Fmoc-N-Me-Asp(OtBu)-OH

Microtiter plate-format optodes could be assembled by casting bulk-response membranes into the standard 96-well polypropylene-based plate or by screen printing them on an optically transparent substrate with 96-well pattern. The compositions of thick optode membranes, especially the ratios of poly(vinyl chloride) (PVC) to plasticizer [bis-(2-ethylhexyl) sebacate (DOS)], were carefully optimized to provide reproducible and rapid response. Adjusting the ratio of PVC to DOS by 1:6, bulk-response membranes containing neutral carrier (4-tert-butyl calix[4]arene tetraacetic acid tetraethyl ester for sodium-selective membrane or valinomycin for potassium-selective membrane) and lipophilic pH indicator (ETH 5294) could exhibit equilibrium response in 5 min. The practical utility of microtiter plate-format optodes has been examined by determining clinically relevant electrolytes in serum samples. It was demonstrated that microtiter plate-format optodes can provide high sample throughput (approximately 100 samples in less than 5 min), analytical performance comparable to that of a potentiometric clinical analyzer, and additional information on electrolytes using the same samples prepared for other colorimetric measurements.

The bond distances and bond angles of the title compound, C(23)H(25)NO(6), are consistent with values typically found for fluoren-9-ylmethoxy-carbonyl-protected amino acids. The conformations of the backbone and the side chain are slightly different from those of l-aspartic acid. The crystal structure exhibits two inter-molecular hydrogen bonds, forming a two-dimensional sheet structure parallel to the ab plane.

Phosphorescence spectra of nonphosphorescent or very weakly phosphorescent new UV absorbers, 2-methylphenyl cinnamate (MePC), 2-methylphenyl 4-methoxycinnamate (MePMC) and 2-methylphenyl 4-ethoxycinnamate (MePEC) have been observed by using external heavy atom effects of ethyl iodide in ethanol at 77 K. The lowest excited triplet (T(1)) energies of these new UV absorbers are lower than those of a widely used UV-A absorber, 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), in both keto and enol forms. The intermolecular triplet-triplet energy transfer from photolabile BM-DBM to MePMC was observed by measuring the time-resolved phosphorescence spectra. Electron paramagnetic resonance spectra have been observed for the T(1) states of these new UV absorbers in ethanol at 77 K by using benzophenone as a triplet sensitizer. The observed T(1) lifetimes, zero-field splitting (ZFS) parameters and molecular orbital calculations of the ZFS parameters suggest that T(1) states of these new UV absorbers posses mainly (3)ππ* character.

Quinol esters 2b, 2c, and 3b and sulfonamide 4c were investigated as possible precursors to 4-alkylaryloxenium ions, reactive intermediates that have not been previously detected. These compounds exhibit a variety of interesting reactions, but with one possible exception, they do not generate oxenium ions. The 4-isopropyl ester 2b predominantly undergoes ordinary acid- and base-catalyzed ester hydrolysis. The 4-tert-butyl ester 2c decomposes under both acidic and neutral conditions to generate tert-butanol and 1-acetyl-1,4-hydroquinone, 8, apparently by an SN1 mechanism. This is also a minor decomposition pathway for 2b, but the mechanism in that case is not likely to be SN1. Decomposition of 2c in the presence of N3- leads to formation of the explosive 2,3,5,6-tetraazido-1,4-benzoquinone, 14, produced by N3--induced hydrolysis of 8, followed by a series of oxidations and nucleophilic additions by N3-. No products suggestive of N3--trapping of an oxenium ion were detected.