Plant calorimetry. Part 2. Modeling the differences between apples and oranges

In a previous review we discussed calorimetric methods for the study of plant metabolism. Since that review, a number of papers describing calorimetric measurements examining plant growth, stress responses and effects of temperature have appeared. This recent work is reviewed here.

In addition to the experimental work, a mechanistic model linking respiration rates to growth has been published. This model is derived from both mass and enthalpy balance equations. It describes specific growth rate and substrate carbon conversion efficiency as functions of the metabolic heat rate, the rate of CO₂ production, the mean oxidation state of the substrate carbon produced by photosynthesis, and enthalpy changes for conversion of photosynthate to biomass and CO₂. Application of this model to understanding the basis for variation in growth rates among individual genotypes in plants is reviewed.

The effects of environment on the plant respiration-growth relation has been an important focus for plant calorimetry studies. Climatic temperature is one of the most important variables determining growth. Extremes of temperature determine limits of growth, and diurnal variation and mean temperature have a major influence on growth rate. Calorimetric measurements of respiratory rates as a function of temperature can be used to relate the temperature influence on respiratory metabolism to the temperature influence on growth rate. These studies have also discovered the existence of an isokinetic point within the range of normal growth temperatures. Studies of temperature dependence are reviewed and the results analyzed in terms of the recently published mechanistic model.     

氢气存在下煤焦水蒸气气化： II 修正随机孔模型的建立

采用热天平对神府煤1200℃快速热解焦进行常压水蒸气/惰性气气化及水蒸气/氢气气化。考察神府煤焦在875℃~950℃时与水蒸气/惰性气的气化反应和水蒸气/氢气的气化反应特性,两者的特征曲线明显不同。不加氢的水蒸气气化反应速率随碳转化率的增加缓慢而均匀地下降;加氢水蒸气气化反应速率随碳转化率的增加先迅速降低,而后降低较缓慢。此种形式的气化曲线以往的动力学模型很难进行模拟,研究根据随机孔模型提出了一个新的气化动力学模型。此模型拟合的数据与实验数据比较,证明了修正的随机孔模型可以更好的模拟煤焦的加氢水蒸气气化,相关系数达到0.996以上。用修正模型求得的神府煤焦加氢水蒸气气化的活化能为251.990kJ/mol,指前因子为5.97877×10⁹min^-1。     

PHOTOREDUCTION OF ZINC PORPHIN BY ASCORBIC ACID*

Abstract— Zinc porphin is photoreduced to zinc chlorin through an intermediate dihydroporphin (PH₂) by ascorbic acid in ethanol containing 1% to 10% (v/v) piperidine. Under the same conditions zinc chlorin is more slowly photoreduced to zinc tetrahydroporphin. The reactions leading to chlorin are photosensitized by the product chlorin and so are autocatalytic in red light. Quantum yields for these reactions range up to 0.05.Other aliphatic amines catalyze these reactions, but at rates peculiar to the amine. The immediate product of reduction of zinc porphin, PH₂, is distinguished by an intense band at 437 nm; it reverts to porphin in the dark in the presence of oxygen or dehydroascorbic acid. Its conversion to chlorin is effected by light absorbed by porphin or chlorin, but not by light absorbed by PH₂ itself. A suggested structure for PH₂, compatible with the observed reactions, has added hydrogens on one bridge carbon and one β-pyrrole carbon. The possibility of an analogy between these reactions and the biochemical conversion of protochlorophyll to chlorophyll is discussed.     

Determination of the enthalpy change for anabolism by four methods

The enthalpy change for anabolism is needed to model the growth/respiration relation in plants. If all CO₂ production is assigned to catabolism, the anabolic reaction becomes C_substrate→C_products+xO₂ with an enthalpy change, ΔH_b. Four methods are proposed for determining ΔH_b: (a) From the difference in the heats of combustion of substrate and anabolic products (i.e. newly grown tissue). (b) From the composition of newly grown tissue and application of Thornton’s rule. (c) From independently measured values of the specific growth rate, R_SG, and of the product (R_SG ΔH_b). The product (R_SG ΔH_b) equals (−ΔH_CO2R_CO2−R_q) where R_CO2 is the specific rate of CO₂ production by respiration, ΔH_CO2 is the heat of combustion of respiratory substrate per mole of CO₂ and R_q is the specific metabolic heat rate. ΔH_b is then calculated as the ratio (R_SG ΔH_b)/R_SG. (d) From (ΔH_b=−(R_q/R_CO2+ΔH_CO2) [(1−)/] where is the substrate carbon conversion efficiency obtained from a total carbon balance. The first three methods have been tested and compared on oat seedlings and the last on corn seedlings. ΔH_b values from all four methods are in reasonable agreement despite the different assumptions involved.     

