Conformational Flexibility in Hydrated Sugars: The Glycolaldehyde-Water Complex

Juan-Ramon Aviles-Moreno, Jean Demaison and Thérèse R. Huet

Laboratoire de Physique des Lasers, Atomes et MoléculesUMR 8523 CNRS – Université Lille 1, 59655 Villeneuve d’Ascq Cedex, France

OSU International Symposium on Molecular Spectroscopy meeting, June 19-23, in Columbus, Ohio, USA

17307,0 17307,2 17307,4 17307,6

Frequency (MHz)

CC-W-1

0+

0-

CC-W-1

CC-W-2

-80 -60 -40 -20 0 20 40 60 80

100

150

200

250

300

Hydroxyl group /deg

Fre

e O

H w

ater

gro

up /d

eg

CC-W-1

CC-W-2

CC-W-1

CC-W-1

Glycolaldehyde: the simplest sugar

structural formula : CH2OHCHO

• Marstokk, K.-M.; Møllendal, H. J. Mol. Struct. 1970, 5, 205-213.• Butler, R. A. H.; De Lucia, F. C. ; Petkie, D. T.; Møllendal, H. ; Horn, A. ; Herbst, E. Ap. J. Supp. Ser. 2001, 134, 319-321.• Weaver, S. L. W.; Butler, R. A. H.; Drouin, B. J.; Petkie, D. T.; Dyl, K. A.; De Lucia, F. C. ; Blake G. A. Ap. J. Supp. Ser. 2005, 158, 188-192.

• Ratajczyk, T.; Pecul, M.; Sadlej, J.; Helgaker, T. J. Phys. Chem. A 2004, 108, 2758-2769.• Senent, M. L. J. Phys. Chem. A 2004, 108, 6286-6293.

Experimental : micro-wave and millimeter-wave datas

Ab initio calculations : structure + energy of 4 conformers (MP2/aug-cc-pVTZ and MP4/cc-pVQZ)

A=18.474 GHzB=6.548 GHzC=4.984 GHzμa=0.4D μb=2.3D μc=0.0D

Glycolaldehyde 1 CC (C2v) (E = 0.0 kJ/mol)

2 TTE = 14.63 kJ/mol

3 TGE = 15.39 kJ/mol

4 CTE = 21.72 kJ/mol

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Hydrated glycolaldehyde (GA-W)

Structures optimized at the B3LYP/6-311++G(2df,p) level of theory Energies: the Gaussian-3 (G3) compound method was used in its

G3MP2B3 version as implemented in Gaussian 03 The two lowest experimentally accessible energy structures were also

optimized using the B3LYP/aug-cc-pVTZ level of theory.

CC-W-1 (0 kJ/mol)

197.5

186.4

CC-W-2 (2.12 kJ/mol)

186.0

197.4

CC-W-3 (4.03 kJ/mol)

194.4

209.6

CC-W-4 (5.83 kJ/mol)

200.0

214.2

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Conformers CC-W-1 and CC-W-2

CC-W-1 CC-W-2

GA skeleton:

4O-7H/pm 97.6 97.5

3C-4O-7H/deg 110.88 111.49

1O-2C-3C-4O/deg - 10.5 10.8

7H-4O-3C-2C/deg 46.9 44.1

Water skeleton:

9H-10O/pm 97.2 97.1

11H-10O/pm 96.2 96.1

9H-10O-11H/deg 106.42 106.57

GA-W:

7H-10O/pm 186.5 186.6

9H-1O/pm 195.4 195.2

10O-9H-3C-2C/deg 161.1 169.6

11H-10O-1O-2C/deg 135.5 255.5

CC-W-1 (0 kJ/mol)

197.5

186.4

Principal Bond Lengths, Bond Angles, and Dihedral Angles (B3LYP/aug-cc-pVTZ )

CC-W-2 (2.12 kJ/mol)

186.0

197.4

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The experimental setup

Microwave Fourier transform spectrometer (6-20 GHz) coupled to a supersonic molecular jet

* GA dimer: crystalline mixture of stereoisomers (Sigma Aldrich, purity 98%)

Heated nozzle T= 363 K

Mirror

Inside the

cavity…

Glycolaldehyde *Carrier gas P= 3 bars (Ne)

Carrier gas+ H2O

H2O cavityCo

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9000 10000 11000 12000 13000 14000 15000 160001E-7

1E-6

1E-5

1E-4

1E-3

Inte

nsi

ty (

a. u.)

Frequency (MHz)

2 12-1 11

2 02-1 01

2 12-1 01

2 11-1 10

3 03-2 12 3 13-2 12

3 03-2 02

9000 10000 11000 12000 13000 14000 15000 160001E-7

1E-6

1E-5

1E-4

1E-3

Inte

nsi

ty (

a. u.)

