聚苹果酸- 聚乙二醇- 叶酸纳米共聚物的合成和生物活性的研究

目的:制备聚苹果酸-聚乙二醇-叶酸(PMLA-PEG-FA)纳米共聚物,为构建多功能靶向药物转运系统提供前期工作.方法:配体叶酸(FA)通过α-羟基-ω-醛基聚乙二醇(HO-PEG-CHO)以腙键连接在经过水合肼修饰的聚苹果酸的主链上.核磁共振光谱表征纳米共聚物的结构,动态透析法研究腙键响应不同pH值的断键特性,监测不同pH值共聚物中叶酸的稳定性.并采用SMCC-7721人体肝癌细胞测定该纳米共聚物的细胞毒性.结果:1、经核磁共振表征PMLA-PEG-FA共聚物合成完成.2、在pH5.5、pH6.5及pH7.4的PBS缓冲体系中,6h后配体叶酸累积释放率分别为88.1％,85.3％和41.6％.3、MTT实验证实PMLA-PEG-FA无毒性.结论:PMLA-PEG-FA有望成为智能靶向药物载体.     

共载依克立达和阿霉素的PBM-Hz-PEG纳米粒制备与性能研究

摘要 目的：研究不同比例依克立达（ELC）和阿霉素（DOX）的联合抗肿瘤效果,确定最佳联用比例。以生物可降解材料聚苹果酸苄基酯（PBM）为载体包封两种药物,得到一种酸敏感纳米胶束。方法：以L-天冬氨酸为原料通过内酯开环法制备PBM,并以酸敏感的腙键（Hz）连接PEG,得到嵌段聚合物PBM-Hz-PEG,红外光谱和核磁氢谱对其结构进行表征。动态透析法制备纳米胶束,测定纳米胶束的粒度、分散系数（PDI）、临界胶束浓度（CMC）及其载药量（DL）、包封率（EE）。动态透析法模拟胶束的体外释药性能,采用三阴性乳腺癌MDA-MB-231细胞系考察载药纳米胶束的体外细胞毒性。结果：①ELC能够增敏DOX,二者摩尔比为1:3时有最强肿瘤抑制作用。②经红外光谱和核磁共振氢谱表征,嵌段共聚物PBM-Hz-PEG成功合成。③空白纳米胶束的粒径为69.67±11.55 nm,PDI为0.245 ± 0.026,CMC值为3.9 μg?mL^-1;载药纳米胶束粒径略大,粒径在96.92 ~ 113.47 nm之间,ELC和DOX的载药量与投料比一致。④载药纳米胶束在pH 7.4和pH 6.0时的药物释放率曲线和体外细胞毒性试验证实载药胶束具有良好的酸敏特性。结论：ELC和DOX联用有较强的肿瘤抑制作用,PBM是二者的优良载体。该PBM-Hz-PEG纳米胶束载药率高,其特有的酸敏性能够有效降低药物对正常组织的毒副作用,具有肿瘤组织富集释放特性,有望成为一种新型智能释药平台。     

长春新碱PEG-PE胶束的制备及其对乳腺癌细胞生长的抑制

为提高长春新碱(VCR)的抗肿瘤活性并降低其毒副作用,利用聚乙二醇衍生化磷脂酰乙醇胺(PEG-PE)聚合物胶束作为载体制备了包载VCR的PEG-PE胶束(VCR胶束),对其理化性质和体外抗肿瘤活性进行研究.采用透射电镜观察胶束的外观形态,动态光散射法测定粒径和粒度分布,HPLC法测定包封率和体外释放度,MTT法测定VCR胶束及游离VCR对MCF-7细胞的毒性.透射电镜负染照片显示,VCR胶束呈不规则的球状结构,粒度分布窄而均一,平均粒径在(11.1±0.1)nm;VCR能有效被PEG-PE胶束包载,VCR与PEG-PE的摩尔比在1∶2～1∶10的范围内包载量均大于95%;体外释放度和耐稀释试验结果表明,VCR胶束在HBS和血清(pH7.0)两种释放介质中稳定,释放符合一级动力学释药模型;体外细胞毒试验表明,VCR胶束能显著提高VCR对MCF-7细胞生长的抑制作用.制得的VCR纳米胶束具有良好的稳定性、较高包封率和显著提高VCR的抗肿瘤活性,表明PEG-PE胶束将是VCR的一个高效输送载体.     

