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1.
The redox potentials of the oriented films of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins (bR), prepared by adsorbing purple membrane (PM) sheets or its mutant on a Pt electrode, have been examined. The redox potentials (V) of the wild-type bR were −470 mV for the 13-cis configuration of the retinal Shiff base in bR and −757 mV for the all-trans configuration in H2O, and −433 mV for the 13-cis configuration and −742 mV for the all-trans configuration in D2O. The solvent isotope effect (ΔV=V(D2O)−V(H2O)), which shifts the redox potential to a higher value, originates from the cooperative rearrangements of the extensively hydrogen-bonded water molecules around the protonated CN part in the retinal Schiff base. The redox potential of bR was much higher for the 13-cis configuration than that for the all-trans configuration. The redox potentials for the E194Q mutant in the extracellular region were −507 mV for the 13-cis configuration and −788 mV for the all-trans configuration; and for the E204Q mutant they were −491 mV for the 13-cis configuration and −769 mV for the all-trans configuration. Replacement of the Glu194 or Glu204 residues by Gln weakened the electron withdrawing interaction to the protonated CN bond in the retinal Schiff base. The E204 residue is less linked with the hydrogen-bonded network of the proton release pathway compared with E194. The redox potentials of the D96N mutant in the cytoplasmic region were −471 mV for the 13-cis configuration and −760 mV for the all-trans configuration which were virtually the same as those of the wild-type bR, indicating that the D to N point mutation of the 96 residue had no influence on the interaction between the D96 residue and the CN part in the Schiff base under the light-adapted condition. The results suggest that the redox potential of bR is closely correlated to the hydrogen-bonded network spanning from the retinal Schiff base to the extracellular surface of bR in the proton transfer pathway.  相似文献   

2.
We have obtained by Fourier transformed infra-red (FTIR)-spectroscopy BR-K, BR-L and BR-M difference spectra of bacteriorhodopsin regenerated with isotopically labelled retinals. Thereby, we are able to assign reliably the C14–C15 and C=N stretching vibrations of the various intermediates. The lower C14–C15 stretching vibration frequency in L as compared with 13-cis protonated Schiff base model compounds indicates a 13-cis, 14-s-cis configuration of the retinal in this species. The unusually low C=N stretching vibration in K at 1615 cm−1 indicates less stabilization of the positive charge at the Schiff base by the protein environment. Based on these results, a mechanism is suggested by which the stored light energy is transformed into proton transfers.  相似文献   

3.
We discuss to what extent the vibrational spectra of bacteriorhodopsin that have been observed and assigned by Smith et al. (1, 2) by means of resonance Raman and by Gerwert and Siebert (EMBO (Eur. Mol. Biol. Organ.) J. In press) by means of infrared absorption experiments are in agreement with a photo-cycle of bacteriorhodopsin that involves the sequence BR, IO(all-trans) → K(13,14-cis) → L(13,14-cis) → M(13-cis) → N(13-cis) → O(all-trans). Our discussion is based on a quantumchemical modified neglect of diatomic overlap [MNDO] calculation of the vibrational spectra of the relevant isomers of the protonated retinal Schiff base. In particular, we investigated in these calculations the effects of different charge environments on the frequencies of the relevant C-C single bond stretching vibrations of these isomers.  相似文献   

4.
We discuss to what extent recent vibrational spectra of 14-2H, 15-2H and 14,15-2H isotopically labelled L550 provide evidence for the occurrence of 13-cis, 14-s-trans or 13-cis, 14-s-cis chromophore structures in bacteriorhodopsin's photocycle. The discussion is based on a quantum chemical (MNDO) vibrational analysis of four molecular fragments as models for the retinal chromophore in bacteriorhodopsin.  相似文献   

5.
The resonance Raman spectrum of the reaction center of Rhodopseudomonas sphaeroides G1C as well as those of the cis-trans isomers of β-carotene (all-trans, 9-cis, 13-cis, 15-cis and 9-cis, 13-cis- (or 9-cis, 13′-cis)) have been recorded at liquid N2 temperature by use of the 457.9, 488.0 and 514.5 nm excitation lines. Comparison of the spectra indicated that the carotenoid in the reaction center takes the 15-cis configuration.  相似文献   

