Frontier orbitals of trivalent cages: (3,6) cages and (4,6) cages

A qualitative molecular-orbital treatment and group-theoretical analysis reveals the nature of the frontier orbitals of (3,6) and (4,6) polyhedral cages, consisting of a hexagonal network with triangular and square defects, respectively. Leapfrog (3,6) cages have two nonbonding filled orbitals. Leapfrog (4,6) cages have a high HOMO-LUMO gap, while nonleapfrog (4,6) cages with octahedral symmetry have a very small HOMO-LUMO gap. The symmetry of the frontier orbitals is determined.     

Copper(II) ion hydrolysis in aqueous solution

A copper(II) ion-selective-electrode potentiometric method was used to determine the first and second hydrolysis constants of Cu²⁺. Special techniques prevented copper(II) hydroxide precipitation, and copper(II) carbonate and cipper(II) organic complexation during the titration of the experimental solution over the pH range 6.8–8.4. The large change in the total copper concentration during the titration due to adsorption of copper onto the vessel walls was accounted for by measuring the total copper concentration at each pH by atomic absorption spectrophotometry. The two hydrolysis constants were determined at 25°C in 0.7 and 0.05m NaClO₄ media. The measured stability constants are independent of the copper concentration and yield similar zero ionic strength values. Also, the stepwise equilibrium constants decrease as the ligand number increases.     

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.     

Solvothermal preparation of iron phosphonate cages

Three new iron(Ⅲ) phosphonate cage-like complexes with [Fe 4 ], [Fe 9 ] and [Fe 14 ] cores have been synthesized by solvothermal reaction with various starting materials. Magnetic studies show overall antiferromagnetic interaction presented in these cages.     

Density-functional theory study of Iron(III) hydrolysis in aqueous solution

Fe(III) hydrolysis in aqueous solution has been investigated using density-functional methods (DFT). All possible structures arising from different tautomers and multiplicities have been calculated. The solvation energy has been estimated using the UAHF-PCM method. The hydrolysis free energies have been estimated and compared with the available experimental data. The different hydrolysis species have distinct geometries and electronic structures. We have shown that improvement of theory level in calculating the electronic energy does not necessarily improve the estimated free energies in aqueous solution since the UAHF-PCM is a simple method that neglects specific interactions with the solvent. Therefore, it is important to have the correct balance between theory level used in the electronic calculation and the UAHF-PCM. The PBE/TZVP/UAHF-PCM method has been found to describe correctly the hydrolysis energies of Fe(III), deviating about 3.0 kcal mol(-1) from experimental values.     

The hydrolysis of phosphoranes in aqueous dioxane

The entropy of activation for the hydrolysis of pentaphenoxyphosphorane in 25% aqueous dioxane is ?188 J/mol deg. The enthalpy of activation is 22.5 kJ/mol, which is small for the relatively slow reaction. This suggests that the reaction is a multistep process having a preliminary equilibrium with a negative heat of reaction. This conclusion is supported by the results obtained for the hydrolysis of C₆H₅ [OCH(CF₃)₂]₂. A kinetic isotope effect k_H2O/k_D2O of 3.46 was found for the latter reaction. Orders in water were obtained, and a mechanism of hydrolysis is proposed.     

Paraoxon and parathion hydrolysis by aqueous molybdenocene dichloride (Cp2MoCl2): first reported pesticide hydrolysis by an organometallic complex

We report the first case of an organometallic complex that effectively hydrolyzes the organophosphate pesticides parathion and paraoxon. The complex is the water-soluble compound bis(eta 5-cyclopentadienyl)molybdenum(IV) dichloride (1), which hydrolyzes parathion to produce ethanol and deethyl parathion in a biphasic reaction in D2O. Rate accelerations were 130 and 10(5) at pH 7 and 3, respectively. Paraoxon is readily hydrolyzed by 1 to yield p-nitrophenol and diethyl phosphate with rate accelerations of 2300 and 27 at pH 7 and 3, respectively. Kinetic data for paraoxon hydrolysis by 1 are consistent with a process that involves intermolecular (delta S++ = -49 +/- 10 eu) hydroxide attack on the phosphate triester in which the aquated 1 serves as a coordinated Lewis acid that activates the organophosphate. Interestingly parathion hydrolysis by 1 occurs via nucleophilic attack at the alpha-carbon of the phosphorothioate pesticide that involves C-O bond cleavage. These parathion results represent one of the few cases of this type of unusual hydrolytic chemistry and the first case of an organometallic complex that accelerates organophosphate pesticide hydrolysis.     

