Metallomicellar Catalysis: Hydrolysis of Phosphodiester with Cu(II) and Zn(II) Complexes in Micellar Solution

Abstract

The effects of two metal complexes of 2,2′‐dipyridylamine (bpya) ligand, [(bpya)Cu]Cl₂ and [(bpya)Zn]Cl₂, in promoting the hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) have been kinetically investigated in Brij35 micellar solution and at 298 K, pH ranging from 6.41 to 8.6. In neutral micellar solution at 298 K, pH 7.02, the rate constants for the catalytic hydrolysis of BNPP by [(bpya)Cu]Cl₂ and [(bpya)Zn]Cl₂ are 1.2 × 10⁶ times and 1.5 × 10⁵ times higher than those for the spontaneous hydrolysis, respectively. Kinetic studies show that the active species in the catalytic hydrolysis of BNPP is the aquo‐hydroxy form, and the relative kinetic and thermodynamic parameters indicate that the mechanism of the reaction involves intramolecular nucleophilic attack on the metal center‐bound diester.     

Adsorption of Hg(II) Ions onto Binary Biopolymeric Beads of Carboxymethyl Cellulose and Alginate

The removal of Hg(II) ions from aqueous solution by adsorption onto cross-linked polymeric beads of carboxymethyl cellulose (CMC) and sodium alginate was studied at fixed pH (6) and room temperature 28 ± 0.2°C. The cross-linked polymeric beads were characterized by FTIR spectra. Sorption capacity of the polymer for the mercury ions was investigated in aqueous media consisting different amounts of mercury ions (2.5 to 100 mg dm^?3) and at different pH values (2 to 8). Adsorption behavior of Hg(II) ions could be modeled using both the Langmuir and Freundlich isotherms. The dynamic nature of adsorption was quantified in terms of several kinetic constants such as rate constants for adsorption (k₁) and Lagergreen rate constant (K_ad). The influence of various experimental parameters such as effect of pH, contact time, solid-to-liquid ratio, salt effect, and temperature effect etc. were investigated on the adsorption of Hg(II) ions.     

Removal of Rhodamine-B from Aqueous Solution by Adsorption onto Crosslinked Alginate Beads

The biosorption of rhodamine-B from aqueous solution using crosslinked alginate beads was studied by contact method at fixed pH ?3 and room temperature (28 ± 0.2°C). Both the Freundlich and Langmuir isotherm models could describe the adsorption equilibrium of the rhodamine-B onto crosslinked alginate beads. The influence of various experimental parameters such as pH, temperature, effect of concentration and time were evaluated. It was observed that the adsorption capacity of rhodamine-B onto alginate beads decreased with increase in pH and temperature above room temperature.     

Adsorption Mechanism of Comb Polymer Dispersants at the Cement/Water Interface

Comb polymers are commonly used as dispersants to stabilize highly concentrated cement suspensions. The effectiveness of such polymeric additives to stabilize these suspensions is determined to a large extent by the amount adsorbed. In this study we investigated the adsorption characteristics of various comb dispersant containing different graft densities on surfaces of cement particle. The effect of inorganic salts on their adsorption was also examined in order to elucidate their adsorption mechanism. The results show that the adsorption of comb polymer dispersants on cement surface conforms approximately to Langmuir's adsorption isotherm and the characteristic plateau A _s and adsorption free energy ΔG_ads are largely dependent on the anionic group content of the comb polymers. The A _s and ΔG_ads increase with increasing anionic group content. This information suggests that the adsorption of comb polymers on cement surfaces is dominated by electrostatic interaction between COO-groups on the comb polymers and the positive surface of the cement. This conclusion is supported by effects of inorganics such as calcium and sulfate ions, and diffuse reflectance FTIR spectroscopy. The implication of results for tuning polymers for the required performance in cement manufacture should be noted.     

One-dimensional Vanadyl Phosphate Containing the Tancoite-like {vIvO（HPO4）2}2- Chain

A vanadyl phosphate containing a new member of tancoite-like single chain, （DAPH2）[VIVO（HPO4）2]·xH20 （x ≈ 0.2, DAP = 1,3-diaminopropane, C3H10N2）, has been synthesized under hydro（solvo）thermal conditions. It crystallizes in orthorhombic space group P21212 （No. 18） with a = 7.1730（14）, b = 19.252（4）, c = 8.6557（17） A, Z= 4, V= 1195.3（4）A3, C3H14.38N2P2VO9.19, Mr = 338.47, Dc = 1.881 g/cm3,μ（MoKa） = 1.138 mm-1 and F（000） = 692. The final full-matrix least-squares refinement converged to R = 0.0408, wR = 0.1046 for 2498 observed reflections with I 〉 2σ（I） and R = 0.0456 and wR = 0.1080 for all data （2750） and S = 1.001. Its one-dimensional 1 structure consists of tancoite-like ∞1 {vIVO（HPO4）2}2- single chains surrounded by DAPH22＋ ions and water molecules. The single chain is built from trans-corner-sharing octahedral {VIV= O…VIV} backbone loop-branched by HPO4 groups like staple forming a new member of tancoite single chain. Due to the special coordination of VIVO6, the ∞1 {VO（HPO4）2-} chain adopts a larger M-O-M angle （V-O-V = 135°） than those of tancoite chains reported before. The corner-sharing linear {VIV = O…VIV} chain structure also leads to a one-dimensional weak antiferromagnetic interaction at low temperature. The magnetic measurements confirm the 4＋ valence state of vanadium. IR and TG results of the title compound are also discussed.     

Determination of phosphate in freshwater samples by flow-injection with lucigenin chemiluminescence

Lucigenin chemiluminescence (CL) in conjunction with flow-injection analysis (FIA) is used for the determination of phosphate in freshwater samples. The procedure is based on the formation of molybdophosphoric heteropoly acid (MoP–HPA) by the reaction of phosphate and ammonium molybdate under acidic conditions. CL emission was observed as a result of oxidation of lucigenin in aqueous sodium hydroxide solution in the presence of MoP–HPA. Calibration was linear up to 500?µg?L^?1 (r ^2?=?0.9998; n?=?8), with a detection limit (S/N?=?3) of 0.95?µg?L^?1. An injection throughput of 120 h^?1, and relative standard deviation (RSD; n?=?4) of 1.3–3.2% were achieved in the concentration range studied. An on-line chelating column was used to remove interfering cations. The method was applied to freshwater samples, and the results (51?±?1.0 – 107?±?2.0?µg?L^?1) did not differ significantly from results obtained using a spectrophotometric method (52.5?±?1.0 – 102?±?2.0?µg?L^?1) at 95% confidence level (t-test).     

Infrared and Raman spectra of magnesium ammonium phosphate hexahydrate (struvite) and its isomorphous analogues. IX: Spectra of protiated and partially deuterated cubic magnesium caesium phosphate hexahydrate

Infrared and Raman spectra of cubic magnesium caesium phosphate hexahydrate, MgCsPO₄·6H₂O (cF100), and its partially deuterated analogues were analyzed and compared to the previously studied spectra of the hexagonal analogue, MgCsPO₄·6H₂O (hP50). The vibrational spectra of the cubic and hexagonal dimorphic analogues are similar, especially in the regions of HOH stretching and bending vibrations. In the difference IR spectrum of the slightly deuterated analogue (<5% D), one distinctive band appears at 2260 cm⁻¹ with a small shoulder at around 2170 cm⁻¹, but only one band is expected in the region of the OD stretchings of isotopically isolated HDO molecules. The small weak band could possibly result from second-order transitions (a combination of HDO bending and some libration of the same species) rather than statistical disorder of the water molecules. By comparing the IR spectra in the region of external vibrations of water molecules of the protiated compound recorded at RT (room temperature) and at LNT (liquid nitrogen temperature) and those in the series of the partially deuterated analogues, it can be stated with certainty that the bands at 924 and 817 cm⁻¹ result from librations of water molecules, rocking and wagging respectively. And the band at 429 cm⁻¹ can be safely attributed to a stretching Mg–O_w mode. In the ν₃(PO₄) and ν₄(PO₄) region in the infrared spectra, one band in each is observed, at 995 and 559 cm⁻¹, respectively. In the region of the ν₁ modes, in the Raman spectrum of the protiated compound, one very intense band was observed at 930 cm⁻¹ which is only insignificantly shifted to 929 cm⁻¹ in the spectrum of the perdeuterated compound. The band at 379 cm⁻¹ in the Raman spectrum could be assigned to the ν₂(PO₄) modes. With respect to the phosphate ion vibrations, the comparison between the two polymorphic forms of MgCsPO₄·6H₂O and their deuterated compounds shows that ν₁(PO₄) and ν₃(PO₄) appear at lower wavenumbers in the cubic phase than in the hexagonal phase. These data are in full agreement with the lower repulsion potential at the cubic lattice sites compared with that for the hexagonal lattice sites.     

Synthesis of C‐Glycosyl Phosphate and Phosphonate,Analogues of N‐Acetyl‐α‐d‐Glucosamine 1‐Phosphate

Synthesis of α‐C‐ethylene phosphate and phosphonate as well as α‐C‐methylene phosphate analogues of N‐acetyl‐α‐d‐glucosamine 1‐phosphate is reported starting from the common perbenzylated 2‐acetamido‐2‐deoxy‐α‐C‐allyl glucoside. Anomerisation of the corresponding amino α‐C‐glucosyl aldehyde to the β‐aldehyde was observed. Thus, both amino α‐ and β‐C‐glucosyl methanol were obtained after reduction.     

The Aqueous Ca2+ System,in Comparison with Zn2+, Fe3 +, and Al3 +: An Ab Initio Molecular Dynamics Study

Herein, we report on the structure and dynamics of the aqueous Ca²⁺ system studied by using ab initio molecular dynamics (AIMD) simulations. Our detailed study revealed the formation of well‐formed hydration shells with characteristics that were significantly different to those of bulk water. To facilitate a robust comparison with state‐of‐the‐art X‐ray absorption fine structure (XAFS) data, we employ a 1st principles MD‐XAFS procedure and directly compare simulated and experimental XAFS spectra. A comparison of the data for the aqueous Ca²⁺ system with those of the recently reported Zn²⁺, Fe³⁺, and Al³⁺ species showed that many of their structural characteristics correlated well with charge density on the cation. Some very important exceptions were found, which indicated a strong sensitivity of the solvent structure towards the cation′s valence electronic structure. Average dipole moments for the 2nd shell of all cations were suppressed relative to bulk water.