自交联共轭亚油酸囊泡的钙稳定性及钙响应性研究

脂肪酸囊泡(FAV)是一种成分简单、安全价廉的载体,可以起到与脂质体或微胶囊类似的作用。本实验以廉价易得且具有生理活性、自组装活性和自交联活性的共轭亚油酸(CLA)为分子砌块,通过自交联反应制备稳定的共轭亚油酸囊泡(CLA-FAV)。研究了该自交联CLA-FAV的钙稳定性及钙响应性。揭示了自交联CLA-FAV作为潜在活性物包埋空间和释放通道具有钙刺激响应性,可能成为一种潜在的钙响应型载体,为CLA-FAV应用在化妆品及洗涤用品行业提供了新思路。     

烷基磷酸酯与共轭亚油酸形成杂化囊泡的研究

脂肪酸囊泡(FAV)的中空壳核结构能够包埋活性分子。为改善FAV仅在其p Ka附近形成的缺陷,以拓宽FAV的应用范围,将安全性和温和性阴离子表面活性剂烷基磷酸酯钾盐(MAPK)添加到共轭亚油酸中,通过动态激光光散射(DLS)和透射电子显微镜(TEM)研究了囊泡化的pH窗口,发现9%MAPK存在时就可以在中性至酸性环境中形成杂化FAV,不明显改变原有FAV的形貌及粒径,且随着MAPK添加量的增大,杂化FAV的pH窗口有逐渐拓宽的趋势。这一结果显示了杂化FAV在化妆品和个人卫生护理用品等领域的应用前景。     

N-甲基-N,N-双十二烷基壳聚糖盐酸盐的合成及自组装囊泡性能

以壳聚糖为原料制备N-甲基-N,N-双十二烷基壳聚糖盐酸盐(TMC),用FT-IR、EA对产物进行表征,溶解性实验表明TMC溶于乙醇等有机溶剂。采用乙醇注射法制备TMC囊泡,研究不同pH值介质中制得的载亲/疏水药物TMC囊泡的Zeta电位、粒径大小及分布、储存稳定性、载药及释放性能。结果表明,制得的TMC自组装囊泡Zeta电位为39.5~46 mV,粒径为50~100 nm,多分散系数为0.17~0.26,静置30天后仍保持稳定。Langmuir膜行为表明在较低pH值下TMC更易自组装,制备介质pH值不同对囊泡的粒径、药物释放行为影响较大,而释药环境pH值对囊泡的药物释放行为影响较小。     

氟碳化合物FC-77——脂质体囊泡的制备及性能研究

通过19F NMR、紫外可见光谱、激光粒度仪、Zeta电势和透射电子显微镜等方法研究了生理条件下(pH7.4)FC-77与脂质体囊泡的相互作用。结果表明,脂质体囊泡使得FC-77分子的紫外吸收光谱发生明显位移;FC-77使得脂质体囊泡的粒径和电势均增加。进一步的研究表明,FC-77能够引起囊泡双层膜通透性的降低。为开发FC-77的脂质体药物、增加FC-77的临床利用率提供了基础。     

甲氨蝶呤囊泡的制备和体外释放性能研究

用非离子表面活性剂和胆固醇为原料,采用薄膜分散法制备甲氨蝶呤囊泡,通过透析法分离未包封的药物,紫外分光光度法测定包封率和体外释药性。结果显示,Span 60与胆固醇形成的囊泡(VSpan 60∶VCHOL=5∶3),在50℃超声40 m in的条件下,对0.60 g/L的甲氨蝶呤包封率可达65%以上,在模拟胃流体和模拟肠流体中均有良好的缓释作用。     

长春新碱纳米缓释新剂型的制备及性能研究

采用非离子表面活性剂在亲水介质中进行自组装,成功制备了双分子层硫酸长春新碱囊泡,并对其制备条件、粒径分布、囊泡形态、包封率及体外释放进行了探究。实验结果表明,通过电子显微镜观察分析,制备的双分子层硫酸长春新碱囊泡呈现规则的球形形态,并具有较为均匀的尺寸分布。紫外分光光度计测定结果显示,囊泡具有较高包封率,能够有效封装药物。体外释放实验显示,双分子层硫酸长春新碱囊泡具有良好的药物缓释性能,释放速率稳定且符合预期缓释效果。研究结果为双分子层硫酸长春新碱囊泡作为药物递送系统的应用提供了有力支持。     

