肽链体系中的长程电子转移: 酪氨酸与色氨酸间电子转移的理论研究

用电子转移的半经典模型和量子化学半经验方法对色氨酸-酪氨酸二肽体系进行电子转移动力学参数计算.用AM1方法分别优化给体、受体和桥体几何构型,用线性反应坐标的构造了给体和受体分子间电子转移的双势阱,得到两透热势能面交叉处的反应坐标为R=(约等于)0.10,并确定了反应的内重组能及反应热.对色氨酰酪氨酸和酪氨酰色氨酸体系进行闭壳层HF自洽场计算,按Koopmans定理计算体系分子轨道分裂能值A(三角形),在R约为0处发现了A(三角形)的极小值,从而获得色氨酰酪氨酸及酪氨酰色氨酸体系分子内电子转移的电子转移矩阵元V~D~A分别为0.96kJ.mol^-^1和0.87kJ.mol^-^1.采用Marcus双球模型估算反应的溶剂重组能为64.60kJ.mol^-^1。     

Combining UV photodissociation with electron transfer for peptide structure analysis

The combination of near‐UV photodissociation with electron transfer and collisional activation provides a new tool for structure investigation of isolated peptide ions and reactive intermediates. Two new types of pulse experiments are reported. In the first one called UV/Vis photodissociation–electron transfer dissociation (UVPD‐ETD), diazirine‐labeled peptide ions are shown to undergo photodissociation in the gas phase to form new covalent bonds, guided by the ion conformation, and the products are analyzed by electron transfer dissociation. In the second experiment, called ETD‐UVPD wherein synthetic labels are not necessary, electron transfer forms new cation–peptide radical chromophores that absorb at 355 nm and undergo specific backbone photodissociation reactions. The new method is applied to distinguish isomeric ions produced by ETD of arginine containing peptides. Copyright © 2015 John Wiley & Sons, Ltd.     

Theoretical study of long range electron transfer in Phthalimide–Peptide–Methyl Aminoacetate Model molecules

Long-range electron transfer (ET) matrix elements (V_PS), rate constants (k_ET) and reorganization energies for ET from phthalimide radical (pha) moiety to methyl aminoacetate radical (aa) moiety in pa–(gly)_n = 0–6–aa (pa = C₆H₄(CO)₂N–(CH₂CO), gly = glycine, aa = HNCH₂COOCH₃) ionic molecules have been investigated using two-state variational method (TSVM) and classical rate model. Calculations on V_PS reveal that the overlap between the frontier orbitals of two diabatic states is quite small, which leads to a small value of V_PS. k_ET has a minimum at the range n = 1–3 for β-strand conformation, but linearly increases as the peptide chain length (n) increases for pro II-helix conformation. These results are in good agreement with the experimental predictions. Relevant ET mechanisms are elucidated. The transition energies for charge transfer in such systems are also calculated to test the influences of local dipoles on the potentials of the donor and acceptor. For comparison electron couplings in [pa–(gly)_n = 1,3–aa]⁺ cations are calculated and the effects of electron correlation on inner reorganization energies in pha + pha^−/+ self-exchange reactions are examined at different levels of theory respectively. Calculated results are discussed also.     

Extracellular electron transfer in microbial biocorrosion

Biocorrosion by microbial biofilms is also termed microbiologically influenced corrosion (MIC). For many decades in MIC research, people focused on corrosive metabolites. In the past decade, researchers started to apply bioenergetics to MIC science research. They realized that extracellular oxidation of a metal can supply electrons for microbial respiration, which causes MIC. Because these electrons must be transported to the cytoplasm via extracellular electron transfer (EET), this kind of MIC is called EET-MIC, which is different from metabolite-MIC (M-MIC). Advances have been made to decipher inward EET involved in MIC. Carbon source starvation and electron mediator acceleration have been used to study impact of EET on MIC. More recently, manipulations of electron mediator-related genes have been used to elucidate EET in MIC. EET in energy metabolism in microbiology and EET for MIC are intertwined. Well-established corrosion research tools, especially electrochemical methods that are highly sensitive, are useful for microbiologists to study EET.     

Dynamic electron transfers in B2H6 and Cu(PH3)2(BH4)

In order to investigate the coupling of molecular vibrations and electron distribution, dynamic electron transfers in B₂H₆ and Cu(PH₃)₂(BH₄) are lated by using a new variational method. In both molecules, the dynamic electron density near bridging hydrogen atoms decreases to form the density valley by exciting specific vibrational modes. On the other hand, in both sides of the valley density hills grow up. For these molecules, similar contour maps are given by the modes with different symmetry which have large contribution of the bridging ligands. While the dynamic electron transfer of B₂H₆ arises in symmetric form, the vibrational modes of the Cu complex gives the asymmetric redistribution of the dynamic electron density. This is attributed to the difference of the symmetry between the two molecules.     

