Spontaneous transformations

Polymorphism. Many crystalline polyolefins, particularly polymers of a-olefins with linear alkyl groups, can exist in several polymorphic modifications. The type of polymorph depends on crystallisa tion conditions. Isotactic PB can exist in five crystal forms form I (twinned hexagonal), form II (tetragonal), form III (orthorhombic), form P (untwinned hexagonal), and form IP (37—39). The crystal stmctures and thermal parameters of the first three forms are given in Table 3. Form II is formed when a PB resin crystallises from the melt. Over time, it is spontaneously transformed into the thermodynamically stable form I at room temperature, the transition takes about one week to complete. Forms P, IP, and III of PB are rare they can be formed when the polymer crystallises from solution at low temperature or under pressure (38). Syndiotactic PB exists in two crystalline forms, I and II (35). Form I comes into shape during crystallisation from the melt (very slow process) and form II is produced by stretching form-1 crystalline specimens (35). 

Unimolecular reaction (Section 11.4) A reaction that occurs by spontaneous transformation of the starting male-rial without the intervention of other reactants. For example, the dissociation of a tertiary alkyl halide in the S l reaction is a unimolecular process. 

The ecstatic tenor of Khunrath s rhetoric is itself perhaps modelled on the spiritus rhetoricus of Erasmus early hermeneutics in which he had explored the spiritual sense of a text as being a force of divine grace that could spontaneously transform the reader. It was the personal experience of the sense of scripture that Erasmus had favoured in the Enchiridion Hence, also the outcries of Hallelujah and Lob Herr that punctuate, or conclude, Khunrath s writings. 

In the same paper, Rutherford and Soddy also suggested that elements were undergoing spontaneous transformation. The use of the word transformation smacked of alchemy and Rutherford was loath to use it, but by then it seemed clear that elements were really changing and that radioactivity may therefore be considered as a manifestation of subatomic change (Rutherford and Soddy 1902). 

Probucol (4,4/-[(l-methylethylidene)bis(thio)]-bis-[2,6-bis(l,l-dime-thylethyl)phenol]) is a cholesterol-lowering drug that has been reported to exist in two forms [27]. Form II has been found to exhibit a lower melting point onset relative to Form I, and samples of Form II spontaneously transform to Form I upon long-term storage. The structures of these two polymorphic forms have been reported, and a summary of the crystallographic data obtained in this work is provided in... 

The obtained results have shown that cell cultures of tumor origin are more sensitive to phototoxic damage induced by solid-phase C60 than the cultures of nontumor origin (normal or spontaneously transformed ones) - the effect that could be interesting for the perspective of possible fullerene usage in photodynamic therapy of tumors. 

Unlike rodent cells that readily undergo spontaneous transformation [46-50], human cells tend to be very refractory to this process [51, 52] and will undergo spontaneous transformation only on rare occasions [53, 54], The biochemical and molecular mechanisms that underlie such an event are not yet clearly elucidated however, it is likely that there have been preneoplastic insults that have occurred to initiate spontaneous transformation. Of the few reports... 

Takahashi, K., Y. Sawasaki, J. Hata, K. Mukai, and T. Goto. 1990. Spontaneous transformation and immortalization of human endothelial cells. In Vitro Cell Dev Biol 26(3 Pt 1) 265-74. 

In practice, the primary objective of chemical thermodynamics is to estabhsh a criterion for determining the feasibility or spontaneity of a given physical or chemical transformation. For example, we may be interested in a criterion for determining the feasibility of a spontaneous transformation from one phase to another, such as the conversion of graphite to diamond, or the spontaneous direction of a metabohc reaction that occurs in a cell. On the basis of the first and second laws of thermod5m-amics, which are expressed in terms of Gibbs s functions, several additional theoretical concepts and mathematical functions have been developed that provide a powerful approach to the solution of these questions. 