Ni单原子催化剂表面CO2电还原动力学的电化学谱学解析

针对Ni单原子催化剂表面的CO₂电还原反应(CO₂RR), 提出了以Ni为活性位点的“单中心”机理以及同时借助Ni位点还原和碳氮锚定位水解的“双功能”机理. 依据稳态极化的实验结果, 开展了CO₂RR的动力学解析与模型参数的敏感性分析; 借助暂态模型方程, 分别获取可表达CO₂RR线性与非线性频响特征的电化学阻抗谱(EIS)与总谐波失真(THD)谱. 研究结果表明, CO₂的溶解分压对CO₂RR活性影响最显著. 若CO₂RR遵循“单中心”机理, Ni位点COOH_ads的形成为速率控制步骤; 但若为“双功能”机理, 碳氮锚定位的水解与Ni位点的CO_2,ads还原同为速率控制步骤. EIS理论上可用于区分CO₂RR的“单中心”机理与“双功能”机理; 与之相比, THD谱在CO₂RR的机理识别中并无优势.     

不同条件下离体大鼠肝脏线粒体能量代谢微量热分析

为了探究线粒体的能量代谢过程,本文以离体大鼠肝脏线粒体为模型,利用多通道、高灵敏度的热活性检测仪TAM Ⅲ,实时监测了不同线粒体浓度、不同底物、不同缓冲液、几种呼吸抑制剂以及Ca²⁺和线粒体渗透转换孔抑制剂CsA存在时线粒体的能量代谢,获得了完整的热功率―时间曲线,并通过计算得到了线粒体能量代谢的热动力学参数。通过分析发现：（1）线粒体浓度越大,代谢越快;（2）直接底物琥珀酸钠使线粒体代谢更快;（3）高浓度Ca²⁺能够刺激线粒体快速产热,且在长期代谢进程中,线粒体渗透转换孔抑制剂CsA并不能改变Ca²⁺造成的影响;（4）不同缓冲液对线粒体代谢的影响基于其组分的不同,缓冲液中含有呼吸底物;（5）呼吸抑制剂都能抑制线粒体的能量代谢,尤其是复合物IV的抑制剂NaN₃,高浓度下使代谢停止。     

A theoretical investigation of the adsorption surface sites of the activated MgCl2

The adsorption of carbon monoxide on activated MgCl₂ has been investigated within DFT using different models of the MgCl₂ surface. All the models were Mg₆Cl₁₀ clusters with two saturating OH groups. It has been found that the adsorption sites within the models based on the geometry of the ideal MgCl₂ crystal are stronger than they are in the experiment. It has also been found that relaxed clusters based on the geometry of the relaxed MgCl₂ surface present more accurate models of the MgCl₂ surface and account the relaxation effects properly. IR spectra of carbon monoxide bounded to three different adsorption sites calculated within relaxed clusters approximation is in excellent agreement with the experimental data. Such an agreement allows us to conclude that adsorption sites of the activated MgCl₂ surface in general are 3-, 4- and 5-fold Mg atoms and the structure of these sites follows the structure of corresponded relaxed MgCl₂ crystallographic faces.     

XRD和Raman法评估热解气氛中H_2和CO对半焦化学结构的影响

采用XRD和Raman光谱分析方法研究了神木煤在热解主要温度区间(450-750℃)及在三种热解气氛(N_2、含H_2及含CO)下的化学结构演变规律,并比较了两种方法所获结构参数的相关性。结果表明,原煤在N_2气氛下热解制备的半焦,其炭微晶尺寸在横向上不断增长,纵向上层面间距逐渐增大,堆垛高度在650℃左右剧烈转变; Raman参数A_(D_1)/A_G增加,而A_G/A_(all)降低,表明半焦有序性结构比例降低。热解气氛中的H_2促进了炭微晶结构的纵向发展,提高了小分子基团的转化程度,使得半焦有序化程度升高。热解气氛中的CO对炭微晶结构参数影响小于H_2气氛,但在700℃以下,CO因析炭作用产生的致密炭颗粒包裹于半焦表面,导致半焦炭有序化程度提高。半焦的L_c与A_G/A_(all)及d_(002)与A_(D_1)/A_G之间存在一定相关性; L_a与A_(D_1)/A_G呈较好的正相关性。     

