Activation Energy For Motion Research Articles

Nearly Barrierless Polarization Switching Mechanisms in ZrO2 Having Perpendicular In-Plane Domain Walls.

The polarization switching mechanism in ferroelectric ZrO2 involves the nucleation and subsequent migration of nonpolar domain boundaries; however, the fundamental mechanism driving this process remains inadequately understood. The present study introduces a mechanism for nearly barrierless polarization switching in 180° domain walls, facilitated by a the half-unit-cell nonpolar phase between oppositely polarized domains. Based on density functional theory (DFT) calculations, two types of 180° domain walls are explored, featuring head-to-head and tail-to-tail polarization boundaries, with nonpolar orthorhombic Pbcm and tetragonal P42/nmc phases as the respective domain walls. The calculations reveal exceptionally low energy barriers of 17.5 and 10.1 meV for migrating these Pbcm and P42/nmc boundaries by half a unit cell through the domains. An evaluation of the impact of defects on domain wall motion is achieved by introducing 2% oxygen vacancies or 3% Si doping, which induces a significant increase in the barrier motion activation energy, suggesting that defects serve as barriers to polarization switching.

Dynamics of Polyalkylfluorene Conjugated Polymers: Insights from Neutron Spectroscopy and Molecular Dynamics Simulations.

The dynamics of the conjugated polymers poly(9,9-dioctylfluorene) (PF8) and poly(9,9-didodecylfluorene) (PF12), differing by the length of their side chains, is investigated in the amorphous phase using the temperature-dependent quasielastic neutron scattering (QENS) technique. The neutron spectroscopy measurements are synergistically underpinned by molecular dynamics (MD) simulations. The probe is focused on the picosecond time scale, where the structural dynamics of both PF8 and PF12 would mainly be dominated by the motions of their side chains. The measurements highlighted temperature-induced dynamics, reflected in the broadening of the QENS spectra upon heating. The MD simulations reproduced well the observations; hence, the neutron measurements validate the MD force fields, the adopted amorphous model structures, and the numerical procedure. As the QENS spectra are dominated by the signal from the hydrogens on the backbones and side chains of PF8 and PF12, extensive analysis of the MD simulations allowed the following: (i) tagging these hydrogens, (ii) estimating their contributions to the self-part of the van Hove functions and hence to the QENS spectra, and (iii) determining the activation energies of the different motions involving the tagged hydrogens. PF12 is found to exhibit QENS spectra broader than those of PF8, indicating a more pronounced motion of the didodecyl chains of PF12 as compared to dioctyl chains of PF8. This is in agreement with the outcome of our MD analysis: (i) confirming a lower glass transition temperature of PF12 compared to PF8, (ii) showing PF12 having a lower density than PF8, and (iii) highlighting lower activation energies of the motions of PF12 in comparison with PF8. This study helped to gain insights into the temperature-induced side-chain dynamics of the PF8 and PF12 conjugated polymers, influencing their stability, which could potentially impact, on the practical side, the performance of the associated optoelectronic active layer.

Mechanically Interlocked Polymers with Dense Mechanical Bonds.

