Spatial distribution pattern and correlation of dominant species in the arbor layer at a 25 hm2 forest plot in Lushan Mountain, China.

To explore the spatial pattern of zonal tree species in the subtropical subalpine mountain area on Lushan Mountain, a 25 hm2 forest plot was established in Yangtianping area of Lushan Mountain following the technical specification of CTFS in 2021. We classified these species into evergreen conifer species, deciduous broad-leaved species and evergreen broad-leaved species based on their leaf shape and deciduous or not to analyze the spatial pattern of dominant species of different types by spatial point pattern method. The results showed that Pinus taiwanensis, Cornus kousa subsp. chinensis, Platycarya strobilacea, Castanea henryi, Quercus serrata, Cornus controversa, Eurya muricata, Litsea elongata, and Eurya hebeclados were dominant species. Among these species, P. taiwanensis was the constructive one. The spatial pattern of dominant species was clustered at a certain scale, and gradually became to randomly distribution with the increases of scales. Evergreen conifer species was independent with deci-duous broad-leaved species and evergreen broad-leaved species at small scales, but was negatively correlated with them at large scales. Deciduous broad-leaved species and evergreen broad-leaved species were obviously negatively correlated with each other. Deciduous broad-leaved species were positively correlated or independent with each other at small scales, but were negatively correlated with each other at large scales. Evergreen broad-leaved species were positively correlated at small scales, independent at medium scales, and negatively correlated with each other at large scales.

Regioselective conversions of H4pdta (1,2-propanediaminetetraacetic acid) and H4eed3a to their triacetates on peroxotitanates.

1,2-Propanediaminetetraacetic acid (H4pdta = C11H18O8N2) is degraded selectively to 1-methyl-1,2-propanediaminetriacetic acid (H3pd3a = C9H16O6N2) with a yield of 75% at room temperature, while N-(2-hydroxyethyl) ethylenediaminetriacetic acid (H4eed3a = C10H18O7N2) is converted with difficulty to ethylenediaminetriacetic acid (H3ed3a = C8H14O6N2) on peroxotitanates(iv), showing the influence of the uncoordinated leaving group. Various species in the reaction sequence are isolated and fully characterized, including (NH4)[Ti(O2)(Hpdta)]·H2O (1), (NH4)3[Ti(O2)(pdta)H(pdta)(O2)Ti]·7H2O (2), (NH4)[Ti(O2)(pd3a)]·H2O (3) and (NH4)[Ti(O2)(Heed3a)]·H2O (5). Peroxo dimer 2 forms a strong intramolecular hydrogen bond [2.451(3) Å] as an intermediate in the peroxo Ti-pdta system, which results in the absence of a fully deprotonated species of peroxo pdta titanate. A catalytic reaction of the peroxo titanate (NH4)3[Ti(O2)(pdta)H(pdta)(O2)Ti]·7H2O (2) for the conversion of pyridine to pyridine N-oxide shows 94% conversion at 80 °C.

Photoinduced Formation of Peroxide Ions on La2O3 and Nd2O3 under O2: Effects of Excitation Wavelength and Crystal Structure.

Photoinduced formation of peroxide ions on La2O3 and Nd2O3 under O2 was studied by in-situ microprobe Raman spectroscopy with attention focused on the effect of excitation wavelength and crystal structure on the O2(2-) formation. It was found that photoexcitations at 633, 532, 514, and 325 nm can induce O2(2-) formation over La2O3 at 450 °C. By contrast, photoexcitation at 785 nm does not cause formation of O2(2-) up to 500 °C. Photoexcitation at 325 nm can induce O2(2-) formation on cubic Nd2O3 at 25 °C, but cannot induce O2(2-) formation on hexagonal Nd2O3 up to 200 °C. The significant difference in the behavior of O2(2-) formation over the Nd2O3 samples of the two structures can be related to the difference in the capacity to adsorb O2. Since the number of oxygen vacancies in cubic Nd2O3 is larger than that in the hexagonal one, the former has a higher capacity than the latter to adsorb O2. As a result, cubic Nd2O3 is more favorable to the reaction of O2 with O(2-) to generate O2(2-). The structural similarity between cubic Nd2O3 and Nd2O2(O2) may be another factor in favor of peroxide formation.

