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Purification of phosphoric acid by melt crystallization

Purification of phosphoric acid by melt crystallization

Phosphoric acid is an inorganic acid. It is widely used in chemical, food, fertilizer and electronic industries according to its purity (industrial grade, food grade, technical grade and electronic grade). It can be produced by two different processes, the dry process and the wet process [Wah80]. Due to the high energy consumption of the dry process, the wet process is the most often used process to produce phosphoric acid from phosphate ore. However, many impurities such as iron, aluminum, magnesium, fluorine and sulfate remain as impurities in the found products. Electronic grade phosphoric acid can be used to etch circuits and displays in electronic industry. Any impurities may change the properties or destroy the devices. Therefore, an efficient technique of purification is needed. There are several methods to purify and to get a pure phosphoric acid such as solvent extraction [Ahm07], ion exchange [Ell06], electroosmosis [Koo99] and crystallization [Ris25]. Crystallization, as a highly efficient, low cost and environmental friendly method, is therefore considered here as a potential purification step. Much research has been carried out in the field of the phosphoric acid concerning physical properties of phosphoric acid [Dav69, Jia11], the phase diagram with water [Smi09, Jia12b], the metastable zone width of phosphoric acid with different impurities [Kim06, Ma09a, San10], the growth of the phosphoric acid hemihydrate crystals in a suspension crystallization using FBRM for measurements [Ma09b, Ma10b], suspension melt crystallization of phosphoric acid [Wan12] and modeling of layer melt crystallization [Jia12a].
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Determination of Anion Transference Number and Phosphoric Acid Diffusion Coefficient in High Temperature Polymer Electrolyte Membranes

Determination of Anion Transference Number and Phosphoric Acid Diffusion Coefficient in High Temperature Polymer Electrolyte Membranes

The passage of an electrical current through phosphoric acid doped polymer membranes involves parasitic migration of the acid, which imposes a critical issue for long-term operation of the high temperature polymer electrolyte membranes fuel cell (HT-PEMFC). To elucidate the phenomenon, a three-layered membrane is constructed with embedded micro reference electrodes to measure phosphoric acid redistribution in a polybenzimidazole based membrane. Under a constant load, a concentration gradient develops due to the acid migration, which drives the back diffusion of the acid and eventually reaches a steady state between migration and diffusion. The acid gradient is measured as a difference in local ohmic resistances of the anode- and cathode-layer membranes by electrochemical impedance spectroscopy. The phosphoric acid diffusion coefficient through the acid doped membrane is about 10 −11 m 2 s −1 , at least one order of magnitude lower than that of aqueous phosphoric acid solutions. The anion (H 2 PO 4 − ) transference number is found to range up to 4% depending on current density, temperature and atmospheric humidity of the cell, implying that careful control of the operating parameters is needed in order to suppress the vehicular proton conduction as a degradation mitigation strategy.
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Determination of Anion Transference Number and Phosphoric Acid Diffusion Coefficient in High Temperature Polymer Electrolyte Membranes

Determination of Anion Transference Number and Phosphoric Acid Diffusion Coefficient in High Temperature Polymer Electrolyte Membranes

phosphoric acid fuel cell (PAFC) community assumes that the an- ion transference number under its normal operating conditions is around 0.1. 41 It must be noted that the electrolyte in phosphoric acid fuel cells is contained in a ceramic matrix with a thickness about 200 µm, 42 with different mass transport properties than in a polymer membrane. The water uptake capabilities of the phosphoric acid is diminished as more benzimidazole is present within the system, caus- ing phosphoric acid doped PBI to have a different acid composition in comparison to that of the PAFC. 29 Also, the PAFC typically contains much more phosphoric acid than a HT-PEMFC. It seems reasonable that a fraction of 10% of the current involves the acid migration in PAFC while only 2% to 4% in HT-PEMFC. This may also corre- late with the very low acid loss reported for HT-PEMFC operation. The effect of acid migration may also explain the observed increase in degradation of HT-PEMFC at very high current densities. 43 The coupled effect of acid migration and back diffusion was also dis- cussed for the operation of fuel cells with poly-perflourosulfonic acid membranes. 44 In that case the very low diffusion coefficient of the acid is assumed to be responsible for the very poor performance.
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In Operando Neutron Radiography Analysis of a High-Temperature Polymer Electrolyte Fuel Cell Based on a Phosphoric Acid-Doped Polybenzimidazole Membrane Using the Hydrogen-Deuterium Contrast Method

