Presence Of Acetate Anions Research Articles

π-Conjugation effects on excited-state intermolecular proton-transfer reactions of anthracene-urea derivatives in the presence of acetate anions.

This study investigated emissive urea compounds with an anthryl moiety on one side and a substituent group (biphenyl, naphthyl, benzyl, or cyclohexyl) on the other side across from the urea group. This was performed to determine the contribution of π-conjugation on a substituent group to excited-state intermolecular proton-transfer (ESPT) reactions in the presence of acetate anions. Fluorescence lifetime measurements revealed that the rate constant of the ESPT reaction from the normal form to the tautomer form increased with the length of the π-conjugation. Considering that there were a few differences among the wavelengths of the fluorescence maxima for the anthracene-urea derivatives in the presence of acetate anions, we observed that the extension of π-conjugation promoted tautomer formation. This maintained the energy levels of the normal and tautomer forms in the excited state. Furthermore, an anthracene-urea derivative without π-conjugation did not undergo a reverse ESPT reaction, implying that π-conjugation is considerably involved in the reverse ESPT reaction from the tautomer form to the normal form.

Electronic state of a fluoranthene–urea compound and the kinetics of its emissive tautomer state in the presence of acetate anions

The fluorescence spectrum of 3FU–Ac around 600 nm agrees well with that of 3FU–DBU, indicating that the electronic state of tautomer has a proton-abstracted structure.

Iodide CIMS and <i>m</i>∕<i>z</i> 62: the detection of HNO<sub>3</sub> as NO<sub>3</sub><sup>−</sup> in the presence of PAN, peroxyacetic acid and ozone

Abstract. Chemical ionisation mass spectrometry (CIMS) using I− (the iodide anion), hereafter I-CIMS, as a primary reactant ion has previously been used to measure NO3 and N2O5 both in laboratory and field experiments. We show that reports of large daytime mixing ratios of NO3 and N2O5 (both usually present in detectable amounts only at night) are likely to be heavily biased by the ubiquitous presence of HNO3 in the troposphere and lower stratosphere. We demonstrate in a series of laboratory experiments that the CIMS detection of HNO3 at m/z 62 using I− ions is efficient in the presence of peroxy acetyl nitric anhydride (PAN) or peroxyacetic acid (PAA) and especially O3. We have characterised the dependence of the sensitivity to HNO3 detection on the presence of acetate anions (CH3CO2-, m/z 59, from either PAN or PAA). The loss of CH3CO2- via conversion to NO3- in the presence of HNO3 may represent a significant bias in I-CIMS measurements of PAN and PAA in which continuous calibration (e.g. via addition of isotopically labelled PAN) is not carried out. The greatest sensitivity to HNO3 at m/z 62 is achieved in the presence of ambient levels of O3 whereby the thermodynamically disfavoured, direct reaction of I− with HNO3 to form NO3- is bypassed by the formation of IOx-, which reacts with HNO3 to form, for example, iodic acid and NO3-. The ozone and humidity dependence of the detection of HNO3 at m/z 62 was characterised in laboratory experiments and applied to daytime, airborne measurements in which good agreement with measurements of the I−(HNO3) cluster ion (specific for HNO3 detection) was obtained. At high ozone mixing ratios, we show that the concentration of I− ions in our ion–molecule reactor (IMR) is significantly depleted. This is not reflected by changes in the measured I− signal at m/z 127 as the IOx- formed does not survive passage through the instrument but is likely detected after fragmentation to I−. This may result in a bias in measurements of trace gases using I-CIMS in stratospheric air masses unless a calibration gas is continuously added or the impact of O3 on sensitivity is characterised.

A Dual Emissive Coumarin-urea Derivative with an Electron-withdrawing Substituent in the Presence of Acetate Anion.

