The Role of the Polyethylene Glycol in the Organization of Gold Nanorods at the Air-Water and Air-Solid Interfaces.

The organization of metallic nanoparticles into assembled films is a complex process. The type of nanoparticle stabilizing ligand and the method for creating an organized layer can profoundly affect the optical properties of the resulting nanoparticle assembly. Investigations of the ligand structure and nanoparticle interactions can provide a greater understanding of the design of the assembly process and the quality of the resulting materials. One of the functionalization methods in the preparation of specific gold nanorods is the utilization of thiol-terminated poly(ethylene glycol). This generates gold nanorods capable of forming stable monolayers at the air-water interface upon dispersion in a suitable organic solvent. Herein, we show that depending on the molecular weight of the poly(ethylene glycol), the structures obtained at the air-water and air-solid interfaces differ in the arrangement. The studied structures were characterized by using spectroscopic and microscopic techniques, and the structural type was correlated with the polymer type. Insoluble and stable Langmuir monolayers composed of higher-molecular-weight gold nanorods with poly(ethylene glycol) were formed only in the presence of an additional stabilizer that prevented the formation of gold nanorods in aqueous solutions. At the air-solid interface, conformational changes in poly(ethylene glycol) induced the aggregation of gold nanorods, which became closely packed under the influence of surface pressure. The presented results suggested that the arrangement of two-dimensional layers of gold nanorods could be tailored using poly(ethylene glycol) of various molecular weights.

The Mechanism of Wear Reduction in the Ni-CaF2 Composite Material: Raman and Confocal Microscopy Insights.

A powder metallurgy process was used to produce high temperature self-lubricating composites based on Ni, with varying content of calcium fluoride (10 wt.% and 20 wt.%). The wear properties of the samples were investigated by a pin-on-disc test at elevated temperature, up to 600 °C. Aside from standard techniques for the sample characterization, confocal microscopy and micro-Raman spectroscopy were used for the first time for this type of sample. These methods were used to examine the changes in topography and to detect the distribution of the tribofilm on sample surfaces. The addition of solid lubricant particles decreased the coefficient of friction and improved the tribological properties, because of the tribofilm which formed on sample surfaces.

Recent Advances in Metallic Nanoparticle Assemblies for Surface-Enhanced Spectroscopy.

Robust and versatile strategies for the development of functional nanostructured materials often focus on assemblies of metallic nanoparticles. Research interest in such assemblies arises due to their potential applications in the fields of photonics and sensing. Metallic nanoparticles have received considerable recent attention due to their connection to the widely studied phenomenon of localized surface plasmon resonance. For instance, plasmonic hot spots can be observed within their assemblies. A useful form of spectroscopy is based on surface-enhanced Raman scattering (SERS). This phenomenon is a commonly used in sensing techniques, and it works using the principle that scattered inelastic light can be greatly enhanced at a surface. However, further research is required to enable improvements to the SERS techniques. For example, one question that remains open is how to design uniform, highly reproducible, and efficiently enhancing substrates of metallic nanoparticles with high structural precision. In this review, a general overview on nanoparticle functionalization and the impact on nanoparticle assembly is provided, alongside an examination of their applications in surface-enhanced Raman spectroscopy.

Gold-Based Nanoparticles Systems in Phototherapy - Current Strategies.

BACKGROUND: The understanding of the action mechanism of the nanoparticles systems consisting of metallic nanoparticles and dyes or cytostatic molecule is crucial for searching and designing the ideal, novel drugs. In this review, we have considered moleculefunctionalized metallic nanoparticle systems for phototherapy. METHODS: We performed a thorough search of the high-quality peer-reviewed literature on metallic nanoparticles systems in phototherapy, focusing on their biological importance and the action mechanism. RESULTS: 138 papers were included in the mini-review. The majority of them discussed the way of metallic nanoparticles functionalization and its impact on the biological activity of a hybrid system. CONCLUSION: In this work, we show numerous medically and chemically important development strategies of hybrid types of drugs which can be used in phototherapy. These systems have a high affinity to the tumor cells surface proteins which transport the nanoparticles directly into a cell. The application of functionalized metallic nanoparticles in phototherapy improved photophysical properties lowered cytotoxicity of commonly used photosensitizers and facilitated the development of the third generation photosensitizers. Furthermore, this type of nanoparticles could also be used as a cytostatic drug carrier in the chemo or combined anticancer therapies.

Photo-switching of a non-ionic azobenzene amphiphile in Langmuir and Langmuir-Blodgett films.

