Zheng Guo

Liquid lipases for enzymatic concentration of n-3 polyunsaturated fatty acids in monoacylglycerols via ethanolysis: Catalytic specificity and parameterization

This work examined catalytic specificity and fatty acid selectivity of five liquid lipases C. antarctica lipase A and B (CAL-A/B), and lipase TL (T. lanuginosus), Eversa Transfrom and NS in ethanolysis of fish oil with the aim to concentrate n-3 PUFAs into monoacylglycerols (MAGs) products. Lipase TL, Eversa Transform & NS entail a much faster reaction and produce higher MAGs yield (>30%); whereas CAL-A obtains the highest concentration of n-3 PUFAs/DHA/EPA into MAGs products (88.30%); followed by lipase NS (81.02%). 13C NMR analysis indicates that CAL-B and lipase TL are sn-1,3 specific; but CAL-A and lipase Eversa Transform are non-regiospecific or weak sn-2 specific; which plausibly explains high enrichment effect of the latter two lipases. All liquid lipases are observed reusable for a certain times (lipase Eversa Transform up to 12 times), demonstrating their competitive advantage over immobilized form for industrial application because of their higher activity and cheaper operation cost.

Synthesis of silicon-doped reduced graphene oxide and its applications in dye-sensitive solar cells and supercapacitors

Heteroatom-doping of graphene is of fundamental importance to enable a wide range of optoelectronic and energy storage devices while exploring their basic material properties. Herein, a facile and low-cost method is presented to synthesize the silicon-doped reduced graphene oxide (Si-rGO) via annealing treatment of triphenylsilane and graphene oxide. Compared to the pristine reduced graphene oxide (rGO), Si-rGO exhibits significant enhancement in electrocatalytic and electrochemical properties: when Si-rGO is used as a metal-free electrocatalyst in counter electrodes in dye-sensitized solar cells (DSSCs), the conversion efficiency is increased by 29.6%; when Si-rGO is used as an active electrode in a supercapacitor, the specific capacity is increased by 48.5%. This suggests that silicon doping can effectively improve the electrocatalytic ability and electrochemical performance. It is promising for Si-rGO to be used as a metal-free catalytic and active material.

The near-ideal catalytic property of Candida antarctica lipase A to highly concentrate n-3 polyunsaturated fatty acids in monoacylglycerols via one-step ethanolysis of triacylglycerols.

Declining quantity/quality of available n-3 polyunsaturated fatty acids (n-3 PUFAs) resources demand innovative technology to concentrate n-3 PUFAs from low quality oils into value-added products/health-beneficial ingredients rich in n-3 PUFAs. This work proposed the catalytic property and specificity of an ideal enzyme required to tackle this task and identified Candida antarctica lipase A (CAL-A) is such a near-ideal enzyme in practice, which concentrates n-3 PUFAs from 25% to 27% in oils to a theoretically closer value 90% in monoacylglycerols (MAGs) via one-step enzymatic ethanolysis. Non-regiospecificity and high non-n-3 PUFAs preference of CAL-A are the catalytic feature to selectively cleave non-n-3 PUFAs in all 3 positions of triacylglycerols (TAGs); while high ethanol/TAGs ratio, low operation temperature and high tolerance to polar ethanol are essential conditions beyond biocatalyst itself. C-13 Nuclear magnetic resonance ((13)C NMR) analysis and competitive factor estimation verified the hypothesis and confirmed the plausible suggestion of catalytic mechanism of CAL-A.

Mining catalytic promiscuity from Thermophilic archaea: an acyl-peptide releasing enzyme from Sulfolobus tokodaii (ST0779) for nitroaldol reactions

This work demonstrates that the thermophiles can be a rich source to mine catalytic promiscuity, whereby an acyl-peptide releasing enzyme from Sulfolobus tokodaii (ST0779) is identified to be a promising biocatalyst to mediate the Henry (nitroaldol) reaction. Compared to Porcine Pancreatic Lipase (PPL), ST0779 displayed superior catalytic efficiency kcat/Km (6–8 fold higher) and enantioselectivity ee% (90–99%). The catalytic versatility of ST0779 was validated as the enzyme displayed activity towards a broad scope of substituted benzaldehydes, and the electron effects of the benzaldehyde substituents were analyzed by Hammett plotting. Accordingly, this work not only presents a novel enzyme capable of catalyzing the Henry reaction with higher yield and enantioselectivity than ever reported, but also demonstrates the huge potential of Thermophilic archaea to be an optimal source for mining novel enzymes for biocatalytic promiscuity, which could provide a variety of potent biosynthesis tools to yield diverse kinds of molecules.

