Light-Induced Acidification by the Antiviral Agent Hypericin

The naturally occurring polycyclic quinone hypericin possesses light-induced antiviral activity against the human immunodeficiency virus (HIV) and other closely related enveloped lentiviruses such as equine infectious anemia virus (EIAV). We have previously argued that hypericin undergoes a fast proton transfer reaction in its singlet state (J. Phys. Chem. 1994, 98, 5784). We have also presented evidence that the light-induced antiviral activity of hypericin does not depend upon the formation of singlet oxygen (Bioorg. Med. Chem. Lett. 1994, 4, 1339). It is demonstrated here that steady-state illumination of a solution containing hypericin effects a pH drop. When hypericin and an indicator dye, 3-hexadecanoyl-7-hydroxycoumarin,a re both imbedded in vesicles, hypericin transfers a proton to the indicator within a time commensurate to its triplet lifetime. Proton transfer to the indicator is not observed when the indicator is protonated or when the system is oxygenated. Since hypericin is known to form triplets and to generate singlet oxygen with high efficiency, this latter result is taken to confirm triplet hypericin as a source, but not necessarily the only source, of proton

Photophysics of a novel optical probe: 7-azaindole

7-Azaindole is the chromophoric side chain of the nonnatural amino acid 7-azatryptopha11, which we have shown can be incorporated into bacterial protein and is amenable to peptide synthesis. Timeresolved fluorescence measurements of 7-amindole are performed as a function of solvent, pH, and temperature in order to characterize its behavior and to establish criteria for the interpretation of its photophysics when it is incorporated into, or interacts with, proteins. The first time-resolved measurements of 7-azaindole in water are presented. The dependence of the fluorescence properties of 7-azaindole in water with respect to that in various solvents of differing polarity and the temperature dependence of the fluorescence lifetimes of 7-azaindole in H20 and D20, and in CHBOH and CH30D, suggest that the fuorescent species of 7-azaindole in water is a tautomerized excited-state solutesolvent complex. Time-resolved fluorescence measurements as a function of temperature verify the existence in methanol of a ground-state precursor to the 7-azaindole *tautomer” species. Upon optical excitation, this precursor decays into the tautomer in less than 30 ps. Our results are used to rationalize the sensitivity of the fluorescence lifetime of a synthetic peptide containing 7-azatryptophan alone in aqueous solution and in complex with a protein

Structure and Energetics of Ground-State Hypericin: Comparison of Experiment and Theory

Calculations of the energies of the ground-state un-ionized tautomers of hypericin have been performed at the RMP2/6-31G(d) level of theory, using geometries obtained with the 3-21G basis set and Hartree−Fock wave functions. It is found that only the so-called normal form is likely to be populated at room temperature and that only two of the three possible double tautomers correspond to minima on the potential energy surface. The effect of continuum aqueous solvation on the tautomer energies is negligible. The O---O distances between which the proton is transferred are reported and are consistent with that required for an adiabatic proton transfer, i.e., ∼2.5 Å. All 156 vibrational frequencies are tabulated and may be viewed at www.msg.ameslab.gov. For example, the vibrations in the range 320−660 cm-1 are coupled with O---O vibrations. The vibrations that are most clearly O---O vibrations occur in the range 400−500 cm-1. Twisting of the backbone occurs in a wide range of frequencies, from 230 to 1150 cm-1, while the motion corresponding to an inversion of the (nonplanar) backbone occur at very low frequencies, 80−150 cm-1. The results of these calculations are discussed in terms of ground-state heterogeneity of hypericin that has been invoked to explain its spectra and excited-state kinetics

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

Novel noninvasive in situ probe of protein structure and dynamics

7-Amtryptophan is an ideal noninvasive in situ probe of protein structure and dynamics and provides an alternative to the use of ,tryptophan. 7-Azatryptophan affords a single-exponential fluorescence decay in aqueous solution, unlike tryptophan. Its absorption and fluorescence spectra are distinguishable from those of tryptophan. Its fluorescence spectrum and lifetime are sensitive to the environment. It can be used in peptide synthesis, and it can be incorporated into bacterial protein. These facts render 7-azatryptophan a unique probe that has the potential for widespread use

Paradigms and Controversies in the Treatment of HIV-Related Burkitt Lymphoma

Burkitt lymphoma (BL) is a very aggressive subtype of non-Hodgkin's lymphoma that occurs with higher frequency in patients with HIV/AIDS. Patients with HIV-related BL (HIV-BL) are usually treated with high-intensity, multi-agent chemotherapy regimens. The addition of the monoclonal antibody Rituximab to chemotherapy has also been studied in this setting. The potential risks and benefits of commonly used regimens are reviewed herein, along with a discussion of controversial issues in the practical management of HIV-BL, including concurrent anti-retroviral therapy, treatment of relapsed and/or refractory disease, and the role of stem cell transplantation

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

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

Equilibrium solutions of the shallow water equations

A statistical method for calculating equilibrium solutions of the shallow water equations, a model of essentially 2-d fluid flow with a free surface, is described. The model contains a competing acoustic turbulent {\it direct} energy cascade, and a 2-d turbulent {\it inverse} energy cascade. It is shown, nonetheless that, just as in the corresponding theory of the inviscid Euler equation, the infinite number of conserved quantities constrain the flow sufficiently to produce nontrivial large-scale vortex structures which are solutions to a set of explicitly derived coupled nonlinear partial differential equations.Comment: 4 pages, no figures. Submitted to Physical Review Letter