Sigman effect

Electrical properties of tissue and cell suspensions were reviewed by Schwan (1957). Membrane capacitance and conductance for pancreatic P-cells were measured by an electrokinetic method (Pethig et al. 2005 Grimnes and Martinsen 2008). The conductivity of blood is dependent on blood velocity this is the Sigman effect (Sigman et al. 1937). 

ICG is impedance plethysmography based upon the measurement of thoracic electrical bioimpedance. It may also include a component from the resistivity dependence on blood flow (Sigman effect). If so this is not a plethysmographic but a blood velocity component. Usually a measuring frequency of 50—100 kHz has been used. A thoracic electrical bioimpedance measurement picks up both cardiac and respiration signals. The ambition is that the SV [L] and therefore CO [L/min] can be calculated with ICG, as well as the total thoracic fluid volume, for example, according to Eq. 10.1 v = GpL. ... 

Sigman et al. have optimized their system too [45]. A study of different solvents showed that the best solvent was f-BuOH instead of 1,2-dichloroethane, which increased the conversion and the ee. To ensure that the best conditions were selected, several other reaction variables were evaluated. Reducing the catalyst loading to 2.5 mol % led to a slower conversion, and varying temperature from 50 °C to 70 °C had little effect on the selectivity factor s. Overall, the optimal conditions for this oxidative kinetic resolution were 5 mol % of Pd[(-)-sparteine]Cl2, 20 mol % of (-)-sparteine, 0.25 M alcohol in f-BuOH, molecular sieves (3 A) at 65 °C under a balloon pressure of O2. 

Sigman and Jorgenson490 have found that zinc(II) catalyzes the transesterification reaction between N- (/3-hydroxy ethyl) ethylenediamine and 4-nitrophenyl picolinate. This reaction involves a reactive mixed ligand complex (152) in which the zinc(II) ion perturbs the p/fa of the hydroxyethyl group of N-(/3-hydroxyethyl)ethylenediamine to provide a high effective concentration of the nucleophile. Intramolecular nudeophlic attack then occurs at the carbonyl group of p-nitrophenyl picolinate. This system provides a somewhat unique example of intramolecular... 

Sigman and Jacobsen reported the first example of a metal-catalyzed enantioselective Strecker-type reaction using a chiral Alnl-salen complex (salen = N,N -bis(salicyhdene)-ethylenediamine dianion) [4]. A variety of N-allylimines 4 were evaluated in the reaction catalyzed by complex 5 to give products 6, which were isolated as trifluoroacetamides in good yields and moderate-to-excellent enantioselectivities (Scheme 3). Substituted arylimines 4 were the best substrates, while alkyl-substituted imines afforded products with considerably lower ee values. Jacobsen and co-workers also reported that non-metal Schiff base catalysts 8 and 9 proved to be effective in the Strecker reaction of imines 7 with hydrogen cyanide to afford trifluoroacetamides 10 after reaction with trifluoroacetic anhydride, since the free amines were not stable to chromatography (Scheme 4) [5]. 

It is possible to compare these results with those reported in the literature for supercritical C02. Hyatt ( 8) reports it values for C02 from -0.52 to -0.0 which compares very favorably with the present value of -0.55 at a reduced density of 0.43. Sigman et al. (9) used a number of solutes to determine n values for C02 at fluid densities of 0.86, 0.68, and 0.46 g/cm3 of -0.12, -0.22, and -0.45, respectively. The present values at similar densities are -0.05, -0.10, and -0.25. The source of this discrepancy is unknown, although Sigman et al. attribute the variation in n values among their various indicators to specific solute effects. 

TorteU, P., DiTuUio, G., Sigman, D., and Morel, F. (2002). CO2 effects on taxomonic composition and nutrient utilization in an Equatorial Pacific phytoplankton assemblage. Mar. Ecol. Prog. Ser. 236, 37-43. 

Fig. 6.3 Total dissolved C (DIC + DOC) versus alkalinity plots showing (a) relationships between different oceanic water bodies and the effects of net changes in dissolved CaC03 and C02 (after Broecker 1974) (b) variation in pC02 (shown by diagonal isobars in units of atmospheres) for surface water of 35%o salinity at 20 °C, and the effects of changes in dissolved CaC03 and export of organic matter (after Sigman Boyle 2000).

Zinc ion is essential for the catalytic activities of both yeast and liver alcohol dehydrogenase. Until recently, model systems have been notably unsuccessful in accounting for the participation of Zn(II) in the enzyme-catalyzed oxidoreductive interconversion of aldehyde and alcohol. The studies of Creighton and Sigman (20) and of Shinkai and Bruice (21, 22) conclusively demonstrate that Lewis (general) acid catalysis by Zn + (and other divalent metal ions) can effectively promote aldehyde reduction by the reduced 1,4-dihydropyridine moiety. 

Sigman E, Kolin A, Katz LN, Jochim K. 1937. Effect of motion on the electrical conductivity of the blood. Am J Physiol 118,708-719. 

Derossis AM, BothweU J, Sigman HH, Fried GM. The effect of practice on performance in a laparoscopic simulator. Surg Endosc 1998 12(9) 1117—20. 

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