Squaraines as reporter units: insights into their photophysics, protonation, and metal-ion coordination behaviour

The synthesis, photophysical properties, protonation, and metal-ion coordination features of a family of nine aniline-based symmetrical squaraine derivatives are reported. The squaraine scaffold displays very attractive photophysical properties for a signalling unit. These dyes show absorption and weakly Stokes-shifted, mirror-image-shaped emission bands in the visible spectral range and there are no hints of multiple emission bands. The mono-exponential fluorescence decay kinetics observed for all the derivatives indicate that only one excited state is involved in the emission. These data stress the interpretation that squaraines can be regarded as polymethine-type dyes. From a coordination chemistry point of view, the squaraines possess four potential binding sites; that is, two nitrogen atoms from the anilino groups and two oxygen atoms from the central C(4)O(2) four-membered ring. These coordination sites are part of a cross-conjugated pi-system and coordination events with protons or certain metal ions affect the electronic properties of the delocalised pi-system dramatically, resulting in a rich modulation of the colour of the squaraines. The absorption band at around 640 nm is blue-shifted when coordination at the anilino nitrogen atoms occurs, whereas coordination to the C(2)O(4) oxygen atoms results in the development of red-shifted bands. Addition of more than one equivalent of protons or metal cations could additionally entail mixed N,O- or N,N-coordinated complexes, manifested in the development of a broad band at 480 nm or complete bleaching in the visible range, respectively. Analysis of the spectrophotometric titration data with HYPERQUAD yielded the macroscopic and microscopic stability constants of the complexes. Theoretical modelling of the various protonated species by molecular mechanics methods and consideration of some of the title dyes within the framework of molecular chemosensing and molecular-scale "logic gates" complement this contribution.     

A mesoporous 3D hybrid material with dual functionality for Hg2+ detection and adsorption

Dual-function hybrid material U1 was designed for simultaneous chromofluorogenic detection and removal of Hg(2+) in an aqueous environment. Mesoporous material UVM-7 (MCM41 type) with homogeneously distributed pores of about 2-3 nm in size, a large specific surface area exceeding 1000 m(2) g(-1), and nanoscale particles was used as an inorganic support. The mesoporous solid is decorated with thiol groups that were treated with squaraine dye III to give a 2,4-bis(4-dialkylaminophenyl)-3-hydroxy-4-alkylsulfanylcyclobut-2-enone (APC) derivative that is covalently anchored to the inorganic silica matrix. The solid was characterised by various techniques including X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and nitrogen adsorption. This hybrid solid is the chemodosimeter for Hg(2+) detection. Hg(2+) reacts with the APC fragment in U1 with release of the squaraine dye into the solution, which turns deep blue and fluoresces strongly. Naked-eye Hg(2+) detection is thus accomplished in an easy-to-use procedure. In contrast, U1 remains silent in the presence of other thiophilic transition metal ions, alkali and alkaline earth metal ions, or anions ubiquitously present in water such as chloride, carbonate, sulfate, and phosphate. Material U1 acts not only as chemodosimeter that signals the presence of Hg(2+) down to parts-per-billion concentrations, but at the same time is also an excellent adsorbent for the removal of mercury cations from aqueous solutions. The amount of adsorbed mercury ranges from 0.7 to 1.7 mmol g(-1), depending on the degree of functionalisation. In addition, hybrid material U1 can be regenerated for both sensing and removal purposes. As far as we know, U1 is the first example of a promising new class of polyfunctional hybrid supports that can be used as both remediation and alarm systems by selective signalling and removal of target species of environmental importance. Model compounds based on silica gel (G1), fumed silica (F1), and micrometre-sized MCM-41 scaffolds (M1) were also prepared and studied for comparative purposes.     

Correlation of global electrophilicity with the activation energy in single-step concerted reactions

The experimental energy of activation (Ea) of the single-step concerted oxidation process of aliphatic primary alcohols by quinolinium bromochromate (QBC) are correlated with the theoretically evaluated global electrophilicity values (w) [as proposed by Parr et al. (J. Am. Chem. Soc. 1999, 121, 1922)]. Conceptual justification in favor of correlating w of the substrate with Ea involved in a single-step concerted reaction is also discussed. The evaluated w values at HF/cc-pVTZ and MP2/6-31G(d,p) methods are found to be as expected (when we consider structural aspects), although there are some inconsistencies in other methods [e.g., HF/6-31G(d,p), B3LYP/cc-pVTZ, BLYP/dnp, PW91/dnp, PWC/dnp, VWN/dnp]. The reasons for the inconsistencies, even with a superior B3LYP/cc-pVTZ method, are discussed thoroughly. It is observed that the higher the value of w, the more the value of Ea involved in the process of oxidation of primary alcohols by QBC. The present study also reveals that the apparent success of insignificant (i.e., much smaller) local electrophilicity values (S+O(OH)), evaluated using Hirshfeld population analysis (HPA), in explaining observed trend of experimental Ea values turns out to be ambiguous when more significant (i.e., much larger) local nucleophilicity values (S-O(OH)) are also compared. This is evident from the corresponding correlation coefficient values.     