Fourier transform IR product study of the reaction of CFO radicals with O2 at 298 K

Experimental results are presented of a Fourier transform IR product study at 298 K of the reaction system CFO+O₂ at oxygen pressures between 3 and 250 mbar. Pulsed photolysis of oxalyl fluoride (CFO)₂ or formyl fluoride (CHFO) at 193 nm was used to produce CFO. As stable products we detected bis-fluoroformyl peroxide, carbonyl fluoride and carbon dioxide. The yields of the peroxide and of CF₂O were measured as a function of [O₂]/[precursor] and are discussed qualitatively.     

基于g-C3N4的Z型光催化体系研究进展

导电聚合物型光催化材料g-C₃N₄有着独特的电子结构、稳定的化学性能和显著的可见光催化活性。基于g-C₃N₄的Z型光催化体系(Z-g-C₃N₄)的催化效率高、电子-空穴复合率低而备受关注,在光催化领域展现出了巨大的应用潜力。本文阐述了Z-g-C₃N₄型光催化反应体系的作用机理,综述了Z-g-C₃N₄在光催化领域的研究进展,介绍了Z-g-C₃N₄在产氢、转化CO₂、降解有机物等光催化领域的应用,讨论了pH值、导电介质等因素对Z-g-C₃N₄光催化性能的影响。最后指出了Z-g-C₃N₄光催化体系在研究过程中面临的问题和研究方向。     

The organometallic chemistry of nitrogenases

Nitrogenases mediate the reduction of many substrates other than dinitrogen and a summary is given. Several chemical systems that mimic aspects of nitrogenase reactivity, including transition metal complexes of alkynes and olefins, are outlined. Their protonation has been studied and their relevance to reduction of alkynes and olefins by nitrogenase is assessed. Cyclopropene is reduced by molybdenum nitrogenase to propene and cyclopropane. The reactions of cyclopropene with different transition metal complexes are discussed and a study of interactions of cyclopropenes with models for the active site of the nitrogenase enzyme are described. These models include transition metal hydrides, such as [FeH(H₂)(dmpe)₂][BPh₄] and [MoH₄(dppe)₂] reducing 3,3-dimethylcyclopropene and cyclopropene. Products observed upon protonation and deuteration of several platinum-cyclopropene complexes are presented and a mechanism for their formation is proposed.     

二氧化碳电化学还原的研究进展

利用低品阶的可再生电能,将二氧化碳(CO_2)电化学还原生成高附加值的化学品或燃料,既可以"变废为宝"、减少CO_2排放,又能将可再生能源转变为高能量密度的燃料储存,具有重要的现实意义。电化学还原CO_2的研究,是目前世界范围内的研究热点,许多标志性的重要研究成果不断涌现。本文首先简要介绍了CO_2电化学还原的基本原理,然后概述了近5年来在其电催化剂材料和反应机理相关的实验与理论研究方面的昀新研究进展,昀后对其发展趋势进行了展望。     

Supported carbon molecular sieve membranes based on a phenolic resin

The preparation of a composite carbon membrane for separation of gas mixtures is described. The membrane is formed by a thin microporous carbon layer (thickness, 2 μm) obtained by pyrolysis of a phenolic resin film supported over a macroporous carbon substrate (pore size, 1 μm; porosity, 30%). The microporous carbon layer exhibits molecular sieving properties and it allows the separation of gases depending on their molecular size. The micropore size was estimated to be around 4.2 Å. Single and mixed gas permeation experiments were performed at different temperatures between 25°C and 150°C, and pressures between 1 and 3.5 bar. The carbon membrane shows high selectivities for the separation of permanent gases like O₂/N₂ system (selectivity≈10 at 25°C). Gas mixtures like CO₂/N₂ and CO₂/CH₄ are successfully separated by means of prepared membranes. For example, the membrane prepared by carbonization at 700°C shows at 25°C the following separation factors: CO₂/N₂≈45 and CO₂/CH₄≈160.     

