H+反应对土壤重金属分级提取形态分析的影响

探讨了普遍存在于重金属分级提取形态分析体系中的H+浓度的影响因素,分析了H+反应与提取剂的选择性、金属离子的重分配现象的关系,以及H+浓度对分级提取法数据结果的影响,并对分级提取方法作了进一步的改进.研究表明提取剂pH、提取体系、土壤理化性质及土壤/溶液比是影响H+反应的主要因素;H+反应可降低提取剂选择性,减弱金属离子的重分配能力,影响分析结果的有效性,且对于不同的重金属离子、不同的提取体系,H+反应所造成的影响不同.     

H+反应对土壤重金属分级提取形态分析的影响

探讨了普遍存在于重金属分级提取形态分析体系中的H 反应的影响因素,分析了H 反应与提取剂的选择性、金属离子的重分配现象的关系,以及H 反应对分级提取法数据结果的影响,并对分级提取方法作了进一步的改进。研究表明提取剂pH、提取体系、土壤理化性质及土壤 溶液比是影响H 反应的主要因素;H 反应可降低提取剂选择性,减弱金属离子的重分配能力,影响分析结果的有效性,且对于不同的重金属离子、不同的提取体系,H 反应所造成的影响不同。     

Surface modification of III–V semiconductors: chemical processes and electronic properties

The possibilities of controlling the surface electronic properties of III–V semiconductors by varying the adsorption chemistry are analyzed. Variations of the adsorption process parameters and the adsorbate reactivity are able to affect the surface atomic and electronic structure of the semiconductor. The adsorbate reactivity is considered within the framework of the density functional theory using the reactivity indices. The easiest way to affect the reactivity of a particular adsorbate is to create a solvation shell around it, as is possible in both liquid solutions and the gas phase (microsolvation). Solvation of ions before their adsorption by different solvents affects considerably the relative nucleophility of the central atom in the ion, which results in a different charge transfer mechanism from the surface states on adsorption, and thus, in a different modification of the surface electronic structure of the semiconductor. The effect of halogen, sulfur and metal atoms reactivity on the electronic structure of the resulting adsorbate-covered surface of III–V semiconductor is discussed.     

Aging of gold nanoparticles: ligand exchange with disulfides

Aging of thiolate protected gold nanoparticles (AuNPs) results in reduced reactivity in the disulfide exchange as monitored by electron paramagnetic resonance (EPR) spectroscopy with a bisnitroxide disulfide incoming ligand. Factors determining the reactivity of the aged particles were investigated. The presence of different binding sites on the surface of AuNPs and a surface reorganization process during aging can explain observed reactivity trends.     

Revisiting the reactivity of different carbon bases: A theoretical study

Quantum chemical calculations are performed on different carbon bases to understand the origin of their reactivity. Both carbon(0) and carbon(II) bases may show very high values of second proton affinity as well as bond dissociation energies for gem‐dimetallation. Thus, their distinction becomes blurred when subjected to electrophilic attack. However, unlike carbon(0) bases, carbon(II) bases are ambiphilic in nature owing to the presence of a σ symmetric lone pair and a vacant π orbital concentrated on the central carbon atom. Thus, they may show different reactivity when subjected to nucleophilic attack. This reactivity difference may be considered as another distinction between these two classes of compounds. © 2013 Wiley Periodicals, Inc.     

Reactivity of long conjugated systems: selectivity of Diels-Alder cycloaddition in oligofurans

Taking advantage of the synthetic availability and solubility of long oligofurans, their reactivity toward dienophiles was studied as a model for the rarely investigated reactivity of long conjugated systems. Unlike oligoacenes, the reactivity of oligofurans decreases or remains constant with increasing chain length. Terminal ring cycloadducts of oligofurans are kinetically and thermodynamically favored, whereas central ring cycloadducts are preferred in oligoacenes, because of the different driving forces in the two reactions: π-conjugation in oligofurans and aromatization/dearomatization in oligoacenes.     

