Dielectric saturation of water in a membrane protein channel

Water molecules in confined geometries like nanopores and biological ion channels exhibit structural and dynamical properties very different from those found in free solution. Protein channels that open aqueous pores through biological membranes provide a complex spatial and electrostatic environment that decreases the translational and rotational mobility of water molecules, thus altering the effective dielectric constant of the pore water. By using the Booth equation, we study the effect of the large electric field created by ionizable residues of an hour-glass shaped channel, the bacterial porin OmpF, on the pore water dielectric constant, ew. We find a space-dependent significant reduction (down to 20) of ew that may explain some ad hoc assumptions about the dielectric constant of the protein and the water pore made to reconcile model calculations with measurements of permeation properties and pKa’s of protein residues. The electric potential calculations based on the OmpF protein atomic structure and the Booth field-dependent dielectric constant show that protein dielectric constants ca. 10 yield good agreement with molecular dynamics simulations as well as permeation experiment

Dual Purpose Measurements with Displacement Sensors

[EN] In this paper we show a laboratory experience describing the possibility to build a sensor using a coil to measure small thicknesses of materials with the possibility of measuring temperature simultaneously, with the same built sensor. Its operation is based on the following facts: An electric current (a.c), flows through a coil and a magnetic field appears producing self-induction characterized by an electromotive force induced in the coil, when a conductive piece is situated in front of the coil. That permits us to obtain information about the distance between the coil and the conductive piece. When this separation thickness is changing, the magnetic field around the coil changes, because the self-induction coefficient (L) is also changing. Using resistance and impedance measurements (voltage in our case) in the coil, an expression has been obtained for the determination of the thickness of a non-conductive sheet placed between a metallic plate and the coil. Calibration measurements of resistance with temperature have been obtained. The thermodynamic analysis is also presented showing the equation of state of the system between the voltage, temperature and the thickness of the non-conductive sample. The linear thermal-expansion coefficient of the sample is also determined.The authors gratefully acknowledge the support provided by the projects ENE/2015-69203-R from Ministerio de Economia y Competitividad (MINECO) (Spain), and DGAPA-PAPIIT IG100618 and DGAPA-PAPIIT IN-114818 (México) and also thanks to Raúl Reyes Ortíz and Alberto López Vivas for technical assistance.Andrio, A.; Del Castillo, LF.; Compañ Moreno, V. (2020). Dual Purpose Measurements with Displacement Sensors. European Journal of Physics Education. 11(2):24-34. https://doi.org/10.20308/ejpe.v11i2.279S243411

Enhanced Conductivity of Composite Membranes Based on Sulfonated Poly(Ether Ether Ketone) (SPEEK) with Zeolitic Imidazolate Frameworks (ZIFs)

The zeolitic imidazolate frameworks (ZIFs) ZIF-8, ZIF-67, and a Zn/Co bimetallic mixture (ZMix) were synthesized and used as fillers in the preparation of composite sulfonated poly(ether ether ketone) (SPEEK) membranes. The presence of the ZIFs in the polymeric matrix enhanced proton transport relative to that observed for SPEEK or ZIFs alone. The real and imaginary parts of the complex conductivity were obtained by electrochemical impedance spectroscopy (EIS), and the temperature and frequency dependence of the real part of the conductivity were analyzed. The results at different temperatures show that the direct current (dc) conductivity was three orders of magnitude higher for composite membranes than for SPEEK, and that of the SPEEK/ZMix membrane was higher than those for SPEEK/Z8 and SPEEK/Z67, respectively. This behavior turns out to be more evident as the temperature increases: the conductivity of the SPEEK/ZMix was 8.5 x 10-3 S·cm-1, while for the SPEEK/Z8 and SPEEK/Z67 membranes, the values were 2.5 x 10-3 S·cm-1 and 1.6 x 10-3 S3cm-1, respectively, at 120 ºC. Similarly, the real and imaginary parts of the complex dielectric constant were obtained, and an analysis of tan d was carried out for all of the membranes under study. Using this value, the diffusion coefficient and the charge carrier density were obtained using the analysis of electrode polarization (EP)

