Physico-chemical characteristics of humic substances of major soil associations of Bihar (India)

Humic acid (HA) and fulvic acid (FA) extracted from fourteen surface soil samples (0–20 cms) belonging to nine major Soil Association Groups scattered over different agro-climatic situations, were characterized by elemental and functional group analysis, E₄/E₆ ratios, coagulation behaviour and distribution of carbon in different soil humus fractions. The E₄/E₆ ratio of FA extracted from different soils was wider than that of HA. The coagulation behaviour of HA and FA fractions and also of cultivated and forest soils showed marked differences. The variations in the ratios of HAC:FAC (0.31 to 1.0) among different soils were indicative of the degree of humification under the influence of vegetation and agroclimatic conditions. The elemental composition of HA and FA, in general, indicated a higher carbon and nitrogen content and C/N ratio in the former than in the latter fraction. On the contrary, the oxygen content of FA was higher compared to that of HA. The carbon contents of HA extracted from the cultivated and forest soils of Hazaribagh were almost equal, as were also the carbon contents of HA from the cultivated and forest soils from Ranchi. Total acidity of FA of the soils selected in the present study was higher than that of HA. The functional groups such as carboxyl, phenolic hydroxyl and carbonyl were present in the two fractions in varying proportions.     

Platinum(II) phosphonate complexes derived from endo-8-camphanylphosphonic acid

The reactions of cis-[PtCl₂L₂] [L = PPh₃, PMe₂Ph or L₂ = Ph₂P(CH₂)₂PPh₂ (dppe)] with endo-8-camphanylphosphonic acid (CamPO₃H₂) and Ag₂O in refluxing dichloromethane gave platinum(II) phosphonate complexes [Pt(O₃PCam)L₂]. The X-ray crystal structure of [Pt(O₃PCam)(PPh₃)₂]·2CHCl₃ shows that the bulky camphanyl group, rather than being directed away from the platinum, is instead directed into a pocket formed by the Pt and the two PPh₃ ligands. This allows the O₃P-CH₂ group to have a preferred staggered conformation. The complexes were studied in detail by NMR spectroscopy, which demonstrates non-fluxional behaviour for the sterically bulky PPh₃ and dppe derivatives, which contain inequivalent phosphine ligands in their ³¹P NMR spectra. These findings are backed up by theoretical calculations on the PPh₃ and PPhMe₂ derivatives, which show, respectively, high and low energy barriers to rotation of the camphanyl group in the PPh₃ and PPhMe₂ complexes. The X-ray crystal structure of CamPO₃H₂ is also reported, and consists of hydrogen-bonded hexameric aggregates, which assemble to form a columnar structure containing hydrophilic phosphonic acid channels surrounded by a sheath of bulky, hydrophobic camphanyl groups.     

Enhancement and inhibition of luminol chemiluminescence by phenolic acids

We explored the behaviour of a series of phenolic acids used as enhancers or inhibitors of luminol chemiluminescence by three different methods to determine if behaviour was associated with phenolic acid structure and redox character. All the phenolic acids inhibited chemiluminescence when hexacyanoferrate(III) was reacted with the phenolic acids before adding luminol. The redox character of these compounds was clearly related to structure. When hexacyanoferrate(III)-luminol-O₂ chemiluminescence was initiated by phenolic acid-luminol mixtures some phenolic acids behaved as enhancers of chemiluminescence, and others as inhibitors. We propose a mechanism to explain these findings. We found direct relationships between the redox character of the phenolic acids and the enhancement or inhibition of the chemiluminescence of the luminol–H₂O₂–peroxidase system and we propose mechanism to explain these phenomena.     

Relaxation time measurements of hyaluronic acid

The N-acetyl-groups of hyaluronic acid and its sodium salts are shown to have pH-dependent T₁, T₂ and NOE values, unlike all other carbonatoms and protons. This behaviour at high temperatures can be explained by assuming that parts of the helical structure are converted into random coil by H-bond breaking. Moreover, the concentration of Na⁺, Mg²⁺, or Ca²⁺ is shown to have no influence on the relaxational behaviour of HA.     

O-Atom Scrambling in the Aqueous Isomerization of Pernitrous Acid

Raman spectroscopy has been used to determine the isotopic distribution of oxygen during the isomerization of pernitrous acid to nitrate in¹⁸OH₂. Decomposition of unlabeled pernitrous acid in carbon-dioxide-free phosphate-buffered solutions of¹⁸OH₂at pH 6.8 results in the incorporation of 13 ± 1%¹⁸O into the nitrate product with no detectable double-isotopic incorporation and 83% of the product having complete retention of its oxygen atoms. The mechanistic implications of this are contrasted for three frequently considered pathways for peroxide bond cleavage and it is concluded that the results are most consistent with the formation of reactive intermediate which can either rearrange or undergo hydrolytic O-atom exchange with water.     

Gallic acid oxidation by turnip peroxidase

Both ellagic and gallic acids non competitively inhibited guaiacol oxidation by turnip peroxidase. The K_i values were 3 and 26 μm for ellagic and gallic acid respectively. Enzymatic oxidation of gallic acid by the isolated major turnip peroxidase was characterized with respect to spectral behaviour, affinity constant and pH effect. The K_m for H₂O₂ and gallic acid are 2.5 and 8.0 mM for turnip peroxidase. The pH optimum for gallic acid oxidation is about 6.5 and the rate constant k₄ decreased with the increase of pH in presence of both guaiacol and Gallic acid. When the gallic acid oxidation products were subjected to chromatographic analysis, it was found to be converted mainly to ellagic and an unknown quinone.     

Solution structure of molybdic acid from Raman spectroscopy and DFT analysis

Protonation of produces the well-characterized polymolybdates, but at concentrations below 10⁻³ M the dominant species is monomeric molybdic acid, H₂MoO₄. It is likely to be the species adsorbed on manganese oxide, a process thought to control levels in the ocean, because of the strong proton dependence of adsorption. The molecular structure of H₂MoO₄ is elusive, since it occurs only in dilute solutions. Using 244 nm laser excitation, near resonance with O → Mo charge-transfer electronic transitions of H₂MoO₄, we have detected a 919 cm⁻¹ Raman band assignable to ν_sMoO. Using DFT, we have computed geometries and vibrational modes for the various structures consistent with the H₂MoO₄ formula. We tested the computations on a series of Mo(VI) oxo complexes with known vibrational frequencies, at several levels of theory. Best agreement with experimental values, at reasonable computational cost, was obtained with the B3LYP functional, employing a LANL2DZ ECP basis set for Mo and the 6-311+G(2df,p) basis set for O and H. Among the possible H₂MoO₄ structures only those based on the MoO₃ unit, with one, two or three coordinated water molecules, gave a scaled frequency for ν_sMoO that was within two standard deviations of 919 cm⁻¹. Best agreement was obtained for MoO₃(H₂O)₃. The MoO₂ and MoO structures gave frequencies that were too high. The Mo(OH)₆ structure could be excluded, because its vibrational frequencies shift down strongly upon H/D exchange, whereas the 919 cm⁻¹H₂MoO₄ band shifts up 1 cm⁻¹ in D₂O.     

Hydrothermal investigation of the lanthanide (Ln=La, Ce, Pr, Nd, Sm) 2,6-pyridinedicarboxylate system

In this paper, two new dipicolinate complexes, Ln₂(dipic)₃(H₂O)₃ (1) with Ln=La, Ce, Pr, Nd, Sm and Ce₃(dipic)₅(H₂O)₂ (2), are described. Hydrothermal synthesis, crystal structure and thermal behaviour of both compounds are described, as well as the magnetic behaviour of the trinuclear complex (2). The structures consist of LaO₇N₂, LaO₇N (1) and CeO₇N, CeO₆N₃ (2) polyhedra linked to form three-dimensional networks. The magnetic study of 2 confirms that it corresponds to a Ce(III)-Ce(IV) molecular compound and that the magnetic interaction is certainly antiferromagnetic. According to the thermogravimetric analysis, thermal decomposition of compounds 1 starts at about 100-130 °C, when 2 is thermally stable up to 250 °C.     

