Temperature Dependence of the Excited-State Intramolecular Proton Transfer Reaction in Hypericin and Hypocrellin A

The excited-state intramolecular proton-transfer reactions of hypericin and hypocrellin A are measured as a function of temperature in an ethanol/methanol mixture. The data yield activation energies of 0.044 ± 0.008 and 2.12 ± 0.070 kcal/mol for hypericin and hypocrellin A, respectively. The negligible activation energy of hypericin is consistent with previous suggestions that the proton-transfer reaction is adiabatic (K. Das et al., J. Phys. Chem. 1997,101A, 3241.) and that a very low-amplitude displacement in at least one other coordinate be taken into account in order to describe the reaction dynamics. The proton transfer for hypocrellin is also considered to occur in the adiabatic regime, but the significant activation energy suggests that a larger amplitude motion than that for the case of hypericin comprises part of the reaction coordinate. Much of the barrier cited above for hypocrellin A results from the temperature dependence of the viscosity of the solvent mixture. The viscosity independent part of the activation barrier is 0.41 ± 0.088 kcal/mol

Photoionization and dynamic solvation of the excited states of 7-azaindole

The excited-state photophysics of the biological probe, 7-azaindole, are examined in water and methanol. Electrons in a presolvated state absorbing in the infrared appear within the excitation pulse width of 130 fs. 330 i 100 fs is required for the presolvated electron to achieve the spectrum characteristic of the completely solvated electron. An excited-state transient absorbance decays in -350 fs for 7-azaindole and its methylated analog, N1-methyl-7-azaindole (1M7AI), in the region 400-450 nm in water and methanol. The instantaneous appearance of the electron in the infrared is attributed to the decay of the lLb excited-state that overlaps the \u27La excited state of 7-azaindole. The rapid decay of the excited-state transient absorbance is attributed to preferential, dynamic solvation of the \u27La state. 7-Azaindole thus provides an interesting example of a molecule whose excited state is continuously and dynamically solvated but which also produces a species, e,,-, whose solvation appears to occur in a stepwise process

Using 7-Azatryptophan To Probe Small Molecule-Protein Interactions on the Picosecond Time Scale: The Complex of Avidin and Biotinylated 7-Azatryptophan

The utility of 7-azatryptophan as an alternative to tryptophan for optically probing protein structure and dynamics is demonstrated by investigating the complex of egg-white avidin and biotinylated 7-azatryptophan. We report the synthesis of biotinylated 7-azatryptophan and optical measurements of its complex with avidin. Although there are four biotin binding sites, the emission from the 7-azatryptophan tagged to biotin decays by a single exponential, whereas the tryptophyl emission from avidin requires two exponentials in order to be adequately fit. Fluorescence depolarization measurements of the complex probed by emission from 7-azatryptophan reveal both rapid (-80 ps) and much longer-lived decay. The former component is attributable to the local motion of the probe with respect to the protein; the latter component represents overall protein tumbling. In addition, energy transfer from tryptophan to 7-azatryptophan and a blue-shift in the spectrum of biotinylated 7-azatryptophan are observed upon formation of the complex. Modified strategies of effecting optical selectivity are also discussed