Effect of time of annealing on gas permeation through coextruded linear low-density polyethylene (LLDPE) films

[EN] The effect of annealing on the permeation of oxygen, nitrogen, and carbon dioxide through coextruded linear low-density polyethylene (LLDPE) films is studied. The results indicate that the permeability coefficient P of nitrogen does not show a definite dependence on the time of annealing, ta, whereas for the other gases this parameter increases with ta. The analysis of the variation of the diffusion coefficient of O2 and N2 with ta indicates that D undergoes a sharp decrease from ta ) 0 to ta ) 2 h, but for larger times of annealing the diffusion parameter only undergoes a slight diminution; on the contrary, the diffusion coefficient of CO2 gradually decreases with increasing ta. The fact that annealing increases the solubility of the gases in the polymer films suggests that thermal treatments may favor the formation of microcavities or molecular packing defects in the crystalline amorphous interface that can accommodate individual site molecules without disturbing the natural dissolution process in the rubbery region of the polymer matrix. Finally, free volume theories are not sensitive enough to interpret the effect of annealing on the permeation characteristics of coextruded LLDPE films.This work was supported by the DGICYT through Grant PB95-0134-C02.Compañ Moreno, V.; Andrio, A.; Lopez, ML.; Alvarez, C.; Riande, E. (1997). Effect of time of annealing on gas permeation through coextruded linear low-density polyethylene (LLDPE) films. Macromolecules. 30:3317-3322. http://hdl.handle.net/10251/147741S331733223

Enhanced conductivity of sodium versus lithium salts. Sodium metallacarboranes as electrolyte

