摘要:

AbstractSodium hyaluronate (NaHy) and sodium carboxymethyl cellulose (NaCMC) behave similarly with respect to concentration.N3of an added 1 : 1 electrolyte. The second virial coefficientA2(light scattering) is identical within experimental error at a given.N3. The limiting viscosity number [η] also varies withN3−1/2in similar fashion for samples of similar [η] of the two polymers. Differences in Na+activity in salt‐free solutions are interpreted on the basis of weaker Na+binding in NaHy, presumably due to the greater charge separation along its chain backbone. Added electrolyte is excluded in dialysis more strongly by NaHy (or its acid form) than by NaCMC. The Flory parameter Φ is smaller in good solvents for NaHy, as for many other polyelectrolytes, than for nonionic po

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractCalculations of the dependence of the conformational energy and the rotational strength of the amiden–π* electronic transition (in a series of α‐helical polyhel‐α‐ amino acids with different side chains) on conformation have been carried out. The conformational energies were computed by procedures developed in this laboratory; the computation of rotational strengths was carried out by the method of Schellman and Oriel, with a slight modification. Polyamino acids with both nonpolar and polar side chains were considered; in the latter case, it was assumed that the only influence of the polar side chain was on the backbone conformation and on the electrostatic field which perturbs the amide chromophore of the backbone. Only conformations in the range of backbone dihedral angles of the right‐ and left‐handed a‐helices were considered, and the assumption of regularity (i.e., uniformity of dihedral angles in every residue) was made. The rotational strength per residue was found to vary markedly with chain length (in oligomers of up to 40 residues long); both the conformational energy per residue and the rotational strength per residue were found to vary significantly with the backbone conformation, which in turn depends on the nature of the side chain. The geometry of the hydrogen bond in the α‐helical backbone is the most important factor which influences the dependence of the rotational strength on conformation. The implications of these results, for the interpretation of experimental circular dichroism and optical rotatory dispersion

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractIn order to test theoretical predictions that poly‐L‐valine can exist in an α‐helical conformation, water‐soluble block copolymers ofL‐valine andD,L‐lysine were prepared. By carrying out the synthesis on a resin support (with the use ofN‐carboxyanhydrides) contamination of the individual blocks by any unreacted monomer from the previous block was avoided. A single glycine residue was incorporated at the C‐terminus of the chain for use in amino acid analyses. Using optical rotatory dispersion and circular dichroism criteria, about 50% of the short valine block of (D,L‐lysine HCl)18‐(L‐valine)15‐(D,L‐lysine‐HCl)16‐glycine was found to be in the right‐handed α‐helical conformation in 98% aqueous methanol, in water, the polymer appears to be a dimer, with the valine block being involved in the formati

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractHeat‐denatured DNA from HeLa cells interacts with natural as well as synthetic polysaccharides. Glucose does not inhibit the interaction nor will it produce it. Polysaccharides with a molecular weight of 10000 or greater are required before the interaction takes plac

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractA series of copolymers of β‐p‐nitrobenzylL‐aspartate with β‐benzylL‐aspartate and with β‐mcthylL‐aspartatc in helix‐supporting and helix‐breaking conditions have been reexamined by using ultraviolet isotropic, absorption, optical rotatory dispersion, and circular dichroism techniques. Many different conformations are apparent, depending on solvent and temperature. Chloroform, trifluoroethanol, and methylene dichloride support the left‐handed helical conformation of the copolymers containing less than about 20 mole‐% nitroaromatic residues and the right‐handed helical conformation of the copolymers containing more than approximately 30 mole‐% nitroaromatic residues. In trifluoroacetic acid all the copolymers are in a random‐coil conformation. In hexa‐fluoroacetone trihydrate and in trimethyl phosphate, the copolypeptides with low nitroaromatic residues content are predominantly in a disordered conformation, while those with high nitroaromatic residues content show a right‐handed helical array. Reversible helix‐ramlom‐coil transitions are observed with increasing temperature in trimethyl phosphate. An example of right‐handed‐left‐handed helix reversible transition with temperature is reported in a chloroform‐trimethyl phosphate (2:1) mixture. Nitrobenzyl‐nilrobenzyl side‐chain interactions in chloroform, but not in trifluoroacetic acid or in trimethyl phosphate, have been confirmed. For the first time we report the circular dichroism spectra in which then‐π* peptide band of a left‐h

