Spin-state-dependent oxygen sensitivity of iron dithiolates: sulfur oxygenation or disulfide formation

The oxygen sensitivity of two related iron(III) dithiolate complexes of the ligand [4,7-bis-(2′-methyl-2′-mercatopropyl)-1-thia-4,7-diazacyclononane], (bmmp-TASN)FeCN (1) and (bmmp-TASN)FeCl (2), has been examined. Oxygen exposure of the low-spin complex 1 yields the disulfonate complex (bmmp-O₆-TASN)FeCN (3) as an olive-green solid with characteristic peaks in the IR spectrum at 1262, 1221, 1111, 1021, 947, 800, and 477 cm⁻¹. The corresponding nickel dithiolate, (bmmp-TASN)Ni (4), yields the related disulfonato derivative, (bmmp-O₆-TASN)Ni (5) upon addition of H₂O₂ (IR bands at 1258, 1143, 1106, 1012, 800, and 694 cm⁻¹. Oxygen exposure of the high-spin complex 2 results in disulfide formation and decomplexation of the metal with subsequent iron-oxo cluster formation. Complexes 1 and 2 were examined using density functional theory calculations. A natural bond order/natural localized molecular orbital covalency analysis reveals that the low-spin complex 1 contains Fe–S_thiolate bonds with calculated covalencies of 75 and 86%, while the high-spin complex 2 contains Fe–S_thiolate bonds with calculated covalencies of 11 and 40%. The results indicate the degree of covalency of the Fe–S bonds plays a major role in determining the reaction pathway associated with oxygen exposure of iron thiolates. The X-ray structures of 1, 4, and 5 are reported. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Loss of hyaluronate-dependent coat during myoblast fusion

Cultured myoblasts were found to exhibit extensive, Streptomyces hyaluronidase-sensitive pericellular coats as revealed by exclusion of particles (fixed red blood cells). These coats are not discernible subsequent to fusion of the myoblasts to form myotubes. The myoblasts contained 2.5 times more hyaluronate attached to their cell surface than myotubes when the data was expressed per unit of protein, but no change in hyaluronate was evident on a per DNA basis. Hyaluronidase activities in the cultures were equivalent when expressed per unit of protein. We conclude that, although the myotubes accumulate larger amounts of protein than myoblasts, there is no compensatory increase in hyaluronate.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.