Investigations for Modification of Polyacrylamide-Bentonite by Phytic Acid and its Usability in Fe3+, Zn2+ and UO2 2+ Adsorption

Composite of polyacrylamide-bentonite (PAA-B) was prepared by direct polymerisation of PAA in a suspension of bentonite (B). Adsorption and thermodynamic features of phytic acid (Phy) adsorption onto B, PAA and PAA-B, and those of Fe³⁺, Zn²⁺, UO₂ ²⁺ adsorption onto PAA-B and its modification by Phy (PAA-B-Phy) have been investigated. The reusability, storagability, ion selectivity and recoverability of sorbed ions with 1 M HCl have also been considered.The chemical and physical structure of adsorbents has been characterised by means of FT-IR and XRD. All adsorption isotherms for Phy and the ions were L-type of the Giles classification except, the one which is S type for adsorption of Phy onto PAA. The maximum adsorption capacities for the ions adsorbed were in order of UO₂ ²⁺ > Fe³⁺ > Zn²⁺ for PAA-B and Zn²⁺ > Fe³⁺ > UO₂ ²⁺ for PAA-B-Phy. Langmuir equilibrium constants for the adsorption of ions onto PAA-B-Phy were significantly higher than those found for PAA-B; the magnitude of increase for UO₂ ²⁺ was about 100. The thermodynamic parameters indicated that adsorption reactions are spontaneous in terms of adsorption free enthalpy.The chemical structure of PAA-B-Phy was not changed at the end of the studies of reusability and storagability. The composite was selective for UO₂ ²⁺ of the ions of interest.The composite of PAA-B and its modification by Phy have been used for the first time in this investigation. It is proposed that the composites can be practically used in the investigations and applications of adsorption.     

Stacking of triphenylene: characterization of the potential energy surface

The interaction potential energy of triphenylene dimer has been calculated with Møller–Plesset second-order perturbation theory for various geometrical configurations. Different types of geometrical perturbations such as rotation, displacements and their combinations are studied in terms of their effects on the stability of the dimer. Minimum energy conformers for face to face, rotated, parallel displaced and T-shape structures are obtained. For the unsubstituted triphenylene, the 35° rotation of one of the monomers results in the global minimum. However, the dimer is still very flexible in terms of displacements. A helical structure seems to be the most stable form for the trimer. For large stacked clusters, the two body forces dominate the interactions while at small monomer–monomer separation, three body terms behave like z ^?9 where z is the vertical distance between two adjacent monomers.     

Interferometry with entangled atoms

A quantum gravity-gradiometer consists of two spatially separated ensembles of atoms interrogated by pulses of a common laser beam. The laser pulses cause the probability amplitudes of atomic ground-state hyperfine levels to interfere, producing two, motion-sensitive, phase shifts, which allow the measurement of the average acceleration of each ensemble, and, via simple differencing, of the acceleration gradient. Here we propose entangling the quantum states of atoms from the two ensembles prior to the pulse sequence, and show that entanglement encodes their relative acceleration in a single interference phase which can be measured directly, with no need for differencing. Received 6 June 2002 / Received in final form 25 October 2002 Published online 28 January 2003     

Comments on “A more precise statement of Hamilton's principle”

Among the problems C. D. Bailey has questioned in a recent paper (Ref. 1) are a precise and general formulation of Hamilton's variational principle and the establishment of a sufficiency criterion for this to be a minimum principle. In this paper, we will try to answer these questions using the geometric theory of classical mechanics.     

Synthesis and EPR studies of porphyrazines with bulky substituents

Magnesium porphyrazinate substituted with eight 4-tert-butylphenylthio-groups on the peripheral positions has been synthesized by cyclotetramerization of 1,2-bis(4-tert-butylphenylthio)maleonitrile in the presence of magnesium butanolate. The metal-free derivative was obtained by its treatment with trifluoroacetic acid and further reaction of this product with copper(II) acetate, zinc(II) acetate and cobalt(II) acetate led to the metal porphyrazinates (M = Cu, Zn, Co). These new compounds have been characterized by elemental analysis, together with FT-IR, ¹H NMR, UV–Vis spectral data. By using EPR technique, room temperature paramagnetic properties of Cu(II) doped porphyrazine sample as powder and solution forms were measured. The first-derivative EPR signals taken from as powder and solution forms shows that the sample is axially symmetric. The trend g_∥ > g_⊥ > 2 indicates that the unpaired electron is located mainly in the _dx2-y2${\mathrm{d}}_{x^2-y^2}$ orbital (²B₁ as ground state).     

Intermolecular interactions in nitrogen-containing aromatic systems

π–π and CH···N interactions are vital in biological systems. In this study, stacking and hydrogen-bonded interactions in pyrazine and triazine dimers were investigated by density functional theory combined with symmetry-adapted perturbation theory (DFT-SAPT) and counterpoise (CP)-corrected supermolecular MP2, SCS-MP2, B3LYP-D and CCSD(T) calculations. All interaction energies were computed using the optimized structures at the CP-corrected SCS/aug-cc-pVDZ level, which gave 1–2 kJ/mol lower interaction energies than the ones computed at the MP2 level. For both dimers, doubly hydrogen-bonded and cross-(displaced) stacked orientations were found to be the lowest energy ones. The reference CCSD(T) calculations favored the former structure in both dimer systems, whereas MP2 and SCS-MP2 located the latter as the lowest energy isomer. In particular, the former was found to be lower in energy than the latter by 2.28 and 1.01 kJ/mol at the CCSD(T)/aug-cc-pVDZ level for pyrazine and triazine, respectively. B3LYP-D produced interaction energies in agreement with the CCSD(T) at the equilibrium geometries, but it overestimates them at the short range and underestimates at the long intermonomer separations. Furthermore, it tends to give smaller equilibrium distances compared to the CCSD(T). DFT-SAPT method was in a good agreement with the reference CCSD(T) calculations. This suggests that DFT-SAPT can be employed to compute the full potential energy surface of these dimers. Moreover, DFT-SAPT calculations showed that the electrostatic and dispersion contributions are the most important energy components stabilizing these dimers. The present study aims to show which theoretical method is the most promising one for the investigation of intermolecular interactions dominated by π–π and CH···N. Therefore, the findings obtained in this study can be used to unravel the structures of nucleic acid bases and other systems stabilized by π–π and CH···N interactions.     

Weakly bound finite systems: (?He)N-Rb?(3Σu), clustering structures from a quantum Monte Carlo approach

We report here ((4)He)(N)-Rb(2)((3)Σ(u)) complexes, 2 ≤ N ≤ 20, analysed through a quantum diffusion Monte Carlo stochastic approach. The calculations show that the spin stretched dimer molecule is bound outside the pure He sub-complex, due to the stronger He-He potential as compared with the He-Rb(2) interaction, while the rare gas atom moiety presents, in turn, a shell-like structure with ten He adatoms completing the first shell. Our results agree with previous findings on this and similarly weakly interacting systems.