Molecular positive cooperativity

In this part, two series of 44 copolymers with coiled main-chain structures and 45 copolymers with stiff main-chain conformations were described. It was concluded that both optically inactive 42 and 43 adopt helical conformations with an equal proportion of P and M screw senses by means of UV and CD spectra as well as molecular mechanics calculations. A marked positive cooperative induction effect of the preferential screw sense in 44 and 45 copolymers was found. However, there is a marked difference in the helical cooperativity between 44 and 45, probably because of the differences in their global and local conformations. This difference can be related to the persistence of the helical conformation against defects allowing change of... 

Positive cooperativity is a basic characteristic of molecular amplification devices, since once initiated, the subsequent steps of the assembly are facilitated. It represents a non-linear process and confers features of an error filter, only the correct input will in principle lead to the cooperative structure generation. 

RNA but of both handednesses. Upon appending a single homochiral residue such as L-lysine at the carboxy terminus of the helix, the peptide nucleic acid polymers predominantly fold into duplexes of a single handedness. This phenomenal positive cooperativity can be considered a form of molecular amplification. Additional examples on spontaneous and induced formations of helical morphologies were reviewed [114,182]. 

The structural and functional properties of human hemoglobin (Hb) have been the subject of study for decades, stimulated by the intriguing characteristic of positive cooperativity. How do the four subunits that compose the Hb tetramer communicate with one another The answer to this question has been sought primarily through the comparison of deoxy with oxy Hb. However, to understand the molecular mechanism of a chemical reaction, it is necessary to characterize the intermediate(s) of the process, and the reaction of Hb with O2 is no exception. 

From the rate studies the macrotricyclic quaternary ammonium host 25 emerges as an efficient though very simple enzyme model It is a water soluble compound of well defined structure and size which possesses one molecular cavity (active site). Substrate binding occurs there in a specific fashion and may initiate catalysis in certain reactions. The rate effects demonstrate reaction — as well as substrate specificity and originate in principal from entropic and enthalpic diminution of the rate limiting free enthalpy barrier. Even kinetic positive cooperativity can be observed. 

Biology thrives near a movable cusp of insolubility, and the forces that, in a positively cooperative manner, power the molecular machines of biology drive paired oil-like domains of proteins back and forth between association (insolubility) and dissociation (solubility), and excursions too far in either direction into the realms of insolubility or solubility spell disease and death. 

Most significantly, however, the molecular basis for positive cooperativity and the result of increased functional efficiency in designed elastic-contractile model proteins has been experimentally determined to be the competition for water that occurs between oil-like domains and charged groups constrained to coexist within a protein structure (see immediately below and Chapter 5, section 5.1.7.4). This represents the principal statement of the Mechanistic Assertion. 

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