Dimeric 1,3-propanediaminetetraacetato lanthanides as the precursors of catalysts for the oxidative coupling of methane.

From neutral solutions, dimeric 1,3-propanediaminetetraacetato lanthanides (NH4)2[Ln2(1,3-pdta)2(H2O)4]·8H2O [Ln = La, 1; Ce, 2] and K2[Ln2(1,3-pdta)2(H2O)4]·11H2O [Ln = La, 3; Ce, 4] (1,3-H4pdta = 1,3-propanediaminetetraacetic acid, C11H18N2O8) were isolated in high yields. The reaction of excess strontium nitrate with 1 resulted in the formation of a two dimensional coordination polymer [La2(1,3-pdta)2(H2O)4]n·[Sr2(H2O)6]n·[La2(1,3-pdta)2(H2O)2]n·18nH2O (5) at 70 °C. Complexes 1-4 show a similar central molecular structure. The lanthanide ions are coordinated by two nitrogen atoms, four carboxy oxygen atoms from one 1,3-pdta ligand, two from the neighboring 1,3-pdta ligand forming a four-membered ring and two water molecules. Complex 5 has two kinds of dimeric lanthanum unit and extends into a 2D coordination polymer through strontium ions and bridged oxygen atoms, and forms a fourteen membered ring linked by oxygen atoms from carboxy groups of pdta. Complexes 1-4 are soluble in water. The (13)C{(1)H} NMR experiments for complex 1 were tested in solution. Thermal products from 1 and 5 show good catalytic activities towards the oxidative coupling reaction of methane (OCM). The conversion of methane and selectivity to C2 reached 29.7% and 51.7% at 750 °C for the product of 5. From TGA, XRD and SEM analyses, the thermal products from 1 and 5 are rod- and poly-shaped, which are assigned as lanthanum oxocarbonate and a mixture of La2O3, SrCO3 and La2O2CO3 for 1 and 5, respectively. The precursor method is favorable for the formation of regular shaped mixed oxides.

Effect of calcination temperature and pretreatment with reaction gas on properties of Co/γ-Al2O3 catalysts for partial oxidation of methane.

The effects of calcination temperature and feedstock pretreatment on the catalytic performance of Co/γ-Al(2)O(3) catalysts were studied for partial oxidation of methane (POM) to synthesis gas, with emphasis on the role of feedstock pretreatment. The physicochemical properties of the catalysts were characterized by N(2) adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), H(2) temperature-programmed reduction (H(2) -TPR), and Raman spectroscopy. The results showed that the pretreatment of the catalyst by reaction gas significantly improved the catalytic activity and stability for the POM reaction. On the other hand, the effect of calcination temperature was less significant. Although the initial activity was increased by an increased calcination temperature, the catalyst without the feedstock pretreatment suffered a rapid deactivation. The reaction-atmosphere pretreatment was revealed as a process that mainly modified the surface structure of the catalyst. In that process, the formation of a CoAl(2)O(4) -like compound led to high Co metal dispersion after reduction, and the transformation of the carrier into α-Al(2)O(3) occurred over the catalyst surface. Both the high dispersion of cobalt and the presence of α-Al(2)O(3) surface phase were assumed as the important factors resulting in an excellent catalytic performance in terms of high activity and high stability.

Mechanistic aspects of photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) under oxygen.

The photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) was studied by in situ microprobe Raman spectroscopy using a 325 nm laser as excitation source. It was found that the Raman bands of peroxide ions at 833-843 cm(-1) began to grow at the expense of the Ln(3+)-O(2-) bands at 333-359 cm(-1) when the Ln2O3 samples under O2 were continuously irradiated with a focused 325 nm laser beam at temperatures between 25-150 °C. The intensity of the peroxide Raman band was found to increase with increasing O2 partial pressure, whereas no peroxide band was detected on the Ln2O3 under N2 as well as on the samples first irradiated with laser under Ar or N2 followed by exposure to O2 in the dark. The experiments using (18)O as a tracer further confirmed that the peroxide ions are generated by a photo-induced reaction between O2 and the lattice oxygen (O(2-)) species in Ln2O3. Under the excitation of 325 nm UV light, the transformation of O2 to peroxide ions on the surface of the above lanthanide sesquioxides can even take place at room temperature. Basicity of the lattice oxygen species on Ln2O3 also has an impact on the peroxide formation. Higher temperature or laser irradiation power is required to initiate the reaction between O2 and O(2-) species of weaker basicity.

