摘要:

Energy transfer between photoexcited flavin and cytochrome c has been investigated in order to estimate intermolecular forces between flavin and cytochrome c. The quenching of the fluorescence of flavin by cytochrome c excited at 372 nm was found to be much greater than that excited at 465 nm. This dependence of the quenching on the exciting wavelength is considered to be due to the “prerelaxational” fast energy transfer. From the analysis of the quenching of the fluorescence of FMN and lumiflavin by cytochrome c excited at 465 nm, it was concluded that 1) the quenching is mainly controlled by resonance energy transfer, and 2) the heterogeneous dispersion state of molecules due to electrostatic forces makes the critical transfer distance,R0, of the resonance process longer than the real distance. For the quenching of the fluorescence of flavodoxin by cytochrome c, it was found that complex formation is a dominant process and is controlled to a great extent by electrostatic forces. Furthermore, fluorescence decay curves were measured by a single-photon counting method in order to estimate the dynamic processes of flavin fluorescence. The results also showed that the resonance process exists in the energy transfer between flavin and cytochrome c.

ISSN:0022-233X    

DOI:10.1080/00222338908051986

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

cis-Diamminedichloroplatinum(II) binds covalently to the bases of DNA and exhibits a number of distinct modes of binding that can influence the structure of DNA. Of these, the intrastrand crosslink to adjacent guanines appears responsible for unwinding of supercoiled DNA and stimulating S1 nuclease activity. Investigation of the binding that occurs in chromatin reveals that the antitumor drug also forms crosslinks between DNA and the HMG proteins 1, 2, and E in micrococcal nuclease-accessible regions, in addition to protein-protein crosslinks between the LMG proteins. From the studies on both DNA and chromatin, we propose 1) a model for the interaction of, and the general location of, these HMG proteins in chromatin and 2) novel mechanisms for the possible action ofcis-diamminedichloroplatinum(II) in cancer chemotherapy.

ISSN:0022-233X    

DOI:10.1080/00222338908051987

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

3,8,13,17-Tetramethyl-7,12-divinyl-2,18-bis(18-hydroxyoctadecyl propionate) porphinato zinc (BHPZn) and a model compound, dimethyl ester of protoporphinato zinc (DMPZn), were synthesized and incorporated into the hydrophobic region of bilayer membrane of dipalmitoylphosphatidylcholine (DPPC) liposome. The introduction of long alkyl groups onto the porphyrin ring is effective for restriction of porphyrin aggregation in the bilayer membrane of DPPC liposome. When the molar ratio of DPPC lipid to porphyrin is above 100, the spectrum of BHPZn in the liposome suggests that it is in a typically monomeric state. Quenching of BHPZn fluorescence in the hydrophobic bilayer membrane by hydrophilic quenchers is slow and shows smaller Stern-Volmer constants, while the quenching by hydrophobic quenchers shows much larger Stern-Volmer constants than that of the model compound, DMPZn. These results suggest that the location of the porphyrin ring of BHPZn is fixed at a certain depth in the hydrophobic bilayer membrane of DPPC liposome, and that that of DMPZn is widely distributed in the whole hydrophobic region.

ISSN:0022-233X    

DOI:10.1080/00222338908051988

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In this paper a new type of activation of polymer-metal complexes on an enzyme immobilized in them will be described. The polymer is partially quaternized poly(dimethylaminomethylstyrene) (PQPD). The metals (Me) include the fourth-period transition elements trivalent chromium and divalent iron, cobalt, nickel, copper, zinc, and manganese. Glucose oxidase (GO) is the enzyme. These complexed metallic ions had some activation effects on GO for most PQPD-Me-GO complexes. Specifically, the activity of the GO was increased up to 1.8-fold by chromium ion in the complex compared to immobilized GO without metal ion. The extent of activation of the polymer-metal complexes on GO was found to be related to the ionic radius and could be expressed quantitatively by a regression equationa= (4.5 – 42.3r) × 100, wherearepresents the relative activity of the immobilized enzyme andrrepresents the metal ion radius in the polymer-metal-enzyme complex.

ISSN:0022-233X    

DOI:10.1080/00222338908051989

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A new type of polyether-polyester block copolymer (MPEE) consisting of two components of polyethers (PTMGT and PEGT) as soft segment and one polyester (PET) as hard segment has been synthesized. It has also been investigated in comparison with blended polyether-polyester block copolymer (BPEE) consisting of the same composition ratio of hard and soft segments and both of the two polyethers (PTMG and PEG). It was found that 1) Improvement of blood compatibility of polyether-polyester block copolymer can be achieved by introducing the hydrophilic component PEG into it; 2) generally the blood compatibility of MPEE is better than that of BPEE; 3) at a specific molar ratio of PTMGT-PET to PEGT-PET (60/40), the blended copolymer (BPEE 60/40) shows the best blood compatibility, as well as the best mechanical properties. This might be related to smaller-size microphaseseparated structures. The relationship between blood compatibility and structure of the copolymer is discussed. Polyether-polyester block copolymer containing hydrophilic and hydrophobic components might be a useful material with antithrombogenicity.

