Exploration of the complex Ni2(MBD)4 (MBD = 2-mercaptobenzimidazole) (C1) having different coordinated Ni atoms as a photocatalyst for hydrogen evolution is made. For comparison, the bimetallic Ni2(MBT)4 (MBT = 2-mercaptobenthiazole) (C2) complex with the same coordinated Ni atoms was synthesized. Both of the complexes have been successfully constructed for photo-induced hydrogen production using organic dyes as photosensitizers and triethanolamine (TEOA) as the effective electron donor by visible light (>400 nm) in acetonitrile-water solution. The time-dependence of H2 generation and DFT computational studies demonstrate that the complex C1 is more active than C2 for H2 evolution. The mechanisms of photocatalytic hydrogen generation for C1 and C2 involve different protonation sites resulting from the differences between the two structures.

The visual information we receive during natural vision changes rapidly and continuously. The visual system must adapt to the spatiotemporal contents of the environment in order to efficiently process the dynamic signals. However, neuronal responses to luminance contrast are usually measured using drifting or stationary gratings presented for a prolonged duration. Since motion in our visual field is continuous, the signals received by the visual system contain an abundance of transient components in the contrast domain. Here using a modified reverse correlation method, we studied the properties of responses of neurons in the cat primary visual cortex to different contrasts of grating stimuli presented statically and transiently for 40 ms, and showed that neurons can effectively discriminate the rapidly changing contrasts. The change in the contrast response function (CRF) over time mainly consisted of an increment in contrast gain (CRF shifts to left) in the developing phase of temporal responses and a decrement in response gain (CRF shifts downward) in the decay phase. When the distribution range of stimulus contrasts was increased, neurons demonstrated decrement in contrast gain and response gain. Our results suggest that contrast gain control (contrast adaptation) and response gain control mechanisms are well established during the first tens of milliseconds after stimulus onset and may cooperatively mediate the rapid dynamic responses of visual cortical neurons to the continuously changing contrast. This fast contrast adaptation may play a role in detecting contrast contours in the context of visual scenes that are varying rapidly.

DJ. Organization of hue selectivity in macaque V2 thin stripes. J Neurophysiol 102: 2603-2615, 2009. First published July 1, 2009. doi:10.1152/jn.91255.2008. V2 has long been recognized to contain functionally distinguishable compartments that are correlated with the stripelike pattern of cytochrome oxidase activity. Early electrophysiological studies suggested that color, direction/disparity, and orientation selectivity were largely segregated in the thin, thick, and interstripes, respectively. Subsequent studies revealed a greater degree of homogeneity in the distribution of response properties across stripes, yet color-selective cells were still found to be most prevalent in the thin stripes. Optical recording studies have demonstrated that thin stripes contain both color-preferring and luminance-preferring modules. These thin stripe color-preferring modules contain spatially organized hue maps, whereas the luminance-preferring modules contain spatially organized luminancechange maps. In this study, the neuronal basis of these hue maps was determined by characterizing the selectivity of neurons for isoluminant hues in multiple penetrations within previously characterized V2 thin stripe hue maps. The results indicate that neurons within the superficial layers of V2 thin stripe hue maps are organized into columns whose aggregated hue selectivity is closely related to the hue selectivity of the optically defined hue maps. These data suggest that thin stripes contain hue maps not simply because of their moderate percentage of hue-selective neurons, but because of the columnar and tangential organization of hue selectivity. I N T R O D U C T I O NEarly electrophysiological studies of area V2 emphasized the segregation of receptive field properties in different cytochrome oxidase stripes. These studies suggested that thin stripes contained color-selective cells, interstripes contained orientation-selective cells, and thick stripes contained disparity and end-stopped cells (e.g., DeYoe and Van Essen 1985;Hubel and Livingstone 1987;Livingstone and Hubel 1988;Shipp and Zeki 2002). Subsequent investigations emphasized a greater homogeneity of neuronal properties across stripes, suggesting that orientation-and color-selective cells were found in nearly equal percentages across all three stripes (Gegenfurtner 2003;Gegenfurtner et al. 1996;Levitt et al. 1994;Shipp and Zeki 2002). In contrast to these electrophysiological findings, optical recordings of intrinsic cortical activity have consistently demonstrated color-preferring modules or hue maps only in thin stripes, orientation-selective modules in both thick and interstripes, and binocular disparity and direction maps only in thick stripes (e.g., Chen et al. 2008;Lu and Roe 2008;Roe and Ts'o 1995;Ts'o et al. 2001;Xiao et al. 2003). If the neuronal selectivity for color, orientation, direction, and/or disparity is largely homogeneous across V2 cytochrome oxidase stripe compartments, why are different feature maps localized to different stripe compartments?In our previo...