Effects of diclofenac on EPC liposome membrane properties

In this work the interaction of a non-steroidal anti-inflammatory drug (NSAID), diclofenac, with egg yolk phosphatidylcoline (EPC) liposomes, used as cell-membrane models, was quantified by determination of the partition coefficient. The liposome/aqueous phase partition coefficient was determined by derivative spectrophotometry, fluorescence quenching, and measurement of zeta-potential. Theoretical models based on simple partition of the diclofenac between two different media, were used to fit the experimental data, enabling the determination of K_p. The three techniques used yielded similar results. The effects of the interaction on the membranes characteristics were further evaluated, either by studying membrane potential changes or by effects on membrane fluidity. The liposome membrane potential and the size and size-homogeneity of liposomes were measured by light scattering. The effects of diclofenac on the internal viscosity or fluidity of the membrane were determined by use of spectroscopic probes—a series of n-(9-anthroyloxy) fatty acids in which the carboxyl terminal group is located at the interfacial region of the membrane and the fluorescent anthracene group is attached at different positions along the fatty acid chain. The location of the diclofenac on the membrane was also evaluated, by fluorescence quenching using the same series of fluorescent probes. Because the fluorescent anthracene group is attached at different positions along the fatty acid chain, it is possible to label at a graded series of depths in the bilayer. The interactions between the drug and the probe are a means of predicting the location of the drug on the membrane.     

衍生荧光法测定盐酸西布曲明

通过衍生反应，建立了用荧光光度法测定盐酸西布曲明的新方法。并对衍生体系、反应条件、产物稳定性等进行了研究。实验确定丙二酸和乙酸酐混合试剂与盐酸西布曲明在75℃的水浴中加热15min，所得产物发射强荧光，最大激发波长λcx=456nm，最大发射波长λem=496nm。在上述波长下，荧光强度与盐酸西布曲明的质量浓度在0．11～9．5μg／mL范围内呈良好的线性关系，检出限为13．4ng／mL，标准加入回收率在95．4％～104．2％。用于曲美胶囊中盐酸西布曲明的测定。     

乌拉地尔的荧光光谱研究及测定

建立了一种测定制剂中乌拉地尔的荧光分光光度法。用荧光分光光度法研究了不同溶剂和pH下乌拉地尔的荧光光谱性质。在pH5.0缓冲溶液中,在3.30×10-7～1.65×10-5mol/L浓度范围内,285nm紫外光的激发下,乌拉地尔在365nm处的荧光强度与浓度呈良好的线性关系。线性相关系数为0 9975,测定片剂和针剂的平均回收率分别为99.0%和99.8%,相对标准偏差小于3 0%。     

Optimization of DNA-tagged liposomes for use in microtiter plate analyses

Dye-encapsulating unilamellar DNA oligonucleotide-tagged liposomes were prepared and characterized for use as signal-enhancing reagents in a microtiter plate sandwich-hybridization analyses of single-stranded RNA or DNA sequences. The liposomes were synthesized using the reversed-phase evaporation method and tagged with DNA oligonucleotides by adding cholesteryl-modified DNA reporter probes to the initial lipid mixture. Liposomes were prepared using probe coverages of 0.0013–0.103 mol% of the total lipid input, several hydrophobic and poly(ethylene glycol)-based spacers between the cholesteryl anchor and the probe, and liposome diameters ranging from 200 nm to 335 nm. Their signal enhancement functionality was compared by using them in microtiter plate sandwich-hybridization assays for the detection of single-stranded DNA sequences. In these assays, an optimal reporter probe concentration of 0.103 mol%, a liposome diameter of 274 nm, and a phospholipid concentration of 0.3 mM were found. The length between the cholesteryl anchor and the probe was optimal when a spacer composed of TEG+(CH₂O)₃ was used. Under optimal conditions, a detection limit of 0.5 nM for a truncated synthetic DNA sequence was found with a coefficient of variation of 4.4%. A 500-fold lower limit of detection using fluorescence was found using lysed dye-encapsulating liposomes versus a single fluorescein-labeled probe. Finally, when this method was applied to the detection of atxA RNA extracted from E.coli SG12036-pIu121 and amplified using NASBA, a minimum extracted concentration of RNA of 1.1×10⁻⁷ μg/μL was found.     

Partition Equilibrium on the Interface Between a Charged Membrane and a Mixed Electrolyte Aqueous Solution

Ionic partition equilibrium on a charged membrane immersed in a mixed electrolyte solution was systematically investigated and several models were established for the determination of partition coefficients.On the basis of theoretical models,the effects of the concentration ratio λof the fixed group(charged density) to reference electrolyte,the concentration ratio η between the two electrolytes existing in the solution and the valence of the electrolyte ions on the partition equilibrium in a positively charged membrane were analyzed and simulated within the chosen parameters in detail.The obtainable results can also be applicable to a sytem of mixed electrolytes contacting with a negatively charged membrane.The theoretical calculations were confirmed with the experimental data of model mixed electrolytes,NaCl HCl and CaCl2 NaCl partitioned in the system of self-made negatively charged membrane-sulphonated poly (phenylene oxide)(SPPO) with different charge densities.     

Universal liposomes: preparation and usage for the detection of mRNA

Dye-encapsulating liposomes can serve as signaling reagents in biosensors and biochemical assays in place of enzymes or fluorophores. Detailed here is the use and preparation of streptavidin-coupled liposomes which offer a universal approach to biotinylated target detection. The universal approach provides two advantages, i.e. only one type of liposome is necessary despite varying target and probe sequences and the hybridization event can take place in the absence of potential steric hindrance occurring from liposomes directly conjugated to probes. One objective of this work was to optimize the one-step conjugation of SRB-encapsulating liposomes to streptavidin using EDC. Liposome, EDC, streptavidin concentrations, and reaction times were varied. The optimal coupling conditions were found to be an EDC:carboxylated lipid:streptavidin molar ratio of 600:120:1 and a reaction time of 15 min. The second goal was to utilize these liposomes in sandwich hybridization microtiter plate-based assays using biotinylated reported probes as biorecognition elements. The assay was optimized in terms of probe spacer length, probe concentration, liposome concentration, and streptavidin coverage. Subsequently, the optimized protocol was applied to the detection of DNA and RNA sequences. A detection limit of 1.7 pmol L⁻¹ and an assay range spanning four orders of magnitude (5 pmol L⁻¹−50 nmol L⁻¹) with a coefficient of variation ≤5.8% was found for synthetic DNA. For synthetic RNA the LOQ was half that of synthetic DNA. A comparison was made to alkaline phosphatase-conjugated streptavidin for detection which yielded a limit of quantitation approximately 80 times higher than that for liposomes in the same system. Thus, liposomes and the optimized sandwich hybridization method are well suited for detecting single-stranded nucleic acid sequences and compares favorably to other sandwich hybridization schemes recently described in the literature. The assay was then used successfully for the clear detection of mRNA amplified by nucleic acid sequence-based amplification (NASBA) isolated from as little as one Cryptosporidium parvum oocyst. The detection of mRNA from oocysts isolated from various water sample types using immunomagnetic separation was also assessed. Finally, to prove the wider applicability and sensitivity of this universal method, RNA amplified from the atxA gene of Bacillus anthracis was detected when the input to the preceding NASBA reaction was as low as 1.2 pg. This highly sensitive liposome-based microtiter plate assay is therefore a platform technology allowing for high throughput and wide availability for routine clinical and environmental laboratory applications.     

A fluorescence spectroscopic study of the interaction between epristeride and bovin serum albumine and its analytical application

A new spectrofluorimetric method to determine epristeride (EP) has been developed, which based on the EP has a strong ability to quench the intrinsic fluorescence of bovine serum albumin (BSA). There was the relationship between the fluorescence quenching intensity of BSA (ΔF = F_BSA − F_BSA-EP) and the concentration EP. The quenching mechanism was investigated with the quenching type, the association constants, the number of binding sites and basic thermodynamic parameters. The method had been successfully applied to the analysis of EP in real samples and the obtained results were in good agreement with the results of official method-HPLC.     

