Biosorption of heavy metal ions by brown seaweeds from southern coast of Korea

Heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, Cu²⁺, and Cr₂O₇ ^2?) were biosorbed by brown seaweeds (Hizikia fusiformis, Laminaria japonica, and Undaria pinnatifida) collected from the southern coast of South Korea. The biosorption of heavy metal ions was pH-dependent showing a minimum absorption at pH 2 and a maximum biosorption at pH 4 (Pb²⁺, Cd²⁺, Mn²⁺, and Cr₂O₇ ^2?) or pH 6 (Cu²⁺). Biosorption increased most noticeably for pH changes from 2 to 3. In the latter pH range, biosorption increased, because a higher pH decreased the electrostatic repulsion between metal ions and functional groups on the seaweed. In the pH range of 2 ～ 4, biosorption of negatively-charged chromium species (Cr₂O₇ ^?2) followed the pattern of positively-charged metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺). This suggests that the most prevalent chromium species were positively-charged Cr³⁺, reduced from Cr⁶⁺ in Cr₂O₇ ^?2. Whereas positively-charged heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) reached a plateau after the maximum level, biosorption of chromium ions decreased noticeably between pH 5 and 8. Kinetic data showed that biosorption by brown seaweed occurred rapidly during the first 10 min, and most of the heavy metals were bound to the seaweed within 30 min. Equilibrium adsorption data for a lead ion could fit well in the Langmuir and Freundlich isotherm models with regression coefficients (R ²) between 0.93 and 0.98.     

Biosorption of hexavalent chromium using biofilm of <Emphasis Type="Italic">E. coli</Emphasis> supported on granulated activated carbon

The optimization of hexavalent chromium biosorption has been studied by using three different biosorbents; biofilm of E. coli ASU 7 supported on granulated activated carbon (GAC), lyophilized cells of E. coli ASU 7 and granulated activated carbon. Supporting of bacteria on activated carbon decreased both the porosity and surface area of the GAC. Significant decrement of surface area was correlated to the blocking of microspores as a result of the various additional loads. The experimental data of adsorption was fitted towards the models postulated by Langmuir and Freundlich and their corresponding equations. The maximum biosorption capacity for hexavalent chromium using biofilm, GAC and E. coli ASU 7 were 97.70, 90.70, 64.36 mg metal/g at pH 2.0, respectively. Biosorption mechanism was related mainly to the ionic interaction and complex formation. Based on the experimental conditions, the presence of bacteria could be enhanced the capacity of activated carbon to adsorb hexavalent chromium ions from aqueous solutions.     

Biosorption of chromium to fungi

Eighteen fungal strains were isolated from water and soil samples and tested for their ability to enrich chromium. The microorganism with the highest enrichment capacity, a zygomycete (Mucor hiemalis MP/92/3/4), was chosen for detailed investigations. Some basic tests such as the pH-dependence, the kinetics of the enrichment and the metal selectivity were carried out with the two most frequent oxidation states of chromium, the trivalent cation (Cr³⁺) and the hexavalent anion (CrO₄ ^2–). With Cr³⁺ the enrichment showed a saturation kinetic reaching 70% of the maximum capacity after about 30 min, whereas with CrO₄ ^2– a linear time course with a much lower metal enrichment was observed. The highest level of enrichment for Cr³⁺ was observed at pH 5.5 (21.4 mg/g dry wt), and for CrO₄ ^2– at pH 1 (4.3 mg/g dry wt). Investigations concerning the metal enrichment selectivity resulted in the following series of decreasing ion uptake: Cr³⁺ > Cu²⁺ > Pb²⁺ > Ag⁺ > Al³⁺ > Co²⁺ > Zn²⁺ > Ni²⁺ > Fe²⁺ > Mo⁵⁺ > Cd²⁺ > ^2– > CrO₄ ^2– > VO^3–, calculated on a molar basis. Trivalent chromium caused a staining of the outer cell wall region in transmission electron microscopy. The localization of chromium in the stained outer layers of the cell wall could be verified by electron energy loss spectroscopy. The enrichment of Cr³⁺ by M. hiemalis seemed to be mainly a passive biosorption to the cell wall, whereas for the uptake of CrO₄ ^2– intracellular accumulation as well as biosorption is possible.     

Chromium ions inactivate electron transport and enhance superoxide generation in vivo in pea (Pisum sativum L. cv. Azad) root mitochondria

The effect in vivo of hexavalent chromium (Cr⁶⁺) on the respiratory electron transport activity and production of superoxide (O₂^–) radicals, was studied in submitochondrial particles (SMPs) prepared from mitochondria isolated from roots of 15‐day‐old pea (Pisum sativum L. cv. Azad) plants exposed to environmentally relevant (20 µm ) and acute (200 µm ) concentrations of chromium for 7 d. A concentration ‐dependent inactivation of electron transport activity from both NADH to O₂ (NADH oxidase) and succinate to O₂ (succinate oxidase) was observed. The electron transport activity was more sensitive to Cr⁶⁺ with NADH as the substrate than with succinate as the substrate. Although NADH dehydrogenase and succinate dehydrogenase were less affected, NADH: cytochrome c oxidoreductase and succinate: cytochrome c oxidoreductase activities were prominently affected by Cr⁶⁺. Cytochrome oxidase was the most susceptible complex of mitochondrial membranes to Cr⁶⁺, exhibiting maximal inactivation of activity both at 20 and 200 µm chromium concentrations. Cr⁶⁺ increased the generation of O₂^– radicals. This effect was more evident at 200 than at 20 µm . A significant increase in lipid peroxidation of mitochondrial membranes at 200 µm Cr⁶⁺ was the physiological impact of the metal‐induced enhanced generation of O₂^– radicals. An increase in superoxide dismutase (SOD) activity at 20 µm Cr⁶⁺ towards enhanced production of O₂^– radicals appeared to be a defence response in pea root mitochondria that, however, could not be sustained at 200 µm Cr⁶⁺. The results obtained concerning inactivation of mitochondrial electron transport and subsequent enhancement in the generation of O₂^– radicals suggest that root mitochondria are an important target of Cr⁶⁺‐induced oxidative stress in pea.     

Conformations of helical Aib peptides containing a pair of l‐amino acid and d‐amino acid

A pair of l ‐leucine (l ‐Leu) and d ‐leucine (d ‐Leu) was incorporated into α‐aminoisobutyric acid (Aib) peptide segments. The dominant conformations of four hexapeptides, Boc‐l ‐Leu‐Aib‐Aib‐Aib‐Aib‐l ‐Leu‐OMe (1a), Boc‐d ‐Leu‐Aib‐Aib‐Aib‐Aib‐l ‐Leu‐OMe (1b), Boc‐Aib‐Aib‐l ‐Leu‐l ‐Leu‐Aib‐Aib‐OMe (2a), and Boc‐Aib‐Aib‐d ‐Leu‐l ‐Leu‐Aib‐Aib‐OMe (2b), were investigated by IR, ¹H NMR, CD spectra, and X‐ray crystallographic analysis. All peptides 1a,b and 2a,b formed 3₁₀‐helical structures in solution. X‐ray crystallographic analysis revealed that right‐handed (P) 3₁₀‐helices were present in 1a and 1b and a mixture of right‐handed (P) and left‐handed (M) 3₁₀‐helices was present in 2b in their crystalline states. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Bacterial Reduction of Hexavalent Chromium: Kinetic Aspects of Chromate Reduction by Enterobacter cloacae HO1

Kinetic aspects of the bacterial reduction of hexavalent chromium (chromate: CrO^2-₄) were investigated using Enterobacter cloacae strain HO1. E. cloacae strain HO1 could reduce hexavalent chromium to the trivalent form (Cr³⁺) anaerobically. High concentrations of CrO^2-₄ inhibited the reduction, and a substrate inhibition model gave a good fit to the observed data. The rate of chromate reduction was proportional to cell density. The effect of temperature on the reduction rate followed the Arrhenius equation. The rate of chromate reduction was also dependent on pH and the concentrations of carbon and energy sources in the culutre medium. Amino acids including asparagine, methionine, serine and threonine were utilized effectively as carbon and energy sources for chromate reduction.     

Removal of Chromium(VI) Ions from Synthetic Solutions by the Fungus Penicillium purpurogenum

The ability of Penicillium purpurogenum to bind high amounts of chromium(VI) from aqueous solutions is demonstrated. Cr(VI) adsorption capacity increases with time during the first four hours and then leveled off toward the equilibrium adsorption capacity. Biosorption of Cr(VI) ions reached equilibrium in four hours. Binding of Cr(VI) ions with Penicillium purpurogenum biomass was clearly pH dependent. Cr(VI) loading capacity increased with increasing pH. The adsorption of Cr(VI) ions reached a plateau value at a pH of approx. 6.0. The maximum capacity of adsorption of Cr(VI) ions onto the fungal biomass was 36.5 mg/g. Adsorption behavior of Cr(VI) ions can be approximately described with the Langmuir equation. When applying the Langmuir model, the maximum adsorption capacity (Q_max) and the Langmuir constant were found to be 40 mg/g and 3.9 × 10^–3 mg/L. Elution of Cr(VI) ions was performed by means of 0.5 M HCl. It was possible to use the biomass of Penicillium purpurogenum for six cycles for biosorption.     

Removal of chromium using Rhizobium leguminosarum

The chromium (Cr^III and Cr^VI) removal capability of Rhizobium leguminosarum was checked by estimating the amount of chromium in the medium before and after inoculation. To determine the efficiency of R. leguminosarum in removal of chromium, the influence of physical and chemical parameters such as temperature, pH and different concentrations (0.1–1.0 mM) of trivalent (Cr^III) and hexavalent (Cr^VI) chromium were studied. The chromium removal in aqueous solution by different size of active and inactivated biomass and immobilized cells of R. leguminosarum in a packed-bed column was also carried out. Results showed that in a medium containing up to 0.5 mM concentration of both Cr^III and Cr^VI, R. leguminosarum showed optimal growth. The maximum chromium removal was at pH 7.0 and 35°C. Active biomass removed 84.4 ± 3.6% of Cr^III and 77.3 ± 4.3% of Cr^VI in 24 h of incubation time. However, inactivated biomass removed maximum chromium after 36 h of incubation. Immobilized bacterial cells in a packed-bed column removed 86.4 ± 1.7% of Cr^III and 83.8 ± 2.2% of Cr^VI in 16 and 20 h of incubation time, respectively.     

Biosorption of Cr(VI) onto marine Aspergillus niger: experimental studies and pseudo-second order kinetics

The removal of hexavalent chromium from aqueous solution was studied in batch experiments using dead biomass of three different species of marine Aspergillus after alkali treatment. All the cultures exhibited potential to remove Cr(VI), out of which, Aspergillus niger was found to be the most promising one. This culture was further studied employing variation in pH, temperature, metal ion concentration and biomass concentration with a view to understand the effect of these parameters on biosorption of Cr(VI). Higher biosorption percentage was evidenced at lower initial concentration of Cr(VI) ion, while the sorption capacity of the biomass increased with rising concentration of ions. Biomass as low as 0.8 g l⁻¹ could biosorb 95% Cr(VI) ions within 2,880 min from an aqueous solution of 400 mg l⁻¹ Cr(VI) concentration. Optimum pH and temperature for Cr(VI) biosorption were 2.0 and 50°C, respectively. Kinetic studies based on pseudo second order models like Sobkowsk and Czerwinski, Ritchie, Blanchard and Ho and Mckay rate expressions have also been carried out. The nature of the possible cell–metal ion interactions was evaluated by FTIR, SEM and EDAX analysis.     

Biosorption Performance of Multimetal Resistant Fungus Penicillium chrysogenum XJ-1 for Removal of Cu2+ and Cr6+ from Aqueous Solutions

Adsorption for heavy metals via biomaterials such as fungal biomass presents a practical remediation technique for polluted water. Among all known filamentous fungi, Penicillium chrysogenum is widespread in nature and can serve as a biosorbent for heavy metals. In the current study, the ability of P. chrysogenum XJ-1 to remove copper (Cu²⁺) and chromium (Cr⁶⁺) from water was evaluated. The maximum biosorption capacity of XJ-1 for Cu²⁺ reached 42.83 ± 0.57 mg g^?1 dry biomass at pH 5.0 after the equilibrium time of 1.5 h. The maximum biosorption capacity for Cr⁶⁺ at pH 3.0 reached 52.69 ± 1.68 mg g^?1 dry biomass after the equilibrium time of 1.5 h. The biosorption data of XJ-1 biomass were well fitted to the Freundlich isotherm model and the pseudo-second-order Lagergren kinetic model. Laundry powder-treated and HCl-treated XJ-1 biomass significantly enhanced its adsorption capacity to Cu²⁺ and Cr⁶⁺, respectively. HCl and NaOH were suitable desorbents for Cu²⁺/Cr⁶⁺ loading biomass, respectively. Fourier transform infrared spectroscopy analyses revealed that hydroxyl, amine, and sulfonyl groups on the biosorbent contributed to binding Cu²⁺ and Cr⁶⁺ and that carbonyl and carboxyl groups were also vital binding sites of Cu²⁺. Scanning electron microscopy and energy-dispersive x-ray (SEM-EDX) analyses confirmed that considerable amounts of metals were precipitated on the cell surface of XJ-1. Our results suggested that XJ-1 might be used to purify multimetal-contaminated water. This low-cost and eco-friendly biomass of XJ-1 seems to have a broad use in the restoration of metal-contaminated water.     

Potential of Live Spirulina platensis on Biosorption of Hexavalent Chromium and Its Conversion to Trivalent Chromium

Microalga biomass has been described worldwide according their capacity to realize biosorption of toxic metals. Chromium is one of the most toxic metals that could contaminate superficial and underground water. Considering the importance of Spirulina biomass in production of supplements for humans and for animal feed we assessed the biosorption of hexavalent chromium by living Spirulina platensis and its capacity to convert hexavalent chromium to trivalent chromium, less toxic, through its metabolism during growth. The active biomass was grown in Zarrouk medium diluted to 50% with distilled water, keeping the experiments under controlled conditions of aeration, temperature of 30°C and lighting of 1,800 lux. Hexavalent chromium was added using a potassium dichromate solution in fed-batch mode with the aim of evaluate the effect of several additions contaminant in the kinetic parameters of the culture. Cell growth was affected by the presence of chromium added at the beginning of cultures, and the best growth rates were obtained at lower metal concentrations in the medium. The biomass removed until 65.2% of hexavalent chromium added to the media, being 90.4% converted into trivalent chromium in the media and 9.6% retained in the biomass as trivalent chromium (0.931 mg.g^?1).     

Substrate specificity of a recombinant d‐lyxose isomerase from Serratia proteamaculans that produces d‐lyxose and d‐mannose

Aims: Characterization of substrate specificity of a d ‐lyxose isomerase from Serratia proteamaculans and application of the enzyme in the production of d ‐lyxose and d ‐mannose. Methods and Results: The concentrations of monosaccharides were determined using a Bio‐LC system. The activity of the recombinant protein from Ser. proteamaculans was the highest for d ‐lyxose among aldoses, indicating that it is a d‐ lyxose isomerase. The native recombinant enzyme existed as a 54‐kDa dimer, and the maximal activity for d‐ lyxose isomerization was observed at pH 7·5 and 40°C in the presence of 1 mmol l^?1 Mn²⁺. The K_m values for d ‐lyxose, d ‐mannose, d ‐xylulose, and d ‐fructose were 13·3, 32·2, 3·83, and 19·4 mmol l^?1, respectively. In 2 ml of reaction volume at pH 7·5 and 35°C, d ‐lyxose was produced at 35% (w/v) from 50% (w/v) d ‐xylulose by the d‐ lyxose isomerase in 3 h, while d ‐mannose were produced at 10% (w/v) from 50% (w/v) d ‐fructose in 5 h. Conclusions: We identified the putative sugar isomerase from Ser. proteamaculans as a d ‐lyxose isomerase. The enzyme exhibited isomerization activity for aldose substrates with the C2 and C3 hydroxyl groups in the left‐hand configuration. High production rates of d‐ lyxose and d ‐mannose by the enzyme were obtained. Significance and Impact of the Study: A new d‐ lyxose isomerase was found, and this enzyme had higher activity for d ‐lyxose and d ‐mannose than previously reported enzymes. Thus, the enzyme can be applied in industrial production of d ‐lyxose and d ‐mannose.     

Controlling the helical screw sense of peptides with C‐terminal L‐valine

One chiral L ‐valine (L ‐Val) was inserted into the C‐terminal position of achiral peptide segments constructed from α‐aminoisobutyric acid (Aib) and α,β‐dehydrophenylalanine (Δ^ZPhe) residues. The IR, ¹H NMR and CD spectra indicated that the dominant conformations of the pentapeptide Boc‐Aib‐ΔPhe‐(Aib)₂‐L ‐Val‐NH‐Bn (3) and the hexapeptide Boc‐Aib‐ΔPhe‐(Aib)₃‐L ‐Val‐NH‐Bn (4) in solution were both right‐handed (P) 3₁₀‐helical structures. X‐ray crystallographic analyses of 3 and 4 revealed that only a right‐handed (P) 3₁₀‐helical structure was present in their crystalline states. The conformation of 4 was also studied by molecular‐mechanics calculations. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Biosorption of Chromium,Cadmium, and Cobalt from Aqueous Solution by Immobilized Living Cells of Chryseomonas luteola TEM 05

Abstract

In this work, the potential use of the immobilized cells of Chryseomonas luteola TEM 05 for the removal of Cr⁺⁶, Cd⁺² and Co⁺² ions from aqueous solutions was investigated. The living cells of C. luteola TEM 05 were firstly entrapped both in carrageenan and chitosan coated carrageenan gels and then used in biosoption of the metal ions in batch reactors at pH 6.0, 25°C, in 100 mg L^?1 of each metal solution. Besides this, a process of competitive biosorption of these metal ions was also described and compared to single metal ion adsorption in solution. According to the immobilization results, the replacement of KCl by KCl-chitosan as gelling agent improved the mechanical strength and thermal stability of the gel. In addition, the C. luteola TEM 05 immobilized carrageenan-chitosan gel system was quite more efficient for the fast adsorption of metal ions from aqueous solution than the carrageenan gels without biomass.     

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.     

Enhancement of Lead(II) Biosorption by Microalgal Biomass Immobilized onto Loofa (Luffa cylindrica) Sponge

A unicellular green microalga, Chlorella sorokiniana, was immobilized on loofa (Luffa cylindrica) sponge and successfully used as a new biosorption system for the removal of lead(II) ions from aqueous solutions. The biosorption of lead(II) ions on both free and immobilized biomass of C. sorokiniana was investigated using aqueous solutions in the concentration range of 10–300 mg/L. The biosorption of lead(II) ions by C. sorokiniana biomass increased as the initial concentration of lead(II) ions increased in the medium. The maximum biosorption capacity for free and immobilized biomass of C. sorokiniana was found to be 108.04 and 123.67 mg lead(II)/g biomass, respectively. The biosorption kinetics were found to be fast, with 96 % of adsorption within the first 5 min and equilibrium reached at 15 min. The adsorption of lead(II) both by free and immobilized C. sorokiniana biomass followed the Langmuir isotherm. The biosorption capacities were detected to be dependent on the pH of the solution; and the maximum adsorption was obtained at a solution pH of about 5. The effect of light metal ions on lead(II) uptake was also studied and it was shown that the presence of light metal ions did not significantly affect lead(II) uptake. The loofa sponge‐immobilized C. sorokiniana biomass could be regenerated using 0.1 M HCl, with up to 99 % recovery. The desorbed biomass was used in five biosorption‐desorption cycles, and no noticeable loss in the biosorption capacity was observed. In addition, fixed bed breakthrough curves for lead(II) removal were presented. These studies demonstrated that loofa sponge‐immobilized biomass of C. sorokiniana could be used as an efficient biosorbent for the treatment of lead(II) containing wastewater.     

Lead biosorption by different morphologies of fungus Mucor indicus

Biosorption characteristics of Pb⁺² ions from aqueous solution were investigated using fungus Mucor indicus biomass treated with NaOH. Biosorption was measured as a function of biomass morphology, pH, biomass concentration, contact time, and metal concentration. The morphology of M. indicus biomass was manipulated towards filamentous or yeast-like forms. The highest and lowest biosorption capacities were observed for purely filamentous and yeast-like forms, respectively. Models of Langmuir, Freundlich, Temkin, and Scachard were applied to describe adsorption isotherm and fitted appropriately. Biosorption kinetics was successfully described using Ho’s pseudo-second-order model. Maximum and minimum values of biosorption capacity of Pb²⁺ were 22.1 and 12.1 mg g⁻¹ for purely filamentous and yeast-like morphologies, respectively. Increasing pH resulted in higher biosorption of Pb⁺² ions up to pH 5.5. Biosorption capacity of individual Pb⁺² ions was reduced in the presence of other metal ions in bi- or multi-metal ion experiments. Metal ions adsorption by the biomass could be eluted effectively with HNO₃.     

