Magneto-optical methods for magnetoplasmonics in noble metal nanostructures

The use of magneto-optical techniques to tune the plasmonic response of nanostructures is a hot topic in active plasmonics, with fascinating implications for several plasmon-based applications and devices. For this emerging field, called magnetoplasmonics, plasmonic nanomaterials with strong optical response to magnetic field are desired, which is generally challenging to achieve with pure noble metals. To overcome this issue, several efforts have been carried out to design and tailor the magneto-optical response of metal nanostructures, mainly by combining plasmonic and magnetic materials in a single nanostructure. In this tutorial we focus our attention on magnetoplasmonic effects in purely plasmonic nanostructures, as they are a valuable model system allowing for an easier rationalization of magnetoplasmonic effects. The most common magneto-optical experimental methods employed to measure these effects are introduced, followed by a review of the major experimental observations that are discussed within the framework of an analytical model developed for the rationalization of magnetoplasmonic effects. Different materials are discussed, from noble metals to novel plasmonic materials, such as heavily doped semiconductors.Comment: Tutorial article. 17 pages, 12 figure

ЕФЕКТ НА ЕКЗОГЕННИЯ ПОЛИАМИН ДИЕТИЛЕНТРИАМИН ВЪРХУ ОКСИДАТИВНИТЕ ПРОМЕНИ И ФОТОСИНТЕЗАТА В ТРЕТИРАНИ С АРСЕН ЦАРЕВИЧНИ РАСТЕНИЯ (Zea mays L.)

The antioxidant effect of the exogenous polyamine Diethylentriamine (DETA) on the oxidative changes in young maize plants treated with different As concentrations was studied. The plants were grown in a climatic box in a Hogland-Arnon nutrient solution. Arsenic was applied as Na3As04 in concentrations 0, 2 and 5 mg dm-3 (pH 5.5). The polyamine DETA (concentration 10-4 М) was added to the nutrient environment of some of the plants 24 hours prior to the As treatment. Five days later the lipid peroxidation level, the peroxidase activity, the growth and leaf gasexchange, and the protein and plastid pigments content were studied. The physiological analyses proved that DETA had positive effect on the As-treated maize plants by increasing the leaf gas-exchange, the plastid pigments content and soluble protein. The exogenous polyamine DETA, applied 24 hours prior to the As treatment, decreased considerably the lipid peroxidation level and the peroxidase itself in maize plants. DETA had protective effect on the As-induced oxidative stress, but in order to clarify its role as an antioxidant, more detailed and profound studies should be made.Проучен беше aнтиоксидантният ефект на екзогенния полиамин Диетилентриамин (ДЕТА) върху оксидативните промени в млади царевични растения, третирани с различни концентрации арсен. Растенията бяха отгледани в климатичен бокс в хранителна среда на Хогланд-Арнон. Арсенът (As) беше приложен като Na3As04 в концентрации 0, 2 и 5 mg dm-3 (pH 5.5). Полиаминът ДЕТА (концентрация 10-4 М), беше прибавен към хранителната среда на част от растенията 24 h преди третирането с Аs. След пет дни беше отчетено нивото на липидната пероксидация, активността на ензима пероксидаза, растежът и листният газообмен, и съдържанието на белтък и пластидни пигменти. Физиологичните анализи показаха, че полиаминът Дета оказва положителен ефект върху третираните с арсен царевични растения, като повишава листния газообмен, съдържанието на пластидни пигменти и разтворим белтък. Екзогенният полиамин Дета, приложен 24 преди третирането с As намалява съществено нивото на липидната пероксидация и ензима пероксидаза в царевичните растения. Изследванията показват, че ДЕТА изпълнява протекторен ефект срещу As-индуцирания оксидативен стрес, но за изясняване на неговата роля като антиоксидант са необходими по-детайлни и задълбочени изследвания

Chiral Four-Wave-Mixing signals with circularly-polarized X-ray pulses

Chiral four-wave-mixing signals are calculated using the irreducible tensor formalism. Different polarization and crossing angle configurations allow to single out the magnetic dipole and the electric quadrupole interactions. Other configurations can reveal that the chiral interaction occurs at a given step within the nonlinear interaction pathways contributing to the signal. Applications are made to the study of valence excitations of S-ibuprofen by chiral Stimulated X-ray Raman signals at the Carbon K-edge and by chiral visible 2D Electronic Spectroscopy.teraction pathways contributing to the signal.Comment: 33 pages, 10 figure

Conformational effects on the Circular Dichroism of Human Carbonic Anhydrase II: a multilevel computational study