We investigated the fluorescent properties, including the excited-state intermolecular proton transfer, of urea derivatives comprising a coumarin ring, which is a widely used fluorophore. We prepared two different coumarin-urea derivatives, 6CU and 7CU, which bear a urea-based substituent at the 6 and 7 positions of a coumarin ring, respectively. In the presence of the acetate ion, 7CU showed additional tautomer fluorescence emission with respect to 6CU, indicating that tautomer formation depends on the positions of the urea-based substituent on the coumarin ring. Thus, the resonance structures of urea derivatives might play an important role in the behavior of dual fluorescence, which is an important phenomenon applicable to photochemical anion sensing. Moreover, in order to further improve the fluorescence properties of the mentioned derivatives, a CF3 group was introduced in a phenyl ring opposite to a coumarin ring. The fluorescence quantum yield of 7CUCF3 thus synthesized was 65 times as large as that of 7CU, an observation that renders 7CUCF3 a suitable anion sensor candidate. The results of this study will contribute to the development of new molecular designs for highly fluorescent sensing.

Solution-processed fabrication of perfectly (2 0 0)-oriented lead selenide thin films

To the best of our knowledge, the solution-processed fabrication of perfectly (2 0 0)-oriented lead selenide (PbSe) films on various substrates, including glass, transparent conducting glass, and polyethylene terephthalate (PET) substrates, has been achieved for the first time. Herein, the effects of orientation parameters, including the acetate anion effect, crystallization temperature, and chemical composition, on solution-processed PbSe thin films were examined. Particularly, the presence of acetate anions in the precursor solution strongly affected the degree of orientation. X-ray diffraction analysis was employed, and X-ray diffraction pole-figure polar distance was scanned by rotating the sample about the incident beam direction. The experimental results confirmed the formation of perfectly (2 0 0)-oriented PbSe films.

Brønsted versus Lewis Acid Type Anion Recognition by Arylboronic Acids.

Interactions between arylboronic acids and a series of anions as tetrabutylammonium salts in DMSO and MeCN were studied by (1)H and (11)B NMR as well as spectrophotometrically. Boronic acids act as Brønsted acid type receptors through hydrogen bonding with B(OH)2 hydroxyl groups toward Cl(-), Br(-), HSO4(-), and AcO(-), but they act as Lewis acid type receptors toward F(-) and H2PO4(-), which form tetrahedral adducts with the B(III) center of boronic acids, although there is also evidence for some contribution of hydrogen bonding with these anions. The Hammett plot for the binding constants of AcO(-) with 3- and 4-substituted phenylboronic acids in DMSO is nonlinear, with a small negative slope for electron-donating and weakly electron-accepting substituents and a large positive slope for strongly electron-accepting substituents. 3-Nitrophenylboronic acid recognizes zwitterions of amino acids in DMSO, and its UV absorption maximum undergoes a significant red shift in the presence of acetate anions, providing a means for sensing anions optically. Arylboronic acids as Brønsted acid type receptors show relatively low sensitivity to solvent polarity and are equally or even more efficient than widely employed proton donors such as ureas or dicarboxamides.

Kinetic analysis of photoinduced reactions in hydrogen-bonded complexes of anthracene-urea with anions

Abstract Transient absorption measurement of urea-anthracene species n PUA ( n = 1, 2, 9; PUA = 1-anthracen- n -yl-3-phenylurea) in the presence of acetate anions (tetrabutylammonium acetate, TBAAc) gave relatively long-lived transient species with lifetimes of ∼100 μs, which were unaffected by O 2 . The lifetimes showed significant temperature dependence, which allowed us to determine Δ H ‡ and Δ S ‡ . Δ S ‡ had a large negative value, in contrast to Δ H ‡ , indicating that the dissipation process of the transient species was entropy-controlled. A linear relationship between T Δ S ‡ and Δ H ‡ suggested entropy–enthalpy compensation, which is generally found in host–guest systems with hydrogen bonding. These findings allowed us to assign the transient species as X , which is the ground state responsible for longer wavelength emissions, and conclude that the dissipation of the transient species corresponded to recovery of the complex in the ground state. We propose a reaction scheme for the photochemical process applying to urea derivatives in the presence of anions.

