Inner‐shell chemical shift of DNA/RNA bases and inheritance from their parent purine and pyrimidine

Inner‐shell electronic structures, properties and ionization spectra of DNA/RNA bases are studied with respect to their parent pyrimidine and purine species. Density functional theory B3LYP/aug‐cc‐pVTZ has been employed to produce the geometries of the bases, whereas LB94/et‐pVQZ//B3LYP/aug‐cc‐pVTZ is used to calculate site‐related Hirshfeld charges and core (vertical) ionization energies, as well as inner‐shell spectra of C1s, N1s and O1s for DNA/RNA bases and their parent pyrimidine and purine species. The site‐dependent variations of properties indicate the changes and inheritance of chemical environment when pyrimidine and purine become substituted. In general, although the changes are site‐dependent, they are also ring‐dependent. Pyrimidine bases change less significantly with respect to their parent pyrimidine than the purine bases with respect to their parent purine. Pyrimidine bases such as uracil, thymine and cytosine inherit certain properties from their parent pyrimidine, such as the Hirshfeld charge distributions and the order of core ionization energy level etc. No particular sites in the pyrimidine derivatives are engaged with a dramatic chemical shift nor with energy crossings to other sites. For the core shell spectra, the purine bases inherit very little from their parent purine, and guanine exhibits the least similarities to the parent among all the DNA/RNA bases.     

The Use of Solid‐Phase Supports for Derivatization in Chromatography and Spectroscopy

Abstract

Derivatization, or chemical modification of analytes, is often required for species that are only weakly detectable by common spectroscopic methods. Derivatization is most commonly performed in homogeneous solution or using phase‐transfer catalyzed reactions. However, the use of solid phase supports for performing the same reactions has a number of advantages. The sample can be “cleaned up” on the same phase, eliminating interfering matrix components or excess reagent. The process naturally concentrates the analyte, providing higher sensitivity, but also, under favorable circumstances, provides for more efficient reactions relative to solutions of the same original concentration. This review explores the uses to which such supports have been put, primarily in fluorescence derivatization for chromatographic applications. Some of the considerations in applying these techniques are described, and they are shown to be an extremely useful format for derivatization.     

Synthesis of highly substituted 2,3-dihydropyrimido[4,5-<Emphasis Type="Italic">d</Emphasis>]pyrimidin-4(1<Emphasis Type="Italic">H</Emphasis>)-ones from 4,6-dichloro-5-formylpyrimidine,amines and aldehydes

A practical strategy was developed for the preparation of highly substituted 2,3-dihydropyrimido[4,5-d]pyrimidin-4(1H)-ones from 4,6-dichloro-5-formylpyrimidine, primary amines, and aldehydes. The key step for this synthesis entails a cyclization reaction involving an intramolecular amide addition to an iminium intermediate formed in situ from 4-amino-pyrimidine-5-carboxamide 2 and aldehydes to form the pyrimido[4,5-d]pyrimidine core with a strategically placed 5-Cl group for further derivatization. The utility of this methodology was demonstrated through the preparation of a 27-membered library of representative 2,3-dihydropyrimido[4,5-d]pyrimidin-4(1H)-ones in moderate to good yields.     

Analysis of organic functional groups by X-ray photoelectron spectroscopy and chemical derivatization

A technique for analyzing alcohol and carboxyl functional groups on the surfaces of organic materials that combines X-ray photoelectric spectroscopy with chemical derivatization is developed. Side reactions that can accompany chemical derivatization are revealed. The experimental conditions of reactions for analyzing alcohol and carboxyl groups are determined.     

四氯苯醌与嘧啶类核酸碱基的光化学氢抽取和电子转移反应

采用纳秒时间分辨的激光闪光光解实验技术,研究了四氯苯醌(TCBQ)分子与两种嘧啶核酸碱基(胸腺嘧啶和尿嘧啶)分子在355nm激发下的光化学反应动力学. 355 nm将TCBQ分子布居到激发三重态³TCBQ^*,高反应活性的³TCBQ^*与碱基分子发生两个平行的反应,氢抽取反应和电子转移反应,分别对应生成瞬态光谱上观测到的两个光反应产物TCBQH·和TCBQ·^-. 这两个反应同时生成的碱基自由基和碱基阳     

Quantification of oxygenated species on a diamond-like carbon (DLC) surface

This paper discusses the use of chemical derivatization methods for surface chemical composition analysis of diamond-like carbon (DLC) films synthesized through plasma-enhanced chemical vapor deposition with X-ray photoelectron spectroscopy (XPS). The main challenge in applying chemical derivatization reactions for titration of organic functional groups on the DLC surface is that sub-surface oxygenated species are not accessible to the derivatizing agent. As a simple approximation, a functional group that can be quantified unambiguously with XPS can be used as an internal reference to estimate the accessible-to-inaccessible ratio, and this information can be used to estimate the total amount of other functional groups from the chemical-derivatization-assisted XPS analysis. The use of this principle to obtain the surface composition of hydroxyl, ether, carbonyl, and carboxyl groups in the oxidized surface region of the DLC film was demonstrated.     

