Negative Counterion Research Articles

Charge carrier dynamics in conducting polymer PEDOT using abinitio molecular dynamics simulations.

As conducting polymers become increasingly important in electronic devices, understanding their charge transport is essential for material and device development. Various semi-empirical approaches have been used to describe temporal charge carrier dynamics in these materials, but there have yet to be any theoretical approaches utilizing abinitio molecular dynamics. In this work, we develop a computational technique based on abinitio Car-Parrinello molecular dynamics to trace charge carrier temporal motion in archetypical conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). Particularly, we analyze charge dynamics in a single PEDOT chain and in two coupled chains with different degrees of coupling and study the effect of temperature. In our model we first initiate a positively charged polaron (compensated by a negative counterion) at one end of the chain, and subsequently displace the counterion to the other end of the chain and trace polaron dynamics in the system by monitoring bond length alternation in the PEDOT backbone and charge density distribution. We find that at low temperature (T = 1K) the polaron distortion gradually disappears from its initial location and reappears near the new position of the counterion. At the room temperature (T = 300K), we find that the distortions induced by polaron, and atomic vibrations are of the same magnitude, which makes tracking the polaron distortion challenging because it is hidden behind the temperature-induced vibrations. The novel approach developed in this work can be used to study polaron mobility along and between the chains, investigate charge transport in highly doped polymers, and explore other flexible polymers, including n-doped ones.

Quantifying Free Carriers in Doped SWCNTs: An Optical and Magnetic Resonance Approach

Single-walled carbon nanotubes (SWCNTs) have become increasingly important for opto-electronic devices due to their strong optical absorption, tunable carrier densities, and large carrier mobilities. To produce electricity in applications like photovoltaics and sensors, after light absorption the bound exciton must be separated into free charges carriers. However, the nature of charges in s-SWCNTs is still unclear and a way to quantify them has remained elusive. To better understand free carriers in doped semiconducting SWCNTs we employ a new class of molecular charge-transfer dopants, functionalized dodecaborane (DDB) molecules, to tune the charge carrier density. These DDB dopants form delocalized hole charge carriers on the SWCNTs due to the spatial separation between nanotube surface and the boron cluster containing the negative counterion. Importantly, the fluorine-decorated DDB dopants have strong 19F resonances, characteristic of the negatively charged molecules, that can quantify the absolute concentrations of DDB- and SWCNT+. As such, we use a combined approach of steady state optical spectroscopy and 19F NMR studies. Optical spectroscopy allows to track the excitonic absorption quenching and trion signature due to charge carrier density while correlating it to the concentration of carriers extracted from NMR experiments. This combined methodology allows for quantitative determination of a molar extinction coefficient for free carriers in semiconducting SWCNTs. This molar extinction coefficient can then be used in further studies to determine the yield and mobility of free carriers generated in a variety of samples and applications, for example at a heterojunction in photovoltaic devices, to determine quantitative charge transfer efficiencies and dynamics.

CLCN7, a gene shared by autosomal recessive and autosomal dominant osteopetrosis.

After the discovery of abundant v-ATPase complexes in the osteoclast ruffled membrane it was obvious that in parallel a negative counter-ion needs to be transported across this membrane to allow for efficient transport of protons into the resorption lacuna. While different candidate proteins were discussed the osteopetrosis phenotype of Clcn7 knockout mice suggested that the chloride/proton-exchanger ClC-7 might be responsible for transporting the negative charge. In the following, individuals with autosomal recessive osteopetrosis (ARO) were found to carry biallelic CLCN7 pathogenic variants. Shortly thereafter, heterozygous pathogenic variants were identified as the exclusive cause of autosomal dominant osteopetrosis type 2 (ADO2). Since in most cell types other than osteoclasts ClC-7 resides in late endosomes and lysosomes, it took some time until the electrophysiological properties of ClC-7 were elucidated. Whereas most missense variants lead to reduced chloride currents, several variants with accelerated kinetics have been identified. Evidence for folding problems is also known for several missense variants. Paradoxically, a heterozygous activating variant in ClC-7 was described to cause lysosomal alteration, pigmentation defects, and intellectual disability without osteopetrosis. The counter-intuitive 2 Cl-/H+ exchange function of ClC-7 was shown to be physiologically important for intravesicular ion homeostasis. The lysosomal function of ClC-7 is also the reason why individuals with CLCN7-ARO can develop a storage disorder and neurodegeneration, a feature that is variable and difficult to predict. Furthermore, the low penetrance of heterozygous pathogenic CLCN7 variants and the clinical variability of ADO2 are incompletely understood. We aim to give an overview not only of the current knowledge about ClC-7 and its related pathologies, but also of the scientists and clinicians that paved the way for these discoveries.

