Retention behaviour of Cs(I), Sr(II), Tc(VII) and Np(V) on smectite-rich clay

The smectite-rich natural clay is being considered as a backfill and buffer material for Indian repository programme. In the present study, batch sorption measurements have been performed at trace concentrations for one of the minor actinide elements [Np(V)] and for the long lived fission products, Cs(I), Sr(II), and Tc(VII) on purified and conditioned smectite-rich clay at varying conditions of pH and ionic strength. In case of Cs(I) and Sr(II) the sorption was found to increase with pH. At any pH the sorption was found to decrease with increasing ionic strength of the suspension maintained with NaCl. Further, at any pH the sorption of Sr(II) is less than the corresponding value for Cs(I). This is indicative of effect of size selectivity on the sorption by the clay. Tc(VII), on the other hand, is poorly retained by the clay, which can be explained in terms of the negative charge on the TcO₄ ^? ion, which has negligible interaction with the predominantly negatively charged clay surface. In the case of Np(V), the sorption was found to increase albeit, slowly compared to Cs(I) and Sr(II) with pH, and it with no effect of ionic strength on the sorption at all pH values. This suggests that Np(V) primarily interacts with the surface sites via inner sphere complexation mechanism.     

Highly regioselective rhodium(II)-catalysed carbenoid insertion reaction into sp CH bond: a general method for the synthesis of 3,3a-dihydro-2H,5H-pyrrolo[1,2-a]quinoline-1,4-dione ring system

A simple and high yielding general method for the synthesis of 3,3a-dihydro-2H,5H-pyrrolo[1,2-a]quinoline-1,4-dione derivatives through a highly regioselective rhodium(II)-catalysed carbenoid sp² C-H insertion reaction on suitably substituted γ-lactam diazocarbonyl compounds is described.     

2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-derived [Ru(II)(tptz)(acac)(CH3CN)]+ and mixed-valent [(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(CH3CN)]+

Mononuclear [Ru(II)(tptz)(acac)(CH3CN)]ClO4 ([1]ClO4) and mixed-valent dinuclear [(acac)2Ru(III){(mu-tptz-Eta+)-}Ru(II)(acac)(CH3CN)]ClO4 ([5]ClO4; acac = acetylacetonate) complexes have been synthesized via the reactions of Ru(II)(acac)2(CH3CN)2 and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In [1]ClO4, tptz binds with the Ru(II) ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO4, tptz bridges the metal ions unsymmetrically via the tridentate neutral N,N,N mode with the Ru(II) center and cyclometalated N,C- state with the Ru(III) site (motif F). The activation of the coordinated nitrile function in [1]ClO4 and [5]ClO4 in the presence of ethanol and alkylamine leads to the formation of iminoester ([2]ClO4 and [7]ClO4) and amidine ([4]ClO4) derivatives, respectively. Crystal structure analysis of [2]ClO4 reveals the formation of a beautiful eight-membered water cluster having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom of the perchlorate ion, which, in turn, makes short (C-H- - - - -O) contacts with the neighboring molecule, leading to a H-bonding network. The redox potentials corresponding to the Ru(II) state in both the mononuclear {[(acac)(tptz)Ru(II)-NC-CH3]ClO4 ([1]ClO4) > [(acac)(tptz)Ru(II)-NH=C(CH3)-OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)Ru(II)-NH2-C6H4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)Ru(II)-NH=C(CH3)-NHC2H5]ClO4 ([4]ClO4)} and dinuclear {[(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(NC-CH3)]ClO4 ([5]ClO4), [(acac)2Ru(III){(mu-tptz-H+(N+-O-)2)-}Ru(II)(acac)(NC-CH3)]ClO4 ([6]ClO4), [(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(NH=C(CH3)-OC2H5)]ClO4 ([7]ClO4), and [(acac)2Ru(III){(mu-tptz-Eta+)-}Ru(II)(acac)(NC4H4N)]ClO4 ([8]ClO(4))} complexes vary systematically depending on the electronic nature of the coordinated sixth ligands. However, potentials involving the Ru(III) center in the dinuclear complexes remain more or less invariant. The mixed-valent Ru(II)Ru(III) species ([5]ClO4-[8]ClO4) exhibits high comproportionation constant (Kc) values of 1.1 x 10(12)-2 x 10(9), with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display Ru(II)- and Ru(III)-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in the visible region and ligand-based transitions in the UV region. In spite of reasonably high K(c) values for [5]ClO4-[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR region up to 2000 nm. The paramagnetic Ru(II)Ru(III) species ([5]ClO4-[8]ClO4) displays rhombic electron paramagnetic resonance (EPR) spectra at 77 K (g approximately 2.15 and Deltag approximately 0.5), typical of a low-spin Ru(III) ion in a distorted octahedral environment. The one-electron-reduced tptz complexes [Ru(II)(tptz.-)(acac)(CEta3CN)] (1) and [(acac)2Ru(III){(mu-tptz-Eta+).2-}Ru(II)(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.     

