三种水杨醛类席夫碱的合成与性质研究

以取代水杨醛和3-氨基噻吩为原料合成了三种水杨醛类席夫碱,探讨了水杨醛结构中酚羟基对位取代基结构变化对于该席夫碱探针的激发态内质子转移过程、pH响应和金属离子响应的影响。研究结果表明,改变取代基团的推、吸电子能力,可调节酚氧负离子对活泼氢的束缚能力,进而影响这些席夫碱分子的激发态内质子转移性能。同时,酚氧负离子的电荷密度也决定了其与阳离子的配位能力,从而表现出不同结构的席夫碱对金属离子的选择性和灵敏性差异。     

Photophysical Properties and OLED Applications of Phosphorescent Platinum(II) Schiff Base Complexes

The syntheses, crystal structures, and detailed investigations of the photophysical properties of phosphorescent platinum(II) Schiff base complexes are presented. All of these complexes exhibit intense absorption bands with λ_max in the range 417–546 nm, which are assigned to states of metal‐to‐ligand charge‐transfer (¹MLCT) ¹[Pt(5d)→π*(Schiff base)] character mixed with ¹[lone pair(phenoxide)→π*(imine)] charge‐transfer character. The platinum(II) Schiff base complexes are thermally stable, with decomposition temperatures up to 495 °C, and show emission λ_max at 541–649 nm in acetonitrile, with emission quantum yields up to 0.27. Measurements of the emission decay times in the temperature range from 130 to 1.5 K give total zero‐field splitting parameters of the emitting triplet state of 14–28 cm^?1. High‐performance yellow to red organic light‐emitting devices (OLEDs) using these platinum(II) Schiff base complexes have been fabricated with the best efficiency up to 31 cd A^?1 and a device lifetime up to 77 000 h at 500 cd m^?2.     

A physiochemical study of azo dyes: DFT based ESIPT process

Azo linked dye derivatives were synthesized and characterized by NMR, mass and elemental analysis. An excited state intramolecular proton transfer (ESIPT) in hydroxy Schiff base has been analyzed, and found that two distinct ground state isomers of I and II are responsible for the observed dual emission. DFT calculation on energy, dipole moment, charge distribution of the rotamers in the ground and excited states support the ESIPT process. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. By varying the addition of base concentration to hydroxy Schiff base, two isobestic points were found which confirm the equilibrium among the trans enol form, anion and the cis enol form. Fluorescence quenching with metal ions reveal that hydroxy Schiff base can be used as a new fluorescence sensor to detect the Cu(2+) ion.     

Key role of electrostatic interactions in bacteriorhodopsin proton transfer

The first proton transport step following photon absorption in bacteriorhodopsin is from the 13-cis retinal Schiff base to Asp85. Configurational and energetic determinants of this step are investigated here by performing quantum mechanical/molecular mechanical minimum-energy reaction-path calculations. The results suggest that retinal can pump protons when in the 13-cis, 15-anti conformation but not when 13-cis, 15-syn. Decomposition of the proton transfer energy profiles for various possible pathways reveals a conflict between the effect of the intrinsic proton affinities of the Schiff base and Asp85, which favors the neutral, product state (i.e., with Asp85 protonated), with the mainly electrostatic interaction between the protein environment with the reacting partners, which favors the ion pair reactant state (i.e., with retinal protonated). The rate-limiting proton-transfer barrier depends both on the relative orientations of the proton donor and acceptor groups and on the pathway followed by the proton; depending on these factors, the barrier may arise from breaking and forming of hydrogen bonds involving the Schiff base, Asp85, Asp212, and water w402, and from nonbonded interactions involving protein groups that respond to the charge rearrangements in the Schiff base region.     

