Copper complexes for fluorescence-based NO detection in aqueous solution

Two copper(II) complexes containing dansylated ligands were investigated as turn-on fluorescence-based nitric oxide (NO) sensors. Upon addition of NO (g), the quenched fluorescence of both complexes was restored in both organic and buffered aqueous solutions, which is caused by the formation of a diamagnetic Cu(I) species and protonation of the sulfonamide functionality of the ligands. The NO detection limit of these Cu(II) complexes is 10 nM.     

Pyrenoviologen-based fluorescent sensor for detection of picric acid in aqueous solution

Two highly emissive pyrenoviologen derivatives were synthesized and used to fabricate fluorescent sensors for detection of picric acid(PA) with good sensitivity and selectivity.The sensitivity of the sensor was attributed to the specific electrostatic association effect of the cationic pyrenoviologens to the picrate anions,which also gave the sensor special selectivity among other compounds with similar structure.The electron transfer between them was attributed to the fluorescence response.Fluorescence lifetime measurements revealed that the quenching is static in nature.The novel and efficient pyrenoviologen derivatives-based sensors offered a strategy to fabricate real-life PA sensor.     

Pyrenoviologen-based fluorescent sensor for detection of picric acid in aqueous solution

Two highly emissive pyrenoviologen derivatives were synthesized and used to fabricate fluorescent sensors for detection of picric acid (PA) with good sensitivity and selectivity.     

Mechanism for basic hydrolysis of N-nitrosoguanidines in aqueous solution

A kinetic study was carried out on the hydrolysis of two N-nitrosoguanidines, 1-nitroso-1-methyl-3-tolylsulfonylguanidine (TSGNO) and 1-nitroso-1-methyl-3-benzoylguanidine (BCGNO). We observed an absence of buffer catalysis using H(2)PO(4)(-)/HPO(4)(2)(-), H(3)BO(3)/H(2)BO(3)(-), and HCO(3)(-)/CO(3)(2)(-) regulators and a complex dependency of the rate constant on the pH. We discovered the existence of three simultaneous reaction paths: spontaneous decomposition of the neutral form of the N-nitrosoguanidine, decomposition of the monoanion, and decomposition through the form of the dianion. The analysis of the kinetic data has allowed us to obtain the acidity constant for the formation of the monoanion of the N-nitrosoguanidine, with values of p = 11.5. The reaction rate for the process through the monoanion, k(2), decreases as the acidity increases. The application of the principle of nonperfect synchronization shows that the basicity and reactivity do not correlate when there exists a possibility of stabilization of the negative charge by resonance. This behavior is consistent with the mechanism E1cB whereby the stabler the negative charge, the slower the elimination reaction. When dealing with the case of the elimination through the neutral form we observe that the reaction rate increases together with the capacity of stabilization of the positive charge on the nitrogen atom adjacent to the imino group. For the reaction through the dianion we used a maximum value of k(3) = 10(10) s(-)(1) to estimate the value of p for the formation of the dianion of the N-nitrosoguanidine, obtaining values of p < 24.     

A new ratiometric ESIPT sensor for detection of palladium species in aqueous solution

An aqueous ratiometric ESIPT sensor with a 87 nM (15.4 ppb) detection limit was successfully synthesized and applied for detection of all oxidation states of palladium species.     

A fluorescence turn-on probe for the detection of thiol-containing amino acids in aqueous solution and bioimaging in cells

A turn-on fluorescent probe, based on a water-soluble terphenyl derivative, for the detection of cysteine and homocysteine is reported. The aldehyde groups in the probe play crucial roles in providing reaction with thiol groups in the amino acids, leading to a formation of thiazolidine (from cysteine) or thiazinane ring (from homocysteine). As a result, the new formation of such rings alters the electronic property of the conjugated system in the probe and results in emission enhancement. The probe in aqueous solution exhibits a remarkable increase in its quantum yield upon exposure to cysteine (up to 20-fold) and to homocysteine (up to 700-fold), while slight quenching is observed in the presence of glutathione. Moreover, an investigation on time-resolved fluorescence spectra of the probe in the presence of cysteine and homocysteine reveals potential discriminatory detection of cysteine and homocysteine. Bioimaging of the thiols in live HeLa cells was successfully applied.     

