PROCEEDINGS

PURE AND APPLIED CHEMISTRY INTERNATIONAL

CONFERENCE 2013 (PACCON2013)

ISBN 978-974-384-495-9

COMMITTEE of PACCON2013

Academic Committee

International Academic Advisory Committee:

Prof. Dr.Peter Wolschann University of Vienna, Austria

Prof. Dr. Seiji Mori Ibaraki University, Japan

Prof. Dr. Jen-Shinag Yu National Chiao Tung University, Taiwan

Prof. Dr. Shigeo Goto Nagoya University, Japan

Prof. Dr. Pierpaolo Zuddas University Pierre et Marie Curie Paris-Sorborne, France

Prof. Dr. Minoru Isobe National Tsing Hua University, Taiwan

Prof.Dr. Kato Koichi Okazaki Institute for Integrative Bioscience, Japan

Prof.Dr. Toshio Nishikawa Nagoya University, Japan

Prof. Dr. Edman Tsang University of Oxford, UK

Prof.Dr. Irene K.P. Tan Institute of Biological Sciences, University of Malaya, Malaysia

Academic Advisory Committee:

Prof. Dr. Somsak Rujiravong Chulabhorn Graduate Institute

Assoc.Prof. Dr. Surin Laosooksathit Vice-President of Chemical Society of Thailand,

King Mongkut's Institute of Technology North Bangkok

Assoc. Prof. Dr. Supa Hannongbua Vice-President of Chemical Society of Thailand, Kasetsart

University

Assoc. Prof. Dr.Vudhichai Parasuk Chulalongkorn University

Academic Committee :

Chairperson : Assoc.Prof.Dr. Thanuttkhul

Mongkolaussavarat

Chulabhorn Graduate

Institute

Vice-Chairperson : Dr. Chuleeporn Puttnual Faculty of Science, Burapha

University

Dr. Chatchawin Petchlert

Dr. Anocha Sooksomboon

Analytical Chemistry Assoc. Prof. Dr. Orawon Chailapakul Chulalongkorn University

Inorganic Chemistry Prof. Dr. Thawatchai Tantulani Chulalongkorn University

Organic Chemistry and

Medicinal Chemistry

Assoc. Prof. Tirayut Vilaivan Chulalongkorn University

Physical and Computational

Chemistry

Assoc. Prof. Dr. Vudhichai Parasuk Chulalongkorn University

Material Sciences and

Technology

Prof.Dr. Jumras Limtrakul Kasetsart University

Polymer Chemistry Assoc.Prof.Dr. Ittipol Jangchud King Mongkut's Institute of

Technology Ladkrabang

Petroleum Chemistry and Assoc. Prof. Dr. Tawan Sooknoi King Mongkut's Institute of

Catalysis Technology Ladkrabang

Environmental Chemistry Prof. Dr. Chongrak Polprasert Thammasart University

Industrial Chemistry and

Innovation

Prof. Dr Suttichai Assabumrungrat Chulalongkorn University

Cosmetics Assoc. Prof. Dr Varaporn Junyaprasert Mahidol University

Chemical Education Asst. Dr. Ekasith Somsook Mahidol University

Biological/Biophysical

Chemistry and Chemical

Biology

Prof. Dr. Piamsook Pongsawasdi Chulalongkorn University

Bioinformatics Asst. Prof. Dr. Marasri

Ruengjitchatcaahawalya

King Mongkut's Institute of

Technology Thonburi

Free radicals / Antioxidants Prof. Emer. Dr. MaitreeSuttajit Phayao University

Food safety and Food

Chemistry

Assoc. Prof. Dr. SiriratKokpol Chulalongkorn University

Organizing Committee

Conference Chairman: Prof.Dr. Sompol Phongthai,

M.D

President of Burapha University

Advisory Organizing

Committee:

