Carbon nanotube functionalization with carboxylic derivatives: a DFT study

Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including –COOX (X?=?H, CH₃, CH₂NH₂, CH₃Ph, CH₂NO₂, and CH₂CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of ?0.23 to ?7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is ?CH₂NO₂?>?CH₂CN?>?H?>?CH₂Ph?>?CH₃?>?CH₂NH₂. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for ?H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of ?CH₂NO₂ and _?CH₂CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.     

Theoretical studies on the unimolecular decomposition of nitroglycerin

To improve the understanding of the unimolecular decomposition mechanism of nitroglycerin (NG) in the gas phase, density functional theory calculations were performed to determine various decomposition channels at the B3LYP/6-311G** level. For the unimolecular decomposition mechanism of NG, we find two main mechanisms: (I) homolytic cleavage of O-NO₂ to form ?NO₂ and CH₂ONO₂CHONO₂CH₂O?, which subsequently decomposes to form ?CHO, ?NO₂, and 2CH₂O; (II) successive HONO eliminations to form HONO and CHO-CO-CHO, which subsequently decomposes to form CH₂O?+?2CO₂ and ?CHO?+?CO. We also find that the former channel has slightly smaller activation energy than the latter one. In addition, the rate constants of the initial process of the two decomposition channels were calculated. The results show that the O-NO₂ cleavage pathway occurs more easily than the HONO elimination.     

Theoretical rate constant of methane oxidation from the conventional transition-state theory

The potential energy surface for the first step of the methane oxidation CH₄?+?O₂?CH₃?+?HO₂ was studied using the London-Eyring-Polanyi-Sato equation (LEPS) and the conventional transition-state theory (CTST). The calculated activation energy and rate constant values were in good agreement with the experimental and theoretical values reported in the literature using the shock tube technique and coupled cluster method respectively. The rate equation from CTST, although simple, provides good results to study the H-shift between methane and the oxygen molecules.     

Characterization of halogen···halogen interactions in crystalline dihalomethane compounds (CH2Cl2, CH2Br2 and CH2I2): a theoretical study

To improve understanding of the unimolecular decomposition mechanism of 1,2,4-butanetriol trinitrate (BTTN) in the gas phase, density functional theory calculations were performed to determine various decomposition pathways at the B3LYP/6-311G** level. Two main mechanisms for the unimolecular decomposition of BTTN were found. In the first, homolysis of one of the O–NO₂ bonds occurs to form ?NO₂ and CH₂ONO₂CHONO₂CH₂CH₂O?, which subsequently decomposes to form CH₃CHO + ?CHO + 3NO₂ + HCHO. In the second, successive HONO elimination reactions yield three HONO and OHCCH₂CHONO₂CH₂ONO₂ fragments, which subsequently decompose to form CH₃CHO + 2CO + 3HONO. We also found that the first pathway has a slightly lower activation energy than the second. The results show that the pathway involving O–NO₂ cleavage is slightly more energetically favorable than that involving HONO elimination.     

Theoretical study on the functionalization of BC2N nanotube with amino groups

Using density functional theory calculations, we investigated properties of a functionalized BC₂N nanotube with NH₃ and five other NH₂-X molecules in which one of the hydrogen atoms of NH₃ is substituted by X = ?CH₃, ?CH₂CH₃, ?COOH, ?CH₂COOH and ?CH₂CN functional groups. It was found that NH₃ can be preferentially adsorbed on top of the boron atom, with adsorption energy of ?12.0 kcal mol^?1. The trend of adsorption-energy change can be correlated with the trend of relative electron-withdrawing or -donating capability of the functional groups. The adsorption energies are calculated to be in the range of ?1.8 to ?14.2 kcal mol^?1, and their relative magnitude order is found as follows: H₂N(CH₂CH₃) > H₂N(CH₃) > NH₃ > H₂N(CH₂COOH) > H₂N(CH₂CN) > H₂N(COOH). Overall, the functionalization of BC₂N nanotube with the amino groups results in little change in its electronic properties. The preservation of electronic properties of BC₂N coupled with the enhancement of solubility renders their chemical modification with either NH₃ or amino functional groups to be a way for the purification of BC₂N nanotubes.     

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.     

A two-layer ONIOM study of thiophene cracking catalyzed by proton- and cation-exchanged FAU zeolite

A two-layer ONIOM study on the hydrodesulfurization mechanism of thiophene in H-FAU and M-FAU (M?=?Li⁺, Na⁺, and K⁺) has been carried out. The calculated results reveal that in H-FAU, for a unimolecular mechanism, the rate-determining step is hydrogenation of alkoxide intermediate. The assistance of H₂O and H₂S molecules does not reduce the difficulty of the C-S bond cracking step more effectively. A bimolecular hydrodesulfurization mechanism is more favorable due to the lower activation barriers. The rate-determining step is the formation of 2-methylthiophene, not the C-S bond cracking of thiophene. Moreover, the ring opening of thiophene is much easier to occur than the desulfurization step. A careful analysis of energetics indicates that H₂S, propene, and methyl thiophene are the major products for the hydrodesulfurization process of thiophene over H-FAU zeolite, in good agreement with experimental findings. In M-FAU zeolites, both unimolecular and bimolecular cracking processes are difficult to occur because of the high energy barriers. Compared to the case on H-FAU, the metal cations on M-FAU increase the difficulty of occurrence of bimolecular polymerization and subsequent C-S bond cracking steps.

Open image in new window

Graphical abstract Hydrodesulfurization process of thiophene can take place in H-FAU zeolite. Two different mechanisms, unimolecular and bimolecular ones, have been proposed and evaluated in detail. The bimolecular mechanism is more favorable due to lower activation barrier as described in the picture above. Our calculated data indicate that H₂S, propene, and methylthiophene are the major products, in good agreement with experimental observations. The effect of metal cations on the reaction mechanism is also investigated in this work.

     

Density functional theory study on the reaction mechanism of synthesizing 1,3-dimethyl-2-imidazolidinone by urea method

We report a first-principles density functional theory investigation on tailoring the fundamental reaction mechanism of synthesizing 1,3-dimethyl-2-imidazolidinone (DMI) through the urea method with water serving as both solvent and catalyst. The nucleophilic cyclization reaction is implemented by two ammonia removal steps. One –NH group of dimethylethylenediamine (DMEDA) first attacks the carbon atom of urea, eliminating one –NH₃ group and forming an intermediate state CH₃NHC₂H₄N(CH₃)CONH₂ (IM^I). IM^I subsequently undergoes the cyclization process through a secondary ammonia removal via similar manner. Without water, the two ammonia removal steps are both slightly exothermic with high activation barriers (~50 kcal mol^-1). As water participated in the reaction, the kinetics of the two steps can be significantly improved, respectively. The role that water plays, beside as solvent, more importantly, is to serve as a proton exchange bridge. Due to the spatial configuration, the direct proton migration from the N atoms of ethylenediamine to urea is difficult to occur. The water bridge facilitates the proton migration by shortening the migration distance. As a consequence, the activation barriers are considerably lowered down to ~30 kcal mol^-1, indicating a strong catalytic effect from water. In contrast, the three possible side reactions of IM^I, even catalyzed by water, have higher activation barriers due to strong steric inhibitive effect and consequently become difficult to occur at the same condition. The current computational understanding on the prototypical reaction to DMI can be extended to guide developing more efficient routes to synthesize imidazolidinone derivatives through the urea method.     

DFT comparison of the OH-initiated degradation mechanisms for five chlorophenoxy herbicides

To compare the OH-initiated reaction mechanisms of five chlorophenoxy herbicides, density functional theory (DFT) calculations of reactions in which ·OH attacks one of three active positions on each herbicide were carried out at the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) level. For each herbicide, the calculation results show that ·OH addition to the C1 atom, which is the nexus between the benzene ring and the side group, possesses the lowest energy barrier among the three kinds of reactions, indicating that ·OH addition–substitution of the side chain is the most energetically and kinetically favorable reaction mechanism. Comparisons among the herbicides show that the mechanisms are affected by the steric hindrance and the electronegativities of the –CH₃ and –Cl groups. When comparing the addition of ·OH to the C1 site among the five herbicides, the activation energy for the reaction of ·OH with DCPP reaction is the lowest (3.61 kcal mol^?1), while that for the ·OH and 4-CPA reaction was the highest (5.91 kcal mol^?1). ·OH addition to the C4 site presents the highest energy barriers among the three kinds of reactions, indicating that the para Cl is difficult to break down. When comparing the H-atom abstraction reactions of the five herbicides, the H atoms in the –CH₂– group of 2,4-D are the easiest for ·OH to abstract, whereas those of DCPP and MCPP are more difficult to abstract, due to the steric hindrance of the –CH₃ group. Additionally, the results obtained from the PCM calculations reveal that most of the reactions occur more easily in water than in gas, though the mechanisms involved are the same as those discussed above.     

Characterization of radicals arising from oxidation of commercially-important essential oils

Inappropriate use of essential oils may entail risks to human health due to mutational events, carcinogenic effects, genetic damages and sensitizing effect caused by generation of reactive oxygen species. In order to detect radicals that are expected to form during their oxidation, we measured the electron spin resonance (ESR) spectra of a standard reaction mixture (I) containing 25?μM flavin mononucleotide, 0.018% several essential oils (or 0.015% geraniol), 1.9 M acetonitrile, 20?mM phosphate buffer (pH 7.4), 0.1 M α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) and 1.0?mM FeSO₄(NH₄)₂SO₄ irradiated with 436?nm visible light (7.8 J/cm²). The ESR peak heights of the standard reaction mixture (I) of the essential oils increased in the following order: tea tree?>?palmarosa?>geranium?>?clary sage?>?petitgrain?>?lavender?>?bergamot?>?frankincense?>?ravintsara?>?ylang ylang?>?lemongrass?>?niaouli?>?eucalyptus globulus?>?peppermint. The ESR peak height of the standard reaction mixture (I) of geraniol, a main component of palmarosa, was comparable to the one of palmarosa (97?±?19% of palmarosa). Furthermore, high performance liquid chromatography (HPLC)-ESR analyses of the standard reaction mixture (I) of palmarosa and geraniol gave the same peaks. The results suggest that the radicals formed in the standard reaction mixture (I) of palmarosa are derived from geraniol. HPLC-ESR-mass spectrometry analyses detected m/z 294 ions, 4-POBN/5-hydroxy-3-methyl-3-pentenyl radical adducts and m/z 320 ions, 4-POBN/C₇O₂H₉ radical adducts in the standard reaction (I) of geraniol. The 5-hydroxy-3-methyl-3-pentenyl and C₇O₂H₉ radicals may be implicated in the sensitizing effect of palmarosa.     

Kinetics investigation of the hydrogen abstraction reaction between CH<Subscript>3</Subscript>SS and CN radicals

The reaction mechanisms and rates for the H abstraction reactions between CH₃SS and CN radicals in the gas phase were investigated with density functional theory (DFT) methods. The geometries, harmonic vibrational frequencies, and energies of all stationary points were obtained at B3PW91/6-311G(d,p) level of theory. Relationships between the reactants, intermediates, transition states and products were confirmed, with the frequency and the intrinsic reaction coordinate (IRC) analysis at the same theoretical level. High accurate energy information was provided by the G3(MP2) method combined with the standard statistical thermodynamics. Gibbs free energies at 298.15 K for all of the reaction steps were reported, and were used to describe the profile diagrams of the potential energy surface. The rate constants were evaluated with both the classical transition state theory and the canonical variational transition state theory, in which the small-curvature tunneling correction was included. A total number of 9 intermediates (IMs) and 17 transition states (TSs) were obtained. It is shown that IM1 is the most stable intermediate by the largest energy release, and the channel of CH₃SS?+?CN?→?IM3?→?TS10?→?P1(CH₂SS?+?HCN) is the dominant reaction with the lowest energy barrier of 144.7 kJ mol^?1. The fitted Arrhenius expressions of the calculated CVT/SCT rate constants for the rate-determining step of the favorable channel is k =7.73?×?10⁶? T ^1.40exp(?14,423.8/T) s^?1 in the temperature range of 200–2000 K. The apparent activation energy E _a(app.) for the main channel is ?102.5 kJ mol^?1, which is comparable with the G3(MP2) energy barrier of ?91.8 kJ mol^?1 of TS10 (relative to the reactants).     

An ab initio study of the formation of alkoxy radicals by reactions of simple alkenes with the OH radical

The formation of ethoxy, propoxy and butoxy radicals in the reactions of ethene, propene, cis- and trans-2-butene with the OH radical has been modeled in the gaseous phase at the MP2/6-31+G(d) level. All the possible reaction pathways have been investigated, and the structures as well as the energetics have been determined. The reactants, prereaction complexes, transition states and products located along the alkene-OH radical reaction coordinates have been discussed thoroughly. The rate determining step for these reactions is the conversion of hydroxyalkyl radicals to alkoxy radicals. The reaction barriers and exothermicities for these small alkenes are more or less identical for the compounds studied. Nevertheless, addition of OH to the central carbon atom of propene is slightly favored kinetically and thermodynamically (1 kcal mol^-1) over the others.     

Computational insights into structural and optical properties of P-containing and N-containing ligands capped CdSe clusters

ABSTRACT

The ligand effects on the structures and properties (energetics, binding energies, charge distribution and optical properties) of the (CdSe)_n clusters (n?=?3, 6, and 10) with P-containing (PH₃, PH₂Me, PHMe₂ and PMe₃) and N-containing (NH₃, NH₂Me, NHMe₂ and NMe₃) have been studied using density functional theory. The P atom and N atom in the ligands interact with Cd and form Cd–P and Cd–N bonds. The influence of P-containing ligands can be enhanced with increasing CH₃ of ligands, while the N-containing ligands influence slightly change. A blueshift in absorption band was predicted for the clusters with increasing CH₃ of P-containing ligands. We also found that the calculated binding energies for various ligands are found to decrease in the order PMe₃?>?NH₂Me?>?NHMe₂?>?NH₃?>?NMe₃?>?PHMe₂?>?PH₂Me?>?PH₃. The use of hydrogen atom for modelling of the CdSe cluster passivating ligands is found to yield unphysical results as well.     

Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity

Temperate pastures are often managed with P fertilizers and N₂-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N₂O) emissions and reduced methane (CH₄) uptake. However, the diel and inter-daily variation in N₂O and CH₄ flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N₂O and CH₄ flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N₂O and CH₄ flux was measured continuously in a High P (23 kg P ha^?1 yr^?1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha^?1 yr^?1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH₄ uptake was similar (?6.3?±?SE 0.3 to ?8.6?±?0.4 μg C m^?2 hr^?1) as were mean N₂O emissions (6.5 to 7.9?±?0.8 μg N m^?2 hr^?1), although N₂O flux in the No P pasture did not respond to changing soil water conditions. N₂O emissions were greatest in the Low P sheep camp (12.4 μg?±?1.1 N m^?2 hr^?1) where there were also net CH₄ emissions of 5.2?±?0.5 μg C m^?2 hr^?1. There were significant, but weak, relationships between soil water and N₂O emissions, but not between soil water and CH₄ flux. The diel temperature cycle strongly influenced CH₄ and N₂O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N₂O emissions, or reduce CH₄ uptake, during this 4 week measurement period, but the lack of an N₂O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N₂O and CH₄ trace gas balance.     