[EN] The development of new types of ion conducting materials is one of the most important challenges in the field of energy. Lithium salt polymer electrolytes have been the most convenient, and thus the most widely used in the design of the new generation of batteries. However, in this work, we have observed that Na+ ions provide a higher conductivity, or at least a comparable conductivity to that of Li+ ions in the same basic material. This provides an excellent possibility to use Na+ ions in the design of a new generation of batteries, instead of lithium, to enhance conductivity and ensure wide supply. Our results indicate that the dc-conductivity is larger when the anion is [Co(C2B9H11)(2)](-), [COSANE](-), compared to tetraphenylborate, [TPB](-). Our data also prove that the dc-conductivity behavior of Li+ and Na+ salts is opposite with the two anions. At 40 C-omicron, the conductivity values change from 1.05 x 10(-2) S cm(-1) (Li[COSANE]) and 1.75 x 10(-2) S cm(-1) (Na[COSANE]) to 2.8 x 10(-3) S cm(-1) (Li[TPB]) and 1.5 x 10(-3) S cm(-1) (Na[TPB]). These findings indicate that metallacarboranes can be useful components of mixed matrix membranes (MMMs), providing excellent conductivity when the medium contains sufficient amounts of ionic components and a certain degree of humidity.This research has been supported by the ENE/2015-69203-R and CTQ2013-44670-R projects, granted by the Ministerio de Economia y Competitividad (MINECO), Spain; the Generalitat de Catalunya (2014/SGR/149) and FP7-OCEAN-2013: Proposal number: 614168. C. V. thanks COST CM1302 project. I. F. is enrolled in the PhD program of the UAB.Fuentes, I.; Andrio, A.; Teixidor, F.; Viñas, C.; Compañ Moreno, V. (2017). Enhanced conductivity of sodium versus lithium salts. Sodium metallacarboranes as electrolyte. Physical Chemistry Chemical Physics. 15177(15186):15177-15186. https://doi.org/10.1039/c7cp02526bS15177151861517715186Bakangura, E., Wu, L., Ge, L., Yang, Z., & Xu, T. (2016). Mixed matrix proton exchange membranes for fuel cells: State of the art and perspectives. Progress in Polymer Science, 57, 103-152. doi:10.1016/j.progpolymsci.2015.11.004Lufrano, F., Baglio, V., Staiti, P., Antonucci, V., & Arico’, A. S. (2013). Performance analysis of polymer electrolyte membranes for direct methanol fuel cells. Journal of Power Sources, 243, 519-534. doi:10.1016/j.jpowsour.2013.05.180Jiang, S. P. (2014). Functionalized mesoporous structured inorganic materials as high temperature proton exchange membranes for fuel cells. J. Mater. Chem. A, 2(21), 7637-7655. doi:10.1039/c4ta00121dHeo, Y., Im, H., & Kim, J. (2013). The effect of sulfonated graphene oxide on Sulfonated Poly (Ether Ether Ketone) membrane for direct methanol fuel cells. Journal of Membrane Science, 425-426, 11-22. doi:10.1016/j.memsci.2012.09.019Mishra, A. K., Kim, N. H., Jung, D., & Lee, J. H. (2014). Enhanced mechanical properties and proton conductivity of Nafion–SPEEK–GO composite membranes for fuel cell applications. Journal of Membrane Science, 458, 128-135. doi:10.1016/j.memsci.2014.01.073Rambabu, G., & Bhat, S. D. (2014). Simultaneous tuning of methanol crossover and ionic conductivity of sPEEK membrane electrolyte by incorporation of PSSA functionalized MWCNTs: A comparative study in DMFCs. Chemical Engineering Journal, 243, 517-525. doi:10.1016/j.cej.2014.01.030Kango, S., Kalia, S., Celli, A., Njuguna, J., Habibi, Y., & Kumar, R. (2013). Surface modification of inorganic nanoparticles for development of organic–inorganic nanocomposites—A review. Progress in Polymer Science, 38(8), 1232-1261. doi:10.1016/j.progpolymsci.2013.02.003Zeng, J., He, B., Lamb, K., De Marco, R., Shen, P. K., & Jiang, S. P. (2013). Phosphoric acid functionalized pre-sintered meso-silica for high temperature proton exchange membrane fuel cells. Chemical Communications, 49(41), 4655. doi:10.1039/c3cc41716fPaddison, S. J. (2003). Proton Conduction Mechanisms at Low Degrees of Hydration in Sulfonic Acid–Based Polymer Electrolyte Membranes. Annual Review of Materials Research, 33(1), 289-319. doi:10.1146/annurev.matsci.33.022702.155102Peighambardoust, S. J., Rowshanzamir, S., & Amjadi, M. (2010). Review of the proton exchange membranes for fuel cell applications. International Journal of Hydrogen Energy, 35(17), 9349-9384. doi:10.1016/j.ijhydene.2010.05.017Kreuer, K.