Liquid-assisted solid-state reaction: assembly of (6,3) and (10,3) hydrogen-bonded networks based on [M(Hbiim)3] by oxidation of [M(H2biim)3]2+ complexes in the presence of acetate anions

Two complexes [Ru(Hbiim)3] (1) and [Co(Hbiim)3]·3H2O (2) (H2biim = 2,2′-biimidazole) were synthesized quantitatively and rapidly via a “liquid-assisted” solid-state reaction approach. The reaction occurs within minutes of grinding together [Ru(H2biim)3](PF6)2 or [Co(H2biim)3]Cl2 and NH4OAc with a few drops of H2O2 as an oxidant and solvent, concomitant with colour changes. The structures of the compounds obtained from the solid-state reaction were confirmed by comparison of their PXRD patterns with simulations based on their single crystal structures. Complex 1 is a 3-fold interpenetrating three-dimensional hydrogen bonded polycatenate network based on a (6,3) net, complex 2 is a double-layer network linked by the lattice water molecules and the Hbiim ligands viahydrogen bonds. For comparison with the solid-state reaction, control reactions were also carried out in solution. Complex 1 was also afforded from the solution reaction. However, a new phase [Co(Hbiim)3]·0.5EtOH (3) was obtained from solution, rather than 2, although it also crystallized from an identical solution of EtOH–water. Complex 3 is a 4-fold interpenetrating three-dimensional hydrogen bonded polycatenate network based on a (10,3)-b net. Interesting, the [M(H2biim)3]2+ (M = Ru and Co) species can be oxidized to the corresponding [M(Hbiim)3] species by oxygen in the presence of acetate anions, which play a determined role in the redox reaction. The deprotonation of the [M(H2biim)3]2+ species triggered by the acetate anions greatly increases the electron density at the M(II) center and shifts the oxidation potentials of M(II) complex to a less positive value. This may provide an effective approach for the generation of high status metal complexes via supramolecular interactions.

Anion‐Templated Formation of Supramolecular Multinuclear Assemblies

The use of anions as supramolecular building motifs is reported herein. The interaction of various anions with [Zn(salphen)] complexes (salphen = N,N'-phenylenebis(salicylideneimine)) has been studied, with a particular focus on assembly formation in the presence of acetate anions. Strong association of the latter with the Zn metal centre of the salphen complex was quantified by UV/Vis titration studies. The [Zn(salphen)]-OAc assemblies were further characterized by NMR spectroscopy and X-ray analysis and revealed that the acetate anions can function as bridging modules between two [Zn(salphen)] units. The binding strength of a second complex to the acetate anion may be regulated by the substitution pattern of the salphen ligand. The anion-templated assembly formation was further demonstrated by the supramolecular synthesis of a trinuclear Zn(3) assembly. These results hold promise for the directed assembly formation of [Zn(salphen)] complexes with biologically relevant carboxylates, such as amino acids, and potentially new bio-sensing materials.

HDTMA in the interlayers of high-charged Llano vermiculite

AbstractX-ray diffraction shows that ordered interlayer structures form when high-charged Llano vermiculite is reacted with HDTMA-Br or HDTMA-acetate, but the structures differ from those given by low-charged vermiculites. The differences arise in two ways; firstly when both HDTMA+ cations and HDTMA-Br (or -acetate) ion pairs are present as interlayer guest species, a superstructure forms which is less commensurate with the host structure of high-charge vermiculite than it is for lower-charged material. Secondly, although a commensurate 3a × b interlayer superstructure forms when HDTMA+ cations are the only interlayer guests, an increasing number of charge-balancing cations must be accommodated as the layer charge increases. This results in some structural disorder which is only observed in the diffraction pattern of HDTMA+-intercalated, high-charge vermiculite. Organic ion pairs tend to order along widely spaced rows corresponding to the intersections of two sets of scattering planes. For the acetate form, one set of planes has spacings of 3.52 Å, but for the bromide form the value is 3.67 Å. Scattering planes in the second set have spacings of 4.02 Å, independently of counter-anion size. These two sets of planes diverge from one another by ∼10°. Ordering is more apparent in the presence of acetate anions than it is for the smaller Br− anions. In the high-charged intercalates, from which organic ion pairs have been removed, HDTMA+ cations occupy positions on a centered two-dimensional superlattice and also randomly, some interstitial positions as necessitated by layer charge.

