35106401
Controlled modification of biomolecules by ultrashort laser pulses in polar liquids
Targeted chemical modification of peptides and proteins by laser pulses in a biologically relevant environment, i.e. aqueous solvent at room temperature, allows for accurate control of biological processes. However, the traditional laser methods of control of chemical reactions are applicable only to a small class of photosensitive biomolecules because of strong and ultrafast perturbations from biomolecule-solvent interactions. Here, we report excitation of harmonics of vibration modes of solvent molecules by femtosecond laser pulses to produce controlled chemical modifications of non-photosensitive peptides and proteins in polar liquids under room conditions. The principal modifications included lysine formylation and methionine sulfoxidation both of which occur with nearly 100% yield under atmospheric conditions. That modification occurred only if the laser irradiance exceeded certain threshold level. The threshold, type, and extent of the modifications were completely controlled by solvent composition, laser wavelength, and peak irradiance of ultrashort laser pulses. This approach is expected to assist in establishing rigorous control over a broad class of biological processes in cells and tissues at the molecular level.
40295099
Laser control of molecular processes.
The last 20 years have seen enormous strides in our understanding of the detailed dynamics of elementary chemical reactions ( 1 -3). With this understanding well in hand, attention has turned to controlling, rather than passively observing, molecular collision processes. Theoretical and computational advances, supported by preliminary experimental results, now clearly indicate that efficient control over molecular processes is possible. We review these advances in detail below. The primary goal of practical chemistry is to produce desired molecular products in substantial yield. For decades, enhanced productivity was attained by thermodynamic techniques, e.g. variations in pressure and temperature. Recently, efforts have been directed toward using properties of lasers to enhance desired product yield selectively. Initial efforts attempted to utilize high laser power (4-Sc) to manipulate molecules; control was based on introducing into the system Hamiltonian, laser­ molecule coupling terms of comparable size to interatomic potentials. A second thrust, "mode-selective excitation," emphasized selective excitation of particular bonds, which encourage reaction toward one channel. These
24489549
Coherent nonlinear spectroscopy: from femtosecond dynamics to control.
This review focuses on the study of the dynamics of isolated molecules and their control using coherent nonlinear spectroscopic methods. Emphasis is placed on topics such as bound-to-free excitation and the study of concerted elimination reactions, free-to-bound excitation and the study of bimolecular reactions, and bound-to-bound excitation and the study of intramolecular rovibrational dynamics and coherence relaxation. For each case the detailed time-resolved information reveals possible strategies to control the outcome. Experimental results are shown for each of the reactions discussed. The methods discussed include pump-probe and four-wave mixing processes such as transient grating and photon echo spectroscopy. Off-resonance transient-grating experiments are shown to be ideal for the study of ground state dynamics, molecular structure, and the molecular response to strong field excitation.
4988490
Experimental coherent laser control of physicochemical processes.
The observation of coherent dynamics ensuing from the excitation of molecular systems by femtosecond laser pulses is at the heart of femtochemistry. The time-dependent evolution of coherent superpositions of quantum states, the physical basis for the observation of coherent dynamics and their manipulation are of central importance to coherent control of physicochemical processes. In the early days of femtochemistry, there was significant skepticism regarding the type of information that could be learned from spectroscopic experiments using very short pulses. There were arguments that one could infer the dynamics from frequency-resolved experiments and that the femtosecond experiments did not offer new information. It was also assumed that experiments with very short pulses would smear the available spectroscopic information because of their broad bandwidths. Approximately two decades after the initial experiments, it has become clear that femtosecond experiments have opened an extremely valuable window into the dynamic behavior of atomic and molecular systems that is influencing how we think about physics, chemistry, and biology. In particular, we highlight the fact that some of the highest resolution spectroscopic measurements being carried out employ femtosecond laser pulses. These experiments, specifically those taking advantage of rotational coherence, provide resolution that rivals microwave spectroscopy. The reason spectroscopic information is not lost in femtochemistry experiments is coherence, a property that can be