A comparative study of myoglobin stability in the presence of Hofmeister anions of ionic liquids and ionic salts

To reveal the impact of ionic liquids (ILs) on the stability of proteins, a series of ILs possessing same 1-butyl-3-methylimidazolium cation [Bmim]⁺ with a set of Hofmeister anions such as SCN⁻, HSO₄⁻, Cl⁻, Br⁻, CH₃COO⁻ and I⁻ were used and their effects on the myoglobin (Mb) structure and stability were studied. For the sake of comparison and also to explore the extent of the stabilization behavior of ILs toward Mb stability, we have chosen a set of ionic salts (I_s) of a fixed sodium cation (Na⁺) with the same series of anions such as SCN⁻, SO₄⁻², Cl⁻, Br⁻, CH₃COO⁻ and I⁻. UV–vis, fluorescence and circular dichroism (CD) spectroscopic techniques were used in order to investigate the stability behavior of Mb in ionic species (I_s and ILs). The results reveal that both I_s and ILs had a negative influence on the stability of Mb. Apparently, the flexibility in the native structure of Mb gradually increases with the increase in the concentration of I_s and ILs at pH 7.0. Therefore, a sharp decrease in the transition temperature (T_m) of the native Mb is observed in the presence of I_s and ILs.     

TOXICITY OF BISULFITE TO PHOTOSYNTHESIS AND RESPIRATION1

Inhabition of photosynthesis in Chloroccoum sp by bisulfileion was the reciprocal of the light intensity curve. Respiration was least affected of the bisulfite after endogenous substrate was reduced by incubation in darkness. Maximum areduction in growth occurred with bisulfile treatment at or above optimal growth temperatures. Maximum phytotoxicity correlated with conditions resulting in maximum metabolic activity. The order of toxicity was –H₂SO₃HSO₃^?SO₃.     

Long distance nitrogen air pollution effects on lichens in Europe

The epiphytic lichen flora of 25 European ICP-IM monitoring sites, all situated in areas remote from air pollution sources, was statistically related to measured levels of SO₂in air, NH₄⁺, NO₃⁻ and SO₄²⁻ in precipitation, annual bulk precipitation, and annual average temperature. Significant regression models were calculated for eleven acidophytic species. Several species show a strong negative correlation with nitrogen compounds. At concentrations as low as 0·3 mg N l⁻¹in precipitation, a decrease of the probability of occurrence is observed for Bryoria capillaris, B. fuscescens, Cetraria pinastri, Imshaugia aleurites and Usnea hirta. The observed pattern of correlations strongly suggests a key role of NH₄⁺ in determining the species occurrence, but an additional role of NO₃⁻ cannot be ruled out. Some species show a distinct response to current levels of SO₂as well. It may be concluded that long distance nitrogen air pollution has strong influence on the occurrence of acidophytic lichen species.     

THE BIOSYNTHESIS OF 3-METHOXY-4-HYDROXYPHENYLGLYCOL SULPHATE BY LIVER AND BRAIN

—3-Methoxy-4-hydroxyphenylglycol (MHPG) formed a sulphate conjugate when incubated with ATP, Mg²⁺ ions, Na₂³⁵SO₄ and the high-speed supernatant preparations of rabbit or rat brain. The same reactions could be catalysed by similar enzyme preparations from liver. The sulphated product was separated and identified by paper chromatography. On acid hydrolysis, it released both Na₂³⁵SO₄ and the free glycol. The measurement of this labelled sulphate was used as a specific assay procedure for determining the overall sulphoconjugatory process. The pH optimum of the reaction is 7.8. For rabbit brain, the K_m for Na₂SO₄ determined for the activating system is 3.6 × 10⁻⁴m , and that for MHPG for the sulphotransferase reaction is 1.05 × 10⁻⁴m . The specific enzyme activity, expressed as nmol ³⁵SO₄ incorporated/h/mg protein for a 30-min assay is as follows: rat brain, 2.8; rabbit brain, 1.6; rat liver, 33.4and rabbit liver, 15.0. Dithiothreitol at 3 mm concentration had no significant effect on the sulphation of MHPG in all these preparations.     

