Leveling effects of ammonium salts on thermal stabilities of polyethylene glycols.

In this work, the thermal stabilities of a series of polyethylene glycols (PEG 4000, 6000 and 10000) were investigated after compositing with different kinds of inorganic salts, such as ammonium molybdate tetrahydrate (AMT), NH4VO3, (NH4)2SO4, NH4NO3, Na2SO4, Na2MoO4. It was first observed that all the ammonium salts exerted leveling effects for the thermal stabilities of the PEGs. In other words, the presence of the ammonium salts caused the occurrence of the maximum decomposition rates of the PEGs with the same repeat sequence but different chain lengths at almost the same temperatures. Leveling effects were defined by three parameters: leveling spans, leveling degrees and dispersion degrees of leveling. Further experiments revealed that leveling effects also occur in similar types of polymers: polypropylene glycols (PPG 2000, 3000 and 4000). A series of independent experiments including Fourier transformation infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, time-of-flight mass spectrometry, conductivity and field-emission scanning electron microscopy were performed to explore the origin of leveling effects. We consider that the interaction between inorganic ions and polymer molecules and the Hofmeister effect of ions in solution are two important factors affecting the stability of salt­polymer composites, because they can contribute to decrease the interaction between the polymer chains, leading to changes in the conformation and pyrolysis mode of polymers. We believe that the finding of leveling effects would be significant for both basic and applied research of soft matter.

Molecule-ion interaction and its effect on electrostatic interaction in the system of copper chloride and ß-cyclodextrin.

The present work was devoted to an experimental investigation of the molecule-ion interaction between copper chloride (CuCl(2)) and ß-cyclodextrin (CD) and its effect on the electrostatic interaction between Cu(2+) and Cl(-) ions. Our results gave an explicit description of the mutual effect between the interactions. First, the molecular arrangement and surface feature of ß-CD experienced a fundamental structural change after interaction with Cu(2+) and Cl(-) ions, which was ascribed to a good separation of Cu(2+) from Cl(-) ions in ß-CD matrix. Second, arguments based on electronic structural analysis provided a direct indication of the change in charge density distributions of Cu(2+) and Cl(-) ions in the presence of ß-CD. Third, the actual occurrence of a second signal in the course of water release at a higher temperature suggested that the Cu(2+) ions were trapped in the form of hydrates in the crystal interstice of ß-CD molecules. Fourth, comparison of the mass spectra indicated that the thermal decomposition of ß-CD in the presence of CuCl(2) produced a series of interesting molecular ions: C(3)H(2)OH(+), C(4)H(3)OH(+), C(5)H(4)OH(+), and C(7)H(6)OH(+). We consider that this study is helpful in providing a new approach to the evaluation of the extent of the mutual effect between an inorganic salt and an organic molecule.

Modification in structure, phase transition, and magnetic property of metallic gallium driven by atom-molecule interactions.

The present work supports a novel paradigm in which the surface structure and stacking behavior of metallic gallium (Ga) were significantly influenced by the preparation process in the presence of organic small molecules (ethanol, acetone, dichloromethane, and diethyl ether). The extent of the effect strongly depends on the polarity of the molecules. Especially, a series of new atom-molecule aggregates consisting of metallic Ga and macrocyclic hosts (cyclodextrins, CDs) were prepared and characterized by various techniques. A comprehensive comparative analysis between free metallic Ga and the Ga samples obtained provides important and at present rare information on the modification in structure, phase transition, and magnetic property of Ga driven by atom-molecule interactions. First, there is a notable difference in microstructure and electronic structure between the different types of Ga samples. Second, differential scanning calorimetry analysis gives us a complete picture (such as the occurrence of a series of metastable phases of Ga in the presence of CDs) that has allowed us to consider that Ga atoms were protected by the shielding effect provided by the cavities of CDs. Third, the metallic Ga distributed in the aggregates exhibits very interesting magnetic property compared to free metallic Ga, such as the uniform zero-field-cooled and field-cooled magnetization processes, the enhanced responses in magnetization to temperature and applied field, and the fundamental change in shape of magnetic hysteresis loops. These significant changes in structural transformation and physical property of Ga provide a novel insight into the understanding of atom-molecule interactions between metallic atoms and organic molecules.

