共查询到20条相似文献,搜索用时 31 毫秒
1.
The use of pH-sensitive liposomes for acid-triggered site-specific drug delivery is one of the more promising approaches to improve the therapeutic index of drugs. Here, we report the synthesis, assembly, and hydrolysis of the first ortho ester phosphocholine (OEPC). The acid hydrolysis of OEPC liposomes consists of a lag phase and a burst phase. The lag time is pH-dependent-the lower the pH, the shorter the time. Upon acid hydrolysis, the OEPC liposomes were transformed into leaky metastable vesicles that rapidly collapsed in the presence of albumin. OEPC, when formulated with cationic lipid, significantly enhanced the transfection efficiency compared with that of the pH-insensitive formulation. 相似文献
2.
Noriyuki Kumazawa Yulia S. Mel'Nikova Kenichi Yoshikawa 《Macromolecular Symposia》1996,106(1):219-223
We report a new method to prepare giant liposome with the size of several tens micrometers, entrapping DNA molecule within the closed phospholipid membrane. The formation of such liposomes has been confirmed through the observation with fluorescence microscopy. 相似文献
3.
《Chemical physics letters》2002,350(3-4):305-310
We studied the effect of daunomycin, a cancer chemotherapeutic agent, on a model cellular system in which folded compact DNA was encapsulated inside a cell-sized phospholipid liposome. Real-time observation with fluorescence microscopy revealed that, upon the addition of daunomycin, entrapped DNA was first elongated and then cut into fragments. A blebbing transition of the membrane was also observed. A theoretical model is proposed to explain the blebbing phenomenon induced by daunomycin, taking into account its effect on the asymmetry between the outer and inner layers of the membrane. 相似文献
4.
Kato N Prime J Katagiri K Caruso F 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5718-5723
We report the preparation of aqueous liposome dispersions of J-aggregates formed by the amphiphilic merocyanine dye (MD). A series of liposome-forming lipids were dispersed together with MD J-aggregates at different molar ratios of MD to lipid. The MD J-aggregate dispersions prepared with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at the MD to DMPC ratio of 0.16 exhibit good dispersibility; that is, they can be readily redispersed without any flocculation even after their precipitation. By use of different counterions for the MD molecules, two types of J-aggregate dispersions, one that exhibits an absorption band (J-band) at 635 nm (type I) and the other at 600 nm (type II), were obtained. As an example of the use of MD J-aggregates liposome dispersions, the thermochromic transformation of MD J-aggregates was demonstrated. When the dispersions are heated, J-aggregates of type I transformed into type II at a certain temperature (T(disp)). The parameters that control the speed of the transformation and the value of T(disp) were determined. 相似文献
5.
The temporal relativistic principle, recently established for calorimetric systems in the framework of the theory of the topoenergetic behaviour of composite systems, is extended to general thermal measuring systems. A thermal measuring system is defined as a measuring system in which the conversion of a response function is measured as a result of a stepwise perturbation in temperature. The process of crystallization revealed by different thermal measuring systems is considered for a series of compounds for which the processes are identical in nature, but differ in amplitude, so that an external affine relationE=n K + m is verified between the activation energyE and the amplitude termK. It results that the polarity of a transformation process is a characteristic proper to the temporal reference system of the considered measuring system and can be expressed by the signs of the parametersE and/orn.
Zusammenfassung Das gemäßigte relativistische Prinzip das unlängst für die kalorimetrischen Systeme im Rahmen der Theorie des topoenergetischen Verhaltens der zusammengesetzten Systeme festgelegt worden ist, wird auf allgemeine thermische Meßsysteme ausgedehnt. Ein thermisches Meßsystem wird als ein Meßsystem definiert, in dem die Umwandlung einer Antwortfunktion als Ergebnis einer stufen weisen Temperaturstörung gemessen wird. Der durch verschiedene thermische Meßysteme bestimmte Kristallisationsverlauf wird als eine Serie von Mischungen betrachtet, für welche die Beschaffenheit des Vorganges identisch, jedoch die Amplituden verschieden sind, so daß eine externe AffinitätsbeziehungE=n K + m zwischen der AktivierungsenergieE und dem AmplitudenausdruckK erfüllt werden kann. Es ergibt sich, daß die Polarität eines Umwandlungsprozesses charakteristisch für das temporale Bezugs-system des betreffenden Meßsystems ist und durch das Zeichen der ParameterE und/odern ausgedrückt werden kann.
, , . . , , , , . - E=nK+m . , E ( ).相似文献
6.