Storage of abnormal oxidants ‘∑1’, ‘∑2’ and ‘∑3’ in photosynthetic water oxidases inhibited by Cl−-removal

The Cl⁻ requirement of photosynthetic O₂ evolution was studied by thermoluminescence measurements with purified Photosystem II-containing membrane particles from chloroplast thylakoids. When Cl anions had been removed from the particles either by an alkaline shock in a Cl⁻-free medium, or by treatment with SO²⁻₄, the pattern of the thermoluminescence emission after illumination with increasing numbers of flashes suggested that the oxidant storage in the water oxidase could only proceed up to the final step. The final step itself. i.e., the advance to the water-oxidizing S₄ state, apparently was blocked. An upward shift of the emission temperatures of the thermoluminescence bands was seen both in the absence and in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethyl urea, indicating that the stored oxidants had redox properties different from those of normal, Cl⁻-sufficient preparations. These properties were readily interconvertible by addition or removal of Cl⁻. We postulate that in Cl⁻-deficient water oxidases abnormal S₁, S₂ and S₃ states, symbolized as ∑₁, ∑₂ and ∑₃, respectively, are formed which are in a Cl⁻-dependent equilibrium with the corresponding normal S states. An oxidation of ∑₃ to a ∑₄ state is not possible. It is proposed that Cl⁻ controls the oxidation potential of the stored oxidants by regulating events associated with the binding and/or oxidative modification of water molecules at the water oxidase.     

Electron-acceptor loadings affect chloroform dechlorination in a hydrogen-based membrane biofilm reactor

Chloroform (CF) can undergo reductive dechlorination to dichloromethane, chloromethane, and methane. However, competition for hydrogen (H₂), the electron-donor substrate, may cause poor dechlorination when multiple electron acceptors are present. Common acceptors in anaerobic environments are nitrate (NO₃⁻), sulfate (SO₄²⁻), and bicarbonate (HCO₃⁻). We evaluated CF dechlorination in the presence of HCO₃⁻ at 1.56 e⁻ Eq/m²-day, then NO₃⁻ at 0.04–0.15 e⁻ Eq/m²-day, and finally NO₃⁻ (0.04 e⁻ Eq/m²-day) along with SO₄²⁻ at 0.33 e⁻ Eq/m²-day in an H₂-based membrane biofilm reactor (MBfR). When the biofilm was initiated with CF-dechlorination conditions (no NO₃⁻ or SO₄²⁻), it yielded a CF flux of 0.14 e⁻ Eq/m²-day and acetate production via homoacetogenesis up to 0.26 e⁻ eq/m²-day. Subsequent addition of NO₃⁻ at 0.05 e⁻ Eq/m²-day maintained full CF dechlorination and homoacetogenesis, but NO₃⁻ input at 0.15 e⁻ Eq/m²-day caused CF to remain in the reactor's effluent and led to negligible acetate production. The addition of SO₄²⁻ did not affect CF reduction, but SO₄²⁻ reduction significantly altered the microbial community by introducing sulfate-reducing Desulfovibrio and more sulfur-oxidizing Arcobacter. Dechloromonas appeared to carry out CF dechlorination and denitrification, whereas Acetobacterium (homoacetogen) may have been involved with hydrolytic dechlorination. Modifications to the electron acceptors fed to the MBfR caused the microbial community to undergo changes in structure that reflected changes in the removal fluxes.     

Sorption of caesium,iodine and sulphur in solution to the adaxial leaf surface of broad bean (Vicia faba L.)

The interception by crop canopies of radionuclides in rainfall can be important in determining radiation exposures to animals and man. Data were obtained on the sorption and desorption of radionuclides on the adaxial surfaces of fully expanded bean leaves by exposing them to ionic forms of caesium (Cs⁺), iodine (I⁻) or sulphur (SO₄²⁻) over a six order of magnitude concentration range. The accumulation of each element was determined as a time course over a 48 h period using radioactive labels (¹³⁷Cs, ¹²⁵I or ³⁵S, respectively). Time- and concentration-dependent sorption of each element to the leaf surface was analysed to determine: (a) the leaf surface-solution distribution coefficient (K_d) at equilibrium and (b) the sorption and desorption rate coefficients for each element over the range of concentrations investigated. It was expected that Cs⁺ would show a stronger tendency to sorb to the leaf surface than both I⁻ and SO₄²⁻ because of the cation exchange properties of the cuticular membrane. The K_d for Cs⁺ was approximately 90× greater than that for SO₄²⁻ but 5× less than that for I⁻. This is thought to be due to either (a) the highly organophilic nature of iodide and the relatively high iodine number of cuticular waxes on plant leaf surfaces or (b) the possible oxidation of I⁻ to I⁰ or IO₃⁻, with consequently enhanced leaf surface sorption. Based on data obtained in this study, ranges and best estimates of sorption and desorption rate coefficients are presented for Cs⁺, I⁻ and SO₄²⁻ for use in modelling the interception of radioactive Cs, I and S in rainfall by crops.     

Ideal enantiomeric resolution by recrystallization of a racemic compound (part 4): Relationship between enantiomeric resolution phenomenon and crystal properties

A new example of a racemate showing unusual enantiomeric resolution phenomenon, in which simple recrystallization of the racemate leads to remarkable enantiomeric enrichment of either enantiomer up to 100% ee in the mother liquor, has been found. This compound is (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]-ethyl]dimethylsulfonium p-nitrobenzenesulfonate [EtOCH₂CH(OH)CH₂OC₆H₄NHCOCH₂CH₂SMe₂⁺O₂NC₆H₄SO₃⁻] [(±)-SN]. By repeating recrystallization of (±)-SN and the resulting deposited crystals successively and collecting the resulting enantiomerically enriched mother liquors with the same chirality sense, highly efficient enantiomeric resolution of the racemate into its separate enantiomers has been accomplished. The relationship between the occurrence of this enantiomeric resolution phenomenon and the crystal properties has been investigated with respect to SN and its aryl- and alkylsulfonate derivatives. The mode of enantiomeric resolution of (±)-SN was similar to that of para-substituted benzenesulfonate derivatives (±)-ST (4-MeC₆H₄SO₃⁻) and (±)-SC (4-ClC₆H₄SO₃⁻) previously reported, whereas the unsubstituted derivative (±)-SB (C₆H₅SO₃⁻) and alkysulfonate derivatives (±)-SO (n-C₈H₁₇SO₃⁻) and (±)-SM (CH₃SO₃⁻) did not show such an enantiomeric resolution phenomenon. The crystalline form of the former racemates that underwent the enantiomeric resolution was racemic compounds, while the latter were mixed crystals (solid solutions) composed of the respective optical antipodes. Chirality 9:220–224, 1997. © 1997 Wiley-Liss, Inc.     

Conformational properties of l-fucose and the tetrasaccharide building block of the sulfated l-fucan from Lytechinus variegatus

Although the 3D structure of carbohydrates is known to contribute to their biological roles, conformational studies of sugars are challenging because their chains are flexible in solution and consequently the number of 3D structural restraints is limited. Here, we investigate the conformational properties of the tetrasaccharide building block of the Lytechinus variegatus sulfated fucan composed of the following structure [l-Fucp4(SO₃⁻)-α(1-3)-l-Fucp2,4(SO₃⁻)-α(1-3)-l-Fucp2(SO₃⁻)-α(1-3)-l-Fucp2(SO₃⁻)] and the composing monosaccharide unit Fucp, primarily by nuclear magnetic resonance (NMR) experiments performed at very low temperatures and using H₂O as the solvent for the sugars rather than using the conventional deuterium oxide. By slowing down the fast chemical exchange rates and forcing the protonation of labile sites, we increased the number of through-space ¹H–¹H distances that could be measured by NMR spectroscopy. Following this strategy, additional conformational details of the tetrasaccharide and l-Fucp in solution were obtained. Computational molecular dynamics was performed to complement and validate the NMR-based measurements. A model of the NMR-restrained 3D structure is offered for the tetrasaccharide.     

Toxicity of flue gas components from cement plants in microalgae CO2 mitigation systems

Microalgae-based CO₂ capture from flue gas is an attractive mitigation strategy in the cement industry. However, NO _x and SO _x components might be harmful to microalgae. We performed toxicity assays, under 2 % (v/v) CO₂ and using nitrite, sulfite, or bisulfite salts, on an environmental isolate, identified as Desmodesmus abundans (The University of Texas at Austin (UTEX), no. 2976) and Scenedesmus sp. UTEX1589. Nitrite and sulfite did not inhibit growth at the tested concentrations (0–1,067 ppm (w/v) NO₂ ^? and 0–254 ppm (w/v) SO₃ ^2?); however, bisulfite was toxic above 39 ppm. Non-toxic concentrations of both sulfur-based compounds stimulated growth, but significantly higher growth rates were only observed for HSO₃ ^?. Within a narrower range, NO _x and SO _x served as a sole nutrient source. Overall, biomass production and growth rates of the environmental isolate were greater. A novel strategy to buffer high concentrations of HSO₃ ^? (200 ppm) was developed by adding cement kiln dust (CKD), a byproduct and flue gas component. The results suggest that CKD also provided other beneficial growth components and that sulfur optimization of the culture medium significantly increased carbon assimilation, particularly in D. abundans. In additional simulations of typical flue gas conditions in a modern cement plant (320, 40, and 40 ppm (w/v) of NO₂ ^?, SO₃ ^2?, and HSO₃ ^?, respectively, and 25 % (v/v) CO₂), along with the incorporation of 300 ppm CDK, growth of D. abundans was supported. Although further studies are needed, direct utilization of flue gas might be possible with the environmental isolate, where NO _x , SO _x , and CKD are all beneficial components of the mitigation system.     

Reaction of trans-dichlorobis(ethylenediamine)nickel(III) in aqueous hydrochloric acid

Both EPR and electronic absorbance spectroscopy have been used to follow the disappearance of [Ni^III(en)₂Cl₂]⁺ in aqueous HCI solutions. The rate of Ni(III) reduction is influenced by both the H⁺ and Cl^? concentrations, although the rate is not linear with respect to the concentration of either species. A mechanism is proposed in which the first step in the reaction is the proton-induced chelate ring opening which is followed by the reduction of Ni(III) by chloride ions. In the presence of H₂SO₄ the coordinated Cl^? ions are rapidly replaced by HSO_4^? ions and the resulting complex is much more stable, even in a 6 N acid solution.     

Tin-119 NMR studies on diorganoyltin(IV)dihalides and triorganoyltin(IV)halides; Formation and stereochemistry of adducts

The reactions of R₂SnX₂ (R = Ph, Me; X = Cl, Br) with excess halide, tributylphosphine, tricyclohexylphosphine and tributylphosphine oxide have been investigated in dichloromethane solution by tin-119 and phosphorus-31 NMR techniques. R₂SnX₂ form five coordinate 1:1 adducts with halide and phosphine (phos) ligands whilst both 1:1 and 1:2 adducts are formed with tributylphosphine oxide (L). Tin-119 spectra imply that Ph₂SnX₂(phos) has the phosphine in the equatorial position of a trigonal bipyramid. At low temperature there is evidence for a slow intramolecular twist mechanism between octahedral isomers of Ph₂SnCl₂L₂. The stereochemistry of the complexes Ph₂SnX₂L₂ differ between chloro and bromo compounds and no mixed halide complex is observed. In the case of the bromo system only, the 1:3 adduct [Ph₂SnBrL₃]⁺Br⁻ is formed. Ph₃SnCl does not react with phosphines but it does give 1:1 adducts with Cl⁻, L and pyridine. All the adducts have similar tin-119 chemical shifts which is consistent with the phenyl groups being equatorial in the five coordinate trigonal bipyramidal adducts. Ph₄Sn does not form adducts with X⁻, L or phosphine.     

Partitioning of amylase produced by Aspergillus niger in solid state fermentation using aqueous two-phase systems

Equilibrium data of aqueous two-phase systems composed of polyethylene glycol (4000 g mol⁻¹ or 6000 g mol⁻¹) and Li₂SO_4, (NH₄)₂SO₄ or Na₂SO₄ at pH 6.5 and 25 °C were obtained. The efficiency of these in the partition of amylases derived from Aspergillus niger was determined. The experimental data of binodal curves and tie lines were used to estimate the group interaction parameters using the UNIFAC model. Additionally, the influence of phases on the activity of the enzymes was investigated. The results indicate that the polymer molar mass did not influence the biphasic region size. However, the cations under study presented differences in induction to phase formation. It was verified that the systems formed with the Na⁺ presented a larger biphasic region. The increase in the molar mass of the polymer caused the increase in the exclusion volume from 3970.732 g mol⁻¹ to 5700.873 g mol⁻¹. The transfer Gibbs free energy of enzymes presented values between −1296.30 kJ mol⁻¹ and −2867.70 kJ mol⁻¹, that is, the process was spontaneous for all systems studied. The systems formed by (NH₄)₂SO₄ and PEG 4000 g mol⁻¹ presented the best K_e result (3.421) and theoretical recovery of 80.35 %.     