Fluorescence quenching of etilefrine by acetate anion

Acid dissociation in the excited state of antihypotensor drug etilefrine [2-(ethylamino1-3-hydroxyphenyl)ethanol] is studied. Fluorescence of etilefrine decreases at pH<7 and is related to phenolic group dissociation. However, intensity of etilefrine fluorescence diminishes as the concentration of the acetate anion increases at pH>7. Analyses of the absorption and fluorescence spectra of aqueous solutions of etilefrine in the presence of acetate anions have been made. Considering the existence of an equilibrium in the excited state the values of 3.47×10 −9 and 0.216×10 −9 M −1 s −1 have been obtained for the rate constants for direct and inverse reactions, respectively. Moreover, the lifetime ( τ 0′=0.58×10 −9 s) and quantum yield (0.01) of non-protonated etilefrine have been determined. Our results seem to support the existence of a dynamic quenching process based on a proton transfer mechanism induced by acetate anions. This process could represent a serious inconvenience in analytical fluorimetric techniques taking into account that the acetic acid/acetate pair is commonly used as a buffer. Additional fluorescence quenching by H + ions could be involved in acid aqueous mediums. At high concentrations of acetic acid, a value of 2.98×10 −9 M −1 s −1 for the bimolecular constant for the quenching by H + has been calculated.

2-Naphthol-phosphatidylethanolamine: A fluorescent phospholipid analogue for excited-state proton transfer studies in membranes

The fluorescence properties of the phospholipid derivative,N-[1-(2-naphthol)]-phosphatidylethanolamine (NAPH-PE), have been studied by steady-state and time-resolved fluorescence techniques. The new probe is a naphthol adduct of phosphatidylethanolamine. The emission spectrum of the fluorescent phospholipid depends on the pH and on the proton acceptor concentration as expected for a typical two-state excited-state proton transfer reaction. In ethanol solutions at an apparent pH of 6.7 and in the presence of acetate anion (0.14M), a biexponential decay is obtained from global analysis of the data. The lifetimes,τ 1=3.9 ns andτ 2=6.2 ns. are constant across the spectral region 350-460 nm. The decay-associated spectra and the species-associated spectra reproduce well the profiles reported for a two-state excited-state proton transfer reaction. The fluorescent phospholipid has been incorporated into dimyristoyllecithin and dipalmitoyllecithin vesicles. Although lower proton transfer is found, the reaction appears to be dependent on the gel-to-liquid-crystalline phase transition of the lipid membrane. In addition, the steady-state anisotropy of NAPH-PE measured as a function of temperature trace the phase transition of the two vesicle systems. Thus, it is shown that the physical state of the bilayer affects a reaction which takes place at the membrane surface. In the presence of acetate ions (0.3M), global analysis, performed in terms of fluorescence decay parameters, recovers preexponential coefficients that are consistent with an excited-state proton transfer reaction. The short lifetime drops from 3.9 to 0.44 ns without significant changes of the longer-lifetime component.

Effects of copper cation and acetate anion on the growth of PbO 2 on a SnO 2/Ti substrate

The effects were examined of copper(II) cations and acetate anions on the nucleation, growth and electrochemically active surface area of lead dioxide on a SnO 2/Ti electrode. The nucleation rate of electrodeposited lead dioxide was greater in the presence of Cu(II), but smaller in the presence of acetate anions when compared with that of pure PbO 2. The growth rate of the nuclei of PbO 2 was greater for acetate-doped PbO 2 but it was smaller for Cu(II)-modified PbO 2 in comparison with pure PbO 2. The acetate-doped PbO 2 was grown in the form of hemispheres, whereas the Cu(II)-modified PbO 2 was in the form of multi-sided pyramids whose growth axes are directed towards the center of the sphere. The average size of crystal aggregates for electrodeposited lead dioxide became enlarged in the presence of Cu(II). The morphology of the PbO 2 film was smooth in appearance in the presence of acetate anions. The growth of PbO 2 on the SnO 2/Ti substrate was demonstrated not to be an instantaneous process, but is preceded by progressive nucleation with preferential island growth. PbO 2 doped with the acetate anion resulted in a significant increase of the electrochemically active surface area ( Q *); by contrast, values of Q * for lead dioxide modified with Cu(II) decreased.

Relationship of the physical and enzymic properties of Escherichia coli recA protein to its strand exchange activity

We have shown that performing the recA protein catalyzed strand exchange reaction in the presence of acetate anions, rather than chloride which is commonly used, greatly increases the rate of the reaction. The initial rate of the reaction in an acetate-based buffer is approximately 3-4 times higher in the presence of Escherichia coli single-stranded DNA binding protein (SSB protein) and 2 times higher in its absence than the initial rate in chloride. To determine the enzymatic basis for this stimulatory effect of acetate buffer, we investigated the relationship between a number of physical and enzymatic properties of recA protein and the strand exchange reaction. We have found that although the acetate anion has some effect on the aggregation properties and the single-stranded DNA-dependent ATPase activity of recA protein, these effects cannot explain the enhanced strand exchange activity in an acetate-based buffer. We do find, however, that two aspects of recA protein activity closely parallel the ability of this protein to catalyze strand exchange. The first is the ability of recA protein to displace SSB protein from single-stranded DNA, an event critical to presynaptic complex formation. RecA protein is able to resist displacement by SSB protein at a lower magnesium concentration in acetate than in chloride buffer. The magnesium ion concentration dependence of strand exchange coincides exactly with this behavior. The second activity correlated to strand exchange is the duplex DNA-dependent ATPase activity of recA protein. We find that over a wide variety of sodium chloride and sodium acetate concentrations, this duplex DNA-dependent ATPase activity is linearly related to the amount of product formed in the strand exchange reaction. We postulate that this duplex DNA-dependent ATPase activity is important in the denaturation of the duplex DNA during the branch migration step of strand exchange and have also determined that this reaction is quite efficient, with the number of ATP molecules hydrolyzed per base pair exchanged being 0.75 +/- 0.25. In addition, recA protein catalyzed strand exchange between circular single-strand and linear duplex DNA molecules is shown to be irreversible, and a possible explanation for this irreversibility is presented.

Excited-state proton transfer of equilenin and dihydroequilenin: interaction with bilayer vesicles.

The two-state excited-state proton-transfer process for d-equilenin [d-3-hydroxyestra-1,3,-5(10),6,8-pentaen-17-one] and dihydroequilenin is found to depend both on pH and on proton acceptor concentration. Both the protonated and deprotonated forms of the excited molecule are fluorescent. As is the case for 2-naphthol, the excited-state pKa (pKa*) is substantially lower than the ground-state pKa. Fluorescence decay studies have been performed as a function of emission wavelength in aqueous solutions at pH 6.9 in the presence of acetate anion (0.1 M). At this pH, both back-reaction from the excited-state and ground-state heterogeneity are minimal. A monoexponential decay is found in the blue region of the spectrum and a biexponential decay on the red edge. The lifetimes measured across both regions are constant, with a negative preexponential term, characteristic of an excited-state reaction, evident at longer wavelengths. Decay-associated spectra (DAS), the preexponential terms associated with the measured lifetimes, have been acquired for these aqueous solutions. Equilenin and dihydroequilenin are found to adsorb to dimyristoyllecithin (DML) vesicles. Rates for excited-state proton transfer are greatly reduced when dihydroequilenin adsorbs to vesicles. The accessibility of the bound probe to acetate as a proton acceptor depends on the cholesterol content of the vesicles.

