Studies on the controllable transformation of ferrihydrite

Ferrihydrite was prepared by two different procedures. Ferrihydrite-1 was prepared by dropping NaOH solution into Fe(III) solution. Ferrihydrite-2 was prepared by adding Fe(III) and NaOH solutions into a certain volume of water simultaneously. Our earlier results obtained at ∼100 °C have shown that the structure of ferrihydrite-2 favors its solid state transformation mechanism. Further research reveals that the structure of ferrihydrite-2 favors its dissolution re-crystallization mechanism at a temperature of ≤60 °C. Based on the transformation mechanism of ferrihydrite at different temperatures, the controllable transformation from ferrihydrite to various iron (hydr)oxides such as lepidocrocite, goethite, hematite and magnetite can be achieved by adjusting the pH, transformation temperature, transformation time, the amount of Fe(II) as well as the preparation procedures of ferrihydrite. The results in the present paper give a nice example that the transformation of a precursor can be controlled with the help of mechanism.     

A temperature correction procedure for temperature inhomogeneity in dilatometer specimens

Dilatometry is a thermo-analytical technique used to measure the expansion or shrinkage of materials during heating or cooling, whether or not in association with a phase transformation. A temperature correction procedure has been developed to correct for the temperature inhomogeneity that exists in an inductively heated specimen during the heating/cooling process and to represent the dilation as a function of a homogeneous temperature. As an example, taking an Fe-5.91 at.% Ni specimen and subjecting it to two different cooling rates, the temperature correction has been performed for the temperature range where the austenite to ferrite phase transformation takes place as well as for the pure austenite and ferrite phases close to the temperature range of the transformation.     

Silica Nanoparticles-mediated Stable Genetic Transformation in Nicotiana tabacum

Nanoparticles as gene carriers become popular in the mammalian cells, whereas the application of them in plant cells is still very limited. Herein lies a report on silica nanoparticles(SiNPs) modified with positively charged poly-L-lysine(PLL) successfully delivering plasmid-encoded β-glucuronidase(GUS) gene into tobacco with the help of gene gun. The stable transgenic tobacco plants mediated by SiNPs can be obtained. Furthermore, we revealed the quantity of gene and types of receptor materials could affect the expression efficiency. In comparison to conventional gold particles-mediated transformation, the silica nanoparticles-mediated stable genetic transformation enhances transformation efficiency, potentially overcoming transgenic silencing. Our results demonstrate the great potential of SiNPs as gene carrier in plant genetic transformation and prove a novel approach for plant genetic decoration.     

Generalized Euler transformation in extracting useful information from divergent (asymptotic) perturbation series and the construction of Padé approximants

Euler transformation for accelerating convergence of a series is considered in the context of handling divergent (asymptotically convergent) perturbation series. A generalized (parametrized) version of this transformation is developed, based on the conjecture of Dalgarno and Stewart, which works better. Viewed from this standpoint, the Padé approximants follow as a special case of the parametrized Euler transformation (PET ), as is the case with the μ transformation procedure of Feenberg in a perturbative context. The PET is shown to serve as a more general method of handling a divergent series and is able to appreciate the construction and convergence behavior of specific sequences of Padé approximants. The role of parametrization in the context of the Z^?1 perturbation theory of atoms is also noted and the workability of the adopted strategy is demonstrated by choosing some specific test cases.     

Adsorption‐Induced Structural Phase Transformation in Nanopores

We report a new type of structural transformation occurring in methane adsorbed in micropores. The observed methane structures are defined by probability distributions of molecular positions. The mechanism of the transformation has been modeled using Monte Carlo method. The transformation is totally determined by a reconstruction of the probability distribution functions of adsorbed molecules. The methane molecules have some freedom to move in the pore but most of the time they are confined to the positions around the high probability adsorption sites. The observed high‐probability structures evolve as a function of temperature and pressure. The transformation is strongly discontinuous at low temperature and becomes continuous at high temperature. The mechanism of the transformation is influenced by a competition between different components of the interaction and the thermal energy. The methane structure represents a new state of matter, intermediate between solid and liquid.     

