Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms.

Triazatriangulenium (TATA) and trioxatriangulenium (TOTA) ions are particularly suited systems to mount functional molecules onto atomically flat surfaces such as Au(111). The TATA and TOTA units serve as platforms that absorb onto the surface and form ordered monolayers, while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA's are known to exhibit extremely fast cis→trans isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism. We now prepared norbornadienes (NBD) and quadricyclanes (QC) attached to TATA and TOTA platforms which can be used to check if these accelerated rates and the spin change mechanism also apply to [2 + 2] cycloreversions (QC→NBD).

Diazocine-functionalized TATA platforms.

Recently, it has been shown that the thermochemical cis→trans isomerization of azobenzenes is accelerated by a factor of more than 1000 by electronic coupling to a gold surface via a conjugated system with 11 bonds and a distance of 14 Å. The corresponding molecular architecture consists of a platform (triazatriangulenium (TATA)) which adsorbs on the gold surface, with an acetylene spacer standing upright, like a post in the middle of the platform and the azobenzene unit mounted on top. The rate acceleration is due to a very peculiar thermal singlet-triplet-singlet mechanism mediated by bulk gold. To investigate this mechanism further and to examine scope and limitation of the "spin-switch catalysis" we now prepared analogous diazocine systems. Diazocines, in contrast to azobenzenes, are stable in the cis-configuration. Upon irradiation with light of 405 nm the cis-configuration isomerizes to the trans-form, which slowly returns back to the stable cis-isomer. To investigate the thermal trans→cis isomerization as a function of the conjugation to the metal surface, we connected the acetylene spacer in meta (weak conjugation) and in para (strong conjugation) position. Both isomers form ordered monolayers on Au(111) surfaces.

Long-Distance Rate Acceleration by Bulk Gold.

We report on a very unusual case of surface catalysis involving azobenzenes in contact with a Au(111) surface. A rate acceleration of the cis-trans isomerization on gold up to a factor of 1300 compared to solution is observed. By using carefully designed molecular frameworks, the electronic coupling to the surface can be systematically tuned. The isomerization kinetics of molecules with very weak coupling to the metal is similar to that found in solution. For their counterparts with strong coupling, the relaxation rate is shown to depend on the spin-density distribution in the triplet states of the molecules. This suggests that an intersystem crossing is involved in the relaxation process. Aside from their impact on catalytic processes, these effects could be used to trigger reactions over long distances.

Modular Synthetic Route to Monofunctionalized Porphyrin Architectures.

The synthesis of a borylated Ni2+ porphyrin and its application as a versatile precursor for building up functional ortho-substituted tetraaryl porphyrin architectures is reported. This precursor porphyrin provides the basis for efficient modular syntheses of porphyrin compounds with covalently attached axial ligands which are important as enzyme model complexes, electron transfer dyads, and many other applications. In the present study, the precursor porphyrin was used for the synthesis of molecular spin switches which previously showed high potential as photoresponsive contrast agents for magnetic resonance imaging.

Is there a role for conventional MRI and MR diffusion-weighted imaging for distinction of skull base chordoma and chondrosarcoma?

BACKGROUND: Chordoma and chondrosarcoma are locally invasive skull base tumors with similar clinical symptoms and anatomic imaging features as reported in the literature. PURPOSE: To determine differentiation of chordoma and chondrosarcoma of the skull base with conventional magnetic resonance imaging (cMRI) and diffusion-weighted MR imaging (DWI) in comparison to histopathological diagnosis. MATERIAL AND METHODS: This retrospective study comprised 96 (chordoma, n = 64; chondrosarcoma, n = 32) patients with skull base tumors referred to the Paul Scherrer Institute (PSI) for proton therapy. cMRI signal intensities of all tumors were investigated. In addition, median apparent diffusion coefficient (ADC) values were measured in a subgroup of 19 patients (chordoma, n = 11; chondrosarcoma, n = 8). RESULTS: The majority 81.2% (26/32) of chondrosarcomas displayed an off-midline growth pattern, 18.8% (6/32) showed clival invasion, 18.8% (6/32) were located more centrally. Only 4.7% (3/64) of chordomas revealed a lateral clival origin. Using cMRI no significant differences in MR signal intensities were observed in contrast to significantly different ADC values (subgroup of 19/96 patients examined by DWI), with the highest mean value of 2017.2 × 10(-6 )mm(2)/s (SD, 139.9( )mm(2)/s) for chondrosarcoma and significantly lower value of 1263.5 × 10(-6 )mm(2)/s (SD, 100.2 × 10(-6 )mm(2)/s) for chordoma (P = 0.001/median test). CONCLUSION: An off-midline growth pattern can differentiate chondrosarcoma from chordoma on cMRI in a majority of patients. Additional DWI is a promising tool for the differentiation of these skull base tumors.

Fanconi's syndrome, acute renal failure, and tonsil ulcerations after colloidal bismuth subcitrate intoxication.

A 22-year-old woman ingested 5.4 g of colloidal bismuth subcitrate (CBS) in a suicide attempt. After ingestion, she presented with Fanconi's syndrome and acute renal failure to our unit. On the third day after ingestion, she was anuric. Ulcerations of both tonsils were observed 8 days after intoxication. Sodium-2,3-dimercapto-1-propanesulfonate (DMPS) is shown to be an effective chelating agent of heavy metal intoxications, but it has only a small effect on elimination of bismuth salts in patients with renal insufficiency without hemodialysis. In our case, we initiated hemodialysis and intravenous treatment with DMPS 60 hours after intoxication. By repeated measurements of bismuth concentrations in serum and dialyzed fluid, we showed its successful elimination. Serum bismuth level decreased from 640 microg/L to 15 microg/L within 6 days. With elimination of bismuth, renal function improved, and tonsil ulcerations healed. Hemodialysis was discontinued on day 14. Follow-up examination 6 weeks later showed normal renal function. Clinicians should be aware that acute renal failure and tonsil ulcerations can occur after CBS intoxication. Generally, acute renal failure caused by CBS intoxication is reversible. Treatment with the chelating agent DMPS in combination with hemodialysis is highly effective in reducing the serum bismuth level in patients with acute renal failure.