Readily Available Fluorescence Probes for Zinc Ion in Aqueous Solution of Neutral pH

Zinc ion in aqueous solution of neutral pH was detected by a probe that is readily obtained by simply mixing commercially available cyclen (a Zn(II) receptor) and lumazine or lumichrome (a heterocyclic fluorophore containing an imide moiety as partial structure) in an equal molar ratio. The initially generated cyclen-Zn(II) complex interacts with lumazine to form a cyclen-Zn(II)-lumazine complex whereby the intensity of fluorescence is enhanced. These Zn(II) probes showed excellent selectivity for Zn(II) over other divalent metal ions such as Pb(II), Cu(II), Co(II), Ni(II), and good selectivity over Cd(II). The X-ray crystal structure of the cyclen-Zn(II)-lumazine complex revealed that the cyclen-chelated Zn(II) binds deprotonated lumazine at the N-1.     

Facile Synthesis of 1,2-Dialkyl-3-Phenyl-4-Quinolinones

The synthesis of 1,2-dialkyl-3-phenyl-4-quinolinones (1) is readily accomplished by a low-temperature reaction of an N-alkylisatoic anhydride with the therraodynamic potassium enolate of phenyl-acetone. The reaction has also been extended to encompass the synthesis of the more complex 2-(3-hydroxy-propyl)-3-(4-fluorophenyl)-1-methyl-4(1H)-quinolinone (10).     

Spectrophotometric Evidence for the Formation of a Mixed Bismuth-Phosphorus Heteropoly Acid

Abstract

Spectrophotometric evidence is presented to show that bismuth interacts with phosphate and molybdate in acid solution to form a mixed bismuth-phosphorus heteropoly acid. The complex is similar to 12-molybdophosphoric acid by virtue of its degree of dissociation in both concentrated and dilute acid solutions. The complex is more stable than 12-molybdophosphoric acid because it is formed when bismuth is added to a solution of 12-molybdophosphoric acid. The proposed bismuth-phosphorus compound is reduced much more readily to a heteropoly blue than is 12-molybdophosphoric acid, a fact that has contributed to a false belief that the bismuth may have been acting catalytically in the reduction of 12-molybdophosphoric acid.     

CO2 activation by metal−ligand-cooperation mediated by iridium pincer complexes

Abstract

Herein we report the reversible activation of CO₂ by the dearomatized complex [(^tBuPNP*)Ir(COE)] (1) and by the aromatized complex [(^tBuPNP)Ir(C₆H₅)] (2) via metal-ligand cooperation (MLC) (^tBuPN = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine; ^tBuPNP* = deprotonated PNP; COE = cyclooctadiene). The [1,3]-addition of CO₂ to 1 and 2 is reversible at ambient temperature. While the dearomatized complex 1 reacts readily at ambient temperature with CO₂ in THF or benzene, complex 2 reacts with CO₂ upon heating in benzene at 80 °C or at ambient temperature in THF. The novel aromatized complex [(^tBuPNP)IrCl] (10) does not react with CO₂. Based on the reactivity patterns of 1, 2, and 10 with CO₂, we suggest that CO₂ activation via MLC takes place only via the dearomatized species, and that in the case of 2 THF plays a role as a polar solvent in facilitating formation of the dearomatized hydrido phenyl complex intermediate (complex II).     

Stereochemistry and the use of H2/D2 mixtures as probes into the mechanism of hydrogenations catalyzed by cationic rhodium (DIPHOS) complexes

The stereochemistry of the hydrogenation of 4-tert-butylmethylenecyclohexane (1) and the use of D₂ or D₂/H₂ mixtures in place of H₂ furnishes evidence that hydrogenations using the catalyst precursor [Rh(DIPHOS)(COD)]⁺BF ₄ ⁻ proceed via more than one mechanism. This evidence includes the effect of changes in pressure and added triethylamine upon the kinetics and isomerization of 1, as well as the distribution of the added deuterium in the products of the reaction of 1 or norbornene with either D₂ or H₂/D₂ mixtures. That an alkene necessarily causes the equilibration of H₂/D₂ mixtures, although it need not involve any of the alkenes’s hydrogen atoms (e.g., norbornene), provides a clue to the process by which the mononuclear mechanism proposed by Halpern, which is dominant near one atmosphere of H₂, merges into another with increasing pressure. It has been proposed that the cationic complex [Rh(DIPHOS)S₂]⁺ is transformed in the presence of an alkene and hydrogen into a binuclear hydrido complex, such as those described by Sivak and Muetterties (1979) and Fryzuk (1982), which represent a far more active catalyst than its mononuclear precursor. Such an intermediate should readily catalyze the H₂-D₂ equilibration and the isomerization of an alkene in the presence of D₂ without necessarily introducing deuterium into the product. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 88–97. Deceased. The text was submitted by the authors in English. This work was conducted at the University of Arkansas.     

