Nanoscopic Channels Research Articles

Interplay of Hydropathy and Heterogeneous Diffusion in the Molecular Transport within Lamellar Lipid Mesophases

Lipid mesophases are being intensively studied as potential candidates for drug-delivery purposes. Extensive experimental characterization has unveiled a wide palette of release features depending on the nature of the host lipids and of the guest molecule, as well as on the environmental conditions. However, only a few simulation works have addressed the matter, which hampers a solid rationalization of the richness of outcomes observed in experiments. Particularly, to date, there are no theoretical works addressing the impact of hydropathy on the transport of a molecule within lipid mesophases, despite the significant fraction of hydrophobic molecules among currently-available drugs. Similarly, the high heterogeneity of water mobility in the nanoscopic channels within lipid mesophases has also been neglected. To fill this gap, we introduce here a minimal model to account for these features in a lamellar geometry, and systematically study the role played by hydropathy and water-mobility heterogeneity by Brownian-dynamics simulations. We unveil a fine interplay between the presence of free-energy barriers, the affinity of the drug for the lipids, and the reduced mobility of water in determining the net molecular transport. More in general, our work is an instance of how multiscale simulations can be fruitfully employed to assist experiments in release systems based on lipid mesophases.

Selectively Enhanced Electrocatalytic Oxygen Evolution within Nanoscopic Channels Fitting a Specific Reaction Intermediate for Seawater Splitting.

Abundant availability of seawater grants economic and resource-rich benefits to water electrolysis technology requiring high-purity water if undesired reactions such as chlorine evolution reaction (CER) competitive to oxygen evolution reaction (OER) are suppressed. Inspired by a conceptual computational work suggestingthat OER is kinetically improved via a double activation within 7Å-gap nanochannels, RuO2 catalysts are realized to have nanoscopic channels at 7, 11, and 14Å gap in average (dgap ), and preferential activity improvement of OER over CER in seawater by using nanochanneled RuO2 is demonstrated. When the channels are developed to have 7Å gap, the OER current is maximized with the overpotential required for triggering OER minimized. The gap value guaranteeing the highest OER activity is identical to the value expected from the computational work. The improved OER activity significantly increases the selectivity of OER over CER in seawater since the double activation by the 7Å-nanoconfined environments to allow an OER intermediate (*OOH) to be doubly anchored to Ru and O active sites does not work on the CER intermediate (*Cl). Successful operation of direct seawater electrolysis with improved hydrogen production is demonstrated by employing the 7Å-nanochanneled RuO2 as the OER electrocatalyst.

Chemorobust 4p-5p {InPb}-organic framework for efficiently catalyzing cycloaddition of CO2 with epoxides and deacetalization-Knoevenagel condensation

Due to that the high charge density and small radius render In3+ cation a stronger Lewis acidity, multifunctional nanoporous In-MOFs have become one of the most promising catalysts for their high activity. Herein, the solvothermal self-assembly by employing 2,4,6-tri (2,4-dicarboxyphenyl)pyridine (H6TDP) as organic linker leads to a robust honeycomb skeleton of {[(CH3)2NH2][InIIIPbII(TDP) (H2O)]⋅3DMF⋅3H2O}n (NUC-52) with the merits of nanoscopic channels, high porosity (61.3%), large specific surface area, and thermal stability. To the best of our knowledge, this is the first 4p-5p heterometallic {InIIIPbII} cluster-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 7-coordinated Pb2+ ions, 4-coordinated In3+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Performed catalytic experiments exhibited that activated NUC-52 owned the high catalytic activity on the cycloaddition reactions of styrene oxide with CO2 under mild conditions with excellent turnover number (2475) and turnover frequency (619 h−1). Moreover, activated NUC-52 could greatly accelerate the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile. Hence, this work lays down the groundwork for constructing heterometallic cluster-based nanoporous MOFs with excellent Lewis acidic catalysis and chemical stability, which should be ascribed to the reasonable coordination arrangement between organic ligands and distinct metal ions according to the hard–soft acid–base (HSAB) theory.