多孔炭材料在纤维素催化转化中的应用

生物质作为自然界唯一可再生的有机碳资源,其利用受到了越来越多的关注。特别是随着能源和环境危机的日益加重,将生物质中非可食用部分催化转化为燃料及具有高附加值的化学品被认为是高效、环保、原子经济的绿色过程。同时,多孔炭材料具有丰富的孔道结构、优异的水热稳定性和大比表面积,是生物质催化转化反应中最常用的载体材料之一。兼之炭材料表面极性、亲疏水性的可调变性,及对酸碱溶剂的反应惰性,也使其无论在学术研究还是在工业应用中都具有特殊的优势。另外,随着纳米炭材料科学的飞速发展,合成孔径、形貌、及表面官能团可控的介孔炭和具有多级孔道结构的多孔炭材料成为可能,将其应用到纤维素催化转化过程中,对深入理解孔道结构、表面官能团对纤维素转化的作用,揭示催化反应作用机制,指导炭基催化剂的设计合成,均具有重要意义。在本综述中,我们首先对纤维素转化中多孔炭的孔道结构和表面官能团性质的独特作用进行了阐述。由于商业活性炭的孔径一般在微孔尺度,但纤维素及可溶低聚糖的分子体积较大,因而其在活性炭中的传质受到了极大的限制。通过模板法获得的介孔炭材料,可实现孔径在2–10 nm的可控合成,大大提高了反应物的扩散速率,使之能与催化活性位有效接触。但孔道过于狭长,在反应过程中堵塞的可能性增高,进而导致催化剂失活;因此,在介孔孔道的基础上,建立互通的多级孔道结构对反应物、中间物、和产物的扩散,及催化活性的保持更为有利。另一方面,炭材料表面的含氧官能团不仅具有加强1,4-糖苷键吸附的作用,还可以作为酸性活性中心催化水解反应的进行;尤其是在传统的水相纤维素催化转化过程中,亲水表面对多孔炭催化剂与反应物的接触非常有利。本文以纤维素水解及纤维素水解加氢反应为例,展开讨论了多孔炭作为固体酸及双功能催化剂载体的应用。在水解反应中,纤维素首先在热水中降解为可溶低聚糖,之后再与活性炭表面官能团反应;其中多孔炭的比表面积、酸量、及酸强度均是促进水解发生的正向因素。在水解加氢反应中,炭载贵金属催化剂作为最常用的加氢催化剂,可获得以六元醇为主的纤维素转化产物。除了加氢作用之外,贵金属小颗粒被证实可以通过氢溢流作用提供水解所需的H+,同时,正价的贵金属也可促进反应过程中的氢转移。另一方面,由于钨物种可催化逆羟醛缩合反应的发生,因此在反应体系中引入钨物种时,水解加氢的主要产物由六元醇变为乙二醇。需要特别指出的是,在纤维素催化水解加氢的过程中,多孔炭材料作为载体同样具有非常重要的作用：一方面,三维介孔的孔道结构不仅有利于反应物、产物的扩散,也有利于加氢金属催化剂的分散,进而提高金属的催化加氢能力;另一方面,当炭材料的表面化学性质改变时,也会影响产物的选择性分布,例如当炭表面显碱性时,由于异构化作用,丙二醇成为主要产物。本文最后,我们列举了一些新型多孔炭材料,包括杂原子改性的多孔炭材料和金属氧化物-炭复合多孔材料的合成方法及其在纤维素催化转化乃至生物质转化中的潜在应用。     

Organic-Free Interzeolite Transformation in the Absence of Common Building Units

Zeolite crystals can be used as seeds or aluminosilicate sources in syntheses to control polymorphs and/or reduce the quantity of organics used as structure-directing agents. A frequently invoked hypothesis for interzeolite transformations is that zeolites share some underlying similarity in structure, most notably in cases pertaining to organic-free syntheses. Herein, we show for the first time that ZSM-5 (MFI) can be directly obtained from USY (FAU) through an interzeolite transformation between parent–daughter structures lacking common building units in the absence of a structure-directing agent and seeds. We show that interzeolite transformation leads to a crystalline product with fewer defects. Our findings also reveal that ZSM-5 is a metastable intermediate that undergoes further transformation to mordenite (MOR) and quartz. The MFI-to-MOR transition is counter to reported trends for which transformations lead to structures with reduced molar volume. Herein, we propose mechanistic arguments that suggest the driving force for interzeolite transformation is more complex than guidelines posited in the literature.     

