An atomic scale mechanism for the antimalarial action of chloroquine from density functional theory calculations

The X-ray crystal structures of complexes between the antimalarial drugs quinine, quinidine and halofantrine and their biological target, iron(III) ferriprotoporphyrin IX (FePPIX), have been reported in the literature (de Villiers et al. in ACS Chem Biol 7:666, 2012; J Inorg Biochem 102:1660, 2008) and show that all three drugs utilize their zwitterionic alkoxide forms to coordinate to the iron atom via Fe–O bonds. In this work, density functional theory calculations with implicit solvent corrections have been used to model the energetics of formation of these complexes. It is found that the cost of formation of the active zwitterionic form of each drug is more than offset by the energy of its binding to FePPIX, such that the overall energies for complexation of all three drugs with FePPIX are moderately favourable in water, and rather more favourable in n-octanol as solvent. The calculations have been extended to develop an analogous model for the complex between FePPIX and chloroquine, whose structure is not presently known from experiment.     

Oxygen‐Initiated Stereoselective Thermal Isomerisation of a Cyclobutane Derivative in the Solid State

Solid‐state [2+2] photochemical cycloaddition reactions have been extensively studied after the classical work of Schmidt in the 1960s. Of these, trans‐1,2‐bis(4′‐pyridyl)ethylene (bpe) is one of the well‐studied alkenes to synthesize tetrakis(4‐pyridyl)cyclobutane (tpcb). However, almost all the solid‐state [2+2] cycloaddition reactions of bpe yielded, almost exclusively, one of the four possible isomers, namely, the rctt‐tpcb (r=regio c=cis and t=trans). Here we describe a stereoselective synthesis of the tetrahedrally disposed rtct‐tpcb by the solid‐state thermal isomerization of the rctt‐isomer in atmospheric air. We propose that this isomerization occurs through a topochemical unimolecular mechanism by a radical chain pathway, initiated by molecular oxygen. This is supported by the nature of products formed in air and nitrogen, detection of a radical in ESR spectral studies, ESI‐MS crossover experiments, VT PXRD studies along with QM, MD and docking calculations. The formation of a unique isomer by thermal isomerization may be a general phenomenon to quantitatively synthesize other useful stereoisomers from the existing isomers of cyclobutane derivatives.     

Incorporation of ovalbumin within cationic octadecylamine monolayer and a comparative study with zwitterionic DPPC and anionic stearic acid monolayer

In this communication we demonstrated the incorporation of water-soluble surface-active protein OVA within an insoluble cationic ODA monolayer and compared with zwitterionic (DPPC) and anionic (SA) monolayer. The incorporation of OVA is found to be more in ODA as compared to that of DPPC and SA. The kinetics of protein adsorption in lipid monolayer gives the idea that unfolding of OVA is less in case of DPPC than SA and ODA. The pi-A isotherm and compressibility study gives the information about the different states of the protein-lipid mixed monolayer. At higher pressure, OVA tend to squeeze out from the lipids monolayer. High-resolution field emission scanning electron microscope (FE-SEM) images confirm this observation. The surface morphology of DPPC-OVA LB film is far better than ODA-OVA and SA-OVA LB film. OVA forms large irregular aggregates on SA and ODA monolayer. Fluorescence study reveals that protein structure is perturbed more in SA and ODA system compared to that of DPPC. The overall results indicate that DPPC monolayer is better to get protein lipid mixed film than SA and ODA monolayer.     

Adsorption of 2-aminobenzothiazole on colloidal silver particles: an experimental and theoretical surface-enhanced Raman scattering study

Surface-enhanced Raman scattering (SERS) spectra of the biologically important 2-aminobenzothiazole (2-ABT) molecule adsorbed on silver hydrosols are compared with its FTIR spectrum and normal Raman spectroscopy (NRS) spectrum in the bulk and in solution. The optimized structural parameters and the computed vibrational wavenumbers of the compound have been estimated from ab initio (Hatree-Fock) and density functional calculations. Some vibrational modes of the molecule have been reassigned. Concentration-dependent SERS spectra of the molecule reveal the existence of two types of vertically adsorbed species on colloidal silver particles, whose relative population varies with the adsorbate concentrations. The adsorption geometry and structural parameters of one type of adsorbed species are related to the NRS spectrum of the chemically prepared and theoretically modeled 2-ABT-Ag(I) coordination compound.     

