Showing papers on "Intramolecular force published in 1977"
TL;DR: In this paper, the influence of donor and acceptor substituents on the second and third order hyperpolarizabilities β and γ of large conjugated molecules such as stilbene and styrene derivatives was investigated.
Abstract: We have investigated the influence of donor and acceptor substituents on the second and third order hyperpolarizabilities β and γ of large conjugated molecules such as stilbene and styrene derivatives. This was performed by two independent measurements of β and γ using the techniques of dc electric‐field induced second‐harmonic generation and tunable four‐wave mixing in liquids and solutions. For trans−stilbene derivatives, β and γ are typically 10 times larger than for the corresponding benzene compounds, and are strongly correlated with the mesomeric effect of the substituents. A series of disubstituted molecules with strong donor–acceptor intramolecular charge transfer exhibit very large β, and it is shown that this enhancement can be predicted from the basic properties of the first electronic excited state.
1,391 citations
351 citations
01 Jan 1977
253 citations
TL;DR: Cell surface proteins of cultured cells are disulfide bonded to a greater degree than are total cellular proteins, and the "large external transformation-sensitive" (LETS) protein, a major surface protein, is present almost exclusively indisulfide-bonded complexes including homodimers and also higher aggregates held together by disulfides bonds or concovalent interactions.
Abstract: Cell surface proteins of cultured cells are disulfide bonded to a greater degree than are total cellular proteins. In particular, the "large external transformation-sensitive" (LETS) protein, a major surface protein, is present almost exclusively in disulfide-bonded complexes including homodimers and also higher aggregates held together by disulfide bonds or concovalent interactions. Other cell surface proteins also appear to be involved in disulfide bonding, both intramolecular and intermolecular. In virally transformed cells, LETS protein and its disulfide complexes are absent and certain other disulfide-bonded proteins are also not observed.
164 citations
138 citations
TL;DR: A neutron diffraction study of squaric acid (C4H2O4; 3,4−dihydroxy−3,cyclobutene•1,2−dione) at 25°C has been carried out.
Abstract: A neutron diffraction study of squaric acid (C4H2O4; 3,4‐dihydroxy‐3‐cyclobutene‐1,2‐dione) at 25°C has been carried out. Space group P21/m, a=6.143(2), b=5.286(2), c=6.148(2) A, β=89.96(2) °, Z=2. The structure has been refined with 67 variable parameters on 1026 reflections, comprising one hemisphere of the reciprocal lattice to yield a conventional crystallographic R value of 0.025. An anisotropic extinction correction was applied, and 66 reflections severely effected by extinction were not used in the final cycles of refinement. The squaric acid molecules are linked by strong hydrogen bonds to form infinite planar layers in the crystallographic mirror planes. The hydrogen bond lengths are H⋅⋅⋅O 1.034 and O⋅⋅⋅O 2.554 A, the O−H⋅⋅⋅O angle is 177.5°. Average intramolecular bond distances are C–O 1.288, C=O 1.229, C–C 1.500 and 1.462, and C=C 1.414 A.
128 citations
TL;DR: The primary kinetic isotope effect for benzylic hydroxylation is measured by a method utilizing intramolecular competition, using the symmetrical substrate 1,3-diphenylpropane-1,1-d2.
118 citations
TL;DR: In this paper, the authors compare entropy changes in intermolecular and intramolecular reactions and determinations of the intrinsic energy of the bond arising by non-covalent interaction between enzyme and substrate.
Abstract: Why are enzyme-catalyzed reactions so much faster than uncatalyzed reactions, and why are enzymes so specific? What is the effect of mere approximation of enzyme and substrate, and what is the influence of the strain energy? Attempts to answer these questions have led to comparisons between entropy changes in intermolecular and intramolecular reactions, and to determinations of the intrinsic energy of the bond arising by non-covalent interaction between enzyme and substrate
110 citations
TL;DR: In this article, the interaction site cluster series is derived for the Helmholtz free energy of a molecular mixture in which molecules can interconvert by chemical reactions, and the free energy functional is shown to be a minimum with respect to variations of the intramolecular distribution functions.