ONE-STEP ELECTROCHEMICAL SYNTHESIS OF PEDOT BASED COMPOSITES FOR SUPERCAPACITOR APPLICATIONS

The aim of this work was to determine the optimal synthesis conditions for the preparation of a poly(3,4-ethylenedioxythiophene) (PEDOT) layer by the electrochemical method from an electrolyte containing graphene oxide (GO) and a sodium dodecylsulfate (SDS) micellar solution. Besides an SDS anion, GO is also incorporated within the PEDOT layer as a negative counter ion. Therefore, this is a one-step electrochemical method for a PEDOT/GO composite layer preparation. The results displayed that PEDOT composites were successfully synthesised by applying a potential in the value range from 0.94 to 1.00 V, and with a synthesis duration of up to 600 s. It was concluded that the optimal concentration of EDOT monomer is 0.02 mol dm-3, and SDS 0.01 mol dm-3. The incorporation of GO into the PEDOT layer improved the polymer response in KCl solution influencing the pseudocapacitive properties, which is significant for its supercapacitor applications. The morphological and structural properties of the obtained layers were characterized by means of scanning electron microscopy and ultraviolet-visible spectrophotometry. The pseudocapacitive properties were determined in a 0.1 mol dm-3 KCl solution by using cyclic voltammetry and electrochemical impedance spectroscopy methods.

Electronic and Optical Properties of Protonated Triazine Derivatives

The peculiar electronic and optical properties of covalent organic frameworks (COFs) are largely determined by protonation, a ubiquitous phenomenon in the solution environment in which they are synthesized. The resulting effects are non-trivial and appear to be crucial for the intriguing functionalities of these materials. In the quantum-mechanical framework of time-dependent density-functional theory, we investigate from first principles the impact of protonation of triazine and amino groups in molecular building blocks of COFs in water solution. In all considered cases, we find that proton uptake leads to a gap reduction and to a reorganization of the electronic structure, driven by the presence of the proton and by the electrostatic attraction between the positively charged protonated species and the negative counterion in its vicinity. Structural distortions induced by protonation are found to play only a minor role. The interplay between band-gap renormalization and exciton binding strength determines the energy of the absorption onsets: when the former prevails on the latter, a red-shift is observed. Furthermore, the spatial and energetic rearrangement of the molecular orbitals upon protonation induces a splitting of the lowest-energy peaks and a decrease of their oscillator strength in comparison with the pristine counterparts. Our results offer quantitative and microscopic insight into the role of protonation on the electronic and optical properties of triazine derivatives as building blocks of COFs. As such, they contribute to rationalize the relationships between structure, property, and functionality of these materials.

Sublimable Cationic Iridium(III) Complexes with 1,10-Phenanthroline Derivatives as Ancillary Ligands for Highly Efficient and Polychromic Electroluminescence.

A novel series of four sublimable cationic iridium(III) complexes have been prepared with 1,10-phenanthroline derivatives as ancillary ligands and the same negative counter-ion, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, which has a large steric hindrance and widely dispersed charges, thereby increasing the ionic radii, reducing the electrostatic interaction, and thus improving the volatility. Their structural, photophysical, electrochemical, and thermal properties have been fully characterized. Upon excitation, these compounds show polychromic emission varying from green to orange in solution, which are blue-shifted in the solid state to different extents due to π-π conjugate effects in the ancillary ligands and the resulting molecular aggregation. OLEDs fabricated by vacuum evaporation deposition demonstrated desirable device performance with high efficiency and brightness, exhibiting various electroluminescent colors dependent upon doping concentration.