Effect of serotonin depletion on seizures learning-memory in pilocarpine-induced epileptic rats / 中国应用生理学杂志

<p><b>OBJECTIVE</b>To investigate the relationship between serotonin (5-HT) and epilepsy and the mechanism of learning-memory in pilocarpine (PILO)-induced epileptic rats after 5,7-dihydroxytryptamine (5,7-DHT) microinjection in median raphe nucleus.</p><p><b>METHODS</b>Adult S D rats were randomly divided into 3 groups: PILO group, PILO+ 5,7-DHT group, vehicle control group; PILO group was divided into two groups by status epilepticus (SE): PILO + SE group and PILO - SE group. The rats' seizures and cortex electroencephalography (EEG) were observed by video EEG. The rats' spatial learning-memory was evaluated by Morris water maze. Finally, serotonergic neuron in raphe nuclei was observed by immunohistochemistry.</p><p><b>RESULTS</b>After treatment of 5,7-DHT (PILO + 5,7-DHT group), the success rate, the mortality and the frequency of chronic spontaneous seizures in pilocarpine-induced epilepsy model were all improved. Compared with the control group, the number of serotonergic neuron in raphe nuclei was decrease in PILO + SE group (P < 0.05). Moreover, it's extremely decrease in PILO + 5,7-DHT group (P < 0.01). Compared with control group, the mean escape latency was prolonged, the times of crossing target was decreased and the retention time in target zone was shortened in PILO + SE group (P < 0.05), but there was no significant difference between PILO + SE group and PILO + 5,7-DHT group.</p><p><b>CONCLUSION</b>Depletion of serotonin may facility the rats' epileptic seizures, but we could not interpret which may cause epileptic rats' cognitive deficit.</p>

In situ Raman and pulse reaction study on the partial oxidation of methane to synthesis gas over a Pt/Al2O3 catalyst.

Catalytic partial oxidation of methane (POM) to synthesis gas (syngas) over Pt/Al(2)O(3) was investigated by in situ microprobe Raman and pulse reaction methods with attention focused on the mechanism of syngas formation in the oxidation zone (i.e., the catalyst zone in which O(2) was still available in the reaction feed). It was found that the amount of platinum oxide in the catalyst under POM conditions was below the detection level of Raman spectroscopy. Raman bands of carbon species that originated from methane dissociation were detected at the entrance of the catalyst bed under working conditions. The results of the pulse reaction study on POM as well as steam and CO(2) reforming of methane at 700 °C with a contact time of less than 1 ms over the catalyst suggest that pyrolysis of methane on reduced platinum sites followed by coupling of two surface hydrogen atoms to H(2) and partial oxidation of surface carbon species to CO are the major reactions responsible for syngas formation in the oxidation zone. Under the experimental conditions, steam and CO(2) reforming of methane play only a minor role in syngas formation in the same reaction zone. The contribution of the last two reactions increases with increasing contact time.

Brønsted-NH(4)(+) mechanism versus nitrite mechanism: new insight into the selective catalytic reduction of NO by NH(3).

