Adsorptive removal of phenol from aqueous solution with zeolitic imidazolate framework-67.

ZIF-67(zinc-methylimidazolate framework-67), one of the zeolitic imidazolate frameworks (ZIFs), was used for the removal of phenol from aqueous solutions via adsorption and shows high adsorption capacity for phenol. The thermodynamic and kinetic adsorption behavior of ZIF-67 for phenol in water with concentration ranging from 50 to 300 ppm were investigated in a batch reactor and a ZIF-67 packed column, respectively. The effects of pH, contact time, zeta potential of the adsorbent and temperature on the adsorption behavior were evaluated, and the results demonstrated that the adsorption is primarily brought about by a specific favorable interaction (electrostatic interaction) between phenol and ZIF-67 surface. The suitability of the Langmuir adsorption model to the equilibrium data was investigated for each phenol-adsorbent system, which the results showed that the equilibrium data for all the phenol-sorbent systems fitted the Langmuir model. Thermodynamic parameters such as Gibbs free energy are calculated from the experimental data at different temperatures. The adsorbent could be perfectly regenerated at 120 °C with little loss in the adsorption ability.

Mechanism of photoisomerization of 1-naphthyl-2-phenylethylenes in organic glasses.

Photoisomerization reactions of cis isomers of 1-beta-naphthyl-2-phenylethylene, an o-methylated homolog and 1-alpha-naphthyl-2-phenylethylene in organic glasses at liquid nitrogen temperature were studied. Reactions were followed by changes in UV-absorption spectra of the irradiated samples. Formation of an unstable trans-photoproduct was detected only with the o-methylated homolog. The results are consistent with high regioselective Hula-twist photoisomerization at the benzylic sites of the three compounds examined. Calculated data on relative energies of the conformers of both the cis and the trans isomers are in agreement with the suspected conformational population of the starting materials and the photoproducts.

Mechanisms of photoisomerization of polyenes in confined media: from organic glasses to protein binding cavities.

Photochemical reactivities of model organic systems (stilbene and diphenylbutadiene) in organic glasses were first examined and compared with those in solution and in organized media. These observations were in turn compared with reactivities of polyene chromophores in protein binding cavities (specifically PYP, rhodopsin and bacteriorhodopsin). The obvious conclusion is that the preference for the most volume-conserving Hula-twist mechanism isomerization in organic glasses is because of the close interaction between the guest and the host molecules. In organized media (zeolites, crystals and protein binding cavities), the residual empty space coupled with any specific guest-host interactions that are characteristic of a given system, could lead to involvement of the more volume-demanding one-bond-flip (i.e. torsional relaxation) or bicycle-pedal or an extended HT process in photoisomerization.

Spectroscopic and computational studies on the coordination-driven self-assembly complexes (ZnL)2 and (NiL)2 [L= bis(2,4-dimethyldipyrrin-3-yl)methane].

FT-IR, FT-Raman and electronic absorption spectroscopies were utilized in conjunction with density functional theory (DFT) calculations to investigate the ground and excited states of self-assembled dinuclear dimeric helicates (ZnL)2 and (NiL)2 [L = bis(2,4-dimethyldipyrrin-3-yl)methane]. These studies afford a detailed description of the ground-state geometric and electronic structures of (ZnL)2 and (NiL)2 and provide a comparison with similar geometrical metal-porphyrins. The results demonstrate that enlarging the basis set used in the DFT calculations results in an obvious alteration of the calculated bond lengths but negligible alteration of the calculated bond angles. The predicted spectra are in good agreement with the experimental ones with the deviations generally less than 30 cm(-1). In comparison with vibrational spectra of metal-porphyrins, the breathing vibration of the pyrrole ring is shifted by over 100 cm(-1) toward higher wavenumber due to local conjugation of molecular geometry. Time-dependent density functional theory (TD-DFT) provides a good description of the excitation energy. Because of the break in symmetry, the absorption band (corresponding to the Q-band of porphyrin) of (ZnL)2 and (NiL)2 is no longer weak. Local conjugation makes the absorption wavelength of (NiL)2 and (ZnL)2 shift to the blue compared with those of NiP and ZnP.

Stilbene analogs in Hula-twist photoisomerization.

Photoisomerization of several cis- or Z-stilbene analogs and two E-analogs in low temperature organic glasses was examined. From a mechanistic view-point, the compounds can be divided into three types: (i) those giving identical Hula-twist (HT) and one-bond-flip (OBF) products, (ii) those giving a single HT product that is different (hence distinguishable) from the OBF product and (iii) those showing two distinct HT processes but only one OBF process. Examples for all three types of analogs are provided emphasizing the most informative Type-II (stilbene analogs with identical but unsymmetrically substituted phenyl rings), including linear as well as conformationally constrained compounds. Conditions necessary for establishing HT and OBF processes are defined. Proper choice and design of model systems are essential for establishing or eliminating HT mechanism(s) of isomerization.