In Operando Neutron Radiography Analysis of a High-Temperature Polymer Electrolyte Fuel Cell Based on a Phosphoric Acid-Doped Polybenzimidazole Membrane Using the Hydrogen-Deuterium Contrast Method

In order to observe the transport phenomena or structural changes in a PEFC that operates at high temperature, some effective techniques have already been applied. For example, Maier et al. [ 5 , 6 ] used synchrotron X-ray radiography to perform phosphoric acid distribution and re-distribution inside MEAs (membrane electrode assemblies), which were considered as one of the first real in operando attempts within operating high temperature PEFCs. In these studies, the redistribution of the acid from the open cell voltage (OCV) condition, to the load condition was analyzed on the basis of the in-plane direction of the cell, with membrane expansions and contractions at the micrometer scale being explained by the hydration and dehydration of phosphoric acid in the membrane, which is highly affected by the water partial pressure within the cell. A few years later, in operando Raman spectroscopy in high temperature PEFCs was conducted by Majerus et al. [ 7 ]. In that work, a change of different acid concentrations was noted when current load changes occurred, which proved that Raman spectroscopy was a useful tool for investigating the relationship between phosphoric acid and polymer, as well as the chemical processes within the membrane under operating conditions. However, there have been no further reports of this measurement. In the meantime, a successful segmentation of the quantitative determination of phosphoric acid content and concentration in the gas diffusion layers of high temperature PEFC MEAs was first reported by using 3D X-ray tomographic microscopy images [ 8 ]. Moreover, in-operando electron paramagnetic resonance (EPR) is considered to be an appropriate method to investigate the chemical degradation mechanism of polymer electrolytes in fuel cells. The first attempt at using this technique in high temperature PEFCs was undertaken by Niemoeller et al. [ 9 ]. However, the electrochemical performance of the cell was not given.
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Electrochemical Corrosion Study of Metallic Materials in Phosphoric Acid as Bipolar Plates for HT-PEFCs

Electrochemical Corrosion Study of Metallic Materials in Phosphoric Acid as Bipolar Plates for HT-PEFCs

High-temperature polymer electrolyte fuel cells (HT-PEFCs) op- erate in the range of 120–180 ◦ C and currently employ phosphoric acid doped polybenzimidazole membranes. This in turn represents a quite aggressive environment for the components of a fuel cell. Presently, bipolar plates are made of graphitic composite materials. Significant drawbacks are the apparent corrosion rates, a high effort of manu- facturing and the uptake of phosphoric acid. Previous studies have demonstrated a wide range of corrosion current densities for different types of graphite up to the level of 1 mA cm −2 in ∼100 wt% H
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In Operando Neutron Radiography Analysis of a High-Temperature Polymer Electrolyte Fuel Cell Based on a Phosphoric Acid-Doped Polybenzimidazole Membrane Using the Hydrogen-Deuterium Contrast Method

In Operando Neutron Radiography Analysis of a High-Temperature Polymer Electrolyte Fuel Cell Based on a Phosphoric Acid-Doped Polybenzimidazole Membrane Using the Hydrogen-Deuterium Contrast Method

