Strong chromate-adsorbent based on pyrrolic nitrogen structure: An experimental and theoretical study on the adsorption mechanism.

Chromate is considered a toxic contaminant in various water sources because it poses a risk to animal and human health. To meet the stringent limits for chromium in water and wastewater, pyrrolic nitrogen structure was investigated as a chromate adsorbent for aqueous solutions, employing a polypyrrole coating on carbon black. The characteristics of the adsorbent were analyzed by high-resolution transmission electron microscopy, energy-filtered transmission electron microscopy, and X-ray photoelectron spectroscopy. Chromate was adsorbed as both Cr(III) and Cr(VI). The chromate adsorption capacity increased (from 50.84 to 174.81 mg/g) with increasing amounts of pyrrole monomers (from 50 to 86%) in the adsorbent. The adsorption capacity was well-correlated with the pyrrolic nitrogen content (from 2.06 to 6.57 at%) in the adsorbent, rather than other types of nitrogen. The optimized adsorption capacity (174.81 mg/g in the equilibrium batch experiment and 211.10 mg/g at an initial pH of 3) was far superior to those of conventional adsorbents. We investigated the mechanism behind this powerful chromate adsorption on pyrrolic nitrogen via physical/chemical analyses of the pH-dependent adsorption behavior, supported by first-principles calculation based on density functional theory. We found that Cr(III) and Cr(VI) adsorption followed different reaction paths. Cr(III) adsorption occurred in two sequential steps: 1) A Jones oxidation reaction (JOR)-like reaction of Cr(VI) with pyrrolic N that generates Cr(III), and 2) Cr(III) adsorption on the deprotonated pyrrolic N through Cr(III)-N covalent bonding. Cr(VI) adsorption followed an alternative path: hydrogen-bonding to the deprotonation-free pyrrolic N sites. The pH-dependent fractional deprotonation of the pyrrolic N sites by the JOR-like reaction in the presence of chromate played an important role in the adsorption.

Theoretical prediction of the complexation behaviors of antitumor platinum drugs with cucurbiturils.

The inclusion complex formation ability between CB[n] (n = 6-9) and Pt-drugs (oxaliplatin, nedaplatin, carboplatin, and cisplatin) in gas phase as well as water phases has been investigated using the using density functional theory. The results reveal the existence of several stable inclusion complexes in aqueous solution with high solvation energies compared to the guest and host molecule. It has been shown that the formation of complexes between CB[6] and Pt-drugs resulted in structural change in the CB[6], with the calculated deformation energies being higher for the inclusion complexes. The inclusion complexes are stabilized by the hydrogen bonding and the charge transfer between the Pt-drugs and the CB[n] host. Calculated enthalpy and Gibbs free energy of formation in aqueous solution revels that the formation of CB[7]-oxaliplatin is spontaneous, and hence its experimental synthesis is feasible. Among the CB's studied, CB[8]-Pt-drug inclusion complexes have exothermic enthalpy and low Gibbs free energy of formation. Computed (1)NMR spectra in CB[7]-oxaliplatin showed high chemical shielding for the cyclohexane ring, indicating the existence of charge transfer in the inclusion complex. The amine protons in the guest Pt-drugs are shielded due to the hydrogen bonding interaction with CB's oxygen portal.

Modular, homochiral, porous coordination polymers: rational design, enantioselective guest exchange sorption and ab initio calculations of host-guest interactions.

Two new, homochiral, porous metal-organic coordination polymers [Zn(2)(ndc){(R)-man}(dmf)]⋅3DMF and [Zn(2)(bpdc){(R)-man}(dmf)]⋅2DMF (ndc=2,6-naphthalenedicarboxylate; bpdc=4,4'-biphenyldicarboxylate; man=mandelate; dmf=N,N'-dimethylformamide) have been synthesized by heating Zn(II) nitrate, H(2)ndc or H(2)bpdc and chiral (R)-mandelic acid (H(2)man) in DMF. The colorless crystals were obtained and their structures were established by single-crystal X-ray diffraction. These isoreticular structures share the same topological features as the previously reported zinc(II) terephthalate lactate [Zn(2)(bdc){(S)-lac}(dmf)]⋅DMF framework, but have larger pores and opposite absolute configuration of the chiral centers. The enhanced pores size results in differing stereoselective sorption properties: the new metal-organic frameworks effectively and stereoselectively (ee up to 62 %) accommodate bulkier guest molecules (alkyl aryl sulfoxides) than the parent [Zn(2)(bdc){(S)-lac}(dmf)]⋅DMF, while the latter demonstrates decent enantioselectivity toward precursor of chiral anticancer drug sulforaphane, CH(3)SO(CH(2))(4)OH. The new homochiral porous metal-organic coordination polymers are capable of catalyzing a highly selective oxidation of bulkier sulfides (2-NaphSMe (2-C(10)H(7)SMe) and PhSCH(2)Ph) that could not be achieved by the smaller-pore [Zn(2)(bdc){(S)-lac}(dmf)]⋅DMF. The sorption of different guest molecules (both R and S isomers) into the chiral pores of [Zn(2)(bdc){(S)-lac}(dmf)]⋅DMF was modeled by using ab initio calculations that provided a qualitative explanation for the observed sorption enantioselectivity. The high stereo-preference is accounted for by the presence of coordinated inner-pore DMF molecule that forms a weak C-H...O bond between the DMF methyl group and the (S)-PhSOCH(3) sulfinyl group.

Titanium-doped nickel clusters TiNi(n) (n = 1-12): geometry, electronic, magnetic, and hydrogen adsorption properties.

Using the first principles method, we study the growth behavior and electronic and magnetic properties of TiNi(n) (n = 1-12) clusters to clarify the effect of Ti modulation on the nickel nanostructures. Furthermore, chemisorption of H(2) was studied to understand the chemical reactivity of H(2) on the small Ni- and Ti-doped Ni clusters. The calculations are performed using the plane wave pseudopotential approach under the density functional theory and generalized gradient approximation for the exchange and correlation functional. The optimized geometries of TiNi(n-1) clusters indicate that the substitution of Ti brings a substantial structural reconstruction from 3D structure to a layer structure in which Ti atom is found to coordinate with Ni atoms to a maximum extent. This is accompanied by a significant enhancement in binding energies and reduction in chemical reactivity. Furthermore, the magnetic moments of the small Ti-doped Ni clusters are quenched because of the antiferromagnetic alignment of the Ti electrons. The lowest-energy structure of H(2) chemisorbed on Ni clusters shows that hydrogen prefers to adsorb on the edge site with two hydrogen atoms on these clusters in neighboring sites as the preferred arrangement. The incorporation of Ti atom improves the chemisorption energy of Ni clusters. Bader charge analysis indicates that with the formation of metal hydride, the H atoms withdraw charges from the metal centers, making them lose an electron, and carry a positive charge over them. Furthermore, Ti doping is found to enhance the chemical reactivity of Ni clusters.