Intramolecular Stabilization Research Articles

Electrochemical solution and solid-state investigations on conjugated oligomers and polymers of the α-thiophene and the p-phenylene series

A study of the solution and solid-state electrochemical properties of defined oligomers of the α-thiophene and the p-phenylene series with chain lengths 2 ⩽ N ⩽ 16 is presented. Upon p-doping of the oligomers in the solid state their solid-state polymerization on the electrode was observed. The investigations clearly demonstrate that the important steps of the electropolymerization of conducting polymers take place exclusively in the solid state on the electrode. The degree of polymerization strongly depends on the anodic electrode potential. At low potentials polymers with long, ideally-linked chains are formed, whereas at high potentials strongly cross-linked polymers are generated. A new charge storage mechanism for conjugated oligomers and polymers is presented taking into account the morphology of the materials. We propose a two-step mechanism to explain hysteresis effects observed in voltammograms for charging processes on these materials. In the first stage of the charging process we assume that the originally twisted segments become more planar, enabling a better delocalization of charges along the chain (intramolecular stabilization). This is the prerequisite for the second step, an intermolecular stabilization through interactions between neighbouring charged segments, leading to the delocalization of the excess charges over several segments and, therefore, to further stabilization of the system.

Intramolekular stabilisierte Übergangsmetallamide: 2‐(Dimethylaminomethyl)pyrrolyl‐Komplexe des Titan(III), Vanadium(III), Chrom(III), Cobalt(II) und Nickel(II)

Intramolecularly Stabilized Metal Amides: 2‐(Dimethylaminomethyl)pyrrolyl Complexes of Titanium(III), Vanadium(III), Chromium(III), Cobalt(II) and Nickel(II)By the metallation of 2‐(dimethylaminomethyl)pyrrol (HL) with butyllithium the lithium pyrrolide LiL (1) was obtained. The reactions of 1 with TiBr3 · 3 THF, VBr3 · 3 THF, CrBr3 · 3 THF, CoBr2 · 2 THF, and NiBr2 · 1.67 THF result in the formation of the 2‐(dimethylaminomethyl)pyrrolyl complexes of type ML3 (2–4), and ML2 (5, 6), respectively. The structures of these new compounds are discussed on the basis of magnetic and visible absorption measurements. An X‐ray crystal structure determination of 4 reveals a strongly distorted octahedral environment of the chromium atom with facial arrangement of the ligands.

Effect of Third Strand Orientation on Oligonucleotide Intramolecular Triplex Stability

Effect of Third Strand Orientation on Oligonucleotide Intramolecular Triplex Stability

Reaction of AgOCN with NO, NO2, ClNO2, ClNO, and BrNO: Evidence of the Formation of OCN−NO2and OCN−NO

Reactions of silver cyanate with binary nitrogen oxides, NO and NO2, and ternary nitrogen oxohalides, ClNO2, ClNO, and BrNO, were studied by means of gas phase IR spectroscopy. The experimental data for the neat reactions of AgOCN with NO2 and AgOCN with ClNO2 are compatible with the formation of an intermediate, short-lived OCN−NO2 molecule, which undergoes cleavage−rearrangement to give N2O and CO2. In contrast, NO does not react with AgOCN. The reaction of XNO (X = Cl, Br) and AgOCN is much more complex, leading to a mixture of NO, NO2, N2O, CO2, NCNCO, and X(CO)NCO. A reaction mechanism that involves the formation of neutral nitrosyl isocyanate, OCN−NO, has been proposed as the initial step. The two neutral intermediates, OCN−NO2 and OCN−NO, were computed by ab initio methods at the correlated MP2 level of theory and are discussed in terms of intramolecular stabilization by donor−acceptor interaction (negative hyperconjugation).

Nitration of hydrogen cyanide with nitryl tetrafluoroborate

The reaction of hydrogen cyanide at 0 °C in CFCl3, purified nitrile-free nitromethane or tetrahydrothiophene 1,1-dioxide gave dinitrogen monoxide, N2O and COn(n= 1 or 2). The same products were obtained in a solvent-free neat reaction of HCN(g) and NO2+BF4–(s). The experimental data are in accord with the intermediate formation of neutral CN–NO2. This intermediate then undergoes cleavage–rearrangement to give N2O and CO. In a subsequent reaction carbon monoxide is oxidized by unreacted NO2+BF4– to give CO2 and the corresponding nitrosyl salt, NO+BF4–. The reaction was followed by low-temperature 14N NMR spectroscopy and the identity of the products established by 14N NMR and IR spectroscopy. The two isomers CN–NO2 and NC–NO2 were computed ab initio at the correlated MP2 level of theory and are discussed in terms of intramolecular stabilization by donor–acceptor interaction (negative hyperconjugation).

