A review on the synthesis of TiO<Subscript>2</Subscript> nanoparticles by solution route

TiO₂ can be prepared in the form of powder, crystals, or thin films. Liquid-phase processing is one of the most convenient and utilized methods of synthesis. It has the advantage of allowing control over the stoichiometry, production of homogeneous materials, formation of complex shapes, and preparation of composite materials. However, there may be some disadvantages such as expensive precursors, long processing times, and the presence of carbon as an impurity. In comparison, the physical production techniques, although environment friendly, are limited by the size of the produced samples which is not sufficient for a large-scale production. The most commonly used solution routes in the synthesis of TiO₂ are reviewed.     

Magnetic field dependence of photo-CIDNP MAS NMR on photosynthetic reaction centers of Rhodobacter sphaeroides WT

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is observed in frozen and quinone depleted photosynthetic reaction centers of the purple bacteria Rhodobacter sphaeroides wild type (WT) by (13)C solid-state NMR at three different magnetic fields. All light-induced signals appear to be emissive at all three fields. At 4.7 T (200 MHz proton frequency), the strongest enhancement of NMR signals is observed, which is more than 10 000 above the Boltzmann polarization. At higher fields, the enhancement factor decreases. At 17.6 T, the enhancement factor is about 60. The field dependence of the enhancement appears to be the same for all nuclei. The observed field dependence is in line with simulations that assume two competing mechanisms of polarization transfer from electrons to nuclei, three-spin mixing (TSM) and differential decay (DD). These simulations indicate a ratio of the electron spin density on the special pair cofactors is 3:2 in favor of the L-BChl during the radical cation state. The good agreement of simulations with the experiments raises expectations that artificial solid reaction centers can be tuned to show photo-CIDNP in the near future.     

Dissociation constants of some derivatives of 5-amino isophthalic acid in mixed solvents

The dissociation constants of some derivatives of 5-amino isophthalic acid have been measured by Calvin Bjerrum pH titration method in DMF-water and DMSO-water (60: 40 v/v) systems at 308.15 K. It is observed that dissociation constant depends on the solvent and substituents group present in the compound.     

Dynamic internal cavities of dendrimers as constrained media. A study of photochemical isomerizations of stilbene and azobenzene using poly(alkyl aryl ether) dendrimers

Dendritic microenvironments defined by dynamic internal cavities of a dendrimer were probed through geometric isomerization of stilbene and azobenzene. A third-generation poly(alkyl aryl ether) dendrimer with hydrophilic exterior and hydrophobic interior was used as a reaction cavity in aqueous medium. The dynamic inner cavity sizes were varied by utilizing alkyl linkers that connect the branch junctures from ethyl to n-pentyl moiety (C(2)G3-C(5)G3). Dendrimers constituted with n-pentyl linker were found to afford higher solubilities of stilbene and azobenzene. Direct irradiation of trans-stilbene showed that C(5)G3 and C(4)G3 dendrimers afforded considerable phenanthrene formation, in addition to cis-stilbene, whereas C(3)G3 and C(2)G3 gave only cis-stilbene. An electron-transfer sensitized trans-cis isomerization, using cresyl violet perchlorate as the sensitizer, also led to similar results. Thermal isomerization of cis-azobenzene to trans-azobenzene within dendritic microenvironments revealed that the activation energy of the cis- to trans-isomer was increasing in the series C(5)G3 < C(4)G3 相似文献   

Experimental Determination of a Third Derivative of G. (III): Differential Pressure Perturbation Calorimetry (II)

