Ultrafast Vibrational Energy Transfer Research Articles

Ultrafast Vibrational Energy Transfer between Protein and Cofactor in a Flavoenzyme.

Protein motions and enzyme catalysis are often linked. It is hypothesized that ultrafast vibrations (femtosecond–picosecond) enhance the rate of hydride transfer catalyzed by members of the old yellow enzyme (OYE) family of ene-reductases. Here, we use time-resolved infrared (TRIR) spectroscopy in combination with stable “heavy” isotopic labeling (2H, 13C, 15N) of protein and/or cofactor to probe the vibrational energy transfer (VET) between pentaerythritol tetranitrate reductase (a member of the OYE family) and its noncovalently bound flavin mononucleotide (FMN) cofactor. We show that when the FMN cofactor is photoexcited with visible light, vibrational energy is transferred from the flavin to the surrounding protein environment on the picosecond timescale. This finding expands the scope of VET investigation in proteins, which are limited by suitable intrinsic probes, and may have implications in the understanding of the mechanism of recently discovered photoactive flavoenzymes.

Ultrafast Vibrational Energy Transfer through the Covalent Bond and Intra- and Intermolecular Hydrogen Bonds in a Supramolecular Dimer by Two-Dimensional Infrared Spectroscopy.

In this work, the structural fluctuations and vibrational energy transfer dynamics in a supramolecular homodimer model, which is composed of 2-(9-anthracene)ureido-6-(1-undecyl)-4[1H]-pyrimidinone (UPAn) with quadruple intermolecular and single intramolecular hydrogen bonds (HBs), have been examined using ultrafast two-dimensional infrared (2D IR) and steady-state IR spectroscopies. A less structurally fluctuating intermolecular HB is found between the pyrimidinone C═O and ureido N-H groups. However, a larger structurally fluctuating intramolecular HB is suggested by the equilibrium and dynamical line-shape measurements of the ureido C═O stretch. Further, dynamical time-dependent 2D IR diagonal and off-diagonal signals show that intra- and intermolecular vibrational energy transfer processes occur on the picosecond timescale, where the latter is more efficient due to intermolecular hydrogen bonding interaction and through-space interaction.

Ultrafast Vibrational Energy Transfer from Photoexcited Carbon Nanotubes to Proteins

Carbon nanotube (CNT) and protein complexes are one of the most important nanomaterials in physical and biological fields, especially for building biomedical systems based on their unique electronic and optical properties. However, there is little knowledge about ultrafast vibrational phenomena and energy flow in CNT-protein complexes. Here, we study the ultrafast vibrational energy transfer (VET) from photoexcited carbon nanotubes to adsorbed materials, such as protein and surfactant, by observing relaxation dynamics of coherent radial breathing modes (RBMs) of CNT. As a result, we found the vibrational relaxation time of the RBMs depends on phonon density of states (PDOS) of adsorbed materials. Our findings are particularly useful for designing a highly efficient phonon energy flow system from photo-excited CNT to biomaterials, and such vibrational energy transfer can be controlled by the PDOS originated from the structure of coupled biomaterials.

Observation of Ultrafast Vibrational Energy Transfer in Fibrinogen and Fibrin Fibers.

We study the secondary structure of the blood protein fibrinogen using two-dimensional infrared spectroscopy. With this technique, we identify the amide I′ vibrational modes of the antiparallel β-sheets and turns of fibrinogen. We observe ultrafast energy flow among these amide I′ vibrational modes with a time constant of ∼7 ps. This energy transfer time constant does not change significantly upon fibrin fiber formation, indicating that the secondary structure of the fibrinogen monomers remains largely unchanged in the polymerization process.

Ultrafast Vibrational Energy Transfer in Catalytic Monolayers at Solid-Liquid Interfaces.

We investigate the ultrafast vibrational dynamics of monolayers from adsorbed rhenium-carbonyl CO2-reduction catalysts on a semiconductor surface (indium-tin-oxide (ITO)) with ultrafast two-dimensional attenuated total reflection infrared (2D ATR IR) spectroscopy. The complexes are partially equipped with isotope-labeled (13C) carbonyl ligands to generate two spectroscopically distinguishable forms of the molecules. Ultrafast vibrational energy transfer between the molecules is observed via the temporal evolution of cross-peaks between their symmetric carbonyl stretching vibrations. These contributions appear with time constant of 70 and 90 ps for downhill and uphill energy transfer, respectively. The energy transfer is thus markedly slower than any of the other intramolecular dynamics. From the transfer rate, an intermolecular distance of ∼4-5 Å can be estimated, close to the van der Waals distance of the molecular head groups. The present paper presents an important cornerstone for a better understanding of intermolecular coupling mechanisms of molecules on surfaces and explains the absence of similar features in earlier studies.

Influence of the alkyl side-chain length on the ultrafast vibrational dynamics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (CnmimNTf2) ionic liquids.

