Surface functionalized spherical nanoparticles: an optical assessment of local chirality

Electromagnetic radiation propagating through any molecular system typically experiences a characteristic change in its polarization state as a result of light-matter interaction. Circularly polarized light is commonly absorbed or scattered to an extent that is sensitive to the incident circularity, when it traverses a medium whose constituents are chiral. This research assesses specific modifications to the properties of circularly polarized light that arise on passage through a system of surface-functionalized spherical nanoparticles, through the influence of chiral molecules on their surfaces. Non-functionalized nanospheres of atomic constitution are usually inherently achiral, but can exhibit local chirality associated with such surface-bound chromophores. The principal result of this investigation is the quantification of functionally conferred nanoparticle chirality, manifest through optical measurements such as circularly polarized emission. The relative position of chiral chromophores fixed to a nanoparticle sphere are first determined by means of spherical coverage co-ordinate analysis. The total electromagnetic field received by a spatially fixed, remote detector is then determined. It is shown that bound chromophores will accommodate both electric and magnetic dipole transition moments, whose scalar product represents the physical and mathematical origin of chiral properties identified in the detected signal. The analysis concludes with discussion of the magnitude of circular differential optical effects, and their potential significance for the characterization of surface-functionalized nanoparticles

Observations of radio pulsars and their physical implications

Pulsars are rapidly rotating neutron stars from which we observe strong radio emissions. Observed changes in pulsar rotation frequency can suggest the presence of a binary companion. Pulsars with high rotation frequencies are almost always found in binaries. This is well explained by the theory of pulsar spin-up: matter is accreted to the neutron star from a main sequence companion. This increases the neutron star’s rotation speed due to the conservation of angular momentum, a process called recycling. If the binary is a double neutron star system, spin periods will be higher due to incomplete recycling. Double neutron star systems provide some of the most stringent tests of gravity, however their population is small and the key indicators for their evolution are poorly constrained. This work presents and discusses the results from observations of five recycled radio pulsar signals. PSR J1829+2456 is a member of a double neutron star system. Observations over three consecutive years have allowed measurement of the system’s proper motion and component masses, found to be1.306±0.007M and 1.299 ± 0.007M for the neutron star and its companion, respectively. The proper motion implies a low-to-moderate space velocity of∼50 km s−1which, in tandem with the measured masses and mild orbital eccentricity, suggests the system is the result of a low-kick, symmetric ultra-stripped iron core-collapse supernova. PSRs J1851+0010, J1853+0008, J1936+1805 and J1936+2142 were discovered by the Pulsar Arecibo L-band Feed Array (PALFA) survey collaboration. The former two are believed to be members of double neutron star systems. Component masses for both systems have been measured with the companion of PSR J1851+0010 being1.15 ± 0.04M: possibly the lowest mass neutron star discovered to-date. These systems are thought to have evolved in a similar way to PSR J1829+2456. Time dependent pulse width analysis is consistent with this hypothesis. PSR J1936+1805 is an isolated pulsar with a rotation frequency of≈17rotations per second. This may be a disrupted binary: a pulsar that was once part of a binary system that did not survive long-term. PSR J1936+2142 is believed to be a neutron star-white dwarf binary with an orbital period of 0.757days. The observed pulse frequency decay implies this pulsar is old, with a characteristic age of eleven billion years. Orbital parameters suggest that this system is an intermediate mass binary pulsar

Point source generation of chiral fields:measures of near- and far-field optical helicity

To consider the relationship between different measures of chirality in an optical field, the simplest case is considered: direct spontaneous emission of circularly polarized light by a point source. In the electromagnetic fields radiated from a suitably chiral source, such as a low-symmetry chiral molecule undergoing radiative decay, optical helicity is exhibited in the extent of a difference in left- and right-handed circular polarization components. There are several practical measures for quantifying the emergence of ensuing optical helicity, exhibiting different forms of dependence on the properties of the emitter and the positioning of a detector. By casting each measure in terms of an irreducible helicity density, connections and distinctions can be drawn between results expressible in either classical or quantum form

Structural analysis of the architecture and in situ localization of the main S-layer complex in Deinococcus radiodurans

Bacterial surface layers are paracrystalline assemblies of proteins that provide the first line of defense against environmental shocks. Here, we report the 3D structure, in situ localization, and orientation of the S-layer deinoxanthin-binding complex (SDBC), a hetero-oligomeric assembly of proteins that in Deinococcus radiodurans represents the main S-layer unit. The SDBC is resolved at 11-Å resolution by single-particle analysis, while its in situ localization is determined by cryo-electron crystallography on intact cell-wall fragments leading to a projection map at 4.5-Å resolution. The SDBC exhibits a triangular base with three comma-shaped pores, and a stalk departing orthogonally from the center of the base and oriented toward the intracellular space. Combining state-of-the-art techniques, results show the organization of this S-layer and its connection within the underlying membranes, demonstrating the potential for applications from nanotechnologies to medicine

Crystallization of the Photosystem II core complex and its chlorophyll binding subunit CP43 from transplastomic plants of Nicotianatabacum

Photosystem II from transplastomic plants of Nicotiana tabacum with a hexahistidine tag at the N-terminal end of the PsbE subunit (α-chain of the cytochrome b559) was purified according to the protocol of Fey et al. (BBA 12:1501–1509, 2008). The protein sample was then subjected to two additional gel filtration runs in order to increase its homogeneity and to standardize the amount of detergent. Large three dimensional crystals of the core complex were obtained. Crystals of one of its chlorophyll binding subunits (CP43) in isolation grew in very similar conditions that differed only in the concentration of the detergent. Diffraction of Photosystem II and CP43 crystals at various synchrotron beamlines was limited to a resolution of 7 and 14 Å, respectively. In both cases the diffraction quality was insufficient for an unambiguous assignment of the crystallographic lattice or space group

