Group folded conformation

Some proteins contain covalent disulfide (S— S) bonds that link the sulfhydryl groups of cysteinyl residues. Formation of disulfide bonds involves oxidation of the cysteinyl sulfhydryl groups and requires oxygen. Intrapolypeptide disulfide bonds further enhance the stability of the folded conformation of a peptide, while interpolypeptide disulfide bonds stabilize the quaternary structure of certain oligomeric proteins. 

It was an outstanding experience to plan, organize and realize this book, and to work with such a distinguished group of contributors. I hope that the readers will enjoy the work they did. I won new friends during this book project, one of which is Pierre-Alain Carrupt. He prepared the cover graphics, which represents the molecular lipophilicity potentials for my PhD molecule verapamil in its extended and folded conformation. 

Fig. 7. Stereoview of the crystal structure of water solvated host 5 (folded conformation). The structure is held together by host-host and host-solvent hydrogen bonding interactions. Within the solvation layer there are chains of circular H-bonds between the molecules of water (crystal data a - 8.227, b = 8.964, c - 16.945 A, a = 89.64, / = 97.51, y = 114.28°, space group Pi taken from Ref,3S>)...

Fig. 8. Stereoscopic illustration of the inclusion compound of host 5 (folded conformation) with acetic acid and 2 mol of water. Host-host and host-water hydrogen bonding interactions stabilize the structure. The solvation layers consist of cyclic carboxy dimers of acetic acid surrounded by water species (crystal data a = 7.857, b = 11.379,c = 13.831 A,a = 92.50,/i = 101.21, y = 101.12°, space group Pi taken from Ref. 351)...

Based on the three-dimensional structure of CHS, we proposed that the initiation/elongation/cyclization cavity serves as a structural template that selectively stabilizes a particular folded conformation of the linear tetraketide, allowing the Claisen condensation to proceed from C6 to Cl of the reaction intermediate.14 In contrast, CTAL formation can occur either in solution or alternatively while sequestered in the enzyme active site. In either case, enolization of the C5 ketone followed by nucleophilic attack on the Cl ketone with either a hydroxyl group (in solution) or the cysteine thiolate (enzyme bound) as the leaving group results in CTAL. Similar lactones are commonly formed as by-products of in vitro reactions in other PKS systems.36 38... 

Figure 4-7. Folded conformation of the salen complex. Rs = Alkyl RL = aryl R1, R2 = FI, alkyl, or aryl R3 = bulky group. Reprinted with permission by Elsevier Science Ltd., Ref. 94. 

The mechanistic basis of 3 and 4 is a double application of the argument used for the YES operation with 1. Each receptor in 3 is capable of launching a PET process if the lumophore is powered up by ultraviolet excitation. In other words, the fluorescence of the 9-cyanoanthracene unit is efficiently quenched by either the amine or the 1,2-dioxybenzene group within the benzo-15-crown-5 ether unit. These quenching processes are predictable from thermodynamic calculations or from related bimolecular quenching experiments in the literature. The small separation of the amine from the lumophore ensures rapid PET kinetics. On the other hand, the presence of four bonds between the benzo-15-crown-5 ether and the lumophore is probably responsible for the incomplete quenching seen between this pair. No information is yet available regarding possible folded conformations of 3. 

P2i2,2i Z = 4 Dx = 1.57 R = 0.13 for 1,860 intensities. The molecule is in the folded conformation, but differs greatly in a number of the torsions around the backbone bonds found in the sodium salt85 of CDP-choline. Furthermore, the conformation of the D-ribosyl group here is C-3 -endo (28.3°). The glycosyl disposition is anti (33.1°), and the orientation around the exocyclic, C-4 -C-5 bond is -57.4°. The pyrophosphate group has a staggered orientation around the... 

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