Circular Dichroism (CD) spectroscopy is a powerful method for investigating conformational changes in proteins and therefore has numerous applications in structural and molecular biology. Here a computational investigation of the CD spectrum of the Human Carbonic Anhydrase II (HCAII), with main focus on the near-UV CD spectra of the wild-type enzyme and it seven tryptophan mutant forms, is presented and compared to experimental studies. Multilevel computational methods (Molecular Dynamics, Semiempirical Quantum Mechanics, Time-Dependent Density Functional Theory) were applied in order to gain insight into the mechanisms of interaction between the aromatic chromophores within the protein environment and understand how the conformational flexibility of the protein influences these mechanisms. The analysis suggests that combining CD semi empirical calculations, crystal structures and molecular dynamics (MD) could help in achieving a better agreement between the computed and experimental protein spectra and provide some unique insight into the dynamic nature of the mechanisms of chromophore interactions

DNA-based Self-Assembly of Chiral Plasmonic Nanostructures with Tailored Optical Response

Surface plasmon resonances generated in metallic nanostructures can be utilized to tailor electromagnetic fields. The precise spatial arrangement of such structures can result in surprising optical properties that are not found in any naturally occurring material. Here, the designed activity emerges from collective effects of singular components equipped with limited individual functionality. Top-down fabrication of plasmonic materials with a predesigned optical response in the visible range by conventional lithographic methods has remained challenging due to their limited resolution, the complexity of scaling, and the difficulty to extend these techniques to three-dimensional architectures. Molecular self-assembly provides an alternative route to create such materials which is not bound by the above limitations. We demonstrate how the DNA origami method can be used to produce plasmonic materials with a tailored optical response at visible wavelengths. Harnessing the assembly power of 3D DNA origami, we arranged metal nanoparticles with a spatial accuracy of 2 nm into nanoscale helices. The helical structures assemble in solution in a massively parallel fashion and with near quantitative yields. As a designed optical response, we generated giant circular dichroism and optical rotary dispersion in the visible range that originates from the collective plasmon-plasmon interactions within the nanohelices. We also show that the optical response can be tuned through the visible spectrum by changing the composition of the metal nanoparticles. The observed effects are independent of the direction of the incident light and can be switched by design between left- and right-handed orientation. Our work demonstrates the production of complex bulk materials from precisely designed nanoscopic assemblies and highlights the potential of DNA self-assembly for the fabrication of plasmonic nanostructures.Comment: 5 pages, 4 figure

Reprogramming the assembly of unmodified DNA with a small molecule

The ability of DNA to store and encode information arises from base pairing of the four-letter nucleobase code to form a double helix. Expanding this DNA ‘alphabet’ by synthetic incorporation of new bases can introduce new functionalities and enable the formation of novel nucleic acid structures. However, reprogramming the self-assembly of existing nucleobases presents an alternative route to expand the structural space and functionality of nucleic acids. Here we report the discovery that a small molecule, cyanuric acid, with three thymine-like faces reprogrammes the assembly of unmodified poly(adenine) (poly(A)) into stable, long and abundant fibres with a unique internal structure. Poly(A) DNA, RNA and peptide nucleic acid all form these assemblies. Our studies are consistent with the association of adenine and cyanuric acid units into a hexameric rosette, which brings together poly(A) triplexes with a subsequent cooperative polymerization. Fundamentally, this study shows that small hydrogen-bonding molecules can be used to induce the assembly of nucleic acids in water, which leads to new structures from inexpensive and readily available materials

Chirality of Matter Shows Up via Spin Excitations

Right- and left-handed circularly polarized light interact differently with electronic charges in chiral materials. This asymmetry generates the natural circular dichroism and gyrotropy, also known as the optical activity. Here we demonstrate that optical activity is not a privilege of the electronic charge excitations but it can also emerge for the spin excitations in magnetic matter. The square-lattice antiferromagnet Ba$_2$CoGe$_2$O$_7$ offers an ideal arena to test this idea, since it can be transformed to a chiral form by application of external magnetic fields. As a direct proof of the field-induced chiral state, we observed large optical activity when the light is in resonance with spin excitations at sub-terahertz frequencies. In addition, we found that the magnetochiral effect, the absorption difference for the light beams propagating parallel and anti-parallel to the applied magnetic field, has an exceptionally large amplitude close to 100%. All these features are ascribed to the magnetoelectric nature of spin excitations as they interact both with the electric and magnetic components of light

Fluorescent Pigment and Phenol Glucosides from the Heartwood of Pterocarpus marsupium

The fluorescence shown by extracts of the heartwood of Pterocarpus marsupium is attributed to salts of the new compound 1, whose structure was elaborated using detailed spectroscopic/ spectrometric studies. The plant material also contains the nonfluorescent compounds 2 and 3. The absolute configuration of 1 was determined by experimental and theoretically calculated electronic CD spectra, while that of 3 was deduced from ECD comparison with reported results in the α-hydroxydihydrochalcone series