Silicate complexes of sugars in aqueous solution

Certain sugars react readily with basic silicic acid to form soluble 2/1 (sugar/silicic acid) silicate complexes. Failure of monohydroxy compounds to give soluble products under these conditions indicates that the sugar silicates are chelates: five-membered diolato rings. Only furanose forms react. Pyranose sugars are stable under these conditions. Because all glycosides fail to react with silicic acid under these conditions, reaction appears to involve the anomeric position (C1 in aldoses, C2 in ketoses), which has a more acidic hydroxy group. Reaction is completed only when the anomeric hydroxy group is cis to an adjacent hydroxy group. The appropriate furanose form must have sufficient natural abundance and solubility to provide an observable product, as measured by (29)Si and (13)C NMR spectroscopy. These structural and practical constraints rationalize the successful reaction of the monosaccharides ribose, xylose, lyxose, talose, psicose, fructose, sorbose, and tagatose and the disaccharides lactulose, maltulose, and palatinose. Glucose, mannose, galactose, and sucrose, among others, failed to form complexes. This high selectivity for formation of sugar silicates may have ramifications in prebiotic chemistry.     

A novel fluorescent sensor for hydrophobic amines in aqueous solution

A novel fluorescent tweezer was designed and synthesised to sense hydrophobic amines in aqueous solution. Association of the guest was driven by both hydrophobic effect and electrostatic interactions, with the hydrophobic interactions being dominant. The affinity and selectivity of the sensor for amine-based stimulants are reported.     

Squarete complexes of uranyl ions in aqueous solution

The stability constants of UO ₂ ²⁺ -squarate complexes are measured at ionic strengths of 0.05M, 0.06M, 0.075M, 0.09M, 0.1M (squaric acid-perchloric acid) using a solvent extraction method at a pH of 1.1 and a temperature of 25 °C. The extractant used is dinonylnaphthalenesulfonic acid in n-heptane. The aqueous phase was made of a mixture of squaric and perchloric acid and²³³U radio tracer. The stability constants of squarate complexes of UO ₂ ²⁺ is seen to decrease linearly with the square root of the ionic strength.     

Chromogenic and fluorescent chemodosimeter for detection of fluoride in aqueous solution

We have developed a chromogenic and fluorescent chemodosimeter 1 based on the release of resorufin for F- (TBA+ and Na+ salts). This dosimeter 1 displayed drastic dual changes in UV-vis absorption and fluorescence emission intensities selectively for F- over other anions in CH3CN/H2O (50:50, v/v) as well as in acetonitrile.     

High-temperature degradation of polyacrylic acid in aqueous solution

Poly(acrylic acid) (PAA) was decarboxylated in aqueous solution as a function of pH and ionic strength in the temperature range 100–350°C. Degradation kinetics were first order with respect to acid functionality. The rate of decarboxylation at high pH (E_α = 51.1 kcal/mol) was much slower than that at low pH (E_α = 20.3 kcal/mol). At intermediate pH, the reactivity was found to depend on the degree of dissociation of PAA as a functions of ionic strength, pH, and temperature. No monomer was observed in the reaction product. © 1996 John Wiley & Sons, Inc.     

Sol-gel-based optical sensor for the detection of aqueous amines

We present an optical sensor for the detection of aqueous amines obtained by incorporating chromoionophore XV (ETH^T 4001) into sol-gel thin films. Acid- and base-catalyzed sol-gel processes were studied to prepare stable ormosil layers using various amounts of organically modified sol-gel precursor such as methyltriethoxysilane (MTriEOS). The sensor layers were coated with a protective layer of microporous white polytetrafluoroethylene (PTFE) in order to prevent interference from ions and ambient light. The measurements were carried out in a flow-through cell in the reflection mode. Acid-catalyzed ormosil layers (pH 1) based on the copolymerization of tetraethoxysilane (TEOS) and MTriEOS did not show any change in signal upon exposure to aqueous amine solutions, while base-catalyzed sensor layers (pH 3 and 13) showed significant changes in signal. The response time (t ₁₀₀) for the base-catalyzed sensor layer L3 (pH 13) upon exposure to different solutions containing 0–608 mmol L⁻¹ aqueous propylamine was 20–30 s, the regeneration time was 70 s and the detection limit was 0.1 mmol L⁻¹. The sensor response was reproducible and reversible. The porous ormosil layers permit dry sensor storage conditions.     

