The site of ionization (protonation and deprotonation) of hydroxamic acids (RCONHOH) has been investigated by heteronuclear (14N, l5N, 170) N M R relaxation and NOE experiments (R = Me, Ph) and ab initio theoretical methods (R = H, Me, Ph). Theoretical calculations indicate that nitrogen deprotonation is favored in all cases. Electric field gradient calculations have been used to estimate the change in nuclear quadrupolar coupling constants at 0 and N upon ionization and compared to experimental line width changes. N M R relaxation rate and NOE measurements in aqueous solution indicate that acetohydroxamic acid (R = Me) in water is predominantly an oxygen acid, whereas benzohydroxamic acid (R = Ph) is predominantly a nitrogen acid in methanol. Acetohydroxamic acid (m* = 0.25, pKBH+ = -1.15) is protonated at the carbonyl oxygen.

A two-thiol reactive lanthanide-DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) chelate, CLaNP-3 (CLaNP=caged lanthanide NMR probe), was synthesized for the rigid attachment to cysteine groups on a protein surface, and used to obtain long-range-distance information from the {15N,1H} HSQC spectra of the protein-lanthanide complex. The DOTA ring exhibits several isomers that are in exchange; however, single resonances were observed for most amide groups in the protein, allowing determination of a single, apparent magnetic-susceptibility tensor. Pseudocontact shifts caused by Yb-containing CLaNP-3 were observed for atoms at 15-35 A from the metal. By using Gd-containing CLaNP-3, relaxation effects were observed, allowing distances up to 30 A from the paramagnetic center to be determined accurately. Similar results were obtained with a Gd-DTPA (diethylene-triaminepentaacetic acid) chelate, CLaNP-1, bound in the same bidentate manner to the protein. This study demonstrates that bidentate attachment of a paramagnetic probe enables determination of long-range distances.

The site of protonation of several types of amide bases (carboxylic amides and thioamides, sulfenamides, sulfinamides, sulfonamides, nitrosamides, nitramides, cyanamides, and phosphorous and phosphoric acid triamides) has been investigated through a combination of quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase (by MP2 calculations) and in water (by the IPCM continuum solvation method). Relevant NMR properties of the involved heteronuclei (nuclear shielding and electric field gradient) were calculated at the GIAO-HF level, and compared with chemical shifts and relaxation rates experimentally measured in 14 N, 17 O, and 31 P spectra. It is shown that such a combination of theoretical and experimental tools allows a dependable prediction of spectral parameters and ultimately of the protonation site of amides. The reliability of common assumptions, like the comparison of spectral parameters of polyfunctional bases and monofunctional models, is also scrutinized and tested.

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Stability constants were measured for complexes formed between a modified DTPA ligand and the metal ions Gd(III), Eu(III), Fe(III), Ca(II), Cu(II), and Zn(II) at 25 degrees C in 0.1 M NaClO4. The gadolinium complex of this ligand is MS-325, a novel blood pool contrast agent for magnetic resonance imaging currently undergoing clinical trials. Stability constants were determined by 4 different methods: direct pH titration, pH titration with competition by EDTA, competition with DTPA using an HPLC-MS detection system, and competition with Eu(III) by monitoring equilibrium by luminescence spectroscopy. The 1:1 stability constants, log beta101, are the following: Gd, 22.06 (23.2 in 0.1 M Me4NCl); Eu, 22.21; Fe, 26.66; Ca, 10.45; Cu, 21.3; Zn, 17.82. The exchange kinetics of the Gd complex, MS-325, with the radioactive tracer (152,154)Eu were studied at 25 degrees C in 0.1 M NaClO4. The exchange reaction has acid-dependent and acid-independent terms. The rate expression is given by the following: R = k(a)[GdL][H]2 + kb[GdL][Gd][H] + kc[GdL][Gd]. The rate constants were determined to be the following: k(a) = 1.84 x 10(6) M(-2) x min(-1), kb = 2.87 x 10(3) M(-2) x min(-1), kc = 3.72 x 10(-3) M(-1) x min(-1). MS-325 is 2-3 times more stable than GdDTPA at pH 7.4 and is 10-100 times more kinetically inert.

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This paper describes the synthesis and in-depth characterization of two new porphyrogenic macrocycles 1 and 2, and provides an evaluation of these molecules as photosensitizer agents. By tuning the reaction conditions and starting from readily available 1,9-diformyl-5-phenyldipyrromethane (4) and tripyrrane dicarboxylic acid (3), both the nonaromatic isopentaphyrin 1, composed of a 24 pi-electron macrocycle, and the aromatic pentaphyrin 2, composed of a 22 pi-electron macrocycle, were obtained in good yield and purity. Confocal laser microscopy and cytofluorimetry studies showed that the newly synthesized pentaphyrins penetrate the cell membranes and localize mainly in the cytoplasm. In the absence of light, 1 and 2 exhibit a nonsignificant cytotoxic effect at concentrations up to 3 mug/mL. In contrast, the synthesized pentaphyrins, when delivered to cells at 1.5 or 3 microg/mL and irradiated with white light (8 mW/cm(2)), promoted a strong and dose-dependent phototoxic effect in four different cell lines. FACS and caspase-3/7 activation assays demonstrated that the pentaphyrins cause cell death by apoptosis.