摘要:

AbstractMeasurements have been made of the nuclear magnetic relaxation timesT1andT2of the protons of water in hair. These are interpreted as showing that water molecules in hair exist in a continuous range of environments with a wide spread of rates of molecular rotation. Even at high water contents most of the water molecules are much less mobile than molecules in bulk water. The term “mobility” is given a quantitative mean

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041002

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

年代:1966

数据来源: WILEY

摘要:

AbstractStudies of the properties of copolymers ofN‐carboxy sarcosine anhydride with otherN‐carboxy α‐amino acid anhydrides have shown that the secondary structure may be a function of the type of initiator used. In particular, when polysarcosine is the initiator, and the “chain effect” becomes possible, blocklike character appears in the copolymer. This is the result of selective and rapid polymerization ofN‐unsubstitutedN‐carboxy α‐amino acid anhydrides by the chain‐effect mechanism. In suitable circumstances, therefore, the latter may be used to induce order into copolymeriz

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041003

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

年代:1966

数据来源: WILEY

摘要:

AbstractSpectrophotometric acid titrations of DNA samples of different GC content were performed at different wavelengths. From the acid titration profile and absorbance changes of deoxycytidine‐5′‐monophosphate and DNA the extent of protonated cytosine within the DNA double‐stranded molecule was estimated (pK3.65 at 25°C. in 0.02MKCl). At constant counterion concentration and temperature the maximum of protonated cytosine in DNA before denaturation occurs depends on the base composition and can exceed 50%. The thermal stability of the DNA secondary structure is strongly reduced with increasing amount of ionized cytosine residues. The degree of protonation of cytosine in DNA is decreased with increasing counterion conce

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041004

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

年代:1966

数据来源: WILEY

摘要:

AbstractStudies were made of the influence of hydrostatic pressure on the helix–coil transitions of poly (A + U) and poly (A + 2U). The results were analyzed by a thermodynamic treatment which emphasized the cooperative aspect of the transitions. The helix‐to‐coil volume changes were found to be small and negative indicating pressure stabilization of the coil form. The significance of the results with respect to other denaturation measurements was disc

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041005

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe optical rotatory dispersion curves of the proflavine cation were measured in the spectral range 400–500 mμ. No optical activity was observed for the free cation but a large positive Cotton effect appeared in the presence of DNA. The effect of ionic strength, denaturation of the DNA, and the DNA/proflavine ratio were studied. The dependence of the magnitude of the Cotton effect on the DNA/proflavine ratio suggests that a nearest‐neighbor interaction between bound proflavine molecules is necessary for optical activity. A simple statistical treatment was made which indicated that only a small number of proflavine molecules are required in close proximity for optical activity to occur. Denaturation of the DNA did not destroy the optical activity, which shows that long runs of DNA double helix are not necessary for optical activity of the ligand molecules. The optical rotatory dispersion curves of acridine orange which was bound to DNA were also measured. Two Cotton effects of opposite sense could be distinguished, the relative magnitudes of which depended on the DNA/acridine orange ratio and the state of denaturation of the DNA. The apparent differences from the proflavine‐DNA system can to a large extent be explained in terms of the tendency of acridine orange to form aggr

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041006

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

年代:1966

数据来源: WILEY

摘要:

AbstractWater‐insoluble films of poly‐L‐lysine, crosslinked with formaldehyde, were suspended in aqueous media and their relative lengths measured as a function of pH. A sharp transition of the polymer was observed in the pH range which corresponded with that observed in polylysine solutions by optical rotation or dilatometry. In NaBr and NaCl solutions the coiled form of the polylysine film shrinks with increasing salt concentration, but in NaHCO3solution the extent of the contraction is larger, and the coil–helix transition of polylysine occurs at lower pH when NaHCO3is added to the medium. If one assumes the formation of amino carbamate in this case, this phenomenon can be well explained. Urea does break up the hydrogen bonds in helical polylysine film, but not completely. This result is interesting compared with that obtained for poly(L‐glutamic acid). After the coil–helix transition region was found by film experiments, the volume change associated with the coil‐to‐helix transition was measured and found to be about 1–l.5 ml. per amino residue after taking electrostatic interaction into consideration. This value is nearly same as that obtained for poly(L‐glutamic acid). By contrast, the value for poly‐γ‐benzyl‐L‐glutamate was reported to be −0.077 ml./mole of repeating unit. So it is still necessary to determine the magnitude and direction of the volume change for

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041007

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

年代:1966

数据来源: WILEY

摘要:

AbstractFrom observations on model compounds having two or more benzene rings and structures analogous to high polymers of interest (polystyrene and aromatic polypeptides), we conclude that interactions of pairs of benzene rings sufficiently strong to cause observable excimer emission requires that these rings be separated by no more than 2–3 A. and that they be in an approximately parallel‐stacked, face‐to‐face arrangement. If a molecule does not have such a configuration of its aromatic rings in its ground‐state conformation, strong excimer emission can still occur provided there is a conformation with the appropriate ring configuration which can be attained within the radiative lifetime of the exci

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041008

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

年代:1966

数据来源: WILEY

摘要:

AbstractPrevious fluorescence and phosphorescence studies of aromatic model compounds have been extended to polymers: “atactic” and isotactic polystyrene, seven aromatic poly‐(amino acids), and two proteins. We have confirmed previous observations that both forms of polystyrene exhibit strong excimer fluorescence emission at room temperature but not at 77°K. Of the poly(amino acids) (all observed in helix‐supporting solvents), poly‐L‐phenylalanine, poly(α‐benzyl‐L‐aspartic acid), and poly‐1‐benzyl‐L‐histidine likewise show excimer emission at room temperature but not at 77°K., while poly‐L‐tyrosine, poly‐L‐tryptophan, poly(γ‐benzyl‐L‐glutamic acid), and poly‐S‐benzyl‐L‐cysteine exhibit no excimer emission at either temperature. The aromatic residues of bovine serum albumin exhibit only “normal” fluorescence, but, lysozyme appears to be unique among proteins in showing excimer‐like tryptophan emission in the native state; its luminescence becomes “normal” upon denaturation. It appears very probable that none of these polymers has a ground‐state conformation in which the aromatic groups have face‐to‐face orientations appropriate for excimer interaction. It is concluded that at room temperature absorption of light can cause local “melting” of regular (usually helical) structures and thus, in some polymers, permit the attainment of a face‐to‐face arrangement of aromatic rings within the radiative lifetime of their excited singlet states. In certain other polymers (for reasons not clear at present), and in all polymers at 77°K., this does not occur. This concept is extended to provide a bettor basis for understandin

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041009

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

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041010

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

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360041001

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

年代:1966

数据来源: WILEY