Abstract: The interaction site cluster series is derived for the Helmholtz free energy of a molecular mixture in which molecules can interconvert by chemical reactions. This series expresses the free energy as a functional of the single‐molecule (intramolecular) distribution functions. Variations of this functional are studied. It is shown that when the total numbers of atoms in the mixture are fixed, the free energy functional is a minimum with respect to variations of the intramolecular distribution functions. Further, this variational principle is shown to be equivalent to the cluster series formulas derived earlier [J. Chem. Phys. 65, 2925 (1976)] for chemical equilibrium constants and intramolecular distribution functions of nonrigid molecules in condensed phases.
101 citations
TL;DR: In this paper, the reduction of FeCl2 in THF in the presence of excess trimethylphosphine (L) leads to a compound of the composition L4Fe (1).
Abstract: Die Reduktion von FeCl2 in THF fuhrt in Gegenwart von uberschussigem Trimethylphosphin ( L) zu einem Komplex der Zusammensetzung L4Fe (1). Dieser liegt in Losung infolge einer intramolekularen CH-Spaltung weitgehend als Eisen(II)-Hydridkomplex L3(H)[(CH3)2PCH2]Fe (1 b) vor, steht aber im Gleichgewicht mit seinem Eisen(0)-Isomeren (1 a). — Niedrige Oxidationsstufen begunstigende Liganden verschieben dieses Gleichgewicht und bilden die Komplexreihen L3L′2Fe (L′ CO, P(OCH3)3, ½ Isopren) (2c–e) und L2L′3Fe (L′ CO, P(OCH3)3) (3a, b). — Reaktionen mit Protonensauren verlaufen dagegen (vorwiegend) uber den Eisen(II)-Komplex. Dabei lassen bruckenbildende Saureanionen die Reaktion in eine Disproportionierung zu L4FeH2 (4) und polymeren Eisen(II)-salzen einmunden. Bei der Methanolyse erfolgt, abhangig von Temperatur und Losungsmittel, neben einer OH-Spaltung auch eine CH-Spaltung des Methanols, das dabei (teilweise) zu CO oxidiert und so in L3(CO)FeH2 (6) eingebaut wird.
Functional Derivatives of Trimethylphosphine, II. Ambivalent Behaviour of Tetrakis(trimethylphosphine)iron: The Equilibrium of the Isomers
The reduction of FeCl2 in THF in the presence of excess trimethylphosphine ( L) leads to a compound of the composition L4Fe (1). As a result of an intramolecular CH-fission this complex exists in solution almost completely as an iron(II) hydride complex L3(H)[(CH3)2PCH2]Fe (1 b), but is in an equilibrium with its iron(0) isomer (1 a). — Ligands favouring low oxidation states shift this equilibrium to give the complexes L3L′2Fe (L′ CO, P(OCH3)3, ½ isoprene) (2c–e) and L2L′3Fe (L′ CO, P(OCH3)3) (3a, b). — On the other hand protic acids (predominantly) react with the iron(II) complex. Hereby, bridging anions give rise to a disproportionation reaction yielding L4FeH2 (4) and iron(II) polymers. In the course of the methanolysis, depending on nature of the solvent and temperature, a CH-fission reaction is observed, besides the OH-cleavage of methanol, which is thereby (partly) oxidized to give CO as a substituent in L3(CO)FeH2 (6).
90 citations
TL;DR: In this paper, the influence of the molecular weight on the relative quantum yield of the pyrene groups has been analyzed according to the general kinetic treatment of diffusion controlled quenching processes.
TL;DR: The C′= O and Cα signals in the NMR spectra of valinomycin have been assigned and the vicinal 1H…13C coupling constants have been determined by double and triple heteronuclear resonance, leading to unequivocal determination of the torsion angles φ and of the population distribution of the Cα-Cβ rotational states.