-D. (1996). Proton Conductivity:  Materials and Applications. Chemistry of Materials, 8(3), 610-641. doi:10.1021/cm950192aKreuer, K.-D., Paddison, S. J., Spohr, E., & Schuster, M. (2004). Transport in Proton Conductors for Fuel-Cell Applications:  Simulations, Elementary Reactions, and Phenomenology. Chemical Reviews, 104(10), 4637-4678. doi:10.1021/cr020715fWang, C., Chalkova, E., Lute, C. D., Fedkin, M. V., Komarneni, S., Chung, T. C. M., & Lvov, S. N. (2010). Proton Conductive Inorganic Materials for Temperatures Up to 120°C and Relative Humidity Down to 5%. Journal of The Electrochemical Society, 157(11), B1634. doi:10.1149/1.3486113Hara, S. (2002). Proton-conducting properties of hydrated tin dioxide as an electrolyte for fuel cells at intermediate temperature. Solid State Ionics, 154-155, 679-685. doi:10.1016/s0167-2738(02)00517-9Yang, Q., Kapoor, M. P., & Inagaki, S. (2002). Sulfuric Acid-Functionalized Mesoporous Benzene−Silica with a Molecular-Scale Periodicity in the Walls. Journal of the American Chemical Society, 124(33), 9694-9695. doi:10.1021/ja026799rMargolese, D., Melero, J. A., Christiansen, S. C., Chmelka, B. F., & Stucky, G. D. (2000). Direct Syntheses of Ordered SBA-15 Mesoporous Silica Containing Sulfonic Acid Groups. Chemistry of Materials, 12(8), 2448-2459. doi:10.1021/cm0010304Jin, Y. G., Qiao, S. Z., Xu, Z. P., Diniz da Costa, J. C., & Lu, G. Q. (2009). Porous Silica Nanospheres Functionalized with Phosphonic Acid as Intermediate-Temperature Proton Conductors. The Journal of Physical Chemistry C, 113(8), 3157-3163. doi:10.1021/jp810112cFujita, S., Koiwai, A., Kawasumi, M., & Inagaki, S. (2013). Enhancement of Proton Transport by High Densification of Sulfonic Acid Groups in Highly Ordered Mesoporous Silica. Chemistry of Materials, 25(9), 1584-1591. doi:10.1021/cm303950uPonomareva, V. ., & Lavrova, G. . (2001). The investigation of disordered phases in nanocomposite proton electrolytes based on MeHSO4 (Me=Rb, Cs, K). Solid State Ionics, 145(1-4), 197-204. doi:10.1016/s0167-2738(01)00957-2Vijayakumar, M., Bain, A. D., & Goward, G. R. (2009). Investigations of Proton Conduction in the Monoclinic Phase of RbH2PO4 Using Multinuclear Solid-State NMR. The Journal of Physical Chemistry C, 113(41), 17950-17957. doi:10.1021/jp903408vHara, S., Takano, S., & Miyayama, M. (2004). Proton-Conducting Properties and Microstructure of Hydrated Tin Dioxide and Hydrated Zirconia. The Journal of Physical Chemistry B, 108(18), 5634-5639. doi:10.1021/jp0370369Kozawa, Y., Suzuki, S., Miyayama, M., Okumiya, T., & Traversa, E. (2010). Proton conducting membranes composed of sulfonated poly(etheretherketone) and zirconium phosphate nanosheets for fuel cell applications. Solid State Ionics, 181(5-7), 348-353. doi:10.1016/j.ssi.2009.12.017Abbaraju, R. R., Dasgupta, N., & Virkar, A. V. (2008). Composite Nafion Membranes Containing Nanosize TiO[sub 2]∕SnO[sub 2] for Proton Exchange Membrane Fuel Cells. Journal of The Electrochemical Society, 155(12), B1307. doi:10.1149/1.2994079Chalkova, E., Fedkin, M. V., Wesolowski, D. J., & Lvov, S. N. (2005). Effect of TiO[sub 2] Surface Properties on Performance of Nafion-Based Composite Membranes in High Temperature and Low Relative Humidity PEM Fuel Cells. Journal of The Electrochemical Society, 152(9), A1742. doi:10.1149/1.1971216Sahu, A. K., Selvarani, G., Pitchumani, S., Sridhar, P., & Shukla, A. K. (2007). A Sol-Gel Modified Alternative Nafion-Silica Composite Membrane for Polymer Electrolyte Fuel Cells. Journal of The Electrochemical Society, 154(2), B123. doi:10.1149/1.2401031González-Cardoso, P., Stoica, A.