Effects of chromium compounds on plasma membrane Mg2+-ATPase activity of BHK cells.

An ATPase activity stimulated by divalent ions (Mg²⁺, Ca²⁺, Mn²⁺, Zn²⁺) has been observed in intact hamster fibroblasts cultured in vitro (BHK line). Such activity has been determined by the incubation (30 min at 37°C) of washed cell suspensions (about 1 mg of proteins) in a medium containing 100 mM NaCl, 20 mM KCl, 15 mM Tris—HCl (pH 7.4), 10 mM NaHCO₃, 5 mM glucose and equimolar concentrations of ATP and divalent cation. Mg²⁺-ATPase activity is insensitive to ouabain and lacks specificity towards nucleoside triphosphate substrates. AMP and ADP are not hydrolyzed under these conditions. Apparent K_m of 0.76 mM and V_max of 1.46 μmol Pi · mg proteins^?1 · h^?1 have been calculated for Mg-ATP complex. This ATPase is an ectoenzyme, therefore its activity could be used as a suitable index of the action of chemicals like chromium compounds known for their cytotoxic effects on membrane functions.Salts of trivalent (CrCl₃) and hexavalent (K₂Cr₂O₇) chromium at concentrations ranging from 1 mM to 5 mM inhibit Mg²⁺-ATPase. The inhibition by K₂Cr₂O₇ is observed after pretreatment of the cells with this compound followed by its absence from the assay medium “per se” for Mg²⁺-ATPase, and it is referred to the alterations of membrane bound enzyme structures by the oxidizing hexavalent chromium. The inhibition by CrCl₃ is mainly evident when this compound is present in the incubation medium, and is referred to the interaction of trivalent chromium with Mg²⁺-ATP as it is partially reversed by increasing Mg²⁺-ATP concentration.     

Taraxerol 4‐Methoxybenzoate,an in vitro Inhibitor of Photosynthesis Isolated from Pavonia multiflora A. St‐Hil. (Malvaceae)

A phytochemical study of Pavonia multiflora A. St ‐Hil . (Malvaceae) led to the isolation through chromatographic techniques of 10 secondary metabolites: vanillic acid ( 1 ), ferulic acid ( 2 ), p‐hydroxybenzoic acid ( 3 ), p‐coumaric acid ( 4 ), loliolide ( 5 ), vomifoliol ( 6 ), 4,5‐dihydroblumenol A ( 7 ), 3‐oxo‐α‐ionol ( 9 ), blumenol C ( 10 ), and taraxerol 4‐methoxybenzoate ( 8 ), the latter being a novel metabolite. Their structures were identified by ¹H‐ and ¹³C‐NMR, using one‐ and two‐dimensional techniques, and X‐ray crystallography. In this work, we report the effect of compounds 5 and 8 on several photosynthetic activities in an attempt to search for new compounds as potential herbicide agents that affect photosynthesis. Both compounds inhibited the electron flow from H₂O to methyl viologen; therefore, they act as Hill reaction inhibitors. Using polarographic techniques and studies of the fluorescence of chlorophyll a, the interaction sites of these compounds were located at photosystem II.     

Difference in the structures of alanine tri‐ and tetra‐peptides with antiparallel β‐sheet assessed by X‐ray diffraction,solid‐state NMR and chemical shift calculations by GIPAW

Alanine oligomers provide a key structure for silk fibers from spider and wild silkworms.We report on structural analysis of l ‐alanyl‐l ‐alanyl‐l ‐alanyl‐l ‐alanine (Ala)₄ with anti‐parallel (AP) β‐structures using X‐ray and solid‐state NMR. All of the Ala residues in the (Ala)₄ are in equivalent positions, whereas for alanine trimer (Ala)₃ there are two alternative locations in a unit cell as reported previously (Fawcett and Camerman, Acta Cryst., 1975, 31, 658–665). (Ala)₄ with AP β‐structure is more stable than AP‐(Ala)₃ due to formation of the stronger hydrogen bonds. The intermolecular structure of (Ala)₄ is also different from polyalanine fiber structure, indicating that the interchain arrangement of AP β‐structure changes with increasing alanine sequencelength. Furthermore the precise ¹H positions, which are usually inaccesible by X‐ray diffraction method, are determined by high resolution ¹H solid state NMR combined with the chemical shift calculations by the gauge‐including projector augmented wave method. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 13–20, 2014.