Recovery Of Br Research Articles

In Situ Growth of MOF from Wood Aerogel toward Bromide Ion Adsorption in Simulated Saline Water.

Utilizing metal-organic framework (MOF) materials for the extraction of bromide ions (Br-) from aqueous solutions, as an alternative to chlorine gas oxidation technology, holds promising potential for future applications. However, the limitations of powdered MOFs, such as low utilization efficiency, ease of aggregation in water, and challenging recovery processes, have hindered their practical application. Shaping MOF materials into application-oriented forms represents an effective but challenging approach to address these drawbacks. In this work, a novel Ag-UiO-66-(OH)2@delignified wood cellulose aerogel (CA) adsorbent is synthesized using an oil bath impregnation method, involving the deposition of UiO-66-(OH)2 nanoparticles onto CA and the uniform dispersion of Ag0 nanoparticles across its surface. CA, characterized by the intertwined cellulose nanofiber structure and a highly hydrophilic surface, serves as an ideal substrate for the uniform growth of UiO-66-(OH)2 nanoparticles, which, in turn, spontaneously reduce Ag+ to form distributed Ag0 nanoparticles due to the abundant hydroxyl groups provided. Leveraging the well-defined biological structure of CA, which offers excellent mass transfer channels, and the highly dispersed Ag adsorption sites, Ag-UiO-(OH)2/CA exhibits remarkable adsorption capacity (642 mg/gAg) under optimized conditions. Furthermore, an integrated device is constructed by interconnecting Ag-UiO-(OH)2/CA adsorbents in series, affirming its potential application in the continuous recovery of Br-. This study not only presents an efficient Ag-UiO-(OH)2/CA adsorbent for Br- recovery but also sheds light on the extraction of other valuable elements from various liquid ores.

An Evaluation of Three Halogens (Cl, Br, and I) Data from a Geological Survey of Japan Geochemical Reference Materials by Radiochemical Neutron Activation Analysis

Fifteen Geological Survey of Japan (GSJ) geochemical reference materials were analyzed to determine the contents of three halogens (Cl, Br, and I) by using instrumental neutron activation analysis (INAA) and/or radiochemical NAA (RNAA). Two reference materials (JCp-1 and JSO-1) were analyzed using both INAA and RNAA. Although there were discrepancies in Cl and Br for JCp-1 between the INAA and RNAA data, probably due to sample heterogeneity, the INAA and RNAA data for JSO-1 were consistent with each other, within less than 7%, indicating that our RNAA data are reliable. With the repeated analyses of JR-3, the external repeatability of the data obtained using RNAA was evaluated to be 18% for Cl, 11% for Br, and 19% for I. Our RNAA data are in agreement with literature values using NAA for the three halogens, as well as those using isotope dilution mass spectrometry and ion chromatography for Cl. Systematically lower values when using neutron irradiation noble gas mass spectrometry (NI-NGMS) and inductively coupled plasma mass spectrometry (ICP-MS) with pyrohydrolysis can be observed, implying that there are losses for noble gas nuclides produced through the beta-decay of the neutron capture halogen nuclides in NI-NGMS and the non-quantitative recovery of Br and I during procedures in ICP-MS, respectively.

A novel photo-assisted electrochemically switched ion exchange technology for selective recovery of bromide ions

Effective recovery of high-value-added bromide ion (Br−) from aqueous solutions is significant because of its high application value. Electrochemically switched ion exchange (ESIX) has been proven as a valid method for the selective capture and recovery of target ions. As the photocatalysts are also used as the electroactive materials in the ESIX process, the light illumination could promote the excitation of electrons for the improvement of ion capture capacity. Herein, taking advantage of synergetic effect between photo and electric field we propose a novel photo-assisted electrochemically switched ion exchange (P-ESIX) strategy for the first time. As a try, Br−-vacancy BiOBr film is used as an ideal electrode material in P-ESIX system for the recovery of Br−, which not only possesses photo/electron bi-activity, but also exhibits high selectivity towards Br−. Compared with the traditional ESIX, this P-ESIX displays superior capture performances with a photo-assisted adsorption capacity growth rate of 23.09% with 1.23 times higher Br− adsorption capacity at 0.8 V applied potential. The capture capacity of Br− in P-ESIX reaches 106.80 mg g−1 with excellent stability. Meanwhile, P-ESIX working mechanism is deeply analyzed based on experiments and DFT calculations. This novel technology provides a new direction in separation field to achieve higher capture efficiency for the target ions.

