Oxalyl amide derivatives bearing 4-dodecyloxy-stilbene as a cis−trans photoisomerizing unit were synthesized. The trans derivative acted as a versatile gelator of various organic solvents, whereas ...the corresponding cis derivative showed a poor gelation ability or none at all. In diluted solution (c = 2.0 × 10-5 mol dm-3, ethanol), the cis isomer was photochemically converted into the trans isomer within 4 min. Depending on the radiation wavelength, the trans isomer was stable or liable to photodecomposition. When exposed to irradiation, a concentrated solution of the cis isomer (c = 2.0 × 10-2 mol dm-3, ethanol) turned into a gel. The FT-Raman, FT-IR, and 1H NMR spectra demonstrated that the gelation process occurred because of a rapid cis → trans photoisomerization followed by a self-assembly of the trans molecules. Apart from the formation of hydrogen bonding between the oxalyl amide parts of the molecules, confirmed by FT-IR spectroscopy, it was assumed that the π−π stacking between the trans-stilbene units of the molecule and a lipophilic interaction between long alkyl chains were the interactions responsible for gelation.
Among novel bis-nucleobase-phenanthridinium conjugates bis-uracil analogue stabilized significantly more effective poly-dA-poly-dT and poly-AH(+)-poly-AH(+) than adenine analogue and reference ...compound . For the alternating poly-dAdT-poly-dAdT however, the binding preference is lost, pointing to the importance of specific interactions of uracils of with homopolynucleotides containing consecutive adenines.
Extra virgin olive oil samples were collected from different geographical areas of Central Dalmatia region in Croatia including locations both on the coast and islands. This set included 41 oils of ...cultivar Oblica, 1 per cultivars Coratina and Leccino, and 5 of mixed cultivars Lastovka and Oblica. Attenuated total reflectance (ATR) spectra of non-treated samples were recorded and principal component analysis (PCA) was carried out on a set of obtained spectra, as well as their first and second derivatives. The quality of PCA models was assessed using leave-one-out cross-validation and optimal number of principal components was determined. In the case of ATR spectra, the first principal component accounted for 42.92 % of the total variance among the samples and the optimal number of components was 6, whereas in the case of second derivatives the first principal component accounted for 95.76 % of the total variance and the optimal number of components was 3. Classification of olive oils on the basis of geographical origin was proposed and underlying spectral differences among the spectra were determined by investigating principal component loadings. These differences arise as a result of variations in fatty acid composition. It was found out that ATR in combination with PCA could easily distinguish between samples collected from the coastal area and those from the islands. Classification results were further confirmed by using spherical principal components procedure, projection pursuit and robust PCA, as well as hierarchical cluster analysis.(doi: 10.5562/cca2377) Keywords: Croatia, extra virgin olive oils, ATR-FTIR spectroscopy, principal component analysis, cluster analysis
Nanocrystalline Y2O3:Ho was synthesized by solution combustion method with ethylene glycol as fuel. Material was characterized using powder X-ray diffraction and transmission electron microscopy ...(TEM). X-ray diffraction and TEM showed that the material is nanostructured. Luminescence properties were studied using Raman spectrometers with excitation in near infrared (NIR) and visible regions. The visible and NIR luminescence spectra of nanocrystalline Y2O3:Ho show some important differences from those of bulk material. The convenience of using Raman instruments for studying luminescence of lanthanide ions is demonstrated.