Assoc.Prof.Dr. Supawan

Tantayanon

President of Chemical Society of

Thailand

Assoc.Prof.Dr. Surin

Laosooksathit

Vice-President of Chemical Society of

Thailand

Assoc.Prof.Dr. Supa

Hannongbua

Vice-President of Chemical Society of

Thailand

Assist.Prof.Dr. Usavadee

Tantivaranurak

Dean of Faculty of Science, Burapha

University

Local Organizing Committee :

Chairperson: Assist.Prof.Dr. Usavadee Tantivaranurak

Committee : Dr. Chuleeporn Puttnual

Dr. Chatchawin Petchlert

Asst,Prof.Dr.Prapasiri Barnette

Asst,Prof.Dr. Jaray Jaratjaronpong

Dr. Nattapong Srisook

Dr. Nawasit Rakbamrung

Dr. Kanchaya Honglertkongsakul

Asst,Prof.Dr.Krisana Chinnasarn

Dr. Salil Chanroj

Dr. Anocha Suksomboon

Dr. Anuttara Udomprasert

Secretary :

Assist.Prof Dr. Ekaruth Srisook

Assistant Secretary : Dr. Karaked Tedsri

Dr. Panata Wanichwatanadecha

Dr. Songklod Sarapusit

Scientific Committee : Dr.Pornpen Atorngitjawat

Dr.Sirirat Chanvaivit

Asst,Prof.Dr.Jittima Charoenpanich

Asst,Prof.Dr.Supranee Kaewpirom

Dr. Somchart Maenpuen

Dr. Chatchawin Petchlert

Asst,Prof.Dr.Suchaya Pongsai

Asst,Prof.Dr.Ubolluk Rattanasak

Asst,Prof.Dr.Rungnapha Saeeng

Asst,Prof.Dr.Somsak Sirichai

Dr. Uthaiwan Siriou

Asst,Prof.Dr.Pitak Sootanan

Asst,Prof.Dr.Klaokwan Srisook

Asst,Prof.Dr.Jomjai Suksai

Asst,Prof.Dr.Orasa Suriyaphan

Dr. Prapapan Techasauvapak

Dr. Karaked Tedsree

Asst,Prof.Dr.Thanida Trakulsujaritchok

Organizers : Faculty of Science, Burapha University

Chemical Society of Thailand

P u r e a n d A p p l i e d C h e m i s t r y I n t e r n a t i o n a l C o n f e r e n c e 2 0 1 3

ELUCIDATING THE STRUCTURAL CHARACTERISTICS OF

1,4-POLYISOPRENE BASED ON QUANTUM CHEMICAL CALCULATIONS

Pornpan Pungpo1,*

, Saisamorn Lumlong1, Peter Wolschann

2,

Alfred Karpfen3 and Dieter Baurecht4

1 Department of Chemistry, Faculty of Science, Ubon Ratchathani University,

85 Sthollmark Rd., Warinchamrap, Ubonratchathani 34190, Thailand 2Department of Pharmaceutical Technology and Biopharmaceutics, Faculty of Life Sciences,

University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria 3 Institute for Theoretical Chemistry, University of Vienna, Währinger Straße 17, A-1090 Vienna, Austria

4 Institute of Physical Chemistry, University of Vienna, Althanstrasse 14, Vienna A-1090, Austria

* Author for correspondence; E-Mail: pornpan_ubu@yahoo.com, Tel. +66 45 353400 ext 4124, Fax. +66 45 288379

Abstract: Natural rubber has been used extensively in

many applications and products. Polyisoprene, mostly

cis-1,4-polyisoprene, is the main component in natural

rubber latex. Although the crystal structures of natural

rubber were previously studied, but no acceptable crystal

structure has been reported. Therefore, quantum

chemical calculations were performed on five systems of

monomer, dimer, trimer, tetramer and pentamer of 1,4-isoprene as the representative of cis-1,4-polyisoprene

with the aim to elucidate the structural behaviours and

conformation analysis of cis-1,4-polyisoprene. The

optimized geometries of five molecular targets were

carried out using high level of M062X calculations with

6-31G(d) and cc-pVDZ basis sets. The vibrational

frequencies of the optimized structures were then

calculated. The trend of calculated spectroscopic

properties agrees well with the experimentally

vibrational frequency spectra derived from the

experimental ATR-IR. The results obtained from the

present study are fruitful for better understanding of the

structural and vibrational spectra of cis-1,4-polyisoprene

within molecular level.

