Adsorption Capacity of Silica SBA-15 and Titanosilicate ETS-10 toward Indium Ions.

Indium is an extremely important element for industry that is distributed in the Earth's crust at very low concentrations. The recovery of indium by silica SBA-15 and titanosilicate ETS-10 was investigated at different pH levels, temperatures, times of contact and indium concentrations. A maximum removal of indium by ETS-10 was achieved at pH 3.0, while by SBA-15 it was within the pH range of 5.0-6.0. By studying kinetics, the applicability of the Elovich model for the description of indium adsorption on silica SBA-15 was shown, while its sorption on titanosilicate ETS-10 fitted well with the pseudo-first-order model. Langmuir and Freundlich adsorption isotherms were used to explain the equanimity of the sorption process. The Langmuir model showed its applicability for the explanation of the equilibrium data obtained for both sorbents, the maximum sorption capacity obtained using the model constituted 366 mg/g for titanosilicate ETS-10 at pH 3.0, temperature 22 °C and contact time 60 min, and 2036 mg/g for silica SBA-15 at pH 6.0, temperature 22 °C and contact time 60 min. Indium recovery was not dependent on the temperature and the sorption process was spontaneous in nature. The interactions between the indium sulfate structure and surfaces of adsorbents were investigated theoretically using the ORCA quantum chemistry program package. The spent SBA-15 and ETS-10 could be easily regenerated by using 0.01 M HCl and reused with up to 6 cycles of adsorption/desorption with a decrease in the removal efficiency between 4% and 10% for SBA-15 and 5% and 10% for ETS-10, respectively.

Aminopolycarboxylic Acids-Functionalized Chitosan-Based Composite Cryogels as Valuable Heavy Metal Ions Sorbents: Fixed-Bed Column Studies and Theoretical Analysis.

Over the years, a large number of sorption experiments using the aminopolycarboxylic acid (APCA)-functionalized adsorbents were carried out in batch conditions, but prospective research should also be directed towards column studies to check their industrial/commercial feasibility. In this context, sorption studies of five-component heavy metal ion (HMI) solutions containing Zn2+, Pb2+, Cd2+, Ni2+, and Co2+ in equimolar concentrations were assessed in fixed-bed columns using some APCA-functionalized chitosan-clinoptilolite (CS-CPL) cryogel sorbents in comparison to unmodified composite materials. The overall sorption tendency of the APCA-functionalized composite sorbents followed the sequence Co2+ < Zn2+ < Cd2+ ≤ Pb2+ < Ni2+, meaning that Co2+ ions had the lowest affinity for the sorbent's functional groups, whereas the Ni2+ ions were strongly and preferentially adsorbed. To get more insights into the application of the composite microbeads into continuous flow set-up, the kinetic data were described by Thomas and Yoon−Nelson models. A maximum theoretical HMI sorption capacity of 145.55 mg/g and a 50% breakthrough time of 121.5 min were estimated for the column containing CSEDTA-CPL cryogel sorbents; both values were much higher than those obtained for the column filled with pristine CS-CPL sorbents. In addition, desorption of HMIs from the composite microbeads in dynamic conditions was successfully achieved using 0.1 M HCl aqueous solution. Moreover, a theoretical analysis of APCA structures attached to composite adsorbents and their spatial structures within the complex combinations with transition metals was systematically performed. Starting from the most stable conformer of EDTA, coordinative combinations with HMIs can be obtained with an energy consumption of only 1 kcal/mole, which is enough to shift the spatial structure into a favorable conformation for HMI chelation.

Experimental Studies on the Removal of Aluminium Ions from Synthetic Aqueous Solution by Hydroxyapatites.

In this work we have presented the results obtained in the adsorption behavior of hydroxyapatite with different treatment towards aluminium ions from synthetic wastewaters. Experiments were performed in batch technique at different pH values, temperatures, sorbent dosage, contact time and initial aluminium concentration. The thermodynamic studies on the adsorption process of aluminium onto hydroxyapatite indicated that the process is spontaneous and endothermic. The Langmuir, Freundlich, Flory-Huggins, Dubinin-Radushkevich and Temkin equilibrium models were applied to the description of experimental data. The adsorption of aluminium follows the Langmuir adsorption isotherm. The kinetics of adsorption was evaluated using the pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models. The rate of aluminium adsorption was successfully described by a pseudo-second-order kinetic model. The obtained results indicated that hydroxyapatite treated with Pluronic P123 surfactant has a higher sorption capacity toward aluminium ions (117.65 mg g-1) than hydroxyapatite treated with Pluronic F127 surfactant (109.89 mg g-1) while untreated hydroxyapatite exhibited the lowest one (104.17 mg g-1).

