Cooperative phenomena

The molecules retain their essential character In all cases studied. This implies that the spontaneous dissociation observed under certain circumstances for H2O must be a cooperative phenomenon involving more than one H2O molecule. 

Above a specific temperature, the Curie temperature, a ferroelectric substance becomes paraelectric since the thermal vibrations counteract the orientation of the dipoles. The coordinated orientation of the dipoles taking place during the ferroelectric polarization is a cooperative phenomenon. This behavior is similar to that of ferromagnetic substances, which is the reason for its name the effect has to do nothing with iron (it is also called seignette or rochelle electricity). 

The term ferromagnetism reflects the fact that iron shows this effect, but it is by no means restricted to iron or iron compounds. Ferromagnetism is a cooperative phenomenon, i.e. many particles in a solid behave in a coupled manner. Paramagnetic atoms or ions exert influence on each other over extended regions. 

When located at opposite ends (or at conjugated positions) in a molecular system, a donor and an acceptor do more than simply add up their separate effects. A cooperative phenomenon shows up, involving the entire disubstituted molecule, known as charge transfer (C.T.). Such compounds are colored (from pale yellow to red, absorption from 3,000 to 5,000 A) and show high U.V. absorption oscillator strength. "Figure 2 helps understand the enhancement of optical nonlinearity in such a system. 

The cooperative phenomenon of complexation was also observed for a heteronuclear polymer complex, e.g., the PVP-Cu,Mn mixed metal ion system (Tab. I). Although the complex forming ability of Mn ion itself is weak, the formation constant (K) for the Mn... 

It is well known that the transfer of nonpolar molecules from nonpolar to polar surroundings results in a decrease in the partial molar volume of the solute. The dimerization studies also show that there is a similar volume decrease when two monomers form a dimer. This volume decrease is of the order of 20 cm3 mol-1. It is difficult to understand how there can be first a volume decrease when the nonpolar molecules are transferred from the nonpolar to the polar environment and then a further volume decrease when two molecules come together and partly reverse the first transfer. It is a little dangerous to speak of the partial reversal of a process we know so little about. It is believed that the hydrophobic hydration is a cooperative phenomenon, in which the exact microstructure of water is very important for the occupied volume. How this microstructure changes when two molecules associate in a hydrophobic interaction is not par-... 

The formation of multisubunit complexes (for example, protein complexes). Such complex formation is usually a cooperative phenomenon. 

The helical structure of PLL plays an important role in transferring information on oxygenation to the neighboring heme groups. We call this cooperative phenomenon the pseudo-allosteric effect of the PLL-heme complex. 

Thus we find that a smaller a induces cooperation of peptide units to create a longer helical sequence, provided the environmental conditions are in favor of helix formation. This is the reason why a is often called the cooperativity parameter for the formation of helical sequences, or a polypeptide with a smaller a is referred to as more cooperative. It is crucial to understand that helix formation in polypeptides is a cooperative phenomenon. 

High concentrations of urea produce an increase in viscosity and changes in absorption and rotation spectra. The transition as a function of urea concentration is steep, implying a cooperative phenomenon involv-... 

At low temperatures, rj will be unity because all of the Cu atoms will be localized on A sites. 1 But the degree of disorder increases as the temperature increases until the Cu and Zn atoms are mixed randomly on the two sublattices and 77 = 0. This process, called a positional (order + disorder) transition, is often described as a cooperative phenomenon because it becomes easier to produce additional disorder once some disorder is generated. In the vicinity of a critical temperature, the order parameter rj behaves like the density difference (pi — pg) near the gas-liquid critical point. Thus,... 

In the literature, DNA condensation was frequently interpreted as a highly cooperative phenomenon, in other words, the transition was regarded as steep but continuous. For example, Widom and Baldwin (1983)... 

Transition from normal conductivity to superconductivity is a virtual perfect second-order phase transition that is, there is no latent heat or a sharp finite discontinuity in the specific heat therefore, it is a cooperative phenomenon. 

The theoretical treatment of a solid-state transition involving covalent (localized) vs. conduction (delocalized) electronic transformation was first enunciated by Mott [44], By considering the Pauli Exclusion Principle and the electron-electron interaction during the transformation, it was shown that such transition will be critically dependent upon the inter-atomic distances. The number of electrons already existing in the conduction state will in turn influence the critical inter-atomic distances and the transition therefore, it is necessarily a cooperative phenomenon. Later, in a theoretical treatment of the same subject, but based on a different context, Goodenough [45] has shown that the transition is likely to be second-order if the number of electrons per like atom is non-integral. Further, a crystallographic distortion is a prominent manifestation of such a transition. 

Thermodynamically, it can be reasoned that the major contribution of heat generation or absorption must have come from source other than the lattice, i.e., such as electrons and changes in their thermodynamic state. Similar phenomena exist in stretching a piece of rubber or other cooperative phenomenon such as the transition between ordinary helium to helium-11. 

Whether the orbital ordering is a cooperative phenomenon in TDAE-C60 or not still remains an open question. If it is a cooperative phenomenon, one can indeed apply the approach of Asei et al. [122] with a starting Hamiltonian... 

If electron ordering introduces a change in lattice symmetry, it is a cooperative phenomenon, and Tt is well defined, though it may exhibit considerable thermal hysteresis. If it introduces no change in the lattice symmetry, it need not be a cooperative phenomenon, and Tt may spread over a considerable ( 100°C) temperature interval. 

The CD exampies ail involve direct inclusion of the guest within the cavity of the CD. The poiar orientation of the soiid arises as a resuit of the crystal habit of the CD. For the thiourea and TOT complexes, the inclusion compiexation is a cooperative phenomenon between host and guest. The nature of the polar orientation, and its apparent commonality, deserve speciai comment. We have prepared nearly 25 examples of inclusion compiexes of poiar molecules in various matrices as part of this work. Only... 

That segregation makes no difference with a first order reaction is scarcely surprising, for a first order reaction is in a sense a spontaneous thing which happens to a molecule independently of other similar molecules. For a second order reaction we should expect a difference in conversion, for this is essentially a cooperative phenomenon between neighboring molecules. Consider the irreversible reaction with rate k c — For complete molecular mixing... 

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