Coupling experiment

An LC-LC coupling experiment system can be performed by employing a commercially available HPLC apparatus and involving various combinations of HPLC columns, eluents, additives, switching devices and detectors. 

The successful clinical use of titanium and cobalt-chromium alloy combinations has been reported Lucas etal. also investigated this combination using electrochemical studies based on mixed potential and protection potential theories. Verification of these studies was made by direct coupling experiments. The electrochemical studies predicted coupled corrosion potentials of -0.22 V and low coupled corrosion rates of 0.02 ft A/cm. Direct coupling experiments verified these results. The cobalt-titanium interfaces on the implants were macroscopically examined and no instances of extensive corrosion were found. Overall, the in-vitro corrosion studies and the examination of retrieved prostheses predicted no exaggerated in-vivo corrosion due to the coupling of these cobalt and titanium alloys. 

Work by the US Bureau of Mines" involving galvanic couple experiments showed that the normally low corrosion rates of molybdenum were reduced further by contact with aluminium, SAE 1 430 steel or magnesium in aerated solutions of synthetic sea water or 3% sodium chloride. 

The US Bureau of Mines found the chemical and galvanic corrosion behaviour of both the TZM and Mo-30W alloy to be generally equal or superior to that of unalloyed molybdenum in many aqueous solutions of acids, bases and salts. Notable exceptions occurred in 6-1 % nitric acid where both alloys corroded appreciably faster than molybdenum. In mercuric chloride solutions the TZM alloy was susceptible to a type of crevice corrosion which was not due to differential aeration. The alloys were usually not adversely affected by contact with dissimilar metals in galvanic couple experiments, but the dissimilar metals sometimes corroded galvanically. Both alloys were resistant to synthetic sea water spray at 60°C. 

In Chapfer 7.2, J.H. Frank and R.S. Barlow describe the basic characteristics of non-premixed flames wifh an emphasis on fundamenfal phenomena relevant to predictive modeling. They show how the development of predictive models for complex combustion systems can be accelerated by combining closely coupled experiments and numerical simulations. 

In the first coupling experiments Mullen et al. used the monomer 10 as a cisitrans diastereomeric mixture. When the diastereoisomers are separated by... 

Scheme 15 Cross-coupling experiments to obtain mechanistical evidence (a) complex 67 (5 mol%), PhMgBr, THF [9]...

There are a few precautions that should be noted when doing a CDI activation and coupling experiment. First, CDI itself is extremely unstable to aqueous environments, much more so than the active imidazolyl carbamate that s formed after PEG activation. Therefore, the activation step must be done in a solvent that is free of water. If unacceptable amounts of water are present, CDI will be immediately broken down to C02 and imidazole. The evolution of bubbles upon addition of CDI to a PEG solution is the telltale sign of high water content. Only freshly obtained solvents analyzed to be extremely low in moisture or those dried over a molecular sieve should be used. A water content of less than 0.1 percent in the solvent is usually all right for a CDI activation procedure. 

Scalar coupled experiments COSY and TOCSY The correlated spectroscopy (COSY) experiment is one of the most simple 2D-NMR pulse sequences in terms of the number of RF pulses it requires [32]. The basic sequence consists of a 90-C-90-acquire. The sequence starts with an excitation pulse followed by an evolution period and then an additional 90° pulse prior to acquisition. Once the time domain data are Fourier transformed, the data appear as a diagonal in... 

The reaction is considered to proceed via a silyl anion mechanism, although the possibility of a radical-based mechanism has also been discussed.115,125 In order to clarify the mechanism, coupling experiments on a 1 1 mixture of chlorotrimethylsilane, 27 (reduction potential <—3.0 V),126 and chlorotriphenylsilane, 28 (reduction potential vs. standard calomel electrode (SCE) < —3.0 V),120 were performed, in which the mixed coupling product 1,1,1-trimethyl-2,2,2-triphenyldisilane, 29, and the homocoupling product hexaphenyldisilane, 30, only, were found,125 as indicated in Scheme 15. 

The procedure works when each detected spin B can be selectively decoupled from a spin C, although other couplings may be present. If this is the case, the spectra obtained in the coupled experiment and the reference experiment are identical except for the additional splitting due to the coupling of interest J(l>, C). This splitting can be determined by convolution ( in Fig. 7.8) of the decoupled spectrum with a stick doublet to yield the coupled spectrum. 

Tab. 6.5 Selected Heck coupling experiments with polymeric amphiphiles (experimental data are listed in Scheme 6.6, reaction time=7 h).

A positive sign has also been found for P-O-CH involving a pentaco-ordinated phosphorus (in phosphonitrilics).(1969,68) As no J(P-O-CH) values are in the vicinity of zero it is unlikely that this coupling experiences sign reversal it may be taken as positive in all cases. As a consequence, this is not so for J(P-0-C-CH), especially for the above mentioned phosphites. 

Figure 3-18 (a) Fit of an H20t profile (from low to high H20t) from a diffusion-couple experiment. The misfit at x —120 imi is attributed to the convolution effect (limited spatial resolution of the measurements), (b) The dependence of DhjO, on H20t from the fit in (a). From Zhang and Behrens (2000). 

Figure 3-28 H2O diffusion profile for a diffusion-couple experiment. Points are data, and the solid curve is fit of data by (a) error function (i.e., constant D) with 167 /irn ls, which does not fit the data well and (b) assuming D = Do(C/Cmax) with Do = 409 /im ls, which fits the data well, meaning that D ranges from 1 /rm /s at minimum H2O content (0.015 wt%) to 409 firn ls at maximum H2O content (6.2 wt%). Interface position has been adjusted to optimize the fit. Data are adapted from Behrens et al. (2004), sample DacDC3.

For the calculation of convective dissolution rate of a falling crystal in a silicate melt, the diffusion is multicomponent but is treated as effective binary diffusion of the major component. The diffusivity of the major component obtained from diffusive dissolution experiments of the same mineral in the same silicate melt is preferred. Diffusivities obtained from diffusion-couple experiments or other types of experiments may not be applicable because of both compositional effect... 

Figure 3-18 H2O profile from a diffusion-couple experiment 243...

Reports in the literature that isolate any of these processes are rare and often require unusual conditions. For example, in addition to the oxazoI-5(4//)-one studies described above, Kemp and Rebek[27l were able to use kinetic isotope effects to distinguish the enolization mechanism from oxazol-5(4//)-one formation in a simple peptide coupling experiment. a-2H-Labeled Bz-L-Leu-OH and Z-Gly-Phe-OH were prepared and coupling reactions to H-Gly-OEt were carried out. In cases where oxazol-5(4//)-one formation is rate-determining, such as with Bz- L-Leu-OH, the isotope effect kHlkD is equal to 1 because the a-proton is not removed until after this rate-determining step. In contrast, enolization requires the direct removal of the a-proton, and the isotope effect measured for this mechanism was as high as 2.9 with Z-Gly-Phe-OH. Therefore, a measurement of the isotope... 

The search for stable diaminocarbenes dates back to the early 1960s and is associated with the name of Wanziick." At that time the preparation of the 1,3-diphenyl imidazolidin-2-ylidenes (Ilia) was first examined (Scheme 8.4). Precursors of Ilia included the dimeric and electron-rich olefin IIIa 2 and the chloroform adduct 3a of the desired carbene. By means of cross-coupling experiments, however, it was shown that IIIa 2 was not in equilibrium with the two carbene units. On the other... 

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