Electrolyte and Temperature Effects on Third-Order Susceptibility in Sum-Frequency Generation Spectroscopy of Aqueous Salt Solutions

Sum-frequency generation (SFG) spectra from charged solid–liquid interfaces include significant contribution from third-order susceptibility χ⁽³⁾, which mainly originates from induced water orientation in the electric double layer. We quantitatively evaluate the χ⁽³⁾ susceptibility by molecular dynamics simulation in aqueous electrolyte solutions with varying concentrations and temperatures. We found that the value of χ⁽³⁾ decreases with increasing concentration or temperature and that the perturbation on χ⁽³⁾ is quite well-correlated with that on the dielectric constant ϵ of the solution. This correlation is understood as both quantities are commonly governed by the response of molecular orientation to the electric field. Accurate evaluation of χ⁽³⁾ in various conditions is important in quantitative estimate of the third-order effect on the SFG spectroscopy, particularly in conditions of high surface charge and ion concentration

Hydrogen-Bonding Structure at Zwitterionic Lipid/Water Interface

Interface structure of water/[3-palmitoyl-2-oleoyl-d-glycero-1-phosphatidylcholine] (POPC) lipid layer is investigated with molecular dynamics (MD) simulation by analyzing the recent heterodyne-detected vibrational sum-frequency generation (HD VSFG) spectroscopy. The MD simulation clearly reproduced the experimental HD VSFG spectrum of imaginary susceptibility (Im­[χ]), which exhibits two positive bands in the OH stretching vibrations of water. With the help of decomposition MD analysis, we found three kinds of interfacial water in relation to the HD VSFG spectrum. The low-frequency positive band is attributed to the water pointing toward the lipid side, whose orientation is influenced by negatively charged phosphate and positively charged choline of POPC. The high-frequency positive band is attributed to the water bonding with the carbonyl groups of the lipid. The gap between the two positive bands indicates the interfacial water pointing toward the bulk water phase in the vicinity of the choline groups

Why is Benzene Soluble in Water? Role of OH/π Interaction in Solvation

The XH/π interaction (X = C, N, or O) plays an essential role in a variety of fundamental processes in condensed phase, and it attracts broad interests in the fields of chemistry and biochemistry in recent years. This issue has a direct relevance to an intriguing phenomenon that a benzene molecule exhibits a negative solvation free energy of −0.87 kcal/mol in ambient water though it is a typical nonpolar organic solute. In this work, we developed a novel method to analyze the free energy δμ due to the electron density fluctuation of a solute in solution to clarify the mechanism responsible for the affinity of benzene to bulk water. Explicitly, the free energy δμ is decomposed into contributions from σ and π electrons in π-conjugated systems on the basis of the QM/MM method combined with a theory of solutions. With our analyses, the free energy δμ_π arising from the fluctuation of π electrons in benzene was obtained as −0.94 kcal/mol and found to be the major source of the affinity of benzene to water. Thus, the role of π electrons in hydration is quantified for the first time with our analyses. Our method was applied to phenyl methyl ether (PME) in water solution to examine the substituent effects of the electron donating group (EDG) on the hydration of a π-conjugated system. The delocalization effect of the π electrons on hydration was also investigated performing the decomposition analyses for ethene and 1,3-butadiene molecules in water solutions. It was revealed that the stabilization due to δμ_π for butadiene (−0.76 kcal/mol) is about three times as large as that for ethene (−0.26 kcal/mol), which suggests the importance of the delocalization effect of the π electrons in mediating the affinity to polar solvent

Origin of Vibrational Spectroscopic Response at Ice Surface

Since the basal plane surface of ice was first observed by sum frequency generation, an extraordinarily intense band for the hydrogen­(H)-bonded OH stretching vibration has been a matter of debate. We elucidate the remarkable spectral feature of the ice surface by quantum mechanics/molecular mechanics calculations. The intense H-bonded band is originated mostly from the “bilayer-stitching” modes of a few surface bilayers, through significant intermolecular charge transfer. The mechanism of enhanced signal is sensitive to the order of the tetrahedral ice structure, as the charge transfer is coupled to the vibrational delocalization

Sputter Deposition toward Short Cationic Thiolated Fluorescent Gold Nanoclusters: Investigation of Their Unique Structural and Photophysical Characteristics Using High-Performance Liquid Chromatography

We herein present the preparation of short, bulky cationic thiolate (thiocholine)-protected fluorescent Au nanoclusters via sputter deposition over a liquid polymer matrix. The obtained Au nanoclusters showed near-infrared fluorescence and had an average core diameter of 1.7 ± 0.6 nm, which is too large compared to that of the reported fluorescent Au nanoclusters prepared via chemical means. We revealed the mechanism of formation of this unique material using single-particle electron microscopy, optical measurements, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography fractionations. The noncrystallized image was observed via single-particle high-angle annular dark-field scanning transmission electron microscopy observations and compared with chemically synthesized crystalline Au nanoparticle with the same diameter, which demonstrated the unique structural characteristic speculated via XPS. The size fractionation and size-dependent fluorescence measurement, together with other observations, indicated that the nanoclusters most probably contained a mixture of very small fluorescent species in their aggregated form and were derived from the sputtering process itself and not from the interaction between thiol ligands

Surface Structure of Organic Carbonate Liquids Investigated by Molecular Dynamics Simulation and Sum Frequency Generation Spectroscopy

The vapor–liquid interface structures of two typical organic carbonates, propylene carbonate (PC) and dimethyl carbonate (DMC), are investigated in collaboration of sum frequency generation (SFG) spectroscopy and molecular dynamics (MD) simulation. The present general molecular model for organic carbonates well reproduces various liquid properties, including density, heat of vaporization, and infrared, Raman and SFG spectra. The MD simulation revealed contrasting interface structures between PC and DMC. The PC interface exhibits layered structure of oscillatory orientation, while the DMC interface is quite random. The structural feature of the PC interface is mainly attributed to dimer formation of PC molecules. We elucidated that the different surface structures are manifested in their Im­[χ⁽²⁾] SFG spectra in the CO stretching band, showing opposite signs of bipolar peaks between the two liquids

Correlation of phosphorylation at Tyr-342 of FOXP3 with transcriptional regulation.

