利用化学修饰的细菌视紫红质薄膜进行光学信息存储的研究

细菌视紫红质(bacteriorhodopsin,bR)具有独特的光、化学和热稳定性.bR光循环中间态M态的最大吸收峰相对于始态明显地发生蓝移,所以基于bR(→)M的光致变色模型可以为光学应用尤其是信息存储提供一个机制.但是野生型bR 中M态的寿命很短,不适合用来进行信息存储.本文采用化学添加剂的方法,将bR/聚乙烯醇(PVA)薄膜的中间态M态的寿命显著延长.用此化学修饰的bR薄膜作为记录介质进行缩微图像存储,所得到的图像具有较高的对比度和较长的保存时间.此实验首次实现了在化学修饰的bR薄膜上基于bR始态和中间态M态的双稳态模型在光学信息存储上的应用.     

锌(Ⅱ)存在下灯盏花素与BSA相互作用的光谱分析

运用荧光光谱、吸收光谱研究了灯盏花素(Breviscapinun,BR)与牛血清白蛋白(Bovine Serum Albumin,BSA)的相互作用.BR对BSA的荧光光谱具有猝灭作用,其猝灭机制为静态-动态联合猝灭,BSA发射峰蓝移.Zn2+的存在使得BSA发射峰蓝移程度降低,猝灭常数、结合常数、结合位点数减小.在较大浓度Zn2+存在下,BR与BSA作用的相关系数增大,猝灭机制变为静态猝灭.从Zn2+与BR的竞争作用,热力学参数的变化、配位化合物的形成3个方面分析了影响BR与BSA作用的因素.     

生物滤池中生物膜和出水悬浮物的元素分析和红外光谱比较

对生物滤池中不同高度的生物膜和出水悬浮物的碳氢氮三元素和红外光谱进行了分析比较.元素分析结果表明,悬浮物的无机成份比生物膜高.悬浮物和生物膜的红外吸收光谱图主要由蛋白质的吸收带、碳水化合物的吸收带组成.1655 cm-1处的吸收峰为酰胺Ⅰ带,是C=O的伸缩振动,1542 cm-1的吸收峰是酰胺Ⅱ带,是N-H的弯曲振动和C-N的伸缩振动,1240 cm-1是酰胺Ⅲ带,是C-N的伸缩振动和N-H的弯曲振动引起的.1460 cm-1处的吸收峰为CH3和CH2的弯曲振动峰.悬浮物的蛋白质特征峰强度比生物膜低,而1050cm-1处的吸收峰强度比生物膜大.     

含蒽醌基双分子膜的电子光谱

用荧光和紫外光谱研究了新合成的含蒽醌(2,6)生色基的单链双亲性分子(ANQU)在水溶液中形成的双分子膜聚集体结构。ANQU在稀水溶液中的吸收光谱比其在乙醇稀溶液中的谱峰有较大的红移；其凝胶态相对于液晶态的吸收谱亦有明显红移。结果表明,ANQU双分子膜中分子的堆积方式是J-聚集,蒽醌生色基以头对尾取向方式排列。变温荧光光谱观察双分子膜中蒽醌生色基的荧光光谱强度和峰位极敏感地受到双分子膜物理状态变化的影响。     

聚乙烯醇纤维金属配合物的合成和表征

以聚乙烯醇纤维(PVA)为配体原料,分别与FeCl3、NiCl2、CuCl2和Pb(Ac)2反应,制备了宏观上仍保持原纤维形态的PVA Fe(Ⅲ)、PVA Ni(Ⅱ)、PVA Cu(Ⅱ)、PVA Pb(Ⅱ)纤维配合物(用PVA M表示).用红外光谱仪分别对PVA和4种配合物在4000～400cm-1范围进行傅立叶变换红外光谱测量,对各PVA M的FTIR主要吸收峰做了经验归属,并与PVA的相应吸收峰做对比分析,结果表明,与金属离子形成配合物后,PVA分子中O—H氢键缔合状态被破坏,向高波数位移了65～86cm-1,PVA中的羟基氧与金属离子发生配位作用.PVA Fe(Ⅲ)的XPS显示,PVA中O1s只出现532.5eV单峰,而PVA Fe(Ⅲ)中O1s分裂为531.4eV和532.3eV两个峰,且Fe2p只有一个峰710.9eV,比FeCl3的结合能值711.2eV下降,说明OH氧与Fe3+形成配位键.     