In order to observe the transport phenomena or structural changes in a PEFC that operates at high temperature, some effective techniques have already been applied. For example, Maier et al. [ 5 , 6 ] used synchrotron X-ray radiography to perform phosphoric acid distribution and re-distribution inside MEAs (membrane electrode assemblies), which were considered as one of the first real in operando attempts within operating high temperature PEFCs. In these studies, the redistribution of the acid from the open cell voltage (OCV) condition, to the load condition was analyzed on the basis of the in-plane direction of the cell, with membrane expansions and contractions at the micrometer scale being explained by the hydration and dehydration of phosphoric acid in the membrane, which is highly affected by the water partial pressure within the cell. A few years later, in operando Raman spectroscopy in high temperature PEFCs was conducted by Majerus et al. [ 7 ]. In that work, a change of different acid concentrations was noted when current load changes occurred, which proved that Raman spectroscopy was a useful tool for investigating the relationship between phosphoric acid and polymer, as well as the chemical processes within the membrane under operating conditions. However, there have been no further reports of this measurement. In the meantime, a successful segmentation of the quantitative determination of phosphoric acid content and concentration in the gas diffusion layers of high temperature PEFC MEAs was first reported by using 3D X-ray tomographic microscopy images [ 8 ]. Moreover, in-operando electron paramagnetic resonance (EPR) is considered to be an appropriate method to investigate the chemical degradation mechanism of polymer electrolytes in fuel cells. The first attempt at using this technique in high temperature PEFCs was undertaken by Niemoeller et al. [ 9 ]. However, the electrochemical performance of the cell was not given.
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Characterization of phosphoric acid doped polybenzimidazole membranes

Characterization of phosphoric acid doped polybenzimidazole membranes

39 magnitude in the acid doping level range from 0 - 6 moles per repeating unit of the polymer at 150 °C. On the other hand, nevertheless how the cell is assembled, the catalyst layer of the cell would have some amount of phosphoric acid due to the phosphoric acid redistribution [5]. Maier et al. [87] prepared the MEAs by assembled un-doped membrane with pre-acid doped gas diffusion electrodes (GDEs). They estimated that after the assembly the acid doping level in the membrane was about 2 molecules phosphoric acid per repeating unit of the polymer. The rest phosphoric acid existed in the catalyst layer. In addition, they found that the total resistance of the MEAs decreased with the increase of current density. Kwon et al. [88] assembled MEAs with doped membranes and dry GDEs. They found that after assembly at room temperature a total amount of about 40 % phosphoric acid moved into catalyst layers for cathode and anode. By comparing the flooded cell (with 50% phosphoric acid in catalyst layers) and non-flooded cell (with 40% phosphoric acid in catalyst layers), they further found that the charge transfer resistance of the flooded cell was larger than that of the non-flooded cell. Chen et al. [89] investigated the charge transfer resistance of fuel cells as functions of current density and operating temperature. They found that the charge transfer resistance decreased with the increase of the temperature and current density. The effect of temperature on charge transfer resistance was also found by Zhang et al. [90]. Souse et al. [91] reported the current density at 0.4V of HT-PEFCs as a function of phosphoric acid loading in catalyst layers at 150 °C. They demonstrated that the current density increased between a volume fraction of 5% and 30% of phosphoric acid in catalyst layers. The optimum current density was estimated to be reached between 30% and 55%, and for the phosphoric acid content in catalyst layer above 55% the current density started to fall caused by the flooding effect of phosphoric acid.
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Lignocellulose Fractionation Using Recyclable Phosphoric Acid: Lignin, Cellulose, and Furfural Production

Lignocellulose Fractionation Using Recyclable Phosphoric Acid: Lignin, Cellulose, and Furfural Production

The practical use of phosphoric acid as catalyst may be hampered by its costs; [35] however, such biorefinery concepts might become econom- ically viable with optimal heat integration, efficient recycling of the acid, and lowering the energy consumption of the process. Thus, integrated concepts, in which several marketable prod- ucts are generated and the catalyst can be recycled, are needed. In this work, a holistic concept is put forth, evaluating the use of phosphoric acid for lignocellulose pretreatment and pentose dehydration in a biphasic system. By using the same catalyst- solvent system for both reaction steps, downstream processing might be simplified, although the use of other biogenic solvents [e. g., cyclopentyl methyl ether (CPME) [36–38]
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Assessment of Layer-By-Layer Modified Nanofiltration Membrane Stability in Phosphoric Acid

