Phi angle

Yang Y, Sohuster M, Blumioh B and Spiess FI W 1987 Dynamio magio-angle spinning NMR speotrosoopy exohange-induoed sidebands Chem. Phys. Lett. 139 239-43... 

Castillo R, Ramos S and Ruiz-Garcia J 1996 Direct observation of Langmuir films of Cgg and C- g using Brewster angle microscopy J. Phys. Chem. 100 15 235-41... 

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Theoiy permits the approximation of the maximum size of a bubble that can adhere to a submerged horizontal surface if the contact angle between bubble and sohd (angle formed by solid-hquid and liquid-gas interfaces) is known [Wark, ]. Phys. Chem.,. 37, 623 (1933) Jakob, Mech. Eng., 58, 643 (1936)]. Because the bubbles that actually rise from a surface are always considerably smaller than those so calculated and inasmuch as the contact angle is seldom known, the theoiy is not direc tly useful. 

Since the peptide units are effectively rigid groups that are linked into a chain by covalent bonds at the Ca atoms, the only degrees of freedom they have are rotations around these bonds. Each unit can rotate around two such bonds the Ca-C and the N-Ca bonds (Figure 1.6). By convention the angle of rotation around the N-Ca bond is called phi (<[)) and the angle around the Ca-C bond from the same C atom is called psi (y). 

Figure 1.6 Diagram showing a polypeptide chain where the main-chain atoms are represented as rigid peptide units, linked through the atoms. Each unit has two degrees of freedom it can rotate around two bonds, its Ca-C bond and its N-Ca bond. The angle of rotation around the N-Ca bond is called phi (cj)) and that around the Co-C bond is called psi (xj/). The conformation of the main-chain atoms is therefore determined by the values of these two angles for each amino acid.

The conformation of the whole main chain of a protein is determined by two conformational angles, phi (0) and psi (i(f), for each amino acid. Only certain combinations of these angles are allowed because of steric hindrance between main-chain atoms and side-chain atoms, except for glycine. 

P. G. Snyder, M. C. Rost, G. H. Bu-Abbud, J. A. WooUam, and S. A. Alterovitz. /. ofAppL Phys. 60, 3293, 1986. First use of computer drawn three-dimensional surfaces (in wavelength and angle of incidence space) for ellipsometric parameters r and A and their sensitivities. 

Kieffer, J., Investigation of the transitional pore stmeture of activated carbon fibers by small-angle neutron scattering, J. Appl. Phys., 1992, 72(12), 5649 5656. 

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J. Putz, R. Holyst, M. Schick. Nonmonotonic behavior of a contact angle on approching critical endpoints. Phys Rev A 46 3369-3312, 1992. Phys Rev E 46 3035, 1993. 

Apostolov A.A. and Fakirov S., Effect of the length on the deformation behaviour of polyetheresters as revealed by smah angle x-ray scattering, J. Macromol. Set, Phys. B, 31, 329, 1992. 

Regions of ordered secondary structure arise when a series of aminoacyl residues adopt similar phi and psi angles. Extended segments of polypeptide (eg, loops) can possess a variety of such angles. The angles that define the two most common types of secondary structure, the a helix and the (5 sheet, fall within the lower and upper left-hand quadrants of a Ramachandran plot, respectively (Figure 5-1). 

Figure 5-1. Ramachandran plot of the main chain phi (< ) and psi (T) angles for approximately 1000 nonglycine residues in eight proteins whose structures were solved at high resolution. The dots represent allowable combinations and the spaces prohibited combinations of phi and psi angles. (Reproduced, with permission, from Richardson JS The anatomy and taxonomy of protein structures. Adv Protein Chem 1981 34 167.)...

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