Formation and stability of proton-amine-inorganic anion complexes in aqueous solution

Interaction of some amines with inorganic ligands was studied potentiometrically in aqueous solutions at 25°C at different ionic strengths. The systems taken into account were: meta-PP, meta-TPP, en-PP, en-TPP, en-HPO ₄ ^2– , dap-SO ₄ ^2– , tetren-HPO ₄ ^2– , 6da-PP and 8da-TPP (meta=methylamine, en=ethylenediamine, tetren=tetraethylenepentamine, dap=1,2-diaminopropane, 6da=1,6-hexanediamine, 8da=1,8-octanediamine, PP=pyrophosphate, TPP=tripolyphosphate). Several ALH_r species are formed for all the studied mixed systems (A=amine, L =inorganic ligand), and in some cases A_pL_qH_r species were also found. The stability of mixed proton-ligand-ligand species is proportional to the charges involved in the complexation reaction and, to some extent, it depends on steric characteristic of the ligands. A simple relationship has been found between formation constants of mixed ligand species and charges involved in the complexation reaction. The ionic strength dependence of formation constants has been taken into account, and it was found that, also for these types of mixed complexes, a general equation independent of the nature of the reactants can be used.     

Kinetics of hydrolysis of xylometazoline (XYL) in aqueous solution

The effect of pH (over the range of 2.10 - 11.90) and temperature (from 353 K to 363 K) on the stability of xylometazoline (XYL) has been studied by high performance liquid chromatography (HPLC). Using the dependence of log k vs pH, the hydrolysis of both the undissociated and dissociated XYL-molcules has been described by micro rate constants k₁ and k₂. Thermodynamic parameters (activation energy, enthalpy and entropy) of the composition reaction were calculated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Computational study on hydrolysis of cefotaxime in gas phase and in aqueous solution

We are presenting a theoretical study of the hydrolysis of a β‐lactam antibiotic in gas phase and in aqueous solution by means of hybrid quantum mechanics/molecular mechanics potentials. After exploring the potential energy surfaces at semiempirical and density functional theory (DFT) level, potentials of mean force have been computed for the reaction in solution with hybrid PM3/TIP3P calculations and corrections with the B3LYP and M06‐2X functionals. Inclusion of the full molecule of the antibiotic, Cefotaxime, in the gas phase molecular model has been demonstrated to be crucial since its carboxylate group can activate a nucleophilic water molecule. Moreover, the flexibility of the substrate implies the existence of a huge number of possible conformers, some of them implying formation of intramolecular hydrogen bond interaction that can determine the energetics of the conformers defining the different states along the reaction profile. The results show PM3 provides results that are in qualitative agreement with DFT calculations. The free energy profiles show a step‐wise mechanism that is kinetically determined by the nucleophilic attack of a water molecule activated by the proton transfer to the carboxylate group of the substrate (the first step). However, since the main role of the β‐lactamase would be reducing the free energy barrier of the first step, and keeping in mind the barrier obtained from second intermediate to products, population of this second intermediate could be significant and consequently experimentally detected in β‐lactamases, as shown in the literature. © 2012 Wiley Periodicals, Inc.     

