Phase Transition Temperature Of Liposomes Research Articles

Effect of Indole-3-Carbinol on Dimyristoylphosphatidylcholine Multilamellar Vesicles.

This study reports the interaction of indole-3-carbinol (I3C), which is a chemopreventive reagent, with an artificial model membrane {(dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (MLVs)}, using the intrinsic fluorescence properties of I3C, extrinsic fluorescence properties of Nile Red (NR), differential scanning calorimetry (DSC), dynamic light scattering (DLS), and confocal microscopy. The intrinsic fluorescence of I3C helps to provide information about its location, partitioning ability, and sensitivity toward the phase-transition temperature of liposomes, confirmed by cetylpyridinium chloride (CPC) quenching study, partition coefficient values {(4.60 ± 0.1) × 105 (solid gel phase) and (7.29 ± 0.1) × 105 M-1 (liquid crystalline phase)} and temperature-dependent emission behavior of I3C. I3C perturbs the DMPC MLVs above 15 mol %, as observed using the fluorescence properties of NR, DSC, and DLS data. This perturbation occurs as a consequence of interfacial hydration of the DMPC MLVs, which was clearly indicated by the fluorescence properties (emission intensity, fluorescence lifetime, and nonextensive distribution analysis) of NR.

DSC for evaluating the encapsulation efficiency of lidocaine-loaded liposomes compared to the ultracentrifugation method

This study reports the investigation of liposomal formulations of lidocaine in the form of a free base (LID). LID was encapsulated into large multilamellar vesicles composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Samples of a mass ratio of LID with respect to DMPC ranging from 1 to 10% were investigated. The effects of the increasing LID concentration on the bilayer membrane were determined in terms of size, polydispersity index, zeta potential, encapsulation efficiency (EE %) and partition coefficient. Furthermore, differential scanning calorimetry (DSC) studies were also carried out to analyze the effect of LID on the liposome phase transition temperature and to calculate the EE % with an unfrequented method. The EE % results obtained by different experimental procedures were quite ambiguous, but the DSC measurements confirmed the ultracentrifugation direct method. The calculated partition coefficients of these two methods were in good agreement, too. Our research revealed a less known application field of DSC, as a fast and reliable tool to determine EE%.

Possibilities of acoustic thermometry for controlling targeted drug delivery

Model acoustic thermometry experiments were conducted during heating of an aqueous liposome suspension. Heating was done to achieve the liposome phase transition temperature. At the moment of the phase transition, the thermal acoustic signal achieved a maximum and decreased, despite continued heating. During subsequent cooling of the suspension, when lipids again passed through the phase transition point, the thermal acoustic signal again increased, despite a reduction in temperature. This effect is related to an increase in ultrasound absorption by the liposome suspension at the moment of the lipid phase transition. The result shows that acoustic thermography can be used to control targeted delivery of drugs mixed in thermally sensitive liposomes, the integrity of which is violated during heating to the phase transition temperature.

Effect of Encapsulation on Phase Transition Temperature of Liposomes. Binding Sites in HSA

The degree of encapsulation of 5-fluorouracil (5-FU) and vinorelbine (VIN) to dipalmitoylphosphatidylcholine (DPPC) liposomes was estimated using UV-vis spectroscopy. The phase transition temperature was determined by the differential scanning calorimetry (DSC). 5-FU incorporates in more extend to liposomes than VIN and affects phase transition temperature of phospholipide forming liposomal membrane. There is only a slight influence of VIN on the 5-FU encapsulation in liposome vesicle while 5-FU affects significantly the VIN content in the liposome vesicles. The binding sites of VIN and 5-FU in HSA determined by fluorescence quenching method were confirmed by computer simulation.