<p>(A) Comparison of the phosphorylation levels of FOXP3 mutants. The level of phosphorylated (top) and total (middle) FOXP3 immunoprecipitated and constitutively-active mutant of LCK (LCK CA) in cell lysates (bottom) was detected using Western blotting. Phosphorylation of Y330F and Y342F mutants of FOXP3 was greatly decreased compared with FOXP3 WT. (B) Comparison of MMP9 expression regulated by FOXP3 mutant. MMP9 expression was analyzed using a zymography assay (top). FOXP3, LCK CA, and actin expression was determined using Western blotting (middle). MMP9 expression level was normalized with actin (bottom). FOXP3 Y342F mutant was unable to suppress MMP9 unlike FOXP3 WT and Y330F mutant. The data represents the mean ± S.E. of three independent experiments. The asterisks indicate statistically significant differences (<i>p</i> < 0.01, Fisher's LSD test). (C) Real-time PCR analysis of <i>MMP9</i> in FOXP3 Y342F expressing cells. <i>MMP9</i> expression in FOXP3 Y342F cells was significantly increased compared with FOXP3 WT cells. The data represents the mean ± S.E. of three independent experiments. The asterisks indicate statistically significant differences (<i>p</i> < 0.01, Tukey-Kramer test). (D) <i>In </i><i>vitro</i> kinase assay. Analysis of phosphorylation of MBP-FOXP3 and MBP-FOXP3 Y342A (arrow) by LCK. Phosphorylation of MBP-FOXP3 (Y342A) was remarkably decreased compared with that of MBP-FOXP3 (WT). (E) Western blotting analysis using an anti-pTyr-342-specific antibody. FOXP3 and FOXP3 Y342F were immunoblotted with the anti-pTyr342 antibody. The antibody detected phosphorylation of FOXP3 only when LCK was co-transfected. (F) Levels of invasive cells. The cell number that invaded matrigel was normalized with cell counts that invaded the control insert. FOXP3 Y342F cells showed higher invasive rates than FOXP3 WT cells. The data represents the mean ± S.E. of six independent experiments. The asterisks indicate statistically significant difference (<i>p</i> < 0.01, Tukey-Kramer test).</p

Phosphorylation of FOXP3 by LCK Downregulates MMP9 Expression and Represses Cell Invasion

<div><p>Forkhead Box P3 (FOXP3) is a member of the forkhead/winged helix family of the transcription factors and plays an important role not only as a master gene in T-regulatory cells, but also as a tumor suppressor. In this study, we identified lymphocyte-specific protein tyrosine kinase (LCK), which correlates with cancer malignancy, as a binding partner of FOXP3. FOXP3 downregulated LCK-induced <i>MMP9</i>, <i>SKP2</i>, and <i>VEGF-A</i> expression. We observed that LCK phosphorylated Tyr-342 of FOXP3 by immunoprecipitation and <i>in vitro</i> kinase assay, and the replacement of Tyr-342 with phenylalanine (Y342F) abolished the ability to suppress MMP9 expression. Although FOXP3 decreased the invasive ability induced by LCK in MCF-7 cells, Y342F mutation in FOXP3 diminished this suppressive effect. Thus we demonstrate for the first time that LCK upregulates FOXP3 by tyrosine phosphorylation, resulting in decreased MMP9, SKP2, and VEGF-A expression, and suppressed cellular invasion. We consider that further clarification of transcriptional mechanism of FOXP3 may facilitate the development of novel therapeutic approaches to suppress cancer malignancy. </p> </div

Real-time PCR analyses for <i>SKP2</i> and <i>VEGF-A</i>.

<p>(A) Real-time PCR analyses of <i>SKP2</i> expression and (B) <i>VEGF-A</i> expression. Gene expression was normalized with <i>18S </i><i>rRNA</i> gene expression. FOXP3 WT suppressed the genes upregulated by LCK, while FOXP3 Y342F lost that capability. The data represents the mean ± S.E. of six independent experiments (*<i>p</i> < 0.05, *<i>p</i> < 0.01; Tukey-Kramer test). The data represents the mean ± S.E. of three independent experiments. The asterisks indicate statistically significant difference (<i>p</i> < 0.01, Tukey-Kramer test). </p

Alignment of amino acid sequence of FOXP3.

<p>ClustalW was used for the multiple alignment of amino acid sequence of FOXP3 from <i>Homo sapiens</i>, <i>Macaca fascicularis</i>, <i>Felis catus</i>, <i>Equus caballus</i>, <i>Bos taurus</i>, <i>Mus musculus</i>, <i>Rattus norvegicus</i>, <i>Xenopus tropicalis</i>, and <i>Danio rerio</i>. Black, red, and blue areas indicate identical, high, and low homologous amino acid residues, respectively. The tyrosine residues are represented by residue numbers. </p