A Strained Aminoazoniatricyclene Species: Result of an Intramolecular Stabilization of a Cyclopropaniminium Ion by an Amino Moiety

Ab initio calculations of the cationic intermediates of a cyclopropane-forming process of 1,4-diamino-6-chlorocyclohexene precursors predict the 3α-aminobicyclohexane-6-iminium ion 6c to be more stable than its 3β-isomer 7c. The latter, however, stabilizes itself by intramolecular cyclization leading to aminoazoniatricyclene species 9c. The aminocyclohexenyl cation 8c proved to have no minimum on both the MP2 and the MP4(SDTQ) potential energy surfaces. Optimization of species 8c causes a ring closure reaction to give iminium analogues 6c or 7c. The potential energy curve of this transformation 6c → 8c → 7c was calculated. Experimentally, solvolysis of chloro enamine isomers 4a and 5a was studied as a simple access to these cationic intermediates: 3α-amino 6-iminium ion 6a leading to 3α-amino 6-semiaminal 12 is generated exclusively from trans chloro enamine 4a and as main intermediate (67%) from cis chloro enamine 5a. In the latter case, aminoazonia compound 9a is formed as a byproduct (33%) which decomposes in water to give 3β-amino 6-semiaminal 13 via 3β-amino 6-iminium ion 7a. Aminoazoniatricyclene species 9a is obtained as stable tetrafluoroborate in acetonitrile or dichloromethane by reaction of chloro enamine isomers 4a or 5a with AgBF4-. 1H and 13C NMR spectral and X-ray structural data are given for this strained tricyclic system 9a.

A 3D-QSAR study of anticoccidial triazines using molecular shape analysis.

A set of 54 anticoccidial triazine analogs were analyzed in terms of molecular shape analysis, MSA, with the goal of constructing a three-dimensional quantitative structure-activity relationship (3D-QSAR). This same dataset was previously investigated using alternate QSAR methods including comparative molecular field analysis (CoMFA). A complete 3D-QSAR was realized using MSA which included (a) identification of the active conformation of each individual analog, (b) the relative intramolecular stability of each analog in its active conformation, (c) general intramolecular stability requirements for activity, (d) a statistically significant correlation equation, and (e) mapping of the receptor space explored by the analogs. The MSA-3D-QSAR indicates that the steric shape and dipole moment of each analog governs its activity. The MSA-3D-QSAR correlation equations are more predictive than other QSARs as measured by cross-validation correlation coefficients.

Syntheses and Structures of Intramolecularly Stabilized Organoaluminium Compounds

AbstractThe reaction of LiAr (Ar = 2‐[(dimethylamino)methyl]phenyl) with AlCl3, MeAlCl2, and Me2AlCl in a 1:1 ratio yields the corresponding organoaluminium compounds ArAlCl2, ArAl(Cl)Me, and ArAlMe2 (1–3). The alanes Ar2AlCl and Ar2AlMe (4 and 5) were synthesized from AlCl3 and MeAlCl2 with two equivalents of LiAr. The products ArAl(Cl)R [R = tBu, C(SiMe3)3] 6 and 7 are formed by the reaction of LiR with 1. The Lewis acid 1 adds the bases iPrNH2 and THF to yield the adducts 1 · iPrNH2 and 1 · THF. The structures of the products were deduced from the 1H‐, 13C‐, and 27Al‐NMR spectra and were confirmed by X‐ray structural determinations of 5 and 1 · iPrNH2.

Cyclische amine als intramolekulare hilfsliganden in π-komplexen des titans

New monocyclopentadienyl complexes of titanium(IV) with linked pyrrolidine( N) and piperidine( N) functions as σ-donating pendant groups were synthesized from their silylated cyclopentadiene precursor compounds and TiCl 4. The first single-crystal X-ray structure of a titanium complex with an intramolecular nitrogen donor stabilization is reported.

