Controlled release of volatiles under mild reaction conditions: from nature to everyday products

Volatile organic compounds serve in nature as semiochemicals for communication between species, and are often used as flavors and fragrances in our everyday life. The quite limited longevity of olfactive perception has led to the development of pro-perfumes or pro-fragrances--ideally nonvolatile and odorless fragrance precursors which release the active volatiles by bond cleavage. Only a limited amount of reaction conditions, such as hydrolysis, temperature changes, as well as the action of light, oxygen, enzymes, or microorganisms, can be used to liberate the many different chemical functionalities. This Review describes the controlled chemical release of fragrances and discusses additional challenges such as precursor stability during product storage as well as some aspects concerning toxicity and biodegradability. As the same systems can be applied in different areas of research, the scope of this Review covers fragrance delivery as well as the controlled release of volatiles in general.     

Dithiocarbamates as Precursors in Organic Chemistry; Synthesis and Uses

Abstract

Organic dithiocarbamates have received great attention due to their interesting chemistry and wide utility as radical precursors and intermediates in organic synthesis. They also have found many of applications, that is, in agriculture and medicine. They are in use as pesticides, as well as in the rubber industries as vulcanization accelerators; and as antioxidants. Because they exhibit strong metal-binding capacity, they can act as in inhibitors of enzymes and have a profound effect on biological systems. Moreover, they have found application in the treatment of cancer and HIV.     

Aptamers: molecular tools for analytical applications

Aptamers are artificial nucleic acid ligands, specifically generated against certain targets, such as amino acids, drugs, proteins or other molecules. In nature they exist as a nucleic acid based genetic regulatory element called a riboswitch. For generation of artificial ligands, they are isolated from combinatorial libraries of synthetic nucleic acid by exponential enrichment, via an in vitro iterative process of adsorption, recovery and reamplification known as systematic evolution of ligands by exponential enrichment (SELEX). Thanks to their unique characteristics and chemical structure, aptamers offer themselves as ideal candidates for use in analytical devices and techniques. Recent progress in the aptamer selection and incorporation of aptamers into molecular beacon structures will ensure the application of aptamers for functional and quantitative proteomics and high-throughput screening for drug discovery, as well as in various analytical applications. The properties of aptamers as well as recent developments in improved, time-efficient methods for their selection and stabilization are outlined. The use of these powerful molecular tools for analysis and the advantages they offer over existing affinity biocomponents are discussed. Finally the evolving use of aptamers in specific analytical applications such as chromatography, ELISA-type assays, biosensors and affinity PCR as well as current avenues of research and future perspectives conclude this review.     

Asymmetric multicomponent reactions (AMCRs): the new frontier

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.     

The Role of Microencapsulation in Food Application

Modern microencapsulation techniques are employed to protect active molecules or substances such as vitamins, pigments, antimicrobials, and flavorings, among others, from the environment. Microencapsulation offers advantages such as facilitating handling and control of the release and solubilization of active substances, thus offering a great area for food science and processing development. For instance, the development of functional food products, fat reduction, sensory improvement, preservation, and other areas may involve the use of microcapsules in various food matrices such as meat products, dairy products, cereals, and fruits, as well as in their derivatives, with good results. The versatility of applications arises from the diversity of techniques and materials used in the process of microencapsulation. The objective of this review is to report the state of the art in the application and evaluation of microcapsules in various food matrices, as a one-microcapsule-core system may offer different results according to the medium in which it is used. The inclusion of microcapsules produces functional products that include probiotics and prebiotics, as well as antioxidants, fatty acids, and minerals. Our main finding was that the microencapsulation of polyphenolic extracts, bacteriocins, and other natural antimicrobials from various sources that inhibit microbial growth could be used for food preservation. Finally, in terms of sensory aspects, microcapsules that mimic fat can function as fat replacers, reducing the textural changes in the product as well as ensuring flavor stability.     