Molecule-ion interaction and its effect on coordination interaction.

The present work revealed the presence of the molecule-ion interaction between ethylenediaminetetraacetic acid disodium salt (Na(2)H(2)EDTA) and ß-cyclodextrin (CD) on the basis of observable changes in crystal patterns and thermal behaviors before and after interaction. Results from electric conductivity measurements confirmed this presence and showed that the extent of the molecule-ion interaction was associated with the concentration of ß-CD. More importantly, the molecule-ion interaction led to a decreased coordination interaction of Na(2)H(2)EDTA and copper chloride, and this decrease exhibited a concentration dependence of ß-CD. Similar phenomena were also observed in the case of several analogs of Na(2)H(2)EDTA by UV-vis spectroscopy. A possible explanation was proposed on the basis of the hypothesis that there was a competitive relationship between the molecule-ion interaction and the coordination interaction. Further, nuclear magnetic resonance measurements provided important information on the difference in interaction modes of ß-CD with H(2)EDTA(2-) and [Cu(EDTA)](2-). We are of the opinion that the results would provide a significant bridge between coordination chemistry and supramolecular chemistry and help us further understand factors related to different interactions in multicomponent systems.

Thermal decomposition behavior of sodium arsenite in the presence of carbonized beta-cyclodextrin.

The thermal decomposition behavior of sodium arsenite (SA) was greatly affected by carbonized beta-cyclodextrin (CD), possessing the releases of four forms of gaseous arsenic molecules according to gas chromatography coupled to time-of-flight mass spectrometry with programmed temperature operation. Also, the decomposition temperature of beta-CD was lowered in the presence of SA.

Striking structural transformation from cyclic oligosaccharide to aromatic series by means of the effect of lithium carbonate based on gas chromatography coupled to time-of-flight mass spectrometry.

An interesting paradigm in which the conformation of glucopyranose of beta-CD in the presence of Li(2)CO(3) is transformed into both an aromatic structure, such as the heterocyclic compound C(6)H(6)O(+) with a prominent relative abundance (RA) and the tropylium ions C(3)H(3)(+), C(5)H(5)(+), and C(7)H(7)(+) at comparatively low temperatures, and a linear structure such as C(18)H(30)O(+) and C(4)H(10)O(3)(+) is reported in the present work. The efficient transformation (higher RA, lower temperature) from a sugar structure to an aromatic structure is ascribed to the contribution of the molecule-ion interaction between beta-CD and Li(2)CO(3). Such a transformation is significant because it provides new insight into the link between supramolecular chemistry and other fields such as organic synthesis, biomineralization, environmental protection, and energy utilization.

Old drugs, new tricks: the effect of molecule-ion interactions on the precipitation-dissolution equilibrium of lithium carbonate in aqueous solution and on the chiral recognition of cyclodextrins to D-,L-tryptophan.

In the present work, the influence of molecule-ion interactions on the precipitation-dissolution equilibrium of a typical inorganic drug, lithium carbonate (Li2CO3), in water and on the chiral recognition behaviors and binding abilities of alpha-, beta-, gamma-, and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (CD) to D- and L-tryptophan (Trp) was investigated. Our results revealed that the solubility of Li2CO3 was increased to a large extent and the phase solubility diagram of Li2CO3 belonged to the AN type. This finding provided a new insight into the link between molecule-ion interactions and precipitation-dissolution equilibriums of poorly dissolving inorganic salts. Furthermore, despite having a negative effect on the isomer recognition behaviors, the molecule-ion interaction between CDs and Li2CO3 effectively increased the binding abilities of these CDs to both D- and L-Trp synchronously. The observation gave an important implication that buffer solutions consisting of inorganic salts are used with caution in molecular recognition fields between host and guest or between acceptor and donor. Further analyses confirmed the interaction among Li2CO3, beta-CD, and L-Trp using an electrospray ionization mass spectrum.

Synthesis, structure, magnetism and photocatalysis of α-Fe2O3 nanosnowflakes.