ConspectusMechanically interlocked polymers (MIPs) such as polyrotaxanes and polycatenanes are polymer architectures that incorporate mechanical bonds, which represent a compelling frontier in polymer science. MIPs with cross-linked structures are known as mechanically interlocked networks (MINs) and are widely utilized in materials science. Leveraging the motion of mechanical bonds, MINs hold the potential for achieving a combination of robustness and dynamicity. Currently, the reported MINs predominantly consist of networks with discrete mechanical bonds as cross-linking points, exemplified by well-known slide-ring materials and rotaxane/catenane cross-linked polymers. The motion of these mechanically interlocked cross-linking points facilitates the redistribution of tension throughout the network, effectively preventing stress concentration and thereby enhancing material toughness. In these instances, the impact of mechanical bonds can be likened to the adage "small things can make a big difference", whereby a limited number of mechanical bonds substantially elevate the mechanical performance of conventional polymers. In addition to MINs cross-linked by mechanical bonds, there is another type of MIN in which their principal parts are polymer chains composed of dense mechanical bonds. Within these MINs, mechanical bonds generally serve as repeating units, and their unique properties stem from integrating and amplifying the function of a large amount of mechanical bonds. Consequently, MINs with dense mechanical bonds tend to reflect the intrinsic properties of mechanical interlocked polymers, making their exploration critical for a comprehensive understanding of MIPs. Nevertheless, investigations into MINs featuring dense mechanical bonds remain relatively scarce.This Account presents a comprehensive overview of our investigation and insights into MINs featuring dense mechanical bonds. First, we delve into the synthetic strategies employed to effectively prepare MINs with dense mechanical bonds, while critically evaluating their advantages and limitations. Through meticulous control of the core interlocking step, three distinct strategies have emerged: mechanical interlocking followed by polymerization, supramolecular polymerization followed by mechanical interlocking, and dynamic interlocking. Furthermore, we underscore the structure-property relationships of MINs with dense mechanical bonds. The macroscopic properties of MINs originate from integrating and amplifying countless microscopic motions of mechanical bonds, a phenomenon we define as an integration and amplification mechanism. Our investigation has revealed detailed motion characteristics of mechanical bonds in bulk mechanically interlocked materials, encompassing the quantification of motion activation energy, discrimination of varying motion distances, and elucidation of the recovery process. Additionally, we have elucidated their influence on the mechanical performance of the respective materials. Moreover, we have explored potential applications of MINs, leveraging their exceptional mechanical properties and dynamicity. These applications include enhancing the toughness of conventional polymers, engineering mechanically adaptive and multifunctional aerogels, and mitigating Li protrusion as interfacial layers in lithium-ion batteries. Finally, we offer our personal perspectives on the promises, opportunities, and key challenges in the future development of MINs with dense mechanical bonds, underscoring the potential for transformative advancements in this burgeoning field.

Similarities and Differences among Protein Dynamics Studied by Variable Temperature Nuclear Magnetic Resonance Relaxation.

Understanding and describing the dynamics of proteins is one of the major challenges in biology. Here, we use multifield variable-temperature NMR longitudinal relaxation (R1) measurements to determine the hierarchical activation energies of motions of four different proteins: two small globular proteins (GB1 and the SH3 domain of α-spectrin), an intrinsically disordered protein (the C-terminus of the nucleoprotein of the Sendai virus, Sendai Ntail), and an outer membrane protein (OmpG). The activation energies map the motions occurring in the side chains, in the backbone, and in the hydration shells of the proteins. We were able to identify similarities and differences in the average motions of the proteins. We find that the NMR relaxation properties of the four proteins do share similar features. The data characterizing average backbone motions are found to be very similar, the same for methyl group rotations, and similar activation energies are measured. The main observed difference occurs for the intrinsically disordered Sendai Ntail, where we observe much lower energy of activation for motions of protons associated with the protein-solvent interface as compared to the others. We also observe variability between the proteins regarding side chain 15N relaxation of lysine residues, with a higher activation energy observed in OmpG. This hints at strong interactions with negatively charged lipids in the bilayer and provides a possible mechanistic clue for the "positive-inside" rule for helical membrane proteins. Overall, these observations refine the understanding of the similarities and differences between hierarchical dynamics in proteins.

High-temperature electrical energy storage performances of dipolar glass polymer nanocomposites filled with trace ultrafine nanoparticles

• PEI dipolar glasses with high T g and -CF 3 or -SO 2 - are synthesized rationally. • Trace ultrafine nanoparticles enhance permittivity markedly and keep low loss. • A mechanism of the enhancement is proposed in terms of mobility of dipolar groups. • The nanocomposites exhibit excellent high-temperature energy storage performances. The urgent demand for high-temperature dielectrics toward capacitive energy storage arises from numerous emerging harsh-environment high-temperature applications such as electric vehicles, aerospace power conditioning, downhole oil explorations. For these applications, it is imperative to enhance the discharge energy density of polymer-based dielectrics at elevated temperature. Herein, a trace composite approach is proposed and demonstrated. Two types of polyetherimides (PEIs)-based dipolar glasses are designed, synthesized and composited with trace amount of ultrafine Al 2 O 3 nanoparticles. PEIs-based dipolar glasses with high T g (~250 °C) and much enhanced electrical polarization are constructed by introducing dipolar groups (-CF 3 ) and sulfonyl groups (-SO 2 -) with high dipolar moment (~4.30 D) in the polymer chains. The incorporation of ultrafine Al 2 O 3 nanoparticles increases the electrical polarization and keeps low loss. The remarkable permittivity enhancement via the ultrafine filling could be ascribed to more active mobility of dipolar groups characterized by activation energy of movement and the correlation of arrangement of dipolar groups in the chains with this effect is also revealed. These results will contribute to deeply understanding and rationally designing high-performance polymer-based nanocomposites orienting to high-temperature electrical energy storage.