Remarkably enhanced activity and substrate affinity of lipase covalently bonded on zwitterionic polymer-grafted silica nanoparticles

Enzymes are promising biocatalysts for the production or degradation of chemical compounds, but low stabilities of free enzymes restrict their industrial applications. Therefore, development of effective immobilization methods to maintain or increase enzyme activity and stability remains a challenge. In this work, a novel support made of zwitterionic polymer-grafted silica nanoparticles (p-SNPs) was fabricated and Candida rugosa lipase (CRL) was covalently attached onto the p-SNPs. The zwitterionic polymer was a product of the reaction between poly(maleic anhydride-alt-1-octadecene) and N,N-dimethylenediamine and contained a cetane side chain. The hydrolytic activity, reaction kinetics, thermal stability, pH tolerance, storage stability and reusability of the immobilized CRL (SNPs-CRL) were investigated. It revealed that the specific activity of SNPs-CRL was two to four times higher than the free CRL in the temperature range of 25-60u202f°C. It is considered mainly due to the interfacial activation effect regulated by the cetane side chains of the zwitterionic polymer. Kinetic studies revealed remarkable improvement of the enzymatic reaction efficiency by the immobilized enzyme as demonstrated by the significant increases of the reaction rate constant and the decreases of Michaelis constant (i.e., increase of enzyme-substrate affinity) determined with two different substrates (p-nitrophenyl acetate and p-nitrophenyl palmitate). Moreover, the immobilization improved the enzyme stabilities and SNPs-CRL displayed good reusability. Finally, the SNPs-CRL was proven to catalyze the hydrolysis of methyl mandelate to produce mandelic acid at an activity three times higher than the free enzyme. The results indicate that zwitterionic polymers deserved further development for enzyme immobilization.

Adding functionality to milk-based protein: Preparation, and physico-chemical characterization of β-lactoglobulin-phenolic conjugates

Multi-functional phenolic emulsifiers were prepared by covalently coupling β-Lactoglobulin (βLg) to caffeic acid (CA) using crosslinker chemistry at different pH conditions (pH 2.5, 6.0, and 8.5). The resulting bioconjugates were characterized by MALDI-TOF MS, differential scanning calorimetry (DSC), fluorescence-quenching, infrared and circular dichroism spectroscopies. Furthermore, the emulsifying and antioxidant properties of βLg-CA conjugates were evaluated and compared to native β-Lactoglobulin and the non-covalent β-lactoglobulin/caffeic complex (βLg/CA). Results showed: 1) An optimal molar ratio (8:1) of caffeic acid to βLg was obtained at pH 6; 2) DPPH activity of βLg-CA increases as the number of CA units coupled increases; 3) βLg-CA conjugates displayed comparable or superior water solubility than native βLg and βLg/CA. Moreover, DSC results showed that coupling of CA with βLg significantly increased the thermal stability of βLg. In summary, βLg-CA conjugates can act as effective antioxidant emulsifiers and stabilizers and may find application in food and cosmetic industries.

Synthesis and characterization of O-acylated-ω-hydroxy fatty acids as skin-protecting barrier lipids.

A series of O-acylated-ω-hydroxy fatty acids (Acyl acids) of up to 34 carbons were synthesized and characterized through DSC, FTIR and Langmuir isotherm measurements to identify potential replacements to petrolatum, a highly used occlusive technology that if unrefined, it can potentially be classified as carcinogenic. Fourier transform infrared spectroscopy studies demonstrated that long acyl acids engender orthorhombic packing; packing behavior that is predominant in the lipid matrix of healthy stratum corneum, the outmost layer of the skin. In addition, Differential Scanning Calorimetry (DSC) and Langmuir isotherm studies suggested that the length of the hydrocarbon chain and the position of the ester bond influence the molecular organization of the acyl acids. For instance, 16-(tetradecanoyloxy)hexadecanoic acid (30 carbons) displayed a higher melting point (mp=68°C) than 10-(stearoyloxy)decanoic acid (28 carbons; mp=63°C) and 10-(tetradecanoyloxy)decanoic acid (24 carbons; mp=55°C) according to DSC. Moreover, Langmuir isotherm studies showed that mixtures of acyl acid with distearoylphosphatidylcholine improved packing behavior. Finally, Water Vapor Transmission Rate (WVTR) measurements showed that the compounds in fact decrease WVTR compared to untreated control (P<0.001) which demonstrates the potential of these ingredients as occlusive technologies to combat skin barrier diseases.

