Thermal and structural properties of surfactant–picrate compounds

The novel surfactant?Cpicrate compounds were synthesized and characterized by thermal and XRD analysis. The synthesis, based on the electrostatic interactions of components in polar solvents, was carried out using picric acid and cationic surfactants (dodecyltrimethylammonium, didodecyldimethylammonium, and tridodecylmethylammonium halide). The idea was to investigate the dependence of physico-chemical properties and thermal transitions of picrate?Csurfactant compounds with raising number of dodecyl chains sited on the same ammoniumm head group. The equimolar mixed aqueous solutions are characterized as lyotropic, strongly promoted by picrate anion. The main crystal structure feature of investigated picrates is layered structure with stacked aromatic rings of one picrate molecule on the top of the other one via strong ?С??? interactions and connection to the alkylammonium molecules with their nitro groups by C?CH??O hydrogen bonds. Surfactant?Cpicrate bilayer-like structures are interrupted with layers of polar heads and picrate counterions and the observed width of such a bilayers are functions of more complex structural behaviors which ensures alternation in space of equal numbers of positive and negative charges. Although some of the surfactants used posses thermotropic porperties, like examined tridodecylmethylammonium chloride, no thermotropic mesomorphism is detected in solid state of investigated surfactant?Cpicrate compounds. The thermodynamic parameters of solid?Cliquid thermal transitions depend linear on the number of dodecyl chains, and for double- and triple-tailed picrate compounds the marked temporal hysteresis of the melt crystallization is registered.     

Silver cluster-biomolecule hybrids: from basics towards sensors

We focus on the functional role of small silver clusters in model hybrid systems involving peptides in the context of a new generation of nanostructured materials for biosensing. The optical properties of hybrids in the gas phase and at support will be addressed with the aim to bridge fundamental and application aspects. We show that extension and enhancement of absorption of peptides can be achieved by small silver clusters due to the interaction of intense intracluster excitations with the π-π* excitations of chromophoric aminoacids. Moreover, we demonstrate that the binding of a peptide to a supported silver cluster can be detected by the optical fingerprint. This illustrates that supported silver clusters can serve as building blocks for biosensing materials. Moreover, the clusters can be used simultaneously to immobilize biomolecules and to increase the sensitivity of detection, thus replacing the standard use of organic dyes and providing label-free detection. Complementary to that, we show that protected silver clusters containing a cluster core and a shell liganded by thiolates exhibit absorption properties with intense transitions in the visible regime which are also suitable for biosensing applications.     

Binding motifs of silver in prion octarepeat model peptides: a joint ion mobility, IR and UV spectroscopies, and theoretical approach

Transition metal-ion complexation is essential to the function and structural stability of many proteins. We studied silver complexation with the octarepeat motif ProHisGlyGlyGlyTrpGlyGln of the prion protein, which shows competitive sites for metal chelation including amide, indole and imidazole groups. This octapeptide is known as a favourable transition metal binding site in prion protein. We used ion mobility spectrometry (IMS), infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations (DFT) to identify the binding motifs of a silver cation on HisGlyGlyGlyTrp peptide as well as on peptide subsequences. Ultra-violet photodissociation (UVPD) and collision induced dissociation mass spectrometry together with the time-dependent density functional method was then exploited to study the influence of binding sites on optical properties and on the ground and excited states reactivity of the peptide. We show that the metal cation is bound to the π-system of the indole group and a nitrogen atom of the imidazole group and that charge transfers from the indole group to the silver cation occur in excited electronic states.     

Electronic structure similarities in Pb(x)Sb(y)(-) and Sn(x)Bi(y)(-) clusters

The geometric and electronic structure of Pb(x)Sb(y)(-) and Sn(x)Bi(y)(-) clusters are investigated by photoelectron spectroscopy and theoretical methods. It is found that PbSb(2)(-) and SnBi(2)(-) have similar spectroscopic patterns, reflecting correlations in electronic nature that are a result of their isoelectronic character and common geometries. Analogous findings are presented for Pb(2)Sb(2)(-) and Sn(2)Bi(2)(-). Further, we investigate the effect of altering the total valence count, and separately the geometry, on spectroscopic patterns. We conclude that these heavy p-block elements are interchangeable and that the electronic structure correspondence can be preserved regardless of elemental composition. This represents an extension of the traditional concepts of periodicity, where elements of similar valence configuration are grouped into columns. Instead, elements from different columns may be combined to yield similarities in chemistry, given the overall valence count is preserved.     

Photochemical and phototoxic properties of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate, a new quinoline derivative

The present study demonstrates photoinduced generation of superoxide radical anion and singlet oxygen upon UVA irradiation of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate (DNQC), and its cytotoxic/phototoxic effects on murine leukemia L1210 cells. The formation of reactive oxygen species (ROS) was investigated by EPR spectroscopy using in situ spin trapping technique and 4-hydroxy-2,2,6,6-piperidine (TMP) for singlet oxygen ((1)O(2)) detection. The EPR spectra monitored upon photoexcitation of aerated solutions of DNQC in dimethylsulfoxide evidenced the efficient activation of molecular oxygen via Types I and II mechanisms. The cytotoxic/phototoxic effects of DNQC, analysis of cell cycle, induction of apoptosis/necrosis, DNA damage and molecular mechanism of apoptotic death of L1210 cells in dark and in the presence of UVA irradiation were compared. DNQC induced a different cytotoxic/phototoxic effect, which was concentration- and time-dependent. The four highest tested concentrations of non-photoactivated and photoactivated DNQC induced immediate cytotoxic/phototoxic effect after 24h cultivation of L1210 cells. This effect decreased with the time of treatment. The irradiation increased the sensitivity of leukemia cell line on DNQC, but the cell sensitivity decreased with time of processing. Quinolone derivative DNQC significantly induced direct DNA strand breaks in L1210 cells, which were increased with the irradiation of cells. The DNA damage generated by DNQC alone/with combination of UVA irradiation induced cell arrest in G(0)/G(1) and G(2)/M phases, decrease in the number of L1210 cells in Sphase and apoptotic cell death of certain part of cell population after 24 h of influence. DNQC alone/with combination of UVA irradiation induced apoptosis in L1210 cells through ROS-dependent mitochondrial pathway.