Computer simulation of viscous fingering in a lifting Hele-Shaw cell with grooved plates

We simulate viscous fingering generated by separating two plates with a constant force, in a lifting Hele-Shaw cell. Variation in the patterns for different fluid viscosity and lifting force is studied. Viscous fingering is strongly affected by anisotropy. We report a computer simulation study of fingering patterns, where circular or square grooves are etched on to the lower plate. Results are compared with experiments.     

Copper(II)‐Catalyzed Nitroaldol (Henry) Reactions: Recent Developments

Self‐assembled copper(II) complexes are described as effective catalysts for nitroaldol (Henry) reactions on water. The protocol involves a heterogeneous process and the catalysts can be recovered and recycled without loss of activity. Further, C2‐symmetric N,N′‐substituted chiral copper(II) salan complexes are found to be more effective catalysts than chiral copper(II) salen complexes for reactions in homogeneous catalysis, with high enantioselectivities. The reactions involve bifunctional catalysis, bearing the properties of a Brønsted base, as well as a Lewis acid, to effect the reaction in the absence of external additives.     

Relative Cartier divisors and Laurent polynomial extensions

If \(i:A\subset B\) is a commutative ring extension, we show that the group \({\mathcal I}(A,B)\) of invertible A-submodules of B is contracted in the sense of Bass, with \(L{\mathcal I}(A,B)=H^0_{\mathrm {et}}(A,i_*{\mathbb Z}/{\mathbb Z})\). This gives a canonical decomposition for \({\mathcal I}(A[t,\frac{1}{t}],B[t,\frac{1}{t}])\).     

Electronic structure and spectroscopic properties of 6‐aminophenanthridine and its derivatives: Insights from density functional theory

6‐Aminophenanthridine (6AP) and its derivatives show important biological activities as antiprion compounds and inhibitors of the protein folding activity of the ribosome. Both of these activities depend on the RNA binding property of these compounds, which has been recently characterized by fluorescence spectroscopy. Hence, fundamental insights into the photophysical properties of 6AP compounds are highly important to understand their biological activities. In this work, we have calculated electronic structures and optical properties of 6AP and its three derivatives 6AP8CF₃, 6AP8Cl, and 6APi by density functional theory (DFT) and time‐dependent density functional theory (TDDFT). Our calculated spectra show a good agreement with the experimental absorption and fluorescence spectra, and thus, provide deep insights into the optical properties of the compounds. Furthermore, comparing the results obtained with four different hybrid functionals, we demonstrate that the accuracy of the functionals varies in the order B3LYP > PBE0 > M062X > M06HF. © 2015 Wiley Periodicals, Inc.     

Periodic trends and complexation chemistry of tetravalent actinide ions with a potential actinide decorporation agent 5-LIO(Me-3,2-HOPO): A relativistic density functional theory exploration

A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An⁴⁺ ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide–ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide–ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th⁴⁺ to Pu⁴⁺. A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant π-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency.     

Cryptand derived fluorescence signaling systems for sensing Hg(II) ion: A comparative study

Two laterally non-symmetric aza-oxa cryptands have been derivatized with the electron-withdrawing fluorophore, 7-nitrobenz-2-oxa-1,3-diazole to obtain the corresponding mono-, bis- and tris-products. In each case, no appreciable emission is observed when the fluorophore is excited due to an efficient photoinduced intramolecular electron transfer (PET) from the lone pair on nitrogen present in the bridges. In the presence of a number of transition and heavy metal ions, their emission characteristics change. The electron-withdrawing ability of the fluorophore drastically alters the binding ability of the cryptand such that Hg(ii) affords largest enhancement of fluorescence. In contrast, mono-, bis- and tris-anthryl (electron-donating) derivatives of these cryptands do not exhibit any selectivity towards Hg(ii) and affords low fluorescence enhancement. Also, the difference in cavity dimension of the o-cryptand and m-cryptand plays a crucial role in terms of selectivity.     

A new resin glycoside from Ipomoea maxima

A new resin glycoside (1) was isolated from the aerial part of Ipomoea maxima, together with three known compounds, pescaprein XX (2), stoloniferin X (3), and stoloniferin IX (4). The structure of 1 was elucidated on the basis of 1D NMR spectroscopy, a fragmentation study by APCIMS, and HRESIMS analysis.