Even-numbered Homologues Research Articles

New homologues of chiral cyclohexylhemicucurbit[n]urils

The existence of new 7-, 8-, 9- and 10-membered homologues of chiral cyclohexylhemicucurbituril is reported. The barrel-shaped (all-R)-cyclohexylhemicucurbit[8]uril ((all-R)-cycHC[8]) was isolated and its complexes with anions were detected in negative ion mode MS. Here, 7-, 9- and 10-membered homologues were detected by HPLC–HRMS. Geometries of all reported macrocycles were calculated using quantum chemical methods, which showed that even-numbered homologues were barrel-shaped and odd-numbered homologues were asymmetrical barrel-shaped with unequal dimensions of the openings. The size of the ((all-R)-cycHC[8]) cavity was comparable to CB[8] and it probably can serve as a chiral host.

Direct evidence from hydropyrolysis for the retention of long alkyl moieties in black carbon fractions isolated by acidified dichromate oxidation

Chemical oxidation with acidified potassium dichromate is one of the more commonly used of a range of available methods for the quantification of black carbon (BC) in soils and sediments. There are potential uncertainties with this method however, with indications that not all non-BC material is susceptible to oxidation. An emerging approach to BC quantification is hydropyrolysis (hypy), in which pyrolysis assisted by high hydrogen pressure facilitates the reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum that is predominantly composed of >7 ring aromatic domains.Here, results from the hypy of the BC fraction isolated by dichromate oxidation (BCdox) from a BC-rich soil are presented, which demonstrated that 88% of the total carbon initially defined as BC was stable under hypy conditions (defined as BChypy). More notably, hypy allowed the non-BChypy fraction to be characterised. In addition to a number of PAHs, the non-BChypy fraction was also found to contain a significant abundance of n-alkanes, with a marked predominance of even-numbered homologues. These compounds are probably derived from lipids, hydrogenated during hypy, which survived dichromate oxidation due to their hydrophobic nature. Hypy of the dichromate oxidation residue from a sample of Green River shale, known to contain no BC of pyrogenic origin revealed that the significant apparent BCdox content (BC/OC=5.7%) was also largely due to the presence of n-alkanes within the oxidation residues. The distribution of these compounds, biased towards longer chain homologues with no significant even/odd preference, indicated that they were largely derived from long n-alkyl chains within this highly aliphatic matrix.Hypy therefore provides compelling direct evidence for the incomplete removal of non-BC material by dichromate oxidation from both a BC-rich soil and a BC-free oil shale, with the molecular characterisation of the non-BChypy fraction allowing the potential sources of this material to be deduced.

Very-long-chain hydroxyaldehydes from the cuticular wax of Taxus baccata needles

In the cuticular wax of Taxus baccata needles, homologous series of very-long-chain 1,5-alkanediols and 5-hydroxyaldehydes were identified by various chemical transformations with product assignment using GC–MS. The 1,5-alkanediols had chain lengths ranging from C 28 to C 38, with strong predominance of even carbon numbers and a maximum at C 32 (29%). The series of 5-hydroxyaldehydes comprised chain lengths C 24 and C 26–C 36, and showed a pronounced prevalence of even-numbered homologues. 5-Hydroxyoctacosanal was the most abundant compound of the series (42%). The 5-hydroxyaldehydes together amounted to 0.4 μg/cm 2, corresponding to 1.2% of total wax of the needles. A polyketide-like biosynthetic pathway is proposed based on the (similar) chain length distributions and functional group patterns for both compound classes.

Alkanes of foliar epicuticular waxes from five cycad genera in the zamiaceae

The n-alkane distribution patterns from 31 specimens in the meso-American cycad genera Ceratozamia, Dioon, Zamia and two Australian taxa, reported from GC analysis, complement a previously published investigation of the African genus, Encephalartos and complete a survey of the Zamiaceae. The significant proportions of n-alkane homologues with short (< n-C 25) carbon chains, the extended distribution range ( n-C 26 to n-C 33) and a general absence of prevalence of odd- over even-numbered homologues collectively provides evidence for a monophyletic origin of the Zamiaceae and distinguishes the cycads chemotaxonomically from other gymnosperms and from angiosperms. Exceptions to the general trend are seen in Dioon califanoi, which shows an angiosperm-like bias towards odd-numbered carbon alkanes, and to a lesser extent in two species of Ceratozamia and three of Zamia. Alkane distribution profiles do not allow any distinction between the genera of the Zamiaceae and show little species specificity.