Fe(II) hydrolysis in aqueous solution: A DFT study

Species arising from Fe(II) hydrolysis in aqueous solution have been investigated using density-functional methods (DFT). The different tautomers and multiplicities of each species have been calculated. The solvation energy has been estimated using the UAHF–PCM method. The hydrolysis free energies have been estimated and compared with the available experimental data. The different hydrolysis species have distinct geometries and electronic structures. The estimated ionization potential of the hydrolyzed species is linearly dependent to the number of hydroxyls present in the complex. The estimated Fe(II)/Fe(III) oxidation potential is in good agreement with previously published results about 0.29 V larger than the experimental value. The results highlight the importance of the chemical speciation in describing electron transfer processes at a molecular level. The PBE/TZVP/UAHF–PCM method has been found to describe correctly the hydrolysis free energies of Fe(II) with an average error about 5 kcal mol⁻¹ from the experimental values.     

Ionic strength dependence of formation constants-XVIII. The hydrolysis of iron(III) in aqueous KNO(3) solutions

The hydrolysis of iron(III) was studied potentiometrically at different ionic strengths in KNO(3) aqueous solutions, at 25 degrees C, to determine the dependence of hydrolysis constants on ionic strength (nitrate media), to check the existence of nitrate-ferric ion interactions, and to confirm the formation of high polymeric species. Under the experimental conditions 0.03 I (KNO(3)) 1M, 0.3 C 12 mM, the species Fe(OH)(2+), Fe(2)(OH)(4+)(2), Fe(OH)(+)(2) and Fe(12)(OH)(2+)(34) were found, and the hydrolysis constants log beta(11) = 2.20, log beta(12) = -2.91, log beta(22) = -5.7, log beta(12,34) = -48.9 (I = 0M) were calculated. The ionic strength dependence of hydrolysis constants is quite close to that found for several protonation and metal complex formation constants reported elsewhere.     

The formation of polymer vesicles or "peptosomes" by polybutadiene-block-poly(L-glutamate)s in dilute aqueous solution

Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subsequent ring-opening polymerization of N-carboxyanhydrides and were characterized by NMR, IR, SEC, and circular dichroism. These polymers, when appropriately designed, form so-called "polymersomes" or "peptosomes", vesicles composed of modified protein units. The size and structure of the vesicles are determined by dynamic light scattering, small-angle neutron scattering, and freeze-fracture electron microscopy. It is also shown that the size of the peptosomes does not depend on the pH; that is, the solvating peptide units can perform a helix-coil transition without serious changes of the vesicle morphology.     

Fast preparation of nanocrystalline cellulose by microwave-assisted hydrolysis

In this work we report on the procedure for fast and controlled preparation of nanocrystalline cellulose (NCC) from commercially available microcrystalline cellulose using microwave-assisted hydrolysis. By varying the sulfuric acid concentration and hydrolysis temperature, an average hydrodynamic diameter of NCC between 126 and 1,310 nm with corresponding yields between 16 and 82 %, respectively, was obtained in a very short reaction time of 10 min. An additional advantage of the described procedure is its high reproducibility and ability to fine-tune the average NCC particle size by adjusting the reaction conditions, i.e., the sulfuric acid concentration and/or reaction temperature.     