Comparative studies on some metrics for external validation of QSPR models

Quantitative structure-property relationship (QSPR) models used for prediction of property of untested chemicals can be utilized for prioritization plan of synthesis and experimental testing of new compounds. Validation of QSPR models plays a crucial role for judgment of the reliability of predictions of such models. In the QSPR literature, serious attention is now given to external validation for checking reliability of QSPR models, and predictive quality is in the most cases judged based on the quality of predictions of property of a single test set as reflected in one or more external validation metrics. Here, we have shown that a single QSPR model may show a variable degree of prediction quality as reflected in some variants of external validation metrics like Q2(F1), Q2(F2), Q2(F3), CCC, and r2(m) (all of which are differently modified forms of predicted variance, which theoretically may attain a maximum value of 1), depending on the test set composition and test set size. Thus, this report questions the appropriateness of the common practice of the "classic" approach of external validation based on a single test set and thereby derives a conclusion about predictive quality of a model on the basis of a particular validation metric. The present work further demonstrates that among the considered external validation metrics, r2(m) shows statistically significantly different numerical values from others among which CCC is the most optimistic or less stringent. Furthermore, at a given level of threshold value of acceptance for external validation metrics, r2(m) provides the most stringent criterion (especially with Δr2(m) at highest tolerated value of 0.2) of external validation, which may be adopted in the case of regulatory decision support processes.     

Acetanilide mediated reversible assembly and disassembly of Au nanoparticles

Herein we report the generation of Au nanoparticles (NPs) by sparingly soluble acetanilide in water. We also report the formation of linear chain-like superstructures of self-assembled Au NPs, in the presence of excess acetanilide. This was achieved in two different ways. In the first method, acetanilide was added, with increasing concentration, into aqueous HAuCl(4) to produce Au NPs as well as for the formation of assembly, which varied according to the concentration of acetanilide. The other route involved formation of spherical Au NPs at the lowest concentration of acetanilide, which was followed by the formation of assembly of various lengths upon further addition of variable amount of acetanilide. The assemblies were stable in aqueous solution for days with characteristic UV-vis absorption spectra consisting of two peaks. While the wavelength of the first peak remained the same, the position of the second peak changed to longer wavelength with increasing acetanilide concentration. Interestingly, the linear chain-like arrays could be broken into individual particles by first dilution of the solution concentration followed by treatment with ultrasonic waves. The individual Au NPs again formed linear chain-like arrays upon addition of excess acetanilide.     

An attempt towards coordination supramolecularity from Mn(II), Ni(II) and Cd(II) with a new hexadentate [N4O2] symmetrical Schiff base ligand: Syntheses,crystal structures,electrical conductivity and optical properties

To explore the influence of non-covalent weak force interactions, mainly exerted by carboxylic groups, on the formation of supramolecular architectures of transition metal complexes and their electrical conduction processes, a new symmetrical [N₄O₂] hexadentate Schiff base ligand, 1,8-N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine, abbreviated to H₄fsatrien, and its complexes of Ni(II), Cd(II) and Mn(II) have been synthesized using in situ condensation of the ligand components in the presence of metal ions. The complexes were structurally characterized by elemental analyses, IR, UV–Vis, NMR, ESR, molar conductivity and magnetic measurements. The crystal structures of all the complexes have been determined by a single crystal X-ray diffraction study. The 1-D, 2-D and 3-D networks of the complexes are formed by π–π stacking, C–H?π interactions and mono or bifurcated H-bonding. The electronic structures of the complexes have been examined using the DFT method. Solid-state properties (e.g. electrical conductivity at different temperatures and optical properties) of the Ni(II) and Mn(II) complexes have also been studied and, depending on the temperature, the conductivity of the complexes is found to be insulating and semiconducting (intrinsic and extrinsic) in nature. The optical band gap (E_gd) of complexes (1) and (3) is found to be 2.57 and 2.30 eV, respectively.     

Photoinduced intramolecular charge transfer phenomena in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid

A donor acceptor substituted aromatic system 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid (DMAPPDA) has been synthesized and its spectral properties have been explored on the basis of steady state absorption and fluorescence spectroscopy. Spectral features point largely towards a possible occurrence of photoinduced intramolecular charge transfer process from the donor NMe2 group to the acceptor acid group. Solvent dependency of the large Stokes' shifted emission band and the calculated large excited state dipole moment support the polar character of the charge transfer excited state. Quantum yield calculations and effect of addition of acid and base on the steady state spectra were also performed to further scrutinize the excited state CT character.     

Syntheses, crystal structures and magnetic properties of two dicopper(II) complexes and a zigzag 1-D Cu(II) complex of a bidentate pyridyl-pyrazole ligand

Two new dinuclear copper compounds, [Cu₂(pypz)₂(N₃)₂(NO₃)₂] (1) and [Cu₂(pypz)₂(OH)₂(NO₃)₂] (2), and one 1-D polymeric Cu(II) complex, [Cu(pypz)(dca)₃]_n (3) [‘pypz’ = (3,5dimethyl-1-(2′-pyridyl)pyrazole) and dca = (dicyanamide)], have been synthesized and characterized crystallographically and spectroscopically. Complex 1 is pseudo-octahedral, adjacent Cu atoms are connected by a pair of μ(1,1) azido groups and the structure is stabilized by π-π interactions between two pyridyl moieties from two different neighboring complex molecules. Complexes 2 and 3 are square pyramidal. The hydroxo bridged complex 2 is further stabilized through H-bonding. The 1-D polymeric chain of 3 is bridged by an end-to-end dicyanamide bridge and it propagates along the crystallographic b axis, whilst the polymer chains are stacked one upon another along the crystallographic c axis. Low temperature magnetic measurement shows that complexes 1 and 2 are ferromagnetic (J values are 30.81 and 14.79 cm⁻¹, respectively), whereas due to larger Cu-Cu distances, complex 3 shows weak ferromagnetism.     

Interval Valued (∈,∈ ∨q)-Fuzzy Filters of MTL-Algebras

The concepts of interval valued (∈,∈ ∨q)-fuzzy Boolean, MV - and G- filters in a MTL-algebra are introduced. The properties of these generalized fuzzy filters are studied and in particular, the relationships between these fuzzy filters in an MTL-algebra are investigated.