Deep eutectic solvent (des) as a new solvent for lipase-catalyzed synthesis of glyceryl monocaffeate via transesterification / Puteri Norathirah Megat Abu Bakar
Cecair ionik dan pelarut eutektik (DES) telah dikenal pasti sebagai pelarut alternatif yang mesra alam. Walau bagaimanapun, laporan kajian terbaru tentang cecair ionik telah menunjukkan bahawa bahan mentahnya (kation berasaskan imidazolium) memberi kesan toksik yang terhadap alam sekitar. Penggunaan DES sebagai pengganti cecair ionik memberi sinar baru bagi aplikasi tindak balas menggunakan lipase. Tiada sebarang kajian mengenai tindak balas menggunakan lipase bagi menghasilkan gliseril monokafeat (GMC) di dalam DES. Pengubahsuaian asid kafeik (CA) kepada GMC berpotensi untuk meluaskan aplikasi aktiviti biologi CA di dalam sistem berasaskan air dan minyak. Transesterifikasi antara etil kafeat (EC) dan gliserol untuk menghasilkan GMC telah dijalankan dengan menyaring parameter-parameter berikut yang memberi kesan terhadap tindak balas iaitu jumlah enzim daripada 250 U sehingga 1500 U, kandungan air bermula daripada 0 % (v/v) sehingga 40 % (v/v), kelajuan pusingan di antara 100 rpm dan 250 rpm, nisbah molar substrat etil kafeat dan gliserol daripada 1:40 sehingga 1:90, masa tindak balas bermula daripada 0 minit sehingga 240 minit dan suhu di antara 30 ºC hingga 60 ºC. Penukaran etil kafeat sebanyak 88.4 % telah diperolehi pada 1250 U jumlah enzim, 20 % (v/v) kandungan air, 200 rpm kelajuan pusingan, 1:50 nisbah molar substrate etil kafeat dan gliserol, 30 minit masa tindak balas dan 40 ºC suhu. Mekanisma kinetik dan parameter kinetik telah dijalankan untuk menentukan kadar awal tindak balas untuk pelbagai kepekatan substrat. Hasil menunjukkan bahawa tindak balas menggunakan lipase bagi menghasilkan GMC di dalam DES mematuhi mekanisme Ping Pong Bi-Bi dengan Vmax, 10.9 mmol min-1; KmEC, 126.5 mmol dan KmGly, 1842.7 mmol. Seterusnya, kajian tentang tenaga pengaktifan telah dijalankan dengan mempelbagaikan suhu daripada 30 ºC sehingga 55 ºC dan menghasilkan nilai sebanyak 50.4 kJ/mol. Akhir sekali, metodologi tindak balas permukaan (RSM) berdasarkan reka bentuk komposit pusat (CCD) telah dijalankan untuk memperoleh nilai optimum dengan penukaran EC diperolehi sebanyak 94.71±0.06 % daripada faktor berikut yang signifikan iaitu: jumlah enzim, 705 U; jumlah air, 20 % (v/v) dan masa tindak balas, 113 minit. Secara kesimpulannya, DES berpotensi sebagai pelarut bagi tindak balas menggunakan lipase. __________________________________________________________________________
Ionic liquids and deep eutectic solvent (DES) have been identified as greener alternatives solvents. Nevertheless, ionic liquid has been reported to display toxicity to the environment due to its starting material (i.e. imidazolium-based cation). Therefore, the design of DES for ionic liquids substitution has shown a bright future for implementation in lipase-catalyzed reaction. Lipase-catalyzed reaction of glyceryl monocaffeate (GMC) in DES has not yet been reported. The modification of caffeic acid (CA) into GMC could potentially be widen the application of CA’s biological activities in water and oil-based system. The transesterification of ethyl caffeate (EC) and glycerol to produce GMC was carried out by screening these parameters that affect the reaction such as enzyme loading between 250 U to 1500 U, water content within 0 % (v/v) and 40 % (v/v), agitation speed ranged from 100 rpm to 250 rpm, substrates molar ratio of ethyl caffeate and glycerol from 1:40 to 1:90, reaction time between 0 to 240 minutes and temperatures ranged from 30 ºC to 60 ºC. Final conversion of ethyl caffeate at 88.4% was obtained at 1250 U of enzyme loading, 20 % (v/v) of water content, 200 rpm of agitation speed, 1:50 substrates molar ratio of ethyl caffeate and glycerol, 30 minutes of reaction time and 40 ºC of temperature. The kinetic mechanism and kinetic parameters were investigated to determine the initial rate of reaction of various substrates concentration. The results demonstrated that lipase-catalyzed synthesis of GMC in DES obeyed Ping Pong Bi Bi mechanism with Vmax, 10.9 mmol min-1; KmEC, 126.5 mmol and KmGly, 1842.7 mmol. Next, the study on the activation energy was conducted by varying temperature from 30 ºC to 55 º C and resulted in the value of activation energy was 50.4 kJ/mol. Finally, response surface methodology (RSM) based on face-centered central composite design (CCD) was studied to obtain the following optimum conditions with 94.71±0.06 % final conversion of EC from significant factors: enzyme loading, 705 U; water content, 20 % (v/v) and reaction time, 113 minutes. Therefore, it can be concluded that DES could serve as a potential solvent for lipase-catalyzed reaction.
Deep eutectic solvent (des) as a new solvent for lipase-catalyzed synthesis of glyceryl monocaffeate via transesterification / Puteri Norathirah Megat Abu Bakar
Deep eutectic solvent (des) as a new solvent for lipase-catalyzed synthesis of glyceryl monocaffeate via transesterification_Puteri Norathirah Megat Abu Bakar _K4_2019_MYMY