Designing Molecular Probes To Prolong Intracellular Retention: Application to Nitroxide Spin Probes.

Targeted delivery of molecular probes into cells enables cellular imaging through optical and magnetic modalities. Probe molecules that are well retained by cells can accumulate to higher intracellular concentrations, and thus increase the signal-to-noise ratio of, and widen the temporal window for, imaging. Here we synthesize a paramagnetic spin probe bearing six ionic functional groups and show that it has long intracellular half-life (>12 h) and exceptional biostability in living cells.

Ncm, a Photolabile Group for Preparation of Caged Molecules: Synthesis and Biological Application.

Ncm, 6-nitrocoumarin-7-ylmethyl, is a photolabile protective group useful for making "caged" molecules. Ncm marries the reliable photochemistry of 2-nitrobenzyl systems with the excellent stability and spectroscopic properties of the coumarin chromophore. From simple, commercially available starting materials, preparation of Ncm and its caged derivatives is both quick and easy.

Baeyer-Villiger Rearrangement of a Substituted Pyrrole by Oxone.

Pyrroloxyls have been reported to exhibit very narrow EPR spectral lines, essential for imaging. En route to pyrroloxyls, we observed an unexpected Baeyer-Villiger rearrangement, leading to loss of aromaticity and formation of a 4,5-dihydro-1-ketopyrrole.

A study on the photophysics of 9-amino-10-cyanoanthracene: probing its dual absorption and emission behavior.

The photophysics of a donor-acceptor substituted chromophore, 9-amino-10-cyanoanthracene (ACAN), has been investigated in polar and nonpolar solvents to understand its intriguing dual absorption and emission behavior. Steady-state and time-resolved fluorescence studies clearly indicate that the short wavelength emission band of ACAN arises from the higher excited singlet state, S2, while the longer wavelength emission band arises from the intramolecular charge transfer (ICT) state, S1. Interestingly, both these states can be populated by direct excitation from the ground state.

Dimethyl 5-acetyl-1-hy-droxy-4-methyl-1H-pyrrole-2,3-di-carboxyl-ate, an oxidation-resistant N-hy-droxy-pyrrole.

The title compound, C11H13NO6, exhibits an intra-molecular O-H⋯O=C hydrogen bond between the N-hydroxyl H atom and carbonyl O atom of the neighboring acetyl group. This finding contradicts a previously published model in which the hydrogen bond was postulated to occur with the neighboring carbomethoxy group. This relatively strong hydrogen bond [O-H⋯O: D = 2.

Ethyl 2,5-di-tert-butyl-5-eth-oxy-4-oxo-4,5-di-hydro-1H-pyrrole-3-carboxyl-ate.

The title compound, C17H29NO4, contains a chiral center and crystallizes as a racemate. The asymmetric unit consists of two non-equivalent mol-ecules, in which the carbeth-oxy groups have markedly different orientations [C(=O)CC(OEt)=O torsion angles = 59.3 (2) and 156.

Characterizing caged molecules through flash photolysis and transient absorption spectroscopy.

Caged molecules are photosensitive molecules with latent biological activity. Upon exposure to light, they are rapidly transformed into bioactive molecules such as neurotransmitters or second messengers. They are thus valuable tools for using light to manipulate biology with exceptional spatial and temporal resolution.

(2)H,(15)N-substituted nitroxides as sensitive probes for electron paramagnetic resonance imaging.

Electron paramagnetic resonance imaging (EPRI) using nitroxides is an emergent imaging method for studying in vivo physiology, including O(2) distribution in various tissues. Such imaging capabilities would allow O(2) mapping in tumors and in different brain regions following hypoxia or drug abuse. We have recently demonstrated that the anion of 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl (2) can be entrapped in brain tissue to quantitate O(2) concentration in vivo.

The effect of structure on nitroxide EPR spectral linewidth.

Nitroxides with narrow linewidths are essential for low-frequency EPR spectroscopy and in vivo EPR imaging. In developing a framework for designing narrow-line nitroxides, we sought to understand the unexpectedly narrow line width of 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyl (5). Computational modeling revealed that the carbonyl double bond in the 4-position allows conformational diversity that results in the observed narrowing of the EPR spectral line.

Optimization of labile esters for esterase-assisted accumulation of nitroxides into cells: a model for in vivo EPR imaging.

Nitroxide-based electron paramagnetic resonance (EPR) imaging agents are useful quantitative probes of O2 concentration in vivo in real time. Lipophilic, labile alkanoyloxymethyl esters of nitroxides can cross the blood-brain barrier, and after hydrolysis, the corresponding anionic nitroxide is intracellularly entrapped at levels sufficient to permit O2 measurements. The utility of nitroxides as EPR imaging agents depends critically on their ability to accumulate in the brain to high levels.

Photochemical gating of intracellular Ca2+ release channels.

We have synthesized BiNiX, a caged methylxanthine agonist for the ryanodine receptor (RyR) — the major calcium channel that mediates Ca release from intracellular Ca stores in electrically excitable cells. BiNiX is easily loaded into living cells through incubation with its acetoxymethyl (AM) ester. Delivery of focused UV light pulses to the loaded cell releases paraxanthine focally and rapidly to activate RyRs to release Ca, thus elevating intracellular Ca concentration to initiate Ca-dependent signaling cascades.

Caged vanilloid ligands for activation of TRPV1 receptors by 1- and 2-photon excitation.

Nociceptive neurons in the peripheral nervous system detect noxious stimuli and report the information to the central nervous system. Most nociceptive neurons express the vanilloid receptor, TRPV1, a nonselective cation channel gated by vanilloid ligands such as capsaicin, the pungent essence of chili peppers. Here, we report the synthesis and biological application of two caged vanilloids: biologically inert precursors that, when photolyzed, release bioactive vanilloid ligands.

Endocannabinoid signaling dynamics probed with optical tools.

Intercellular signaling dynamics critically influence the functional roles that the signals can play. Small lipids are synthesized and released from neurons, acting as intercellular signals in regulating neurotransmitter release, modulating ion channels on target cells, and modifying synaptic plasticity. The repertoire of biological effects of lipids such as endocannabinoids (eCBs) is rapidly expanding, yet lipid signaling dynamics have not been studied.

Ncm-D-aspartate: a novel caged D-aspartate suitable for activation of glutamate transporters and N-methyl-D-aspartate (NMDA) receptors in brain tissue.

The D-isomer of aspartate is both a substrate for glutamate transporters and an agonist of N-methyl-D-aspartate (NMDA) receptors. To monitor the behavior of these receptors and transporters in intact tissue we synthesized a new photo-labile analogue of D-aspartate, N-[(6-nitrocoumarin-7-yl)methyl]-D-aspartic acid (Ncm-D-aspartate). This compound was photolyzed rapidly (t(1/2)=0.

Unique roles of SK and Kv4.2 potassium channels in dendritic integration.

Focal activation of glutamate receptors in distal dendrites of hippocampal pyramidal cells triggers voltage-dependent Ca(2+) channel-mediated plateau potentials that are confined to the stimulated dendrite. We examined the role of dendritic K(+) conductances in determining the amplitude, duration, and spatial compartmentalization of plateau potentials. Manipulations that blocked SK-type Ca(2+)-activated K(+) channels, including apamin and BAPTA dialysis, increased the duration of plateau potentials without affecting their amplitude or compartmentalization.