The urea-water complexurea-water complex observed by jet cooled Fourier-transform

microwave spectroscopy and studied by ab initio calculations.

J.-R. AVILES-MORENO, A. CUISSET, T. DELEPORTE, T.R. HUET, D. PETITPREZ.

Physique des Lasers, Atomes et Molécules

UMR 8523 CNRS – Université Lille 1, 59655 Villeneuve d’Ascq Cedex, France

60th OSU International Symposium on Molecular Spectroscopy

June 20-24, 2005

ContentContent Motivations:

Urea: history and structure

Urea-water complexUrea-water complex

Ab initio structure of the Urea-water complex

Experimental set-up: MB-MWFTS

Experimental spectrum:

Lines with H2O

Lines with D2O

Determination of a first experimental structure

Conclusions and outlook

•One of the Nature’s simplest biomolecule.

•A simplest diamide with 3 coordination sites.

•Important role in pharmaceutical chemistry

•Powerfull protein denaturing agent

•Anti-viral agent

Urea: history and structureUrea: history and structure (NH2)2C=O

b

a

• In the solid phase : planar a (C2v symmetry), intensive network of H-bonds

• In the gas phase : nonplanar and relatively floppy

microwave spectra b

ab initio calculations

MP2 / 6-311++G(d,p)

most stable conformer : anti form

a A S. Swaminathan et al, Acta Crystallogr., Sect B : struct. Sci. 40, 398, (1984)

b P. D. Godfrey, R. D. Brown and A. N. Hunter, J. Mol. Struct. 413-414, 405, (1997)

Urea: history and structureUrea: history and structure (NH2)2C=O

E/ kJ/mol

148 192180

5 kJ/mol

2

1

b

a

Conformer Plane C2v

1 Conformer Anti C2

2 Conformer Syn Cs

b

a

• To study the micro-solvation process of bio-molecules : possible bridge between the gas phase and the liquid phase

• To understand the hydrogen bond formation.

• Possible comparison between physico-chemical data

coming from experiment and ab initio calculations.

UREA - WATER COMPLEX : motivation of the workUREA - WATER COMPLEX : motivation of the work

1 Conformer H11 Anti Cs

ab

Ab initio calculations at the B3LYP / aug-cc-pVTZ level of theory

Similar to formamide-water: F.J. Lovas et al J. Chem. Phys. 88(2) 722-729(1988)

UREA - WATER COMPLEX : UREA - WATER COMPLEX : Ab initioAb initio structure structure

0

1

3

0.7

3.6

130 180 230

2

Dihedral angle H11-O10-O2-C1 / °

E/ kJ/mol

P.-O. Astrand, A. Wallqvist, G. Karlström, J. Chem. Phys. 100 (1994) 1262.

ab1.85 Å

2.09 Å

• Spectra recorded with a pulsed-nozzle MB-MWFTS in the 6-20 GHz frequency range.

• Optimization of the signal : T(K), carrier gas and pressure

Heated nozzle T= 363-403 K

Mirror

Inside resonator

Carrier gas P= 2-5 barCarrier gas+ H2O

Urea powder

H2O40 mm

Teflon

Experimental set-up: MB-MWFTSExperimental set-up: MB-MWFTS

• Large survey scan in the 6-20 GHz frequency range with a mixture of :

((1414NHNH22))2 2 C=OC=O + HH22OO ((1515NHNH

22))2 2 C=OC=O + HH22OO

((1414NHNH22))2 2 C=OC=O + DD22OO ((1515NHNH

22))2 2 C=OC=O + DD22OO

• 4 strong lines around 12 GHz12 GHz which can be identified as

the JJka,kcka,kc==111111-0-00000 b-type transitions.

• Other lines around 17 GHz do not match with the urea-

water complex (Jka,kc=212-101 transition for example).

