Spotlights on Recent JACS ... - ACS Publications

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Spotlights Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

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Spotlights on Recent JACS Publications

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ULTRABRIGHT DYES ENABLE SELECTIVE IMAGING OF LIPID DROPLETS Lipid droplets that bob along in cells are involved in many physiological processes, such as cell-membrane formation and biochemical signaling. As a result, they play a role in metabolic disorders and diseases, including obesity, diabetes, and cancer. One of the challenges researchers face when studying lipid droplets is finding an appropriate dye to serve as a probe to track droplet movementone that switches from the “off” to the “on” state and gives a clear and steady signal when it travels from an aqueous environment to a hydrophobic environment. Most dyes in current use are rather nonselective for hydrophobic media and will stain lipid bilayers that make up cell membranes, creating background color noise that is hard to decipher. Mayeul Collot and co-workers present a family of ultrabright fluorophores that are selective for lipid droplets and work over a range of wavelengths from yellow to the near-infrared (DOI: 10.1021/jacs.7b12817). The fluorophores, which are merocyanine dyes containing an indolenine unit and an adjacent dioxaborine-barbiturate unit, selectively stain lipid droplets to track their movement and their distribution, both between live cultured cells and in tissues, with very low background noise. The new fluorogenic probes also allow for multi-color imaging, thanks to their narrow absorption and emission bands in the visible range. Christine Herman, Ph.D.

GENETICALLY ENCODED AMINO ACID ANALOGUE ENABLES “NEXT-GENERATION CLICK CHEMISTRY” Imbuing proteins in living cells with new chemical functionality and reactivity opens up potential applications in chemical biology, drug discovery, and biotherapeutics. Advances in genetic engineering have enabled researchers to expand the genetic code to include unnatural amino acids (Uaas). Now, a new class known as latent bioreactive Uaas enables selective formation of new covalent bonds between proteins in living cells (DOI: 10.1021/jacs.8b01087). Researchers led by Lei Wang genetically encode the unnatural amino acid fluorosulfate-L-tyrosine into proteins in both bacterial and mammalian cells and demonstrate subsequent reactivity in live cells with neighboring proteins. The bonds are formed when the Uaa reacts with lysine, histidine, and tyrosine residues via a sulfur−fluoride exchange reaction, generating both intra-protein bridges and inter-protein cross-links. The study expands the diversity of proteins amenable to cross-linking reactivity via sulfur−fluoride exchange chemistry, with the potential to empower general proteins with the next generation of click chemistry. Christine Herman, Ph.D.

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“BREATHING” POLYMERSOMES: NANOREACTORS WITH A PROGRAMMABLE ON−OFF SWITCH Polymersomes are a class of artificial vesicles formed with a polymer-based membrane that can encapsulate molecular cargo in solution. When properly equipped, a polymersome can execute a task in response to external stimuli, such as transporting the cargo across the membrane barrier or serving as a nanoreactor for an enzymatic reaction. In a new example, Jan van Hest and colleagues report the creation of a biocatalytic polymersome that offers users pH control over enzyme activation (DOI: 10.1021/jacs.8b02387). The team encapsulates two enzymes within vesicles: urease, which helps control pH, and horseradish peroxidase, which drives a catalytic reaction. In a high pH environment, the vesicles are in an “off” state as the polymers are deprotonated and the vesicles shrink to become impermeable. The addition of acid and urea lowers the pH and causes the vesicles to swellto “take a breath”. In this “on” state, reactants can pass through the polymer membrane and react with horseradish peroxidase. As urease converts the urea into ammonia, the pH rises, causing the vesicles to shrink again. This on−off cycle can be repeated. Programmable polymersomes acting as nanoreactors can offer users more control compared to classical nanoreactors that operate in a thermodynamically controlled one-way transition. Christine Herman, Ph.D.

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AN ENVIRONMENTALLY FRIENDLIER ROUTE FOR PRODUCING MESOPOROUS MATERIALS The highly ordered mesoporous silica material SBA-15 is used in a range of applications, including molecular sieves, catalysts, drug delivery, gas sensing, ion exchange, and photovoltaics. SBA-15 is obtained by catalytic synthesis from tetraethyl orthosilicate (TEOS) dissolved in water. However, this reaction requires eco-unfriendly acidic conditions for the supply of the hydrogen ions that catalyze the reaction. Jihong Yu and co-workers have demonstrated a new approach for synthesizing SBA-15 that works without resorting to acid (DOI: 10.1021/jacs.8b00093). They instead use hydroxyl free radicals in water induced via physical or chemical methods. Calculations show that •OH is more efficient than H+ in catalyzing the synthesis of the mesoporous material. In a series of experiments, the researchers demonstrate the formation of SBA-15 from TEOS dissolved in water by exposing the mixture to UV light, without adding acid. The UV irradiation generates the free radicals. The team also can obtain the required free radicals chemically by adding sodium persulfate as an oxidizing agent or by using a mixture of hydrogen peroxide and ferrous oxide for a similar result. The researchers verify the formation of the mesopores in these experiments with TEM images of the obtained SBA-15 samples. Alexander Hellemans © XXXX American Chemical Society

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DOI: 10.1021/jacs.8b03930 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX