Toward cell circuitry: Topological analysis of enzyme reaction networks via reaction route graphs

The first step toward developing complete cell circuitry is to build quantitative networks for enzyme reactions. The conventional King-Altman-Hill (KAH) algorithm for topological analysis of enzyme networks, adapted from electrical networks, is based on “Reaction Graphs” that, unlike electrical circuits, are not quantitative, being straightforward renderings of conventional schematics of reaction mechanisms. Therefore, we propose the use of “Reaction Route (RR) Graphs” instead, as a more suitable graph-theoretical representation for topological analysis of enzyme reaction networks. The RR Graphs are drawn such that they are not only useful for visualizing the various reaction routes or pathways, but unlike Reaction Graphs possess network properties consistent with requisite kinetic, mass balance, and thermodynamic constraints. Therefore, they are better than the conventional Reaction Graphs for topological representation and analysis of enzyme reactions, both via the KAH methodology as well as via numerical matrix inversion. The difference between the two is highlighted based on the example of a single enzyme reaction network for the conversion of 7,8-dihydrofolate and NADPH into 5,6,7,8-tetrahydrofolate and NADP⁺, catalyzed by the enzyme dihydrofolate reductase.     

Quantitative Planar Chromatographic Analysis of Pantoprazole Sodium Sesquihydrate and Domperidone in Tablets

JPC – Journal of Planar Chromatography – Modern TLC - A simple, rapid, and reliable HPTLC method has been established and validated for determination of pantoprazole sodium...     

Light‐Triggered,Spatially Localized Chemistry by Photoinduced Electron Transfer

It is of immense interest to exert spatial and temporal control of chemical reactions. It is now demonstrated that irradiation can trigger reactions specifically at the surface of a simple colloidal construct, obtained by adsorbing polyethyleneimine on fluorescent colloidal particles. Exciting the fluorescent dye in the colloid affords photoinduced electron transfer to spatially proximal amine groups on the adsorbed polymer to form free radical ions. It is demonstrated that these can be harnessed to polymerize acrylic acid monomer at the particle surface, or to break up colloidal assemblies by cleaving a cross‐linked polymer mesh. Formation of free radical ions is not a function of the size of the colloid, neither is it restricted to a specific fluorophore. Fluorophores with redox potentials that allow photoinduced electron transfer with amine groups show formation of free radical ions.     

Amphiphilic Polymer Nanoparticles: Characterization and Assessment as New Drug Carriers

An amino‐acid‐based hydrophobically modified biocompatible copolymer, poly[(sodium N‐acryloyl‐L ‐valinate)‐co‐(N‐octylacrylamide)] was synthesized and characterized. Techniques such as fluorescence probes, DLS, and TEM were used to investigate its aggregation behavior in aqueous solution. The copolymer was observed to form micellar aggregates having diameters in the nanometer range in aqueous solution (pH = 8) through inter‐chain hydrophobic association. This behavior was found to be similar to that of poly[(sodium N‐acryloyl‐L ‐valinate)‐co‐(N‐dodecylacrylamide)]. The compact micellar nanostructures were observed to be stable with respect to changes of pH and temperature. The encapsulation and release of griseofulvin, a hydrophobic model drug, was studied.

     

The geometry and the analytic properties of isotropic multiresolution analysis

In this paper we investigate Isotropic Multiresolution Analysis (IMRA), isotropic refinable functions, and wavelets. The main results are the characterization of IMRAs in terms of the Lax–Wiener Theorem, and the characterization of isotropic refinable functions in terms of the support of their Fourier transform. As an immediate consequence of these results, there are no compactly supported (in the space domain) isotropic refinable functions in many dimensions. Next we study the approximation properties of IMRAs. Finally, we discuss the application of IMRA wavelets to 2D and 3D-texture segmentation in natural and biomedical images.     