Earlier we constructed a differential pressure perturbation calorimeter, in order to determine directly a third derivative of the Gibbs energy G, the partial molar entropy-volume cross fluctuation density of solute B, ^SVd_[(B)dot]^{mathit{SV}}delta_{dot{mathrm{B}}}, in a binary aqueous solution of B. Our attempt was basically successful, as described elsewhere (J. Solution Chem. 39:431–440, 2010). However, the uncertainty of the results for ^SV δ _B was several percent. One of the purposes of our direct experimental determination was to obtain a fourth derivative quantity graphically with some confidence. For this purpose, data of the third derivative quantity are necessary with uncertainties of less than one per cent. Various difficulties that we had on the first generation apparatus were attended to, and a new apparatus was constructed. The new experimental results for aqueous 2-butoxyethanol are found to be at least several-fold better. Hence, we were able to evaluate the fourth derivative quantity for the first time. The physical meaning of the fourth derivatives may become clearer in comparative studies when such data become available for aqueous solutions of other solutes including mono-ols and poly-ols. A project is underway to that effect.     

A thermal study of some Schiff bases derivative of α-napthylamine

Thermal analyses of some Schiff bases, derivative of α-napthylamine, were performed by the DSC, TG and DTA techniques. The thermograms were used to determine various kinetic parameters, such as the order of degradation (n), energy of activation (E), frequency factor (A), and entropy change (ΔS), by the Freeman-Carroll method. The text was submitted by the authors in English.     

Kinetics and Mechanism of the Oxidation of Some Aldoses by Cerium(IV)

Abstract

The kinetics of oxidation of some aldoses by cerium(IV) have been studied spectrophotometrically in sulphuric acid medium. The reactions are second order; first order with respect to both cerium(IV) and aldose concentration. The reaction rate decreases with increase in sulphuric acid concentration. The mechanisms for the reactions are discussed.     

The Effect of N-methylation on Photophysical Properties of 3-Aminoquinoline

It has been reported previously that the photophysics of 3-aminoquinoline (3AQ) is governed by a flip–flop motion of its amino group in apolar solvents and intersystem crossing in polar solvents. The nonradiative rates are governed by more than one solvent parameters, like polarity and hydrogen bonding ability of the solvent. So, 3AQ is not a well-behaved probe of any individual solvent parameter. In the present work, 3AQ has been modified synthetically; replacing an amino hydrogen atom with a methyl group and photophysical properties were studied in 22 different apolar, polar-aprotic and polar-protic solvents. It is found that Stokes’ shifts and fluorescence quantum yields exceptionally low in apolar solvents as compared to those in other solvents. Such substitution causes a decrease in the extent of the effect of the hydrogen bonding ability of the solvent and that nonradiative rate become a more regular function of polarity. However, the flip–flop appears to continue to be the major nonradiative pathway, as the nonradiative rates decrease with increase in micropolarity.     

A review on stabilization of carbon nanotube nanofluid

Journal of Thermal Analysis and Calorimetry - CNT nanoparticles have high tensile strength, excellent thermal transfer properties, and optimal chemical and physical stability. The lack of CNT...     

Electron spin density distribution in the special pair triplet of Rhodobacter sphaeroides R26 revealed by magnetic field dependence of the solid-state photo-CIDNP effect

Photo-CIDNP (photochemically induced dynamic nuclear polarization) can be observed in frozen and quinone-blocked photosynthetic reaction centers (RCs) as modification of magic-angle spinning (MAS) NMR signal intensity under illumination. Studying the carotenoidless mutant strain R26 of Rhodobacter sphaeroides, we demonstrate by experiment and theory that contributions to the nuclear spin polarization from the three-spin mixing and differential decay mechanism can be separated from polarization generated by the radical pair mechanism, which is partially maintained due to differential relaxation (DR) in the singlet and triplet branch. At a magnetic field of 1.4 T, the latter contribution leads to dramatic signal enhancement of about 80,000 and dominates over the two other mechanisms. The DR mechanism encodes information on the spin density distribution in the donor triplet state. Relative peak intensities in the photo-CIDNP spectra provide a critical test for triplet spin densities computed for different model chemistries and conformations. The unpaired electrons are distributed almost evenly over the two moieties of the special pair of bacteriochlorophylls, with only slight excess in the L branch.