Search results for "Effects"
showing 10 items of 2634 documents
Molybdenum(VI)-dioxo complexes with sterically bulky thiocarboxylate ligands. Reactions with aliphatic thiols and electrochemical properties
1991
Abstract Under acid conditions, the reaction of (Bu n 4 N)2[Mo VI O 2 (O 2 CC(S)Ph 2 ) 2 ] with aliphatic thiols yields the monomeric [Mo V O(O 2 CC(S)Ph 2 ) 2 ] − as unique complex product. The experimental pseudo-first order rate constant with respect to the Mo(VI) complex was found to be K =6.1 × 10 −5 s −1 . At neutral pH, however, an unstable Mo(IV) species was formed which was also electrochemically detected in a reversible Mo(V,IV) couple. [Mo V O(O 2 CC(S)Ph 2 ) 2 ] − appears to be obtained by the reaction of [Mo IV O(O 2 CC(S)Ph 2 ) 2 ] 2− with unreacted [Mo VI O 2 (O 2 CC(S)Ph 2 ) 2 ] 2− . Steric features on the ligand (gemdiphenyl groups) explain that the latter reaction does not…
O-Nitroaryldioxolanes for Protection of Pheromones. Study of the Photodelivery of Carbonyl Compounds
2001
o-Nitrophenyldioxolanes 1 to 12 have been prepared and the rate of their photocleavage determined. Steric congestion in the molecule causes a decrease of the reaction rate. The decrease in the rate is especially important in the presence of a nitro group in a second phenyl ring.
ChemInform Abstract: o-Nitroaryldioxolanes for Protection of Pheromones. Study of the Photodelivery of Carbonyl Compounds.
2010
o-Nitrophenyldioxolanes 1 to 12 have been prepared and the rate of their photocleavage determined. Steric congestion in the molecule causes a decrease of the reaction rate. The decrease in the rate...
Informational rigidity in mesitylene-based calix[4]arenes adopting a 1,3-alternate conformation
2000
Abstract Two chiral derivatives of a mesitylene-based calix[4]arene known to exist in the 1,3-alternate conformation were prepared by the attachment of homochiral residues to the four exo -hydroxy groups. Thus, the enantiotopic protons of the central scaffold became diastereotopic, leading to a doubling of their 1 H NMR signals in one example. From the temperature independence of the NMR spectrum, a lower limit of 24.2 kcal/mol could be estimated for the barrier of ring inversion. MM3 calculations confirm the 1,3-alternate conformation as the energy minimum, and estimate a barrier of 25.7 kcal/mol for the 1,3-alternate-to-1,3-alternate* interconversion process. This high barrier is due to t…
Triphenyl moieties as building blocks for obtaining molecular glasses with nonlinear optical activity
2012
The incorporation of trityl and triphenylsilyl groups into low molecular weight molecules allows the formation of stable molecular glasses. A series of materials based on the N-phenyldiethanolamine core was synthesized bearing different azobenzenes and benzylydene-1,3-indandione as active chromophores. Molecular hyperpolarizability of the synthesized compounds was calculated by a restricted Hartree–Fock method with basis 6-31G(d,p) and measured in solutions by hyper-Rayleigh scattering. Non-linear optical (NLO) activity of the thin glassy films was confirmed after a corona poling procedure. Thermal sustainability of the NLO response of up to 85 °C was achieved. Quantum chemical calculations…
Conformational properties and folding analysis of a series of seven oligoamide foldamers
2016
33 crystal structures (11 unsolvated and 22 solvates) of a series of seven oligoamide foldamers were analysed. The crystal structures revealed that despite the structural and environmental differences the series of foldamers prefer only two general conformations, a protohelical @-conformation and a sigmoidal S-conformation. Both conformations also have preferred crystal packing motifs and solvate forming tendencies. Hydrogen bonding was found to be the most decisive factor in conformational preference, but steric properties, the type of the peripheral substituents, as well as solvent and aromatic interactions were also found to have an effect on the conformational details and crystal form. …
Multipolar interactions in the D pocket of thrombin: large differences between tricyclic imide and lactam inhibitors.
2006
Two series of tricyclic inhibitors of the serine protease thrombin, imides (+/-)-1-(+/-)-8 and lactams (+/-)-9-(+/-)-13, were analysed to evaluate contributions of orthogonal multipolar interactions with the backbone C=O moiety of Asn98 to the free enthalpy of protein-ligand complexation. The lactam derivatives are much more potent and more selective inhibitors (K(i) values between 0.065 and 0.005 microM, selectivity for thrombin over trypsin between 361- and 1609-fold) than the imide compounds (Ki values between 0.057 and 23.7 microM, selectivity for thrombin over trypsin between 3- and 67-fold). The increase in potency and selectivity is explained by the favorable occupancy of the P-pocke…
Syntheses, spectroscopic and structural properties of phenoxysilyl compounds : X-ray structures, FT-IR and DFT calculations
2013
Abstract The reaction of silicon disulfide with alkylphenols yields tetraphenoxysilane, cyclodisilthiane and silanethiol. The outcome of the reaction depends on the presence of the steric hindrance in the ortho position on the reacting phenol. New products of the reaction of silicon disulfide with phenols are characterized by FT-IR, NMR, X-ray diffraction and DFT calculations. The intramolecular interactions in the compounds are mainly XH---π (X = C, S) whereas the intermolecular interactions are either very weak CH---π/CH---O contacts found in aryloxysilane or electrostatic dipole–dipole attraction in cyclodisilthiane and silanethiol. The S–H---π interactions in the obtained silanethiol ar…
Stereocontrolled synthesis of five diastereomers of trimethyl 3-aminocyclopentane-1,2,4-tricarboxylates
2013
Abstract The sterically controlled oxidative cleavage of N - protected di exo - and di endo -substituted norbornene β-amino acids/esters resulted in four trimethyl 3-aminocyclopentane-1,2,4-carboxylate diastereomers. The sodium methoxide mediated isomerization of the four diastereomers in all cases yielded the thermodynamically most stable all- trans stereoisomer as a single product.
Bulky, Dendronized Iridium Complexes and their Photoluminescence
2019
Solution-processed blue emitters are essential for low-cost organic light-emitting diodes (OLEDs) but still face challenges due to their poor color purity, low efficiency and limited operational stability. Herein, by extending the conjugation of ultraviolet-emissive, facial tris(diphenylbenzimidazolyl)iridium (Ir) (fac-(dpbic)3Ir), we introduce two new types of solution-processed emitters, i.e. triisopropylsilylethynyl(TIPSE)-substituted fac-(dpbic)3Ir (2) and fac-(dpbic)3Ir-based polyphenylene dendrimers D1 and D2. The emissions of Ir-complex 2 and the dendrimers were successfully pushed toward a pure and sky blue color, respectively, due to the dominant 3π–π* nature of their emissive exci…