Measurements of transmembrane pH differences of low extents in bacterial chromatophores

In chromatophores from photosynthetic bacteria the interaction of the fluorescent monoamine, 9-amino, 6-chloro, 2-methoxyacridine (ACMA), with the membrane is evaluated and described by an S-shaped adsorption isotherm. This phenomenon is hysteretic, as indicated by the difference between the adsorption and desorption branches of the binding isotherm. Maximal saturation of adsorption is reached at one ACMA per one to four lipid molecules, indicating that the probe binds in its neutral form. Adsorption of the probe on the membrane causes a large quenching of its fluorescence, which is explaind as being due to hypochromic effects following stacking and aggregation in a medium of low dielectric constant. A further quenching of fluorescence is brought about by imposing artificially induced transmembrane pH's. This latter phenomenon titrates in at increasing pH values and approaches saturation when pH is 2. The dependence of pH on the observed quenching of fluorescence is predicted by considering a model based on the equilibrium distribution of the amine between two phases at different pH's, in which adsorption of the probe on the membrane is used to evaluate its free concentration in the inner and outer compartments of the chromatophore vesicle. It is proposed that the equation thus obtained should be used to measure pH from the quenching of ACMA fluorescence.Abbreviations pH transmembrane pH difference between the inner and outer compartments - Q quenching of fluorescence - BChl Bacteriochlorophyll - ACMA 9-amino-6-chloro-2-methoxyacridine - 9AA 9-aminoacridine - Tricine N-tris-(hydroxymethyl)methylglycine - MES 2-morpholinoethanesulfonic acid - FCCP carbonylcyanide-p-trifluoro-methoxy-phenylhydrazone - CCCP carbonylcyanide-m-chloro-phenylhydrazone     

POTENTIAL USE OF LEAF BIOMASS,ARAUCARIA HETEROPHYLLA FOR REMOVAL OF Pb+2

The present investigation attempt to analyze the biosorption behavior of novel biosorbent, Araucaria heterophylla (green plant) biomass, for removal of Pb⁺² from solution as the function of initial metal ion concentration, pH, temperature, sorbent dosage and biomass particle size. The maximum biosorption was found to be 95.12% at pH 5 and biosorption capacity (q_e) of Cd⁺² is 9.643 mg/g. The Langmuir and Freundlich equilibrium adsorption isotherms were studied and observed that Freundlich model is best fit than the Langmuir model with correlation coefficient of 0.9927. Kinetic studies indicated that the biosorption process of Cd⁺² followed well pseudo second order model with R² 0.999. The process is exothermic and, spontaneous. The chemical functional groups –OH, CH₂ stretching vibrations, C?O of alcohol, C?O of amide, P?O stretching vibrations, –CH, were involved in the process. The XRD pattern of the A. heterophylla was found to be mostly amorphous in nature. The SEM studies showed Pb⁺² biosorption on selective grains of the biosorbent. It was concluded that A. heterophylla leaf powder can be used as an effective, low cost, and environmentally friendly biosorbent for the removal of Pb⁺² from aqueous solution.     

Adsorption of Basic violet 16 from aqueous solutions by waste sugar beet pulp: kinetic,thermodynamic, and equilibrium isotherm studies

Waste sugar beet pulp has been used as adsorbent for the removal of a hazardous cationic dye, Basic violet 16, from its aqueous solution. Adsorption of the dye was studied as function of time, pH of the solution, dosage of the adsorbent, sieve size of the particles, concentration of the dye, and temperature. The initial pH of the dye solution did not affect the chemistry of the dye molecule and the surface of beet pulp. Langmuir and Freundlich adsorption isotherms were successfully employed, and on the basis of these models, the thermodynamic parameters were evaluated. Adsorption of Basic violet 16 on beet pulp was found to be an exothermic reaction. Time contact studies showed that more than 80% adsorption of the dye is achieved in less than 1 h. Kinetics investigations confirmed both pseudo-first-order and pseudo-second-order behaviors; on the other hand, it shows that the intraparticle diffusion step is not the only rate-controlling step in all concentrations.     

Modifying dipalmitoylphosphatidylcholine monolayers by n-hexadecanol and dipalmitoylglycerol

The monolayer structure of pure dipalmitoylphosphatidylcholine (DPPC) and equimolar mixtures of DPPC/n-hexadecanol (C(16)OH) and DPPC/dipalmitoylglycerol (DPG) are studied by the film balance technique and grazing incidence X-ray diffraction measurements. At 20 degrees C, the binary systems exhibit complete miscibility. In contrast to pure DPPC monolayers, a condensing effect is observed in the presence of both non-phospholipid additives; but the phase transition behavior differs. The tilt angle of the hydrocarbon chains in the DPPC/C(16)OH mixture is significantly smaller than in pure DPPC monolayers. The tilt of the chains is even further reduced in the mixed monolayer of DPPC/DPG. A comparison of the three systems reveals distinct structural features such as phase state, chain tilt, and molecular area over a wide range of surface pressures. Therefore, these monolayers provide a highly suitable model to investigate the influence of structural parameters on biological processes occurring at the membrane surface, e.g. enzymatic reactions and adsorption events.     

Bioavailability of phosphorus in agriculturally loaded rivers in southern Finland

The potential bioavailability of phosphorus in agriculturally loaded rivers of southern Finland was determined by an algal bioassay and the release of the potentially bioavailable particulate P was estimated by sorption studies. According to the bioassay 0 to 13.2 per cent (mean 5.1%) of the particulate P in river water samples was potentially bioavailable. Dissolved reactive P (DRP) in river waters appeared to be totally bioavailable whereas the dissolved unreactive P appeared not to be utilized by algae. In addition to river waters two lake sediment samples were also assayed. In these samples 0 and 2.6% of the P was bioavailable. The potential bioavailability of particulate P in agriculturally loaded rivers obtained in this study was lower than that reported in studies from other countries. The difference was assumed to arise partly from methodological factors and partly from the nature of the Finnish soils. The EPC (equilibrium phosphate concentration) values indicated that during the period when most of the agricultural loading enters the lakes in Finland, potentially bioavailable P is not released from the particles because of the relatively high DRP concentration in the receiving waters. However, during the algal production period the DRP concentration in lakes decreases below the EPC and potentially bioavailable particulate P is desorbed. The increase in pH during this period may further enhance the desorption of P.     

ZnCl2-Modified Activated Carbon from Biomass Coir Pith for the Removal of 2-Chlorophenol by Adsorption Process

Coir pith, a waste biomass, from coconut coir industry was used to prepare activated carbon with ZnCl₂ and employed for the removal of 2-chlorophenol (2-CP) from aqueous solution and wastewater. Zinc chloride–activated coir pith carbon (ZnCPC) was prepared by mixing coir pith with ZnCl₂ in the ratio 2:1 and carbonized at 700°C for 1 h. ZnCPC was characterized using standard physicochemical methods, Brunaver, Emmett, and Teller (BET) surface area, and scanning electron microscopy (SEM) studies. Batch mode adsorption studies were carried out to evaluate the effect of contact time, initial concentration, adsorbent dose, pH, and temperature. The Langmuir adsorption capacity Q ₀ was found to be 149.3 mg g^?1. Kinetic studies showed that the adsorption obeyed second-order and Bangham's model. Equilibrium adsorption data fit better into Langmuir, Freundlich, and D-R isotherms. pH effect and desorption studies showed that ion-exchange mechanism was involved in the adsorption process. Effect of temperature was not significant. Quantitative removal of 2-CP from synthetic wastewater was also achieved. ZnCPC is economically effective compared to commercial activated carbon, because the raw material is abundantly and freely available and it can be used effectively in the treatment of water contaminated with 2-CP.     

Lags in the response of plant assemblages to global warming depends on temperature-change velocity

Aim

Current global warming is driving changes in biological assemblages by increasing the number of thermophilic species while reducing the number of cold-adapted species, leading to thermophilization of these assemblages. However, there is increasing evidence that thermophilization might not keep pace with global warming, resulting in thermal lags. Here, we quantify the magnitude of thermal lags of plant assemblages in Norway during the last century and assess how their spatio-temporal variation is related to variables associated with temperature-change velocity, topographic heterogeneity, and habitat type.

Location

Norway.

Time period

1905–2007.

Major taxa studied

Vascular plants.

Methods

We inferred floristic temperature from 16,351 plant assemblages and calculated the floristic temperature anomaly (difference between floristic temperature and baseline temperature) and thermal lag index (difference between reconstructed floristic temperature and observed climatic temperature) from 1905 until 2007. Using generalized least squares models, we analysed how the variation in observed lags since 1980 is related to temperature-change velocity (measured as magnitude, rate of temperature change, and distance to past analogous thermal conditions), topographic heterogeneity, and habitat type (forest versus non-forest), after accounting for the baseline temperature.

Results

The floristic temperature anomaly increases overall during the study period. However, thermophilization falls behind temperature change, causing a constantly increasing lag for the same period. The thermal lag index increases most strongly in the period after 1980, when it is best explained by variables related to temperature-change velocity. We also find a higher lag in non-forested areas, while no relationship is detected between the degree of thermal lag and fine-scale topographic heterogeneity.

Main conclusions

The thermal lag of plant assemblages has increased as global warming outpaces thermophilization responses. The current lag is associated with different dimensions of temperature-change velocity at a broad landscape scale, suggesting specifically that limited migration is an important contributor to the observed lags.     

Biosorption of Arsenic from Contaminated Water onto Solid Psidium guajava Leaf Surface: Equilibrium,Kinetics, Thermodynamics,and Desorption Study

A batch study on the removal of As(III) and As(V) ions from contaminated water by biosorption using powdered Psidium guajava (Guava) leaf as biosorbent was carried out in the present work. FT-IR (Fourier transform infrared) and SEM (scanning electron microscopy) were used to characterize the surface of the biosorbent. The effect of sorption parameters such as pH, temperature (T _c), adsorbent dose (D _c), and contact time (t _c) were studied. At optimum treatment conditions, the maximum uptake of 1.06 mg of As(III) per gram and 2.39 mg of As(V) per gram onto the surface of biosorbent were obtained. Langmuir and Freundlich isotherm models were examined for sorption equilibrium at various temperatures. The sorption isotherm was favorable with the Freundlich model with the experimental data. Furthermore, higher uptake kinetics was tested for the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model appeared to be the more suitable model to describe arsenic biosorption. ΔG ₀ values were negative at all temperatures, confirming the feasible and spontaneous nature of the biosorption process. Solvent desorption studies help in understanding the mechanism of the adsorption process and also to check the stability of the loaded/spent adsorbents. HCl was found to show maximum effectiveness in the desorption of both As(III) and As(V) with the comparison of other solvents.     

Hexavalent chromium removal from aqueous solutions by a novel powder prepared from Colocasia esculenta leaves

In this study, batch removal of hexavalent chromium from aqueous solutions by powdered Colocasia esculenta leaves was investigated. Batch experiments were conducted to study the effects of adsorption of Cr(VI) at different pH values, initial concentrations, agitation speeds, temperatures, and contact times. The biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectrometer analysis. The biosorptive capacity of the adsorbent was dependent on the pH of the chromium solution in which maximum removal was observed at pH 2. The adsorption equilibrium data were evaluated for various adsorption isotherm models, kinetic models, and thermodynamics. The equilibrium data fitted well with Freundlich and Halsey models. The adsorption capacity calculated was 47.62 mg/g at pH 2. The adsorption kinetic data were best described by pseudo-second-order kinetic model. Thus, Colocasia esculenta leaves can be considered as one of the efficient and cheap biosorbents for hexavalent chromium removal from aqueous solutions.     

Sorption of chromium(VI) from aqueous solution by cassava (Manihot sculenta Cranz.) waste biomass

The sorption of highly toxic Cr(VI) ions by cassava waste biomass was quantitatively investigated. The sorption was found to be influenced by several physico-chemical factors such as agitation speed, temperature, contact time, pH, and sorbent/sorbate ratio. The adsorption data at equilibrium were fitted to Freundlich and Langmuir isotherms. The monolayer sorption capacity was found to be 61.79 mg of Cr(VI) per gram of biomass. The kinetics of Cr(VI) adsorption to pure cassava-tuber-bark wastes were determined based on a pseudo-second-order-rate model using the batch-sorption technique at a temperature of 30 degrees. The kinetics data suggest that the adsorption process is exothermic, and that the rate-limiting step is physisorption. Negative DeltaG(ads) values indicate that the adsorption is spontaneous and exothermic in nature. Also, under optimal conditions (in agitated 1M H(2)SO(4) at 30 degrees), the cassava waste biomass appears to be recyclable.