Spontaneous and Directed Symmetry Breaking in the Formation of Chiral Nanocrystals

The homochirality of biomolecules remains one of the outstanding puzzles concerning the beginning of life. Chiral amplification of a randomly perturbed racemic mixture of chiral molecules is a well-accepted prerequisite for all routes to biological homochirality. Some models have suggested that such amplification occurred due to asymmetric discrimination of chiral biotic or prebiotic molecules when they adsorbed onto crystalline surfaces. While chiral amplification has been demonstrated on surfaces of both chiral and achiral crystals, the mechanism that would produce an enantiomeric imbalance in the chiral surfaces themselves has not been addressed. Here we report strong chiral amplification in the colloidal synthesis of intrinsically chiral lanthanide phosphate nanocrystals, quantitatively measured via the circularly polarized luminescence of the lanthanide ions within the nanocrystals. The amplification involves spontaneous symmetry breaking into either left- or right-handed nanocrystals below a critical temperature. Furthermore, chiral tartaric acid molecules in the solution act as an external chiral field, sensitively directing the amplified nanocrystal handedness through a discontinuous transition between left- and right-handed excess. These characteristics suggest a conceptual framework for chiral amplification, based on the statistical thermodynamics of critical phenomena, which we use to quantitatively account for the observations. Our results demonstrate how chiral minerals with high enantiomeric excess could have grown locally in a primordial racemic aqueous environment.Comment: 9 pages, 4 figure

Spontaneous patterning of quantum dots at the air-water interface

Nanoparticles deposited at the air-water interface are observed to form circular domains at low density and stripes at higher density. We interpret these patterns as equilibrium phenomena produced by a competition between an attraction and a longer-ranged repulsion. Computer simulations of a generic pair potential with attractive and repulsive parts of this kind, reproduce both the circular and stripe patterns. Such patterns have a potential use in nanoelectronic applications

The solvation of Cl − , Br − , and I − in acetonitrile clusters: Photoelectron spectroscopy and molecular dynamics simulations

We present the photoelectron spectra of Cl−, Br−, and I− solvated in acetonitrile clusters (CH3CN) n with n=1–33, 1–40, and 1–55, respectively, taken with 7.9 eV photon energy. Anion–solvent electrostatic stabilization energies are extracted from the measured vertical electron binding energies. The leveling of stabilization energies beyond n=10–12 for the three halides signifies the completion of the first solvation layer. This is different from the behavior of anion–water clusters which probably do not fill the first solvation layer, but rather form surface solvation states. Classical molecular dynamics simulations of halide–acetonitrile clusters reproduce the measured stabilization energies and generate full solvation shells of 11–12, 12, and 12–13 solvent molecules for Cl−, Br−, and I−, respectively. Ordered shell structures with high stability were found for the clusters of Cl−, Br−, and I− with n=9, 9, and 12. This special stability is reflected in the intensity distribution of the clusters in the mass spectra. Larger anion–acetonitrile clusters have the molecules beyond the first solvation layer packed in a small droplet which is attached to the first layer. It is suggested that in general, anions solvated in large clusters of polar solvents, might be located close to their surface

Parallel fabrication and single-electron charging of devices based on ordered, two-dimensional phases of organically functionalized metal nanocrystals

A parallel technique for fabricating single-electron, solid-state capacitance devices from ordered, two-dimensional closest-packed phases of organically functionalized metal nanocrystals is presented. The nanocrystal phases were prepared as Langmuir monolayers and subsequently transferred onto Al-electrode patterned glass substrates for device construction. Alternating current impedance measurements were carried out to probe the single-electron charging characteristics of the devices under both ambient and 77 K conditions. Evidence of a Coulomb blockade and step structure reminiscent of a Coulomb staircase is presented

Aluminum Nanoparticles with Hot Spots for Plasmon-Induced Circular Dichroism of Chiral Molecules in the UV Spectral Interval

Plasmonic nanocrystals with hot spots are able to localize optical energy in small spaces. In such physical systems, near-field interactions between molecules and plasmons can become especially strong. This paper considers the case of a nanoparticle dimer and a chiral biomolecule. In our model, a chiral molecule is placed in the gap between two plasmonic nanoparticles, where the electromagnetic hot spot occurs. Since many important biomolecules have optical transitions in the UV, we consider the case of Aluminum nanoparticles, as they offer strong electromagnetic enhancements in the blue and UV spectral intervals. Our calculations show that the complex composed of a chiral molecule and an Al-dimer exhibits strong CD signals in the plasmonic spectral region. In contrast to the standard Au- and Ag-nanocrystals, the Al system may have a much better spectral overlap between the typical biomolecule's optical transitions and the nanocrystals' plasmonic band. Overall, we found that Al nanocrystals used as CD antennas exhibit unique properties as compared to other commonly studied plasmonic and dielectric materials. The plasmonic systems investigated in this study can be potentially used for sensing chirality of biomolecules, which is of interest in applications such as drug development.Comment: 31 pages, 7 figure

