N435 Enzymatic Degradation Difference and Molecular Modeling of Hydrophilic Modified PBS-based Copolymer†

doi:10.7503/cjcu20140966

Abstract

Abstract:

By lipase Novozym435, enzymatic degradation of copolymers poly(butylene succinate-diglycolic butanediol)ester[P(BS-co-BDGA)] and poly(butylene succinate-diethylene glycol succinate)ester[P(BS-co-DEGS)] which contain ether oxygen bond at different positions of alcohol binding segment and acid binding segment in the main chain of PBS, was performed in the aqueous system. And molecular docking simulations explore the recognition of enzyme on hydrophilic substrate and the interaction mechanisms. In order to study the degradation law of PBS modified copolymers, the mass loss rate, hydrophilicity and thermal properties of the copolymer films and the degradation products were investigated. The results show that: with the passage of time, mass loss rate of the copolymer films is increased, increasing the hydrophilicity and the thermal decomposition temperature; after degradation for 5 d, oligomeric species of P(BS-co-BDGA) are more than P(BS-co-DEGS). Combined with the results of molecular docking, P(BS-co-BDGA) ester bond of ether bond in an acid binding segment docking with the Novozym435 enzyme active sites is more stable than P(BS-co-DEGS) ester bond of ether bond in an alcohol binding segment, so under the action of the enzyme. The degradation effect of P(BS-co-BDGA) is better than P(BS-co-DEGS); and in the synthesized composition range, when the addition amount of DGA is 20%(molar fraction), degradation effect is best.

Key words: Polybutylene succinate, Oxygen ether bond, Lipase Novozym 435, Enzymatic degradation, Molecular docking simulation

CLC Number:

O631

TrendMD:

ZHANG Min, ZHANG Yi, LI Chengtao, QIN Jiaxiang, Gao Rang, MA Xiaoning, QIU Jianhui. N435 Enzymatic Degradation Difference and Molecular Modeling of Hydrophilic Modified PBS-based Copolymer^†[J]. Chem. J. Chinese Universities, 2015, 36(3): 568.

Figures/Tables 12

Table 1 Composition and relactive parameters of copolymers

Run	Copolymer	10^-4 M_n	10^-4 M_w	M_w/M_n	Run	Copolymer	10^-4 M_n	10^-4 M_w	M_w/M_n
1	PBS	5.08	10.98	2.16	6	P(BS-co-5%BDGA)	5.48	10.55	2.07
2	P(BS-co-5%DEGS)	4.40	8.17	1.86	7	P(BS-co-10%BDGA)	5.40	13.36	2.48
3	P(BS-co-10%DEGS)	5.20	9.99	1.92	8	P(BS-co-15%BDGA)	4.73	12.54	2.23
4	P(BS-co-15%DEGS)	4.50	9.04	2.01	9	P(BS-co-20%BDGA)	4.91	11.37	2.96
5	P(BS-co-20%DEGS)	4.52	9.13	2.02

Fig.1 1H NMR spectra of copolymers P(BS-co-DEGS)(A) and P(BS-co-BDGA)(B)

Fig.2 Schematic representation of BSB, DEGSDEG and BDGAB

Fig.3 Mass loss of copolymers P(BS-co-DEGS)(---) and P(BS-co-BDGA)(—) during degradation

Table 2 Contact angle of the copolymer

Copolymer	Water contact angle, θ/(°)		Copolymer	Water contact angle, θ/(°)
Copolymer	Before degradation		After degradation of 2 d	Before degradation	After degradation of 2 d
PBS	72.76	67.03	P(BS-co-5%BDGA)	71.46	62.09
P(BS-co-5%DEGS)	68.30	54.12	P(BS-co-10%BDGA)	70.26	51.11
P(BS-co-10%DEGS)	66.18	49.63	P(BS-co-15%BDGA)	65.62	45.03
P(BS-co-15%DEGS)	66.07	42.42	P(BS-co-20%BDGA)	62.57	37.93
P(BS-co-20%DEGS)	64.78	40.65

Fig.4 Curves of decomposition temperature before and after degradation of copolymers P(BS-co-DEGS)(A) and P(BS-co-BDGA)(B)

