Long-chain Homologues Research Articles

New fluorogenic triacylglycerol analogs as substrates for the determination and chiral discrimination of lipase activities

A new type of fluorogenic and isomerically pure 1(3)-O-alkyl-2,3 (3,2)-diacyl glycerols was synthesized that can be used as substrate for the determination of lipase activities. These compounds contain a fluorescent pyrene acyl chain and, as a potent quencher of pyrene fluorescence, a trinitrophenylamino acyl residue. In their intact form, the fluorogens show only low fluorescence intensity. Upon lipase-induced or chemical hydrolysis of the substrates, however, the fluorophore and quencher separate from each other. This leads to a gradual increase in pyrene fluorescence, reflecting the time-dependent progress of lipolysis and, under substrate saturation conditions, lipase activity. This lipase assay is continuous and does not require separation of substrate and reaction products. Short- and long-chain homologues as well as optical isomers of the fluorogenic alkyldiacyl glycerols were hydrolyzed by pancreatic lipase, hepatic lipase, and lipo-protein lipase at highly different rates depending on the substrate or enzyme preparation and source (e.g., postheparin plasma or cultured cells). It is proposed that a useful set of enantiomeric and/or homologous substrates in combination with appropriate reaction media might be applied to the selective determination of a lipase in a mixture of lipases, e.g., hepatic and lipoprotein lipase in PHP, for medical diagnostics.

Location of ubiquinone homologues in liposome membranes studied by fluorescence anisotropy of diphenyl-hexatriene and trimethylammonium-diphenyl-hexatriene

The measurements of diphenyl-hexatriene (DPH) and trimethylammonium-diphenyl-hexatriene (TMA-DPH) fluorescence anisotropy in dipalmitoylphosphatidylcholine (DPPC) and egg yolk lecithin (EYL) liposomes containing different concentrations of various ubiquinone (UQ) homologues have been performed. UQ-4 induced the highest DPH anisotropy increase in DPPC liposomes, whereas for higher UQ homologues the anisotropy was lowered with the increase of UQ side-chain length. These differences were less pronounced in EYL liposomes. It was concluded that at a higher content in the membranes (3–4 mol%), the short-chain ubiquinones are arranged parallel to lipid fatty acid chains, whereas long-chain homologues are progressively removed from the lipid acyl chains into the midplane region of the membrane. At the lower (1–2 mol%) concentrations, long-chain quinones seem to be evenly distributed within the membrane, especially in EYL membranes. UQ-10 in EYL liposomes perturbed TMA-DPH to a similar extend as the short-chain ubiquinones indicating that UQ-10 penetrates the interface regions of the membrane where its redox reactions occur. The localization and physical state of UQ-10 in native membranes is discussed.

Long-chain polyprenyl acetates in Murraya exotica

Polyprenyl acetates with an average number of isoprene residues of eight to 13 were isolated from the leaves of Murraya exotica, the content being 0.12% of the dry weight. Spectroscopic analysis revealed that all the polyprenyl acetates were long-chain homologues with the following sequence of isoprene residues: ω- trans, two- trans, four to nine cis and cis- α-terminal.

Novel results on the adsorption of ionic surfactants at the air/water interface — sodium- n-alkyl sulphates

Equilibrium surface tension vs. concentration isotherms of aqueous, surface-chemically pure solutions of the homologous series of sodium n-alkyl sulphates (from C 7 to C 14) have been evaluated using a new surface equation of state approach. All adsorption parameters (standard free energy of adsorption, interaction parameter, saturation adsorption) and the CMC reveal a pronounced even/odd effect. Surprisingly, it was found that the cross-sectional areas of the short-chain homologues decrease with increasing chain length, reaching a minimum value for C 10 and C 11. However the cross-sectional areas of the longer-chain homologues (C n ≥ C 12) increase again drastically with increasing chain length. This novel effect is attributed to increasing electrostatic repulsion within the adsorption layer caused by increasing Debye lengths of the stronger surface-active homologues. The good agreement between the data for the cross-sectional area of sodium- n-dodecyl sulphate, as obtained from the new surface equation of state approach, from the Gibbs equation and from crystal structure analysis, make us suggest that it is unreasonable to apply an additional factor in the Gibbs equation for ionic amphiphiles as long as the counterion is very small in comparison with the oppositely charged amphiphilic molecule.