A simple flowcell for reaction monitoring by NMR

A simple, cheap and flexible flowcell based on a standard 5 mm NMR tube, designed for the monitoring of reactions but of wide applicability, is described. No modification of the NMR instrument is needed, allowing the system to be employed with any conventional NMR probe and magnet. The system is robust and economical in use of reagents, and can be used for studying both homogeneous and heterogeneous reactions. Copyright © 2010 John Wiley & Sons, Ltd.     

Direct electron transfer reaction of glucose oxidase at bare silver electrodes and its application in analysis

The direct electron transfer reaction of glucose oxidase (GOx) at a bare silver electrode is verified. The electron transfer number n = 2, electron transfer coefficient α = 0.45 and rate constant of the electrochemical reaction K_s = 0.1 s⁻¹ are obtained. This communication presents a multimolecular adsorption model to explain the properties of the direct electron reaction between GOx and bare silver electrodes. The residual valence force may be an important factor to ensure a direct electron transfer reaction on the bare electrode. On the basis of the experimental fact that only biologically active GOx exhibits electrochemical activity in solution, a facile analytical method for analyzing the active GOx concentration is developed. The results determined correspond very well to that of a spectrometric method.     

TTF-porphyrin dyads as novel photoinduced electron transfer systems

A TTF-linked porphyrin dyad and its zinc complex have been synthesized as novel photosystems with a redox-active pendant. The two chromophores of these dyads are not interactive in the absorption spectra, but the fluorescence of the porphyrin chromophore is dramatically quenched by intramolecular electron transfer from the TTF pendant.     

A novel photoinduced electron transfer reaction of N-alkylphenothiazines in carbon tetrachloride

U.V. irradiation of N-alkylphenothiazines (1a—c) in carbon tetrachloride produced 3-(phenothiazin-N'-yl-carbonyl)-N′-alkylphenothiazine (2a—b) and/or 3-(N′-alkylphenothiazin-3′-yl-carbonyl)-N-alkylphenothiazine (3b—c) together with the radical cation carbon tetrachloride salt 1~( ·)CCl_4~(-·)(4a—c), presumably via a photoinduced electron transfer mechanism.     

A possible role of histidine residues in long-range electron transfer in proteins

Metal–histidine complexes are recurrent structural motifs in proteins exhibiting long-range electron transfer (ET), being involved both as electron donor or acceptor groups and as bridges which mediate ET between other cofactors. That observation suggests that the histidine residue could play an active role in ET, beyond that of simply binding the metal ion. Density functional theory and ab initio computations, performed on a simplified model system of the ET chain in semisynthetic Zinc cytochromes, confirm that expectation, suggesting that the nitrogen site of the histidine ring can exchange both a proton and a whole hydrogen atom with its redox partners. This finoling indicates that proton-assisted ET appears to be a plausible mechanism in this system.Contribution to Jacopo Tomasi Honorary Issue     

Optimized precursor ion selection for labile ions in a linear ion trap mass spectrometer and its impact on quantification using selected reaction monitoring

The fragmentation of fragile ions during the application of an isolation waveform for precursor ion selection and the resulting loss of isolated ion intensity is well‐known in ion trap mass spectrometry (ITMS). To obtain adequate ion intensity in the selected reaction monitoring (SRM) of fragile precursor ions, a wider ion isolation width is required. However, the increased isolation width significantly diminishes the selectivity of the channels chosen for SRM, which is a serious problem for samples with complex matrices. The sensitive and selective quantification of many lipid molecules, including ceramides from real biological samples, using a linear ion trap mass spectrometer is also hindered by the same problem because of the ease of water loss from protonated ceramide ions. In this study, a method for the reliable quantification of ceramides using SRM with near unity precursor ion isolation has been developed for ITMS by utilizing alternative precursor ions generated by in‐source dissociation. The selected precursor ions allow the isolation of ions with unit mass width and the selective analysis of ceramides using SRM with negligible loss of sensitivity. The quantification of C18:0‐, C24:0‐ and C24:1‐ceramides using the present method shows excellent linearity over the concentration ranges from 6 to 100, 25 to 1000 and 25 to 1000 nM, respectively. The limits of detection of C18:0‐, C24:0‐ and C24:1‐ceramides were 0.25, 0.25 and 5 fmol, respectively. The developed method was successfully applied to quantify ceramides in fetal bovine serum. Copyright © 2014 John Wiley & Sons, Ltd.     

