Peroxidase-dependent fluorescence decrease of carboxyfluorescein and its enhancement by liposome encapsulation

The fluorescence intensity of 5(6)-carboxyfluorescein (CF) was decreased by addition of horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The reaction inside a liposome containing CF and HRP on addition of H₂O₂ was measured fluorometrically after destruction of the liposome with Triton X-100. The reaction efficiency was higher than that without liposome because CF and HRP were concentrated inside the latter. The determination of H₂O₂ can be performed with a smaller amount of HRP by liposome encapsulation.     

Conformational effects induced by guest encapsulation in an enantiopure water-soluble cryptophane

A new water-soluble cryptophane 1 derivative (penta-hydroxyl cryptophane-A) has been synthesized from cryptophanol-A and the chiroptical properties of its two enantiomers MM-1 and PP-1 have been studied by polarimetry, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD). Cryptophane 1 shows specific circular dichroism responses upon complexation that depend on the size of the guest and on the nature of the counterion (Li(+), Na(+), K(+), Cs(+)) present in the solution. In LiOH and NaOH solutions, chiroptical changes induced by the encapsulation of guests and by the presence of cations in the vicinity of hosts can be interpreted from molecular dynamics (MD) and ab initio calculations by subtle conformational changes of the bridges. In KOH solution, the exchange dynamics is dependent on the size of the guest molecules, whereas in CsOH solution no encapsulation effect is observed whatever the size of the guest molecule. This last behavior comes from the fact that host 1 exhibits a very high affinity for cesium cations.     

Effect of pH and counterions on the encapsulation properties of xenon in water-soluble cryptophanes

In the ¹²⁹Xe NMR‐based biosensing approach in which the hyperpolarized noble gas is transported to biological receptors for a sensitive molecular imaging, cryptophanes are excellent xenon host systems. However to avoid formation of self‐organized systems, these hydrophobic cage molecules can be rendered water soluble by introduction of ionic groups. We show that the sensitivity of xenon to its local environment and the presence of these ionic functions can lead to interesting properties. For a first water‐soluble cryptophane derivative, we show that a precise monitoring of the local pH can be performed. For a second cryptophane, the presence of ionic groups close to the cryptophane cavity modifies the xenon binding constant and in–out exchange rate. The latter allows the tuning of physical properties of xenon–cryptophane interactions without resorting to a change of the cavity size. These results open new perspectives on the influence of chemical modifications of cryptophanes for optimizing the biosensor properties.     

Guest encapsulation in a water-soluble molecular capsule based on ionic interactions

We report on the synthesis and characterization of a water-soluble molecular capsule based on multiple ionic interactions. The assembly has been studied by means of 1H NMR, ESI-MS spectroscopy, and isothermal titration calorimetry (ITC), showing an association constant in water, Ka, of 3.3 x 104 M-1. The achieved water solubility of the system opens the possibility of using this supramolecular assembly for molecular recognition in pure water. Encapsulation studies have been performed and are reported in this Communication.     

Acceleration of amide bond rotation by encapsulation in the hydrophobic interior of a water-soluble supramolecular assembly

The hydrophobic interior cavity of a self-assembled supramolecular assembly exploits the hydrophobic effect for the encapsulation of tertiary amides. Variable-temperature (1)H NMR experiments reveal that the free energy barrier for rotation around the C-N amide bond is lowered by up to 3.6 kcal/mol upon encapsulation. The hydrophobic cavity of the assembly is able to stabilize the less polar transition state of the amide rotation process. Carbon-13 labeling studies showed that the (13)C NMR chemical shift of the carbonyl resonance increases with temperature for the encapsulated amides, which suggests that the assembly is able to favor a twisted form of the amide.     

Formation mechanism of the macrovoids induced by surfactant additives

In the present work, it is shown that addition of surfactants in the casting solution can induce or suppress macrovoids in polymeric membranes, depending on the miscibility between the added surfactant and the coagulant. Dual-bath experiments, in which casting solution was immersed in one coagulant for a very short time (<2 s) and then removed to a second bath containing different coagulants, were performed to investigate the formation process of macrovoids induced by surfactants. The results suggest that the initiation of macrovoids is completed in the first bath and the growth of macrovoids begins in the first bath but continues in the second bath. It was observed that the size of macrovoids is insensitive to the coagulant used in the second bath, which can be accounted for by proposing that the growth of macrovoids is mainly due to imbibing solvent from the surrounding polymer solution. To verify the above proposal, results from optical study and analysis of the growth speed of macrovoids are also presented.     

Encapsulation of doxorubicin into liposomes by a freeze-thawing method using buffer solution

When doxorubicin was encapsulated into liposomes by freeze-thawing, the percentage of encapsulated doxorubicin (EN%) was found to vary according to the type of buffer solution used. The reason for this was investigated in the present report. Drug-free liposomes prepared by hydration were mixed with doxorubicin dissolved in a certain type of buffer solution that shows a pH decrease on freezing, and this mixture was subjected to freeze-thawing. Doxorubicin was encapsulated by the liposomes due to the difference in pH between freezing and thawing. EN% depended on the pH of the buffer solution before freezing and increased significantly at over pH 7. About 60% of doxorubicin was encapsulated into liposomes after the Ist freeze-thawing cycle, and EN% was increased gradually with the number of freeze-thawing cycles. The addition of sugar to the experimental system was seen to affect doxorubicin encapsulation and the particle size of liposomes.     