A Rapid Acid Digestion Technique for the Simultaneous Determination of Bromine and Iodine in Fifty‐Three Chinese Soils and Sediments by ICP‐MS

Bromine and iodine are important tracers for geochemical and environmental studies. In this study, a rapid acid digestion (HNO3 + HF) with ammonia dilution for the simultaneous determination of bromine and iodine in soils and sediments using ICP‐MS was developed. The recoveries of Br and I were controlled by the synergic effect of temperature and time. It took only 15 min at 140 °C for the complete recovery of Br and I in sediment (GSD‐2) and soil (GSS‐24) reference materials, which is a process that needs 2–6 h at 90 °C. A serious loss of Br and I was found at a higher digestion temperature of 190 °C. A 5% v/v NH4OH dilution effectively eliminated the memory effects and stabilised the signals of Br and I. Moreover, ammonia dilution also avoided the corrosiveness of HF on the sample introduction system and torch of ICP‐MS. Tellurium is a more suitable internal standard element than In in the ammonia medium. To avoid the adsorption of residues of dissolution on Te, addition of Te should be carried out after centrifuging the solution. The developed method was successfully applied to determine Br and I in fifty‐three Chinese soil and sediment reference materials. This simple method shows great potential for the rapid determination of Br and I in large batches of geological and environmental samples commonly analysed for mineral exploration and environmental geochemistry studies.

Reorganization of sensory input at brainstem in hemifacial spasm and postparalytic facial syndrome.

We hypothesized the filtering of sensory input from face and hand at brainstem may reorganize in hemifacial spasm (HFS) and postparalytic facial syndrome (PFS). Thus, we examined the prepulse inhibition of blink reflex (BR-PPI) in HFS and PFS. We included 12 healthy subjects, 13 patients with HFS, and 11 patients with PFS. Baseline BR, BR recovery at interstimulus interval (ISI) of 300ms and BR-PPI at ISI of 100ms were performed on the right sides of healthy subjects and on both sides of patients. Within-subject analysis showed baseline BR and BR-PPI were similar between asymptomatic and symptomatic sides of patients with HFS whereas BR recovery was higher on the symptomatic side. In the PFS group, latency of R2 during baseline BR recording was longer (p=0.022) and R2 amplitude (p=0.046) was reduced on the symptomatic side compared to asymptomatic side. Reduction of R2 area in BR-PPI recordings was also the lowest in HFS compared to other two groups (p=0.000); however, it was also lower in patients with PFS compared to healthy subjects (p=0.018). BR-PPI was decreased on both sides of patients. The mean R2 recovery was higher on both sides of patients with HFS and PFS (p=0.007). Filtering of facial sensory input is decreased probably to monitor and to correct the sequence of facial movements in these disorders.

Conversion of HBr to Br2 in the flue gas from the combustion of waste printed circuit boards in post-combustion area

It is crucial to prevent the secondary pollution when recycling wastes. During the recycling of waste printed circuit boards by the pyrometallurgical process, bromine in the raw materials is normally released in the form of HBr/Br2 into the flue gas. In the present work, for the first time the conversion of HBr to Br2 during the cooling of flue gas in the post combustion area (PCA) was studied to provide evidences for the control of PBDD/Fs and the recycling of Br.The 1200 °C flue gas was cooled down at various cooling rates in a lab-scale system. The influence of PCA operating conditions, i.e., cooling temperature (Tc), residence time in the cooling zone (RTcz) and Oxygen partial pressure (PO2), on the conversion ratio was studied systematically. And the study was based on the newly developed method to determine HBr and Br2 contents in the flue gas at various temperatures.For each RTcz, i.e., 0.3, 0.5 and 0.7s, the ratio first increases with decreasing Tc to a maximum value at Tcmax and then decreases as Tc further drops. Tcmax depends on RTcz. For Tc = 200 °C and RTcz = 0.3s, approximately 31.1% HBr is converted to Br2. This is 51% lower than the highest. Moreover, at lower Tc and longer RTcz, the ratio can be less than that at higher Tc and shorter RTcz, vice versa. Accordingly, when cooling the system to a certain temperature, the shorter the RTcz is, the lower the conversion ratio will be. PO2 slightly influences the ratio. These are vital to the determination of Br sources for PBDD/Fs formation in PCA, which is valuable for the future pollution control. Besides, extension of the cooling time in the lower temperature range (from 200 °C at RTcz = 0.3s to 50 °C) within 300s greatly improves the ratio up to 91%. This provides the basis for the Br recovery rather than removal by chemical agents.

The possible role of the vagal nervous system in the recovery of the blood pressure control after cardiac arrest: a porcine model study

Previous studies have proved that the baroreceptor reflex (baroreflex) control of heart rate can be used for stratification of post-infarction population and, in general, cardiovascular disease populations. Many methods have been proposed to estimate the so-called baroreflex sensitivity (BRS) expressed as ms mmhg−1. Most of the studies that exploit BRS focus mainly on acute myocardial infarction (AMI) and there are no important works that investigate the role of BRS immediately after cardiac arrest (CA). The present work is a continuation of the published work of Ristagno et al ( Shock 41 72–8). In particular, the main objectives are: (1) to study the evolution of BRS after CA and following cardiopulmonary resuscitation (CPR); (2) to verify if the recovery of cardiovascular stability and arterial blood pressure is accompanied by a recovery of BR in a porcine model; (3) to investigate the possible causes of the BRS variations in response to CA and following cardiopulmonary resuscitation. All the BRS estimators adopted in this study show a significant decrease after CA. However, partial recovery is obtained in the last hours of post resuscitation. Analysis of impulse response showed a decrease in peak delay after CA and was significantly shorter 4 hours after CPR. This finding hints at a compensation mechanism: a faster response when baroreflex gain is not fully restored. The increase in the speed of baroreflex response is in line with the hypothesis of a key role of the parasympathetic nervous system, which is known to act at a higher firing rate.

On the Mechanism of the Plasmonic Field Enhancement of the Solar-to-Electric Energy Conversion by the Other Photosynthetic System in Nature (Bacteriorhodopsin): Kinetic and Spectroscopic Study

We have recently reported Ag nanoparticles (AgNPs) plasmonic field enhancement of the Bacteriorhodopsin (bR) photocurrent observed during its proton pump photocycle in solution. We proposed a mechanism based on the plasmonic field enhancement of the blue light effect which bypasses the slow part of the photocycle and increases the rate of proton production and thus the observed photocurrent. In this present work, we studied the AgNPs plasmonic field effect on the spectroscopy and kinetics of the bR proton pumping photocycle. We examined the blue light effect on both the recovery rate of bR and the decay rate of the M intermediate by using 532-nm short-pulsed laser excitation of bR in the presence of AgNPs and continuous-wave blue light exposure. Our observation showed that the recovery of bR and the decay of the M intermediate are both greatly accelerated in the presence of both AgNPs and blue light simultaneously. This gives support for the proposed mechanism of the enhanced proton current in the presence of AgNPs with a plasmon band in the blue region. It was found experimentally that the 40 nm-AgNPs enhancement of the blue light effect on the decay rate is around 400× larger than that of 8 nm-AgNPs. This is found to be in agreement with the known dependence of the plasmonic field on size and the overlap of the plasmonic extinction band with the absorption band of the M intermediates.

Dissipation of Bromide and Metribuzin Affected by Tillage and Crop Residue Management in Subarctic Alaska

Prudent use of agricultural fertilizers and herbicides is paramount for sustaining or improving surface and ground water quality in Subarctic regions, but little information is available that documents the loss of chemicals from agricultural lands in the Subarctic. This study aimed to ascertain more clearly how time of application and land management practices affect the loss of bromide and metribuzin in a Subarctic soil. Potassium bromide (KBr), a surrogate for nitrate, and metribuzin, commonly used to control broadleaf weeds, were applied in the autumn of 1996 and the spring of 1997 to a silt loam that had been subjected to conventional tillage (CT), minimum tillage (disk once [DO]), and no tillage (NT) since 1983. Superimposed on the tillage treatments were the removal or retention of barley (Hordeum vulgare L.) stubble and loose straw. Loss of these chemicals was ascertained by sampling the soil profile at the time of heading of barley, before freeze-up of the soil in autumn, and after spring thaw until September 1998. Tillage and residue treatments did not influence the recovery of autumn-applied or spring-applied Br. However, recovery of Br diminished with time: about 30% of the Br applied in autumn and 45% of that applied in spring remained in the soil profile by September 1998. Tillage, but not residue, treatments influenced the recovery of metribuzin. Recovery of metribuzin at the termination of this study was 6% or more in NT soil and 2% or less in CT and DO soil; greater recovery in NT soil was presumably a result of slower degradation in NT than in CT and DO. This study suggests that bromide (and thus nitrate) and metribuzin are more prone to leaching when applied in autumn and that tillage practices affect retention of metribuzin, but not nitrate, in the soil of Subarctic Alaska.

Comparative environmental analysis of waste brominated plastic thermal treatments

The aim of this research activity is to investigate the environmental impact of different thermal treatments of waste electric and electronic equipment (WEEE), applying a life cycle assessment methodology. Two scenarios were assessed, which both allow the recovery of bromine: (A) the co-combustion of WEEE and green waste in a municipal solid waste combustion plant, and (B) the staged-gasification of WEEE and combustion of produced syngas in gas turbines. Mass and energy balances on the two scenarios were set and the analysis of the life cycle inventory and the life cycle impact assessment were conducted. Two impact assessment methods (Ecoindicator 99 and Impact 2002+) were slightly modified and then used with both scenarios. The results showed that scenario B (staged-gasification) had a potentially smaller environmental impact than scenario A (co-combustion). In particular, the thermal treatment of staged-gasification was more energy efficient than co-combustion, and therefore scenario B performed better than scenario A, mainly in the impact categories of "fossil fuels" and "climate change". Moreover, the results showed that scenario B allows a higher recovery of bromine than scenario A; however, Br recovery leads to environmental benefits for both the scenarios. Finally the study demonstrates that WEEE thermal treatment for energy and matter recovery is an eco-efficient way to dispose of this kind of waste.

A novel chemically modified carbon paste electrode based on a new mercury(II) complex for selective potentiometric determination of bromide ion

A new modified carbon paste electrode based on a recently synthesized mercury (II) complex of a pyridine containing proton transfer compound as a suitable carrier for Br− ion is described. The electrode has a linear dynamic range between 3.00×10−2 and 1.0×10−5 M with a near-Nernastian slope of 61.0±0.9 mV per decade and a detection limit of 4.0×10−6 M (0.32 ppm). The potentiometric response is independent of the pH of the solution in the pH range 4.0–8.3. The electrode possesses the advantages of low resistance, fast response and good over a variety of other anions. It was applied as an indicator electrode in potentiometric titration of bromide ions and for the recovery of Br− from tap water.

Transport and deposition of Bacillus subtilis through an intact soil column

Bacterial transport in unsaturated soils is much less well understood than in saturated conditions, especially for intact soils. This paper aims to investigate the fate and transport of bacteria in intact soils with different water saturations, and particularly the effect of low suction (and hence removal of water flow in the largest macropores). An intact soil column (0.50 m diameter by 0.70 m depth) with a tension infiltrometer was used to investigate the transport and deposition of Bacillus subtilis endospores (i.e. dormant and persistent bacteria) during saturated and unsaturated flows. Soil porosity and pore size distribution were measured. Porosity decreased with depth and macropores were concentrated in the topsoil. Three tensiometers and a temperature sensor were installed along the soil column to monitor matric suction and temperature. Breakthrough curves for bacteria and chemical tracer Br– at 0 and 0.5 kPa suction were obtained during the 3-month leaching experiment. Bacterial breakthrough occurred earlier than the inert chemical tracer, which is consistent with effects of pore size exclusion. Also, saturated flow gave a significantly higher concentration and recovery ratio of leached bacteria, i.e. 51% v. 0.88%. Recovery of Br– in leachate at both suctions reached >85%. The column was destructively sampled for deposited endospores at the completion of leaching. Bacterial deposition was concentrated in the top 0.10 m, then decreased abruptly and was relatively constant with column depth, although showing some irregularity at the bottom of the column.

C1 Coupling via bromine activation and tandem catalytic condensation and neutralization over CaO/zeolite compositesElectronic supplementary information (ESI) available: additional figures. See http://www.rsc.org/suppdata/cc/b3/b314118g/

We demonstrate here an alternative scheme for C(1) coupling by way of methane bromination, followed by concurrent bromomethane condensation and quantitative HBr neutralization; regeneration of the metal oxide with O(2) with recovery of Br(2) completes the cycle.

