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Are C-H∙∙∙O interactions linear? Are C-H∙∙∙O interactions linear? The case of aromatic CH donors The case of aromatic CH donors

DuDuššanan Ž. Ž. VeljkoviVeljkoviććaa,, Goran Goran V. JanjiV. Janjiććbb, , SneSnežžanaana DD. . ZariZariććaa

aaDepartment of Chemistry, University of Belgrade, Studentski trg Department of Chemistry, University of Belgrade, Studentski trg 16, 11000 Belgrade, Serbia16, 11000 Belgrade, Serbia

e-mail: vdusan@chem.bg.ac.rse-mail: vdusan@chem.bg.ac.rsbbICTM, Njegoševa 12, 11 000 Belgarde, SerbiaICTM, Njegoševa 12, 11 000 Belgarde, Serbia

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Non-covalent C-H∙∙∙O interactions are Non-covalent C-H∙∙∙O interactions are of great importance in chemistry, of great importance in chemistry, biology and biochemistrybiology and biochemistry

They play prominent role in crystal They play prominent role in crystal packing, conformational control, packing, conformational control, stabilizing protein structures and stabilizing protein structures and DNA base pairsDNA base pairs

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WWater/aromatic ater/aromatic interactions interactions

OH/π interaction C-H…O interaction

Parallel alignment interactions

Aromatic molecules can form few types of weak hydrogen bonds:Aromatic molecules can form few types of weak hydrogen bonds:

B. D. Ostojić, G. V. Janjić, S. D. Zarić, Chemical Communications (48), 6546-6548, (2008). G. V. Janjić, D. Veljković, S. D. Zarić, Crystal Growth & Design (2011), in press

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Directionality of C-H∙∙∙O Directionality of C-H∙∙∙O interactionsinteractions

One of the most important One of the most important characteristics of hydrogen bondscharacteristics of hydrogen bonds

Based on directionality it was shown Based on directionality it was shown that the C–H···O interactions, that the C–H···O interactions, although can be weak, are hydrogen although can be weak, are hydrogen bonds and not the van der Waals bonds and not the van der Waals interactionsinteractions

T. Steiner and G. R. Desiraju, Chem. Commun., (1998), 891-892.

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However…However…

Are C-H∙∙∙O interactions REALLY Are C-H∙∙∙O interactions REALLY

linear?linear?

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Geometry of C–H•••O interactions of aromatic Geometry of C–H•••O interactions of aromatic C–H donors was studied using crystal C–H donors was studied using crystal structures from the Cambridge Structural structures from the Cambridge Structural Databank (CSD)Databank (CSD)

Crystal structures involving CCrystal structures involving C66-H aromatic -H aromatic groups and oxygen atoms were screened for groups and oxygen atoms were screened for intermolecular contactsintermolecular contacts

Following systems with oxygen atom were Following systems with oxygen atom were taken: HOH (non-coordinated), HOZ, Ztaken: HOH (non-coordinated), HOZ, Z11OZOZ22, , O=CZ and O=YZ (Z, ZO=CZ and O=YZ (Z, Z11, and Z, and Z22 are not are not hydrogen atoms, Y is not carbon atom) hydrogen atoms, Y is not carbon atom)

Data screeningData screening

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The preference for linear geometries The preference for linear geometries in in

C–H∙∙∙O interactions of aromatic C-C–H∙∙∙O interactions of aromatic C-H groups was observed by the H groups was observed by the distributions of angle α distributions of angle α

To obtain more reliable data cone To obtain more reliable data cone correction was used correction was used

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Cone correctionCone correction

The angle covered by an angular The angle covered by an angular interval interval ΔαΔα is smaller for nearly is smaller for nearly linear angles linear angles αα then for bent ones then for bent ones

Angular distribution must be Angular distribution must be weighted by a correction factor weighted by a correction factor 1/sin1/sinαα to properly reflect angular to properly reflect angular preferencespreferences

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For the purpose of this analysis, we used For the purpose of this analysis, we used parameters which were directly retrieved parameters which were directly retrieved from CSD (H…O distance d, angle from CSD (H…O distance d, angle αα), as well ), as well as parameters which were derived (distances as parameters which were derived (distances R, r and angle R, r and angle φφ).).

