Steroid-porphyrin conjugate for saccharide sensing in protic media

A new saccharide receptor in protic media has been designed and synthesized. The receptor combines advantages of steroids, which are responsible for saccharide binding, and of the porphyrin moiety acting as a signalling component of the molecule due to changes in UV-vis electronic spectra. The synthesis is based on condensation of steroid aldehyde with pyrrole to form the porphyrin unit with four protected steroid moieties. After deprotection, meso-substituted porphyrin contains 12-hydroxy groups on the steroidal part. The receptor is soluble in aqueous solutions and exhibits high complexation affinity towards saccharides. Because the receptor extensively aggregates in water, most of the experiments were performed in 50% aqueous 2-propanol where aggregation is significantly eliminated. Binding is evidenced by spectral changes in the Soret region of the receptor in UV-vis absorption spectra allowing the evaluation of the binding constants. Additional confirmation of binding is obtained using 1H NMR, Raman and IR spectroscopies and the surface plasmon resonance technique. The receptor exhibits higher selectivity for oligosaccharides over monosaccharide. The results point to the importance of a combination of multiple binding via H-bonding and hydrophobic interactions.     

Phase Transition of a Structure II Cubic Clathrate Hydrate to a Tetragonal Form

The crystal structure and phase transition of cubic structure II (sII) binary clathrate hydrates of methane (CH₄) and propanol are reported from powder X‐ray diffraction measurements. The deformation of host water cages at the cubic–tetragonal phase transition of 2‐propanol+CH₄ hydrate, but not 1‐propanol+CH₄ hydrate, was observed below about 110 K. It is shown that the deformation of the host water cages of 2‐propanol+CH₄ hydrate can be explained by the restriction of the motion of 2‐propanol within the 5¹²6⁴ host water cages. This result provides a low‐temperature structure due to a temperature‐induced symmetry‐lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition.     

On optimality of two adaptive choices for the parameter of Dai–Liao method

Orthonormal matrices are a class of well-conditioned matrices with the least spectral condition number. Here, at first it is shown that a recently proposed choice for parameter of the Dai–Liao nonlinear conjugate gradient method makes the search direction matrix as close as possible to an orthonormal matrix in the Frobenius norm. Then, conducting a brief singular value analysis, it is shown that another recently proposed choice for the Dai–Liao parameter improves spectral condition number of the search direction matrix. Thus, theoretical justifications of the two choices for the Dai–Liao parameter are enhanced. Finally, some comparative numerical results are reported.     

Pore Aperture Control Toward Size-Exclusion-Based Hydrocarbon Separations

Metal–organic frameworks (MOFs) have been proposed as a promising material for non-thermal chemical separations owing to their high structural diversity and tunability. Here, we report the synthesis of a zinc-based MOF containing a three-dimensional (3D) linker, bicyclo[2.2.2]octane-1,4-dicarboxylic acid, with high thermal stability towards the separation of hexane isomers. The incorporation of the 3D linker enhances the structural stability and provides well-defined pore apertures/channels with sub-Ångstrom precision. This precision allowed for the separation of similarly sized hexane isomers based on subtle differences in their kinetic diameters. Multi-component liquid phase batch experiments confirmed the separation of hexanes mixture into linear, monobranched, and dibranched isomers. This work represents a significant milestone in the construction of stable Zn-based MOFs and the incorporation of 3D linkers as a potential solution to challenging separations.     

Surface Arginine Saturation Effect on Unfolding Reaction of Firefly Luciferase: A Thermodynamic and Kinetic Perspective

Replacement of some hydrophobic solvent‐exposed residues in Lampyris turkestanicus luciferase with arginine increases thermostability of this enzyme. Herein, thermodynamic and kinetic of unfolding reactions of wild type (WT), E354R/356R, E354R/356R‐I232R and E354R/356R‐Q35R/L182R/I232R variants, has been investigated. Fluorescence and Far‐UV circular dichroism measurements using urea as a chemical denaturant indicated that the value of for all variants is greater than that of WT enzyme. Analysis of m‐values, as a measure of difference in the solvent accessible surface area between the native and denatured states of protein, revealed that higher stability of mutants is related to their higher degree of compactness in the folded state. Results of unfolding kinetic experiments showed that all variants have three‐exponential behavior in which they unfolded with three rate constants and corresponding amplitudes. Increasing the rate constants of fast unfolding phase in mutants relative to WT protein may be attributed to more compactness and more kinetic sensitivity of their folded state to urea. However, more population of WT protein was unfolded from fast unfolding phase. Results of this investigation highlight kinetic stability of luciferase via a slow rate of unfolding.     

Two-Level method for the total fractional-order variation model in image deblurring problem

Numerical Algorithms - Image deblurring with total fractional-order variation model is used to improve the quality of the deblurred images. This model is very efficient in preserving edges and...     

A molecular dynamics study of ethanol-water hydrogen bonding in binary structure I clathrate hydrate with CO2

Guest-host hydrogen bonding in clathrate hydrates occurs when in addition to the hydrophilic moiety which causes the molecule to form hydrates under high pressure-low temperature conditions, the guests contain a hydrophilic, hydrogen bonding functional group. In the presence of carbon dioxide, ethanol clathrate hydrate has been synthesized with 10% of large structure I (sI) cages occupied by ethanol. In this work, we use molecular dynamics simulations to study hydrogen bonding structure and dynamics in this binary sI clathrate hydrate in the temperature range of 100-250 K. We observe that ethanol forms long-lived (>500 ps) proton-donating and accepting hydrogen bonds with cage water molecules from both hexagonal and pentagonal faces of the large cages while maintaining the general cage integrity of the sI clathrate hydrate. The presence of the nondipolar CO(2) molecules stabilizes the hydrate phase, despite the strong and prevalent alcohol-water hydrogen bonding. The distortions of the large cages from the ideal form, the radial distribution functions of the guest-host interactions, and the ethanol guest dynamics are characterized in this study. In previous work through dielectric and NMR relaxation time studies, single crystal x-ray diffraction, and molecular dynamics simulations we have observed guest-water hydrogen bonding in structure II and structure H clathrate hydrates. The present work extends the observation of hydrogen bonding to structure I hydrates.     

A note on the global convergence theorem of the scaled conjugate gradient algorithms proposed by Andrei

In (Andrei, Comput. Optim. Appl. 38:402?C416, 2007), the efficient scaled conjugate gradient algorithm SCALCG is proposed for solving unconstrained optimization problems. However, due to a wrong inequality used in (Andrei, Comput. Optim. Appl. 38:402?C416, 2007) to show the sufficient descent property for the search directions of SCALCG, the proof of Theorem?2, the global convergence theorem of SCALCG, is incorrect. Here, in order to complete the proof of Theorem?2 in (Andrei, Comput. Optim. Appl. 38:402?C416, 2007), we show that the search directions of SCALCG satisfy the sufficient descent condition. It is remarkable that the convergence analyses in (Andrei, Optim. Methods Softw. 22:561?C571, 2007; Eur. J. Oper. Res. 204:410?C420, 2010) should be revised similarly.     

On the sufficient descent property of the Shanno’s conjugate gradient method

Satisfying in the sufficient descent condition is a strength of a conjugate gradient method. Here, it is shown that under the Wolfe line search conditions the search directions generated by the memoryless BFGS conjugate gradient algorithm proposed by Shanno satisfy the sufficient descent condition for uniformly convex functions.