Protonation and dimerization reactions of cyclopentadienylrhodiumcarbonylphosphine and phosphite derivatives

Eight cyclopentadienylrhodiumcarbonylphosphine and phosphite complexes have been prepared and their IR, ¹H, and ³¹P NMR spectra recorded. A good correlation between carbonyl stretching frequencies and rhodium-phosphorous coupling constants has been observed. Reaction of these compounds with trifluorosulfonic acid, HCF₃SO₃, forms the expected cationic rhodium-hydride species which were examined using ¹H and ³¹P NMR spectroscopy. Similar reactions between trifluoroacetic acid, HCF₃CO₂, and the phosphine compounds gave evidence of rapid proton exchange at the metal. Reaction between trifluoroacetic acid and cyclopentadienylrhodiumcarbonylphosphite compounds yielded new sets of rhodium-hydride resonances which were shown to be due to the formation of dinuclear rhodium complexes and cyclopentadienylrhodiumbis(phosphite) complexes which arise under the reaction conditions. A Scheme for the formation of these reaction products is presented which is consistent with all of the experimental data.     

Effects of Sulfite on Metabolism in Isolated Mesophyll Cells from Papaver somniferum

Exposure (30 minutes) of leaf-free mesophyll cells from the C-3 plant, Papaver somniferum, to concentrations of sulfite (SO₂ + HSO₃⁻ + SO₃⁻) up to 20 millimolar stimulated the rate of CO₂ incorporation as much as 30%. The sulfite rapidly affects the metabolism of newly incorporated CO₂. Ammonia incorporation into glutamine and subsequent transamination reactions were stimulated during the short term exposure periods while glycolate metabolism apparently was inhibited by bisulfite at two points in the pathway. The results further indicate that glycolate is the major precursor of glycine in these cells. Prolonged periods of exposure (24 hours) to sulfite had somewhat different effects on carbon metabolism: the high concentrations (10 to 20 millimolar) severely inhibited all aspects of cellular metabolism while lower concentrations (1 millimolar) appeared to inhibit ammonia incorporation but stimulated synthesis of sucrose and starch.     

Effects of Anions on Swelling, Respiration, and Phosphorylation of Isolated Corn Mitochondria

The effects of a series of anions on swelling, respiration, and oxidative phosphorylation of corn mitochondria were studied. Active mitochondrial swelling similar to that found with HPO₄⁻² was demonstrated in the presence of IO₃⁻, NO₂⁻, MoO₄⁻², SO₄⁻², HAsO₄⁻², acetate, S₂O₃⁻², SeO₄⁻², CrO₄⁻², and WoO₄⁻². In general, those anions which caused active swelling also released respiration and reduced the efficiency of oxidative phosphorylation with exogenous NADH as substrate. The degree of passive swelling in the presence of certain of the monovalent anions was found to approximate the order of the lyotropic series (SCN⁻ > CIO₄⁻ > I⁻ > NO₃⁻ > CI⁻).     

A New Enzyme Species of p-Hydroxybenzoate Hydroxylase during Oxygenating Process Observed by the Stopped-flow Method

Sulfite ion (HSO₃ ^-) is one of the products when elemental sulfur is oxidized by the hydrogen sulfide:ferric ion oxidoreductase of Thiobacillus ferrooxidans AP19-3. Under the conditions in which HSO₃ ^- is accumulated in the cells, the iron oxidase of this bacterium was strongly inhibited by HSO₃ ^-. Since cytochrome c oxidase is one of the most important components of the iron oxidase enzyme system in T. ferrooxidans, effects of HSO₃ ^- on cytochrome c oxidase activity were studied with the plasma membranes of HSO₃ ^--resistant and -sensitive strains of T. ferrooxidans, OK1-50 and AP19-3. The enzyme activity of AP19-3 compared with OK1-50 was strongly inhibited by HSO₃ ^-. To investigate the inhibition mechanism of HSO₃ ^- in T. ferrooxidans, cytochrome c oxidases were purified from both strains to an electrophoretically homogeneous state. Cytochrome c oxidase activity of a purified OK1-50 enzyme was not inhibited by 5 mM HSO₃ ^-. In contrast, the same concentration of HSO₃ ^- inhibited the enzyme activity of AP19-3 50%, indicating that the cytochrome c oxidase of OK1-50 was more resistant to HSO₃ ^- than that of AP19-3. Cytochrome c oxidases purified from both strains were composed of three subunits. However, the molecular weight of the largest subunit differed between OK1-50 and AP19-3. Apparent molecular weights of the three subunits of cytochrome c oxidases were 53,000, 24,000, and 19,000 for strain AP19-3 and 55,000, 24,000, and 19,000 for strain OK1-50, respectively.     

The high-affinity binding site for manganese on the oxidizing side of Photosystem II

Electron donation to Photosystem II (PS II) by diphenylcarbazide (DPC) is interrupted by the presence of endogenous Mn in PS II particles. Removal of this Mn by Tris treatment greatly stimulates the electron transport with DPC as donor. Binding of low concentration of exogenous Mn(II) to Tris-treated PS II particles inhibits DPC photooxidation competitively with DPC. This phenomenon was used to locate a highly specific Mn(II) binding site on the oxidizing side of Photosystem II with dissociation constant about 0.15 μM. The binding of Mn(II) is electrostatic in nature. Its affinity depends not only on the ionic strength, but also on the anion species of the salt in the medium. The effectiveness in decreasing the affinity follows the order F⁻ > SO²⁻₄ > CH₃COO⁻ > CI⁻ > Br⁻ > NO₃⁻. This observation is interpreted as follows: smaller ions, like F⁻, CH₃COO⁻, and larger ions, like SO²⁻₄, have inhibitory effects on Mn(II) binding, whereas ions with optimal size, like Cl⁻, Br⁻ and NO₃⁻, can stabilize the binding, resembling the anion requirement for reactivation of Cl⁻-depleted chloroplasts. We suggest that the binding site for Mn(II) we observed is the site for the endogenous Mn in the O₂-evolving complex of PS II. This site remains after Tris treatment, which removes all the endogenous Mn as well as the three extrinsic proteins, indicating that it is on the intrinsic component(s) of PS II reaction centers. Furthermore, the Cl⁻ requirement for O₂ evolution may be attributed, at least partly to its stabilizing effect on Mn binding.     

Synthesis,characterization, and evaluation of (E)-methyl 2-((2-oxonaphthalen-1(2H)-ylidene)methylamino)acetate as a biological agent and an anion sensor

An amino acid based and bidentate Schiff base, (E)-methyl 2-((2-oxonaphthalen-1(2H)-ylidene)methylamino)acetate (ligand), was synthesized from the reaction of glycine-methyl ester hydrochloride with 2-hydroxy-1-naphthaldehyde. Characterization of the ligand was carried out using theoretical quantum–mechanical calculations and experimental spectroscopic methods. The molecular structure of the compound was confirmed using X-ray single-crystal data, NMR, FTIR and UV–Visible spectroscopy, which were in good agreement with the structure predicted by the theoretical calculations using density functional theory (DFT). Antimicrobial activity of the ligand was investigated for its minimum inhibitory concentration (MIC) to several bacteria and yeast cultures. UV–Visible spectroscopy studies also shown that the ligand can bind calf thymus DNA (CT-DNA) electrostatic binding. In addition, DNA cleavage study showed that the ligand cleaved DNA without the need for external agents. Energetically most favorable docked structures were obtained from the rigid molecular docking of the compound with DNA. The compound binds at the active site of the DNA proteins by weak non-covalent interactions. The colorimetric response of the ligand in DMSO to the addition of equivalent amount of anions (F⁻, Br⁻, I⁻, CN⁻, SCN⁻, ClO₄⁻, HSO₄⁻, AcO⁻, H₂PO₄⁻, N₃⁻ and OH⁻) was investigated and the ligand was shown to be sensitive to CN⁻ anion.     

Bark pH and susceptibility to toxic air pollutants as independent causes of changes in epiphytic lichen composition in space and time

Abstract:The lichen composition on wayside Quercus robur in the Netherlands was related to bark properties (pH, EC, NH₄⁺, SO₄²⁻, NO₃⁻) and levels of air pollution (SO₂and NH₃). The pH of the bark and the susceptibility to toxic substances appear to be the two major primary factors affecting epiphytic lichen composition. These factors have independent effects on the lichen composition. Most of the so-called nitrophytic species appear to have a low sensitivity to toxic effects of SO₂; their only requirement being a high bark pH. An increased bark pH appears to be the primary cause of the enormous increase in nitrophytic species and the disappearance of acidophytic species over the last decade in the Netherlands. Measurements of ambient NH₃concentrations in air show that there is a nearly linear relationship between the NH₃concentration and the abundance of nitrophytes on Quercus. The abundance of nitrophytes was not correlated with SO₂concentrations. Most of the acidophytic species appear very sensitive to NH₃since in areas with concentrations of 35 μg m⁻³or more, all acidophytic species have disappeared. Current methods using species diversity to estimate or monitor SO₂air pollution need some modification, otherwise the air quality may be erroneously considered to be relatively good in areas with high NH₃levels.