Local Structure and Dynamics in Methylammonium, Formamidinium, and Cesium Tin(II) Mixed-Halide Perovskites from 119Sn Solid-State NMR.

Organic–inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability in comparison to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a 119Sn solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of 119Sn can span 6 orders of magnitude in this class of compounds, which makes judicious choice of experimental NMR parameters essential for the reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/Cl compositions. We elucidate the degradation pathways of Cs-, MA-, and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar products, regardless of the A-site cation and halide. We detect the presence of metallic tin among the degradation products, which we suggest could contribute to the previously reported high conductivities in tin(II) halide perovskites. 119Sn NMR chemical shifts are a sensitive probe of the halide coordination environment as well as of the A-site cation composition. Finally, we use variable-temperature multifield relaxation measurements to quantify ion dynamics in MASnBr3 and establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact.

Quantitative analysis of local fine structure on diffusion of point defects in passive film on Ti

The diffusion of point defects in passivation determines all physico-electrochemical processes in materials corrosion and protection. In this study, a multiscale quantitative methodology was developed to reveal the diffusivity of oxygen vacancies on titanium surface (～5.0 nm thickness) in 1.0 M H2SO4 solution based on X-ray absorption fine structure (XAFS), combining with electrochemical impedance spectroscopy (EIS) and Mott-Schottky. EIS equivalent circuit exhibits that the high electronic field across passive film is 1.06 × 106 V cm–1. Mott-Schottky space charge capacitance indicates n-type semiconducting film with the donor density of ～1021 cm–3. Three important structure parameters have been firstly proposed from XAFS theoretical calculation at Ti K-edge to quantitatively describe the point defects transport between metal/film/solution interfaces. The half-jump distance equals half Ti–Ti distance subtly changing with oxidation potentials. The coordination coefficient is defined as the probability of activation jump from Ti–O coordination. And the Debye-Waller factor of structure disorder is related to the donor density of Mott-Schottky. Overall, the diffusivity of oxygen vacancies is in the range of (1.84–4.71) × 10–17 cm2 s–1 under the electric field, which determines the interfacial equilibrium of passivation and dissolution during potentiodynamic polarization. And the activation energy for motion has a minimum of 0.89 eV at 1.5 V. This multiscale quantitative methodology predicts well the potential dependent steady-state in the corrosive system.

Bridging Structural and Dynamical Models of a Confined Sodium Nitroprusside Complex

Sodium nitroprusside (SNP), an active pharmaceutical ingredient, is encapsulated in biocompatible amorphous silica matrices and characterized by solid-state NMR. Through complementary NMR and pair distribution function (PDF) study, we previously showed that when confined in 1–2 nm sized nanopores of an amorphous silica matrix, the complex displays a “liquid like” isotropic motion (NMR) but still retains an associated anion/cation preferential arrangement (PDF). In this study, we present new insights into the physical state of the confined drug to explain the coexistence of these two seemingly contradictory characteristics. By performing temperature-dependent T1 relaxation experiments on the samples with different hydration levels, we retrieve respective motional activation energies for all three guest species inside the pores (sodium cations, nitroprusside anions, and water). For the hydrated samples, we identify a temperature range where results ascertain isotropic but correlated ionic motion of the SNP ...

Can Multielectron Intercalation Reactions Be the Basis of Next Generation Batteries?