Transparent ultrathin SiO2 nanowire aerogel displaying novel properties when interacting with water: A promising versatile functional platform

With low density, high porosity, and outstanding physicochemical stability, ceramic nanowire aerogels and sponges exhibit various interesting properties. Herein, an ultrathin silica nanowire aerogel (SiO2 NWs-A) was achieved via a facile chemical vapor deposition route. In addition to good mechanical and thermal performances, properties resulting from active water-aerogel interactions are revealed, i.e., outstanding transparency, strong capillary effect, enhanced compressive strength (a reversible strain of ∼62%), switchable wettability and robust shape retention ability when filled with water. The physical mechanism related to these interesting properties is demonstrated basically according to its unique features (distinctly reduced nanowire diameter, enriched nanoscopic gap channels, and reinforced network). To demonstrate the superiority, an advantageous solar vapor generation system (hydrophilic NWs-A/reduced graphene oxide (rGO)/ hydrophobic NWs-A) was obtained by integrating these favorable characteristics, giving rise to remarkably promoted vapor evaporation rate and energy efficiency compared to the rGO hydrophobic NWs-A device. These results contribute to the structural design and functional exploration of nanowire aerogels.

Regulating and Directionally Controlling Electron Emission from Gold Nanorods with Silica Coatings.

Dielectric coatings offer a versatile means of manipulating hot carrier emission from nanoplasmonic systems for emerging nanocatalysis and photocathode applications, with uniform coatings acting as regulators and nonuniform coatings providing directional photocurrent control. However, the mechanisms for electron emission through dense and mesoporous silica (SiO2) coatings require further examination. Here, we present a systematic investigation of photoemission from single gold nanorods as a function of dense versus mesoporous silica coating thicknesses. Studies with dense coatings on gold nanostructures clarify the short (∼1 nm) attenuation length responsible for severely reduced transmission through the silica conduction band. By contrast, mesoporous silica is much more transmissive, and a simple geometric model quantitatively recapitulates the electron escape probability through nanoscopic porous channels. Finally, photoelectron velocity map imaging (VMI) studies of nanorods with coating defects verify that photoemission occurs preferentially through the thinner regions, illustrating new opportunities for designing photocurrent distributions on the nanoscale.

Nanochannel-based {BaZn}-organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation.

Herein, the rare combination of BaII (5s) and ZnII (3d) in the presence of the structure-oriented TDP6- ligand generated the nanochannel-based hybrid material {[(CH3)2NH2]2[BaZn(TDP)(H2O)]·DMF·5H2O}n (NUC-51, H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which possesses excellent physicochemical characteristics such as nanoscopic channels, high porosity, large specific surface area, and high heat/water-resistance. To the best of our knowledge, this is the first 3D [BaIIZnII(CO2)6(H2O)]-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 4-coordinated Zn2+ ions, 7-coordinated Ba2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Catalytic experiments exhibited that activated NUC-51a possesses a high catalytic activity on the cycloaddition reactions of epoxides with CO2 at 55 °C, which can be ascribed to its structural advantages of nanoscale channels and rich bifunctional active sites. Moreover, NUC-51a could significantly accelerate the deacetalization-Knoevenagel condensation reaction in DMSO solvent at 70 °C.

Distinct Chemistries Explain Decoupling of Slip and Wettability in Atomically Smooth Aqueous Interfaces.