Improved hemocompatibility of silk fibroin fabric using layer‐by‐layer polyelectrolyte deposition and heparin immobilization

ABSTRACTSilk fibroin has long been used as implantable surgical sutures and it has acceptable mechanical properties and patency rates in animal models and in clinical end‐uses. However, fibroin has been shown to be hemolytic and can cause damage to red blood cells. So to be used as an implantable vascular prosthesis its hemocompatibility needs to be improved. This study has taken two sequential steps to address this problem. First, to create a positively charged layer on the fibroin fibers' surface, a 1.5 and 2.5 bilayers polyelectrolyte surface deposition layer‐by‐layer technique was used with the positive counterion poly(allylamine hydrochloride) and the negative counterion poly(acrylic acid). Second, negatively charged low molecular weight heparin was then immobilized on these positively charged self‐assembled surfaces. The presence of the heparin was confirmed with Alcian Blue staining and a toluidine blue assay, and the increased roughness and hydrophilicity of the modified surfaces were characterized by scanning electron microscopy, contact angle measurements, and atomic force microscopy. In addition, a negligible hemolytic effect, reduced protein adsorption, and a higher concentration of free hemoglobin measured by a kinetic clotting time test were found to be enhanced with the use of 2.5 bilayers compared to the 1.5 bilayers self‐assembly technique. Given the success of these preliminary results, it is anticipated that this novel approach of surface modification and heparin immobilization will demonstrate long‐term patency during future animal trials of small caliber silk fibroin vascular grafts. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40772.

Association constants and distribution functions for ion pairs in binary solvent mixtures: Application to a cyanine dye system

The computations of the association constants K(ass) were performed at the microscopic level for the ion pair Cy(+)I(-) composed of the complex cyanine dye cation Cy(+) coupled to the negative iodine counterion. The wide array of K(ass) values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy(+)I(-) by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy(+)I(-) system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the K(ass).

Na+-dependent HCO3− Import by the slc4a10 Gene Product Involves Cl− Export

The slc4a10 gene encodes an electroneutral Na(+)-dependent HCO(3)(-) importer for which the precise mode of action remains unsettled. To resolve this issue, intracellular pH (pH(i)) recordings were performed upon acidification in the presence of CO(2)/HCO(3)(-) by 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) fluorometry of stably slc4a10-transfected NIH-3T3 fibroblasts. slc4a10 expression induced a significant Na(+)-dependent pH(i) recovery, which was accompanied by an increase in the intracellular Na(+) concentration evaluated by use of the Na(+)-sensitive fluorophore CoroNa Green. The estimated Na(+):HCO(3)(-) stoichiometry was 1:2. Cl(-) is most likely the counterion maintaining electroneutrality because (i) Na(+)-dependent pH(i) recovery was eliminated in Cl(-)-depleted cells; (ii) acute extracellular Cl(-) removal led to a larger alkalization in slc4a10-transfected cells than in control cells; and (iii) the 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS)-sensitive and Na(+)- and HCO(3)(-)-dependent (36)Cl(-)-efflux during pH(i) recovery was significantly greater in acidified slc4a10-transfected cells than in control cells. Charged amino acids specific to slc4a gene family members that transport Na(+) and are expected to move more HCO(3)(-) molecules/turnover were targeted by site-directed mutagenesis. Na(+)-dependent pH(i) recovery was reduced in each of the single amino acid mutated cell lines (E890A, E892A, H976L, and H980G) compared with wild type slc4a10-transfected cells and completely eliminated in quadruple mutant cells. In conclusion, the data suggest that slc4a10 expressed in mammalian cells encodes a Na(+)-dependent Cl(-)/HCO(3)(-) exchanger in which four specific charged amino acids seem necessary for ion transport.