Assessment of Layer-By-Layer Modified Nanofiltration Membrane Stability in Phosphoric Acid

Abstract: Nanofiltration (NF) can enable P recovery from waste streams via retaining multivalent impurities from spent pickling acid. However, with the currently available membranes, an economically feasible process is impossible. Layer-by-layer modified NF membranes are a promising solution for the recovery of P from acidic leachate. LbL membranes show a high level of versatility in terms of fine tuning for ion retention, which is necessary to achieve sufficient phosphorus yields. However, the stability of layer-by-layer modified membranes during phosphoric acid (H 3 PO 4 ) filtration needs to be further investigated. In our study, we show that a polyethersulfone hollow fiber membrane modified with four or eight bi-layers was stable during immersing and filtering of a 15% H 3 PO 4 solution. A sulfonated polyethersulfone (sPES)-based hollow fiber LbL membrane was only stable during filtration. Thus, we show the importance of applying real process conditions to evaluate membranes. Another important aspect is the influence of the high ionic strength of the feed solution on the membrane. We show that a high ionic strength led to a decrease in Mg retention, which could be increased to 85% by adjusting the process parameters.
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Electrochemical Corrosion Study of Metallic Materials in Phosphoric Acid as Bipolar Plates for HT-PEFCs

Electrochemical Corrosion Study of Metallic Materials in Phosphoric Acid as Bipolar Plates for HT-PEFCs

The required corrosion current densities lower than 1 μA cm −2 for anodic and cathodic conditions 4 could not be achieved. Based on the results from this study, it is not feasible to employ bare commercially available stainless steels or Ni-based alloys as metallic bipolar plates for HT-PEFC application. On the one hand, the typical operating temperature of a HT-PEFC lies within a range of 160–180 ◦ C and this would imply even higher corrosion rates than obtained in this work at 130 ◦ C. And on the other hand, it should be also taken into account that in a fuel cell there is distinctly less phosphoric acid in contact with the bipolar plate ( ∼1 mg cm −2 ). Consequently, corrosion is going to be reduced or even inhibited due to a saturation of the present wetted acid film. Further it has to be considered that the enhanced concentration of metal cations will increase the pH in the thin acid film and thus change the stability of passivation. Both effects are important parts of ongoing research activities. To overcome corrosion and the rise of the contact resistance but to keep the benefits of metals, one possibility could be applying conductive and inert coatings. Studies on various promising ceramic and graphitic coatings are currently in progress. Additionally, the increase of the interfacial contact resistance, which results from passivation of metallic materials, is also going to be considered.
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Synthesis of microporous polymeric BINOL-deríved phosphoric acids and applications in hetererogeneous asymmetric organocatalysis

Synthesis of microporous polymeric BINOL-deríved phosphoric acids and applications in hetererogeneous asymmetric organocatalysis

The proposed mechanism by Kobayashi group was that the reaction proceeds by an aza-ene- type pathway. This work inspired Terada and coworkers to further explore and develop a highly efficient organocatalytic reaction using a BINOL derived phosphoric acid catalyst (see Scheme 49). They showed that BINOL-derived phosphoric acid is capable of catalyzing addition of enamides or enecarbamates to N-benzoylimines with high enantioselectivity. Hydrolysis of the addition product leads to chiral β-keto amines which are structurally useful moiety in several important bioactive molecules.
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Biosynthesis of Stizolobinic Acid and Stizolobic Acid in the Etiolated Seedlings of Stizolobium hassjoo 

Biosynthesis of Stizolobinic Acid and Stizolobic Acid in the Etiolated Seedlings of Stizolobium hassjoo 

