Construction of different dimensional inorganic-organic hybrid materials based on polyoxometalates and metal-organic units via changing metal ions: from non-covalent interactions to covalent connections

Five POM-based hybrid materials have been designed and synthesized based on different metal ions under hydrothermal conditions, namely, [Zn(Hfcz)(H(2)O)(3)](H(3)fcz)(SiMo(12)O(40)).3H(2)O (1), [Cd(2)(Hfcz)(6)(H(2)O)(2)](SiMo(12)O(40)).H(2)O (2), [Co(2)(Hfcz)(2)(SiW(12)O(40))](H(3)fcz)(2)(SiW(12)O(40)).10H(2)O (3), [Ni(2)(Hfcz)(4)(H(2)O)(2)](SiW(12)O(40)).5H(2)O (4) and [Ag(4)(Hfcz)(2)(SiMo(12)O(40))] (5), where Hfcz is fluconazole [2-(2,4-difluorophenyl)-1,3-di(1H-1,2,4-triazol-1-yl)propan-2-ol]. Their crystal structures have been determined by X-ray diffraction, elemental analyses, IR spectra, and thermogravimetric analyses (TGA). There are 1D mono and double chain-like metal-organic units in compounds 1 and 2, respectively. Polyoxometalates and metal-organic units co-crystallize through hydrogen bonds. In compound 3, metal-organic sheets are pillared by one kind of polyanion through covalent connections to generate a sandwich double-sheet. The other kind of polyanion acts as a counter-ion and lies in two adjacent sandwich double-sheets through non-covalent interactions. Polyanions covalently link metal-organic sheets to extend to an unusual 3D 5-connected framework with the (4(4).6(6)) topology in 4. In compound 5, polyanions link metal-organic chains to form a sheet through covalent connections. It is interesting that compound 5 shows an intricate (4,5,10)-connected framework with (4(4).6(2))(4)(4(8).6(2))(2)(4(14).6(19).8(12)) topology based on two kinds of Ag cations as four-connected and five-connected nodes, and polyanions as ten-connected nodes, when AgO interactions are considered. It represents the highest connected network topology presently known for polyoxometalate systems. The structural differences among 1-5 indicate the importance of different metal-organic units, coordination modes of polyanions for framework formation, and the interactions between polyanions and metal-organic units. In addition, the luminescent properties of compounds 1, 2 and 5, and electrochemical behaviours of compounds 1-5 have been investigated.     

Molecular simulation study of temperature effect on ionic hydration in carbon nanotubes

Molecular dynamics simulations have been performed to investigate the hydration of Li(+), Na(+), K(+), F(-), and Cl(-) inside the carbon nanotubes at temperatures ranging from 298 to 683 K. The structural characteristics of the coordination shells of ions are studied, including the ion-oxygen radial distribution functions, the coordination numbers, and the orientation distributions of the water molecules. Simulation results show that the first coordination shells of the five ions still exist in the nanoscale confinement. Nevertheless, the first coordination shell structures of cations change more significantly than those of anions because of the preferential orientation of the water molecules induced by the carbon nanotube. The first coordination shells of cations are considerably less ordered in the nanotube than in the bulk solution, whereas the change of the first coordination shell structures of the anions is minor. Furthermore, the confinement induces the anomalous behavior of the coordination shells of the ions with temperature. The first coordination shell of K(+) are found to be more ordered as the temperature increases only in the carbon nanotube with the effective diameter of 1.0 nm, implying the enhancement of the ionic hydration with temperature. This is contrary to that in the bulk solution. The coordination shells of the other four ions do not have such behavior in the carbon nanotube with the effective diameter ranging from 0.73 to 1.00 nm. The easier distortion of the coordination shell of K(+) and the match of the shell size and the nanotube size may play roles in this phenomenon. The exchange of water molecules in the first coordination shells of the ions with the solution and the ion diffusion along the axial direction of the nanotube are also investigated. The mobility of the ions and the stability of the coordination shells are greatly affected by the temperature in the nanotube as in the bulk solutions. These results help to understand the biological and chemical processes at the high temperature.     

Spatial arrangement of alpha-cyclodextrins in a rotaxane. Insights from free-energy calculations

The rotaxane formed by alpha-cyclodextrins (alpha-CDs) threaded onto a poly(ethylene glycol) (PEG) chain was investigated in the gas phase and in an aqueous solution by means of molecular dynamics simulations. The free-energy difference between the three possible spatial arrangements of consecutive alpha-CD--viz.. head-to-head (HH), head-to-tail (HT), and tail-to-tail, was determined using free-energy perturbation calculations. These simulations reveal that the interaction of alpha-CD with the PEG chain is very similar in the two surroundings, whereas the mutual interaction of the macrocycles is stronger in the gas phase than in the aqueous solution. Moreover, difference in the overall interaction appears to stem primarily from changes in the electrostatic contribution. Analysis of intermolecular hydrogen bonds indicates that hydrogen bonds created between alpha-CD and water molecules weaken the hydrogen-bonding interaction of adjacent alpha-CDs. Comparison of the free-energy differences characteristic of the three possible spatial arrangements of contiguous alpha-CDs reveals that the HH motif of the rotaxane is the most stable in the gas phase due to the hydrogen-bond formation between the secondary hydroxyl groups of the two alpha-CDs, and the slight preference for the HT motif in aqueous solution, which can be related to the directionality of the dipole moment borne by the macrocycles in these two motifs.     

A simple and efficient colorimetric anion sensor based on a thiourea group in DMSO and DMSO-water and its real-life application

An efficient colorimetric sensor with a thiourea moiety as binding sites and p-nitrophenylhydrazine as a signaling unit has been synthesized by only one single-step procedure. Selectivity for anions with the distinct geometry (tetrahedral, trigonal planar and spherical) has been investigated in dry DMSO and even in DMSO/H(2)O (95:5, v/v) solutions through the naked-eye experiment, UV-vis titration and (1)H NMR titration techniques. In particular, the fluoride of toothpaste can be detected qualitatively by the sensor 1.     

A convenient one-pot synthesis of 2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives and their further transformations

The trifluoromethyl containing heterocycles, 2-hydroxy-4-aryl-3-(thien-2-oyl)-2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives 4, were synthesized via a one-pot three-component reaction of aldehyde 1 with 1,3-cyclohexanedione 2 and 4,4,4-trifluoro-1-(thien-2-yl)butane-1,3-dione 3 in the presence of a catalytic amount of Et₃N. The effect of bases and solvents on the reaction efficiency and yield was briefly investigated. Treatment of 4 with an excess amount of NH₄OAc in ethanol afforded 2-trifluoromethyl-1H-quinolin-5-one derivatives 5. Refluxing of 4 with TsOH in CHCl₃ gave the corresponding dehydrated products 8.     

Lewis acid-catalyzed Prins-type reactions of methylenecyclopropylcarbinols with aldehydes and aldimines

Lewis acid-catalyzed Prins-type reactions of methylenecyclopropylcarbinols with aldehydes and aldimines proceeded smoothly to give the corresponding 3-oxa-bicyclo[3.1.0]hexane units via 5-exo cyclization in good to high total yields.     

A dynamic lattice searching method with interior operation for unbiased optimization of large Lennard-Jones clusters

For improving the efficiency of dynamic lattice searching (DLS) method for unbiased optimization of large Lennard-Jones (LJ) clusters, a variant of the interior operation (IO) proposed by Takeuchi was combined with DLS. The method is named as DLS-IO. In the method, the IO moves outer atoms with higher energy toward the coordinates center, i.e., (0, 0, 0), of a cluster and a local minimization (LM) follows each IO. This makes the interior atoms more compact and the outer atoms more uniformly distributed with lower potential energy. Therefore, the starting structure for DLS operations is closer to the global optimum compared with the randomly generated structures. On the other hand, a method to identify the central atom is proposed for the central vacancy problem. Optimizations of LJ(500), LJ(561), LJ(660), LJ(665), and LJ(670) were investigated with the DLS-IO, and the structural transition during the optimization was analyzed. It was found that the method is efficient and unbiased for optimization of large LJ clusters, and it may be a promising approach to be universally used for structural optimizations.     

