Infrared and ab initio studies of hydrogen bonding and proton transfer in the complexes formed by pyrazoles

The results of experimental studies and quantum mechanical calculations of vibrational spectra and structure of hydrogen bonded complexes formed by pyrazole (P) and 3,5-dimethylpyrazole (DMP) are presented. IR spectra of pyrazoles in solutions, gas phase, and solid state have been investigated in wide range of concentrations and temperatures. It has been found that in the gas phase both P and DMP reveal the equilibrium between monomers, dimers, and trimers. In solutions the equilibrium between monomers and trimers dominates, no bands, which can be attributed to dimers were detected. DMP retains the trimer structure in solid state, while in the case of pyrazole P, formation of the crystal provides another type of association. Geometrical and spectral characteristics of dimers and trimers, obtained by ab initio calculations, are presented and compared with experimental data.

IR spectra of solutions containing P and DMP with a number of acids (acetic and trifluoroacetic acids, pentachlorophenol, HBr) have been studied in parallel with ab initio calculations. It has been found that pentachlorophenol forms with pyrazoles complexes with one strong hydrogen bond O–HN, while NH pyrazole group remains unbonded. With carboxylic acids DMP forms 1:1 cyclic complexes with two hydrogen bonds. In the case of acetic acid, the complex in CH₂Cl₂ solution reveals molecular structure with OHN and C=OHN bonds, in accordance with results of the calculations. For trifluoroacetic acid, the calculations predict the molecular structure to be energetically more stable in the case of the isolated binary complex (in gas phase), while the experimental spectrum of CH₂Cl₂ solution gives an evidence of the proton transfer with formation of the cyclic ionic pair with two NH⁺O⁻ bonds. The agreement with experimental results can be improved by taking into account the influence of environment in the framework of Onsager or Tomasi models. The shape of proton potential function of the complexes and medium effect on its parameters, resulted from experimental data and calculations, are discussed. It has been found that the number of potential minima and their relative depth depend strongly on the method of calculations and the basic set. Under excess of trifluoroacetic acid, the formation of 2:1 acid–DMP complex has been detected. Spectral characteristics and results of calculations point to the cyclic structure of this complex, which includes homoconjugated bis-trifluoroacetate anion and DMPH⁺ cation. With HBr both studied pyrazoles were found to form ionic complexes including one or two pyrazole molecules per one acid molecule and correspondingly monocation or homoconjugated cation BHB⁺.     

过渡金属离子(Cu2+、Cd2+)对藻红蛋白单体的漂白机制

藻胆蛋白是一组同源捕光色素蛋白,由多肽链及相连的开链四吡咯环色团构成。多肽链对色团的调控形成不同藻胆蛋白的特征吸收及荧光光谱。这些色团是藻蓝胆素(吸收带590～670 nm)、藻红胆素(吸收带530～570 nm)和藻尿胆素(吸收带490～500nm)。藻尿胆素由于在共轭体系中含有较少的双键,所以与前二者比,在较短波长有吸收。它们总是与藻红胆素伴生,在藻胆蛋白中作为敏化基团存在。     

ELECTRON TRANSFER FROM CHLOROPHYLL a TO QUINONE IN MONO- AND MULTILAYER ARRAYS

Abstract— Mono- and multilayers of chlorophyll a (Chl a )– lecithin have been prepared on quartz slides, by means of the Blodgett-Langmuir technique, for fluorescence studies. Self-quenching of the Chl a fluorescence has been observed in Chl a -lecithin single layer excited with a laser light at 632.8 nm. The fluorescence yield is reduced by 50% at a concentration of 7 ± 10¹² Chl a molecules cm⁻². Chl a fluorescence quenching, by adding N,N -distearoyl-1,4-diaminoanthraquinone (SAQ), has been studied. in a single layer, in pure Chl a and also at various dilutions of Chl a in lecithin. The results are explained in terms of a dynamic quenching rather than in terms of a permanent complex formation, at the ground state, between Chl a and SAQ. The fluorescence quenching has been interpreted as the result of an electron transfer from excited Chl a to SAQ, and rate constants of 8.3 ± 10⁻⁵ cm² molecule⁻¹ S⁻¹ and 2.4 ± 10⁻⁴ cm² molecule⁻¹ s⁻¹ have been found for pure diluted Chl a , respectively. Ten per cent of the diluted Chl a fluorescence always remains unquenchable and independent of the quinone concentration. In multilayers, where SAQ and Chl a are in different layers, there is no fluorescence quenching for pure or diluted Chl a even when the chromophores are in two adjacent layers. This happens only if SAQ is not able to diffuse from one layer to another. A minimum value of 22.4 nm has been found for the singlet exciton diffusion length in pure Chl a multilayers.     