The analysis of alkyl-capped alcohol ethoxylates and alcohol ethoxycarboxylates from alcohol ethoxylates by atmospheric pressure chemical ionization mass spectrometry

Alcohol ethoxylates (AEs) are nonionic surfactants. They are industrially important compounds that have historically been difficult to analyze, with the best results to date achieved through derivatization (e.g., silylation) followed by analysis by gas chromatography/mass spectrometry (GC/MS). Recently, mass spectrometric techniques such as field desorption (FD), time-of-flight secondary ion mass spectrometry (TOF-SIMS), fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) have been employed to analyze surfynol(R) 4xx. In an effort to produce low-cost alkyl-capped AEs and anionic detergents from AEs, a fast and reliable measure of the product yields and conversions from AEs is required in research. We found that the product yields and conversions from reactions of AEs, obtained by the employment of atmospheric pressure chemical ionization (APCI), were in good agreement with those obtained from proton nuclear magnetic resonance spectroscopy ((1)H-NMR). Therefore, APCI can be used as a validated tool for studying AE reactions. Mixtures that contain either silylated or unsilylated ethoxylates and/or carboxylates yield the same APCI mass spectra. Copyright -Copyright 1999 John Wiley & Sons, Ltd.     

Coupling-isomerization-coupling sequences switched on by propargyl alcohol-enone-isomerization

The coupling-isomerization-reaction (CIR) of an electron-deficient halide 1 with 1-(p-bromo phenyl) propyne-1-ol (2) leads to an in-situ activation of the carbon-bromine bond towards oxidative addition and has been elaborated to a consecutive CIR-coupling sequence where subsequent palladium catalyzed coupling reactions such as Sonogashira, CIR, Heck, or Suzuki reactions allow a rapid construction of more complex frameworks in a one-pot reaction and in moderate to good yields.     

Ultrasound and microwave assisted synthesis of dihydroxyacetophenone derivatives with or without 1,2-diazine skeleton

A thorough study concerning O-alkylation and α-bromination of dihydroxyacetophenone (DA) and N-alkylation of 1,2-diazine, under ultrasound (US) and microwave (MW) irradiation as well as under conventional thermal heating (TH) is presented. Under US and MW irradiation the yields are higher, the amount of used solvent decreases substantially, the reaction time decreases considerable (from hours or days to minutes) and the consumed energy decreases, consequently the O-alkylation, α-bromination and N-alkylation methods could be considered environmentally friendly. A selective and efficient way to either bis-O-alkylation or mono-O-alkylation of DA has been found, the relative position of the two hydroxyl groups on the phenyl moiety being compulsory. A selective and efficient way for α-bromination in heterogeneous catalysis of DA derivatives under US irradiation is presented. The N-alkylation reaction of DA under US and MW irradiation proved to be the most convenient setup procedure for these types of reactions. Overall, the use of US proved to be more efficient than MW or TH.     

Selective detection of organic compounds on modified polymer surfaces using TOF-SIMS in combination with derivatization

This investigation encompasses work in the development of TOF-SIMS methodology for the characterization of compounds formed during polymer surface modification. TOF-SIMS was used in this study in combination with selective derivatization reactions with hydroxyl group specific reagents. Derivatization techniques with group specific reagents provide a means of identifying functional groups in a complex matrix, along with significant enhancement of detection limits. The study proceeded in three steps. First, derivatives of organic compounds as a model compound were monitored to determine the suitability for detecting oxygenated species. Second, useful derivatization reactions were tested on functional groups in the synthetic polymer chains. Third, the methods thus developed were applied to polymer surfaces treated by plasma source ion implantation (PSII). 2-Fluoro-1-methylpyridinium derivatives were useful for characterization of organic alcohols and phenolic compounds. Analysis of organic compounds derivatized by these methods on polymeric materials demonstrated clearly that analysis in the presence of a carbonaceous matrix is possible. The results yielded evidence for the formation of hydroxyl species as the polymer is modified by PSII technique.     