叶酸介导的普鲁兰多糖- 阿霉素聚合物前药的制备及生物学性能初探

目的:制备叶酸介导的普兰多糖-阿霉素聚合物前药(FA-MP-DOX),实现阿霉素药物的靶向控制释放。方法:将普鲁兰多糖用马来酸酐进行修饰后,通过酰胺键键合阿霉素制备得到普鲁兰多糖-阿霉素(MP-DOX),继而酯键键合叶酸制备得到叶酸介导的普鲁兰多糖-阿霉素聚合物前药(FA-MP-DOX)。红外光谱、核磁共振光谱表征聚合物药物的结构,动态透析法模拟体外释药特性,监测不同pH值聚合物药物中阿霉素的释药特性,同时采用人口腔表皮样癌细胞(KB细胞)测定聚合物药物体系的细胞毒性。结果:①经核磁共振表征FA-MP-DOX聚合物合成完成。②在pH2.5、pH5.0及pH7.4的PBS缓冲体系16h中,阿霉素药物累积释放率分别为49.1%,30.3%和15.3%,证实FA-MP-DOX中阿霉素的释放具有pH依赖性。③细胞实验证实FA-MP-DOX的细胞毒性高于阿霉素和MP-DOX。结论:FA-MP-DOX聚合物药物有望成为阿霉素智能型控释和靶向性药物载体。     

叶酸介导的普鲁兰多糖-阿霉素聚合物前药的制备及生物学性能初探

目的：制备叶酸介导的普兰多糖-阿霉素聚合物前药（FA-MP-DOX）,实现阿霉素药物的靶向控制释放。方法：将普鲁兰多糖用马来酸酐进行修饰后,通过酰胺键键合阿霉素制备得到普鲁兰多糖-阿霉素（MP-DOX）,继而酯键键合叶酸制备得到叶酸介导的普鲁兰多糖-阿霉素聚合物前药（FA-MP-DOX）。红外光谱、核磁共振光谱表征聚合物药物的结构,动态透析法模拟体外释药特性,监测不同pH值聚合物药物中阿霉素的释药特性,同时采用人口腔表皮样癌细胞（KB细胞）测定聚合物药物体系的细胞毒性。结果：①经核磁共振表征FA-MP-DOX聚合物合成完成。②在pH2.5、pH5.0及pH7.4的PBS缓冲体系16h中,阿霉素药物累积释放率分别为49.1%,30.3%和15.3%,证实FA-MP-DOX中阿霉素的释放具有pH依赖性。③细胞实验证实FA-MP-DOX的细胞毒性高于阿霉素和MP-DOX。结论：FA-MP-DOX聚合物药物有望成为阿霉素智能型控释和靶向性药物载体。     

聚苹果酸- 羟喜树碱前药的合成和性质初探

目的:化学全合成聚苹果酸(poly(β-malic acid),PMLA),将其作为高分子药物载体,制备聚苹果酸-羟喜树碱前药(PMLA-HCPT)。研究其体外释药特点和体外细胞毒性。方法:以L-天冬氨酸为原料,通过化学方法全合成PMLA,通过酰胺键键合羟基喜树碱(HCPT)。通过红外光谱、核磁共振光谱表征该前药的结构,利用体外动态透析的方法模拟体外释药特点,用高效液相色谱法测定不同pH值聚合物药物中前喜树碱的释药特性。采用人卵巢癌HO-8910细胞系研究该前药的体外毒性。结果:①经核磁共振表征PMLA-HCPT前药合成完成。②在pH 5.6、pH 6.8及pH 7.4的PBS缓冲体系16 h中,羟喜树碱药物累积释放率分别为76.8%,47.2%和18.1%,证实PMLA-HCPT中羟喜树碱的释放具有pH依赖性。③细胞实验证实PMLA-HCPT的细胞毒性和游离的HCPT相比没有降低。结论:PMLA是一种良好的药物载体材料,PMLA-HCPT有望成为具有pH敏感性的聚合物前药。     

