Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

The Huisgen 1,3-dipolar cycloaddition reaction of organic azides and alkynes has gained considerable attention in recent years due to the introduction in 2001 of Cu(1) catalysis by Tornoe and Meldal, leading to a major improvement in both rate and regioselectivity of the reaction, as realized independently by the Meldal and the Sharpless laboratories. The great success of the Cu(1) catalyzed reaction is rooted in the fact that it is a virtually quantitative, very robust, insensitive, general, and orthogonal ligation reaction, suitable for even biomolecular ligation and in vivo tagging or as a polymerization reaction for synthesis of long linear polymers. The triazole formed is essentially chemically inert to reactive conditions, e.g. oxidation, reduction, and hydrolysis, and has an intermediate polarity with a dipolar moment of ∼5 D. The basis for the unique properties and rate enhancement for triazole formation under Cu(1) catalysis should be found in the high ∆G of the reaction in combination with the low character of polarity of the dipole of the noncatalyzed thermal reaction, which leads to a considerable activation barrier. In order to understand the reaction in detail, it therefore seems important to spend a moment to consider the structural and mechanistic aspects of the catalysis. The reaction is quite insensitive to reaction conditions as long as Cu(1) is present and may be performed in an aqueous or organic environment both in solution and on solid support.

Cu-catalyzed azide-alkyne cycloaddition.

The field of chemical sensing is becoming ever more dependent upon novel materials. Polymers, crystals, glasses, particles, and nanostructures have made a profound impact and have endowed modern sensory systems with superior performance. Electronic polymers have emerged as one of the most important classes of transduction materials; they readily transform a chemical signal into an easily measured electrical or optical event. Although our group reviewed this field in 2000,1 the high levels of activity and the impact of these methods now justify a subsequent review as part of this special issue. In this review we restrict our discussions to purely fluorescence-based methods using conjugated polymers (CPs). We further confine our detailed coverage to articles published since our previous review and will only detail earlier research in this Introduction to illustrate fundamental concepts and terminology that underpin the recent literature.

Chemical sensors based on amplifying fluorescent conjugated polymers.

National Institute of Standards and Technology における超伝導研究及び生活

基礎講座 電気泳動(Electrophoresis)

Greener approaches to organic synthesis using microreactor technology.

Organic synthesis is a powerful enterprise that continues to develop more selective and efficient chemical methods and synthetic routes. To synthesize complex molecules, whether in academic laboratories or industrial manufacturing, reactions are often performed iteratively in batch reactors. Although these stepwise methods are effective, they are also very wasteful. The pharmaceutical industry, for example, produces 25–100 kg of waste for every kilogram of a complex molecule synthesized. Though chemists are constantly striving to devise more efficient syntheses, recent reminders of a resource-limited world underscore the need for more sustainable methods and technologies to synthesize molecules of importance. The application of new technologies, such as microreactors, to organic synthesis can be used to achieve this goal. Microreactors are a developing technology used to perform safer, more efficient, and more selective chemical transformations in microchannels or narrow-bore tubing. The many advantages associated with conducting reactions in flow are attributed to large surface-area-to-volume ratios that allow precise reaction control through rapid heat transfer and mixing. The syntheses can be scaled up by running a single reactor for extended periods of time or by the addition of more identical flow reactors in parallel, a process known as numbering up. Although most applications of microreactors in organic synthesis have focused on single-step reactions, recent examples have demonstrated multistep reaction sequences in flow. 28–32] Our group has a long-standing interest in the development of new methodologies that enable the rapid and efficient synthesis of important small molecules. Specifically, we have aimed to run multistep reaction sequences in one pot (i.e. in batch reactors) or in series (i.e. in microreactors). 34] We report herein a three-step, continuous-flow synthesis of ibuprofen, a high-volume, nonsteroidal anti-inflammatory drug (NSAID), using a simplified microreactor that eliminates the need for purification and isolation steps. To achieve this continuous-flow synthesis, a careful retrosynthetic analysis of ibuprofen was performed, considering the synthesis of ibuprofen as an entity, as opposed to a series of independent reactions steps. Reactions therefore had to be designed such that byproducts and excess reagents from one reaction were compatible with downstream reactions. In this way, reactions could be performed in sequence without any breaks in the synthesis. The general three-step synthesis of ibuprofen we investigated is outlined in Scheme 1.

The continuous-flow synthesis of Ibuprofen.

The system is designed so that pH alters the absorption cross-section, energy migration efficiency, and emission efficiency ofthe fluoresceinamine (FA) dye appended off of polymer 2.Inthis case, the dye acts as a shunt, withdrawing energy from theconjugated polymer. At high pH, FA is highly absorptive andhighly fluorescent, while at low pH, the dye’s extinction coef-ficient decreases and the fluorescence is lost. In our case,electrostatic binding of anionic polymer 2 onto the cationic surfaceformed by depositing 1 directly onto a glass substrate provides afacile method for placing the appended FA in close proximity tothe conjugated polymer.

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Signal Amplification of a “Turn-On” Sensor: Harvesting the Light Captured by a Conjugated Polymer

Ion‐Specific Aggregation in Conjugated Polymers: Highly Sensitive and Selective Fluorescent Ion Chemosensors

[reaction: see text] On the basis of reaction rate data, we have proposed a new mechanism for the Baylis-Hillman reaction involving the formation of a hemiacetal intermediate. We have determined that the rate-determining step is second order in aldehyde and first order in DABCO and acrylate. We have shown that this mechanism is general to aryl aldehydes under polar, nonpolar, and protic conditions using both rate data and two isotope effect experiments.

D. Tyler McQuade

Papers

Greener approaches to organic synthesis using microreactor technology.

The continuous-flow synthesis of Ibuprofen.

Signal Amplification of a “Turn-On” Sensor: Harvesting the Light Captured by a Conjugated Polymer

Ion‐Specific Aggregation in Conjugated Polymers: Highly Sensitive and Selective Fluorescent Ion Chemosensors

A new interpretation of the Baylis-Hillman mechanism.