Lowering the overpotential for the electrochemical conversion of CO2 to useful products is one of the grand challenges in the Department Of Energy report, “Catalysis for Energy”. In a previous paper, we showed that CO2 conversion occurs at low overpotential on a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4)-coated silver catalyst in an aqueous solution of EMIM-BF4. One of the surprises in the previous paper was that the selectivity to CO was better than 96% on silver, compared with ∼80% in the absence of ionic liquid. In this article, we use sum frequency generation (SFG) to explore the mechanism of the enhancement of selectivity. The study used platinum rather than silver because previous workers had found that platinum is almost inactive for CO production from CO2. The results show that EMIM-BF4 has two effects: it suppresses hydrogen formation and enhances CO2 conversion. SFG shows that there is a layer of EMIM on the platinum surface that inhibits hydrogen formation. CO2, however, can react with the EMIM layer to form a complex such as CO2-EMIM at potentials more negative than −0.1 V with respect to a standard hydrogen electrode (SHE). That complex is converted to adsorbed CO at cathodic potentials of −0.25 V with respect to SHE. These results demonstrate that adsorbed monolayers can substantially lower the barrier for CO2 conversion on platinum and inhibit hydrogen formation, opening the possibility of a new series of metal/organic catalysts for this reaction.

Corrections Fig. 2B shows SCP3 cells transduced with a vector constitutively expressing red fluorescent protein (RFP, Upper) and a vector expressing green fluorescent protein (GFP) under the control of a TGF-␤ responsive promoter (Lower). An erroneous, unpaired set of images was used in the ϩTGF-␤ panels of the previously published version of this figure.'' The corrected figure and its legend appear below. This correction does not affect the conclusions of the article.

The amide I vibrational mode, primarily associated with peptide-bond carbonyl stretches, has long been used to probe the structures and dynamics of peptides and proteins by infrared (IR) spectroscopy. A number of ab initio-based amide I vibrational frequency maps have been developed for calculating IR line shapes. In this paper a new empirical amide I vibrational frequency map is developed. To evaluate its performance, we applied this map to a system of isotope-edited CD3-ζ membrane peptide bundles in aqueous solution. The calculated 2D-IR diagonal linewidths vary from residue to residue and show an asymmetric pattern as a function of position in the membrane. The theoretical results are in fair agreement with experiments on the same system. Through analysis of the computed frequency time-correlation functions, it is found that the 2D-IR diagonal widths are dominated by contributions from the inhomogeneous frequency distributions, from which it follows that these widths are a good probe of the extent of local structural fluctuations. Thus the asymmetric pattern of linewidths follows from the asymmetric structure of the bundle in the membrane.

Heterodyned 2D-IR, frequency resolved photon echo, and pump−probe spectroscopies were collected to study the couplings and anharmonicities of cytidine and guanosine bases in DNA. Cytidine and guanosine anharmonicities were measured to be 9 and 14 cm-1, respectively. Strong cross-peaks were observed between the guanosine (G) and cytosine (C) carbonyl stretches in the 2D-IR spectra of the self-complementary oligonucleotide dG5C5 (5‘-GGGGGCCCCC-3‘). The spectra are interpreted in terms of inter- and intrastrand couplings between the carbonyl modes, and an excitonic Hamiltonian, based on transition dipole coupling, was used to fit the 2D-IR spectra. The accuracy of this model is discussed in light of observed couplings to the ring modes.

Summary The pH-controlled M2 protein from Influenza is a critical component of the virus, serving as a target for aminoadamantane anti-flu agents that block its H+ channel activity. To better understand its H+-gating mechanism, we investigated M2 in lipid bilayers with a new combination of IR spectroscopies and theory. Linear FTIR spectroscopy was utilized to measure the precise orientation of the backbone carbonyl groups, and 2D-IR spectroscopy was utilized to identify channel-lining residues. At low pH (open-state), our results match previously published ss-NMR and X-ray structures remarkably well. However, at neutral pH (closed-state), our measurements point to a large conformational change, that is consistent with the transmembrane α-helices rotating by one amino acid register: a structural rearrangement not previously observed. The combination of isotope-labelled FTIR and 2D-IR spectroscopies, alongside simulations, provides a non-invasive mean of interrogating structures of membrane proteins in general and ion channels in particular.