三明治型酞菁稀土配合物M(Pc)2电子吸收光谱的离子半径效应

系统研究了对称三明治型二层酞菁稀土配合物M(Pc)₂在300～800 nm范围内的电子吸收光谱，首次采用导数光谱对光谱区域内的叠加谱带及肩带进行了分离，并求算了相应吸收的摩尔吸光系数。结果表明，该系列酞菁稀土配合物的Soret带都分裂两个吸收峰，配合物的吸收谱带除位于Soret带低能一侧和酞菁π阴离子自由基吸收高能一侧的吸收以外均随镧系收缩发生蓝移,但Soret带蓝移程度较小，其余谱带吸收波长与稀土离子半径呈现线性关系；配合物电子吸收光谱中,叠加谱带相邻两吸收峰的强度比随镧系收缩发生规律性变化,与稀土离子半径也存在良好的线性关系,表现出明显的离子半径效应。     

胆酸和脱氧胆酸分子的远红外与THz吸收光谱研究

胆酸和脱氧胆酸是胆汁酸中的主要成分, 是人体中重要的生物表面活性剂. 两种分子只相差一个羟基, 在远红外和太赫兹波段有不同的吸收光谱. 胆酸分子的太赫兹(THz)吸收光谱有1.26 THz(42 cm-1)和2.02 THz(67 cm-1)两个吸收峰, 脱氧胆酸分子的THz吸收光谱有1.13, 1.26, 1.69和2.17 THz(即38, 42, 56, 72 cm-1)等几个吸收峰. 两个分子的THz吸收光谱都包含有1.26 THz(42 cm-1) 峰, 反映出二者结构的相似性. 它们的远红外光谱都有部分频率相近的谱带, 但对比之下可以观察到峰位位移和相对峰强的改变. 指认了两种物质的某些可能与羧基振动有关的特征吸收峰. 为找出THz光谱隐含的信息, 利用Omnic程序采用二阶导数方法来处理THz光谱数据, 观察到多个子峰, 说明分子结构中可能存在更复杂的氢键状态. 实验结果表明, 远红外和THz吸收光谱是研究生物分子及鉴别生物分子结构的很好方法.     

现场表面拉曼光谱研究Fe-Mo合金诱导共沉积

现场表面拉曼光谱结果显示，在0．2mol·L-1Na2MoO4,pH＝4．0的溶液中，电位正于0．5V（vsSCE）时只观察到多钼酸盐的拉曼峰（940、880和450cm-1）．负于-0．5V时，出现中心位于730cm-1的宽峰．同时电极表面有蓝色膜生成．表明混合氧化态（MO（Ⅳ），MO（Ⅴ））氧化膜的形成．730cm-1的峰在-1．9V时仍然存在，说明氧化膜没有被进一步还原．在钼酸钠溶液中同时含有0．1mol·L-1FeSO4和0．2mol·L-1柠檬酸时，中间态氧化膜的拉曼峰的中心移到740cm-1．且峰强度随着电位从-1．3V负移到-1．9V而逐渐减弱并最终消失．电极表面沉积层呈银白色，说明由于Fe2 的存在，钼的中间态氧化膜的结构发生了变化，能够被进一步还原形成Fe－Mo合金，表现出诱导共沉积的特征．     

六元卟啉Hexaphyrin(1.1.1.1.1.1)的Pd(Ⅱ)金属配合物光电性质的理论研究

通过密度泛函和含时密度泛函方法对六元卟啉的钯金属配合物进行了系统的研究,探讨了几种金属配合物光学性质的变化.对于具有26π电子体系3个单金属配合物在Q带的最大吸收峰顺序为λmax(D26Pd)>λmax(R26Pd)>λmax(M28Pd),这同它们的ΔEH-L成反比.其中D26Pd和M28Pd的跃迁来自于π→π*的ILCT的跃迁,而R26Pd有部分金属d轨道参与到跃迁,跃迁性质为ILCT/MLCT.它们的B带的强吸收峰同自由状态下的配体的吸收光谱比较,配合物的吸收峰发生了约20nm左右的蓝移,吸收主要贡献都是来自于d(metal)→π*的MLCT的跃迁.非芳香性配合物M28Pd2α的跃迁性质则不同,无论是Q带还是B带都没有发现金属的参与,而且吸收强度明显降低.     

