Spatial configuration of single-stranded polynucleotides. Calculations of average dimensions and Nmr coupling constants

The probability distributions of the torsional angles (Φ′, ω′, ω, Φ, and ψ), which fix the structure of nucleotide backbone, have been calculated using the results of energy calculations based on extended Huckel theory (EHT), complete neglect of differential overlap (CNDO), perturbative configuration interaction using localized orbitals (PCILO), and classical potential functions (CPF) methods. Statistical average values of the vicinal ¹H? ¹H, ¹H? ³¹P, and ¹³C? ³¹P nmr coupling constants 〈J〉 have been calculated from the generalized Karplus relations using the probability distribution in the Φ′, Φ, and ψ space. Experimental 〈J〉 values for polyribouridylic acid (polyU) support the theoretical predictions for these torsional angles. Using Monte Carlo technique, random coils of single-stranded polynucleotides have been simulated and the mean-square end-to-end distance 〈r²〉 has been calculated. Molecular orbital methods (EHT, CNDO, and PCILO) suggest considerable flexibility around O? P bonds, leading to fairly small values for the characteristic ratio (C_∞ ～ 4). Observed values of the unperturbed characteristic ratio for polynucleotides are quite large (C_∞ ～ 18) suggesting a relatively rigid nucleotide backbone. The results based on molecular orbital calculations can be reconciled with the experimental values by introducing an additional stabilization of ～2 kcal mol^?1 for the predicted minimum energy ragion (Φ′ ～ 240°, ω′ ～ 290°, ω 290°, Φ 180°, and ψ 60°). Such a stabilization may arise from the association of water molecules and metal ions with the phosphate group and (or) Coulomb interaction between neighboring phosphate groups. The calculations provide a semiquantitative estimate of torsional rigidity in the nucleotide backbone.     

Multispectroscopic studies of the interaction of folic acid with glycated human serum albumin

Abstract

The interaction between glycated human serum albumin (gHSA) and folic acid (FA) was investigated by various spectroscopic techniques, such as fluorescence, circular dichroism, UV–vis absorption spectroscopy and electrophoretic light scattering technique. These methods characterize the binding properties of an albumin–folic acid system. The binding constants values (K_a) at 300 and 310 K are about 10⁴ M^?1. The standard enthalpy change (ΔH) and the standard entropy change (ΔS) were calculated to be ～?20?kJ mol^?1 and ～16 J mol^?1 K^?1, respectively, which indicate characteristic electrostatic interactions between gHSA and folic acid. The CD studies showed that there are no significant conformational changes in the secondary structure of the protein. Moreover, the zeta potential measurements proved that under physiological conditions the gHSA–folic acid complex shows instability. No significant changes in the secondary structure of the protein and reversible drug binding are the desirable effect from pharmacological point of view.

Communicated by Ramaswamy H. Sarma     

Quantification of algal biofilms colonising building materials: chlorophyll a measured by PAM-fluorometry as a biomass parameter

Abstract

The aim of this study was to quantify algal colonisation on anthropogenic surfaces (viz. building facades and roof tiles) using chlorophyll a (chl a) as a specific biomarker. Chl a was estimated as the initial fluorescence F₀ of ‘dark adapted’ algae using a pulse-modulated fluorometer (PAM-2000). Four isolates of aeroterrestrial green algae and one aquatic isolate were included in this study. The chl a concentration and F₀ showed an exponential relationship in the tested range between 0 and 400 mg chl a m^?2. The relationship was linear at chl a concentrations <20 mg m^?2. Exponential and linear models are presented for the single isolates with large coefficients of determination (exponential: r² > 0.94, linear: r² > 0.92). The specific power of this fluorometric method is the detection of initial algal colonisation on surfaces in thin or young biofilms down to 3.5 mg chl a m^?2, which corresponds to an abundances of the investigated isolates between 0.2 and 1.5 million cells cm^?2.     

Static and dynamic properties of mid-size liquid n- alkanes,C12∼C400: a molecular dynamics simulation study

ABSTRACT

In this paper, we have extended our previous study of the static and dynamic properties (self-diffusion coefficient D_self and friction coefficient ζ) of liquid n-alkane systems up C₄₀₀ at several temperatures (～2300?K) using molecular dynamics (MD) simulations in the canonical ensembles. For the small n-alkanes with n?≤?120 (n: the chain length), the chains are clearly ?R² _ee?/6?R² _g? ≥ 1 (1.06 ～ 1.44), which leads to the conclusion that the liquid n-alkanes are far away from the ideal chain regime. But for the n-alkanes of n?≥?160, the chains are ?R² _ee?/6?R² _g? ≈ 1, indicating that they are Gaussian. It is found that the long chains of these n-alkanes at high temperatures show abnormalities in density and friction coefficient. We observed a clear transition in the power law dependence of n-alkane self-diffusion coefficient on the molecular weight (M) of n-alkane, D_self ～ M^?γ, occurs in the range C₁₂₀～C₁₆₀ at temperatures of 318, and 618?K, corresponding to a crossover from the ‘oligomer’ to the ‘Rouse’ regime. The entanglement lengths (N_e) are calculated by the Z1 code and discussed shortly.     

Fluctuations of an alpha-helix.

Fluctuations in backbone dihedral angles in the α-helical conformation of homopolypeptides are studied based on an assumption that the conformational energy function of a polypeptide consisting of n amino-acid residues can be approximated by a 2n-dimensional parabola around the minimum point in the range of fluctuations. A formula is derived that relates 〈Δθ_iΔθ_j〉, the mean value of the product of deviations of dihedral angles ?_i and ψ_i (collectively designated by θ_i) from their energy minimum values, with a matrix inverse to the second derivative matrix F ,_n of the conformational energy function at the minimum point. A method of calculating the inverse matrix F _n^?1 explicitly is given. The method is applied to calculating 〈Δθ_iΔθ_j〉 for the α-helices of poly(L -alanine) and polyglycine. The autocorrelations 〈(Δ?_i)²〉 and 〈(Δψ_i)²〉 at 300°K are found to be about 66 deg² and 49 deg², respectively, for poly(L -alanine), and 84 deg² and 116 deg², respectively, for polyglycine. The length of correlations of fluctuations along the chain is found for both polypeptides to be about eight residues long.     

Solution properties and chain flexibility of pullulan in aqueous solution

Molecular characteristics for pullulan, a polysaccharide produced by a fungus Aureobasidium pullulans, were measured by light scattering, viscometry, and gel-permeation chromatography. From the experimental data the Mark-Houwink-Sakurada viscosity equation in water at 25°C was determined for samples having the molecular weight M ranging from 48 × 10³ to 2.18 × 10⁶ g mol^?1 as [η] = (1.91 ± 0.02) × 10^?2M_w^0.67±0.01 (in cm³ g^?1); and as molecular weight decreased, the slope of the viscosity equation decreased, although the molecular weight values below 30 × 10³ g mol^?1 evaluated by gel-permeation chromatography were somewhat unreliable. The unperturbed dimensions 〈R²〉₀^1/2 of pullulan were estimated by determining the expansion factor α_s, from the theoretical combination of theories for the interpenetration function Ψ and those for α_s. The 〈R²〉₀/M value estimated from this procedure in 6.7 × 10^?17 cm² mol g^?1. We concluded that the polysaccharide chain that is linked by the α-1,6-glucosidic linkage behaves like a flexible chain in aqueous solution.     

Design,synthesis, MTT assay,DNA interaction studies of platinum(II) complexes

The square planar Pt(II) complexes of the type [Pt(Lⁿ)(Cl₂)] (where Lⁿ = L^1?3 = thiophene-2-carboxamide derivatives and L^4?6 = thiophene-2-carbothioamide derivatives) have been synthesized and characterized by physicochemical and various spectroscopic studies. MIC method was employed to inference the antibacterial potency of complexes in reference to free ligands and metal salt. Characteristic binding constant (K_b) and binding mode of complexes with calf thymus DNA (CT-DNA) were determined using absorption titration (0.76–1.61 × 10⁵ M^?1), hydrodynamic chain length assay and fluorescence quenching analysis, deducing the partial intercalative mode of binding. Molecular docking calculation displayed free energy of binding in the range of –260.06 to –219.63 kJmol^?1. The nuclease profile of complexes towards pUC19 DNA shows that the complexes cleave DNA more efficiently compared to their respective metal salt. Cytotoxicity profile of the complexes on the brine shrimp shows that all the complex exhibit noteworthy cytotoxic activity with LC₅₀ values ranging from 7.87 to 15.94 μg/mL. The complexes have been evaluated for cell proliferation potential in human colon carcinoma cells (HCT 116) and IC₅₀ value of complexes by MTT assay (IC₅₀ = 125–1000 μg/mL).     

Evaluation of growth and phycobiliprotein composition of cyanobacteria isolates cultivated in different nitrogen sources

Phycobiliproteins, light-harvesting pigments found in cyanobacteria and in some eukaryotic algae, have numerous commercial applications in food, cosmetic, and pharmaceutical industries. Colorant production from cyanobacteria offers advantages over their production from higher plants, as cyanobacteria have fast growth rate and high photosynthetic efficiency and require less space. In this study, three cyanobacteria strains were studied for phycobiliprotein production and the influence of sodium nitrate, potassium nitrate and ammonium chloride on the growth and phycobiliprotein composition of the strains were evaluated. In the batch culture period of 12 days, Phormidium sp. and Pseudoscillatoria sp. were able to utilize all tested nitrogen sources; however, ammonium chloride was the best nitrogen source for both strains to achieve maximum growth rate μ?=?0.284?±?0.03 and μ?=?0.274?±?0.13 day^?1, chlorophyll a 16.2?±? 0.5 and 12.2?±? 0.2 mg L^?1, and phycobiliprotein contents 19.38?±?0.09 and 19.99?±?0.14% of dry weight, whereas, for Arthrospira platensis, the highest growth rate of μ?=?0.304?±?0.0 day^?1, chlorophyll a 19.1?±?0.5 mg L^?1, and phycobiliprotein content of 22.27?±?0.21% of dry weight were achieved with sodium nitrate. The phycocyanin from the lyophilized cyanobacterial biomass was extracted using calcium chloride and food grade purity (A₆₂₀/A₂₈₀ ratio >?0.7) was achieved. Furthermore, phycocyanin was purified using two-step chromatographic method and the analytical grade purity (A₆₂₀/A₂₈₀ ratio >?4) was attained. SDS-PAGE demonstrated the purity and presence of two bands corresponding to α- and β-subunits of the C-phycocyanin. The results showed that Phormidium sp. and Pseudoscillatoria sp. could be good candidates for phycocyanin production.     

Performance of bioelectrochemical systems inoculated with Desmodesmus sp. A8 under different light sources

Light source can affect the stomata opening, photosynthesis process, and pigment content in microalgae cells. In this study, growth rate, chlorophyll a (chl a) content, and electrogenic capability of Desmodesmus sp. A8 were investigated under incandescent and fluorescent lamps. Growth rate, productivity, and chl a content of strain A8 exposed to incandescent light were recorded as 0.092 ± 0.010 day^?1, 0.019 ± 0.008 g L^?1 day^?1, and 15.10 ± 1.40 mg L^?1, which decreased to 0.086 ± 0.006 day^?1, 0.012 ± 0.004 g L^?1 day^?1, and 10.06 ± 1.59 mg L^?1, respectively, under fluorescent light. The stable current density of bioelectrochemical systems inculcated with strain A8 under incandescent and fluorescent lamps were 249.76 and 158.41 mA m^?2 at ?0.4 V vs. Ag/AgCl, coupling with dissolved oxygen within biofilm decreasing from 15.91 to 10.80 mg L^?1. This work demonstrated that illuminating microalgae under an incandescent lamp can improve biomass production and electrogenic capabilities.     

Solvent‐dependent conformation of amylose tris(phenylcarbamate) as deduced from scattering and viscosity data