Measurement of radioactivity was carried out in a liquid scintillation spectrometer (Beckman, model LS250). The dioxane scintillation fluid contained 4 g of PPO, 0.2 g of POPOP, 60 g of naphthalene, 100 ml of absolute methanol, 20 ml of ethylene glycol per litre of dioxane (counting efficiency 83 — 85%). The radioactivity on paper chromato­ grams from small scale feeding experiments was determined after combustion of the marked radio­ active spots corresponding to stizolobinic or stizo­ lobic acid with a sample oxidizer (Packard Tri- Carb, model 305). A mixture of 15 g of PPO and 1 g of bis-MSB dissolved in 1 litre of toluene was used as the scintillant (counting efficiency 51 — 69%). Radioautographs of paper chromatograms were ob­ tained conventionally by exposing the papers to X-ray films.
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Synthesis of 5-AminoIevulinic Acid 

Synthesis of 5-AminoIevulinic Acid 

T herefore, it is often used for biochem ical investiga­ tions and a sim ple synthesis would be useful. Till now , a number o f synthesis have been described, which are m ostly tim e-consum ing or result in difficult to clean product(s) (for a com plete list see [1 — 3]). Som e years ago, M cD onald [4] published the bromi- nation o f levulinic acid yielding 3-bromo- and 5-brom olevulinic acid which can be separated by dis­ tillation. We obtained 5-am inolevulinic acid from 5-brom olevulinic acid by a 2-step sequence (Gabriel- synthesis and hydrolysis) in 33% overall yield (Fig. 2).
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Activation of the Glutamic Acid-Dependent Acid Resistance System in Escherichia coli BL21(DE3) Leads to Increase of the Fatty Acid Biotransformation Activity

Activation of the Glutamic Acid-Dependent Acid Resistance System in Escherichia coli BL21(DE3) Leads to Increase of the Fatty Acid Biotransformation Activity

Product analysis by GC/MS The concentrations of remaining carboxylic acids in the medium such as ricinoleic acid, n-hep- tanoic acid, and ω-hydroxyundec-9-enoic acid were determined as described previously [ 5 ]. The reaction medium was mixed with an equal volume of ethyl acetate containing palmitic acid as an internal standard. The organic phase was harvested after vigorous vortexing and was then subjected to derivatization by adding N-methyl-N-(trimethylsilyl) trifluoroacetamide (TMS). The TMS derivatives were analyzed using a Thermo Ultra Trace GC system connected to an ion trap mass detector (Thermo ITQ1100GC-ion Trap MS, Thermo Scientific, and India- napolis, IN, USA). The derivatives were separated on a non-polar capillary column (30 m length, 0.25 μm film thickness, HP-5MS, Agilent Technologies, Palo Alto, CA, USA). A linear temperature gradient was programmed as 90°C, 5°C/min to 280°C. The injection port temper- ature was 230°C. Mass spectra were obtained by electron impact ionization at -70 eV. Scan spectra were obtained within the range of 100–600m/z. Selected ion monitoring (SIM) was used for the detection and fragmentation analysis of the reaction products.
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Chemistry of Fenchonesulfonic Acid Derivatives 

Chemistry of Fenchonesulfonic Acid Derivatives 

{ ( 1 R) -3,3-Dimethyl-2-oxobicyclo[2.2.1 ]hept-l -yl}- methanesulfonyl chloride (3) and { ( 1 S, Z)-l-chloro- 7,7-dimethylbicyclo [2.2.1 ]hept-2-y lidenejmethane- sulfonyl chloride (10): To fenchonesulfonic acid (25 g, 0.1 mol of the m onohydrate), thionyl chlo­ ride (100 ml) was added, and the mixture kept at 50 °C for 12 h. The excess of thionyl chloride was removed in vacuum. Recrystallization from hex­ ane gave fenchone sulfonyl chloride (3), having properties identical to those described [12], yield 7 0-9 0 % . The m other liquors contained a mixture of 3 and 10 which could not be separated, but NM R data for 10 could be obtained from the mix­ ture (Tables I and II).
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Acid sulfate soils: Processes and assessment

