Polymethylene Bridges Research Articles

Square Planar–Octahedral Equilibrium of Bismacrocyclic Ni(II)Ni(II) Complexes with a Polymethylene Bridge of Various Lengths

Abstract Bismacrocyclic Ni(II)Ni(II) complexes, i.e., 7,7′-polymethylenebis[2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene]dinickel(II) perchlorates with polymethylene bridges of 2-6-C length, exist in the equilibrium between square planar and octahedral forms in water. The equilibrium shifts toward the octahedral side as the polymethylene bridge is shortened.

Interactions and photoreactivity of 8-alkoxypsoralens with thymine. A model approach.

Abstract— To investigate the interactions and the photoreactions in solution between thymine and psoralen, model compounds have been synthesized in which a thymine molecule is linked to a psoralen ring by a polymethylene bridge. Two series of compounds have been studied and compared as models for the two major drugs 5‐MOP and 8‐MOP. We report here the results obtained in the 8‐alkoxypso‐ralen series. In water, intramolecular ring‐ring stacking interactions were evidenced using UV and 1H NMR spectroscopies. In organic solvents such as ethanol, these interactions disappear completely. The photoreactivity of the models was examined in relation to their ground state interaction properties. in water and in ethanol. Slow photolysis of the pyrone ring of psoralen occurs whatever the length of the linking chain (3 to 12 methylenes). No intramolecular thymine‐psoralen photoaddition nor psoralen photodimerization were observed. These results are discussed with regards to the behavior of the 5‐alkoxy models which lead selectively to the 3,4 psoralen‐thymine photoadduct.

ChemInform Abstract: Host‐Guest Complexation. Part 46. Cavitands as Open Molecular Vessels Form Solvates.

AbstractThe preparation of a series of cavitands possessing four (→ (V)) or three (→ (VI)) polymethylene bridges is described; most of them are synthesized by a route similar to that shown for (Va).

Electrochemical Studies on Metal–Metal Interactions in Bismacrocyclic Ni(II) Complexes

Abstract Studies on five Ni(II) complexes, i.e., 7,7′-polymethylenebis[2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene]dinickel(II) per-chlorates with polymethylene bridges of 2–6-C length, by cyclic voltammetry and differential pulse polarography, have revealed that the half-wave potentials of the [NiIINiII]/[NiIINiIII] and [NiIINiIII]/[NiIIINiIII] couples are not changed among the hexa- to tetramethylene derivatives but shifted toward the positive side in the following order: tetramethylene<trimethylene<ethylene derivative. These results are explainable in terms of the electrostatic repulsion due to these two metal ions.

ChemInform Abstract: (7)‐ and (9)(3,5)Troponophanes and the Corresponding Hydroxytropyliophanes.

AbstractThe cyclohexenones (I) containing a polymethylene bridge are converted to the cycloheptenones (II) which undergo bromination and dehydrobromination, producing the dienones (III).

Angular Distortions at Tetracoordinate Carbon Planoid Configurations in Substituted Spiro[4.4]nonanes

AbstractThe configuration of the spiro centre in polycyclic compounds containing a spiro[4.4]nonane substructure is analyzed in terms of symmetry coordinates. As revealed by X‐ray structures of such compounds, the local distortions around the quaternary C‐atom are dominated by a decrease of the ring‐bond angles at the spiro centre and a twist of one ring relative to the other. The planoid deformations given by the planarization index PC are comparatively small for spiro[4.4]nonanes, which contain either no additional bridges between the rings or only α,β′–or β,β′‐polymethylene bridges. This indicates that the local strain in the spiro C(C)4 fragments is rather small.

Polyaza Cavity-shaped Molecules. VIII. Ruthenium(II) complexes with 3,3′-annelated derivatives of 2-(2′-pyridyl)quinoline and 2-(2′-pyridyl)-1,8-naphthyridine

Mixed ligand complexes of the type Ru(bpy) 2L 2+ have been prepared where L is a 3,3′-polymethylene bridged derivative of 2-(2′-pyridyl)-quinoline or 2- (2′-pyridyl)-l,8-naphthyridine. In the electronic absorption spectra for these species the long wavelength band associated with the MLCT stare shows two components whose separation increases with increasing delocalizing ability of the ligand L. This same interpretation may be invoked to explain a shift of the first reduction wave to more positive potential. Both of these features do not vary appreciably as a function of the polymethylene bridge length.

