Electrochemically driven organic monolayer formation on silicon surfaces using alkylammonium and alkylphosphonium reagents

The functionalization of silicon surfaces with organic monolayers, bound through Si–C bonds, is an area of wide interest due to the technological promise of organosilicon hybrid devices, but also to investigate fundamental surface reactivity. In this paper, the use of alkylammonium and alkylphosphonium cations as sources of organic moieties to bind to hydrogen-terminated flat and porous silicon is demonstrated. Tetraalkylammonium, tetraalkyl/arylphosphonium reagents, and alkyl pyridinium salts can be utilized, but trialkylammonium salts cannot as they yield substantial surface oxidation. Under electrochemical conditions, either potentiostatic or galvanostatic modes, alkyl groups derived from the ammonium or phosphonium salts are grafted to the silicon surface and are bound through Si–C bonds. Covalent attachment of the organic monolayers to the surface was demonstrated by XPS, AFM scribing, and FTIR. The mechanism may proceed via reduction of the ammonium salt yielding alkyl radicals, R, which may be reduced to R⁻ and attack surface Si–Si bonds, leading to Si–C bonds, or the formation of silyl anions (≡Si⁻) under the cathodic conditions followed by nucleophilic attack on the trialkylammonium cation.     

An easy and fast ultrasonic selective S-alkylation of hetaryl thiols at room temperature

A series of 2-alkylthio derivatives of hetaryl thiols were synthesized by selective S-alkylation with alkyl halides (bromides and iodides) with ultrasonic irradiation at room temperature. The reaction was found to be generally applicable to hetaryl thiol derivatives with different substituents in the aromatic nucleus and various alkyl halides. The reaction gives high to excellent yields of products with high purity.     

长期不同施肥处理对黑土根际土壤有机碳结构组分的影响

土壤有机碳是农业生态系统的关键驱动和调节者,特别是根际微域有机碳动态对土壤碳素循环和矿质营养元素释放起着重要作用。研究长期不同化肥和有机肥施用下大豆根际土壤有机碳、活性有机碳以及有机碳结构的变化规律,深入了解根际有机碳固持和稳定机制,为完善农田生态系统碳固持和农田可持续发展提供科学依据和理论支撑。该研究依托黑土长期定位试验,采用化学分析、固态¹³C-核磁共振(¹³C-NMR)等方法研究大豆根际土壤有机碳含量、活性有机碳含量和有机碳结构组分变化规律。结果表明,与非根际土壤相比,大豆根际土壤有机碳含量显著增加,长期施肥处理能够显著增加根际土壤有机碳和低活性有机碳含量,以常量有机肥加氮磷钾(MNPK)处理提升效果最好。核磁共振实验结果表明,与不施肥处理相比,MNPK处理明显增加根际土壤烷基碳、烷氧基碳比例以及烷基碳/烷氧基碳比值,降低芳香基碳和芳香碳/总碳比值,在非根际土壤中尤其显著;常量氮磷钾(NPK)处理增加芳香基碳比例和芳香碳/总碳比值,在根际土壤中烷基碳比例和烷基碳/烷氧基碳比值增加,烷氧基碳比例降低,非根际土壤测试结果相反。综上所述,MN...     

First ultrasound-mediated one-pot synthesis of N-substituted amides

Ultrasound irradiation, an efficient and innocuous technique of reagent activation for synthesizing organic compounds, has been applied with success to transform seven carboxylic acids to fourteen secondary amides in good to excellent yields. The reaction has worked well either with aryl or alkyl carboxylic acids as well as with aromatic or aliphatic amines. This methodology is expeditious and reliable for preparing secondary carboxamides which in many cases are embedded in the C-5 side-chain of 1,2,4-oxadiazoles (14, 15, 17–27). The elemental analyses of new compounds (19–27) in conjunction with the spectral data of all synthesized amides gave an idea about their structures, while the crystallographic data of one of the compounds (26) supplied information concerning the configurational behavior of the amidic part and also the conformational aspect of the entire molecule in the crystalline state.     

Water and oil wettability of hybrid organic–inorganic titanate–silicate thin films deposited via a sol–gel route

Hybrid organic–inorganic titanate–silicate thin films were deposited on silicium wafer via a sol–gel route. Hybrid sols were formulated by mixing an inorganic titanium alkoxide solution with solutions of hybrid organic–inorganic silicon alkoxides partially substituted with non-hydrolysable alkyl chains. Three organo-silicate precursors were used to introduce methyl, octyl, or hexadecyl chains in the oxide network. Physico-chemical and morphological properties of derived hybrid films have been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and atomic force microscopy. Contact angle measurements have also been performed to assess the water and mineral oil wettability of hybrid films. Wettability properties of these films are discussed with respect to physico-chemical and morphological features. It is shown that increasing the fraction and length of alkyl chains in the oxide network conjointly increases water and oil contact angles measured on such hybrid films.     