In this work, a simple one-step hydrothermal method was developed to synthesize high-quality α-Fe2O3 nanoparticles with a snowflake-like microstructure. First, a series of binary supramolecular aggregates were prepared by a non-covalent combination between a polymer such as polyvinylpyrrolidone (PVP) and a complex such as potassium ferrocyanide (PF). Then, the aggregates were used as the precursors of the one-step hydrothermal reactions. The snowflake-like nanostructure has six-fold symmetry as a whole, and each petal is symmetric. This synthesis method has the characteristics of simplicity, rapidity, reliance, and high yield, and can be used for creating high-quality α-Fe2O3 nanoparticles. Moreover, our results show that the molar ratio of PVP to PF, reaction time and temperature play important roles in the generation of a complete snowflake structure from different angles. Also, the snowflake-like α-Fe2O3 nanostructure exhibits a much higher coercivity (2997 Oe) compared to those reported by others, suggesting a strong hysteresis behaviour, which promises potential applications in memory devices, and other fields. Further, the α-Fe2O3 nanosnowflakes show a much higher photocatalytic degradation activity for cationic organic dyes such as crystal violet, rhodamine 6G than for anionic dyes such as methyl orange. A possible photocatalytic mechanism was proposed for explaining the selectivity of the photocatalytic oxidation reaction of organic dyes. We believe that this study provides a direct link among coordination compounds of transition metals, their supramolecular aggregates with polymers, and controlled hydrothermal synthesis of high-quality inorganic metal oxide nanomaterials.

A comparative study on the binding behaviors of beta-cyclodextrin and its two derivatives to four fanlike organic guests.

Four fanlike organic compounds, 1-ethoxybenzene (EOB), 1-butoxybenzene (BOB), 1-dodecyloxybenzene (DOB), and 1-(dodecyloxy)-2-methoxybenzene (DOMB), were chosen as guests, and beta-cyclodextrin (beta-CD) and its two derivatives, mono(2-O-2-methyl)-beta-CD and mono(2-O-2-hydroxy-propyl)-beta-CD, were chosen as hosts. Energy changes involved in host-guest inclusion processes were clearly obtained by applying semiempirical PM3 calculations. According to this, probable structures of the host-guest inclusion complexes were proposed. The inclusion systems in aqueous solution were investigated by UV-vis spectroscopy and nuclear magnetic resonance ((1)H NMR) titration, and the formation constants (K) of the inclusion complexes were determined using the Benesi-Hildebrand equation. Moreover, two solid inclusion complexes of beta-CD with EOB and DOB were prepared and characterized by Fourier transform infrared spectra, X-ray powder diffraction, (1)H NMR, electrospray ionization mass spectrometry, and thermogravimetric analyses. Results showed that the host-guest stoichiometries in the inclusion complexes were all 1:1 both in solid state and in aqueous solution. As for the same host, the values of K increased in the order EOB < BOB < DOB, in strong association with the fan handle in the fanlike molecules; that is to say, the K values increased with increasing carbon chain length of substituent on benzene ring. In addition, the K values of DOMB complexes were larger than those of DOB complexes for the same CD, indicating that the introduction of an extra o-methoxyl group on DOB further stabilized the CD inclusion complexes. The decomposition activation energies of EOB-beta-CD and DOB-beta-CD were very similar but significantly larger than that of free beta-CD.

A comparative study on the thermal decomposition behaviors between beta-cyclodextrin and its inclusion complexes of organic amines.

How does a complexed organic guest change its thermal stability during the heating process? How does the guest release influence the decomposition behavior of the complexed host? To answer these questions, in-situ Fourier transform infrared spectroscopy and gas chromatography coupled to time-of-flight mass spectrometry with programmed temperature were employed in the present work. The careful comparisons among the thermal decomposition behaviors of free beta-cyclodextrin (beta-CD) and its inclusion complexes of ethylenediamine and diethylenetriamine indicated that the release of the amines was not a simple physical process without the rupture of chemical bonds but was instead a complex process together with the fragments from complexed beta-CD. In short, the release and decomposition of the complexed amines drove the decomposition of the complexed beta-CD in their respective inclusion complexes. It was found that the thermal decomposition behavior of the complexed beta-CD was influenced by the complexed amines dependent on the nature of the amines, and at the same time, beta-CD had, to a certain extent, changed the temperature of the phase-change, release, and decomposition of organic amines by the formation of inclusion complexes with them.

