The measurement of lipid phosphate is proposed as an indicator of microbial biomass in marine and estuarine sediments. This relatively simple assay can be performed on fresh, frozen or frozen-lyophilized sediment samples with chloroform methanol extraction and subsequent phosphate determination. The sedimentary lipid phosphate recovery correlates with the extractible ATP and the rate of DNA synthesis. Pulse-chase experiments show active metabolism of the sedimentary phospholipids. The recovery of added C-labeled bacterial lipids from sediments is quantitative. Replicate analyses from a single sediment sample gave a standard deviation of 11%. The lipid extract can be fractionated by relatively simple procedures and the plasmalogen, diacyl phospholipid, phosphonolipid and non-hydrolyzable phospholipid content determined. The relative fatty acid composition can be readily determined by gas-liquid chromatography.The lipid composition can be used to define the microbial community structure. For example, the absence of polyenoic fatty acids indicates minimal contamination with benthic micro-eukaryotes. Therefore the high content of plasmalogen phospholipids in these sediments suggests that the anaerobic prokaryotic Clostridia are found in the aerobic sedimentary horizon. This would require anaerobic microhabitats in the aerated zones.

We have synthesized a triamidoamine ligand ([(RNCH(2)CH(2))(3)N](3)(-)) in which R is 3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3) (hexaisopropylterphenyl or HIPT). The reaction between MoCl(4)(THF)(2) and H(3)[HIPTN(3)N] in THF followed by 3.1 equiv of LiN(SiMe(3))(2) led to formation of orange [HIPTN(3)N]MoCl. Reduction of MoCl (Mo = [HIPTN(3)N]Mo) with magnesium in THF under dinitrogen led to formation of salts that contain the ((Mo(N(2)))(-) ion. The (Mo(N(2)))(-) ion can be oxidized by zinc chloride to give Mo(N(2)) or protonated to give MoN=NH. The latter was found to decompose to yield MoH. Other relevant compounds that have been prepared include (Mo=N-NH(2))(+) (by protonation of MoN=NH), M=1;N, (Mo=NH)(+) (by protonation of M=N), and (Mo(NH(3)))(+) (by treating MoCl with ammonia). (The anion is usually (B(3,5-(CF(3))(2)C(6)H(3))(4))(-) = (BAr'(4))(-).) X-ray studies were carried out on (Mg(DME)(3))(0.5)[Mo(N(2))], MoN=NMgBr(THF)(3), Mo(N(2)), M=N, and (Mo(NH(3)))(BAr'(4)). These studies suggest that the HIPT substituent on the triamidoamine ligand creates a cavity that stabilizes a variety of complexes that might be encountered in a hypothetical Chatt-like dinitrogen reduction scheme, perhaps largely by protecting against bimolecular decomposition reactions.

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Of great si&icance in both biological and synthetic systems are two-electron processes in which a divalent atom such as oxygen is completely transferred between two reaction partners.' Until now, the endogenous three-electron atom transfer process has been limited to examples of intermetallic nitrogen atom transfer as exemplified by the reaction (TTP)Cr + N=Mn(TTP) -(TTP)CFN 4-Mn(TTP).2 In the present work we establish a three-electron redox process in which a nitrogen atom from nitrous oxide is transferred to a molybdenum(II1) coordination complex.The complex Mo(NRAr)3 (1; R = C(CD3)2CH3, Ar = 33-C6H3Me2) was prepared for this work since d3 1 could conceivably engage in three-electron redox processes. Of the various possibilities, N-atom transfer was a particularly attractive target since stable nitrido complexes of the kind N=MoX3 (X = alkyl,3 amide? or &oxide5) are known. In a typical preparation, M o C~~( T H F )~~ (4.164 "01) and Li(NRAr)(OEt2)7 (8.315 m o l ) were added to 70 mL of cold (-100 "C) ether, and the mixture was stirred for 2.5 h after warming to 28 "C. The precipitated LiCl and excess MoC13(THF)3 were removed by filtration. Analysis of the filtrate by 2H NMR spectroscopy showed only one major product, with a relatively sharp (Avll2 = 35 Hz) signal at 64.6 ppm corresponding to the 2H-labeled tert-butyl groups in paramagnetic M O ( N R A~)~.~ The filtrate was concentrated and cooled to -35 "C under an argon atmosphere to produce orange-red, crystalline Mo(NRAr)3 (mp 126-128 "C, yield 70%)? MO(NR&)3 (1) is extremely oxygen-and (1) Holm, R. H.; Donahue,