ChemInform Abstract: Synthesis and Rearrangement of Intramolecularly Stabilized 1σ2,3. sigma.2‐Diphosphaallylic Cations into Intramolecularly Stabilized 1. sigma.1,3σ3‐Diphosphaallylic Cations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Formation of Intramolecularly Stabilized Diazaphosphorinane Derivatives with the Trimethylethylenediamine and the Tetramethylguanidine Group as Substituents at Phosphorus: Investigation of Intramolecular Me2N → P Interactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Three-dimensional molecular shape analysis-quantitative structure-activity relationship of a series of cholecystokinin-A receptor antagonists.

The three-dimensional molecular shape analysis-quantitative structure-activity relationship (3D-MSA-QSAR) technique has been applied to develop correlations between the calculated physicochemical properties and the in vitro activities of a series of 3-(acylamino)-5-phenyl-2H-1,4-benzodiazepine cholecystokinin-A (CCK-A) antagonists. 3D-MSA-QSARs were developed for varying subsets of 53 analogs (J. Med. Chem. 1988, 31, 2235-2246). An active conformation is hypothesized for these compounds using the loss in biological activity-loss in conformational stability principle. After placing all compounds in the active conformation and performing pairwise molecular shape analysis, it was determined that not any one analog serves as the best shape reference compound. Nonidentical volumes of allowed receptor space are mapped out by different antagonists. A shape reference compound that consists of selected overlapped structures expands the definition of the accessible receptor space. This type of mutant improves the predicted activity of analogs over the value predicted if only one compound is chosen as the reference. Molecular shape, as represented by common overlap steric volume and nonoverlap steric volume, is the major factor contributing to the affinity of this class of compounds. Intramolecular conformational stability, as measured by the difference in energy of the active conformation and the global minimum energy conformation, is also important. It is further concluded from the 3D-MSA-QSAR models that part of the binding pocket for the 3-amido substituent has a preference for lipophilicity. The method used in this study of fragmenting the antagonist into spheres of varying radii and measuring lipophilicity isolates the substructure with highest probability of interacting with the receptor. Two indicator variables marking the presence of an N-methyl group and an o-fluoro atom on the 5'-phenyl substituent of the benzodiazepine ring structure also contribute significantly to the 3D-MSA-QSAR models. The 3D-MSA-QSAR results have led to the proposal of a 3D pharmacophore model for the benzodiazepine CCK-A antagonists.

Synthesis and Rearrangement of Intramolecularly Stabilized 1.sigma.2,3.sigma.2-Diphosphaallylic Cations into Intramolecularly Stabilized 1.sigma.1,3.sigma.3-Diphosphaallylic Cations

Synthesis and Rearrangement of Intramolecularly Stabilized 1.sigma.2,3.sigma.2-Diphosphaallylic Cations into Intramolecularly Stabilized 1.sigma.1,3.sigma.3-Diphosphaallylic Cations

The role of cysteine residues in glucose-transporter-GLUT1-mediated transport and transport inhibition.

The role of cysteine residues in transport function of the glucose transporter GLUT1 was investigated by a mutagenesis-expression strategy. Each of the six cysteine residues was individually replaced by site-directed mutagenesis. Expression of the heterologous wild-type or mutant glucose transporters and transport measurements at two hexose concentrations (50 microM and 5 mM) were undertaken in Xenopus oocytes. The catalytic activity of GLUT1 was retained, despite substitution of each single cysteine residue, which indicated that no individual residue is essential for hexose transport. This finding questions the involvement of oligomerization or intramolecular stabilization by a single disulphide bond as a prerequisite for transporter activation under basal conditions. Application of the impermeant mercurial thiol-group-reactive reagent p-chloromercuribenzenesulphonate (pCMBS) to the external or internal surface of plasma membrane demonstrated that cysteine-429, within the sixth external loop, and cysteine-207, at the beginning of the large intracellular loop which connects transmembrane segments 6 and 7, are the residues which are involved in transport inhibition by impermeant thiol-group-reactive reagents from either side of the cell. These data support the predicted membrane topology of the transport protein by transport measurements. If residues other than the cysteines at positions 429 or 207 are exposed to either side of the plasma membrane by conformational changes, they do not contribute to the transport inhibition by pCMBS. Application of pCMBS to one side of the plasma membrane also inhibited transport from the opposite direction, most likely due to the hindrance of sugar-induced interconversion of transporter conformation.

