Malaysian Journal of Analytical Sciences Vol 26 No 1 (2022): 109 - 118

 

 

 

 

THE CONJUGATION AND CHARACTERISATION OF THERMORESONSIVE POLY (N-ISOPROPYLACRYLAMIDE) WITH TERNATIN BIOMOLECULE

 

(Konjugasi dan Pencirian Poli (N-Isopropilakrilamida) dengan Biomolekul Ternatin)

 

Adrina Zulkifli, Farahiyah Najah Ab Samad, Nukman Ameen Rosli, Nurul Aina Jamaluddin, Nor Nadiah Mohamad Yusof, Noor Faizah Che Harun*

 

Green Chemistry and Sustainable Engineering Technology, Polymer Technology Section,

Universiti Kuala Lumpur (UniKL) MICET, Lot 1988, Kawasan Perindustrian Bandar Vendor, Taboh Naning, 78000 Alor Gajah, Melaka, Malaysia

 

*Corresponding author: noorfaizah@unikl.edu.my

 

 

Received: 15 September 2021; Accepted: 4 January 2022; Published: 25 February 2022

 

 

Abstract

Poly (N-isopropylacrylamide) (PNIPAAm) is a well-known thermoresponsive polymer that shows a reversible coil-to-globule transition at the lower critical solution temperature (LCST) (32 ^oC) in aqueous solution. Chemically modified PNIPAAm with hydrophilic/hydrophobic compound will tune its LCST. Below the LCST, PNIPAAm and its conjugate behave as an extended coil form in an aqueous solution, whereas it shrinks into a globule form above the LCST. In this study, a direct conjugate of PNIPAAm with a ternatin biomolecule and their physicochemical characterizations were investigated. Ternatin biomolecule is an anti-adipogenic cyclic peptide that has a potential as a new treatment approach for obesity and metabolic disorders. Poly (N-isopropylacrylamide)-chain transfer agent (PNIPAAm-CTA) was synthesized through reversible addition fragmentation chain transfer (RAFT) polymerization using 2-(Dodecylthiocarbonothioyltho)-2-methylpropanoic acid (DDMAT) as chain transfer reagent. One end-group of PNIPAAm-CTA was subsequently modified with maleimide to form PNIPAAm-Maleimide through aminolysis reaction. Thereafter, a carboxylic end-group of PNIPAAm-Maleimide was directly conjugated with a hydroxyl group of ternatin biomolecule (PNIPAAm-Ternatin) through esterification method. The chemical structure, molecular weight (Mw) and molecular weight distribution (Mw/Mn) of PNIPAAm were determined through the proton nuclear magnetic resonance (¹H-NMR), Fourier transform infrared (FTIR) and size exclusion chromatography (SEC) measurements. Moreover, the LCST of PNIPAAm and its conjugate were determined through light scattering intensity analysis. The results indicated that upon heating the solutions of PNIPAAm and its conjugates in 10 mM HEPES solution pH 7.4 at 25 ^oC-40 ^oC, PNIPAAm-CTA, PNIPAAm-Maleimide and PNIPAAm-Ternatin solutions started to increase their light intensities at 32 ^oC, 34 ^oC and 35 ^oC, respectively. In conclusion, chemical structure modification of PNIPAAm could tune their LCST.

 

Keywords: poly (n-isopropylacrylamide), raft polymerization, ternatin biomolecule, conjugation, lower critical solution temperature

 

Abstrak

N-isopropilakrilamida) (PNIPAAm) adalah polimer termoresponsif terkenal yang menunjukkan peralihan gegelung-ke-globule yang boleh berbalik pada suhu larutan kritikal rendah (LCST) (32 ^oC) dalam larutan akueus. PNIPAAm yang diubahsuai secara kimia dengan sebatian hidrofilik/hidrofobik akan mengubahkan LCSTnya. Pada suhu di bawah LCST, PNIPAAm dan konjugatnya berbentuk gegelung di dalam larutan akueus, manakala ia akan mengecut menjadi bentuk globul pada suhu di atas LCST Dalam kajian ini, konjugasi secara langsung PNIPAAm dengan biomolekul ternatin dan sifat fizikokimianya dikaji. Biomolekul ternatin adalah peptida siklik anti-adipogenik. Ia berpotensi sebagai rawatan baharu untuk obesiti dan gangguan metabolik. Poli (N-isopropilakrilamida)-agen pemindahan rantai (PNIPAAm-CTA) disintesis melalui polimerisasi radikal hidup menggunakan asid 2-(dodekilthiokarbonothioiltho)-2-metilpropanoik(DDMAT) sebagai reagen pemindahan rantai. Selepas itu, satu kumpulan akhir pada PNIPAAm-CTA diubahsuai dengan maleimida untuk membentuk PNIPAAm-Maleimida melalui tindak balas aminolisis. Kemudian, kumpulan akhir karboksilik PNIPAAm-Maleimida dihubungkan secara langsung dengan kumpulan hidroksil pada biomolekul ternatin (PNIPAAm-Ternatin) melalui kaedah esterifikasi. Struktur kimia, berat molekul (Mw) dan taburan berat molekul (Mw/ Mn) bagi PNIPAAm dikaji melalui analisis proton resonans magnetik nuklear (¹H-NMR), spektroskopi inframerah Fourier transformasi (FTIR) dan kromatografi ekslusi saiz (SEC). Seterusnya, sifat LCST bagi PNIPAAm dan konjugatnya dikaji melalui analisis intensiti penyerakan cahaya. Hasilnya, setelah larutan PNIPAAm dan konjugat dalam larutan HEPES 10 mM pH 7.4 dipanaskan pada suhu 25-40 ^oC, intensiti cahaya bagi PNIPAAm-CTA, PNIPAAm-Maleimida dan PNIPAAm-Ternatin mula meningkat pada 32 ^oC, 34 ^oC dan 35 ^oC. Kesimpulannya, pengubahsuaian struktur kimia PNIPAAm dapat mengubah sifat LCST polimer.

 

Kata kunci:  poli (n-isopropilakrilamida), pempolimeran raft, biomolekul ternatin, konjugasi, suhu larutan kritikal rendah

 

 

 

Graphical Abstract

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