New Cross-Linking Quinoline and Quinolone Derivatives for Sensitive Fluorescent Labeling

A variety of contemporary analytical platforms, utilized in technical and biological applications, take advantage of labeling the objects of interest with fluorescent tracers-compounds that can be easily and sensitively detected. Here we describe the synthesis of new fluorescent quinoline and quinolone compounds, whose light emission can be conveniently tuned by simple structural modifications. Some of these compounds can be used as sensitizers for lanthanide emission in design of highly sensitive luminescent probes. In addition, we also describe simple efficient derivatization reactions that allow introduction of amine- or click-reactive cross-linking groups into the fluorophores. The reactivity of synthesized compounds was confirmed in reactions with low molecular weight nucleophiles, or alkynes, as well as with click-reactive DNA-oligonucleotide containing synthetically introduced alkyne groups. These reactive derivatives can be used for covalent attachment of the fluorophores to various biomolecules of interest including nucleic acids, proteins, living cells and small cellular metabolites. Obtained compounds are characterized using NMR, steady-state fluorescence spectroscopy as well as UV absorption spectroscopy.     

Multi-component electrocatalyst for low-temperature fuel cells synthesized via sonochemical reactions

This review presents recent advances in multi-component electrocatalysts for low-temperature fuel cells (FCs) synthesized via sonochemical reactions. As a feasible approach to develop novel electrocatalysts that can overcome the many problems of the prevailing Pt electrocatalysts, Pt- or Pd-based alloy and core–shell M@Pt nanoparticles (NPs) have been pursued. Synthesizing NPs with desirable properties often turn out to be challenging. Sonochemistry generates extreme conditions via acoustic cavitation, which have been utilized in the syntheses of various Pt and Pd NPs and Pt- and Pd-based alloy NPs. Especially, it has been reported that several M@Pt core–shell NPs can be synthesized by sonochemistry, which is hard to achieve by other methods. The principles of sonochemistry are presented with examples. Also alloy NPs and core–shell NPs synthesized by sonochemistry and those by other methods are compared.     

International Perspective on Government Nanotechnology Funding in 2005

The worldwide investment in nanotechnology research and development (R&D) reported by national government organizations and EC has increased approximately 9-fold in the last 8 years – from $432 million in 1997 to about $4,100 million in 2005. The proportion of national government investments for: academic R&D and education are between 20% (Korea, Taiwan) and 65% (US), industrial R&D – between 5% (US) and 60% (Korea, Taiwan), and core facilities and government laboratories – about 20–25% in all major contributing economies. This evaluation uses the NNI definition of nanotechnology (that excludes MEMS or microelectronics), and is based on direct information and analysis with managers of nanotechnology R&D programs in the respective countries.     

Recent advances of ultrasound-assisted Maillard reaction

Maillard reaction (MR) is one of the most important chemical reactions in the food science domain with a long history of more than 100 years. As for ultrasound-assisted MR (US-MR), it has gradually drawn attention in a recent decade. Purpose of this paper is to provide a systematic review on recent advances of US-MR in model systems, glycation of protein, and food processing. Fundamental studies on simple MR model systems (i.e. reducing sugar and amino acid) have reported a promoted generation of colored and volatile MR products (MRPs). Critical steps influenced by US and possible mechanisms have been elucidated simultaneously. Other studies focused on modification of proteins which undergoes a glycation between proteins and saccharides as the initial stage of MR. Since the MR rate is extremely low in the presence of protein and saccharide, US becomes a promising mean of promoting the glycation. As a result, a number of functional properties of glycated protein obtained by US are significantly promoted, which extend their utilization in the food industry. The rest of studies reviewed in this article are concentrated on applying US to process real foods. Many attributes changed during US-assisted processing are induced by MR. Positive aspects brought by the promoted US-MR include enhanced antioxidant capacity and organoleptic properties (e.g. desirable color, low bitterness, enhanced flavor, etc.), as well as inhibited hazards (e.g. advanced glycation end-products, acrylamide, etc.) formed in the processed foods. Meanwhile, the promoted MR by US may also inevitably bring some negative aspects to the processed foods due to unfavored yellowish/browning colors, off-flavors and hazard components.     