The Lyomesophase Formation Zone and the Rheolcgical Characteristics of Binary Sodium Alkylsulfate Aqueous Systems

Abstract A description is given of the concentration dependence of lyomesophase formation by even-numbered homologues of sodium alkylsulfate. The similarity of the data obtained by rheological investigations to those of lyotropic polymer systems is shown.

Composition of Epicuticular Wax on Opuntia engelmannii

Alkanes and esthers contributed up to 97% of the total epicuticular wax on cladophylls of glasshouse-grown Texas pricklypear cactus (Opuntia engelmannii var. texana [Gr.] Weniger). Alkane content increased with cladophyll age. Ester content decreased from 56% on buds to 17% on older cladophylls. Alkanes consisted of both odd- and even-numbered homologues, but odd-numbered alkanes predominated. The most prevalent carbon numbers (Cn) of alkanes from buds were C15 through C25, while those of fully expanded cladophylls produced in the year of or the year prior to sampling were C29 through C35. Both odd- and even-numbered ester components were also present, mostly C16, C18, and C30 on all cladophylls.

Thermotropic phase behavior of phosphatidylcholines with omega-tertiary-butyl fatty acyl chains

The thermotropic phase behavior of a homologous series of phosphatidylcholines containing acyl chains with omega-tertiary butyl groups was studied by differential scanning calorimetry, Fourier transform infrared spectroscopy, and 31P-nuclear magnetic resonance spectroscopy (31P-NMR). Upon heating, aqueous dispersions of these lipids exhibit single transitions which have been identified as direct conversions from Lc-like gel phases to the liquid-crystalline state by both infrared and 31P-NMR spectroscopy. The calorimetric data indicate that the thermodynamic properties of the observed transition are strongly dependent upon whether the acyl chains contain an odd- or an even-number of carbon atoms. This property is manifest by a pronounced odd/even alternation in the transition temperatures and transition enthalpies of this homologous series of lipids, attributable to the fact that the odd-numbered compounds form gel phases that are more stable than those of their even-numbered counterparts. The spectroscopic data also suggest that unlike other lipids which exhibit the so-called odd/even effect, major odd/even discontinuities in the packing of the polymethylene chains are probably not the dominant factors responsible for the odd/even discontinuities exhibited by these lipids, because only subtle differences in the appropriate spectroscopic parameters were detected. Instead, the odd/even alternation in the physical properties of these lipids may be attributable to significant differences in the organization of the carbonyl ester interfacial regions of the lipid bilayer and to differences in the intermolecular interactions between the terminal t-butyl groups of the odd- and even-numbered homologues. Our results also suggest that the presence of the bulky t-butyl groups in the center of the lipid bilayer reduces the conformational disorder of the liquid-crystalline polymethylene chains, and promotes the formation of Lc-like gel phases. However, these Lc-like gel phases are considerably less ordered than those formed by saturated, straight-chain lipids.

An infrared spectroscopic study of the thermotropic phase behavior of phosphatidylcholines containing ω-cyclohexyl fatty acyl chains

The thermotropic phase behavior of an odd- and an even-numbered member of the homologous series of 1,2-di-ω-cyclohexylphosphatidylcholines was studied using Fourier transform infrared spectroscopy. The results obtained indicate that the pronounced discontinuities in the behavior of the odd- and even-numbered homologoues observed by differential scanning calorimetry can be attributed to differences in the organization of their respective gel states. The single phase transition exhibited by the odd-numbered compounds upon heating is shown by infrared spectroscopy to be a direct transition from α condensed, subgel-like phase (L c phase) to the liquid-crystalline state (L α phase). In contrast, the multiple transitions exhibited by the even-numbered homologues are shown to be due to the initial conversion of an L β-like phase to a more loosely packed gel phase, followed by the acyl chain-melting transition. Moreover, the major changes in the interaction between the acyl chains, and in the organization of the interfacial region of the bilayers formed by the even-numbered homologous, occur at temperatures below that of the chain onset-melting phase transition. The infrared spectroscopic changes observed also suggest that above the chain-melting transition, the odd- and even-numbered homologues form similar liquid-crystalline phases that are more ‘ordered’ than those of normal saturated straight-chain phosphatidylcholines. Most likely this is because the large size and the intrinsic rigidity of the ω-cyclohexyl group reduces the conformational disorder of the liquid-crystalline state by ‘damping’ all acyl chain motions. The formation of a relatively ordered liquid-crystalline state may be the critical property exploited by the thermoacidophylic organisms in which ω-cyclohexyl fatty acids naturally occur.

