Hydrogen sulfide evolved from an acidified sample is pre-concentrated by permeation in a stationary alkaline acceptor solution enclosed in a silicone rubber sample loop. Depending on the sample volume pre-concentrated, the applicable analytical range spans low micrograms/L to tens of mg/L for both methods. The methylene blue method is more sensitive by a factor of approximately 30 and actually permits practical determinations in the sub-micrograms/L levels. The limit of detection (LOD) for the nitroprusside method ranges from 20 micrograms/L for a 20 microL sample by conventional flow-injection determination (no membrane, throughput 30 samples/h) to less than 2 micrograms/L for 12 mL sample pre-concentrated in the membrane system (throughput 5 samples/h). The membrane is highly resistant to fouling and permits analysis of untreated wastewater samples bearing suspended solids, oil, grease, etc. without any pretreatment. No significant interference is observed with either chemistry. Although the nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential. Viable reaction mechanisms are proposed for both of these chemistries.

[reaction: see text] Receptor-mediated imaging and therapy of diseased tissue is rapidly gaining favor in the medical community. The synthesis and facile aqueous/organic coupling of a peripheral-type benzodiazepine receptor ligand to a cyclen-based fluorophore is described herein. The contrast agent QM-CTMC-PK11195, when chelated with lanthanides, produces bright luminescence and good MRI contrast and can potentially serve as an imaging and demarcation agent for certain types of cancers.

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Phenoxathiin cation radical perchlorate (PO.+ClO4(-)) added stereospecifically to cyclopentene, cyclohexene, cycloheptene, and 1,5-cyclooctadiene to give 1,2-bis(5-phenoxathiiniumyl)cycloalkane diperchlorates (4-7) in good yield. The diaxial configuration of the PO+ groups was confirmed with X-ray crystallography. Unlike additions of thianthrene cation radical perchlorate (Th.+ClO4(-)) to these cycloalkenes, no evidence for formation of monoadducts was found in the reactions of PO.+ClO4(-). This difference is discussed. Addition of Th.+ClO4(-) to five trans alkenes (2-butene, 2-pentene, 4-methyl-2-pentene, 3-octene, 5-decene) and four cis alkenes (2-pentene, 2-hexene, 2-heptene, 5-decene) gave in each case a mixture of mono- and bisadducts in which the configuration of the alkene was retained. Thus, cis alkenes gave erythro monoadducts and threo bisadducts, whereas trans alkenes gave threo monoadducts and erythro bisadducts. In these additions to alkenes, cis alkenes gave predominantly bisadducts, while trans alkenes (except for trans-2-butene) gave predominantly monoadducts. This difference is explained. 1,2-Bis(5-phenoxathiiniumyl)cycloalkanes (4-7) and 1,2-bis(5-thianthreniumyl)cycloalkanes underwent fast elimination reactions on activated alumina forming, respectively, 1-(5-phenoxathiiniumyl)cycloalkenes (8-11) and 1-(5-thianthreniumyl)cycloalkenes (12-16). Among adducts of Th.+ClO4(-) and alkenes, monoadducts underwent fast ring opening on alumina to give (5-thianthreniumyl)alkenes, while bisadducts underwent fast eliminations of H+ and thianthrene (Th) to give (5-thianthreniumyl)alkenes also. Ring opening of monoadducts was a stereospecific reaction in which the configuration of the original alkene was retained. Thus, erythro monoadducts (from cis alkenes) gave (E)-(5-thianthreniumyl)alkenes and threo monoadducts (from trans alkenes) gave (Z)-(5-thianthreniumyl)alkenes. Among bisadducts, elimination of a proton and Th occurred and was more complex, giving both (E)- and (Z)-(5-thianthreniumyl)alkenes. These results are explained. Configurations of adducts and (5-thianthreniumyl)alkenes were deduced with the aid of X-ray crystallography and (1)H and (13)C NMR spectroscopy. In the NMR spectra of (E)- and (Z)-(5-thianthreniumyl)alkenes, the alkenyl proton of Z isomers always appeared at a lower field (0.8-1.0 ppm) than that of E isomers.