Sulfur Lone Pairs Control Topology in Heterotrimetallic Complexes: An Experimental and Theoretical Study.

Heterotrimetallic complexes with (N2S2)M metallodithiolates, M = Ni2+, [Fe(NO)]2+, and [Co(NO)]2+, as bidentate chelating ligands to a central trans-Cr(NO)(MeCN) unit were characterized as the first members of a new class, NiCrNi, FeCrFe, CoCrCo. The complexes exhibit a cisoid structural topology, ascribed to the stereoactivity of the available lone pair(s) on the sulfur donors, resulting in a dispersed, electropositive pocket from the N/N and N/S hydrocarbon linkers wherein the Cr-NO site is housed. Computational studies explored alternative isomers (transoid and inverted cisoid) that suggest a combination of electronic and steric effects govern the geometrical selectivity. Electrostatic potential maps readily display the dominant electronegative potential from the sulfurs which force the NO to the electropositive pocket. The available S lone pairs work in synergy with the π-withdrawing ability of NO to lift Cr out of the S4 plane toward the NO and stabilize the geometry. The metallodithiolate ligands bound to Cr(NO) thus find structural consistency across the three congeners. Although the dinitrosyl [(bme-dach)Co(NO)-Mo(NO)(MeCN)-(bme-dach)Co(MeCN)][PF6]2 (CoMoCo') analogue displays chemical noninnocence and a partial Mo-Co bond toward (N2S2)Co'(NCCH3) in an "asymmetric butterfly" topology [Guerrero-Almaraz P.Inorg. Chem.2021, 60(21 (21), ), 15975-15979], the stability of the {Cr(NO)}5 unit prohibits such bond rearrangement. Magnetism and EPR studies illustrate spin coupling across the sulfur thiolate sulfur bridges.

Microscopic computed tomography-based virtual histology of embryos.

Advances in imaging technologies and computational capabilities have made possible novel methods for phenotypic assessments and visualization of detailed anatomical structures of whole embryos. We recently reported a rapid and inexpensive technique for achieving high-resolution virtual histology for phenotyping assessment of mouse embryos (Johnson et al., PLoS Genet 2:e61, 2006). By en bloc staining in a solution of electron-dense osmium tetroxide followed by volumetric X-ray computed tomography, whole embryos can be imaged at isometric resolutions as high as 2.5 µm, depending on the size of the specimen. The datasets generated by these techniques are compatible with state-of-the-art computational methods of organ pattern analysis. This method of Microscopic Computed Tomography (microCT)-based Virtual Histology of embryos allows one to rapidly and accurately phenotype transgenic embryos or to engage in developmental and reproductive toxicology studies of investigational drugs at better resolution, less time, and less expense than traditional histology, magnetic resonance microscopy, or the classical Wilson and Staples procedures.