The diffusion and calibration properties for three commercially available microdialysis membranes (polycarbonate-polyether (PC), polyacrylonitrile (PAN), and cuprophan (CUP)) were evaluated. The analytes studied had molecular weights between 94 (phenol) and 1355 (vitamin B12). For each analyte-membrane pair, an effective membrane diffusion coefficient was calculated. Effective membrane diffusion coefficients varied considerably between the microdialysis membranes. For Vitamin B12, CUP and PAN membranes gave relative recovery values of greater than 20% at 0.5 microl min(-1), while the PC membrane had a 1% recovery. When backpressure was applied. PC and PAN membranes exhibited more ultrafiltration than CUP membranes. Ultrafiltration did not affect analyte relative recovery through either PC or PAN membranes. Effective membrane diffusion coefficients were not significantly altered for some membrane-analyte combinations when exposed to 4% bovine serum albumin or 0.3% fibrinogen. These data suggest that reductions in relative recovery during long-term microdialysis sampling experiments may be due to other physiologically relevant proteins or to tissue reactions near the dialysis membrane.

Rotational transitions for four isotopomers of diethynyl sulfide, S(CCH)2, were observed by using a pulsed nozzle Fourier transform microwave spectrometer. Vibration−rotation interaction constants obtained from ab initio calculated force fields were used to convert the ground-state rotational constants to equilibrium values. The latter were used to derive structural parameters, several of which are not in good agreement with those obtained from high level ab initio calculations. The structure has planar C 2 v symmetry with the following parameters:  d(SC) = 1.708(20) Å, d(C⋮C) = 1.211(10) Å, d(CH) = 1.061(10) Å, ∠(CSC) = 100.5(5)°, ∠(SC⋮C)outside   angle = 174.4(15)°, ∠(C⋮CH)inside   angle = 177.0(25)°. The structure of bis(phenylethynyl) sulfide, S(C⋮CC6H5)2, was determined by X-ray crystallography. The unit cell contains two inequivalent molecules. The structural parameters are (average of both species; uncertainties represent 1σ) d(SC) = 1.695(4) Å, d(C⋮C) = 1.198(2) Å, d(CCphenyl) = 1.440(4) Å, ∠(CSC) = 101.4(9)°, ∠(SC⋮C) = 176.4(19)°, and ∠(C⋮CCphenyl) = 178.2(8)°. The phenyl groups are twisted out of the C−S−C plane from 20 to 85° such that each phenyl ring is oriented nearly 90° to its intramolecular mate. The structural parameters are compared with several other sulfides and with hydrocarbons containing acetylenic linkages. The nonlinearity about the acetylenic bond follows a pattern seen in other similar species, although it is more pronounced in S(CCH)2 than in hydrocarbons. These data constitute the first experimental structural studies on uncomplexed diethynyl sulfides.