阳极改性对微生物燃料电池处理秸秆水解物性能影响

以玉米秸秆稀酸水解液为阳极底物,用污水处理厂活性污泥为产电微生物菌源构建双室微生物燃料电池(MFC),采用三种不同方法改性阳极碳毡,并对其MFC产电性能进行研究。结果表明,以未改性碳毡(CC)、HNO_3酸解CC(HNO_3/CC)、壳聚糖改性CC(chitosan/CC)、PDADMAC/α-Fe_2O_3层层自组装改性碳毡(PDADMAC/α-Fe_2O_3/CC)的MFC的最大产电量分别为248、315、452和522 mV,最大功率密度分别为54.6、92.7、203.8和248.1 mW/m~2,COD的去除率分别为82.21%、81.46%、82.53%和86.44%。循环伏安曲线显示,PDADMAC/α-Fe_2O_3层层自组装改性的阳极碳毡具有较高的氧化还原电位。电化学阻抗谱图表明,PDADMAC/α-Fe_2O_3层层自组装改性碳毡的极化内阻最小,为7Ω。几种改性材料为阳极的MFC性能依次为PDADMAC/α-Fe_2O_3/CC壳聚糖/CCHNO_3/CC空白CC。     

垃圾衍生燃料热解半焦气化过程中HCl与H2S析出规律

通过水平管式气化炉和化学吸收法,对比研究了矿化垃圾热解半焦（ARC）和常规垃圾热解半焦（NRC）在水蒸气和CO₂气化过程中腐蚀性气体（HCl和H₂S）的析出特性,考察了气化温度、气化介质类型和流量对腐蚀性气体析出特性的影响。当气化温度升至950℃,ARC在水蒸气气化过程中的碳气化率、HCl和H₂S产率分别为66.1%、100%和74.9%,而其在CO₂气化过程中的碳气化率、HCl和H₂S产率分别为77.8%、100%和2.9%;NRC在水蒸气气化过程中的碳气化率、HCl和H₂S产率分别为98.8%、100%和53.7%,而其在CO₂气化过程中的碳气化率、HCl和H₂S产率分别为100%、96.2%和10.3%。以NRC为原料,考察了水蒸气和CO₂流量对其HCl和CO₂析出特性的影响。NRC的HCl和H₂S产率均随水蒸气流量增加而增加,但当水碳比大于等于3.3时,其促进作用不再明显。NRC的HCl产率随CO₂流量的增加而增加,而H₂S产率随CO₂流量的增加而减小。     

高灵敏线粒体靶向近红外二氧化硫荧光探针的开发及细胞、小鼠成像研究

二氧化硫(SO₂)及其衍生物(亚硫酸盐、亚硫酸氢盐等)作为活性硫物种的重要组成部分,与生命体的生理过程有着密切的关系.此外,摄入过量的SO₂会对呼吸系统造成不可修复的损伤,例如呼吸系统损伤、心脑血管和神经疾病等.近红外发射荧光探针具有较强的组织穿透能力,可以有效地检测活体内的生物分子.因此,设计了一种基于迈克尔加成(Michael Addition)机理的线粒体靶向近红外SO₂荧光探针XA-SO₂.溶液光谱实验表明,该探针XA-SO₂对SO₂有着显著的选择性和灵敏度,并且具有快速检测SO₂的能力.值得注意的是,该荧光探针XA-SO₂具有较好的细胞膜渗透能力,成功检测到了细胞外/内源性SO₂.更重要的是,该探针XA-SO₂能够有效地在细胞的线粒体上富集,有望实现细胞线粒体内SO₂的动态检测.     

Equilibrium constants and kinetics of carbon monoxide insertion in alkyl complexes of ruthenium(II)

The equilibrium constants of the reaction of cis, trans-[Ru(CO)₂(PMe₃)₂(CH₃)I] (Mc) with carbon monoxide to give cis, trans[Ru(CO)₂(PMe₃)₂ (COMe)i] (Ac) and trans, trans[Ru(CO)₂(PMe₃)₂(COMe)I] (At) were measured at various temperatures in toluene. The thermodynamic parameters are compared with those obtained for the isoelectronic complexes of iron, and the trend is discussed. The kinetics of the carbonylation reaction of Mc, as well as those of the inverse decarbonylation reaction of At were measured. The kinetics of the carbonylation of the new complex trans, trans-[Ru(CO)₂(PMe₃)₂(CH₃)I] (Mt) were also investigated. All the results afford further support to the previously proposed CO insertion mechanism occurring via methyl migration. The comparison of these kinetic results with those of isoelectronic complexes of iron indicates that ruthenium is more reactive than iron, which is reflected by its greater aptitude to act as catalyst in many processes.     