The concept of programmable and reconfigurable soft matter has emerged in science in the last few decades and can be realized by photoisomerization of azobenzene derivatives. This possibility results in great application potential of these compounds in optical storage devices, molecular junctions of electronic devices, command layers of liquid crystal displays or holographic gratings. In this paper, we present the results of a study on the organization and isomerization of the non-ionic and amphiphilic methyl 4-[(E)-2-[4-(nonyloxy)phenyl]diazen-1-yl]benzoate (LCA) in a 2D layer architecture of Langmuir and Langmuir-Blodgett (LB) films supported by spectroscopic studies on LCA chloroform solutions. Our investigation has shown a significantly different molecular organization of LCA depending on the ratio of trans and cis isomers in the monolayers. Taking advantage of a relatively low packing density and aggregation strength in the cis-LCA monolayer, we demonstrated the reversible isomerization in the LB film initially formed of LCA molecules in the cis form, while in the trans-LCA monolayer this effect was not observed. Our approach allows the formation of a switchable monolayer made of the amphiphilic LCA showing liquid crystalline properties without introducing an ionic group into the molecule structure, mixing with another compound or changing the subphase pH to provide free space for the molecules' isomerization.

Intrinsic Photoprotective Mechanisms in Chlorophylls.

Photosynthetic energy conversion competes with the formation of chlorophyll triplet states and the generation of reactive oxygen species. These may, especially under high light stress, damage the photosynthetic apparatus. Many sophisticated photoprotective mechanisms have evolved to secure a harmless flow of excitation energy through the photosynthetic complexes. Time-resolved laser-induced optoacoustic spectroscopy was used to compare the properties of the T1 states of pheophytin a and its metallocomplexes. The lowest quantum yield of the T1 state is always observed in the Mg complex, which also shows the least efficient energy transfer to O2 . Axial coordination to the central Mg further lowers the yield of both T1 and singlet oxygen. These results reveal the existence of intrinsic photoprotective mechanisms in chlorophylls, embedded in their molecular design, which substantially suppress the formation of triplet states and the efficiency of energy transfer to O2 , each by 20-25 %. Such intrinsic photoprotective effects must have created a large evolutionary advantage for the Mg complexes during their evolution as the principal photoactive cofactors of photosynthetic proteins.

The effect of Cu doping on the mechanical and optical properties of zinc oxide nanowires synthesized by hydrothermal route.

Zinc oxide (ZnO) is a wide-bandgap semiconductor material with applications in a variety of fields such as electronics, optoelectronic and solar cells. However, much of these applications demand a reproducible, reliable and controllable synthesis method that takes special care of their functional properties. In this work ZnO and Cu-doped ZnO nanowires are obtained by an optimized hydrothermal method, following the promising results which ZnO nanostructures have shown in the past few years. The morphology of as-prepared and copper-doped ZnO nanostructures is investigated by means of scanning electron microscopy and high resolution transmission electron microscopy. X-ray diffraction is used to study the impact of doping on the crystalline structure of the wires. Furthermore, the mechanical properties (nanoindentation) and the functional properties (absorption and photoluminescence measurements) of ZnO nanostructures are examined in order to assess their applicability in photovoltaics, piezoelectric and hybrids nanodevices. This work shows a strong correlation between growing conditions, morphology, doping and mechanical as well as optical properties of ZnO nanowires.

The impact of solvents on the singlet and triplet states of selected fluorine corroles - absorption, fluorescence, and optoacoustic studies.

This paper examines the influence of aprotic solvents on the spectroscopic properties as well as the energy deactivation of two free-base corrole dyes substituted with C6F5 and/or 4-NO2C6H4 groups. Absorption, fluorescence and laser-induced optoacoustic spectroscopy have been used to follow the singlet and triplet states of fluorine corroles belonging to the A2B and A3 type in toluene (TL), chloroform (CL), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and also in solvent mixtures. Changes in the absorption and fluorescence spectra are influenced by the type of solvent mixture. The fluorescence behaviors of the two investigated corroles were extremely different - fluorescence of the nitro-corrole in TL is dramatically quenched in the presence of DMF. In contrast, fluorescence quenching of fluorine corroles in DMF-TL mixtures is substantially weakened. Absorption, fluorescence, triplet population as well as singlet oxygen generation parameters are evaluated. The spectral experimental data are supported by quantum chemical calculations - time-dependent density functional theory (TD-DFT) and cyclic voltammetry experiments. The presented results are discussed from a viewpoint of aggregation, tautomerization, and deprotonation effects occurring in the corroles.

Multiwavelength excitation of photosensitizers interacting with gold nanoparticles and its impact on optical properties of their hybrid mixtures.