Polyaza cavity shaped molecules. 11. Ruthenium complexes of annelated 2,2'-biquinoline and 2,2'-bi-1,8-naphthyridine

Ruthenium(II) complexes of the type RuL/sub 3/(PF/sub 6/)/sub 2/ and Ru(bpy)/sub 2/L(PF/sub 6/)/sub 2/ have been prepared, where bpy = 2,2'-bipyridine and L is a 3,3'-polymethylene-bridged derivative of 2,2'biquinoline or 2,2'-bi-1,8-naphthyridine. Effects associated with steric crowding and nonplanarity of the bridged ligands are reflected in the coordination geometry of the RuL/sub 3//sup 2 +/ complexes. These effects can be partially evaluated by consideration of NMR shielding effects and interpretation of /sup 1/H spin-spin couplings along the polymethylene bridge. The energies of the long-wavelength MLCT absorption are sensitive to the delocalizing ability of the ligand as well as the effectiveness of coordination as dictated by steric effects. Varying the dihedral angle of the 1,4-bidentate chelating moiety affects the intensity more than the energy of charge transfer to the ligands. The oxidation potentials for the tris(biquinoline) complexes are more positive than for Ru(bpy)/sub 3//sup 2 +/ while those of the tris(binaphthyridine) complexes are more negative. 22 references, 7 figures, 5 tables.

Oligothymidylates Substitubs en Position 3’ Par un Derive De L'Acridine

Abstract Oligothymidylates covalently linked at the 3′position to an acridine dye derivative via a polymethylene bridge have been synthetized by the phosphotriester method in solution.

Crystal and molecular structure of a highly hindered iron(II) porphyrin complex

The crystal structure of a carbonyl–1-methylimidazole–iron(II) porphyrin complex with one highly hindered face has been determined; the structural parameters indicate that the twelve membered polymethylene bridging chain does not induce steric deformation of the axial carbonyl ligand.

Molecular-mechanical analysis of the structure of strained organic molecules. Communication 3. Substituted bicyclo[1.1.0]butanes

1. The complex use of the MM/2 molecular mechanics method and quantum chemical calculations was proposed for the description of the structural and thermochemical characteristics of bicyclo [1.1.0]butane and its polycyclic derivatives, which have not previously been studied experimentally. 2. The structural and energetic consequences of substitution of different positions in the bicyclobutane molecule were analyzed, and the determining role of a change in the dihedral angle between the planes of the three-member rings and the degree of pyramidicalness of the inverted tetrahedral bridge carbon atoms was demonstrated. 3. A new variant of inclusion of the bicyclobutane fragment in the polycyclic backbone structure due to linkage of positions 1 and exo-2 by a polymethylene bridge was proposed, and the tetramethylene bridge formed in this six-member ring is optimum.

Spin exchange in nitroxyl biradicals of the imidazoline series with polymethylene bridges

1. Seven nitroxyl biradicals with polymethylene bridges that contain imidazoline and imidazoline oxide radical fragments were synthesized. 2. The principles of electron spin exchange in these biradicals were established by EPR spectroscopy. It was shown that, in these biradicals, direct exchange, which takes place as the radical fragments draw together in solution due to thermal motion, is realized in them. 3. The thermodynamic parameters of the conformational transitions in the biradicals were determined.

Precursors to aromatic units in coal

Previous oxidation experiments with bituminous coal have produced fluorenone, benzophenone and anthraquinone carboxylic acids. Precursors to these acids were speculated to be fluorene, diphenylmethane, anthracene and 9,10-dihydroanthracene derivatives. Oxidation experiments suggested that polymethylene bridges between aromatic units may also act as precursors to these acids.

ChemInform Abstract: INTRAMOLECULAR CYCLOADDITION OF TWO ACYL‐1,4‐BENZOQUINONE MOIETIES ON PHOTOLYSIS

AbstractDie intramolekulare Photocyclisierung der Bis‐(′hinone (V) zu den tetracyc isehen Verbindungen (VI) ist als Diels‐Alder‐Addition einer C = C‐Doppelbindung des einen Chinons an die Dienol‐Gruppierung aufzufassen, die durch Enolisierung der dem anderen Chinon benachbarten Brücken‐Keto‐Funktion entsteht.

Oligodeoxynucleotides covalently linked to intercalating dyes as base sequence-specific ligands. Influence of dye attachment site.