Hybrid solar cells using nanorod zinc oxide electrodes and perylene monoimide–monoanhydride dyes

Hybrid solar cells have been fabricated using perylene monoimide–monoanhydride dyes with nanorod zinc oxide electrodes as electron transporting layers. We have investigated the influence of the spacer alkyl chain length of perylene monoimide–monoanhydride (PMIMA) dyes on the device performance in hybrid solar cells using nanorod zinc oxide electrodes. Nanorod zinc oxide electrodes with 50–150 nm of diameter were synthesized in the presence of PEG400 by using microwave heating method. We observed that the dyes with longer and brunched alkyl chains exhibit higher efficiencies in hybrid solar cells. We report the highest efficiency obtained with zinc oxide nanorods under standard conditions for perylene monoimide–monoanhydride derivative with PMIMA_1 that performs 400 mV open circuit voltage, 2.81 mA/cm² short-circuit current and 0.59% overall conversion efficiency.     

Aqueous sonolytic decomposition of polycyclic aromatic hydrocarbons in the presence of additional dissolved species

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) results in a first-order loss of the PAHs (k=0.010–0.027 s⁻¹). When sonication occurred in the presence of other organic compounds, the degradation rate constant was reduced quite dramatically. This reduction is believed to come about through scavenging of radicals by the matrix chemical. When oxygen was bubbled into the PAH solution before sonication, the degradation rate constant was elevated. Nitrogen purging resulted in decreased rate constants. These results indicate that oxygen was an important precursor in the degradation of the PAHs. Organic compounds, including humic acid, benzoic acid, and sodium dodecyl sulfate, decreased PAH degradation rate constants by scavenging oxygen derived reactive transients.     

Surface modification of layered silicates. I. Factors affecting thermal stability

The resistance of modification molecules bound to montmorillonite platelet surfaces towards structural damage at high temperature is a major parameter guiding the formation of optimal interface between the filler and polymer phases in a nanocomposite material. As nanocomposites are generated by melt-blending of modified mineral and polymer, it is necessary to quantify the thermal resistance of the filler surface modification at the compounding conditions because different modifications differ in chain length, chemical structure, chain density, and thermal performance. A number of different alkyl ammonium modifications were exchanged on the montmorillonites with cation exchange capacities in the range 680–900?µequiv.?g^?1 and their thermal behaviour was characterised using high resolution thermogravimetric analysis. Quantitative comparisons between different modified minerals were achieved by comparing temperature at 10% weight loss as well peak degradation temperature. Various factors affecting thermal stability, such as length and density (or number) of alkyl chains in the modification, presence of excess modification molecules on the filler surface, the chemical structure of the surface modifications, etc. were studied. The TGA findings were also correlated with X-ray diffraction of the modified platelets.     

Coupled high and low-frequency ultrasound remediation of PFAS-contaminated soils

Solids such as soils and sediments contaminated with per- and polyfluorinated alkyl substances (PFAS) from exposure to impacted media, e.g., landfill leachate or biosolids, direct contaminated discharge, and contaminant transport from atmospheric deposition, have caused significant environmental pollution. Such solids can act as secondary sources of PFAS for groundwater and surface water contamination. There are currently no proven technologies that can degrade PFAS in soil and sediments in a cost-effective, environmentally-friendly, and energy-efficient manner. This study examines the use of coupled high and low-frequency ultrasound in desorbing and degrading PFAS in soil, thereby achieving concurrent treatment and destruction of PFAS in soil. Two common PFAS, namely perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), were used to evaluate treatment performance in soils with both low and high organic matter contents. The test results showed that the ultrasound treatment could significantly reduce PFAS concentrations in artificially contaminated soil; however, no significant degradation was achieved. Ultrasound treatment did improve desorption of PFAS from solid particles, particularly from the highly absorbent organic soil; 68.8 ± 1.8% of PFOA and 45.4 ± 4.1% of PFOS were leached from the soil after ultrasound treatment compared to only 28 ± 0.2% of PFOA and 1 ± 3.1% of PFOS after desorption in water. This work shows that sonication treatment is an effective technology for the removal of PFAS from solids, however, the presence of solids in the solid–liquid slurry can negatively impact ultrasonic cavitation, inhibiting the sonolytic degradation of desorbed PFAS.     