Ultrarelativistic Bondi--Hoyle Accretion I: Axisymmetry

An ultrarelativistic relativistic study of axisymmetric Bondi--Hoyle accretion onto a moving Kerr black hole is presented. The equations of general relativistic hydrodynamics are solved using high resolution shock capturing methods. In this treatment we consider the ultrarelativistic limit wherein one may neglect the baryon rest mass density. This approximation is valid in the regime where the internal energy of the system dominates over the rest mass energy contribution from the baryons. The parameters of interest in this study are the adiabatic constant $\Gamma$, and the asymptotic speed of the fluid, $v_\infty$. We perform our simulations in three different regimes, subsonic, marginally supersonic, and supersonic, but the primary focus of this study is the parameter regime in which the flow is supersonic, that is when $v_\infty \ge c_{s}^{\infty}$. As expected from previous studies the supersonic regimes reveal interesting dynamics, but even more interesting is the presence of a bow shock in marginally supersonic systems. A range of parameter values were investigated to attempt to capture possible deviations from steady state solutions, none were found. To show the steady state behaviour of each of the flows studied we calculate the energy accretion rates on the Schwarzschild radius. Additionally, we also find that the accretion flows are dependent on the location of the computational boundary, that if the computational boundary is located too close to the black hole the calculated flow profiles are marred with numerical artifacts. This is a problem not found in previous relativistic models for ultrarelativistic hydrodynamic systems.Comment: 16 pages, 15 figures, Typos correcte

Role of Solvent in Excited-State Proton Transfer in Hypericin

The excited-state proton transfer of hypericin is monitored by the rise time (-6-1 2 ps in the solvents investigated) of the component of stimulated emission corresponding to the formation of the long-lived (-5 ns) fluorescent tautomer. The assignment of this excited-state process to proton transfer has been verified by noting that a hypericin analog (mesonaphthobianthrone) lacking labile protons is not fluorescent unless its carbonyl groups are protonated. Recent experimental studies on other systems have suggested that three solvent properties play important roles in excited-state proton transfer: viscosity, hydrogen-bonding character, and dynamic solvation. We find that for hypericin, in a range of protic, aprotic, hydrogen-bonding, and non-hydrogen-bonding solvents in which the viscosity changes by a factor of 60 and the average solvation time changes by a factor of 100, the excited-state proton-transfer rate of hypericin is uncorrelated with these properties and varies not more than a factor of 2 (- 6-1 2 ps) at room temperature. The relative contribution of the bulk solvent polarity is considered, and the role of intramolecular vibrations of hypericin on the proton-transfer rate is discussed

Domain Structure of the Staphylococcus aureus Collagen Adhesin

Sequence analysis of surface proteins from Gram-positive bacteria indicates a composite organization consisting of unique and repeated segments. Thus, these proteins may contain discrete domains that could fold independently. In this paper, we have used a panel of biophysical methods, including gel permeation chromatography, analytical ultracentrifugation, circular dichroism, and fluorescence spectroscopy, to analyze the structural organization of the Staphylococcus aureus collagen adhesin, CNA. Our results indicate that the structure, function, and folding of the ligand-binding domain (A) are not affected by the presence or absence of the other major domain (B). In addition, little or no interaction is observed between the nearly identical repeat units within the B domain. We propose that CNA is indeed a mosaic protein in which the different domains previously indicated by sequence analysis operate independently

Hypericin, Hypocrellin, and Model Compounds: Primary Photoprocesses of Light-Induced Antiviral Agents

The excited-state photophysics of the light-induced antiviral agents hypericin and hypocrellin are compared with those of the hexa- and tetramethoxy analogues of hypericin. The results are consistent with the interpretation of the primary photoprocess in hypericin and hypocrellin as that of excited-state intramolecular proton or atom transfer

Inverse monoids and immersions of 2-complexes

It is well known that under mild conditions on a connected topological space $\mathcal X$, connected covers of $\mathcal X$ may be classified via conjugacy classes of subgroups of the fundamental group of $\mathcal X$. In this paper, we extend these results to the study of immersions into 2-dimensional CW-complexes. An immersion $f : {\mathcal D} \rightarrow \mathcal C$ between CW-complexes is a cellular map such that each point $y \in {\mathcal D}$ has a neighborhood $U$ that is mapped homeomorphically onto $f(U)$ by $f$. In order to classify immersions into a 2-dimensional CW-complex $\mathcal C$, we need to replace the fundamental group of $\mathcal C$ by an appropriate inverse monoid. We show how conjugacy classes of the closed inverse submonoids of this inverse monoid may be used to classify connected immersions into the complex