2-Phenyliminomethylphenols, 2-phenylaminomethylphenols and their copper(II) complexes

Syntheses of 2-phenyliminomethylphenols (I) and 2-phenylaminomethylphenols (II) are described. Acid dissociation constants, determined potentiometrically, for the amines (II) are related to substituent constants; values are not obtained for Schiff bases(I) due to their hydrolysis. IR spectra of the amines (II) indicate chelate ring formation via OH⋯N hydrogen bonding. NMR spectra for Schiff bases (I) are consistent with the phenol-imine tautomer, not the ketone-amine tautomer. Ligands (I) form bis-complexes with copper(II) while the amines (II) form copper(II) complexes in the presence of acetate anion; magnetic measurements for these indicate no metal-metal interaction in the solid state.

The effect of acetates on the activity of cobalt bromide catalysts

With a view to assess the effect of acetates of the groups Ia and IIon the activity of cobalt bromide catalyst, oxidation of mesitylene and pseudo-cumene in a temperature range of 90 to °C has been investigated. At 100°C the acetate anions retarded the oxidation in the initial stage and increased selectivity of the oxidation of mesitylene to 3,5-dimethylbenzaldehyde, which intermediate was formed to a concentration of 42 mol%. The presence of acetates also affected distribution of isomers of aromatic dicarboxylic acids and the contents of aldehydo acids. The resultant effect of the simultaneous presence of acetate anions and nitrogen compounds on the activity of cobalt bromide catalysts depended on the nitrogen compound; with aminoacetic acid and hexamethylenediamine the oxidation rate and yields of aromatic acids were markedly increased. As conductance measurements indicated, the presence of acetates enhanced the formation of ionic forms of the complexes.

ChemInform Abstract: EFFECTS OF CYCLIZATION AND RING SIZE ON COMPLEX FORMATION BETWEEN PENTA‐AMINE LIGANDS AND COPPER(II)

AbstractGleichgewichte und Kinetik der Komplexbildung zwischen den Makrocyclen (I) und Cu(II) wurden untersucht.

Effects of cyclization and ring size on complex formation between penta-amine ligands and copper(II)

Equilibria and kinetics of complex formation between CuII and the macrocyclic penta-amines 1,4,7,10,13-penta-azacyclopentadecane (L1), 1,4,7,10,13-penta-azacyclohexadecane (L2), and 1,4,7,11,14-penta-azacycloheptadecane (L3) have been investigated. Thermodynamic functions for formation of the 1 : 1 complex have been determined polarographically: for L1, L2, and L3, respectively, log KCuL 28.3, 27.1, and 23.8, –ΔH 32.9, 32.7, and 27.2 kcal mol–1, and ΔS 22, 14, and 18 cal K–1 mol–1(at / 0.2 mol dm–3 and 25 °C). The large stability enhancements caused by the cyclization of penta-amines are due to a favourable enthalpy factor, in contrast to the entropy-favoured macrocyclic effects of tetra-amines. Kinetic studies have established the rate laws for the complex formation in acetate buffer as d[CuL]/dt=k2H[Cu(O2CMe)+][H2L2+]+k3H[Cu(O2CMe)+][H3L3+], and in unbuffered acid solution as d[CuL]/dt =k2H′[Cu2+][H2L2+]+k3H′[Cu2+][H3L3+]. (The macrocyclic complexes formed are a mixture of [CuL]2+ and [Cu(HL)]3+ depending on the acidity.) The rate constant k2H′ for the diprotonated ligand species increases from 105 to 107 dm3 mol–1 s–1 as the macrocyclic ring opens, approaching the value found for 3,6,9-triazaundecane- 1, 11 -diamine (L4). The rate constant k3H′ for the triprotonated species increases similarly from zero to 102 dm3 mol–1 s–1, although falling below the corresponding value for L4. The presence of acetate anions as a buffer significantly accelerates the reactions involving proton-congested species. The implications for substitution reactions of protonated macrocyclic ligands are discussed.