Despite essentially identical crystallography and equilibrium structuring of water, nanoscopic channels composed of hexagonal boron nitride and graphite exhibit an order-of-magnitude difference in fluid slip. We investigate this difference using molecular dynamics simulations, demonstrating that its origin is in the distinct chemistries of the two materials. In particular, the presence of polar bonds in hexagonal boron nitride, absent in graphite, leads to Coulombic interactions between the polar water molecules and the wall. We demonstrate that this interaction is manifested in a large typical lateral force experienced by a layer of oriented hydrogen atoms in the vicinity of the wall, leading to the enhanced friction in hexagonal boron nitride. The fluid adhesion to the wall is dominated by dispersive forces in both materials, leading to similar wettabilities. Our results rationalize recent observations that the difference in frictional characteristics of graphite and hexagonal boron nitride cannot be explained on the basis of the minor differences in their wettabilities.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal-Organic Frameworks.

Cyclization of propargylamines with CO2 to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique CuI /CuII mixed valence copper-based framework {[(CuI 6 I5 )Cu3 II L6 (DMA)3 ](NO3 )⋅9DMA}n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO2 , and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h-1 , which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO2 without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between CuI /CuII and uncoordinated amino groups promotes highly efficient and green conversion of CO2 . Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO2 source.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal–Organic Frameworks

AbstractCyclization of propargylamines with CO2 to obtain 2‐oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble‐metal catalysts with organic bases as co‐catalysts under harsh conditions. We have synthesized a unique CuI/CuII mixed valence copper‐based framework {[(CuI6I5)Cu3IIL6(DMA)3](NO3)⋅9DMA}n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO2, and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h−1, which is much higher than that of reported noble‐metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO2 without solvents and co‐catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between CuI/CuII and uncoordinated amino groups promotes highly efficient and green conversion of CO2. Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO2 source.

Cytokinins Stimulate Plasmodesmatal Transport in Leaves.

Plant cells are connected by plasmodesmata (PD), nanoscopic channels in cell walls that allow diverse cytosolic molecules to move between neighboring cells. PD transport is tightly coordinated with physiology and development, although the range of signaling pathways that influence PD transport has not been comprehensively defined. Several plant hormones, including salicylic acid (SA) and auxin, are known to regulate PD transport, but the effects of other hormones have not been established. In this study, we provide evidence that cytokinins promote PD transport in leaves. Using a green fluorescent protein (GFP) movement assay in the epidermis of Nicotiana benthamiana, we have shown that PD transport significantly increases when leaves are supplied with exogenous cytokinins at physiologically relevant concentrations or when a positive regulator of cytokinin responses, ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 5 (AHP5), is overexpressed. We then demonstrated that silencing cytokinin receptors, ARABIDOPSIS HISTIDINE KINASE 3 (AHK3) or AHK4 or overexpressing a negative regulator of cytokinin signaling, AAHP6, significantly decreases PD transport. These results are supported by transcriptomic analysis of mutants with increased PD transport (ise1–4), which show signs of enhanced cytokinin signaling. We concluded that cytokinins contribute to dynamic changes in PD transport in plants, which will have implications in several aspects of plant biology, including meristem patterning and development, regulation of the sink-to-source transition, and phytohormone crosstalk.

Confined Water's Dielectric Constant Reduction Is Due to the Surrounding Low Dielectric Media and Not to Interfacial Molecular Ordering.

Liquid water confined within nanometer-sized channels exhibits a surprisingly low dielectric constant along the direction orthogonal to the channel walls. This is typically assumed to result from a pronounced heterogeneity across the sample: the dielectric constant would be bulk-like everywhere except at the interface, where it would be dramatically reduced by strong restrictions on interfacial molecules. Here we study the dielectric properties of water confined within graphene slit channels via classical molecular dynamics simulations. We show that the permittivity reduction is not due to any important alignment of interfacial water molecules, but instead to the long-ranged anisotropic dipole correlations combined with an excluded-volume effect of the low-dielectric confining material. The bulk permittivity is gradually recovered only over several nanometers due to the impact of long-range electrostatics, rather than structural features. This has important consequences for the control of, e.g., ion transport and chemical reactivity in nanoscopic channels and droplets.