A Supramolecular Palladium Catalyst Displaying Substrate Selectivity by Remote Control

Inspired by enzymes such as cytochrome P-450, the study of the reactivity of metalloporphyrins continues to attract major interest in the field of homogeneous catalysis. However, little is known about benefitting from the substrate-recognition properties of porphyrins containing additional, catalytically relevant active sites. Herein, such an approach is introduced by using supramolecular ligands derived from metalloporphyrins customized with rigid, palladium-coordinating nitrile groups. According to different studies (NMR and UV/Vis spectroscopy, XRD, control experiments), the supramolecular ligands are able to accommodate pyridine derivatives as substrates inside the porphyrin pocket while the reactivity occurs at the peripheral side. By simply tuning a remote metal center, different binding events result in different catalyst reactivity, and this enzyme-like feature leads to high degrees of substrate selectivity in representative palladium-catalyzed Suzuki–Miyaura reactions.     

Farewell to the HSAB treatment of ambident reactivity

The concept of hard and soft acids and bases (HSAB) proved to be useful for rationalizing stability constants of metal complexes. Its application to organic reactions, particularly ambident reactivity, has led to exotic blossoms. By attempting to rationalize all the observed regioselectivities by favorable soft-soft and hard-hard as well as unfavorable hard-soft interactions, older treatments of ambident reactivity, which correctly differentiated between thermodynamic and kinetic control as well as between different coordination states of ionic substrates, have been replaced. By ignoring conflicting experimental results and even referring to untraceable experimental data, the HSAB treatment of ambident reactivity has gained undeserved popularity. In this Review we demonstrate that the HSAB as well as the related Klopman-Salem model do not even correctly predict the behavior of the prototypes of ambident nucleophiles and, therefore, are rather misleading instead of useful guides. An alternative treatment of ambident reactivity based on Marcus theory will be presented.     

A comparative study of the degradation of different starches using thermal analysis

Four starches obtained from different sources were treated to thermal analysis and their mechanisms of degradation were deciphered using a rising temperature method of evaluation. A comparison of the solid state reactivity between the four starches was made, using a method known as the alpha(s)-alpha(r) method. By this method, it was possible to differentiate between four starches of completely different plant origin. Potato starch and rice starch were found to have the highest reactivity.     

Copolymerization of a dendronized monomer with styrene and different acrylates: Determination of reactivity ratios

The reactivity ratios for the copolymerization of a first‐generation dendronized monomer with styrene and different acrylates are determined. The obtained ratios as well as the copolymer compositions that can be expected are discussed in detail. The influence of the dendron on the polymerization potential of the monomer is estimated by comparing its reactivity to those of linear systems as well as using higher generations of the dendronized monomer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Unsymmetrically substituted ethane as a new and efficient initiator for the polymerization of methyl methacrylate and styrene

In this paper, we present a compound, 2,3-diphenyl butyronitrile (DPBN), which can be used as a new and efficient radical initiator for the polymerization of methyl methacrylate (MMA) and styrene (St). Very different from other compounds as a carbon-carbon initiator, DPBN is an unsymmetrically substituted ethane and works with high initiation reactivity at lower temperatures. This new compound as an initiator exhibits various advantages, such as easy preparation, high initiation reactivity, safe use and storage, and convenient handling.     

1,3-Dipolar cycloadditions of new 2,5-bifunctionalized five-membered cyclic nitrones

A new family of five-membered cyclic nitrones bearing functional groups at positions 2 and 5 were tested in 1,3-cycloadditions with various dipolarophiles. These reactions gave the corresponding cycloadducts as single diastereomers in high yields. The reaction scope was examined, 23 compounds were isolated and fully characterized. The comparison of the reactivity was carried out by a study of reaction conversions while different nitrones or dipolarophiles were used. In addition, the exceptional reactivity of nitrone bearing benzylamino group in position 2 was studied. The formation of the nitrone complex and evaluation of its reactivity in 1,3-DC is presented.     

