Extraordinary Electrical Conductance through Amorphous Nonconducting Polymers under Vibrational Strong Coupling.

Enhancing the electrical conductance through amorphous nondoped polymers is challenging. Here, we show that vibrational strong coupling (VSC) of intrinsically nonconducting and amorphous polymers such as polystyrene, deuterated polystyrene, and poly(benzyl methacrylate) to the vacuum electromagnetic field of the cavity enhances the electrical conductivity by at least 6 orders of magnitude compared to the uncoupled polymers. Remarkably, the observed extraordinary conductance is vibrational mode selective and occurs only under the VSC of the aromatic C-H(D) out-of-plane bending modes of the polymers. The conductance is thermally activated at the onset of strong coupling and becomes temperature-independent as the collective strong coupling strength increases. The electrical characterizations are performed without external light excitation, demonstrating the role of vacuum electromagnetic field-matter strong coupling in enhancing long-range transport even in amorphous nonconducting polymers.

Plasmonic Resonant Nanoantennas Induce Changes in the Shape and the Intensity of Infrared Spectra of Phospholipids.

Surface enhanced infrared absorption spectroscopic studies (SEIRAS) as a technique to study biological molecules in extremely low concentrations is greatly evolving. In order to use the technique for identification of the structure and interactions of such biological molecules, it is necessary to identify the effects of the plasmonic electric-field enhancement on the spectral signature. In this study the spectral properties of 1,2-Dipalmitoyl-sn-glycero-3 phosphothioethanol (DPPTE) phospholipid immobilized on gold nanoantennas, specifically designed to enhance the vibrational fingerprints of lipid molecules were studied. An AFM study demonstrates an organization of the DPPTE phospholipid in bilayers on the nanoantenna structure. The spectral data were compared to SEIRAS active gold surfaces based on nanoparticles, plain gold and plain substrate (Si) for different temperatures. The shape of the infrared signals, the peak positions and their relative intensities were found to be sensitive to the type of surface and the presence of an enhancement. The strongest shifts in position and intensity were seen for the nanoantennas, and a smaller effect was seen for the DPPTE immobilized on gold nanoparticles. This information is crucial for interpretation of data obtained for biological molecules measured on such structures, for future application in nanodevices for biologically or medically relevant samples.

Modifying Woodward-Hoffmann Stereoselectivity Under Vibrational Strong Coupling.

Vibrational strong coupling (VSC) has recently been shown to change the rate and chemoselectivity of ground-state chemical reactions via the formation of light-matter hybrid polaritonic states. However, the observation that vibrational-mode symmetry has a large influence on charge-transfer reactions under VSC suggests that symmetry considerations could be used to control other types of chemical selectivity through VSC. Here, we show that VSC influences the stereoselectivity of the thermal electrocyclic ring opening of a cyclobutene derivative, a reaction which follows the Woodward-Hoffmann rules. The direction of the change in stereoselectivity depends on the vibrational mode that is coupled, as do changes in rate and reaction thermodynamics. These results on pericyclic reactions confirm that symmetry plays a key role in chemistry under VSC.

On the Role of Symmetry in Vibrational Strong Coupling: The Case of Charge-Transfer Complexation.

It is well known that symmetry plays a key role in chemical reactivity. Here we explore its role in vibrational strong coupling (VSC) for a charge-transfer (CT) complexation reaction. By studying the trimethylated-benzene-I2 CT complex, we find that VSC induces large changes in the equilibrium constant KDA of the CT complex, reflecting modifications in the ΔG° value of the reaction. Furthermore, by tuning the microfluidic cavity modes to the different IR vibrations of the trimethylated benzene, ΔG° either increases or decreases depending only on the symmetry of the normal mode that is coupled. This result reveals the critical role of symmetry in VSC and, in turn, provides an explanation for why the magnitude of chemical changes induced by VSC are much greater than the Rabi splitting, that is, the energy perturbation caused by VSC. These findings further confirm that VSC is powerful and versatile tool for the molecular sciences.

Modification of Enzyme Activity by Vibrational Strong Coupling of Water.

Vibrational strong coupling (VSC) has recently emerged as a completely new tool for influencing chemical reactivity. It harnesses electromagnetic vacuum fluctuations through the creation of hybrid states of light and matter, called polaritonic states, in an optical cavity resonant to a molecular absorption band. Here, we investigate the effect of vibrational strong coupling of water on the enzymatic activity of pepsin, where a water molecule is directly involved in the enzyme's chemical mechanism. We observe an approximately 4.5-fold decrease of the apparent second-order rate constant kcat /Km when coupling the water stretching vibration, whereas no effect was detected for the strong coupling of the bending vibration. The possibility of modifying enzymatic activity by coupling water demonstrates the potential of VSC as a new tool to study biochemical reactivity.

Quantum Strong Coupling with Protein Vibrational Modes.

In quantum electrodynamics, matter can be hybridized to confined optical fields by a process known as light-matter strong coupling. This gives rise to new hybrid light-matter states and energy levels in the coupled material, leading to modified physical and chemical properties. Here, we report for the first time the strong coupling of vibrational modes of proteins with the vacuum field of a Fabry-Perot mid-infrared cavity. For two model systems, poly(l-glutamic acid) and bovine serum albumin, strong coupling is confirmed by the anticrossing in the dispersion curve, the square root dependence on the concentration, and a vacuum Rabi splitting that is larger than the cavity and vibration line widths. These results demonstrate that strong coupling can be applied to the study of proteins with many possible applications including the elucidation of the role of vibrational dynamics in enzyme catalysis and in H/D exchange experiments.

Shear-stress-induced conformational changes of von Willebrand factor in a water-glycerol mixture observed with single molecule microscopy.

The von Willebrand factor (VWF) is a human plasma protein that plays a key role in the initiation of the formation of thrombi under high shear stress in both normal and pathological situations. It is believed that VWF undergoes a conformational transition from a compacted, globular to an extended form at high shear stress. In this paper, we develop and employ an approach to visualize the large-scale conformation of VWF in a (pressure-driven) Poiseuille flow of water-glycerol buffers with wide-field single molecule fluorescence microscopy as a function of shear stress. Comparison of the imaging results for VWF with the results of a control with λ-phage double-stranded DNA shows that the detection of individual VWF multimers in flow is feasible. A small fraction of VWF multimers are observed as visibly extended along one axis up to lengths of 2.0 µm at high applied shear stresses. The size of this fraction of molecules seems to exhibit an apparent dependency on shear stress. We further demonstrate that the obtained results are independent of the charge of the fluorophore used to label VWF. The obtained results support the hypothesis of the conformational extension of VWF in shear flow.