溶剂对四苯基卟啉氯化锰飞秒瞬态吸收光谱的影响

采用稳态和飞秒瞬态吸收光谱技术研究了四苯基卟啉氯化锰MnⅢ(TPP)Cl在甲苯(TOL)、二氯甲烷(DCM)、乙腈(ACN)和N,N-二甲基甲酰胺(DMF)四种溶剂中的光物理性质.结果表明随溶剂极性的增加,其紫外-可见吸收光谱的B带与Q带与飞秒瞬态对应的漂白信号均发生蓝移.随着MnⅢ(TPP)Cl二氯甲烷溶液浓度的增加, ⁵S₂态寿命无明显变化,⁵S₁态和⁵T₁态寿命依次变短.在四种溶剂中,非极性溶剂甲苯中的⁵S₂态寿命最长而⁵S₁和⁵T₁态寿命最短,这与⁵S₂→⁵S₁能差最大, ⁵S₁→5S0能差最小对应.从弱极性DCM到极性更大的DMF时, ⁵S₁和...     

Ultrafast electronic and vibrational dynamics of stabilized A state mutants of the green fluorescent protein (GFP): Snipping the proton wire

Two blue absorbing and emitting mutants (S65G/T203V/E222Q and S65T at pH 5.5) of the green fluorescent protein (GFP) have been investigated through ultrafast time resolved infra-red (TRIR) and fluorescence spectroscopy. In these mutants, in which the excited state proton transfer reaction observed in wild-type GFP has been blocked, the photophysics are dominated by the neutral A state. It was found that the A* excited state lifetime is short, indicating that it is relatively less stabilised in the protein matrix than the anionic form. However, the lifetime of the A state can be increased through modifications to the protein structure. The TRIR spectra show that a large shifts in protein vibrational modes on excitation of the A state occurs in both these GFP mutants. This is ascribed to a change in H-bonding interactions between the protein matrix and the excited state.     

Enhanced Activity and Substrate Specificity by Site-Directed Mutagenesis for the P450 119 Peroxygenase Catalyzed Sulfoxidation of Thioanisole

P450 119 peroxygenase was found to catalyze the sulfoxidation of thioanisole and the sulfonation of sulfoxide in the presence of tert-butyl hydroperoxide (TBHP) for the first time with turnover rates of 1549 min⁻¹ and 196 min⁻¹ respectively. Several mutants were designed to improve the peroxygenation activity and thioanisole specificity by site-directed mutagenesis. The F153G/T213G mutant gave an increase of sulfoxide yield and a decrease of sulfone yield. Moreover the S148P/I161T/K199E/T214V mutant and the K199E mutant with acidic Glu residue contributed to improving the product ratio of sulfoxide to sulfone. Addition of short-alkyl-chain organic acids to the P450 119 peroxygenase-catalyzed sulfur oxidation of thioanisole was investigated. Octanoic acid was found to induce a preferred sulfoxidation of thioanisole catalyzed by the F153G/T213G mutant to give approximately 2.4-fold increase in turnover rate with a k_cat value of 3687 min⁻¹ relative to that of the wild-type, and by the F153G mutant to give the R-sulfoxide up to 30 % ee. The experimental control and the proposed mechanism for the P450 119 peroxygenase-catalyzed sulfoxidation of thioanisole in the presence of octanoic acid suggested that octanoic acid could partially occupy the substrate pocket; meanwhile the F153G mutation could enhance the substrate specificity, which could lead to efficiently regulate the spatial orientation of thioanisole and facilitate the formation of Compound I. This is the most effective catalytic system for the P450 119 peroxygenase-catalyzed sulfoxidation of thioanisole.     

Aequorin mutants with increased thermostability

Bioluminescent labels can be especially useful for in vivo and live animal studies due to the negligible bioluminescence background in cells and most animals, and the non-toxicity of bioluminescent reporter systems. Significant thermal stability of bioluminescent labels is essential, however, due to the longitudinal nature and physiological temperature conditions of many bioluminescent-based studies. To improve the thermostability of the bioluminescent protein aequorin, we employed random and rational mutagenesis strategies to create two thermostable double mutants, S32T/E156V and M36I/E146K, and a particularly thermostable quadruple mutant, S32T/E156V/Q168R/L170I. The double aequorin mutants, S32T/E156V and M36I/E146K, retained 4 and 2.75 times more of their initial bioluminescence activity than wild-type aequorin during thermostability studies at 37 °C. Moreover, the quadruple aequorin mutant, S32T/E156V/Q168R/L170I, exhibited more thermostability at a variety of temperatures than either double mutant alone, producing the most thermostable aequorin mutant identified thus far.     