manipulated to control physicochemical processes by a number of different approaches, which will be reviewed here. This review presents a summary of some of the most salient contributions to the field of coherent laser control from an experimentalist’s perspective. While a number of theoretical papers have made key contributions to the field, it is from the experimental successes, as well as failures, that we can best learn how to implement new strategies and develop future applications. Coherent laser control, in the context of this review, encompasses experiments in which the coherent properties of the laser and/or the molecule are required for controlling a particular physicochemical process. We distinguish for each of the experiments between coherence in the laser field(s), * To whom correspondence should be addressed. Phone (517) 3559715 (ext-315). Fax (517) 353-1793. E-mail dantus@msu.edu. 1813 Chem. Rev. 2004, 104, 1813−1859
4950270
Control of quantum phenomena: past, present and future
Quantum control is concerned with active manipulation of physical and chemical processes on the atomic and molecular scale. This work presents a perspective of progress in the field of control over quantum phenomena, tracing the evolution of theoretical concepts and experimental methods from early developments to the most recent advances. Among numerous theoretical insights and technological improvements that produced the present state-of- the-art in quantum control, there have been several breakthroughs of foremost importance. On the technology side, the current experimental successes would be impossible without the development of intense femtosecond laser sources and pulse shapers. On the theory side, the two most critical insights were (i) realizing that ultrafast atomic and molecular dynamics can be controlled via manipulation of quantum interferences and (ii) understanding that optimally shaped ultrafast laser pulses are the most effective means for producing the desired quantum interference patterns in the controlled system. Finally, these theoretical and experimental advances were brought together by the crucial concept of adaptive feedback control (AFC), which is a laboratory procedure employing measurement-driven, closed-loop optimization to identify the best shapes of femtosecond laser control pulses for steering quantum dynamics towards the desired objective. Optimization in AFC experiments is guided by a learning algorithm, with stochastic methods proving to be especially effective. AFC of quantum phenomena has found numerous applications in many areas of the physical and chemical sciences, and this paper reviews the extensive experiments. Other subjects discussed include quantum optimal control theory, quantum control landscapes, the role of theoretical control
8804783
Coherent Control of Retinal Isomerization in Bacteriorhodopsin
Optical control of the primary step of photoisomerization of the retinal molecule in bacteriorhodopsin from the all-trans to the 13-cis state was demonstrated under weak field conditions (where only 1 of 300 retinal molecules absorbs a photon during the excitation cycle) that are relevant to understanding biological processes. By modulating the phases and amplitudes of the spectral components in the photoexcitation pulse, we showed that the absolute quantity of 13-cis retinal formed upon excitation can be enhanced or suppressed by ±20% of the yield observed using a short transform-limited pulse having the same actinic energy. The shaped pulses were shown to be phase-sensitive at intensities too low to access different higher electronic states, and so these pulses apparently steer the isomerization through constructive and destructive interference effects, a mechanism supported by observed signatures of vibrational coherence. These results show that the wave properties of matter can be observed and even manipulated in a system as large and complex as a protein.
4419832
Quantum control of energy flow in light harvesting
Coherent light sources have been widely used in control schemes that exploit quantum interference effects to direct the outcome of photochemical processes. The adaptive shaping of laser pulses is a particularly powerful tool in this context: experimental output as feedback in an iterative learning loop refines the applied laser field to render it best suited to constraints set by the experimenter. This approach has been experimentally implemented to control a variety of processes, but the extent to which coherent excitation can also be used to direct the dynamics of complex molecular systems in a condensed-phase environment remains unclear. Here we report feedback-optimized coherent control over the energy-flow pathways in the light-harvesting antenna complex LH2 from Rhodopseudomonas acidophila, a photosynthetic purple bacterium. We show that phases imprinted by the light field mediate the branching ratio of energy transfer between intra- and intermolecular channels in the complex's donor–acceptor system. This result illustrates that molecular complexity need not prevent coherent control, which can thus be extended to probe and affect biological functions.