Mimicking enzymes: cooperation between organic functional groups and metal ions in the cleavage of phosphate diesters

A series of ligands derived from the bis-2-pyridinylmethylamine structure, which bear either additional hydroxyl or aromatic amino groups, were prepared and their Zn(II) complexes were studied as catalysts for the cleavage of bis-p-nitrophenyl phosphate (BNP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) diesters. A comparative kinetic study indicated that the insertion of organic groups, capable of acting as nucleophiles or as hydrogen-bond donors, substantially increases the hydrolytic activity of the metal complex. Dissection of the effects of the individual groups revealed that the increase in reactivity can reach up to three orders of magnitude. The improved efficiency of the systems studied, combined with the benefits resulting from the low pK(a) value of the active nucleophile, result in an acceleration of the BNP cleavage at pH 7 of six orders of magnitude. The pH-dependent reactivity profiles follow a bell-shaped curve and the maximum reactivity is observed at pH 9. The mechanism of the reactions and the structure of the complexes were investigated in detail by means of kinetic analysis, NMR spectroscopy experiments, and theoretical calculations. The reactivity of the complexes that cleave HPNP closely resembles the reactivity observed for BNP, but the accelerations achieved are lower as a result of different reaction mechanisms.     

MNDO and MINDO/3 study of the reactivity of 3-pyrrolin-2-one tautomers and derivatives

MINDO/3 and MNDO methods have been applied to the study of the reactivity of 3-pyrrolin-2-one tautomers and derivatives. The different parameters that can influence the reactivity from the frontier molecular orbital point of view (atomic charge distribution, frontier orbital energy and frontier orbital reactivity indices) are compared and evaluated with respect to the experimental reactivity already known.     

工业气化装置原料煤及残余物气化反应特性研究

考察了某工业气化装置中的原煤、滤饼及除沫器灰渣在不同温度下与水蒸气和CO₂的气化反应特性,采用扫描电子显微镜和吸附仪测试了样品的初始结构及表面特性。研究表明,采用相同气化剂进行气化反应时,原煤的气化活性要高于除沫器灰渣,而除沫器灰渣的气化活性则与滤饼相近,但略好于滤饼。这主要是由于三种样品的表面和内部结构存在很大的差异。由于水蒸气和CO₂与样品的反应机理存在差异,使得样品的水蒸气气化活性比CO₂气化活性高三倍左右。     

TTT Analysis of a powder coating system based on polyester resin and triglycidyl-isocyanurate

The gelation of a powder coating and its matrix based on a saturated carboxyl functional polyester resin and triglycidyl isocyanurate of different diastereomer racemate composition was investigated by rotational viscometry. The iso-T_cure diagrams have been determined directly by isothermal viscometric measurements and the gelation curves for the TTT-diagram have been constructed. To the measured section of the gelation curves power functions could be fitted and with their help the reactivity of the investigated systems were compared. The ratio of the two diastereomer racemates of TGIC has a significant effect on the reactivity of the coating, as it was also supported by DSC measurements. β-TGIC is of highest reactivity, and by increasing its ratio in TGIC, reactivity increases, and adversely effects the performance of the powder coating. Commercial TGIC-s have similar reactivity, comparable to that of high α-TGIC. The reactivity of the matrix is higher than that of the powder.     

Effect of tertiary diamines on anionic polymerization of polar vinyl monomers

Tertiary diamines that exhibit chelating capability to lithium are shown to decrease the reactivity of growing species when used in classical anionic polymerization of methacrylic monomers. Out of the different diamines investigated, sparteine turns out to be the most efficient chelating agent. The beneficial effect of the latter additives on the overall reactivity of methacrylic anions was exploited to prepare poly(MMA) samples of controlled size at room temperature. The decrease in reactivity was also demonstrated from a kinetic point of view, upon measuring the actual rate constant of propagation using vinyl pyridine as model monomer.