4. Characteristics of cellulose acetates 4.1 Characterization and physical properties of cellulose acetates

An overview is provided of the basic features of cellulose acetate of various degree of substitution in the solid and liquid crystalline state as well as in solution. These features represent a necessity for an understanding of the properties of these cellulose derivatives and further for mixed esters, which are not presented in this paper. Specifically, the crystal structure of cellulose triacetate will be addressed as well as structures in dilute and semi-dilute solutions. Thermal, viscoelastic and further properties in the solid state are discussed as well as flow behavior of solutions and their application in molecular weight determination, including false viscosity of commercial 2.5 cellulose acetates.     

Nanocelluloses: a new family of nature-based materials

Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.     

Experimental and theoretical challenges in the chemistry of noncovalent intermolecular interaction and clustering

The weak, noncovalent interactions among molecules at long range and as close as van der Waals contact form a crucial contemporary frontier for chemical physics, one with many challenges for experimental as well as theoretical investigation. Certain of these challenges have been met in the last two decades, but as recognition of the complexity of phenomena governed or affected by weak interaction has grown, new challenges have arisen. We discuss a number of these challenges in the context of recent developments and progress, highlighting both disparate objectives of theory and experiment in this area as well as their crucial interplay.     

Low-field NMR for quality control on oils

Oil is a prominent, but multifaceted material class with a wide variety of applications. Technical oils, crude oils as well as edibles are main subclasses. In this review, the question is addressed how low-field NMR can contribute in oil characterization as an analytical tool, mainly with respect to quality control. Prerequisite in the development of a quality control application, however, is a detailed understanding of the oils and of the measurement. Low-field NMR is known as a rich methodical toolbox that was and is explored and further developed to address questions about oils, their quality, and usability as raw materials, during production and formulation as well as in use.     

N,N-dimethylformamide: a multipurpose building block

Often used as a common solvent for chemical reations and utilized widely in industry as a reagent, N,N-dimethylformamide (DMF) has played an important role in organic synthesis for a long time. Numerous highly useful articles and reviews discussing its utilizations have been published. With a focus on the performance of DMF as a multipurpose precursor for various units in numerous reactions, this Minireview summarizes recent developments in the employment of DMF in the fields of formylation, aminocarbonylation, amination, amidation, and cyanation, as well as its reaction with arynes.     

Determination of Selenium Species in Environmental Samples

 The essential nature of selenium as well as its toxicity depend on the concentration and the chemical forms in which this element is present in a given sample. Dissolved inorganic selenium can be found in natural water and soil as selenides, selenite and selenate. Organoselenium compounds present in air, soil and plants are volatile methylselenides, trimethylselenonium ion and several selenoamino acids. This review is a summary of recent research on the determination of selenium species in environmental samples such as water, air, soil and plants. Stability of selenium species in solutions and their storage is also discussed. In the metabolic pathway in the body selenide could act as the common intermediate for inorganic and organic Se sources as well as the checkpoint between further utilisation and excretion of selenium. Received May 30, 2001; accepted October 19, 2001; published online July 15, 2002     

离子液体在有机合成中的应用研究进展

离子液体由于具有特殊的性质, 包括低挥发性、大极性、良好的热稳定性、通过调整阴阳离子选择不同的溶解性等特点, 已经作为反应介质或催化剂广泛应用于有机合成领域, 引起了人们足够的兴趣. 与传统有机溶剂反应相比, 离子液体相反应得到的产物收率高, 选择性好, 加快部分类型反应的速率, 后处理简单以及离子液体催化剂体系简单, 回收后, 可多次重复使用. 综述了离子液体作为反应介质或催化剂在有机合成传统反应类型中的最新研究成果, 主要包括: 偶联反应、Michael加成、Baylis-Hillman反应、Diels-Alder反应、Aldol缩合、Knoevenagel缩合、环化反应、烷基化及酰基化反应和氧化还原反应.     