具有pH响应及细胞核靶向功能的胶束的体内抗肿瘤活性的研究

目的:研究具有pH响应性及细胞核靶向功能的,由细胞穿透肽Tat修饰的聚乙二醇-聚己内酯共聚物胶束(PECL/DA-Tat-M)的体内抗肿瘤活性。方法:用溶剂挥发法制备了胶束,通过透射电镜(TEM)观察胶束形貌和大小。考察在不同pH条件下胶束的药物释放行为。在Bal b/c雌性小鼠的乳腺脂肪垫注射鼠源4T1乳腺癌细胞,建立小鼠乳腺癌原位模型,通过尾静脉向荷瘤小鼠注射具有pH响应及细胞核靶向功能的载药胶束。记录18天治疗期内肿瘤的体积、小鼠体重以及存活率的变化情况,并进行肿瘤组织的免疫组化研究。结果:TEM结果显示PECL/DA-Tat-M胶束呈球形结构,粒径在80 nm左右。在72小时内,胶束在pH 5.0条件释放80%的药物,而在pH 7.4条件下仅释放11%的药物。PECL/DA-Tat-M胶束组小鼠的肿瘤生长最缓慢,在治疗第18天,非靶向胶束(PECL-M)组肿瘤体积为0.82 cm3,PECL/DA-Tat-M组的肿瘤体积仅有0.51 cm3。生理盐水(Saline)组和空白胶束(PECL/DA-Tat-blank M)组的小鼠的肿瘤生长较为迅速,体积分别是PECL/DA-Tat-M胶束组肿瘤体积的4.43倍和3.76倍,差异具有统计学意义(P0.05或P0.01);各组小鼠经过治疗后体重均呈现出上升趋势;治疗期后第42天,PECL/DA-Tat-M胶束组和非靶向胶束(PECL-M)组小鼠的存活率分别为60%和40%,其他组的小鼠均在39天内全部死亡(n=5);肿瘤组织免疫组化分析结果表明PECL/DA-Tat-M载药胶束能有效抑制肿瘤生长,其抑瘤率(IR)、及肿瘤细胞凋亡率(AR)明显高于其他组,差异具有统计学意义(P0.05)。结论:具有pH响应及细胞核靶向功能的胶束(PECL/DA-Tat-M)具有良好的体内抗乳腺癌活性。     

D-甘露糖修饰聚合物胶束的制备及其在靶向药物输送中的应用

聚合物胶束作为药物载体具有良好的稳定性和生物相容性,提高疏水性药物溶解性等优势,是一类很有应用潜力的药物传输系统。本研究以合成的共价键连D-甘露糖的双亲性聚合物分子(PGMA-Mannose)为药物载体,包载抗癌药物阿霉素(DOX)制备具有甘露糖受体靶向性和pH敏感药物释放特性的新型载药聚合物胶束。利用激光共聚焦显微镜和MTT细胞毒性评价方法对载药胶束的细胞内吞摄取和毒性进行评价。实验结果表明,载药胶束能特异性识别人乳腺癌细胞MDA-MB-231表面过度表达的甘露糖受体,被癌细胞大量摄取并在细胞溶酶体酸性环境内释放药物,而载药胶束在表面甘露糖受体低表达的HEK293细胞中只有少量摄取。与原药DOX相比,该载药胶束对癌细胞的毒性显著提高,而对正常细胞的毒性较低。因此,该PGMA-Mannose聚合物胶束有望成为一种新型的靶向药物输送系统应用于癌症的治疗。     

