Electron spin resonance, magnetic circular dichroism, and optical absorption spectra of a paramagnetic Rh 2ϩ complex are investigated in Rh 3ϩ doped solution-grown NaCl single crystals. x irradiation of the crystals at 77 K followed by a warm-up to room temperature results in the formation of a stable low-spin Jahn-Teller distorted RhCl 6 4Ϫ complex possessing D 4h symmetry. The unpaired electron is largely localized in the 4d z 2 orbital of the Rh 2ϩ (4d 7 ) which is involved in a type molecular bond with two symmetrically placed Cl Ϫ ions along ͗001͘. The magnetic circular dichroism and optical absorption measurements at 1.4 K reveal two main bands around 12 200 cm Ϫ1 and 16 200 cm Ϫ1 . Within the octahedral Tanabe-Sugano formalism of the Rh 2ϩ these two absorptions are associated with two vibronically allowed 2 E g → 2 T 1g , 2 T 2g molecular transitions. This assignment is in quantitative agreement with the analysis of the g matrix components. A small MCD feature at 15 200 cm Ϫ1 is tentatively associated with two coinciding 2 E g → 2 T 1g , 2 T 2g transitions of another, probably a ligand-exchanged, Rh 2ϩ center.

Corneal blindness is the fourth leading cause of visual impairment. Of specific interest is blindness due to a dysfunctional corneal endothelium which can only be treated by transplanting healthy tissue from a deceased donor. Unfortunately, corneal supply does not meet the demand with only one donor for every 70 patients. Therefore, there is a huge interest in tissue engineering of grafts consisting of an ultra‐thin scaffold seeded with cultured endothelial cells. The present research describes the fabrication of such artificial Descemet membranes based on the combination of a biodegradable amorphous polyester (poly (d,l‐lactic acid)) and crosslinkable gelatins. Four different crosslinkable gelatin derivatives are compared in terms of processing, membrane quality, and function, as well as biological performance in the presence of corneal endothelial cells. The membranes are fabricated through multi‐step spincoating, including a sacrificial layer to allow for straightforward membrane detachment after production. As a consequence, ultrathin (<1 µm), highly transparent (>90%), semi‐permeable membranes could be obtained with high biological potential. The membranes supported the characteristic morphology and correct phenotype of corneal endothelial cells while exhibiting similar proliferation rates as the positive control. As a consequence, the proposed membranes prove to be a promising synthetic alternative to donor tissue.

Unlike the photographically important silver halides, large NaCl single crystals can be grown from solution. In such NaCl crystals, with doping comparable to practical AgCl and AgBr microcrystals, three stable Rh centers were detected and studied by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). The primary center was identified as a nonlocally compensated [RhCl6]4− complex, at variance with earlier reported EPR work. By lack of sufficient EPR and/or ENDOR evidence, the identity of the two other Rh related centers with orthorhombic and isotropic symmetry respectively, remains rather speculative.

Three different paramagnetic [RhCl6]4− complexes were detected in x-ray irradiated solution-grown NaCl single crystals: RhCl64−⋅nVac, n=2, 1, 0. These complexes all have a 4d7 ground state, with the unpaired electron spin mainly in a 4dz2 orbital and differ only by the presence of two, one, or none next-nearest cation vacancy (Vac). The RhCl64−⋅2Vac is formed at 77 K and partially converts into RhCl64−⋅1Vac at about 190 K. At room temperature the RhCl64−⋅0Vac is dominant, but traces of the RhCl64−⋅1Vac and RhCl64−⋅2Vac centers remain. A thermally induced reorientation motion of the 4dz2 molecular orbital is used to explain the temperature dependence of the RhCl64−⋅1Vac electron spin resonance spectrum.

Articles you may be interested inIdentification of electron and hole traps in lithium tetraborate ( Li 2 B 4 O 7 ) crystals: Oxygen vacancies and lithium vacancies Rh 3ϩ -doped NaCl single crystals grown from aqueous solution were studied with electron paramagnetic resonance and electron nuclear double resonance after irradiation at liquid nitrogen temperature. ͓RhCl 6 ͔ 4Ϫ complexes with two next-nearest neighbor charge compensating vacancies have been detected. The two vacancy-Rh 2ϩ axes make an angle of 90 0 to each other and are perpendicular to the center symmetry axis. After warming the sample, this center with C 2v symmetry decays consecutively into two other ͓RhCl 6 ͔ 4Ϫ centers reported earlier in Rh 3ϩ -doped NaCl and AgCl Bridgman crystals on the one hand, and/or in solution-grown NaCl:Rh 3ϩ crystals irradiated at room temperature on the other hand.