Determination of octanol/water partition coefficients for long-chain homologs of orcinol from cereal grains.

Polycratic reversed-phase high-performance liquid chromatography (RPHPLC) was used for estimation of the octanol/water partition coefficient for three highly hydrophobic long chain orcinol homologs. The homologs studied (C 15:0, C 17:0 and C 19:0) showed high preference for hydrophobic phase as evidenced by their high octanol/water partition coefficient (log Po/w) values of 7.02-7.74; 8.71-9.47 and 10.49-11.32 for the 95% prediction interval, respectively. Experimentally estimated values were compared with log P values calculated with the use of several fragmental systems. The experimental values of log Po/w are in best agreement to those calculated with the use of the Klopman system (Klopman, G., Namboodiri, K. & Schochet, M., 1985, J. Comput. Chem. 6, 28-38). The lack of appropriate standard compounds with known log Po/w in the range over 6 markedly affected the accuracy of experimental determinations.

Phenols and Quinones from Leaves ofPrimula obconica

Abstract Besides primin 1 and its hydroquinone, miconidin 2, surface extracts of Primula obconica contain their longer chain homologues 1a and 2a. In addition to several derivatives of 2, namely the methyl ethers 3 and 4 and the acetate 5, the resorcinol 6 and its methyl ether 7 are found. The structures of the compounds were elucidated by spectroscopic methods and - if necessary - by comparison with synthetic references. The possible biosynthesis of these natural products is discussed.

Crystalline - Smectic C - Cubic - Isotropic - Nematic - Isotropic Polymorphism: Synthesis and Unexpected Behaviour of a New Series of Double-Swallow-Tailed Mesogens

Abstract A new homologous series of six-ring double-swallow-tailed mesogens was prepared and investigated. Liquid-crystalline properties strongly depend on the length of the terminal alkyl chains. Six different phase sequences could be detected, two of them were unknown up to now. The derivatives DS-5 …7 show smectic C, cubic and nematic phases, the longer-chain homologues DS-10 … 14,16 have columnar phases. The substance DS-8 exhibits the most interesting phase sequence cr - SC- cub - Ire - N - I. DS-8 represents the second pure compound with a stable reentrant isotropic phase. Optical, X-ray, and further investigations provide arguments to propose the structures of the different phases.

The Invention of Radical Reactions. XXXIII. Homologation Reactions of Carboxylic Acids by Radical Chain Chemistry

Various carbon radicals can be generated from carboxylic acids via the corresponding Barton esters. These radicals can be used for the synthesis of longer chain homologues of the original acids.

Novel inhibitory action of tunicamycin homologues suggests a role for dynamic protein fatty acylation in growth cone-mediated neurite extension.

In neuronal growth cones, the advancing tips of elongating axons and dendrites, specific protein substrates appear to undergo cycles of posttranslational modification by covalent attachment and removal of long-chain fatty acids. We show here that ongoing fatty acylation can be inhibited selectively by long-chain homologues of the antibiotic tunicamycin, a known inhibitor of N-linked glycosylation. Tunicamycin directly inhibits transfer of palmitate to protein in a cell-free system, indicating that tunicamycin inhibition of protein palmitoylation reflects an action of the drug separate from its previously established effects on glycosylation. Tunicamycin treatment of differentiated PC12 cells or dissociated rat sensory neurons, under conditions in which protein palmitoylation is inhibited, produces a prompt cessation of neurite elongation and induces a collapse of neuronal growth cones. These growth cone responses are rapidly reversed by washout of the antibiotic, even in the absence of protein synthesis, or by addition of serum. Two additional lines of evidence suggest that the effects of tunicamycin on growth cones arise from its ability to inhibit protein long-chain acylation, rather than its previously established effects on protein glycosylation and synthesis. (a) The abilities of different tunicamycin homologues to induce growth cone collapse very systematically with the length of the fatty acyl side-chain of tunicamycin, in a manner predicted and observed for the inhibition of protein palmitoylation. Homologues with fatty acyl moieties shorter than palmitic acid (16 hydrocarbons), including potent inhibitors of glycosylation, are poor inhibitors of growth cone function. (b) The tunicamycin-induced impairment of growth cone function can be reversed by the addition of excess exogenous fatty acid, which reverses the inhibition of protein palmitoylation but has no effect on the inhibition of protein glycosylation. These results suggest an important role for dynamic protein acylation in growth cone-mediated extension of neuronal processes.

Fatty Acids: Evolution in Relation to Neurobiology

Metabolism of long-chain polyunsaturated fatty acids derived from 18:2ω−6 and 18:3ω−3 by chain elongation – desaturation is essential for synthesis of complex structural lipids, leukotrienes, thromboxanes, and prostaglandins. These essential fatty acids are required for normal function in developing tissues and appropriate maturation of a wide variety of physiological processes. During development, fetal accretion of long-chain metabolites of ω−6 and ω−3 fatty acids may result from maternal or placental synthesis and transfer or, alternatively, from the metabolism of 18:2ω−6 and 18:3ω−3 to longer chain homologues by the fetus. After birth the infant must synthesize or be fed the very long chain polyunsaturated fatty acids of C20 and C22 type derived from 18:2ω−6 and 18:3ω−3.Metabolism of ω−6 and ω−3 fatty acids utilizes the same enzyme system and is competitive. When levels of dietary ω−3 and ω−6 C18 fatty acids are altered, the levels of metabolites of these precursor fatty acids change in specific brain membranes, influencing membrane lipid dependent functions. For example, a diet unbalanced in very long chain ω−3 and ω−6 fatty acids may increase brain membrane ω−3 fatty acid content when 20:5ω−3 is fed, while decreasing membrane fatty acid content of the ω−6 series of competing fatty acids. As 20:4ω−6 is quantitatively and qualitatively important to brain phospholipid, significant reduction in brain levels of 20:4ω−6 may be less than optimal. The impact of these compositional changes on brain function is not yet clear.The authors in this symposium address how this general area of essential fatty acid metabolism is relevant to the evolution of man, growth and development of fish, function of the retina and neural tissue, cognitive development of infants, and infant nutrition.

Calorimetric and spectroscopic studies of the polymorphic phase behavior of a homologous series of n-saturated 1,2-diacyl phosphatidylethanolamines

The polymorphic phase behavior of a homologous series of n-saturated 1,2-diacyl phosphatidylethanolamines was investigated by differential scanning calorimetry, 31P-nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Upon heating, aqueous dispersions of dried samples of the short- and medium-chain homologues (n < or = 17) exhibit single, highly energetic transitions from a dry, crystalline form to the fully hydrated, liquid-crystalline bilayer at temperatures higher than the lamellar gel-liquid-crystalline phase transition exhibited by fully hydrated samples. In contrast, the longer chain homologues (n > or = 18) first exhibit a transition from a dehydrated solid form to the hydrated L beta gel phase followed by the gel-liquid-crystalline phase transition normally observed with fully hydrated samples. The fully hydrated, aqueous dispersions of these lipids all exhibit reversible, fairly energetic gel-liquid-crystalline transitions at temperatures that are significantly higher than those of the corresponding phosphatidylcholines. In addition, at still higher temperatures, the longer chain members of this series (n > or = 16) exhibit weakly energetic transitions from the lamellar phase to an inverted nonlamellar phase. Upon appropriate incubation at low temperatures, aqueous dispersions of the shorter chain members of this homologous series (n < or = 16) form a highly ordered crystal-like phase that, upon heating, converts directly to the liquid-crystalline phase at the same temperature as do the aqueous dispersions of the dried lipid. The spectroscopic data indicate that unlike the n-saturated diacyl phosphatidylcholines, the stable crystal-like phases of this series of phosphatidylethanolamines describe an isostructural series in which the hydrocarbon chains are packed in an orthorhombic subcell and the headgroup and polar/apolar interfacial regions of the bilayer are effectively immobilized and substantially dehydrated. Our results suggest that many of the differences between the properties of these phosphatidylethanolamine bilayers and their phosphatidylcholine counterparts can be rationalized on the basis of stronger intermolecular interactions in the headgroup and interfacial regions of the phosphatidylethanolamine bilayers. These are probably the result of differences in the hydration and hydrogen bonding interactions involving the phosphorylethanolamine headgroup and moieties in the polar/apolar interfacial regions of phosphatidylethanolamine bilayers.

