Upper bounds for the first dirichlet eigenvalue of a tube around an algebraic complex curve of ℂ<Emphasis Type="Italic">P</Emphasis><Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>(<Emphasis Type="Italic">λ</Emphasis>)

We give an upper bound for the first Dirichlet eigenvalue of a tube around a complex curve P of ℂP ⁿ (λ) which depends only on the radius of the tube and the degrees of the polynomials defining P. The bound is sharp on a totally geodesic ℂP ¹(λ) and gives a gap between the eigenvalue of a tube around ℂP ¹(λ) and around other complex curves.     

Some sixth order zero-finding variants of Chebyshev-Halley methods

A zero-finding technique in which the order of convergence is improved and nonlinear equations are solved more efficiently than they are solved by traditional iterative methods is derived. Composing a modified Chebyshev-Halley method with a variant of this method that just introduces one evaluation of the function the iterative methods presented are obtained. By carrying out this procedure the output numerical results show that the new methods compete in both order and efficiency with the modified Chebyshev-Halley methods.     

Pyridoxamine,a scavenger agent of carbohydrates

Pyridoxamine has been found to inhibit protein glycation and to avoid the formation of advanced glycation end‐products (AGEs). One of the mechanisms by which pyridoxamine can inhibit glycation involves the scavenger of carbonyl groups with glycation capacity. In this work, we conducted a kinetic study of the reactions of pyridoxamine with various carbohydrates under physiological pH and temperature. The reactions involving hexoses were found to give a tricyclic compound ( 5 ) in addition to pyridoxal and pyridoxine. Such a tricyclic compound inhibits the Amadori rearrangement and the formation of other carbonyl compounds with glycating properties. The reactions involving pentoses gave compound 7 and pyridoxal—by transamination of the Schiff base. The transamination reaction enhances the inhibitory action of pyridoxamine. The formation rate constants for the Schiff base, k₃, were found to be similar to those for the reactions of D ‐glucose with amino acids, which suggests competition between pyridoxamine and terminal amino residues in proteins for glycating sites in sugars. These constants are dependent on the electrophilic character of the carbonyl carbon in the carbohydrate. © 2007 Wiley Periodicals, Inc. 39: 154–167, 2007     

Efficient implementation of the analytical second derivatives of hartree–fock and hybrid DFT energies within the framework of the conductor-like polarizable continuum model

Calculation of vibrational frequencies for solvated systems is essential to study reactions in complex environments. In this paper, we report the implementation of the analytical self-consistent field Hessian at the Hartree–Fock and density functional theory levels in the framework of the conductor-like polarizable continuum model (C-PCM) into the ORCA quantum chemistry suite. The calculated vibrational frequencies agree very well with those computed through numerical differentiation of the analytical gradients. The deviation between both sets of data is smaller than 3 cm⁻¹ for frequencies larger than 200 cm⁻¹ and smaller than 5 cm⁻¹ for the low-frequency regime (100 cm⁻¹ < ω < 200 cm⁻¹). The accuracy of the frequencies is not significantly affected by the size of the density functional theory (DFT) integration grid, with a deviation lower than 0.5 cm⁻¹ between data computed with the smallest and that with the largest DFT grid size. The calculation of the analytical Hessian is between 3 and 12 times faster than its numerical counterpart. The C-PCM terms only add an overhead of 10–30% relative to the gas phase calculations. Finally, for acetone, the (B3LYP) values for the frequency shifts obtained in going from the gas phase to liquid acetone are in agreement with experiment. © 2019 Wiley Periodicals, Inc.     

An Adamantyl Amino Acid Containing Gramicidin S Analogue with Broad Spectrum Antibacterial Activity and Reduced Hemolytic Activity

The cyclic cationic antimicrobial peptide gramicidin S (GS) is an effective topical antibacterial agent that is toxic for human red blood cells (hemolysis). Herein, we present a series of amphiphilic derivatives of GS with either two or four positive charges and characteristics ranging between very polar and very hydrophobic. Screening of this series of peptide derivatives identified a compound that combines effective antibacterial activity with virtually no toxicity within the same concentration range. This peptide acts against both Gram‐negative and Gram‐positive bacteria, including several MRSA strains, and represents an interesting lead for the development of a broadly applicable antibiotic.     

Enhancing Dual-State Emission in Maleimide Fluorophores through Fluorocarbon Functionalisation

Herein, a library of trifluoroethyl substituted aminomaleimide derivatives are reported with small size and enhanced emissions in both solution and solid-state. A diCH₂CF₃ substituted aminochloromaleimide exhibits the most efficient dual-state emission (Φ_f >50 % in solution and solid-state), with reduced quenching from protic solvents. This is attributed to the reduction of electron density on the maleimide ring and suppressed π-π stacking in the solid-state. This mechanism was explored in-depth by crystallographic analysis, and modelling of the electronic distribution of HOMO-LUMO isosurfaces and NCI plots. Hence, these dual-state dyes overcome the limitations of single-state luminescence and will serve as an important step forward for this rapidly developing nascent field.     

Effect of Diamine Bridge on Reactivity of Tetradentate ONNO Nickel(II) Complexes

Two new square planar ONNO nickel(II) complexes C2_core and C3_core have been synthesized and characterized by single crystal X-ray diffraction, NMR spectroscopy, thermogravimetry, and DFT calculations. The experimental results revealed the effect of the length of diamine bridge in the ligand on the behavior of the studied complexes in the reaction with N-heterocyclic aromatic amines, while DFT calculations provided a basis for the rationalization of this observation. The complex with propylenediamine bridge ( C3_core ) readily reacts with pyridine and its derivatives to form high-spin (paramagnetic) complexes with octahedral geometry as characterized by X-ray diffraction; electron-donating substituents on the pyridine ring facilitate the coordination of axial ligands. In contrast, the complex with ethylenediamine bridge ( C2_core) does not undergo such a reaction because of the high deformation energy of the core required for the formation of C2_Py complex.     

Ruthenium(III) and iridium(III) complexes with nicotine

A new chloride-dimethylsulfoxide-ruthenium(III) complex with nicotine trans-[Ru^IIICl₄(DMSO)[H-(Nicotine)]] (1) and three related iridium(III) complexes; [H-(Nicotine)]trans-[Ir^IIICl₄(DMSO)₂] (2), trans-[Ir^IIICl₄(DMSO)[H-(Nicotine)]] (3) and mer-[Ir^IIICl₃(DMSO)(Nicotine)₂] (4) have been synthesized and characterized by spectroscopic techniques and by single crystal X-ray diffraction (1, 2, and 4). Protonated nicotine at pyrrolidine nitrogen is present in complexes 1 and 3 while two neutral nicotine ligands are observed in 4. In these three inner-sphere complexes coordination occurs through the pyridine nitrogen. Moreover, in the outer-sphere complex 2, an electrostatic interaction is observed between a cationic protonated nicotine at the pyrrolidine nitrogen and the anionic trans-[Ir^IIICl₄(DMSO)₂]^¯ complex.