Adsorption of CO2 and H2 on Nitrogen-doped Porous Carbon from Ionic Liquid Precursor

Nitrogen-doped mesoporous carbon material was prepared via a simple one-step thermolysis method via the carbonization of ionic liquid, 1-cyanomethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([MCNIm]⁺[Nf₂T]^-). The nanostructure of the resultant carbon material was characterized by X-ray diffraction(XRD) and transmission electron microscopy(TEM) and the types of N-containing groups of the carbon material were investigated by X-ray photoelectron spectroscopy(XPS). The N-content of the carbon material is 18.6%(mass fraction) based on the elemental analysis. The produced mesoporous carbon material was further used as the solid sorbent for H₂ and CO₂. The hydrogen uptake capacity and H₂ isosteric heat of the carbon material were discussed. Furthermore, the nitrogen-containing carbon material as good sorbent shows relatively high adsorption and separation ability for CO₂ from CH₄, for which the heat of CO₂ adsorption(Q_st) is 31.8 kJ/mol. The mesoporous structure and nitrogen functionality make the carbon material with high adsorption capacity and selectivity for CO₂ and ability to store H₂, indicating that this kind of nitrogen-doped carbon material originated from ionic liquids is a promising sorbent material for high-performance separation and adsorption.     

Ab initio prediction of MnOH2/MnOH2 electron transfer reactivity at electron correlation level

An ab initio calculation of electron transfer reactivity of Mn²⁺OH₂/Mn³⁺OH₂ redox system, in gas and in solution, has been made in this paper. The detailed geometry optimization and the scanning of the potential energy surfaces have been carried out at UMP2 (full)/6-311+G^* level. The relevant energy quantities (such as the activation energy and the binding energy) are calculated at different levels of theory (HF, MP2, MP3, MP4 and QCISD and corresponding spin-projection PUHF, PMP2 and PMP3) with the same basis set (6-311+G^*). Both all-electrons and valence electrons have been correlated in energy calculations. The electronic transmission coefficient is calculated using the ab initio potential energy surface slopes and the coupling matrix element determined from the two-state model and the Slater-type d-electron wave functions. The pair distribution function is obtained using both a classical sphere approximation scheme and a novel scheme. The relevant kinetic parameters are obtained at different ab initio levels in terms of the new model. The contact-distance dependence of these parameters and the applicability of the presented models are also discussed.     

Nitrogen-doped Carbon Coated Na3V2(PO4)3 with Superior Sodium Storage Capability

Cathodes with high cycling stability and rate capability are required for ambient temperature sodium ion batteries in renewable energy storage application. Na₃V₂(PO₄)₃ is an attractive cathode material with excellent electrochemical stability and fast ion diffusion coefficient within the 3D NASICON structure. Nevertheless, the practical application of Na₃V₂(PO₄)₃ is seriously hindered by its intrinsically poor electronic conductivity. Herein, solvent evaporation method is presented to obtain the nitrogen-doped carbon coated Na₃V₂(PO₄)₃ cathode material, delivering enhanced electrochemical performances. N-Doped carbon layer coating serves as a highly conducting pathway, and creates numerous extrinsic defects and active sites, which can facilitate the storage and diffusion of Na⁺. Moreover, the N-doped carbon layer can provide a stable framework to accommodate the agglomeration of the electrode upon electrode cycling. N-Doped carbon coated Na₃V₂(PO₄)₃(NC-NVP) exhibits excellent long cycling life and superior rate performances than bare Na₃V₂(PO₄)₃ without carbon coating. NC-NVP delivers a stable capacity of 95.9 mA·h/g after 500 cycles at 1 C rate, which corresponds to high capacity retention(94.6%) with respect to the initial capacity(101.4 mA·h/g). Over 91.3% of the initial capacity is retained after 500 cycles at 5 C, and the capacity can reach 85 mA·h/g at 30 C rate.