Nitrogen‐15 and Bromide Tracers of Nitrogen Fertilizer Movement in Irrigated Wheat Production

AbstractIn irrigated agricultural systems, NO3 leaching is believed to result from high fertilizer rates combined with the need to periodically leach salts from surface soil horizons. The purpose of this research is to estimate N fertilizer movement in the soil of commercial fields of flood‐irrigated wheat (Triticum spp.) while documenting best management practices (BMPs). Potassium bromide and 15N labeled ammonium sulfate were applied as tracers of N fertilizer movement to 1‐ × 1‐m microplots replicated 9 or 10 times in three commercial fields of flood‐irrigated wheat. The soil was sampled at harvest to a depth of 2.4 to 4.0 m. More fertilizer was applied at two out of three sites and more irrigation water was applied at all sites than recommended by BMPs. Bromide recovery in the soil and plant tissue at harvest was 29, 68, and 61% of that applied at the three sites. Most of the 15N measured in the soil profile was contained in the 0‐ to 0.3‐m increment of soil. Recovery on 15N in the soil and plant tissue at harvest was 54, 54, and 69% of that applied. The Br recovery data suggests that 32 ± 28% (standard deviation) of the 15N applied may have leached. The highest leaching potential was measured at the site that adhered to BMPs for N fertilizer management but had the most permeable soil. Nitrate leaching in flood‐irrigated wheat production seems inevitable even if BMPs for N fertilizer management are followed.

Bacteriorhodopsin's intramolecular proton-release pathway consists of a hydrogen-bonded network.

In its proton-pumping photocycle, bacteriorhodopsin releases a proton to the extracellular surface at pH 7 in the transition from intermediate L to intermediate M. The proton-release group, named XH, was assigned in low-temperature FT-IR studies to a single residue, E204 [Brown, L. S., Sasaki, J., Kandori, H., Maeda, A., Needleman, R. , and Lanyi, J. K. (1995) J. Biol. Chem. 270, 27122-27126]. The time-resolved room-temperature step-scan FT-IR photocycle studies on wild-type and E204Q-, and E204D-mutated bacteriorhodopsin, which we present here, show in contrast that the FT-IR data give no evidence for deprotonation of E204 in the L-to-M transition. Therefore, it is unlikely that E204 represents XH. On the other hand, IR continuum absorbance changes indicate intramolecular proton transfer via an H-bonded network to the surface of the protein. It appears that this H-bonded network is spanned between the Schiff base and the protein surface. The network consists at least partly of internally bound water molecules and is stabilized by E204 and R82. Other not yet identified groups may also contribute. At pH 5, the intramolecular proton transfer to the surface of the protein seems not to be disturbed. The proton seems to be buffered at the surface and later in the photocycle released into the bulk during BR recovery. Intramolecular proton transfer via a complex H-bonded network is proposed to be a general feature of proton transfer in proteins.

Measuring Instantaneous Solute Flux and Loading with Time Domain Reflectometry

AbstractTime domain reflectometry (TDR) can be used to measure water content and conservative tracer concentration in soils. An important contribution of TDR for assessing or monitoring water‐soluble contaminant loading in real time under transient flow may be possible because of the ability to acquire rapid, multiplexed measurements of variables necessary for calculating loading — the water flux and resident contaminant concentration. An empirically derived equation relating resident soil Br− concentration (CBr, mg L−1) to apparent soil bulk electrical conductivity (σa, dS m−1) and soil water content (θ, m3 m−3) was established for Sparta sand (mesic, uncoated Typic Quartzipsamment). This equation has the form CBr = ασaγθδ, where α, γ, and δ are empirical constants. Using TDR, we conducted real‐time monitoring of a Br− tracer transported through a repacked Sparta sand soil column at four depths. Under steady‐state and transient‐flow experiemntal conditions and assuming a unit gradient and uniform vertical flow, instantaneous water flux at each monitored depth was estimated from TDR‐acquired θ data and soil hydraulic conductivity. For steady‐state conditions, recovery of Br− ranged from 72% at 15 cm to 133% at 45 cm, while water recovery averaged 92% for all depths. Under transient conditions, Br− recovery ranged from 65% at 15 cm to 121% at 60 cm. Percentages of Br− recovery were congruent across depths between steady‐ and transient‐flow experiments, leading us to conjecture that nonhomogeneous flow patterns and pockets of immobile water had developed within the column.

Degradation of methyl bromide by methanotrophic bacteria in cell suspensions and soils.