Noncovalent synthesis in aqueous solution and spectroscopic characterization of multi-porphyrin complexes

The interactions of the tetracationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (H(2)TMPyP) and its metallo derivatives (MTMPyP) (where M=copper(II), zinc(II), and gold(III) with the octa-anionic form (at neutral pH) of 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)calix[4]arene (C(4)TsTc) lead to a series of complex species whose stoichiometry and porphyrin sequence can be easily tuned. Crystallographic, spectroscopic, and diffusion NMR studies converge towards a common picture in which a central 1:4 porphyrin/calixarene unit serves as a template for the formation of more complex species. These species arise by successive, stepwise addition of single porphyrin molecules above and below the plane of the 1:4 central core to ultimately give a 7:4 complex. Noticeably, the stoichiometry of the various complex species corresponds to the actual concentration ratio of porphyrins and calixarenes in solution allowing the stoichiometry of these species to be easily tuned. This behavior and the remarkable stability of these species allow homo-porphyrin and hetero-(metallo)porphyrin species to be formed with control of not only the stoichiometry but also the sequence of the porphyrin array. The flexibility and ease of this approach permit, in principle, the design and synthesis of porphyrin arrays for predetermined purposes. For example, we have shown that it is very easy to design and obtain mixed porphyrin species in which a foreseen photoinduced electron-transfer is indeed observed.     

Redox energetics and kinetics of uranyl coordination complexes in aqueous solution

Detailed voltammetric results for five uranyl coordination complexes are presented and analyzed using digital simulations of the voltammetric data to extract thermodynamic (E(1/2)) and heterogeneous electron-transfer kinetic (k(0) and alpha) parameters for the one-electron reduction of UO(2)(2+) to UO(2)(+). The complexes and their corresponding electrochemical parameters are the following: [UO(2)(OH(2))(5)](2+) (E(1/2) = -0.169 V vs Ag/AgCl, k(0) = 9.0 x 10(-3) cm/s, and alpha = 0.50); [UO(2)(OH)(5)](3-) (-0.927 V, 2.8 x 10(-3) cm/s, 0.46); [UO(2)(C(2)H(3)O(2))(3)](-) (-0.396 V, approximately 0.1 cm/s, approximately 0.5); [UO(2)(CO(3))(3)](4-) (-0.820 V, 2.6 x 10(-5) cm/s, 0.41); [UO(2)Cl(4)](2-) (-0.065 V, 9.2 x 10(-3) cm/s, 0.30). Differences in the E(1/2) values are attributable principally to differences in the basicity of the equatorial ligands. Differences in rate constants are considered within the context of Marcus theory of electron transfer, but no specific structural change(s) in the complexes between the two oxidation states can be uniquely identified with the underlying variability in the heterogeneous rate constants and electron-transfer coefficients.     

Mixed proton complexes of aminoacids and carboxylic ligands in aqueous solution

Formation and stability of proton-mixed ligand complexes have been studied for the systems H(+)-lysine-aspartic acid, H(+)-lysine-succinic acid and H(+)-glycine malonic acid, in aqueous solution at 25 degrees , by potentiometric technique using the (H(+))-glass electrode. For all these systems it has been found that the species ABH(j) (A and B, first and second ligand, respectively; j = 1, 2, ... m + n - 1; m and n are the maximum protonation degrees of the two ligands, respectively) are formed. The stability of these species is discussed with respect to various factors and, in particular, as a function of speciation problems.     

Ion chromatographic determination of hydrolysis products of hexafluorophosphate salts in aqueous solution

In this work, hydrolysis of three different hexafluorophosphate salts in purified water was investigated. Aqueous samples of lithium hexafluorophosphate (LiPF₆), sodium hexafluorophosphate (NaPF₆) and potassium hexafluorophosphate (KPF₆) were prepared and stored for different times. Ion chromatography (IC) with UV as well as non-suppressed and suppressed conductivity detection was used for the analysis of the reaction products. For the detection and identification of the formed decomposition products, an IC method using IonPac AS14A 250 mm × 4.0 mm i.d. column and 2.5 mM KHCO₃–2.5 mM K₂CO₃ eluent was established. Besides hexafluorophosphate, four other anionic species were detected in fresh and matured aqueous solutions. The hydrolysis products fluoride (F⁻), monofluorophosphate (HPO₃F⁻), phosphate (HPO₄²⁻) and difluorophosphate (PO₂F₂⁻) were found and were unambiguously identified by means of standards or electrospray ionization mass spectrometry (ESI-MS). It was shown that stability of hexafluorophosphate solutions depends on the nature of the counter ion and decreases in the order potassium > sodium > lithium.