Three novel dimolybdenum dimers [Mo2(DAniF)3]2(μ-OSCC6H4CSO), [Mo2(DAniF)3]2(μ-O2CC6H4CS2), and [Mo2(DAniF)3]2(μ-S2CC6H4CS2) (DAniF = N,N'-di(p-anisyl)formamidinate) have been synthesized and characterized by single-crystal X-ray diffractions. Together with the terephthalate analogue, the four compounds, denoted as [O2-O2], [OS-OS], [S2-S2], and [O2-S2], have similar molecular skeletons and Mo2···Mo2 separations (∼12 Å), but varying sulfur contents or symmetry. The singly oxidized complexes [O2-O2](+), [OS-OS](+), [S2-S2](+), and [O2-S2](+) display characteristic intervalence transition absorption bands in the near- and mid-IR regions, with differing band energy, intensity, and shape. Applying the geometrical length of the bridging group "-CC6H4C-" (5.8 Å) as the effective electron transfer distance, calculations from the Mulliken-Hush equation yield electronic coupling matrix elements (H(ab)) in the range 600-900 cm(-1). Significantly, this series presents a transition from electron localization to "almost-delocalization" as the carboxylate groups of the bridging ligand are successively thiolated. In terms of Robin-Day's scheme, [S2-S2](+) is best described as an intermediate between Class II and III, while [O2-O2](+) and [OS-OS](+) belong to Class II. It is unusual that the Class II-III transition occurs in such a weakly coupled system (H(ab) < 1000 cm(-1)). This is attributed to the d(δ)-p(π) conjugation between the Mo2 center and bridging ligand. By electrochemical and spectroscopic methods, the internal energy difference for [O2-S2](+) is determined to be 2250 ± 80 cm(-1), which controls the charge distribution of the cation radical. The experimental results and theoretical analyses illustrate that the unsymmetrical geometry leads to unbalanced electronic configurations and asymmetrical redox and optical behaviors.

Three symmetrical and one unsymmetrical dimolybdenum dimers, namely, [Mo2(DAniF)3]2(E2CC6H4CE2) (DAniF = N,N′-di(p-anisyl)formamidinate and E = O or S), are structurally and electronically closely related. The mixed-valence cation radicals display well-defined metal to ligand (ML), ligand to metal (LM), and metal to metal (MM) charge transfer absorption bands. Successive thiolations of the complexes result in steady increases of the electronic coupling between the two [Mo2] units. The electronic coupling matrix elements (H ab) calculated from the Hush model fall in the range of 600–900 cm–1, which are remarkably consistent with the results from the CNS superexchange formalism. Spectroscopic analyses suggest that the intramolecular electron transfer occurs by electron-hopping and hole-hopping in concert. The rate constants (k et) are estimated in the range of 1011–1012 s–1 for the symmetrical analogues and 107 s–1 for the unsymmetrical species. The ultrafast electron transfer in such a weakly coupled system (H ab < 1000 cm–1) is attributed to the d(δ)–p(π) conjugation between the dimetal centers and the bridge.

Abstract. To investigate the effect of trace amounts of water on plastic deformation of feldspar, we fabricated synthetic polycrystalline aggregates of pure anorthite from a glass. The glass powder was either densifted and crystallized at 1473 K and 0.1 MPa or hot isostatically pressed at 1443 K and 300 MPa confining pressure. Fourier transform infrared spectrometry indicates a water content of 0.002 -0.0035 wt % (300 -550 H per 106 Si) for specimens prepared at atmospheric pressure. Hot -isostatically pressed samples contain 0.05 wt % to 0.1 wt % (8000 -15000 H per 106 Si), depending on whether they were crystallized from glass powder predried at 1073 K for 2 -3 days or from glass powder as received. In the wet samples, < 1 vol % glass was found.

Three symmetrical dimolybdenum dimers bridged by 4,4′-biphenyldicarboxylate and the partially and fully thiolated derivatives have been synthesized and studied with respect to electronic coupling and intramolecular electron transfer. As generally denoted by [Mo 2 ]−(ph) 2 −[Mo 2 ], the complexes are differentiated by the [Mo 2 ] units but have a biphenylene spacer in common, where [Mo 2 ] = [Mo 2 (DAniF) 3 (EE′C)] with auxiliary ligands DAniF (N,N′-di(p-anisyl)formamidinate) and donor atoms E and E′ (O or S). The radical cations {[Mo 2 ]−(ph) 2 −[Mo 2 ]} + , prepared by one-electron oxidation of the corresponding neutral precursor, exhibit a characteristic intervalence (IV) charge transfer absorbance in the near-IR spectra. The electronic coupling matrix elements (H ab ) calculated from the Mulliken−Hush expression vary in the range of 245−415 cm −1 depending on the number of sulfur atoms in the [Mo 2 ] units. These parameters are also calculated by CNS superexchange formalism, in which only the electron-hopping pathway is taken into account because of the lack of ligand to metal charge transfer absorptions in the spectra. The results show remarkable alignment between the two different methods. Thus, the mixed-valence complexes are assigned to weakly coupled Class II in terms of Robin−Day's classification. Under the Marcus−Hush theoretical framework, the adiabatic electron transfer rate constants (k et ) are optically determined in the range of 10 9 − 10 11 s −1 . The fastest electron transfer is observed in the fully thiolated species. In comparison with the reported (ph) 1 series, a relatively small attenuation factor, ca. β(H ab ) 0.17, is also estimated for the tetrathiolated system.

We have recently developed a bioreactor that can apply both shear and compressive forces to engineered tissues in dynamic culture. In our system, alginate hydrogel beads with encapsulated human mesenchymal stem cells (hMSCs) were cultured under different dynamic conditions while subjected to periodic, compressive force. A customized pressure sensor was developed to track the pressure fluctuations when shear forces and compressive forces were applied. Compared to static culture, dynamic culture can maintain a higher cell population throughout the study. With the application of only shear stress, qRT-PCR and immunohistochemistry revealed that hMSCs experienced less chondrogenic differentiation than the static group. The second study showed that chondrogenic differentiation was enhanced by additional mechanical compression. After 14 days, alcian blue staining showed more extracellular matrix formed in the compression group. The upregulation of the positive chondrogenic markers such as Sox 9, aggrecan, and type II collagen were demonstrated by qPCR. Our bioreactor provides a novel approach to apply mechanical forces to engineered cartilage. Results suggest that a combination of dynamic culture with proper mechanical stimulation may promote efficient progenitor cell expansion in vitro, thereby allowing the culture of clinically relevant articular chondrocytes for the treatment of articular cartilage defects.