ISSN:0022-233X    

DOI:10.1080/00222338908051990

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Recent work on the crystallographic and morphological structure of semicrystalline PEO complexes with alkali metal salts is described. The thermal properties of the materials and the influence of solvent on complex formation is also considered. The dependence of the ionic conductivity of the complexes on their morphology, the temperature and ionic association is discussed and some current work relating to the mechanism of conduction is considered. The various strategies which have been adopted to suppress crystallinity and so to optimize ionic conductivity, including networks, “comb” structures, and linear copolymers, are reviewed. The morphological organization and mesogenic behavior of some novel crystalline complexes of PEO with organo-alkali salts, such as sodium phenolates and naphtholates, are discussed. Some PEO composite materials which have mixed electronic-ionic mechanisms of conductivity are also described.

ISSN:0022-233X    

DOI:10.1080/00222338908051991

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Oligo(oxyethylene) methacrylate, MEO, has been synthesized as a basic material to design a polymeric solid electrolyte. The homopolymer P(MEO) has a glass transition temperature of -78°C. P(MEO) solubilizes inorganic salts without solvent, and the dissociated ions migrate fast to give very high ionic conductivity, above 10−5S/cm for ac. Although the ac conductivity is high, the current decreases gradually under dc conditions. This is improved by the design of an ionic conductor using only cations. Poly[oligo(oxyethylene) methacrylate-co-alkali metal methacrylate], P(MEO-MAM), is prepared as an organic solid electrolytes which allows cationic single-ion conduction. The ionic conductivity of the films depends on the electrolyte content, the dissociation energy of the comonomeric electrolytes, and the degree of segmental motion surrounding the ions in the polymer matrix. The ionic conductivity of Li or K is around 10−6S/cm in these polymeric systems at 80°C. The plot of logarithmic conducticity vs reciprocal absolute temperature is a curved line. The Williams-Landel-Ferry parameters, calculated from the temperature dependence of the conductivity, coincided with theoretical values within a certain range. The single-ion conduction in these films is concluded to be affected considerably by the segmental motion of the matrix polymer. This is also confirmed by the Vogel-Tammann-Fulcher plot.

ISSN:0022-233X    

DOI:10.1080/00222338908051992

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Complex formation of poly(ethylene oxide) (PEO) with divalent barium and strontium salts was investigated in methanol. In these systems the complexation was accompanied by a considerable degree of ionic association. An analytical model for the polymer-ion complexation based on a one-dimensional lattice model was proposed. According to this model, the electrostatic effects between the bound ions were separated from the total free energy change of the binding. Three binding constants, i.e., the ionic association constantKA, the cation binding constant,Kc, and the anion binding constant,Ka, could be estimated.KAfor barium and strontium salts was comparable, and the effect of counteranions onKAwas not large.Kcfor barium salts was almost independent of the kind of counteranion and larger than that for corresponding strontium salts, indicating stronger polymer-ion interaction for barium salts. The anion binding constant,Ka, was strongly dependent upon the kind of anion, and the order was CI−<Br−<SCN−<CIO4−.The pronounced ion binding for larger anions may be explained by the more favorable free energy change of desolvation. Finally, the concentration of free and bound ionic species was determined as a function of PEO concentration.

ISSN:0022-233X    

DOI:10.1080/00222338908051993

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Electrothermomechanical film (ETMF) is a cellular, biaxially oriented plastic film which is coated with electrically conductive layers. It is an elastic impedance. ETMF relates electrical, mechanical, and thermal energies as well as parameters. The functional basis of the film comprises the compression of gases, the mechanical parameters of the film, and the electric or magnetic field. By exploiting these basic characteristics, the film can be used in measuring techniques, in acoustics, in ultrasonics, in motion elements, in energy transformation, etc.

ISSN:0022-233X    

DOI:10.1080/00222338908051994

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The electrochemical and electrochromic properties of polymer films containing a conductive powder (SnO2/TiO2) have been investigated. The films are complexes of polytetramethyleneviologen and poly(p-styrenesulfonic acid). It was found that the coloration (purple) and bleaching rates of the composite films increase markedly with increasing conductive powder content(x). The coloring and bleaching of the composite film withx= 95 wt% were about 7 and 44 times faster, respectively, than those for an equivalent film without conductive powder. This increase in the rate of color change by introduction of a conductive powder was found to be correlated with the apparent diffusion coefficient (Dapp) for the diffusionlike charge-transport process within the composite films which increases with increasingx. TheDappfor the reduction process of the film withx= 95 wt% was larger by about 3 orders of magnitude than that for the unfilled film.

ISSN:0022-233X    

DOI:10.1080/00222338908051995

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor