Proton entrapment in acidic lipid membranes: Intramolecular vs. intermolecular hydrogen bonding.
Item
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Title
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Proton entrapment in acidic lipid membranes: Intramolecular vs. intermolecular hydrogen bonding.
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Identifier
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AAI9315507
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identifier
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9315507
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Creator
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Syz-Chin, Jing-Yi.
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Contributor
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Adviser: Thomas H. Haines
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Date
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1993
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Biochemistry | Biology, Molecular | Biology, Animal Physiology
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Abstract
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Hydrogen-bonding of anionic lipids in two different model membrane systems were examined in this thesis. The first is the chlorosulfolipid system found in fresh-water algae Ochromonas danica. The second is a unique acid-anion found in cardiolipin.;Ochromonas danica grows optimally at pH 4.5. The plasma and flagellar membranes of this organism are mainly composed of 1,14-docosane-disulfates with from 1-6 chloro groups replacing hydrogens on an otherwise saturated chain. These chlorosulfolipids constitute over 90% of the polar lipids of the membrane. To explore the basis for stable bilayer formation by chlorosulfolipids the sulfatide mixture was isolated and purified from O. danica and reconstituted into vesicles using oleic acid and cholesterol as a comparable model system. Examination of the reconstituted vesicles by EM (electron microscopy) and PCS (photon correlation spectroscopy) indicated that the secondary sulfate of the alkyl disulfate lipids is in the protonated form in the low dielectric presumably by intermolecular hydrogen bonding.;The second part of this thesis is to examine the possibility of acid-anion formation and thus the intramolecular hydrogen bonding in the headgroup of cardiolipin (CL). Both CL and its deoxy analogue (dCL, the central hydroxyl of the glycerol is replaced by a hydrogen atom) were prepared as bilayers and titrated against 1 and 2 equivalents of KOH. The titration curves showed that the pK's of CL (pK{dollar}\sb1{dollar} = 2.8; pK{dollar}\sb2{dollar} = 7.5) are very different from that of the deoxy analogue of CL (pK{dollar}\sb1{dollar} = 2.8; pK{dollar}\sb2{dollar} = 3.8). This is interpreted to mean that the central hydroxyl group of CL forms an intramolecular hydrogen bond to one of the phosphate groups forming a unique acid-anion altering the second pK. The second phosphate if protonated, forms a hydrogen bond with a pair of electrons on the hydroxyl. The hydroxyl thus participates in two hydrogen bonds, one as a donor and one as an acceptor. This permits the single proton to resonate between the two phosphates.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