Two-Phase Thin-Layer Chromatography

Abstract

Thin layer chromatography (TLC) is normally carried out on single-phase (adsorbent) plates. However, it may be necessary to use nore than one adsorbent to achieve the separation of complex mixtures. Literature reports indicate that the use of mixed phases in TLC is not very common, possibly because the plates are difficult to prepare and precoated single-phase plates of different absorbents are readily available (silica gel, reversed phase, cellulose. alumina, etc.).     

A copper(II) complex of 1,4,7-triazacyclononane featuring acetate pendant: an efficient DNA cleavage agent

A new water-soluble copper(II) complex, Cu(TACNA)Br?·?0.375H₂O (1) [TACNA?=?1,4,7-triazacyclononane-N-acetate], has been synthesized to serve as artificial nucleases. The X-ray crystal structure of 1 indicates that one bromide and an oxygen from acetate pendant coordinate to copper(II) in addition to the nitrogen atoms in the TACN macrocycle, resulting in a five-coordinate complex with square-pyramidal geometry. The interaction of 1 with calf thymus DNA (ct-DNA) has been investigated by UV absorption and fluorescence spectroscopies, and the mode of ct-DNA binding for 1 has been proposed. In the absence of external agents, supercoiled plasmid DNA cleavage by 1 was performed under aerobic condition; the influences on DNA cleavage of different complex concentrations and reaction times were also studied. The cleavage of plasmid DNA likely involves oxidative mechanism.     

Synthesis,crystal structure,DNA binding,and DNA cleavage of a zinc complex containing N,N-bis(2-pyridylmethyl)amine

A water-soluble zinc complex, [Zn(bpea)Cl₂] (1) (bpea?=?N,N-bis(2-pyridylmethyl)ethylamine), was prepared to serve as a nuclease mimic. The complex was characterized by X-ray, infrared, and UV spectroscopy. Interactions of the complex with calf thymus-DNA (ct-DNA) have been investigated by UV absorption and fluorescence spectroscopies; the mode of ct-DNA binding for 1 has been proposed. DNA cleavage activities by 1 were performed in the absence of external agents. The influences of different complex concentrations or reaction times on DNA cleavage were studied.     

Untersuchung Der Kcmplexbildung Von Thallium(III) Mit 1-Phenyl-3-Methyl-4-Benzoylpyrazolon-5

Abstract

A study has been made of the method used for extracting the complex formed between thallium(III) and PhMBP. It has been demonstrated that thallium(III) can be readily extracted as a complex with PhMBP by organic solvents at low pH. The extraction of thallium(III) has been studied as a function of pH, concentration of reagent, nature of solvent, duration of contact of the phases and concentration of thallium(III). It has been established that thallium(III) forms a complex with PhMBP of the type MA_n, where n=3. The stability constants and distribution constant of the neutral complex has been calculated by the method of Leden-Rydberg.     

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

This work presents a detailed study of the photo-induced spin-state dynamics of the photochromic iron(II) complex 1, where the metal ion is in the field of a tripodal hexa-imine ligand with protolysable phenol groups. The nature of the complex’s ground state has been identified as a spin singlet by ¹H NMR and steady-state UV/vis spectroscopies, and its distorted octahedral structure was analyzed via crystal structure determination. Sub-picosecond and nanosecond time-resolved laser flash photolysis experiments identify the long-lived quintet state of 1 as the selective product of photoexcitation in the UV/vis spectral region. Thermal barriers of spin-state interconversion as a function of solvent and added base are derived from temperature-dependent rates of transient decay. Ground-state recovery is found to be significantly affected by the solvent and is strongly enhanced, in particular, by base-driven solvolysis of the ligand’s phenol groups. Partial spontaneous deprotonation of the phenolic hydroxyl groups of 1 seems to prevail on metal oxide surfaces, i.e. on alumina. Composite materials, like 1 at Al₂O₃, that retain the characteristic spectral features of the parent iron(II) complex can be readily obtained by wet impregnation of hydrous alumina with solutions of 1.     