Optimization of Verapamil Drug Analysis by Excitation-Emission Fluorescence in Combination with Second-order Multivariate Calibration

Excitation emission fluorescence matrices (EEMs) of Verapamil drug were obtained by direct and by derivatization fluorescence spectroscopy. The fluorescence excitation and emission wavelengths were displaced to longer wavelengths and the fluorescence intensity was enhanced upon derivation with respect to the native fluorescence of the drug. The complete EEM of the native fluorescence of the drug and of the derivatization product were rapidly acquired by using a charged-coupled device detector (CCD), which is advantageous in terms of speed in the analysis, with respect to the use of a conventional photomultiplier detector. The EEMs were analyzed by several second-order multivariate calibration methods exploiting the second order advantage. The three-dimensional decomposition methods used, based in different assumptions about the trilinearity of the three way data structure under analysis, were parallel factor analysis (PARAFAC), bilinear least squares (BLLS), parallel factor analysis 2 (PARAFAC2) and multivariate curve resolution—alternating least squares (MCR-ALS). The determination was performed by using the standard addition approach. The figures of merit of the PARAFAC and BLLS methods were calculated, obtaining a lower limit of detection with the derivatization procedure, when compared with the direct measurement of the fluorescence of the drug. In Verapamil drug the best estimations were found with the BLLS and the MCR-ALS models. In the quantification of Verapamil in a pharmaceutical formulation the best estimation, when compared with the result obtained by the US Pharmacopeia high performance liquid chromatography approach, was obtained by direct fluorescence spectroscopy with MCR-ALS and by derivatization fluorescence spectroscopy with the PARAFAC2 model.     

Efficient H2O2/CH3COOH oxidative desulfurization/denitrification of liquid fuels in sonochemical flow-reactors

The oxidative desulfurization/denitrification of liquid fuels has been widely investigated as an alternative or complement to common catalytic hydrorefining. In this process, all oxidation reactions occur in the heterogeneous phase (the oil and the polar phase containing the oxidant) and therefore the optimization of mass and heat transfer is of crucial importance to enhancing the oxidation rate. This goal can be achieved by performing the reaction in suitable ultrasound (US) reactors. In fact, flow and loop US reactors stand out above classic batch US reactors thanks to their greater efficiency and flexibility as well as lower energy consumption. This paper describes an efficient sonochemical oxidation with H₂O₂/CH₃COOH at flow rates ranging from 60 to 800 ml/min of both a model compound, dibenzotiophene (DBT), and of a mild hydro-treated diesel feedstock. Four different commercially available US loop reactors (single and multi-probe) were tested, two of which were developed in the authors’ laboratory. Full DBT oxidation and efficient diesel feedstock desulfurization/denitrification were observed after the separation of the polar oxidized S/N-containing compounds (S ⩽ 5 ppmw, N ⩽ 1 ppmw). Our studies confirm that high-throughput US applications benefit greatly from flow-reactors.     

Absorption effects in halo-nucleus core or nucleon stripping reactions

Inclusive halo-nucleus core or nucleon stripping reactions are considered on the basis of a potential three-body model using the eikonal and adiabatic approximations. Clear analytical expressions for the cross sections of these reactions are obtained, and numerical calculations for ¹¹Be halo nucleus are performed. Constituent absorption by the target nucleus substantially influences the integral and differential (with respect to longitudinal momentum) nucleon stripping cross section. It is demonstrated that the differential core stripping cross section contains more complete information on the unperturbed wave function of the halo nucleus.     

多功能胶囊催化剂在多相催化中的应用研究进展

Capsule catalysts composed of pre-shaped core catalysts and layer zeolites have been widely used in the tandem reactions where multiple continuous reactions are combined into one process. They show excellent catalytic performance in heterogeneous catalysis, including the direct synthesis of middle isoparaffins or dimethyl ether from syngas, as compared to the conventional hybrid catalysts. The present review highlights the recent development in the design of capsule catalysts and their catalytic applications in heterogeneous catalysis. The capsule catalyst preparation methods are introduced in detail, such as hydrothermal synthesis method, dual-layer method, physically adhesive method and single crystal crystallization method. Furthermore, several new applications of capsule catalysts in heterogeneous catalytic processes are presented such as in the direct synthesis of liquefied petroleum gas from syngas, the direct synthesis of para-xylene from syngas and methane dehydroaromatization. In addition, the development in the design of multifunctional capsule catalysts is discussed, which makes the capsule catalyst not just a simple combination of two different catalysts, but has some special functions such as changing the surface hydrophobic or acid properties of the core catalysts. Finally, the future perspectives of the design and applications of capsule catalysts in heterogeneous catalysis are provided.     

Relations between the differential cross sections for diffractive processes of nucleon stripping and halo-nucleus core stripping

A comparative analysis of the nucleon stripping and core stripping reactions induced by a halo nucleus is presented on the basis of certain models for diffractive processes. It follows from calculations for the halo nucleus 11Be that the transverse momentum distribution of nucleons for core stripping (as the longitudinal momentum distribution) is less distorted by absorption in a target than the distribution of core fragments for nucleon stripping. The obtained relations between the cross sections for the stripping reactions simplify interpretation of the calculation results.