Additive-Free, Visible-Light-Enabled Decarboxylative Alkylation of Enamides.

Enamides are versatile precursors for synthesizing bioactive compounds. As their alkylations often require perstoichiometric amounts of oxidants, transition metals, or photocatalysts, we herein report a simple alternative for their alkylations by just using visible light to irradiate the mixture of the readily available N-hydroxyphthalimide esters and enamides without an additive. The reaction involves the photoactivation of a π-π stacking EDA complex between the substrates.

Visible-Light-Induced Selective Photolysis of Phosphonium Iodide Salts for Monofluoromethylations.

The sigma (σ)-hole effect has emerged as a promising tool to construct novel architectures endowed with new properties. A simple yet effective strategy for the generation of monofluoromethyl radicals is a continuing challenge within the synthetic community. Fluoromethylphosphonium salts are easily available, air- and thermally stable, as well as simple-to-handle. Herein, we report the ability of the σ-hole effect to facilitate the visible-light-triggered photolysis of phosphonium iodide salts, a charge-transfer complex, selectively giving fluoromethyl radicals. The usefulness and versatility of this new protocol are demonstrated through the mono-, di-, and trifluoromethylation of a variety of alkenes.

Visible-Light-Triggered Iodinations Facilitated by Weak Electrostatic Interaction of N-Heterocyclic Carbenes.

N-heterocyclic carbenes (NHCs) are well-known as ligands and organocatalysts, but there is no recognition for their catalytic role as a stabilizer through electrostatic interaction rather than electron donation. By utilizing the electrostatic interaction, we herein describe the success of a visible-light-triggered radical-radical cross-coupling of N-alkenoxypyridinium salts and NaI, giving a variety of α-iodo ketones. Computational studies characterize the stabilization role of NHCs.

A centrifugation-assisted visual detection of SNP in circulating tumor DNA using gold nanoparticles coupled with isothermal amplification.

Detection of single-nucleotide polymorphism (SNP) in circulating tumor DNA (ctDNA) is challenging because of the large DNA fragmentation (∼150 nt) and the strong background of normal cell free DNA (cfDNA). Here we developed a rapid centrifugation-assisted colorimetric assay using gold nanoparticles (AuNPs) coupled with isothermal amplification to detect a SNP (G to C mutation) in KRAS, p.G13D in ctDNA. Compared to conventional AuNP aggregation assays, our assay contains four unique design concepts. Firstly, a centrifugation step is introduced at the end of the reaction that significantly enhances the colorimetric readout by providing visually distinct precipitation for the SNP ctDNA. Secondly, to achieve a fast turnover rate for clinical pM demand, a "critical linker concentration" concept is introduced to the assay. Thirdly, in order to achieve an unambiguous differentiation of the SNP ctDNA from wild type cfDNA and the control sample without DNA, a "color code conversion" strategy is employed, where a complementary sequence of the linker DNA is introduced to manipulate the AuNP aggregation. Finally, ethylenediaminetetraacetic acid is used for enzyme inactivation only at room temperature while stabilizing the AuNP solution from unwanted aggregation. Our assay coupling two amplification strategies (isothermal amplification and centrifugation-assisted assembly) is capable of both quantitative and qualitative differentiation of SNP in ctDNA of ∼150 nt at a clinically relevant concentration and 67 pM limit of detection and in the presence of 99% normal cfDNA background. This assay can be used for point-of-care colon cancer diagnosis and prognosis with a fast turnover time (<2 h).

Correction to "Gold Nanorods Embedded in Polymeric Film for Killing Bacteria by Generating Reactive Oxygen Species with Light".

[This corrects the article DOI: 10.1021/acsabm.9b00343.].

Gold Nanorods Embedded in Polymeric Film for Killing Bacteria by Generating Reactive Oxygen Species with Light.

For the first time, anisotropic gold nanorods (AuNRs) were embedded with a photosensitizer dye (crystal violet) in polyurethane (PU) matrix to create the effective antimicrobial film, capable of killing Gram-negative bacteria on its surface when exposed to white light. The dye, when activated with white light, interacts with the AuNRs to generate reactive oxygen species (ROS), which kill bacteria. With a proper control of the aspect ratio (2.1-2.4) and coating of the AuNRs, the film can be tuned to reduce the bacteria population of one to four orders of magnitude (1-log to 4-log) under 11 klux of light, for an exposure to light between 1 to 3 h. Particularly it could reduce 104 cfu/cm2 to the level of 1-5 cfu/cm2 in 3 h of light exposure. This was a desired performance for use on hospital surfaces. In addition, the system showed antimicrobial effect only when exposed to light, which eliminated the concern for a cumulative toxic effect on subjects exposed to the material for a long period of time and limited the time given to the bacteria to develop resistance against the system. Furthermore, this process of sterilization could be carried out by a commercially available white light lamp, which when in use did not interrupt the normal routine operation of the environment.

Formulation of DNA chimera templates: Effects on emission behavior of silver nanoclusters and sensing.

Single strand DNA (ssDNA) chimeras consisting of a silver nanoclusters-nucleating sequence (NC) and an aptamer are widely employed to synthesize functional silver nanoclusters (AgNCs) for sensing purpose. Despite its simplicity, this chimeric-templated AgNCs often leads to undesirable turn-off effect, which may suffer from false positive signals caused by interference. In our effort to elucidate how the relative position of NC and aptamer affects the fluorescence behavior and sensing performance, we systematically formulated these NC and aptamer regions at different position in a DNA chimera. Using adenosine aptamer as a model, we tested the adenosine-induced optical response of each design. We also investigated the effect of linker region connecting NC and aptamer, as well as different NC sequence on the sensing performance. We concluded that locating NC sequence at 5'-end exhibited the best response, with immediate fluorescence enhancement observed over a wide linear range (1-2500 µM). Our experimental findings help to explain the emission behavior and sensing performance of chimeric conjugates of AgNCs, providing an important means to formulate a better aptasensor.

Electrochemical impedance sensing of DNA hybridization on conducting polymer film-modified diamond.

The impedimetric sensing of DNA hybridization on polyaniline/polyacrylate (PANI/PAA)-modified boron-doped diamond (BDD) electrode has been investigated. An ultrathin film of PANI-PAA copolymer was electropolymerized onto the diamond surfaces to provide carboxylic groups for tethering to DNA sensing probes. The electrochemical impedance and the intrinsic electroactivity of the polymer-diamond interface were analyzed after the hybridization reaction with target and non-target DNA. The impedance measurement shows changes in the impedance modulus as well as electron-transfer resistance at the stage of probe DNA immobilization (single-strand), as well as after hybridization with target DNA (double-strand). DNA hybridization increases the capacitance of the polymer-DNA layer and reduces the overall impedance of the DNA-polymer-diamond stack significantly. The polymer-modified BDD electrode shows no detectable nonspecific adsorption, with good selectivity between the complementary DNA targets and the one-base mismatch targets. The detection limit was measured to be 2 x 10(-8) M at 1000 Hz. Denaturing test on the hybridized probe and subsequent reuse of the probe indicates chemical robustness of the sensor. Our results suggest that electropolymerization followed by the immobilization of biomolecules is a simple and effective way of creating a functional biomolecular scaffold on the diamond surface. In addition, label-free electrochemical impedance method can provide direct and noninvasive sensing of DNA hybridization on BDD.