Facile one-pot synthesis of highly monodisperse nickel microspheres with raised nickel dots and their adsorption performance for heavy metal ions.

This report describes the facile solvothermal synthesis of highly monodispersed nickel microspheres with surfaces uniformly covered by nickel dots. Synthesis parameters including reaction times and reagent concentrations significantly influence the microspheric particle characteristics. The novelty of the synthetic method in this work is twofold: first, the controlled synthesis of Ni metallic microspheres using ethylene glycol as the precursor of a reductant and urea as the origin of OH(-) has never been reported. Second, there are few studies on the construction of Ni microspheres covered by uniform Ni dots using a one-step solvothermal method. Importantly, the as-prepared Ni microspheres show an improved ability to remove Cd(2+) ions even at high concentrations in water and a unique adsorption isotherm having an increasing adsorption capacity for Cd(2+) ions. The presence of Ni dots was considered to play an important role in the onset of the adsorption process. We believe that this work opens up new and possibly exciting opportunities in the field of adsorption of heavy metal ions.

Construction of Cu3Mo2O9 nanoplates with excellent lithium storage properties based on a pH-dependent dimensional change.

One-, two- and three-dimensional nanostructures of copper molybdenum oxide hydroxide were successfully constructed by a simple approach through a pH-dependent dimensional transformation of ammonium copper molybdate. Thin nanoplates of copper molybdate, which were obtained by sintering the two-dimensional nanobelts of copper molybdenum oxide hydroxide, exhibited remarkably high reversible lithium storage capacity, good rate capability and excellent cycling stability.

Self-assembled metastable γ-Ga2O3 nanoflowers with hexagonal nanopetals for solar-blind photodetection.

Metastable γ-Ga2O3 nanoflowers assembled from hexagonal nanopetals are successfully constructed by the oxidation of metallic Ga in acetone solution. The nanoflowers with a hollow interior structure exhibit a short response time and a large light-current-dark-current ratio under a relatively low bias voltage, suggesting an especially important potential application in solar-blind photodetection.

Low-temperature carbonization and more effective degradation of carbohydrates induced by ferric trichloride.

The present work is devoted to an attempt to understand the effect of an inorganic salt such as ferric trichloride (FeCl(3)) on the carbonization and degradation of carbohydrates such as ß-cyclodextrin (CD), amylose, and cellulose. Our data revealed two important observations. First, the presence of FeCl(3) led to the occurrence of a low carbonization temperature of 373 K. This is a rare phenomenon, in which carbonization improvement is present even if a small amount of FeCl(3) was added. Experimental results had provided evidence for the fact that a redox process was started during the low-temperature carbonization of ß-CD, causing the reduction of FeCl(3) to ferrous chloride (FeCl(2)) by carbon materials formed in the carbonization process in air. However, the reduction process of FeCl(3) produced the in situ composite nanomaterial of Fe-FeCl(2) combination in nitrogen. Second, a molecule-ion interaction emerged between FeCl(3) and the carbohydrates in aqueous solution, resulting in a more effective degradation of the carbohydrates. Moreover, our results demonstrated that FeCl(3) played the role of a catalyst during the degradation of the carbohydrates in solution. We believe that the current work not only has a significant potential application in disposal of waste carbohydrates but also could be helpful in many fields such as environmental protection, biomass energy development, and inorganic composite nanomaterials.

A controllable transformation in copper valence states and its applications.