Theoretical study of the reaction mechanism of CH<Subscript>3</Subscript>NO<Subscript>2</Subscript> with NO<Subscript>2</Subscript>, NO and CO: the bimolecular reactions that cannot be ignored

The intriguing decompositions of nitro-containing explosives have been attracting interest. While theoretical investigations have long been concentrated mainly on unimolecular decompositions, bimolecular reactions have received little theoretical attention. In this paper, we investigate theoretically the bimolecular reactions between nitromethane (CH₃NO₂)—the simplest nitro-containing explosive—and its decomposition products, such as NO₂, NO and CO, that are abundant during the decomposition process of CH₃NO₂. The structures and potential energy surface (PES) were explored at B3LYP/6-31G(d), B3P86/6-31G(d) and MP2/6-311?+?G(d,p) levels, and energies were refined using CCSD(T)/cc-pVTZ methods. Quantum chemistry calculations revealed that the title reactions possess small barriers that can be comparable to, or smaller than, that of the initial decomposition reactions of CH₃NO₂. Considering that their reactants are abundant in the decomposition process of CH₃NO₂, we consider bimolecular reactions also to be of great importance, and worthy of further investigation. Moreover, our calculations show that NO₂ can be oxidized by CH₃NO₂ to NO₃ radical, which confirms the conclusion reached formerly by Irikura and Johnson [(2006) J Phys Chem A 110:13974–13978] that NO₃ radical can be formed during the decomposition of nitramine explosives.     

Reactions of methylcobalamin with tin and lead compounds

Reactions of CH₃[Co] with (CH₃)_nM^(4?n)+ (n = 2, 3; M = Sn, Pb) at concentrations high enough to detect (CH₃)₄M in the head space (yields 7.08×10^?5?2.06×10^?5%), indicate that dismutation is the major route of production. Similarly, kinetic reactions at lower concentrations show that no demethylation of CH₃[Co] by (CH₃)₃M⁺ (M = Sn, Pb) occurs after 60 days. From the methylation of SnCl₂ by CH₃[Co] at pD 1.0 and under aerobic conditions, the following hydrolysis species were observed in the 400 MHz ¹H NMR spectrum: CH₃- Sn(OH)Cl₂·2H₂O (63.6%), [CH₃Sn(OH)(H₂O)₄]²⁺ (17.6%) and CH₃Sn(OH)₂Cl·nH₂O (18.8%). No methylation products were observed from similar reactions with Pb(II) salts.     

Theoretical studies on identity SN2 reactions of lithium halide and methyl halide: A microhydration model

Reactions of lithium halide (LiX, X = F, Cl, Br and I) and methyl halide (CH₃X, X = F, Cl, Br and I) have been investigated at the B3LYP/6-31G(d) level of theory using the microhydration model. Beginning with hydrated lithium ion, four or two water molecules have been conveniently introduced to these aqueous-phase halogen-exchange S_N2 reactions. These water molecules coordinated with the center metal lithium ion, and also interacted with entering and leaving halogen anion via hydrogen bond in complexes and transition state, which to some extent compensated hydration of halogen anion. At 298 K the reaction profiles all involve central barriers ΔE _cent which are found to decrease in the order F > Cl > Br > I. The same trend is also found for the overall barriers (ΔE _ovr ) of the title reaction. In the S_N2 reaction of sodium iodide and methyl iodide, the activation energy agrees well with the aqueous conductometric investigation.     

The addition reactions of germylenoid H<Subscript>2</Subscript>GeAlCl<Subscript>3</Subscript> with ethylene: a theoretical investigation