Preparation of trityl cations in faujasite micropores through supercritical CO 2 impregnation

In this paper, we investigated on the preparation of three zeolite encapsulated-trityl cations (trityl, dimethoxytrityl and methoxytrityl) using supercritical CO 2 (scCO 2) as the processing media. Since the studied trityl cations had a size larger than the diameter of the zeolite channels, the fabrication was based on a ship-in-a-bottle procedure using benzene, benzaldehyde, anisole, diphenylcarbinol and benzophenone as building blocks. The different cations were prepared by nucleophilic substitution, using the inner supercage of the acid zeolite as both a microreactor and a negative counterion for the trityl cation. The obtained impregnated samples were purified by cleaning with a continuous flow of scCO 2. Loaded amounts of ca. 8 wt.% were obtained following the supercritical procedure. The successful formation of the cation was confirmed by using optical spectroscopies, such as UV–vis diffuse reflectance and FTIR spectroscopies.

Thin Layer Chromatography for the Separation and Analysis of Acidic Carbohydrates

Thin layer chromatography (TLC) is routinely used by synthetic organic chemists and natural products chemists working on a variety of types of molecules. Carbohydrate chemists and biochemists in the past largely relied on paper chromatography for rapid and inexpensive analysis. Carbohydrates are highly polar molecules and often require derivatization to be analyzed by TLC. Acidic carbohydrates pose an even more difficult challenge as they contain a formal negative charge and counterion, and can interact with commonly used stationary phases. This review describes TLC methods that have been developed for the analysis of acidic monosaccharides, disaccharides, and oligosaccharides derived from natural sources.

Highly Enantioselective Biphasic Iminium‐Catalyzed Epoxidation of Alkenes. On the Importance of the Counterion and of N(sp2)C(sp3) Rotamers

Abstractmagnified imageDiastereomeric biaryliminium cations made of an (Ra)‐5,5′,6,6′,7,7′,8,8′‐octahydrobinaphthyl core and exocyclic appendages derived from (S)‐ or (R)‐3,3‐dimethylbutan‐2‐amine are effective asymmetric epoxidation catalysts for unfunctionalized alkenes. Herein, we report that the negative counterion of the iminium salts has to be chosen wisely. While the hexafluoroantimonate anion [SbF6−] is optimal for reliable results, one has to be careful about other anions and tetraphenylborate [BPh4−] in particular. We also detail that the so far unexplained “lack” of stereochemical control from the chiral exocyclic appendage in this type of catalysts is due to the existence of atropisomers around the N(sp2)C(sp3) bond that links the azepinium core to the exocyclic stereocenter. Finally, we develop a general model to predict with certainty the high selectivity in the formation of non‐racemic epoxides of defined absolute configuration.

Raising the gold standard

Gold is the current star of metal catalysis, but most gold catalysts cannot control which mirror-image version of a molecule forms during a reaction. The answer lies with the positive catalyst's negative counter-ion.

Ligand Effects on ESR and Optical Properties of Gold Atoms in γ Irradiated Organic Solid Solutions at 77 K

Ligand effects on ESR and optical properties of Au0 atoms produced at 77 K in gamma irradiated solid solutions of AuCl/MTHF and AuCl/EtOH with and without HCl were investigated. Four groups of ESR lines were observed at 73 K more clearly around the magnetic fields at about 250, 280, 340, and 400 mT for both gamma irradiated MTHF and EtOH solid solutions with HCl than those without HCl. The values of a and g(J) calculated by Breit-Rabi analysis showed a remarkable dependence on the solvent polarity. It was confirmed that the signals were the hyperfine quartet corresponding to the transitions between the Zeeman levels of Au0 atoms with nuclear spin of 3/2 in the ground state, 2S(1/2). It was also confirmed that Au0 atoms produced after gamma irradiation were located in the nuclear environment of isotropic interaction with surrounding ligand molecules. Delocalization of the unpaired spin density of Au0 onto ligands is found to be as large as one in the case of Cu0 atoms. Our previous hypothesis of the occurrence of configuration mixing of d valence orbital into the wave function of the atom in its 2S(1/2) was strongly supported. The dependence of the ESR, optical absorption, and the steady-state emission and excitation characteristics on solvent polarity was cleared in this study. We observed two kinds of emissions i.e., a band at 385 nm and a set of emission bands at 456, 482, 484, and 520 nm. These correspond to two bands out of the six kinds of emissions observed previously. The bands were attributed to exciplex (Au0 x Ln...Au+)* and the excited Au0 atoms trapped in a large cavity, respectively. The negative counterion of Au+ of the gold compound plays an important role for the formation of the exciplexes.

