共查询到20条相似文献，搜索用时 31 毫秒
1.
用荧光光谱法结合紫外可见吸收光谱法、圆二色谱法(CD)研究了1-(2-吡啶偶氮)-2-萘酚(PAN)与牛血清白蛋白(BSA)的相互作用。研究表明,PAN与BSA发生了生成复合物的静态猝灭作用;紫外可见吸收光谱辅证了PAN对牛血清白蛋白的猝灭机制属于静态猝灭;利用Van’t Hoff方程计算体系的热力学参数焓变(ΔH)和熵变(ΔS),ΔH和ΔS的值均小于0,表明两者主要以氢键和范德华力作用力结合;圆二色谱法研究表明,PAN指示剂引起BSA二级结构的改变。 相似文献
2.
Conformations of signal peptides induced by lipids suggest initial steps in protein export 总被引：21，自引：0，他引：21
Despite the requirement for a functional signal sequence in protein export, little is known of the conformational properties and membrane interactions of these highly hydrophobic amino terminal extensions on nearly all exported proteins. The Escherichia coli lambda phage receptor signal sequence was studied in phospholipid monolayers by circular dichroism and Fourier transform infrared spectroscopy; the signal peptide was shown to prefer an alpha-helical conformation when inserted into the lipid phase. However, interaction with the lipid surface without insertion induced the signal sequence, which is unstructured in bulk aqueous solution, to adopt a beta structure. These observations are combined in a model for the initial steps in signal sequence-membrane interaction in vivo. 相似文献
3.
Treatment of human red blood cell membranes with phospholipase C releases 68 to 74 percent of the total membrane phosphorus into solution, through hydrolysis of membrane phospholipids to diglycerides and water-soluble phosphorylated amines. In spite of this drastic change, the membrane remains intact in phase microscopy, and the average protein conformation in the membranes, as determined by circular dichroism measurements in the ultraviolet, is unaffected. These results are readily explained by a model of membrane structure that is stabilized by hydrophobic interactions and in which the polar and ionic heads of lipids are on the outer surfaces of the membrane, in contact with the bulk aqueous phase and accessible to the action of phospholipase C. 相似文献
4.
The chiral fullerene C(76) was kinetically resolved by asymmetric osmylation providing an example of an optically active allotrope of a pure element. C(76) recovered from the treatment of racemic C(76) with OsO(4) and a chiral alkaloid ligand, showed a specific rotation [alpha](D) of -4000 degrees (> 97 percent enantiomeric excess) and a circular dichroism spectrum corresponding to the ultraviolet spectrum. Regenerated C(76) formed by reducing the asymmetrically osmylated C(76) with SnCl(2) was enriched in the opposite enantiomer. Analysis of the local curvature of the C(76) molecule indicated that OsO(4) should selectively add to 2 of the 30 types of bonds in C(76). This regioselectivity was supported chromatographically and interpreted in terms of the kinetic resolution. 相似文献
5.
Far-ultraviolet stopped-flow circular dichroism 总被引：2，自引：0，他引：2
A stopped-flow circular dichroism instrument, with a total accessible wavelength range of 200 to 750 nanometers, has been constructed and provides a spectroscopic method for kinetic investigations of a wide array of fast reactions in which optical activity changes in absorbing regions are involved. An important biochemical application depends on the far-ultraviolet capability, which allows observation of the rapid alterations in backbone conformation associated with folding and unfolding reactions of proteins. Results obtained by following two such reactions at 222 nanometers represent direct monitoring by circular dichroism of rapid secondary structure changes in proteins. 相似文献
6.
The orbital parameters of a satellite revolving around 22 Kalliope indicate that the bulk density of this main-belt asteroid is 2.37 +/- 0.4 grams per cubic centimeter. M-type asteroids such as Kalliope are thought to be the disrupted metallic cores of differentiated bodies. The low-density indicates that Kalliope cannot be predominantly composed of metal and may be composed of chondritic material with approximately 30% porosity. The satellite orbit is circular, suggesting that Kalliope and its satellite have different internal structures and tidal dissipation rates. The satellite may be an aggregate of impact ejecta from an earlier collision with Kalliope. 相似文献
7.