Novel Synthetic Nanopores for Single-Molecule Biosensing Applications

Studying biomolecular systems at the single-molecule level in contrast to the ensemble-averaged measurement approaches has opened a new era in probing structural and dynamic properties of biomolecules. Nanopore biosensing technology (the youngest in this family) has been developed over the past two decades as a label-free, single-molecule sensing platform for biopolymers and small molecules. In nanopore-based sensing, as a biomolecule is pulled through a nanoscopic channel, either within a protein assembly embedded in an organic membrane (biological nanopore) or a synthetically-fabricated channel in a solid-state membrane (solid-state nanopore), partial physical obstruction of the pore is detected as a characteristic transient disruption in the ionic current. These signals are then compiled and statistical analysis is used to probe structural elements of the biomolecules. in solid-state nanopores, the total sensing resolution of a nanopore is defined by the geometry of the pore, i.e., a nanopore with diameter and thickness comparable to the structural element of the biomolecule being studied is required for the highest sensing resolution. Therefore, ultra-thin membranes of two-dimensional (2D) materials provide the highest resolution possible, surpassing that of protein nanopores, owing to their single or a few-atomic-layer thickness. Herein, we investigate the application of freestanding thin membranes of MXenes, an emerging family of 2D materials with a layered structure of transition metals carbides, nitrides, or carbonitrides, in nanopore technology. For biomolecular sensing, the synthetic membrane is fabricated in wafer-scale by the precise self-assembly of one-nanometer-thick MXene sheets. In addition, by harnessing the unique electrical and electrochemical properties of MXenes and their versatile chemistry to modify some fundamental components and characteristics of a traditional nanopore's sensing modality to eliminate the adverse effect of access resistance on smearing the sensing resolution, our proposed MXene-based nanopore platform could outperform existing nanopore sensing paradigms.

Highly Robust 3s-3d {CaZn}-Organic Framework for Excellent Catalytic Performance on Chemical Fixation of CO2 and Knoevenagel Condensation Reaction.

In terms of ligand-directed synthetic strategy, multifunctional metal-organic frameworks (MOFs) could be assembled by employing organic ligands with nitrogen-containing heterocycles, which could serve as Lewis base sites in crystallized porous frameworks. Here, the acidic one-pot hydrothermal reaction of CaCl2, Zn(NO3)2, and 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) generates one robust honeycomb-shaped double-walled material of {[(CH3)2NH2]2[CaZn(TDP)(H2O)]·3DMF·3H2O}n (NUC-21), which has the excellent physicochemical characteristics of nanoscopic channels, high porosity (58.3%), large specific surface area, and high heat/water-resisting property. To the best of our knowledge, this is the first 3s-3d dinuclear [CaZn(CO2)6(OH2)]-based nanoporous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including four-coordinated Zn2+ ions, four-coordinated Ca2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. As expected, because of the coexistence of Lewis acid-base nature, desolvated NUC-21 displays satisfactory catalytic activity on the chemical cycloaddition of various epoxides with CO2 into the corresponding alkyl carbonates under comparatively mild conditions. Furthermore, the efficient conversion of benzaldehydes and malononitrile confirms that NUC-21 is simultaneously a bifunctional heterogeneous catalyst for Knoevenagel condensation reactions. Hence, the achievements broaden the way for assembling nanoporous multifunctional MOFs by employing ligand-directed synthetic strategy, which can accelerate the transformation from simple structural research to socially demanding applications.

Scale Effects in Nanoscale Heat Transfer for Fourier's Law in a Dissimilar Molecular Interface.