嵌段共聚物聚乙二醇-聚苹果酸苄基酯载药胶束的制备及性质研究

目的：为构建聚合物胶束药物运载体系,制备嵌段共聚物聚乙二醇-聚苹果酸苄基酯载药胶束并测定其性质。方法：以L-天冬氨酸为原料,重氮化、环化后经开环聚合得到聚苹果酸苄基酯。氨基聚乙二醇通过酰胺键连接到β-聚苹果酸苄基酯上形成两亲性嵌段共聚物,喜树碱做药物模型制备载药胶束。动态光散射法测定胶束粒径、评价胶束稳定性,高效液相法测定喜树碱载药率和包封率,芘荧光法与动态光散射法测定临界胶束浓度。结果：喜树碱包封率72%,载药率6%,临界胶束浓度为40μg.mL-1。随着聚苹果酸苄基酯分子量减小,胶束稳定性增强。结论：聚乙二醇-聚苹果酸苄基酯在疏水链/亲水链分子量比值为2-4时在水中可自组装形成纳米胶束,可作为性能优良的聚合物药物载体。     

新型γ-聚谷氨酸自组装纳米胶束的制备及用于蛋白载体的研究

对水溶性的γ-聚谷氨酸(γ-PGA)进行了接枝改性,合成了两亲性γ-聚谷氨酸(γ-PGA)接枝衍生物,采用超声探头法制备胆甾醇基γ-PGA自组装胶束,并以卵清蛋白(OVA)作为模型蛋白,研究其载药和释药性能.结果表明,制备的两亲性胆甾醇基γ-PGA自组装胶束平均粒径为299.6+ 27.3nm,粒径的多分散系数较窄(0.17),且具有较低的细胞毒性;其疏水核-亲水壳的纳米微结构对蛋白药物显示了良好载药性能,对OVA载药量可达118.8 μg/mg,包封率33.5％;体外释药结果显示,负载OVA的甾醇基γ-PGA自组装胶束能延缓蛋白的释放,释药速率与介质pH密切相关.     

Enhanced oral bioavailability and anticancer activity of novel curcumin loaded mixed micelles in human lung cancer cells

BackgroundCurcumin has a wide range of pharmacological activities including antioxidant, anti-inflammatory, antidiabetic, antibacterial, wound healing, antiatherosclerotic, hepatoprotective and anti-carcinogenic. However, its clinical applications are limited owing to its poor aqueous solubility, multidrug pump P-gp efflux, extensive in vivo metabolism and rapid elimination due to glucuronidation/sulfation.PurposeThe objective of the current work was to prepare novel curcumin loaded mixed micelles (CUR-MM) of Pluronic F-127 (PF127) and Gelucire^® 44/14 (GL44) in order to enhance its oral bioavailability and cytotoxicity in human lung cancer cell line A549.Study design3² Factorial design was used to assess the effect of formulation variables for optimization of mixed micelle batch.MethodsCUR-MM was prepared by a solvent evaporation method. The optimized CUR-MM was evaluated for size, entrapment efficiency (EE), in vitro curcumin release, cytotoxicity and oral bioavailability in rats.ResultsThe average size of CUR-MM was found to be around 188 ± 3 nm with an EE of about 76.45 ± 1.18% w/w. In vitro dissolution profile of CUR-MM revealed controlled release of curcumin. Additionally, CUR-MM showed significant improvement in cytotoxic activity (3-folds) and oral bioavailability (around 55-folds) of curcumin as compared to curcumin alone. Such significant improvement in cytotoxic activity and oral bioavailability of curcumin when formulated into mixed micelles could be attributed to solubilization of hydrophobic curcumin into micelle core along with P-gp inhibition effect of both, PF127 and GL44.ConclusionThus the present work propose the formulation of mixed micelles of PF127 and GL44 which can act as promising carrier systems for hydrophobic drugs such as curcumin with significant improvement in their oral bioavailability.     

