From aggregated state

Many proteins frequendy require the assistance of other protein molecules called molecular chaperonins, for assuming the fine tertiary stmcture in vivo. In E. coli, two such chaperonin molecules bind transientiy to newly synthesized polypeptide monomers, preventing them from aggregating prematurely, until the polypeptides attain their folded state (10). 

Gum-Saline. Gum is a galactoso—gluconic acid having molecular weight of approximately 1500. First used (16) in kidney perfusion experiments, gum—saline enjoyed great popularity as a plasma expander starting from the end of World War I. The aggregation state of gum depends on concentration, pH, salts, and temperature, and its coUoid oncotic pressure and viscosity are quite variable. Conditions were identified (17) under which the viscosity would be the same as that of whole blood. 

Figure 6.9 Influence of electrolyte concentration on colloid stability ( denotes change from a stable to an aggregated state)...

Hounslow, M.J., 1990b. Nucleation, growth and aggregation rates from steady-state experimental data. American Institution of Chemical Engineers Journal, 36, 1748-1753. 

It is important to distinguish between the concept of method and the concept of technique . Method defines the aggregative state of the original material (e.g., liquid or gaseous state) from which crystals form directly. Each method is employed by means of several techniques. ... 

When the free enthalpy of reaction AG for the transformation of the structure of a compound to any other structure is positive, then this structure is thermodynamically stable. Since AG depends on the transition enthalpy AH and the transition entropy AS, and AH and AS in turn depend on pressure and temperature, a structure can be stable only within a certain range of pressures and temperatures. By variation of the pressure and/or the temperature, AG will eventually become negative relative to some other structure and a phase transition will occur. This may be a phase transition from a solid to another solid modification, or it may be a transition to another aggregate state. 

Water can be found, in all three aggregate states, almost everywhere in the universe as ice in the liquid phase on the satellites of the outer solar system, including Saturn s rings and in the gaseous state in the atmospheres of Venus, Mars and Jupiter and in comets (as can be shown, for example, from the IR spectra of Halley s comet). The OH radical has been known for many years as the photodissociation product of water. 

Fig. 4 Idealized surface pressure n versus area A isotherm detailing the inferred molecular orientation and aggregation states during a compression cycle. Reprinted with permission from Arnett et al, 1989. Copyright 1989 American Chemical Society.

Nuckolls and Katz have synthesized discotic liquid crystalline molecules in which the core is a helix in its own right.37 Nonracemic helicene 33 was found to assemble into a columnar mesophase in which the helicenes stack on top of each other. CD spectroscopy showed a strong increase of the Cotton effect upon going from the molecularly dissolved state to the aggregated state, exhibiting an amplification of chirality. These helical columns give rise to a strong expression of chirality because the intrinsic shape of the helicenes... 

Figure 7.1 Illustration of different aggregation states obtained (from left to right) by increasing temperature crystal (K), smectic C (SmC), nematic (N) and isotropic (I). Row a shows macroscopic appearance of samples in row b, short-range microscopic ordering is represented (each bar represents a molecule) thermotropic phase diagram of row c illustrates relevant transition temperatures (Tm melting temperature Tsmc-N transition temperature between SmC and N Tc clearing temperature) row d shows different texture of different states as seen through polarizing microscope (with crossed polars, isotropic phase appears black).

In practice, there is often not a sharp change from one state to another, and the plots are frequently curved over the temperature range in which aggregation becomes important. 

So far, we have considered cross-section balance between one hydrophilic part and one hydrophobic part. We can also consider a different type of cross-section balance between one hydrophilic part and two hydrophobic parts. This is possible because the molecular area of CnAzoCmN+Br is almost equal to twice that of the chain cross-section. In this case, we will obtain a tilt angle of 23° from the relation of Sm cos0=2 Sc. This is another stable state of CnAzoCmN+Br, known as the interdigitated H-aggregation state which is observed in several compounds with m-ns2. 

Now we shall elucidate factors which determine the J- and H-aggregation state. At first, we shall consider the H-aggregation state obtained from structure analyses of single crystals. In the layered structure, the methyl moiety at the end of the hydrophobic chain is in contact with... 

Based on the above qualitative discussion of the characteristics of the Jt-A curves, we now provide a useful kinetic model for the molecular aggregation. Let [S] and [D] be the concentration of PhDA2-8 molecules in the "regular" and "aggregated states, respectively. The "regular" state corresponds to the usual conformation of a surfactant molecule at the interface, i.e., the hydrophilic head faces the hydrophilic environment and the hydrophobic tail is expelled from the interface towards the hydrophobic environment. Then the aggregation can be described as... 

An effective thickness of the layer where the fluorescence is observed is assumed to be the depth where the excitation light intensity is 1/e of the initial value. The thickness was calculated to be 1.4 im from an absorption coefficient of the film at 295 nm (excitation wavelength). Therefore, the observed fluorescence spectral change is due to that of aggregate states of EPy in the depth region of 1.4 fin from the ablated surface. Actually, it is well known in a PMMA matrix that the excimer band is due to the ground state dimer of the dopant (23). 

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