PubMed · 1273255
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J Eisinger. 1976. Energy transfer and dynamical structure.. https://doi.org/10.1017/s0033583500002134
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
A 100 ns molecular dynamics simulation of penta-alanine in explicit water is performed to study the reversible folding and unfolding of the peptide. Employing a standard principal component analysis (PCA) using Cartesian coordinates, the resulting free-energy landscape is found to have a single minimum, thus suggesting a simple, relatively smooth free-energy landscape. Introducing a novel PCA based on a transformation of the peptide dihedral angles, it is found, however, that there are numerous free energy minima of comparable energy (less than or approximately 1 kcal/mol), which correspond to well-defined structures with characteristic hydrogen-bonding patterns. That is, the true free-energy landscape is actually quite rugged and its smooth appearance in the Cartesian PCA represents an artifact of the mixing of internal and overall motion. Well-separated minima corresponding to specific conformational structures are also found in the unfolded part of the free energy landscape, revealing that the unfolded state of penta-alanine is structured rather than random. Performing a connectivity analysis, it is shown that neighboring states are connected by low barriers of similar height and that each state typically makes transitions to three or four neighbor states. Several principal pathways for helix nucleation are identified and discussed in some detail.
Internal energies and energy distributions were studied using the 'survival yield' method developed previously. In addition to conventional benzylpyridinium salts, protonated esters (fragmenting by rearrangement) and protonated leucine enkephalin were also used, extending the validity of the technique. Fragmentation processes were studied in the cone voltage region and modeled by the RRKM-based MassKinetics program. The results show that the shapes of the energy distributions are similar to thermal distributions. The mean internal energies are very similar for all compound classes studied, and show a linear increase with collision energy in the 10-50 eV region.
Dual excited states of nickel(II) meso-tetra(4-sulfonatophenyl)porphyrin (NiTPPS) and nickel(II) meso-tetraphenylporphyrin (NiTPP) have been investigated by two-pump-one-probe transient absorption spectrometry. By dual excited states, we mean molecular entities that have absorbed two photons to generate molecular states with electronic excitation in two distinct regions of metalloporphyrin. Two successive pulses of 400 and 550 nm were used for excitation. The first pulse (400 nm) produced an S2 state of the porphyrin pi-system, which deactivated to give rise to an S1 state and subsequently produce a metal-centered (d,d) state. The second (550 nm) pulse selectively targeted an S0 --> S1 transition of those molecules having an excited metal center and was delivered to the sample approximately 40 ps after the first excitation event. At this time, the ground state of the tetrapyrrole pi-system was already regenerated and the excitation was localized at the metal center. The kinetic profiles of the NiTPPS transients in DMSO revealed biexponential decays with time constants of 0.6 and 4 ps. Photoexcitation of NiTPP in toluene and NiTPPS in water resulted in similar behavior. A mechanism for the Ni(II) porphyrin dual excited state deactivation involving the formation of an intramolecular charge transfer state has been proposed.