无溶剂体系中酶催化合成共轭亚油酸甘油酯

采用直接酯化法,以共轭亚油酸(简称CLA)和甘油为原料,用脂肪酶Novozym 435催化合成共轭亚油酸甘油酯。结果表明:n(甘油)/n(CLA)=5,酶添加量为体系总质量的4%,65℃反应6 h后,共轭亚油酸的转化率为98.18%。所得共轭亚油酸甘油酯为淡黄色油状透明液体,酸价低于3,Novozym 435的操作半衰期为30 h。     

CO2/N2可逆单层囊泡-网状结构转变研究

以聚乙二醇6000与α-溴代异丁酰溴进行酯化反应得到大分子引发剂PEG6000-Br,使用原子转移自由基聚合(ATRP)法合成了对称三嵌段且聚合度相等的聚甲基丙烯酸二甲胺乙酯-聚乙二醇-聚甲基丙烯酸二甲胺乙酯(PDM_(165)-PEG_(165)-PDM_(165))。利用FTIR和~1HNMR对其结构进行了表征。以p H、电导率测试证明了聚合物溶液的CO_2/N_2循环可逆性,聚合物溶液中通入CO_2后,5 min内,溶液p H值即从7.74下降至5.47,溶液电导率从0.176 m S/cm迅速上升至0.405 m S/cm;继而向溶液中通入N_2,经过30 min后,溶液的p H值和电导率都恢复到初始值。冷冻透射电镜(Cryo-TEM)观察得知,聚合物在水中可自组装形成单层囊泡,通入CO_2后,叔胺被质子化,囊泡解离形成网状结构,导致溶液黏度从3 m Pa·s上升至12 m Pa·s,叔胺质子化由~1HNMR证明,N原子附近的氢位移从δ2.3、2.7、4.1向低场分别移动至δ2.8、3.2、4.3。     

头孢曲松钠囊泡的研制

以司盘(Span)和胆固醇(CHOL)为膜材,用超声法制备了头孢曲松钠囊泡,通过透射电镜考查其形态和构造,并研究了其在模拟胃液和模拟肠液中的释放情况。实验表明,Span 40与CHOL用量比为5∶3时形成的囊泡,对0.60 mg/mL的注射用头孢曲松钠的包封率可达60%以上,在模拟胃液和模拟肠液中均有缓释作用。     

介孔二氧化硅的合成及表征

首先利用脂肪醇聚氧乙烯醚硫酸钠(AES)与十六烷基三甲基溴化铵(CTAB)在水溶液中自组装形成囊泡体系,然后在囊泡体系中pH=9.2条件下以正硅酸四乙酯(TEOS)作为硅源,合成了介孔二氧化硅。用动态光散射仪(DLS),透射电镜(TEM),X射线衍射仪(XRD)和低温氮吸附仪等对囊泡体系和介孔二氧化硅样品进行了表征。结果表明,在浓度均为0.01 mol·L-1的AES溶液与CTAB溶液体积比为1∶1时得到了直径约为50 nm的囊泡体系。在2.88°处出现了介孔二氧化硅材料的特征衍射峰。测得介孔二氧化硅材料的平均孔径为3.5 nm,比表面积为670 m2·g-1。     

Investigation of Micellization and Vesiculation of Conjugated Linoleic Acid by Means of Self‐Assembling and Self‐Crosslinking

Bioactive and biocompatible conjugated linoleic acid (CLA) has been only considered as a food or medicine ingredient due to its rare natural occurrence. In this work, the surface activities and pH‐induced self‐assembling behaviors of the semi‐synthetic CLA molecules into micelles or vesicles were systematically investigated. First, the self‐assembling of CLA was studied in detail, and it was found that aside from temperature and ionic strength, pH is the prominent factor affecting the self‐assembling of CLA. Moreover, stable CLA ufasomes (unsaturated fatty acid liposomes) in uniform size were obtained by self‐crosslinking of the CLA ufasomes, and the morphologies of the crosslinked CLA assemblies were recorded by transmission electron microscopy, which made known the pH‐induced formation of the CLA ufasomes or the CLA micelles. The crosslinked CLA assemblies presented improved properties such as a higher calcium stability, a lower lime soap dispersing requirement and a better solubilization ability than that of the CLA molecules themselves or the pre‐crosslinked linoleic acids. These investigations could be helpful for comprehensively understanding effects of environment factors on self‐assembling behaviors of conjugated fatty acids and responsive polymerization of polymerizable surfactants.     