Preparation, Characterization, and Pharmacodynamics of Thermosensitive Liposomes Containing Docetaxel

A novel thermosensitive liposome (TL) containing docetaxel (DTX) was designed to enhance DTX-targeted delivery and antitumor effect. TL loading DTX (DTX-TL) were prepared by thin film hydration. The mean particle size of the liposomes was about 100 nm, and the drug entrapment efficiency was more than 95%. The phase transition temperature of liposomes was about 42 °C. In vitro drug release showed that drug released at 37 °C was obviously less than that at 42 °C. For in vivo experiments, the human breast tumor model was established by subcutaneous xenotransplantation on nude mice; liposomes and injection containing DTX were injected i.v. in nude mice, followed by exposure of the tumors to hyperthermia (HT) for 30 min after administration. The tumor inhibition ratio of DTX-TL group was significantly higher than the normal injection group. Combining TL with HT enhanced the delivery of DTX and thereby its antitumor effects. The liposomes reported in this paper could potentially produce viable clinical strategies for improved targeting and delivery of DTX for the treatment of breast cancer.

Ionic Liquid Expedites Partition of Curcumin into Solid Gel Phase but Discourages Partition into Liquid Crystalline Phase of 1,2-Dimyristoyl-sn-glycero-3-phosphocholine Liposomes

The hydrolysis of curcumin in alkaline and neutral buffer conditions is of interest because of the therapeutic applicability of curcumin. We show that hydrolysis of curcumin can be remarkably suppressed in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes. The fluorescence of curcumin sensitively detects the phase transition temperature of liposomes. However, at greater concentrations, curcumin affects the phase transition temperature, encouraging fusion of two membrane phases. The interaction of curcumin with DMPC is found to be strong, with a partition coefficient value of Kp = 2.78 × 10(5) in the solid gel phase, which dramatically increases in the liquid crystalline phase to Kp = 1.15 × 10(6). The importance of ionic liquids as green solvents has drawn interest because of their toxicological effect on human health; however, the impact of ionic liquids (ILs) on liposomes is not yet understood. The present study establishes that ILs such as 1-methyl-3-octylimidazolium chloride (moic) affect the permeability and fluidity of liposomes and thus influence parition of curcumin into DMPC liposomes, helping in the solid gel phase but diminishing in the liquid crystalline phase. The Kp value of curcumin does not change appreciably with moic concentration in the solid gel state but decreases with moic concentration in the liquid crystalline phase. Curcumin, a rotor sensitive to detect phase transition temperature, is applied to investigate the influence of ionic liquids such as 1-methyl-3-octylimidazolium chloride, 1-buytl-3-methyl imadazolium tetrafluoroborate, and 1-benzyl-3-methyl imidazolium tetrafluoroborate on DMPC liposome properties. 1-Methyl-3-octylimidazolium chloride lowers the phase transition temperature, but 1-buytl-3-methyl imidazolium tetrafluoroborate and 1-benzyl-3-methyl imidazolium tetrafluoroborate do not perceptibly modify the phase transition temperature; rather, they broaden the phase transition.

Influence of lipid composition on the phase transition temperature of liposomes composed of both DPPC and HSPC

Objective: Phase transition of the lipid membrane is one of the most important properties of liposomes. The objective of this study was to investigate the influence of molar ratio of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and hydrogenated soy phosphatidylcholine (HSPC) on the phase transition temperature (Tm) of the liposomes.Materials and methods: The Tms of the liposomes with different phosphatidylcholine (PC) composition were determined by calcein release test and differential scanning calorimetry (DSC).Results: Only one phase transition was observed for liposomes composed of both DPPC and HSPC, indicating that DPPC and HSPC might combine into one phase with single phase transition. The Tm of the liposomes composed of both DPPC and HSPC was directly dependent on the molar ratio of the two PCs. Moreover, DPPC percentage and Tm relationship could be fitted with a linear equation (r2 > 0.98). In addition, the serum stability of the liposomes at 37°C was directly increased with the increase of DPPC percentage. When 10% DSPE-PEG2000 was added, the significant increase of calcein release at Tm and decrease at 37°C were observed.Discussion: It is easy to obtain liposomes with a Tm in between that of DPPC and HSPC by modifying the molar ratio of DPPC and HSPC.Conclusion: With the modification of Tm, the liposomes containing various ratios of DPPC and HSPC may have promising application potential in the field of thermosensitive liposomes (TSLs). After 10% DSPE-PEG2000 is added, a formulation of sterically stabilized liposomes with the proper thermal sensitivity can be obtained.