Triarylamine on Nanocrystalline TiO2 Studied in Its Reduced and Oxidized State by Photoelectron Spectroscopy

The electronic and molecular structures of an electrochemically reduced and oxidized triarylamine layer (((3-ethyl(p-N,N-dimethylamino)phenyl)amino)propyl-1-phosphonic acid) adsorbed on a nanocrystalline TiO2 film have been investigated. Photoelectron spectroscopy (PES) measurements on electrochemically prepared surfaces and density functional theory (DFT) calculations for the free triarylamine molecule were performed. The major electronic difference between the reduced and oxidized state of the triarylamine molecules appears on the nitrogen atom. In the PES measurement a shift of the N 1s signal of 1.5 eV toward higher binding energies was measured between triarylamine in its reduced and oxidized states. The molecular structure of the surface layer was found to depend on the electrolyte used in the electrochemical preparation. The oxidized triarylamine molecule is positively charged and must therefore be accompanied by a negative counterion. The identity of the counterion was found to influence electron transfer between adjacent molecules, as explained by geometrical differences of the surface layer. During the measurements the PES N 1s signal was affected by the continuous X-ray illumination. Interestingly, a reversible photoreduction of the oxidized triarylamine was observed. The effect is accounted for by X-ray induced electron hole-pair generation in the TiO2 and subsequent electron transfer from the TiO2 conduction band to the singly occupied molecular orbital of the adsorbed molecule.

How vertebrate and invertebrate visual pigments differ in their mechanism of photoactivation.

In vertebrate visual pigments, a glutamic acid serves as a negative counterion to the positively charged chromophore, a protonated Schiff base of retinal. When photoisomerization leads to the Schiff base deprotonating, the anionic glutamic acid becomes protonated, forming a neutral species that activates the visual cascade. We show that in octopus rhodopsin, the glutamic acid has no anionic counterpart. Thus, the "counterion" is already neutral, so no protonated form of an initially anionic group needs to be created to activate. This helps to explain another observation-that the active photoproduct of octopus rhodopsin can be formed without its Schiff base deprotonating. In this sense, the mechanism of light activation of octopus rhodopsin is simpler than for vertebrates, because it eliminates one of the steps required for vertebrate rhodopsins to achieve their activating state.

Properties of interacting aspartic acid and lysine residues in the lactose permease of Escherichia coli.

The side chains of the interacting pair Asp237(helix VII)-Lys358(helix XI) or Asp240(helix VII)-Lys319(helix X) in the lactose permease of Escherichia coli were extended by replacement with Glu and/or Arg or by site-specific derivatization of single-Cys replacement mutants. Iodoacetic acid was used to carboxymethylate Cys, or methanethiosulfonate derivatives [Akabas, M. H., Stauffer, D. A., Xu, M., & Karlin, A. (1992) Science 258, 307] were used to attach negatively charged ethylsulfonate or positively charged ethylammonium groups. Replacement of Asp237 with Glu, carboxymethyl-Cys, or sulfonylethylthio-Cys yields active permease with Lys or Arg at position 358. Similarly, the permease tolerates replacement of Lys358 with Arg or ammonioethylthio-Cys with Asp or Glu at position 237. Remarkably, moreover, permease with Lys, Arg, or ammonioethylthio-Cys in place of Asp237 is highly active when Lys358 is replaced with Asp or Glu, in agreement with the conclusion that the polarity of the charge interaction can be reversed without loss of activity [Sahin-Tóth, M., Dunten, R. L., Gonzalez, A., & Kaback, H. R. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 10547]. In contrast, replacement of Asp240 with Glu abolishes lactose transport, and permease with carboxymethyl-Cys, at position 240 is inactive when paired with Lys319, but it exhibits significant activity with Arg319. Interestingly, sulfonylethylthio-Cys substitution for Asp240 also results in significant transport activity. Permease with Arg or ammonioethylthio-Cys in place of Lys319 exhibits high activity with Asp240 as the negative counterion, but no lactose transport is observed when either of these modifications is paired with Glu240.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of the retinal protonated Schiff base counterion in rhodopsin