НЕЛИНЕЙНАЯ УСТОЙЧИВОСТЬ СИНУСОИДАЛЬНОЙ ВЕЛАРОИДАЛЬНОЙ ОБОЛОЧКИ

The nonlinear analysis of thin-walled shells is not a rarity, particularly the nonlinear strength one. Many works are devoted to linear and nonlinear analyses of shells of classical form: cylindrical, spherical, hemispherical, shallow, conical. The concept of shells of complex geometry appears when the coefficients of the first and second quadratic forms of their middle surfaces are functions of the curvilinear coordinates. Concerning nonlinearity, it is generally accepted that four different sources of nonlinearity exist in solid mechanics: the geometric nonlinearity, the material nonlinearity and the kinetic nonlinearity. The above theoretical aspect of the nonlinearity, applied to a sinusoidal velaroidal shell with the inner radius r0=1m, the outer radius R=20m and the number of waves n= 8, will give rise to the investigation of its nonlinear buckling resistance. The building material is a concrete. The investigation emphasizes more on the material and the geometric nonlinearities, which are more closed to the reality. Finite element model of the shell consists of 6400 elements and 3280 nodes, the total number of nodal unknown - 18991. For surface modelling was used flat shell elements with six degrees of freedom in the node. The boundary conditions cor- respond to hinged bearing on the outer and inner contours. The result of the investigation is the buckling force of the shell under self-weight and uniformly vertically distributed load on its area, the corresponding numerical values of displacements and the buckling modeБольшое количество исследований посвящено линейному анализу напряженно - деформированного состояния (НДС) оболочек классической формы: цилиндрической, сферической, полусферической и конической. Однако НДС тонких оболочек сложной геометрии исследовано недостаточно. Понятие оболочек сложной геометрии возникает тогда, когда коэффициенты первой и второй квадратичных форм их срединных поверхностей представляют собой довольно сложные функции криволинейных координат. В статье рассматривается материальная нелинейная устойчивость железобетонной синусоидальной велароидальной оболочки с внутренним радиусом r0 =1 м, внешним радиусом R = 20 м и числом волн n = 8. Оболочка нагружалась нагрузкой от собственного веса и снеговой равномерно распределенной нагрузкой интенсивностью 0,252 т/м2. Численные расчеты проводились в программных комплексах LIRA-SAPR 2013 и STARK ES 2015. Конечноэлементная модель оболочки состоит из 6400 элементов и 3280 узлов, общее число узловых неизвестных - 18991. Для моделирования поверхности использовались плоские оболочечные элементы, имеющие шесть степеней свободы в узле. Граничные условия соответствовали шарнирному опиранию по наружному и внутреннему контурам. В результате расчетов были получены значения перемещений и формы потери устойчивости

Reversible Metal-Insulator Transition in Ordered Metal Nanocrystal Monolayers Observed by Impedance Spectroscopy

Low frequency impedance spectroscopy was applied on a Langmuir monolayer of alkylthiol passivated 35 Å diameter silver quantum dots, as a function of interparticle separation distance. As interparticle spacing decreases below 30% of particle diameter, a reduction in interparticle charge tunneling time is observed. On further compression, the complex impedance of the films undergoes a transition from a parallel RC equivalent circuit to an inductive circuit. Optical reflectance changes in the films are consistent with the deduced metal-insulator transition

Universal imprinting of chirality with chiral light by employing plasmonic metastructures

Chirality, either of light or matter, has proved to be very practical in biosensing and nanophotonics. However, the fundamental understanding of its temporal dynamics still needs to be discovered. A realistic setup for this are the so-called metastructures, since they are optically active and are built massively, hence rendering an immediate potential candidate. Here we propose and study the electromagnetic-optical mechanism leading to chiral optical imprinting on metastructures. Induced photothermal responses create anisotropic permittivity modulations, different for left or right circularly polarized light, leading to temporal-dependent chiral imprinting of hot-spots, namely imprinting of chirality. The above effect has not been observed yet, but it is within reach of modern experimental approaches. The proposed nonlinear chiroptical effect is general and should appear in any anisotropic material; however, we need to design a particular geometry for this effect to be strong. These new chiral time-dependent metastructures may lead to a plethora of applications.Comment: Main (29 pages, 6 figures) and supplemental (46 pages, 35 figures