The randomization of 11 bases in the theophylline-binding domain generated a library containing millions of different theophylline riboswitch variants. The dual genetic selection of this molecular library successfully led to the identification of a caffeine-specific synthetic riboswitch. When a chloramphenicol-resistance gene was expressed under control of this caffeine riboswitch, E. coli cells showed chloramphenicol resistance only in the presence of caffeine. For a colorimetric or fluorescence assay, the caffeine riboswitch gene was inserted upstream of the B-galactosidase (LacZ) or green fluorescence protein (GFP) gene, respectively. When tested with various concentrations of caffeine, the enzymatic activity of LacZ or the fluorescence intensity of GFP was proportional to the amount of caffeine, clearly indicating the caffeine-dependent gene regulation by the caffeine riboswitch. The caffeine synthetic riboswitch can be further developed as a biosensor to detect caffeine in complex biological samples such as urine and blood.

Porous silicon (pSi) is a unique nanostructured form of the elemental semiconductor Si. Due to its useful properties governed by its surface chemistry and porous morphology, pSi has been studied in the last few decades in diverse fields extending from electronic device technology to bio-relevant applications.1 Recently, one-dimensional porous nanotubes based on elemental Si (pSiNTs) with a tunable structure (sidewalls, inner void space and lengths) have been successfully synthesized.2 The well-defined structure of pSiNTs offers ample opportunities to study newly emerging properties of this material and innovative applications in multiple areas. For example, recent reports have revealed the use of SiNTs as an efficient template for loading superparamagnetic nanoparticles (Fe3O4), lithium storage and cycling, as well as acting as a template for formation of organometal perovskite nanostructures.3-5
Platinum (Pt) nanoparticles, both free-standing as well as anchored on various surfaces, have attracted widespread attention in nanocatalysis, electronics, and chemotherapeutics.6 In this work, it is suggested that pSiNTs after being functionalized with 3-(aminopropyl)triethoxysilane (APTES) can serve as a platform for Pt nanocrystal (Pt NC) formation. Particularly, incubation of APTES-functionalized SiNTs in potassium tetrachloroplatinate (II) (K2PtCl4) solution under ambient conditions subsequently yields Pt nanoclusters with sizes ranging from 1-3 nm on SiNTs. From high-resolution transmission electron microscopy (HRTEM), nanocrystals with characteristic lattice spacings associated with Pt (d = 0.21 nm) are observed on the nanotubes. The amount of Pt deposited on SiNTs can be sensitively tuned from 20-60 wt% (characterized by TEM Energy Dispersive X-ray Analysis, EDX) by varying concentration of K2PtCl4 and immersion time in this Pt salt precursor.
These findings suggest a new approach to prepare Pt NCs that are of potential benefit to a broad number of applications by using pSiNTs as a template. Further investigations into the properties of the newly discovered Pt NCs-SiNT composites are imperative to evaluate useful applications of this material.
REFERENCES
[1] Porous Silicon for Biomedical Applications, H. Santos, Ed. Cambridge: Woodhead Publishing, 2014.
[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Commun., 2013, 49, 5760-5762.
[3] P. Granitzer, K. Rumpf, R. Gonzalez, J. Coffer, M. Reissner, Nanoscale Res. Lett. 2014, 9, 413.
[4] R. Gonzalez-Rodriguez, N. Arad-Vosk, N. Rozenfeld, A. Sa'ar, J. L. Coffer, Small, 2016, 12, 4477-4480.
[5] A. T. Tesfaye, R. Gonzalez, J. L. Coffer, T. Djenizian, ACS Appl. Mater. Interfaces, 2015, 7, 20495-20498.
[6] A. Chen, and P. Holt-Hindle, Chem. Rev., 2010, 110, 3767-3804.

Atomic partial charges obtained from computed wavefunctions are widely used for interpreting quantum chemistry simulations and chemical reactivities of molecules, solids, surfaces, and nanoparticles. In many cases, partial charge alone gives an incomplete picture of reactivity: PhS(-) is a better nucleophile compared to PhO(-) in SN2 reactions with MeI, though PhO(-) has a more negative charge on the nucleophilic atom, the carbons of benzene and cyclobutadiene, or those of diamond, graphene, and C60, possess nearly identical partial charges and very different reactivities, deprotonated amides perform nucleophilic attack via the less negative nitrogen, rather than the more negative oxygen, in anionic cyclization of o-alkynyl benzamides, halide anions F(-), Cl(-), Br(-) and I(-) have identical charges but different nucleophilicities, carbons in aromatic benzene and anti-aromatic cyclobutadiene have nearly identical partial charges, but different reactivities. Our atomic overlap distance complements computed partial charges by measuring the size of orbital lobes that best overlap with the wavefunction around an atom. Compact, chemically stable atoms tend to have overlap distances smaller than chemically soft, unstable atoms. Combining atomic charges and overlap distances captures trends in aromaticity, nucleophilicity, allotrope stability, and substituent effects. Applications to recent experiments in organic chemistry (counterintuitive Lewis base stabilization of alkenyl anions in anionic cyclization), nanomaterials chemistry (facile doping of the central atom in Au7 hexagons) and selective binding of ligands in proteins illustrate this combination’s predictive power.

Amaryllidaceae isoquinoline alkaloids, as well as their analogs, have long been of interest in research for drug discovery due to their biologically active nature. Many of these compounds have been found to be anti-tumor agents.1 Moreover, there have also been studies that show the effectiveness of these molecules against diseases such as Yellow Fever and other RNA-containing flaviviruses.2 Though these compounds are pharmaceutical drug prospects, their low natural abundance lowers that potential.3 For this reason, many synthetic chemists have pursued novel routes to synthesize a wide variety of these compounds.
Techniques toward the synthesis of Pancratistatin-type natural products are presented herein. Manipulations were tested and optimized on a model system to save both time and funds while developing a synthetic pathway to be utilized in the formation of more complex compounds. Setbacks such as controlling the stereochemistry of a tetrasubstituted alkene reduction have been encountered. However, adjustments are being made to avoid such difficulties. Ideally, the proposed scheme will ultimately allow for the synthesis of multiple biologically active Phenanthridone analogs.

Hippadine and pratosine are lycorine-type pharmacologically active Amaryllidaceae alkaloids. Various total syntheses of these natural products have been developed. However, most of these synthetic routes require prohibitively expensive materials and/or achieve yields that are subpar, making these schemes unlikely to be used in an industrial setting. Current research involves developing better synthetic methods for these two alkaloids starting with a 6,7-disubstituted isoquinoline. These syntheses are appealing since they utilize readily available starting materials and avoid expensive catalysts. The key step in the synthetic scheme centers around an intramolecular de Mayo photocyclization which involves a reaction between an alkene moiety in the isocarbostyril system and a 1,3-diketone (a functionalized tether on nitrogen), which forms a third ring in the structure of the molecule. When the photochemical reaction was attempted, an unexpected cyclic photoproduct was obtained; fortunately, this product is a cyclic hemiketal of the expected 1,5-dicarbonyl compound. A base-catalyzed aldol addition affords the final ring in the system; dehydration of this product affords a β-enone that can be transformed to a diene. Oxidation of the diene with DDQ affords the target natural products after simple chromatographic purification. This new synthetic pathway circumvents the need for catalysts that are either expensive or contain metals such as palladium or iridium; moreover, our method allows for the synthesis of various natural and unnatural alkaloids in high yields by modification of the N-tether.