Intra- and Inter-Molecular Spin Coupling in Phenalenyl Dimeric Systems.

Phenalenyl is a triangular aromatic molecule made of three fused benzene rings, carrying an unpaired electron, and many of its derivatives show crystal structures with stacked radicals. Here, we investigate the inter-molecular binding in phenalenyl dimers by state-of-the-art computational methods and phenomenological models. Aside from being important for the supramolecular assembly of such radical molecules, the theoretical insight is relevant in methodological aspects, due to the interplay of long-range exchange coupling effects and van der Waals forces. We used comparative wave function-based and density functional theories. Drawing the potential energy surfaces as a function of inter-planar separation and mutual rotation of the monomer units, we found an interesting pattern which is not discovered in previous computational reports on the title systems. The dependence can be nicely interpreted by a transparent phenomenological model based on an orbital overlap paradigm of exchange coupling. We also brought forth a simplified phenomenological valence bond (VB) model of inter-molecular coupling, which is realized on the background of the VB spin model inside of the aromatic monomers and calibrated with the corresponding ab initio data. As the systems can be considered good candidates with potential applications in spintronics and organic magnetism, the theoretical rationalization opens up prospective ways to realize such promises.

Direct evidence for binding of aluminum to NAP anti-amyloid peptide and its analogs.

NAP (NAPVSIPQ) is a small peptide derived from the activity-dependent neuroprotective protein (ADNP), which provides neuroprotection against amyloid-ß peptide toxicity associated with Alzheimer disease. Several metal ions are able to promote the formation of amyloid-ß peptide oligomers and protofibrils in human brain tissue. Although the relationship between metal ions and amyloid-ß peptide peptides is extensively investigated, that with the NAP peptide is less understood. Nevertheless, our previous research revealed unexpected iron binding to NAP peptide and its analogs. However, a link between aluminum ions, Alzheimer disease and amyloid-ß peptide or NAP peptides still remains controversial. Therefore, we have investigated the possible binding of aluminum ions to NAP peptide and its four analogs. Indeed, MALDI-ToF mass spectrometry (MS), including MS/MS study, and Fourier transform infrared (FT-IR) spectroscopy revealed an unexpected pattern of aluminum ion binding to both NAP peptide and its analogs. Our results have been discussed with respect to NAP protection against Alzheimer disease-related neurotoxicity.

On the Charge-Transfer Excitations in Azobenzene Maleimide Compounds: A Theoretical Study.

Photoswitchable systems with charge-transfer (CT) transitions have gained much attention during the recent years because of their many emerging applications. CT transitions themselves are of fundamental importance from physical, chemical, engineering, and molecular modeling points of view because they depend on the modified intramolecular electronic structure. CT transitions in azobenzene (AB) were observed when substituted with the maleimide (MI) functional group. This work represents a systematic theoretical study of excited states of the AB-MI structures of eight azo derivatives. In addition to the two main azo transitions (π → π* and n → π*), our calculations show a CT occurring between the azo moiety as a donor and the MI group as an acceptor. The CT mechanism can be characterized based on both the number and the position of the MI fragments. MI groups in the azo structure result in low-energy transitions, changing the order of the main transitions by introducing a CT character. Calculations using both density functional theory (DFT) and high-end molecular orbital theories confirm the CT character of these derivatives, although the order of excited states was found to differ depending on the chosen level of theory. We present here the first theoretical investigation of the electronic excited states (nπ*CT and ππ*CT) and corresponding transitions for this class of compounds. The computational results showed that the CT mechanism in AB-MI derivatives can occur via two pathways: planar and twisted. Our findings are expected to be of substantial interest, especially in the area of molecular optoelectronics and in the design of responsive materials.

Adsorptive Performance of Soy Bran and Mustard Husk Towards Arsenic (V) Ions from Synthetic Aqueous Solutions.

