Polarization of near-forward-scattered light from particulate substrates illuminated at near-grazing angles

Laboratory photopolarimetric measurements of light scattered by substrates consisting of semitransparent particles with sizes significantly larger than the wavelength show a polarization shoulder at small scattering angles near θ=10-30° in addition to the Brewster maximum positioned near θ=50°. With ray-tracing simulations, we find that the shoulder appears to be related to light passing through particles in the upper layers of the substrates. We study the dependence on particle absorption and packing density of particulate substrates. The studies show that the shoulder weakens with increased absorption and packing density.     

Detection of dust grains vibrations with a laser heterodyne receiver of scattered light

We present the results of measurement of grains vibrations under external action in gas and liquid with a laser heterodyne receiver of scattered radiation. For investigation of dynamic characteristics of particles we made the laser heterodyne receiver with sensitivity about 2×10⁻¹⁷ W/Hz and source of probing with radiation power 1 mW. In our pilot experiments, measurement of vibration amplitude of nanoparticles in gas (cigarette smoke) and microparticles in fluid (toothpaste in water) was made. We measured values of vibration amplitudes about 20–30 nm.     

Discrete dipole approximation simulations of light reflection from flat non-transparent particles with rough surfaces

We study light reflection from flat particles with rough surfaces and fractal statistics of topography. Discrete dipole approximation method is used to solve the problem of light scattering. Refractive indices corresponding to a metal and a transient material with conductive properties are taken. The sizes of particles are much larger than the wavelength of incident light and the roughness scales are larger, comparable to and smaller than the wavelength. The influence of the fractal dimension parameter and the amplitude of heights of random topography on reflectance and on the angular profile of the specular reflection peak is considered. Our calculations demonstrate that topography amplitude is very important for reflectance and fractal dimension is responsible for the angular dispersion of the specular reflection peak.     

Effective dichroism in forward scattering by inhomogeneous birefringent medium

The Mueller matrix model for inhomogeneous medium characterized by simultaneous linear and circular birefringence for single scattering in the forward direction is derived. We find that the presence of inhomogeneity results in the occurrence of new polarization effects. In particular, forward scattering by inhomogeneous birefringent medium exhibits linear and circular dichroism. We show that in the case of weak depolarization (when Cloude's entropy is less than 0.5), the initial parameters for linear and circular birefringence can be obtained from deterministic Mueller matrix associated with the largest eigenvalue of Cloude's coherency matrix. Sample calculations are given for quartz.     

Functional Detergents Containing an Imidazole Ring and Typical Fragments of α-Nucleophiles Underlying Micellar Systems for Cleavage of Esters of Prosphorus Acids

1-Cetyl-3-(2-oximinopropyl)imidazolium, 1-cetyl-3-(2-oxaminoethyl-2-one)imidazolium, and 1-cetyl-3-(2-amino-2-oximinoethyl)imidazolium halides were synthesized.These compounds form in water solutions functional zwitter-ionic micelles as surfactants. The cleavage kinetics of 4-nitrophenyl diethyl phosphate, 4-nitrophenyl ethyl ethylphosphonate, and 4-nitrophenyl tosylate in micelles of the functional detergents and combined micelles of the functional detergents with cetyltrimethylammonium chloride are adequately described in a framework of a simple pseudophase distribution model, and the micellar systems of the detergents are typical -nucleophilic reagents. An equation was suggested for quantitative estimation of the micellar effect of the surfactants that took into account the change in the nucleophilic and basic characteristics of the -nucleophilic center of the detergent and also the influence of the reagents concentrating on transition of the reaction from the water into micelle phase. The maximum acceleration of the S N 2-reaction in the micelles of the functional zwitter-ionic detergents for the cleavage of 4-nitrophenyl diethyl phosphate and 4-nitrophenyl tosylate reached 3500 and 75 000 (oximate surfactant), 3300 and 66 000 (amidoximate surfactant ), and 4800 and 12200 (hydroxamate surfactant) times respectively. New functional detergents underlie unique supernucleophilic micellar system affording extremely high cleavage rates of organophosphorus substrates-ecotoxicants.     

Designing a New Class of Bases for Nucleic Acid Quadruplexes and Quadruplex‐Active Ligands

A new class of quadruplex nucleobases, derived from 3‐deazaguanine, has been designed for various applications as smart quadruplex ligands as well as quadruplex‐based aptamers, receptors, and sensors. An efficient strategy for modifying the guanine quadruplex core has been developed and tested by using quantum chemistry methods. Several potential guanine derivatives modified at the 3‐ or 8‐position or both are analyzed, and the results compared to reference systems containing natural guanine. Analysis of the formation energies (BLYP‐D3(BJ)/def2‐TZVPP level of theory, in combination with the COSMO model for water) in model systems consisting of two and three stacked tetrads with Na⁺/K⁺ ion(s) inside the internal channel indicates that the formation of structures with 3‐halo‐3‐deazaguanine bases leads to a substantial gain in energy, as compared to the corresponding reference guanine complexes. The results cast light on changes in the noncovalent interactions (hydrogen bonding, stacking, and ion coordination) in a quadruplex stem upon modification of the guanine core. In particular, the enhanced stability of the modified quadruplexes was shown to originate mainly from increased π–π stacking. Our study suggests the 3‐halo‐3‐deazaguanine skeleton as a potential building unit for quadruplex systems and smart G‐quadruplex ligands.     

