Oligothiophenes and Synthesis Thereof

Novel oligothiophenes and intermediates therefor are disclosed together with a process for synthesizing them. The oligothiophenes are in the form of a helix which contains five-membered rings unsaturated heterocycles that are cross-conjugated and annelated into a helix

Exchange Coupling Mediated Through-Bonds and Through- Space in Conformationally-Constrained Polyradical Scaffolds: Calix[4]arene Nitroxide Tetraradicals And Diradical

Calix[4]arenes constrained to 1,3-alternate conformation and functionalized at the upper rim with four and two tert-butylnitroxides have been synthesized, and characterized by X-ray crystallography, magnetic resonance (EPR and 1H NMR) spectroscopy, and magnetic studies. The 1,3-alternate nitroxide tetraradical and diradical provide unique polyradical scaffolds for dissection of the throughbond and through-space intramolecular exchange couplings. In addition, detailed magnetic studies of the previously reported calix[4]arene nitroxide tetraradical, which possesses cone conformation in solution, reveal conformational dependence of exchange coupling. Through-bond coupling between the adjacent nitroxide radicals is mediated by the nitroxide-m-phenylene-CH2-m-phenylenenitroxide coupling pathway, and through-space coupling is found between the diagonal nitroxide radicals at the conformationally-constrained N···N distance of 5–6 Å. Magnetic studies of the calix[4]arene polyradical scaffolds in frozen solutions show that the through-bond exchange coupling in the 1,3-alternate calix[4]arene tetraradical is antiferromagnetic, while that in cone calix[4]arene tetraradical is ferromagnetic. The through-space exchange couplings are antiferromagnetic in both cone and 1,3-alternate calix[4]arene tetraradical, as well as in the 1,3-alternate calix[4]arene diradical. The exchange coupling constants (|J/k|) are of the order of 1 Kelvin

Synthesis and Reduction Kinetics of Sterically Shielded Pyrrolidine Nitroxides

A series of sterically shielded pyrrolidine nitroxides were synthesized and their reduction by ascorbate (vitamin C) indicate that nitroxide 3 – a tetraethyl derivative of 3-carboxy-PROXYL – is reduced at the slowest rate among known nitroxides, i.e., at a 60-fold slower rate than that for 3- carboxy-PROXYL

BRUSH-ARM STAR POLYMER IMAGING AGENTS AND USES THEREOF

Disclosed are methods, compositions, reagents, systems, and kits to prepare nitroxide-functionalized brush-arm star polymer organic radical contrast agent (BASP-ORCA) as well as compositions and uses thereof. Various embodiments show that BASP-ORCA display unprecedented per-nitrox-ide and per-molecule transverse relaxivities for organic radical contrast agents, exceptional stability, high water solubility, low in vitro and in vivo toxicity, and long blood compartment half-life. These materials have the potential to be adopted for tumor imaging using clinical high-field 1H MRI techniques

Impact of Electron-Electron Spin Interaction on Electron Spin Relaxation of Nitroxide Diradicals and Tetraradical in Glassy Solvents Between 10 and 300 K

To determine the impact of electron-electron spin-spin interactions on electron spin relaxation rates, 1/T1 and 1/Tm were measured for nitroxide monoradical, diradical, and tetraradical derivatives of 1,3-alternate calix[4]arenes, for two pegylated high-spin nitroxide diradicals, and for an azine-linked nitroxide diradical. The synthesis and characterization by SQUID (superconducting quantum interference device) magnetometry of one of the high-spin diradicals, in which nitroxides are conformationally constrained to be coplanar with the m-phenylene unit, is reported. The interspin distances ranged from about 5-9 Å, and the magnitude of the exchange interaction ranged from \u3e150 to \u3e0.1 K. 1/T1 and 1/Tm were measured by long-pulse saturation recovery, three-pulse inversion recovery, and two-pulse echo decay at X-band (9.5 GHz) and Q-band (35 GHz). For a diradical with interspin distance about 9 Å, relaxation rates were only slightly faster than for a monoradical with analogous structure. For interspin distances of about 5-6 Å, relaxation rates in glassy solvents up to 300 K increased in the order monoradical \u3c diradical \u3c tetraradical. Modulation of electron-electron interaction enhanced relaxation via the direct, Raman, and local mode processes. The largest differences in 1/T1 were observed below 10 K, where the direct process dominates. For the three diradicals with comparable magnitude of dipolar interaction, 1/Tm and 1/T1 were faster for the molecules with more flexible structures. Relaxation rates were faster in the less rigid low-polarity sucrose octaacetate glass than in the more rigid 4:1 toluene/chloroform or in hydrogen-bonded glycerol glasses, which highlights the impact of motion on relaxation

A Spirocyclohexyl Nitroxide Amino Acid Spin Label for Pulsed EPR Distance Measurements

Site-directed spin labeling (SDSL) and electron paramagnetic resonance (EPR) spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide α-amino acid and its N-(9- fluorenylmethoxycarbonyl) (Fmoc) derivative, has been synthesized that exhibit slow enough spin echo dephasing to permit accurate distance measurements by pulse EPR at temperatures up to 125 K in 1:1 water:glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR to the study of structure and conformation for peptides and proteins

A Spirocyclohexyl Nitroxide Amino Acid Spin Label for Pulsed EPR Distance Measurements

Site-directed spin labeling (SDSL) and electron paramagnetic resonance (EPR) spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide α-amino acid and its N-(9- fluorenylmethoxycarbonyl) (Fmoc) derivative, has been synthesized that exhibit slow enough spin echo dephasing to permit accurate distance measurements by pulse EPR at temperatures up to 125 K in 1:1 water:glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR to the study of structure and conformation for peptides and proteins