With the objective of contributing to the buildup of mathematical tools for anaerobic process simulation, an algorithm for
the dynamic simulation of pH was developed. The dynamic simulation of the gaseous phase variables was also considered. The
pH algorithm was validated for a watery system, obtaining good agreement between predicted and experimental data. The applied
methodology provides a differential equation that allows the inclusion of pH as a state variable of the system that can be
easily included in a general mathematical model of anaerobic digestion using matrix notation. This methodology also allows
a noticeable decrease in computing time in simulations. A dynamic anaerobic digestion model of complex substrates taken from
the literature was completed with the developed algorithms, and it was used to predict the response of an anaerobic reactor
against overloading and against the presence of pH-dependent inhibitors with satisfactory results. 相似文献
7.
Vesicles are of great interest as drug delivery system or models for cell membranes. For many applications, it is necessary
to produce vesicles which are unilamellar, monodisperse, easy to adjust in size, and which can be filled with various types
of active compounds. In a series of experiments, we produced giant vesicles with dimension of several millimeters by phase
transfer processes. This new technique allowed synthesizing defined vesicles with lipid and surfactant membranes. The preparation
of these aggregates occurred in two steps. First, we filled some amount of water into a cuvette and covered this liquid with
an oil phase. Surfactants or lipids were solved either in the water or the oil phase. In the second step, a water droplet
filled with methyl blue and saccharose was formed with a syringe in the oil phase. Due to density difference, the water droplet
passed the plane oil/water interface and during this process it was transformed into a vesicle. The giant liposomes, thus
formed, showed a high sensitivity against variations of the osmotic pressure, and their stability reached from seconds to
hours. Due to the phase transfer process, the vesicle membranes often contained incorporated lenses of oil. If this hydrophobic
liquid was released from the membrane, the vesicles decayed into smaller liposomes with a broad particle size distribution. 相似文献
8.
9.
Preciado S Vicente-García E Llabrés S Luque FJ Lavilla R 《Angewandte Chemie (International ed. in English)》2012,51(28):6874-6877
When a door closes, a window opens! The use of geometrically or electronically restricted imines for Povarov-type processes does not afford the anti-Bredt tetrahydroquinolines, but leads instead to highly functionalized structures through novel reaction pathways (see picture; LA=Lewis acid). The exploration of "forbidden" routes constitutes a valuable approach in the search for new multicomponent reactions. 相似文献
10.
The switching process in a ferroelectric liquid crystal cell is of great interest. The precise way in which the optic tensor structure reorientates during switching between states is, however, difficult to determine. Here we consider the use of guided modes and surface plasmon-polaritons as techniques for the investigation of this. It is seen that because of the nature of the dynamic processes the guided mode data is inconclusive, but surface plasmon-polariton data show the surface reorientation mechanism. 相似文献
11.
Abstract The switching process in a ferroelectric liquid crystal cell is of great interest. The precise way in which the optic tensor structure reorientates during switching between states is, however, difficult to determine. Here we consider the use of guided modes and surface plasmon-polaritons as techniques for the investigation of this. It is seen that because of the nature of the dynamic processes the guided mode data is inconclusive, but surface plasmon-polariton data show the surface reorientation mechanism. 相似文献
12.
The octamethylene chains in [8](2,4)-1,5-dicarbomethoxy-3-oxaquadricyclane and in [8](1,4)-7-oxanorbornadiene both undergo two dynamic processes, which have been identified by NMR spectroscopy. The slower process involves a swinging of the octano bridge. the octamethylene chains in di-[8](1,4)-7-oxanorbornadienerhodium chloride show the same processes. In addition, two other processes are observed in this complex: a degenerate one, involving a rotation of the 7-oxanorbornadiene ligands around the rhodium—oxygen axes, and non-degenerate one, involving an exchange of free and coordinated 7-oxanorbornadiene. 相似文献
13.