Effect of the crosslinking with 1,1,1-trimethylolpropane trimethacrylate on 5-fluorouracil release from poly(2-hydroxyethyl methacrylate) hydrogels

The aim of this study is to examine the influence of crosslinking density on 5-Fluorouracil release from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels crosslinked with 1,1,1-trimethylolpropane trimethacrylate (TPT). PHEMA hydrogels were synthesized by bulk polymerization with different proportions of TPT (1 – 10 wt%) as crosslinker agent and ammonium persulphate as initiator, enabling polymerization in the feed mixture in the presence of water. As a result, 5-FU could be trapped by including it as a sodium salt in the feed mixture of polymerization. Discs with 5-FU loads between 1 – 16 mg/disc were obtained. Swelling and 5-FU release kinetics studies were carried out in saline solution at 310 K. The diffusion studies were in accordance with Fick's second law during the initial stages, enabling the diffusion coefficients of the process to be determined. The time required for discs to reach total 5-FU release was between 35 h and 160 h and was a function of crosslinking density of the gels and 5-FU load of the discs. Received: 12 July 1996/Revised version: 8 October 1996/Accepted: 15 October 1996     

Sources and Bioactive Properties of Conjugated Dietary Fatty Acids

The group of conjugated fatty acids known as conjugated linoleic acid (CLA) isomers have been extensively studied with regard to their bioactive potential in treating some of the most prominent human health malignancies. However, CLA isomers are not the only group of potentially bioactive conjugated fatty acids currently undergoing study. In this regard, isomers of conjugated α‐linolenic acid, conjugated nonadecadienoic acid and conjugated eicosapentaenoic acid, to name but a few, have undergone experimental assessment. These studies have indicated many of these conjugated fatty acid isomers commonly possess anti‐carcinogenic, anti‐adipogenic, anti‐inflammatory and immune modulating properties, a number of which will be discussed in this review. The mechanisms through which these bioactivities are mediated have not yet been fully elucidated. However, existing evidence indicates that these fatty acids may play a role in modulating the expression of several oncogenes, cell cycle regulators, and genes associated with energy metabolism. Despite such bioactive potential, interest in these conjugated fatty acids has remained low relative to the CLA isomers. This may be partly attributed to the relatively recent emergence of these fatty acids as bioactives, but also due to a lack of awareness regarding sources from which they can be produced. In this review, we will also highlight the common sources of these conjugated fatty acids, including plants, algae, microbes and chemosynthesis.     

Body Compositional Changes and Growth Alteration in Chicks from Hens Fed Conjugated Linoleic Acid

Effects of feeding conjugated linoleic acid (CLA) to hens on progeny chick development and composition at hatch (NHC) and three weeks of age (TWC) were assessed. CLA (0 or 0.5%, composed of mixed isomers of cis-9,trans-11 or trans-10,cis-12-CLA) was fed to hens with either safflower (SO) or olive oil (OO) (3 or 3.5%) to assure successful hatch for 2 weeks prior to collection for incubation. Maternal CLA feeding had no effect on hatchability, but improved egg fertility (p < 0.05). Maternal feeding of CLA with SO increased 21 day-old progeny growth, while CLA with OO decreased growth (oil*CLA, p < 0.05). In 25 day-old chicks (TWC), but not NHC, maternal CLA decreased the proportion of total body water (p < 0.05) and increased body ash (p < 0.05). While monounsaturated fatty acids were decreased and saturated fatty acids increased in eggs and NHC from hens fed CLA, no differences in fatty acid composition were observed in chicks at 25 days of age from hens fed CLA. Maternal CLA feeding resulted in the presence of c9,t11 and t10,c12-CLA in NHC, but only c9,t11 in the TWC. In conclusion, hens fed CLA led to improved fertility and altered body composition at 3 weeks of age.     