The present study revealed a surprising valence transformation of copper (Cu) in the sintering process of mixtures of copper chloride dihydrate (CuCl(2)·2H(2)O) with ß-cyclodextrin (ß-CD) in ambient atmosphere. Such a transformation in Cu valence states can be modulated by changing the initial molar ratio (IMR) of CuCl(2)·2H(2)O to ß-CD in the mixtures. Firstly, as the value of IMR decreased, the content of cuprous chloride (CuCl) decreased, while the content of cupric oxide (CuO) increased gradually. That is to say, there is an unambiguous IMR-dependence of the contents of CuCl and CuO formed. However, such a controllable valence transformation from Cu(II) to Cu(I) to Cu(II) did not happen in nitrogen atmosphere. Secondly, the in situ composite of CuCl and CuO produced a highly ordered structure of self-assembled nanowires, intertwined, with a diameter of 30 to 50 nm. Furthermore, electronic structural analysis provided direct evidence that the Cu-Cl and Cu-O bonds in this composite material were simultaneously impaired by self-assembled growth. Finally, we noticed that the photoluminescence property of CuCl was regulated through the formation of composites with CuO. In addition, this in situ composite synthesis technique was used to modify the magnetic property of CuO. Furthermore, the anomalous ferromagnetic behaviour of the CuO nanocrystal was observed and explained. In short, this work not only demonstrates a flexible and easily controllable valence transformation of Cu, but also provides a novel approach for constructing inorganic nanocomposite materials. We believe that the implications of these findings are important and make significant contributions to the development of inorganic chemistry and material science.

The physical properties and unusual pyrolysis behaviour of a supramolecular complex of ß-cyclodextrin and potassium ferrioxalate.

The thermal pyrolysis behaviour of a complex of ß-cyclodextrin (CD) and potassium ferrioxalate (PF) was analyzed using gas chromatography coupled to time-of-flight mass spectrometry. Two rare inorganic ions: CO(2)(2+) and O(4)(+), neither of which was found in the cases of free ß-CD and PF, were synchronously observed during the decomposition of the complex. Our observations led to proposed formation mechanisms of the ions, in which the structural transformation of a metastable intermediate ion (C(2)H(4)O(3)(+)) was employed to qualitatively explain our data. Besides this, the formation, structure and magnetic properties of the complex were evaluated carefully. First, XPS analysis indicates a decrease of electron densities of Fe(III) ions in the presence of ß-CD. We think that this is due to an effect of the noncovalent complexation between PF and ß-CD. This gives an indication on the effect of second sphere coordination of ß-CD on the electronic structure of the Fe(III) in the first coordination sphere. Second, structural changes in stacking modes and morphologies provide further support for the noncovalent complexation. For example, the surface feature of the complex gives us an impression that both ß-CD and PF are evenly dispersed with each other. Also, the complex presents a uniform sponge-like porous nanostructure with diameters of less than 50 nm. This seems to be an important reason for those changes that occurred in the thermal analysis. Finally, the result of magnetic experiments implies that the coordination compound PF upon complexation with ß-CD will experience a gradual decrease in magnetization with the increase of magnetic fields. These observations have significant implications for a better understanding of the importance of the construction and deconstruction of a second sphere coordination in modifying the physical properties of an σ-coordination compound.

Important effects of lithium carbonate on stoichiometry and property of the inclusion complexes of polypropylene glycol and ß-cyclodextrin.

The present work reveals a significant influence of lithium carbonate (Li(2)CO(3)) on stoichiometry, yield, spectral property, and thermal behavior of the inclusion complex formed by polypropylene glycol (PPG) and ß-cyclodextrin (CD). First, the presence of Li(2)CO(3) in aqueous solution leads to the formation of an inclusion complex PPG-(ß-CD)(6), which is completely different from that precipitated from pure water. This finding is supported by the result of a similar experiment in the case of lithium chloride, demonstrating that the self-assembling behavior of PPG, a flexible oligomer, and ß-CD, a rigid oligomer, in solution can be mediated by additions of the lithium salts. Second, powder X-ray diffraction patterns indicate that the lithium salts in solution play a considerable role in fabricating three-dimensional structures of the complex. Third, the difference in stoichiometry and microstructure of the complexes precipitated from different media is reflected by the difference of their thermal properties. Finally, the results of viscosity, surface tension, and conductivity measurements provide positive support on the effect of the lithium salts on the physical property of PPG solution. Taken together, these observations provide a novel framework for understanding functions of inorganic salts in designing and constructing supramolecules.

Noncovalent interaction of polyethylene glycol with copper complex of ethylenediaminetetraacetic acid and its application in constructing inorganic nanomaterials.