We collect and critically analyze extensive literature data, including our own, on three important kinetic processes--viscous flow, crystal nucleation, and growth--in lithium disilicate (Li(2)O·2SiO(2)) over a wide temperature range, from above T(m) to 0.98T(g) where T(g) ≈ 727 K is the calorimetric glass transition temperature and T(m) = 1307 K, which is the melting point. We found that crystal growth mediated by screw dislocations is the most likely growth mechanism in this system. We then calculated the diffusion coefficients controlling crystal growth, D(eff)(U), and completed the analyses by looking at the ionic diffusion coefficients of Li(+1), O(2-), and Si(4+) estimated from experiments and molecular dynamic simulations. These values were then employed to estimate the effective volume diffusion coefficients, D(eff)(V), resulting from their combination within a hypothetical Li(2)Si(2)O(5) "molecule". The similarity of the temperature dependencies of 1/η, where η is shear viscosity, and D(eff)(V) corroborates the validity of the Stokes-Einstein/Eyring equation (SEE) at high temperatures around T(m). Using the equality of D(eff)(V) and D(eff)(η), we estimated the jump distance λ ~ 2.70 ? from the SEE equation and showed that the values of D(eff)(U) have the same temperature dependence but exceed D(eff)(η) by about eightfold. The difference between D(eff)(η) and D(eff)(U) indicates that the former determines the process of mass transport in the bulk whereas the latter relates to the mobility of the structural units on the crystal/liquid interface. We then employed the values of η(T) reduced by eightfold to calculate the growth rates U(T). The resultant U(T) curve is consistent with experimental data until the temperature decreases to a decoupling temperature T(d)(U) ≈ 1.1-1.2T(g), when D(eff)(η) begins decrease with decreasing temperature faster than D(eff)(U). A similar decoupling occurs between D(eff)(η) and D(eff)(τ) (estimated from nucleation time-lags) but at a lower temperatureT(d)(τ) ≈ T(g). For T > T(g) the values of D(eff)(τ) exceed D(eff)(η) only by twofold. The different behaviors of D(eff)(τ)(T) and D(eff)(U)(T) are likely caused by differences in the mechanisms of critical nuclei formation. Therefore, we have shown that at low undercoolings, viscosity data can be employed for quantitative analyses of crystal growth rates, but in the deeply supercooled liquid state, mass transport for crystal nucleation and growth are not controlled by viscosity. The origin of decoupling is assigned to spatially dynamic heterogeneity in glass-forming melts. 相似文献
14.
Birnbaumer G Küpcü S Jungreuthmayer C Richter L Vorauer-Uhl K Wagner A Valenta C Sleytr U Ertl P 《Lab on a chip》2011,11(16):2753-2762
Although liposomes have many outstanding features such as biocompatibility, biodegradability, low toxicity and structural diversity, and are successfully applied in many areas of chemistry and biotechnology, a lack of characterization standards and quality control tools are still inhibiting the translation of liposome technology into clinical routine. The greatest obstacle to clinical scale commercialization is the inability to ensure liposome formulation stability because small size variations or altered surface chemistries can significantly influence in vivo distribution and excretion kinetics that could in turn lead to unpredictable therapy outcomes. To enhance the product development process we have developed a microfluidic biochip containing embedded dielectric microsensors capable of providing quantitative results on formulation composition and stability based on the monitoring of the unique electric properties of liposomes. Computational fluid dynamic (CFD) simulations confirmed that microfluidics offer reproducible and well-defined measurement conditions where a moving liposome suspension within a microchannel behaves like a bulk material. Results of this study demonstrate the ability of microfluidics, in combination with dielectric spectroscopy and multivariate data analysis methods, to identify nine different liposomes. We also show that various liposome modifications such as membrane-bound surface proteins, lipid bilayer soluble drugs, as well as protein and dye encapsulations, can be detected in the absence of any labels or indicators. Since shelf-life stability of a liposome formulation is regarded of prime importance for regulatory approval and clinical application, we further provide a possible practical application of the developed liposome analysis platform as a high-throughput tool for industrial quality insurance purposes. 相似文献
15.
Hellberg D Scholz F Schubert F Lovrić M Omanović D Hernández VA Thede R 《The journal of physical chemistry. B》2005,109(30):14715-14726
The adhesion of liposomes on a mercury electrode leads to capacitive signals due to the formation of islands of lecithin monolayers. Integration of the current-time transients gives charge-time transients that can be fitted by the empirical equation Q(t) = Q(0) + Q(1)(1 - exp(-t/tau(1))) + Q(2)(1 - exp(-t/tau(2))), where the first term on the right side is caused by the docking of the liposome on the mercury surface, the second term is caused by the opening of the liposome, and the third term is caused by the spreading of the lecithin island on the mercury surface. The temperature dependence of the two time constants tau(1) and tau(2) and the temperature dependence of the overall adhesion rate allow determination of the activation energies of the opening, the spreading, and the overall adhesion process both for gel-phase 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and for liquid-crystalline-phase DMPC liposomes. In all cases, the spreading is the rate-determining process. Negative apparent activation energies for the spreading and overall adhesion process of liquid-crystalline-phase DMPC liposomes can be explained by taking into account the weak adsorption equilibria of the intact liposomes and the opened but not yet spread liposomes. A formal kinetic analysis of the reaction scheme supports the empirical equation used for fitting the charge-time transients. The developed kinetic model of liposome adhesion on mercury is similar to kinetic models published earlier to describe the fusion of liposomes. The new approach can be used to probe the stability of liposome membranes. 相似文献
16.