Intercalation compounds form the basis of essentially all lithium rechargeable batteries. They exhibit a wide range of electronic and crystallographic structures. The former varies from metallic conductors to excellent insulators. The latter often have layer structures or have open tunnel structures that can act as the hosts for the intercalation of a wide range of metal cation and other guest species. They are fascinating materials with almost infinitely variable properties, with the crystal structure controlling the identity and the amount of the guest species that may be intercalated and subsequently removed. The electronic structure controls not only the degree of electron transfer to the host, but also defines the degree of the electrostatic interactions a mobile ion experiences; thus, a metallic host will provide a minimizing of those interactions, whereas in an ionic lattice the interactions will be much greater and the mobile ion will experience a much higher activation energy for motion. This becomes more important for multivalent cations such as Mg2+. Today's lithium batteries are limited in capacity, because less than one lithium ion is reversibly intercalated per transition metal redox center. There may be an opportunity to increase the storage capacity by utilizing redox centers that can undergo multielectron reactions. This might be accomplished by intercalating multiple monovalent cations or one multivalent cation. In this Account, we review the key theoretical and experimental results on lithium and magnesium reversible intercalation into two prototypical materials: titanium disulfide, TiS2, and vanadyl phosphate, VOPO4. Both of these materials exist in two or more phases, which have different molar volumes and/or dimensionalities and thus are expected to show a range of diffusion opportunities for battery active guest ions such as lithium, sodium, and magnesium. One major conclusion of this Account is that reversibly intercalating two lithium ions into a host lattice while maintaining its crystal structure is possible. A second major conclusion is that theoretical studies are now sufficiently mature that they can be relied upon to predict the key free energy values of simple intercalation reactions, i.e., the energy that might be stored. This could help to focus future choices of battery couples. In hindsight, theory would have predicted that magnesium-based intercalation cells are not a viable electrochemical option, relative to lithium cells, from either power or energy density considerations. However, the fundamental study of such reactions will lead to a better understanding of intercalation reactions in general, and of the critical importance of crystal structure in controlling the rates and degree of chemical reactions.

Effect of quenching method on Li ion conductivity of Li5La3Bi2O12 solid state electrolyte

Effect of the quenching method on conductivity of Li5La3Bi2O12 ceramics prepared by sol-gel process was studied. In a synthesis process, lithium hydroxide, acetic bismuth, and acetic lanthanum were used as starting materials, while water was used as solvent. The temperature to synthesize the high density Li5La3Bi2O12 with cubic garnet type structure is 750°C for 8h in air with 10% excess lithium salt. The samples were prepared by the same synthesis route with the only difference from cooling methods. The samples were characterized by XRD, SEM, 6Li MAS NMR and ionic conductivity measurement. The XRD patterns of Li5La3Bi2O12 ceramics showed that there was a single phase oxides with garnet-like structure by the furnace cooling and the quenching method. The Li5La3Bi2O12 electrolyte by the furnace cooling exhibits the highest total ionic conductivity of 2.0×10−5Scm−1 at 22°C, and that by the quenching method exhibits the highest conductivity of 2.0×10−4Scm−1 with a motional activation energy of 0.36eV, which is an order of magnitude higher than that by the furnace cooling. The reason is that the relative density of Li5La3Bi2O12 by the quenching method is higher than that by the furnace cooling. The SEM images are also shown that the density of Li5La3Bi2O12 is very high by the quenching method and there exists lots of pores by the furnace cooling. And the 6Li-MAS-NMR results indicate the Li5La3Bi2O12 samples by the quenching method possess high Li ion mobility.

Synthesis and Ion Conductivity of Li7La3Nb2O13 Ceramics with Cubic Garnet-Type Structure

In the paper, the synthesis and transport properties of the Li7La3Nb2O13 compounds by a solid state reaction are reported for the first time. The optimized conditions to synthesize the Li7La3Nb2O13 ceramics is 1175°C for 24 h with 10% excess lithium salt. The refined lattice constant is 12.8207 Å. Qualitative phase analysis by X-ray powder diffraction patterns combined with the Rietveld method reveals garnet type compounds as major phases. Lithium ion conductivity of Li7La3Nb2O13 was studied by AC impedance method. Li7La3Nb2O13 ceramics exhibits the highest total ionic conductivity of 2.2 × 10−5 S cm−1 at room temperature with a motional activation energy of 0.39 eV. The SEM images of surface and cross-sections for sintered Li7La3Nb2O13 pellets are shown that their density is also very high.

