Experimental and theoretical spectral properties of ethyl 2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetate doped sol-gel materials: new materials with potential optical application

Silica xerogels and monoliths, containing ethyl 2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetate (K4) or Sm^{3 +} ions and K4 are prepared by sol-gel technique. NMR investigations, UV/Vis, IR- and luminescence spectral properties of K4 in solution and in monoliths are presented. The IR-spectroscopic properties of the prepared sol-gel materials are examined by applying the reduced-difference procedure to non-polarized IR-spectra. The results show that the sol-gel medium did not interact with K4 as well as in the presence of Sm³⁺ ions the K4 form a [Sm(L)₂(H₂O)₄] × (NO₃)₃ complex in the matrix. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mercury binding sites in thiol-functionalized mesostructured silica

Thiol-functionalized mesostructured silica with anhydrous compositions of (SiO(2))(1)(-)(x)()(LSiO(1.5))(x)(), where L is a mercaptopropyl group and x is the fraction of functionalized framework silicon centers, are effective trapping agents for the removal of mercuric(II) ions from water. In the present work, we investigate the mercury-binding mechanism for representative thiol-functionalized mesostructures by atomic pair distribution function (PDF) analysis of synchrotron X-ray powder diffraction data and by Raman spectroscopy. The mesostructures with wormhole framework structures and compositions corresponding to x = 0.30 and 0.50 were prepared by direct assembly methods in the presence of a structure-directing amine porogen. PDF analyses of five mercury-loaded compositions with Hg/S ratios of 0.50-1.30 provided evidence for the bridging of thiolate sulfur atoms to two metal ion centers and the formation of chain structures on the pore surfaces. We find no evidence for Hg-O bonds and can rule out oxygen coordination of the mercury at greater than the 10% level. The relative intensities of the PDF peaks corresponding to Hg-S and Hg-Hg atomic pairs indicate that the mercury centers cluster on the functionalized surfaces by virtue of thiolate bridging, regardless of the overall mercury loading. However, the Raman results indicate that the complexation of mercury centers by thiolate depends on the mercury loading. At low mercury loadings (Hg/S < or = 0.5), the dominant species is an electrically neutral complex in which mercury most likely is tetrahedrally coordinated to bridging thiolate ligands, as in Hg(SBu(t))(2). At higher loadings (Hg/S 1.0-1.3), mercury complex cations predominate, as evidenced by the presence of charge-balancing anions (nitrate) on the surface. This cationic form of bound mercury is assigned a linear coordination to two bridging thiolate ligands.     

Studies on the uncertainties in quantitative EPR estimations due to the construction of the cavities used

The magnitude of the continuous wave electron paramagnetic resonance (CW-EPR) response of a given sample is governed by several cavity parameters. Two of them are the distribution of the modulation magnetic flux density and the microwave magnetic component over the sample length. Their mutual configuration could have a significant influence on quantitative EPR estimations. In the present paper, we report the results obtained with 14 different cavities of TE₁₀₂, TE₁₀₄, TM₁₁₀ and TM₀₁₁ modes commercially available and used in many EPR laboratories with respect to the magnitude of their EPR response as a function of the sample length. The results show that due to their technical construction the widely used cavities in CW-EPR spectroscopy could be classified into three types in which: (i) the distribution of the microwave magnetic component in the cavity coincides with the modulation magnetic flux; (ii) the modulation magnetic flux is wider than the microwave magnetic component in the cavity. In this type, the magnitude of the EPR response along the sample length is governed only by the distribution of the microwave magnetic component in the cavity, (iii) the modulation magnetic flux is narrower than to the microwave magnetic component in the cavity. In the cavities of this type, the magnitude of the EPR response is governed by the distribution of the modulation magnetic flux. Whereas, in both former types, the EPR response corresponds to the full length of the sample along the z-axis of the cavity, an EPR silent zone appears in the latter type. In some of them this zone takes ca. 40% of their full length. Therefore, the assumption that the EPR active zone corresponds to the full cavity length (along the sample axis) is not valid for the latter type cavities. Their use will give 2-3% error within a series of samples, but the results will be burdened by a systematic error and could not be compared with the data obtained with another cavity even on the same spectrometer. In view of this, we should be familiar with the features of every cavity before using it for quantitative EPR estimations. Two ways are recommended to overcome the effect of EPR silent zones of an unknown cavity in order to get comparable results in quantitative EPR estimations: (i) to use samples of less than 5-6 mm length, symmetrically situated with respect to the cavity center in consecutive procedures of estimations independently of the cavity type, (ii) in the cases of simultaneous recording of unknown sample and a standard they both should be homogeneously mixed or coaxially situated along their full length.     