6.
Channelrhodopsin-2 mediates phototaxis in green algae by acting as a light-gated cation channel. As a result of this property, it is used as a novel optogenetic tool in neurophysiological applications. Structural information is still scant and we present here the first resonance Raman spectra of channelrhodopsin-2. Spectra of detergent solubilized and lipid-reconstituted protein were recorded under pre-resonant conditions to exclusively probe retinal in its electronic ground state. All-trans retinal was identified to be the favoured configuration of the chromophore but significant contributions of 13-cis were detected. Pre-illumination hardly changed the isomeric composition but small amounts of presumably 9-cis retinal were found in the light-adapted state. Spectral analysis suggested that the Schiff base proton is strongly hydrogen-bonded to a nearby water molecule.  相似文献   

7.
Five dissymmetric tridentate Schiff base ligands, containing a mixed donor set of ONN and ONO were prepared by the reaction of benzhydrazide with the appropriate salicylaldehyde and pyridine-2-carbaldehyde and characterized by FT-IR, 1H and 13C NMR. The complexes of these ligands were synthesized by treating an ethanolic solution of the appropriate ligand and one equivalent Et3N with an equimolar amount of MnCl2 · 4H2O or alternatively by a more direct route in which an ethanolic solution of benzhydrazide was added to ethanolic solution of appropriate salicylaldehyde and MnCl2 · 4H2O solution to yield [MnCl(L1)(H2O)2], [Mn(L2)2(H2O)2], [MnCl(L3)], [MnCl(L4)] and [MnCl2(H2O)(L5)]. The hydrazone Schiff base ligands and their manganese complexes including HL1-4 and L5 (HL1 = benzoic acid (2-hydroxy-3-methoxy-benzylidene)-hydrazide, HL2 = benzoic acid (2,3-dihydroxy-benzylidene)-hydrazide, HL3 = benzoic acid (2-hydroxy-benzylidene)-hydrazide, HL4 = benzoic acid (5-bromo-2-hydroxy-benzylidene)-hydrazide, L5 = benzoic acid pyridine-2-yl methylene-hydrazide) were characterized on the basis of their FT-IR, 1H and 13C NMR, and molar conductivity. The crystal structures of HL1 and [MnCl2(H2O)L5] have been determined. The results suggest that the Schiff bases HL1, HL2, HL3, and HL4 coordinate as univalent anions with their tridentate O,N,O donors derived from the carbonyl and phenolic oxygen and azomethine nitrogen. L5 is a neutral tridentate Schiff base with N,N,O donors. ESI-MS for the complexes Mn-L2,3,5 provided evidence for the presence of multinuclear complexes in solution. Catalytic ability of Mn-L1-5 complexes were examined and found that highly selective epoxidation (>95%) of cyclohexene was performed by iodosylbenzene in the presence of these complexes and imidazole in acetonitrile.  相似文献   

8.
Using highly purified ornithine decarboxylase isolated from androgen-treated mice, [1R-2H]putrescine was generated by the decarboxylation of l-ornithine in D2O, and [1S-2H]putrescine was generated from [2-2H]ornithine by carrying out the decarboxylation in H2O. Chirality of the putrescines was then determined from the 200-MHz 1H NMR spectra of their bis-camphanamides in the presence of Eu(fod)3. These results demonstrated that decarboxylation had taken place with retention of configuration.  相似文献   

9.
Kinetics were determined for the four transients K590, L540, M410, O660 of the photochemical cycle of bacteriorhodopsin (BR570) both in 1H2O and in 2H2O over a wide temperature range. Breaks in the Arrhenius plots, observed at 25–32 for the longest-lived transients coincide with a transition point in the microviscosity of the membrane as measured by depolarization of an added fluorescent probe. The earliest isotope effect occurs in the decay of L540, and is present in the subsequent formation and decay of M410 and O660. Thus in the light-driven proton pump of BR570, proton ejection from the Schiff base correlates with decay of L504 and reprotonation occurs with the decay of both M410 and O660 back to BR570.  相似文献   