ЯКР 35CL И ЗАТОРМОЖЕННАЯ ПОДВИЖНОСТЬ В МОЛЕКУЛЯРНОМ КОМПЛЕКСЕ CL2·БЕНЗОЛ

Temperature dependences of the resonance frequency and the spin-lattice relaxation time of the chlorine nuclei are investigated in the equimolecular addition compound of chlorine with benzene in the temperature range between 77 K and the melting point. The experimental data reveal a complex picture of thermally activated molecular motion involving both components of this compound. At temperatures 77–130 K the quadrupole relaxation is determined by the action of three types of molecular motions: 1– background molecular librations, 2– reorientational movement of the benzene rings, modulating the electric field gradient at the chlorine nuclei, created by donor-acceptor interaction of the partner molecules, and 3– reorientational movement of the chlorine molecules at a rate less than the NQR frequency, causing the broadening of the 35 Cl spectral line and its fading out at 130 K. In this temperature region consistent separation of the respective contributions to the chlorine relaxation rate is made and the quantitative parameters of the movements defined. At higher temperatures, the development of hindered rotation of the chlorine molecules leads to the appearance of the resonance signal again at 150 K to ~4 MHz lower in frequency, and the relaxation time of the chlorine nuclei increases with increasing temperature. Both these facts indicate that the reorientation rate of the chlorine molecules becomes much higher than the nuclear quadrupole resonance frequency. By analogy with the known NQR data for 1,2-dichloroethane these results show that the “fast” reorientation of the chlorine molecule occurs about the axis that forms the angle ~14° with the Cl–Cl direction. The spin-lattice relaxation time of the chlorine nuclei, as measured in the field of both “slow” and “fast” reorientations, revealed that the activation energy of motion in these areas varies considerably (~22.5 kJ/mol and ~6.2 kJ/mol, respectively). The set of obtained data allows to conclude that at the temperatures 130–150 K in the sample, apparently, there are structural changes, leading to a sharp change in the mobility of the chlorine molecules. Received 0 7 .0 6 .201 6 ; accepted 23 .0 6 .201 6

Evaluation of Dislocation Mobility in Wurtzite Semiconductors

ABSTRACTThe indentation hardness and yield strength of various wurtzite-structured semiconductors, such as AlN, GaN, InN, and ZnO, were summarized together with those of 6H-SiC. From analysis of the data, the activation energy for motion of an individual dislocation was deduced to be 2–2.7 and 0.7–1.2 eV in GaN and ZnO, respectively, and the evaluated activation energy for dislocation motion showed a dependence on the dislocation energy in the minimum length. The results were evaluated in terms of homology and the basic mechanism of the dislocation process. Dislocation motion is thought to be primarily controlled by the atomic bonding character of the semiconductors.

Water rotation barriers on protein molecular surfaces

The experimental characterization of hindered-rotation barriers and mapping the energetic heterogeneity of water molecules bound to the molecular “surface” of proteins is critical for understanding the functional interaction of proteins with their environment. Here, we show how to achieve this goal by an original wide-line NMR procedure, which is based on the spectral motional narrowing phenomenon following the melting (thawing) process of interfacial ice. The procedure highlights the differences between globular and intrinsically disordered proteins and it enables to delineate the effect of solvent on protein structure, making a distinction between point mutants, monomeric and oligomeric states, and characterizing the molecular interactions taking part in different cellular processes. We put this unique experimental approach introducing novel physical quantities and quantifying the heterogeneous distribution of motional activation energy of water in the interfacial landscape into a historical perspective, demonstrating its utility through a variety of globular and disordered proteins.

Magnetic flux creep in HTSC films

In weak magnetic fields, precision measurements of the magnetic moment relaxation in thin epitaxial films YBa2Cu3O7−δ are performed. The exponents µ of the dependence of the vortex motion activation energy on the current are determined in a wide temperature range. Despite the low vortex density, the data obtained indicate the collective nature of their creep, which is probably caused by the strong interaction of vortices through the space surrounding the film.

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide)-based lithium polyether-ester-sulfonate ionomers

Nuclear magnetic resonance spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. (1)H and (7)Li spin-lattice relaxation times (T(1)) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T(1) values along with the presence of minima in T(1) as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similar activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though lithium hopping is about ten times slower than the segmental motion. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and quasi-elastic neutron scattering experiments.

Use of B2O3 to improve Li+-ion transport in LiTi2(PO4)3-based ceramics

Substitution of B for Ti in Li1+xTi2−xBx(PO4)3 introduces x mobile Li+ ions per formula unit in the solid-station range 0<x≤0.2. The B2O3 is also an aid to sintering dense ceramics with more uniform particle size. With x=0.2, the room-temperature Li+-ion conductivity is σLi=2.0×10−4Scm−1 with a motional activation energy of 0.48eV. For x>0.2, an intergranular B2O3-rich second phase impedes intergranular Li+-ion transport.

