顺磁共振和紫外光谱法研究SDS-PEO体系的相互作用

合成更疏水的自旋探针4 羰基 2,2,6,6 四甲基哌啶氮氧自由基 2,4 二硝基苯腙.用顺磁共振（ESR）和紫外光谱法研究了十二烷基硫酸钠（SDS） 0.5 ％(w,质量分数)聚氧乙烯（PEO）体系的分子间相互作用. ESR结果表明,此水溶液体系的微极性随SDS浓度增大而减小,并且SDS与PEO聚集体具有更加紧密的堆积结构使其结合处具有较大的微粘性, SDS与PEO间的相互作用导致PEO分子链伸展. UV表明自旋探针分子可能靠近胶束的表面存在, 2,4 二硝基苯肼基团可能位于靠近SDS的硫酸根基团,定向于SDS胶束的表面,氮氧自由基基团短距离渗透到SDS胶束的碳氢核.     

Electron Spin Resonance of α-(Alkoxycarbonyl)alkyl Radicals in Solution

High-resolution ESR. spectra of the radicals CH₂COOR, CH₃CHCOOR and (CH₃)₂CCOOR with R?CH₃, CH₂CH₃, CH(CH₃)₂ and C(CH₃)₃ in liquid solution confirm planar energy-minimum structures with substantial barriers to internal rotation about the ?, CO-bonds (?40 kJ/mol) and partial π-electron delocalization. The assignments of coupling constants to protons in isomeric positions and the conclusions on radical structures are supported by INDO-calculations.     

Electron Spin Resonance of Oxiranyl Radicals in Solution: Configurational Stabilities and Rearrangement Reactions

Several alkyl substituted oxiranyl radicals derived by hydrogen abstraction from oxiranes are observed in solution by ESR.-spectroscopy. The ESR.-spectra demonstrate that oxiranyl radicals have pyramidal configurations at the radical carbon atom and undergo inversion. Alkyl substituted oxiranyls rearrange by ring opening to α-keto alkyl radicals. The rates of inversion decrease and the rates of rearrangement increase with alkyl substitution. The activation parameters of these processes are given for several cases and are related to radical structure. Line broadening effects caused by inversion allow the determination of relative signs of γ-CH₃-coupling constants.     

Electron Spin Resonance Analysis of Semiquinone Free Radicals of Aquatic and Soil Fulvic and Humic Acids

Abstract

We analyzed the solid state and aqueous solution electron spin resonance (esr) spectra of Oyster River and Podzol soil fulvic and humic acids. Because the aqueous solution esr spectra mimic the behavior of the model compound para-benzosemiquinone, we conclude that semiquinone free radicals predominate in fulvic acid. In addition a decrease in spin concentration at a potential of 0.20 volts (vs. SCE) demonstrates that the semiquinone radicals are at least partially responsible for the reducing capability of humic materials. From the above results we devised a quantitative semiquinone analysis for humic materials.     

Observation of the Neophyl Radical Rearrangement by Electron Spin Resonance Spectroscopy

The rearrangement of the 2-methyl-2-phenylpropyl (or neophyl) radical 1 to the 1-methyl-1-benzylethyl radical 2 is observed by ESR. spectroscopy during photolysis of di-t-butylperoxide in t-butylbenzene at 270–360 K. The energy of activation of the rearrangement is determined to be (43 ± 9) kJ mol^?1.     

Effect of the UV Modification of α-Crystallin on Its Ability to Suppress Nonspecific Aggregation