Charge transfer complexes of adenosine-5'-monophosphate and cytidine-5'-monophosphate with water-soluble cobalt(II) Schiff base complexes in aqueous solution

Water-soluble cobalt(II) tetradentate Schiff base complexes have been shown to form charge transfer (CT) complexes with a series of nucleoside monophosphates including adenosine-5'-monophosphate (AMP) and cytidine-5'-monophosphate (CMP). The investigated water-soluble cobalt(II) Schiff base complexes are (i) disodium[{bis(5-sulfo-salicylaldehyde)-o-phenylenediiminato}cobalt(II)], Na2[Co(SO3-salophen)] (1); (ii) disodium[{bis(5-sulfo-salicylaldehyde)-4,5-dimethyl-o-phenylenediiminato}cobalt(II)], Na2[Co(SO3-sal-4,5-dmophen)] (2) and (iii) disodium[{bis(4-methoxy-5-sulfo-salicylaldehyde)-4,5-dimethyl-o-phenylenediiminato}cobalt(II)], Na(2)[Co(SO3-4-meosal-4,5-dmophen)] (3). The formation constant and thermodynamic parameters for charge transfer complex formation of water-soluble cobalt(II) Schiff base complexes with nucleoside monophosphates were determined spectrophotometrically in aqueous solution at constant ionic strength (I = 0.2 mol dm(-3) KNO3) under physiological condition (pH 7.0) and at various temperatures between 288 and 308 K. The stoichiometry has been found to be 1:1 (water-soluble cobalt(II) Schiff base complex: nucleoside monophosphate) in each case. Our spectroscopic and thermodynamic results show that the interaction of water-soluble cobalt(II) Schiff base complexes with the investigated nucleoside monophosphates occurs mainly through the phosphate group. The trend of the interaction according to the cobalt(II) Schiff base complexes due to electronic and steric factors is as follows: Na2[Co(SO3-salophen)] > Na2[Co(SO3-sal-4,5-dmophen)] > Na2[Co(SO3-4-meosal-4,5-dmophen)]. Also the trend of the interaction of a given cobalt(II) Schiff base complex according to the nucleoside monophosphate is as follows: CMP > AMP.     

Synthesis,structures, photoluminescence,and theoretical investigations on two new Zn(II)/Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands

Abstract  

Two new neutral mononuclear Zn(II) and Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands, [Zn(paH)₂(OAc)₂]·2CH₃OH (paH = pyridine-2-amidoxine, HOAc = acetic acid) (1), and [Mn(paH)₂(OAc)₂]·C₂H₅OH·2H₂O (2), have been prepared and characterized structurally by X-ray crystallography. 1 and free paH exhibit photoluminescence at room temperature in solid state, which is rare so fare for metal complexes with oxime-based ligand. The emissions of 1 and free paH arise from the metal-perturbed paH-based π → π* ligand-to-ligand charge transfer transition (LLCT) and π → π* charge transfer transition in nature, respectively, in terms of the density functional theory level calculations and molecular orbital analyses.     

SPECTROSCOPY OF POLYENES–III. ABSORPTION AND EMISSION SPECTRAL INVESTIGATION OF POLYENE SCHIFF BASES AND PROTONATED SCHIFF BASES RELATED TO VISUAL PIGMENTS

Abstract— A number of n -butylamine Schiff bases of polyenals related to retinals as homologues and analogues, and their protonated forms, have been studied for absorption and emission spectral properties. The polyene Schiff bases exhibit the same general features in their absorption spectra as those of the parallel polyenals except that the ^lB_u←¹A_g and π*← n singlet transitions are at substantially higher energy in the Schiff bases (the shift being larger for the π *← n transition). The Schiff bases with short polyene chainlength ( n = 2, 3 where n is the number of double bonds including C=N) do not fluoresce or phosphoresce in 3-methylpentane in the temperature range 298–77 K. The Schiff bases with intermediate chainlength ( n = 4, 5) show fluorescence at 77 K with intensity strongly dependent on the nature of solvent. The Schiff bases with relatively long chainlength ( n = 5–7) show strong or moderately strong fluorescence at 77 K and very weak fluorescence at 298 K ( n = 7) with intrinsic radiative lifetimes much longer than those estimated from the oscillator strength of the low-energy, strong absorption band (¹B_u←¹ A_g ). A discussion on the possible state order and nature of the fluorescing state of the various polyene Schiff base systems is presented.     

