Density, DSC, X-ray and NMR measurements through the gel and lamellar phase transitions of 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC: observation of slow relaxation processes and mechanisms of phase transitions

J. W. Jones, L. Lue, A. Saiani, G. J. T. Tiddy

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Dialkyl lecithin dispersions in water exhibit two phase transitions upon cooling from the lamellar phase (L-alpha). At the main transition (T-M) the L-alpha phase changes to a ripple (gel) phase (P-beta ') which then transforms to a second gel phase (L-beta ') at the "pretransition'' (T-P). We have made accurate density measurements through the various phases for two lecithins having unequal chains: 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC). The measurements were carried out over five heat/cool cycles from 5 to 55 degrees C, followed by cooling back to 5 degrees C. The samples were then held at 50 degrees C for 24 hours, followed by a further three cool/heat cycles. For SMPC we observe an increase in density of the gel phases over the first 5 cycles, followed by much smaller changes after incubation at 50 degrees C. The lamellar phase also shows an increase in density, albeit much smaller. This parallels the behaviour of 1,2-di-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-di-myristoyl-sn-glycero-3-phosphatidylcholine (DMPC) reported earlier (Jones et al., Liquid Crystals 32, 1465 (2005)). For MSPC we observe a decrease in density within the gel phases while T-P almost disappears after the first cycle. The lamellar phase shows little evidence of any change with each cycle. Within the lamellar phases there is a marked reduction in density on approaching T-M, which is attributed to the formation of transitory gel phase domains. Additional measurements by DSC and X-ray diffraction show that the changes in densities are not accompanied by large changes in transition enthalpies or phase structures. NMR data indicate that the pretransitional event within the L-alpha phase is accompanied by ordering of the alkyl chains. The results indicate that the exact nature of the lipid alkyl chains could play a key role in the formation of gel phase patches within membrane bilayers. Their detailed chemical structures merit more attention than by simply assuming a uniform "bending energy'' to describe the behaviour.

LanguageEnglish
Pages5452-5469
Number of pages18
JournalPhysical Chemistry Chemical Physics
Volume14
Issue number16
DOIs
Publication statusPublished - 2012

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Relaxation processes
Phase transitions
Gels
Nuclear magnetic resonance
gels
X rays
nuclear magnetic resonance
cycles
x rays
Lecithins
Phosphatidylcholines
Cooling
cooling
Liquid Crystals
heat
Phase structure
ripples
Dispersions
lipids
1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine

Keywords

  • lipid alkyl chains
  • NMR measurement
  • lamellar phase

Cite this

@article{1b1383734be64091949bc10fa64b0c69,
title = "Density, DSC, X-ray and NMR measurements through the gel and lamellar phase transitions of 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC: observation of slow relaxation processes and mechanisms of phase transitions",
abstract = "Dialkyl lecithin dispersions in water exhibit two phase transitions upon cooling from the lamellar phase (L-alpha). At the main transition (T-M) the L-alpha phase changes to a ripple (gel) phase (P-beta ') which then transforms to a second gel phase (L-beta ') at the {"}pretransition'' (T-P). We have made accurate density measurements through the various phases for two lecithins having unequal chains: 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC). The measurements were carried out over five heat/cool cycles from 5 to 55 degrees C, followed by cooling back to 5 degrees C. The samples were then held at 50 degrees C for 24 hours, followed by a further three cool/heat cycles. For SMPC we observe an increase in density of the gel phases over the first 5 cycles, followed by much smaller changes after incubation at 50 degrees C. The lamellar phase also shows an increase in density, albeit much smaller. This parallels the behaviour of 1,2-di-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-di-myristoyl-sn-glycero-3-phosphatidylcholine (DMPC) reported earlier (Jones et al., Liquid Crystals 32, 1465 (2005)). For MSPC we observe a decrease in density within the gel phases while T-P almost disappears after the first cycle. The lamellar phase shows little evidence of any change with each cycle. Within the lamellar phases there is a marked reduction in density on approaching T-M, which is attributed to the formation of transitory gel phase domains. Additional measurements by DSC and X-ray diffraction show that the changes in densities are not accompanied by large changes in transition enthalpies or phase structures. NMR data indicate that the pretransitional event within the L-alpha phase is accompanied by ordering of the alkyl chains. The results indicate that the exact nature of the lipid alkyl chains could play a key role in the formation of gel phase patches within membrane bilayers. Their detailed chemical structures merit more attention than by simply assuming a uniform {"}bending energy'' to describe the behaviour.",
keywords = "lipid alkyl chains, NMR measurement, lamellar phase",
author = "Jones, {J. W.} and L. Lue and A. Saiani and Tiddy, {G. J. T.}",
year = "2012",
doi = "10.1039/c2cp23136k",
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journal = "Physical Chemistry Chemical Physics",
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TY - JOUR

T1 - Density, DSC, X-ray and NMR measurements through the gel and lamellar phase transitions of 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC

T2 - Physical Chemistry Chemical Physics

AU - Jones, J. W.