Frequency (MHz)

2 12-1 11

2 02-1 01

2 12-1 01

2 11-1 10

3 03-2 12 3 13-2 12

3 03-2 02

2 12-1 11

2 02-1 01

2 12-1 01

2 11-1 10

3 03-2 12 3 13-2 12

3 03-2 02

GA-W: (JKaKc)’-(JKaKc)’’

The microwave spectrum of GA-W Signals: GA (red dots), water dimer (blue circles), GA-W (assigned lines)

Decomposition products: Acetic acid, formic acid and formaldehyde (high T). Methyl formate was not detected

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GA-W: the molecular parameters

Constants 0+ 0-

A/MHz 5616.5972(13) 5616.6051(13)

B/MHz 3483.4258(14) 3483.4321(14)

C/MHz 2285.7921(8) 2285.7929(8)

J/kHz 6.45(4) 6.47(4)

JK/kHz -14.24(14) -14.50(14)

K/kHz 21.94(11) 21.31(11)

J/kHz 1.958(20) 1.934(20)

K/kHz 5.16(25) 6.00(25)

Std/kHz 4.1 4.3

/amu.Å2 -13.9648(2) -13.9645(2)

The Doppler components are splitted (30 kHz):

17307,0 17307,1 17307,2 17307,3 17307,4 17307,5 17307,6

5,00E-008

1,00E-007

1,50E-007

2,00E-007

Frequency (MHz)

Inte

nsity

(a. u

.)

0+

0

17307,0 17307,1 17307,2 17307,3 17307,4 17307,5 17307,6

5,00E-008

1,00E-007

1,50E-007

2,00E-007

Frequency (MHz)

Inte

nsity

(a. u

.)

0+

0

Semirigid rotor: Ir representation, A reduction. = -0.28.

Large amplitude motion associated with two equivalent structures ?

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Conformational assignment

Exp. CC-W-1 CC-W-2 CC-W-3 CC-W-4

VTZ (2df,p) VTZ (2df,p) (2df,p) (2df,p)

A/MHz 5616.6 5551.8 5545.0. 5577.8 5559.2 9883.4 17731.3

B/MHz 3483.4 3595.6 3592.4 3553.6 3562.5 1887.4 1675.5

C/MHz 2285.8 2309.4 2309.1 2277.1 2283.4 1877.9 1545.3

/amu.Å2 -13.96 -12.75 -12.96 -10.88 -11.44 -49.78 -3.09

a/D strong -1.2 -1.1 -1.6 -1.5 -0.5 0.1

b/D medium 0.6 0.7 1.2 1.3 1.5 0.6

c/D - 0.2 0.2 2.4 2.5 1.4 0.0

The identity of the experimentally detected conformer is CC-W-1

CC-W-1 (0 kJ/mol)

197.5

186.4

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Tunneling effect

Structure of the transition state TS 1 (17.72 kJ/mol):

Simple model:

« Mirror »

TS 1

CC-W-1 CC-W-1

17307,0 17307,1 17307,2 17307,3 17307,4 17307,5 17307,6

5,00E-008

1,00E-007

1,50E-007

2,00E-007

Frequency (MHz)

Inte

nsity

(a. u

.)

0+

0

17307,0 17307,1 17307,2 17307,3 17307,4 17307,5 17307,6

5,00E-008

1,00E-007

1,50E-007

2,00E-007

Frequency (MHz)

Inte

nsity

(a. u

.)

0+

0

The conformational flexibility was investigated through a two dimensional potential energy surface calculated along the hydroxyl group (i. e. the 7H-4O-3C-2C dihedral angle) and the free OH water group (i. e. the 11H-10O-1O-2C dihedral angle) coordinates, and associated with the two most stable conformers (CC-W-1 and CC-W-2).

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Conformational flexibility

The grid was built by steps of 5 degrees, as a function of the energy by optimizing the structure of the 1440 grid points at the B3LYP/6-31G* level of the theory. The structure of all the maxima and minima was also optimized at the B3LYP/6-311++G(2df,p) level. Finally the energy of the maxima and minima was calculated at the MP2/cc-pVQZ level of theory.

Results:

TS1: 17.72 kJ/mol

TS2: 4.36 kJ/mol

TS3: 4.98 kJ/mol

CC-W-1: 0 kJ/mol

CC-W-2: 2.36 kJ/mol-80-60-40-20

020

4060

80

02468

10121416182022

100150

200250

300

CC-W-1

CC-W-2

TS 1

TS 3 TS 2Co

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Conformational flexibility

The splitting of the lines is due to a tunneling effect between two equivalent structures of the CC-W-1 conformers.

The energetically favourable path involves TS2, CC-W-2, and TS3.

-80 -60 -40 -20 0 20 40 60 80

100

150

200

250

300

Hydroxyl group (7H-4O-3C-2C/deg)

Fre

e O

H w

ate

r gro

up (

11H

-10O

-1O

-2C

/deg)

CC-W-1

CC-W-2

TS2

TS3

TS2

TS3

TS1

CC-W-1

CC-W-2

CC-W-1TS1

CC-W-1

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Acknowledgment

The Institut du Développement des Ressources en Informatique Scientifique (contract IDRIS 51715, France)

The Programme National de Physico-Chimie du Milieu Interstellaire (PCMI, France)

17307,0 17307,2 17307,4 17307,6

Frequency (MHz)

CC-W-1

0+

0-

CC-W-1

CC-W-2

-80 -60 -40 -20 0 20 40 60 80

100

150

200

250

300

Hydroxyl group /deg

Fre

e O

H w

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gro

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eg

CC-W-1

CC-W-2

CC-W-1

CC-W-1

Manuscript submitted to the J. Am. Chem. Soc.

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