Nuclear quadrupole resonance and thermally activated molecular mobility in solids: Reorientations of symmetric molecular species and pseudorotation in trigonal-bipyramidal molecules

The specific features revealed in the behavior of temperature dependences of the spin-lattice relaxation time t 1 of quadrupole nuclei involved in different types of thermally activated motions in crystals have been analyzed under the assumption that there exists a temperature dependence of the activation energy of motion. An expression for the spin-lattice relaxation rate has been obtained. This expression includes the effect under consideration and provides an adequate explanation for numerous anomalies in the behavior of the experimental dependences t 1(T), which were revealed in the case of the motion of molecular fragments with a relatively large volume. A nontraditional method for evaluating the activation energy of motion under these conditions has been proposed.

Proton transport in doped La-metaphosphate glasses

The electrical properties of [La (1 − x) M x ]–P 3O 9 metaphosphate glasses, where M is Ba, Sr, Ca, and 0 ≤ x ≤ 0.8 were investigated in the 300–500 °C range. The protonic conductivity increases two orders of magnitude from the unsubstituted to the 60% substituted glass reaching a maximum conductivity of about 10 − 5 S/cm at 450 °C. The activation energy is found to be approximately independent of concentration though dependent on the type of modifying substitutional cation, and decreases from about 1.04 eV for Ca and Sr to ∼ 0.96 eV for Ba. AC impedance measurements were used to find the DC ionic conductivities. Mean ion travel distances at the frequencies, ν Ζ * or ν Μ *, associated with the maximum in Z″ or M″ were found to be up to 30 times larger than the average oxygen spacing in the glasses. While diffusion coefficients derived from conductivities, D σ , were vastly lower than an uncorrelated diffusion coefficient computed from first principles, the travel distance at ν Z * or ν Z * derived from a simple random walk expression using D Γ , was surprisingly close to those derived from the more rigorous statistical treatments. The ratio ξ = D σ / D Γ ≪ 1 may be interpreted as indicative of highly correlated ion motion and strongly reduced mean attempt frequencies, together with a mean activation energy for motion increased by Δ E = E σ − E Γ over that of the uncorrelated intertetrahedral motion of an ideal crystal characterized by D Γ .

Effects of amantadine on the dynamics of membrane-bound influenza A M2 transmembrane peptide studied by NMR relaxation

The molecular motions of membrane proteins in liquid-crystalline lipid bilayers lie at the interface between motions in isotropic liquids and in solids. Specifically, membrane proteins can undergo whole-body uniaxial diffusion on the microsecond time scale. In this work, we investigate the (1)H rotating-frame spin-lattice relaxation (T (1rho)) caused by the uniaxial diffusion of the influenza A M2 transmembrane peptide (M2TMP), which forms a tetrameric proton channel in lipid bilayers. This uniaxial diffusion was proved before by (2)H, (15)N and (13)C NMR lineshapes of M2TMP in DLPC bilayers. When bound to an inhibitor, amantadine, the protein exhibits significantly narrower linewidths at physiological temperature. We now investigate the origin of this line narrowing through temperature-dependent (1)H T (1rho) relaxation times in the absence and presence of amantadine. Analysis of the temperature dependence indicates that amantadine decreases the correlation time of motion from 2.8 +/- 0.9 mus for the apo peptide to 0.89 +/- 0.41 micros for the bound peptide at 313 K. Thus the line narrowing of the bound peptide is due to better avoidance of the NMR time scale and suppression of intermediate time scale broadening. The faster diffusion of the bound peptide is due to the higher attempt rate of motion, suggesting that amantadine creates better-packed and more cohesive helical bundles. Analysis of the temperature dependence of ln(T_1rho(-1)) indicates that the activation energy of motion increased from 14.0 +/- 4.0 kJ/mol for the apo peptide to 23.3 +/- 6.2 kJ/mol for the bound peptide. This higher activation energy indicates that excess amantadine outside the protein channel in the lipid bilayer increases the membrane viscosity. Thus, the protein-bound amantadine speeds up the diffusion of the helical bundles while the excess amantadine in the bilayer increases the membrane viscosity.