Dietary Fat Does Not Overcome trans-10, cis-12 Conjugated Linoleic Acid Inhibition of Milk Fat Synthesis in Lactating mice

Trans-10, cis-12 conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis in the cow and similarly reduces milk fat in rodents. The objective of this study was to determine whether dietary fat can overcome CLA inhibition of milk fat concentration in lactating mice. Wild type C57Bl/6J mice (n = 31) were fed semipurified diets containing either low fat (LF; 4% fat) or high fat (HF; 23.6% fat) starting 4–6 days postpartum. Dietary fat was increased by inclusion of high oleic sunflower oil. After 2 days on the experimental diets, lactating dams were orally dosed with either water (control) or trans-10, cis-12 CLA (20 mg/day) for 5 days. CLA treatment decreased pup growth similarly in both HF and LF diets. Milk fat percent was increased over 16% by the HF diet and decreased over 12% by CLA, but there was no interaction of dietary fat and CLA. Both CLA and the HF diet reduced the proportion of short- and medium-chain fatty acids that originate from de novo synthesis, and there was no interaction of diet and CLA. CLA had no effect on the percent of preformed fatty acids, but the HF diet increased their abundance. Dietary fat and CLA both modified mammary expression of lipogenic enzymes and regulators, but no interactions were observed. In conclusion, CLA reduced milk fat concentration and litter growth, but these effects were not overcome by increased dietary fat from high oleic sunflower oil. CLA inhibition of milk fat in the mammary gland is not substrate dependent, and the mechanism is independent from dietary supply of oleic acid.     

Directed sequential synthesis of conjugated linoleic acid isomers from Δ7, 9 to Δ12, 14

Position and configuration isomers of conjugated linoleic acid (CLA), from 7, 9‐ through 12, 14‐C18:2, were synthesized by directed sequential isomerizations of a mixture of rumenic (cis‐9, trans‐11 C18:2) and trans‐10, cis‐12 C18:2 acids. Indeed, the synthesized conjugated fatty acids cover the range of unsaturated systems as found in milk fat CLA. The two‐step sequence consisted in initial sigmatropic rearrangement of cis/trans CLA isomers at 200 °C for 13 h under inert atmosphere (Helium, He), followed by selenium‐catalyzed geometrical isomerization of double bonds at 120 °C for 20 h under He. Product analysis was achieved by gas‐liquid chromatography using a 120 m polar capillary column coated with 70% cyanoalkylpolysiloxane equivalent polymer. Migration of conjugated systems was geometrically controlled as follows: the cis‐C_n, trans‐C_n+2 double bond system was rearranged through a pericyclic [1, 5] sigmatropic mechanism into a trans‐C_n‐1, cis‐C_n+1 unsaturated system, while the trans‐C_n, cis‐C_n+2 double bond system was rearranged through a similar pericyclic mechanism into a cis‐C_n+1, trans‐C_n+3 unsaturated system. Selenium‐catalyzed geometrical isomerization under mild conditions then allowed cis/trans double bond configuration transitions, resulting in the formation of all cis, all trans, cis‐trans and trans‐cis isomers. A sequential combination of the two reactions resulted in a facile controlled synthesis of CLA isomers, useful for the chromatographic identification of milk fat CLA, as well as for the preparation of CLA standard mixture.     

Autoxidation of the furan fatty acid ester, methyl 9,12-epoxyoctadeca-9,11-dienoate

The objective of this study was to identify autoxidation products of methyl 9,12-epoxyoctadeca-9,11-dienoate (F_9,12). Previous work has shown that F_9,12 is a product both of autoxidation and singlet oxygen oxidation of the methyl ester derivative of conjugated linoleic acid (CLA). F_9,12, 95% pure, was synthesized from methyl ricinoleate. The synthetic F_9,12 was heated at 50°C in sealed tubes containing air. Each tube contained 6 mg F_9,12 and 1 mg methyl stearate as an internal standard. Samples were taken at 4.5, 7, 23, 46.5, 69.5, and 93 h. The oxidized F_9,12 was dissolved in isooctane and analyzed by gas chromatography (GC), GC-direct deposition-Fourier transform infrared spectroscopy, and GC-electron ionization mass spectrometry. CLA methyl ester was oxidized in a similar manner. Under these conditions, the half-lives of CLA and F_9,12 were 40 and 35 h, respectively. Oxidation products of F_9,12 that were identified included: 5-hexyl-2-furaldehyde (I), methyl 8-oxooctanoate (II), methyl 13-oxo-9,12-epoxytrideca-9,11-dienoate (III), methyl 8-oxo-9,12-epoxy-9,11-octadecadienoate (IV), and methyl 13-oxo-9,12-epoxy-9,11-octadecadienoate (V).     