Studies on catalytic hydrogenation of citral by water-soluble palladium complex

The hydrogenation of citral has been studied in biphasic system using water-soluble PdCl₂(TPPTS)₂ as catalyst. The selectivity to form citronellal increased with increasing pH values of the aqueous phase. At the same pH value, the selectivity was higher when the hydrogenation was carried out in the presence of Na₂CO₃ than in the presence of NaOH. The main product was citronellal and a maximum yield of 93% had been obtained using Na₂CO₃ solution at pH 11.6. The CC bond in citronellal could be further hydrogenated to form dihydrocitronellal when the hydrogenation was carried out in distilled water at pH 6.0. The yield of dihydrocitronellal could reach 93% with prolonged reaction time to 6 h. Therefore, high yields of either citronellal or dihydrocitronellal could be obtained from citral by selecting the corresponding reaction conditions.     

Mechanochemical preparation of water-soluble composites based on quercetin

The solubility and antioxidant activity of the bioflavonoid quercetin was increased from its mechanochemically prepared solid composites with metal carbonates and carbohydrate compounds.     

Studies on the biomimetic membrane interaction between liposome and realgar nanoparticles

The liposome of small unilamellar vesicles (SUV) made from phosphatidylcholine-cholesterol mixtures was used as a simple model for biomimetic membranes. The studies on the interaction between the liposome and realgar nanoparticles (NPs) demonstrate that the phospholipid is one of the key targeted molecules of realgar NPs, used by surface plasmon resonance (SPR) technology, fluorescence polarization, Raman spectroscopy, nuclear magnetic resonance (NMR) and atom force microscope (AFM). It was observed that th...     

纳米雄黄与脂质体仿生膜的相互作用研究

本工作以卵磷脂与胆固醇组成的磷脂小单层脂质体（small unilamelarvesicles,suv）作为仿生膜的简单模型,采用表面等离子共振技术（SPR）、荧光偏振、拉曼（Raman）光谱、核磁共振（NMR）及原子力显微镜（AFM）研究纳米雄黄与SUV仿生膜的相互作用,证实了磷脂是纳米雄黄作用的关键靶分子．随纳米雄黄结合,SUV仿生膜的相对粘度聃值增大,膜的流动性减小．Raman光谱数据计算表明,作用后膜的纵向有序性参数s。。及横向有序性参数Slat值增大,说明纳米雄黄的结合使磷脂膜的脂酰基链全反式构型比例上升,膜的流动性减小．由Raman光谱和引PNMR结果推测,磷脂极性头部是纳米雄黄与磷脂的主要结合位点。AFM实时观测,纳米雄黄通过在膜表面打“孔”或“洞”的方式,损坏磷脂膜．     

A facile method for preparation of green and antibacterial hydrogel based on chitosan and water-soluble 2,3-dialdehyde cellulose

Cellulose - Chitosan (CS) has been widely used to prepare natural hydrogel duo to its characteristics. However, most of the methods of preparing CS-based hydrogel are complicated and not green,...     

丙氨酸肽脂的合成与脂质体制备

以十六酸、十六烷基胺、Boc保护丙氨酸、6-溴己酰氯、三甲胺为主要原料,通过EDC(1-乙基-(3-二甲基氨基丙基)碳二亚胺)缩合、氢化锂铝还原酰胺形成胺等反应合成丙氨酸肽脂,最终得率为39.9%,高分离温度(35℃)可提高产物得率。丙氨酸肽脂不需要胆固醇与辅助类脂可独立形成脂质体,通过激光粒度仪、透射电子显微镜进行初步检测,脂质体平均粒径为97.4±15.5nm,表面电位为+63.53±1.53 m V。     

Studies on formation mechanism of polypyrrole microtubule synthesized by template‐free method

The influence of the polymerization time and rate as well as the solution's ionic strength on the morphology, conductivity, and molecular structure of the polypyrrole (PPy) microtubule [synthesized by the template‐free method in the presence of β‐naphthalene sulfonic acid (β‐NSA) as the dopant] were investigated. It was found that the formation of the PPy‐NSA microtubule was a slow and self‐assembled growth process. Moreover, the β‐NSA dopant played a “templatelike” role in the formation of tubular PPy‐NSA, which might be relative to its surfactant characters. This assumption was further confirmed by the phenomenon that the morphology of PPy‐NSA could be modified by increasing the ionic strength by adding inorganic salt. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 997–1004, 2001     

Studies on the encapsulation of diclofenac in small unilamellar liposomes of soya phosphatidylcholine

The encapsulation of acid (AD) and sodium diclofenac (SD) in small unilamellar liposomes (SUV) as well as the interactions of the drug with the bilayer was studied. SUV was prepared by sonication from multilamellar liposomes containing soya phosphatidylcholine and diclofenac at various proportions. The size distribution obtained from dynamic light scattering showed that the incorporation of SD decreases significantly the size of the liposomes suggesting that the drug interacts with the bilayer of the liposomes. This size decrease is related with the phase transition of liposomes to mixed micelar solution. The encapsulation of the hydrophilic dye indocyanine green in the aqueous compartment of liposomes showed that the rate of captured dye decreases with SD concentration suggesting the transition of liposomes to mixed micelles. The (31)P NMR analysis indicates that SD interacts with the phosphate of phosphatidylcholine head groups. A schematic model for interaction of SD with phosphatidylcholine of the liposomes in which the diclofenac anion interacts with the ammonium group of the phospholipid and the dichlorophenyl ring occupies a more internal site of bilayer near phosphate group was proposed.     

The effect of additives on organolithiums

The effect of additives on the “apparent” acidities of weak carbon acids as measured versus lithiated amides is found to be small (< 2 pK units). TMEDA is found to be the most effective in accelerating the rates of deprotonation of triphenylmethane.