High-energy conformation

Reduce stress on molecules caused hy a simulation at elevated tern peratiires. The cooling process, called sim n lated annealing, takes new, high energy conformational slates toward stable conformations. 

A molecule has three nondegenerate conformers (Fig. 5-8). One is 450 x 10 J above the ground state, and the second high-energy conformer is 900 x 10 J above the ground state. What are the percentages of each of the three conformers relative to the total number of molecules in a sample of the normal conformational mixture at 300 K ... 

B. In vacuo calculation of a librated state of the Gramicidin channel showing the peptide NH moieties to be librated into the channel. This is a relatively high energy conformation, some 8 kcal/mole higher than in A. C. M. Venkatachalam and D. W. Urry, unpublished results... 

The molecule is twisting and bending around all of the time, and the conformation with the bracelet-shaped skeleton is just one of the possible conformations. The molecule probably spends very little of its time like this (it is a relatively high energy conformation), but this is the conformation that we will use to draw our Fischer projection. 

In the relaxation phase of muscle contraction, the S-1 head of myosin hydrolyzes ATP to ADP and Pj, but these products remain bound. The resultant ADP-Pj-myosin complex has been energized and is in a so-called high-energy conformation. 

Another cycle then commences with the hydrolysis of ATP (step 1 of Figure 49-6), re-forming the high-energy conformation. 

In order to obtain more information about the receptor-active conformation of muscimol, X-ray structure analysis, and ab initio quantum chemical studies have been applied to this compound (14). The flexibility of muscimol exclusively resides in the side chain (O-C-C-N bond) and a calculated potential energy curve for the rotation about this bond of muscimol in its zwitterionic form is shown in Fig. 3. These studies have demonstrated that in order for muscimol to obtain the conformation displayed by THIP, a conformational energy of 8.9 kcal/mol is required, which makes it less likely that the receptor-active conformation of muscimol corresponds to that of THIP. On the contrary, the conformation of THIP seems to mimic a high-energy conformation of muscimol as shown on the energy curve in Fig. 3, where the dihedral angles corresponding to the solid-state conformations of the muscimol zwitterion and the THIP cation are denoted. 

Is there any ground-state destabilization of the substrate by bond-angle strain or binding in a high-energy conformation ... 

The lowest energy conformational process in 2,2-dimethyl-l,3-dioxocane is the conversion of (433) to (434) via the boat-boat intermediate (BB-1,3) which has C2 symmetry. The methyl groups (A and B) in (433) and (434) have exchanged sites. This process is actually similar to the high energy conformational process in 1,3-dioxocane itself. This crossover of mechanisms is shown diagrammatically in Figure 1. 

Neglecting high energy conformations, cis-1,4,5,8-tetramethylperhy-dro[2,3-b]pyrazinopyrazine (416) exists as an enantiomeric pair of confor-mers 417 and 418 interconverting by ring inversion. For the trans isomer, only conformations 419 and 420 need to be considered. A 13C- and H-NMR... 

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