New molecules with high and specific affinity for nucleic acid base sequences have been synthesized. They involve an oligodeoxynucleotide covalently attached to an intercalating dye. Visible absorption spectroscopy and fluorescence have been used to investigate the binding of poly(rA) to octadeoxythymidylates substituted by a 9-aminoacridine derivative in different positions along the oligonucleotide chain. The 9-amino group of the acridine dye was linked through a polymethylene bridge to the 3'-phosphate, the 5'-phosphate, the fourth internucleotidic phosphate or to both the 3'- and 5'-phosphates. Different interactions of the acridine dye were exhibited by these different substituted oligodeoxynucleotides when they bind to poly(rA). The interaction was shown to be specific for adenine-containing polynucleotides. The stability of these complexes was compared with that of oligodeoxynucleotides substituted by an alkyl group on the 3'-phosphate. The increase in stability due to the presence of the intercalating dye has been determined from the comparison of melting temperatures. These results are discussed with respect to the strategy of synthesis of a new class of molecules with high affinity and high specificity for nucleic acid base sequences.

Intramolecular Cycloaddition of Two Acyl-1,4-benzoquinone Moieties on Photolysis

Abstract Upon irradiation a regio- and stereoselective cycloaddition occurred intramolecularly between two acyl-1,4-benzoquinone moieties connected by a polymethylene bridge. The regio- and stereoselectivities are different from those of the corresponding intermolecular cycloaddition; this was interpreted in terms of the Diels-Alder reaction between an acyl-1,4-benzoquinone moiety and a photochemically produced dienol.

Binuclear platinum complexes with polymethylene bridges: a neighbouring atom effect in oxidative addition

Binuclear platinum complexes with polymethylene bridges: a neighbouring atom effect in oxidative addition

Synthetic models related to dna-intercalating molecules a study of the ring-ring stacking interactions between 8-alkoxypsoralen and thymine.

As a contribution to the problem of the intercalation and photobinding of psoralens to DNA, model compounds were prepared in which the psoralen ring is linked to thymine by a polymethylene bridge. The ring-ring intramolecular interaction in the models was assessed by hypochromism measurement in the UV.

Sterically hindered co-ordination sites in metal complexes. Part 2. Structural characterisation of two ligand conformations in the nickel(II) complex of the ‘fly-over’ ligand 2,2′-tetramethylenedioxydi(8-N-salicylideneiminonaphthalene)

The crystal and molecular structure of the title complex has been determined at 295 K from three-dimensional X-ray diffraction data measured by counter techniques. The complex crystallises in the monoclinic space group P21/c with a= 18.631(1), b= 35.524(2), c= 9.756(1)A, β= 111.21(1)°, U= 6 019.6 A3, and Z= 8. The structure has been solved by conventional Patterson and Fourier techniques and refined by block-diagonal least squares to final residuals of R= 0.043, R′= 0.058 for 7 179 independent reflections with I/σ(I) 3.0. The trans-planar ‘capped’ structure proposed in Part 1 is confirmed (Ni–O, mean 1.820 A; Ni–N, mean 1.910 A) although it emerges that the dimensions and shape of the cavity are markedly sensitive to which of two conformations is adopted by the polymethylene bridging group. The details of the structures of the two independent molecules are discussed with respect to the potential of Schiff-base compounds of this type to serve as possible models for oxygen carriers in biological systems.

Macrocyclic enzyme model systems. Concurrent nucleophilic–electrostatic bifunctional catalysis by [20]paracyclophanes in deacylation of p-nitrophenyl carboxylates

Deacylation of p-nitrophenyl laurate (PNPL) and palmitate (PNPP) was accelerated in alkaline solution by the presence of a 10-hydroxyimino[20]paracyclophane derivative. A [20]paracyclophane which bears a quaternary ammonium group on the benzene ring and a nucleophilic hydroxyimino-group on the polymethylene bridge (2a) greatly enhanced the reaction rate due to an electrostatic effect provided by the positively charged substituent, whereas a 10-hydroxyimino[20]paracyclophane derivative bearing a carboxylate group on the benzene group (2c) enhanced the rate only slightly and the parent oxime (2b) showed the intermediate catalytic activity. The kinetics of deacylation are consistent with a reaction mechanism which involves pre-equilibrium complex formation between an ester substrate and a paracyclophane oxime, followed by pseudo-intramolecular acyl transfer from the incorporated substrate to the deprotonated hydroxyimino-group of a paracyclophane macrocycle. The paracyclophane oximes exhibited comparatively large binding constants (103–105 l mol–1) in the decreasing sequence (2b) > (2c) > (2a). The reactivity of the subsequent intracomplex acyl transfer was characterized by the nature of an electric charge on the benzene group and decreases in the sequence (2a)(2b) > (2c). The apparent second-order rate constant for acylation of (2a) with PNPL exceeds that for the reaction of chymotrypsin with p-nitrophenyl acetate. The ammonium salt (2a) is thus claimed as a novel enzyme model which exhibits both favourable hydrophobic binding ability towards an appropriate ester substrate and nucleophilic–electrostatic bifunctional catalysis giving rise to significant rate acceleration in its decomposition.