Tryptanthrin derivatives as Toxoplasma gondii inhibitors—structure–activity-relationship of the 6-position

A panel of derivatives of the natural product tryptanthrin was synthesized and screened for its in vitro activity against the intracellular parasite Toxoplasma gondii. We concentrated on the modification of the 6-keto group of tryptanthrin and prepared a series of oximes, hydrazones and alcohols based on tryptanthrin. We evaluated parasite growth inhibition and host cell cytotoxicity. Our results indicate that in particular alcohol analogs are promising candidates for further investigation.     

Self-Assembling Raloxifene Loaded Mixed Micelles: Formulation Optimization, <Emphasis Type="Italic">In Vitro</Emphasis> Cytotoxicity and <Emphasis Type="Italic">In Vivo</Emphasis> Pharmacokinetics

Raloxifene (RLX) has been strongly recommended for postmenopausal women at high risk of invasive breast cancer and for prevention of osteoporosis. However, low aqueous solubility and reduced bioavailability hinder its clinical application. The objective of this study was to explore the potential of RLX loaded mixed micelles (RLX-MM) using Pluronic F68 and Gelucire 44/14 for enhanced bioavailability and improved anticancer activity on human breast cancer cell line (MCF-7). RLX-MM were prepared by solvent evaporation method and optimized using 3² factorial design. The average size, entrapment efficiency and zeta potential of the optimized formulation were found to be 190?±?3.3 nm, 79?±?1.3%, 13?±?0.8 mV, respectively. In vitro study demonstrated 74.68% drug release from RLX-MM in comparison to 42.49% drug release from RLX dispersion. According to the in vitro cytotoxicity assay, GI₅₀ values on MCF-7 breast cancer cell line for RLX-MM and free RLX were found to be 22.5 and 94.71 μg/mL, respectively. Significant improvement (P?<?0.05) in the anticancer activity on MCF-7 cell line was observed in RLX-MM over RLX pure drug. Additionally, oral bioavailability of RLX-MM was improved by 1.5-fold over free RLX when administered in female Wistar rats. Incorporation of RLX in the hydrophobic core and improved solubility of the drug due to hydrophilic shell attributed to the enhanced cytotoxicity and bioavailability of RLX-MM. This research establishes the potential of RLX loaded mixed micelles of Pluronic F68 and Gelucire 44/14 for improved bioavailability and anticancer activity on MCF-7 cell line.     

Norbornene derived doxorubicin copolymers as drug carriers with pH responsive hydrazone linker

The synthesis and complete characterization of both norbornene-derived doxorubicin (mono 1) and polyethylene glycol (mono 2) monomers are clearly described, and their copolymerization by ring-opening metathesis polymerization (ROMP) to get the block copolymer (COPY-DOX) is vividly elaborated. The careful design of these conjugates exhibits properties like well-shielded drug moieties and well-defined nanostructures; additionally, they show solubility in both water and biological medium and also have the important tendency of rendering acid-triggered drug release. The drug release profile suggests the importance of having the hydrazone linker that helps to release the drug exactly at the mild acidic conditions resembling the pH of the cancerous cells. It is also observed that the drug release from micelles of COPY-DOX is significantly accelerated at a mildly acidic pH of 5.5-6, compared to the physiological pH of 7.4, suggesting the pH-responsive feature of the drug delivery system with hydrazone linkages. Confocal laser scanning microscopy (CLSM) measurements indicate that these COPY-DOX micelles are easily internalized by living cells. MTT assays against HeLa and 4T cancer cells showing COPY-DOX micelles have a high anticancer efficacy. All of these results demonstrate that these polymeric micelles that self-assembled from COPY-DOX block copolymers have great scope in the world of medicine, and they also symbolize promising carriers for the pH-triggered intracellular delivery of hydrophobic anticancer drugs.     