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe dichroic ratios of T5st‐O and T2H bacteriophage DNA molecules were measured throughout the ultraviolet region of the spectrum. Two methods of DNA orientation were studied: (1) orientation in solution in a Shimadzu flow dichroism instrument attached to a Beckman DU spectrophotometer, and (2) alcohol precipitation of the DNA from solution and orientation in a thin film on the quartz face of a humidity chamber. Spectra in the latter case were recorded using a Gary Model 14 spectrophotomcter fitted with Glan prisms. The lower wavelength limit was 215 mμ in both systems. The DNA preparations were carefully characterized as to spectral purity, sedimentation coefficient, hyperchromicity, protein content, and DNA content. In addition, the structure of the DNA oriented in films was inferred from x‐ray diffraction patterns of fibers of the precipitated DXA. The A and B configurations of DNA in films could not be distinguished by the dichroic ratio measuiements. The dichroic ratio obtained for the film‐oriented DNA at high relative humidity shows the same wavelength dependence as for the flow‐oriented DNA. The same wavelength dependence for DNA in the fibrous state and in solution, when considered together with the x‐ray diffract ion results, indicates that DNA in solution maintains an orientation of bases which is similar to that in fibers. I1Or both solutions and films of DNA, the dichroic ratio is constant from 290mμ to 240 mμ and increases at wavelengths below 240 mμ. The increased parallel absorption below 240 mμ is consistent with the existence of ann→π* transition. The inherent molecular dichroic ratio is found to be the same for T5st‐O DNA and T2H DNA in solution, and is a maximum of 0.

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThis paper gives a very simple method based on the characteristic property of the electric free energy to calculate the repulsive force between parallel rodlike macroions in a solution as a function of the charge density on rods. The total extensive force (∂f/∂X) of an assembly ofmrods of lengthland charge numbern(charge density −neo/l) at small extensionXin the absence of low molecular sals is given bywherezis the valency of counterions andQ(=neO2/εkTl) is a dimensionless quantity representing the charge density. The repulsion between two parallel rods is given by puttingm= 2. At large charge densities the repulsion is very much smaller than the direct coulomb force between charged rods, even at small distances. The addition of low molecular salts does not depress the repulsion appreciably, as long as the average concentration of salt ions is much smaller than the concentration of counterions accumulated in the space between rods. The effect of fluctuation of the coumerion distribution is also analyzed, and it is found that the attractive force due to the ion fluctuation may predominate over the above repulsive force in the case of polyvalent counterions and rods of high charge densities at small dis

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractIf the collagen triple helix is so built as to have one set of NH ⃛ O hydrogen bonds of the type N3H3(A) ⃛ O2(B), then it is possible to have a linkage between N1H1(B) and O1(A) through the intermediary of a water molecule with an oxygen O 1Wleading to the formation of the hydrogen bonds N1(B) ⃛ O 1Wand O 1W(A). In the same configuration, another water molecule with an oxygen O 1Wcan link two earbonyl oxygens of chains A and B forming the hydrogen bonds O 2WO1(A) and O 2WO0(B). The two water oxygens also become receptors at the same time for CH ⃛ O hydrogen bonds. Thus, the neighboring chains in the triple helix are held together by secondary valence bond linkages occurring regularly sit intervals of about 3 Å along the length of the protofibril. The additional water molecules occur on the periphery of the proto‐fibril and will contribute their full share towards stabilizing the structure in the solid state. In solution, they will be disturbed by the medium unless they are protected by long side groups. It appears that this type of two‐bonded structure, in which one NH ⃛ O bond is to a water molecule, can explain several observations on the stability and hydrogen exchange properties of collagen itself and related synthetic polypeptides. The nature of the water bonds and their strength are found to be better in the one‐bonded structure proposed from Madras than in the one having the c

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe study of the structure of KBr–amylose begun by Senti and Witnauer has been extended by a three‐dimensional crystallographic analysis and by stereochemical considerations. Location of Br−at (0.200, 0.200, 0.000) and K+at (0.540, 0.540, 0.000) was obtained from the three‐dimensional map of vector interactions. By using known parameters for theD‐glucose residue and accurate space‐filling models, an amylose helix was constructed to meet the fiber repeat spacing of 16.1 Å. The helix was determined to be left‐handed, and the correct space group for KBr–amylose isP43212. Placement of the helix in the unit cell resulted from structure factor calculations; minima in the grid ofRvalues were checked with space‐filling models to establish the final structure. Both ions are located in a waterlike environment. The oxygen atoms O(2), O(3), and O(4) from glucose residues on adjacent chains co

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1968.360061101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY