Conserved water-mediated recognition and dynamics of NAD+ (carboxamide group) to hIMPDH enzyme: water mimic approach toward the design of isoform-selective inhibitor

Inosine monophosphate dehydrogenase (IMPDH) enzyme involves in GMP biosynthesis pathway. Type I hIMPDH is expressed at lower levels in all cells, whereas type II is especially observed in acute myelogenous leukemia, chronic myelogenous leukemia cancer cells, and 10?ns simulation of the IMP–NAD⁺ complex structures (PDB ID. 1B3O and 1JCN) have revealed the presence of a few conserved hydrophilic centers near carboxamide group of NAD⁺. Three conserved water molecules (W1, W, and W1′) in di-nucleotide binding pocket of enzyme have played a significant role in the recognition of carboxamide group (of NAD⁺) to D274 and H93 residues. Based on H-bonding interaction of conserved hydrophilic (water molecular) centers within IMP–NAD⁺-enzyme complexes and their recognition to NAD⁺, some covalent modification at carboxamide group of di-nucleotide (NAD⁺) has been made by substituting the –CONH₂group by –CONHNH₂ (carboxyl hydrazide group) using water mimic inhibitor design protocol. The modeled structure of modified ligand may, though, be useful for the development of antileukemic agent or it could be act as better inhibitor for hIMPDH-II.     

An insight to the dynamics of conserved water-mediated salt bridge interaction and interdomain recognition in hIMPDH isoforms

Inosine monophosphate dehydrogenase (IMPDH) is involved in de novo biosynthesis pathway of guanosine nucleotide. Type II isoform of this enzyme is selectively upregulated in lymphocytes and chronic myelogenous leukemia (CML) cells, and is an excellent target for antileukemic agent. The molecular dynamics simulation results (15?ns) of three unliganded 1B3O, 1JCN, and 1JR1 structures have clearly revealed that I_N, I_C (N- and C-terminal of catalytic domains) and C₁, C₂ (cystathionine-beta-synthase-1 and 2) domains of IMPDH enzyme have been stabilized by six conserved water (center) mediated salt bridge interactions. These conserved water molecules could be involved in interdomain or intradomain recognition, intradomain coupling, and charge transfer processes. The binding propensity of cystathionine-beta-synthase domain to catalytic domain (through conserved water-mediated salt bridges) has provided a new insight to the biochemistry of IMPDH. Stereospecific interaction of I_N with C₂ domain through conserved water molecule (K109–W^II ₁–D215/D216) is observed to be unique in the simulated structure of hIMPDH-II. The geometrical/structural consequences and topological feature around the W^II ₁ water center may be utilized for isoform specific inhibitor design for CML cancer.

An animated Interactive 3D Complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:1     

城市小型景观水体溶存N2O浓度及排放通量特征

淡水生态系统是大气中N₂O的重要排放源,受到国内外广泛关注。城市小型景观水体作为区域淡水系统的重要组成,具有环境容量小,受人类活动干扰强烈,其N₂O排放特征及影响机制并不清楚。选择重庆大学城8个典型景观水体和2个城市外围的自然水体（对照）作为研究对象,利用顶空法和漂浮箱法对水体溶存N₂O浓度及排放通量进行季节性监测,并通过分析生境特征及水环境特征,探究城市小型景观水体N₂O排放特征及关键影响因素。结果表明：1）小型景观水体TN、NO₃^--N、NH₄⁺-N、NO₂^--N含量总体偏低但变异性极强（变化范围分别为0.31-1.47 mg/L、0.05-0.79 mg/L、0.03-0.14 mg/L、0.00-0.04 mg/L）,硝态氮是主要的氮形态;景观水体氮丰度远高于外围的自然水体;2）10个小型水体N₂O浓度范围为16.51-158.96 nmol/L,平均为（47.60±21.47） nmol/L,均处于过饱和状态;漂浮箱法实测8个景观水体N₂O排放通量均值为（0.13±0.05）mmol m^-2 d^-1,是对照水体的1.3-5.2倍,高于大部分已有研究结果,是大气N₂O的排放热源;3）景观水体N₂O排放通量与水体各形态氮含量呈显著的正相关关系,较高的N负荷和强烈的氮转化过程是导致景观水体成为N₂O排放热源的主要因子,水体N含量可以作为景观水体N₂O排放强度的有效指示因子;同时水生植物分布对水体N₂O排放影响显著,有植物分布的水域比开敞水域高1.4倍;4）漂浮箱法和边界层模型法对小型景观水体N₂O排放通量的监测结果呈较好的线性关系,但不同季节仍存在着一定差异,需要进一步优化模型估算方法;5）水体N₂O排放通量对温度的季节性变化较为敏感,呈夏季最高,春、秋季次之,冬季最低的季节模式。本研究强调,城市小型景观水体具有较高的N₂O排放速率,在区域氮循环及全球淡水系统温室气体排放清单中具有不可忽视的作用,在未来研究中应得到更多关注。     

Conserved Water Molecular Dynamics of the Different X-ray Structures of Rusticyanin: An Unique Aquation Potentiality of the Ligand Bonded Cu++ Center

Abstract

The invariant water molecular interaction involving in the Rusticyanin of Thiobacillus ferrooxidans is thought to be important for its molecular complexation with other proteins at differential acidophilic situation. The comparative analysis of the different x-ray, energy minimized, and auto solvated structures of Rusticyanin revealed the presence of five specific invariant bound water molecules (among the ~ 150 water molecules per monomer) in the crystals. The five W 205, W 206, W 112, W 214, and W 221 water molecules (in Rusticyanin PDB code: 1RCY) were seem to be invariant in all the seven structures (PDB codes: 1RCY, 1A3Z, 1A8Z, 1E3O, 1GY1, 1GY2, 2CAL). Among the five conserved water molecules the W 221 (of 1 RCY or the equivalent water molecules in the other oxidized form of Rusticyanin structures) had endowed an interesting coordination potentiality to Cu⁺² ion during the energy minimization. The W 221 was observed to approach toward the tetrahedrally bonded Cu⁺² ion through the opposite (or trans) route of metal-bonded Met 148. This direct water molecular coordination affected the tetrahedral geometry of Cu⁺² to trigonal bipyramidal. Presumably this structural dynamics at the Cu⁺² center could involve in the electron transport process during protein-protein complexation.     

The Structure,Role, and Regulation of Type 1 Protein Phosphatases

Abstract

Type 1 protein phosphatases (PP-1) comprise a group of widely distributed enzymes that specifically dephosphorylate serine and threonine residues of certain phosphoproteins. They all contain an isoform of the same catalytic subunit, which has an extremely conserved primary structure. One of the properties of PP-1 that allows one to distinguish them from other serine/threonine protein phosphatases is their sensitivity to inhibition by two proteins, termed inhibitor 1 and inhibitor 2, or modulator. The latter protein can also form a 1:1 complex with the catalytic subunit that slowly inactivates upon incubation. This complex is reactivated in vitro by incubation with MgATP and protein kinase F_A/GSK-3. In the cell the type 1 catalytic subunit is associated with noncatalytic subunits that determine the activity, the substrate specificity, and the subcellular location of the phosphatase. PP-1 plays an essential role in glycogen metabolism, calcium transport, muscle contraction, intracellular transport, protein synthesis, and cell division. The activity of PP-1 is regulated by hormones like insulin, glucagon, α- and β-adrenergic agonists, glucocorticoids, and thyroid hormones.     

硝化细菌群的富集及其去除城镇寡营养河道中氨氮污染的应用

[背景]随着工农业的发展,污水排放导致的氨氮超标逐渐成为水体污染的重要因素,脱氮已成为人们研究的重点.目前脱氮方法主要集中于硝化细菌的硝化作用,其将氨氮转化为硝酸盐氮,从而减少水体中氨氮的污染.由于工业废水和农业污水中的有机物含量较高,而且异养硝化细菌具有生长较快等优势,因此对异养菌的研究多于自养菌.然而现有的异养硝化...     