Self-preservation and structural transition of gas hydrates during dissociation below the ice point: an in situ study using Raman spectroscopy.

The hydrate structure type and dissociation behavior for pure methane and methane-ethane hydrates at temperatures below the ice point and atmospheric pressure were investigated using in situ Raman spectroscopic analysis. The self-preservation effect of sI methane hydrate is significant at lower temperatures (268.15 to 270.15 K), as determined by the stable C-H region Raman peaks and AL/AS value (Ratio of total peak area corresponding to occupancies of guest molecules in large cavities to small cavities) being around 3.0. However, it was reduced at higher temperatures (271.15 K and 272.15 K), as shown from the dramatic change in Raman spectra and fluctuations in AL/AS values. The self-preservation effect for methane-ethane double hydrate is observed at temperatures lower than 271.15 K. The structure transition from sI to sII occurred during the methane-ethane hydrate decomposition process, which was clearly identified by the shift in peak positions and the change in relative peak intensities at temperatures from 269.15 K to 271.15 K. Further investigation shows that the selectivity for self-preservation of methane over ethane leads to the structure transition; this kind of selectivity increases with decreasing temperature. This work provides new insight into the kinetic behavior of hydrate dissociation below the ice point.

Changes in functional connectivity of ventral anterior cingulate cortex in heroin abusers.

BACKGROUND: Previous studies with animal experiments, autopsy, structural magnetic resonance imaging (MRI) and task-related functional MRI (fMRI) have confirmed that brain functional connectivity in addicts has become impaired. The goal of this study was to investigate the alteration of resting-state functional connectivity of the ventral anterior cingulate cortex (vACC) in the heroin abusers' brain. METHODS: Fifteen heroin abusers and fifteen matched healthy volunteers were studied using vACC as the region-of interest (ROI) seed. A 3.0 T scanner with a standard head coil was the imagining apparatus. T2*-weighted gradient-echo planar imaging (GRE-EPI) was the scanning protocol. A ROI seed based correlation analysis used a SPM5 software package as the tool for all images processing. RESULTS: This study showed a functional connection to the insula vACC in heroin abusers. Compared with controls, heroin users showed decreased functional connectivity between the nucleus accumbens (NAc) and vACC, between the parahippocampala gyrus/amgdala (PHC/amygdala) and vACC, between the thalamus and vACC, and between the posterior cingulated cortex/precuneus (PCC/pC) and vACC. CONCLUSION: The altered resting-state functional connectivity to the vACC suggests the neural circuitry on which the addictive drug has an affect and reflects the dysfunction of the addictive brain.

The role of organic glasses in cis/trans photoisomerization at low temperatures.

Low temperature photoisomerization of stilbene and 1,4-diphenyl-1,3-butadiene derivatives was found to vary depending on the organic glass employed in such studies. Examination of the combined results showed that the variation was more likely to arise from the rigidity of the organic glass at the temperature of irradiation rather than the composition of the organic glass; that is, the observed results are consistent with the possible softening of the glass that surrounds the excited substrate in the same manner as detected in the photolysis of ethyl iodide reported by Porter and co-workers. These observations successfully account for the apparent "disagreement" of reports from the Hawaii and the Florida State groups on the mechanism of photoisomerization in low temperature glasses.

New aspects of diphenylbutadiene photochemistry. Regiospecific hula-twist photoisomerization.

In EPA glass at liquid nitrogen temperature, the E,E isomer of diphenylbutadiene (DPB) was photostable, while both the Z,E and Z,Z isomers underwent selective HT isomerization at center 1 giving the stable conformer of the double-bond isomerized trans product. That HT-1 was involved rather than the OBF process was shown by results of o,o'-dimethyl-DPB. Formation of unstable trans product corresponded to simultaneous configurational and conformational isomerization. The regioselectivity was found not sensitive to a substituent effect, as shown by the similar reactivity in p,p'- or o,o'-bistrifluoromethyl-DPB.

Steric effects in hula-twist photoisomerization. 1,4-dimethyl- and 2,3-dimethyl-1,4-diphenylbutadienes.

1,4-Dimethyl-1,4-diphenylbutadiene was shown to be able to execute regiospecific HT-1 photoisomerization around a methyl group when irradiated in a low-temperature organic glass, albeit at reduced efficiency. 2,3-Dimethyl-1,4-diphenylbutadiene exhibited a different type of steric effect, causing the E,E-isomer to undergo regiospecific HT-1 photoisomerization.