Transcript sev-benz ozu.pptx

Structure of the
SEVOFLURANE-BENZENE
complex as determined by CP-FTMW spectroscopy
Nathan A. Seifert, Daniel P. Zaleski, Justin L. Neill, Brooks H. Pate
University of Virginia
Alberto Lesarri, Montserrat Vallejo
Universidad de Valladolid
Emilio J. Cocinero, Fernando Castano
Universidad de País Vasco, Bilbao
Isabelle Kleiner
Laboratoire Interuniversitaire des Systèmes Atmosphériques
Sevoflurane Monomer
• Last year, Lesarri et al.1 published a
microwave and ab-initio study of
the sevoflurane monomer.
• A DFT study of the torsional
potential energy surface of the
monomer reveals a single global
minimum (CG), with two equivalent
local minima (TR) corresponding to
180° degree rotations of the isopropyl
group
1 A.
Lesarri, et al. Phys. Chem. Chem. Phys. 2010, 12, 9624-9631
• Global minimum structure fit
experimentally, as well as 5
isotopologues corresponding to
sevoflurane singly substituted
with 13C at all four positions, as
well as the 18O substitution.
Previous Study
Last year, Dom et al. published an IR/Raman study of the sevoflurane-benzene complex
Two clusters observed in Raman and IR slit jet and in liquid xenon cryosolution:
Most abundant;
formation enthalpies
similar but isopropylbonded species is
entropically favored
J. J. J. Dom et al. Phys. Chem. Chem. Phys., 2011, 13, 14142.
Why Benzene?
• Although the mechanism for anesthetic action
is currently not well understood, studies suggest
a path via direct binding to synaptic
ligand/voltage-gate ion channel proteins2.
• MD studies with the related ether anesthetic,
halothane, suggest binding to hydrophobic residues,
such as in nicotinic acetylcholine receptor
(figure on left)3.
Conclusion
Benzene provides a suitable choice
to study non-covalent, potentially
biochemically relevant, interactions with
sevoflurane.
• Additionally, a CD/NMR study from 2005 of
sevoflurane with a four-α-helix bundle
suggests binding interactions to phenylalanine
residues4 in the bundle.
2
N.P. Franks, et al. Nature, 1998, 396, 324.
Brannigan, et al. PNAS. 2010, 107, 14122-14127.
4 R. Pidikiti, et al. Biochem. 2005, 44, 12128-12135.
3 G.
Experimental
24 Gs/s
AWG
2-8 GHz (top figure5):
• Spectra taken with both perpendicular (as shown)
and coaxial alignments.
• Coaxial alignment, although limited to one
nozzle, narrows linewidths not only by minimizing
Doppler broadening, but also by lengthening the T2
dephasing time:
• FID collection time doubles from 40 to 80 μs
• Perpendicular limited to 2 nozzles.
• ~25 kHz FWHM in coaxial, ~120 kHz in
perpendicular
6.5-18 GHz (bottom figure6):
• Only perpendicular arrangement used
• 3 nozzles
5 J.L.
Neill, et al. J. Mol. Spec. 2011, 269, 21-29.
Brown, et al. Rev. Sci. Instru. 2008, 59, 053103.
