Pyrazole‐substituted Near‐infrared Cyanine Dyes Exhibit pH‐dependent Fluorescence Lifetime Properties

Near‐infrared heptamethine cyanine dye is functionalized with pyrazole derivatives at the meso‐position to induce pH‐dependent photophysical properties. The presence of pyrazole unsubstituted at ¹N‐position is essential to induce pH‐dependent fluorescence intensity and lifetime changes in these dyes. Replacement of meso‐chloro group of cyanine dye IR820 with ¹N‐unsubstituted pyrazole resulted in the pH‐dependent fluorescence lifetime changes from 0.93 ns in neutral media to 1.27 ns in acidic media in DMSO. Time‐resolved emission spectra (TRES) revealed that at lower pH, the pyrazole consists of fluorophores with two distinct lifetimes, which cor‐responds to pH‐sensitive and non‐pH‐sensitive species. In contrast, ¹N‐substituted pyrazoles do not exhibit pH response, suggesting excited state electron transfer as the mechanism of pH‐dependent fluorescence lifetime sensitivity for this class of compounds.     

Experimental shift allowance in the deconvolution of SIMS depth profiles

We study the deconvolution of the secondary ion mass spectrometry (SIMS) depth profiles of silicon and gallium arsenide structures with doped thin layers. Special attention is paid to allowance for the instrumental shift of experimental SIMS depth profiles. This effect is taken into account by using Hofmann's mixing‐roughness‐information depth model to determine the depth resolution function. The ill‐posed inverse problem is solved in the Fourier space using the Tikhonov regularization method. The proposed deconvolution algorithm has been tested on various simulated and real structures. It is shown that the algorithm can improve the SIMS depth profiling relevancy and depth resolution. The implemented shift allowance method avoids significant systematic errors of determination of the near‐surface delta‐doped layer position. Copyright © 2013 John Wiley & Sons, Ltd.     

Model‐independent structure and resonant X‐ray spectra of intermediate smectic phases

It is shown that the orientational structure of intermediate smectic phases can be determined using the symmetry properties of the general free energy with arbitrary orientational coupling between smectic layers, without addressing a particular model. The structure of three‐ and four‐layer intermediate phases, obtained in this way, corresponds to experimental data. The same method enables one to predict the structure of intermediate phases with periodicity of five and six layers, which have not been observed experimentally so far. The resonant X‐ray spectra of the five‐ and six‐layer intermediate phases with predicted structure have also been calculated. These spectra are characterized by a number of features which enable one to distinguish five‐layer and six‐layer intermediate phases from phases with smaller periods.     

Influence of chirality on the mesophase of side chain polymers with phenyl benzoate pendant groups

To reveal the structure of an amorphous mesophase with a hidden liquid crystalline structure (ISm*) in a chiral side chain polymer, P8*M, its racemic isomer has been synthesized along with two more RS‐copolymers with controlled enantiomer excess. The phase behaviour of the copolymers was studied comparatively by DSC and X‐ray scattering. Optical rotatory dichroism was measured for thin films of P8*M and two homologue polymers, differing in the polymeric main chain, by the size of the chiral terminal group and by its absolute configuration. A helical superstructure with pitch of about 250?nm is indicated within the ISm* mesophase. Its structure as a short pitch TGB phase hase been proven conclusively.     

A sensitive chromatographic determination of hydrazines by naphthalene-2,3-dialdehyde derivatization

A new high-performance liquid chromatography (HPLC) method for the sensitive simultaneous determination of hydrazine (Hy), monomethylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) based upon the derivatization of hydrazines with naphthalene-2,3-dialdehyde and the separation of the derivatives on Zorbax Eclipse AAA column in a single chromatographic run under acidic conditions (pH 2.4) was developed. Hydrazine and monomethylhydrazine derivatives were found to be strongly fluorescent at λ_ex?=?273?nm, λ_em?=?500?nm. It was shown that UDMH derivative can be detected as non-fluorescent hydrazone at 290?nm by UV-detection. Limits of detection were 0.05?µg?·?L^?1 for Hy and MMH, and 1?µg?·?L^?1 for UDMH for the injection volume of 100?µL. The method was validated for water sample analysis. It proved to be selective, accurate and precise with the supplementary advantage of the simple and rapid sample preparation.     

The effect of organic sorbates on water associated with environmentally important sorbents: estimating and the LFER analysis

The effect of organic sorbates on the water associated with naturally occurring sorbents is of significant interest since it probes the hydration of a sorbate-specific microenvironment and its role in a compound partitioning between various environmental compartments. This effect was described in a thermodynamically strict way by converting the sorption isotherms of organic vapors on variously hydrated sorbents into the derivatives relating the change in the amount of water associated with a sorbent to the change in the amount of an organic sorbate. Further, these derivatives were analyzed by means of the Linear Free Energy Relationship (LFER). The analysis included the sorption data for various organic vapors on such environmentally important sorbents as quartz, metal oxides, calcite, clay minerals and humic acid. From the LFER analysis it followed that (i) organic sorbate polarizability contributions from n- and π-electrons resulted in driving water into the sorbent phase; (ii) the increasing volume of the organic compounds involved expelling water molecules; (iii) the increasing hydrogen-bond acidity and basicity of organic sorbates resulted in expelling water from inorganic surfaces but in enhancing hydration of the humic phase. In contrast to inorganic surfaces, when sorbed on strongly hydrated humic acid, the majority of organic sorbates containing oxygen, nitrogen or sulfur atoms drive water into the sorbent phase. Several molecules of water may need to be cosorbed by a humic sorbent for each sorbed molecule of an organic compound thus supporting the possibility of the concomitant participation of a number of water molecules in organic sorbate–humic matter interactions.     

Transition Metal Complexes of a Salen–Fullerene Diad: Redox and Catalytically Active Nanostructures for Delivery of Metals in Nanotubes

A covalently‐linked salen–C₆₀ (H₂L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C₆₀ cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen–C₆₀ introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal–salen–C₆₀ complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene‐containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single‐, double‐ and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen–C₆₀ complexes in heterogeneous catalysis.     

Estimation Problems for Periodically Correlated Isotropic Random Fields

Spectral theory of isotropic random fields in Euclidean space developed by M. I. Yadrenko is exploited to find a solution to the problem of optimal linear estimation of the functional

$$ A\zeta ={\sum\limits_{t=0}^{\infty}}\,\,\,{\int_{S_n}} \,\,a(t,x)\zeta (t,x)\,m_n(dx) $$

which depends on unknown values of a periodically correlated (cyclostationary with period T) with respect to time isotropic on the sphere S _n in Euclidean space E ⁿ random field ζ(t, x), t?∈?Z, x?∈?S _n . Estimates are based on observations of the field ζ(t, x)?+?θ(t, x) at points (t, x), t?=???1,???2, ..., x?∈?S _n , where θ(t, x) is an uncorrelated with ζ(t, x) periodically correlated with respect to time isotropic on the sphere S _n random field. Formulas for computing the value of the mean-square error and the spectral characteristic of the optimal linear estimate of the functional Aζ are obtained. The least favourable spectral densities and the minimax (robust) spectral characteristics of the optimal estimates of the functional Aζ are determined for some special classes of spectral densities.