The dependence of the heat transfer of a nanoscopic liquid channel residing at the solid–liquid interface is traditionally ascribed to the temperature jump, interfacial thermal resistance, wettability, and heat flux. Other contributions stemming from the channel width dependence such as the boundary position are typically ignored. Here, we conducted nonequilibrium molecular dynamics simulations to better understand the relation between channel width and boundary positions located at the solid–liquid interface. The system under investigation is a simple liquid confined between the solid from nanochannels of different sizes (3.27–7.35 nm). In this investigation, the existence of the correlation between the boundary position and the channel width is observed, which follows an exponential function. The thermal conductivity of the boundary positions is compared with the experimental value and Green–Kubo prediction to verify the actual boundary position. Atomistic simulation reveals that the solid–liquid boundary position, which matches the experimental value of thermal conductivity, varies with the channel width because of the intermolecular force and the phonon mismatch of the solid and the liquid.

Fast Switching of Bright Whiteness in Channeled Hydrogel Networks.

Beside pigment absorption and reflection by periodic photonic structures, natural species often use light scattering to achieve whiteness. Synthetic hydrogels offer opportunities in stimuli‐responsive materials and devices; however, they are not conventionally considered as ideal materials to achieve high whiteness by scattering due to the ill‐defined porosities and the low refractive index contrast between the polymer and water. Herein, a poly(N‐isopropylacrylamide) hydrogel network with percolated empty channels (ch‐PNIPAm) is demonstrated to possess switchable bright whiteness upon temperature changes, obtained by removing the physical agarose gel in a semi‐interpenetrating network of agarose and PNIPAm. The hydrogel is highly transparent at room temperature and becomes brightly white above 35 °C. Compared to conventional PNIPAm, the ch‐PNIPAm hydrogel exhibits 80% higher reflectance at 800 nm and 18 times faster phase transition kinetics. The nanoscopic channels in the ch‐PNIPAm facilitate water diffusion upon phase transition, thus enabling the formation of smaller pores and enhanced whiteness in the gel. Furthermore, fast photothermally triggered response down to tens of milliseconds can be achieved. This unique property of the ch‐PNIPAm hydrogel to efficiently scatter visible light can be potentially used for, e.g., smart windows, optical switches, and, as demonstrated in this report, thermoresponsive color displays.

Monte Carlo simulation of the implantation profile of e+ in nanochanneled silicon

The process of implantation and diffusion of positron in nanochanneled silicon crystals has been simulated in detail through the Monte Carlo technique. Our implantation simulations evidenced the fraction of empty volume inside the sample to be the decisive factor in the determination of the shape of the implantation profile, with the specific shape of the nanoscopic structure playing a marginal role for implantation processes with an energy above 3 keV. Moreover we observed that, due to the high density of surfaces inside of the silicon sample, the subsequent diffusion process is highly suppressed and that thermalized positrons reach the surface of a nanoscopic channel close to their implantation depth. Due to this suppression of the diffusion process, 60–80% of the positrons implanted at an energy comprised between 4 and 13 keV will reach, at thermal energy, the surface of a channel without escaping the sample or undergoing annihilation.

Electrical Spin Injection and Detection in Silicon Nanowires with Axial Doping Gradient.

The interest in spin transport in nanoscopic semiconductor channels is driven by both the inevitable miniaturization of spintronics devices toward nanoscale and the rich spin-dependent physics the quantum confinement engenders. For such studies, the all-important issue of the ferromagnet/semiconductor (FM/SC) interface becomes even more critical at nanoscale. Here we elucidate the effects of the FM/SC interface on electrical spin injection and detection at nanoscale dimensions, utilizing a unique type of Si nanowires (NWs) with an inherent axial doping gradient. Two-terminal and nonlocal four-terminal lateral spin-valve measurements were performed using different combinations from a series of FM contacts positioned along the same NW. The data are analyzed with a general model of spin accumulation in a normal channel under electrical spin injection from a FM, which reveals a distinct correlation of decreasing spin-valve signal with increasing injector junction resistance. The observation is attributed to the diminishing contribution of the d-electrons in the FM to the injected current spin polarization with increasing Schottky barrier width. The results demonstrate that there is a window of interface parameters for optimal spin injection efficiency and current spin polarization, which provides important design guidelines for nanospintronic devices with quasi-one-dimensional semiconductor channels.