Indole Editing Enabled by HFIP-Mediated Ring-Switch Reactions of 3-Amino-2-Hydroxyindolines

This work reports the novel reactivity of hemiaminal as a precursor for indole editing at the multi-site. The HFIP-promoted indole editing of indoline hemiaminals affords 2-arylindoles through a ring-switch sequence. The key to success of this transformation is to use a cyclic hemiaminal as an α-amino aldehyde surrogate under transient tautomeric control. This transformation features mild reaction conditions and good yields with broad functional group tolerance. The utility of this transformation is presented through the one-pot protocol and the synthesis of isocryptolepine.     

纳米锐钛矿相变的原位XRD研究

钛氧化物具有3种物相：锐钛矿、板钛矿和金红石，其中，锐钛矿和板钛矿为室温稳定相．在温度较高的条件下会向热力学更稳定的金红石相转变。锐钛矿向金红石的相变是热力学亚稳定相向稳定相的转变，由于这种相变过程不存在平衡温度．分析研究其相变过程无论从理论方面还是从实际应用方面均具有重要的意义。     

Characterization of atenolol transformation products in ozonation by using rapid resolution high-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry

This experiment investigated the transformation pathway of atenolol, a widely used β-blocker, in the ozonation process through the identification of generated intermediate compounds. In order to characterize the contribution of ozone and hydroxyl radical (•OH) in the transformation of atenolol, ozonation were performed at pH 2, 7 and 9. 15 major transformation products have been identified based on the chromatographic behavior of these compounds and the information obtained from accurate mass MS and MS/MS spectra. By comparing to the elution pattern of the identified transformation products and its fragmentation pattern in the MS/MS spectrum, a variety of isomers of the transformation products were characterized.Identified transformation products of atenolol are including its mono-, di and tri-hydroxylated derivatives as well as the aliphatic and aromatic ring breakdown products. Transformation of atenolol in the ozonation involved hydroxylation reaction, aromatic ring opening reaction, oxidation and cleavage of 2-hydroxy-3-(isopropylamino)propoxy group of atenolol. In ozonation, aromatic ring of atenolol was transformed through the reaction with both ozone and •OH whereas the aliphatic chain of atenolol was degraded mainly through the reaction with •OH. The results also indicated that both •OH and ozone involved in the aromatic ring opening reaction.     

Effective Floquet Hamiltonian for spin I = 1 in magic angle spinning NMR using contact transformation

Contact transformation is an operator transformation method in time-independent perturbation theory which is used successfully in molecular spectroscopy to obtain an effective Hamiltonian. Floquet theory is used to transform the periodic time-dependent Hamiltonian, to a time-independent Floquet Hamiltonian. In this article contact transformation method has been used to get the analytical representation of Floquet Hamiltonian for quadrupolar nuclei with spin I = 1 in the presence of an RF field and first order quadrupolar interaction in magic angle spinning NMR experiments. The eigenvalues of contact transformed Hamiltonian as well as Floquet Hamiltonian have been calculated and a comparison is made between the eigenvalues obtained using the two Hamiltonians.     

Palladium-catalyzed asymmetric allylic alkylation of electron-deficient pyrroles with meso electrophiles

Pyrroles can serve as competent nucleophiles with meso electrophiles in the Pd-catalyzed asymmetric allylic alkylation. The products from this transformation were obtained as a single regio- and diastereomer in high yield and enantiopurity. A nitropyrrole-containing nucleoside analogue was synthesized in seven steps to demonstrate the synthetic utility of this transformation.     