27421402
Controlling the efficiency of an artificial light-harvesting complex
Adaptive femtosecond pulse shaping in an evolutionary learning loop is applied to a bioinspired dyad molecule that closely mimics the early-time photophysics of the light-harvesting complex 2 (LH2) photosynthetic antenna complex. Control over the branching ratio between the two competing pathways for energy flow, internal conversion (IC) and energy transfer (ET), is realized. We show that by pulse shaping it is possible to increase independently the relative yield of both channels, ET and IC. The optimization results are analyzed by using Fourier analysis, which gives direct insight to the mechanism featuring quantum interference of a low-frequency mode. The results from the closed-loop experiments are repeatable and robust and demonstrate the power of coherent control experiments as a spectroscopic tool (i.e., quantum-control spectroscopy) capable of revealing functionally relevant molecular properties that are hidden from conventional techniques.
121865632
Coherent Control of Decoherence
We demonstrate experimentally that closed loop control of the excitation of a prototypical quantum system (molecular vibrations) can mitigate the effects of the environment (rotations) by enabling the search for a decoherent resistant subspace.
11061625
Absorption spectrum (380-700 nm) of pure water. II. Integrating cavity measurements.
Definitive data on the absorption spectrum of pure water from 380 to 700 nm have been obtained with an integrating cavity technique. The results are in good agreement with those recently obtained by our group with a completely independent photothermal technique. As before, we find that the absorption in the blue is significantly lower than had previously been generally believed and that the absorption minimum is at a significantly shorter wavelength, i.e., 0.0044 ? 0.0006 m(-1) at 418 nm. Several spectroscopic features have been identified in the visible spectrum to our knowledge for the first time.
120888557
Minimally disruptive laser-induced breakdown in water.
We produce minimally disruptive breakdown in water by using tightly focused 100-fs laser pulses and demonstrate the potential use of this technique in microsurgery of the eye. Using time-resolved imaging and piezoelectric pressure detection, we measure the magnitude and speed of propagation of the pressure wave produced in the breakdown. Compared with breakdown with longer pulses, here there is a much lower energy threshold for breakdown of 0.2 µJ, a smaller shock zone diameter (11 µm for 1‐µJ pulses), and consistent energy deposition.
13286690
Nonlinear intensity dependence in the infrared multiphoton excitation and dissociation of methanol pre-excited to different energies
We report quantitative dissociation yields for the reaction CH3OH (v(OH))-->nhnu CH3+OH induced by infrared multiphoton excitation of methanol pre-excited to various levels of the OH stretching vibration (v(OH)=0, 1, 3, 5). The yields are measured by detecting OH using laser induced fluorescence. It is demonstrated that for low levels of pre-excitation (v(OH)=0, 1, 3) there is a substantial nonlinear intensity dependence, as a higher yield is found for self mode-locked CO2 laser pulses (with higher peak intensity) as compared to single mode pulses of the same laser fluence, but lower peak intensity. In contrast, at high levels of preexcitation (v(OH)=5) this nonlinear intensity dependence is absent. Quantitative model calculations are carried out using a case B/case C master equation approach that takes nonlinear intensity dependence into account. The calculations are consistent with the experimental results and confirm the prediction that an important part of the selectivity of the CO2 laser excitation step in infrared laser assisted photofragment spectroscopy of CH3OH is due to this nonlinear intensity dependence. We discuss further consequences of these experimental observations and theoretical predictions, which are also extended to infrared multiphoton excitation of C2H5OH. Infrared (C-O) chromophore band strengths are reported for CH3OH and C2H5OH. (C) 2002 American Institute of Physics.
97359581
Vibrational relaxation and spectral evolution following ultrafast OH stretch excitation of water
Ultrafast anti-Stokes Raman measurements of OH stretching excitations (3000–3600 cm � 1 ) in water show an � 0:4 ps spectral evolution from the red to the blue that is similar to what is seen in the Raman spectrum of water heated to 90C. The lifetime of OH stretching excitations T1 ¼ 0:7 ps. A small portion of the spectrum on the blue edge of the band decays more slowly with T1 ¼ 1:1 ps. A previous measurement of T1 � 0:3 ps for water [J. Chem. Phys. 117 (2002) 1708] is reinterpreted shown to consistent with the present work. 2003 Elsevier Science B.V. All rights reserved.