About the Mechanism of the Reaction Cuprous Dialkyl Thiophosphates with the Alkynyl Halides

Abstract

Cuprous dialkyl thiophosphates are convenient reagents for the synthesis of the organophosphorus compounds with the α-acetylenic bond in the alkthiolic radical, and for steric hindered S-propargyl thiophosphates. X-ray investigation established that the crystal is constructed of the tetramer molecules Cu₄[(EtO)₂PSO]₄.¹ The tetramer is a tetrahedral claster of Cu atoms coordinated with four three-dentant chelate-bridged diethyl thiophosphate ligands. Firmly coordinated diethyl thiophosphate ligand in the copper complex does not possess nucleophilic properties and does not react with alkyl bromide. EPR spectroscopy established that the ethynylation of cuprous dialkyl thiophosphate by the substituted ethynyl bromides proceeds via the paramagnetic cupric complex formation. The latter, being unstable under usual conditions, decomposes with the formation of substituted S-ethynyl thiophosphates and CuBr.² Sterically hindered halides of the propargyl type are not liable to Sn2 reaction with the potassium salts of dialkyl thiophosphoric acids, but they readily react with the cuprous salts of these acids yielding S-propargyl thiophosphates. This process is a redox one and it proceeds via the paramagnetic cupric complex formation.     

A Kinetic Study of the Reaction Between Glutathione and Iron(III) in the pH Range from 1 to 3

Anaerobic reactions of iron(III) with glutathione (GSH) have been studied kinetically using stopped-flow spectrophotometry. One mixing reduced GSH with iron(III) a very rapid increase in absorbance with a broad peak centred at 620 nm was recorded. The rapid formation of the blue complex was followed by a decomposition step at a slower rate, yielding a colourless product. GSH reduces iron(III) readily in aqueous solution to yield the iron(II) GSH complex.     

Ion Interaction Chromatographic Separation of Amino Acids Using a Basic-Tetraalkylammonium Salt Mobile Phase

Abstract

A basic mobile phase containing a tetraalkylammonium (R₄N⁺) salt was used to enhance the retention of free amino acids (AA) in their anion form on a polystyrene divinylbenzene copolymeric (Hamilton PRP-1) nonpolar stationary phase adsorbent. Major variables, which can be readily manipulated to alter this retention and resolve complex AA mixtures, are: structure and concentration of R₄N⁺ salt, type and amount of organic modifier in the mobile phase solvent, concentration and selectivity of the counteranion present, and mobile phase pH and ionic strength. Mobile phase gradients based on a pH change, or an ionic strength change and their combination, while all other variables are constant, were evaluated for the separation of complex AA mixtures. Detection was accomplished by absorbance or fluorescence after a post-column ortho-phthalaldehyde reaction.     

Synthesis and crystal structure of the Sm(ButNCHCHNBut)2(bpy) complex

Reaction of Sm(bpy)₄ (bpy is 2,2′-bipyridyl) with di-tert-butyldiazabutadiene (dad) in tetrahydrofuran (THF) affords the mixed-ligand complex Sm(dad)₂(bpy) (1). Complex1 was isolated as black paramagnetic crystals readily soluble in THF, 1,2-dimethoxyethane (DME), toluene, and ether. Compound1 was characterized by IR and ESR spectroscopy, X-ray diffraction analysis, and by the results of magnetic measurements. Based on the difference between the Sm−N bond lengths and on the data of IR spectroscopy, the following formal charge distribution in the molecule of complex1 was proposed: Sm³⁺(dad)²⁻(dad)¹⁻(bpy)⁰. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1860–1862, October. 1997.     

Protonation of Tetrapropoxy-4-tert-butylcalix[4]arene: NMR Study of Interaction and Probable Structures of the Product

Using ¹H and ¹³C NMR spectroscopy, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H₃O⁺ ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d ₅. It was shown that 1 readily forms an equimolecular complex with H₃O⁺. The equilibrium constant K of its formation is 2.6 at 296 K. Exchange between bound and free 1 is fast even under mild excess of HDCC, the correlation time τ_ex being about 0.13 ms. NMR shows that H₃O⁺ is bound to the aryl-oxygen atoms and this binding forces the calixarene cup to adopt a more open and symmetrical conformation. This conclusion is in full accord with high precision quantum DFT calculations which find one structure of the complex corresponding to a global energy minimum, in which the H₃O⁺ ion is bound to three of the oxygen atoms by strong hydrogen bonds and to the remaining oxygen by two weaker hydrogen bonds. The calixarene part is forced into a C₄ symmetrical opened form.

When stored for weeks, the complex gradually transforms into other forms, most probably its hydrates, according to spectral evidence and DFT calculations.     

