Micro-Raman spectroscopic analysis of liquid-liquid phase separation.

Liquid-liquid phase separation (LLPS) plays a significant role in various biological processes, including the formation of membraneless organelles and pathological protein aggregation. Although many studies have found various factors that modulate the LLPS process or the liquid-to-solid phase transition (LSPT) using microscopy or fluorescence-based methods, the molecular mechanistic details underlying LLPS and protein aggregation within liquid droplets remain uncharacterized. Therefore, structural information on proteins inside liquid droplets is required to understand the mechanistic link to amyloid formation. In the present study, we monitored droplet formation related to protein fibrillation using micro-Raman spectroscopy in combination with differential interference contrast (DIC) microscopy to study the conformational change in proteins and the hydrogen-bonding (H-bonding) structure of water during LLPS. Interestingly, we found that the O-D stretching band for water (HOD in H2O) inside the droplets exhibited a distinct Raman spectrum from that of the bulk water, suggesting that the time-dependent change in the hydration environment in the protein droplets during the process of LLPS can be studied. These results demonstrate that the superior spatial resolution of micro-Raman spectroscopy offers significant advantages in investigating the molecular mechanisms of LLPS and following LSPT processes.

Molecular Photothermal Effect on the 2D-IR Spectroscopy of Acetonitrile-Based Li-Ion Battery Electrolytes.

Advancements in Li-ion battery (LIB) technology hinge on an understanding of Li-ion solvation and charge transport dynamics. Ultrafast two-dimensional infrared (2D-IR) spectroscopy has been used to investigate these dynamics in electrolytes by probing chemical exchange processes through time-dependent cross-peak analysis. However, accurate interpretation is complicated by factors such as vibrational energy transfer and molecular photothermal effect (MPTE), affecting cross-peak evolution. Pinpointing the precise origin of these cross-peaks has posed a significant challenge in time-resolved IR spectroscopic studies of LIB electrolytes. Here, we trace the origin of 2D-IR cross-peaks of LIB electrolytes utilizing acetonitrile as a solvent. Time-dependent analysis of LiSCN and CH3SCN mixtures in CD3CN revealed distinctive MPTE features. Furthermore, direct observation of intermolecular MPTE through two-color IR pump-probe spectroscopy lends support to the findings. Our results emphasize the non-negligible artifacts induced by MPTE and the necessity of considering these effects to accurately observe the ultrafast dynamics within LIB electrolytes.

Direct observation of protein structural transitions through entire amyloid aggregation processes in water using 2D-IR spectroscopy.

Amyloid proteins that undergo self-assembly to form insoluble fibrillar aggregates have attracted much attention due to their role in biological and pathological significance in amyloidosis. This study aims to understand the amyloid aggregation dynamics of insulin (INS) in H2O using two-dimensional infrared (2D-IR) spectroscopy. Conventional IR studies have been performed in D2O to avoid spectral congestion despite distinct H-D isotope effects. We observed a slowdown of the INS fibrillation process in D2O compared to that in H2O. The 2D-IR results reveal that different quaternary structures of INS at the onset of the nucleation phase caused the distinct fibrillation pathways of INS in H2O and D2O. A few different biophysical analysis, including solution-phase small-angle X-ray scattering combined with molecular dynamics simulations and other spectroscopic techniques, support our 2D-IR investigation results, providing insight into mechanistic details of distinct structural transition dynamics of INS in water. We found the delayed structural transition in D2O is due to the kinetic isotope effect at an early stage of fibrillation of INS in D2O, i.e., enhanced dimer formation of INS in D2O. Our 2D-IR and biophysical analysis provide insight into mechanistic details of structural transition dynamics of INS in water. This study demonstrates an innovative 2D-IR approach for studying protein dynamics in H2O, which will open the way for observing protein dynamics under biological conditions without IR spectroscopic interference by water vibrations.

IrCo nanocacti on CoxSy nanocages as a highly efficient and robust electrocatalyst for the oxygen evolution reaction in acidic media.

Developing highly efficient Ir-based electrocatalysts for the oxygen evolution reaction (OER) has been an important agenda in spearheading the water splitting technology. In this study, the synthesis of IrCo nanocacti on CoxSy nanocages (ICS NCs) is demonstrated by utilizing CoO@CoxSy nanoparticles as reactive nanotemplates. In addition to the high catalytic activities with a low overpotential of 281 mV at 10 mA cm-2 and an outstanding mass activity of 1285 mA mgIr-1 at 1.53 V, the ICS NCs endure a prolonged OER test for over 100 h, greatly outperforming other previously reported Ir-based electrocatalysts. This work suggests that the unique hetero-nanostructure of IrCo/CoxSy induces in situ S doping during electrochemical oxidation and the beneficial effect of S doping on the enhanced stability of ICS NCs for the OER.