In a hybrid mixture of organic (dye) and inorganic (metallic nanoparticles) components, the optical properties of a dye can be easily controlled by tailoring the shape or the concentration of the noble metal nanoparticles (NPs). The influences of multiexcitation (multiwavelength excitation) of photosensitizers (pheophorbide a and hematoporphyrin) on the interactions with pegylated Au-NPs and on the photophysical parameters of the dyes are studied. Detailed, systematic fluorescence quenching studies were performed in the mixtures of different contents of Au-NPs, and interpreted together with the results of quantum singlet oxygen yield examinations. According to the results, the fluorescence of the two dyes studied was effectively quenched in the presence of Au-NPs, mainly because of the resonance energy transfer between the donor (dye) and the acceptor (Au-NPs). Stern-Volmer quenching constants were determined by a few orders of magnitude higher than those describing the photochemical quenching process. In hybrid mixtures analyzed, the mechanism of energy transfer between the donor and the acceptor was nanometal surface energy transfer. Furthermore, different behavior of the mixtures on excitation with the wavelengths from the Soret and Q bands of the dyes and with those corresponding to the surface plasmon resonance band of Au-NPs was analyzed. Moreover, for certain concentrations of Au-NPs and for certain excitation wavelengths, an increase in singlet oxygen generation was observed. The results obtained indicate the significance of further studies of photosensitizers in hybrid mixtures with NPs.

Unlocked nucleic acids: implications of increased conformational flexibility for RNA/DNA triplex formation.

Unlocked nucleic acids (UNAs) have been introduced at specific positions in short model DNA hairpins and RNA/DNA triplexes for the first time. UNA residues destabilize the hairpins and decrease triplex thermodynamic stability or suppress triplex formation for most of the evaluated structures. Nevertheless, the incorporation of UNA residues at certain positions of dsDNA was found to be energetically favourable or at least did not affect triplex stability. Notably, the most thermodynamically stable UNA-modified triplexes exhibited improved stability at both acidic and physiological pH. The specificity of the interactions between the triplex-forming oligonucleotide and dsDNA was characterized using EMSA for the most thermodynamically stable structures, and triplex dissociation constants were determined. One of the modified triplexes exhibited an improved Kd in comparison with the unmodified triplex. CD and thermal difference spectra indicated that UNA residues do not alter the overall structure of the most thermodynamically stable triplexes. In addition, incubation of the modified oligonucleotides with human serum indicated that the UNAs demonstrate the potential to improve the biological stability of nucleic acids.

Near and Far-Field Properties of Nanoprisms with Rounded Edges.

Photonic devices can be developed, and their working principle can be understood only by considering the phenomena taking place at the nanoscale level. Optical properties of plasmonic structures depend on their geometric parameters and are sensitive to them. Recently, many advanced methods for the preparation of nanostructures have been proposed; however still, the geometric parameters are inaccurate. Numerical simulations provide a powerful tool for the analysis of plasmonic nanostructures. To the best of our knowledge, there are not many papers on near-field and far-field properties of single nanoprism and nanoprism dimer, the so-called bowtie, with rounded edges. For this purpose, Finite Integration Technique implemented to the CST Microwave Studio was used. Besides the edge rounding, an additional modification of the resonance modes was investigated, achieved by placement of a spherical nanoparticle in the gap between the prisms. Results of numerical simulations indicate that the radius of the curvature edges strongly affects the plasmon peak localization, and this effect cannot be neglected in plasmonic device design. Increase in the radius of edge curvature causes main extinction cross-section peak blueshift in all cases analyzed. Moreover, our calculations imply that the nanoparticle in the gap between prisms strongly influences the dependence of spectral properties on the radius curvature.

Adsorption properties of biologically active derivatives of quaternary ammonium surfactants and their mixtures at aqueous/air interface. I. Equilibrium surface tension, surfactant aggregation and wettability.

The adsorption properties of surfactant mixtures containing two types of quaternary derivatives of lysosomotropic substances: alkyl N,N-dimethylalaninates methobromides and alkyl N,N-dimethylglycinates methobromides were studied. Quantitative and qualitative description of the adsorption process was carried out on the basis of experimentally obtained equilibrium surface tension isotherms. The results indicated that most of the systems studied revealed synergistic effect both in adsorption and wetting properties. In vitro studies on human cancer cells were undertaken and the data obtained showed that the mixtures suppressed the cancer cells' proliferation more effectively than individual components. Results of preliminary research on the interaction of catanionic mixtures with phospholipids suggested a possibility of a strong penetration of cell membranes by the mixtures investigated.