细菌光合反应中心突变体原初电子转移机理的理 论研究

利用量子化学DFT从头计算方法,计算经过突变的细菌光合反应中心HM202L原始电子给体和其他色素分子的电子结构,然后对其原初电子转移机理进行探讨。结果表明：1)超分子D-2A的HOMO主要是由定域在其组成单元BChl~L分子上的原子轨道组成,而它的LUMO主要是由定域在其组成单元MBPheo~M分子上的原子轨道组成。这表明它在基态的激发态时分别存在超分子内的电荷分离态[BChl~L^--MBPheo~M^+]和[BChl~L^+-MBPheo~M^-]。同时也说明了D-2A阳离子态的正电荷完全分布在组成单元细菌叶绿素分子BChl~L上,与实验事实相符。2)HM202L细菌光合反应中心原初电子转移反应存在由ABCha~L^h^*驱动的电子转移反应。     

Chlorophyll triggered one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones via photo induced electron transfer reaction

The photocatalytic potential of chlorophyll has been investigated for the facile synthesis of dihydropyrimidinones utilizing concentrated solar irradiation towards sustainable energy solutions. This, one-pot, multicomponent Biginelli reaction, which involves a photoinduced electron transfer (PET) mechanism, affords a green and efficient approach for the transformation of the commercial aldehydes, β-keto ester and urea into valuable 3,4-dihydropyrimidin-2(1H)-ones with wide substrate scope and diversity. These improved reaction conditions allow the formation of a variety of substituted dihydropyrimidinones with high yields and purity in a short duration of time and mild reaction conditions.     

Complex formation followed by internal electron transfer: The reaction between cysteine and iron(III)

Summary A kinetic study of the anaerobic oxidation of cysteine (H₂ L) by iron(III) has been performed over thepH-range 2.5 to 12 by use of a stopped-flow high speed spectrophotometric method. Reaction is always preceded by complex formation. Three such reactive complex species have been characterized spectrophotometrically: FeL ⁺ (_max=614 nm, =2 820 M^–1cm^–1); Fe(OH)L (_max=503 nm; shoulder at 575 nm, =1 640 M^–1cm^–1); Fe(OH)L ₂ ^2– (_max=545 nm; shoulder at 445 nm, =3 175 M^–1 cm^–1). Formation constants have been evaluated from the kinetic data: Fe³⁺+L ^2– FeL ⁺: logK ₁ ^M =13.70±0.05; Fe(OH)²⁺+L ^2– Fe(OH)L: logK ₁ ^MOH =10.75±0.02; Fe(OH)L+L ^2– Fe(OH)L ₂ ^2– ; logK ₂ ^MOH =4.76±0.02. Furthermore the hydrolysis constant for iron(III) was also obtained: Fe(OH)²⁺+H⁺ Fe _aq ³⁺ : logK ^FeOH=2.82±0.02). Formation of the mono-cysteine complexes, FeL ⁺ and Fe(OH)L, is via initial reaction of Fe(OH)²⁺ with H₂ L (k=1.14·10⁴M^–1s^–1), the final product depending on thepH. FeL ⁺ (blue) formed at lowpH decomposes following protonation with a second-order rate constant of 1.08·10⁵M^–1s^–1. Fe(OH)L (purple) decomposes with an apparent third order rate constant ofk=3.52·10⁹M^–2s^–1 via 2 Fe(OH)L+H⁺ products, which implies that the actual (bimolecular) reaction involves initial dimer formation. Finally, Fe(OH)L ₂ ^2– (purple) is remarkably stable and requires the presence of Fe(OH)L for electron transfer. A rate constant of 8.36·10³M^–1s^–1 for the reaction between Fe(OH)L and Fe(OH)L ₂ ^2– is evaluated.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Rational design of novel photoinduced electron transfer type fluorescent probes for sodium cation

We have developed novel fluorescence probes for sodium cation based on photoinduced electron transfer (PeT). In this study, we rationally designed new probes and succeeded in achieving fluorescence enhancement upon sodium ion binding by reducing the HOMO energy level of the chelator group within the probe molecule. Our new probes show low pH dependency, possibly because of their simple structures. Our results confirm the value of rational probe design based on PeT.     

Quantum electron transfer processes induced by thermo-coherent state

When the reactant surface is not in a thermal equilibrium, but in a thermo-coherent state we have derived the rate and discussed about the quantum features of the rate. In the limit of very low and very high temperature the expressions are derived analytically and compared with the case of thermal distribution. We have investigated the dependence of temperature on the rate due to displacement, distortion of the harmonic potential energy surfaces of the reactant and product manifold.