10.
To assign the observed vibrationsl modes in the resonance Raman spectrum of the retinylidene chromophore of rhodopsin, we have studied chemically modified retinals. The series of analogs investigated are the n-butyl retinals substituted at C9 and C13. The results obtained for the 11-cis isomer have clearly assigned the CCH3 vibrational frequencies observed in the spectrum of the retinylidene chromophore. The data show that the C(9)CH3 stretching vibration can be assigned to the vibrational mode observed in the 1017 cm?1 region, and the vibration detected at 997 cm?1 can be assigned to the C(13CH3 vibration. The C(5)CH3 stretching mode does not contribute to the vibrations observed in this region. The splitting in the C(n)CH3 (n = 9, 13) vibration is characteristic of the 11-cis conformation. The results on the modified retinals do not support the hypothesis that the splitting arises from equilibrium mixtures of 11-cis, 12-s-cis and 11-cis, 12-s-trans in solution. Thus, this splitting cannot be used to determine whether the chromophore in rhodopsin is in a 12-s-cis or 12-s-trans conformation. However, our results demonstrate that there are other vibrational modes in the spectra which are sensitive to this conformational equilibrium and we use the presence of a strong ~ 1271 cm?1 mode in bovine and squid rhodopsin spectra as an indication that the chromophore in these pigments is 11-cis, 12-s-trans.  相似文献   

11.
Raman, infra-red and multinuclear NMR spectroscopy were used to establish the structure of several TiX4·2L adducts (X=F, Cl, Br; L=Lewis base) in inert solvents. In contrast to the analogous SnX4·2L adducts where a cis-trans equilibrium prevails, most of the TiX4·2L adducts studied were found to have only the cis configuration. Trans isomers were observed but their formation was dependent on the donor ability of the ligand. In dichloromethane solution, the adducts with L=Me2O, Me2S, (MeOCH2-)2, Et2S, THT, Me2Se, MeCN, Me2CO, Cl(MeO)2PO, Cl2(MeO)PO, Cl3PO and Cl2(Me2N)PO were found to have the cis configuration only. For the adducts with L=THF, Cl(Me2N)2PO and TMPA, a cis-trans equilibrium was observed. The thermodynamic parameters were measured for cis-trans isomerization for TiCl4·2TMPA in CHCl3; these parameters are: Kiso277=[trans] / [cis]=0.36, ΔH°iso=− 1.3 ± 1.3 kJ/mol, ΔS°iso=−13.1 + 7.5 J/mol K, and ΔV°iso= − 1.3+0.8 cm3/mol. A complex equilibrium involving cis and trans isomers and the ionic complex [TiCl3·3HMPA]Cl was found to occur for the TiCl4 adduct with L=HMPA. 1H NMR was used to establish the relative stabilities of the cis adducts and the following sequence was obtained: Me2O ∼ MeCN < Me2CO < Me2S < Me2Se < Cl(MeO)2PO < TMPA < CI(Me2N)2PO.  相似文献   

12.
Two new zinc complexes, Zn(HL1)2 (1) and [Zn2(H2L2)(OAc)2]2 (2) [H2L1 = Schiff base derived from o-vanillin and (R)-(+)-2-amino-3-phenyl-1-propanol, H3L2 = Schiff base derived from o-vanillin and 2-amino-2-ethyl-1,3-propanediol], have been synthesized and characterized by single crystal X-ray diffraction, elemental analyses, TG analyses, solid fluorescence, IR, UV-Vis and circular dichroism spectra. The structural analysis shows that complex 1 has a right-handed double helical chain along the crystallographic b axis. A homochiral 3D supramolecular architecture has been further constructed by intermolecular C-H··· π, O-H···O and C-H···O interactions. Complex 2 includes two crystallographically independent binuclear zinc molecules. The two binuclear zinc molecules are isostructural. The 2-D sheet supramolecular structure was formed by intermolecular hydrogen bonding interaction. The fluorescence of ligands and complexes in DMF at room temperature are studied. The interactions of two complexes with calf thymus DNA (CT-DNA) are investigated using UV-Vis, CD and fluorescence spectroscopy. The results show that complex 1 exhibits higher interaction with CT-DNA than complex 2. In addition, in vitro cytotoxicity of the complexes towards four kinds of cancerous cell lines (A549, HeLa, HL-60 and K562) were assayed by the MTT method. Investigations on the structures indicated that the chirality and nuclearity of zinc complexes play an important role on cytotoxic activity.  相似文献   

