Atomic layer coating of hafnium oxide on carbon nanotubes for high-performance field emitters

Carbon nanotubes coated with hafnium oxide exhibit excellent electron emission characteristics, including a low turn-on voltage, a high field enhancement factor, and exceptional current stability. Their enhanced emission performance was attributed to a decrease in the work function and an increase in the electron density of states at the carbon nanotube Fermi level closest to the conduction band minimum of hafnium oxide. In addition, the enhanced current stability was attributed to the ability of hafnium oxide to protect the carbon nanotubes against ions and free radicals created in the electron field emission process. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650471]ArticleAPPLIED PHYSICS LETTERS. 99(15):153115 (2011)journal articl

A Rare Case of Radial Arteriovenous Fistula After Coronary Angiography

The percutaneous transfemoral approach has been routinely used for cardiac catheterization and coronary angioplasty. Local vascular complications following angioplasty are seen in 5% to 10% of patients, especially in those who need prolonged anticoagulation. Transradial access for coronary procedures dramatically reduces access site complications. We report a rare case of radial arteriovenous fistula, which developed after coronary angiography perfomed using the transradial approach

A Rare Case of Radial Arteriovenous Fistula After Coronary Angiography

The percutaneous transfemoral approach has been routinely used for cardiac catheterization and coronary angioplasty. Local vascular complications following angioplasty are seen in 5% to 10% of patients, especially in those who need prolonged anticoagulation. Transradial access for coronary procedures dramatically reduces access site complications. We report a rare case of radial arteriovenous fistula, which developed after coronary angiography perfomed using the transradial approach

Multilayer Two-Dimensional Water Structure Confined in MoS_2

The conflicting interpretations (square vs rhomboidal) of the recent experimental visualization of the two-dimensional (2D) water confined in between two graphene sheets by transmission electron microscopy measurements, make it important to clarify how the structure of two-dimensional water depends on the constraining medium. Toward this end, we report here molecular dynamics (MD) simulations to characterize the structure of water confined in between two MoS_2 sheets. Unlike graphene, water spontaneously fills the region sandwiched by two MoS_2 sheets in ambient conditions to form planar multilayered water structures with up to four layer. These 2D water molecules form a specific pattern in which the square ring structure is formed by four diamonds via H-bonds, while each diamond shares a corner in a perpendicular manner, yielding an intriguing isogonal tiling structure. Comparison of the water structure confined in graphene (flat uncharged surface) vs MoS_2 (ratchet-profiled charged surface) demonstrates that the polarity (charges) of the surface can tailor the density of confined water, which in turn can directly determine the planar ordering of the multilayered water molecules in graphene or MoS_2. On the other hand, the intrinsic surface profile (flat vs ratchet-profiled) plays a minor role in determining the 2D water configuration

Atomic layer coating of hafnium oxide on carbon nanotubes for high-performance field emitters

Carbon nanotubes coated with hafnium oxide exhibit excellent electron emission characteristics, including a low turn-on voltage, a high field enhancement factor, and exceptional current stability. Their enhanced emission performance was attributed to a decrease in the work function and an increase in the electron density of states at the carbon nanotube Fermi level closest to the conduction band minimum of hafnium oxide. In addition, the enhanced current stability was attributed to the ability of hafnium oxide to protect the carbon nanotubes against ions and free radicals created in the electron field emission process. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650471]ArticleAPPLIED PHYSICS LETTERS. 99(15):153115 (2011)journal articl

Water interaction differences determine the relative energetic stability of the polyproline II conformation of the alanine dipeptide in aqueous environments

Although subsequent studies have provided extensive support for the 1968 Tiffany and Krimm proposal (Biopolymers 6, 1379) that the polyproline II (PPII) conformation is a significant component of the structure of unordered polypeptide chains, two issues are still not fully resolved: the PPII persistence length in a chain and the source of its relative stability with respect to the β‐conformation. We examine the latter question by studying the B97‐D/6‐31++G ** energy, in the absence and presence of a reaction field, of the alanine dipeptide hydrated by various amounts of explicit waters and resolving this into its three components: the energies of the individual solvated peptides and water structures plus the interaction energy involving them. We find that the relative stability of the PPII conformation is determined mainly by the difference in the interaction energies of the water structures in the near‐peptide layers. © 2012 Wiley Periodicals, Inc. Biopolymers 97: 789–794, 2012.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92429/1/22064_ftp.pd

Temperature dependence of protein dynamics simulated with three different water models

The effect of variation of the water model on the temperature dependence of protein and hydration water dynamics is examined by performing molecular dynamics simulations of myoglobin with the TIP3P, TIP4P, and TIP5P water models and the CHARMM protein force field at temperatures between 20 and 300 K. The atomic mean-square displacements, solvent reorientational relaxation times, pair angular correlations between surface water molecules, and time-averaged structures of the protein are all found to be similar, and the protein dynamical transition is described almost indistinguishably for the three water potentials. The results provide evidence that for some purposes changing the water model in protein simulations without a loss of accuracy may be possible

Ultrafast 2D-IR and optical Kerr effect spectroscopy reveal the impact of duplex melting on the structural dynamics of DNA

Changes in the structural and solvation dynamics of a 15mer AT DNA duplex upon melting of the double-helix are observed by a combination of ultrafast two-dimensional infrared (2D-IR) and optical Kerr-effect (OKE) spectroscopies. 2D-IR spectroscopy of the vibrational modes of the DNA bases reveal signature off-diagonal peaks arising from coupling and energy transfer across Watson-Crick paired bases that are unique to double-stranded DNA (ds-DNA). Spectral diffusion of specific base vibrational modes report on the structural dynamics of the duplex and the minor groove, which is predicted to contain a spine of hydration. Changes in these dynamics upon melting are assigned to increases in the degree of mobile solvent access to the bases in single-stranded DNA (ss-DNA) relative to the duplex. OKE spectra exhibit peaks that are assigned to specific long-range phonon modes of ds- and ss-DNA. Temperature-related changes in these features correlate well with those obtained from the 2D-IR spectra although the melting temperature of the ds-DNA phonon band is slightly higher than that for the Watson-Crick modes, suggesting that a degree of long-range duplex structure survives the loss of Watson-Crick hydrogen bonding. These results demonstrate that the melting of ds-DNA disrupts helix-specific structural dynamics encompassing length scales ranging from mode delocalisation in the Watson-Crick base pairs to long-range phonon modes that extend over multiple base pairs and which may play a role in molecular recognition of DNA

Vibrational Spectroscopic Map, Vibrational Spectroscopy, and Intermolecular Interaction

© 2020 American Chemical Society. Vibrational spectroscopy is an essential tool in chemical analyses, biological assays, and studies of functional materials. Over the past decade, various coherent nonlinear vibrational spectroscopic techniques have been developed and enabled researchers to study time-correlations of the fluctuating frequencies that are directly related to solute-solvent dynamics, dynamical changes in molecular conformations and local electrostatic environments, chemical and biochemical reactions, protein structural dynamics and functions, characteristic processes of functional materials, and so on. In order to gain incisive and quantitative information on the local electrostatic environment, molecular conformation, protein structure and interprotein contacts, ligand binding kinetics, and electric and optical properties of functional materials, a variety of vibrational probes have been developed and site-specifically incorporated into molecular, biological, and material systems for time-resolved vibrational spectroscopic investigation. However, still, an all-encompassing theory that describes the vibrational solvatochromism, electrochromism, and dynamic fluctuation of vibrational frequencies has not been completely established mainly due to the intrinsic complexity of intermolecular interactions in condensed phases. In particular, the amount of data obtained from the linear and nonlinear vibrational spectroscopic experiments has been rapidly increasing, but the lack of a quantitative method to interpret these measurements has been one major obstacle in broadening the applications of these methods. Among various theoretical models, one of the most successful approaches is a semiempirical model generally referred to as the vibrational spectroscopic map that is based on a rigorous theory of intermolecular interactions. Recently, genetic algorithm, neural network, and machine learning approaches have been applied to the development of vibrational solvatochromism theory. In this review, we provide comprehensive descriptions of the theoretical foundation and various examples showing its extraordinary successes in the interpretations of experimental observations. In addition, a brief introduction to a newly created repository Web site (http://frequencymap.org) for vibrational spectroscopic maps is presented. We anticipate that a combination of the vibrational frequency map approach and state-of-the-art multidimensional vibrational spectroscopy will be one of the most fruitful ways to study the structure and dynamics of chemical, biological, and functional molecular systems in the future