Helix diameter

The unit cell is tetragonal, with a symmetry approximating P2i2 2i. The cell dimensions are a = b= 18.87 A (1.887 nm) and c = 7.99 A (799 pm). The helix diameter is 13.3 A (1.33 nm). One ethylenediamine molecule for every two D-glucose residues is indicated. The location of the ethylenediamine molecule in the lattice was discussed. The structure is almost identical to that of the amy-lose-dimethyl sulfoxide complex. 

The average DNA helix diameter used in modeling applications such as the ones described here includes the diameter of the atomic-scale B-DNA structure and— approximately—the thickness of the hydration shell and ion layer closest to the double helix [18]. Both for the calculation of the electrostatic potential and the hydrodynamic properties of DNA (i.e., the friction coefficient of the helix for viscous drag) a helix diameter of 2.4 nm describes the chain best [19-22]. The choice of this parameter was supported by the results of chain knotting [23] or catenation [24], as well as light scattering [25] and neutron scattering [26] experiments. 

Form Turn direction Bases/360° Helix diameter (mn)... 

The most widely known ordered structure in polypeptides is the a-helix. When the repeating units are amino acid residues of l configuration, the a-helix is right-handed i.e., the chain backbone follows the pattern of the thread of a right-hand screw. Each turn of the helix is made up of 3.6 residues, so the helix is nonintegral. An exact repeat of the backbone structure occurs every 18 monomeric units. This repeat corresponds to five turns of the helix, with a linear translation along the axis of 27 A and a pitch of 5.4 A. The helix diameter, neglecting side chains, is about 6 A. 

Calculate the heat-transfer coefficient for a fluid with a flow rate of 100 lb/h (45.36 kg/h) and the physical properties outlined in Example 7.18. The inside diameter of the tube is 0.62 in (0.016 m), and the tube is fabricated into a helical coil with a helix diameter of 24 in (0.61 m). 

Let us continue with the case of L/D = 500, the same as that of the pipeline reactor with a diameter of 0.413 m. Considering the helix diameter to be 10 times the pipe diameter, D = 4.13 m. 

An increase in the helix diameter provides a larger capacity, so that larger samples can be run. For a given length of tube, the partition efficiency decreases with the increase of the helix diameter. 

For a given length of tube, the partition efficiency decreases with the increase of the helix diameter. 

Other than B-form DNA, there are other forms of DNA that are more distorted from Watson and Crick ideality. These include A-form, C-form, D-form and T-form DNA. Of these, A-form DNA is the most similar to B-form DNA (Figure 1.73). The only major difference is that the 2 -deoxy-/3-D-ribofuranose rings of A-form DNA exist in an alternative C -endo twist conformation (Figures 1.71 and 1.73). Consequently, the helix diameter is wider and there are 11 base pair residues per turn (Table 1.2). A-form DNA also possesses shallow major and minor grooves. Z-form DNA, by contrast, is radically different from B-form... 

The structure of deoxyribonucleic acid was determined in 1953 by Watson and Crick to consist of two antiparallel strands of deoxyribonucleic acid coiled around a common axis in a double helix (Fig. 6.6). The purine and pyrimidine bases are on the inside of the helix, whereas the phosphate and deoxyribose units are on the outside. The planes of the bases are perpendicular to the axis of the helix. The planes of the sugars are at approximately 70° to those of the bases. The helix diameter is 20 A adjacent bases are separated by 3.4 A along the... 

A polymer solution is to be heated from IS C to 27°C before use as a thinner in a wall paint. The heating is to be carried out in a stainless steel vessel (1 m diameter) fitted with an anchor agitator of diameter equal to 0.9 m which is rotated at 100 RPM. The tank which is filled up to 0.8 m depth is fitted with a helical coil (helix diameter 0.8 m) made of 25 mm od and 22 mm id copper tube (total external heat transfer area of 2 m ). Hot water at a mean temperature of 45°C (assumed to be approximately constant) is fed to the coil at a rate of 30 kg/min. 

According to the Watson-Crick model, two helically arranged chains are wound around each other to produce a double helix in double-strand deoxyribonucleic acids (Figure 29-2). The double helix rotates upward in a clockwise direction (P-helix). The screwlike rotation of the strands causes periodically recurring large and small furrows to occur at 2.2 or 1.2 nm. Thus, after 3.4 nm or ten base pairs, a complete rotation has occurred. The double helix diameter is about 2 nm. 

Internal Loop Interhelica Angle O Helix Axis Displacement (A) OverAJnder- Winding (°) Internal Curvature o Helix Diameter (Min/Max) Major Groove (A) Minor Groove (A)... 

Usually, as-grown nanotubes form ropes which consist of 10-1000 individual CNTs of different helixes, diameters, and therefore conductivity. As it is important for nanoelec-tronic devices to be composed of CNTs of the same electronic properties, ropes of CNTs would not be appropriate. Therefore, individual CNTs were isolated through the son-ication of carboxylated SWNT bundles in DMF. Smalley and coworkers noticed that the carboxylated SWNTs were attracted to -NH2-functionalized surfaces the carboxylated SWNTs were not observed on -CH3-functionalized surfaces. On the basis of this observation, it was possible to position individual CNTs by chemically functionalizing nano-pattems on Si02. The process was accomplished by (i) preparing a hydrophobic Si surface on Si02 using... 

Figure 14. Top view (right) and side view (left) of a homo-DNA backbone in idealized confcMmation where tension angle 5 is changed from 60 to 80 and 1(X) (tension axis 5 perpendicular to projection plane of top view). 6 = 60 linear strand 5 = 1(X) helical strand, helix diameter ca. 13 A [2].

The number of monomers per turn (n) and the pitch in the axial direction per residue (h) is highly variable in a hollow helical conformation. The value of n is between 2 and 10, whereas h can be near its limit value of 0. The conformation of a P(1 3)-glucan, with n = 5.64 and h = 3.16 A, is shown in Fig. 4.12, b. The helial conformation can be stabilized in various ways. When the helix diameter is large, inclusion (clathrate) compounds can be formed (Fig. 4.13, a cf. 4.4.4.14.3). More extended or stretched chains, with smaller helix diameter. 

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