Proton Motion Research Articles

Antimicrobial and Conductive Nanocellulose-Based Films for Active and Intelligent Food Packaging.

Bacterial nanocellulose (BNC) is becoming an important substrate for engineering multifunctional nanomaterials with singular and tunable properties for application in several domains. Here, antimicrobial conductive nanocomposites composed of poly(sulfobetaine methacrylate) (PSBMA) and BNC were fabricated as freestanding films for application in food packaging. The nanocomposite films were prepared through the one-pot polymerization of sulfobetaine methacrylate (SBMA) inside the BNC nanofibrous network and in the presence of poly(ethylene glycol) diacrylate as cross-linking agent. The ensuing films are macroscopically homogeneous, more transparent than pristine BNC, and present thermal stability up to 265 °C in a nitrogen atmosphere. Furthermore, the films have good mechanical performance (Young’s modulus ≥ 3.1 GPa), high water-uptake capacity (450–559%) and UV-blocking properties. The zwitterion film with 62 wt.% cross-linked PSBMA showed bactericidal activity against Staphylococcus aureus (4.3–log CFU mL−1 reduction) and Escherichia coli (1.1–log CFU mL−1 reduction), and proton conductivity ranging between 1.5 × 10−4 mS cm−1 (40 °C, 60% relative humidity (RH)) and 1.5 mS cm−1 (94 °C, 98% RH). Considering the current set of properties, PSBMA/BNC nanocomposites disclose potential as films for active food packaging, due to their UV-barrier properties, moisture scavenging ability, and antimicrobial activity towards pathogenic microorganisms responsible for food spoilage and foodborne illness; and also for intelligent food packaging, due to the proton motion relevant for protonic-conduction humidity sensors that monitor food humidity levels.

Proton conductivity in a hureaulite-type compound, Mn5[(PO4)2(PO3(OH))2](HOH)4

The manganese endmember of hureaulite (Mn-hureaulite, Mn2+5(PO4)2(PO3(OH))2(HOH)4 with a minor trace of Sr2+) was synthesized under various hydrothermal conditions to yield high-quality crystals up to 1 mm in length. The deuterated samples were investigated using high-resolution neutron powder diffraction (HRNPD) at 12 K and 298 K to understand the proton conductivity in the context of dynamically disordered hydrogen bond networks (DDHBN). Results from Rietveld analysis on HRNPD data combined with bond valence sum (BVS) mismatch landscapes and maximum-entropy methods (MEM) revealed protonic motions confined by two semihelical chains as a DDHBN within 8-membered ring channels running along the crystallographic c axis. A DC bulk conductivity value of 4.5x10-5 Scm-1 at 498 K was evaluated from the high-frequency (HF) relaxation mode in impedance spectroscopy (IS) of Mn-hureaulite powder samples. IS spectra acquired at 398-498 K were fitted to two serially connected RC-circuits, equivalent to inter- and intragrain charge transport. A low activation energy of 0.31(3) eV between 398 K and 473 K indicates the ease of site-exchanging protons over DDHBN in the title compound.

Quantum Trajectory Dynamics Based on Local Approximations to the Quantum Potential and Force.

The quantum nature of nuclei often affects molecular structure and properties, which are associated with the motion of protons and other light nuclei at low temperature. However, incorporation of the nuclear quantum effects into theoretical studies of large molecular systems is an outstanding challenge in theoretical chemistry. In this paper, the de Broglie-Bohm formulation of the time-dependent Schrödinger equation is used as a framework for the development of approximate quantum corrections to the dynamics of a trajectory ensemble, representing a time-dependent wave function. Specifically, the trajectory-centered local Least Square Fit (L-LSF) to the trajectory attributes is introduced, formally analyzed and illustrated on model potentials, typically used to benchmark approximate and semiclassical dynamics methods. The L-LSF method improves the dynamics accuracy, compared to the globally defined approximations, developed previously, and is shown to converge to the exact (generally impractical for large systems) limit of quantum dynamics.

Measurement of the Spin Tune Using the Coherent Spin Motion of Polarized Protons in a Storage Ring.

This Letter reports the first spin tune measurement at high energies (24 and 255GeV) with a driven coherent spin motion. To maintain polarization in a polarized proton collider, it is important to know the spin tune of the polarized proton beam, which is defined as the number of full spin precessions per revolution. A nine-magnet spin flipper has demonstrated high spin-flip efficiency in the presence of two Siberian snakes [H. Huang etal., Phys. Rev. Lett. 120, 264804 (2018).10.1103/PhysRevLett.120.264804]. The spin flipper drives a spin resonance with a given frequency (or tune) and strength. When the drive tune is close to the spin tune, the proton spin direction is not vertical anymore, but precesses around the vertical direction. By measuring the precession frequency of the horizontal component, the spin tune can be precisely measured. A driven coherent spin motion and fast turn-by-turn polarization measurement are keys to the measurement. The vertical spin direction is restored after turning the spin flipper off and the polarization value is not affected by the measurement. The fact that this manipulation preserves the polarization makes it possible to measure the spin tune during the operation of a high energy accelerator.

