Steric and electronic control of an ultrafast isomerization.

Synthetic control of the influence of steric and electronic factors on the ultrafast (picosecond) isomerization of penta-coordinate ruthenium dithietene complexes (Ru((CF3)2C2S2)(CO)(L)2, where L = a monodentate phosphine ligand) is reported. Seven new ruthenium dithietene complexes were prepared and characterized by single crystal X-ray diffraction. The complexes are all square pyramidal and differ only in the axial vs. equatorial coordination of the carbonyl ligand. Fourier Transform Infrared (FTIR) spectroscopy was used to study the ν(CO) bandshapes of the complexes in solution, and these reveal rapid exchange between two or three isomers of each complex. Isomerization is proposed to follow a Berry psuedorotation-like mechanism where a metastable, trigonal bipyramidal (TBP) intermediate is observed spectroscopically. Electronic tuning of the phosphine ligands L = PPh3, P((p-Me)Ph)3, ((p-Cl)Ph)3, at constant cone angle is found to have little effect on the kinetics or thermodynamic stabilities of the axial, equatorial and TBP isomers of the differently substituted complexes. Steric tuning of the phosphine ligands over a range of phosphine cone angles (135 < θ < 165°) has a profound impact on the isomerization process, and in the limit of greatest steric bulk, the axial isomer is not observable. Temperature dependence of the FTIR spectra was used to obtain the relative thermodynamic stabilities of the different isomers of each of the seven ruthenium dithietene complexes. This study details how ligand steric effects can be used to direct the solution state dynamics on the picosecond time scale of discrete isomers energetically separated by <2.2 kcal mol-1. This work provides the most detailed description to date of ultrafast isomerization in the ground states of transition metal complexes

Immunolocalization of CGRP, NPY and PGP 9.5 in guinea pig skin

By means of immunoperoxidase and immune-alkaline phosphatase methods the immunoreactivities to neuropeptides: neuropeptide Y (NPY), calcitonin gene related peptide (CGRP) and a pan-neuronal marker, the protein gene product 9.5 (PGP 9.5), were evaluated in guinea pig deep dorsal skin specimens. CGRP immunoreactive (CGRP-IR) and NPY-immunoreactive (NPY-IR) nerve fibres were dispersed in the papillary dermis and sometimes inside the hair roots and among the sebaceous gland cells. Such localized nerve fibres have not so far been described. In the subcutaneous layer nerve trunks were found composed of CGRP-IR and NPY-IR nerve fibres. Some of these indicated vestigial or negative immunoreactivity to PGP 9.5