A multichannel thiacalix[4]arene-based fluorescent chemosensor for Zn2+, F− ions and imaging of living cells

Abstract

The fluorescent sensor (3) based on the 1,3-alternate conformation of the thiacalix[4]arene bearing the coumarin fluorophore, appended via an imino group, has been synthesised. Sensing properties were evaluated in terms of a colorimetric and fluorescence sensor for Zn²⁺ and F^?. High selectivity and excellent sensitivity were exhibited, and ‘off-on’ optical behaviour in different media was observed. All changes were visible to the naked eye, whilst the presence of the Zn²⁺ and F^? induces fluorescence enhancement and the formation of a 1:1 complex with 3. In addition, 3 exhibits low cytotoxicity and good cell permeability and can readily be employed for assessing the change of intracellular levels of Zn²⁺ and F^?.     

Direct Resolution of Secondary Tert-Butylphenylphosphine Oxide

Abstract

Secondary phosphine oxides constitute an important class of organophosphorus compounds and are higly useful as versatile phosphinoylating agents and as ligands ^[1,2] They are however not readily available in the optically active form.^[3–5] We wish to demonstrate that P-chiral secondary teri-butylphenylphosphine oxide (I) can be promptly resolved into enantiomers by means of its diastereoisomeric complexes with L-O,O-dibenzoyltanaric acid (L-DBTA) Dissolution of equimolar amounts of racemic I and L-DBTA in the 4 I benzene acetone mixture yields crystalline II complex containing exclusively the R-enantiomer of the starting phosphine oxide The complexed S-enantiomer is obtained from the mother liquor by crystallization from benzene The enantiomers of I are freed from their L-DBTA complexes by simple washing with aqueous NaOH Both enantiomers of 1 of very high optical purity are thus obtained from a single batch These enantiomers have subsequently been tested for their configurational stability in selected synthetic applications.     

Complexation of Indole-3-acetic Acid with Iron(III): Influence of Coordination on the π-Electronic System of the Ligand

Summary.  The iron(III) complex of indole-3-acetic acid (1) was prepared, and its physicochemical properties, mode of iron(III) coordination, and electronic structure were studied using UV/Vis, diffuse reflectance infrared Fourier transform (DRIFT), and transmission ⁵⁷Fe M?ssbauer spectroscopic techniques. The data obtained provide evidence that iron(III) is not only coordinated by the carboxylic O-donor atom, but also via the conjugated π-electronic system of the pyrrole moiety involving both the non-shared electronic pair of the heteroatom and the C(2)*C(3) double bond. Considering the well-known increased sensitivity of the pyrrole residue in indole derivatives to oxidation as compared to the benzene ring, as well as the formation of a triple complex (peroxidase-1-O₂) proposed for the enzymatic 1 oxidative degradation mechanism involving as a key step the Fe³⁺ → Fe²⁺ transition in the enzyme form as discussed in literature, it is concluded that iron(III) coordination with 1 can influence the redox properties of the pyrrole ring by affecting its π-electronic system. Received September 17, 2000. Accepted (revised) October 31, 2000     

Syntheses,crystal structures,and urease inhibitory properties of copper(II) and zinc(II) complexes with 2-bromo-4-chloro-6-[(2-dimethylaminoethylimino)methyl]phenol

A new copper(II) complex, [CuL(μ _1,1-N₃)] _n (1), and a new zinc(II) complex, [ZnL(μ ₂-acetato-O, O′)₂] _n (2) (HL = 2-bromo-4-chloro-6-[(2-dimethylaminoethylimino)methyl]phenol), were prepared and characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray diffraction. Complex 1 is an end-on azide-bridged polynuclear copper(II) complex and 2 is a syn–anti bidentate acetate-bridged polynuclear zinc(II) complex. Each metal in the complex is five-coordinate with square-pyramidal geometry. Complex 1 shows good urease inhibitory properties, while 2 does not.     

Effects of Acetone,Ethanol, Isopropanol and Dimethyl Sulfoxide on Amylose-Iodine Complex†

Abstract

The amylose-iodine (AI) complex formation was studied by absorption spectra in water and water-containing varying proportions of ethanol, acetone, isopropanol and dimethyl sulfoxide (DMSO). Complex formation is most favored in pure water and decreases as the proportion of nonaqueous solvent is increased. A decrease in the absorbance intensity at around 615 nm (for AI complex) is accompanied by a peak shift towards 550 nm and an increased absorbance at around 350 nm (for unbound iodine). The amount of the nonaqueous solvent added, as well as the order in which it is added relative to amylose and iodine solution; change remarkably the extent of the AI complex formation. A mechanism of the complex formation is proposed.