyclic bond angles' and torsion angles show small but systematic deviations from the pseudorotation equations derived for equilateral rings. Based on observed correlations with the four parameters, reasonably accurate coordinates for exocyclic atoms, including hydrogen atoms, could also be obtained. Coordinates for model β‐D‐furanoside fragments with preferred χ and δ orientations and variable pseudorotation parameters, covering a part of the N ⇌ S interconversion pathway, are presented. Their usefulness in future theoretical and experimental studies on nucleic acid conformations, both in the solid state and in solution, is discussed.
Stereospecific Methanol Elimination and Hidden Hydrogen Transfer in Cyclic Diesters under Electron Impact
Authors: Bar‐Shai Rivka , Bortinger Arie , Sharvit Joseph , Mandelbaum Asher
Published: November 2013

Elimination of CH3OH under electron impact occurs in trans‐1,2‐ and 1,3‐dicarbomethoxycycloalkanes to a greater extent than in the cis‐isomers. In the trans‐diesters, one of the α‐hydrogen atoms is abstracted in the course of the elimination. In the methyl esters of cyclohexane 1,4‐dicarboxylic acids, the elimination of CH3OH is also specific to the trans‐isomer, but the abstracted hydrogen atom does not originate at the α‐position. This result is explained by a stereospecific hidden hydrogen migration step, preceding the elimination.
Two Syntheses of [2.2.2] (1,2,3)Cyclophane
Authors: Neuschwander Brent , Boekelheide V.
Published: November 2013

Two syntheses are presented for [2.2.2] (1,2,3)cyclophane (7), the remaining member of the symmetrical [2n]cyclophanes whose preparation has not previously been described. The first method involved the dimerization of 2,6‐bis (4′, 4′‐dimethyl‐2′‐oxazolinyl)toluene (1 ) to give 2 which, on hydrolysis, produced the tetracarboxylic acid 3. Conversion of 3, via the acid chloride (4 ), to the tetraol 5, followed by treatment with phosphorus tribromide yielded the tetrabromide 6. The overall scheme was then completed by reaction of 6 with phenyllithium to give [2.2.2] (1,2,3) cyclophane (7 ). An alternate, more convenient, method began with the pyrolysis of 2,6‐bis (chloromethyl)toluene (8 ) to give 3‐chloromethylbenzocyclobutene (9 ). Formation of the Grignard of 9, followed by reaction with ferric chloride, yielded the dimer 10. Pyrolysis of 10 then gave [2.2.2] (1,2,3)cyclophane (7).
Pyrolysis and Isomerization Reactions of Multiply‐bridged Cyclophanes
Authors: Hopf Henning , Kleinschroth Jürgen , Murad Abo El‐Fetouh El‐Sayed
Published: November 2013

When subjected to pyrolysis in para‐di‐isopropylbenzene (270°C, 40h) [2.2.2] (1,2,4)cyclophane (5 ) is cleaved to 2,9‐dimethyldibenzo[a,e]cyclooctadiene (8 ). Under comparable conditions (290°C, 65h), [2.2.2.2] (1,2,3,5)cyclophane (6 ) is converted to 6,11‐dimethyl[2.2.2] (1,2,3)cyclophane (9 ), the first derivative of a symmetrical [2n]cyclophane carrying three consecutive ethano bridges. The isomeric [2.2.2.2]‐ (1,2,3,4)cyclophane (7 ), on the other hand, cannot be induced to undergo carbon‐carbon‐bond cleavage followed by hydrogen abstraction. Under the influence of aluminiumtrichloride/hydrogenchloride hydrocarbon 5 isomerizes to the unsymmetrical [2.2.2] (1,2,4) (1,2,5)cyclophane (10 ), whereas 6 and 7 are stable under these conditions. The thermal stability and propensity of multiply‐bridged cyclophanes to undergo isomerization reactions is discussed.
Diels‐Alder Reactivity of Polycyclic Aromatic Hydrocarbons. III. New Experimental and Theoretical Results
Authors: Biermann D. , Schmidt W.
Published: November 2013