95797575
Vibrational relaxation of pure liquid water
Multicolor infrared ultrafast spectroscopy is applied to investigate the vibrational relaxation dynamics in liquid water at room temperature. In a sequence of experiments, both the stretching and the bending mode are photoexcited and probed. A unified model, capable of the reproduction of as much as 150 transients, yielded cross-sections and relaxation times for the stretching and bending modes. It is further demonstrated, that the energy from the initially excited stretching vibration is partitioned to the bending modes of approximately two water molecules.
13101769
Vibrational Spectroscopy and Dynamics of Water.
We present an overview of recent static and time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state, as well as of crystalline and amorphous ice forms. The structure and dynamics of the complex hydrogen-bond network formed by water molecules in the bulk and interphases are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed, from conventional infrared and Raman spectroscopy to femtosecond pump-probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. Additionally, we discuss novel approaches, such as two-dimensional sum-frequency generation, three-dimensional infrared, and two-dimensional Raman terahertz spectroscopy. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges. Furthermore, we outline future perspectives of vibrational spectroscopy for water researches.
36347637
Quantum Interference in the Vibrational Relaxation of the O-H Stretch Overtone of Liquid H2O.
Using femtosecond two-color infrared pump-probe spectroscopy, we study the vibrational relaxation of the O-H stretch vibrations of liquid H2O after excitation of the overtone transition. The overtone transition has its maximum at 6900 cm(-1) (1.45 μm), which is a relatively high frequency in view of the central frequency of 3400 cm(-1) of the fundamental transition. The excitation of the overtone leads to a transient induced absorption of two-exciton states of the O-H stretch vibrations. When the overtone excitation frequency is tuned from 6600 to 7200 cm(-1), the vibrational relaxation time constant of the two-exciton states increases from 400 ± 50 fs to 540 ± 40 fs. These values define a limited range of relatively long relaxation time constants compared to the range of relaxation time constants of 250-550 fs that we recently observed for the one-exciton O-H stretch vibrational state of liquid H2O ( S. T. van der Post et al., Nature Comm. 2015 , 6 , 8384 ). We explain the high central frequency and the limited range of relatively long relaxation time constants of the overtone transition from the destructive quantum interference of the mechanical and electrical anharmonic contributions to the overtone transition probability. As a result of this destructive interference, the overtone transition of liquid H2O is dominated by molecules of which the O-H groups donate relatively weak hydrogen bonds to other H2O molecules.
19389012
Anharmonic exciton dynamics and energy dissipation in liquid water from two-dimensional infrared spectroscopy.
Water's extended hydrogen-bond network results in rich and complex dynamics on the sub-picosecond time scale. In this paper, we present a comprehensive analysis of the two-dimensional infrared (2D IR) spectrum of O-H stretching vibrations in liquid H2O and their interactions with bending and intermolecular vibrations. By exploring the dependence of the spectrum on waiting time, temperature, and laser polarization, we refine our molecular picture of water's complex ultrafast dynamics. The spectral evolution following excitation of the O-H stretching resonance reveals vibrational dynamics on the 50-300 fs time scale that are dominated by intermolecular delocalization. These O-H stretch excitons are a result of the anharmonicity of the nuclear potential energy surface that arises from the hydrogen-bonding interaction. The extent of O-H stretching excitons is characterized through 2D depolarization measurements that show spectrally dependent delocalization in agreement with theoretical predictions. Furthermore, we show that these dynamics are insensitive to temperature, indicating that the exciton dynamics alone set the important time scales in the system. Finally, we study the evolution of the O-H stretching mode, which shows highly non-adiabatic dynamics suggestive of vibrational conical intersections. We argue that the so-called heating, commonly observed within ∼1 ps in nonlinear IR spectroscopy of water, is a nonequilibrium state better described by a kinetic temperature rather than a Boltzmann distribution. Our conclusions imply that the collective nature of water vibrations should be considered in describing aqueous solvation.
207592678
Hydrogen bond dynamics in primary alcohols: a femtosecond infrared study.
