Solvent deuteration

Another way of perturbing the commitments is solvent deuteration. Change of the carbon kinetic isotope effect in the case of E. coli enzyme indicates that the proton transfer precedes the decarboxylation step ... 

Recently, a series of derivative ligands, [L19]4-—[L23]4-, has been reported (32,62), where the acetophenone chromophore in [L18]4- is replaced by a dipyrazolylpyridine chromophore. These form lanthanide complexes that are stable in aqueous solution, and which possess very promising photophysical attributes. The europium and terbium complexes of all these ligands have long lifetimes (1.3-1.4 ms for europium and 2.3-2.8 ms for terbium) in water that are largely unchanged by solvent deuteration, indicating the effective exclusion of solvent from the primary coordination sphere. 

The use of a C-enriched building block anchored to a resin makes the gel-phase spectrum selective for the appearance of the new C signal, and the enrichment allows much shorter acquisition times (133, 134) a real-time kinetic was reported for the alkylation of amines with C-enriched bromoacetic acid (135). An example from our laboratories (136) shows the formation of a cyanohydrin on SP is monitored by C-enriched gel-phase NMR using C-benzaldehyde. The appearance of the cyanohydrin signal (63.2 ppm) and its increase at different reaction times is easily monitored by comparison with the constant signals of the solvent (deuterated benzene, 133-126 ppm. Fig. 1.19, spectra A-D). A major drawback of this technique is the cost and the limited availability of C-enriched building blocks, which currently severely limits its application. 

Euan, C.H. Urry, D.W. Solvent deuteration enhancement of hydrophobicity—DSC study of the inverse temperature transition of elastin-based polypeptides. Journal of Physical Chemistry 1991, 90, 7896-7900. 

Our present knowledge of the helix-coil transition in synthetic polypeptides, with particular reference to the poly-y-benzyl-h-glutamate-dichloroacetic acid-1,2-dichloroethane system, is briefly reviewed. Recent results concerning the effect of solvent composition and of polypeptide and solvent deuteration on the thermodynamic properties of the transition show that both the thermodynamics and presumably the molecular mechanism of the transition are generally more complicated than had been previously supposed. 

In DEE/MgBrr, THE. and THF/MgCU. solvent deuteration gives a 12- Wi increase in (CpMgBr). If s is a solution reaction, this disproves the A models (AAD and ADD) delinitively. 

Data for THE show otherwise [20[. Solvent deuteration increases the yield of RMgBr by 15%. decreases its enantiomeric excess, decreases the yield of RH(D), and increases its enantiomeric excess. These effects rcllect a deuterium isotope effect that diverts R- from s to r. The increase in (RMgBr) indicates that I5% of RBr gives R-that are diverted in this manner. The discrepancy between this value and the lower (RH), 5-6%. found in THF is probably due lo quantitative uncertainties in the analyses. 

As in the CpBr case (above in Section 7.2.9I. dculerating DEE has a different result, il has no measurable effect on (RMgBr) or (RH). consisteiu with the proposition that there is no effect on the product distribution at all I20). This is probably an illusion. If no products other than RMgBr and RH had been determined for reactions of CpBr. the results would have been similar and ihe effecis of solvent deuteration on yields (RR) and (SS) w ould have been missed. For l-bromo-l-mclhyl-... 

Solvent Deuterated Form Chemical Shift (Multiplicity) ... 

One of the major problems facing distance determination by pulsed EPR on spin labeled membrane proteins is the short relaxation time (generally around 1 ps). Solvent deuteration is routinely used (10-20 vol% deuterated glycerol as cryopro-tectant for membrane-embedded or detergent-solubilized samples, or deuterated buffer) to slow down the nitroxide relaxation, thus extending the range of distance measurement and sensitivity. However, the problems coimected to the too fast relaxation time called for a systematic analysis of all factors modifying the... 

Solvent molecules may also be situated in the outer sphere of complex cations. For instance, Fung [Fu 67] used NMR examinations to demonstrate the outer-sphere association between the complex cation tris(ethylenediamine) cobalt(III) and the solvent (deuterated dimethyl sulphoxide-D20). 

Table 3j. Solvent deuteration effect on inverse temperature transition. (13) ...

An equally important trend is a reduction in column size and a concomitant increase in analytical speed. Short columns can reduce analysis time, and efficiency may be as high as 5000 theoretical plates since the particle size of the packing material is 3 /u.m. The analysis time is about 1 minute. A standard HPLC column has a diameter of 4.6 mm as compared to 2, 1, or even 0.5 mm for the new columns. The small size of these columns allows the use of more expensive solvents deuterated solvents might be used when it is necessary to analyze the collected samples by NMR. The use of ultramicrobore (50-/u.m diameter) columns allows feeding of the eluted peaks directly into a mass spectrometer of FTIR instrument. 

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