Molecular ordering of organosulfur compounds on Au(111) and Au(100): Adsorption from solution and in ultrahigh vacuum

Low-energy electron diffraction and reflection-absorption infrared spectroscopy were used to study the monolayers formed by the adsorption of n-alkane thiols [HS(CH2)mCH3] on both (111) and (100) single-crystal gold substrates. Samples were prepared by dosing either from solution (m=15, 17, 18, and 21) or in ultrahigh vacuum (m=0–9). On Au(111), ordered surface structures are obtained which can be indexed as (n√3×√3)R30°, where n varies from 1 to 6. On Au(100), the adsorption of short chain thiols leads to the formation of a c(2×2) overlayer while the longer chain homologs show additional diffraction spot splittings. It is also found that chain length influences both the character of the diffraction seen and perturbs the reactive sticking probability of molecules dosed in UHV. Infrared studies reveal that the polymethylene chains of the monolayers formed on Au(100) are comprised of nearly all-trans conformations and are less canted than the comparable structures formed on Au(111). A simple model is proposed to account for the differences seen on the two surfaces and a mechanism for the adsorption and assembly of organic thiols into ordered monolayer phases on gold is presented.

Quantitative analysis of alkylbenzenesulfonate surfactants using continuous-flow fast atom bombardment spectrometry

A quantitative method for the analysis of linear alkylbenzenesulfonates (LAS) has been developed using continuous-flow fast atom bombardment and tandem mass spectrometry. Simultaneous analysis of all LAS homologues is possible by scanning the parent ions of m/z 183, which is a product ion common to all LAS subjected to collisionally induced dissociation. Similarly, branched alkylbenzenesulfonate (ABS) can be analyzed by scanning the parent ions of m/z 197. Samples were concentrated using solid-phase extraction on C{sub 18} disks. Because separation is not required, samples can be analyzed in 4 min or less using flow injection analysis. Quantitation is linear from 1 to at least 100 ng; the detection limit is 1 ng injected, corresponding to 0.5 {mu}g/L in 1-L water samples. This method has been used to determine LAS concentrations in samples taken from a wastewater treatment plant and in river water. In this activated sludge treatment plant, removal of LAS from wastewater occurred by adsorption to sludge as well as by biodegradation. Relative concentrations of longer chain homologues in sludge were higher than in the plant influent, indicating that these homologues accumulate on sludge. LAS adsorbed to sludge were eventually degraded in the plant`s aerobic sludge digester. 19 refs., 8more » figs., 2 tabs.« less

Improved inhibitors of glucosylceramide synthase.

