Surface-enhanced Raman scattering in the ultraviolet spectral region: UV-SERS on rhodium and ruthenium electrodes

We report the first observation of surface-enhanced Raman scattering (SERS) excited with ultraviolet (UV) light from transition metal electrodes. Adsorbed pyridine and SCN- on rough rhodium (Rh) and ruthenium (Ru) electrodes, respectively, have been studied using 325 nm laser excitation. In contrast, the best enhancers in the visible and near infrared, silver and gold, do not produce UV-SERS. The experimental data of UV-SERS are in agreement with our preliminary theoretical calculation based on the electromagnetic enhancement mechanism. The enhancement factor is about 2 orders of magnitude for the Rh and Ru electrodes when they are excited at 325 nm.     

Fenton-type treatment: state of the art

The different currently used Fenton-type treatments, either chemically or electrochemically generated, are reviewed. A particular attention is devoted to the traditional Fe++/H2O2 chemical process and to the indirect electrochemical oxidation which uses in situ generated hydrogen peroxide. Mechanisms and experimental conditions employed for the optimisation of each technology are reported; moreover advantages and main limitations are discussed.     

Electrochemical and surfaced-enhanced Raman spectroscopic investigation of CO and SCN- adsorbed on Au(core)-Pt(shell) nanoparticles supported on GC electrodes

Core-shell Au-Pt nanoparticles were synthesized by using a seed growth method and characterized by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy. Au(core)-Pt(shell)/GC electrodes were prepared by drop-coating the nanoparticles on clean glassy carbon (GC) surfaces, and their electrochemical behavior in 0.5 M H2SO4 revealed that coating of the Au core by the Pt shell is complete. The electrooxidation of carbon monoxide and methanol on the Au(core)-Pt(shell)/GC was also examined, and the results are similar to those obtained on a bulk Pt electrode. High quality surface-enhanced Raman scattering (SERS) spectra of both adsorbed CO and thiocyanate were observed on the Au(core)-Pt(shell)/GC electrodes. The potential-dependent SERS features resemble those obtained on electrochemically roughened bulk Pt or Pt thin films deposited on roughened Au electrodes. For thiocyanate, the C-N stretching frequency increases with the applied potential, yielding two distinctly different dnu(CN)/dE. From -0.8 to -0.2 V, the dnu(CN)/dE is ca. 50 cm(-1)/V, whereas it is 90 cm(-1)/V above 0 V. The bandwidth along with the band intensity increases sharply above 0 V. At the low-frequency region, Pt-NCS stretching mode at 350 cm(-1) was observed at the potentials from -0.8 to 0 V, whereas the Pt-SCN mode at 280 cm(-1) was largely absent until around 0 V and became dominant at more positive potentials. These potential-dependent spectral transitions were attributed to the adsorption orientation switch from N-bound dominant at the negative potential region to S-bound at more positive potentials. The origin of the SERS activity of the particles is briefly discussed. The study demonstrates a new method of obtaining high quality SERS on Pt-group transition metals, with the possibility of tuning SERS activity by varying the core size and the shell thickness.     

Europium(II) and ytterbium(II) cyclic organohydroborates with agostic interactions