The z‐average mean‐square radius of gyration 〈S²〉_z, the particle scattering function P(k), the second virial coefficient, and the intrinsic viscosity [η] have been determined for amylose tris(phenylcarbamate) (ATPC) in methyl acetate (MEA) at 25°C, in ethyl acetate (EA) at 33°C, and in 4‐methyl‐2‐pentanone (MIBK) at 25°C by light and small‐angle X‐ray scattering and viscometry as functions of the weight‐average molecular weight in a range from 2 × 10⁴ to 3 × 10⁶. The first two solvents attain the theta state, whereas the last one is a good solvent for the amylose derivative. Analysis of the 〈S²〉_z, P(k), and [η] data based on the wormlike chain yields h (the contour length or helix pitch per repeating unit) = 0.37 ± 0.02 and λ^?1 (the Kuhn segment length) = 15 ± 2 nm in MEA, h = 0.39 ± 0.02 and λ^?1 = 17 ± 2 nm in EA, and h = 0.42 ± 0.02 nm and λ^?1 = 24 ± 2 nm in MIBK. These h values, comparable with the helix pitches (0.37–0.40 nm) per residue of amylose triesters in the crystalline state, are somewhat larger than the previously determined h of 0.33 ± 0.02 nm for ATPC in 1,4‐dioxane and 2‐ethoxyethanol, in which intramolecular hydrogen bonds are formed between the C?O and NH groups of the neighbor repeating units. The slightly extended helices of ATPC in the ketone and ester solvents are most likely due to the replacement of those hydrogen bonds by intermolecular hydrogen bonds between the NH groups of the polymer and the carbonyl groups of the solvent. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 729–736, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Quantifying the contribution of land use to N<Subscript>2</Subscript>O,NO and CO<Subscript>2</Subscript> fluxes in a montane forest ecosystem of Kenya

Increasing demand for food and fibre by the growing human population is driving significant land use (LU) change from forest into intensively managed land systems in tropical areas. But empirical evidence on the extent to which such changes affect the soil-atmosphere exchange of trace gases is still scarce, especially in Africa. We investigated the effect of LU on soil trace gas production in the Mau Forest Complex region, Kenya. Intact soil cores were taken from natural forest, commercial and smallholder tea plantations, eucalyptus plantations and grazing lands, and were incubated in the lab under different soil moisture conditions. Soil fluxes of nitrous oxide (N₂O), nitric oxide (NO) and carbon dioxide (CO₂) were quantified, and we approximated annual estimates of soil N₂O and NO fluxes using soil moisture values measured in situ. Forest and eucalyptus plantations yielded annual fluxes of 0.3–1.3 kg N₂O–N ha^?1 a^?1 and 1.5–5.2 kg NO–N ha^?1 a^?1. Soils of commercial tea plantations, which are highly fertilized, showed higher fluxes (0.9 kg N₂O–N ha^?1 a^?1 and 4.3 kg NO–N ha^?1 a^?1) than smallholder tea plantations (0.1 kg N₂O–N ha^?1 a^?1 and 2.1 kg NO–N ha^?1 a^?1) or grazing land (0.1 kg N₂O–N ha^?1 a^?1 and 1.1 kg NO–N ha^?1 a^?1). High soil NO fluxes were probably the consequence of long-term N fertilization and associated soil acidification, likely promoting chemodenitrification. Our experimental approach can be implemented in understudied regions, with the potential to increase the amount of information on production and consumption of trace gases from soils.     

A critical evaluation of models for complex molecular dynamics: application of NMR studies of double- and single-stranded DNA

The nature of internal and overall motions in native (double-stranded) and denatured (single-stranded) DNA fragments 120–160 base pairs (bp) long is examined by molecular-dynamics modeling using ¹³C-nmr spin-relaxation data obtained over the frequency range of 37–125 MHz. The broad range of ¹³C frequencies is required to differentiate among various models. Relatively narrow linewidths, large nuclear Overhauser enhancements (NOEs), and short T₁ values all vary significantly with frequency and indicate the presence of rapid, restricted internal motions on the nanosecond time scale. For double-stranded DNA monomer fragments (147 bp, 24 Å diam at 32°C), the overall motion is that of an axially symmetric cylinder (τ_x = ～10^?6 s;τ_Z = ～1.8 × 10^?8s), which is in good agreement with values calculated from hydrodynamic theory (τ_x = ～1.8 × 10^?6 s; τ_Z = ～2.7 × 10^?8 s). The DNA internal motion can be modeled as restricted amplitude internal diffusion of individual C? H vectors of deoxyribose methine carbons C1′, C3′, and C4′, either with conic boundary conditions (τ_w = ～4 × 10^?9 s, θ_cone = ～21°) or as a bistable jump (τ_A = τ_B = ～2 × 10^?9 s, θ = ～15°). We discuss the critical role in molecular-dynamics modeling played by the angle (β) that individual C? H vectors make with the long axis of the DNA helix. Heat denaturation brings about increases in both the rate and amplitude of the internal motion (described by the wobble model with τ_W = ～0.2 × 10^?9 s, θ_cone = ～50°), and overall motion is affected by becoming essentially isotropic (τ_x = τ_Z = ～5 × 10^?8 s) for the single-stranded molecules. Since ¹³C-nmr data obtained at various DNA concentrations for C2′ of the deoxyribose ring is not described well by the above models, a new model incorporating an additional internal motion is proposed to take into account the rapid, extensive, and weakly coupled motion of C2′.     

Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica

The effects of several physiological parameters on H₂ production rate in the unicellular halotolerant cyanobacterium Aphanothece halophytica were investigated. Under nitrogen deprivation, the growth of cells was inhibited, but H₂ production rate was enhanced approximately fourfold. Interestingly, cells grown under sulfur deprivation exhibited a decrease in cell growth, H₂ production rate, and bidirectional hydrogenase activity. Glucose was the preferred sugar source for H₂ production by A. halophytica, but H₂ production decreased at high glucose concentrations. H₂ production rate was optimum when cells were grown in the presence of 0.75 M?NaCl, or 0.4 μM?Fe³⁺, or 1 μM?Ni²⁺. The optimum light intensity and temperature for H₂ production were 30 μmol photons m^?2?s^?1 and 35 °C, respectively. A two-stage culture of A. halophytica was performed in order to overcome the reduction of cell growth in N-free medium. In the first stage, cells were grown in normal medium to accumulate biomass, and in the second stage, H₂ production by the obtained biomass was induced by growing cells in N-free medium supplemented with various chemicals for 24 h. A. halophytica grown in N-free medium containing various MgSO₄ concentrations had a high H₂ production rate between 11.432 and 12.767 μmol H₂ mg?chlorophyll a (chl a)^?1?h^?1, a 30-fold increase compared to cells grown in normal medium. The highest rate of 13.804 μmol H₂ mg?chl a ^?1?h^?1 was obtained when the N-free growth medium contained 0.4 μM Fe³⁺. These results suggested the possibility of using A. halophytica and some other halotolerant cyanobacteria thriving under extreme environmental conditions in the sea as potential sources for H₂ production in the future.     

Relation of certain infrared bands to conformational changes of cellulose and cellulose oligosaccharides

The i.r. spectra of D-glucose and cellulose oligosaccharides up to cellopentaose have been compared with those of cellulose at various temperatures between that of liquid nitrogen and ～250°. Significant changes in frequency and intensity of the bands at ～3400 cm^?1 were observed. The a_1372cm^?1/a_2900cm^?1 ratio for each carbohydrate studied decreased gradually as the temperature was increased above ambient. The change of the band intensifies at 1429 and 893 cm^?1 with temperature was also investigated. The observed spectral changes are assumed to be associated with changes of hydrogen bonding.     

Kinetics and thermodynamics of catalysis and thermal inactivation of a novel α-amylase (Tp-AmyS) from Thermotoga petrophila

Abstract

This research is focussed on kinetic, thermodynamic and thermal inactivation of a novel thermostable recombinant α-amylase (Tp-AmyS) from Thermotoga petrophila. The amylase gene was cloned in pHIS-parallel1 expression vector and overexpressed in Escherichia coli. The steady-state kinetic parameters (V_max, K_m, k_cat and k_cat/K_m) for the hydrolysis of amylose (1.39?mg/min, 0.57?mg, 148.6?s^?1, 260.7), amylopectin (2.3?mg/min, 1.09?mg, 247.1?s^?1, 226.7), soluble starch (2.67?mg/min, 2.98?mg, 284.2?s^?1, 95.4) and raw starch (2.1?mg/min, 3.6?mg, 224.7?s^?1, 61.9) were determined. The activation energy (E_a), free energy (ΔG), enthalpy (ΔH) and entropy of activation (ΔS) at 98?°C were 42.9?kJ mol^?1, 74?kJ mol^?1, 39.9?kJ mol^?1 and ?92.3 J mol^?1 K^?1, respectively, for soluble starch hydrolysis. While ΔG of substrate binding (ΔG_E-S) and ΔG of transition state binding (ΔG_E-T) were 3.38 and ?14.1?kJ mol^?1, respectively. Whereas, EaD, Gibbs free energy (ΔG*), increase in the enthalpy (ΔH*) and activation entropy (ΔS*) for activation of the unfolding of transition state were 108, 107, 105?kJ mol^?1 and ?4.1 J mol^?1 K^?1. The thermodynamics of irreversible thermal inactivation of Tp-AmyS revealed that at high temperature the process involves the aggregation of the protein.     