If two blocks of metal, one at a high temperature and the other at a low temp-eramre Tj [Fig. 6.10(a)] are separated by a perfect heat insulator, and the system as a whole is surrounded by a thermal blanket that permits no transfer of heat in or out, then no change in internal energy can occur with time. If the insulator between the blocks is removed, the hotter block will decrdease in temperature and the cooler one will increase in temperature until the uniform temperamre T2 is reached. This transformation is spontaneous. At/ is zero. But a loss of capacity to perform work has occurred. In the initial state, we could insert a thermocouple lead in the block at Ts and another in that at Tj and obtain electrical work. Insertion of thermocouple leads in the same positions in the double block at T2 cannot generate any work. At the conclusion of the spontaneous transformation without the thermocouple, the internal energy is stiU the same as that at the outset, but it is no longer in a condition where it has the capacity to do work. 

Spontaneous transformations occur aU around us aU the time. Hence, A5, for a section of space encompassing each such transformation and its affected surroundings, is a positive number. This realization led Clausius to his famous aphorism ... 

S. Sugiura, M. Nakajima, N. Kumazawa, S. Iwamoto, and M. Seki Characterization of Spontaneous Transformation-Based Droplet Formation During MicroChannel Emulsification. J. Phys. Chem. B 106, 9405 (2002). 

To assess the protective abilities of these chelators, a spontaneously transformed cell line of oligodendroglia origin (OLN 93) was chosen as a model for neural cells. These cells were previously used to demonstrate a remarkable sensitivity to genotoxic stress, culminating in cell death when both divalent iron and H2O2 were added to cells °. ... 

The homologous cumulene 44 prepared by an analogous vinylidene insertion reaction is spontaneously transformed to the dimer 45.46 By contrast the stable tert-butyl derivative 46 undergoes thermal cycloaddition at one of the inner double bonds giving 47. The structure of this dimer was confirmed by X-ray diffraction.47... 

There are also risks associated with the long-term expansion of stem cells in culture, such as transformation and aneuploidy. Such modifications of the intrinsic properties of the cells can potentially lead to the development of malignancy in the patient following transplantation. In the protocol developed by Osiris, MSCs are expanded until the number of adult stem cells has increased over 3000-fold [327297], [327352]. Recent studies have reported that MSCs expanded in culture have an intrinsic propensity towards spontaneous transformation after a certain number of population doublings ( 250) [660856], [660857],... 

Although the living nature of anionic polymerization of styrene testifies to the relative stability of the carbanion at the chain end, observations indicate that it may undergo spontaneous transformations.182 Polystyryl sodium in THF was shown to undergo termination involving hydride elimination followed by proton transfer ... 

The values of these three parameters are all negative, as expected for a spontaneous transformation. It is also logical that entropy is decreased when the analyte moves from the mobile phase into the stationary phase where it is essentially fixed. Because of this, Van t Hoff s equation can be used in a fairly rigorous way to predict the effect of the temperature on the retention times of the analytes. 

This compound was prepared by Dessaignes in 1857 [98]. The compound is unstable and is spontaneously transformed into dioxosuccinic acid (Kekule [99], Thiele and Dralle [100] and others [101]). 

E. C. Szarvasky found that the electrolysis of hydroxylamine was accompanied by the spontaneous transformation of hydroxylamine into ammonia. Secondary reactions always occur—the base being reduced to ammonia at the cathode and at the anode oxidized to nitrogen oxides. F. Balia found that with various electrodes the percentage current yield of NaN02 NaN03 in the electrolytic oxidation of hydroxylamine with anodes of different metals was as follows ... 

A. Kupferberg, G. Teller and P. Behr, Metabolism of 7(5-hydroxycholesterol in astrocyte primary cultures and derived spontaneously transformed cell lines correlation between the esterification on C-3-OH by naturally occurring fatty acids and cytotoxicity, Biochim. Biophys. Acta 1046 (1990) 106-109. 

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