二氢蒽醌用于荧光猝灭法测定痕量汞

荧光动力学分析法常以罗丹明类、荧光素类、桑色素等作为指示物,用蒽醌作为指示物较少见。本文报道了以2,3二-氢-9,10二-羟基-1,4蒽-醌(R)为指示物,荧光动力学分析法测定痕量汞的新方法。直接用硼酸代替三氯化铝加硫酸封环一步法制得1,4二-羟基-9,10蒽-醌,再经冰醋酸和锌粉还原     

分子荧光法测定水中的微量铁

基于Fe（Ⅱ）与邻菲口罗啉生成络合物使其荧光猝灭的特性,讨论了在室温下,pH 5.5的乙酸-乙酸铵的缓冲介质中,以λex=270 nm为激发波长,于eλm=365 nm波长处测定该络合物荧光强度。结果表明Fe（Ⅱ）质量浓度在0.8-120.0 ng/mL范围内与络合物的荧光强度具有良好的线性关系,相关系数0.9994,检出限0.50 ng/mL。对60 ng/mL的Fe RSD（n=9）为2.8%。Fe的回收率为98.03%-102.9%。方法已用于水中微量铁的测定。     

Suppression of aggregation-induced fluorescence quenching in pyrene derivatives: photophysical properties and crystal structures

Two new pyrene-based fluorophores, namely 1-[4-(2,2-diphenylvinyl)phenyl]pyrene (PVPP) and 1,3,6,8-tetrakis[4-(2,2-diphenylvinyl)phenyl]pyrene (TPVPP), were synthesized through Suzuki coupling reaction and well characterized. PVPP successfully suppresses the fluorescence quenching of pyrene units in the solid state, displaying aggregation-induced enhanced emission. Despite the same substituent, TPVPP shows a different fluorescent behavior. On the basis of the crystal structures, the distinct optical behavior is discussed and clarified. The intermolecular C-H?π interaction has a dramatic effect on their photophysical properties in the solid state.     

Potentiometric determination of octanol-water and liposome-water partition coefficients (log P) of ionizable organic compounds

The logarithm of the octanol-water partition coefficient, log P, is a key physicochemical property for both pharmaceutical drugs and agrochemicals. It is also required by legislation as part of the physicochemical properties profile for high volume production chemicals. This Letter describes a simple method for determining log P values (over a wide range from −0.8 to 5.3) for 12 organic weak acids and bases using potentiometric titrations, with octanol or phosphatidyl choline liposomes as the partitioning medium. Such titrations take comparatively little time (about 30-45 min per titration), are easy to implement, and can be carried out with an inexpensive laboratory titrator.     

Interaction of magnolol with bovine serum albumin: a fluorescence-quenching study

The interaction of magnolol with bovine serum albumin(BSA) was studied using fluorescence spectroscopy under physiological conditions. The binding constants, K, and the ratio of quantum yields of protein fluorescence for complex and free protein, f, at 298 K, 304 K, and 310 K were obtained; the values were 6.799×10⁵ L mol^–1, 5.541×10⁵ L mol^–1, and 4.344×10⁵ L mol^–1 and 0.17, 0.30, and 0.34, respectively. The standard enthalpy change (H°) and the standard entropy change (S°) were calculated to be –28.53 kJ mol^–1 and 15.88 J mol^–1 K^–1, which indicated that hydrophobic forces played major role in the interaction of magnolol and BSA. The binding average distance between magnolol and BSA (4.32 nm) was obtained on the basis of the theory of Förster energy transfer.     

Second derivative spectrophotometric determination of partition coefficients of phenothiazine derivatives between human erythrocyte ghost membranes and water

The absorption spectra of six phenothiazine derivatives, chlorpromazine, triflupromazine, promazine, promethazine, trifluoperazine and prochlorperazine, measured in the solutions containing various amounts of human erythrocyte ghosts (HEG) showed bathocromic shifts according to the amount of HEG. Due to the strong background signals caused by HEG, the baseline compensation was incomplete, even though the sample and the reference solutions contained the same amount of HEG, hence further spectral information could not be obtained. The second derivative spectra of these absorption spectra clearly showed the derivative isosbestic points, indicating that the residual background signal effects were entirely eliminated. The derivative intensity differences of the phenothiazines (ΔD values) before and after the addition of HEG were measured at a specific wavelength. Using the ΔD values, the partition coefficients (K_p) of these drugs were calculated and obtained with R.S.D. of below 10 %. The fractions of partitioned phenothiazines calculated from the K_p values agreed well with the experimental values. The results indicate that the derivative method can be applicable to the determination of partition coefficients of drugs to HEG without any separation procedures.     