Emergence of correlated proton tunnelling in water ice.

Several experimental and theoretical studies report instances of concerted or correlated multiple proton tunnelling in solid phases of water. Here, we construct a pseudo-spin model for the quantum motion of protons in a hexameric H2O ring and extend it to open system dynamics that takes environmental effects into account in the form of O-H stretch vibrations. We approach the problem of correlations in tunnelling using quantum information theory in a departure from previous studies. Our formalism enables us to quantify the coherent proton mobility around the hexagonal ring by one of the principal measures of coherence, the l 1 norm of coherence. The nature of the pairwise pseudo-spin correlations underlying the overall mobility is further investigated within this formalism. We show that the classical correlations of the individual quantum tunnelling events in long-time limit is sufficient to capture the behaviour of coherent proton mobility observed in low-temperature experiments. We conclude that long-range intra-ring interactions do not appear to be a necessary condition for correlated proton tunnelling in water ice.

Demonstration of the value of diffusion weighted MR imaging for differentiation of benign from malignant breast lesions

Background: Radiologic evaluation of breast lesions is being achieved through several imaging modalities. Mammography has an established role in breast cancer screening and diagnosis. Still however, it shows some limitations particulary in dense breast.
 Methods : Magnetic resonance imaging is an attractive tool for the diagnosis of breast tumors1 and the use of magnetic resonance imaging of the breast is rapidly increasing as this technique becomes more widely available.1 As an adjunct to mammography and ultrasound, MRI can be a valuable addition to the work-up of a breast abnormality. MRI has the advantages of providing a three-dimensional view of the breast, performing with high sensitivity in dense breast tissue and using non-ionizing radiation.2
 Results : Recent advances in MRI have shown the potential in bridging the gap between sensitivity and specificity. Methods based on differences in physiological, cellular and biochemical characteristics of malignant, benign and normal tissues were developed to monitor changes in diffusion. Among these techniques is diffusion- weighted MRI (DWI).3
 Diffusion-weighted magnetic resonance imaging detects Brownian motion of water protons, thus reflecting the biologic character of tissue. The apparent diffusion coefficient (ADC) is used to quantify the Brownian motion4-5
 Conclusion :The use of DWI for breast tumors has recently been considered in clinical application, and many studies have shown lower ADC values for breast cancer compared to normal breast tissue or benign tumors 3.

Protic Ionic Liquids Based on the Alkyl-Imidazolium Cation: Effect of the Alkyl Chain Length on Structure and Dynamics.

Protic ionic liquids are known to form extended hydrogen-bonded networks that can lead to properties different from those encountered in the aprotic analogous liquids, in particular with respect to the structure and transport behavior. In this context, the present paper focuses on a wide series of 1-alkyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [HC nIm][TFSI], with the alkyl chain length ( n) on the imidazolium cation varying from ethyl ( n = 2) to dodecyl ( n = 12). A combination of several methods, such as vibrational spectroscopy, wide-angle X-ray scattering (WAXS), broadband dielectric spectroscopy, and 1H NMR spectroscopy, is used to understand the correlation between local cation-anion coordination, nature of nanosegregation, and transport properties. The results indicate the propensity of the -NH site on the cation to form stronger H-bonds with the anion as the alkyl chain length increases. In addition, the position and width of the scattering peak q1 (or the pre-peak), resolved by WAXS and due to the nanosegregation of the polar from the nonpolar domains, are clearly dependent on the alkyl chain length. However, we find no evidence from pulsed-field gradient NMR of a proton motion decoupled from molecular diffusion, hypothesized to be facilitated by the longer N-H bonds localized in the segregated ionic domains. Finally, for all protic ionic liquids investigated, the ionic conductivity displays a Vogel-Fulcher-Tammann dependence on inverse temperature, with an activation energy Ea that also depends on the alkyl chain length, although not strictly linearly.

Photoinduced Proton Transfer of GFP-Inspired Fluorescent Superphotoacids: Principles and Design.