1. Introduction

Natural rubber from the tropical tree Hevea

brasiliensis, has been used to provide about one-

quarter of rubber based products trading worldwide [1-

2]. Natural rubber is a mixture of polyisoprene and

small amounts of other organic compounds as well as

proteins, fatty acids, resins and inorganic materials

(salts). Natural polymer of cis-1,4-polyisoprene is a

major component in natural rubber [3-4]. The crystal

structure of natural rubber has been studied by many

researchers [5-7]. However, no acceptable crystal

structure has been reported.

To predict the structural and vibrational modes of

1,4-polyisoprene, the quantum chemical calculations

based on the density functional theory (DFT) had been

performed. Five models based on number of 1,4-

polyisoprene monomers were used in this study. The

obtained results aid to fruitful the information data of

1,4-polyisoprene structures and vibrational frequencies

for spectroscopic characteristics of natural rubber.

2. Materials and Methods

2.1 Structures of 1,4-polyisoprene and quantum

chemical calculations

The structural models of 1,4-polyisoprene (n =1-5)

were constructed using the standard tool in

Guassview3.07 program as shown in Figure 1.

HC C

CH2

CH3

H2C HHn=1-5

Figure 1 General structure of 1,4-polyisoprene

Five models of 1,4-polyisoprene (n =1-5) were

calculated using Gaussian09 program. Fully geometry

optimizations and the related vibrational frequency

spectra calculations were performed using high level

density functional theory of the highly parametrized,

empirical exchange correlation functionals M062X

calculations with 6-31G(d) and cc-pVDZ basis sets.

3. Results and Discussion

3.1 The geometry optimizations of 1,4-polyisoprene

Five systems of the molecular structures of 1,4-

polyisoprene in the ground state (in vacuo) were

optimized using M062X calculations with 6-31G(d)

basis set. To validate the systems used in this study,

the distance from the backbone carbon to carbon atom

and the angles of 1,4-polyisoprene results obtained

from the calculations were compared with the

experimental data [5], as listed in Table 1. The results

show that two systems of 1,4-polyisoprene, trimer and

tetramer systems, are high correspondence to the

experimental data.

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Therefore, trimer and tetramer of 1,4-polyisoprene

systems can be accurately used as the representative

model of 1,4-polyisoprene for further study. To

validate the methods of calculations, the geometry

optimization using M062X with 6-31G (d) and cc-

pVDZ basis sets were performed. The bond lengths

and bond angles of 1,4-polyisoprene tetramer derived

from the calculations and experimental data were

compared as reported in Table 2. The results show that

the structural information derived from cc-pVDZ basis

set is high correspondence to the experimental data

compared to those of the calculated results obtained

from the 6-31G(d) basis set. Therefore, M062X

calculations with cc-pVDZ basis set are chosen for

further study. The optimized structures of 1,4-

polyisoprene trimer and tetramer calculated using

M062X/cc-pVDZ are illustrated in Figure 2.