Second‐order rate constants for the Diels‐Alder reaction of aromatic hydrocarbons comprising up to 13 condensed benzene rings with maleic anhydride have been measured under standardized conditions. The position of attack was deduced from the UV spectra of the adducts. A number of theoretical models was examined as to how far they reproduce the observed rate data and positional selectivities. All except Fukui's frontier orbital concept were successful. These include Brown's para‐localization model, second‐order perturbation theory using Hückel orbital energies and AO coefficients, Clar's sextet theory and Herndon's structure count method. The latter two models provide a particularly attractive basis for discussing structure/reactivity relationships. Inter alia, they lead to the discovery of “isocanonical” series, i.e., to homologous series in which corresponding members have the same theoretical reactivity index and therefore the same rate constant, despite widely differing topologies.
The Relationship Between Zinc Protoporphyrin Levels in Blood and Lead‐Induced Anemia
Authors: Blumberg W. E.
Published: November 2013

The production of zinc protoporphyrin by the erythrocyte has been shown to be a good indicator of lead intoxication. The relationship between zinc protoporphyrin levels in blood and lead‐induced anemia are examined. Serum iron parameters show that the anemia is not related to the lack of availability or transport of iron, but to faulty utilization by the reticulocyte. Although zinc protoporphyrin is produced in response to both lead intoxication and iron deficiency, it is pointed out that plasma iron and lead levels provide a method for differentiating between them.
The Electronic Configurations of Catalases and Peroxidases in their High Oxidation States: A Definitive Assessment
Authors: Dolphin David
Published: November 2013

The highest oxidation states of catalase and horseradish peroxidase contain two oxidizing equivalents more than the resting ferrihemoproteins. While numerous electronic configurations for these primary complexes have been suggested, the most widely accepted formulation is that of an Fe(IV) (S = 1) porphyrin π‐cation radical (S = 1/2). The evidence for and against these electronic configurations is reviewed and assessed.
Influence of Sex Hormones on Relative Quantities of Multiple Species of Cytochrome P‐450 in Rat Liver Microsomes: A Possible Answer to the Sexual Differences in Metabolic Activities of Rat Liver Microsomes
Authors: Fujita Shoichi , Chevion Mordechai , Peisach Jack
Published: November 2013

EPR spectra of rat liver microsomes from male, female and hormonally‐treated castrated hepatectomized rats were studied. The spectra, especially in the region of gmax, suggested a heterogeneity of local environments of the low spin ferric heme indicative of multiple structures for cytochrome P‐450. Certain features in the spectrum correlated with sexual differences. It is suggested that the changes in the relative amplitudes of the EPR features represent differences in the relative abundance of the individual proteins in the mixture that, in turn, are related to the sexual differences of metabolic patterns for reactions catalyzed by cytochrome P‐450.
Photosynthetic Oxygen Evolution and the Water Splitting Enzyme
Authors: Barber J. , Nakatani H. Y. , Mansfield R.
Published: November 2013

A brief review is given of the present knowledge of the mechanism by which higher plants and algae bring about the photooxidation of water. Emphasis is placed on the role of manganese in this process and a summary is given of recent efforts from several laboratories to isolate the “water‐splitting enzyme”. Experimental evidence is presented that, in contrast to earlier beliefs, the Mn not removed by washing chloroplast thylakoids with high concentrations of Tris (hydroxymethyl) amino methane could be involved in O2 evolution. This manganese is equivalent to about 2 Mn per photosystem two reaction centre. Also presented are details of the isolation of a heme‐protein from spinach chloroplasts which may be intimately associated with the water splitting process. This protein has a native molecular weight of approximately 232 k Daltons and has characteristics similar to those of a catalase type enzyme. The possibility of involvement of peroxide formation during the water splitting process is discussed.
Orientation and Energy Transfer in Chlorophyll Monolayers Diluted with Hexadecane. Fluorescence and Sensitized Fluorescence
Authors: Gonen Oded , Levanon Haim , Patterson L. K.
Published: November 2013

The fluorescence and force‐area behavior of chlorophyll a (Chl a) monomolecular films diluted with hydrocarbon on an aqueous subphase is reported. It is found that the diluent hexadecane, instead of conventional fatty alcohols, results in a substantial increase in the fluorescence yield of Chl a. The luminescence intensity varies nonmonotonically with respect to the intermólecular distance. A model for the mutual orientation of the chlorophyll pigments and the consequent energy transfer processes in terms of a Förster mechanism is proposed. For a random distribution of the Chl a molecules in the monolayer (k2 = 2/3) an average value of 43° is calculated for the angle between the molecular planes and the water surface. This model yields a value of 23 Å for the Förster R0. Also, a value of 58° is derived for the angle between the Q‐band transition moment and the line of intersection between the molecular plane and water surface. When a mixture of Chl a and Chl b in the monolayers is being excited at the absorption band of the latter pigment, typical fluorescence of Chl a is being detected. This sensitization process can also be interpreted in terms of the orientational model of the Chl molecules as presented in this work.
Thermal Decomposition of Copper(II) Squarate
Authors: Brown Michael E. , Galwey Andrew K. , Beck Michael W.
Published: November 2013

