Oxygen diffusion in poly(dimethyl siloxane) using fluorescence quenching. I. Measurement technique and analysis

The transport properties of oxygen in poly(dimethyl siloxane) have been measured using the method of quenching of fluorescence. This paper discusses the uniqueness of this method and its use in measuring the diffusion coefficient of oxygen in unfilled PDMS. The results show (1) a large value for the diffusion coefficient of oxygen in pure PDMS at 25°C, D = 3.55 × 10^?5 cm²/s, (2) a low value of the acitivation energy, E_D = 4.77 kcal/mole, which was not temperature dependent in the ranges evaluated, and (3) a large value of the preexponential term, D₀ = 0.115 cm²/s. The diffusion coefficient was found to be independent of both the oxygen concentration and fluorophor concentration in the pressure and temperature ranges used in these experiments. The import of these experiments lies in their application to a unique biomedical oxygen sensor which is fast, sensitive, and does not consume oxygen.     

Acidity functions of aqueous fluorinated acid solutions by differential pulse polarography

The acidity functions of aqueous trifluoroacetic and trifluoromethanesulphonic acid mixtures, and aqueous hexafluoropropane-2, 2-diol solutions, have been determined by differential pulse polarography. The apparent shift of the half-wave potential for the ferrocene—ferricinium couple, as the solvent composition is changed, is used to indicate the change in potential of a glass electrode; acidity is measured as the H_GF acidity function. The densities of two of these solvent systems as a function of composition are also reported. Trifluoromethanesulphonic acid—water mixtures represent the strongest aqueous acid solvent system so far studied.     

The synthesis of some substituted macrocyclic ether-ester compounds

A series of macrocyclic ether-esters has been prepared by treating various glycols with adipoyl chloride and various substituted malonyl, succinyl and glutaryl chlorides. The prepared compounds include: 15-ethyl- and 15-phenyl-1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (5 and 6); 15-methyl-, 15-phenyl-, cis-cyclohexo-[o]-and benzo-[o]-1,4,7,10,13-pentaoxacycloheptadecane-14,17-dione (7–10); trans,trans-1,4,7,10,13,18,21,24,27,30-de-caoxacyclotetratriacontane-15, 32-diene-14,17,31,34-tetraone (11); 1,4,7,10,13-pentaoxacyclooctadecane-14,18-dione (12); 15,15,16,16,17,17-hexafluoro- and 16-methyl-1,4,7,10,13-pentaoxacyclooctadecane-14,18-dione (13 and 14); 1,4,7,10-tetraoxacyclohexadecane-11,16-dione (15); and 1,4,7,10,13-pentaoxacyclononadecane-14,19-dione (16).     

Development of an effective chiral auxiliary for hydroxyalkyl radicals

The development of an effective chiral auxiliary for hydroxyalkyl radicals is delineated. Both the 2-tetrahydropyranyl (THP) and tri-O-benzyl-2-deoxy-alpha-D-glucopyranosyl (GLU) auxiliaries resulted in diastereoselective radical additions to methyl acrylate at -78 degrees C (ds = 6/1 and 11/1, respectively). The developing stereochemistry at the radical center was completely under auxiliary control. Correlation experiments showed that the D-GLU auxiliary led to attack on the radical Si-face. The selectivity of these radical additions dropped-off considerably when the more reactive 2-nitropropene trap was employed. Computational studies suggested that the observed facial selectivity was due primarily to entropic factors in the transition state but that a smaller temperature-dependent enthalpic contribution was also involved. It was hypothesized that incorporation of a quaternary center at C-6 (THP numbering) would restore the facial selectivity with more reactive radical traps by restricting the orientations available to the incoming alkene. In the event, the trans-6-tert-butyltetrahydropyranyl (tBu-THP) auxiliary resulted in very good diastereoselection with 2-nitropropene (ds = 35/1 at -78 degrees C, 15/1 at 0 degrees C, and 8/1 at RT) as did the tri-O-benzyl-6,6-dimethyl-2-alpha-D-deoxyglucopyranosyl (diMe-GLU) auxiliary during additions to ethyl alpha-trifluoroacetoxyacrylate (ds = 10/1 at 0 degrees C). A protocol for recovery of the sugar-derived chiral auxiliaries was also established. This work sets the stage for the development of a novel approach to 1, 3, 5.(2n + 1) polyols based on iterative radical homologation as well as the application of these pyranosidic auxiliaries to other synthetically important reactions.     

Mass transfer of oxygen in poly(2-hydroxyethyl methacrylate)

The diffusion coefficient of oxygen in poly(2-hydroxyethyl methacrylate) has been explicitly measured using an optical technique based on fluorescence quenching. This measurement represents the first explicit determination of D in PHEMA. A diffusion coefficient of oxygen in PHEMA of 1.36 × 10^?7 cm²/s at 20°C was obtained from this measurement. This value is shown to agree well with permeability data for PHEMA, the free volume theory of diffusion, and with values of D that have been explicitly measured in other methacrylate hydrogels.     

Spectra and structure of organogermanes: Part XX. Infrared and Raman spectra of (CH3)3GeNCO and (CH3)3GeNCS

The infrared and Raman spectra of gaseous and solid (CH₃)₃ GeNCO and solid (CH₃)₃GeNCS have been recorded over the frequency range 20–4000 cm^?1 . The Raman spectra of the liquids have also been recorded. Assignments of the normal modes have been made on the bases of band types, Raman depolarization values, and characteristic frequencies. Spectral data indicate that (CH₃)₃ GeNCO is non-linear in all phases and that (CH₃)₃GeNCS has a linear or quasi-linear heavy atom skeleton in the fluid phases.     

Sesquiterpenoids—27: X-ray crystallographic analysis of istanbulin-B,A 1-oxo-eremophilenolide

The stereochemistry of istanbulin-B has been defined by X-ray crystal-structure analysis. Rings A and B are transfused, with the Me groups at C(4) and C(5) cis. The α,β-unsaturated,γ -lactone ring is essentially planar. Crystals of istanbulin-B are orthorhombic, space group P2₁2₁,2₁, with a = 6.729(2), b = 13.447(3), c = 14.721(3)Â,and Z = 4. The crystal structure was determined by direct phasing and the atomic parameters were subsequently adjusted by least-squares calculations that converged at R 38% over 1179 diffractometer |F_a| values     

Synthesis,spectroscopic studies,and x-ray crystallographic analysis of the organotin carbohydrate: 1,2∶3,4-di-O-isopropylidene-6-O-triphenylstannylmethyl-α-D-galactopyranose

The title organotin carbohydrate, C₃₁H₃₆O₆Sn, has been synthesized and its molecular structure has been determined in solution and in the solid state. NMR, infrared, mass and X-ray crystallographic techniques were used. The chiral molecules crystallize in the monoclinic space group P2₁ withZ=2. The triphenyltin and carbohydrate moieties are linked by a trans methylene-oxygen-methylene arrangement. The pyranosyl ring adopts a twist-boat conformation and the isopropylidene rings adopt different (half-chair and envelope) forms. Solution and solid-state conformations are similar as only three ¹³C shift values are greater than 2ppm; the ¹¹⁹Sn value is 12 ppm.