The divalent lanthanide bis((cyclooctane-1,5-diyl)dihydroborate) complexes {K(THF)4}2{Ln{(mu-H)2BC8H14}4} (Ln = Eu, 3; Yb, 4) were prepared by a metathesis reaction between (THF)(x)LnCl2 and K[H2BC8H14] in THF in a 1:4 molar ratio. Although the reaction ratios were varied between 1:3 and 1:6, complexes 3 and 4 were the only lanthanide 9-BBN hydroborates produced. Because of disorder of THF in crystals of 3 and 4, good single-crystal X-ray structural data could not be obtained. However, when the potassium cation was replaced by the tetramethylammonium cation or when MeTHF (2-methyltetrahydrofuran) was employed in place of THF, good quality crystals were obtained. Complexes [NMe4]2[Ln{(mu-H)2BC8H14}4] (Ln = Eu, 5; Yb, 6) were afforded by metathesis reactions of NMe4Cl with 3 and 4 in situ. On the basis of the single-crystal X-ray diffraction analysis, the four 9-BBN tetrahydroborate ligands are tetrahedrally arranged around the lanthanide cation in 5 and 6. The two structures differ in that one alpha-C-H bond from each of the four {(mu-H)2BC8H14}4 units exhibits an agostic interaction with Eu(II) in 5 but, in complex 6, only two of the alpha-C-H bonds form agostic interactions with Yb(II). Complexes {K(MeTHF)3}2{Ln{(mu-H)2BC8H14}4} (Ln = Eu, 7; Yb, 8) were produced by employing MeTHF in place of THF. The structures of 7 and 8 display connectivity between the anion {Ln{(mu-H)2BC8H14}4}2- and the cation {K(MeTHF)3}+, in which the potassium not only interacts directly with the hydrogens of the Ln-H-B bridged bonds but is also involved in agostic interactions with alpha-C-H bonds. By systematically examining the structures of complexes 3-8 and taking into account the previously reported complexes (THF)4Ln{(mu-H)2BC8H14}2 (Ln = Eu, 1; Yb, 2), it is concluded that Eu(II) appears to have a better ability to form agostic interactions than Yb(II) because of its larger size, even though Yb(II) has a higher positive charge density.     

Layer-by-layer assembly of polyoxometalates into microcapsules

The polyoxometalate (POM) chemistry world has been experiencing an unparalleled development of rapid synthesis of new compounds and slow development of POM-based functional materials and devices. Meanwhile, researchers in the microcapsule world, encouraged by the introduction of the layer-by-layer method, are pursuing good components for constructing functional capsule devices. Here, in view of the versatile properties that POM-based microcapsules may possess, various types of POM-polyelectrolyte composite microcapsules were constructed using the layer-by-layer method. Microscopy reveals that polyoxometalates form nanoparticles on the shell in the presence of cationic polyelectrolytes. These nanoparticles connected with polyelectrolytes constitute the shell and support the microcapsule from collapse after drying, and this is an interesting characteristic different from those of common composite and polyelectrolyte capsules. Fourier transform infrared (FTIR), UV-vis absorption, and X-ray photoelectron spectroscopy (XPS) were used to examine the properties of the POMs in the microcapsules. The obtained microcapsules exhibit higher thermal stability than polyelectrolyte microcapsules. Furthermore, the functions of POMs were maintained when they were assembled into microcapsules. It is proved that microcapsules bearing POMs with redox activity can provide a reduction environment, which can lead to the realization of in situ synthesis of materials, and that microcapsules with photoluminescent POMs as a component can also have a photoluminescent property, providing a way to develop functional capsule devices. This work may provide an opportunity to enrich both the polyoxometalate chemistry and the capsule field.     

Synthesis and Properties of Polyetherketones Containing Sulfide and Phthalazinone

High molecular weight copoly(ether ketone)s (PEK) based on 4-(4-hydroxyphenyl)-1-phthalazinone (DHPZ)/4,4′-thiobisphenol (TBP)/4,4′-diflourodiphenylketone (DFK) were prepared by nucleophilic substitution polycondensation. The copolymers were characterized by FT- and ^1H-NMR. Thermal properties and solubility of copolymers were studied.     

Spectroscopy, NMR and DFT studies on molecular recognition of crown ether bridged chiral heterotrinuclear salen Zn(II) complex

A barium-containing crown ether bridged chiral heterotrinuclear salen Zn(II) complex BaZn2L(ClO4)2, where L is a folded dinuclear chiral (R,R)-salen ligand, has been synthesized and characterized by elemental analysis, 1H NMR, UV-vis, IR, circular dichroism (CD) spectra, and mass spectra. As a folded dinuclear chiral host, its recognition with achiral guests (imidazole derivatives), rigid bidentate guest (1,4-diazobicyclo[2,2,2]octane, DABCO) and chiral guests (amino acid methyl esters) was investigated by means of UV-vis spectrophotometric titration, CD spectra. The association constants of D-amino acid methyl esters are found to be higher than those of their L-enantiomer. The sandwich-type binding of BaZn2L(ClO4)2-DABCO supramolecular assembly was specially studied via 1H NMR titration and 1H ROESY. To understand the recognition on molecular level, density functional theory (DFT) calculations on B3LYP/LanL2DZ were performed on the minimal energy conformations of host, guests, and host-guest complexes. The minimal energy conformations were obtained by molecular mechanics (MM) optimization and molecular dynamics (MD) simulation. The results of single point energy, HOMO energy, and charges transfer were analyzed. The results of theoretical calculations are in good agreement with the experimental data.     