A physiochemical study of excited state intramolecular proton transfer process-Luminescent chemosensor by spectroscopic investigation supported by ab initio calculations

A group of novel Schiff base derivatives were synthesized and characterized by NMR spectra, X-ray, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy Schiff base (SB4) has been studied using emission spectroscopy and it was detected that the two distinct ground state isomers of I and II are responsible for the emission. The comparison of the emission wavelength in hydrocarbon solvent strongly supports that trans enol form predominates over the cis enol form for Schiff base (SB4). With increasing base concentration of the solutions of hydroxy substituted Schiff bases (SB4 and SB5), two isobestic points are found which confirm the equilibrium among the trans enol form, anion and the cis enol form. The fluorescence of (SB4) quenched markedly with the gradual addition of Cu(2+) but the fluorescence properties of (SB5) was influenced by other metal ions. Therefore Schiff base (SB5) can be used as a new fluorescence sensor to detect the quantity of Cu(2+) ion in any sample solution depending on the relative intensity change. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base derivatives were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state.     

Electronic structures of heme a of cytochrome c oxidase in the redox states—Charge density migration to the propionate groups of heme a

The electronic structures of heme a of cytochrome c oxidase in the redox states were studied, using hybrid density functional theory with a polarizable continuum model and a point charge model. We found that the most stable electronic configurations of the d electrons of the Fe ion are determined by the orbital interactions of the d orbitals of the Fe ion with the π orbitals of the porphyrin ring and the His residues. The redox reaction of the Fe ion influences the charge density on the formyl group through the π conjugation of the porphyrin ring. In addition, we found the charge transfer from the Fe ion to the propionate group of heme a in the redox change despite the lack of the π‐conjugation. We elucidated that the charge propagation originates from the heme a structure itself and that the origin of the charge delocalization to the heme propionate is the orbital interactions between the d orbital of the Fe ion and the p orbitals of the carboxylate part of the heme propionate via the π conjugation of the porphyrin ring and the σ* orbital of the C? C bond of the propionate group. The electrostatic effect by surrounding proteins enhances the charge transfer from the Fe ion to the propionate group. These results indicate that heme propionate groups serve electron mediators in electron transfer as well as electrostatic anchors, and that proteins surrounding the active site reinforce the congenital abilities of the cofactors. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Synthesis, characterization, spectroscopic and thermodynamic studies of charge transfer interaction of a new water-soluble cobalt(II) Schiff base complex with imidazole derivatives

The water-soluble cobalt(II) tetradentate Schiff base complex [Co(II)L](ClO4)(2), L: (N,N'-bis(5-[(triphenylphosphonium)-methyl]salicylidine)-o-phenylenediamineperchlorate has been synthesized and characterized. This complex forms charge transfer (CT) complexes with imidazole and 1-methylimidazole. The formation constant, molar absorptivity (epsilon'), and thermodynamic parameters for charge transfer complexes formation of cobalt(II) Schiff base complexes with imidazole derivatives were determined by using UV-vis spectrophotometric method in aqueous solutions at constant ionic strength (I=0.2mol dm(-3) KNO3) at pH 6.0 and various temperatures between 292 and 315K.     

邻香兰素氨基酸Schiff碱化合物的合成及构象研究

Schiff碱是指含有亚甲氨基－PC＝N－的化合物,这类化合物因Schiff于1864年首先发现而得名。一些Schiff碱及其过渡金属配合物对肿瘤和病菌有一定的抑制作用^[1-3]。1970年,Hodnett^[4,5]制得几种Schiff碱,实验发现它们对老鼠肌肉内的Walker206瘤有抑制生长的作用,它们和某些金属形成的螯合物效果更好。Schiff碱配体可以作为螯合剂、生物活性剂、分析试剂和催化剂等,在科学研究和化工生产中有着广泛应用^[6,7]。本文报道一类新型的Schiff碱－邻香兰素氨基酸化合物的合成和构象研究,采用分子动力学模拟退火搜索方法对4人邻香兰素Schiff碱化合物的不同构型分子进行了构象研究,在搜索出的系列低能构象中分别找出全局最低能量构象,以此为初始构象进行了PM3量子化学计算。4个化合物的分子骨架结构如图1所示。     

The role of the carboxylate ion in models of acyl-chymotrypsin

Two exquisite models of the acyl-chymotrypsin intermediate, one designed by Bruice and another by Bender, were studied to elucidate the role of the carboxylate ion in the catalytic triad of serine proteases. However, opposing conclusions were drawn from these studies. Computational chemistry analysis of these models indicates that the carboxylate ion plays an insignificant role in the former model because of the correct orientation and the distance of the imidazole group without the carboxylate ion. However, in the latter model, the carboxylate ion serves to orient and place the imidazole group at the correct position. This analysis suggests that an important role of the carboxylate ion in serine proteases is to position the imidazole group to be an effective general base catalyst. © 1995 by John Wiley & Sons, Inc.     