COMPLEX FORMATION BETWEEN ETHIDIUM BROMIDE AND THE NUCLEOTIDES AMP AND GMP

Abstract— The antimicrobial drug ethidium bromide (EB) has been found to form molecular complexes with nucleotides, the strongest being those with the purines AMP and GMP. For the EB-AMP and EB-GMP complexes (which we characterized) the values of the ground-state association constant have been found to be 100 and 103 M ^-1, respectively. The fluorescence of the drug is enhanced when complexed to AMP, GMP, and TMP by about 60, 30 and 10%, respectively, whereas it is quenched by about 20% when complexed to CMP. Fluorescence enhancement analysis has yielded the values of 1.1 × 10¹⁰ and 0.7 × 10¹⁰ M ^-1 s^-1 for the excited-state rate constant of complex formation with the former two nucleotides, respectively. About one out of two collisions between an excited EB molecule and an AMP or GMP molecule results in complex formation. The potential implications of these findings for the EB-DNA interaction are discussed.     

Paramagnetic ruthenium(III) cyclometallated complex. Synthesis, spectroscopic studies and electron-transfer properties

The reaction of Ru^II(PPh₃)₃X₂ (X = Cl, Br) with o-(OH)C₆H₄C(H)=N-CH₂C₆H₅ (HL) under aerobic conditions affords Ru^II(L)₂(PPh₃)₂, 1, in which both the ligands (L) are bound to the metal center at the phenolic oxygen (deprotonated) and azomethine nitrogen and Ru^III(L¹)(L²)(PPh₃), 2, in which one L is in bidentate N,O form like in complex 1 and the other ligand is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom (deprotonated) of the benzyl amine fragment. The complex 1 is unstable in solution, and undergoes spontaneous oxidative internal transformation to complex 2. In solid state upon heating, 1 initially converts to 2 quantitatively and further heating causes the rearrangement of complex 2 to the stable RuL₃ complex. The presence of symmetry in the diamagnetic, electrically neutral complex 1 is confirmed by ¹H and ³¹P NMR spectroscopy. It exhibits an Ru^II → L, MLCT transition at 460 nm and a ligand based transition at 340 nm. The complex 1 undergoes quasi-reversible ruthenium(II)—ruthenium(III) oxidation at 1.27V vs. SCE. The one-electron paramagnetic cyclometallated ruthenium(III) complex 2 displays an L → Ru^III, LMCT transition at 658 nm. The ligand based transition is observed to take place at 343 nm. The complex 2 shows reversible ruthenium(III)—ruthenium(IV) oxidation at 0.875V and irreversible ruthenium(III)—ruthenium(II) reduction at −0.68V vs. SCE. It exhibits a rhombic EPR spectrum, that has been analysed to furnish values of axial (6560 cm⁻¹) and rhombic (5630 cm⁻¹) distortion parameters as well as the energies of the two expected ligand field transitions (3877 cm⁻¹ and 9540 cm⁻¹) within the t₂ shell. One of the transitions has been experimentally observed in the predicted region (9090 cm⁻¹). The first order rate constants at different temperatures and the activation parameter ΔH^#/ΔS^# values of the conversion process of 1 → 2 have been determined spectrophotometrically in chloroform solution.     

Iron carbonyl complexes from 2-[2,3-diaza-4-(2-thienyl)buta-1,3-dienyl]thiophene: N---N bond cleavage and cyclometalation

When thienyl Schiff base 1, derived from 2-formylthiophene and hydrazine, reacted with Fe₂(CO)₉ in n-hexane, three major complexes were obtained: (1) a diironhexacarbonyl complex with two 2-thienylmethylideneamido bridging ligands 2, which resulted from the =N---N= bond cleavage of ligand 1; (2) a doubly cyclometalated di-μ-di-(η¹:η²-thienyl; η¹:η¹(N))bis(hexacarbonyldiiron) complex (3); and (3) a cyclometalated (μ-η¹:η²-thienyl; η¹:η¹(N))hexacarbonyldiiron complex (4). Molecular structures of compounds 1a, 1c, and 2a have been determined by single-crystal X-ray diffraction.     