Hydrogen bonding in salicylaldehyde-4-phenylthiosemicarbazone (
1) has been studied by using experimental (NMR, Raman and UV spectroscopies) and quantum chemical (DFT) methods. It has been ...demonstrated that 1 adopted the hydroxy-thione tautomeric form in solution as found also in the solid state and previously indicated by secondary deuterium isotope effects. Apart from the intra-molecular hydrogen bonds new interactions between 1 and solvent molecules were formed as well. Changes in NMR chemical shifts and calculations have pointed towards a formation of inter-molecular three-centered hydrogen bonds in each of the studied complexes involving OH and NH groups of
1 and associated solvent molecules. Stabilization energies of intra-molecular hydrogen bonds were found to decrease with the increase of the solvent polarity. Two-dimensional NOESY spectra indicated conformational changes in solution with respect to the structure observed in the solid state. These were accounted for by a relatively low barrier of the rotation of the N
N single bond thus enabling a molecule to posses a higher conformational flexibility in solution with portions of skewed conformations. The results presented here can help in a better understanding of the role hydrogen bonds can play in bioactivity of related thiosemicarbazone derivatives and their metal complexes.
Raman and surface-enhanced Raman spectra of new DNA/RNA-binding compounds consisting of three imidazole (Im) and three pyridine (Py) rings connected by tripodal polyaminomethylene linkages were ...obtained by the near-infrared excitation at 1064 nm. Study of interactions of Im and Py polyamines with single-stranded RNA polynucleotides (poly A, poly G, poly C, poly U), double-stranded DNA polynucleotides (poly dAdT-poly dAdT, poly dGdC-poly dGdC) and calf thymus DNA (ct-DNA) by surface-enhanced Raman spectroscopy (SERS) reveals unambiguous enhancement of the Raman scattering from the small molecules as well as appearance of new bands in spectra associated mainly with nucleobases. The SERS experiments point toward comparable interactions of Im and Py polyamines with single-stranded purine and pyrimidine polynucleotides. Furthermore, SERS experiments with double stranded polynucleotides reveal the base-pair dependent selectivity of Im and Py, whereby interactions within both, major and minor groove are indicated for poly dAdT-poly dAdT, at variance to preferred binding of Im and Py to only major groove of poly dGdC-poly dGdC. SERS spectra of Im and Py with ct-DNA imply that protonated amino groups of these compounds preferentially interact with N7 atoms (adenine, guanine) while nitrogen in aromatic rings of polyamines might be attracted to C6-NH(2) (adenine), all sites being located at the major groove of the DNA helix. Wavenumber downshift of the imidazole (Im) and pyridine (Py) ring vibrations supports aromatic stacking interactions of imidazole and pyridine aromatic moieties with DNA base-pairs.
Surface-enhanced Raman scattering (SERS) of the cationic and the neutral form of rhodamine 19 octadecylamide (R19OA) has been studied in the silver citrate colloid using NIR excitation at 1064
nm. ...Cationic molecules readily adsorb onto negatively charged silver nanoparticles through a positively charged xanthene part of the molecules resulting in surface enhancement of Raman scattering. Due to a lack of the positive charge in molecular structure, SERS spectrum of neutral molecules is not observed. Nevertheless, a broad band appearing at 1240
cm
−1 in the spectrum of the cationic form indicates conversion of the cationic into the neutral species occurring close to the silver surface. The observed band most likely arises from a vibration of the ring formed in the molecular structure after conversion, but before complete desorption of the neutral molecules from the metal surface. Upon addition of HCl and NaOH in the silver sol, equilibrium is shifted toward the cationic and the neutral form of R19OA, respectively, followed by corresponding changes in the Raman spectrum. In addition, FT-SERS spectra of two rhodamine dyes, rhodamine 19 (R19) and rhodamine 6G (R6G), that are structurally related to R19OA, have been studied under the same experimental conditions for comparison.
Surface-enhanced Raman scattering has been applied to study weak intermolecular interactions between small organic gelling molecules involved in the silver nanoparticle-hydrogel composite formation. ...Assembly and disassembly of the gelator molecules in close vicinity to embedded silver nanoparticles were followed by changes in Raman intensity of the amide II and carboxyl vibrational bands, whereas the strength of the bands related to benzene modes remained constant. This implied that the gelator molecules were strongly attached to the silver particles through the benzene units, while participating in gel structure organization by intermolecular hydrogen bonding between oxalyl amide and carboxyl groups.
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