Cyclic conformation correlate

Figure 5.6. Description of the molecular structure of the parent model protein (GVGVP) , which should be recognized as equivalent to (VPGVG) . (A) A series of P-turns involving residues VPGV. (B) The P-turn obtained from the crystal structure of the cyclic conformational correlate cyclo(GVGVP)3 shown in Figure 5.4B. (C,D) Schematic helical representations without P-turns (in C) and showing p-turns as spacers between turns of a helix, called the P-spiral. (E) Cross-eye stereo view of the poly(GVGVP) p-spiral in side view below and in axis view above. (F) Cross-eye stereo view of the twisted filament composed of three P-spirals. Before passing...

D.W. Urry, D.K. Chang, R. Krishna, D.H. Huang, T.L. Ti-apane, and K.U. Prasad, Two Dimensional Proton Nuclear Magnetic Resonance Studies on Poly(VPGVG) and its Cyclic Conformational Correlate, Cyclo(VPGVG)3. Biopolymers, 28,819-833,1989. 

D.W. Urry, T.L. TVapane, H. Sugano, and K.U. Prasad, Sequential polypeptides of elastin cyclic conformational correlates of the linear polypentapep-tide. J Am Chem Soc 103,2080-2089,1981. 

Concept of cyclic conformations with linear conformational correlates. More information on the details of the PPP yS-spiral can be obtained by considering a series of cyclic analogs. The concept being utilized here is that of cyclic conformations with linear conformational correlates. The idea is that a helix with a large number of residues per turn can have a low pitch and only small changes in torsion angles are sufficient to interconvert between cyclic and linear helical conformations. With this... 

The second application of the CFTI approach described here involves calculations of the free energy differences between conformers of the linear form of the opioid pentapeptide DPDPE in aqueous solution [9, 10]. DPDPE (Tyr-D-Pen-Gly-Phe-D-Pen, where D-Pen is the D isomer of /3,/3-dimethylcysteine) and other opioids are an interesting class of biologically active peptides which exhibit a strong correlation between conformation and affinity and selectivity for different receptors. The cyclic form of DPDPE contains a disulfide bond constraint, and is a highly specific S opioid [llj. Our simulations provide information on the cost of pre-organizing the linear peptide from its stable solution structure to a cyclic-like precursor for disulfide bond formation. Such... 

A number of pyrans, including 3-hydroxy-tetrahydropyran (both axial conformer, 29 and equatorial conformer, 30), 2-methoxy-tetrahydropyran 33, 3-methyl-tetrahydropyran 32, and several 4-substituted tetrahydropyrans, along with 2-methyl-l,3-dioxolane and the rigid cyclic ethers 7-oxabicyclo[2.2.1]heptane and 1,8-cineole, were studied extensively by NMR. These empirical results, in conjunction with the literature data for a variety of acyclic and cyclic ethers, were used to examine the reliability of O-substituent chemical shift models in these systems. The empirical data correlate well with predictions made from the model and it is concluded that ethereal oxygen substituent chemical shifts are due to both steric and electrostatic terms <1998J(P2)1751>. 

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