Recent studies have shown that structural modifications of α-crystallin during lens aging decrease it's effectiveness as a molecular chaperone. Some of these posttranslational modifications have been linked to UV radiation, and this study was undertaken to investigate the effect of UV irradiation on the ability of α-crystallin to suppress nonspecific aggregation. The effect of 3-hydroxykynurenine (3-HK) was also investigated as a model for its glucoside (3-HKG), a main lens chromophore that has been linked to photochemical changes in the human lens. Alpha- and γ-crystallin solutions (1 mg/mL, 1:0.125 wt/wt) were photolyzed (transmission above 295 nm) for various time intervals. Thermal denaturation of γ-crystallin with or without α-crystallin was carried out at 70°C and increases in light scattering were measured at 360 nm. We found that (1) irradiation of γ-crystallin increased its susceptibility to heat-induced scattering. The addition of α-crystallin protects it against thermal denaturation, although its ability to do so decreases the longer γ-crystallin is irradiated and (2) irradiation of α-crystallin decreases its ability to suppress nonspecific aggregation and the presence of 3-HK during irradiation decreases it further. Our results indicate that posttranslational modifications of α-crystallin due to UV irradiation affect the sites and mechanisms by which it interacts with γ-crystallin. The kinetics of γ-crystallin unfolding during thermal denaturation were also analyzed. We found that a simple two state model applies for nonirradiated γ-crystallin. This model does not hold when γ-crystallin is irradiated in the presence or absence of α-crystallin. In these cases, two step or multistep mechanisms are more likely.     

衬底对N@C60分子电子自旋共振谱的影响

N@C₆₀内嵌富勒烯是一种在量子科技领域有较高应用前景的分子。科学家们设计了一系列以内嵌富勒烯分子为基本量子单元的量子计算机模型,而构筑这样的模型具有极高的挑战。其中,由于内嵌富勒烯分子阵列的制备通常需要合适的衬底,而衬底与分子之间的相互作用会影响甚至破坏内嵌N原子的自旋信号。因此研究和理解衬底与内嵌富勒烯分子的相互作用具有重要的意义。本文制备了高质量的N@C₆₀分子,并采用扫描隧道显微镜对其在Au(111)表面的结构及电子态进行表征。通过对比N@C₆₀分子在Au(111)、Si(111)、SiO₂表面的电子自旋共振(ESR)信号随时间及其抽真空处理的变化,表明Au原子的核自旋与内嵌N原子的电子自旋的耦合作用是Au(111)表面N@C₆₀单分子层的ESR谱中内嵌N原子的信号衰减的主要原因。     

Electron Spin Resonance of Trapped Radicals and the Photoinduced Radical Conversion in γ-Irradiated 3-Methylpentane Glasses at 77°K

Studies on the isotropic hyperfine splitting constants of protiated and deuterated 3-methylpentyl radicals produced by γ-ray accompanied with the radical yield determinations reveal that the radicals are distributed in clusters in the matrix. A tentative mechanism with the migration of positive hole is proposed for the formation of UV-induced new radicals following γ-irradiation in 3-methylpentane glasses at 77°K; and to account for all the experimental observation.     

Effect of Strong Irradiation on Raman Magnetic Resonance in an AX Spin System

In Raman magnetic resonance an initially prepared multiple quantum coherence (MQC) in a spin system introduces all the possible single quantum (SQ) and multiple quantum (MQ) NMR signals when an irradiation is applied during the detection period. If the irradiation is weak, the induced signals include those MQs up to the very order of this given MQC, while in the strong irradiation case, those MQs beyond the very order of the given MQC will also appear. An analytical approach based on the product formalism is developed to predict the intensities and frequencies of these induced signals. The analysis provides a complete treatment to cover both cases of weak and strong irradiation. It is also demonstrated with an AX spin system. Experimental results are in qualitative agreement with the analysis.     

Pressure Effect on the Interaction of Hydrogen Atoms with Ethyl Radicals

Hydrogen atoms from the mercury photosensitized decomposition of hydrogen was allowed to interact with ethylene. Product distributions of this interaction were analyzed with the FID-gas-chromatographic technique. Such distribution has been used to interprete, based on a proposed mechanism, the pressure effect on the following chemically activated process: k^P at 35°C has been determined to be 1.7×10^-7sec^-1 from this observed pressure effect.     

Free Radical Formation of p-Nitrophenacyl Esters of Carboxylic Acids and Their Detection by High-Performance Liquid Chromatography with Electron Spin Resonance

Abstract

p-Nitrophenacyl esters derived from p-nitrophenacyl bromide and carboxylic acids were determined by high-performance liquid chromatography with electron spin resonance. p-Nitrophenacyl bromide was used as the pre-column reagent to determine the carboxylic acids. The p-nitrophenacyl esters gave free radicals by hydrolysis with alkaline solution, and then the free radicals were detected with electron spin resonance. The separation of these esters was achieved within 20 min.     