Corrosion inhibition studies on mild steel in HCl by a newly synthesized benzil monohydrazone based Schiff base

The corrosion inhibition effect of newly formulated Schiff base 2-((E)-((E)-2-hydrazone-1, 2-diphenylethylidene) amino phenol) (HDAP) ligand L derived from Benzil monohydrazone and 2-Aminophenol on mild steel in 1 ​M HCl was examined. Electrochemical (Tafel and EIS) and mass loss techniques were employed to evaluate its corrosion protection efficiency. The inhibition efficiency (η %) was elevated with raise in concentration of compound L.Maximum inhibition efficiency of 94.18% was obtained at 0.01 ​M concentration of HDAP from Tafel polarisation curve. From electrochemical impedance (EIS) studies, it was confirmed that increase in concentration of HDAP led to enhancement of the charge transfer resistance. Both physical and chemical types of adsorptions were observed for the Schiff base via π-bonding electrons which obey Langmuir adsorption isotherm. The SEM picture revealed development of a thin layer on metallic surface. Quantum chemical evaluations were conducted to find out the mechanism of corrosion retardation power of HDAP.     

Carboxylate ion dependency in the Cu(II) catalysed asymmetric Henry reaction: Structural characterisation of a tridentate Schiff base complex containing a coordinated carboxylic acid

Six tridentate Schiff base ligands containing tertiary butyl or benzyl substituents were prepared from chiral amino alcohols and salicylaldehyde derivatives. The ligands were employed as catalysts for the Cu(II) catalysed asymmetric Henry reaction. It was discovered that when different carboxylate salts were used instead of copper acetate as the Cu(II) salt, significant changes in the enantioselectivity of the reactions were observed. Addition of Cu(OAc)₂ to the ligand prepared from salicylaldehyde and α,α‐diphenyl‐tert ‐leucinol resulted in the formation of dark green crystals. X‐ray structural analysis of these crystals showed that a square planar monomeric complex had been formed rather than the expected dimer. In the structure, the copper(II) centre is bonded to the tridentate ONO ligand and an acetate ion. There is a strong hydrogen bond between the protonated alcoholic oxygen of the Schiff base ligand and the uncoordinated acetate oxygen atom. These results, taken together, indicate that the carboxylate anion may be an important part of the active intermediate when this type of copper complex is used as a catalyst in the asymmetric Henry reaction.     

catena‐Poly[aquacopper(II)‐μ‐[N‐(1‐oxido‐2‐naphthylmethylene)glycinato‐O,N,O′:O′]]

In the title compound, [Cu(C₁₃H₉NO₃)(H₂O)]_n, the Cu^II ion is in a slightly distorted square‐pyramidal environment, with four short bonds in the basal plane formed by three donor atoms of the Schiff base and a water O atom. A symmetry‐related neighbouring mol­ecule provides an apical carboxylate O atom at a distance of 2.551 (3) Å; this contact leads to the formation of zigzag polymeric chains. In addition, the chain fragments are connected to each other by hydrogen bonding.     

Structuring Redox Polymers Poly[M(Schiff)] (M = Ni,Pd; Schiff = Schiff Bases) on a Molecular Level: Methods and Results of an Investigation

This work is devoted to a consideration of methods of electrochemical synthesis of redox polymers poly[M(Schiff)], where “M” is Ni, or Pd and “Schiff” stands for a four-dentate Schiff base, with a controlled distribution of structural elements (stacks) over the electrode's surface for the optimization of the transport of charge-compensating ions, which is the stage that determines the charge transfer rate in the system under consideration. It is shown that the structuring of these polymers on a molecular level by means of a purposeful selection of the composition of the initial compounds and the conditions of synthesis—the potential of formation and the nature of the solvent and supporting electrolyte—makes it possible to a considerable extent accelerate the charge transfer process in the polymers and improve stability of their electrochemical characteristics.     