Hydrogen-bonded liquids are excellent solvents, in part due to the highly dynamic character of the directional interaction associated with the hydrogen bond. Here we study the vibrational and reorientational dynamics of deuterated hydroxyl groups in various primary alcohols using polarization-resolved femtosecond infrared spectroscopy. We show that the relaxation of the OD stretch vibration is similar for ethanol and its higher homologues (∼0.9 ps), while it is appreciably faster for methanol (∼0.75 ps). The fast relaxation for methanol is attributed to strong coupling of the OD stretch vibration to the overtone of the CH3 rocking mode. Subsequent to excited state relaxation, the dissipation of the excess energy leads to structural relaxation of the alcohol liquid structure. We show that this relaxation of the H-bonded network depends on the alkyl chain length. We find that the anisotropy of the excitation decays by both thermal diffusion from excited OD groups to nonexcited molecules and reorientational motion. The reorientation is described well by a model employing two relaxation times that increase linearly with increasing alcohol size. The short reorientation time is assigned to the partial reorientation of molecules within the alcohol cluster, while the long reorientation times can be attributed to breaking and reforming of hydrogen bonds.
97599610
Multiple timescales in the intramolecular vibrational energy redistribution of highly excited methanol
Highly resolved vibrational overtone spectra of jet-cooled CH3OH, obtained using selective IRLAPS detection of the vibrational transition, reveal rich vibrational structure that carries detailed information on the intramolecular dynamics. Low-resolution single resonance spectra of the jet-cooled molecules exhibit a 50 cm–1 splitting resulting from strong coupling between the OH and CH stretch modes at the energy of the 5νOH band. Subsequent to coherent excitation, this coupling would lead to energy redistribution between the OH and CH on a 100 fs timescale. High-resolution spectra obtained using double-resonance excitation reveal smaller vibrational splittings resulting from weak vibrational couplings that control the longer time dynamics. The extensive vibrational structure in this overtone spectrum of methanol clearly indicates that it is the presence of low-order resonances rather than the total density of vibrational states that control the first 10 ps of vibrational-energy redistribution.
96055726
Measuring vibrational coherence lifetimes in liquid methanol using transient coherent Raman scattering
We demonstrate the measurement of vibrational coherence in liquids using transient coherent Raman scattering. This technique measures the coherence lifetime of vibrational states through the interference of time-delayed coherent Raman-scattered photons using low-power, non-resonant optical pulses. We measure the vibrational lifetime of the 1033 cm−1 mode in liquid methanol. The resulting lifetime agrees with frequency-domain lineshape measurements. This technique is a complementary and in some cases simpler alternative to standard nonlinear spectroscopy techniques.
120547410
Structure and dynamics of monohydroxy alcohols—Milestones towards their microscopic understanding, 100 years after Debye
Abstract In 1913 Debye devised a relaxation model for application to the dielectric properties of water and alcohols. These hydrogen-bonded liquids continue to be studied extensively because they are vital for biophysical processes, of fundamental importance as solvents in industrial processes, and in every-day use. Nevertheless, the way to a microscopic understanding of their properties has been beset with apparently conflicting observations and conceptual difficulties. Much of this remains true for water, but fortunately the situation for monohydroxy alcohols is different. Here, with the experimental progress witnessed in recent years and with the growing recognition of the importance of specific supramolecular structures, a coherent microscopic understanding of the structure and dynamics of these hydrogen-bonded liquids is within reach.
9727351
Ultrafast anisotropy dynamics of water molecules dissolved in acetonitrile.
Infrared pump-probe experiments are performed on isolated H(2)O molecules diluted in acetonitrile in the spectral region of the OH stretching vibration. The large separation between water molecules excludes intermolecular interactions, while acetonitrile as a solvent provides substantial hydrogen bonding. Intramolecular coupling between symmetric and asymmetric modes results in the anisotropy decay to the frequency-dependent values of approximately 0-0.2 with a 0.2 ps time constant. The experimental data are consistent with a theoretical model that includes intramolecular coupling, anharmonicity, and environmental fluctuations. Our results demonstrate that intramolecular processes are essential for the H(2)O stretching mode relaxation and therefore can compete with the intermolecular energy transfer in bulk water.
