Characterization of Nitrosothiols
J. Am. Chem. Soc., Vol. 121, No. 30, 1999 7123
giving a data to parameter ration of 6.6:1). The maximum and minimum
UV/Visible Spectroscopy. Absorption spectra were acquired on
a Hewlett-Packard HP8453 diode array spectrophotometer. For studies
on aqueous systems in anaerobic environments fiber-optic cables
were used to record the spectra in an inert-atmosphere box (Belle
Technology).
residual intensities were 0.203and -0.285 eÅ-3, respectively.
(
b) SNAP. A dark-green crystal with red reflections of S-nitroso-
acetylpenicillamine was selected for structure analysis. A total of 1409
int ) 0.0171) independent reflections were gathered in the 2θ range
of 5.5-50°. The data were not corrected for absorption. The compound
crystallized in the orthorhombic space group P2
(R
Theoretical Calculations. The calculations described here were
2
1 1
2 (Z ) 4) and the
58
performed by using Gaussian94 implemented on a Silicon Graphics
structure was solved by direct methods and refined by least-squares
Iris Indigo workstation. Full optimizations were performed initially at
the restricted Hartree-Fock (HF) level by using the polarized split
valence 6-31G* basis sets before the final optimizations which were
performed by density functional theory with use of Becke’s 3 parameter
functional59 and double-ú sets, 6-311+G*. It has recently been shown
that related nitrogen oxide anions exhibit Hartree-Fock instability and
that an effective method to model this is with Becke’s three-parameter
hybrid functions.60 After determination of the ground-state geometries
for the syn and anti conformations of methylthionitrite the transition
state for their conversion was determined by using the synchronous
2
and a full-matrix least-squares process on F by using structure solution
55
programs from the SHELXTL system. All non-hydrogen atoms were
refined anisotropically whereas the hydrogen atoms were located in
successive Fourier maps and refined isotropically. The final refinement
parameters were R
σ(F) (R ) 0.0289 and wR
parameter ration of 8.0:1). The maximum and minimum residual
1
) 0.0256 and wR
2
) 0.0677 for data with F >
4
1
2
) 0.0795 for all data giving a data to
-
3
intensities were 0.144 and -0.205 eÅ , respectively.
NMR Spectroscopy. NMR spectra were acquired on a Bruker
Advance-400 spectrometer operating at 40.55 MHz for 15N. The sample
was equilibrated for 10 min at each temperature prior to data collection,
6
1
transit-guided quasi-Newton algorithm developed by Schlegel et al.
The optimized transition states were tested by stepping through the
internal reaction coordinate to verify that the saddle separated the
minima described by the anti and syn structures. The reduced geometry
for methylthionitrite was calculated for the anti geometry and gave a
ground state with the structure that corresponds to a local minimal
geometry, as gauged for its frequencies.
2
56 transients were acquired with a 60° pulse, 2.0 s acquisition time,
and 3.5 s delay time. The data were multiplied by an exponential
window function with a 25 Hz line broadening factor prior to Fourier
transformation. Spectra were referenced to an external standard of
Na NO at 0 ppm. Temperature corrections were applied to experi-
2
mental values based upon a calibration of thermocouple performance
against a methanol/ethylene glycol standard.
1
5
56
Raman Spectroscopy. A Solution 633 Raman Laser System
Acknowledgment. This work was made possible by support
from the NIH, grant GM-53828, and a Teacher-Scholar award
from the Henry and Camille Dreyfus Foundation. We thank
Prof. K. C. Carron for the use of his Raman equipment and
assistance in its operation.
(
Detection Limit Technology) was used to acquire spectra for solid
samples of GSNO and SNAP and for a solution of Ph CSNO in
CH Cl . It was necessary to dissolve Ph CSNO due to laser-induced
3
2
2
3
photodecomposition of the solid, and the laser used had an excitation
wavelength of 633 nm.
Infrared Spectroscopy. Spectra were acquired with use of a MIDAC
FTIR spectrophotometer, recording 32 transients at a resolution of 1
cm . Solid spectra were obtained as KBr pellets or as a mull in a
fluorocarbon polymer between KBr plates. Solution spectra were
JA9901314
-
1
57) Formal potentials for the ferrocene+ couple vs SCE: +400 mV,
1/0
(
CH3CN solvent; +460 mV, CH2Cl2 solvent.
recorded by using CH
2
Cl
2
as a solvent.
(58) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
Johnson, B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G.
A.; Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.;
Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-
Gordon, M.; Gonzalez, C.; Pople, J. A.; Frisch, M. J.; Trucks, G. W.;
Schlegel, H. B.; Gill, P. M. W.; Johnson, B. G.; Robb, M. A.; Cheeseman,
J. R.; Keith, T.; Petersson, G. A.; Montgomery, J. A.; Raghavachari, K.;
Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J. V.; Foresman, J. B.;
Cioslowski, J.; Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng,
C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.; Andres, J. L.; Replogle, E.
S.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.;
Baker, J.; Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A., Eds.;
Gaussian, Inc.: Pittsburgh, PA, 1995.
Electrochemistry. Cyclic voltammetry experiments were conducted
by using a BAS50w potentiostat (Bioanalytical Sciences) with a
platinum wire auxiliary electrode, a platinum working electrode, and a
silver reference electrode. Experiments were performed anaerobically
in a Vacuum atmospheres Inert Atmosphere box. Spectroelectro-
chemistry investigations were performed by using an optical cell in
which a platinum gauze working electrode was sandwiched between
two quartz windows. Anaerobic, dry, solvents were used and the sample
purged with argon during the experiment. Absorption spectra were
acquired on a Hewlett-Packard HP8453 diode array spectrophotometer.
In both sets of experiments 0.1 M tetra-n-butylammonium hexa-
fluorophosphate was used as an electrolyte and ferrocene was added
3
7,57
as an internal standard.
(59) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.
(56) There remains some confusion in the literature over the appropriate
(60) Tsai, H.-H.; Hamilton, T. P.; Tsai, J.-H. M.; Harrison, J. G.;
Beckman, J. S. J. Phys. Chem. 1996, 100, 6942-6949.
(61) Peng, C.; Schlegel, H. B. Isr. J. Chem. 1993, 33, 449-54.
(62) Witanowski, M.; Stefaniak, L.; Webb, G. A. Annu. Rep. NMR
Spectrosc. 1993, 25, 1-480.
reference sample and chemical shift scale to use in nitrogen NMR
11,62,63
spectroscopy.
In our experiments nitromethane was used as an external
reference at 0 ppm and signals observed at lower field assigned positive
chemical shifts. Thus, on this scale, MeNO2 δ 0.0 ppm, KNO3 (1 M,
D2O, pD 8) δ -3.5 ppm, NaNO2 (1 M, D2O, pD 9.4) δ 232.0 ppm,
(63) Mason, J. In Multinuclear NMR; Mason, J., Ed.; Plenum Press: New
York, 1987; pp 335-368.
(CH3)3CSNO (0.25 M, d8-toluene) δ 453.5 ppm.