Influence of initial oxygen on the formation of thiol layers

In this study, X-ray photoelectron spectroscopy (XPS) has been used to study thin organic films. For comparison, monolayers were formed on clean and air-exposed metal substrates. Obtained results show that thiols remove contamination oxygen from gold, silver, platinum and copper surfaces. The tightly packed thiolate layers can be formed. In addition, oxygen does not take part in the final bonding of molecules to the surfaces.     

脂肪醇甲酸酯类酞菁铜配合物的合成、表征及荧光性能

报道了四甲酰氯酞菁铜的合成及其与反应得到正丁醇、正戊醇、正己醇、正辛醇、正十二醇5个含脂肪链取代基的酞菁铜衍生物.分别用红外光谱、紫外-可见光谱、元素分析、核磁共振氢谱等方法对这些衍生物进行了结构和取代度的表征,并研究了该系列酞菁铜衍生物在有机溶剂中的溶解性及荧光性能与浓度、取代基的关系.研究结果表明在一般有机溶剂中这些酞菁铜衍生物的溶解性显著提高,荧光强度不随浓度的变化而线性变化、长链要高于短链取代酞菁铜衍生物的荧光强度.     

A Highly Selective Fluorescent Probe for Detection of Biological Samples Thiol and Its Application in Living Cells

Probe 1 was designed and synthesized as a new fluorescent molecular probe for thiols in PBS buffer at physiological condition. This fluorescent molecular probe consists of a thiol reaction moiety bound to a coumarin fluorophore. Its fluorescence quantum yield is low, but a drastic enhancement of fluorescence intensity was observed in the presence of thiols. Possible interference with other analytes was examined. Probe 1 displays a highly selective fluorescent enhancement with thiols, and the probe was successfully applied to thiols determination in intracellular, in human urine and blood samples.     

Abnormal adsorption behavior of dimethyl disulfide on gold surfaces

Adsorption of dimethyl disulfide (DMDS) on gold colloidal nanoparticle surfaces has been examined to check its binding mechanism. Differently from previous results, DMDS molecules adsorbed on the gold surface at high concentration showed the S–S stretching band at 500 cm⁻¹ in surface-enhanced Raman scattering (SERS) spectra, which indicates the presence of intact adsorption of DMDS molecules. However, it was found that the S–S bond of disulfides was easily cleaved on the gold surface at low concentration. These behaviors were not observed for diethyl disulfide (DEDS) or diphenyl disulfide (DPDS). Our results indicate that DMDS molecules with the shortest alkyl chains on the gold surface can be inserted into self-assembled monolayers (SAMs) without the S–S bond cleavage during self-assembly due to insufficient lateral van der Waals interaction and the low adsorption activity of disulfides, whereas DEDS with longer alkyl chains or DPDS with the weak disulfide bond dissociation energy would not. These unusual DMDS adsorption behaviors were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We also compared the bonding dissociation energy of the S–S bonds of various disulfides by means of a density functional theory (DFT) calculation.     

Reactivities of mixed organozinc and mixed organocopper reagents. Part 7. Comparison of the transfer rate of the same group in allylation of mixed and homo diorganozinc reagents

A detailed direct kinetic study has been carried out to compare the reaction rate of transferable group, Ph in mixed phenylzinc reagents, RPhZn (R = n‐alkyl) and in homo diphenylzinc reagent, Ph₂Zn in their reactions with allyl bromide in THF at 25–(?15) °C. Empirical rata law and activation parameters are consistent with a second‐order substitution reaction. The allylation rate of transferable group Ph in RPhZn (R = n‐alkyl) has been found higher than the rate of Ph group in Ph₂Zn. A mechanism which accommodates the kinetic data and higher allylation rate of transferable group Ph in RPhZn than that in Ph₂Zn is given. Copyright © 2013 John Wiley & Sons, Ltd.     

Electronic properties of organic monolayers and molecular devices

We review some of our recent experimental results on charge transport in organic nanostructures such as self-assembled monolayer and monolayers of organic semiconductors. We describe a molecular rectifying junction made from a sequential self-assembly on silicon. These devices exhibit a marked current-voltage rectification behavior due to resonant transport between the Si conduction band and the π molecule highest occupied molecular orbital of the π molecule. We discuss the role of metal Fermi level pinning in the current-voltage behavior of these molecular junctions. We also discuss some recent insights on the inelastic electron tunneling behavior of Si/alkyl chain/metal junctions.     