4589044
Vibrational Relaxation of the Aqueous Proton in Acetonitrile: Ultrafast Cluster Cooling and Vibrational Predissociation.
We study the ultrafast O-H stretch vibrational relaxation dynamics of protonated water clusters embedded in a matrix of deuterated acetonitrile, using polarization-resolved mid-IR femtosecond spectroscopy. The clusters are produced by mixing triflic (trifluoromethanesulfonic) acid and H2O in molar ratios of 1:1, 1:2, and 1:3, thus varying the degree of hydration of the proton. At all hydration levels the excited O-H stretch vibration of the hydrated proton shows an ultrafast vibrational relaxation with a time constant T1 < 100 fs, leading to an ultrafast local heating of the protonated water cluster. This excess thermal energy, initially highly localized to the region of the excited proton, first re-distributes over the aqueous cluster and then dissipates into the surrounding acetonitrile matrix. For clusters with a triflic acid to H2O ratio of 1:3 these processes occur with time constants of 320 ± 20 fs and 1.4 ± 0.1 ps, respectively. The cooling of the clusters reveals a long-living, underlying transient absorption change with high anisotropy. We argue that this feature stems from the vibrational predissociation of a small fraction of the proton hydration structures, directly following the ultrafast infrared excitation.
102322080
Ultrafast vibrational energy flow in water monomers in acetonitrile
Abstract Vibrational relaxation of the OH stretching and bending modes of water monomers in acetonitrile is studied by two-color pump–probe experiments in a frequency range from 1400 to 3800 cm −1 . Measurements with resonant infrared excitation reveal vibrational lifetimes of 6.4 ± 1.0  ps of the OH stretching modes and 4.0 ± 0.5  ps of the OH bending mode. After OH stretching excitation, the OH bending mode shows an instantaneous response, a hallmark of the anharmonic coupling of stretching and bending modes, and a delayed population buildup by relaxation of the stretching via the bending mode. The relaxation steps are discussed within the framework of current theoretical pictures of water’s vibrational relaxation.
97267572
The selective synthesis of acetonitrile from carbon monoxide, hydrogen, and ammonia over MO/SiO2
Abstract The selective synthesis of acetonitrile from CO/H 2 /NH 3 over Mo/SiO 2 was investigated. The effects of temperature, space velocity, and reactant compositions on conversion and selectivity were explored with a two-level factorial designed experiment. High selectivities (37–96% excluding CO 2 ) were achieved at reasonably high conversions (29–64%). The product's carbon number distribution differed significantly from that obtained from a CO/H 2 feed under identical conditions. The results are explained in terms of three competing reactions: water-gas shift, Fischer-Tropsch synthesis, and nitrile synthesis. Other experiments are described that indicate a nitrile synthesis mechanism involving a CN intermediate which further reacts with a carbon species to form the acetonitrile. A mechanistic hypothesis involving an isocyanide ligand is proposed.
93833427
Association and the assignment of the OH overtones in hydrogen bonded alcohols
The long‐standing problem of the assignment of the first overtone of the OH stretching vibration of hydrogen bonded alcohols is examined for the cases of methanol, ethanol, and tertiary butanol. The spectra of the related deuterated alcohols were measured and isotopic isolation experiments were carried out at temperatures ranging from 25° to − 190°C. Dilute solutions were studied as well as the pure liquids. For the latter the second overtones were also measured. The first OH overtones, although overlapped by CH + OH combination bands were definitely identified and the anharmonicity constants were determined. They show a moderate but appreciable increase with respect to free OH stretching vibrations. Bands due to simultaneous excitation or coupling of two contiguous OH groups bound together by hydrogen bonds are also present.
