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Understanding the structure of well-defined anatase TiO 2 surfaces is critical for deciphering site-specific thermal and photoreaction mechanisms on anatase TiO 2 . Using ultrahigh vacuum scanning tunneling microscopy (STM), we have studied the atomic structure of anatase TiO 2 (001) epitaxial thin films grown by oxygen plasma assisted molecular beam epitaxy. Bright rows of the (1×4) reconstructed surface are resolved as three types of features with different sizes. High-resolution STM images taken from the same area at different bias voltages show that these individual features are originated from combinations of two basic atomic building blocks. We propose a modified added molecule model for the anatase TiO 2 (001) surface structure.

Direct imaging of site-specific reactions of individual molecules as a function of temperature has been a long-sought goal in molecular science. Here, we report the direct visualization of molecular coupling of formaldehyde on reduced rutile TiO 2 (110) surfaces as we track the same set of molecules using scanning tunneling microscope (STM) when the temperature is increased from 75 to 170 K. Our previous study showed that formaldehyde preferably adsorbs at bridgingbonded oxygen (O b ) vacancy (V O ) defect site. Herein, images from the same area as the temperature is increased show that V O -bound formaldehyde couples with Ti-bound formaldehyde forming a diolate intermediate. Consequently, exposure of formaldehyde at room temperature leads to diolate as the majority species on the surface and no V O -bound formaldehyde is observed. The diolate species are the key reaction intermediates in the formation of ethylene reported in previous ensemble-averaged studies.

The anticonvulsant gabapentin (GBP) has been shown effective for the treatment of neuropathic pain, although its mechanism of action remains unclear. A recent report has suggested that binding to the ␣ 2 ␦ subunit of voltage-gated calcium channels contributes to its antinociceptive effect, based on the stereoselective efficacy of two analogs: (1S,3R)3-methylgabapentin (3-MeGBP) (IC 50 ϭ 42 nM), which is effective in neuropathic pain models; and (1R,3R)3-MeGBP (IC 50 Ͼ 10,000 nM), which is ineffective (Field et al., 2000). The present study was designed to further examine the profiles of GBP and 3-MeGBP in rat models of acute and persistent pain. Systemic administration of GBP or (1S,3R)3-MeGBP inhibited tactile allodynia in the spinal nerve ligation model of neuropathic pain, whereas (1R,3R)3-MeGBP was ineffective. The antiallodynic effect of GBP, but not (1S,3R)3-MeGBP, was blocked by i.t. injection of the GABA B receptor antagonist [3-[[(3,4-Systemic GBP or (1S,3R)3-MeGBP also inhibited the second phase of formalin-evoked nociceptive behaviors, whereas (1R,3R)3-MeGBP was ineffective. However, both (1S,3R)3-MeGBP and (1R,3R)3-MeGBP, but not GBP, inhibited first phase behaviors. In the carrageenan model of inflammatory pain, systemic GBP or (1R,3R)3-MeGBP failed to inhibit thermal hyperalgesia, whereas (1S,3R)3-MeGBP had a significant, albeit transient, effect. Systemic (1S,3R)3-MeGBP, but not GBP or (1R,3R)3-MeGBP, also produced an antinociceptive effect in the warm water tail withdrawal test of acute pain. These data demonstrate that GBP and 3-MeGBP display different antinociceptive profiles, suggesting dissimilar mechanisms of antinociceptive action. Thus, the stereoselective efficacy of 3-MeGBP, presumably related to ␣ 2 ␦ binding, likely does not completely account for the mechanism of action of GBP.Gabapentin (GBP; Neurontin) is an anticonvulsant that has found increased utility for the treatment of clinical neuropathic pain. Although originally developed for the treatment of spasticity and epilepsy, recent attention has focused on the utility of GBP for the treatment of neuropathic pain based on its efficacy and minimal side-effect profile in clinical trials (Rice and Maton, 2001). In rodent neuropathic pain models, GBP effectively attenuates thermal and mechanical hypersensitivity following peripheral nerve ligation (Xiao and Bennett, 1996;Hunter et al., 1997;Hwang and Yaksh, 1997). GBP has also been shown to inhibit thermal and mechanical hyperalgesia following carrageenan-induced inflammation (Field et al., 1997b;Lu and Westlund, 1999); however, other studies have reported limited effectiveness of GBP for inflammatory pain (Gould et al., 1997;Patel et al., 2001). Additionally, GBP inhibits spontaneous nociceptive behaviors and mechanical hyperalgesia produced by intraplantar formalin or surgical incision, respectively (Field et al., 1997a,b). The antinociceptive effects of GBP in models of neuropathic, inflammatory, and surgical pain appear to be selective for injury-induced hypersensitivity, ...

Chlorohydrocarbons chemisorb dissociatively on Pd surfaces at g200 K and g10 -8 Torr, as shown by high-resolution electron energy loss spectroscopy (HREELS) and C 1s, Cl 2p, and Pd 3d surface core level shifts (SCLS). From CH2Cl2-generated overlayers on Pd(100), hydrogen is removed thermally and carbon is removed by oxidation as CO and CO2, leaving voids between the chlorine (Cl) ensembles that are accessible to other adsorbates. The resulting Cl overlayers are partially ordered depending on initial conditions. The concomitant low-energy electron diffraction (LEED) patterns show that the Cl ensembles are stable to high-temperature reaction cycles. The order-disorder phenomena observed in the temperature range 300-900 K include the generation of domains consisting of Cl only that surround reactive sites of the metal. With CH2Cl2/Pd(100), these domains are formed by lateral packing of 16 Pd/CCl2 units that restrict the supply of O(a) for oxidation of C. Selectivity is switched from CO2 to CO with increasing Cl concentration. Lateral interactions are of two types: mobile O-immobile Cl and mobile O-mobile O. This is reflected in a lowering of the O2 temperature programmed desorption (TPD) maxima with increasing Cl concentration. A statistical-mechanical model is presented for the effects of Cl(a) with phase-equilibration between a dense and a rare phase of O(a).