Recently, there is growing attention on the use of low-cost sorbents in the depollution of contaminated waters. As a consequence, the present work investigates the potential of soy bran and mustard husk as possible sorbent for the removal of arsenic(V) from residual water. Effects of various operating parameters such as: contact time, pH, initial arsenic concentration, pH, sorbent dose, temperature were investigated to determine the removal efficiency of arsenic(V). Thermodynamic parameters that characterize the process indicated that the adsorption is spontaneous and endothermic. The values for the separation factor, RL were less than one which confirms that the adsorption process was favorable. Equilibrium data fitted well to the Langmuir model with a higher adsorption capacity of soy bran (74.07 mg g-1) towards arsenic(V) ions than mustard husk (65.79 mg g-1). It was found that the pseudo-second order kinetic model was the best applicable model to describe the adsorption kinetic data.

On The Density Functional Theory Treatment of Lanthanide Coordination Compounds: A Comparative Study in a Series of Cu-Ln (Ln = Gd, Tb, Lu) Binuclear Complexes.

The nontrivial aspects of electron structure in lanthanide complexes, considering ligand field (LF) and exchange coupling effects, have been investigated by means of density functional theory (DFT) calculations, taking as a prototypic case study a series of binuclear complexes [LCu(O2COMe)Ln(thd)2], where L2- = N,N'-2,2-dimethyl-propylene-di(3-methoxy-salicylidene-iminato) and Ln = Tb, Lu, and Gd. Particular attention has been devoted to the Cu-Tb complex, which shows a quasi-degenerate nonrelativistic ground state. Challenging the limits of density functional theory (DFT), we devised a practical route to obtain different convergent solutions, permuting the starting guess orbitals in a manner resembling the run of the ß electron formally originating from the f8 configuration of the Tb(III) over seven molecular orbitals (MOs) with predominant f-type character. Although the obtained states cannot be claimed as the DFT computed split of the 7F multiplet, the results are yet interesting numeric experiments, relevant for the ligand field effects. We also performed broken symmetry (BS) DFT estimation of exchange coupling in the Cu-Gd system, using different settings, with Gaussian-type and plane-wave bases, finding a good match with the coupling parameter from experimental data. We also caught BS-type states for each of the mentioned series of different states emulated for the Cu-Tb complex, finding almost equal exchange coupling parameters throughout the seven LF-like configurations, the magnitude of the J parameter being comparable with those of the Cu-Gd system.

Conformational effects on the lowest excited states of benzoyl-pyrrolopyridazine: insights from PCM time-dependent DFT.

Time-dependent density functional theory (TD-DFT) computations and steady-state electronic spectroscopy measurements are performed on two recently synthesized pyrrolopyridazines to account for the detrimental effect of benzoyl substitution on the blue fluorescence emission. In the case of the highly fluorescent ester derivative, planar in ground state, we show that TD-DFT using the PBE0 and B3LYP hybrid functionals in the state-specific solvation approach provides an accurate description of absorption and emission properties. In benzoyl-pyrrolopyridazine, the (pretwisted) orientations of the benzoyl group and the solvent polarity are both found to modulate the nature of the lowest excited states. The first excited state has nπ* character at ground-state geometry of the main conformer (carbonyl group facing the diazine ring) in nonpolar solvents and become nearly degenerate with a ππ* state in polar solvents. The latter, lower than the nπ* state at the ground state geometry of a minor conformer, relaxes into a twisted intramolecular charge transfer. Experimental absorption and excitation spectra are consistent with the conformational-dependent picture of the lowest excited state (as derived from TD-DFT). A rather qualitative agreement in predicting the fluorescence emission wavelength is achieved in computations employing the CAM-B3LYP and BH&HLYP functionals, whereas global hybrids with low or moderate amounts of exact exchange exhibit the expected TD-DFT failure with up to 1 eV underestimated transition energies.

The conformers of 3-fluoroalanine. A theoretical study.

Quantum chemical calculations (DFT, SCS-MP2) show that the relative energies of the four principal alanine conformations are only marginally altered by the introduction of a single fluorine substituent into the methyl group. The fluorine gauche effect and attractive interactions of fluorine to the O-H or N-H moieties (formation of hydrogen bridges) do stabilize particular conformers of 3-fluoroalanine. This is true for the neutral molecule both in the gas phase and in aqueous solution (CPCM-model), but also for the zwitterionic forms and the conformers of the related carboxylate ions and also for the respective ammonium ions in aqueous solution. In water (CPCM calculations), the zwitterion is almost equal in energy to the most stable conformer of the neutral 3-fluoroalanine. Compared to alanine the atomic charges of the amino group and the carboxyl function of 3-fluoroalanine are not significantly influenced by the fluorine at C3, which relates to the fact that both experimental pK(a) values are almost equal for alanine and 3-fluoroalanine.