Cell suspensions of Methylococcus capsulatus mineralized methyl bromide (MeBr), as evidence by its removal from the gas phase, the quantitative recovery of Br- in the spent medium, and the production of 14CO2 from [14C]MeBr. Methyl fluoride fluoride (MeF) inhibited oxidation of methane as well as that of [14C]MeBr. The rate of MeBr consumption by cells varied inversely with the supply of methane, which suggested a competitive relationship between these two substrates. However, MeBr did not support growth of the methanotroph. In soils exposed to high levels (10,000 ppm) of MeBr, methane oxidation was completely inhibited. At this concentration, MeBr removal rates were equivalent in killed and live controls, which indicated a chemical rather than biological removal reaction. At lower concentration (1,000 ppm) of MeBr, methanotrophs were active and MeBr consumption rates were 10-fold higher in live controls than in killed controls. Soils exposed to trace levels (10 ppm) of MeBr demonstrated complete consumption within 5 h of incubation, while controls inhibited with MeF or incubated without O2 had 50% lower removal rates. Aerobic soils oxidized [14C]MeBr to 14CO2, and MeF inhibited oxidation by 72%. Field experiments demonstrated slightly lower MeBr removal rates in chambers containing MeF than in chambers lacking MeF. Collectively, these results show that soil methanotrophic bacteria, as well as other microbes, can degrade MeBr present in the environment.

Effect of the arginine-82 to alanine mutation in bacteriorhodopsin on dark adaptation, proton release, and the photochemical cycle.

The pH dependence of the rate constant of dark adaptation (thermal isomerization from all-trans- to 13-cis-bR) drastically changes when Arg82 of bacteriorhodopsin is replaced by an alanine. In the wild type (WT) the rate decreases sharply between pH 2.5 and pH 5. In R82A the sharp decrease is shifted to pH > 7. This correlates with the shift in the pK of the purple-to-blue transition from pH 2.6 in the wild type to pH 7.2 in the mutant (in 150 mM KCl). We propose that the same group that controls the purple-to-blue transition, namely, Asp85, catalyzes dark adaptation. The rate of dark adaptation in the R82A mutant is proportional to the fraction of protonated Asp85, indicating that dark adaptation occurs when Asp85 is transiently protonated. Thermal isomerization is at least 2 x 10(3) times more likely when Asp85 is protonated (blue membrane) than when it is deprotonated (purple membrane). The pH dependence of dark adaptation in the WT can be explained by a model in which the rate of dark adaptation in the WT is also proportional to the fraction of protonated Asp85 and that the pK of Asp85 depends on some other group, X, which deprotonates (or moves away from Asp85) with pK9 and causes the shift in the pK of Asp85 from 2.6 to 7.2. The quantum yield of light adaptation is at least an order of magnitude less in R82A as compared to the WT. The rise time of M formation is very fast in R82A and, unlike the WT, pH independent (1 microsecond versus 85 and 6 microseconds in the WT at pH 7 and 10, respectively). The activation energy of the L to M transition is 6.9 kcal/mol versus 13.5 kcal/mol in the WT. Thus the loss of a positive charge in the active site greatly increases the rate of light-induced deprotonation of the Schiff base. In the R82A mutant, the M decay at pH > 8.8 is much faster than the recovery of initial bR, which suggests a decrease in the rate of back-reaction from N to M. In a suspension of R82A membranes the rate of proton release as measured by the pH-sensitive dye pyranine is delayed by at least 20-fold (in 2 M KCl), while the uptake of protons did not change much (12 ms in the WT versus 8 ms in R82A).(ABSTRACT TRUNCATED AT 400 WORDS)

Distortions in the photocycle of bacteriorhodopsin at moderate dehydration

The photoreaction of bacteriorhodopsin was studied in moderately dehydrated films (relative humidities between 100 and 65%). Time-resolved difference spectra from a gated optical multichannel analyzer, between 100 ns and 100 ms after photoexcitation, were decomposed into sums of difference spectra of the intermediates K, L, M, N, and O, and the kinetics obtained were fitted to various alternative schemes. The data confirm the model of a single reaction sequence with reversible reactions we proposed recently for purple membrane suspensions (Váró, G., and J. K. Lanyi. Biochemistry. 1990. 29:2241-2250) but including reversibility also for the reaction K in equilibrium with L in addition to L in equilibrium with M, M in equilibrium with N, and N in equilibrium with O. With increasing dehydration the kinetics were increasingly dominated by the reverse reactions. As before, fitting the data required the existence of two M species in series: L in equilibrium with M1 in equilibrium with M2 in equilibrium with N. The M1 in equilibrium with M2 reaction was greatly slowed at lower humidities. This step might be the switch for the unidirectional transfer of protons. With increasing dehydration recovery of BR occurred less and less via the N intermediate and increasingly via direct shunts from the two M species. As indicated earlier by electrical measurements with similarly dried bacteriorhodopsin films (Váró, G., and L. Keszthelyi, 1983. Biophys. J. 43:47-51). The latter are pathways not necessarily associated with net proton translocation.