Dimethylsulfoxide contributions

The second factor that contributes to this variability is that in most high throughput screens the compounds are usually only tested once, at a single concentration. Consequently, differences in compound concentration and purity will have a large effect on the accuracy of the assay data. The differences in compound concentration can be due to differences in compound preparation or compound stability in dimethylsulfoxide (DMSO). The concentration of the test compound can even be varied depending on the length of time the DMSO stock solution is exposed to the atmosphere, as DMSO can take up water (69,70). 

P. Suppan, Time-resolved luminescence spectra of dipolar excited molecules in liquid and solid mixtures - dynamics of dielectric enrichment and microscopic motions, Faraday Discuss., (1988) 173-84 L. R. Martins, A. Tamashiro, D. Laria and M. S. Skaf, Solvation dynamics of coumarin 153 in dimethylsulfoxide-water mixtures Molecular dynamics simulations, J. Chem. Phys., 118 (2003) 5955-63 B. M. Luther, J. R. Kimmel and N. E. Levinger, Dynamics of polar solvation in acetonitrile-benzene binary mixtures Role of dipolar and quadrupolar contributions to solvation, J. Chem. Phys., 116 (2002) 3370-77. 

Figure 2 shows the spectral response functions (5,(r), Eq. 1) derived firom the spectra of Fig. 1. In order to adequately display data for these varied solvents, whose dynamics occur on very different time scales, we employ a logarithmic time axis. Such a representation is also useful because a number of solvents, especially the alcohols, show highly dispersive response functions. For example, one observes in methanol significant relaxation taking place over 3-4 decades in time. (Mdtiexponential fits to the methanol data yield roughly equal contributions from components with time constants of 0.2, 2, and 12 ps). Even in sinqrle, non-associated solvents such as acetonitrile, one seldom observes 5,(r) functions that decay exponentially in time. Most often, biexponential fits are required to describe the observed relaxation. This biexponential behavior does not reflect any clear separation between fast inertial dynamics and slower diffusive dynamics in most solvents. Rather, the observed spectral shift usually appears to sirrply be a continuous non-exponential process. That is not to say that ultrafast inertial relaxation does not occur in many solvents, just that there is no clear time scale separation observed. Of the 18 polar solvents observed to date, a number of them do show prominent fast components that are probably inertial in origin. For example, in the solvents water [16], formamide, acetoniuile, acetone, dimethylformamide, dimethylsulfoxide, and nitromethane [8], we find that more than half of the solvation response involves components with time constants of 00 fs.

Estimate the contributions to the van der Waals energy in dimethylsulfoxide at 25° C by considering two molecules in contact as hard spheres with diameters of 491 pm. The dipole moment of dimethyl sulfoxide is 3.96 debyes, its polarizability, 7.99 X 10 nm, and its ionization potential, 9.01 eV. 

Chloroethanol, 2-butoxyethanol, carbon tetrachloride, 1,1,2-trichloroethane, DMF and dimethylsulfoxide gave rise to mortality in guinea pigs exposed percu-taneously (Wahlberg and Roman 1979). Fatalities in man have also been reported. An important aspect is thus that percutaneous absorption contributes to the total body burden, and there are strong motives to reduce percutaneous uptake as well as inhalation of solvents. 

The library of silver-NHC compounds has been greatly expanded due to the contributions of Tacke and coworkers (13a-21) [13-17] and Roland et al. (22a-25b) [18]. Compounds 13a-21 (Figure 6.1), all bearing the acetate ligand, were evaluated for their antimicrobial efficacy against S. aureus and . coli using a qualitative Kirby-Bauer disk-diffusion method. The imidazolium salt precursors, silver acetate, and the vehicle (dimethylsulfoxide) served as controls. The results of the tests were mixed, with a number of compounds having a weak... 

Protic solvents are especially effective at solvating anions. If we use a less effective solvent such as dimethylsulfoxide (DMSO) or dimethylformamide (DMF), the contribution of desolvation should become less. Indeed, the nucleophilicity of F" and HO is enormously increased in these solvents, the ratio of the rates of their Sj 2 reactions to those of the large iodide ion being greater by several powers of ten than it is in a protic solvent such as water or methanol. 

Conductometric titration of alpha acids was in the not so distant past the most common procedure in the brewery laboratories. In this method, a suitable solution of an extracted hop or of the dissolved hop extract is titrated with a solution of lead(ll) acetate and the conductivity plot allows deduction of the results. Many contributions on the conductometry of alpha acids have appeared in the literature. The titration curve can be influenced substantially by changing the titration medium, as we found out for a number of mixed solvents (10), Current methods add either a base or dimethylsulfoxide to improve the determination of the titration endpoint. The Analysis Committee of the European Brewery Convention repeatedly organized collaborative trials to evaluate hop conductometric analysis. The efforts of a Working Group on Hop... 

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