Propiedades fisicoquímicas y evaluación del efecto fotocitotóxico de nuevos agentes terapéuticos

Tesis (Doctora en Ciencias Químicas) - - Universidad Nacional de Córdoba. Facultad de Ciencias Químicas, 2022.Fil: Haniewicz, Cinthia Soledad. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas; Argentina.Esta Tesis Doctoral tuvo como finalidad el desarrollo de nuevos agentes fototerapéuticos para su potencial aplicación en terapia fotodinámica (TFD) y terapia fotodinámica antimicrobiana (TFDA) destinadas al tratamiento de patologías oncológicas y no oncológicas, respectivamente. Ambas alternativas terapéuticas han demostrado resultados promisorios y se sustentan en la utilización de fotosensibilizadores (Fs), compuestos químicos capaces de absorber luz de determinada longitud de onda, generando especies reactivas del oxígeno responsables de la muerte celular. Se sintetizaron nuevos Fs de segunda generación a partir de modificaciones estructurales sobre prototipos de la familia de fenotiazinas, toluidine blue O (TBO) y azure A (AzA), con la finalidad de mejorar su eficacia fotodinámica. Se realizó la bromación de los reactivos de partida ensayando diferentes parámetros de síntesis para obtener los compuestos dibromados de toluidine blue O (TBOBr2), azure C (AzCBr2) y azure A (AzABr2). Los nuevos Fs se analizaron por cromatografía en placa fina, cromatografía líquida de alta eficacia y espectrofotometría UV-Visible. La caracterización por espectrometría de masas de alta resolución y espectroscopia de resonancia magnética nuclear de protones permitió corroborar la estructura de los productos obtenidos. El Fs AzABr2 resultó inestable en las condiciones de almacenamiento (ambiente de nitrógeno, oscuridad y baja temperatura). Por lo expuesto, se evaluaron las propiedades fisicoquímicas y fotoquímicas de TBOBr2 y AzCBr2. Los nuevos Fs bromados evidenciaron valores pKa cercanos al pH fisiológico, presentaron mejores rendimientos cuánticos de producción de oxígeno singlete que su precursor y fueron fotoquímicamente estables. Los estudios de agregación permitieron identificar a las especies monoméricas y agregadas de los Fs evaluando diferentes medios y concentraciones. Se llevaron a cabo ensayos de fotohemólisis in vitro de glóbulos rojos permitiendo inferir un mayor daño celular fotoinducido de TBOBr2 con relación a TBO y AzCBr2. Adicionalmente se determinó que los nuevos derivados presentan actividad fotodinámica principalmente mediante el mecanismo Tipo II.The objective of this doctoral thesis was the development of new phototherapeutic agents for their application in photodynamic therapy (PDT) and antimicrobial photodynamic therapy (APDT) used for the treatment of oncological and non-oncological pathologies, respectively. These therapeutic modalities have shown promising results and are based on the administration of photosensitizers (Ps), chemical compounds that absorb light of the appropriate wavelength and generate reactive oxygen species responsible for cell death. In this context the need to develop new second-generation Ps from structural modifications on prototypes of the phenothiazine family, toluidine blue O (TBO) and azure A (AzA), was raised in order to improve their photodynamic efficiency. The bromination of the starting reagents was carried out by testing different synthesis parameters to obtain the dibrominated compounds of toluidine blue O (TBOBr2), azure C (AzCBr2) and azure A (AzABr2). The new Ps were analyzed by thin layer chromatography, high performance liquid chromatography and UV-Visible spectrophotometry. Characterization by high resolution mass spectrometry and proton nuclear magnetic resonance spectroscopy allowed corroborating the structure of the products obtained. The Ps AzABr2 was unstable under storage conditions (nitrogen environment, darkness and low temperature). Therefore, the physicochemical and photochemical properties of TBOBr2 and AzCBr2 were evaluated. The new brominated Ps showed pKa values close to physiological pH, presented better quantum yield of singlet oxygen production than its precursor and were photochemically stable. On the other hand, the aggregation test made it possible to identify the monomeric and aggregated species of the studied Ps in different media and concentrations. Finally, in vitro photohemolysis red blood cells allowed inferring a higher photodynamic activity of the TBOBr2 in relation to TBO and AzCBr2. Furthermore, it was determined that the new derivatives obtained present their photodynamic activity predominantly through the Type II mechanism.2024-11-30Fil: Haniewicz, Cinthia Soledad. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas; Argentina

The structured organization of Deinococcus radiodurans' cell envelope

Surface layers (S-layers) are highly ordered coats of proteins localized on the cell surface of many bacterial species. In these structures, one or more proteins form elementary units that self-assemble into a crystalline monolayer tiling the entire cell surface. Here, the cell envelope of the radiation-resistant bacterium Deinococcus radiodurans was studied by cryo-electron microscopy, finding the crystalline regularity of the S-layer extended into the layers below (outer membrane, periplasm, and inner membrane). The cell envelope appears to be highly packed and resulting from a three-dimensional crystalline distribution of protein complexes organized in close continuity yet allowing a certain degree of free space. The presented results suggest how S-layers, at least in some species, are mesoscale assemblies behaving as structural and functional scaffolds essential for the entire cell envelope