Single-component solid lipid nanocarriers prepared with ultra-long chain amphiphilic lipids

HYPOTHESISnSynthetic sugar alcohol mono-behenates with high melting points, surface activity and resistance to enzymatic lipolysis, are expected to form stable single-component solid lipid nanocarriers (SC-SLNs). The preparation methods and the polar head group of the molecules should affect the size and drug encapsulation efficiency.nnnEXPERIMENTSnSC-SLNs of sugar alcohol mono-behenates with varied polar heads were prepared using emulsification-diffusion method and melting-probe sonication method. Model lipophilic drug fenofibrate was formulated into nanocarriers. The drug release was assessed using the lipolysis model. The structure and drug distribution of the nanocarriers were studied using AFM and TEM.nnnFINDINGSnBoth the polar head group of the molecules and the preparation methods affect the particle size and size distribution. Nanocarriers prepared with sorbitol mono-behenates showed the smallest mean size (∼100nm with PdI of 0.26). In addition, they displayed high entrapment efficiency of fenofibrate (95%) and long term drug release. Nanocarriers prepared by emulsification-diffusion method entrapped fenofibrate into lipid bilayers. In contrast, Nanocarriers prepared by melting-probe sonication method had a micelle structure with fenofibrate incorporated into a lipid monolayer. This study provides an insight into the systematic development of novel amphiphilic lipids for solid lipid-based drug delivery system.

Catalytic Biodiesel Production Mediated by Amino Acid-Based Protic Salts

Hetero- and homogeneous acid catalysts are effective catalysts for the production of biodiesel from oils containing high free fatty acids. The protic salts synthesized from natural amino acids were examined for catalytic activity and efficiency for the esterification of oleic acid after structural identification and characterization. In the esterification reaction of oleic acid with methanol, [Asp][NO3 ] was the best catalyst, and its high activity correlated to its high Hammett acidity. The optimal reaction conditions for the esterification of oleic acid to achieve 97u2009% biodiesel yield were: 70u2009°C, 10u2009% catalyst loading (w/w, on oleic acid basis), methanol/oleic acid ratio 7.5:1, and 5u2005h. Generally, [Asp][NO3 ] could be a good catalyst for the esterification of oleic acid with alcohols with chain lengths of up to six. The biodiesel yield of 93.86u2009% obtained from palm fatty acid distillate implies that the catalyst has potential for industrial application. A study of the kinetics indicated that the reaction followed pseudo-first-order kinetics with an activation energy and pre-exponential of 57.36u2005kJu2009mol-1 and 44.24×105 u2005min-1 , respectively. The aspartic acid-derived protic salt is a promising, operationally simply, sustainable, renewable, and possibly biodegradable catalyst for the conversion of free fatty acids into biodiesel.

Production of new human milk fat substitutes by enzymatic acidolysis of microalgae oils from Nannochloropsis oculata and Isochrysis galbana

Human milk fat substitutes (HMFs) with four kinds of n-3 fatty acid for infant formula were firstly synthesized using triacylglycerols (TAGs) from Nannochloropsis oculata rich in PA at the sn-2 position and free fatty acids (FFAs) from Isochrysis galbana rich in n-3 polyunsaturated fatty acids (n-3 PUFAs-ALA/SDA/DHA) via solvent-free acidolysis with Novozym 435, Lipozyme 435, TL-IM and RM-IM as biocatalysts. The results show that the resulting HMFs contain total n-3 PUFA of 13.92-17.12% and PA of 59.38-68.13% at the sn-2 position under the optimal conditions (mole ratio FFAs/TAG 3:1, 60°C (Novozym 435 and Lipozyme TL-IM) and 50°C (Lipozyme 435 and RM-IM), lipase loading 10%, reaction time 24h). Moreover, among the tested enzymes, Lipozyme 435, TL-IM, and RM-IM display the fatty acid selectivity towards SDA, LA and ALA, and OA, respectively. Overall, the examined lipases are promising biocatalysts for producing high-value microalgal HMFs in a cost-effective manner.