Structure-Activity Relationships of Novel Salicylaldehyde Isonicotinoyl Hydrazone (SIH) Analogs: Iron Chelation,Anti-Oxidant and Cytotoxic Properties

Salicylaldehyde isonicotinoyl hydrazone (SIH) is a lipophilic, tridentate iron chelator with marked anti-oxidant and modest cytotoxic activity against neoplastic cells. However, it has poor stability in an aqueous environment due to the rapid hydrolysis of its hydrazone bond. In this study, we synthesized a series of new SIH analogs (based on previously described aromatic ketones with improved hydrolytic stability). Their structure-activity relationships were assessed with respect to their stability in plasma, iron chelation efficacy, redox effects and cytotoxic activity against MCF-7 breast adenocarcinoma cells. Furthermore, studies assessed the cytotoxicity of these chelators and their ability to afford protection against hydrogen peroxide-induced oxidative injury in H9c2 cardiomyoblasts. The ligands with a reduced hydrazone bond, or the presence of bulky alkyl substituents near the hydrazone bond, showed severely limited biological activity. The introduction of a bromine substituent increased ligand-induced cytotoxicity to both cancer cells and H9c2 cardiomyoblasts. A similar effect was observed when the phenolic ring was exchanged with pyridine (i.e., changing the ligating site from O, N, O to N, N, O), which led to pro-oxidative effects. In contrast, compounds with long, flexible alkyl chains adjacent to the hydrazone bond exhibited specific cytotoxic effects against MCF-7 breast adenocarcinoma cells and low toxicity against H9c2 cardiomyoblasts. Hence, this study highlights important structure-activity relationships and provides insight into the further development of aroylhydrazone iron chelators with more potent and selective anti-neoplastic effects.     

Effects of Biorelevant Media Components on Dissolution Behaviour of 1,2,4‐Thiadiazole Derivative Designed for Alzheimerʼs Disease Prevention

In this study, dissolution behaviour of 1,2,4‐thiadiazole derivative (1‐[5‐(3‐chloro‐phenylamino)‐1,2,4‐thiadiazol‐3‐yl]‐propan‐2‐ol) displaying an anti‐Alzheimer activity was examined in biorelevant media such as Simulated Gastric Fluid (SGF, pH 1.2), Fasted State Simulated Gastric Fluid (FaSSGF, pH 1.6) and Fasted State Simulated Intestinal Fluid (FaSSIF, pH 6.5). It was found that solubility and dissolution rate of 1,2,4‐thiadiazole derivative under consideration are not strongly dependent on pH, whereas these parameters are significantly affected by the buffer composition. Dissolution was found to be more effective in buffers composed of the surfactant micelles. It was demonstrated that considerable increase in solubility and dissolution rate in SGF is achieved through the interaction of 1,2,4‐thiadiazole derivative with the micelles of sodium dodecyl sulfate. On the contrary, CMC of sodium taurochalate was shifted in the presence of 1,2,4‐thiadiazole derivative, therefore, dissolution process is not so efficient in FaSSIF. Interactions occurring between 1,2,4‐thiadiazole derivative and the components of biorelevant media were investigated in detail by means of UV/VIS spectroscopy, ¹H‐NMR and phase solubility methods.     

Preparation and in vitro and in vivo evaluation of quercetin-loaded mixed micelles for oral delivery

Quercetin (QT) is a plant polyphenol with various pharmacological properties. However, the low water solubility limits its therapeutic efficacy. In the present study, QT-loaded sodium taurocholate-Pluronic P123 (QT-loaded ST/P123) mixed micelles were developed and characterized, and the effect of the formulation on improving the water solubility of QT was investigated. QT-loaded ST/P123 mixed micelles were prepared by thin film hydration-direct dissolution and optimized by uniform design. The optimal formulation possessed high drug loading (12.6%) and entrapment efficiency (95.9%) in small (16.20 nm) spherically-shaped micelles. A low critical micelle concentration indicated that the micelles were stable, and they showed a sustained release pattern, as determined in vitro in simulated gastric fluid and intestinal fluid. Pharmacokinetic evaluation showed the C_max and AUC_0–24 were 1.8-fold and 1.6-fold higher than the QT suspension. The present results indicate that QT-loaded ST/P123 micelles are potential candidates to improve the solubility and oral bioavailability of QT.     