Aristolochene synthase: mechanistic analysis of active site residues by site-directed mutagenesis

Incubation of farnesyl diphosphate (1) with Penicillium roqueforti aristolochene synthase yielded (+)-aristolochene (4), accompanied by minor quantities of the proposed intermediate (S)-(-)germacrene A (2) and the side-product (-)-valencene (5) in a 94:4:2 ratio. By contrast, the closely related aristolochene synthase from Aspergillus terreus cyclized farnesyl diphosphate only to (+)-aristolochene (4). Site-directed mutagenesis of amino acid residues in two highly conserved Mg(2+)-binding domains led in most cases to reductions in both k(cat) and k(cat)/K(m) as well as increases in the proportion of (S)-(-)germacrene A (2), with the E252Q mutant of the P. roqueforti aristolochene synthase producing only (-)-2. The P. roqueforti D115N, N244L, and S248A/E252D mutants were inactive, as was the A. terreus mutant E227Q. The P. roqueforti mutant Y92F displayed a 100-fold reduction in k(cat) that was offset by a 50-fold decrease in K(m), resulting in a relatively minor 2-fold decrease in catalytic efficiency, k(cat)/K(m). The finding that Y92F produced (+)-aristolochene (4) as 81% of the product, accompanied by 7% 5 and 12% 2, rules out Tyr-92 as the active site Lewis acid that is responsible for protonation of the germacrene A intermediate in the formation of aristolochene (4).     

Studies on pyrylretinal analogues of bacteriorhodopsin

The retinal analogues 3-methyl-5-(1-pyryl)-2E,4E-pentadienal (1) and 3,7-dimethyl-9-(1-pyryl)-2E,4E,6E,8E-nonatetr aenal (2), which contain the tetra aromatic pyryl system, have been synthesized and characterized in order to examine the effect of the extended ring system on the binding capabilities and the function of bacteriorhodopsin (bR). The two bR mutants, E194Q and E204Q, known to have distinct proton-pumping patterns, were also examined so that the effect of the bulky ring system on the proton-pumping mechanism could be studied. Both retinals formed pigments with all three bacterioopsins, and these pigments were found to have absorption maxima in the range 498-516 nm. All the analogue pigments showed activity as proton pumps. The pigment formed from wild-type apoprotein bR with 1 (with the shortened polyene side chain) showed an M intermediate at 400 nm and exhibited fast proton release followed by proton uptake. Extending the polyene side chain to the length identical with retinal, analogue 2 with wild-type apoprotein gave a pigment that shows M and O intermediates at 435 nm and 650 nm, respectively. This pigment shows both fast and slow proton release at pH 7, suggesting that the pKa of the proton release group (in the M-state) is higher in this pigment compared to native bR. Hydrogen azide ions were found to accelerate the rise and decay of the O intermediate at neutral pH in pyryl 2 pigment. The pigments formed between 2 and E194Q and E204Q showed proton-pumping behavior similar to pigments formed with the native retinal, suggesting that the size of the chromophore ring does not alter the protein conformation at these sites.     

Engineering P450 Peroxygenase to Catalyze Highly Enantioselective Epoxidation of cis‐β‐Methylstyrenes

P450 119 peroxygenase and its site‐directed mutants are discovered to catalyze the enantioselective epoxidation of methyl‐substituted styrenes. Two new site‐directed P450 119 mutants, namely T213Y and T213M, which were designed to improve the enantioselectivity and activity for the epoxidation of styrene and its methyl substituted derivatives, were studied. The T213M mutant is found to be the first engineered P450 peroxygenase that shows highly enantioselective epoxidation of cis‐β‐methylstyrenes, with up to 91 % ee. Molecular modeling studies provide insights into the different catalytic activity of the T213M mutant and the T213Y mutant in the epoxidation of cis‐β‐methylstyrene. The results of the calculations also contribute to a better understanding of the substrate specificity and configuration control for the regio‐ and stereoselective peroxygenation catalyzed by the T213M mutant.     

