Does water suffer from claustrophobia? The local structural and dynamic properties of water in confined (300–4000 nm) spaces were characterized by an NMR study of the size‐dependent relaxation phenomena, which in turn reflect changes in water mobility and proton transfer. The results are important for understanding fluidics in extended nanospaces and in implementing micro‐/nanofluidic devices.

We fabricated an NMR cell equipped with 10-100 nm scale spaces on a glass substrate (called extended nanospaces), and investigated molecular structure and dynamics of water confined in the extended nanospaces by (1)H NMR chemical shift (delta(H)) and (1)H and (2)H NMR spin-lattice relaxation rate ((1)H- and (2)H-1/T(1)), (1)H NMR spin-spin relaxation rate ((1)H-1/T(2)), and (1)H NMR rotating-frame spin-lattice relaxation rate ((1)H-1/T(1rho)) measurements of H(2)O and (2)H(2)O. The delta(H) and (1)H- and (2)H-1/T(1) results showed that size-confinement produces slower translational motions and higher proton mobility of water, but does not affect the hydrogen-bonding structure and rotational motions. Such unique phenomena appeared in the space size of 40 to 800 nm. However, the (1)H-1/T(1) value at 40 nm was still different from that in 4 nm porous nanomaterial, because translational and rotational motions were inhibited for H(2)O molecules in the nanomaterial. By examining temperature- and deuterium-dependence of the (1)H-1/T(1) values, the molecular translational motions of the confined water were found to be controlled by protonic diffusion invoking a proton hopping pathway between adjacent water rather than hydrodynamic translational diffusion. Furthermore, we clarified that proton exchange between adjacent water molecules in extended nanospaces could be enhanced by the chemical exchange of protons between water and SiOH groups on glass surfaces, ( identical with SiO(-)...H(+)...H(2)O) + H(2)O --> triple bond SiO(-) + (H(3)O(+) + H(2)O) --> triple bond SiO(-) + (H(2)O + H(3)O(+)), based on (1)H-1/T(2) measurements. An enhancement of proton exchange rate of water due to the reduction of space sizes was verified from the results of (1)H-1/T(1rho) values, and the rate of water in the 100 nm sized spaces is larger by a factor of more than ten from that of bulk water. Such size-confinement effects were distinctly observed for hydrogen-bond solvents with strong proton-donating ability, while they did not appear for aprotic and nonpolar solvent cases. Based on these NMR results, we suggested that an intermediate phase, in which protons migrate through a hydrogen-bonding network and the water molecules are loosely coupled within 50 nm from the surface, exists mainly in extended nanospaces. This model could be supported by a three-phase theory based on the weight average of three phases invoking the bulk, adsorbed, and intermediate phases.

A novel air-pressure-based nanofluidic control system was developed and its performance was examined. We found that the flow in a 100 nm scale nanochannel on a chip (called an extended nanospace channel) could be controlled within the pressure range of 0.003-0.4 MPa, flow rate range of 0.16-21.2 pL/min, and residence time range of 24 ms-32.4 s by using the developed nanofluidic control system. Furthermore, we successfully demonstrated an enzyme reaction in which the fluorogenic substrate TokyoGreen-beta-galactoside (TG-beta-gal) was hydrolyzed to the fluorescein derivative TokyoGreen (TG) and beta-galactose by the action of beta-galactosidase enzyme as a calalyst in a Y-shaped extended nanospace channel. The parameters for the reaction kinetics, such as K(m), V(max) and k(cat), were estimated for the nanofluidic reaction, and these values were compared with the results of bulk and microfluidic reactions. A comparison showed that the enzyme reaction rate in the Y-shaped extended nanospace channel increased by a factor of about two compared with the rates in the bulk and micro spaces. We thought that this nanospatial property resulted from the activated protons of water molecules in the extended nanospace. This assumption was supported by the result that the pH dependence of the maximum enzyme activity in the Y-shaped extended nanospace channel was slightly different from that in the bulk and micro spaces.