Effects of chain-chain interaction on the configuration of short-chain alkanethiol self-assembled monolayers on a metal surface.

Surface-specific sum frequency generation vibrational spectroscopy is applied to study the molecular configuration of short-chain n-alkanethiol self-assembled monolayers (SAMs with n = 2-6) on the Au surface. For monolayers with n≥ 3, the alkanethiols are upright-oriented, with the CH3 tilt angle varying between ∼33° and ∼46° in clear even-odd dependency. The ethanethiol monolayer (n = 2) is, however, found to exhibit a distinct lying-down configuration with a larger methyl tilt angle (67°-79°) and a smaller CH2 tilt angle (56°-68°).

An economical single-shot pulse picker without nonlinear effect and dispersion.

An economical and stable single-shot pulse picker design without dispersion, nonlinear effect, and limitation on wavelength is proposed. This design is composed of a periodic pulse blocker (PPB), a control unit, and a mechanical shutter. It has successfully been applied to the commercial high-fluence femtosecond laser with 11-mm beam diameter, 2-mJ pulse energy, and 1-kHz repetition rate.

Surface Potential at Electrolyte/Air Interfaces: A Quantitative Analysis via Sum-Frequency Vibrational Spectroscopy.

We conduct a quantitative phase-sensitive sum-frequency vibrational spectroscopic investigation on the air/water interface with various atmospherically relevant ions in water in submolar concentrations. At electrolyte concentrations below 0.1 M, the spectral changes of the OH-stretching resonance induced by ions exhibit no ion specificity and resemble the lineshape of the third-order nonlinear optical susceptibility of bulk water.

Momentum-dependent sum-frequency vibrational spectroscopy of bonded interface layer at charged water interfaces.

Interface-specific hydrogen (H)-bonding network of water directly controls the energy transfer and chemical reaction pathway at many charged aqueous interfaces, yet to characterize these bonded water layer structures remains a challenge. We now develop a sum-frequency spectroscopic scheme with varying photon momenta as an all-optic solution for retrieving the vibrational spectra of the bonded water layer and the ion diffuse layer and, hence, microscopic structural and charging information about an interface. Application of the method to a model surfactant-water interface reveals a hidden weakly donor H-bonded water species, suggesting an asymmetric hydration-shell structure of fully solvated surfactant headgroups.

Therapeutic Potential of Human Umbilical Cord-Derived Mesenchymal Stem Cells in Recovering From Murine Pulmonary Emphysema Under Cigarette Smoke Exposure.

Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) were shown to have potential for immunoregulation and tissue repair. The objective of this study was to investigate the effects of hUC-MSCs on emphysema in chronic obstructive pulmonary disease (COPD). The C57BL/6JNarl mice were exposed to cigarette smoke (CS) for 4 months followed by administration of hUC-MSCs at 3 × 10 (low dose), 1 × 10 (medium dose), and 3 × 10 cells/kg body weight (high dose).

Potential surrogate quantitative immunomodulatory potency assay for monitoring human umbilical cord-derived mesenchymal stem cells production.

Mesenchymal stem cells (MSCs) play an important role as immune modulator through interaction with several immune cells, including macrophages. In this study, the immunomodulatory potency of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) was demonstrated in the in vivo middle cerebral artery occlusion (MCAo)-induced brain injury rat model and in vitro THP-1-derived macrophages model. At 24 h after induction of MCAo, hUC-MSCs was administered via tail vein as a single dose.

Effects of Human Umbilical Cord-Derived Mesenchymal Stem Cells on the Acute Cigarette Smoke-Induced Pulmonary Inflammation Model.

Cigarette smoke (CS) has been reported to induce oxidative stress and inflammatory process in the lungs. However, the role of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in the regulation of pulmonary inflammation remains unclear. The objective of this study is to investigate the effects of hUC-MSCs on lung inflammation in the acute CS-induced pulmonary inflammation animal model.

Wavelength-scanning second-harmonic generation for determining absolute charge density at aqueous interfaces.

We develop a new, to the best of our knowledge, optical scheme based on second-harmonic generation (SHG) at multiple wavelengths for unequivocal separation of the second-order and the electric-field-induced third-order nonlinear optical contributions from aqueous interfaces. The third-order SHG originating from the field-induced reorientation order of water molecules in the electrical double layer offers an optical label-free and inherent probe to the surface charge density and surface potential in the absolute scales. We verify this wavelength-scanning SHG scheme both theoretically and experimentally, and show that the approach is applicable to water interfaces with bulk ionic strength below 500 µM and can achieve a detection sensitivity for a surface charge density of ∼10/.

