Substituted phenylthioureas have been established as efficient organocatalysts and substituents containing electron withdrawing CF 3 groups have been shown to enhance catalytic efficiency. The effect of the CF 3 groups on binding of catalysts to substrates in solution has however remained elusive. Here, we report on the effect of CF 3 substituted diphenylthioureas on the association with the substrate 1,3-diphenyl-2propenone in solution by using a combination of nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy. We use the ensemble-averaged chemical shift of the thiourea proton as function of substrate concentration to determine the association constants between catalyst and substrate. To experimentally discriminate between free and bound catalyst we use infrared absorption spectra, which show a red-shift of thiourea's N-H stretching vibration upon association with the substrate. With both methods, we find the association constant K to increase from ~1 L/mol to ~20 L/mol with increasing number of CF 3 substituents. This enhanced binding can explain the increased reaction rates observed for CF 3 substituted diphenylthiourea catalysts. For the efficient catalyst containing four CF 3groups (Schreiner's catalyst), the strongest association is observed in toluene as a solvent, while the binding strength is somewhat weaker in dichloromethane, and association to the substrate is not detectable in acetonitrile. Our results thus demonstrate that even weak association between the thiourea catalysts and the ketone can facilitate efficient catalytic conversion. However, the association with the ketone substrates is very susceptible to competing interactions with the solvent.

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Engineered living materials (ELMs) use encapsulated microorganisms within polymeric matrices for biosensing, drug delivery, capturing viruses, and bioremediation. It is often desirable to control their function remotely and in real time. Suitable, genetically engineered microorganisms respond to changes of their environment. Here, we combine this local sensitivity with a nanostructured encapsulation material to sensitize the ELM for infrared light. Previously, blue light has been used to stimulate microorganisms that contain optogenetic modules responsive to those wavelengths without the need for exogenous cofactors. Here, we use plasmonic gold nanorods (AuNR) that have a strong absorption maximum at 808 nm, a wavelength where human tissue is relatively transparent. Biocompatible composites of a Pluronic-based hydrogel and AuNR are prepared without agglomeration; they react to illumination by local heating. We measure a photothermal conversion efficiency of 47 % in transient temperature measurements. Steady-state temperature profiles from local photothermal heating are quantified using infrared photothermal imaging, correlated with measurements inside the gel, and applied to stimulate thermoresponsive bacteria. Using a bilayer ELM construct with the thermoresponsive bacteria and the thermoplasmonic composite gel in two separate but connected hydrogel layers, it is shown that the bacteria can be stimulated to produce a fluorescent protein using infrared light in a spatially controlled manner.