Molecular dynamic simulations study of the effect of salt valency on structure and thermodynamic solvation behaviour of anionic polyacrylate PAA in aqueous solutions

The effect of salt concentration and valency on intermolecular structure and solvation thermodynamic properties of aqueous solution containing polyacrylicacid (PAA) chains and multi-valent salts calcium chloride (CaCl₂) and aluminium chloride (AlCl₃) as a function of charge density was investigated using atomistic molecular dynamic simulations with explicit solvent. Salt-free solution favours the self-association of uncharged (acidic form) PAA chains facilitated by inter-chain hydrogen bonds. The ionised (charged) PAA chains are not associated in salt-free aqueous solutions and undergo self-association in the salt solutions due to bridging effect induced by condensed salt ions in agreement with scattering investigations available in literature. The collapse behaviour of PAA in presence of CaCl₂ and re-expansion behaviour of PAA chains in case of AlCl₃ salt solutions are observed. The rigidity of PAA chains decrease with increase in salt concentration, in agreement with experimental results available in literature. The trivalent salt favours relatively the greater extent of shrinking of PAA chains as well as inter-chain interactions as compared to divalent salts as evident from radius-of-gyration, H-bond and pair-wise solvation enthalpy data. The conformation and hydration behaviour of the acid form of PAA chains are not significantly altered by added salt ions. The hydration behaviour of ionised PAA chains is significantly reduced by added salts due to screening effect of the condensed salt ions. The pair correlation functions of solutions species such as Ca²⁺, Al³⁺, Na⁺ and Cl^? with respect to PAA oxygen show the greater affinity of PAA units with the higher valency Al³⁺ ions over Ca²⁺ and Na⁺ in solution. With increase in concentration of AlCl₃ and CaCl₂ salts, a decrease in effective charge density of ionised PAA chains is observed from the existence of unfavourable PAA–water, PAA–Ca²⁺ and PAA–Al³⁺ interactions.     

Vanadocene complexes of amino acids containing secondary amino group: The first evidence of O,O-bonded carboxylic group to vanadocene(IV) moiety

Reaction of vanadocene dichlorides (Cp₂VCl₂ and (η⁵-C₅H₄Me)₂VCl₂) with amino acids containing secondary amino groups gives three types of complexes: a) compounds with N,O-bonded amino acid, b) O-bonded amino acids and c) O,O-bonded amino acid. The complexes with N,O-bonded amino acid and O-bonded amino acids were observed in the case of l-proline and N-methylglycine (NMG). Reactions with N-phenylglycine (NPG) give O,O-chelates as the sole products. All three types of the complexes were characterized by spectroscopic methods. Structures of [(η⁵-C₅H₄Me)₂V(O-Pro)][BPh₄], [Cp₂V(O-Pro)₂][PF₆]₂, [Cp₂V(N,O-NMG)][BPh₄]·MeOH, [(η⁵-C₅H₄Me)₂V(N,O-NMG)][BPh₄]·MeOH, [Cp₂V(O-NMG)₂][Cl]₂·2H₂O, [(η⁵-C₅H₄Me)₂V(O-NMG)₂][Cl]₂·H₂O and [(η⁵-C₅H₄Me)₂V(O,O-NPG)][BPh₄] were determined by X-ray crystallography.     

Phase behaviour of stearic acid-stearonitrile mixtures: A thermodynamic study in bulk and at the air-water interface

The solid-liquid phase behaviour of stearic acid (SA) and stearonitrile (SN) in binary mixtures was investigated by differential scanning calorimetry (DSC), and the formation of SA-SN mixed monolayers at the air-water interface was followed by surface pressure-area (π-A) measurements and by Brewster angle microscope (BAM) observation. The solid-liquid phase diagram is a eutectic type phase diagram, with the eutectic composition 0.90 < X_SN < 0.95 and T^eut = 40.9 °C. The DSC results also suggest that the two components are immiscible in the solid phase but form a liquid mixture with positive deviations to the ideal behaviour. At the air-water interface, the two components form liquid condensed monolayers in the entire range of compositions, at low surface pressures, while solid mixed monolayers only form at high surface pressures for X_SN < 0.8. Thermodynamic analysis indicates that SA and SN are miscible in the liquid condensed phase, with negative deviations from the ideal behaviour. The variation of the collapse surface pressure of mixed monolayers also indicates miscibility at the air-water interface.     