6 G.G.
50 Gs/s
Results
M05-2X/6-31G+(d,p) calculations suggest a cluster structure containing the sevoflurane
conformer predicted and fit by Lesarri, et al., with a C-H∙∙∙π interaction between the isopropyl
hydrogen and the benzene ring, as shown below:
Parameter
M05-2X
Experimental*
A (MHz)
512.4934
508.0895
B (MHz)
372.8137
358.8252
C (MHz)
350.4249
338.3186
μa (D)
2.34
-
μb (D)
0.33
-
μc (D)
1.68
-
* Experimental constants determined by averaging constants for A1 and B2
torsional symmetry states
Problem: Internal rotation with six-fold symmetry
Internal Rotation
C6 symmetry, high barrier rotor
MP2/6-311G++(d,p) predicts 48 cm-1 barrier
Standard PAM fit with a minimum of
parameters gets good results
• Iα fixed to benzene C constant
(assume rotor axis normal to ring plane)
• A/B/C fixed to average of A and B
state fits (RMS ~2 kHz for each)
A, B, C
fixed
B, C
fixed
All float
N
138 (a)
86 (b)
-
-
Jmax
11 (a)
9 (b)
-
-
RMS (kHz)
92 (a)
55 (b)
75 (a)
43 (b)
63 (a)
34 (b)
V6 = 33(3) cm-1
Internal Rotation
Parameter
Operator
Value
A (MHz)
J a2
502.23(5)
B (MHz)
Jb2
338.03(7)
C (MHz)
J c2
364.95(1)
DJK (kHz)
-J2Ja2
0.64(2)
Dab (MHz)
{Ja , Jb}
17.65(8)
Dac (MHz)
sin(3α){Ja,Jc}
24.1(1)
NV (MHz)
(1-cos(6α))J2
5.5(1)
In terms of input, functionally similar to
a 3-fold rotor with two torsional states;
V6bc (MHz)
(1-cos(6α))(Jb2-Jc2)
14.1(4)
K2 (MHz)
(1-cos(6α))Ja2
-76(5)
These “virtual” torsional states are
connected by fitting higher order
torsion-rotation coupling terms
ρ (unitless)
PαJa
0.1724(6)
F (GHz)
Pα2
[3.453]
V6 (cm-1)
(1-cos(6α))/2
32.8807(3)
Application of BELGI7,8
improves fit dramatically
Fit by combining C6 quartet into
two pairs (B, E2) and (A, E1) in C3 basis:
(B, E2): vt = 1←1
(A, E1): vt = 0←0
5.1 kHz fit for 135 lines up to J =11!
7
8
I. Kleiner and J. T. Hougen, J. Chem. Phys., 2003, 119, 5505.
R. J. Lavrich, et al. J. Chem. Phys. , 2003, 119, 5497-5504.
#
135
RMS (kHz)
5.1
Sevoflurane Monomer
0 .2% SF .2% Benzene Neon coax 258k avg
0.2% SF 0.2% Benzene Neon coax 258k avg
vt = 1←1
vt = 0←0
Substitution Structure
• Experiment performed using .2% / .2% sevoflurane/benzene-d1 in 100 psi Ne
• Using d1 benzene breaks the symmetry of the rotor
• Rotor quartet per transition  6 singlets per transition, each representing a rigid
rotor for a singly deuterated position on benzene
All but D(6) were assigned in 2-8 GHz spectrum. H(6) required sensitivity improvements in
6-18 GHz arrangement to detect.
NS*
D(1)
D(2)
D(3)
D(4)
D(5)
D(6)
A (MHz)
508.0895
505.636
506.204
504.073
503.896
504.460
505.453
B (MHz)
358.8253
356.432
355.462
357.394
356.778
355.831
355.445
C (MHz)
338.3186
335.439
335.479
335.338
336.551
337.133
335.768
9
J. Kraitchman. Am. J. Phys., 21, 1953, 17-24.
* Average of A1 and B2 rotational constants
0.2% sevoflurane/0.2% benzene-d1
Neon, coaxial, 316k avg
Sevoflurane
positions adapted
from Lesarri et al.
Substitution Structure
D(5)
D(1)
D(4)
D(2)
D(3)
D(6)
D(5)
D(4)
D(6) transitions
much weaker
D(3)
D(6)
•
Sevoflurane coordinates taken from Lesarri et al.
•
Benzene experimentally planar, with a small ~5° tilt relative to isopropyl C-H bond
D(6)
2.34 Å
92.35°
95.61°
83.87°
Conclusions & Future Work
Conclusions:
• Substitution structure fit and calculated for the sevoflurane-benzene complex
• ~5 KHz fit for the high-barrier six-fold rotor, with a barrier of approximately 33 cm-1
• Additional work needed on adapting RAM fit to the principal axis frame
• PAM fit still satisfactory on predicting barrier height, as compared to RAM fit
• Suggests that non-rigidity might not play a huge role in perturbing the torsion
Future work:
• Expanding library to other volatile anesthetics
• No success with desflurane (Suprane)/benzene yet
• Isoflurane or halothane have yet to be studied in this context
• New binding candidates?
• Tyrosine has been suggested as a potential binding partner for halothane10 – phenol?
• Other hydrophobic candidates might require laser ablation for gas-phase studies.
10
D.C. Chiara, et al. Biochem. 42, 2003, 13457-13467.
Acknowledgements
Thanks for listening!
Research at UVa was supported by: National Science Foundation MRI-R2 project (0960074).