Dynamics in hydrophilic and hydrophobic molecular chains tethered to MCM41-type mesoporous silica upon wetting and dehydration processes.

Surface modified mesoporous silica materials are important materials for heterogeneous catalysis and are attracting attention as potential drug carriers. The functionality of these materials relies on the physical and chemical properties of the tethers attached to MCM41 silica surface. These chemically linked tails act as molecular brushes, that can capture pollutant molecules, anchor points for catalysts and can host drug molecules. To utilize the full potential of the tailored silica surfaces, one should infer their properties at different levels of solvation. Here, 1H MAS NMR spectroscopy is used to monitor the dynamic properties of two modified MCM41 materials, an aminopropyl tethered MCM41 and an octyl tethered MCM41, through the process of controlled hydration. The surface site resolved measurements demonstrate how the chemical nature of the two tethers governs the way water molecules are directed to the different sites in the porous materials.

Slow oscillations in neural networks with facilitating synapses.

The synchronous oscillatory activity characterizing many neurons in a network is often considered to be a mechanism for representing, binding, conveying, and organizing information. A number of models have been proposed to explain high-frequency oscillations, but the mechanisms that underlie slow oscillations are still unclear. Here, we show by means of analytical solutions and simulations that facilitating excitatory (E(f)) synapses onto interneurons in a neural network play a fundamental role, not only in shaping the frequency of slow oscillations, but also in determining the form of the up and down states observed in electrophysiological measurements. Short time constants and strong E(f) synapse-connectivity were found to induce rapid alternations between up and down states, whereas long time constants and weak E(f) synapse connectivity prolonged the time between up states and increased the up state duration. These results suggest a novel role for facilitating excitatory synapses onto interneurons in controlling the form and frequency of slow oscillations in neuronal circuits.

Short-term synaptic plasticity orchestrates the response of pyramidal cells and interneurons to population bursts.

The synaptic drive from neuronal populations varies considerably over short time scales. Such changes in the pre-synaptic rate trigger many temporal processes absent under steady-state conditions. This paper examines the differential impact of pyramidal cell population bursts on post-synaptic pyramidal cells receiving depressing synapses, and on a class of interneuron that receives facilitating synapses. In experiment a significant shift of the order of one hundred milliseconds is seen between the response of these two cell classes to the same population burst. It is demonstrated here that such a temporal differentiation of the response can be explained by the synaptic and membrane properties without recourse to elaborate cortical wiring schemes. Experimental data is first used to construct models of the two types of dynamic synaptic response. A population-based approach is then followed to examine analytically the temporal synaptic filtering effects of the population burst for the two post-synaptic targets. The peak-to-peak delays seen in experiment can be captured by the model for experimentally realistic parameter ranges. It is further shown that the temporal separation of the response is communicated in the outgoing action potentials of the two post-synaptic cells: pyramidal cells fire at the beginning of the burst and the class of interneuron receiving facilitating synapses fires at the end of the burst. The functional role of such delays in the temporal organisation of activity in the cortical microcircuit is discussed.