Kinetics of oxidation of tyrosine by a model alkoxyl radical

Abstract

Oxidation of tyrosine moieties by radicals involved in lipid peroxidation is of current interest; while a rate constant has been reported for reaction of lipid peroxyl radicals with a tyrosine model, little is known about the reaction between tyrosine and alkoxyl radicals (also intermediates in the lipid peroxidation chain reaction). In this study, the reaction between a model alkoxyl radical, the tert-butoxyl radical and tyrosine was followed using steady-state and pulse radiolysis. Acetone, a product of the β-fragmentation of the tert-butoxyl radical, was measured; the yield was reduced by the presence of tyrosine in a concentration- and pH-dependent manner. From these data, a rate constant for the reaction between tert-butoxyl and tyrosine was estimated as 6?±?1 × 10⁷ M^?1 s^?1 at pH 10. Tyrosine phenoxyl radicals were also monitored directly by kinetic spectrophotometry following generation of tert-butoxyl radicals by pulse radiolysis of solutions containing tyrosine. From the yield of tyrosyl radicals (measured before they decayed) as a function of tyrosine concentration, a rate constant for the reaction between tert-butoxyl and tyrosine was estimated as 7?±?3 × 10⁷ M^?1 s^?1 at pH 10 (the reaction was not observable at pH 7). We conclude that reaction involves oxidation of tyrosine phenolate rather than undissociated phenol; since the pK_a of phenolic hydroxyl dissociation in tyrosine is ～ 10.3, this infers a much lower rate constant, about 3 × 10⁵ M^?1 s^?1, for the reaction between this alkoxyl radical and tyrosine at pH 7.4.     

DFT studies of hydrocarbon combustion on metal surfaces

Catalytic combustion of hydrocarbons is an important technology to produce energy. Compared to conventional flame combustion, the catalyst enables this process to operate at lower temperatures; hence, reducing the energy required for efficient combustion. The reaction and activation energies of direct combustion of hydrocarbons (CH?→?C?+?H) on a series of metal surfaces were investigated using density functional theory (DFT). The data obtained for the Ag, Au, Al, Cu, Rh, Pt, and Pd surfaces were used to investigate the validity of the Brønsted-Evans-Polanyi (BEP) and transition state scaling (TSS) relations for this reaction on these surfaces. These relations were found to be valid (R²?=?0.94 for the BEP correlation and R²?=?1.0 for the TSS correlation) and were therefore used to estimate the energetics of the combustion reaction on Ni, Co, and Fe surfaces. It was found that the estimated transition state and activation energies (E_TS?=??69.70 eV and E_a?=?1.20 eV for Ni, E_TS?=??87.93 eV and E_a?=?1.08 eV for Co and E_TS?=??92.45 eV and E_a?=?0.83 eV for Fe) are in agreement with those obtained by DFT calculations (E_TS?=??69.98 eV and E_a?=?1.23 eV for Ni, E_TS?=??87.88 eV and E_a?=?1.08 eV for Co and E_TS?=??92.57 eV and E_a?=?0.79 eV for Fe). Therefore, these relations can be used to predict energetics of this reaction on these surfaces without doing the time consuming transition state calculations. Also, the calculations show that the activation barrier for CH dissociation decreases in the order Ag ? Au ? Al ? Cu ? Pt ? Pd ? Ni?>?Co?>?Rh?>?Fe.     

Extraction of total phenolic content from Azadirachta indica or (neem) leaves: Kinetics study

The objective of this work is to put forth the optimization and kinetics of total phenolic compounds extraction from Azadirachta indica leaves in a stirred batch extraction. Various experiential extraction parameters have been studied for maximum extraction of the total phenolic compounds. The maximum yield of total phenolic compounds was found to be 10.80?mg?g^?1 of dried neem powder under the optimized conditions. The extraction kinetics behavior followed first-order kinetics with diffusion coefficient ranged from 1.8?×?10^?12 to 3.2?×?10^?12?m² s^?1 for all sets. Activation energy (E_a) value for the extraction of the total phenolic compounds was found to be 22.87?kJ?mol^?1. The kinetic expression model developed by Spiro and Siddique showed a good agreement with the experimental outcomes. The obtained results can be used to scale up the operations for industrial purposes.     