Conformation of blood-group and virus receptor glycoproteins from red cells and secretions 总被引：2，自引：0，他引：2
Optical rotatory dispersion of human blood-group and virus receptor glycoproteins from erythrocytes and secretions was studied in the far-ultraviolet. Erythrocyte membrane blood-group glycoproteins, with potent virus receptor activities, contained significant alpha-helical and extended beta conformations, whereas the glycoproteins of secretions were largely disordered. These conclusions were supported by determination of the Moffitt constants (b(0)) and by measurements of circular dichroism. 相似文献
8.
de Jong JJ Lucas LN Kellogg RM van Esch JH Feringa BL 《Science (New York, N.Y.)》2004,304(5668):278-281
In nature, key molecular processes such as communication, replication, and enzyme catalysis all rely on a delicate balance between molecular and supramolecular chirality. Here we report the design, synthesis, and operation of a reversible, photoresponsive, self-assembling molecular system in which molecular and supramolecular chirality communicate. It shows exceptional stereoselectivity upon aggregation of the molecules during gel formation with the solvent. This chirality is locked by photochemical switching, a process that is subsequently used to induce an inverted chiral supramolecular assembly as revealed by circular dichroism spectroscopy. The optical switching between different chiral aggregated states and the interplay of molecular and supramolecular chirality offer attractive new prospects for the development of molecular memory systems and smart functional materials. 相似文献
9.
Circular dichroism of biological macromolecules 总被引：11，自引：0，他引：11
S Beychok 《Science (New York, N.Y.)》1966,154(754):1288-1299
Circular dichroism, the unequal absorption of right and left circularly polarized light, is a manifestation of optical activity in the vicinity of absorption bands. To the experimental scientist interested in the conformation of macromolecules and in the sensitive response of optical activity to conformational alteration, it offers a relatively new and powerful means of understanding the environment of chromophoric residues. As a tool in the elucidation of electronic spectra, it should be useful to the theoretical scientist in identifying weakly allowed absorption bands as well as in providing rotational parameters which can be compared with the developing theory of optical activity. I have stressed application of circular dichroism, to experimental aspects of protein and nucleic acid conformation in solution. Much is still uncertain in particular quantitative details. However, even these early results shed new light and yield new information on the conformation of these molecules. 相似文献
10.
Epitaxial BiFeO3 multiferroic thin film heterostructures 总被引：2，自引：0，他引：2
Wang J Neaton JB Zheng H Nagarajan V Ogale SB Liu B Viehland D Vaithyanathan V Schlom DG Waghmare UV Spaldin NA Rabe KM Wuttig M Ramesh R 《Science (New York, N.Y.)》2003,299(5613):1719-1722
Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters. 相似文献
11.
目前土壤水分特征曲线（h-θ曲线）的研究普遍采用vanGenuchten模型（简称VG模型）。利用不同取样精度的土壤,将土壤质地（砂土、粘粒、粉粒含量）和容重作为输入值,探讨了使用基于土壤转换函数的BP神经网络模型来预测0～20cm表层土壤水分特征曲线参数,用甘肃称钩河流域小流域的土样进行了预测和误差分析。结果表明,使用线性回归能够减小预测误差与实测值差距;BP神经网络预测饱和体积含水量的准确性比预测剩余体积含水量和田间持水量要高。为了进一步提高预测精度,还应尽可能地包括土壤结构、有机质含量等信息。 相似文献
12.
The compositions of Earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems. Although this suggests that Earth largely accreted from enstatite chondrites, definitive proof of this model has been lacking. By comparing the silicon (Si) isotope signatures of several extraterrestrial materials with terrestrial samples, we show that they cannot be explained by core-formation scenarios involving a bulk Earth of enstatite chondrite composition. Si isotope similarities between the bulk silicate Earth and the Moon preclude the existence of a hidden reservoir in the lower mantle, a necessary condition of the enstatite chondrite model, and require an equilibrium process after the Moon-forming impact. A three-end-member chondritic mixing model for Earth reconciles the Si isotope similarities between enstatite chondrites and Earth. 相似文献
13.
Zinc-dependent structure of a single-finger domain of yeast ADR1 总被引：38，自引：0，他引：38
G Párraga S J Horvath A Eisen W E Taylor L Hood E T Young R E Klevit 《Science (New York, N.Y.)》1988,241(4872):1489-1492
14.