微波促进离子液体相反应在有机合成中的应用

微波促进离子液体相有机合成技术作为一种新型的绿色化学合成法,引起了人们极大的兴趣。在离子液体中,微波辅助下反应快速、收率高、选择性好、后处理简单,离子液体经简单再生后可多次套用。本文综述了以离子液体为反应介质或催化剂的微波辅助技术在多种类型有机反应中的研究成果,主要包括了环合反应、亲核取代反应、金属复分解反应、酰化反应、重排反应、聚合反应、偶联反应、氧化还原反应和选择性脱溴反应等。     

Analytical devices based on light-emitting diodes – a review of the state-of-the-art

A general overview of the development of the uses of light-emitting diodes in analytical instrumentation is given. Fundamental aspects of light-emitting diodes, as far as relevant for this usage, are covered in the first part. The measurement of light intensity is also discussed, as this is an essential part of any device based on light-emitting diodes as well. In the second part, applications are discussed, which cover liquid and gas-phase absorbance measurements, flow-through detectors for chromatography and capillary electrophoresis, sensors, as well as some less often reported methods such as photoacoustic spectroscopy.     

The urea renaissance

Over the last decade the use of urea derivatives as useful reagents, catalysts, and structural features in organic chemistry has increased rapidly. They now find utility as hydrogen-bond donors in organocatalysts and anion transporters, as important scaffolds in supramolecular chemistry, as lithiation directors, amination substrates, and promoters of metalation, and as substrates for novel rearrangement reactions. Highlighted herein is the remarkably rapid and recent development of the chemistry of ureas, which for many years had been considered unreactive, intractable, and of little value.     

烯丙位氧化的几种方法

综述了近年来烯丙位氧化的研究进展，详细讨论了过渡金属及其络合物、硒化 合物在烯丙位氧化中的应用，并简述了丁基锂方法、固相催化方法、生物氧化方法 和次氯酸钠氧化方法在烯丙位氧化中的应用．     

Advances and challenges of MOF derived carbon-based electrocatalysts and photocatalyst for water splitting: A review

Environmental pollution and energy shortage are substantial fears to the modern world's long-term sustainability. Water splitting is an essential technique for eco - friendly and sustainable energy storage, as well as a pollution-free method to produce hydrogen. In this regards Metal–organic frameworks have emerged as the most competent multifunctional materials in recent times, due to its large surface areas, adjustable permeability, easy compositional alteration, and capability for usage as precursors with a wide range of morphological forms. Further, MOF-derived carbon-based nanomaterials also offer significant benefits in terms of tunable morphological features and hierarchical permeability, as well as ease of functionalization, making them extremely effective as catalysts or catalysts supports for a wide variety of important reactions. Recent developments in carbon-based MOFs as catalysts for overall water splitting are discussed in this review. We explore how MOFs and carbon-based MOFs might well be beneficial, as well as which methods should be explored for future development. We divided our review into two sections: photocatalytic and electrocatalytic water splitting, and we gathered published literature on carbon-based MOFs materials for their outstanding activity, offers helpful methods for catalysts design and analysis, as well as difficulties This study highlights the developments in MOF derived materials as photo and electro catalysts by explaining respective approaches for their use in overall water splitting.     

SDS disc electrophoresis of proteins in homogeneous, low-concentrated polyacrylamide gels

In the attempt to separate in a single gel run low- and high-molecular-weight proteins, we present here a multiphasic buffer system designed for this purpose. It avoids the continuous stacking of SDS as it occurs in the 'classical' SDS-PAGE. The system allows complete stacking and destacking of proteins in the 3.5-250 kDa range at acrylamide concentrations as low as 4.5% T (total acrylamide concentration in %) and 2.6% C (degree of cross-linking in %). Taurine is used as the trailing ion in the cathode buffer and in the resolving zone of the gel, and two different counterions (Tris and imidazole) in the stacking zone. The gel system is easy to prepare and, due to the very low acrylamide concentrations, it is ideal for analytical as well as for preparative tasks.     

Potentiometric and voltammetric polymer lab chip sensors for determination of nitrate, pH and Cd(II) in water

Microparticles are phospholipid vesicles shed mostly in biological fluids, such as blood or urine, by various types of cells, such as red blood cells (RBCs), platelets, lymphocytes, endothelial cells. These microparticles contain a subset of the proteome of their parent cell, and their ready availability in biological fluid has raised strong interest in their study, as they might be markers of cell damage. However, their small size as well as their particular physico-chemical properties makes them hard to detect, size, count and study by proteome analysis. In this review, we report the pre-analytical and methodological caveats that we have faced in our own research about red blood cell microparticles in the context of transfusion science, as well as examples from the literature on the proteomics of various kinds of microparticles.