Adaptations of tropical marine microphytobenthic assemblages along a gradient of light and nutrient availability in Suva Lagoon,Fiji

How are microphytobenthic biofilms adapted to the high incident irradiances and temperatures, low inorganic nutrient concentrations and high desiccation stresses on intertidal flats present in tropical environments? This study investigated biofilms subject to different environmental conditions in a range of tropical sites in Suva lagoon, Fiji. PAM fluorescence was used to measure photophysiological responses to the light climate. Biofilm colloidal carbohydrate, extracellular polymeric substances (EPS) and low molecular weight (MW) carbohydrate concentrations and diel carbohydrate production patterns were measured. Average biomass (Chl a) ranged from 15 to 36?mg?m^?2, and was highest in seagrass bed sediments, but biomass was not correlated with water column or sediment porewater nutrient concentrations. Biofilm photophysiology differed significantly along a combined gradient of light and nutrient availability, with F _v/F _m, relative ETR_max and E _k of biofilms highest in mangrove and intertidal main island sites and lowest in subtidal coral reef flats. Subtidal biofilms showed photoinhibition at irradiances > 1000?µmol?m^?2. Significant correlations between Chl a and colloidal carbohydrate concentrations were present (except on intertidal sandflats), and tropical biofilms had higher ratios of colloidal carbohydrate and EPS to Chl a than temperate estuarine biofilms, probably due to a combination of high irradiance and low nutrient availability leading to the production of excess photoassimilates. The percentage of EPS present in the colloidal fraction was highest in coral sand biofilms (42%), which had the lowest nutrient concentrations, compared with other sites (25–32%). Intertidal biofilms predominantly consisted of large motile taxa and showed strong rhythms of vertical migration. During tidal emersion, high sediment temperatures (41?°C), irradiance (>2300?µmol?m^?2?s^?1) and salinity (49‰) stimulated downward migration. In silty sediments, migration resulted in a reduction in photosynthetic activity during the midday period but, in sands with high light penetration (to a depth of > 1700?µm), high production rates of EPS (18.2?µg carbo. µg Chl a^?1 h^?1) and low MW carbohydrate exudates (40.2?µg carbo. µg Chl a^?1 h^?1) occurred. Vertical migration, high E _k and high rates of photoassimilate dumping are all adaptations to living in the tropical intertidal zone. Seagrass and reef flat biofilms consisted of a diverse non-migratory flora of motile and non-motile taxa that were not subject to such extreme temperature and irradiance conditions. Low values of photosynthetic parameters and high colloidal and EPS content indicated that these biofilms were nutrient-limited.     

Feasibility of Typha Latifolia for High Salinity Effluent Treatment in Constructed Wetlands for Integration in Resource Management Systems

High salinity wastewaters have limited treatment options due to the occurrence of salt inhibition in conventional biological treatments. Using recirculating marine aquaculture effluents as a case study, this work explored the use of Constructed Wetlands as a treatment option for nutrient and salt loads reduction. Three different substrates were tested for nutrient adsorption, of which expanded clay performed better. This substrate adsorbed 0.31 mg kg^?1 of NH₄ ⁺?N and 5.60 mg kg^?1 of PO₄ ^3??P and 6.9 mg kg^?1 dissolved salts after 7 days of contact. Microcosms with Typha latifolia planted in expanded clay and irrigated with aquaculture wastewater (salinity 2.4%, 7 days hydraulic retention time, for 4 weeks), were able to remove 94% NH₄ ⁺?N (inlet 0.25 ± 0.13 mg L^?1), 78% NO₂ ^??N (inlet 0.78 ± 0.62 mg L^?1), 46% NO₃ ^??N (inlet 18.83 ± 8.93 mg L^?1) whereas PO₄ ^3??P was not detected (inlet 1.41 ± 0.21 mg L^?1). Maximum salinity reductions of 52% were observed. Despite some growth inhibition, plants remained viable, with 94% survival rate. Daily treatment dynamics studies revealed rapid PO₄ ^3??P adsorption, unbalancing the N:P ratio and possibly affecting plant development. An integrated treatment approach, coupled with biomass valorization, is suggested to provide optimal resource management possibilities.