Proton transfer remains one of the most fundamental processes in chemistry and biology. Superphotoacids provide an excellent platform to delineate the excited-state proton transfer (ESPT) mechanism on ultrafast time scales and enable one to precisely control photoacidity and other pertinent functionalities such as fluorescence. We modified the GFP core ( p-HBDI chromophore) into two series of highly fluorescent photoacids by fluorinating the phenolic ring and conformationally locking the backbone (i.e., biomimetics). The trifluorinated derivatives, M3F and P3F, represent two of the strongest superphotoacids with p Ka* values of -5.0 and -5.5, respectively, and they can efficiently transfer a proton to organic solvents like methanol. Tunable femtosecond stimulated Raman spectroscopy (FSRS) and femtosecond transient absorption (fs-TA) were employed to dissect the ESPT of M3F and P3F in methanol, particularly with structural dynamics information. By virtue of resonantly enhanced FSRS signal and global analysis of fs-TA spectra, we revealed an inhomogeneous ESPT mechanism consisting of three parallel routes following the initial small-scale proton motion and contact ion-pair formation within ∼300 fs: The first route consists of ultrafast protolytic dissociation facilitated by the pre-existing, largely optimized H-bonding chain; the second route is limited by solvent reorientation that establishes a suitable H-bonding wire for proton separation; the third route is controlled by rotational diffusion that requires rotation of the anisotropically reactive photoacid in a bulky solvent with a complex H-bonding structure over larger distances. Furthermore, we provided new design principles of enhancing photoacidity in a synergistic manner: incorporating electron-withdrawing groups into proximal (often as "donor") and distal (often as "acceptor") ring moieties of the dissociative hydroxyl group to lower the ground-state p Ka and increase the Δp Ka, respectively.

The influence of Fermi motion on the comparison of the polarization transfer to a proton in elastic [formula omitted] and quasi-elastic [formula omitted] scattering

A comparison between polarization-transfer to a bound proton in quasi-free kinematics by the A(e→,e′p→) knockout reaction and that in elastic scattering off a free proton can provide information on the characteristics of the bound proton. In the past the reported measurements have been compared to those of a free proton with zero initial momentum. We introduce, for the first time, expressions for the polarization-transfer components when the proton is initially in motion and compare them to the 2H data measured at the Mainz Microtron (MAMI). We show the ratios of the transverse (Px) and longitudinal (Pz) components of the polarization transfer in H2(e→,e′p→)n, to those of elastic scattering off a “moving proton”, assuming the proton's initial (Fermi-motion) momentum equals the negative missing momentum in the measured reaction. We found that the correction due to the proton motion is up to 20% at high missing momentum. However the effect on the double ratio (Px/Pz)A(Px/Pz)H1 is largely canceled out, as shown for both 2H and 12C data. This implies that the difference between the resting- and the moving-proton kinematics is not the primary cause for the deviations between quasi-elastic and elastic scattering reported previously.

Variational and diffusion Monte Carlo simulations of a hydrogen molecular ion in a spherical box**Project supported by the National Key R&D Program of China (Grant No. 2018YFA0305900), the National Natural Science Foundation of China (Grant Nos. 51632002, 51572108, 91745203, 11634004, 11174102, and 1174121), the National Key Research and Development Program of China (Grant No. 2016YFB0201204), the Program for Changjiang Scholars

The variational and diffusion Monte Carlo approaches are used to study the ground-state properties of a hydrogen molecular ion in a spheroidal box. In this work, we successfully treat the zero-point motion of protons in the same formalism with as of electrons and avoid the Born–Oppenheimer approximation in density function theory. The study shows that the total energy increases with the decrease in volume, and that the distance between protons decreases as the pressure increases. Considering the motion of protons, the kinetic energy of the electron is higher than that of the fixed model under the same conditions and increases by 5%. The kinetic energy of the proton is found to be small under high pressure, which is only a fraction of the kinetic energy of the electron.

Intramolecular electron-induced proton transfer and its correlation with excited-state intramolecular proton transfer

Electron-induced proton transfer depicts the proton motion coupled with the attachment of a low-energy electron to a molecule, which helps to understand copious fundamental chemical processes. Intramolecular electron-induced proton transfer is a similar process that occurs within a single molecule. To date, there is only one known intramolecular example, to the best of our knowledge. By studying the 10-hydroxybenzo[h]quinoline and 8-hydroxyquinoline molecules using anion photoelectron spectroscopy and density functional theory, and by theoretical screening of six other molecules, here we show the intramolecular electron-induced proton transfer capability of a long list of molecules that meanwhile have the excited-state intramolecular proton transfer property. Careful examination of the intrinsic electronic signatures of these molecules reveals that these two distinct processes should occur to the same category of molecules. Intramolecular electron-induced proton transfer could have potential applications such as molecular devices that are responsive to electrons or current.

Magnetic properties of hexamethylbenzene

Magnetic susceptibility χ(T) measurements on hexamethylbenzene C6(CH3)6 (HMB) as well as its deuterated analogue C6(CD3)6 (HMB-d18) in the range of 2–300 K are presented. When cooling, an uptick is detected in χ(T) when the external magnetic field is applied along the direction of the molecular planes which coincide with the onset of intra-molecular coupling of the CH3 groups at T'C_H = 110.8 K for HMB and CD3 groups at T'C_D = 126.7 K for HMB-d18. Upon warming, the same discontinuities occur near TC_H = 117.8 K and TC_D = 132.2 K. Near 40 K, a peak anomaly is observed believed to be the system accessing its ground tunneling state. Near 20 K, the divergence of χ(T) suggests the establishment of long-range ordering, viz., inter-molecular gearing of the methyl group rotations. When the external magnetic field is applied perpendicular to the molecular planes, χ(T) is independent of temperature. Our findings reveal how correlated periodic motion of protons, a phenomenon inherent in many molecular solids, exhibits magnetic behavior that has been thus far overlooked.

Potential of NMR relaxometry to unravel the properties of mucilage in several pore sizes

Soil-born exudates such as mucilage are known to affect soil physicochemical properties. Characterization of the gel properties of mucilage at the pore-scale is necessary to gain mechanistic understanding of the underlying processes leading to changes of soil properties. Yet, mucilage intrinsic properties' complicate its in-situ detection. Longitudinal and transverse magnetic relaxation rates measured with 1H Nuclear Magnetic Resonance (NMR) relaxometry have the potential to study mucilage-water interactions in-situ as they are sensitive to restricted molecular motion of water protons in biohydrogels. However, the relations between water mobility and biohydrogel properties in porous media have remained unknown until now.In this study, the mobility of water molecules in chia seed mucilage in porous systems was systematically investigated by means of 1H NMR relaxometry. Chia seed mucilage was used as it has hydrogel properties shared by a range of biological hydrogels found in soil. Glass beads of several sizes were used to study the influence of the pore size on the NMR signal.A conceptual model based on the equations describing the relaxation of water protons in porous media was developed to integrate these gel effects into the NMR parameters. The increased rigidity of the polymer network and its organization in the pore space, which depended on the particle size and the mucilage concentration, were assessed as the gel effects significantly affecting the bulk relaxation. Our approach, which combines the use of NMR along with other imaging methods, is a promising strategy to detect and characterize the properties of biohydrogel in porous media.

On the Measurement of Sachs Form Factors in Processes without and with Proton Spin Flip

The physical meaning of the decomposition of the Rosenbluth formula into two terms containing only squares of Sachs form factors has been established. A new method has been proposed for their independent measurement in the $e \vec{p} \to e \vec{p}$ elastic process when the initial proton at rest is fully polarized along the direction of motion of the final proton.

Modeling and Simulation of a Photosynthetic Solar Cell

Abstract. Solar energy’s potential as a clean, abundant, and economical energy source can be effectively exploited if it is converted to electricity. Photosynthetic solar cells (PSCs) convert sunlight to electricity by using plant cells via photosynthesis and respiration. These processes can be interrupted to provide a path of lesser resistance for the transfer of protons and electrons in a proton exchange membrane fuel cell system. PSCs require no organic fuel, no active feeding system, and produce carbon-neutral power both day and night. In this article, the mechanisms of photosynthesis that generate electrons and protons in the anode chamber are described and modeled. In addition, the concentrations of various species in the anode and cathode chambers, including plant cells, sugars, reducing agents, and catalysts, are modeled as a function of time and used to simulate the electric potential across the fuel cell. The resulting flow of electrons through the external circuit is described. The influence of non-ideal effects is described and modeled, such as the resistance to the motion of protons, reactants, and products through the electrolyte, which contributes to a voltage drop across the cell. The activation energy required for the chemical reactions also contributes to voltage drop. These dynamics are modeled using differential equations for each species. This model can be used to predict the dynamics of a PSC system under various conditions. Keywords: Cell power, Cell voltage, Microbial fuel cell, Modeling, Photosynthetic solar cell, Solar energy.

Proton mobility in Ruddlesden–Popper phase H2La2Ti3O10 studied by 1H NMR

To study protons localization in H1.83K0.17La2Ti3O10·0.17H2O and their motional characteristics, complementary Nuclear Magnetic Resonance (NMR) techniques have been applied. 1H Magic Angle Spinning NMR evidences the presence of different proton containing species. By analyzing the temperature dependence of the 1H MAS NMR spectrum we attribute the observed lines to interlayer H+ in regular sites (isolated and in water rich environment), water protons and protons from various defects. The temperature behaviors of the spectral lines intensities and widths point out that intercalated water molecules are involved in translational motion that is confirmed by spin lattice relaxation rate (R1) and spin-lattice relaxation rate in rotating frame (R1ρ) measurements. It has been shown that for a correct determination of the proton motional parameters the Kohlrausch-Williams-Watts correlation function must be used. Its application results in the following parameters of proton motion in the interlayer space of H1.83K0.17La2Ti3O10·0.17H2O: Ea = 0.194(2) eV, β = 0.28(1), τ0=6.2(1)×10−10 s.

Quantum dynamics calculation of the annihilation spectrum for positron–proline scattering

The annihilation spectrum for positron scattering by the amino acid proline was calculated using local complex potential theory combined with the time-dependent quantum wave packet method. Two nuclear degrees of freedom associated with the motion of the carboxyl group proton were considered in the dynamics. The positronic potential energy surface and positron–electron contact densities were calculated using ab initio multi-component molecular orbital theory. The calculated annihilation spectrum contained several vibrational resonance peaks, which allowed the positron binding energies to be estimated. We also observed a resonance with a very small contribution of zwitterionic proline via proton transfer.

Hydrated Excess Proton Raman Spectral Densities Probed in Floating Water Bridges

Excess proton structures in water remain unclear. The motion and nature of excess protons in water were probed using a supported water bridge structure in electric field (E) with an intensity of ∼106 V/m. The experimental setup generated protons that exhibit a long lifetime. The effect of excess protons in water induced a ∼3% variation in the pH for a 300 V overvoltage at the cathode. The current versus voltage curves show a current space-charge-limited operation. By measuring the space-charge distribution in both the cathode and anode and by adjusting the Mott–Gurney law to the measured excess hydrated proton current and the voltage drop in the cationic space-charge region, the protonic mobility was determined to be ∼200 × 10–8 m2/(V·s) (E ≈ 4 × 106 V/m). This measured mobility, which is typically five times larger than the reported mobility for protons in water, is in agreement with the mechanism outlined by Grotthuss in 1805. The measured mid-Raman spectrum covering 1000–3800 cm–1 range indicates the species character. The hydrated excess proton spectral response through the mid-Raman at 1760 and 3200 cm–1 was attributed to the Zundel complex and the region at ∼2000 to ∼2600 cm–1 response is attributed to the Eigen complex, indicating a core structure simultaneously with a Eigen-like and Zundel-like character, suggesting a rapid fluctuation between these two structures or a new specie.

$$\hbox {H}^{+} + \hbox {O}_2$$ H + + O 2 system revisited: four-state quasidiabatic potential energy surfaces and coupling potentials

The global adiabatic and quasidiabatic potential energy surfaces for the ground and first three excited ( $$1-4\, ^3\text {A}^{\prime \prime }$$ ) electronic states of $$\hbox {H}^{+} +\hbox {O}_2$$ system are reported on a finer grid points in the Jacobi coordinates using Dunning’s cc-pVTZ basis set and internally contracted multi-reference (single and double) configuration interaction method. Ab initio procedures have been used to compute the corresponding quasidiabatic surfaces and radial coupling potentials which are relevant for the dynamical studies of inelastic vibrational excitation and charge transfer processes. Nonadiabatic couplings arising out of relative motion of proton and the vibrational motions of $$\hbox {O}_2$$ between the adiabatic electronic states have also been analyzed. Adiabatic and quasidiabatic potential energy surfaces have been constructed using ab initio procedure for the lowest four 1-4 $$^{3}A''$$ electronic states of $$\hbox {H}^{+}$$ + $$\hbox {O}_{2}$$ collision system. The computed quasidiabatic surfaces and coupling potentials would be helpful in understanding the collision dynamics of inelastic and charge transfer processes in the system.

Model of multiple Dirac eikonal scattering of protons by nuclei

The model of multiple Dirac eikonal scattering (MDES) of incident proton by target-nucleus nucleons is developed, in which new expressions for the elastic [Formula: see text]-scattering amplitudes are obtained from the multiple scattering Watson series with employing the eikonal approximation for the Dirac propagators of the free proton motion between successive scattering acts on nucleons. Based on this model, calculations for the complete set of observables of the elastic [Formula: see text] and [Formula: see text]Pb at 800[Formula: see text]MeV have been performed, using proton–nucleon amplitudes determined from the phase analysis and the nucleon densities obtained from describing the target-nucleus structure in the relativistic mean-field approximation. A comparison has been made of the results of these calculations with analogous calculations on the basis of the Glauber multiple diffraction theory.