Stability unexpected

The substances involved in bioluminescence reactions are usually unstable. Thus, the extraction and purification of bioluminescent substances should be carried out in the shortest possible period of time, usually at a low temperature. It is known through experience that luminescent substances are almost always more stable in the original animal tissues than in extracts when preserved at a low temperature. Therefore, before starting extraction and purification, the stability of the extracts and purified substances should be investigated by carrying out a small-scale pilot experiment. A pilot experiment is also essential in the course of purification to avoid an unexpected loss of the target substance. If a component of the luminescence system is insoluble in common buffer solutions, it must be solubilized to purify it (see C1.3). 

Other similar cyclic structures may present quite unexpected behaviour. Let us give the example of 46, where X is Cl or Br. Such structures are very easily reduced44 (polished platinum microelectrodes are preferred owing to the reaction of mercury with C—X linkages), and the presence of an anion radical of some stability can be demonstrated in the... 

The orbital symmetry rules also help us to explain, as on pages 1083 and 1433, the unexpected stability of certain compounds. Thus, 102 could, by a thermal [1,3] sigmatropic rearrangement, easily convert to toluene, which of course is far more stable because it has an aromatic sextet. Yet 102 has been prepared and is stable at dry ice temperature and in dilute solutions. ... 

Perhaps it is not unexpected and surprising that there is no /3-aryl participation in the solvolysis of triarylvinyl substrates, as the intermediate vinyl cation is especially stable because of charge delocalization into the a-aryl ring and has no need for extra stabilization. 

Experience with chlorofluorocarbons (CFCs), insecticides such as DDT, herbicides and fertilizers has taught us that extended stability of these products may lead to unexpected harmfiil results. An important challenge will be to develop novel products that have a limited stable life and then decompose so that they do not persist in this environment. Examples are the development of plastic packages that decompose and degrade with time and of agricultural chemicals that do not harm unintended targets and are not overly persistent. 

Antibody A52 with its epitope at residues 657-672 [129,139,274,275] inhibited the vanadate-induced crystallization of Ca " -ATPase and decreased the stability of preformed Ca " -ATPase crystals [285]. The vanadate-induced crystals arise by the association of the ATPase monomers into dimers (type A interaction), the dimers into dimer chains (type B interaction), and the dimer chains into 2-dimensional arrays (type C interaction). It is suggested that antibody A52 interferes with type B interactions, preventing the formation of dimer chains, without exerting major effect on the concentration of Ca -ATPase dimers in the membrane. The simplest interpretation of the destabilization of Ca -ATPase crystals by mAb A52 is that binding of the antibody to its antigenic site physically blocks the interaction between ATPase molecules [285]. Considering the large bulk of the antibody, such interference is not unexpected, yet only a few of the antibodies that bind to the Ca -ATPase in native sarcoplasmic reticulum interfered with crystallization. 

Bardaji, M., Laguna, A., Perez, M.R. and Jones, P.G. (2002) Unexpected ring-opening reaction to a new cyanamide-fhiolate ligand stabilized as a dinuclear gold complex. Organometallics, 21, 1877. 

The N4 complexes are rather stable in acidic solutions. However, sometimes the stability is not high enough, particularly so at higher temperatures. It was quite unexpected, therefore, to hud that after pyrolysis at temperatures of 600 to 800°C the catalytic activity of these compounds not only failed to decrease but in some cases even increased. The major result of pyrolysis is a drastic increase in catalyst stability. Tests have been reported where after pyrolysis such catalysts have worked for 4000 to 8000 h without activity loss. The reasons for the conservation of high activity after pyrolysis are not entirely clear. The activity evidently is associated with the central ion that has attained a favorable enviromnent of pyrolysis products. 

In view of this, it is not surprising that dithiocarbamato compounds with copper in the oxidation state + 3 are stable instead it must be regarded as unexpected that Cu(I) dithiocarbamato complexes exist. The latter complexes are not simply monomeric, but they are tetrameric metal cluster compounds. Obviously, the stability must be attributed to the metal-metal bond rather than to the stabilising effect of the ligand. 

Unexpectedly, tho hydrolysis of jV-(2,4-dinitrobenzoyl)imidazole at 25 °C was found to be slower by a factor of 25 in comparison to iV-(4-nitrobenzoyl)imidazole. This lower reactivity of iV-(2,4-dinitrobenzoyl)imidazole was explained by a combination of steric crowding at the reaction center and intramolecular stabilization of the reactant state.[19]... 

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