Theoretical studies of infrared signatures of proton-bound amino acid dimers with homochiral and heterochiral moieties

Proton-bound homochiral and heterochiral dimers, X-H⁺-X, of five amino acids (X = Ser, Ala, Thr, Phe, and Arg) are investigated theoretically using quantum chemical density functional theory (DFT) calculations and molecular dynamics simulations with the aim to unveil diastereomer-specific mid-infrared (mid-IR) absorption bands in the spectral range of 1000 to 1800 cm⁻¹. The theoretical calculations performed in this work imply that all systems, except Ala₂H⁺, have distinct mid-IR absorption bands in homochiral and heterochiral configurations, which make them appropriate systems to be studied experimentally with mid-IR spectroscopy. We show that intermolecular interaction with the side chain, in the form of hydrogen bonding or cation-π interaction, is necessary for chiral effects to be present in the mid-IR spectra of proton-bound dimers of amino acids. We also report new conformers for Ala₂H⁺, Thr₂H⁺, Phe₂H⁺, and Arg₂H⁺, which were not found in earlier studies of these dimers.     

Crystal structure, magnetic properties and Mössbauer studies of [Fe(qsal)2][Ni(dmit)2]

A new compound of formula [Fe(qsal)₂][Ni(dmit)₂] (1) has been synthesised, structurally and magnetically characterised (qsalH = N-(8-quinolyl)salicylaldimine, dmit²⁻ = 1,3-dithiol-2-thione-4,5-dithiolato). Its structural features and its magnetic behaviour were compared with those of [Fe(qsal)₂]-based complexes, and more particularly [Fe(qsal)₂][Ni(dmit)₂] · 2CH₃CN.     

Investigating the binding behaviour of two avidin‐based testosterone binders using molecular recognition force spectroscopy

Molecular recognition force spectroscopy, a biosensing atomic force microscopy technique allows to characterise the dissociation of ligand–receptor complexes at the molecular level. Here, we used molecular recognition force spectroscopy to study the binding capability of recently developed testosterone binders. The two avidin‐based proteins called sbAvd‐1 and sbAvd‐2 are expected to bind both testosterone and biotin but differ in their binding behaviour towards these ligands. To explore the ligand binding and dissociation energy landscape of these proteins, we tethered biotin or testosterone to the atomic force microscopy probe while the testosterone‐binding protein was immobilized on the surface. Repeated formation and rupture of the ligand–receptor complex at different pulling velocities allowed determination of the loading rate dependence of the complex‐rupturing force. In this way, we obtained the molecular dissociation rate (k_off) and energy landscape distances (x_β) of the four possible complexes: sbAvd‐1‐biotin, sbAvd‐1‐testosterone, sbAvd‐2‐biotin and sbAvd‐2‐testosterone. It was found that the kinetic off‐rates for both proteins and both ligands are similar. In contrast, the x_β values, as well as the probability of complex formations, varied considerably. In addition, competitive binding experiments with biotin and testosterone in solution differ significantly for the two testosterone‐binding proteins, implying a decreased cross‐reactivity of sbAvd‐2. Unravelling the binding behaviour of the investigated testosterone‐binding proteins is expected to improve their usability for possible sensing applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectroscopic and elemental investigation of microbial decomposition of aquatic fulvic acid in biological process of drinking water treatment

As humic substances left in treated water tend to form trihalomethans during chlorination, their removal in water treatment processes is a significant concern for drinking water supplies. One of the removal technologies, the biofilm reactor is studied for the microbial decomposition of aquatic fulvic acid (AFA). The AFA is characterized by elemental analysis, UV-Vis, ¹³C-NMR, and IR spectroscopic methods. The spectroscopic and elemental investigation was capable of characterizing the microbial decomposition of AFA. Biologically treated fulvic acid was in a more oxidized state; its spectra displayed a higher degree of condensation of aromatic constituents than influent fulvic acid. Microbial degradation of AFA was more active in the low molecular weight fractions and intensively occurred in the aliphatic fraction.Abbreviations A the absorbance at wavelength - specific absorptivities - AFAs aquatic fulvic acids - AHS aquatic humic substances - COD chemical oxygen demand - Da dalton - DO dissolved oxygen - E₄/E₆ratio a ratio between absorbance at 465 and 665 nm - FA fulvic acid - IR infrared - NMR nuclear magnetic resonance - TOC total organic carbon - UV-Vis ultraviolet-visible     