Anticholinesterase activity of some major intermediates in carbacylamidophosphate synthesis: Preparation,spectral characterization and inhibitory potency determination

Carbacylamidophosphates with the general formula RC(O)NHP(O)R₁R₂ constitute organophosphorus compounds that are used as insecticides, pesticides and ureas inhibitors. In this work, we studied the inhibition potency of CCl₃C(O)NHP(O)Cl₂1, CHCl₂C(O)NHP(O)Cl₂2, CH₂ClC(O)NHP(O)Cl₂3 and CF₃C(O)NHP(O)Cl₂4, which are the major intermediates for carbacylamidophosphates synthesis towards human erythrocyte acetylcholinesterase (hAChe) activity using Ellman's modified kinetic method. Unexpectedly, it was observed that they were not only hydrolytically unstable but also inhibited hAChE in a similar manner to that produced by organophosphorus insecticides. Enzymatic data, bimolecular inhibition rate constants (k_i) and IC₅₀ values for inhibition of hAChE demonstrated that they are irreversible inhibitors and the inhibition potency of compound 2 (IC₅₀ = 88 μM) was the greatest in comparison with compounds 1, 3 and 4. Also the electropositivity of the phosphorus atom and the hydrophobicity of the compounds demonstrated that these two factors play an additional effect and different role in the inhibitory activity of these compounds. Hydrolytic stability of the compounds was determined by ³¹P NMR monitoring of the loss of the parent molecules with D₂O as a function of time. This study considers antiacetylcholinesterase activity according to the structural and the electronic aspects of compounds 1–4, according to IR, ¹H, ¹³C and ³¹P NMR spectral data.     

Carbonic anhydrase inhibition. Insight into the characteristics of zonisamide,topiramate, and the sulfamide cognate of topiramate

Some useful therapeutic agents inhibit certain carbonic anhydrase (CA) isozymes to varying degrees. We have conducted enzyme kinetics studies in a 4-nitrophenyl acetate (4-NPA) hydrolysis assay with the marketed antiepileptic drugs topiramate (1) and zonisamide (2) to determine if their full inhibition of human CA-II and CA-I requires extended preincubation conditions. We found that neither 1 nor 2 requires appreciable preincubation with either enzyme to manifest full inhibitory activity. We also examined the sulfamide cognate of topiramate (3) to characterize its CA inhibitory activity, and confirmed that it is a very weak inhibitor, unlike 1 or 2. In a CO₂ hydration assay, 3 behaved as a very weak, partial inhibitor of CA-II and CA-I. We conclude that topiramate (1), zonisamide (2), and sulfamide 3 do not require extended exposure to human CA-I or CA-II to manifest full inhibitory activity (4-NPA assay).     

172 Role of conserved water molecular triad in the recognition of IMP,NAD+ with Asp 274, Asn 303, Arg 322, and Asp 364 in both the isoform of hIMPDH

Inosine monophosphate dehydrogenase (IMPDH) plays an important role in the Guanosine monophosphate (GMP) biosynthesis pathway. As hIMPDH-II is involved in CML-Cancer, it is thought to be an active target for leukemic drug design. The importance of conserved water molecules in the salt-bridge-mediated interdomain recognition and loop-flap recognition of hIMPDH has already been indicated in some simulation studies (Bairagya et al., 2009, 2011a, 2011b, 2012; Mishra et al., 2012). In this work, the role of conserved water molecules in the recognition of Inosine monophosphate (IMP) and NAD⁺ (co-factor) to active site residues of both the isoforms has been investigated by all atoms MD-Simulation studies. During 25-ns dynamics of the solvated hIMPDH-II and I (1B3O and 1JCN PDB structures), the involvement of conserved water molecular triad (W _M, W _L and W _C) in the recognition of active site residues (Asp 274, Asn 303, Arg 322, and Asp 364), IMP and NAD⁺ has been observed (Figure 1). The H-bonding co-ordination of all three conserved water molecular centers is within 4–7 and their occupation frequency is 1.0. The H-bonding geometry and the electronic consequences of the water molecular interaction at the different residues (and also IMP and NAD⁺) may put forward some rational clues on antileukemic agent design.     