Two-dimensional H2O-Cl2 and H2O-Br2 potential surfaces: an ab initio study of ground and valence excited electronic states

All electron ab initio calculations for the interaction of H2O with Cl2 and Br2 are reported for the ground state and the lowest triplet and singlet Pi excited states as a function of both the X-X and O-X bond lengths (X = Cl or Br). For the ground state and lowest triplet state, the calculations are performed with the coupled cluster singles, doubles, and perturbative triple excitation level of correlation using an augmented triple-zeta basis set. For the 1Pi state the multireference average quadratic coupled cluster technique was employed. For several points on the potential, the calculations were repeated with the augmented quadruple-zeta basis set. The ground-state well depths were found to be 917 and 1,183 cm-1 for Cl2 and Br2, respectively, with the triple-zeta basis set, and they increased to 982 and 1,273 cm-1 for the quadruple-zeta basis set. At the geometry of the ground-state minimum, the lowest energy state corresponding to the unperturbed 1Pi states of the halogens increases in energy by 637 and 733 cm-1, respectively, relative to the ground-state dissociation limit of the H2O-X2 complex. Adding the attractive ground-state interaction energy to that of the repulsive excited state predicts a blue-shift, relative to that of the free halogen molecules, of approximately 1,600 cm-1 for H2O-Cl2 and approximately 2,000 cm-1 for H2O-Br2. These vertical blue-shifts for the dimers are greater than the shift of the band maximum upon solvation of either halogen in liquid water.     

Hybrid materials with nanoscopic anion-binding pockets for the colorimetric sensing of phosphate in water using displacement assays

Mesoporous amino-functionalised solids containing certain dyes have been used as suitable anion hosts in displacement assays for the colorimetric signalling of phosphate in water.     

EPR and optical study of Mn2+ doped ammonium tartrate single crystals

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.     

Thermal study of polypyrrole complexes with vermiculites of different layer charge

We have studied the synthesis of polypyrrole-clay nanocomposites by the in situ oxidative polymerization of pyrrole in the interlayer space of vermiculites with different layer charges from Santa Olalla and Ojén, Spain. Moreover, the influence of different interlayer cations (Na⁺, Mg²⁺, Fe³⁺) on the interaction between pyrrole and the vermiculties was studied. The resulting materials were characterized by means of DTA-TG, XRD, FTIR and Mössbauer spectroscopy. In all samples polymerization of pyrrole was observed, presumably triggered by the structural iron. In most cases it was found to be externally deposited. An uptake of pyrrole in the interlayer space and PPy formation is observed in the case of the Fe³⁺-intercalated Ojén vermiculite, which has a lower layer charge than the Santa Olalla vermiculite.     

Preparation of antibodies and development of a sensitive immunoassay with fluorescence detection for triazine herbicides

Specific polyclonal antibodies against s-triazine herbicides were obtained by preparing immunogens coupling home-synthesized haptens derivatives of simazine (6-chloro-N-ethyl-N′-ethyl-1,3,5-triazine-2,4-diamine) to lysine groups of hemocyanin from keyhole limpets and bovine serum albumin carrier proteins. Three highly sensitive rabbit antisera were obtained and evaluated with a battery of six enzyme tracers derived from triazine structures in an optimized ELISA format. The antiserum As8 and the HRP-2f tracer, which yield the best assay sensitivity for simazine (detection limit 0.11 ± 0.02 μg L⁻¹, IC₅₀ 0.88 ± 0.04 μg L⁻¹), were applied to the development of a sensitive flow-through immunoassay for the analysis of this herbicide. The automated assay was based on a direct competitive immunosorbent assay and fluorescence detection. The optimized method presents an IC₅₀ value of 0.35 ± 0.04 μg L⁻¹ with a detection limit of 1.3 ± 0.9 ng L⁻¹ and a dynamic range from 0.010 to 7.5 μg L⁻¹ simazine. The generic nature of the antiserum was shown by good relative cross-reactivities with other triazines such as atrazine (420%) or propazine (130%) and a lower response to terbutylazine (6.4%) and desethyl-atrazine (2.2%). No cross-reactivity was obtained for nonrelated pesticides such as 2,4-dichlorophenoxyacetic acid or linuron and the assay could be applied as a screening method for triazine herbicides. The total analysis time was 30 min per determination and the immunosensor could be reused for more than 150 cycles without significant loss of activity. The immunosensor has been successfully applied to the direct analysis of simazine in surface water samples at the nanogram per liter level. The results obtained by comparative analysis of the immunosensor with a chromatographic procedure for triazines showed a close correspondence.     

Desvenlafaxine succinate monohydrate

The title compound {systematic name: [2‐(1‐hydroxycyclohexyl)‐2‐(4‐hydroxyphenyl)ethyl]dimethylammonium 3‐carboxypropanoate monohydrate}, C₁₆H₂₆NO₂⁺·C₄H₅O₄⁻·H₂O, is a succinate salt of O‐desmethylvenlafaxine (desvenlafaxine). The present structure is one of four reported polymorphs of this salt, which is a new antidepressant drug. The carboxyl group of the succinate anion adopts a rare anti conformation and is engaged in a very short O—H...O⁻ hydrogen‐bond contact. Both cations and anions are involved separately in the formation of distinct O—H...O hydrogen‐bonded networks. Desvenlafaxine cations and water molecules self‐assemble to generate a honeycomb layer, while the succinate anions form a linear tape structure. These hydrogen‐bonded networks are interlinked via N—H...O and O—H...O hydrogen bonds. The hydrogen‐bonding network is so strong that desolvation and melting occur together at approximately 402 K. Thus, the crystal structure may be used to understand the thermal stability and solubility of the compound at the molecular level.     

Shape of the Ground State Energy Density of Hill’s Equation with Nice Gaussian Potential

Consider Hill’s operator in which the potential q(x) is an almost surely continuous and rotation invariant Gaussian process on the circle x∈[0,1). Viewing the classical Riccati map as a change of measure, we establish functional integral formulas for the probability density function of the ground state energy and also determine the density’s shape.