Return faster

Make or buy Do we have all the expertise in-house, or will outside firms and consultants give a better return, faster results, or more... 

When R—X is enantiomerically enriched exo-2-norbornyl 4-bromobenzenesulfonate (brosylate), 1 in Fig. 4.5, and SOH is aqueous ethanol, for example, solvolysis is accompanied by racemisation. However, the rate of racemisation is faster than the rate of product formation, and starting material isolated before completion of the solvolysis is partially racemised [14]. The most economical interpretation of these results (and much other evidence, see Chapter 7) is that R+ X- includes the achiral nonclassical carbenium ion (3 in Fig. 4.5), and the ion pair undergoes internal return faster than nucleophilic capture. In other words, k- > k2 in Scheme 4.4, the precise value of the ratio k- lk2 depending upon the particular solvent, and the greater this ratio, the closer the initial reversible process approaches a pre-equilibrium. 

By addition ofwater to the nanocomposite electrolyte (1 wt%) the long-term switching behavior could be improved up to 50,000 switching cycles with only small changes on the EC behavior Fig. 35-10(b), Sun, 2002, 2003,2004). The switching kinetics was also improved and the switching in behavior of the EC-devices shortened. The memory effect of the devices made with a wet composite electrolyte was slightly reduced because they return faster to their bleached state than those made with a dry electrolyte. The behavior is nevertheless still adequate for windows as only a 40% relative variation is observed after about 17 h (Sun, 2003, 2004). 

For aspartate transcarbamylase, denaturation of the catalytic trimer by 6 M GuHCl was obtained under the following conditions pH 7.2, temperature 25°C, and enzyme concentration ranging from 10-30 /ig/ml. Native fluorescence and circular dichroism return faster than enzymatic activity (Ghelis and Herve, 1978). 

If it is assumed that ionization would result in complete randomization of the 0 label in the caihoxylate ion, is a measure of the rate of ionization with ion-pair return, and is a measure of the extent of racemization associated with ionization. The fact that the rate of isotope exchange exceeds that of racemization indicates that ion-pair collapse occurs with predominant retention of configuration. When a nucleophile is added to the system (0.14 Af NaN3), k y, is found to be imchanged, but no racemization of reactant is observed. Instead, the intermediate that would return with racemization is captured by azide ion and converted to substitution product with inversion of configuration. This must mean that the intimate ion pair returns to reactant more rapidly than it is captured by azide ion, whereas the solvent-separated ion pair is captured by azide ion faster than it returns to racemic reactant. 

This process is referred to as internal return, i.e., the base returns the proton to the carbanion faster than exchange of the protonated base with other solvent molecules occurs. If internal return is important under a given set of conditions, how would the correlation between kinetics of exchange and equilibrium acidity be affected How could the occurrence of internal return be detected experimentally ... 

The ion pair mechanism initially suggested by Darwish and McLaren28 (equation 2) has received further support from related studies conducted by several other investigators38-42. For example, Fava and coworkers38 have reported that during isomerization in acetic acid, optically active benzhydryl p-toluenesulfmate loses optical activity at a rate which is about two and a half times faster than the rate of sulfone formation, thus indicating that return from an ion-pair species is occurring (equation 3). 

The FDA are allowed 90 days to review a Traditional or Abbreviated 510(k) notification, and just 30 days for a Special 510(k). With the introduction of the Medical Device User Fee and Modernization Act of2002, provision was made for the participation of third-party organisations in the review process. This represents a partial adoption of the concept of Notified Bodies, which prevails in Europe. The FDA have accredited a number of commercial organisations to conduct primary 510(k) reviews of670 types of device. The FDA must then give a final determination within 30 days of receipt of the recommendation of a third-party reviewer. Because they are commercial, third-party reviewers will seek to offer faster review times in return for their review fee. If using a third-party reviewer, the FDA user fee does not apply. The outcome of a successful 510(k) notification is a letter from the FDA clearing the device for commercial sale. 

If return occurs during the bromination of cw-stilbenes and rotation around the C-C bond is faster than collapse of the intermediates to dibromides, this process will lead to fra j-stilbene (Scheme 9). We used this test to check the possibility of return in the bromination of unsubstimted, 4-methyl, 4-trifluoromethyl-, and 4,4 -bis(trifluoromethyl)-stilbenes in DCE (ref. 24). All these olefins gave clean third-order rate constants spanning 7 powers of 10. For each cis-trans couple the cis olefin was brominated 3.5 to 5.5 times faster than the trans isomer. Reactions for products analysis were performed at initial molar ratios of Br2 to olefin of 1 to 2, so that products arose only from the cis olefin, the trans isomer being accumulated in the reaction medium. 

We have previously discussed the possibilities of racemization or inversion of the product RS of a solvolysis reaction. However, the formation of an ion pair followed by internal return can also affect the stereochemistry of the substrate molecule RX. Cases have been found where internal return racemizes an original optically active RX, an example being solvolysis in aqueous acetone of a-p-anisylethyl p-nitrobenzoate, while in other cases partial or complete retention is found, for example, solvolysis in aqueous acetone of p-chloro benzhydryl p-nitrobenzoate. the pathway RX R+X some cases where internal return involves racemization, it has been shown that such racemization is faster than solvolysis. For example, optically active p-chlorobenzhydryl chloride racemizes 30 times faster than it solvolyzes in acetic acid. ... 

A method of aspirating cells from the tumor via insertion of a small-bore needle into the lesion and aspirating. Commonly used to evaluate lymph nodes or other poorly accessible sites, it has the advantage of being faster and less invasive than other biopsy methods however, it does not preserve the architecture of the tumor and may return cells that are undergoing cell death, which negates histologic analysis. 

Surfactants are used to stabilize water-in-oil emulsions and to promote rapid return of injected fluids and a faster return of the well to hydrocarbon production. Although they are expensive, water-soluble fluorochemicals have been shown to be effective in this application (97,98). 

Returning to our discussion of benefits, we note that they fell into two principal areas the time-value of information and the improvement in laboratory productivity. As we saw, assessing the benefits from the time-value of information requires examination of the total process through which that information will be used. For example, using data such as the anticipated improvement in laboratory turn around time, the rate at which material Is produced and its value, and the current the financial losses attributable to scrap or rework, one can estimate the savings in dollars to be accrued (each hour of faulty production avoided through faster lab turnaround time yields as a gain to the firm, the revenue that otherwise would have been lost). 

---