Reactivity of the dinuclear platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2] towards chelating ligands - Bridge cleavage versus formation of acetyl(chloro)platinum(II) complexes

The dinuclear platina-β-diketone [Pt₂{(COMe)₂H}₂(μ-Cl)₂] (1) was found to react with 2-(ROCH₂)C₅H₄N (R =  Me, 2a; H, 2b) yielding a cationic mononuclear platina-β-diketone [Pt{(COMe)₂H}{2-(MeOCH₂)C₅H₄N}]Cl (3) and an acetyl(chloro)platinum(II) complex [Pt(COMe)Cl{2-(HOCH₂)C₅H₄N}] (4), respectively. The reaction of 1 with 8-(methylthio)quinoline (5) resulted in the formation of [Pt(COMe)Cl{8-(MeS)C₉H₆N}] (6). The identities of all complexes were established by microanalysis, ¹H, and ¹³C NMR spectroscopy. Single-crystal X-ray diffraction analysis showed 6 to be square-planar platinum(II) complex with N and C atoms as well as Cl and S atoms in mutually trans positions (configuration index: SP-4-2). In accordance with this, quantum chemical calculations on the DFT level of theory revealed a higher stability of complex 6 having a SP-4-2 configuration vs. the analogous complex in SP-4-3 configuration. The distinctly different reactivity of 1 with 2a on the one hand and with 2b and 5 on the other is discussed in terms of the HSAB concept and a deprotonation/reprotonation reaction.     

Role of Magnetic Exchange Interactions in the Magnetization Relaxation of {3d–4f} Single‐Molecule Magnets: A Theoretical Perspective

Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni₃^IIILn^III} star‐type complexes [Ln=Gd ( 1 ), Dy ( 2 )] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow magnetization relaxation in complex 2 . DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1 . Acute ?Ni?O?Gd bond angles present in 1 instigate a significant interaction between the 4f_xyz orbital of the Gd^III ion and 3d orbital of the Ni^II ions, leading to rare and strong antiferromagnetic Ni???Gd interactions. Calculations reveal the presence of a strong next‐nearest‐neighbour Ni???Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI‐SO calculations performed on complex 2 suggest that the octahedral environment around the Dy^III ion is neither strong enough to stabilize the m_J |±15/2〉 as the ground state nor able to achieve a large ground‐state–first‐excited‐state gap. The ground‐state Kramers doublet for the Dy^III ion is found to be the m_J |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of magnetization (QTM). Using the POLY_ANISO program, we have extracted the J_NiDy interaction as ?1.45 cm^?1. The strong Ni???Dy and next‐nearest‐neighbour Ni???Ni interactions are found to quench the QTM to a certain extent, resulting in zero‐field SMM behavior for complex 2 . The absence of any ac signals at zero field for the structurally similar [Dy(AlMe₄)₃] highlights the importance of both the Ni???Dy and the Ni???Ni interactions in the magnetization relaxation of complex 2 . To the best of our knowledge, this is the first time that the roles of both the Ni???Dy and Ni???Ni interactions in magnetization relaxation of a {3d–4f} molecular magnet have been established.     

Fixed-bed study for adsorptive removal of furfural by activated carbon

In our previous study [A.K. Sahu, V.C. Srivastava, I.D. Mall, D.H. Latye, Sep. Sci. Technol. 43 (5) (2008) 1239], commercial grade activated carbon (ACC) was used for adsorptive removal of furfural from aqueous solution using batch studies. In the present study, continuous fixed-bed adsorption was carried out in ACC packed bed for the removal of furfural from aqueous solution. The effects of important factors namely bed height (Z = 15–60 cm), influent concentration of furfural (C_o = 50–200 mg/l), the flow rate (Q = 0.02–0.04 l/min) and column diameter (D = 2–4 cm) were studied. Capacity of the bed to adsorb furfural was found to increase with an increase in the value of Z, C_o and D; and with decrease in the value of Q. Adams–Bohart, Bed-Depth Service-Time, Thomas, Yoon–Nelson, Clark and Wolborska models were applied to the experimental data for the prediction of the breakthrough point, and to determine the characteristic parameters of the column. Error analysis showed that the Yoon–Nelson model best described the experimental breakthrough curve, while Wolborska model showed good prediction of breakthrough curve for the relative concentration region up to 0.5.