In this study, we try to answer a fundamental question: what is the consequence of the noncovalent interaction between a polymer and a coordination compound? Here, polyethylene glycol (PEG-4000, PEG-b) and copper complex of ethylenediaminetetraacetic acid (H(2)CuY) were employed to solve this problem. A novel adduct (CEP) between H(2)CuY and PEG-b was prepared. Our results indicated several interesting findings. First, the introduction of H(2)CuY had no effect on the stacking structure of PEG-b but led to a large change in surface structure of the polymer. Second, there was a significant difference (117 K) in the maximum degradation temperature between the PEG and the CEP, suggesting that the noncovalent interaction can drastically improve the thermal stability of the PEG. Third, sintering experiments showed that H(2)CuY and CEP produced completely different decomposition products. The former formed Cu crystals in nitrogen and CuO in air, but the latter generated Cu and CuCl crystals with good crystallinity, respectively. Finally, three independent measurements: viscosity, conductivity and nuclear magnetic resonance in solution, provided useful information and insights from both sides of the noncovalent interaction. Probable interaction mechanisms and interaction sites were proposed. We consider that the current research could create the foundation for a new understanding of how the noncovalent adduct interaction between a metallic complex and a polymer relates to the change in physical and chemical properties of the adducted components.

Formation, characterization, and thermal degradation behavior of a novel tricomponent aggregate of beta-cyclodextrin, ferrocene, and polypropylene glycol.

A tricomponent aggregate PPG-Fc-beta-CD formed by polypropylene glycol (PPG), ferrocene (Fc), and beta-cyclodextrin (beta-CD) was obtained and characterized by a series of physical methods, such as (1)H nuclear magnetic resonance, flame atomic absorption spectrometry, high performance liquid chromatography, UV-vis absorption spectroscopy, thermogravimetry, and gas chromatography coupled to time-of-flight mass spectrometry. First, the tricomponent aggregate exhibited a component ratio of 1:28:32 (PPG/Fc/beta-CD) in the solid state, and showed a completely different order in thermal stability when compared with beta-CD: under a nitrogen atmosphere, beta-CD > PPG-Fc-beta-CD, and in a vacuum, PPG-Fc-beta-CD > beta-CD. Second, the appearance of two peculiar points p and q at the end of TG curve of the aggregate gave a strong impression that the degradation rate further increased after the sharp decomposition of the aggregate reached point p and the amount present in the residual fraction at point q about 780.0 K was lower than 1%, both of which were rather different from those reported previously. This finding implied that the molecular assembly resulting from the binding interaction among Fc, PPG, and beta-CD induced more efficiently the degradation of each of them. Third, an interesting phenomenon was found that the order of thermal release of the three assembled components in PPG-Fc-beta-CD was Fc > beta-CD > PPG. Results of this study provide some insight into an initial attempt to construct a supramolecule among a polymer, a coordination compound, and an organic compound.

Meaningful differences in spectral performance, thermal behavior, and heterogeneous catalysis between ammonium molybdate tetrahydrate and its adduct of beta-cyclodextrin.

A novel molecule-ion adduct of ammonium molybdate tetrahydrate (AMT) with beta-cyclodextrin (CD) was prepared in this work. Significant differences in spectral properties between AMT and the adduct AMT-beta-CD were observed by a series of experimental probes, such as powder X-ray diffraction, Fourier transformation infrared spectroscopy, and Raman spectroscopy. Field emission scanning electron microscopy showed that, although the crystal growth of AMT-beta-CD was dominated by the molecular stacking of AMT, the size and morphology of the adduct were rather different from those seen in free AMT. The difference in stacking forms was attributed to the contribution of the molecule-ion interaction between AMT and beta-CD. A drastic improvement in thermal stability of AMT and beta-CD after adduct formation was observed by thermogravimetry analysis, which was confirmed by controlled sintering measurements. This revealed that the adduct interaction between them played an important role in mediating the thermal decomposition process of the adducted components. Furthermore, our results indicated that AMT and its adduct had a different performance in the catalytic desulfurization of thiophene and its derivatives. The fact that the catalytic efficiency of AMT was decreased after adduct formation implied there was a complexation between AMT and beta-CD. Besides, several unusual molecular ions--NH(3)(+), NH(2)(+), and NH(+)--were simultaneously found with gas chromatography coupled to time-of-flight mass spectrometry of free AMT.