Analysis of Paramagnetic Metal Ions of Low Sensitivity by Electron Spin Resonance: Utilisation of Cross Relaxation Phenomenon

Abstract

A quantitative analytical method by electron spin resonance of some paramagnetic ions with very short spin-lattice relaxation times, is devised using the anomalous differential saturation of the hyperfine components of radiation produced and trapped H or D atoms as a probe.     

Characterization of an Unusual LOV Domain Protein in the α-Proteobacterium Rhodobacter sphaeroides

The facultatively phototrophic purple bacterium Rhodobacter sphaeroides 2.4.1 harbors a LOV (light, oxygen and voltage) domain protein, which shows a particular structure. LOV domains perceive blue light by a noncovalently bound flavin and transmit the signal to various coupled output domains. Proteins, that harbor a LOV core, function e.g. as phototropins or circadian clock regulators. Jα helices, which act as linker between the LOV core and the output domain, were shown to be involved in the light-dependent activation of the output domain. Like PpSB2 from Pseudomonas putida , the LOV domain protein of R. sphaeroides is not coupled to an effector domain and harbors an extended C-terminal α helix. We expressed the R. sphaeroides LOV domain recombinantly in Escherichia  coli . The protein binds an FMN as a cofactor and shows a photocycle typical for LOV domain containing proteins. In R. sphaeroides , we detected the protein as well in the cytoplasm as in the membrane fraction, which was not reported for other bacterial LOV domain proteins.     

Manipulating the Through‐Space Spin–Spin Interaction of Organic Radicals in the Confined Cavity of a Self‐Assembled Cage

We show a new approach to manipulating the through‐space spin–spin interaction by utilizing the confined cavity of a self‐assembled M₆L₄ coordination cage. The coordination cage readily encapsulates stable organic radicals in solution, which brings the spin centers of the radicals closer to each other. In sharp contrast to the fact that the radical in solution in the absence of the cage is in a doublet state, in the presence of the cage through‐space spin–spin interaction is induced through cage‐encapsulation effects in solution as well as in the solid state, resulting in the triplet state of the complex. These results were confirmed by ESR spectroscopy and X‐ray crystallography. The quantity of triplet species generated by encapsulation in the cage increases with increasing affinity of the radicals to the cage. We estimated the affinity between several types of guests and the cage in solution by cyclic voltammetry. We also demonstrate that the through‐space interaction of organic radicals within the self‐assembled coordination cage can be controlled by external stimuli such as heat or pH.     

Conformationally Restricted Isoindoline‐Derived Spin Labels in Duplex DNA: Distances and Rotational Flexibility by Pulsed Electron–Electron Double Resonance Spectroscopy

Three structurally related isoindoline‐derived spin labels that have different mobilities were incorporated into duplex DNA to systematically study the effect of motion on orientation‐dependent pulsed electron–electron double resonance (PELDOR) measurements. To that end, a new nitroxide spin label, ^ExIm U , was synthesized and incorporated into DNA oligonucleotides. ^ExIm U is the first example of a conformationally unambiguous spin label for nucleic acids, in which the nitroxide N?O bond lies on the same axis as the three single bonds used to attach the otherwise rigid isoindoline‐based spin label to a uridine base. Continuous‐wave (CW) EPR measurements of ^ExIm U confirm a very high rotational mobility of the spin label in duplex DNA relative to the structurally related spin label ^Im U , which has restricted mobility due to an intramolecular hydrogen bond. The X‐band CW‐EPR spectra of ^ExIm U can be used to identify mismatches in duplex DNA. PELDOR distance measurements between pairs of the spin labels ^Im U , ^Ox U , and ^ExIm U in duplex DNA showed a strong angular dependence for ^Im U , a medium dependence for ^Ox U , and no orientation effect for ^ExIm U . Thus, precise distances can be extracted from ^ExIm U without having to take orientational effects into account.