The microfluidity and dissolution of hydrogenated PC liposome anchored with alkyl grafted poly(amino acid)s

The stability of a polymer hybridized liposome (PHL) was examined with the microfluidic and thermal state of anchored alkyl chains, and with dissolution against deoxycholate (DOC). Poly(asparagine) grafted with octadecylamine (PAsn-g-C 18), poly(aspartic acid) grafted with octadecylamine (PAsp-g-C 18), and poly(aspartic acid) grafted with phytosphingosine (PAsp-g-PHS) were synthesized. The microfluidity of the membrane of the PHL was evaluated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and the phase transition temperature ( T c) was measured by differential scanning calorimetry (DSC). The membrane fluidity of liposomes was increased by the inclusion of amphiphilic graft polymers. The phase transition temperature of liposomes increased by the anchoring of PAsn-g-C 18, while the inclusion of PAsp-g-C 18 or PAsp-g-PHS lowered the T c. The surface charge of PHL of PAsn-g-C 18 was changed by the cationic lipid content. The structural stability of the PHL was affected by variation of the hydrophilic backbone or the hydrophobic moiety of the polymer and PHL of PAsn-g-C 18 was most stable against DOC. An increased degree of substitution of the graft copolymer led to better stability of the PHL. It was found that the polymer characteristics affect the physicochemical strength of the PHL structure, resulting in different degrees of stability enhancement.

Effect of phase transition temperature of liposomes on preparation of fullerene-encapsulated liposomes by the fullerene-exchange reaction

It is shown that the fullerene-exchange reaction from the cyclodextrin cavity to liposomes, to prepare lipid membrane-incorporating fullerenes, occurred above the phase transition temperature (T(m)) of liposomes.

The Effect of Different Lipid Components on the In Vitro Stability and Release Kinetics of Liposome Formulations

Liposomes are colloidal carriers that form when certain (phospho)lipid molecules are hydrated in an aqueous media with some energy input. The ideal liposome formulation with optimum stability will improve drug delivery by decreasing the required dose and increasing the efficacy of the entrapped drug at the target organ or tissue. The most important parameter of interest in this article was to compare the efficacy of three different liposomes formulated with DSPC, DMPC, and DPPC, all saturated neutral phospholipids with different acyl chain lengths and transition temperatures. DMPC has a phase transition temperature (Tc) below 37°C, whereas the other two phospholipids possess Tcs above the physiological temperature. These lipids were then added to a cholesterol concentration of 21% to optimize the stability of the vesicles. The liposomes were prepared by a sonication and incubated in phosphate buffered saline (PBS) at 4°C and 37°C. The encapsulation efficiency, initial size, and drug retention of the vesicles were tested over a 48-hr period employing radiolabeled inulin as a model drug. The phase transition temperature of liposomes, which depends on the Tc of the constituent lipids, was an important factor in liposome stability. Of all the liposomes tested, the greatest encapsulation efficiency was found for the DSPC liposomes (2.95%) that also had the greatest drug retention over 48 hr at both 4°C (87.1 ± 6.8%) and 37°C (85.2 ± 10.1%), none of these values being significantly different from time zero. The lowest drug retention was found for DMPC liposomes for which a significant difference in drug retention was seen after only 15 min at both 4°C (47.3 ± 6.9%) and 37°C (53.8 ± 4.3%). The DPPC liposomes showed a significant difference in drug retention after 3 hr at 4°C (62.1 ± 8.2%) and after 24 hr at 37°C (60.8 ± 8.9%). Following the initial drop at certain time intervals a plateau was reached for all of the liposome formulations after which no significant difference in drug retention was observed. In conclusion, liposomes with higher transition temperatures appear to be more stable in PBS either at 4°C or 37°C, indicating that the increase in acyl chain length (and therefore transition temperature) is directly proportional to stability.