Scholl A Stohr J Luning J Seo JW Fompeyrine J Siegwart H Locquet J Nolting F Anders S Fullerton EE Scheinfein MR Padmore HA 《Science (New York, N.Y.)》2000,287(5455):1014-1016
Antiferromagnetic domains in an epitaxial thin film, LaFeO(3) on SrTiO(3)(100), were observed using a high-spatial-resolution photoelectron emission microscope with contrast generated by the large x-ray magnetic linear dichroism effect at the multiplet-split L edge of Fe. The antiferromagnetic domains are linked to 90 degrees twinned crystallographic regions in the film. The Neel temperature of the thin film is reduced by 70 kelvin relative to the bulk material, and this reduction is attributed to epitaxial strain. These studies open the door for a microscopic understanding of the magnetic coupling across antiferromagnetic-ferromagnetic interfaces. 相似文献
15.
A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves in preferentially exciting single enantiomers in certain regions of space. By probing induced fluorescence intensity, we demonstrated experimentally an 11-fold enhancement over CPL in discrimination of the enantiomers of a biperylene derivative by precisely sculpted electromagnetic fields. This result, which agrees to within 15% with theoretical predictions, establishes that optical chirality is a fundamental and tunable property of light, with possible applications ranging from plasmonic sensors to absolute asymmetric synthesis. 相似文献
16.
Stereodynamic complexes of copper were found to undergo inversion of a helical chiral element upon oxidation or reduction. The amino acid methionine was derivatized by the attachment of two chromophores to the nitrogen atom. The resultant ligands formed stable complexes with Cu(I) and Cu(II) salts. For a derivative of a given absolute chirality, the complexes afford nearly mirror image circular dichroism spectra. The spectral changes originate from reorientation of the nitrogen-attached chromophores due to a conformation interconversion driven by the exchange of a carboxylate for a sulfide ligand. The electrically induced chirality inversion coupled with strong interactions with polarized light is unique and may lead to novel chiral molecular devices. 相似文献
17.
A. V. Pasynkov A. A. Zavalin E. N. Pasynkova N. A. Skorobogatykh 《Russian Agricultural Sciences》2017,43(5):371-375
The change in the main quality parameters for brewing barley grain at fractionation has been studied to develop the method of their regulation. The barley grain of different fractions is proven unequal in the biochemical composition and the technological quality. The fractionation of the grain samples collected from the large homogenous grain bulks and the relevant analyses can provide the possibility to determine a wide range of quality parameters for the specific fractions and their grain-size dependencies. The basic parameters for the technological quality of barley grain in a certain bulk may be changed (raised or lowered) to the regulatory standards or the standards that consumers demand with the use of the appropriate top and (or) bottom sieve installation in the grain cleaning machines of secondary cleaning. 相似文献
18.
Three cysteine-rich proteins of molecular weight 4000 to 7000, containing 4 to 7 gram atoms of cadmium, zinc, and copper per mole were isolated from Pseudomonas putida growing in 3 mM cadmium. The three proteins were induced during different phases of growth, and the smallest (molecular weight 3600; 3 gram atoms of cadmium) was released into the medium when the cells lysed. The results of amino acid analyses and of ultraviolet, circular dichroism, electron paramagnetic resonance, and cadmium-113 nuclear magnetic resonance spectroscopy suggest a novel cadmium(II)-zinc(II)-copper(I) cluster structure for the major protein. 相似文献
19.
A peptide 60 residues in length that corresponds to the homeo domain of Antennapedia (Antp), a protein governing development in Drosophila, was synthesized by segment condensation with protected peptide segments prepared on an oxime resin. A footprinting assay showed that the homeo domain binds specifically to a TAA repeat DNA sequence in the Antp gene. Thus the Antp homeo domain has a sequence-specific DNA binding property. The circular dichroism spectra of the homeo domain peptide showed the presence of a significant amount of alpha-helical structure in aqueous solution and in 50 percent trifluoroethanol. The alpha helicity measured in water appears to depend on the peptide concentration, which suggests that the peptide aggregates. These results support the hypothesis that the homeo domain binds to DNA through a helix-turn-helix motif. 相似文献