A kinetic and thermochemical study has been made of the dehydration, decomposition and oxidation reactions of copper(II) squarate dihydrate, CuC4O4 · 2H2O. In contrast to results obtained for the nickel(II) salt, the copper salt undergoes preliminary dehydration in a temperature range (410–440 K) appreciably below that for decomposition (590–620 K). The anhydrous material is then more stable than nickel squarate (560–600 K). The major decomposition products in nitrogen are Cu and CO and the reaction may proceed further to CuO and CO2 in an oxyen atmosphere. Values for the enthalpies of dehydration, decomposition and oxidation are reported. Isothermal DSC was used to study the kinetics of dehydration and of decomposition and results were analyzed using relative‐rate reduced‐time (RRRT) curves. The dehydration conforms to the Avrami—Erofe'ev expression, whereas the decomposition approximates closely to the contracting area model. Apparent Arrhenius parameters are reported.
Importance of the Phthalocyanine Ring Carbon π‐orbitals in the Electrical Conduction of Metal Phthalocyanine Polymers
Authors: Whangbo Myung‐Hwan , Stewart Kevin Randall
Published: November 2013

The electronic structures of metal phthalocyanine polymers PcMX and MPc were examined by performing tight‐binding band calculations on PcMX (MX = SiO, GeO, AlF, GaF, CrF) and MPc (M = Ni, Co, Fe) chains. The present band structure study suggests that the electrical conductivities of halogen‐doped PcMX and MPc chains are governed by their valence bands a composed of the HOMO a1M of each Pc ring. It is the valence band a that becomes partially empty upon halogen‐doping. The Pc ring π‐orbital a1M is made up of only the carbon p orbitals. By symmetry, none of the s, p and d orbitals of a metal atom M can mix into the a1M orbital. Consequently, the width of the valence band a is solely determined by such factors as the inter‐ring separation and the inter‐ring rotation. It was noted that there should be one, two and three unpaired electrons on each metal atom of CoPc, FePc and PcCrF chains, respectively. Thus halogen‐doped CoPc, FePc and PcCrF are expected to have magnetic properties associated with the unpaired electrons.
Delta Bilirubin: The Fourth Fraction of Bile Pigments in Human Serum
Authors: Wu T.‐W.
Published: November 2013

Delta bilirubin is a strong, possibly covalent complex between bilirubin and an albumin‐like protein, found in the serum of most jaundiced adults. The bili‐albumin complex reacts directly diazo‐positive. An examination of its azo pigments indicates that only one half of the tetrapyrrole is linked to the protein, presumably via an amide bond formed between a propionic acid side chain of bilirubin and an amine group (e.g., ϵ‐NH2 of a lysine) in the albumin backbone; the other (distal) propionic acid chain is largely unesterified. Preliminary analyses of the peptides generated by chemical or enzymic cleavage of the delta fraction suggest a bilirubin bonding region within positions 128–297 of albumin and another involving positions 298–585. Thus, delta bilirubin may represent the first true human biliprotein. The implications of this biliprotein in both the fundamental and applied aspects of bile pigment research are discussed.
Deuterium NMR of Biaxially Ordered Liquid Crystals
Authors: Doane J. William
Published: November 2013

Deuterium NMR spectra and spectral patterns obtained from several different biaxially ordered liquid crystalline phases are reviewed. An interpretation of these spectra in terms of structural and orientational order is given and a comparison is made between some of the phases in order to examine different aspects of biaxiality. In all of the phases presented, the deuterium spectra are interpreted as being time averaged in the fast motion regime. Liquid crystalline phases reviewed include the ribbon phase of lyotropic soaps, the cholesteric, smectic C and smectic G phases of thermotropic materials.
Pd(O) Promoted Transformation of 1,1‐Dialkoxycarbonyl‐2‐(1,3‐butadienyl)cyclopropanes into 2‐Ethenyl‐3‐cyclopentenes
Authors: Morizawa Yoshitomi , Oshima Koichiro , Nozaki Hitosi
Published: November 2013

1,3‐Butadienylcyclopropanes activated by two electron‐withdrawing groups (1) smoothly rearrange to vinylcyclopentene derivatives in the presence of a Pd(O) catalyst under mild conditions. For example, dimethyl 1,3‐butadienylcyclopropane‐1,1‐dicarboxylate 1a reacts with 3 mol% Pd(PPh3)4 in DMSO at 25–60 °C for 30 min to provide dimethyl 2‐ethenyl‐3‐cyclopentene‐1,1‐dicarboxylate 2a in 87% yield. Other data show that the new method is useful in the synthesis of cyclopentene derivatives including dolichodial and iridodiol.
A New Class of Liquid Crystals Containing an Oxirane Ring
Authors: Solladie Guy , Bartsch Richard , Zimmermann Richard G. , Gottarelli Giovanni
Published: November 2013

It is shown that trans stilbene epoxides, appropriately substituted in the 4,4′ positions, lead to a new class of nematic and smectic liquid crystals.
Structural‐Directing Effects in Heterocyclic Schiff Bases
Authors: Hadjoudis E. , Moustakali‐Mavridis I.
Published: November 2013

Structural‐directing effects have been observed in a number of N‐salicylideneaminopyridines affecting their photochromic and thermochromic properties in the crystalline state.
Topochemical Photodimerization of 4‐(3‐Oxo‐3‐phenyl‐l‐propenyl)benzoic Acid and Its Esters
Authors: Hasegawa M. , Arioka H. , Harashina H. , Nohara M. , Kubo M. , Nishikubo T.
Published: November 2013

The photodimerization behaviors of 4‐(3‐oxo‐3‐phenyl‐1‐propenyl)benzoic acid (1) and its esters (2–7) in the crystalline state are investigated. These crystals, except that of the phenyl ester (7), dimerize photochemically to yield the corresponding cyclobutane derivatives in a typical topochemical fashion. Head‐to‐head type cyclobutane derivatives are obtained from crystals of the acid and ethyl ester (1 and 3), whereas head‐to‐tail type derivatives are formed from the other ester crystals (2, 4, 5, and 6). The temperature dependences of these reaction behaviors and the configurations of the photoproducts are correlated with the molecular arrangement in the reactant crystals. Reversible or irreversible behavior of as‐formed dimer crystals, derived from 2 or 4 crystals, is interpreted in terms of accumulated strain energy in the course of the topochemical process.
The Reaction of (Dicarbonyl)(η5‐Cyclopentadienyl)Cobalt with Bis(trimethylsilyl)ethyne. A One‐Step Synthesis of Tetrakis(trimethylsilyl)butatriene
Authors: Fritch John R. , Peter K. , Vollhardt C.
Published: November 2013

Reaction of the two title compounds in a nitrogen‐flushed boiling medium over several days produced a series of cyclobutadiene and trinuclear biscarbyne complexes in addition to the only organic substance, tetrakis(trimethylsilyl)butatriene, formed formally by catalytic dimerization of bis(trimethylsilyl)ethyne. Mechanistic pathways are discussed which might provide the connection between starting materials and products.
Preparation and Reactions of Cyclic Allenes
Authors: Thies Richard W.
Published: November 2013

Recent synthetic, reaction, and stereochemical studies of strained‐ring, medium‐ring and large‐ring allene hydrocarbons are discussed.
Selectivity in the Solvolysis of 1‐Adamantyl Halides in Binary Solvents
Authors: Samuel P. McManus , Zutaut Steven E.
Published: November 2013

The products of solvolysis of 1‐bromoadamantane in twenty‐six binary solvent mixtures were studied. The solvent systems included aqueous aliphatic alcohols, mixtures of trifluoroethanol with water, formic acid, acetic acid, dichloroacetic acid, and hexafluoroisopropanol (HFIP) and mixtures of HFIP with methanol and ethanol. Also, 1‐chloroadamantane was studied in three binary solvents. The relative rates of reaction of the components of each of the binary mixtures (selectivity values) were calculated. These selectivity values provided evidence supporting the hypothesis that both steric bulk and electrophilicity of the solvent components strongly affect the selectivities. Intrinsic nucleophilicity is of lesser importance. The front‐side nucleophilicities are shown to be composition dependent, especially when highly electrophilic solvents are used. It is suggested that solvent sorting may account for this but other possible causes are discussed.
Conformational Analysis of Polypeptides and Proteins for the Study of Protein Folding, Molecular Recognition, and Molecular Design
Authors: Scheraga Harold A.
Published: November 2013