27134527
The growing landscape of lysine acetylation links metabolism and cell signalling
Lysine acetylation is a conserved protein post-translational modification that links acetyl-coenzyme A metabolism and cellular signalling. Recent advances in the identification and quantification of lysine acetylation by mass spectrometry have increased our understanding of lysine acetylation, implicating it in many biological processes through the regulation of protein interactions, activity and localization. In addition, proteins are frequently modified by other types of acylations, such as formylation, butyrylation, propionylation, succinylation, malonylation, myristoylation, glutarylation and crotonylation. The intricate link between lysine acylation and cellular metabolism has been clarified by the occurrence of several such metabolite-sensitive acylations and their selective removal by sirtuin deacylases. These emerging findings point to new functions for different lysine acylations and deacylating enzymes and also highlight the mechanisms by which acetylation regulates various cellular processes.
33640013
N-formylation of lysine in histone proteins as a secondary modification arising from oxidative DNA damage
The posttranslational modification of histone and other chromatin proteins has a well recognized but poorly defined role in the physiology of gene expression. With implications for interfering with these epigenetic mechanisms, we now report the existence of a relatively abundant secondary modification of chromatin proteins, the N6-formylation of lysine that appears to be uniquely associated with histone and other nuclear proteins. Using both radiolabeling and sensitive bioanalytical methods, we demonstrate that the formyl moiety of 3′-formylphosphate residues arising from 5′-oxidation of deoxyribose in DNA, caused by the enediyne neocarzinostatin, for example, acylate the N6-amino groups of lysine side chains. A liquid chromatography (LC)–tandem mass spectrometry (MS) method was developed to quantify the resulting N6-formyl-lysine residues, which were observed to be present in unperturbed cells and all sources of histone proteins to the extent of 0.04–0.1% of all lysines in acid-soluble chromatin proteins including histones. Cells treated with neocarzinostatin showed a clear dose–response relationship for the formation of N6-formyl-lysine, with this nucleosome linker-selective DNA-cleaving agent causing selective N6-formylation of the linker histone H1. The N6-formyl-lysine residue appears to represent an endogenous histone secondary modification, one that bears chemical similarity to lysine N6-acetylation recognized as an important determinant of gene expression in mammalian cells. The N6-formyl modification of lysine may interfere with the signaling functions of lysine acetylation and methylation and thus contribute to the pathophysiology of oxidative and nitrosative stress.
94972561
A convenient method for the N-formylation of secondary amines and anilines using ammonium formate
The N-formylation of secondary amines and anilines using ammonium formate as a formylating agent is described.
95452546
A facile method for the N-formylation of primary and secondary amines by liquid phase oxidation of methanol in the presence of hydrogen peroxide over basic copper hydroxyl salts
Abstract N-formylation reactions by catalytic oxidation of methanol in the presence of primary or secondary amines and hydrogen peroxide has been investigated using a liquid phase reaction system over basic copper hydroxyl salts. A series of basic copper hydroxyl salts was prepared by the conventional precipitation method using aqueous ammonia and sodium hydroxide as precipitating agents. PXRD, SEM, FT-IR, BET were employed for physical characterization of the prepared basic copper hydroxyl salts. The composition of the catalytic material obtained was found dependent on the nature of the anion associated with the copper salt precursor. The copper hydroxyl chloride catalyst has shown the best catalytic performance in terms of the reaction rate and product selectivity whereas for the copper oxide catalyst the reaction rate was extremely slow. It is interesting to observe that 4-piperidone protected with acid-sensitive functional groups such as N-acetyl piperazine and ethylene glycol can also be formylated from moderate to good yields by these catalysts.
55207599
New Route to N-Formylation of Primary Amines with Amino Acids as a Source of CO Using Polyaniline Catalyst
The treatment of primary amines with amino acids as a CO source in the presence of polyaniline emeraldine salts bring about N-formylation to give the corresponding formamides. This route to N-formylation methodology of primary amine represents the first reported example of a CO-transfer via radical mechanism by highly nanoporous polyaniline emeraldine salts catalyst.
97425114
Convenient N-Formylation of Amines in Dimethylformamide with Methyl Benzoate under Microwave Irradiation
-dimethylformamide (DMF) with methyl benzoate as a promoter under microwave irradiation. Although DMF as a formylating source has been employed for the formylation reaction with 2,3-dihydro-1,4-phthalazinedione as a promoter, it needed long reaction time of more than 40 hours and was limited to the formylation of primary amines.
11659422
A remarkably simple protocol for the N-formylation of amino acid esters and primary amines.
A simple, convenient, and wide scope protocol for the N-formylation of amino acid esters and primary amines has been developed utilizing only imidazole in warm DMF.
120872040
Nonlinear protein – nucleic acid crosslinking induced by femtosecond UV laser pulses in living cells
We investigate the interactions between proteins and DNA in solutions of living cells, triggered by UV, 200-fs laser pulses. DNA-protein crosslinking is obtained with two different techniques: conventional chemical or laser-induced. Our results evidence a nonlinear response of the cells to the laser irradiation in the investigated intensity range. The laser induced crosslink efficiency can reach a value approximately twice higher than that obtained with ordinary chemical methods. The experimental results are very well reproduced by a simple phenomenological model based on the interplay between two-photon absorption by DNA bases and cell damage induced by high intensity laser pulse.
10321674
Femtosecond quantum control of molecular bond formation
Ultrafast lasers are versatile tools used in many scientific areas, from welding to eye surgery. They are also used to coherently manipulate light–matter interactions such as chemical reactions, but so far control experiments have concentrated on cleavage or rearrangement of existing molecular bonds. Here we demonstrate the synthesis of several molecular species starting from small reactant molecules in laser-induced catalytic surface reactions, and even the increase of the relative reaction efficiency by feedback-optimized laser pulses. We show that the control mechanism is nontrivial and sensitive to the relative proportion of the reactants. The control experiments open up a pathway towards photocatalysis and are relevant for research in physics, chemistry, and biology where light-induced bond formation is important.
35144093
Ultraviolet laser-induced cross-linking in peptides.
RATIONALE
The aim of this study was to demonstrate, and to characterize by high-resolution mass spectrometry that it is possible to preferentially induce covalent cross-links in peptides by using high-energy femtosecond ultraviolet (UV) laser pulses. The cross-link is readily formed only when aromatic amino acids are present in the peptide sequence.


METHODS
Three peptides, xenopsin, angiotensin I, and interleukin, individually or in combination, were exposed to high-energy femtosecond UV laser pulses, either alone or in the presence of spin trapping molecules, the reaction products being characterized by high resolution mass spectrometry.


RESULTS
High-resolution mass spectrometry and spin trapping strategies showed that cross-linking occurs readily, proceeds via a radical mechanism, and is the highly dominant reaction, proceeding without causing significant photo-damage in the investigated range of experimental parameters.


CONCLUSIONS
High-energy femtosecond UV laser pulses can be used to induce covalent cross-links between aromatic amino acids in peptides, overcoming photo-oxidation processes, that predominate as the mean laser pulse intensity approaches illumination conditions achievable with conventional UV light sources.
97146460
Tables of molecular vibrational frequencies. Consolidated volume II
The compilations of fundamental vibrational frequencies of molecules previously published as Tables of Molecular Vibrational Frequencies Part 5, Part 6, Part 7, and Part 8, which appeared in the Journal of Physical and Chemical Reference Data in 1972, 1973, and 1974, have been revised. This Consolidated Volume II includes data on a total of 212 molecules in addition to those on 223 molecules included in Volume 1 (NSRDS‐NBS 39). Selected values of the fundamental vibrational frequencies are given for each molecule, together with observed infrared and Raman spectral data and citations to the original literature. The selection of vibrational fundamentals has been based on careful studies of the spectral data and comprehensive normal‐coordinate analyses. An estimate of the accuracy of the selected values is included. The tables provide a convenient source of information for those who require vibrational energy levels and related properties in molecular spectroscopy, thermodynamics, analytical chemistry, and o...
119019372
Optics of Femtosecond Laser Pulses
Contents: Short Optical Pulses in Linear Dispersive Media. Self-action of Optical Pulses Self-modulation, Self-compression, Solitons, and Instabilities. Parametric Interactions and Coherent Scattering of Femtosecond Pulses. Fast Phase Control. Compression and Shaping of Optical Pulses. Optical Solitons. Picosecond and Femtosecond Pulses in Optical Information Systems.