多元络合物显色反应中的有机溶剂化效应——铁(Ⅲ)-铬天青S-溴化十六烷基三甲铵-含氧有机溶剂体系

本文研究了Fe(Ⅲ)-铬天青S(CAS)-溴化十六烷基三甲铵(CTAB)体系显色反应的有机溶剂化效应.拟定了测定痕量铁的分光光度法.探讨了溶剂化效应机理.测定了络合物组成及溶剂化数.研究了有机溶剂对CAS离解常数(K_a3,K_a4)及Fe(Ⅲ)-CAS络合物稳定常数的影响.     

FLASH PHOTOLYSIS STUDIES OF OROTIC ACID

Abstract— The triplet state of orotic acid has been studied by flash photolysis. The rate for dimerization has been observed to vary from 2 × 10⁹ M ^-1 sec^-1 at pH 1 where both the triplet and ground state molecules are neutral, to under 10⁸ M^-1 sec^-1 above pH 9 where both the triplet and ground state molecules are doubly ionized. The p K of the triplet state has been measured as 4.6. The rate of oxygen quenching for the triplet is 2–3 × 10⁹ M^-1 sec^-1 while the rate of radiationless decay in solution is 0.73 × 10⁴ sec^-1. The triplet absorption spectra have been measured for the two ionic forms of the triplet.     

Low-temperature heat capacity and standard molar enthalpy of formation of the complex Zn(Thr)SO4·H2O (s)

Low-temperature heat capacities of the complex Zn(Thr)SO₄·H₂O (s) have been precisely measured with a small sample adiabatic calorimeter over the temperature range from 78 to 373 K. The initial dehydration temperature of the complex (T_d=325.50 K) has been obtained by analysis of the heat-capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation by least square method. The standard molar enthalpy of formation of the complex has been determined from the enthalpies of dissolution (Δ_dH_m^Θ) of [ZnSO₄·7H₂O (s) +Thr (s)] and Zn(Thr)SO₄·H₂O (s) in 100 ml of 2 mol dm⁻³ HCl solvent as: Δ_fH_{m,Zn(Thr)SO4·H2O}^Θ=−2111.7±3.4 kJ mol⁻¹. These experiments were made by using an isoperibol solution calorimeter at 298.15 K.     

Study of the mixed-metal lanthanummagnesium-purpurin complex: spectrophotometric determination of yttrium and lanthanides

Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg₂P₅, which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 × 10⁴ l.mole⁻¹.cm⁻¹ at 570 nm and its conditional extraction constant 5 × 10¹³ l⁴.mole⁻⁴. Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 μg has been investigated.     

Extraction and spectrophotometric determination of trace amount of Pd(II) with 2,2'-dithiodianiline

A method for the extraction-spectrophotometric determination of palladium with 2,2′-dithiodianilline (DTDA) is described. DTDA–Pd(II) complex is extracted from an aqueous solution with pH 3 into isobutyl methyl ketone (IBMK) layer. The absorbance is measured at 397 nm and the molar absorptivity found to be 1.47×10⁶ l mol⁻¹ cm⁻¹. The complex system conforms to Beer's law over the range 0.3–220 ng ml⁻¹ palladium (II). The effect of pH (1–6), NaClO₄ concentration, DTDA concentration and shaking time were studied. The ratio of the metal ion to ligand molecules in the complex and its stability constant were found to be 1:1 and 1.45×10⁶, respectively. The tolerance limit for many cations and anions have been determined. Finally the method has been applied successfully to the determination of palladium in synthetic mixtures, alloy and catalyst samples.     

Synthesis of a di(2-picolyl)amino-β-diketone dual-functional ligand that can coordinate to europium(III) for responding to copper(II) and sulfide ions

Lanthanide complex-based luminescent probes/chemosensors have shown great utilities in various biological and environmental assays with time-resolved detection mode to eliminate background noises. In this work, by conjugating di(2-picolyl)amine (DPA) with a tetradentate β-diketone 1,2-bis[4'- (1",1",1",2",2"-pentafluoro-3",5"-pentanedion-5"-yl)benzyl]-4-chlorosulfo-benzene (BPPBCB), a novel dual-functional ligand that can coordinate to Eu³⁺ for responding to Cu²⁺ and S^2- ions in aqueous media, DPA-BPPBCB, has been designed and synthesized. The β-diketone moiety of DPA-BPPBCB can form a strongly luminescent complex with Eu³⁺. Upon reaction with Cu²⁺, accompanied by the formation of heterobimetallic complex Cu²⁺-DPA-BPPBCB-Eu³⁺, the Eu³⁺ luminescence was quenched. While in the presence of S^2-, owing to the high affinity of S^2- to Cu²⁺, stable CuS was formed, which resulted in the release of Cu²⁺ from Cu²⁺-DPA-BPPBCB-Eu³⁺, to restore the luminescence of the Eu³⁺ complex. This unique “on-off-on” luminescence response of the Eu³⁺ complex enabled Cu²⁺ and S^2- ions in aqueous media to be detected with time-resolved luminescence detection mode.     

