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Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. In this study, we show that the nucleation and growth rates are correlated with the thermodynamics of metal–ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31 P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal–ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles. 

Abstract SARS-CoV-2 variants with spike (S)-protein D614G mutations now predominate globally. We therefore compare the properties of the mutated S protein (S G614 ) with the original (S D614 ). We report here pseudoviruses carrying S G614 enter ACE2-expressing cells more efficiently than those with S D614 . This increased entry correlates with less S1-domain shedding and higher S-protein incorporation into the virion. Similar results are obtained with virus-like particles produced with SARS-CoV-2 M, N, E, and S proteins. However, D614G does not alter S-protein binding to ACE2 or neutralization sensitivity of pseudoviruses. Thus, D614G may increase infectivity by assembling more functional S protein into the virion. 

Controlling the size distribution of nanoparticles is important for many applications and typically involves the use of ligands during synthesis. In this study, we show that the mechanism of size focusing involves a dependence of the growth rate on the size of the nanoparticles and the ligand coverage on the surface of the nanoparticles. To demonstrate these effects, we used in situ small angle X-ray scattering (SAXS) and population balance kinetic modeling (PBM) to investigate the evolution of size distribution during the synthesis of colloidal Pd metal nanoparticles. Despite temporal overlap of nucleation and growth, our in situ SAXS show size focusing of the distribution under different synthetic conditions (different concentrations of metal and ligand as well as solvent type). To understand the mechanism of size focusing using PBM, we systematically studied how the evolution of the nanoparticle size distribution is affected by nucleation rate, and dependence of the growth rate constant on ligand surface coverage, and size of the nanoparticles. We show that continuous nucleation contributes to size defocusing. However, continuous nucleation results in different reaction times for the nanoparticle population leading to time and size-dependent ligand surface coverage. Using density functional theory (DFT) calculations and Brønsted–Evans–Polanyi relations, we show that as the population grows, larger nanoparticles grow more slowly than smaller ones due to lower intrinsic activity and higher ligand coverage on the surface. Therefore, despite continuous nucleation, the faster growth of smaller nanoparticles in the population leads to size focusing. The size focusing behaviour (due to faster growth of smaller nanoparticles) was found to be model independent and similar results were demonstrated under different nucleation and growth pathways ( e.g. growth via ion reduction on the surface and/or monomer addition). Our results provide a microscopic connection between kinetics and thermodynamics of nanoparticle growth and metal–ligand binding, and their effect on the size distribution of colloidal nanoparticles. 

A significant negative correlation between the seasonal mean temperature anomaly and the intensity of the intraseasonal temperature oscillation in the northern winter over Northeast China is found during the time period 1959–2011. A stronger intraseasonal oscillation (ISO) is found during an extremely cold winter. The cold winter in Northeast China is a part of zonally oriented large‐scale pattern with a negative (positive) temperature anomaly in mid‐ (high) latitudes and is associated with a negative phase of the North Atlantic Oscillation (NAO). The intraseasonal temperature anomaly originates from high‐latitude Central Eurasia and propagates southeastward. The southeastward propagation is attributed to the upper tropospheric dispersion of Rossby wave energy as a result of coupling of the low‐level temperature and the upper‐level geopotential height. The cause of the negative correlation between the intraseasonal and interannual modes is investigated. A cold winter in Northeast China is associated with a weakened meridional temperature gradient and vertical wind shear north of 50°N. This weakens synoptic variability in situ through baroclinic instability. Because the ISO competes for an energy source with the synoptic motion, the ISO is enhanced north of 50°N. The southeastward propagation of the enhanced ISO mode increased intraseasonal temperature variability over Northeast China. As a result, a cold winter in Northeast China is accompanied by an enhanced ISO variability in situ. The enhanced local ISO could further feedback to the winter mean temperature anomaly through nonlinear advective processes. The diagnosis of the temperature budget indicates that the ISO may interact with motion on other scales to contribute to the winter mean temperature anomaly in situ.