Partition Coefficients in Octanol-Water and Liquid Chromatographic Behavior of Eight Oxygenated Triterpenes Which are Paired Stereo- and Positional Isomers

The chromatographic behavior of eight lanostanoid triterpenes, which are four pairs of C-3 epimers and two pairs of C-3/C-15 positional isomers, were determined by reverse-phase high performance liquid chromatography (RP-HPLC). In the mobile phase systems of acetonitrile-water-acetic acid, methanol-water-acetic acid, and tetrahydrofuran-water-acetic acid, these triterpenes showed a very good linear relationship between capacity factors (k′) and volume fractions of organic modifiers. The partition coefficients (Poet) of these triterpenes in 1-octanol/water and capacity factors (k′) in RP-HPLC, when both expressed in logarithm, correlated linearly. This study showed that RP-HPLC is an effective method to evaluate the molecular hydrophobicity of multi-functional compounds which are stereo- and positional isomers.     

Partition coefficients of organic molecules in squalane and water/ethanol mixtures by molecular dynamics simulations

Accurate partition coefficient data of migrants between a polymer and a solvent are of paramount importance for estimating the migration of the migrant over time, including the concentration of the migrant at infinite time in the two solvents. In this article it is shown how this partition coefficient can be estimated for both a small hydrophilic and a hydrophobic organic molecules between squalane (used here to mimic low density poly ethylene) and water/ethanol solutes using thermodynamic integration to calculate the free energy of solvation. Molecular dynamics simulations are performed, using the GROMACS software, by slowly decoupling of firstly the electrostatic and then the Lennard-Jones interactions between molecules in the simulation box. These calculations depend very much on the choice of force field. Two force fields have been tested in this work, the TraPPE-UA (united-atom) and the OPLS-AA (all-atom). The computational cheaper TraPPE-UA force field showed to be more accurate over the whole range of systems compared to the OPLS-AA force field. Moreover, some of the calculations were done with five different water models to investigate the influence of the specific water model on the calculations. It was found that the combination of the TraPPE-UA force field and the TIP4p water model gave the best results. Based on the methodology proposed in this article, it is possible to obtain good partition coefficients only knowing the chemical structure of the molecules in the system.     

直链醇、烷基苯气相色谱保留指数之比与其正辛醇/水分配系数的相关性

通过研究直链醇、烷基苯等有机物气相色谱保留指数与其正辛醇／水分配系数的关系得出,在极性相异固定相上保留指数之比Im/n与其正辛醇／水分配系数的对数值logkow之间有较好的线性相关性。因而由保留指数能很好的预测分配系数,从而为直链醇、烷基苯分配系数的测定提供了一种简便准确的新方法。     

荧光猝灭法测定次黄嘌呤及机理研究

研究了次黄嘌呤猝灭伊文思蓝的荧光猝灭机理并根据次黄嘌呤对伊文思蓝荧光的猝灭作用建立了测定次黄嘌呤的新方法.线性回归方程为:ρ=6.292×103F-1-26.49,相关系数为0.9990,线性范围为0.20～20.0 μg/mL,检出限为0.14 μg/mL,相对标准偏差(RSD)为2.5%.求算了伊文思蓝与次黄嘌呤的形成常数K=2.63×102L/moL,实验了pH、放置时间、干扰离子等对测定的影响.     

Fourth derivative spectrophotometric determination of fungicide ziram (zinc(II) dimethyldithiocarbamate) in commercial samples and wheat grains

A procedure has been developed for the direct fourth derivative spectrophotometric determination of zinc(II) dimethyldithiocarbamate by converting it into its copper(II) dimethyldithiocarbamate complex, which is then dissolved in Triton X-100. Beer's law is obeyed over the concentration range 0.5–30?µg/mL in the final solution. Various parameters such as the effect of pH and the interference of a number of ions on the determination of Ziram have been studied in detail. The method is sensitive and can be used for the determination of Ziram in commercial samples like Zirax and Ziron containing Ziram and from wheat grains.     

Protein-induced leakage and membrane destabilization of phosphatidylcholine and phosphatidylserine liposomes

By using spectroscopic and colloidal chemistry methods we studied the interactions of globular proteins with phospholipid membranes in relation to protein-promoted membrane fusion. We considered the effect of protein sorption on the destabilization of phosphatidylcholine and phosphatidylserine liposome membranes. Experimentally, we injected the proteins into fluorophore-quencher embedded liposome dispersions and recorded the leakage of fluorophore-quencher from the liposomes' inner compartment, which is due to the protein-induced destabilization of the phospholipid membranes. The release of fluorophore-quencher strongly depends on the protein concentration. The existence of monovalent and polyvalent cations also influences the protein-induced membrane destabilization by affecting the hydrophobic and electrostatic interactions.