An inhibitor of glucosylceramide (GlcCer) synthase, 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), has been reported to deplete cells and mice of their glucosphingolipids. This inhibitor has proved useful for the elucidation of the many functions of this lipid family [reviewed by Radin, N.S. & Inokuchi, J. (1991) Trends Glycosci. Glycotechnol. 3, 200-213]. In the present study, we have synthesized homologs of PDMP having different acyl chains (C6-C18) and compared their effectiveness for the inhibition of GlcCer synthase in vitro and their inhibition of GlcCer, protein, and DNA synthesis in cultured MDCK (Madin-Darby canine kidney) cells. Using MDCK homogenates and mouse brain and liver microsomes, we found that the C6 compound was relatively inactive and that the longer chain compounds did not differ much in inhibitory power. However, the use of intact MDCK cells showed that the longer chain homologs were much more effective in inhibiting GlcCer synthesis, cell growth, and incorporation of [3H]thymidine. Tests with two radioactive homologs showed that the inhibitor with a longer acyl chain was taken up much more effectively by MDCK cells and that this difference explains the much greater effectiveness of this homolog in intact cells. The inhibitors were effective when solubilized either with a nonionic detergent or with bovine serum albumin. The extent of decrease in DNA synthesis was not directly proportional to the decrease in cellular glucosylceramide, possibly because only a low level of the glycolipid is needed for DNA synthesis.

Structures of the subgel phases of n-saturated diacyl phosphatidylcholine bilayers: FTIR spectroscopic studies of 13C = O and 2H labeled lipids

The subgel phases of unlabeled, specifically chain perdeuterated and specifically 13C = O labeled representative samples of the n-saturated diacylphosphatidylcholines were studied by Fourier-transform infrared spectroscopy. Our results indicate that the spectroscopic properties exhibited by the subgel phases of the longer chain homologues are not consistent with that of a pure phase and we suggest that this is because the observed spectrum is a summation of spectroscopic features arising from both their subgel and L beta gel phases. Using spectral subtraction techniques, we obtained a spectrum which we believe is more representative of the pure subgel phase and from it we suggest that the subgel phase of the long chain phosphatidylcholines is an ordered crystallike structure containing two vibrationally inequivalent populations of lipid molecules arranged with the zigzag planes of their hydrocarbon chains parallel. For dipalmitoylphosphatidylcholine, our data indicate that its stable subgel phase is generally similar to that of the longer chain homologues but it is a more ordered structure in which the polar/apolar interfacial region is probably less hydrated. With the medium chain (N = 13-15) compounds, two populations of vibrationally equivalent molecules are also present in the subgel phase, but unlike DPPC and the longer chain homologues, the zigzag planes of their sn1- and sn2- acyl chains are perpendicular to each other, and a sn1-ester C = O group of one of the populations is in relatively close contact with an sn2-ester C = O group of the other population. With the shorter chain (N = 10 - 12) compounds, our data is indicative of a very complex quasi-crystalline assembly in which there may be at least three vibrationally inequivalent populations of lipid molecules with rotationally disordered hydrocarbon chains. Moreover, the conformation of the glycerol backbone may well be very different from that usually expected of this class of phospholipids. With all of these lipids, the structural pictures which emerge from our studies of the various subgel phases are in many aspects incompatible with that deduced from the single crystal x-ray studies of dimyristoylphosphatidylcholine. We suggest that this is because under our experimental conditions, these lipids have effectively been crystallized from water, whereas the sample used for the single-crystal x-ray study was crystallized from organic solvents.

The solution conformations of lidocaine analogues.

IR and 1H NMR studies in CDCl3 and CCl4 of a series of tertiary aminoxylidides with the amino group in the 2 to 6 position of the acyl chain are described. Lidocaine, diethylaminoaceto-2',6'-xylidide, forms an intramolecular five-membered ring hydrogen-bonded monomer at all concentrations in both solvents. beta-Diethyl-amino-propiono-2',6'-xylidide forms an intramolecular six-membered ring hydrogen-bonded monomer in CDCl3 and CCl4 but a trans intermolecularly associated species is the major form present at high concentrations in CCl4. The longer-chain homologues are mixtures of nonassociated trans and cis monomers at low concentrations but associated trans forms predominate at high concentrations. Evidence for the presence of a hydrogen-bonded seven-membered ring intramolecular monomer in CDCl3 for gamma-diethylaminobutyro-2',6'-xylidide is presented. The relationship between the molecular conformation and the partition coefficient is discussed.