Degradation Studies of Polyolefins Incorporating Transparent Nanoparticulate Zinc Oxide UV Stabilizers

Coated and dispersed nanoparticulate zinc oxide is shown to improve ultra violet (UV) stability of polypropylene and high-density polyethylene without changing its characteristic absorption spectrum in the visible region (400–800-nm). The performance of these nanoparticulate UV stabilizers is compared to conventional hindered amine light stabilizers (HALS). QUV accelerated weathering is used to simulate long-term exposure. Positron annihilation lifetime spectroscopy (PALS) is used to provide an indication of physical and chemical changes due to accelerated weathering and is shown to have potential for detecting changes well before other techniques. Visual observation, optical microscopy, carbonyl index, yellowness index and PALS indicate that nanoparticulate zinc oxide gives superior resistance to UV degradation compared to organic HALS at appropriate loading levels.     

Melting Behavior of Organic Nanocrystals Grown in Sol–gel Matrices

We have characterized the thermal stability of organic nanocrystals grown in the pores of sol–gel matrices. The structure has been measured with transmission electron microscopy (TEM) analysis. Depending on the nature of organic molecules and sol–gel matrices, we have modified the dye–matrix interactions and the interfacial structure between nanocrystals and gel-glasses. When the dye–matrix interactions are weak (Van der Waals' bonds), the corresponding interfacial structure observed by TEM is sharp and the nanocrystals melt below the bulk melting point. On the other hand, when the dye–matrix interactions are strong (hydrogen bonds), the interfacial structure is fuzzy and a great superheating of organic nanocrystals is observed in comparison to the bulk melting point of the dye.     

Formation of interfacial layer in Fe-polystyrene system during mechanochemical synthesis in the presence of alkyl surfactants

The structure of surface organic layers formed during the mechanical milling of Fe with polystyrene and alkyl surfactants is studied using NEXAFS and FT-IR spectroscopies. It is shown that the main constituents of the layers formed are condensed aromatic structures (products of the dehydrogenation of an organic medium) that contain covalently bound polystyrene fragments.     

The role of potassium tellurite as tellurium source in mercaptoacetic acid-capped CdTe nanoparticles

Water-soluble CdTe nanoparticles were synthesized in aqueous solution with the assistance of mercaptoacetic acid (MAA) molecules by wet chemical route and microwave-assisted method. A series of cadmium telluride (CdTe) nanoparticles capped with a bifunctional molecule, which contains both thiols and carboxylic acid groups were prepared using different pH values and using potassium tellurite as tellurium source. Thiol-capped nanocrystals of CdTe can be isolated as powders using 2-propanol. The synthesized thiol-capped CdTe were characterized with EDAX, TEM, Raman, FT–IR, UV–Visible absorption, fluorescence spectroscopy and X-ray diffraction (XRD) for the particle size determination and to understand their optical properties. The particles crystallize predominantly in cubic phase with narrow photoluminescence emission. Potassium tellurite as source of tellurium improves the photoluminescence efficiency and also avoids the cumbersome processes associated with H₂Te or NaHTe sources.     

Patterned self-assembled monolayers of alkanethiols on copper nanomembranes by submerged laser ablation

Self-assembled monolayers (SAMs) of alkanethiols are major building blocks for nanotechnology. SAMs provide a functional interface between electrodes and biomolecules, which makes them attractive for biochip fabrication. Although gold has emerged as a standard, copper has several advantages, such as compatibility with semiconductors. However, as copper is easily oxidized in air, patterning SAMs on copper is a challenging task. In this work we demonstrate that submerged laser ablation (SLAB) is well-suited for this purpose, as thiols are exchanged in-situ, avoiding air exposition. Using different types of ω-substituted alkanethiols we show that alkanethiol SAMs on copper surfaces can be patterned using SLAB. The resulting patterns were analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Both methods indicate that the intense laser beam promotes the exchange of thiols at the copper surface. Furthermore, we present a procedure for the production of free-standing copper nanomembranes, oxidation-protected by alkanethiol SAMs. Incubation of copper-coated mica in alkanethiol solutions leads to SAM formation on both surfaces of the copper film due to intercalation of the organic molecules. Corrosion-protected copper nanomembranes were floated onto water, transferred to electron microscopy grids, and subsequently analyzed by electron energy loss spectroscopy (EELS).