Table 3 TGA data of copolymers

Copolymer	Before degradation		After degradation of 3 d		Copolymer	Before degradation		After degradation of 3 d
Copolymer	T_d,5%/℃	T_d,50%/℃		T_d,5%/℃	T_d,50%/℃	T_d,5%/℃	T_d,50%/℃	T_d,5%/℃	T_d,50%/℃
PBS	354.54	408.84	361.65	413.62	P(BS-co-5%BDGA)	355.34	392.57	360.12	401.55
P(BS-co-5%DEGS)	360.92	406.72	368.53	413.07	P(BS-co-10%BDGA)	342.78	395.68	355.50	407.62
P(BS-co-10%DEGS)	361.71	409.49	365.28	409.99	P(BS-co-15%BDGA)	352.76	399.53	357.70	406.06
P(BS-co-15%DEGS)	366.15	409.23	366.36	410.60	P(BS-co-20%BDGA)	352.91	404.20	358.31	406.85
P(BS-co-20%DEGS)	360.50	407.91	361.74	408.56

Fig.5 MALDI-TOF-MS spectra of the degradation products of copolymers P(BS-co-15DEGS)(A) and P(BS-co-15BDGA)(B)

Table 4 m/z of the degradation products of copolyester†

Copolymer	[M+Na⁺], m/z	Product
P(BS-co-DEGS)	485.5	L*S(BS)₂·Na⁺
	501.5	L*S(BS)(DEGS)·Na⁺
	517.5	L*S(DEGS)₂·Na⁺
	657.7	L*S(BS)₃·Na⁺
	673.7	L*S(BS)₂(DEGS)·Na⁺
	689.7	L*S(BS)(DEGS)₂·Na⁺
	711.8	C*(BS)₄·Na⁺
P(BS-co-BDGA)	485.5	L*S(BS)₂·Na⁺
	501.5	LS(BS)(BDGA)·Na⁺; L(BS)₂(DGA)·Na⁺
	517.5	LS(BDGA)₂·Na⁺; L(BS)(BDGA)(DGA)·Na⁺
	533.5	L*(BDGA)₂(DGA)·Na⁺
	587.6	C*(BDGA)₃·Na⁺
	605.6	L*(BDGA)₃·Na⁺
	657.7	L*S(BS)₃·Na⁺
	673.7	LS(BS)₂(BDGA)·Na⁺; L(BS)₃(DGA)·Na⁺
	689.7	LS(BS)(BDGA)₂·Na⁺; L(BS)₂(BDGA)(DGA)·Na⁺
	711.8	C*(BS)₄·Na⁺

Table 5 Docking results of substrate molecules using the AutoDock program

Enzyme	Ligand	$E binding a$ / (kJ·mol^-1)	$E inter - mol b$ / (kJ·mol^-1)	$E vdw c$ / (kJ·mol^-1)	$E elec d$ / (kJ·mol^-1)	$E total e$ / (kJ·mol^-1)	$E torsional f$ / (kJ·mol^-1)
N435 lipase	BSB	-15.73	-34.43	-33.60	-0.84	-5.15	19.96
	DEGSDEG	-17.07	-37.03	-36.40	-0.63	-5.19	19.96
	BDGAB	-21.13	-41.09	-40.25	-0.84	-4.52	19.96

Table 5 Docking results of substrate molecules using the AutoDock program

Enzyme	Ligand	$E binding a$ / (kJ·mol^-1)	$E inter - mol b$ / (kJ·mol^-1)	$E vdw c$ / (kJ·mol^-1)	$E elec d$ / (kJ·mol^-1)	$E total e$ / (kJ·mol^-1)	$E torsional f$ / (kJ·mol^-1)
N435 lipase	BSB	-15.73	-34.43	-33.60	-0.84	-5.15	19.96
	DEGSDEG	-17.07	-37.03	-36.40	-0.63	-5.19	19.96
	BDGAB	-21.13	-41.09	-40.25	-0.84	-4.52	19.96

Fig.6 Substrate-enzyme interactions by docking studies for CALB-DEG(A) and CALB-DGA(B)

Fig.7 Substrate-enzyme interactions by docking studies for CALB-DEG(A) and CALB-DGA(B)

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