Rotation per residue

A large number of stable conformations of both natural and synthetic DNA have been observed. They may be characterized in terms of gross structural parameters such as N, the number of molecular asymmetric units in K turns of the helix h, the axial rise per residue and r, the axial rotation per residue. Both right- and left-handed helices have been observed [13, 43]. In typical cases the molecular asymmetric unit is a mononucleotide but dinucleotide asymmetric units have been found in molecules in which the chemical repeat consists of two nucleotides [11]. The nucleotide conformations can be related to the different helical parameters both in terms of the backbone and conformational angles and features such as the sugar pucker and the base-pair displacement and orientation with respect to the helix axis. 

Rotation per residue, or twist angle, designed as h, refers to the angle between two adjacent base pairs. B-form DNA of Watson-Crick with lObp in one 360° helix turn of DNA the rotation per residue h = 36°. For B-form DNA in solution with 10.5bp per turn, h = 34.3°. 

Pure dimethylphosphite can also be extracted by rotory membranous vertical apparatus with the heat exchange surface of 0.8 m2 and the rotor speed of 307 rotation per minute. In this case the optimal parameters are the following the temperature is 105-110 °C, the residual pressure is 40 GPa. The purity of dimethylphosphite can reach 98%. 

Proteins, with a specific function and isolated from a single source, usually have a homogeneous population of molecules all with the same unique amino acid sequence. Yet with 20 different amino acids possible at each position in a polypeptide chain of n residues, 20 different primary structures are theoretically possible. Furthermore, the great majority of all molecules of a natural protein may exist in a unique conformation despite the degrees of freedom formally permitted by rotation about the peptide backbone (motility) and side chains (mobility). For example, with only 3 conformations defined per residue, a polypeptide chain of 210 residues would have a theoretical possibility of existing in 10 °° different conformations. 

The measurement of the dipole moments of copolymers and its analysis in terms of both sequence distribution and local chain configurations has received attention Modern computer aided analytical procedures provide in ght into the dependence of mean square dipole moment per residue on reactivity ratios, polymer composition and rotamer probabilities. One such calculation for atactic cc ly-(p-chlorostyrene-p-methylstyrene) has shovm that at constant composition, the dipole moment is quite sensitive to the sequence distribution and thus to the reactivity ratios. This dependence would be even more marked for syndiotactic chains. For cop61y(propylene-vinyl chloride) and copoly(ethylene-vinyl chloride) d le moments are again very sequence dependent, much more so than the diaracteristk ratio. It would appear that in copolymer systems dielectric measurements can be a powerful method of investigating sequence distributions. Two copolymers, p-dilcxo-styrene with styrene and with p-methylstyrene have been examined experimentally The meamrements were made on solid amorphous samples above the ass-rubber transition temperature (Tg) and they are consistent with the predictions of the rotational isomeric state model udi known reactivity ratios and rea nable replication probabilities . However, it is the view of this author that deduc-... 

It has been demonstrated that in isotactic polymers of optically active a-olefins the molar optical rotation per monomeric residue can be interpreted in terms of the prevalence of few conformations with very high optical rotation of the same sign, corresponding to those allowed to the structural unit inserted in an one screw sense helix [11]. 

Below a temperature of Toi 260 K, the Ceo molecules completely lose two of their three degrees of rotational freedom, and the residual degree of freedom is a ratcheting rotational motion for each of the four molecules within the unit cell about a different (111) axis [43, 45, 46, 47]. The structure of solid Ceo below Tqi becomes simple cubic (space group Tji or PaS) with a lattice constant ao = 14.17A and four Ceo molecules per unit cell, as the four oriented molecules within the fee structure become inequivalent [see Fig. 2(a)] [43, 45]. Supporting evidence for the phase transition at Tqi 260 K is... 

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