Abstract: The C′= O and Cα signals in the 13C nuclear magnetic resonance (NMR) spectra of valinomycin have been assigned and the vicinal 1H…13C coupling constants have been determined by double and triple heteronuclear resonance. In conjunction with the vicinal H-NCα-H and H-CαCβ-H proton-proton constants, the results led to unequivocal determination of the torsion angles φ and of the population distribution of the Cα-Cβ rotational states. The Φ torsion angles for the hydroxy acid residues were estimated from the vicinal 1H-CαC′-15N constants. The combined data permitted refinement of the conformational states of valinomycin in different solvents. For the KS+ complex of valinomycin the observed couplings are in complete accord with the conformations we had earlier proposed for solutions and that had also been established by X-ray analysis. In the 13C spectra of the valinomycin-Tl+ complex 13C…203,205Tl+ spin-spin couplings were observed for the l and d-valine carbonyls, unequivocal proof of the donor-acceptor interaction with the cation. In media of weak polarity (cyclohexane, chloroform) the conformation of the valinomycin molecule is similar to that of the K+ complex. In such a ‘bracelet’ structure formed by six fused β-turns of type II and II′, the amino acid carbonyls are axial with certain inclination towards the symmetry axis. On formation of a 1:1 complex with a cation the carbonyl orientation changes, now bending towards the center of the molecular cavity. In the ‘propeller’ conformation, predominant in solvents of medium polarity (for instance CCl4/(C2H3)2SO, 3/1) the three β-turns are of type II. The 1H and 13C chemical shifts are interpreted in terms of conformational changes in the valinomycin molecule, intermolecular and intramolecular hydrogen bonds and interaction with the metal cation.
TL;DR: In this article, the authors discuss the activation of alkanes by transition-metal compounds and show that they can be activated by both hard and soft transition metal complexes, and the results of studies on aromatic compounds are used where appropriate to illuminate the work on alkanes.
Abstract: Publisher Summary This chapter discusses the activation of alkanes by transition-metal compounds Alkanes can be activated by both hard and soft transition-metal complexes The reactions discussed are mainly those in which activation is by soft transition metals The first is the activation of C–H bonds in ligands––usually phosphines—and the reactions are stoichiometric The second group is that of the catalysis of hydrogen–deuterium exchange, and the third group is the reactions of alkanes involving transition-metal compounds For groups two and three, the reactions parallel very closely the reactions of aromatic compounds, and the results of studies on aromatic compounds are used where appropriate to illuminate the work on alkanes In an alkane, all the carbon atoms have hydrogen attached to them The first is the activation of C–H bonds in ligands––usually phosphines––and the reactions are stoichiometric Evidence of the activation of C–H bonds in ligands by the transition to which the ligand is attached has come from three sources: intramolecular ring-closure reactions of phosphine ligands, hydrogen–deuterium exchange in phosphine ligands, and compounds with hydrogen in a ligand coordinated to a transition metal Evidence of interactions with compounds having hydrogen in a ligand coordinated to a transition metal is very limited Alkanes appear to react with platinum in an identical manner to benzene; chloromethane and chloroethane can be detected as the reaction products from methane and ethane, respectively
TL;DR: In this article, the normal coordinate analysis of the optical active intra- and intermolecular vibrations of the α-form crystal of glycine was carried out using a modified Urey-Bradley type intramolecular potential.
TL;DR: In this article, the authors concluded that the sandwich structure is not necessary for the intramolecular charge transfer in polar solvents, and that the mechanism of intra-olecular heteroexcimer formation in polar Solvents is different from that in non-polar SolVents.
Abstract: Solvent effects upon fluorescence quantum yields, fluorescence rise and/or decay curves of p-(CH3)2NC6H4–(CH2)n–(9-anthryl) (n=1, 2, 3) and p-(CH3)2NC6H4–(CH2)n–(1-pyrenyl) (n=1, 2, 3) have been investigated in detail It is concluded that the sandwich structure is not necessary for the intramolecular charge transfer in polar solvents and that the mechanism of intramolecular heteroexcimer formation in polar solvents is different from that in nonpolar solvents
TL;DR: In this article, the 1H nmr spectra of N-acetyl-L-proline N-methylamide were observed in various solvents [CCl4, CDCl3, CD3)2CO, (CD3) 2SO, H2O, and D2O] and the results were discussed in terms of the intra- and intermolecular hydrogen bondings.