Tautomerism of rhodanine

Semiempirical (MINDO/3, AM1, PM3, MNDO) and ab initio (4-31G and 4-3IG + dAO/S basis sets) calculations on the relative stabilities and structures of the five potential tautomeric forms of rhodanine are reported. It is shown that all methods (excepting PM3) predict as most stable 2-thioxo-4-thiazolidinone. These results correspond to the known experimental data. The infrared spectrum of rhodanine was recorded for the region 4000-150 cm^–1, and the characteristic bands were compared with AM1 and 4-31G + dAO/S calculated frequencies. The transition states between five pairs of all possible tautomeric forms of the rhodanine were found by the AM1 method.     

Photochemical dehydrogenation of 3-acetyl-3,4-dihydrocoumarin

Summary The ultraviolet irradiation of air-saturated alcoholic solutions of 3-acetyl-3,4-dihydrocoumarin (1) leads to the formation of 3-acetylcoumarin (2) and 3,3-diacetyl-3,3,4,4-tetrahydro-4,4-biscoumarin (3). The presence of molecular oxygen is an indispensable condition for the occurrence of a photodehydrogenation process, which is quantitatively when effected on silica gel.

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Photochemische Dehydrierung von 3-Acetyl-3,4-dihydrocumarin (Kurze Mitt.)

Zusammenfassung Bei UV-Bestrahlung von alkoholischen Lösungen von 3-Acetyl-3,4-dihydrocumarin (1) unter O₂ werden 3-Acetylcumarin (2) und 3,3-Diacetyl-3,3,4,4-biscumarin (3) gebildet. Die Anwesenheit von molekularem O₂ ist für die Photodehydrierung erforderlich, wobei die Umsetzung an Silikagel quantitativ verläuft.

     

Ab initio Studies on polymers

Ab initio crystal orbital calculations have been performed on the infinite all-trans polyene. A structure with r _c=c= 1.346 Å, r _c-c = 1.446 Å, r _c-h = 1.08 Å, and CCC = 125.3 ° was found to be most stable. The most important force constants, the band structure and the density of states were determined as well.     

Prospects of the search for neutrino bursts from supernovae with Baksan large volume scintillation detector

Observing a high-statistics neutrino signal from the supernova explosions in the Galaxy is a major goal of low-energy neutrino astronomy. The prospects for detecting all flavors of neutrinos and antineutrinos from the core-collapse supernova (ccSN) in operating and forthcoming large liquid scintillation detectors (LLSD) are widely discussed now. One of proposed LLSD is Baksan Large Volume Scintillation Detector (BLVSD). This detector will be installed at the Baksan Neutrino Observatory (BNO) of the Institute for Nuclear Research, Russian Academy of Sciences, at a depth of 4800 m.w.e. Low-energy neutrino astronomy is one of the main lines of research of the BLVSD.     