Semiempirical molecular orbital calculations are combined with 13C NMR chemical shifts to localize the counterion in the retinal binding site of vertebrate rhodopsin. Charge densities along the polyene chain are calculated for an 11-cis-retinylidene protonated Schiff base (11-cis-RPSB) chromophore with 1) a chloride counterion at various distances from the Schiff base nitrogen, 2) one or two chloride counterions at different positions along the retinal chain from C10 to C15 and at the Schiff base nitrogen, and 3) a carboxylate counterion out of the retinal plane near C12. Increasing the distance of the negative counterion from the Schiff base results in an enhancement of alternating negative and positive partial charge on the even- and odd-numbered carbons, respectively, when compared to the 11-cis-RPSB chloride model compound. In contrast, the observed 13C NMR data of rhodopsin exhibit downfield chemical shifts from C8 to C13 relative to the 11-cis-RPSB.Cl corresponding to a net increase of partial positive or decrease of partial negative charge at these positions (Smith, S. O., I. Palings, M. E. Miley, J. Courtin, H. de Groot, J. Lugtenburg, R. A. Mathies, and R. G. Griffin. 1990. Biochemistry. 29:8158-8164). The anomalous changes in charge density reflected in the rhodopsin NMR chemical shifts can be qualitatively modeled by placing a single negative charge above C12. The calculated fit improves when a carboxylate counterion is used to model the retinal binding site. Inclusion of water in the model does not alter the fit to the NMR data, although it is consistent with observations based on other methods. These data constrain the location and the orientation of the Glu113 side chain, which is known to be the counterion in rhodopsin, and argue for a strong interaction centered at C12 of the retinylidene chain.

Partial characterization and HPLC isolation of bacteria-produced attractants for the Mexican fruit fly,Anastrepha ludens

Methods were developed to collect and isolate volatile chemicals produced by aStaphylococcus bacterium in tryptic soy culture that are attractive to protein-hungry adult Mexican fruit flies. Centrifugation of bacteria culture yielded a slightly attractive pellet containing most of the bacteria cells and a highly attractive supernatant. Supernatant filtered to remove the remaining bacteria was as attractive as the unfiltered supernatant. Filtrate at pH 7 and above was much more attractive than filtrate at pH 5 and below. Most of the attractiveness was retained on strong cation exchange media under acidic conditions and eluted with base. Attractive principles could not be trapped on adsorbents such as Porapak Q or extracted with organic solvents from aqueous preparations, but they were easily collected by headspace sweeping with steam. The attractive components were efficiently concentrated by rotary evaporation of steam distillate at pH 5, but at higher pH much of the attractiveness distilled. A reverse-phase HPLC method using a negative counter-ion was developed to separate and collect attractive components of concentrated steam distillate. Attractive fractions collected using this method were concentrated and injected onto silica HPLC. Activity eluted from silica in two distinct bands. Results suggest that the most attractive components of the bacterial odor are highly polar, low-molecular-weight amines.

Aspartic acid 85 in bacteriorhodopsin functions both as proton acceptor and negative counterion to the Schiff base.

In bacteriorhodopsin Asp85 has been proposed to function both as a negative counterion to the Schiff base and as proton acceptor in the early stages of the photocycle. To test this proposal further, we have replaced Asp85 by His. The rationale for this replacement is that although His can function as a proton acceptor, it cannot provide a negative charge at residue 85 to serve as a counterion to the protonated Schiff base. We show here that the absorption spectrum of the D85H mutant is highly sensitive to the pH of the external medium. From spectroscopic titrations, we have determined the apparent pK for deprotonation of the Schiff base to be 8.8 +/- 0.1 and the apparent pK for protonation of the His85 side chain to be approximately 3.5. Between pH 3.5 and 8.8, where the Schiff base is protonated, and the His side chain is deprotonated, the D85H mutant is completely inactive in proton transport. Time-resolved studies show that there is no detectable formation of an M-like intermediate in the photocycle of the D85H mutant. These experiments show that the presence of a neutral proton-accepting moiety at residue 85 is not sufficient for carrying out light-driven proton transport. The requirements at residue 85 are therefore for a group that serves both as a negatively charged counterion and as a proton acceptor.