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

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

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

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

Characterization of SARS-CoV-2 nucleocapsid protein oligomers

Oligomers of the SARS-CoV-2 nucleocapsid (N) protein are characterized by pronounced instability resulting in fast degradation. This property likely relates to two contrasting behaviors of the N protein: genome stabilization through a compact nucleocapsid during cell evasion and genome release by nucleocapsid disassembling during infection. In vivo, the N protein forms rounded complexes of high molecular mass from its interaction with the viral genome. To study the N protein and understand its instability, we analyzed degradation profiles under different conditions by size-exclusion chromatography and characterized samples by mass spectrometry and cryo-electron microscopy. We identified self-cleavage properties of the N protein based on specific Proprotein convertases activities, with Cl- playing a key role in modulating stability and degradation. These findings allowed isolation of a stable oligomeric complex of N, for which we report the 3D structure at ∼6.8 Å resolution. Findings are discussed considering available knowledge about the coronaviruses’ infection cycle

Probing the co-evolution of Supermassive Black Holes and their hosts from scaling relations pairwise residuals: dominance of stellar velocity dispersion and host halo mass

The correlations between supermassive black holes (SMBHs) and their host galaxies still defy our understanding from both the observational and theoretical perspectives. Here, we perform pairwise residual analysis on the latest sample of local inactive galaxies with a uniform calibration of their photometric properties and with dynamically measured masses of their central SMBHs. The residuals reveal that stellar velocity dispersion and, possibly host dark matter halo mass , appear as the galactic properties most correlated with SMBH mass, with a secondary (weaker) correlation with spheroidal (bulge) mass, as also corroborated by additional machine learning tests. These findings may favour energetic/kinetic feedback from active galactic nuclei (AGNs) as the main driver in shaping SMBH scaling relations. Two state-of-the-art hydrodynamic simulations, inclusive of kinetic AGN feedback, are able to broadly capture the mean trends observed in the residuals, although they tend to either favour as the most fundamental property, or generate too flat residuals. Increasing AGN feedback kinetic output does not improve the comparison with the data. In the Appendix, we also show that the galaxies with dynamically measured SMBHs are biased high in at fixed luminosity with respect to the full sample of local galaxies, proving that this bias is not a by-product of stellar mass discrepancies. Overall, our results suggest that probing the SMBH–galaxy scaling relations in terms of total stellar mass alone may induce biases, and that either current data sets are incomplete, and/or that more insightful modelling is required to fully reproduce observations

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

Isolation of monomeric photosystem II that retains the subunit PsbS

Photosystem II has been purified from a transplastomic strain of Nicotiana tabacum according to two different protocols. Using the procedure described in Piano et al. (Photosynth Res 106:221-226, 2010) it was possible to isolate highly active PSII composed of monomers and dimers but depleted in their PsbS protein content. A "milder" procedure than the protocol reported by Fey et al. (Biochim Biophys Acta 1777:1501-1509, 2008) led to almost exclusively monomeric PSII complexes which in part still bind the PsbS protein. This finding might support a role for PSII monomers in higher plants