Modulation of Ionic Conductivity of Lipid Bilayer-Based Nanoscopic Channels by Pre-adsorbed Charged Macromolecules as a Tool for their Detection and Quantification

Investigation of transport phenomena in the nanoscopic channels (pores) having the characteristic cross dimension of less than 100 nm is of utmost importance for diverse areas of applied biology, medicine and technology. One of the mainstream lines of development of nanofluidic systems and applications today is creation of biosensors capable of sensing single molecules and manipulating them in a controllable manner. Molecules can be detected based on the measurements of ionic currents through appropriately sized channels: entry into a channel of a molecule with the effective cross-dimension comparable to that of the channel lumen is accompanied by decrease of the ionic current recorded at a given transmembrane potential. The transport properties of such channels can be modulated by coating their walls with lipid bilayers, two-dimensional fluids capable of sustaining transport processes within them. In our present work, we made use of this property of the membranes to develop a method for detecting and controllably transporting single-stranded DNA molecules through channels formed by lipid membrane cylinders with the luminal radius of 5-7 nm. Entry of a DNA molecule into such a channel in the conditions of low (∼10 mM) ion strength proved to be accompanied by detectable increase of its ionic conductivity in a manner dependent on the direction of the electric field gradient. The amplitude of the conductivity increment can be credibly used to quantify the number the DNA molecules within the channel. Besides that, adsorption of DNA molecules on the lipid bilayer surface was shown to render the membrane cylinder the properties of a voltage-dependent channel with ion selectivity. The work was financially supported by the Russian Science Fund No 17-75-30064.

Block Copolymer-Templated Approach to Nanopatterned Metal-Organic Framework Films.

The fabrication of patterned metal-organic framework (MOF) films with precisely controlled nanoscale resolution has been a fundamental challenge in nanoscience and nanotechnology. In this study, nanopatterned MOF films were fabricated using a layer-by-layer (LBL) growth method on functional templates (such as a bicontinuous nanoporous membrane or a structure with highly long-range-ordered nanoscopic channels parallel to the underlying substrate) generated by the microphase separation of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymers. HKUST-1 can be directly deposited on the templates without any chemical modification because the pyridine groups in P2VP interact with metal ions via metal-BCP complexes. As a result, nanopatterned HKUST-1 films with feature sizes below 50 nm and controllable thicknesses can be fabricated by controlling the number of LBL growth cycles. The proposed fabrication method further extends the applications of MOFs in various fields.

Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights.

Proton transfer in the nanoscopic water channels of polyelectrolyte fuel cell membranes was studied using a photoacid, 8-hydroxypyrene-1,3,6-trisulfonic acid sodium salt (HPTS), in the channels. The local environment of the probe was determined using 8-methoxypyrene-1,3,6-trisulfonic acid sodium salt (MPTS), which is not a photoacid. Three fully hydrated membranes, Nafion (DuPont) and two 3M membranes, were studied to determine the impact of different pendant chains and equivalent weights on proton transfer. Fluorescence anisotropy and excited state population decay data that characterize the local environment of the fluorescent probes and proton transfer dynamics were measured. The MPTS lifetime and anisotropy results show that most of the fluorescent probes have a bulk-like water environment with a relatively small fraction interacting with the channel wall. Measurements of the HPTS protonated and deprotonated fluorescent bands' population decays provided information on the proton transport dynamics. The decay of the protonated band from ∼0.5 ns to tens of nanoseconds is in part determined by dissociation and recombination with the HPTS, providing information on the ability of protons to move in the channels. The dissociation and recombination is manifested as a power law component in the protonated band fluorescence decay. The results show that equivalent weight differences between two 3M membranes resulted in a small difference in proton transfer. However, differences in pendant chain structure did significantly influence the proton transfer ability, with the 3M membranes displaying more facile transfer than Nafion.