Dual wavelength lasing of InGaN/GaN axial-heterostructure nanorod lasers.

Optical confinement effects are investigated in InGaN/GaN axial-heterostructure nanolasers. Cylindrical nanorods with GaN/InGaN/GaN structures are prepared using combined processes of top-down and bottom-up approaches. The lasing of InGaN is observed at a low threshold (1 µJ cm-2), which is attributed to an efficient carrier transfer process from GaN to InGaN. The lasing of GaN is also found in the threshold range of 10-20 µJ cm-2 with a superlinear increase in emission intensity and high quality factors (Q = 1000), implying that dual wavelengths of lasing are tunable as a function of excitation intensity. The non-classical Fabry-Pérot modes suggest strong light-matter interactions in nanorods by optical confinement effects. The polarization of lasing indicates that the non-classical modes are in the identical transverse mode, which supports the formation of exciton-polaritons in nanorods. Polariton lasing in a single axial-heterostructure nanorod is observed for the first time, which proposes small-sized light sources with low threshold, polarized light, and tunable wavelengths in a single nanorod.

Modified Distribution-Free Goodness-of-Fit Test Statistic.

Covariance structure analysis and its structural equation modeling extensions have become one of the most widely used methodologies in social sciences such as psychology, education, and economics. An important issue in such analysis is to assess the goodness of fit of a model under analysis. One of the most popular test statistics used in covariance structure analysis is the asymptotically distribution-free (ADF) test statistic introduced by Browne (Br J Math Stat Psychol 37:62-83, 1984). The ADF statistic can be used to test models without any specific distribution assumption (e.g., multivariate normal distribution) of the observed data. Despite its advantage, it has been shown in various empirical studies that unless sample sizes are extremely large, this ADF statistic could perform very poorly in practice. In this paper, we provide a theoretical explanation for this phenomenon and further propose a modified test statistic that improves the performance in samples of realistic size. The proposed statistic deals with the possible ill-conditioning of the involved large-scale covariance matrices.

Tuning Band Alignments and Charge-Transport Properties through MoSe2 Bridging between MoS2 and Cadmium Sulfide for Enhanced Hydrogen Production.

Transition-metal dichalcogenide materials play a major role in the state-of-the-art innovations for energy conversion because of potential applications resulting from their unique properties. These materials additionally show inordinate potential toward the progress of hygienic power sources to deal with increasing environmental disputes at the time of skyrocketing energy demands. Herein, we report earth-abundant, few-layered, MoSe2-bridged MoS2/cadmium sulfide (CdS) nanocomposites, which reduce photogenerated electron and hole recombination by effectively separating charge carriers to achieve a high photocatalytic efficiency. Accordingly, the MoSe2-bridged MoS2/CdS system produced effective hydrogen (193 µmol·h-1) as that of water using lactic acid as a hole scavenger with the irradiation of solar light. The presence of few-layered MoSe2 bridges in MoS2/CdS successfully separates photogenerated charge carriers, thereby enhancing the shuttling of electrons on the surface to active edge sites. To the best of our knowledge, this few-layered MoSe2-bridged MoS2/CdS system exhibits the most effective concert among altogether-reported MoS2-based CdS composites. Notably, these findings with ample prospective for the development of enormously real photocatalytic systems are due to their economically viable and extraordinary efficiency.

Normal Versus Noncentral Chi-square Asymptotics of Misspecified Models.

The noncentral chi-square approximation of the distribution of the likelihood ratio (LR) test statistic is a critical part of the methodology in structural equation modeling. Recently, it was argued by some authors that in certain situations normal distributions may give a better approximation of the distribution of the LR test statistic. The main goal of this article is to evaluate the validity of employing these distributions in practice. Monte Carlo simulation results indicate that the noncentral chi-square distribution describes behavior of the LR test statistic well under small, moderate, and even severe misspecifications regardless of the sample size (as long as it is sufficiently large), whereas the normal distribution, with a bias correction, gives a slightly better approximation for extremely severe misspecifications. However, neither the noncentral chi-square distribution nor the theoretical normal distributions give a reasonable approximation of the LR test statistics under extremely severe misspecifications. Of course, extremely misspecified models are not of much practical interest. We also use the Thurstone data ( Thurstone & Thurstone, 1941 ) from a classic study of mental ability for our illustration.