Acid sulfate soils: Processes and assessment

Most acid sulfate soils are of Holocene age and were mostly formed during and after the early Holocene sea level rise, which induced the formation of thick and extensive pyritic sediments in many coastal plains of the world (Pons et al., 1982). After the sea level rise leveled off around 5000 yrs. BP, sediments with lower pyrite content accumulated in areas with large sedimentation rates and fast coastal accretion (Pons et al., 1982). Under lower sedimentation rates, highly pyritic peats could be deposited. The interplay of sedimentation, sea level rise and paleo-relief was a governing factor for acid sulfate soil formation during the Holocene. These factors controlled the extent and persistence of the intertidal zones and tidal creeks, which were essential for pyrite accumulation. In a general view, the formation of these soils is controlled by changes in sea level, sedimentation rate, paleo-relief, local tectonics, vegetation and the chemical limiting factors for the formation of sulfides as described above. This variety of controls has to be considered in detail to predict acid sulfate soil distribution.
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Synthese des Indolalkaloids α-Cyclopiazonic Acid

Synthese des Indolalkaloids α-Cyclopiazonic Acid

Benzoesäureanhydrid (471 mg, 2.08 mmol) gelöst in DMF (1.6 ml) wird tropfenweise bei 0 °C unter Stickstoffatmosphäre über eine Glasspritze zugegeben und die Reaktion anschließend noch [r]

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Lyophilization of nucleic acid nanoparticles

Lyophilization of nucleic acid nanoparticles

discussed [17]. According to the “preferential exclusion hypothesis”, established for protein stabilization, solutes are preferentially excluded from the surface resulting in the formation of a stabilizing solvent layer [17, 178-179]. However, it is questionable if this hypothesis can be adapted to nucleic acid nanoparticles, as the relatively high amounts of cryoprotectants required point to a nonspecific bulk stabilization [17, 178-179]. Based on the “glass formation or vitrification hypothesis”, nucleic acid nanoparticles are entrapped in the amorphous gassy matrix when the sample is cooled below the glass transition temperature (Tg`) limiting particle mobility and thus, preventing particle aggregation [17, 178]. As some sugars were able to preserve particle size at temperatures well above Tg` vitrification cannot be the only stabilization mechanism [180]. The “particle isolation hypothesis” states that particles have to be sufficiently separated in the freeze-concentrate in order to inhibit particle aggregation, which is observed above a critical excipient to complex ratio [180]. However, these three mechanisms are not suitable to solely explain the stabilization of nucleic acid nanoparticles during freezing. Thus, the influence of freezing on nucleic acid nanoparticles and underlying stabilization mechanisms during freezing will be addressed in detail in Chapter 6.
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Glutamic Acid-l-semialdehyde, a Hypothetical Intermediate in the Biosynthesis of 5-Aminolevulinic Acid 

Glutamic Acid-l-semialdehyde, a Hypothetical Intermediate in the Biosynthesis of 5-Aminolevulinic Acid 

First, selective reduction of the carbonic acid to a prim ary alcohol with diborane or borane-dim ethyl- sulfide complex [19], and second, oxidation of the alcohol to an aldehyde function with pyridinium dichrom ate [20] or other approved reagents (Fig. 4). The reduction of 1 to the alcohol 6 was accomplished easily in 65% yield but the oxidation of 6 failed. T reatm ent of 6 with pyridinium dichrom ate yielded only overoxidized product 1 whereas 6 rem ained un­ changed by treatm ent with pyridiniumchlorochro- m ate [21]. O th er reagents were not tried with regard to the acid lability of the protective groups.
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Aspartic Acid-Aspartate and Glutamic Acid-Glutamate Hydrogen Bonds Having Great Proton Polarizability — IR Investigations 

Aspartic Acid-Aspartate and Glutamic Acid-Glutamate Hydrogen Bonds Having Great Proton Polarizability — IR Investigations 

It is shown th at the structurally symmetrical hydrogen bonds form ed between aspartic acid and aspartate residues and formed between glutamic acid and glutam ate residues are short hydrogen bonds with great proton polarizabilities. The proton potential in these hydrogen bonds is probably a broad flat well. Thus via such hydrogen bonds positive charge can be translocated in proteins.

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