Search results for "Intramolecular force"
showing 10 items of 599 documents
Intramolecular electron transfer between molybdenum and iron mimicking bacterial sulphite dehydrogenase
2014
Diferrocenyl/diferrocenium substituted dioxido molybdenum(VI) complexes [Fe2MoO2] 2(Fc)/[2(FC)]²⁺ mimic the catalytic active site including the redox subunits as well as the catalytic function of bacterial sulphite oxidases.
Reversible switching of the Au(111) work function by near infrared irradiation with a bistable SAM based on a radical donor–acceptor dyad
2019
We describe the modification of the work function (WF) of Au(111) upon deposition of self-assembled monolayers (SAMs) with two donor–acceptor (D–A) systems, one based on a ferrocene-polychlorotriphenylmethyl radical (Fc–PTM) dyad and another on its non-radical dyad analogue. Kelvin Probe Force Microscopy (KPFM) has been used to measure the changes in the Contact Potential Difference (CPD) between the tip and the SAM under application of a cycling sweep of direct current (DC) voltage bias. These measurements showed that both SAMs exhibit a hysteretic behaviour in their WF changes. Interestingly, the hysteresis loop of the radical SAM is notably reduced when irradiated with NIR light, which w…
Regio- and stereo-selectivity in the intramolecular quenching of the excited benzoylthiophene chromophore by tryptophan
2000
Laser flash photolysis studies on the photobehaviour of a series of bichromophoric derivatives bearing benzoylthiophene and tryptophan groups have shown that the efficiency of the intramolecular quenching process depends on both the stereochemistry of the chiral centers and the relative ketone versus tryptophan orientation. Perez Prieto, Julia, Julia.Perez@uv.es
ChemInform Abstract: Photochemical Transformations of Some Neoclerodane and Labdane Diterpene Ketones.
2010
Some neoclerodane (2–4) and labdane (5 and 6) diterpene ketones having a β- or γ-hydroxy function, an α-epoxy group, or an α-olefinic double bond have been irradiated at λ = 313 nm in dry solvents (benzene or methanol). Fruticolone (2) yielded the naturally occurring 5,6-seco-neoclerodan-6,1α-olide derivative fruticolide (1), while hispanolone (5) gave the δ-lactone 8, both transformations involving a Norrish type I photoreaction. The α,β-unsaturated ketone derivative 4 was transformed into 7 by a stereoselective intramolecular [2+2] cycloaddition reaction involving its furanic 13(16)-double bond. Finally, the α-epoxy ketone 6 was rearranged to the 10(98)abeo-labda-7,9-dione derivative 10. …
[Fe(phen)(CN)4]−: a suitable metalloligand unit to build 3d–4f heterobimetallic complexes with mixed bpym-cyano bridges (phen = 1,10-phenantroline, b…
2010
The synthesis, crystal structure and magnetic properties of a new series of mixed 3d–4f complexes with the formula [{FeIII(phen)(CN)3(μ-CN)}4Ln2III(NO3)2(H2O)6(μ-bpym)]·nH2O [Ln = Eu (1), Gd (2), Dy (3) and Ho (4); n = 8 (1, 3 and 4) and 11 (2); phen = 1,10-phenantroline; bpym = 2,2′-bipyrimidine] are discussed here. Compounds 1–4 are centrosymmetric hexanuclear species whose structure is made up of two cyano-bridged {Fe2IIILnIII} heterobimetallic moieties which are connected through a bis-bidentate bpym molecule between the two rare-earth centers. The values of the iron–lanthanide distance across the single cyano-bridge are Fe(1)⋯Eu(1) = 5.5587(8) and Fe(2)⋯Eu(1) = 5.4908(8) A (1), Fe(1)⋯G…
Synthetic transformation of hydroxymatairesinol from Norway spruce (Picea abies) to 7-hydroxysecoisolariciresinol, (+)-lariciresinol and (+)-cyclolar…
2003