Spectroscopic and structural studies of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one and of an unusual T4(2)7(2)6(2)7(2) water tape stabilized by the copper(II) coordination polymer

The solid-state structures of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one (HL) and the copper(II) complex [Cu(L⁻)₂(OH₂)]·2H₂O (1) are established by X-ray crystallography and also by means of physicochemical and spectroscopic methods. The molecules of HL form a self-complementary head-to-tail hydrogen-bonded dimer through C-H?N and C-H?O contacts to give an infinite 1D chain. The copper(II) complex (1) is five-coordinate with distorted trigonal-bipyramidal (TBP) geometry of the N₄O donor atoms. The electronic and EPR data are in agreement with the X-ray structure of 1, showing that HL coordinates to copper(II) centre as a mono-anionic ligand through deprotonated pyridone N atom and the tertiary benzimidazole nitrogen atom to form a neutral complex in which the water molecule occupies the fifth position. The 1D water tape, T4(2)7(2)6(2)7(2) is anchored to the host through hydrogen bonds between coordinated water molecule [O(3w)] as acting double H-donor, pyridone carbonyl groups [O(2) and O(1)] as double H-acceptor and the lattice water molecules [O(4w) and O(5w)] as double H-donor and single H-acceptor).     

Crystal structures of (2R,4R)-2-(polyhydroxyalkyl)-1,3-thiazolidine-4-carboxylic acids: condensation products of l-cysteine with d-hexoses

We report herein the first crystal structures of (4-carboxy-1,3-thiazolidin-2-yl)pentitols [2-(polyhydroxyalkyl)thiazolidine-4-carboxylic acids], condensation products of l-cysteine with d-galactose and d-mannose: 2-(d-galacto-pentahydroxypentyl)thiazolidine-4-carboxylic acid hydrate, Gal-Cys·H₂O (1), and 2-(d-manno-pentahydroxypentyl)thiazolidine-4-carboxylic acid hydrate, Man-Cys·H₂O (2). In 1 and 2 the compounds crystallize as zwitterions, with the carboxylic groups deprotonated and the thiazolidine N atoms protonated. The sugar moiety and carboxylate group are in a cis configuration relative to the thiazolidinium ring, which adopts different conformation: twisted (T) on C^β–S in 1, and S-puckered envelope (E) in 2. The carbon chain of the galactosyl/mannosyl moiety remains in an extended zig-zag conformation. The orientation of the sugar O2 atom with respect to the thiazolidinium S and N atoms is trans–gauche in 1 and gauche–gauche in 2. The molecular conformation is stabilized by the intramolecular N–H?O_Cys contacts in both 1 and 2 and by the additional N–H?O_Man interaction in 2. The crystal packing of orthorhombic 1 and monoclinic 2 is determined mainly by N/O/C–H?O hydrogen bonds forming ribbons linked to each other by direct and water-mediated O/C–H?O/S contacts.     

Copper(II) complexes of methimazole,an anti Grave’s disease drug. Synthesis,characterization and its potential biological behavior as alkaline phosphatase inhibitor

Methimazole (MeimzH) is an anti-thyroid drug and the first choice for patients with Grave’s disease. Two new copper(II) complexes of this drug: [Cu(MeimzH)₂(NO₃)₂].0.5H₂O and [Cu(MeimzH)₂(H₂O)₂](NO₃)₂·H₂O were synthesized and characterized by elemental analysis, dissolution behavior, thermogravimetric analysis and UV-vis, diffuse reflectance, FTIR and EPR spectroscopies. As it is known that copper(II) cation can act as an inhibitor of alkaline phosphatase (ALP), the inhibitory effect of methimazole and its copper(II) complexes on ALP activity has also been investigated.     

Assessment of C:N Ratios and Water Potential for Nitrogen Optimization in Diesel Bioremediation

Sandy clay loam soil contaminated with 5000, 10,000 or 20,000 mg/kg of diesel fuel no. 2 was amended with 0 (ambient nitrogen only), 250, 500, or 1000 mg/kg nitrogen (NH₄Cl) to evaluate the role of C:N ratios and soil water potential on diesel biodegradation efficacy. The soil was incubated at 25°C for 41 days and microbial O₂ consumption measured respirometrically. Highest microbial respiration was observed in the 250 mg N/kg soil treatments regardless of diesel concentration. Higher levels of nitrogen fertilization decreased soil water potential and resulted in an extended lag phase and reduced respiration. Application of 1000 mg/kg nitrogen reduced maximum respiration by 20% to 52% depending on contaminant levels. Optimal C:N ratios among those tested were 17:1, 34:1, and 68:1 for the three diesel concentrations, respectively, and were dependent on contaminant concentration. Nitrogen fertilization on the basis of soil pore water nitrogen (mg N/kg soil H₂O) is independent of hydrocarbon concentration but takes into account soil moisture content. This method accounts for both the nutritional and osmotic aspects of nitrogen fertilization. In the soil studied the best nitrogen augmentation corresponded to a soil pore water nitrogen level of 1950 mg N/kg H₂O at all diesel concentrations.     

生物炭对褐土旱地玉米季氮转化功能基因、丛枝菌根真菌及N2O释放的影响

以豫西旱地玉米农田为研究对象,设置不同生物炭施用量处理（T0：不施用生物炭;T1：施用生物炭20 t/hm²;T2：施用生物炭40 t/hm²）,采用密闭式静态箱法测定N₂O排放通量和荧光定量PCR法分析丛枝菌根（arbuscular mycorrhizal,AM）真菌、氨单加氧酶（amoA）、亚硝酸盐还原酶（nirS、nirK）以及氧化亚氮还原酶（nosZ）的基因丰度,同时测定土壤理化性状的变化。研究结果表明,随着生物炭施用量的增加,土壤pH和含水量呈增加趋势,土壤有机碳、全氮和铵态氮含量显著提高,土壤容重和硝态氮含量显著降低。T1和T2处理土壤有机碳含量分别较T0显著提高38.44%和71.01%;T1和T2处理土壤铵态氮含量分别较T0显著增加15.89%和30.46%;T2处理土壤全氮含量较T0处理显著提高14.87%;T1和T2处理土壤硝态氮含量分别较T0减少10.57%和21.40%。随着生物炭施用量的增加,AM真菌侵染率显著增加,T1和T2处理分别较T0处理提高71.88%和115.88%;AOA、AOB、nirK和nirS基因丰度显著降低;nosZ基因丰度增加。施加生物炭处理的N₂O排放通量和累积排放量均低于不施生物炭处理,具体表现为：T0 > T1 > T2。相关分析表明,生物炭施用量与AM真菌基因丰度呈显著正相关;与nosZ基因丰度呈正相关;与AOA、AOB、nirK、nirS基因丰度呈极显著负相关。N₂O排放通量与AOA、nirK、nirS基因丰度呈极显著正相关;与土壤含水量和土壤硝态氮含量呈显著正相关;与AM真菌、nosZ基因丰度、易提取球囊霉素含量、铵态氮含量呈极显著负相关。集成推进树（ABT）分析表明,AOA对N₂O排放的影响最大,其次是AM真菌和nirS。总之,生物炭处理改善土壤理化性质、提高土壤AM真菌侵染率、调节硝化、反硝化相关功能基因的丰度,减少N₂O气体排放,为旱地农田合理施用生物炭减少N₂O气体排放提供理论依据。     

Synthesis, crystal structure, spectroscopic and magnetic properties of copper(II) complexes with 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine (PyTT)