(a) (b)

Figure 2 The optimized structures of 1,4-polyisoprene

trimer (a) and tetramer (b) calculated using M062X/

cc-pVDZ method

3.2 IR spectra and vibrational frequency results

The IR spectra of 1,4-polyisoprene trimer,

tetramer, and pentamer models were calculated using

M062X calculations with cc-pVDZ basis set as shown

in Figure 3. The calculated vibrational spectra show

similar within the range of 350-4000 cm-1

. Mainly, IR

spectra were found in three regions. First two regions

Table 1. The structural information of the optimized structures of 1,4-polyisoprene obtained from M062X/6-31G (d)

method

Expt. (a)

Calculated models

Mono Di Tri Tetra Penta

Bond length (Angstrom)

C1-C2 1.53 1.501 1.501 1.501 1.501 1.501

C2=C3 1.34 1.337 1.337 1.337 1.337 1.336

C3-C4 1.53 1.506 1.512 1.512 1.512 1.512

C4-C1' 1.54

1.543 1.543 1.543 1.542

Bond angle (degree)

C1-C2=C3 121.2 128.2 126.8 126.9 126.8 126.8

C2=C3-C4 129.0 125.0 123.3 123.4 123.3 123.3

C3-C4-C1’ 108.6 - 111.7 111.8 111.7 111.9

C4-C1’-C2’ 111.4 - 112.1 112.2 112.3 112.0 (a) the experimental data obtained from reference [5]

Table 2. The structural information of the optimized structures of the 1,4-polyisoprene tetramer derived from

different basis sets of calculations

Expt. (a)

M062X

6-31G(d) cc-pVDZ

Bond (Å)

C1-C2 1.53 1.501 1.500

C2=C3 1.34 1.337 1.340

C3-C4 1.53 1.512 1.512

C4-C1' 1.54 1.543 1.541

Angle (degree)

C1-C2=C3 121.2 125.7 126.7

C2=C3-C4 129.0 123.0 123.0

C3-C4-C1’ 108.6 112.1 111.9

C4-C1’-C2’ 111.4 122.1 111.9

(a) the experimental data obtained from reference [5]

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in range of 3000-3250 cm-1

and 1600-1800 cm-1

, are

the functional group regions. The third region, in the

range of 350-1500 cm-1

, is the fingerprint region.

The analysis of vibrational frequencies and

intensities of 1,4-polyisoprene are summarized in

Table 3. As the experimental vibrational frequencies

obtained from the ATR spectroscopy are available [8 ],

the calculated vibrational frequencies were compared.

The vibrational frequencies obtained from M062X/

cc-pVDZ calculations can be analyzed as follows;

Increasing unit numbers of 1,4-polyisoperne from n =

3 to n = 5 result in broader peaks of vibrational spectra

providing more details of vibrational modes. The

calculated spectra obtained show high correspondence

to the experimental data [8]. These results may be explained by the occurred hydrophobic interaction

occurred between methyl group and isoprene backbone

of the larger models of 1,4-polyisoperne. The

vibrational frequency and intensity analysis of the 1,4-

polyisoprene tetramer show the highest

correspondence to the experimental data [8].

Therefore, the results derived from the 1,4-

polyisoperne tetramer were selected for further

analysis regarding mode of vibration.

Figure 3 IR spectrum of 1,4-polyisoprene obtained

from M062X/cc-pVDZ

The modes of vibration information of 1,4-

polyisoprene can be predicted as following details; i)

The peak at 3,152.50 cm-1

is dominated by linkage

asymmetric C-H stretch vibrations of methyl group of

1,4-polyisoprene; ii) the peak at 3,069.60 cm-1

is

dominated by linkage asymmetric C-H stretch in -

CH2-; iii) the peak at 3,042.60 cm-1

belongs to the

mode of symmetric C-H stretch in -CH3 and -CH2-; iv)

the peak at 1,735 cm-1

belongs to the mode of C=C

stretch vibration; v) -CH2- deformation displays in a

range of 1,460-1,480 cm-1

; and vi) the peak at 884.00

cm-1

is dominated by linkage =CH out of plane

bending. The important modes of vibration results

obtained from M062X/cc-pVDZ calculations show good agreement with the experimental ATR

vibrational frequency [6].

Table 3. The vibrational frequencies and intensities of

1,4-polyisoprene

Tri Tetra Penta

cm-1 Int. cm-1 Int. cm-1 Int.