F-Doped Co3O4 photocatalysts for sustainable H2 generation from water/ethanol

p-Type Co(3)O(4) nanostructured films are synthesized by a plasma-assisted process and tested in the photocatalytic production of H(2) from water/ethanol solutions under both near-UV and solar irradiation. It is demonstrated that the introduction of fluorine into p-type Co(3)O(4) results in a remarkable performance improvement with respect to the corresponding undoped oxide, highlighting F-doped Co(3)O(4) films as highly promising systems for hydrogen generation. Notably, the obtained yields were among the best ever reported for similar semiconductor-based photocatalytic processes.     

Investigation of the influence of incomplete fusion on complete fusion of <Superscript>12</Superscript>C-induced reactions at ≈ 4–7.2 MeV/nucleon

In this paper, we present the results of our investigation of reaction dynamics leading to incomplete fusion of heavy ions at moderate excitation energies, especially the influence of incomplete fusion on complete fusion of ¹²C -induced reactions at specific energies ≈ 4–7.2M eV/nucleon. Excitation functions of various reaction products populated via complete and/or incomplete fusions of a ¹²C projectile with ⁹³Nb, ⁵⁹Co and ⁵²Cr targets were measured at several specific energies ≈ 4–7.2 MeV/nucleon, using a recoil catcher technique, followed by off-line γ-ray spectrometry. The measured excitation functions were compared with theoretical values obtained using the PACE4 statistical model code. For representative non-α-emitting channels in the ¹²C + ⁹³Nb system, the experimentally measured excitation functions were, in general, found to be in good agreement with the theoretical predictions. However, for α-emitting channels in the ¹²C + ⁹³Nb, ¹²C + ⁵⁹Co, and ¹²C + ⁵²Cr systems, the measured excitation functions were higher than the predictions of the theoretical model code, which may be credited to incomplete fusion reactions at these energies. An attempt was made to estimate the incomplete fusion fraction for the present systems, which revealed that the fraction was sensitive to the projectile energy and mass asymmetry of the entrance channel.     

Three new dicyclic solutions of (21, 42, 20, 10, 9)-designs

We give three dicyclic solutions of a (21, 42, 20, 10, 9)-design which are new. Though the parameters of this design belong to the series (4t + 1, 8t + 2, 4t, 2t, 2t − 1), 4t + 1 = 21 is not a prime power.     

SWKB formalism for confined quantum systems

A formalism is developed to study spatially confined one‐dimensional quantum mechanical systems in the framework of the supersymmetric Wentzel–Kramers–Brillouin (SWKB) method. The approximation technique is applied to estimate the energy eigenvalues of two confined potentials—the harmonic oscillator V(x)=x² and the screened Coulomb potential V(x)=−V₀sech²x. The results thus obtained are found to be in better agreement with the exact numerical values than are those from the ordinary WKB approach. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 267–273, 2000     

Thermal Cleavage of Cyclobutane Rings in Photodimerized Coordination‐Polymeric Sheets

Three coordination polymers, [Cd₂(pvba)₂(tbdc)(dmf)₂] ( 1 ), [Co₂(pvba)₂(tbdc)(dmf)₂(H₂O)₂] ( 2 ), and [Ni₂(pvba)₂(tbdc)(dmf)₂(H₂O)₂] ( 3 ) (H₂tbdc=2,3,5,6‐tetrabromobenzenedicarboxylic acid, Hpvba=trans‐2‐(4′‐pyridyl)vinylbenzoic acid), were synthesized by solvothermal methods. The solid‐state structures of compounds 1 and 2 were determined by X‐ray crystallography. In compounds 1 and 2 , the bimetallic cores acted as secondary building units that connected the tbdc ligands in one direction and a pair of pvba ligands, which were aligned in a head‐to‐tail parallel manner, in the orthogonal direction to form sheet structures. The C?C bonds in these pvba ligand pairs in all three compounds were well‐aligned to undergo quantitative [2+2] cycloaddition reactions in the solid state under UV irradiation, thereby yielding their cyclobutane derivatives. This photochemical reaction appeared to facilitate structural transformations from one 2D structure into another in the solid state. The photoreactive Co^II‐ and Ni^II coordination polymers exhibited a reversible dehydration–rehydration reaction that was accompanied by color changes from pink to purple and green to yellow, respectively, owing to a change in coordination number from six to five. Magnetic studies showed that compound 2 was an antiferromagnet, which displayed a field‐dependent transition with a critical field (H_c) of 40 kOe at 2 K; the antiferromagnetic interaction between the Co₂ units was strengthened and weakened by dehydration and UV irradiation, respectively. The cyclobutane ligand in the photodimerized products was cleaved on heating to yield a mixture of trans‐ and cis‐isomers of pvba, as monitored by ¹H NMR spectroscopy. The Cd^II coordination polymer underwent quantitative cleavage of the cyclobutane ring whilst the other two underwent partial cleavage.