The copper(II) complexes [Cu(PyTT)₂(H₂O)](NO₃)₂ (A) and [CuCl₂(μ-PyTT)₂CuCl(H₂O)]Cl · 3H₂O (B) were synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, UV-Vis-NIR diffuse reflectance and magnetic susceptibility measurements. In the mononuclear compound A the copper ion is in a distorted square pyramidal geometry, with the equatorial plane formed by two thiazoline nitrogen atoms, one imino nitrogen atom and one water molecule, whereas the axial site is occupied by one imino nitrogen atom. The compound B is dinuclear and both Cu(II) centres present environments that can be described as slightly distorted square pyramidal geometries. The observed molar magnetic susceptibility for A (μ=2.13 BM) allows to exclude metal-metal interactions, supporting a monomeric structural formulation for this compound. In compound B, magnetic susceptibility measurements in the temperature range 6.2-288 K show an intradimer antiferromagnetic interaction (J=−11.8 cm⁻¹).     

Identification,purification and partial characterization of a 70 kDa inhibitor protein of Na+/K+-ATPase from cytosol of pulmonary artery smooth muscle

AimsWe sought to identify, purify and partially characterize a protein inhibitor of Na⁺/K⁺-ATPase in cytosol of pulmonary artery smooth muscle.Main methods(i) By spectrophotometric assay, we identified an inhibitor of Na⁺/K⁺-ATPase in cytosolic fraction of pulmonary artery smooth muscle; (ii) the inhibitor was purified by a combination of ammonium sulfate precipitation, diethylaminoethyl (DEAE) cellulose chromatography, hydroxyapatite chromatography and gel filtration chromatography; (iii) additionally, we have also purified Na⁺/K⁺-ATPase α₂β₁ and α₁β₁ isozymes for determining some characteristics of the inhibitor.Key findingsWe identified a novel endogenous protein inhibitor of Na⁺/K⁺-ATPase having an apparent mol mass of ～ 70 kDa in the cytosolic fraction of the smooth muscle. The IC₅₀ value of the inhibitor towards the enzyme was determined to be in the nanomolar range. Important characteristics of the inhibitor are as follows: (i) it showed different affinities toward the α₂β₁ and α₁β₁ isozymes of the Na⁺/K⁺-ATPase; (ii) it interacted reversibly to the E₁ site of the enzyme; (iii) the inhibitor blocked the phosphorylated intermediate formation; and (iv) it competitively inhibited the enzyme with respect to ATP. CD studies indicated that the inhibitor causes an alteration of the conformation of the enzyme. The inhibition study also suggested that the DHPC solubilized Na⁺/K⁺-ATPase exists as (αβ)₂ diprotomer.SignificanceThe inhibitor binds to the Na⁺/K⁺-ATPase at a site different from the ouabain binding site. The novelty of the inhibitor is that it acts in an isoform specific manner on the enzyme, where α₂ is more sensitive than α₁.     

Nitrous oxide emissions from agricultural fields: Assessment, measurement and mitigation

In this paper we discuss three topics concerning N₂O emissions from agricultural systems. First, we present an appraisal of N₂O emissions from agricultural soils (Assessment). Secondly, we discuss some recent efforts to improve N₂O flux estimates in agricultural fields (Measurement), and finally, we relate recent studies which use nitrification inhibitors to decrease N₂O emissions from N-fertilized fields (Mitigation).To assess the global emission of N₂O from agricultural soils, the total flux should represent N₂O from all possible sources; native soil N, N from recent atmospheric deposition, past years fertilization, N from crop residues, N₂O from subsurface aquifers below the study area, and current N fertilization. Of these N sources only synthetic fertilizer and animal manures and the area of fields cropped with legumes have sufficient global data to estimate their input for N₂O production. The assessment of direct and indirect N₂O emissions we present was made by multiplying the amount of fertilizer N applied to agricultural lands by 2% and the area of land cropped to legumes by 4 kg N₂O-N ha^-1. No regard to method of N application, type of N, crop, climate or soil was given in these calculations, because the data are not available to include these variables in large scale assessments. Improved assessments should include these variables and should be used to drive process models for field, area, region and global scales.Several N₂O flux measurement techniques have been used in recent field studies which utilize small and ultralarge chambers and micrometeorological along with new analytical techniques to measure N₂O fluxes. These studies reveal that it is not the measurement technique that is providing much of the uncertainty in N₂O flux values found in the literature but rather the diverse combinations of physical and biological factors which control gas fluxes. A careful comparison of published literature narrows the range of observed fluxes as noted in the section on assessment. An array of careful field studies which compare a series of crops, fertilizer sources, and management techniques in controlled parallel experiments throughout the calendar year are needed to improve flux estimates and decrease uncertainty in prediction capability.There are a variety of management techniques which should conserve N and decrease the amount of N application needed to grow crops and to limit N₂O emissions. Using nitrification inhibitors is an option for decreasing fertilizer N use and additionally directly mitigating N₂O emissions. Case studies are presented which demonstrate the potential for using nitrification inhibitors to limit N₂O emissions from agricultural soils. Inhibitors may be selected for climatic conditions and type of cropping system as well as the type of nitrogen (solid mineral N, mineral N in solution, or organic waste materials) and applied with the fertilizers.     

First solid state alkaline-earth complexes of monensic acid A (MonH): crystal structure of [M(Mon)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>] (M = Mg,Ca), spectral properties and cytotoxicity against aerobic Gram-positive bacteria

Alkaline-earth metal complexes of the monoanionic form of the polyether ionophore monensin A were isolated for the first time in solid state and were structurally characterized using various spectroscopic methods (IR, NMR, FAB-MS). The stoichiometric reaction of monensic acid (MonH) with M²⁺ (M = Mg, Ca) in the presence of an organic base leads to the formation of mononuclear complexes of composition [M(Mon)₂(H₂O)₂]. The structures of magnesium (1) and calcium (2) monensin complexes in the solid state were established by single crystal X-ray crystallography. The complexes crystallize as [Mg(Mon)₂(H₂O)₂]·5MeCN (1) and [Ca(Mon)₂(H₂O)₂]·H₂O·5MeCN (2) in the monoclinic P21 space group. The alkaline-earth metal ion is placed in a distorted octahedral environment, defined by two monensin anions acting as bidentate ligands in the equatorial plane of the complex as well as by two water molecules occupying the axial positions of the inner coordination sphere. The bactericidal activity of 1 and 2 was evaluated against aerobic Gram-positive microorganisms applying the double layer agar hole diffusion method.     

植物地上部氮素损失及其机理研究现状与展望

植物地上部气态氮化合物挥发是氮素损失的重要途径, 同时也是大气NH₃和N₂O的重要来源, 因此, 研究植物氮素挥发损失对于大气环境保护和提高氮肥利用率具有重要意义。该文综述了各种气态氮化物(NH₃、NO、NO₂、N₂O和N₂)损失及其机理, 结果表明, 活性氮源积累和同化的不平衡, 是植物氮素挥发损失的主要因素; 环境条件(光、温、水、肥、气)和植物生理病害、衰老等因素, 均可引起植物活性氮源积累和同化的不平衡, 导致植物地上部氮素的挥发损失, 但各种气体氮化物能否从叶面挥发, 还要取决于气体氮化物的补偿点; NH₃和N₂O是主要的植物氮素损失形态, 主要氮素挥发损失发生在生育后期, 但不同氮素损失形态对植物生育期的响应并未完全相同。该文较完整地归纳总结了植物氮素挥发损失的作用机理, 指出了目前研究尚需要解决的重要问题: 1)氮素损失形态间的内在关系并不清楚, 尚不能完整地解释植物氮素挥发损失机制, 尤其是酶催化协同机制; 2)植物叶际气态氮化物交换(包括吸收和释放)作用及其机理也未完全清楚, 因而难以正确评估植物氮素的挥发损失; 3)植物衰老对增强氮素挥发损失有明显促进效果, 但有关其生理机制尚不完全清楚; 4)缺乏可行的抑制植物氮素挥发技术方法, 故还难以有效缓解肥料氮的挥发损失, 提高氮肥利用率。