/pdf/degradable-controlled-release-polymers-and-polymeric-1y322ha58z.pdf

Degradable Controlled-Release Polymers and Polymeric Nanoparticles: Mechanisms of Controlling Drug Release

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Coumarin-Based Small-Molecule Fluorescent Chemosensors.

Hydrogen sulfide (H2S), a gaseous species produced by both bacteria and higher eukaryotic organisms, including mammalian vertebrates, has attracted attention in recent years for its contributions to human health and disease. H2S has been proposed as a cytoprotectant and gasotransmitter in many tissue types, including mediating vascular tone in blood vessels as well as neuromodulation in the brain. The molecular mechanisms dictating how H2S affects cellular signaling and other physiological events remain insufficiently understood. Furthermore, the involvement of H2S in metal-binding interactions and formation of related RSS such as sulfane sulfur may contribute to other distinct signaling pathways. Owing to its widespread biological roles and unique chemical properties, H2S is an appealing target for chemical biology approaches to elucidate its production, trafficking, and downstream function. In this context, reaction-based fluorescent probes offer a versatile set of screening tools to visualize H2S pools in living systems. Three main strategies used in molecular probe development for H2S detection include azide and nitro group reduction, nucleophilic attack, and CuS precipitation. Each of these approaches exploits the strong nucleophilicity and reducing potency of H2S to achieve selectivity over other biothiols. In addition, a variety of methods have been developed for the detection of other reactive sulfur species (RSS), including sulfite and bisulfite, as well as sulfane sulfur species and related modifications such as S-nitrosothiols. Access to this growing chemical toolbox of new molecular probes for H2S and related RSS sets the stage for applying these developing technologies to probe reactive sulfur biology in living systems.

/pdf/chemical-probes-for-molecular-imaging-and-detection-of-34y1mdog9w.pdf

Chemical probes for molecular imaging and detection of hydrogen sulfide and reactive sulfur species in biological systems

Capping agents are frequently used in colloidal synthesis to inhibit nanoparticle overgrowth and aggregation as well as to control the structural characteristics of the resulted nanoparticles in a precise manner. Study of the effect of the residual capping agents on particle surface has unveiled various adverse and favorable behaviors in catalytic applications. In essence, while the capping agents usually act as a physical barrier to restrict the free access of reactants to catalytic nanoparticles, they can also be utilized to promote catalytic performance of nanocrystals. Due to the complexity of these effects, a general survey of capping agents in nanocatalysis is therefore necessary. This short review starts from a brief introduction of common capping agents in nanoparticle synthesis and their adverse impact on heterogeneous catalysis. Next, representative progresses in capping agent removal and surfactant-free synthesis for obtaining surface-clean nanocatalysts are summarized. Lastly, we discuss the r...

Removal and Utilization of Capping Agents in Nanocatalysis

The association state of light-responsive block copolymer (BCP) micelles in aqueous solution can be altered, often reversibly, by light. Driven by the potential application in controlled drug delivery, this type of stimuli-responsive polymer micelles has received increasing attention. This Perspective highlights the progress achieved in recent years. On the one hand, we discuss the different approaches of rational BCP design, making use of various photochromic moieties and photochemical reactions, and the underlying mechanisms leading to photoinduced disruption of BCP micelles. On the other hand, we suggest possible future directions in this area, including exploration of new mechanisms and chemistry and solutions to the excitation wavelength problem crucial for biomedical applications.

Light-Responsive Block Copolymer Micelles

A coumarin-based fluorescence chemoprobe was developed and evaluated for the selective and sensitive detection of hydrogen sulfide in degassed PBS buffers and fetal bovine serum. Fluorescence detection of hydrogen sulfide in living cells was also successfully achieved using two-photon confocal fluorescence imaging. Further in situ visualization of endogenous H(2)S was realized in cardiac tissues of normal rats and atherosclerosis (AS) rats.

Fluorescent probe for highly selective and sensitive detection of hydrogen sulfide in living cells and cardiac tissues

Light-responsive drug delivery systems are particularly appealing that are capable of releasing active molecules at the appropriate site and rate. We synthesized a series of photodegradable polymers that can form nanoparticles for drug encapsulation. These particles in aqueous solutions are stable in buffers with different pHs or at evaluated temperatures, while light can trigger the crash of particles and the release of encapsulated substances. The release efficiency can reach up to 90% based on Nile red fluorescence intensity upon 15 min light irradiation. Nanoparticle uptake by phagocytic cells and light-triggered release in cells were observed by fluorescence emission of the hydrolyzed fluorescein diacetate upon photoinduced degradation of these nanoparticles. No significant toxicity of these nanoparticles was found at the concentrations up to 1000 μg/mL before or after light irradiation. Further encapsulation and triggered release of a bioactive model drug (Tagalsin G) was evaluated for RAW 264.7 cells. Tagalsin G encapsulated in nanoparticles did not show cytotoxity to cells, while light triggered the release of Tagalsin G increasing cell death dramatically from 9% to 67%. Our model studies show a new promising strategy to trigger drug release in cells.

Photodegradable polyurethane self-assembled nanoparticles for photocontrollable release.

We synthesized three 20 mer caged circular antisense oligodeoxynucleotides (R20, R20B2 and R20B4) with a photocleavable linker and an amide bond linker between two 10 mer oligodeoxynucleotides. With these caged circular antisense oligodeoxynucleotides, RNA-binding affinity and its digestion by ribonuclease H were readily photomodulated. RNA cleavage rates were upregulated ~43-, 25- and 15-fold for R20, R20B2 and R20B4, respectively, upon light activation in vitro. R20B2 and R20B4 with 2- or 4-nt gaps in the target RNA lost their ability to bind the target RNA even though a small amount of RNA digestion was still observed. The loss of binding ability indicated promising gene photoregulation through a non-enzymatic strategy. To test this strategy, three caged circular antisense oligonucleotides (PS1, PS2 and PS3) with 2'-OMe RNA and phosphorothioate modifications were synthesized to target GFP expression. Upon light activation, photomodulation of target hybridization and GFP expression in cells was successfully achieved with PS1, PS2 and PS3. These caged circular antisense oligonucleotides show promising applications of photomodulating gene expression through both ribonuclease H and non-enzyme involved antisense strategies.

Caged circular antisense oligonucleotides for photomodulation of RNA digestion and gene expression in cells

Morpholino oligomers (MOs) have been widely used to knock down specific genes in zebrafish, but their constitutive activities limit their experimental applications for studying a gene with multiple functions or within a gene network. We report herein a new design and synthesis of caged circular MOs (caged cMOs) with two ends linked by a photocleavable moiety. These caged cMOs were successfully used to photomodulate b-catenin-2 and no tail expression in zebrafish embryos.

/pdf/manipulation-of-gene-expression-in-zebrafish-using-caged-2lzht38no9.pdf

Manipulation of gene expression in zebrafish using caged circular morpholino oligomers

A selective and sensitive fluorescence probe for hydrogen sulfide (H2S) detection was synthesized and evaluated in PBS buffer and fetal bovine serum. The effect of pH on the probe was also studied. In addition, visualization of H2S in Hela cells was achieved using confocal laser scanning fluorescence microscopy.

Chemoselective reduction-based fluorescence probe for detection of hydrogen sulfide in living cells.

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