We search for structures in which the distance We search for structures in which the distance between the O atom of the water molecule between the O atom of the water molecule and the H atom of the Cand the H atom of the C66 - aromatic ring is - aromatic ring is less than 2.8 Å, and the angle α greater than less than 2.8 Å, and the angle α greater than 110°110°

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Non-corrected and corrected distributions of Non-corrected and corrected distributions of angle α for C–H∙∙∙O interactions of C-H angle α for C–H∙∙∙O interactions of C-H aromatic donors with different types of aromatic donors with different types of acceptorsacceptors

0.0

5.0

10.0

15.0

20.0

25.0

110-120

120-130

130-140

140-150

150-160

160-170

170-180

α(˚)

%

H2O

HOZ

Z1OZ2

O=CZ

O=YZ

0.0

5.0

10.0

15.0

20.0

25.0

110-120

120-130

130-140

140-150

150-160

160-170

170-180

α(˚)

%

H2O

HOZ

Z1OZ2

O=CZ

O=YZ

Non-corrected Non-corrected Corrected Corrected

1111

Distributions of angle φ for C–H∙∙∙O Distributions of angle φ for C–H∙∙∙O interactions of CH aromatic donors with interactions of CH aromatic donors with different types of acceptorsdifferent types of acceptors

-5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40

φ(˚)

%

H2OHOZ1Z2OZ1O=CO=Z

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Type of the atom in the o-position influence linearityType of the atom in the o-position influence linearity

Influence of substituents in o-position on linearity of C–H∙∙∙O interactions

0.0

5.0

10.0

15.0

20.0

25.0

30.0

110- 120

120- 130

130- 140

140- 150

150- 160

160- 170

170- 180

α (°)

%

H2O

HOZ

Z2OZ1

O=CZ

O=YZ

0.0

5.0

10.0

15.0

20.0

25.0

30.0

110- 120

120- 130

130- 140

140- 150

150- 160

160- 170

170- 180

α (°)

%

H2OHOZZ2OZ1O=CZO=YZ

0

5

10

15

20

25

30

35

110- 120

120- 130

130- 140

140- 150

150- 160

160- 170

170- 180

α (°)

%

HOZ

Z2OZ1

O=CZ

O=YZ

0

5

10

15

20

25

30

35

110- 120 120- 130 130- 140 140- 150 150- 160 160- 170 170- 180

α (°) coor

%

HOZ

Z2OZ1

O=CZ

O=YZ

H atom in H atom in o-positiono-position

Cl atom in Cl atom in o-positiono-position

Non-corrected CorrectedNon-corrected Corrected

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Diagrams showing the distribution of Diagrams showing the distribution of angle φ for C–H∙∙∙O interactions of C-angle φ for C–H∙∙∙O interactions of C-H aromatic donors with different types H aromatic donors with different types of acceptors. of acceptors.

-5

0

5

10

15

20

25

30

35

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40

φ (°)

%

H2O

HOZ

Z1OZ2

O=CZ

O=YZ

-5

0

5

10

15

20

25

30

35

40

45

0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40

φ (°)

%

HOZ

Z2OZ1

O=CZ

O=YZ

X=H X=H X=ClX=Cl

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Ab initio calculationsAb initio calculations

Ab initio calculations were performed Ab initio calculations were performed on three model systems: benzene-on three model systems: benzene-water, benzene-methanolwater, benzene-methanol and and benzene-acetonebenzene-acetone

Four different orientations of Four different orientations of acceptor molecules were consideredacceptor molecules were considered

Linear Linear BifurcatedBifurcated

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Ab initio calculationsAb initio calculations

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CONCLUSIONSCONCLUSIONS

Preference for the linear contact depends on the Preference for the linear contact depends on the type of the atom in the o-position to the interacting type of the atom in the o-position to the interacting C-H groupC-H group

The C–H•••O interactions of the aromatic The C–H•••O interactions of the aromatic molecules with two hydrogen atoms in the o-molecules with two hydrogen atoms in the o-position do not show preference for the linear position do not show preference for the linear contacts contacts

Nonlinear interactions are not energetically Nonlinear interactions are not energetically disfavored because of simultaneous interactionsdisfavored because of simultaneous interactions

This result is very important because it can help in This result is very important because it can help in the recognizing important C–H···O interactions in the recognizing important C–H···O interactions in biomolecules containing aromatic groups (proteins)biomolecules containing aromatic groups (proteins)D. Veljković, G. V. Janjić, S. D. Zarić, CrysEngComm (2011), accepted

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AcknowledgementAcknowledgement

Prof. SneProf. Snežana Zarićžana Zarić Goran JanjićGoran Janjić Vesna MedakovićVesna Medaković Dragan NinkovićDragan Ninković Dubravka VojislavljevićDubravka Vojislavljević Jelena AndrićJelena Andrić

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THANK YOUTHANK YOU