Molybdenum-catalyzed reduction of molecular dinitrogen under mild reaction conditions

Quite recently we have found two nitrogen fixation systems catalyzed by molybdenum-dinitrogen complexes under mild reaction conditions; one is the transformation of molecular dinitrogen into its synthetic equivalent of ammonia and the other is that into ammonia. A molybdenum-dinitrogen complex bearing two ferrocenyl diphosphines works as a good catalyst in the transformation of molecular dinitrogen into silylamine, where up to 226 equiv are produced based on the catalyst. A dinitrogen-bridged dimolybdenum complex bearing a PNP-type pincer ligand works as a good catalyst in the direct transformation of molecular dinitrogen into ammonia, where up to 23 equiv are produced based on the catalyst. We believe that both systems provide a new aspect in the development of novel nitrogen fixation.     

Fe(II)-induced transformation from ferrihydrite to lepidocrocite and goethite

The transformation of Fe(II)-adsorbed ferrihydrite was studied. Data tracking the formation of products as a function of pH, temperature and time is presented. The results indicate that trace of Fe(II) adsorbed on ferrihydrite can accelerate its transformation obviously. The products are lepidocrocite and/or goethite and/or hematite, which is different from those without Fe(II). That is, Fe(II) not only accelerates the transformation of ferrihydrite but also leads to the formation of lepidocrocite by a new path. The behavior of Fe(II) is shown in two aspects—catalytic dissolution-reprecipitation and catalytic solid-state transformation. The results indicate that a high temperature and a high pH(in the range from 5 to 9) are favorable to solid-state transformation and the formation of hematite, while a low temperature and a low pH are favorable to dissolution-reprecipitation mechanism and the formation of lepidocrocite. Special attentions were given to the formation mechanism of lepidocrocite and goethite.     

Transient Expression of Minimum Linear Gene Cassettes in Onion Epidermal Cells Via Direct Transformation

A new method without any special devices for direct transformation of linear gene cassettes was developed. Its feasibility was verified through 5′-fluorescent dye (fluorescein isothiocyanate, FITC)-labeled fluorescent tracing and transient expression of a gus reporter gene. Minimal linear gene cassettes, containing necessary regulation elements and a gus reporter gene, was prepared by polymerase chain reaction and dissolved in transformation buffer solution to 100 ng/mL. The basic transformation solution used was Murashige and Skoog basal salt mixture (MS) liquid medium. Hypertonic pretreatment of explants and transformation cofactors, including Ca²⁺, surfactant assistants, Agrobacterium LBA4404 cell culture on transformation efficiency were evaluated. Prior to the incubation of the explants and target linear cassette in each designed transformation solution for 3 h, the onion low epidermal explants were pre-cultured in darkness at 27 °C for 48 h and then transferred to MS solid media for 72 h. FITC-labeled linear DNA was used to trace the delivery of DNA entry into the cell and the nuclei. By GUS staining and flow-cytometry-mediated fluorescent detection, a significant increase of the ratios of fluorescent nuclei as well as expression of the gus reporter gene was observed by each designed transformation solution. This potent and feasible method showed prospective applications in plant transgenic research.     

Optimum heat treatment conditions for masking the bitterness of the clarithromycin wax matrix

The effects of the contents of aminoalkyl methacrylate copolymer E (AMCE) in a wax matrix on the mechanism of polymorphic transformation of glyceryl monostearate (GM) were clarified by evaluating the enthalpy change defined as 1.51 (DeltaH(1)-DeltaH(2))/DeltaH(2), where DeltaH(1) and DeltaH(2) denote the enthalpies in the first and second thermal analyses, respectively. Using this value, K(1), the rate constant of transformation from alpha-form to beta'-form, and K(2), the rate constant of transformation from beta'-form to beta-form, could be obtained. As the ratio of AMCE increased, K(2) increased, but a minimum point existed for K(1). K(1) was always larger than K(2), but gradually approached K(2) as the ratio of AMCE increased. The optimum temperature for the transformation of GM was 50 degrees C, at which the enthalpy change was maximum. To prepare the wax matrix preparation of clarithromycin (CAM), we considered 40 degrees C the optimum treatment temperature for the transformation of GM in a CAM wax matrix compounded from CAM, GM and AMCE, since the matrices were mutually welded at above 45 degrees C during the spray congealing process. Although K(1) and K(2) were almost the same at 40 degrees C, the rate of transformation was accelerated by tumbling. By applying the tumbling that accelerated the transformation of GM in a CAM wax matrix, almost all of the alpha-form disappeared, and the release of CAM from the wax matrix diminished when the enthalpy change was more than 0.8.     

