The power of two-dimensional (2D) IR spectroscopy as a structural method with unprecedented time resolution is greatly improved by the introduction polarization conditions that completely eliminate diagonal peaks from spectra and leave only crosspeaks needed for structure determination. This approach represents key step forward in applications 2D to proteins, peptides, other complex molecules where are often obscured peaks. technique verified on model compound 1,3-cyclohexanedione...

The dynamics of two-dimensional small-polaron formation at ultrathin alkane layers on a silver(111) surface have been studied with femtosecond time- and angle-resolved two-photon photoemission spectroscopy. Optical excitation creates interfacial electrons in quasi-free states for motion parallel to the interface. These initially delocalized self-trap as small polarons localized state within few hundred femtoseconds. then decay back metal picoseconds by tunneling through adlayer potential...

Two-photon photoemission is a promising new technique that has been developed for the study of electron dynamics at interfaces. A femtosecond laser used to both create an excited electronic distribution surface and eject subsequent energy analysis. Time- momentum-resolved two-photon spectra as function layer thickness fully determine conduction band interface. Earlier clean studies showed how lifetimes are affected by crystal structure vacuum image potential. Recent various insulator/metal...

The response functions needed for simulating and fitting two-dimensional infrared spectra are described including the distributions of vibrational frequency, anharmonicity, coupling between vibrators. A simple method that does not involve explicit calculation is introduced to characterize spectral line narrowing properties each quantum paths contributing 2D IR. It shown IR need be collected in both positive negative frequency quadrants order optimize information evaluate these correlations....

We demonstrate rapid vibrational imaging based on sum frequency generation (SFG) microscopy with a collinear excitation geometry. Using the tunable picosecond pulses from high-repetition-rate optical parametric oscillator, vibrationally selective of collagen fibers is achieved submicrometer lateral resolution. furthermore show simultaneous SFG and second harmonic to emphasize compatibility microscope other nonlinear modalities.

We devised a novel two-step reference scheme that can greatly suppress the additive and convolutional noises in heterodyne nonlinear spectroscopy. To optimally remove noise, we fully utilized spectral correlation multi-channel data through linear combination regression algorithm. Using our pump-probe 2D IR spectrometer, demonstrated improve signal-to-noise ratio by 10-30 times reach noise floor of signal detector. The new algorithm is guaranteed to reduce enables use unmatched detectors,...

We demonstrate a phase sensitive, vibrationally resonant sum-frequency generation (PSVR-SFG) microscope that combines high resolution, fast image acquisition speed, chemical selectivity, and sensitivity. Using the PSVR-SFG microscope, we generate amplitude images of second-order susceptibility collagen I fibers in rat tail tendon tissue on resonance with methylene vibrations protein. find shows dependence effective polarity fibril bundles, revealing fibrous domains opposite orientations...

Short peptides are important as lead compounds and molecular probes in drug discovery chemical biology, but their well-known drawbacks, such high conformational flexibility, protease lability, poor bioavailability short half-lives vivo, have prevented potential from being fully realized. Side chain-to-side chain cyclization, e.g., by ring-closing olefin metathesis, known stapling, is one approach to increase the biological activity of that has shown promise when applied 310- α-helical...

BiVO4 photoanodes are promising for solar water splitting, with photogenerated electrons and holes preferentially reacting at top {010} lateral {110} facets, respectively. However, the mechanisms driving this facet-dependent reactivity remain unclear. Here, we investigate photocurrent material heterogeneity using correlative scanning photoelectrochemical microscopy (SPCM), electron beam induced current (EBIC) mapping, mid-IR scattering near-field optical (s-SNOM). SPCM measurements of 62...

We have carried out a comparative study of five ab initio electrostatic frequency maps and semiempirical model for the amide-I -II modes. Unrestrained molecular dynamics simulation 310-helical peptide, Z-Aib-l-Leu-(Aib)2-Gly-OtBu, in CDCl3 is performed using AMBER ff99SB force field, linear two-dimensional infrared (2D IR) spectra are simulated on basis vibrational exciton Hamiltonian model. A new potential-based map N-methylacetamide developed this study. This other by different research...

Two-dimensional infrared (2D IR) spectra of Cα-alkylated model octapeptides Z-(Aib)8-OtBu, Z-(Aib)5-l-Leu-(Aib)2-OMe, and Z-[l-(αMeVal)]8-OtBu have been measured in the amide I region to acquire 2D spectral signatures characteristic 310- α-helical conformations. Phase-adjusted absorptive recorded with parallel polarizations are dominated by intense diagonal peaks, whereas rephasing obtained at double-crossed polarization configuration reveal cross-peak patterns that essential for structure...