Effect of CRL-1343 and HSA-157, non-ionic detergents on the bilayer and hexagonal phase transition temperature

In recently developed non-ionic surfactants called CRL-1343 and HSA-157 (Polyoxyethylene esters of C18 fatty acid, the second compound differs from the first, in having an ester linkage instead of ether link. The second compound, has a hydroxy fatty acid rather than a plain fatty acid component) with low toxicity in vivo, and an ability to reverse the multidrug resistance in human epidermoid carcinoma cells in vitro. The compounds were shown to affect the bilayer and hexagonal phase transition in liposomes. The bilayer phase transition temperature of liposomes composed of dipalmitoylphosphatidylcholine, and encapsulated self quenched doxorubicin, was found to be 40°C, as measured by fluorescence assay. The phase transition measured by this method was found to be in good agreement with the phase transition measured by other techniques such as differential scanning calorimeter (DSC). Addition of the non-ionic detergent HSA-157 to these liposomes, at a concentration of 400 nmol, lowered the transition temperature to 30°C, while adding CRL-1343 to the same control liposomes at concentration of 10 nmol lowered the transition temperature to 28°C. The hexagonal phase transition temperature of N-(7-nitro-2,1,3-benzoxadiazol-4yl) phophatidylethanolamine (NBD-PE) labeled egg PE, was found to be 40°C as determined by fluorescence spectroscopy, and which is in good agreement with DSC measurements. Addition of HSA-157 to the liposomes at the same concentration used before, increased the phase transition temperature to 45°C, while adding CRL-1343 to the same control liposomes at the same concentration used before, increase the hexagonal transition temperature to 50°C. Our results provide an improved knowledge to understand the mechanism of the newly developed non-ionic surfactant in reversing the MDR, and suggest that those surfactants affect the permeability of membranes, by changing their phase transition behavior.

Phase Transitions in Phospholipid Vesicles: Excited State Prototropism of 1-Naphthol as a Novel Probe Concept

1-Naphthol (1-ROH), an excited state acid, undergoes partial dissociation in the excited state in liposome membrane, giving two fluorescence peaks as against a single peak in water. 1-Naphthol distributes between two different sites of different excited state reactivity in liposome, and the relative population in the two different sites changes with any perturbations in the membrane fluidity. This property is made use of in studying the thermotropic phase changes and cholesterol effect on the transition temperature of DMPC (dimyristoylphosphatidylcholine) and DPPC (dipalmitoylphosphatidylchloline) liposomes. The change in the permeability of the membrane due to thermotropic phase changes and the phase transition temperature of liposomes could be easily monitored by fluorescence spectroscopy from a conspicuous change in the emission of the neutral form of 1-naphthol. The applicability of 1-naphthol probe to mixed lipid sytems has also been examined.

Effect of bovine serum on the phase transition temperature of cholesterol-containing liposomes

The phase transition temperature of liposomes composed of dipalmitoylphos-phatidylcholine (DPPC)/hydrogenated soy phosphatidylcholine (HSPC) at a 2:1 molar ratio was estimated in buffer, 30% and 50%) bovine serum by monitoring the leakage of encapsulated self quenched doxorubicin (Dox) from the vesicles when exposed to a temperature increasing from 30–52°C. The results showed that bovine serum caused a slight decrease in the phase transition temperature from 44 to 41 °C in 50% serum. Addition of 50% cholesterol to this liposomal composition resulted in the disappearance of transition temperature in buffer and 30% serum, whereas 50% bovine serum resulted in the reappearance of the transition temperature at 46 °C. The data suggest that bovine serum affects the transition temperature of liposomes in a concentration-dependent manner, and this effect is more pronounced in cholesterol-rich liposomes. The time course for the release of Dox from both kinds of liposomes (cholesterol rich and cholesterol free) during incubation in 50% bovine serum, at temperatures close to the transition temperature (42°, 45 °C), was followed. The results showed an increased leakage of Dox from both kinds of liposomes, at both temperatures. However, liposomes with high cholesterol content released more drug at 42° than at 45 °C. The size of these liposomes was monitored in 10% bovine serum at 25 °C for a period of 1 h using photon correlation spectroscopy. The data showed no variation in the size of both cholesterol-rich and cholesterol-free liposomes for this period, which indicates that bovine serum does not affect the size of either cholesterol-rich or cholesterol-free liposomes.