Probing the vibrational dynamics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (CnmimNTf2) ionic liquids (ILs) using femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) has indicated the ultrafast vibrational energy transfer between counter ions which is governed by interionic interactions and facilitated by hydrogen bonds. In this study, fs-CARS is used to investigate the ultrafast dynamics of the vibrational modes of the CnmimNTf2 ILs with n = 6, 8, 10, and 12 in a spectral region, which involves the imidazolium ring and the alkyl side-chain vibrations. The vibrational Raman modes with wavenumbers around 1418 cm-1 are excited through the CARS process and the ultrafast time evolution of the consequently excited vibrational modes is monitored. The investigation of the life times of the fs-CARS transient signals indicates that the time scale of the dynamics becomes much faster when the alkyl side-chain length of the CnmimNTf2 is longer than n = 8. This observation suggests an increase in the hydrogen bonding interactions due to the nano-structuring of the ionic liquids, which became evident with an increasing length of the alkyl side-chain. This behavior is also found in molecular dynamics simulations. There, an increase of the oxygen density around the C(2)-H moiety of the imidazolium ring, which is the predominant site for hydrogen bond formation, is observed. In other words, the longer the alkyl side-chain, the more reorganization of the ionic liquid into polar and non-polar domains occurs and the higher the probability of finding interionic hydrogen bonds at the C(2)-H position becomes.

Ultrafast vibrational energy transfer at the water/air interface revealed by two-dimensional surface vibrational spectroscopy

Water is very different from liquids of similar molecular weight, and one of its unique properties is the very efficient transfer of vibrational energy between molecules, which arises as a result of strong dipole-dipole interactions between the O-H oscillators. Although we have a sound understanding of such energy transfer in bulk water, we know less about how, and how quickly, transfer occurs at its interface with a hydrophobic phase, because specifically addressing the outermost monolayer is difficult. Here, we use ultrafast two-dimensional surface-specific vibrational spectroscopy to probe the interfacial energy dynamics of heavy water (D(2)O) at the water/air interface. The measurements reveal the presence of surprisingly rapid energy transfer, both between hydrogen-bonded interfacial water molecules (intermolecular), and between O-D groups sticking out from the water surface and those located on the same molecule and pointing towards the water bulk (intramolecular). Vibrational energy transfer occurs on sub-picosecond timescales, and its rates and pathways can be quantified directly.

Ultrafast Vibrational Energy Transfer in the Layers of D2O and CO on Pt(111) Studied with Time-Resolved Sum-Frequency-Generation Spectroscopy

Ultrafast dynamics of vibrational energy transfer in overlayers of D2O and CO on Pt(111) have been investigated by femtosecond time-resolved (TR) IR−visible sum-frequency-generation (SFG) spectrosc...

Ultrafast Vibrational Energy Transfer between Surface and Bulk Water at the Air-Water Interface

We report a femtosecond time-resolved study of water at the neat water-air interface. The O-H stretch vibrational lifetime of hydrogen-bonded interfacial water is measured using surface-specific 4th-order nonlinear optical spectroscopy with femtosecond infrared pulses. The vibrational lifetime in the frequency range of 3200 to 3500 cm(-1) is found to closely resemble that of bulk water, indicating ultrafast exchange of vibrational energy between surface water molecules and those in the bulk.

Ultrafast vibrational energy transfer from O–H stretching modes of liquid water

Vibrational energy transfer from the O–H stretching modes in liquid water is studied by using QM/MM simulations and principal mode analysis (PMA). Two energy relaxation time scales of 0.6–0.7 and 0.3 ps are obtained by decorrelating the vibrational energy into principal modes. The longer time is interpreted as a vibrational energy relaxation (VER) process from the solute to bath, while the shorter time scale is attributed to an intramolecular vibrational energy redistribution (IVR) between the two O–H stretching modes.

Ultrafast vibrational energy transfer in the real world: laser ablation, energetic solids, and hemeproteins

A wide variety of chemical and physical processes that occur in solids produce vibrationally hot (excited) molecules. Recent progress in the theory and experimental measurement of vibrational relaxation and vibrational cooling (VC) in solids is summarized in this paper. Here vibrational relaxation refers to the loss of excitation of the initially prepared state, while VC refers to the return of the hot molecule to its cold ground state. VC is accomplished by energy transfer between the hot molecule and the phonons of the surrounding solid matrix. Both processes occur on the ultrafast time scale in materials that are composed of large molecules. Some real-world applications of VC are discussed. These are processes in which VC plays an important role, including laser ablation and optical damage of polymers, shock-induced chemistry of energetic solids, and hemeprotein photolysis and cooling.

Ultrafast vibrational energy transfer of polyethylene investigated with picosecond laser pulses

Picosecond Raman scattering after infrared excitation is studied for polyethylene films at room temperature. Ultrafast vibrational energy redistribution (⩽ 5 ps) and a comparatively long population lifetime ( T 1 = 260 ± 100 ps) are observed for the CH-stretching modes.