The selective catalytic reduction (SCR) of NO by NH(3) over V(2)O(5)-based catalysts is used worldwide to control NO(x) emission. Understanding the mechanisms involved is vital for the rational design of more effective catalysts. Here, we have performed a systematic density functional theory (DFT) study of a SCR reaction by using cluster models. Three possible mechanisms have been considered, namely (i) a Lewis acid mechanism, (ii) a Brønsted acid mechanism and (iii) a nitrite mechanism. Our calculations down-play the significance of mechanism (i) due to its high barrier as well as the incorrect reaction order. On the other hand, our calculations demonstrate that both mechanisms (ii) and (iii) can lead to a first order reaction with respect to NO with the predicted barriers being consistent with the experimental observations. Thus, we conclude: there exists two competitive pathways for SCR. Mechanism (ii) is dominant when the Brønsted acidity of the catalysts is relatively strong, while mechanism (iii) becomes important when Brønsted acidity is weak or absent. Importantly, we demonstrate that the latter two mechanisms share a common feature where N-N bond formation is ahead of N-H bond cleavage, in contrast to that in mechanism (i). Such a sequence provides an effective way to reduce the side reaction of ammonia combustion since the relatively strong N-N bond has already been formed.

The effect of high frequency stimulation of epileptic foci on the release of glutamate and gamma-aminobutyric acid in hippocampus of the kainic acid-kindled rats / 中国应用生理学杂志

<p><b>OBJECTIVE</b>To observe the dynamics of hippocampal release of glutamate (Glu) and gamma-aminobutyric acid (GABA) in epilepsy (TLE) after administration with high frequency stimulation (HFS).</p><p><b>METHODS</b>The SD were divided into four groups (n =10): (1) Control group (KB) the rats were injected intraperitoneally with saline 0.9%. (2) Kainic acid (KA) group: the rats were injected with KA. (3) Pseudo-deep brain stimulation (DBS) group: the KA-induced rats were implanted with rheophores alone. (4) DBS group: KA induced-rats with DBS in hippocampal epileptic foci. We then collected hippocampal extracellular fluid by microdialysis and the levels of Glu and GABA were measured by high-performance liquid chromatography (HPLC) and fluorescence detection.</p><p><b>RESULTS</b>There was no difference in the baseline of Glu and GABA in the four groups. In contrast, a significant increase in the content of Glu and GABA was shown in the three periods of KA-kindled seizures. Electrical stimulation of hippocampus resulted in a decrease of hippocampal Glu contents, while there was no change in GABA contents. Additionally, HFS of hippocampus normalized the Glu/GABA ratio in the chronic period of seizures.</p><p><b>CONCLUSION</b>The high frequency stimulation of epileptic foci may protect against seizures by modulating the extracellular release of hippocampal Glu.</p>

Mechanisms for O2 dissociation over the BaO (100) surface.

We have investigated the atomic and molecular oxygen adsorptions on the various sites of the BaO (100) surface with both cluster models and the periodic slab models. We found that the atomic oxygen prefers to adsorb on the surface O2- to form the closed-shell peroxides with the binding energies of 83-88 kcal/mol. Such a high exothermicity provides a large driving force for the dissociation of molecular O2 on the BaO surfaces. As molecular oxygen approaches the BaO surfaces, the triplet ground state O2 molecule first binds electrostatically on top of the surface Ba2+ site. It further quenches to the singlet potential energy surface to form a covalently bonded O3(2-) species. We proposed a plausible pathway in which the O3(2-) species acts as the key precursor for further dissociation, leading eventually to the formation of surface peroxides O2(2-). This mechanism is helpful for the understanding of a series of related catalytic processes such as the oxidative coupling of methane, the NOx storage reduction, etc.

Understanding the reactivity of the tetrahedrally coordinated high-valence d0 transition metal oxides toward the C-H bond activation of alkanes: a cluster model study.

We have carried out a theoretical study on the structure-function relationship for the selective oxidation of lower alkanes (C1-C4). The H abstraction mechanism has been examined over the model catalysts of high-valence d0 transition metal oxides in the tetrahedral coordination. The intrinsic connections among the H abstraction barrier, the strengths of the O-H and the M-O bonds, the ability of electron transfer, as well as the energy gap of frontier orbitals of the oxides have been rationalized in terms of thermodynamics cycles and the frontier orbital analysis. In particular, we emphasize the role that the O-H bond strength plays in determining the reactivity of a metal oxide.

pH-dependent isolations and spectroscopic, structural, and thermal studies of titanium citrate complexes.

