Singlet fission (SF) is a process of multi-exciton generation in molecular aggregates where two independent triplet states are formed via an intermediate correlated triplet-triplet (1TT) pair state. SF has been shown to occur within a minimal dimeric unit with chromophores having monomer triplet energies that are half the allowed bright singlet state energy. Recently this idea was challenged by the first report of a cyclophane constructed from naphthalene-di-imide (NDI) units which do not satisfy the triplet energy criteria. In order to uncover electronic nature of the dynamic 1TT stabilization in such supramolecular constructs, herein we have synthesized five new NDI cyclophanes by altering the distance and angle between the NDI units. Using a combination of transient absorption spectroscopy supported by high-level electronic structure calculations, we find that SF is tolerant in these rigid dimeric structures up to distances of 4.5 Å while the rise of the 1TT-state gradually slows down from 400-fs to 4.6-ps concomitant with the decrease in the inter-chromophoric electronic coupling. Our work therefore demonstrates that the thermodynamic criteria of singlet exciton fission isn’t in the Singlet-Triplet energetics of the constitutive monomer rather in the stabilization of the multiexcitonic 1TT pair state in its minimal dimeric unit.
Bacterial endotoxin produces sepsis associated with alterations in body temperature (fever or hypothermia). The intraperitoneal administration of bacterial endotoxin, lipopolysaccharide (LPS; 50 microg/mouse) led to a decrease in colonic temperature starting 1 hr after the injection. The hypothermic effect was accompanied by a significant increase in hypothalamic leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) levels. 5-lipoxygenase inhibitor, zileuton (200 and 400 mg/kg, po) administered 30 min before LPS challenge significantly prevented hypothermia. However, non-selective cyclooxygenase inhibitor, indomethacin (10, 20 mg/kg, po) did not reverse the hypothermic response. Further, pretreatment of mice with zileuton prevented LPS-stimulated increase in hypothalamic LTB4 levels and caused a relatively small increase in PGE2 levels. Indomethacin had no effect on LTB4 levels but it reduced PGE2 levels. These results suggest a possible involvement of leukotrienes in LPS-induced hypothermia and the potential protective role of 5-lipoxygenase inhibitors in endotoxemia.
The title compound, C7H4BrNO3, was isolated as a by-product while attempting to prepare a diselenide. There is a close intramolecular Br⋯O contact [2.984 (2) Å]. The molecules form loosely associated dimers held together by weak intermolecular Br⋯O interactions with the nitro O atoms [Br⋯O = 3.179 (3) Å]. As a result of these interactions, there is also a close Br⋯Br intermolecular contact [3.8714 (6) Å]. In addition, there are weak intermolecular C—H⋯O interactions. The combination of these interactions produces sheets which propagate in the (210) and (\overline{2}10) directions perpendicular to c.
The objective of the present study was to determine the effect of a selective cyclooxygenase-2 (COX-2) inhibitor in in-vivo dextran sodium sulfate (DSS)-stimulated distal colon tissues of the rat. Longitudinal colon tissue sections from DSS-treated rats exhibited noticeable inflammation, altered contraction, increased myleoperoxidase activity, and oxidative stress. When the animals were pretreated with celecoxib, a selective COX-2 inhibitor, the flare of the colon was further worsened in terms of all the parameters studied. There was a reduction in PGE<sub>2</sub> levels on chronic administration of celecoxib in DSS-treated animals. The results of the present study suggest that COX-2 enzyme and prostaglandins derived from COX-2 might play a defensive role in protecting ulceration of the colon akin to that seen in the upper gastrointestinal tract.
The structures, energetics and hydrogen bonding pattern of 13 possible inositol isomers were investigated using<italic>ab initio</italic>calculations and the molecular tailoring approach (MTA).
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Article SULFUR BONDED UNSYMMETRICAL BOROLE COMPLEXES: SYNTHETIC, SPECTROSCOPIC AND BIOCIDAL ASPECTS was published on April 1, 1998 in the journal Main Group Metal Chemistry (volume 21, issue 4).
OPL volume 1323 Cover and Front matter - Volume 1323
Etoricoxib is one of the selective cyclooxygenase inhibitor drug which plays a significant role in the pharmacological management of arthritis and pain. The theoretical investigation of its reactivity is done using Density Functional Theory calculations. Molecular Electrostatic Potential Surface of etoricoxib and its Mulliken atomic charge distribution are used for the prediction of its electrophilic and nucleophilic sites. The detailed analysis of its frontier molecular orbitals is also done.
In the title compound, C17H11Br2N3O4, the dihedral angle between the planes of the naphthalene system and the benzene ring is 52.86 (8)°. The nitro substituent and the attached naphthalene system are almost coplanar [dihedral angle = 5.6 (4)°], probably as a consequence of an intra-molecular N-H⋯O hydrogen bond with the amine group. The nitro substituent attached to the benzene ring is disordered over two sets of sites with occupancies of 0.694 (3) and 0.306 (3). The major component deviates significantly from the ring plane [dihedral angle = 53.6 (2)°]. In the crystal, the mol-ecules are linked into a three-dimensional array by extensive π-π inter-actions involving both the naphthalene and benzene rings [range of centroid-centroid distances = 3.5295 (16)-3.9629 (18) Å] and C-H⋯O inter-actions involving the methyl-ene H atoms and the phenyl-attached nitro group.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The contrasting structure and reactivity of the mono ortho-coordinated aryl- and alkyl-selenium derivatives and 2,6-dibsubstituted aryl- and alkyl-selenium derivatives are described. The 2,6-disubstituted diaryl diselenides with Se$\ctdot$O intramole
Analysis of frontier orbitals of sildenafil has been carried using Density Functional Theory. On the basis of HOMO-LUMO energy, values of global chemical reactivity descriptors such as electronegativity, chemical hardness, softness, chemical potential, electrophilicity index have been calculated. Calculated values of dipole moment, polarizability, hyperpolarizability have also been reported for sildenafil along with its thermodynamic parameters.