Photochromism in p-methylbenzoylthioacetone and related β-thioxoketones

Irradiation of p-methylbenzoylthioacetone with UV or visible light brings about spectral changes characteristic for the photochromic behavior of β-thioxoketones. The nature of the initial species and of the photochromic product can be assigned based on spectral studies of the electronic and IR spectra in rare gas matrices combined with quantum chemical calculations. Additional arguments for the vibrational assignments are provided by using polarized light to induce the phototransformation, and by subsequent measurements of linear dichroism on partially aligned samples. Comparison with the results previously obtained for three related molecules: thioacetylacetone, p-methyl(thiobenzoyl)acetone, and monothiodibenzoylmethane reveals a common pattern of the photochromic reaction. In all four molecules, the initial species corresponds to an intramolecularly hydrogen-bonded enolic molecular structure, and the main photochromic product to an “open”, nonchelated enethiolic counterpart. On the basis of a computational TD-DFT study of ground and excited electronic states, possible mechanisms of the photochromic transformation are discussed.     

Structure-Morphology-Antimicrobial and Antiviral Activity Relationship in Silver-Containing Nanocomposites Based on Polylactide

Green synthesis of silver-containing nanocomposites based on polylactide (PLA) was carried out in two ways. With the use of green tea extract, Ag⁺ ions were reduced to silver nanoparticles with their subsequent introduction into the PLA (mechanical method) and Ag⁺ ions were reduced in the polymer matrix of PLA-AgPalmitate (PLA-AgPalm) (in situ method). Structure, morphology and thermophysical properties of nanocomposites PLA-Ag were studied by FTIR spectroscopy, wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) methods. The antimicrobial, antiviral, and cytotoxic properties were studied as well. It was found that the mechanical method provides the average size of silver nanoparticles in the PLA of about 16 nm, while in the formation of samples by the in situ method their average size was 3.7 nm. The strong influence of smaller silver nanoparticles (3.7 nm) on the properties of nanocomposites was revealed, as with increasing nanosilver concentration the heat resistance and glass transition temperature of the samples decreases, while the influence of larger particles (16 nm) on these parameters was not detected. It was shown that silver-containing nanocomposites formed in situ demonstrate antimicrobial activity against gram-positive bacterium S. aureus, gram-negative bacteria E. coli, P. aeruginosa, and the fungal pathogen of C. albicans, and the activity of the samples increases with increasing nanoparticle concentration. Silver-containing nanocomposites formed by the mechanical method have not shown antimicrobial activity. The relative antiviral activity of nanocomposites obtained by two methods against influenza A virus, and adenovirus serotype 2 was also revealed. The obtained nanocomposites were not-cytotoxic, and they did not inhibit the viability of MDCK or Hep-2 cell cultures.     

α-Effect of hydroxylamine in the transfer of a toluenesulfonyl group in water—Dimethyl sulfoxide mixtures

A kinetic and thermodynamic analysis of the reactions of hydroxylamine with aryltoluenesulfonates in H₂O-DMSO mixtures (0–90 vol.% DMSO) indicated that the neutral and anionic forms of hydroxylamine are strong α-nucleophiles, and the magnitude of the α-effect shows an asymmetric bell shape depending on the DMSO content. This phenomenon is interpreted. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 83–88, March–April, 1999.     

Potent strategy towards strongly emissive nitroaromatics through a weakly electron-deficient core

Nitroaromatics seldom fluoresce. The importance of electron-deficient (n-type) conjugates, however, has inspired a number of strategies for suppressing the emission-quenching effects of the strongly electron-withdrawing nitro group. Here, we demonstrate how such strategies yield fluorescent nitroaryl derivatives of dipyrrolonaphthyridinedione (DPND). Nitro groups near the DPND core quench its fluorescence. Conversely, nitro groups placed farther from the core allow some of the highest fluorescence quantum yields ever recorded for nitroaromatics. This strategy of preventing the known processes that compete with photoemission, however, leads to the emergence of unprecedented alternative mechanisms for fluorescence quenching, involving transitions to dark nπ* singlet states and aborted photochemistry. Forming nπ* triplet states from ππ* singlets is a classical pathway for fluorescence quenching. In nitro-DPNDs, however, these ππ* and nπ* excited states are both singlets, and they are common for nitroaryl conjugates. Understanding the excited-state dynamics of such nitroaromatics is crucial for designing strongly fluorescent electron-deficient conjugates.

Dipyrrolonaphthyridinedione appended with para- or meta-nitrophenyl substituents exhibits strong fluorescence from a ¹ππ* S₁ state.