Ion trap collision-induced dissociation of multiply deprotonated RNA: c/y-ions versus (a-B)/w-ions

The dissociation of model RNA anions has been studied as a function of anion charge state and excitation amplitude using ion trap collisional activation. Similar to DNA anions, the precursor ion charge state of an RNA anion plays an important role in directing the preferred dissociation channels. Generally, the complementary c/y-ions from 5′ P-O bond cleavage dominate at low to intermediate charge states, while other backbone cleavages appear to a limited extent but increase in number and relative abundance at higher excitation energies. The competition between base loss, either as a neutral or as an anion, as well as the preference for the identity of the lost base are also observed to be charge-state dependent. To gain further insight into the partitioning of the dissociation products among the various possible channels, model dinucleotide anions have been subjected to a systematic study. In comparison to DNA, the 2′-OH group on RNA significantly facilitates the dissociation of the 5′ P-O bond. However, the degree of excitation required for a 5′ base loss and the subsequent 3′ C-O bond cleavage are similar for the analogous RNA and DNA dinucleotides. Data collected for protonated dinucleotides, however, suggest that the 2′-OH group in RNA can stabilize the glycosidic bond of a protonated base. Therefore, base loss from low charge state oligonucleotide anions, in which protonation of one or more bases via intramolecular proton transfer can occur, may also be stabilized in RNA anions relative to corresponding DNA anions.     

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by salen CoIII(acetate) complexes

A series of Co^III carboxylate based upon N,N,O,O-tetradentate Schiff base ligand framework have been prepared. X-ray diffraction analysis confirms that these Schiff base Co^III carboxylate are all monomeric species with a six-coordinated central Co in their solid structures. The activities and polycarbonate selectivity of these complexes toward the copolymerization of epoxide (cyclohexene oxide and propylene oxide) and carbon dioxide have been investigated in the presence of bis(triphenylphosphine)iminium chloride. Copolymerization experiments indicate that [bis(α-methyl-3,5-di-tertbutyl-salicylaldehyde) ethylenediiminato] Co^IIIOOCH₃ exhibits the highest activity and polycarbonate selectivity among these Co^III carboxylate. The resultant copolymer contained almost 100 % carbonate linkages with the molecular weight up to 71.8 kg mol^?1 as well as narrow polymer dispersity index (polymer dispersity index?=?1.5). The substituents and the mode of the bridging part between the two nitrogen atoms both exert significant influences upon the progress of the copolymerizations, influencing both the polycarbonate selectivity and the rate of copolymerization.     

RETINAL-OPSIN LINKAGE OF CEPHALOPOD RHODOPSIN

Abstract— The pK_a of the Schiff base of N-retinylidene butylamine was determined in anionic (sodium dodecylsulfate), cationic (cetyltrimethylammonium bromide) and nonionic (polyoxyethylene (9) lauryl ether) detergent solutions. The pK_a of the Schiff base was raised from 6.4 to 9.9 by the effect of the neighboring anion. The rise of the pK_a was affected by the ion strength. Squid metarhodopsin behaved in a manner similar to the model Schiff base in the anionic detergent solution. The cationic group showed the opposite effect on the pK_a of the Schiff base. The retinal Schiff base in rhodopsin might be heavily influenced by adjacent anionic groups. The nature of the interaction is discussed.     

THE INVOLVEMENT OF WATER AT THE RETINAL BINDING SITE IN RHODOPSIN AND EARLY LIGHT-INDUCED INTRAMOLECULAR PROTON TRANSFER

Abstract Extensive dehydration of air-dried films of bovine rod outer segment membranes induces fully reversible changes in the absorption spectrum of rhodopsin, indicative of deprotonation of the retinylidene Schiff base in more than 50% of the rhodopsin molecules in the sample. This suggests that water is involved at the site of the Schiff base protonation in rhodopsin. In contrast, the spectrum of metarhodopsin I is resistant to similar dehydrating conditions, implying a significant difference in the mechanism for protonation in metarhodopsin I. The photochemistry of dehydrated membranes was also explored. Photoexcitation of deprotonated rhodopsin (λ_max 390 nm) induces a large bathochromic shift of the chromophore. The major photoproduct at room temperature was spectrally similar to metarhodopsin I (λ_max, 478 nm). These findings suggest that intramolecular proton transfer involving the Schiff base proton may occur in the earlier stages of the visual cycle, prior to or during the formation of metarhodopsin I.