Experimental spectraExperimental spectra

Tests : with and without water ; different carrier gases (Ne, Ar, He)

T°C = 115 °C carrier gas : Ne at a total pressure of 3 bars

Experimental spectra: Experimental spectra: Lines with HLines with H22OO

14NH2CO14NH2– H2O15NH2CO15NH2 – H2O

0.2 MHz

3.0 MHz

111 000111000

~ 300MHz

15NH2CO15NH2

111 000

14NH2CO14NH2

111000

Hyperfinestructure

Splitting ~ 300MHz

Tests : with and without water ; different carrier gases (Ne, Ar, He)

T°C = 115 °C carrier gas : Ne at a total pressure of 3 bars

Experimental spectra: Experimental spectra: Lines with DLines with D22OO

0.2 MHz

3.0 MHz

14NH2CO14NH2– D2O15NH2CO15NH2– D2O

111000111000

~ 270 MHz

MHz

14NH2CO14NH2– H2O15NH2CO15NH2 – H2O

0.2 MHz

3.0 MHz111 000

111000

~ 300MHz

• Calculation of the water molecule’s cartesian coordinates in the principal inertia axis of urea as a function of 2 internal coordinates (ρ and φ).

• Determination of the complex new inertia tensor, and diagonalisation.

• Calculations of the A, B and C rotational constants for each value of ρ and φ (-40° < ρ < 40° by step of 1° and -90° < φ < 90° by step of 1° )

• Comparison between (A+C)calc and (A+C)obs

Determination of a first experimental structureDetermination of a first experimental structure

principal inertia axis of urea

2 internal rotations for H2O :

ρ : around the 2O-5H axis

φ : rotation of the 11H atom around the 9H-10O bond

H-bond length fixed to 1.9 Å

a

b

ρ

φ

Determination of a first experimental structureDetermination of a first experimental structure

φ (°)

ρ (°)

(MHz)

= | (A+C)calcd- (A+C)obsd | < 10 MHz

for 47° < ρ <50° and 40°< φ <70° 14N14N - H2O

Determination of a first experimental structureDetermination of a first experimental structure

(A+C)calc (A+C)obs

ρ = 47°

φ = 55°

14N14N - H2O 12285 12285

15N15N - H2O 11987 11977

ρ = 49°

φ = 55°

14N14N - D2O 11770 11741

15N15N - D2O 11489 11475

rr 11=1.87Å=1.87Å

rr 22=1.

87Å

=1.

87Å

=90°=90°

Determination of a first experimental structureDetermination of a first experimental structure

Our model Ab initior1 / Å 1.87* 1,85r2 /Å 1.87* 2alpha /° 90 60* Fixed value

• First experimental observation of the urea-water

complex.

• Searching for more urea-water complex lines.

• Possibility of a large amplitude motion of the H11

atom.

• Change of the H-bond length when going from

H2O to D2O.

• In progress: analysis of the hyperfine structure

Conclusions and outlookConclusions and outlook

t

detectionsource

polar gas

t0

Molecules

2

Application rule : maximum polarization for a /2 pulse, i.e.

Physical parameters : : permanent electric dipole moment

: amplitude of the microwave field

: length of the microwave pulse

Source of microwave pulseSource of microwave pulse (2-20 GHz)(2-20 GHz)

Matter-light interactionMatter-light interactionInside a Pérot-Fabry resonatorInside a Pérot-Fabry resonator

Polarization of the polar molecules ;Polarization of the polar molecules ;Rotational coolingRotational cooling

Detection and recording of the signalDetection and recording of the signalEmitted by the molecules Emitted by the molecules

As a function of timeAs a function of time

Fourier transform of the transient signal Fourier transform of the transient signal Frequency analysis Frequency analysis

Experimental set-up: MB-MWFTS

Resonant cavity and pulsed supersonic

beam

Spectral range : 6 – 20 GHz

Sensitivity : 10-11 cm-1

Resolution : 10 kHz

Accuracy : 2.4 kHz

Rot. temp. : 4 K

Pressures :Carrier gas: 1-3 barsMolecules: 10-2 bar

Secondary pumpingLabview interfaceScan : 1GHz/12h

Experimental set-up: MB-MWFTS

Heated nozzle 363 K

Benzamide powder

1.5 bar ArCarrier

gazCavity

Gas mixture

Vacuum-tightrotation transitionand step by step motor

Gaussian envelop(Ws= 42 mm at 12 GHz)

MW pulse

detection

pump

600 mm<d< 650 mm

R=800 mm

s

Interrupteurrapide

t

Impulsion microonde de 1 à 2 s

Synthétiseur2-20 GHz

Cavité PF

Amplificateur

A/D

FI = 30 MHz

Synthétiseur2-20 GHz

Mélangeur

Filtre passe-bande

Amplificateur RF

Convertisseur A/D

s+30 MHz

•Transition rotationnelle•Dédoublement Doppler