Theoretical calculations using the M062X and QCISD methods were performed on the addition reactions of the aluminum germylenoid H₂GeAlCl₃ with ethylene. The most two stable structures of germylenoid H₂GeAlCl₃, i.e., the p-complex and three-membered ring structures, respectively, were employed as reactants. The calculated results indicate that, for the p-complex, H₂GeAlCl₃ there are two pathways, I and II, of which path I involves just one transition state, while path II involves two transition states between reactants and products. Comparing the reaction barrier heights of path I (44.6 kJ mol^?1) and II (37.6 kJ mol^?1), the two pathways are competitive, with similar barriers under the same conditions, while for the three-membered ring structure, another two pathways, III and IV, also exist. Path III has one transition state; however, in path IV, two transition states exist. By comparing their barrier heights, path III (barrier height 39.2 kJ mol^?1) could occur more easily than path IV (barrier height 92.8 kJ mol^?1). Considering solvent effects on these addition reactions, the PCM model and CH₂Cl₂ solvent were used in calculations, and the calculated results demonstrate that CH₂Cl₂ solvent is unfavorable for the reactions, except for path II. In CH₂Cl₂ solvent, paths II and III are more favorable than paths I and IV.     

A theoretical study on the coordination behavior of some phosphoryl,carbonyl and sulfoxide derivatives in lanthanide complexation

The selectivity of phosphoryl P(O)R₃, sulfoxide S(O)R₂, and carbonyl C(O)R₂ (R?=?NH₂, CH₃, OH, and F) derivatives with lanthanide cations (La³⁺, Eu³⁺, Lu³⁺) was studied by density functional theory calculations. Theoretical approaches were also used to investigate energy and the nature of metal–ligand interaction in the model complexes. Atoms in molecules and natural bond orbital (NBO) analyses were accomplished to understand the electronic structure of ligands, L, and the related complexes, L–Ln³⁺. NBO analysis demonstrated that the negative charge on phosphoryl, carbonyl, and sulfoxide oxygen (O_P, O_C, and O_S) has maximum and minimum values when the connected –R groups are –NH₂ and –F. The metal–ligand distance declines as, –F?>?–OH?>?–CH₃?>?–NH₂. Charge density at the bond critical point and on the lanthanide cation in the L–Ln³⁺ complexes varies in the order –F?<?–OH?<?–CH₃?<?–NH₂, due to greater ligand to metal charge transfer, which is well explained by energy decomposition analysis. It was also illustrated that E⁽²⁾ values of Lp(N)?→?σ*(Y–N) vary in the order P=O ? S=O ? C=O and the related values of Lp(N)?→?σ*(Y=O) change as C=O ? S=O ? P=O in (NH₂)_nYO ligands (Y?=?P, C, and S). Trends in the L–Ln³⁺ CP–corrected bond energies are in good accordance with the optimized O_Y?Ln distances. It seems that, comparing the three types of ligands studied, NH₂–substituted are the better coordination ligands.

Open image in new window

Graphical Abstract Density functional theory (B3LYP) calculations were used to compare structural, electronic and energy aspects of lanthanide (La, Eu, Lu) complexes of phosphine derivatives with those of carbonyls and sulfoxides in which the R– groups connected to the P=O, C=O and S=O are –NH₂, –CH₃, –OH and –F.

     

Anion-Mediated Salinity Affecting Methane Production in a Flooded Alluvial Soil

In a laboratory incubation study, effects of amendment with sodium salts of SO₄ ^2?, Cl^? and HCO₃ ^? either singly or as a mixture on CH₄ production in a nonsaline alluvial soil under flooded condition were investigated. Methane production was considerable in the unamended alluvial soil, but was significantly inhibited following amendment with salts of different anions to raise the pore water EC to 8 dS·m^?1. SO₄ ^2? was the most inhibitory to CH₄ production and the degree of inhibition followed the order SO₄ ^2? > salt mixture > HCO₃ ^? > Cl^?. Salt amendment did not adversely affect soil microbial activities as expressed in terms of soil redox potential (Eh) and soil pH. However, readily mineralizable carbon content, an indicator of substrate availability for methanogenic bacteria, differed significantly among the treatments. Most probable number estimates indicated that acetotrophic methanogenic bacterial population was lowest in Cl^?-amended soils followed by SO₄ ^2?-amendment with little or no changes in HCO₃ ^?-amended soils. The data suggested that the inhibition in methanogenesis in saline soils rich in sulphate as in coastal saline soils could be due to competitive inhibition of methanogens, while in inland soils, Cl^? content could be a deciding factor.