Titanium(IV) citrate complexes (NH(4))(2)[Ti(H(2)cit)(3)].3H(2)O (1), (NH(4))(5)[Fe(H(2)O)(6)][Ti(H(2)cit)(3)(Hcit)(3)Ti].3H(2)O (2), Ba(2)[Ti(H(2)cit)(Hcit)(2)].8H(2)O (3), and Ba(3)(NH(4))(7)[Ti(cit)(3)H(3)(cit)(3)Ti].15H(2)O (4) (H(4)cit = citric acid) were isolated in pure form from the solutions of titanium(IV) citrate with various countercations. The isolated complexes were characterized by elemental analyses, IR spectra, and (1)H NMR and (13)C NMR spectra. The formation of titanium(IV) citrate complexes depends mainly on the pH of the solutions, that is, pH 1.0-2.8 for the formation of ammonium titanium(IV) citrate 1, pH 2.5-3.5 for ammonium iron titanium(IV) citrate 2, pH 2.8-4.0 for dibarium titanium(IV) citrate 3, and pH 5.0-6.0 for ammonium barium titanium(IV) citrate 4. X-ray structural analyses revealed that complexes 2-4 featured three different protonated forms of bidentate citrate anions that chelate to the titanium(IV) atom through their negatively charged alpha-alkoxyl and alpha-carboxyl oxygen atoms. This is consistent with the large downfield shifts of the (13)C NMR spectra for the carbon atoms bearing the alpha-alkoxyl and alpha-carboxyl groups. The typical coordination modes of the barium atoms in complexes 3 and 4 are six-coordinated, with three alpha-alkoxyl groups and three beta-carboxyl groups of citrate ions. The strong hydrogen bonding between the beta-carboxylic acid and the beta-carboxyl groups [2.634(8) A for complex 2, 2.464(7) A for complex 3, and 2.467(7) A for complex 4] may be the key factor for the stabilization of the citrate complexes. The decomposition of complex 3 results in the formation of a pure dibarium titanate phase and 4 for the mixed phases of dibarium titanate and barium titanate at 1000 degrees C.

Peroxomolybdate(VI)-citrate and -malate complex interconversions by pH-dependence. Synthetic, structural and spectroscopic studies.

The reaction of potassium molybdate(VI) with biologically relevant ligands, citric and malic acids, in the presence of H2O2 was investigated for the effect of pH variations on the product pattern. That with citric acid led to the formation of the monomeric complex K4[MoO(O2)2(cit)].4H2O (1) in the pH range 7-9, and dimer K5[MoO(O2)(2-)(Hcit)H(Hcit)(O2)2OMo].6H2O (2) (H4cit = citric acid) at pH 3-6 through carboxylate-carboxylic acid hydrogen bonding. The relation with the previously identified K4[MoO3(cit)].2H2O (4) and K4[Mo2O5(Hcit)2].4H2O (5) were shown. These and other intermediates were shown to react in the pH range 3-6 to give a more stable species 2; the reaction sequence was demonstrated either by the protonation from 1 or the deprotonation of [MoO(O2)2(H2cit)](2-) (8). Evidence that 2 exists as a dimer in solution is presented. The reaction with (S)-malic acid afforded Delta-K(2n)[MoO(O2)2((S)-Hmal)]n.nH2O (3) (H3mal = malic acid) that was oxidized further to oxalato molybdate (11) by H2O2. The three complexes 1-3 were characterized by elemental analysis, UV, IR and NMR spectroscopies, in addition to the X-ray structural studies that show citrate and malate being coordinated as bidentate ligands via alpha-alkoxyl and alpha-carboxylate groups. The formation of these complexes is dictated by pH and their thermal stabilities varied with the coordinated hydroxycarboxylate ligands.

Syntheses, crystal structures and biological relevance of glycolato and S-lactato molybdates.