13.
The synthesis and characterization of a new 14- membered tetraazamacrocylic ligand 5,5,7,12,12,14- hexamethyl-1,4,8,11-tetraazacyclotetradecane-N′,N‴- diacetic acid (H2L2) are reported. Cobalt(III),nickel(II) and copper(II) complexes with this ligand were prepared and their IR and visible spectra studied.The molecular structure of the complex NiL2· HBr·H2O was proved by single-crystal X-ray analysis. The compound crystallizes in the space group P21/n, with cell parameters a = 16.7109(13), b = 9.0539(9), c = 17.0277(13) Å, β = 107.46(6)° and Z = 4. The structure was solved by direct and Fourier methods and refined by full matrix least square calculation to R = 0.042 for 4355 observed reflections (I > 3σ(I)). The complex shows a cis-octahedral geometry with the macrocycle coordinated in a folded configuration to four sites around the central nickel atom. The two carboxylate groups of the side chain are on the same side of the approximate plane of the macrocycle.  相似文献   

14.
A mesogenic Schiff base, N,N′-di-(4-hexadecyloxysalicylidene)diaminoethane, H2dhdsde (abbreviated as H2L1) that exhibit smectic-C (SmC) mesophase, was synthesized and its structure studied by elemental analyses, mass, NMR & IR spectra and single crystal XRD (triclinic space group with Z = 1) techniques. Bi-dentate bonding of the Schiff base in the mesogenic LaIII complex was implied on the basis of IR & NMR spectral data. As per the spectral studies of the complexes, the Zwitterionic species of the ligand (H2L1) coordinates to LnIII ion through two phenolate oxygens rendering the overall geometry around the metal ion to distorted square antiprism (Ln = La, Pr, Nd, Sm, Eu) and monocapped octahedron (Ln = Gd, Tb, Dy, Ho).  相似文献   

15.
A novel chiral Schiff base containing α-d-altropyranoside unit, methyl 4,6-O-benzylidene-3-deoxy-3-(2-salicylideneaminoethylamino)-α-d-altropyranoside (3, Me-Alt-NNOH), has been prepared. Treatment of zinc chloride with 3 in the presence of triethylamine afforded a five-coordinated zinc(II) complex [Zn(Me-Alt-NNO)Cl] (4). Both 3 and 4 have been characterized by infrared, 1H NMR, 13C NMR, MS, and elemental analysis. The crystal structure of 4 has been determined by X-ray diffraction. Crystal structure analysis shows that the complex 4 exits a distorted triangular bipyramid geometry and the Schiff base motif acts as a uninegatively charged tetradentate chelating agent. The methoxy and amino groups cis-chelate to the zinc atom and the pyrano-ring is in an ideal 4C1 chair conformation.  相似文献   

16.
A series of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes has been synthesized and characterized by 1H-, 13C-, 119Sn NMR, ESI-MS (electrospray ionization mass spectrometry), IR and 119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The structures of four di-n-butyltin(IV) complexes, viz., nBu2Sn(L3)2 (3), nBu2Sn(L4)2 (4), nBu2Sn(L5)2 (5) and nBu2Sn(L7)2 · 0.5C6H6 (7) (LH = 5-[(E)-2-(aryl)-1-diazenyl)quinolin-8-ol) were determined by single crystal X-ray diffraction. In general, the complexes were found to adopt a distorted cis-octahedral arrangement around the tin atom. These complexes retain their solid-state structure in non-coordinating solvent as evidenced by 119Sn and 13C NMR spectroscopic results. The in vitro cytotoxicity of di-n-butyltin(IV) complexes (3-8) is reported against seven well characterized human tumour cell lines. The basicity of the two quinolinolato donor N and O atoms of the ligands are discussed in relation to the cytotoxicity data.  相似文献   

17.
The chromophore in halorhodopsin (HR) which acts as a light-driven chloride pump in halobacteria shares many properties with its counterpart in bacteriorhodopsin (BR): (i) a similar retinal protein interaction, (ii) trans to cis isomerization and (iii) similar intermediates of its photocycle. One major difference between the two chromoproteins is that the HR chromophore does not become deprotonated during its photocycle. A mechanism for the photocycle of HR is presented, which, in close analogy to an earlier proposed mechanism for BR, involves the sequence of all-trans 13-cis, 14s-cis 13-cis all-trans isomerizations of the chromophore, a Schiff base of retinal. In contrast to the situation in BR the 13-cis, 14s-cis13-cis isomerization is induced not by deprotonation of the retinal Schiff base chromophore but rather by the movement of an anion (Cl-) towards the protonated nitrogen of the Schiff's base. The suggested mechanism involves the Schiff base directly in the chloride translocation in halorhodopsin.  相似文献   

18.
The proton pumping cycle of bacteriorhodopsin (bR) is initiated when the retinal chromophore with the 13-trans configuration is photo-isomerized into the 13-cis configuration. To understand the recovery processes of the initial retinal configuration that occur in the late stage of the photocycle, we have performed a comprehensive analysis of absorption kinetics data collected at various pH levels and at different salt concentrations. The result of analysis revealed the following features of the late stages of the trans photocycle. i) Two substates occur in the O intermediate. ii) The visible absorption band of the first substate (O1) appears at a much shorter wavelength than that of the late substate (O2). iii) O1 is in rapid equilibrium with the preceding state (N), but O1 becomes less stable than N when an ionizable residue (X1) with a pKa value of 6.5 (in 2 M KCl) is deprotonated. iv) At a low pH and at a low salt concentration, the decay time constant of O2 is longer than those of the preceding states, but the relationship between these time constants is altered when the medium pH or the salt concentration is increased. On the basis of the present observations and previous studies on the structure of the chromophore in O, we suspect that the retinal chromophore in O1 takes on a distorted 13-cis configuration and the O1-to-O2 transition is accompanied by cis-to-trans isomerization about C13C14 bond.  相似文献   

19.
The reaction of Cu(ClO4)2·6H2O with the Schiff base derived from 1,1′-(2,6-pyridyl)-bis-1,3-butanedione and 3-amino-1-propanol, (H4L2), yields the complex Cu(H4L2)(ClO4)2·H2O. The crystal structure of this complex is triclinic, R = 0.0521, 5602 reflections. The species is dimeric leading to a binuclear copper(II) complex in which the well- separated (8.93 Å intramolecular and 5.46 Å inter- molecular) copper(II) atoms are in distorted square pyramidal geometries.  相似文献   

20.
The Pd(II) and Pt(II) complexes with triazolopyrimidine C-nucleosides L1 (5,7-dimethyl-3-(2′,3′,5′-tri-O-benzoyl-β-d-ribofuranosyl-s-triazolo)[4,3-a]pyrimidine), L2 (5,7-dimethyl-3-β-d-ribofuranosyl-s-triazolo[4,3-a]pyrimidine) and L3 (5,7-dimethyl[1,5-a]-s-triazolopyrimidine), [Pd(en)(L1)](NO3)2, [Pd(bpy)(L1)](NO3)2, cis-Pd(L3)2Cl2, [Pd2(L3)2Cl4] · H2O, cis-Pd(L2)2Cl2 and [Pt3(L1)2Cl6] were synthesized and characterized by elemental analysis and NMR spectroscopy. The structure of the [Pd2(L3)2Cl4] · H2O complex was established by X-ray crystallography. The two L3 ligands are found in a head to tail orientation, with a Pd?Pd distance of 3.1254(17) Å. L1 coordinates to Pd(II) through N8 and N1 forming polymeric structures. L2 coordinates to Pd(II) through N8 in acidic solutions (0.1 M HCl) forming complexes of cis-geometry. The Pd(II) coordination to L2 does not affect the sugar conformation probably due to the high stability of the C-C glycoside bond.  相似文献   

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