The hydrolysis of pyridilmonoimines in acidic aqueous media

The rates of hydrolysis of some pyridilmonoimines have been investigated in aqueous methanol medium of acetate buffer. The hydrolysis of the studied bases found to be slower than that of benzylideneaniline. It is evident from the dependent of the rate constants upon the buffer concentration that the rate equation has the form of special and general acid catalysis. From the results it is suggested that the rate-determining step appears to be the protonation of the nitrogen atom of the imino group of the monoamines at the employed pH.     

Self-assembled palladium(II) "click" cages: synthesis, structural modification and stability

Readily synthesised and functionalised di-1,2,3-triazole "click" ligands are shown to self-assemble into coordinatively saturated, quadruply stranded helical [Pd(2)L(4)](BF(4))(4) cages with Pd(II) ions. The cages have been fully characterised by elemental analysis, HR-ESMS, IR, (1)H, (13)C and DOSY NMR, DFT calculations, and in one case by X-ray crystallography. By exploiting the CuAAC "click" reaction we were able to rapidly generate a small family of di-1,2,3-triazole ligands with different core spacer units and peripheral substituents and examine how these structural modifications affected the formation of the [Pd(2)L(4)](BF(4))(4) cages. The use of both flexible (1,3-propyl) and rigid (1,3-phenyl) core spacer units led to the formation of discrete [Pd(2)L(4)](BF(4))(4) cage complexes. However, when the spacer unit of the di-1,2,3-triazole ligand was a 1,4-substituted-phenyl group steric interactions led to the formation of an oligomeric/polymeric species. By keeping the 1,3-phenyl core spacer constant the effect of altering the "click" ligands' peripheral substituents was also examined. It was shown that ligands with alkyl, phenyl, electron-rich and electron-poor benzyl substituents all quantitatively formed [Pd(2)L(4)](BF(4))(4) cage complexes. The results suggest that a wide range of functionalised palladium(II) "click" cages could be rapidly generated. These novel molecules may potentially find uses in catalysis, molecular recognition and drug delivery.     

Coupled diffusion produced by hydrolysis of aqueous potassium phosphate

Conductimetric and diaphragm cell techniques have been used to measure diffusion of aqueous potassium phosphate solutions at 25°C from 0.01 to 0.10 mol-dm^–3 (M). A significant portion of the aqueous K₃PO₄ component diffuses as equimolar amounts of potassium hydrogen phosphate and potassium hydroxide produced by hydrolysis: K₃PO₄+H₂O=K₂HPO₄+KOH. Because OH^– diffuses more rapidly than HPO ₄ ^2– , the total flow of KOH exceeds the flow of K₂HPO₄. The extra flow of KOH constitutes coupled transport of a second solute component. Ternary diffusion coefficients that describe interacting flows of K₃PO₄ and KOH components are reported. At low concentrations where phosphate is strongly hydrolyzed, the molar flux of the KOH component produced by diffusion of K₃PO₄ is six times larger than the flux of the K₃PO₄ component. Binary diffusion coefficients for aqueous K₂HPO₄ solutions are also reported. It is shown that ternary transport coefficients for K₃PO₄ solutions can be estimated from the properties of binary solutions of K₂HPO₄ and KOH.     

Kinetics and mechanism of an unique hydrolysis reaction of (hexafluoroacetylacetonato)bis(ethylenediamine)cobalt(III) in aqueous solution

Summary Addition of base to the title complex results in the rapid reversible formation of the hydrolysed species Co(en)₂-(hfac · OH)⁺ in which the coordinated hexafluoroacetylacetonato ligand contains a hydroxyl group on the carbonyl carbon atom. The kinetics of both the forward hydrolysis and reverse acidolysis reactions were followed spectrophotometrically using stopped-flow and T-jump techniques. The corresponding rate constants areca. 3×106 and 1×10⁸ M^–1s^–1, respectively, for various buffer systems at 25 °C and ionic strength 1.0 M. A combination of the kinetic and equilibrium data enables the estimation of the uncatalyzed (spontaneous) forward and reverse reaction components. The results are discussed with reference to similar data reported for the hydrolysis and reverse acidolysis reactions of the uncoordinated acetylacetonato ligand.