Synthesis and characterisation of some 1,4,8,11,15,18,22,25-octa(alkoxymethyl)phthalocyanines; a new series of discotic liquid crystals

A series of 3, 6-bis(alkoxymethyl)phthalonitriles, prepared via Diels–Alder reactions of 2, 5-bis(alkoxymethyl)furans with fumaronitrile, have been converted into the corresponding phthalocyanines. Zn(II) and Cu(II) derivatives of 1,4,8,11,15,18,22,25-octa(heptyloxymethyl)phthalocyanine were also prepared. Examples of the macrocycles were characterised using 1H NMR spectrometry and optical spectroscopy. Those bearing straight chains aggregate in solutions of chloroform and toluene. The octa(butoxymethyl)phthalocyanine and its longer chain homologues exhibit a discotic liquid crystallinephase. Compounds containing branched sidechains are liquid crystals at room temperature.

Synthesis of fluorescent probes for localized membrane fluidity measurements

The synthesis of two long-chain homologues of the fluorescent membrane probes TMA-DPH and DPHpPC is described. The long-chain phosphatidylcholine could be synthesized from palmitoyl-lysophosphatidylcholine and 21-(diphenylhexatrienyl) henicosanoic acid only when the promoting agent was 1,1′-thionyldiimidazole.

Mechanisms of stabilization of biomembranes by alpha-tocopherol: The role of the hydrocarbon chain in the inhibition of lipid peroxidation

The effects of alpha-tocopherol and its homologues with different chain lengths (6-hydroxy-chromanes: C 1, C 6, C 11) on lipid peroxidation in natural membranes (liver microsomes and mitochondria, brain synaptosomes) and liposomes were studied. It was shown that the antioxidant activity of alphatocopherol homologues decreased in the order: C 1 > C 6 > C 11 >alpha-tocopherol (C 16). Using fluorescent measurements, the possible reasons underlying these differences were investigated: (i) the distribution between the aqueous media and nonpolar phase of the membrane, which predetermines the binding of alpha-tocopherol homologues to membranes; (ii) the incorporation of alpha-tocopherol homologues into lipid bilayer; (iii) non-uniform distribution (formation of the clusters) of tocopherol homologues in the lipid bilayer; and (iv) transbilayer mobility of alpha-tocopherol homologues and accessibility of the inhibitors for radical-generating centres under enzymically and non-enzymically induced lipid peroxidation. It was demonstrated that: (i) binding of C 1 with membranes was less efficient than that of longer-chain homologues (C 6, C 11, C 16); (ii) the level of incorporation of alpha-tocopherol homologues into membranes decreased in a succession alpha-tocopherol C 11 > C 6 > C 1; (iii) all alphatocopherol homologues existed in the lipid bilayer not only in a monomeric form but also associated in clusters thus decreasing the efficiency of radical scavenging; (iv) the short-chain alpha-tocopherol homologue, C 1, exhibited a high transbilayer mobility whereas the long-chain one, C 16, underwent no transbilayer migration within tens of minutes. The inhibiting effect of alpha-tocopherol esters and C 1-acetate was predetermined by their hydrolysis in biomembranes; a strong correlation exists between the rate of the ester hydrolysis and their antioxidant activity in the membrane. In liposomes, in which the esterase activity was absent, alpha-tocopherol esters and C 1-acetate exhibited very low lipid peroxidation inhibition.

Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q 0 to Q 10) in preventing (Fe 2+ + ascorbate)-dependent or (Fe 2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQ n , possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q 1–Q 4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q 5–Q 10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q 1 > Q 2 > Q 3 > Q 4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q 5 > Q 6 > Q 7 > Q 8 > Q 9 > Q 10 and iii) the antioxidant efficiency of Q 0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q 1–Q 4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q 6–Q 10 exert no effect. In contrast to ubiquinol Q 10 (ubiquinone Q 10) ubiquinone Q 1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.