Biocompatible Phospholipid-Based Mixed Micelles for Tamoxifen Delivery: Promising Evidences from <Emphasis Type="Italic">In - Vitro</Emphasis> Anticancer Activity and Dermatokinetic Studies

Tamoxifen (TAM) is frequently prescribed for the management breast cancer, but is associated with the challenges like compromised aqueous solubility and poor bioavailability to the target site. It was envisioned to develop phospholipid-based mixed micelles to explore the promises offered by the biocompatible carriers. Various compositions were prepared, employing soya lecithin, polysorbate 80, sodium chloride/dextrose, and water, by self-assembled technique. The formulations were characterized for micromeritics and evaluated for in vitro drug release, hemolysis study, dermatokinetic studies on rodents, and cytotoxicity on MCF-7 cell lines. Cellular uptake of the system was also studied using confocal laser scanning microscopy. The selected composition was of sub-micron range (28.81?±?2.1 nm), with spherical morphology. During in-vitro studies, the mixed micelles offered controlled drug release than that of conventional gel. Cytotoxicity was significantly enhanced and IC₅₀ value was reduced that of the naïve drug. The bioavailability in epidermis and dermis skin layers was enhanced approx. fivefold and threefold, respectively. The developed nanosystem not only enhanced the efficacy of the drug but also maintained the integrity of skin, as revealed by histological studies. The developed TAM-nanocarrier possesses potential promises for safe and better delivery of TAM.     

The complexation of aqueous metal ions relevant to biological applications. 1. Poorly soluble zinc salts and enhanced solubility with added amino acid

Abstract

The effect of added amino acid (glycine, alanine and serine) on the solubility of zinc citrate, zinc succinate and zinc oxalate was investigated. Equilibrated solutions were prepared and titrated to endpoint at pH 5.5 with Na₂EDTA using Xylenol Orange indicator. In every case, a significant enhancement in solubility was seen as the amino acid increased from 1 to 50 molar excess. The increase was non-linear, and, with zinc succinate, showed saturation effects. In these cases, solution composition may be more complicated than initially thought, including mixed-ligand complexes and increasing percent free metal ion as the proportion of amino acid increases.     

Studies on the Critical Micellar Concentration and Phase Transitions of Stearoylcarnitine

The critical micellar concentration (CMC) of stearoylcarnitine was determined at different pH values at room temperature by fluorescence spectroscopy, monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonate (ANS). The CMC was found to vary with pH, increasing from about 10 μM at pH 3.0 to ca. 25 μM at pH 7.0, but decreasing slightly with further increase in pH to approximately 19 μM at pH 10.0. Differential scanning calorimetry (DSC) shows that stearoylcarnitine dispersed in water at low concentration undergoes a broad thermotropic phase transition at 44.5°C, with a transition enthalpy of 15.0 kcal/mol. The transition temperature (T _t) shifts to ca. 50.5°C in the presence of 1 mM EDTA or when the concentration is increased significantly. The turbidity of aqueous dispersions of stearoylcarnitine was found to be considerably high at low temperatures, which decreases quite abruptly over a short temperature range, indicating that a transition occurs from a phase of large aggregates to one of much smaller aggregates, most likely micelles. The phase transition temperature was determined as 29.1°C at pH 3.0, which increased with increasing pH up to a value of 55.3°C at pH 8.6 and remains nearly constant thereafter up to pH 11.2. The pH dependence of CMC and T _t suggest that the pK _a of the carboxyl group of long chain acylcarnitines shifts to higher temperatures upon aggregation (micelles or bilayer membranes).