Stomatal control by both [ABA] in the xylem sap and leaf water status: a test of a model for draughted or ABA-fed field-grown maize

A model of maize stomatal behaviour has been developed, in which stomatal conductance is linked to the concentration of abscisic acid ([ABA]) in the xylem sap, with a sensitivity dependent upon the leaf water potential (Ψ₁). It was tested against two alternative hypotheses, namely that stomatal sensitivity to xylem [ABA] would be linked to the leaf-to-air vapour pressure difference (VPD), or to the flux of ABA into the leaf. Stomatal conductance (g_s) was studied: (1) in field-grown plants whose xylem [ABA] and Ψ₁ depended on soil water status and evaporative demand; (2) in field-grown plants fed with ABA solutions such that xylem [ABA] was artificially raised, thereby decreasing g_s and increasing Ψ₁ and leaf-to-air VPD; and (3) in ABA-fed detached leaves exposed to varying evaporative demands, but with a constant and high Ψ₁. The same relationships between g_s, xylem [ABA] and Ψ₁, showing lower stomatal sensitivity to [ABA] at high Ψ₁, applied whether variations in xylem [ABA] were due to natural increase or to feeding, and whether variations in Ψ₁, were due to changes in evaporative demand or to the increased Ψ₁ observed in ABA-fed plants. Conversely, neither the leaf-to-air VPD nor the ABA flux into the leaf accounted for the observed changes in stomatal sensitivity to xylem [ABA]. The model, using parameters calculated from previous field data and the detached-leaf data, was tested against the observations of both ABA-fed and droughted plants in the field. It accounted with reasonable accuracy for changes in g_s (r² ranging from 0.77 to 0.81). These results support the view that modelling of stomatal behaviour requires consideration of both chemical and hydraulic aspects of root-to-shoot communication.     

Dielectric studies on water in solutions of purified lecithin vesicles

The complex permittivity of sonicated aqueous solutions of purified dimyristoylphosphatidylcholine has been measured as a function of frequency between 3 kHz and 40 GHz. The dielectric spectrum of the samples shows two dispersion/absorption regions, one centered at about 80 MHz the other at about 20.GHz (30°C). Otherwise than in previous studies no additional dispersion/absorption process has been found at frequencies below 10 MHz.The complex dielectric spectrum of the samples is discussed with respect to the dynamical state of solvent water in solutions of single-bilayer vesicles. The main relaxation time of the solvent water, τ₁ ((2πτ₁)^?1 ≈ 20 GHz), is smaller than that of pure water, τ_W, at the same temperature. This effect results from the action of internal depolarizing fields which obviously overcompensate and enhancement of τ₁ due to specific solute/solvent interactions (hydration) as had been previously found with micellar solutions of lysolecithins.It cannot be excluded, that some solvent water shows unusual dynamical behaviour. If there exists a substantial amount of such motionally perturbed water, however, it must be characterized by a relaxation time close to that of the phosphorylcholine zwitterions, τ₂ ((2πτ₂)^?1 ≈ 80 MHz).     

Semisynthesis and properties of a fluorescent phosphatidyl-inositol analogue containing a cis-parinaroyl moiety

A method for the preparation of a fluorescent phosphatidylinositol analogue, 1-acl,-2-prinaroyl-sn-glycero-3-phospho-sn-1-myo-inositol has been developed. This method makes use of yeast phosphatidylinositol as the starting material and includes the following steps: (1) acetylation of the free hydroxyl groups of the inositol moeity; (2) removal of the fatty acid from the sn-2-position of the glycerol moiety by phospholipase A₂; (3) reacylation with parimaroyl anhydride; (4) removal of the protecting acetyl groups by alkaline solvolysis. The identity of the product was established by thin-layer chromatography (TLC), UV absorption spectroscopy, enzymatic degradation and by a transfer assay using the phosphatidylinositol transfer protein from bovine brain.Some properties of the fluorescent phosphatidylinositol analogue are reported.     

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO₂ with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO₂ levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO₂ levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices.