DFT studies on coordination models for adsorption essays of Cu(II) and Ni(II) solutions in modified silica gel with iminodiacetic groups

Research in functionalized inorganic supports faces special challenges regarding the inmobilization of organic chains and efficient computational methods for the quantum chemical modeling of coordination compounds. The silylant 3-cloropropyltriethoxysilyl (R1) was anchored over silica gel in anhydrous conditions, in order to react with diethyl Iminodiacetate (DIDA) to obtain modified silica gel (R2), which was hydrolized in basic conditions previously synthesized and characterized by S _BET, TGA and FTIR spectroscopy to obtain iminodiacetic acid groups IDA to prepare an modified inorganic support (R3) that is able to get hands on metals from the first transition series such as copper and nickel. The obtained experimental values showed that the functionalized grade of R3 corresponds to 0.1598 mmol of the nitrogen indicated that the adsorbed Cu(II) or Ni(II) have the stoichiometry for both cation of 1:1. Based on this relation, the three different structures were proposed to carry out the computational studies using density functional theory (DFT) in its LDA and PW91 with the TZP slater type basis set. The primary coordination sphere of copper(II) or nickel (II) ion in R3 are optimized, structural parameters are calculated, vibrational bands are assigned and energy gaps of frontier orbital (HOMO–LUMO) have been calculated. The calculated results reproduced the experimental data with good agreement. An energy decomposition analysis (EDA) of the different models proposed here was performed and suggest a 1:1 coordination form.     

Automatic Dantzig–Wolfe reformulation of mixed integer programs

Mathematical Programming - Dantzig–Wolfe decomposition (or reformulation) is well-known to provide strong dual bounds for specially structured mixed integer programs (MIPs). However, the...     

The Vortex Filament Equation as a Pseudorandom Generator

In this paper, we consider the evolution of the so-called vortex filament equation (VFE),

$$\mathbf{X}_t = \mathbf{X}_s\wedge\mathbf{X}_{ss}, $$

taking a planar regular polygon of M sides as initial datum. We study VFE from a completely novel point of view: that of an evolution equation which yields a very good generator of pseudorandom numbers in a completely natural way. This essential randomness of VFE is in agreement with the randomness of the physical phenomena upon which it is based.

     

Synthesis of chiral mesoporous silicas with oligo(saccharide) surfaces and their use in separation of stereoisomers

Novel chiral mesoporous silicas (SBA-15 motif) with chemically bonded oligo(saccharides) (1, 3, and 7 glucose units) were obtained through the cocondensation of organosilicon derivatives of the oligo(saccharides) and silica precursors in the presence of polymer surfactant template under mild acidic conditions. The pore order and structure of the materials prepared were characterized by transmission electron microscopy and nitrogen adsorption. The direct application of the oligo(saccharide)-grafted SBA-15 stationary phases in the HPLC separations of stereoisomers was demonstrated for the first time.     

Dwarf Kiwi (Actinidia arguta Miq.), a Source of Antioxidants for a Healthy and Sustainable Diet

The feasibility of using dwarf kiwi fruits (Actinia arguta Miq.) as a healthy and sustainable food, compared to other types of commercial kiwi fruits, was evaluated in the present study. The overall antioxidant capacity of these fruits was assessed by either extraction-dependent methods (ABTS, ORAC) or the direct method called Quick, Easy, New, CHEap, Reproducible (QUENCHER) (DPPH, FRAP, Folin–Ciocalteu), applied for the first time to analyze kiwi fruits. With this methodology, all the molecules with antioxidant capacity are measured together in a single step, even those with high molecular weight or poor solubility in aqueous extraction systems, such as antioxidant dietary fiber. The effect of kiwi extracts on physiological and induced intracellular reactive oxygen species (ROS) production on IEC-6 cells was also analyzed, as well as total phenolic content (TPC) by Fast Blue BB, flavonols, hydroxycinnamic acids, and hydroxybenzoic acids. A. arguta fruits showed the highest values in all the antioxidant assays, being remarkably higher than the other kiwi species for Q-FRAP and Q-DPPH. Dwarf kiwi showed the highest potential in reducing physiological ROS and the highest values of TPC (54.57 mgGAE/g), being hydroxybenzoic acids the main phenolic family found (2.40 mgGAE/g). Therefore, dwarf kiwi fruits are a natural source of antioxidants compared to conventional kiwi fruits, being a sustainable and healthy alternative to diversify fruits in the diet.     

Temperature dependence of ESR anisotropy in La7/8Sr1/8MnO3

We report X-ray diffraction, DC-susceptibility, electron spin resonance (ESR), and dilatometry measurements carried out on an La_7/8Sr_1/8MnO₃ single crystal. Thermal expansion was measured along different crystallographic axes using a three-terminal dilatometer. The sharp anomalies observed in the temperature dependence of Δl/l allowed us to locate the Jahn–Teller transition at T_JT=285(1) K. ESR experiments were carried out in the paramagnetic regime from 220 to 570 K, at 9.4 GHz. We measured the ESR line width ΔH_pp(T) with the magnetic field parallel to the crystallographic directions [1 0 0] and [0 0 1], referred to the orthorhombic (Pbnm) axes. We correlate the temperature dependence of ΔH_pp with the structural changes of the lattice.     

Simulation of CPMAS Signals at High Spinning Speeds

The spin dynamics of anS( )I_Nsystem during the CP mixing time of continuous wave and variable amplitude cross-polarization magic angle spinning (CWCPMAS and VACPMAS) experiments is discussed. The signal enhancement of a low abundantSspin, coupled to a set ofN= 6 coupled spins withI= , is evaluated as a function of the length of the mixing time. For CWCPMAS this signal is first evaluated in the frequency domain and then transformed to the time domain. These calculations provide some additional insight into the CP spin dynamics and enable a practical approach toward the evaluation of CP signals of large spin systems. In addition the adiabatic character of the ramped VACPMAS experiments is discussed andS-spin signals of a spin system withN= 6 are simulated. Estimates of the upper bounds of the CP signals as a function of the number ofIspins in anS( )I_Nsystem are given and compared with the calculated values.     

Polynomial time approximation schemes for dense instances of minimum constraint satisfaction

It is known that large fragments of the class of dense Minimum Constraint Satisfaction (MIN‐CSP) problems do not have polynomial time approximation schemes (PTASs) contrary to their Maximum Constraint Satisfaction analogs. In this paper we prove, somewhat surprisingly, that the minimum satisfaction of dense instances of kSAT ‐formulas, and linear equations mod 2, Ek‐LIN2, do have PTASs for any k. The MIN‐Ek‐LIN2 problems are equivalent to the k‐ary versions of the Nearest Codeword problem, the problem which is known to be exceedingly hard to approximate on general instances. The method of solution of the above problems depends on the development of a new density sampling technique for k‐uniform hypergraphs which could be of independent interest. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 73–91, 2003     

Functionalization of carbon nanofibers (CNFs) through atom transfer radical polymerization for the preparation of poly(tert‐butyl acrylate)/CNF materials: Spectroscopic,thermal, morphological,and physical characterizations

Vapor‐grown carbon nanofibers (CNFs) were oxidized and functionalized for atom transfer radical polymerization (ATRP) of tert‐butyl acrylate (t‐BA) from the surface of the CNFs. The materials were characterized by solubility tests, Fourier‐transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and scanning electron microscopy. The FTIR and electron microscopy results suggest that ATRP process was successfully used to graft poly(tert‐butyl acrylate) (poly(t‐BA)) chains from the surface of the fibers. Raman results strongly indicate the partial degradation of the graphitic layer of CNFs because of the chemical treatments. TGA results suggest that the presence of poly(t‐BA) leads to a decrease of the initial degradation temperature of the fibers. XRD and electron microscopy results indicate that the microstructure of fibers was not destroyed because of the oxidation and functionalization processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3326–3335, 2008