Eri Yoshida 《Supramolecular chemistry》2013,25(4):274-280
The physical conditions to vary the morphology of vesicles formed by amphiphilic poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid) were determined for the self-assembly induced by the nitroxide-mediated photocontrolled/living radical polymerisation performed in an aqueous methanol solution. The copolymer produced micrometre-sized spherical vesicles in the solution with a 30 wt% water content. The vesicles were transformed into a film-like morphology by decreasing the water content, whereas they were changed into nanometre-sized spherical vesicles by increasing it. The concentration of the growing polymer chain also varied the morphology. Large spherical vesicles formed at a low concentration were transformed into much smaller vesicles, followed by rod-like vesicles as a result of increasing the concentration. Furthermore, the stirring speed during the polymerisation-induced self-assembly dominated the morphology. Large elliptical vesicles produced at a low stirring speed changed into spherical vesicles, but decreased the size as the speed increased. 相似文献
17.
Assessing transformation processes of organic contaminants by compound-specific stable isotope analysis 总被引:1,自引:0,他引:1
The analysis of variations in stable isotope composition is becoming an essential approach for evaluating enzymatic and abiotic reactions of organic contaminants in soils and aquatic systems. Different, sometimes complementary analytical techniques are currently used and developed to determine stable isotope ratios in individual organic compounds. Anticipating an increasing demand for compound-specific isotope analysis, this survey compiles information for choosing the most promising analytical approach to an isotope-related problem. To this end, we review the principles of instrumentation for compound-specific isotope analysis and show how they can be exploited to assess contaminant transformation processes. Using chlorinated solvents and triazine herbicides as illustrative examples, we discuss how the isotope-sensitive techniques impact the investigation of stable isotope fractionation in environmental chemistry and microbiology. 相似文献
18.
Mavcic B Babnik B Iglic A Kanduser M Slivnik T Kralj-Iglic V 《Bioelectrochemistry (Amsterdam, Netherlands)》2004,63(1-2):183-187
Giant unilamellar phospholipid vesicles were prepared by the method of electroformation from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC). We studied the influence of different concentrations of the surfactant octaethyleneglycol dodecylether (C(12)E(8)) on the spontaneous shape transformations of POPC vesicles at room temperature. In accordance with previous results, we observed that low concentration of C(12)E(8) increased the speed of the characteristic vesicle shape transformation, starting from the initial shape with thin tubular protrusion, through beaded protrusion where the number of beads gradually decreased, to final spherical shapes with invagination, whereby the average mean curvature of the vesicle membrane monotonously decreased. In contrast, higher concentration of C(12)E(8) initially induced the shape transformation in the "opposite direction": in the protrusion, the number of beads gradually increased and eventually a tube was formed whereby the average mean curvature of the vesicle membrane gradually increased. However, at a certain point, an abrupt shape change took place to yield the vesicle with invagination. In this transition, the average mean curvature of the vesicle membrane discontinuously decreased. After this transition, the vesicle began to shrink and finally disappeared. We discuss possible mechanisms involved in the observed transformations. 相似文献
19.
S. Svane J. Kuntsche F. Steiniger A. Eich L. Duelund V. McKee 《Supramolecular chemistry》2013,25(10):642-653
A dicopper(II) complex can be covalently linked to palmitate/palmitoyl-oleoyl-phosphatidylcholine (PA/POPC) liposomes using the following one-pot strategy: preformed [Cu2(bpbp)(PA)](ClO4)2 (bpbp? = 2,6-bis((N,N′-bis(2-picolyl)amino)methyl)-4-tertbutylphenolato) was incorporated into POPC liposomes with a loading of up to 10 mol%. Despite its shape and charge, the decoration of PA/POPC liposomes with {Cu2(bpbp)}3+ did not disrupt the liposome structure; however, the mean liposome diameter increased from about 130 nm (0 mol% dicopper complex) to about 150 nm (10 mol% dicopper complex). Single-crystal X-ray structures furnish ‘snapshots’ of the pH-dependent solution state derivatives of {Cu2(bpbp)}3+, and model the structure of the [Cu2(bpbp)(PA)]2+ head group at the surface of the liposomes. An impressive plasticity in the intramolecular non-bonded Cu….Cu distance for these ions, ranging from 3 to 4 Å, in [Cu2(bpbp)OH]2+, [Cu2(bpbp)(OAc)(H2O)]2+ and [Cu2(bpbp)(H2O)2]3+ allows for their utility as labile reagents in water. Remarkably, the flexible dicopper site is selective for a single carboxylate ligand, so that [Cu2(bpbp)(PA)]2+ is favoured even in the presence of other chemically similar oxoanions, such as CO32 ? , HCO3? , NO3? , ClO4? , ReO4? and CF3SO3? . 相似文献
20.