Thermally induced formation of conjugated isomers of linoleic acid

Chemical pathways responsible of the conjugation of linoleic acid during heat treatments such as refining (deodorization), frying or cooking processes have been investigated. For this purpose, methyl linoleate was submitted to oxidative and non‐oxidative thermal conditions. The resulting degradation products were mainly composed of geometrical and conjugated fatty acid isomers. Oxidative conditions were obtained using tert‐butyl hydroperoxide under inert atmosphere, and air. The obtained results from both thermal oxidative conditions were compared to non‐oxidative thermal treatment. Higher levels of conjugated linoleic acid were found when linoleate was heated under oxidative conditions. Two distinct mechanisms responsible for the formation of CLA isomers are proposed and discussed. Evidence of formation of 9,11‐C18:2 and 10,12‐C18:2 acids from 9,12‐C18:2 by a free‐radical chain reaction is provided. The first step consists in the formation of a free radical by abstraction of an active bis‐allylic hydrogen. By delocalization of the initial free radical, two allylic free radicals were stabilized and converted into the corresponding CLA isomers via the abstraction of a hydrogen radical from other linoleic acid or oxygenated species. Kinetic observations confirmed the significance of the bimolecular mechanism. Moreover, the proposed mechanism is supported by several pieces of information from the literature on peroxidation of linoleic acid. Under pure thermal conditions and/or for diluted samples, a second pathway to the formation of CLA from heat‐treated linoleic acid is proposed via an intramolecular rearrangement of the pentadienyl structure. This thermal [1,3]‐sigmatropic rearrangement results in a mixture of 9,11 and 10,12 CLA isomers. The formed cis/trans CLA isomers were readily rearranged by a [1,5]‐sigmatropic shift to yield trans‐8,cis‐10 and cis‐11,trans‐13 CLA isomers, respectively.     

Conjugated linoleic acid concentration in processed cheese

The conjugated linoleic acid (CLA) concentration of a variety of processed cheese products ranged between 3.2 to 8.9 mg/g fat. Processing cheddar cheese at temperatures of 80°C and 90°C under atmospheric conditions increased (p < 0.05) CLA content, while processing under nitrogen (70°C, 85°C) had no effect. Increasing concentrations of whey protein concentrate (WPC) and its low molecular weight (LMW) fraction from 0 to 6% increased CLA formation. Six percent WPC and LMW fraction produced a 35% and 19% increase in CLA concentration, respectively, compared to processed cheese. The high molecular weight fraction of WPC did not increase CLA concentration. These results suggest that processing conditions and whey components play a role in CLA formation in processed cheese.     

Semi-IPN hydrogels based on Poly(vinyl alcohol) for controlled release studies of chemotherapeutic agent and their Swelling characteristics

Poly (vinyl alcohol)/poly(acryl amide-co-acrylamidoglycolic acid) (PVA/Poly(Am-co-AGA) based pH sensitive semi interpenetrating (semi-IPN) hydrogels were prepared by free radical polymerization in aqueous solution using N, N-methelene-bis-acryl amide (MBA) as a crosslinker. Different hydrogels with different compositions of AGA and MBA were prepared and characterized by Fourier transform infrared spectroscopy. The developed hydrogels were used for controlled release of 5-fluorouracil (5-FU). The drug entrapment efficiency up to 55% was achieved. The 5-FU loaded gels were characterized by X- ray diffraction and differential scanning calorimetric techniques, to understand the nature of drug in the polymeric matrix. The release of 5-FU through the semi-IPN was completed with in ∼12 h. Swelling studies performed in water have been analyzed with the help of an empirical equation to investigate the diffusion mechanism.