25 research outputs found
Histamine N-methyltransferase Modulates Human Bronchial Smooth Muscle Contraction
To elucidate the modulatory role of histamine-degrading enzymes in
airway constrictor responses, human bronchial strips were studied
under isometric conditions in vitro. Pretreatment of tissues with
the histamine N-methyltransferase (HMT) inhibitor SKF 91488
specifically potentiated the contractile responses to histamine,
causing a leftward displacement of the concentration response curves,
whereas the diamine oxidase inhibitor aminoguanidine had no effect.
This potentiation was attenuated by mechanical removal of the
epithelium. The HMT activity was detected in the human bronchi,
which was less in the epithelium-denuded tissues than the
epithelium-intact tissues. These results suggest that HMT localized
to the airway epithelium may play a protective role against
histamine-mediated bronchoconstriction in humans
Spin density encodes intramolecular singlet exciton fission in pentacene dimers.
The formation of two triplet excitons at the cost of one photon via singlet exciton fission in organic semiconductors can potentially enhance the photocurrent in photovoltaic devices. However, the role of spin density distribution in driving this photophysical process has been unclear until now. Here we present the significance of electronic spin density distribution in facilitating efficient intramolecular singlet exciton fission (iSEF) in π-bridged pentacene dimers. We synthetically modulate the spin density distribution in a series of pentacene dimers using phenyl-, thienyl- and selenyl- flanked diketopyrrolopyrrole (DPP) derivatives as π-bridges. Using femtosecond transient absorption spectroscopy, we find that efficient iSEF is only observed for the phenyl-derivative in ~2.4 ps while absent in the other two dimers. Electronic structure calculations reveal that phenyl-DPP bridge localizes α- and β-spin densities on distinct terminal pentacenes. Upon photoexcitation, a spin exchange mechanism enables iSEF from a singlet state which has an innate triplet pair character