Gigahertz-to-terahertz spectroscopy of macromolecules in aqueous environments provides an important approach for identifying their global and transient molecular structures, as well as directly assessing hydrogen-bonding. We report dielectric properties of zwitterionic dodecylphosphocholine (DPC) micelles in aqueous solutions over a wide frequency range, from 50 MHz to 1.12 THz. The dielectric relaxation spectra reveal different polarization mechanisms at the molecular level, reflecting the complexity of DPC micelle-water interactions. We have made a deconvolution of the spectra into different components and combined them with the effective-medium approximation to separate delicate processes of micelles in water. Our measurements demonstrate reorientational motion of the DPC surfactant head groups within the micelles, and two levels of hydration water shells, including tightly and loosely bound hydration water layers. From the dielectric strength of bulk water in DPC solutions, we found that the number of waters in hydration shells is approximately constant at 950 ± 45 water molecules per micelle in DPC concentrations up to 400 mM, and it decreases after that. At terahertz frequencies, employing the effective-medium approximation, we estimate that each DPC micelle is surrounded by a tightly bound layer of 310 ± 45 water molecules that behave as if they are an integral part of the micelle. Combined with molecular dynamics simulations, we determine that tightly bound waters are directly hydrogen-bonded to oxygens of DPC, while loosely bound waters reside within 4 Å of micellar atoms. The dielectric response of DPC micelles at terahertz frequencies yields, for the first time, experimental information regarding the largest scale, lowest frequency collective motions in micelles. DPC micelles are a relatively simple biologically relevant system, and this work paves the way for more insight into future studies of hydration and dynamics of biomolecular systems with gigahertz-to-terahertz spectroscopy.

Plasmonic nanoparticles can facilitate bond breaking and drive reactions of nearby molecules. Some of these processes involve bond activations which are traditionally challenging to accomplish. However, there is uncertainty in our understanding of the mechanisms through which plasmonic nanoparticles activate bonds and exactly how the plasmon resonance facilitates the bond breakage. Herein, we evaluate Ag n N 2 (n = 4, 6, 8) model systems via real-time time-dependent density functional theory (RT-TDDFT), linear response timedependent density functional theory (LR-TDDFT), and Ehrenfest dynamics with a long-range corrected functional in order to better understand the charge-transfer process between the Ag system and the adsorbed small molecule. We find that charge-transfer states exist between Ag n Σ orbitals and antibonding orbitals of N 2 . Ehrenfest dynamics calculations reveal symmetry-and electric-fielddependent activation of N 2 when coupled to the wire. This study serves as a step toward understanding the time-dependent electron and electron−nuclear dynamics that arise due to the interactions between plasmonic nanowires and small molecules.

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The C-H bond activation of methane using PDI-M≡N [PDI = 2,6-(PhN═CMe)CHN] (M = V, Mn, Fe, Co, Ni, Al, or P) has been studied via three reaction pathways: [2 + 2] addition, hydrogen atom abstraction (HAA), and direct insertion. The activating ligand is a nitride/nitridyl (N), with diiminopyridine (PDI) as the supporting ligand. Calculations show reasonable C-H activation barriers for Co, Ni, Al, and P PDI nitrides, complexes that favor an HAA pathway. ElectrophilicPDI nitride complexes of the earlier metals with a nucleophilic actor ligand-V, Mn, Fe-follow a [2 + 2] addition pathway for methane activation. Free energy barriers for methyl migration, PDI-M(CH)═NH → PDI-M-N(H)CH, are also interesting in the context of alkane functionalization; discriminating factors in this mechanistic step include the strengths of the σ-bond and metal-actor ligand π-bond that are broken and the electrophilicity of the actor ligand to which methyl migrates.

Plasmonic nanoparticles can promote bond activation in adsorbed molecules under relatively benign conditions via excitation of the nanoparticle's plasmon resonance. As the plasmon resonance often falls within the visible light region, plasmonic nanomaterials are a promising class of catalysts. However, the exact mechanisms through which plasmonic nanoparticles activate the bonds of nearby molecules are still unclear. Herein, we evaluate Ag 8 −X 2 (X = N, H) model systems via real-time time-dependent density functional theory (RT-TDDFT), linear response time-dependent density functional theory (LR-TDDFT), and Ehrenfest dynamics in order to better understand the bond activation processes of N 2 and H 2 facilitated by the presence of the atomic silver wire under excitation at the plasmon resonance energies. We find that dissociation is possible for both small molecules at high electric field strength. Activation of each adsorbate is symmetry-and electric field-dependent, and H 2 activates at lower electric field strengths than N 2 . This work serves as a step toward understanding the complex timedependent electron and electron−nuclear dynamics between plasmonic nanowires and adsorbed small molecules.