Peptides investigated by laser desorption—multiphoton ionization mass spectrometry

Laser evaporation of intact neutral molecules into a supersonic beam combined with multiphoton ionization (MUPI) is used to study the fragmentation behaviour of peptides. Owing to the separation of desorption and ionization, an optimization of these processes can be applied to the sample. The investigation of mixtures containing hydrophobic and hydrophilic peptides shows equal probabilities for detection of the two molecules, demonstrating that the neutral yield of both classes of compound is equal in the desorption process. A loss of sensitivity is not observed. By employing the feature of tunable fragmentation, it is possible to sequence peptides in the gas phase. At low laser intensities only the molecular ions are formed. By increasing photon intensities, fragmentation reactions are induced. Owing to the nature of the multiphoton ionization, these mass spectra (at moderate laser powers) contain few and only structurally dependent signals. The molecular ion of the sample investigated is detected in every case.     

Two-color resonance-enhanced multiphoton ionization study of the lowest Rydberg p state of bis(eta6-benzene)chromium and its deuterated derivatives

Two-color resonance-enhanced multiphoton ionization (REMPI) spectra of jet-cooled (eta(6)-C(6)H(6))(2)Cr(1), (eta(6)-C(6)D(6))(2)Cr(2), and (eta(6)-C(6)D(6))(eta(6)-C(6)D(5)H)Cr(3) have been measured with use of the 3d(z)2-->R4p(x,y) Rydberg transition as the first step of the electronic excitation. The 0(0) (0) Rydberg component shifts by 59 and 54 cm(-1) to red when one goes from 1 to 2 and 3, respectively. Surprisingly, the REMPI spectra of 1-3 show very rich vibronic structures revealing both totally symmetric vibrations and degenerate vibrational modes. Presence of intense peaks corresponding to the e(2g) modes in the spectra of 1 and 2 is indicative of Jahn-Teller coupling in the R4p(x,y) Rydberg state. Additional REMPI resonances appear on going from 1 and 2 to 3 as a result of the symmetry reduction. The vibronic components in the spectra of 1-3 were assigned on the basis of the selection rules and comparison with the vibrational frequencies of the 1 and 2 ground-state molecules. The frequencies of over 10 normal vibrations have been determined for the gas-phase 1-3 Rydberg-state molecules from the REMPI experiment. The wavenumber corresponding to the lowest-energy mode (the ring torsion vibration) appears to be 40 cm(-1) in 1 and 35 cm(-1) in the deuterated complexes. The REMPI peaks are homogeneously broadened. The lower lifetime limits for the upper-state components increase on going from the vibrationless level to higher-lying vibronic states and on going from 1 to the deuterated derivatives.     

Two-photon absorption in the collisionless gas phase: lifetimes of new vibrational levels in benzene

Two-photon photoselection has been demonstrated for a molecule in the low pressure gas phase. The excitation has been used to populate new vibrational levels in benzene under isolated molecule conditions down to 0.1 torr. The new states display unusual behaviour as compared to the lifetimes of one-photon excited states. Most unexpectedly the lifetimes of the strongest two-photon inducing mode ν₁₄ is longer than all other lifetimes, including that of the vibrationless ¹B_2u origin. Some theoretical explanations are offered.     

Two-photon spectroscopy in the gas phase: 1B2u ← 1Ag transition of p-difluorobenzene

The two-photon excitation spectrum ¹B_2u ← ¹A_g of p-difluorobenzene in the gas phase is presented and analysed. The normal absorption is electric dipole allowed and shows no vibronic coupling, but the two-photon absorption is electric dipole forbidden and displays rich vibronic structure. Eight vibronic origins are assigned to their excited state fundamentals by analysis of the hot bands and by analogy with benzene. The only previously unassigned ground state frequency, an a_u mode, is active in the spectrum and is accordingly assigned. The sequences and the abundant Fermi resonances accompanying absorption are also partially assigned.     

Spectroscopy in our age

The development of modern spectroscopy is summarized from Bunsen’s detection of atoms as the beginning of spectral analysis to modern molecular spectroscopies including new high resolution techniques for molecular ions. Recent experiments involving long range charge migration in peptides and proteins are outlined. Received: 2 October 2000 / Published online: 11 October 2000     

Methodological approach to the characterization of diacylphosphatidyl cholines in rabbit lung lavage fluid by fast-atom bombardment mass spectrometry

Strong evidence exists that the distribution of phospholipids in the lung is a function of the degree of adult respiratory distress syndrome. The capabilities of positive-ion fast-atom bombardment (FAB) mass spectrometry for the determination of the relative distribution of intact diacylphosphatidylcholine species in lung lavage fluid were investigated. Two different FAB matrices and two different isolation/purification procedures--extraction/thin layer chromatography--high performance liquid chromatography (TLC-HPLC)--have been evaluated. In addition the relative fatty acid composition of the diacylphosphatidylcholines was determined by negative-ion FAB mass spectrometry using the [RCOO]- fragment ion. These results were compared with those obtained by gas chromatographic determination of the fatty acid methylesters.     

Anderson Localization for Schrödinger Operators on ℤ with Strongly Mixing Potentials

In this paper we show that for a.e. x∈[ 0,2 π) the operators defined on as

Distal charge transport in peptides

Biological systems often transport charges and reactive processes over substantial distances. Traditional models of chemical kinetics generally do not describe such extreme distal processes. In this Review, an atomistic model for a distal transport of information, which was specifically developed for peptides, is considered. Chemical reactivity is taken as the result of distal effects based on two-step bifunctional kinetics involving unique, very rapid motional properties of peptides in the subpicosecond regime. The bifunctional model suggests highly efficient transport of charge and reactivity in an isolated peptide over a substantial distance; conversely, a very low efficiency in a water environment was found. The model suggests ultrafast transport of charge and reactivity over substantial molecular distances in a peptide environment. Many such domains can be active in a protein.     

A master equation approach to the dynamics of zero electron kinetic energy (ZEKE) states and ZEKE spectroscopy

We have theoretically studied important dynamic processes involved in zero electron kinetic energy (ZEKE) spectroscopy using the density matrix method with the inverse Born-Oppenheimer approximation basis sets. In ZEKE spectroscopy, the ZEKE Rydberg states are populated by laser excitation (either a one- or two-photon process), which is followed by autoionizations and l-mixing due to a stray field. The discrimination field is then applied to ionize loosely bound electrons in the ZEKE states. This is followed by using the extraction field to extract electrons from the ZEKE levels which have a strength comparable to that of the extraction field. These extracted electrons are measured for the relative intensities of the ion states under investigation. The spectral positions are determined by the applied laser wavelength and modified by the extraction electric field. In this paper, all of these processes are conducted within the context of the density matrix method. The density matrix method can provide not only the dynamics of system's population and coherence (or phase) but also the rate constants of the processes involved in the ZEKE spectroscopy. Numerical examples are given to demonstrate the theoretical treatments.