Glycolato and S-lactato complexes containing the dioxomolybdenum(VI) moiety have been synthesized for studies on the role of the alpha-hydroxycarboxylato anion in the iron molybdenum cofactor of nitrogenase. The ligands in these complexes, vis K2[MoO2(glyc)2].H2O (H2glyc=glycolic acid, C2H4O3) (1) and (Na2[MoO2(S-lact)2])3.13H2O (H2lact=lactic acid, C3H6O3) (2) chelate through their alpha-alkoxyl and alpha-carboxyl oxygen atoms. In contrast, octanuclear K6[(MoO2)8(glyc)6(Hglyc)2].10H2O (3) formed by the reduction of the glycolato complex (1), features three different ligand binding modes: (i) non-bridging and bridging bidentate coordination of alpha-alkoxyl and alpha-carboxyl groups, and (ii) bidentate bridging using alpha-carboxyl group, leaving the alpha-alkoxyl group free. The octanuclear skeleton shows strong metal-metal interactions. The coordination modes in (1) and (2) mimic that of homocitrate to the iron molybdenum cofactor (FeMo-co) of nitrogenase. The bidentate coordination of alpha-alkoxyl and alpha-carboxyl groups shows that bond of alpha-carboxyl group to Mo is less susceptible to the oxidation state of molybdenum compared with the Mo-alpha-alkoxyl bond. This is supported by the dinuclear coordination of alpha-carboxyl group with free alpha-alkoxyl group in glycolato molybdate(V) (3).

Synthesis and characterization of homochiral polymeric S-malato molybdate(VI): toward the potentially stereospecific formation and absolute configuration of iron-molybdenum cofactor in nitrogenase.

Reaction of sodium or potassium molybdate and excess malic acid in a wide range of pH values (pH 4.0-7.0) resulted in the isolation of two cis-dioxo-bis(malato)-Mo(VI) complexes, viz. Na(3)[MoO(2)H(S-mal)(2)] and K(3)[MoO(2)H(S-mal)(2)].H(2)O (H(3)mal=malic acid). The sodium complex is also characterized by an X-ray structure analysis, showing that the mononuclear Mo units are linked together via very strong symmetric CO(2)...H... O(2)C-hydrogen bond [2.432(5) A], forming a polymeric chain. The molybdenum atoms are quasi-octahedrally coordinated by two cis-oxo groups and two bidentate malate ligands via its alkoxy and alpha-carboxyl groups, while the beta-carboxylic and carboxylate groups remain uncomplexed, as the coordination of vicinal carboxylate and alkoxide of homocitrate in FeMo cofactor of nitrogenase. The absolute configuration of the metal center in this S-malato complex is assigned as Lambda and the homochirality within the chain is established as a homochiral form ...Lambda(S)-Lambda(S)-Lambda(S)-Lambda(S)... . It is proposed that the chiral configuration of the metal center in wild-type FeMo-co biosynthesis might be induced by the early coordination of the chiral R-homocitric acid, while a mixture of raceme might be obtained in the biosynthesis of NifV(-) FeMo-cofactor. The absolute configuration of wild-type FeMo-cofactor is assigned as Delta(R).

Mechanistic study of partial oxidation of methane to syngas using in situ time-resolved FTIR and microprobe Raman spectroscopies.

In situ time-resolved Fourier transform infrared (FTIR) and microprobe Raman spectroscopies were used to characterize the reaction mechanisms of the partial oxidation of methane to syngas over SiO(2)- and gamma-Al(2)O(3)-supported rhodium and ruthenium catalysts. The interaction of both pure methane and a methane/oxygen mixture at a stoichiometric feed ratio with an oxygen-rich catalyst surface led to the formation of CO2 and H(2)O as the primary products. For the H(2)-pretreated samples, the reaction mechanisms with the catalysts differ. Only Rh/SiO(2) is capable of catalyzing the direct oxidation of methane to syngas, while syngas formation over Rh/gamma-Al(2)O(3), Ru/SiO(2), and Ru/gamma-Al(2)O(3) can be achieved mainly via a combustion-reforming scheme. The significant difference in the mechanisms for partial oxidation of methane to syngas over the catalysts can be correlated to the differences in the concentration of oxygen species (O(2-)) on the catalyst surface during the reaction, mainly due to the difference in the nature of the metals and supports.