-I., Farràs, P., Pepiol, A., Viñas, C., & Teixidor, F. (2010). Additive Tuning of Redox Potential in Metallacarboranes by Sequential Halogen Substitution. Chemistry - A European Journal, 16(22), 6660-6665. doi:10.1002/chem.200902558Pepiol, A., Teixidor, F., Sillanpää, R., Lupu, M., & Viñas, C. (2011). Stepwise Sequential Redox Potential Modulation Possible on a Single Platform. Angewandte Chemie International Edition, 50(52), 12491-12495. doi:10.1002/anie.201105668Tarrés, M., Arderiu, V. S., Zaulet, A., Viñas, C., Fabrizi de Biani, F., & Teixidor, F. (2015). How to get the desired reduction voltage in a single framework! Metallacarborane as an optimal probe for sequential voltage tuning. Dalton Transactions, 44(26), 11690-11695. doi:10.1039/c5dt01464fTeixidor, F., Viñas, C., Demonceau, A., & Nuñez, R. (2003). Boron clusters: Do they receive the deserved interest? Pure and Applied Chemistry, 75(9), 1305-1313. doi:10.1351/pac200375091305Olid, D., Núñez, R., Viñas, C., & Teixidor, F. (2013). Methods to produce B–C, B–P, B–N and B–S bonds in boron clusters. Chemical Society Reviews, 42(8), 3318. doi:10.1039/c2cs35441aBauduin, P., Prevost, S., Farràs, P., Teixidor, F., Diat, O., & Zemb, T. (2011). A Theta-Shaped Amphiphilic Cobaltabisdicarbollide Anion: Transition From Monolayer Vesicles to Micelles. Angewandte Chemie International Edition, 50(23), 5298-5300. doi:10.1002/anie.201100410Brusselle, D., Bauduin, P., Girard, L., Zaulet, A., Viñas, C., Teixidor, F., … Diat, O. (2013). Lyotropic Lamellar Phase Formed from Monolayered θ-Shaped Carborane-Cage Amphiphiles. Angewandte Chemie International Edition, 52(46), 12114-12118. doi:10.1002/anie.201307357Gassin, P.-M., Girard, L., Martin-Gassin, G., Brusselle, D., Jonchère, A., Diat, O., … Bauduin, P. (2015). Surface Activity and Molecular Organization of Metallacarboranes at the Air–Water Interface Revealed by Nonlinear Optics. Langmuir, 31(8), 2297-2303. doi:10.1021/acs.langmuir.5b00125Ďorďovič, V., Tošner, Z., Uchman, M., Zhigunov, A., Reza, M., Ruokolainen, J., … Matějíček, P. (2016). Stealth Amphiphiles: Self-Assembly of Polyhedral Boron Clusters. Langmuir, 32(26), 6713-6722. doi:10.1021/acs.langmuir.6b01995Uchman, M., Ďorďovič, V., Tošner, Z., & Matějíček, P. (2015). Classical Amphiphilic Behavior of Nonclassical Amphiphiles: A Comparison of Metallacarborane Self-Assembly with SDS Micellization. Angewandte Chemie International Edition, 54(47), 14113-14117. doi:10.1002/anie.201506545Núñez, R., Romero, I., Teixidor, F., & Viñas, C. (2016). Icosahedral boron clusters: a perfect tool for the enhancement of polymer features. Chemical Society Reviews, 45(19), 5147-5173. doi:10.1039/c6cs00159aNúñez, R., Tarrés, M., Ferrer-Ugalde, A., de Biani, F. F., & Teixidor, F. (2016). Electrochemistry and Photoluminescence of Icosahedral Carboranes, Boranes, Metallacarboranes, and Their Derivatives. Chemical Reviews, 116(23), 14307-14378. doi:10.1021/acs.chemrev.6b00198Masalles, C., Borrós, S., Viñas, C., & Teixidor, F. (2000). Are Low-Coordinating Anions of Interest as Doping Agents in Organic Conducting Polymers? Advanced Materials, 12(16), 1199-1202. doi:10.1002/1521-4095(200008)12:163.0.co;2-wMasalles, C., Borrós, S., Viñas, C., & Teixidor, F. (2002). Surface Layer Formation on Polypyrrole Films. Advanced Materials, 14(6), 449-452. doi:10.1002/1521-4095(20020318)14:63.0.co;2-4Fabre, B., Clark, J. C., & Vicente, M. G. H. (2006). Synthesis and Electrochemistry of Carboranylpyrroles. Toward the Preparation of Electrochemically and Thermally Resistant Conjugated Polymers. Macromolecules, 39(1), 112-119. doi:10.1021/ma051508vHao, E., Fabre, B., Fronczek, F. R., & Vicente, M. G. H. (2007). Syntheses and Electropolymerization of Carboranyl-Functionalized Pyrroles and Thiophenes. Chemistry of Materials, 19(25), 6195-6205. doi:10.1021/cm701935nMasalles, C., Teixidor, F., Borrós, S., & Viñas, C. (2002). Cobaltabisdicarbollide anion [Co(C2B9H11)2]− as doping agent on intelligent membranes for ion capture. Journal of Organometallic Chemistry, 657(1-2), 239-246. doi:10.1016/s0022-328x(02)01432-8Masalles, C., Llop, J., Viñas, C., & Teixidor, F. (2002). 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Protonic Conduction of Partially-Substituted CsH2PO4 and the Applicability in Electrochemical Devices