氨基苯甲酸修饰的DTPA螯合物及其弛豫性能

用邻-、对-氨基苯甲酸修饰二乙三胺五乙酸(DTPA),分别得到两种分子中携带芳香基团的双酰胺型DTPA衍生物,合成了它们的顺磁性金属离子螯合物,并研究了其中部分螯合物的inuitroNMRT₁弛豫率(R₁).结果表明,Gd(Ⅲ)DTPA-B4ABA^2-和GdDTPA-B2ABA^2-对水质子的弛豫率R₁分别为5.5和5.4L·mmol^-1·s^-1,接近相应的母体螯合物GdDTPA^2-的R₁值5.2L·mmol^-1·s^-1.     

Rhodamine 6G-based Chemosensor for the Visual Detection of Cu2＋ and Fluorescent Detection of Hg2＋ in Water

A novel water soluble chemosensor 1 based on rhodamine 6G spirolactam scaffold has been synthesized and characterized.Upon addition of a wide range of the environmentally and biologically relevant metal ions,chemosensor 1 shows a colorimetric selective Cu2＋ recognition from colorless to pink confirmed by UV-Vis absorption spectral changes,while it also exhibits a fluorometric selective Hg2＋ recognition by fluorescence spectrometry.An absorption enhancement factor over 17-fold with 1-Cu2＋ complex and a fluorescent enhancement factor over 45-fold with 1-Hg2＋ complex were observed.Their recognition mechanisms were assumed to be a 1：1 stoichiometry for 1-Cu2＋ complex and a 1：2 stoichiometry for 1-Hg2＋ complex,respectively,which were proposed to be different ligation leading to the ring-opening of rhodarnine 6G spirolactam.Furthermore,the detection limits for CU2＋ or Hg2＋ were 3.3 × 10-8 or 1.7x 10-7 mol/L,respectively.     

Extraction-spectrophotometric determination of vanadium with 3,5-dinitrocatechol and Brilliant Green

The formation and extraction of the ion-associates of the vanadium(V)-3,5-dinitrocatechol (DNC) anionic chelate complex with various basic dyes have been studied and a new sensitive extraction—spectrophotometric method for the determination of vanadium based on the system V(V)-DNC-Brilliant Green has been developed. Beer's law is obeyed up to a vanadium concentration of 0.3 μg/ml and the molar absorptivity is 1.7 × 1O⁵ l.mole⁻¹. cm⁻¹ at 630 nm. The molar ratios of the components and the form of the vanadium(V) cation in the extracted compound have been determined, and the formula [VO(OH)(DNC)²⁻₂][BG⁺]₂ is proposed. Titanium, molybdenum, tungsten, EDTA and thiocyanate interfere seriously. The method becomes specific after a preliminary separation of vanadium by its extraction as the BPHA complex from H₂SO₄-HF medium, and is 40 times more sensitive than the spectrophotometric BPHA method. The proposed method has been applied to determination of traces of vanadium (about 10⁻⁵%) in alums.     

INTERACTION BETWEEN HUMAN α1ACID GLYCOPROTEIN (OROSOMUCOID) AND 2-p-TOLUIDINYLNAPHTHALENE-6-SULFONATE

Abstract—
The interaction between human α₁-acid glycoprotein (orosomucoid) and the fluorescent probe, 2- p -toluidinylnaphthalene-6-sulfonate (TNS) has been studied. An association constant of 16.7 (±3) X 10³ M ^-1 was obtained for the complex at 20°C with a stoichiometry of 1:1. From the effect of temperature on the binding process, the standard enthalpy change for the binding is calculated to be ΔH⁰= -18 ± 3 kJ mol^-1 and the standard entropy change ΔS⁰= 19 ± 12 J K^-1 mol^-1. The tryptophan fluorescence of the protein can be described by a sum of three exponentials. Upon TNS binding, the average fluorescence lifetime of the protein in the complex changes much less than the fluorescence intensity. The bound TNS is therefore a very efficient acceptor for the protein fluorescence. The TNS bound to orosomucoid presents two fluorescence lifetimes 1 1 and 4.3 ns. The possible origins of the two lifetimes are discussed.     