Relation of Rigidity of Membrane and Stability of Dipalmitoylphosphatidylcholine Liposomes with Soybean-Derived Sterols Prepared by Reverse Phase Evaporation Vesicle Method.

A soybean-derived sterol mixture (SS) was used to stabilize liposomes prepared from dipalmitoylphosphatidylcholine (DPPC). The effect of SS on the stability and rigidity of liposomes entrapping calcein was investigated by measuring retentivity of calcein in liposomes in vitro and in vivo, and by fluorescence anisotropy, respectively. The entrapment efficiency is directly proportional to the total concentration of DPPC and SS. The presence of SS tends to increase the rigidity of the bilayer above its gel-liquid crystalline phase transition temperature of liposomes, and SS tends to fluidize the bilayer below its gel-liquid crystalline phase transition temperature. The relation between the stability of DPPC-liposomes with SS and the rigidity of liposomal membrane was discussed.

PH-dependence of phase transition of the lipid bilayer of liposomes of stratum corneum lipids

Phase transition of the lipid bilayer of liposomes of stratum corneum lipids, consisting of ceramide, cholesterol, cholesteryl sulfate and palmitic acid, was examined at different pH values by monitoring the fluorescence anisotropy of diphenylhexatriene (DPH). The phase transition temperature decreased about 15°C with decrease of the pH from 6.2 to 4.0. The decrease depended on the content of palmitic acid in liposomes and corresponded with the protonation of the anionic form of fatty acid judging from the fluorescence intensity and fluorescence anisotropy of the cationic trimethylammonium derivative of DPH (TMA-DPH). These results and pH-dependent change in fluorescence anisotropy of 2-(9-anthroyloxy)palmitic acid (2-AP) indicate that perturbation of lamellar lipids is induced by the undissociated form of fatty acids. Stimulation of transdermal penetration of phenol at acidic pH was observed which was consistent with the results on liposomes. A pH-dependent decrease of the phase transition temperature of liposomes was also observed on replacement of palmitic acid by other saturated fatty acids, the decreases being in the order lauric, myristic > palmitic > stearic acid. In the presence of lauric acid at pH 4.0, the fluorescence anisotropy of DPH also decreased at physiological temperatures, this effect being similar to those of long-chain cis-unsaturated fatty acids.

Surface Ionization of Dipalmitoylphosphatidylcholine as Detected by the pH Dependence of the Phase Transition Temperature of Liposomes

AbstractThe surface ionization of lecithin phosphodiester has been studied following the effect of bulk pH on the increment in the gel to liquid‐crystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine (DPPC) liposomes, induced by incorporation of protonated stearylamine. At constant pHb, the increment (Δtm is a monotone increasing function of stearylamine concentration which deviates from linearity, toward lower Δtm values, at high proportions of additive. From plots of Δtm as function of the stearylamine proportion in DPPC liposomes at different pHb values, the initial slopes, as stearylamine concentration approaches zero, is obtained and interpreted as a potentiality for tm elevation of DPPC bilayers. The slope value, seems to be related to the ionization degree of the phosphate group since it increases with bulk pH and levels off above pHb 4 i.e., for zwitterionic lecithin. If the titration curve resulting from normalization of those slope values, is attributed to ionization of lecithin phosphate, an apparent pK of 1.3 is obtained. The consistency of the data analysis is supported by the good fitting found between the experimental results and a theoretical curve based on Henderson‐Hasselbach, Boltzmann, and Gouy‐Chapman equations. Best fit is obtained when the intrinsic interfacial pK, which is the pK in the absence of surface electrostatic effects, is set equal to 4. Such a high intrinsic pK value is explained in terms of the effect of the reduced dielectric constant of the lipid‐water interface, on the ionization of the phosphate group which is a molecular acid and, as such, will be stabilized in a low polarity region.