We have carried out structural determination of capped Cα,α-diethylglycine (Deg) homopeptides with different chain lengths, Ac-(Deg)n-OtBu (n = 2−5), solvated in CDCl3, and investigated vibrational properties the amide I II modes by linear 2D IR spectroscopy, ONIOM calculations, molecular dynamics simulations. experiments were performed region using rephasing pulse sequence under double-crossed polarization nonrephasing a new configuration to measure cross-peak patterns off-diagonal regions....

The dynamics of excited electrons in insulator quantum well states on a metal substrate were determined by femtosecond two-photon photoemission for the first time. Lifetimes are reported three 1--6 atomic layers Xe Ag(111). As image evolve into with increasing coverage, lifetimes undergo an oscillation as layer boundary crosses each node wave function. lifetime data modeled extending two-band nearly free-electron approximation to account presence dielectric layer. shown depend spatial...

We have investigated the onset of secondary structure and evolution two-dimensional infrared (2D IR) spectral patterns as a function chain length with study 310-helical peptides. The results show that 2D IR is highly sensitive to peptide conformation, disorder, size. An extensive set spectra Cα-methylated homopeptides, Z-(Aib)n-OtBu (n = 3, 5, 8, 10), in CDCl3 was measured amide-I region. tripeptide are quite different from those longer signatures begin converge at pentapeptide become almost...

Vibrational couplings between the amide modes are keenly dependent on peptide structure. Site-specific can inform us of molecular conformation in detail. For example, when an amide-I mode couples to amide-II that is three residues away because they brought into proximity presence intramolecular C═O···H−N hydrogen bond, coupling provide direct evidence for single helical turn formation, a proposed key step coil−helix transition. In this work, we measure 2D IR spectra 310-helical hexapeptide,...

Point-scanning sum-frequency generation (SFG) microscopy enables the of images collagen I fibers in tissues by tuning into specific vibrational resonances polypeptide. It is shown that when collagen-rich are visualized near 2954 cm(-1) stretching vibration methylene groups, SFG image contrast higher compared to seen nonresonant second-harmonic (SHG) imaging. Polarization and spectrally resolved analysis signal as a function fiber orientation CH-stretching range spectrum enabled comparative...

Ultrafast relaxation dynamics of electrons at dielectric-metal interfaces reflect the nature electronic interaction with both substrate and adsorbed layer. The full understanding macroscopic electrical transport properties across an interface requires knowledge energies, spatial extent interfacial states, electron scattering length. With femtosecond two-photon photoemission technique, it is possible to directly observe specific energy parallel momentum. Interband intraband in excited surface...

Femtosecond two-dimensional infrared (2D IR) spectroscopy has been applied to study the conformations of a model dipeptide, N-acetyl-l-prolinamide (AcProNH2) in deuterated chloroform (CDCl3). Spectral features amide-I and -II regions are obtained by rephasing (R), nonrephasing (NR), reverse photon echo (RPE) pulse sequences with two polarization conditions. The 2D spectra RPE NR (0, 0, 0) reveal new spectral associated multiple conformers AcProNH2 that difficult discern using R sequence...

We have investigated the sensitivity of two-dimensional infrared (2D IR) spectroscopy to peptide helicity with an experimental and theoretical study Z-[l-(αMe)Val]8-OtBu in CDCl3. 2D IR experiments were carried out amide-I region under parallel double-crossed polarization configurations. In latter configuration, spectra taken rephasing nonrephasing pulse sequences exhibit a doublet feature single peak, respectively. These cross-peak patterns are highly sensitive underlying structure....

In this work, we optimize and further advance a noise reduction scheme for heterodyne spectroscopy. This linearly combines data from reference detectors to predict the statistics in signal detector through an optimized coefficient matrix. We validate visible white-light-continuum 800-nm light sources using un-matched CMOS arrays show that signal-to-noise ratio can approach floor of while only ~5% energy detection. also strategy estimating matrix practical applications. When combined with...

We have combined two-dimensional infrared (2D IR) spectroscopy and isotope substitutions to reveal the vibrational couplings between a pair of amide-I -II modes that are several residues away but directly connected through hydrogen bond in helical peptide. This strategy is demonstrated on 310-helical hexapeptide, Z-Aib-l-Leu-(Aib)2-Gly-Aib-OtBu, its 13C═18O-Leu monolabeled 13C═18O-Leu/15N-Gly bis-labeled isotopomers CDCl3. The isotope-dependent amide-I/II cross peaks clearly show second...