钴与铬天青S、吡啶及其衍生物阳离子表面活性剂体系显色反应的研究

钴与铬天青S、溴化羟十二烷基三甲铵在吡啶的水溶液中可发生灵敏的显色反应,但吡啶作用的机理未论及,且吡啶气味恶臭,不便于应用.为了探讨吡啶在钴多元络合物形成中的增稳作用以及寻找其它含氮中性配位体代替吡啶,对Co(Ⅱ)与CAS,吡啶(Py)及其衍生物(α-氨基吡啶α-AP、5-氯-α-氨基吡啶5-Cl-α-AP),阳离子表面活性剂(CSF)体系进行了系统的研究.     

Simple, rapid and sensitive spectrofluorimetric determination of diflunisal in serum and urine based on its ternary complex with terbium and EDTA

A very simple, rapid and highly sensitive fluorimetric method for the determination of diflunisal in serum and urine is described. The method is based on the formation of a ternary complex between diflunisal, Tb³⁺ and EDTA in alkaline aqueous solutions. This complex exhibits very intense terbium ion luminescence with a main emission maximum at 546 nm when excited at 284 nm. Optimum conditions for the complex formation have been investigated. The detection limit for diflunisal is 2.4 μg 1⁻¹, while the range of application is 0.01–6.00 mg 1⁻¹. The method has been successfully applied for the determination of diflunisal in untreated human serum and urine samples. Analytical recoveries from serum and urine samples spiked with diflunisal were in the ranges of 96.8–101.2% and 98.0–102.0%, respectively.     

铜(Ⅱ)与2-羰基丙酸水杨酰腙配合物的合成、晶体结构和抑菌活性

以2-羰基丙酸水杨酰腙作为配体与五水硫酸铜进行反应,制得配合物Cu(C₁₀H₈N₂O₄)(H₂O)₂(1)和Cu(C₁₀H₈N₂O₄)(CH₃OH)(H₂O)(2)(C₁₀H₈N₂O₄^2-为2-羰基丙酸水杨酰腙负离子),测试了配合物2的单晶结构.该单晶为墨绿色,属三斜晶系,P1空间群.晶胞参数a=0.7538(2)nm,b=1.1431(2)nm,c=0.7500(2)nm,α=93.26(2)^o,β=94.46(2)^o,γ=94.39(2)^o,V=0.6411(2)nm₃,μ=1.731mm^-1,Z=2,D_c=1.792g/cm³,F(000)=342.00,R=0.035,wR=0.048,GOF=1.78.在配合物2内,2-羰基丙酸水杨酰腙负离子中的2个氧原子和1个氮原子、甲醇中的氧原子以及配位水中的氧原子与铜原子配位,形成四方锥结构,其中来自甲醇的配位氧原子位于锥顶;此晶体为外消旋化合物,晶体中存在对映异构体,两者通过氢键连接,形成二聚体,成对出现在晶胞中.根据元素分析、红外和紫外光谱推测配合物1与2的结构相似;抑菌试验结果表明,配合物1对辣椒疫霉菌和烟草赤星菌分别有100%和66.02%的抑制作用.     

Vibrational frequencies of CO adsorbed on silica supported Mo atoms from density functional calculations

The interaction of CO with silica supported molybdenum atoms has been studied by means of density functional calculations and cluster models. Experimentally two bands in the IR spectra of adsorbed CO have been observed at 2170 and 1990 cm⁻¹ with vibrational shifts of +27 and −153 cm⁻¹, respectively, with respect to the gas-phase molecule, the peak at +27 cm⁻¹ has been related to the presence of neutral Mo atoms anchored to two oxygen atoms of the SiO₂ substrate. Possible reactive sites at the Mo/SiO₂ interface have been explored as candidates for CO adsorption. Mo atoms in various formal oxidation states, from +II to +VI, have been considered. Both molecular and cluster models of the Mo/SiO₂ interface have been employed. The analysis shows that a neutral Mo(II) atom, proposed to be responsible for the blue-shift of ν(CO), is not likely to be the origin of the IR band at 2170 cm⁻¹. Only Mo atoms in high oxidation states or Mo cations carrying a real positive charge can account for the positive shifts in the CO frequency.