We have developed a method for the transformation of hydroxymatairesinol to optically pure (+)-lariciresinol and (+)-cyclolariciresinol via the hitherto unreported lignan 7-hydroxysecoisolariciresinol. The two naturally occurring isomers of hydroxymatairesinol were reduced with LiAlH4 to a mixture of two epimers of 7-hydroxysecoisolariciresinol, which were further selectively transformed to (+)-lariciresinol and (+)-cyclolariciresinol by an acid catalysed intramolecular cyclisation reaction. The structure of the major isomer of 7-hydroxysecoisolariciresinol was confirmed by X-ray crystallography and thereby also the absolute configurations of the two isomers of hydroxymatairesinol were unam…
Intramolecular phase separation of copolymer "bottle brushes": No sharp phase transition but a tunable length scale
2006
A lattice model for a symmetrical copolymer "bottle brush" molecule, where two types (A,B) of flexible side chains are grafted with one chain end to a rigid backbone, is studied by a variant of the pruned-enriched Rosenbluth method (PERM), allowing for simultaneous growth of all side chains in the Monte Carlo sampling. Choosing repulsive binary interactions between unlike monomers and varying the solvent quality, it is found that phase separation into an $A$-rich part of the cylindrical molecule and a $B$-rich part can occur only locally. Long range order (in the direction of the backbone) does not occur, and hence the transition from the randomly mixed state of the bottle brush to the phas…
A thermal- and light-induced switchable one-dimensional rare loop-like spin crossover coordination polymer
2019
Rare loop-like isostructural one-dimensional coordination polymer (1D-CP) systems formulated as {Fe(DPIP)2(NCSe)2}n·4DMF (1) and {Fe(DPIP)2(NCSe)2}n·4DMF (2) were obtained by self-assembling FeII and pseudohalide NCX−(X = S, Se) ions in presence of the V-shaped bidentate bridging ligand, namely, N,N′-dipyridin-4-ylisophthalamide (DPIP), and were characterized by elemental analysis, IR spectroscopy, TGA, single crystal X-ray diffraction and powder X-ray diffraction. The magnetic studies show that complex 2 undergoes a complete thermally induced spin crossover (SCO) behavior centered at T1/2 = 120 K with ca. 5 K thermal hysteresis loop and light-induced excited spin state trapping effect (LIE…
Synthesis and characterization of new aromatic tweezers and complex formation with tropylium ion in 1,2-dichloroethane
2001
A series of benzene and pyridine tweezers bearing phenyl, naphthyl and anthryl receptor units was prepared and characterized. The x-ray crystal structure of the 1,3-bis(9-methanolanthracene)methylbenzene ligand (5) is reported. UV–visible and NMR spectroscopy were used to investigate the host–guest chemistry of the new ligands in complexation with tropylium tetrafluoroborate as a model aromatic cationic guest in 1,2-dichloroethane. The appearance of coloured charge-transfer absorption bands demonstrates the complex formation with a tropylium ion. The enlargement of aryl receptor size from phenyl and naphthyl to anthryl increases the stability of complexes. Electron donor–acceptor interactio…
Heterocyclic systems containing antimony (III) -VIII . Hypervalency by intramolecular 1,5-chelation Sb · · · N in rings RSb [ (CH2) 3] 2NR′ (NR′ = NM…
1998
Abstract Eleven antimony compounds RSb [ (CH2) 3] 2 NR′ and eight germanium compounds R2Ge [ (CH2) 3] 2 NR′ (some combinations of R = Cl, I, NCS, OSiPh3, Ph, and NR′ = NMe, NBz, NBui) have been synthesized by diGrignard reactions and subsequent treatment with AgSCN, Ph3SiONa or PhLi. The compounds were compared to 14 Sn, 1 As, 5 Sb and 4 Bi analogues taken from the literature. Evidence is provided for 1,5-chelation Sb · · · N via crystal structure determinations (5+1 (lit) Sb compounds) , 13C- and 29Si-NMR chemical shifts, 12;Sb and 12;I Mossbauer data (11 and 3 Sb compounds, respectively) , cyclic voltammetry (9 Sb compounds) and semi-empirical MO calculations on the Extended Huckel level …