High performance liquid chromatographic method for the determination and pharmacokinetic studies of oxyresveratrol and resveratrol in rat plasma after oral administration of Smilax china extract

A sensitive and simple HPLC method has been developed and validated for the determination of oxyresveratrol (trans-2,4,3',5'-tetrahydroxystilbene, OXY) and resveratrol (trans-3,5,4'-trihydroxystilbene, RES) in rat plasma. The plasma samples were extracted with ethyl acetate and analyzed using HPLC on an Aglient Zorbax SB-C(18) column (250 x 4.6 mm, 5 microm) at a wavelength 320 nm, with a linear gradient of (A) acetonitrile and (B) 0.5% aqueous acetic acid (v/v), at a flow rate of 1.0 mL/min. The method was linear over the range of 0.1265-25.3 microg/mL for OXY and 0.117-23.4 microg/mL for RES. The extraction recovery for OXY, RES and internal standard ranged from 71.1 to 88.3%. The intra- and inter-day precisions were better than 10%, and the accuracy ranged from 89 to 108%. The validated method was used to study the pharmacokinetic profiles of OXY and RES in rat plasma after oral administration of Smilax china root extract.     

Simultaneous determination of cations, zwitterions and neutral compounds using mixed-mode reversed-phase and cation-exchange high-performance liquid chromatography

A novel mixed-mode reversed-phase and cation-exchange high-performance liquid chromatography (HPLC) method is described to simultaneously determine four related impurities of cations, zwitterions and neutral compounds in developmental Drug A. The commercial column is Primesep 200 containing hydrophobic alkyl chains with embedded acidic groups in H(+) form on a silica support. The mobile phase variables of acid additives, contents of acetonitrile and concentrations of potassium chloride have been thoroughly investigated to optimize the separation. The retention factors as a function of the concentrations of potassium chloride and the percentages of acetonitrile in the mobile phases are investigated to get an insight into the retention and separation mechanisms of each related impurity and Drug A. Furthermore, the elution orders of the related impurities and Drug A in an ion-pair chromatography (IPC) are compared to those in the mixed-mode HPLC to further understand the chromatographic retention behaviors of each related impurity and Drug A. The study found that the positively charged Degradant 1, Degradant 2 and Drug A were retained by both ion-exchange and reversed-phase partitioning mechanisms. RI2, a small ionic compound, was primarily retained by ion-exchange. RI4, a neutral compound, was retained through reversed-phase partitioning without ion-exchange. Moreover, the method performance characteristics of selectivity, sensitivity and accuracy have been demonstrated to be suitable to determine the related impurities in the capsules of Drug A.     

A novel catalyst zinc(II) perfluorooctanoate [Zn(PFO)2]-catalyzed three-component one-pot reaction: Synthesis of quinazolinone derivatives in aqueous micellar media

A new type of Lewis acid-surfactant-combined catalyst (LASC), zinc(II) perfluorooctanoate [Zn(PFO)₂], was prepared and applied as a favorable surfactivity catalyst in three-component one-pot cyclocondensation reaction of isatoic anhydride with amines and aldehydes to afford the corresponding quinazolinone derivatives in good yields. Reactions occurred under aqueous micellar media in high atom economy. It was found that this catalyst could be easily quantitatively recovered after the reaction completed and could be reused for at least three cycles without any loss of activity. Furthermore, a mechanism to rationalize the reaction was proposed.