An alternate proton acceptor for excited-state proton transfer in green fluorescent protein: rewiring GFP

The neutral form of the chromophore in wild-type green fluorescent protein (wtGFP) undergoes excited-state proton transfer (ESPT) upon excitation, resulting in characteristic green (508 nm) fluorescence. This ESPT reaction involves a proton relay from the phenol hydroxyl of the chromophore to the ionized side chain of E222, and results in formation of the anionic chromophore in a protein environment optimized for the neutral species (the I* state). Reorientation or replacement of E222, as occurs in the S65T and E222Q GFP mutants, disables the ESPT reaction and results in loss of green emission following excitation of the neutral chromophore. Previously, it has been shown that the introduction of a second mutation (H148D) into S65T GFP allows the recovery of green emission, implying that ESPT is again possible. A similar recovery of green fluorescence is also observed for the E222Q/H148D mutant, suggesting that D148 is the proton acceptor for the ESPT reaction in both double mutants. The mechanism of fluorescence emission following excitation of the neutral chromophore in S65T/H148D and E222Q/H148D has been explored through the use of steady state and ultrafast time-resolved fluorescence and vibrational spectroscopy. The data are contrasted with those of the single mutant S65T GFP. Time-resolved fluorescence studies indicate very rapid (< 1 ps) formation of I* in the double mutants, followed by vibrational cooling on the picosecond time scale. The time-resolved IR difference spectra are markedly different to those of wtGFP or its anionic mutants. In particular, no spectral signatures are apparent in the picosecond IR difference spectra that would correspond to alteration in the ionization state of D148, leading to the proposal that a low-barrier hydrogen bond (LBHB) is present between the phenol hydroxyl of the chromophore and the side chain of D148, with different potential energy surfaces for the ground and excited states. This model is consistent with recent high-resolution structural data in which the distance between the donor and acceptor oxygen atoms is < or = 2.4 A. Importantly, these studies indicate that the hydrogen-bond network in wtGFP can be replaced by a single residue, an observation which, when fully explored, will add to our understanding of the various requirements for proton-transfer reactions within proteins.     

Photoelectrochemical Verification of Proton-Releasing Groups in Bacteriorhodopsin

Light-induced transient currents of bacteriorhodopsin (bR) and its mutants (D96N, D85N, E204Q and E194Q) were measured at the interface of an electrode and the aqueous solution in an electrochemical cell. The transient positive (cathodic) and negative (anodic) photocurrents generated upon the onsets of continuous illumination and of turning off light, respectively, were investigated at different electrolyte pH. The wild type exhibits both positive and negative responses, with the sign of the response inverted at pH lt 5. In D85N the response is entirely suppressed, while D96N lacks the negative response. Laser pulse excitation (532 nm) of bR and the mutants showed the response rise time of the positive transient to be uniformly about 100 μs, indicating that the response is linked to the L to M transition in the photocycle. According to these results the positive and negative signals originate from the proton release and uptake reactions, respectively. Photoexcitation of the mutants E204Q and E194Q that lack protonatable residues at position 204 and 194, respectively, produced a negative response at neutral pH, which indicates that in these proteins proton uptake precedes proton release. This result is consistent with our observations made earlier with pH indicator dyes and demonstrates that Glu-204 and Glu-194 constitute the terminal proton release complex in the extracellular region of bR.     

Coupling Between the Retinal Thermal Isomerization and the Glu194 Residue of Bacteriorhodopsin†

Glu194 is a residue located at the end of F helix on the extracellular side of the light‐induced proton pump bacteriorhodopsin (BR). Currently, it is well recognized that Glu194 and Glu204 residues, along with water clusters, constitute the proton release group of BR. Here we report that the replacement of Glu194 for Gln affects not only the photocycle of the protein but also has tremendous effect on the all‐trans to 13‐cis thermal isomerization. We studied the pH dependence of the dark adaptation of the E194Q mutant and performed HPLC analysis of the isomer compositions of the light‐ and partially dark‐adapted states of the mutant at several pH values. Our data confirmed that E194Q exhibits extremely slow dark adaptation over a wide range of pH. HPLC data showed that a significantly larger concentration of all‐trans isomer was present in the samples of the E194Q mutant even after prolonged dark adaptation. After 14 days in the dark the 13‐cis to all‐trans ratio was 1:3 in the mutant, compared to 2:1 in the wild type. These data clearly indicate the involvement of Glu194 in control of the rate of all‐trans to 13‐cis thermal isomerization.