Local, Single-Molecule Oxidative Cleaving of DNA Origami by C60 on an AFM Tip

Spatially controlled single-molecule oxidation of DNA was performed by photocatalytic generation of singlet oxygen on chemically functionalized AFM tips. A waffle-type DNA origami deposited on a mica surface is site-specifically destroyed by generation of reactive oxygen species at the AFM tip, which was modified with C₆₀-tripod photocatalyst. Upon AFM scanning under photoirradiation, DNA morphology changes, corresponding to oxidative damage were clearly observed at the single-molecule level. The DNA cleavage occurred with strict dependence on photoirradiation and the presence of C₆₀on the AFM tip.

Local, Single-Molecule Oxidative Cleaving of DNA Origami by C60 on an AFM Tip

Spatially controlled single-molecule oxidation of DNA was performed by photocatalytic generation of singlet oxygen on chemically functionalized AFM tips. A waffle-type DNA origami deposited on a mica surface is site-specifically destroyed by generation of reactive oxygen species at the AFM tip, which was modified with C₆₀-tripod photocatalyst. Upon AFM scanning under photoirradiation, DNA morphology changes, corresponding to oxidative damage were clearly observed at the single-molecule level. The DNA cleavage occurred with strict dependence on photoirradiation and the presence of C₆₀on the AFM tip.

OBTAINING NANOSIZED PLATINUM FILMS WITH FRACTAL PROPERTIES

Проведено комплексное исследование морфологии рельефа наноразмерных пленок платины на поверхности слюды с помощью сканирующего зондового (в режиме атомного-силового) и туннельного микроскопов, а также оптического интерференционного профилометра. Описаны характерные особенности нанорельефа поверхности пленок платины различной толщины, включая фрактальные свойства. Получены значения фрактальной размерности для пленок разной толщины при двух альтернативных методах исследования на разных исходных масштабах образцов: на основе данных атомного-силового микроскопа - ̅D = 2,28÷2,35 и сканирующего туннельного микроскопа - ̅D = 2,12÷2,26. Для сравнения приведены экспериментальные данные других авторов. Предложены рекомендации по развитию технологии «выращивания» структур с заданной морфологией поверхности. A comprehensive study of the morphology of the relief of nanosized platinum films on the mica surface was carried out using a scanning probe (in the atomic force mode) and tunneling microscopes, as well as an optical interference profilometer. Characteristic features of the surface nanorelief of platinum films of various thicknesses, including fractal properties, are described. The values of the fractal dimension were obtained for films of different thicknesses using two alternative methods of investigation at different initial scales of samples: based on the data of an atomic force microscope - ̅D = 2,28÷2,35 and a scanning tunneling microscope - ̅D = 2,12÷2,26. For comparison, experimental data of other authors are presented. Recommendations for development of the technology for «growing» structures with a given surface morphology are proposed.

Effect of Hofmeister Anions on Interfacial Properties of Mica Surface in Concentrated Aqueous Solution

The electric double layer (EDL) formed at the water/solid interface is the key to understanding a wide variety of natural phenomena; and nowadays, this knowledge may lead to ideas for technological innovations in the industrial and biomedical fields. The properties of the EDL on a surface directly determine the performance of an EDL-based device. In electrolyte solution, the coions with the same charge sign with the surface are usually ignored. However, they are expected to make a considerable contribution in concentrated conditions when ionic specific effects should be considered. Herein, we investigated the effect of anions in the Hofmeister series, including kosmotropes (Ac−), chaotropes (I−), and intermediate (Cl−), on the properties of the EDL on a negatively charged mica surface by observing intersurface forces using the surface forces apparatus (SFA). The SFA results indicated that at a concentration of 1 M and above, the effect of the monovalent anions in the sodium solutions were mainly correlated with their hydration behaviors. Exclusively in the solutions with strongly hydrated anions, we measured the abnormal long-range repulsions in the diffuse layer region farther away from the surface. By further investigating the solutions with kosmotropic divalent SO42− at relatively low concentrations, we may attribute the observation to the formation of ion pairs and hydrodynamic effects in the presence of concentrated kosmotropic anions. Moreover, these anions can also contribute to the formation of a complete and stable hydration layer near the surface. This work demonstrates the considerable effects of Hofmeister anionic coions on the properties of a simple colloid interface, which has attracted little attention in the past. Therefore, further investigations are desirable in the development of electrolytes and surface materials for the promising EDL-based technologies.

Tuning the morphology of mesoscopic structures of porphyrin macrocycles functionalized by an antimicrobial peptide

The aggregation properties of two peptide–porphyrin conjugates were investigated by optical spectroscopy and microscopy imaging with nanometer resolution. Specifically, a tetraphenylporphyrin platform was functionalized by (L)-magainin, a 23-residue long antimicrobial peptide, and by a (L)-magainin analogue differing from the parent peptide by a single residue substitution, [Formula: see text] an Ala vs. Phe replacement in the position 5 of the peptide chain. Spectroscopic and microscopy results show that this single-site substitution has a small effect on the secondary structure attained by the two peptide analogues, but deeply affects the morphology of the mesoscopic structures deposited on hydrophilic mica from methanol/water solutions. In particular, only the Ala-substituted peptide-porphyrin conjugate was shown to be able to form micrometric fibrils, coating homogeneously a hydrophilic mica surface. These results pave the way for potential applications of porphyrin-peptide compounds in localized photodynamic therapy and for designing solid-state stereoselective sensors.