Conformational energy calculations provide an understanding as to how interatomic interactions lead to the three‐dimensional structures of polypeptides and proteins, and how these molecules interact with other molecules. Illustrative results of such calculations pertain to model systems (α‐helices and β‐sheets, and interactions between them), to various open‐chain and cyclic peptides, to fibrous proteins, to globular proteins, and to enzyme‐substrate complexes. In most cases, the validity of the computations is established by experimental tests of the predicted structures.
Anion Effects in (BEDT‐TTF)2X Salts: Symmetry Induced Superstructures
Authors: Kistenmacher Thomas J.
Published: November 2013

The structural and electrical properties of a series of (BEDT‐TTF)2X salts are systematized in terms of a substructure‐superstructure relationship which is induced by variation in anion symmetry and pictorially represented as a crystallographic family tree. Importantly, it is recognized that the ambient‐pressure superconductors α‐(BEDT‐TTF)2I3, α‐(BEDT‐TTF)2IBr2, and α‐(BEDT‐TTF)2AuI2 have crystal structures coincident with the parent subcell of this crystallographic family tree. Moreover, all first‐generation supercells (doubling of any one subcell vector) are exclusively populated by salts with non‐centrosymmetric anions of tetrahedral symmetry, and, apparently, second‐generation supercells (doubling of any two subcell vectors) are populated by salts with centrosymmetric anions of octahedral symmetry. Finally, trends in structural properties with anion size are briefly considered.
Functionalized Bilayer Membranes as Artificial Transaminase: Modification of the Active Site and Its Consequence in Catalytic Efficiency
Authors: Murakami Yukito , Kikuchi Jun‐Ichi , Akiyoshi Kazunari , Shiratori Nobuyuki
Published: November 2013

The transamination reaction of l‐phenylalanine with pyruvate as catalyzed by the artificial transaminase formed with synthetic bilayer aggregates was examined in aqueous media under mild kinetic conditions. Each catalyst system was constructed with a combination of a synthetic peptide lipid, a hydrophobic vitamin B6 derivative, and metal ions. Modification of the active site in the present artificial transaminase was performed by changing a combination of molecular components constituting the catalytic system. While the catalytic activity was scarcely influenced by differences in aggregate structure, single‐ or multi‐walled bilayer, and in copper‐(II) concentration, molecular structures of the hydrophobic vitamin B6 and an amino acid residue of the peptide lipid had significant effects on the reactivity.
P‐450 Type Activation of Dioxygen by Heterogenized Metal Porphyrins: Comparison with the Corresponding Homogeneous Systems
Authors: Fukuzumi Shunichi , Mochizuki Seiji , Tanaka Toshio
Published: November 2013

The protons of silanol groups on a silica or silica‐alumina surface are replaced by metal(III) porphyrin cations, FeTPP+, MnTPP+, and CoTPP+ (TPP = tetraphenylporphyrin). The heterogenized iron(III) or manganese(III) porphyrin supported on silica thus prepared can activate dioxygen in the presence of excess amounts of NaBH4 and cyclohexene, affording cyclohexanol and cyclohex‐2‐ene‐1‐ol in a 4:1 ratio, which is the same as the ratio observed in the known P‐450 type oxidation of cyclohexene catalyzed by a homogeneous manganese porphyrin (MnTPPCl) in the presence of NaBH4 used as an electron source. The heterogenized iron(III) porphyrin shows a reactivity comparable with that of the corresponding heterogenized manganese(III) porphyrin. On the other hand, substitution of the heterogenized iron(III) porphyrin by the corresponding homogeneous catalyst, FeTPPCl, results in drastic change in the product ratio; the ratio of cyclohexanol to cyclohex‐2‐ene‐l‐ol is reversed, suggesting that the oxidation of cyclohexene proceeds via radical chain autoxidation reactions. The catalytic activity for the P‐450 type oxidation is diminished while FeTPPCl is converted to the μ‐oxo‐dimer (FeTPP)2O. Cobalt(III) porphyrin in a homogeneous system also affords the autoxidation products. Such a mechanistic difference between the homogeneous and heterogeneous metal porphyrins in the oxidation of cyclohexene by dioxygen has been confirmed by kinetic studies in which the P‐450 type oxidation and autoxidation obey different kinetics.