CsH2PO4 is a proton conductor pertaining to the acid salts group and shows a phase transition from monoclinic to cubic phase at 232 ± 2 ◦C under high-steam atmospheres (>30%). This cubic phase gives rise to the so-called superprotonic conductivity. In this work, the influence of the partial substitution of Cs by Ba and Rb, as well as the partial substitution of P by W, Mo, and S in CsH2PO4 on the phase transition temperature and electrochemical properties is studied. Among the tested materials, the partial substitution by Rb led to the highest conductivity at high temperature. Furthermore, Ba and S-substituted salts exhibited the highest conductivity at low temperatures. CsH2PO4 was used as electrolyte in a fully-assembled fuel cell demonstrating the applicability of the material at high pressures and the possibility to use other materials (Cu and ZnO) instead of Pt as electrode electrocatalyst. Finally, an electrolyzer cell composed of CsH2PO4 as electrolyte, Cu and ZnO as cathode and Pt and Ag as anode was evaluated, obtaining a stable production of H2 at 250 ◦C

Proton conductivity through polybenzimidazole composite membranes containing silica nanofiber mats

The quest for sustainable and more efficient energy-converting devices has been the focus of researchers′ efforts in the past decades. In this study, SiO2 nanofiber mats were fabricated through an electrospinning process and later functionalized using silane chemistry to introduce different polar groups −OH (neutral), −SO3H (acidic) and −NH2 (basic). The modified nanofiber mats were embedded in PBI to fabricate mixed matrix membranes. The incorporation of these nanofiber mats in the PBI matrix showed an improvement in the chemical and thermal stability of the composite membranes. Proton conduction measurements show that PBI composite membranes containing nanofiber mats with basic groups showed higher proton conductivities, reaching values as high as 4 mS·cm−1 at 200 °C

Electric Conductivity Study of Porous Polyvinyl Alcohol/Graphene/Clay Aerogels: Effect of Compression

In this work, poly(vinyl alcohol) (PVOH)/graphene (GN) oxide/clay aerogels were prepared using montmorillonite (MMT) and kaolinite (KLT) as fillers. This work paves the way for the development of aerogels filled with MMT or KLT with high conductivity. The mechanical properties of the polymer/clay aerogels are enhanced by incorporating GN into these systems. These composite materials have an enhanced thermal stability, and the combination of PVOH and GN leads to interconnected channels which favored the conductivity when a clay (MMT or KLT) is added to the mixed PVOH/GN matrix. However, after compressing the samples, the conductivities drastically decreased. These results show that the design of solid MMT/GN and KLT/GN composites as aerogels allows maximizing the space utilization of the electrode volume to achieve unhindered ion transport, which seems contrary to the general design principle of electrode materials where a suitable porous structure is desired, such as in our uncompressed samples. These findings also demonstrate the potential of these materials in electrodes, sensors, batteries, pressure-sensing applications, and supercapacitors.Financial support for this research from Ministerio de Economía y Competitividad (project AGL2015-63855-C2-2-R) (MINECO/FEDER) is gratefully acknowledged.The authors acknowledge the Servei Central d’Instrumentació Científica (SCIC-UJI) and Servei Central de Suport a la Investigació Experimental (SCSIE-UV) from Universitat Jaume I and Universitat de València, respectively, for the use of instruments and staff assistance. Authors would like to acknowledge José Ortega and Raquel Oliver for experimental support

Proton conductivity through polybenzimidazole composite membranes containing silica nanofiber mats

The quest for sustainable and more efficient energy-converting devices has been the focus of researchers′ efforts in the past decades. In this study, SiO2 nanofiber mats were fabricated through an electrospinning process and later functionalized using silane chemistry to introduce different polar groups -OH (neutral), -SO3H (acidic) and -NH2 (basic). The modified nanofiber mats were embedded in PBI to fabricate mixed matrix membranes. The incorporation of these nanofiber mats in the PBI matrix showed an improvement in the chemical and thermal stability of the composite membranes. Proton conduction measurements show that PBI composite membranes containing nanofiber mats with basic groups showed higher proton conductivities, reaching values as high as 4 mS·cm−1 at 200 ºC