Anti-Inflammatory,Antidiabetic Properties and In Silico Modeling of Cucurbitane-Type Triterpene Glycosides from Fruits of an Indian Cultivar of Momordica charantia L.

Diabetes mellitus is a chronic disease and one of the fastest-growing health challenges of the last decades. Studies have shown that chronic low-grade inflammation and activation of the innate immune system are intimately involved in type 2 diabetes pathogenesis. Momordica charantia L. fruits are used in traditional medicine to manage diabetes. Herein, we report the purification of a new 23-O-β-d-allopyranosyl-5β,19-epoxycucurbitane-6,24-diene triterpene (charantoside XV, 6) along with 25ξ-isopropenylchole-5(6)-ene-3-O-β-d-glucopyranoside (1), karaviloside VI (2), karaviloside VIII (3), momordicoside L (4), momordicoside A (5) and kuguaglycoside C (7) from an Indian cultivar of Momordica charantia. At 50 µM compounds, 2–6 differentially affected the expression of pro-inflammatory markers IL-6, TNF-α, and iNOS, and mitochondrial marker COX-2. Compounds tested for the inhibition of α-amylase and α-glucosidase enzymes at 0.87 mM and 1.33 mM, respectively. Compounds showed similar α-amylase inhibitory activity than acarbose (0.13 mM) of control (68.0–76.6%). Karaviloside VIII (56.5%) was the most active compound in the α-glucosidase assay, followed by karaviloside VI (40.3%), while momordicoside L (23.7%), A (33.5%), and charantoside XV (23.9%) were the least active compounds. To better understand the mode of binding of cucurbitane-triterpenes to these enzymes, in silico docking of the isolated compounds was evaluated with α-amylase and α-glucosidase.     

α-Tetralone glycosides from the green walnut husks of Juglans mandshurica Maxim. and their cytotoxic activities

Abstract

Five new α-tetralone glycosides, juglanbiosides A-E (1–5), together with an α-tetralone derivative (15) and nine known 1,4-naphthoquinones (6–14) were isolated from the 95% EtOH extract of green walnut husks of Juglans mandshurica Maxim. Their structures were elucidated by comprehensive spectroscopic methods (¹H, ¹³C NMR, DEPT, HSQC, HMBC, CD, HR-ESI-MS). In vitro cytotoxicities of all the isolated compounds were evaluated against BGC-823, HCT-15 and K562 cancer cell lines.

     

(Y,Gd)VO_4∶Eu~(3+)的紫外-真空紫外发光特性

用高温固相法合成了Y1-xGdxVO4∶Eu3 (0≤x≤1)系列单相样品并研究了其发光特性。在254nm激发下,观察到最大强度位于619nm的红色发射峰且其强度在Y/Gd=0.4/0.6时达到最大。在147nm激发下的发射峰与紫外下的一致,发射强度也是在Y/Gd=0.4/0.6时达到最大,大约是商用(Y,Gd)BO3∶Eu3 荧光体的65%。619nm监控下的真空紫外激发光谱由峰值位于158nm,204nm,247nm以及300nm的系列激发带组成,归属于钒酸根的基质吸收以及Gd3 、Y3 和Eu3 的电荷迁移带吸收。相对(Y,Gd)BO3∶Eu3 中Eu3 占据中心对称格位,(Y,Gd)VO4∶Eu3 中Eu3 占据非中心对称格位,其真空紫外下光谱色纯度更好。色坐标分别为(0.632,0.355),(0.672,0.328)。