Affinity of Hydrated Protons at Intrinsic Water/Vapor Interface Revealed by Ion-Induced Water Alignment.

Protons at the water/vapor interface are relevant for atmospheric and environmental processes, yet characterizing their surface affinity on the quantitative level is still challenging. Here we utilize phase-sensitive sum-frequency vibrational spectroscopy to quantify the surface density of protons (or their hydronium form) at the intrinsic water/vapor interface through inspecting the surface-field-induced alignment of water molecules in the electrical double layer of ions. With hydrogen halides in water, the surface adsorption of protons is found to be independent of specific proton-halide anion interactions and to follow a constant adsorption free energy, Δ ≈ -3.

Direct Quantification of Water Surface Charge by Phase-Sensitive Second Harmonic Spectroscopy.

We developed and verified a phase-sensitive second harmonic generation spectroscopic scheme that allows for direct determination of the absolute surface charge density and surface potential of a water interface without the need for prior interfacial information. The method relies on selective probing of surface-field-induced reorientation order of water molecules in the electrical double layer and is, hence, independent of the interfacial molecular bonding structure. Application of this technique to a mixed surfactant monolayer on water suggests the manifest effect of the chain-chain interactions among the monolayer on adsorption of soluble ionic surfactants.

EphA2-positive human umbilical cord-derived mesenchymal stem cells exert anti-fibrosis and immunomodulatory activities via secretion of prostaglandin E2.

Objective: Previous study has demonstrated that EphA2 is a biomarker of mesenchymal stem cells (MSCs) from human placenta or umbilical cord and is able to distinguish MSCs from fibroblasts. In this study, we further examine the potential efficacy of EphA2 human umbilical cord-derived MSCs (hUC-MSCs).

Materials And Methods: MSCs specific markers, EphA2 and CD146 expression on the surface of hUC-MSCs were determined by flow cytometry analysis.

Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2.

We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state.

Unveiling Microscopic Structures of Charged Water Interfaces by Surface-Specific Vibrational Spectroscopy.

A sum-frequency spectroscopy scheme is developed that allows the measurement of vibrational spectra of the interfacial molecular structure of charged water interfaces. The application of this scheme to a prototype lipid-aqueous interface as a demonstration reveals an interfacial hydrogen-bonding water layer structure that responds sensitively to the charge state of the lipid headgroup and its interaction with specific ions. This novel technique provides unique opportunities to search for better understanding of electrochemistry and biological aqueous interfaces at a deeper molecular level.

Probing hydrophilic interface of solid/liquid-water by nanoultrasonics.

Despite the numerous devoted studies, water at solid interfaces remains puzzling. An ongoing debate concerns the nature of interfacial water at a hydrophilic surface, whether it is more solid-like, ice-like, or liquid-like. To answer this question, a complete picture of the distribution of the water molecule structure and molecular interactions has to be obtained in a non-invasive way and on an ultrafast time scale.

Thermal Boundary Resistance between GaN and Cubic Ice and THz Acoustic Attenuation Spectrum of Cubic Ice from Complex Acoustic Impedance Measurements.

A phonon nanoscopy method, based on the picosecond ultrasonics technique, capable of studying the complex acoustic reflection coefficient at frequency up to 1 THz is proposed and demonstrated. By measuring the reflection coefficient at the same surface location at the interface between GaN and air, and between GaN and the material to characterize, we get access to the THz amplitude and phase spectra of the acoustic phonon reflection. The retrieval of both these pieces of information then allows the calculation of the attenuation in a wide range of frequency and gives new insight into the Kapitza anomaly.

Specular scattering probability of acoustic phonons in atomically flat interfaces.

We report a direct determination of the specular scattering probability of acoustic phonons at a crystal boundary by observing the escape of incident coherent phonons from the coherent state during reflection. In the sub-THz frequency range where the phonon wavelength is much longer than the lattice constant, the acoustic phonon-interface interaction is found to agree well with the macroscopic theory on wave scattering from rough surfaces. This examination thus quantitatively verifies the dominant role of atomic-scale corrugations in the Kapitza anomaly observed at 1-10 K and further opens a new path to nondestructively estimate subnanoscale roughness of buried interfaces.

Cr:Forsterite-laser-based fiber-optic nonlinear endoscope with higher efficiencies.

We demonstrate a beam-scanning nonlinear light endoscope based on a flexible fiber bundle. Excited with a femtosecond Cr:Forsterite laser, the degradation in multiphoton multiharmonic excitation efficiency due to the pulse-broadening effect is significantly reduced without utilizing any external devices. The system resolution has been characterized to be 5.