Chemical and photochemical approaches to amino(aryl)silylenes

Generation by two different methods of silylenes stabilized by o-amino(aryl) groups is reported. The halodemetallation of difluoro or dichloro-silanes with Li metal or lithium-naphthalene gave the same product, a stabilized sila-ylide (hypercoordinated silylene). Intramolecular Lewis base stabilization is not sufficient to isolate a monomeric species. The silylenes, however, have been trapped with 2,3-dimethylbutadiene. An unexpected intramolecular rearrangement to silaacenaphthene has been observed in the case of a six-membered ring amino(aryl) coordinated silylene. Photolysis of o-1-[( N, N-dimethylamino)inethyl]-2-[tris(trimethylsilyl)silyl]benzene produced, among other products, Me 3SiSiMe 3 and the sila-ylide, which has been trapped with Et 3SiH and dimethylbutadiene. Our mechanistic interpretation is supported by spectral observation of the photochemically generated reaction intermediates in a 3-methylpentane glass at low temperature.

Direct Polynitroaliphatic Alcohol Addition to Alkenes. 3. Synthesis, Structure and Intramolecular Electron Impact Stability of the Uniquely Structured 2,4-Dimethyl-7,7-dinitro-1,3,5-trioxacyclooctane

Mercury(I) sulfate catalyzed addition between the difunctional 2,2-dinitropropane-1,3-diol (ADIOL) and the divinyl ether (DVE) diene reactants produces either an apparent acyclic acetal oligomer, or the unexpected eight-membered 2,4-dimethyl-7,7-dinitro-1,3,5-trioxacyclooctane. Proton nmr and deuterium labeling of this heterocyclic compound reveals it is comprised of both meso and dl diastereomers caused from its two chiral carbon atoms. Because this heterocycle incorporates both gem-2,2-dinitroalkyl and cyclic trioxane acetal structural fragments into one hybrid saturated ring structure, a novel intramolecular electron impact stability comparison can be made between the structural features representative of the normally unrelated geminal polynitroalkane and cyclic polyoxane compound classes which determine the fragmentation pathway of the subject heterocycle

Group 2 element and related compounds as chemical vapour deposition precursors for high‐temperature superconducting metal oxides

AbstractThe advent of high‐temperature superconducting metal oxides (SMOs) has prompted an increasing number of studies aimed at the development of new routes to their syntheses, in particular in the form of thin films. The preferred method in this regard has been that of chemical vapour deposition (CVD); however, significant difficulties have been associated with the efficacy of commercial precursors for the group 2 metals, in particular those of the bis(β‐diketonates) of barium, whose co‐ordinative unsaturation leads to cluster formation. The development of alternative β‐diketonate precursor systems has focused upon the synthesis of stable Lewis acid‐base complexes by either inter‐ or intramolecular stabilisation. The results of these studies are described herein, along with a review of the research to date on non‐β‐diketonate derivatives of the group 2 metals, including organometallic, halide, amide, carboxylate and alkoxide compounds. On the basis of the results to date, a series of goals for the synthesis of the ideal precursor are discussed.

Intramolecular Base Stabilization of Silicenium Ions: A New Route to Siliconium Ions

The silicon atom is pentacoordinate in cations of salts like 1, which can be prepared, for instance, in a redox reaction of the corresponding silane (with I2, X = I) or transformation with electrophiles like PhCoCl (X = Cl) or Ph3C+BF (X= BF4). These compounds were completely characterized; conductivity titrations confirm that they are ionic.

NMR spectroscopy and conformational analysis of 3-deoxy-3- C-(hydroxymethyl)-1,2:5,6-di- O-isopropylidene-α- d-allofuranose

Homonuclear and heteronuclear 1- and 2-dimensional NMR techniques have been used to establish stereochemical and conformational relationships in the hydroxymethyl furanoside 2. Concurrent with the NMR studies, theoretical calculations were performed on this compound using computer-assisted model building (MacroModel) and molecular mechanics (MM2). From the NOE and J-coupling constraints obtained from NMR experiments, refined structures for this compound in two different solvents have been identified and optimized. The “solvent effects” observed in the NMR spectra for 2 are interpreted in terms of the differences in the requirements for intramolecular electrostatic stabilization in the two solvents.

ChemInform Abstract: Homoleptic Intramolecularly Stabilized Organoindium Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.