Abstract: Concentration and temperature dependences of the 1H nmr spectra of N-acetyl-L-proline N-methylamide were observed in various solvents [CCl4, CDCl3, (CD3)2CO, (CD3)2SO, H2O, and D2O]. The fraction of the cis isomer (with respect to the bond between the acetyl carbonyl carbon and prolyl nitrogen atoms) depends greatly on the solvent used; the fraction of the cis isomer is higher in polar solvents than in nonpolar solvents. It depends also on concentration and temperature in nonpolar solvents but not in polar solvents. In nonpolar solvents the trans isomer mostly exists in the γ-turn structure with an intramolecular hydrogen bond and the cis isomer tends to form molecular aggregates by intermolecular hydrogen bonds. In polar solvents both the cis and trans isomers exist in monomeric forms which interact with solvent molecules. The pH dependences of the N-methyl proton resonances indicate that the γ-turn structure of the trans isomer is present also in aqueous solution, though its population is difficult to determine. Apparent enthalpy and entropy changes for the conversion of the trans isomer to cis isomer are evaluated for various solvents. The results are discussed in terms of the intra- and intermolecular hydrogen bondings.
TL;DR: The role of intramolecular factors in the planarity or near-planarity of the carbon-oxygen framework observed in the α-cap alpha-hydroxy carboxyl moiety of a large number of crystalline α-carboxylates has been investigated using ab initio molecular orbital theory at 4-31G level as mentioned in this paper.
Abstract: The conformational energetics of three ..cap alpha..-hydroxycarbonyl systems (glycolic acid, the glycolate anion, and glycolaldehyde) have been investigated using ab initio molecular orbital theory at the 4-31G level. The major aim of the study was to ascertain the role of intramolecular factors in the planarity or near-planarity of the carbon-oxygen framework observed in the ..cap alpha..-hydroxycarboxyl moiety of a large number of crystalline ..cap alpha..-hydroxy acids and carboxylates, irrespective of the conformation of the ..cap alpha..-hydroxy group. The calculations for the isolated species show that the equilibrium conformations correspond to internally hydrogen-bonded structures. Departures from equilibrium obtained by rotating the ..cap alpha..-hydroxyl group are calculated to cost appreciably less energy than distortions which destroy the planarity of the carbon oxygen framework, a result consistent with the data for the molecules in the crystalline state, where stronger intermolecular hydrogen bonding takes precedence over internal hydrogen bonding. The conformational energetics of the isolated species are discussed in detail, and the nature of the internal hydrogen bonding is analyzed in terms of energy and charge density criteria and by comparison with related intermolecular hydrogen-bonded systems.
TL;DR: In this paper, the intermolecular interactions which occur between the ketoxy group and benzene, and tetrachloromethane are influenced by the intramolecular interaction between the ketoxy and phenyl groups, particularly in the case of acetophenone mixtures.
TL;DR: In this paper, the total electron-nuclear Hamiltonian of a polyatomic molecule, both for nonlinear and linear molecules, has been made on the basis of the formulas for coordinate and impulse transformations from the space fixed system of reference to the molecule-fixed one.
TL;DR: The structure and configuration of an antibiotic, ikarugamycin, have been established to be 1e on the basis of chemical reactions, especially of oxidative degradation, and it is suggested that the as-hydrindacene skeleton arises biogenetically via an intramolecular Diels-Alder reaction as discussed by the authors.
Abstract: The structure and configuration of an antibiotic, ikarugamycin, have been established to be 1e on the basis of chemical reactions, especially of oxidative degradation It is suggested that the as-hydrindacene skeleton arises biogenetically via an intramolecular Diels-Alder reaction
TL;DR: The structure of 5′-oxo-3′,4,4′-triethyl-3,5-dimethyl-1′,5′-dihydro[2.2′]-dipyrromethene 1, a model for bilirubin, has been determined from three dimensional counter data as discussed by the authors.