849.90 17.60 842.00 12.05 864.30 16.28

881.10 12.84 884.00 12.90 872.90 18.01

1,138.00 13.99 1,401.60 10.58 1139.10 21.83

1,410.90 13.05

1411.40 13.01

1,454.30 13.37

1445.70 10.16

1,460.40 19.75 1,462.80 14.05 1460.30 19.52

1,463.40 10.91 1464.70 13.40

1,480.70 12.93 1482.40 10.26

3,038.20 26.69 3034.60 24.05

3036.20 15.61

3036.80 30.80

3,040.20 26.70 3,042.60 39.73 3042.90 16.16

3,043.30 32.11 3,045.00 41.93 3043.60 34.01

3,045.20 35.80 3,045.50 17.10 3045.30 34.17

3,047.90 22.89 3,048.70 31.02 3046.10 34.30

3,048.60 20.99

3047.20 22.99

3,053.70 31.21 3,051.90 34.75 3057.20 77.19

3,054.20 20.83 3059.90 41.90

3,064.40 33.03 3,066.30 25.75 3061.40 11.74

3,068.80 22.30 3,069.60 39.42 3062.20 29.09

3,104.80 17.41 3,102.60 18.25 3101.10 18.44

3,106.10 32.44 3,104.60 15.12 3103.00 12.25

3,107.40 22.02 3104.10 32.00

3,109.40 60.10 3104.50 25.89

3108.00 29.32

3,111.90 20.86 3,111.20 17.37 3110.10 19.23

3,116.20 12.50 3,114.50 13.77 3110.70 13.44

3,116.50 34.76 3,115.50 24.08 3111.70 18.85

3,118.10 25.60 3112.90 16.04

3116.80 29.15

3117.90 10.76

3,121.60 25.08 3,130.80 35.31 3134.80 53.63

3,144.30 10.16 3,141.40 11.17 3143.60 14.72

3,146.30 17.73 3144.90 16.36

3148.60 26.87

3149.60 30.78

3,150.20 14.17 3,150.50 13.10 3151.70 28.32

3,151.90 26.50 3,151.50 10.63 3155.60 36.24

3,155.60 25.85 3,152.50 36.43

3,154.20 26.15

4. Conclusions

The structural and vibrational spectra of 1,4-

polyisoprene were successfully predicted using the

M062X calculations with cc-pVDZ basis set. The 1,4-

polyisoperne tetramer have been chosen as a suitable

model providing the accurate results, regarding to the

structural and vibrational information. The calculated

structural and vibrational properties agree well with

the experimental data. In the present study, the results

provide better insight of the structural and normal

mode of vibration of 1,4-polyisprene at molecular

level.

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Acknowledgements

ASEA-Uninet, OeAD-scholarship, University of

Vienna, Faculty of Science, Ubon Ratchathani

University are gratefully acknowledged for financial

supports.

References

[1] http://www.nmce.com/files/study/rubber.pdf (Retrieved

February 27, 2013).

[2] http://www.imf.org/external/pubs/ft/weo/2012/02/pdf/

text.pdf (Retrieved February 27, 2013).

[3] A. R. Arnold and P. Evans, J. Natl. Rubb. Res. 6 (1991)

75–86.

[4] R.C. Crafts, J.E. Davey, G.P. McSweeney, I.S.

Stephens, J. Natl. Rubb. Res. 5 (1990) 275–285.

[5] Y. Takahashi and T. Kumano, Macromolecules 37

(2004) 4860-4864.

[6] G. Rajkumar, J.M. Squire, and S. Arnott, Macromolecules 39 (2006) 7004-7014.

[7] -Manchado, A. Sanz, A.

Nogales, and T.A. Ezquerra, Macromolecules 44 (2011)

6574-6580.

[8] P. Thawan, N. Srichak and S. Lumlong, Senior project

report for the science and rubber technology program,

Faculty of Science, Ubonratchathani University,

Thailand, 2011.

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