RPA method applied to molecular crystals
A new theory is presented on the excited states of molecular crystals by using the random phase approximation (RPA). The method is applied to the analysis of the absorption spectrum of anthracene crystal. The Davydov splitting for the long axis polarized band is calculated as about 9200 cm−1 while the observed value is 9000 ∼ 12000 cm−1. In the earlier theories, much larger values are reported and a simple dipole-dipole approximation gives the value of 32000 cm−1. The general feature of the crystalline spectra is well predicted.
In order to study possible mediators of the vascular manifestations of passive cutaneous anaphylaxis (PCA), several arachidonic acid metabolites were injected into guinea-pig skin. SRS-A, LTB4, LTC and LTD increased vascular permeability, responses to LTs being enhanced by PGE2. Mepyramine inhibited responses to histamine, but not those to SRS-A and LTs: the latter were inhibited by the SRS-A antagonist FPL-55712. Both mepyramine and FPL-55712 exert limited inhibitory effects on vascular permeability during PCA. Leukotrienes may contribute towards vascular permeability during PCA.