Redox photochemistry of thiouredopyrenetrisulfonate

1-Thiouredopyrene-3,6,8-trisulfonate (TUPS) has recently been used as a photoinduced covalent redox label capable of reducing various cofactors of proteins. A new reaction of this dye, whereby its excited triplet state oxidizes suitable electron donors, is now reported. The characteristic difference spectrum of the reduced radical of TUPS is determined. We also observe the self-exchange electron transfer between two TUPS molecules in their triplet excited states and determine the reaction scheme and the rate constants of the various pathways in the process of triplet depletion. The ability of photoexcited TUPS to withdraw an electron from reduced cytochrome-c is also observed. It is thus demonstrated that TUPS is an appropriate photoinduced covalent redox label for initiating both the oxidative and reductive phases of electron transfer processes in biological macromolecules.     

电感耦合等离子体质谱法测定固体沥青中的稀土元素

原油、沥青中的各种微量元素信息已被应用于油气勘探和油气地球化学研究,然而相关的分析方法较少,而且前处理过程繁琐。本文将微波消解法应用于沥青样品的消解,建立了微波消解-电感耦合等离子体质谱法测定16种稀土元素的方法。不同组合消解试剂优化实验研究表明,HNO3-HF作为消解试剂效果最好,并讨论了样品量、消解条件、质谱干扰等影响因素。该方法样品处理简单,并应用于实际样品的分析,方法的精密度(RSD,n=8)小于6.2%,稀土元素检出限在0.0001~0.013μg/g之间,标准样品分析结果均在推荐值误差范围之内,为沥青类样品中稀土元素分析测定提供了新的参考方法。     

高压密闭消解-电感耦合等离子体质谱法测定煤中稀土元素

煤作为有机物与无机物的复杂混合物,含有多种微量元素,不同的微量元素信息代表不同的地质意义,稀土元素可以提供丰富的沉积环境与物源信息。采用高压消解罐,选用硝酸和氢氟酸混合酸消解样品,建立了电感耦合等离子体质谱法测定16种稀土元素的方法。讨论了样品量、消解试剂、质谱干扰等影响因素,各元素的方法检出限在0.001～0.016μg/g,NIST SRD 1632d煤标准样品实测值和标准值一致,标准样品测定结果与实测样品结果相对标准偏差(RSD,n=11)小于5%,可满足煤中稀土元素的准确测定,为煤类样品中稀土元素测定提供了新的参考方法。     

Porous silicon/photosynthetic reaction center hybrid nanostructure

The purified photosynthetic reaction center protein (RC) from Rhodobacter sphaeroides R-26 purple bacteria was bound to porous silicon microcavities (PSiMc) either through silane-glutaraldehyde (GTA) chemistry or via a noncovalent peptide cross-linker. The characteristic resonance mode in the microcavity reflectivity spectrum red shifted by several nanometers upon RC binding, indicating the protein infiltration into the porous silicon (PSi) photonic structure. Flash photolysis experiments confirmed the photochemical activity of RC after its binding to the solid substrate. The kinetic components of the intraprotein charge recombination were considerably faster (τ(fast) = 14 (±9) ms, τ(slow) = 230 (±28) ms with the RC bound through the GTA cross-linker and only τ(fast) = 27 (±3) ms through peptide coating) than in solution (τ(fast) = 120 (±3) ms, τ(slow) = 1387 (±2) ms), indicating the effect of the PSi surface on the light-induced electron transfer in the protein. The PSi/RC complex was found to oxidize the externally added electron donor, mammalian cytochrome c, and the cytochrome oxidation was blocked by the competitive RC inhibitor, terbutryne. This fact indicates that the specific surface binding sites on the PSi-bound RC are still accessible to external cofactors and an electronic interaction with redox components in the aqueous environment is possible. This new type of biophotonic material is considered to be an excellent model for new generation applications at the interface of silicon-based electronics and biological redox systems designed by nature.     

Mapping local electric fields in proteins at biomimetic interfaces

We present a novel approach for determining the strength of the electric field experienced by proteins immobilised on membrane models. It is based on the vibrational Stark effect of a nitrile label introduced at different positions on engineered proteins and monitored by surface enhanced infrared absorption spectroscopy.     

Complex kinetics of the electron transfer between the photoactive redox label TUPS and the heme of cytochrome c

The photoinduced covalent redox label 8-thiouredopyrene-1,3,6-trisulfonate (TUPS) has been attached to two lysine residues (K8 and K39) at opposite sides of horse heart cytochrome c, as well as to cysteines, at the same positions, introduced by site-directed mutagenesis. Electron transfer between TUPS and the heme of cytochrome c deviates from the expected monoexponential kinetic behavior. Neither the overall rate nor the individual exponential components of electron transfer, as followed by kinetic absorption spectroscopy, correlate with the length of the covalent link connecting the dye with the protein. Molecular dynamics calculations show that TUPS can approach the protein surface and occupy several such positions. This heterogeneity may explain the multiexponential electron-transfer kinetics. The calculated optimal electron-transfer pathways do not follow the covalent link but involve through space jumps from the dye to the protein moiety, effectively decoupling the length of the covalent link and the electron-transfer rates.