AU - Lue, L.

AU - Saiani, A.

AU - Tiddy, G. J. T.

PY - 2012

Y1 - 2012

N2 - Dialkyl lecithin dispersions in water exhibit two phase transitions upon cooling from the lamellar phase (L-alpha). At the main transition (T-M) the L-alpha phase changes to a ripple (gel) phase (P-beta ') which then transforms to a second gel phase (L-beta ') at the "pretransition'' (T-P). We have made accurate density measurements through the various phases for two lecithins having unequal chains: 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC). The measurements were carried out over five heat/cool cycles from 5 to 55 degrees C, followed by cooling back to 5 degrees C. The samples were then held at 50 degrees C for 24 hours, followed by a further three cool/heat cycles. For SMPC we observe an increase in density of the gel phases over the first 5 cycles, followed by much smaller changes after incubation at 50 degrees C. The lamellar phase also shows an increase in density, albeit much smaller. This parallels the behaviour of 1,2-di-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-di-myristoyl-sn-glycero-3-phosphatidylcholine (DMPC) reported earlier (Jones et al., Liquid Crystals 32, 1465 (2005)). For MSPC we observe a decrease in density within the gel phases while T-P almost disappears after the first cycle. The lamellar phase shows little evidence of any change with each cycle. Within the lamellar phases there is a marked reduction in density on approaching T-M, which is attributed to the formation of transitory gel phase domains. Additional measurements by DSC and X-ray diffraction show that the changes in densities are not accompanied by large changes in transition enthalpies or phase structures. NMR data indicate that the pretransitional event within the L-alpha phase is accompanied by ordering of the alkyl chains. The results indicate that the exact nature of the lipid alkyl chains could play a key role in the formation of gel phase patches within membrane bilayers. Their detailed chemical structures merit more attention than by simply assuming a uniform "bending energy'' to describe the behaviour.

AB - Dialkyl lecithin dispersions in water exhibit two phase transitions upon cooling from the lamellar phase (L-alpha). At the main transition (T-M) the L-alpha phase changes to a ripple (gel) phase (P-beta ') which then transforms to a second gel phase (L-beta ') at the "pretransition'' (T-P). We have made accurate density measurements through the various phases for two lecithins having unequal chains: 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC). The measurements were carried out over five heat/cool cycles from 5 to 55 degrees C, followed by cooling back to 5 degrees C. The samples were then held at 50 degrees C for 24 hours, followed by a further three cool/heat cycles. For SMPC we observe an increase in density of the gel phases over the first 5 cycles, followed by much smaller changes after incubation at 50 degrees C. The lamellar phase also shows an increase in density, albeit much smaller. This parallels the behaviour of 1,2-di-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-di-myristoyl-sn-glycero-3-phosphatidylcholine (DMPC) reported earlier (Jones et al., Liquid Crystals 32, 1465 (2005)). For MSPC we observe a decrease in density within the gel phases while T-P almost disappears after the first cycle. The lamellar phase shows little evidence of any change with each cycle. Within the lamellar phases there is a marked reduction in density on approaching T-M, which is attributed to the formation of transitory gel phase domains. Additional measurements by DSC and X-ray diffraction show that the changes in densities are not accompanied by large changes in transition enthalpies or phase structures. NMR data indicate that the pretransitional event within the L-alpha phase is accompanied by ordering of the alkyl chains. The results indicate that the exact nature of the lipid alkyl chains could play a key role in the formation of gel phase patches within membrane bilayers. Their detailed chemical structures merit more attention than by simply assuming a uniform "bending energy'' to describe the behaviour.

KW - lipid alkyl chains

KW - NMR measurement

KW - lamellar phase

U2 - 10.1039/c2cp23136k

DO - 10.1039/c2cp23136k

M3 - Article

VL - 14

SP - 5452

EP - 5469

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 16

ER -