Evaluation of phase transition temperature of liposomes by using tautomerism of benzoylacetoanilide and effects of cholesterol

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEvaluation of phase transition temperature of liposomes by using tautomerism of benzoylacetoanilide and effects of cholesterolM. Ueno, S. Katoh, S. Kobayashi, E. Tomoyama, R. Obata, H. Nakao, S. Ohsawa, N. Koyama, and Y. MoritaCite this: Langmuir 1991, 7, 5, 918–922Publication Date (Print):May 22, 1991Publication History Published online1 May 2002Published inissue 22 May 1991https://doi.org/10.1021/la00053a018RIGHTS & PERMISSIONSArticle Views278Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (509 KB) Get e-Alerts Get e-Alerts

Evaluation of phase transition temperature of liposomes by using the tautomerism of α-Benzoylacetoanilide

The phase transition temperatures for liposomes of dipalmitoyl- and distearoylphosphatidylcholines (abbreviated here as DPPC and DSPC) and for the other liposomes containing small amounts of soybean oil in the bilayer were determined from the changes of absorbance ratios ( R E K ) of enolic form to ketonic form in UV spectra for the tautomer of α-benzoylacetoanilide (BAA) incorporated into the liposomes. R E K values changed with increasing temperature and showed a maximum at a certain temperature. The DPPC liposome showed maximum at the temperature of 41°C corresponding to the phase transition temperature ( T c ) of these lipids. The DSPC liposome showed the maximum at 54°C. The T c values for other liposomes containing soybean oil could be determined in the same way. This method using the tautomerism of BAA was found to be very useful for the determination of the T c .

Enhanced delivery to target cells by heat-sensitive immunoliposomes.

Heat-sensitive immunoliposomes are capable of releasing the entrapped content at the target cell surface upon a brief heating to the phase transition temperature of the liposome membrane. In this study we have examined the delivery efficiency of drugs entrapped in heat-sensitive immunoliposomes. Immunoliposomes composed of dipalmitoyl phosphatidylcholine with entrapped [3H]uridine were incubated with target cells at 4 degrees C. The cell-liposome mixture was then heated to 41 degrees C and the uptake of [3H]uridine into the intracellular pool of phosphorylated uridine-containing molecules was measured. The immunoliposomes showed maximal release of the uridine at 41 degrees C, the phase transition temperature of dipalmitoyl phosphatidylcholine liposomes. The largest accumulation of [3H]uridine in the target cells also took place at 41 degrees C. The initial level of uptake of [3H]uridine released from immunoliposomes by heating was greatly enhanced over that observed for free [3H]uridine and [3H]uridine released from liposomes without attached antibody. The nucleoside uptake inhibitors nitrothiobenzylinosine, dipyridamole, and unlabeled uridine were able to inhibit uptake of [3H]uridine released from immunoliposomes. This supports the hypothesis that the enhanced uptake is due to a heat-induced release of [3H]uridine at the cell surface followed by transport and phosphorylation of [3H]uridine by the target cells. These results indicate the feasibility of using the heat-sensitive immunoliposomes as a target-specific drug delivery system.

Antioxidant Levels in Germinating Soybean Seed Axes in Relation to Free Radical and Dehydration Tolerance

The axis of soybean seeds suffer dehydration injury if they are dried to 10% moisture at 36 hours of imbibition, but tolerate this stress if dried at 6 hours of imbibition. Deesterification of membrane phospholipids has been correlated with the increased permeability and increased lipid phase transition temperatures of membranes from dehydration injured tissues. Deesterification, measured as increased free fatty acid:phospholipid and decreased phospholipid:sterol ratios, occurred primarily when the tissue was in the dry state and did not change significantly (P </= 0.05) with increasing imbibition time.When liposomes were exposed to free radicals in vitro, wide angle x-ray diffraction indicated that the phase transition temperature of liposomes prepared from membrane lipid from 36-hour axes (susceptible) increased from 6 to 31 degrees C. In contrast, those from membrane lipid from 6-hour axes (tolerant) increased from 3 to only 8 degrees C, indicating that the tolerance of free radicals previously observed in these membranes was due to a lipid-soluble component.Lipid-soluble antioxidants were detected in 6-hour imbided axes in much greater quantities than in the 36-hour imbibed axes. The presence of lipid-soluble antioxidants in the membrane apparently contributes to the free radical tolerance of seed membranes observed during the early stages of germination, and these antioxidants may contribute to the dehydration tolerance of this tissue.