An extraordinary cylinder-to-cylinder transition in the aqueous assemblies of fluorescently labeled rod-coil amphiphiles

We report an unprecedented cylinder-to-cylinder transformation in the self-assemblies of pyrene-labeled rod-coil molecules in water. The extraordinary morphological transformation can be monitored by a fluorescence variation from exciplex to excimer emissions, suggesting the rod-packing transition from antiparallel to interdigitated arrangements as a function of PEO coil length.     

等规聚丙烯β晶型向α晶型的相转变行为研究进展

等规聚丙烯(iPP)是典型的多晶型半结晶性聚合物,其常见晶型有单斜(α),三方(β),三斜(γ)以及四方或双四方(e),其中稳定性最好的α晶型和处于亚稳态的β晶型工业和经济价值较大,因此二者之间的相转变行为得到了人们的广泛关注.本文综述了近年来β→α-iPP生长相转变的研究进展.在高临界温度(141°C)和低临界温度(100°C)区间内,β-iPP生长速率高于α-iPP,而温度高于141°C,或低于100°C,由于α-iPP在动力学上占优势,β-iPP会发生向α-iPP的生长转变.但由于α-iPP是热力学上最稳定的晶型,β-iPP熔融重结晶过程也会发生β→α-iPP相转变.此外,拉伸形变过程中也会发生β→α-iPP相转变,广泛用于制备聚丙烯气体交换膜、过滤膜或锂电池隔膜等.目前对变形过程中的β→α-iPP相转变机理还存在争议,本文也对2种主要的机理进行了介绍,并对聚丙烯晶型转变行为的研究方向进行了展望.     

Samarium(II) iodide reduction of isoxazolidines

SmI₂ was used as reducing agent for the N-O bond cleavage in isoxazolidines. The procedure revealed is general and particularly useful for the transformation of 5-spirocyclopropane isoxazolidines to the corresponding β-aminocyclopropanols, a troublesome transformation with other known reagents.     

Characterization of the thermally induced topochemical solid-state transformation of NH4[N(CN)2] into NCN[double bond]C(NH2)2 by means of X-ray and neutron diffraction as well as Raman and solid-state NMR spectroscopy

The mechanism of the solid-solid transformation of NH(4)[N(CN)(2)] into NCN[double bond]C(NH(2))(2), which represents the isolobal analogue of W?hler's historic conversion of ammonium cyanate into urea, has been investigated by temperature-dependent single-crystal and powder X-ray diffraction, neutron powder diffraction, and Raman and solid-state NMR spectroscopy as well as thermoanalytical measurements. The transformation of the ionic dicyanamide into its molecular isomer upon controlled thermal treatment was found to proceed topochemically in the solid state with little molecular motion, giving rise to a single-crystal to single-crystal transformation which manifests itself by a defined metric relation between the unit cells of the two isomers. The exothermic phase transition is thermally activated and was observed to commence at temperatures > or =80 degrees C. The pronounced temperature dependence of the onset of the transformation may be assessed as an indication for the metastability of ammonium dicyanamide at elevated temperatures. Thermal analyses reveal a decrease in the reaction enthalpy (56-13 kJ mol(-1)) at higher heating rates and an average mass loss of 10% gaseous ammonia. Evidence was found for crucial mechanistic steps of the transformation, which is likely to proceed via proton transfer from the ammonium ion to one of the terminal nitrogen atoms of the anion. The protonation is followed by nucleophilic attack of the in situ generated ammonia at the electrophilic nitrile carbon. The proposed mechanistic pathway is based on the results of combined Raman and solid-state NMR spectroscopic as well as neutron powder diffraction measurements.