Vertex and Edge Orbits of Fibonacci and Lucas Cubes

The Fibonacci cube \({\Gamma_{n}}\) is obtained from the n-cube Q _n by removing all the vertices that contain two consecutive 1s. If, in addition, the vertices that start and end with 1 are removed, the Lucas cube \({\Lambda_{n}}\) is obtained. The number of vertex and edge orbits, the sets of the sizes of the orbits, and the number of orbits of each size, are determined for the Fibonacci cubes and the Lucas cubes under the action of the automorphism group. In particular, the set of vertex orbit sizes of \({\Lambda_{n}}\) is \({\{k \geq 1; k |n\} \cup \{k \geq 18; k |2n\}}\), the number of vertex orbits of \({\Lambda_{n}}\) of size k, where k is odd and divides n, is equal to \({\sum_{d | k} \mu (\frac{k}{d})F_{\lfloor{\frac{d}{2}}\rfloor+2}}\), and the number of edge orbits of \({\Lambda_{n}}\) is equal to the number of vertex orbits of \({\Gamma_{n-3}}\). Dihedral transformations of strings and primitive strings are essential tools to prove these results.     

Sol-gel materials doped with 3-(3-(4-(dimethylamino)phenyl)propenoyl)-2H-chromen-2-one: spectroscopic and structural elucidation

Conventional and linear-polarized IR-spectroscopic tools based on reducing-difference procedures for non-polarized and polarized IR-spectra interpretation as well as orientation technique of solids (colloidal suspension in nematic liquid crystal) and UV/vis spectroscopy are applied for investigation of new sol-gel materials with potential optical application of doped organic dye 3-(3-(4-(dimethylamino)phenyl)propenoyl)-2H-chromen-2-one (K2) and Sm3+ ions. The results show that during aging of the monoliths Sm3+ forms an unstable complex with K2, [Sm(K2)(2)(H2O2](NO3)(3), which transforms to [Sm(H2O)(6)](3+) one, typical for gel-Sm3+ system. Quantum chemical ab initio and DFT calculations are reported with a view to support experimental IR-characteristic bands of the system studied.     

Impact of model perfumes on surfactant and mixed surfactant self-assembly

The impact of some model perfumes on surfactant self-assembly has been investigated, using small-angle neutron scattering. A range of different model perfumes, with differing degrees of hydrophilicity/hydrophobicity, have been explored, and in order of increasing hydrophobicity include phenyl ethanol (PE), rose oxide (RO), limonene (LM), linalool (LL), and dihydrogen mercenol (DHM). The effect of their solubilization on the nonionic surfactant micelles of dodecaethylene monododecyl ether (C12EO12) and on the mixed surfactant aggregates of C12EO12 and the cationic dialkyl chain surfactant dihexadecyl dimethyl ammonium bromide (DHDAB) has been quantified. For PE and LL the effect of their solubilization on the micelle, mixed micelle/lamellar and lamellar regimes of the C12EO12/DHDAB mixtures, has also been determined. For the C12EO12 and mixed DHDAB/C12EO12 micelles PE is solubilized predominantly at the hydrophilic/hydrophobic interface, whereas the more hydrophobic perfumes, from RO to DHM, are solubilized predominantly in the hydrophobic core of the micelles. For the C12EO12 micelles, with increasing perfume concentration, the more hydrophobic perfumes (RO to DHM) promote micellar growth. Relatively modest growth is observed for RO and LM, whereas substantial growth is observed for LL and DHM. In contrast, for the addition of PE the C12EO12 micelles remain as relatively small globular micelles, with no significant growth. For the C12EO12/DHDAB mixed micelles, the pattern of behavior with the addition of perfume is broadly similar, except that the micellar growth with increasing perfume concentration for the more hydrophobic perfumes is less pronounced. In the Lbeta (Lv) region of the DHDAB-rich C12EO12/DHDAB phase diagram, the addition of PE results in a less structured (less rigid) lamellar phase, and ultimately a shift toward a structure more consistent with a sponge or bicontinuous phase. In the mixed L1/Lbeta region of the phase diagram PE induces a slight shift in the coexistence from Lbeta toward L1. The addition of LL to the Lbeta (Lv) region of the DHDAB-rich C12EO12/DHDAB phase diagram also results in a reduction in the lamellar structure (less rigid lamellae), and a shift toward a structure more consistent with a sponge or bicontinuous phase, or a coexisting phase of small vesicles. For the mixed L1/Lbeta region of the phase diagram LL induces a shift toward a greater L beta component.