Composition of Wax Made by the Australian Stingless Bee Trigona australis

Analysis of the nest material of T. australis by gas chromatography/chemical ionization-mass spectrometry showed the wax to comprise a hydrocarbon fraction (90%), esters (6%) and free acids . (4%). The major saturated hydrocarbons were C27, C31 and C33 with C2S and C29 being less abundant and C23 and C 3S being present in small amounts. Traces of the intermediate, even-numbered homologues were also found. Hydrocarbons (C31o C 33 and C 3S) which contained one double bond were also present and traces of the diene C3S were detected. The ester fraction did not contain compounds identical with those in beeswax made by the honeybee Apis melli/era and the acid fractions were also quite different. T. australis wax contained the following, saturated free acids: CIO (trace), C12, C14, C16, CIS and C20, monoenoic and dienoic CIS and C 20 and traces of the trienoic CIS. The wax of T. australis is colourless but the brown colour of the nest material derives from the inclusion of masses of pollen (Eucalyptus sp.) and solid material from the inside of the nest tree. The solid residue comprised between 12 and 30% by weight.

Ketogenesis in isolated rat liver mitochondria. II. Factors affecting the rate of β-oxidation

1. During fatty acid oxidation by rat liver mitochondria, the rate of β-oxidation is dependent on the relative amounts of substrate and mitochondrial protein, on the energy state of the mitochondria, on the chain length and the number of double bonds of the fatty acid and on the concentration of various compounds in the reaction medium ( l-carnitine, CoASH, hexokinase, albumin). 2. The rate of β-oxidation of long-chain fatty acids decreases when the ratio of albumin over fatty acid is increased. This effect is most marked in the absence of added carnitine. 3. Addition of excess hexokinase decreases the rate of β-oxidation in the presence of added carnitine. 4. Maximal rates of β-oxidation are observed with octanoate and decanoate (40–60 nmoles acetyl-CoA/min per mg mitochondrial protein at 25 °C). 5. Odd-numbered fatty acids are oxidized at a much lower rate than the even-numbered homologues. In a low-energy state propionyl-CoA accumulates; in a high-energy state in the presence of bicarbonate, Krebs-cycle intermediates accumulate. 6. l-Carnitine enhances the rate of β-oxidation of all fatty acids except butyrate. The stimulatory effect is most pronounced with odd-numbered and with long-chain fatty acids. 7. In the absence of added carnitine the rate of β-oxidation of long-chain fatty acids decreases with the chain length and increases with the number of double bonds. It is suggested that the solubility of the long-chain fatty acids in the aqueous medium is the rate-limiting factor under these conditions. 8. In the presence of carnitine and albumin, palmitate, oleate, linoleate and linolenate are all oxidized at about the same rate (25–30 nmoles/min per mg protein at 25 °C). 9. Propionyl-CoA is not formed as an intermediate during oxidation of unsaturated fatty acids.

Distribution patterns of n-alkanes in human liver, urine and sweat

Paraffins in human liver, urine and sweat were isolated by extraction, molecular sieving, and gas chromatography-mass spectrometry, and the distribution patterns of n-alkanes in these organic materials compared. n-Alkanes in liver (about 10 mg/kg wet wt.) were found to contain 12–33 C-atoms. n-Alkanes with more than 20 C-atoms contained predominately an odd number of C-atoms, whereas in the smaller molecules even-numbered homologues predominated. An excessive concentration of n-nonacosane (C 29H 60) indicates a vegetable diet. In urine n-alkanes (about 1.3 mg/1) containing 13–30 C-atoms were isolated, with a striking predominance of the even-numbered homologues, showing a possible connection between the hydrocarbons in liver and those in urine. In sweat a series of n-alkanes (about 27 mg/g lipid extract from sweat) in the range from 12 to 35 C-atoms was found with a highest concentration of pentacosane (C 25H 52), indicating a similarity to the alkane pattern of human blood serum.