Stefan O. Baumann

Polarization sensitive optical coherence tomography of melanin provides intrinsic contrast based on depolarization

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT. In addition to imaging based on tissue reflectivity, PS-OCT also enables depth-resolved mapping of sample polarization properties such as phase-retardation, birefringent axis orientation, Stokes vectors, and degree of polarization uniformity (DOPU). In this study, PS-OCT was used to investigate the polarization properties of melanin. In-vitro measurements in samples with varying melanin concentrations revealed polarization scrambling, i.e. depolarization of backscattered light. Polarization scrambling in the PS-OCT images was more pronounced for higher melanin concentrations and correlated with the concentration of the melanin granules in the phantoms. Moreover, in-vivo PS-OCT was performed in the retinas of normal subjects and individuals with albinism. Unlike in the normal eye, polarization scrambling in the retinal pigment epithelium (RPE) was less pronounced or even not observable in PS-OCT images of albinos. These results indicate that the depolarizing appearance of pigmented structures like, for instance, the RPE is likely to be caused by the melanin granules contained in these cells.

Unexpected metal-mediated oxidation of hydroxymethyl groups to coordinated carboxylate groups by bis-cyclometalated iridium(III) centers

Two different procedures of the ‘click’ reaction were applied to synthesize a library of 1-aryl- and 4-aryl-functionalized 1H-[1,2,3]triazoles as new ligands for phosphorescent iridium(III) complexes. For three examples, single crystal X-ray analysis was carried out and the structural properties were discussed. The reactive μ-dihydroxy-bridged iridium(III) precursor complex [(ppy)2Ir-μ-(OH)]2 (ppy = 2-phenylpyridinato) was prepared for the complexation of the herein described ligands. During these complexation studies, an unexpected metal-assisted oxidation pathway was observed for the hydroxymethyl-substituted 1-aryl-1H-[1,2,3]triazoles 2d–f leading selectively to a [carboxylate-N3,O]-coordination of the ligands to the iridium(III) centers.

Titanium alkoxo oximates, with surfactant-like properties of the oximate ligands, as precursors for porous TiO2 and mixed oxide sol–gel films

Titanium alkoxo oximates with long-chain alkyl groups were used as sol–gel precursors for simultaneous deceleration of the reaction rates of Ti(OR)4 and creation of porosity upon calcination due to surfactant-like properties. Both titania and hybrid silica–titania films with high surface areas were obtained. Extraction studies showed that only part of the employed oxime is coordinated, but both coordinated and non-coordinated oxim(at)e contribute to pore formation upon heat treatment. Sorption properties of silica–titania hybrid materials were studied by investigating temperature-programmed desorption of toluene.

2-[1-(1-Naphth-yl)-1H-1,2,3-triazol-4-yl]pyridine.

In the crystal structure of the title compound, C17H12N4, the angle between the naphthalene and 1H-1,2,3-triazole ring systems is 71.02 (4)° and that between the pyridine and triazole rings is 8.30 (9)°.

Cleavage of an Iron-Silicon Bond by Hexamethylphosphoric Triamide: Synthesis and Characterization of [SiCl3(HMPA)3]+[Fe(CO)4SiCl3]–

Addition of excess hexamethylphosphoric triamide (HMPA) to cis-Fe(CO)4(SiCl3)2 led to the exclusive formation of the new complex [SiCl3(HMPA)3]+ [Fe(CO)4SiCl3]− by cleavage of an ironsilicon bond. A reaction mechanism is presented, based on density functional theory calculations Graphical Abstract Cleavage of an Iron-Silicon Bond by Hexamethylphosphoric Triamide: Synthesis and Characterization of [SiCl3(HMPA)3]+[Fe(CO)4SiCl3]–

K2[O(HgSO3)3], a new sulfitomercurate with an [OHg3] core.

The structure of dipotassium mu(3)-oxido-tris[sulfitomercurate(II)], K(2)[O(HgSO(3))(3)], is characterized by segregation of the K(+) cations and complex [O(HgSO(3))(3)](2-) anions into layers parallel to (010). The anion has m symmetry and is a new example of a mu(3)-oxido-trimercurate complex with a central [OHg(3)] core. This unit adopts the shape of a flat, almost trigonal, pyramid (mean O-Hg = 2.072 A and mean Hg-O-Hg = 110.8 degrees). The two independent Hg-S bonds have nearly the same length (mean Hg-S = 2.335 A). Due to intermolecular O...Hg donor-acceptor interactions greater than 2.65 A, the O-Hg-S fragments are slightly bent. The [KO(9)] coordination polyhedron of the K(+) cation approaches a distorted tricapped trigonal prism with a [6+1+2] coordination.

K2[Hg(SO3)2]·2.25H2O

The characteristic feature of the structure of the title compound, dipotassium bis(sulfito-κS)mercurate(II) 2.25-hydrate, is a layered arrangement parallel to (001) where each of the two independent [Hg(SO(3))(2)](2-) anions are grouped into centrosymmetric pairs and are surrounded by two K(+) cations to give the overall layer composition {K(2)[Hg(SO(3))(2)](2)}(2-). The remaining cations and the uncoordinated water molecules are situated between these layers. Within the [Hg(SO(3))(2)](2-) anions, the central Hg atoms are twofold coordinated by S atoms, with a mean Hg-S bond length of 2.384 (2) Å. The anions are slightly bent [174.26 (3) and 176.99 (3)°] due to intermolecular O...Hg interactions greater than 2.8 Å. All coordination polyhedra around the K(+) cations are considerably distorted, with coordination numbers ranging from six to nine. Although the H atoms of the five water molecules (one with symmetry 2) could not be located, O...O separations between 2.80 and 2.95 Å suggest a system of medium to weak O-H...O hydrogen bonds which help to consolidate the structural set-up. Differences and similarities between the bis(sulfito-κS)mercurate(II) anions in the title compound and those in the related salts (NH(4))(2)[Hg(SO(3))(2)] and Na(2)[Hg(SO(3))(2)]·H(2)O are discussed.