Effects of chain length,conformation and α-form packing arrangement on theoretical monoacid triglyceride β′-forms

Theoretical β′-form monoacid triglycerides of odd and even chain length having a bend in the glycerol region were prepared by bond rotations from selected α-form conformers. The shapes of such β′-forms depend on the bonds rotated and the direction of rotation. Intermolecular minimization procedures determined best-fit positions around a centralized molecule, which revealed unsymmetrical packing among five of nine different energetically-favored orthorhombic subcell arrangements. Methyl gap energy is influenced more by overall triglyceride conformation than by whether the fatty acid chains have an odd or even number of carbon atoms. Total lattice-packing energies varied little between odd and even chain lengths; thus, many combinations of conformation and subcell arrangement are consistent with known X-ray long spacings and polymorphic behavior of β′-forms.     

On the Crystal Structure of the β′-Form of Triglycerides and Structural Changes at the Phase Transitions LIQ. → α → β′ ← β

Based on X-ray single crystal data of the β′-form of triundecanoin the general features of the molecular arrangement in this crystal form have been derived. The unit cell contains eight molecules arranged according to space group P2_1/c, with alternation of the tilt of the hydrocarbon chains in adjacent bimolecular layers. The structure within the molecular layer is quite similar to that of the β-form; the main difference being the chain packing. A second β″-form, β′₂, of triundecanoin has been observed and it differs from the one mentioned above in the orientation of the chain packing subcell 0° in relation to the true unit cell. The polymorphic transitions have been followed by recording of the diffraction pattern versus temperatures. The polymorphic transitions α · β′ · β can be regarded mainly as different lateral arrangement of a dimeric unit. In the α-form the chains are disordered near the methyl end groups, and due to this disorder the structure is closely related to the lamellar liquid-crystalline phase. It is also possible to classify β′-forms according to short-spacing data into a β′₁-type and a β′₂-type, and these groups can be identified also in complex triglycerides.     

Polymorphism in single-acid triglycerides of positional and geometric isomers of octadecenoic acid

The polymorphism of 25 glycerol trioctadecenoates with double bonds ranging from Δ4-Δ17 was investigated by differential scanning calorimetry. Triglycerides withcis bonds in odd positions Δ7-Δ13 exhibited three intermediate melting (β′-) forms, but those withcis bonds in even positions, exceptcis Δ4, lacked β′-forms. Among thetrans compounds, only Δ11, 13, and 14 showed β′-forms. Thecis andtrans Δ5 triglycerides were unusual, because they readily assumed low melting (α-) forms that were not easily converted to high melting (β-) forms. β-Form mp of compounds in each series (cis ortrans) alternated depending upon double bond position; an even position correlated with high mp. Heats of fusion (ΔH_f) for β-forms, likewise, fluctuated with double bond position but nonuniformly;trans Δ6 had the highest ΔH_f (43 cal/g),cis Δ12 the lowest (21 cal/g).     

Kristallstrukturuntersuchungen an Fettalkoholen und Fettsäuren mit Elektronen- und Röntgenbeugung I

Studies on Crystal Structures of Fatty Alcohols and Fatty Acids Using Electron and X-Ray Diffraction I For the homologous series of even numbered saturated fatty alcohols from dodecanol (C₁₂H₂₅OH) up to hexacosanol (C₂₆H₅₃OH) the almost orthorhombic unit cells of the β₀₁-modifications could be shown by using electron and X-ray diffraction. Fouriersynthesis based on hkO-reflexes showed the presence of a β₀₂-form which has half the edge length c compared to the β₀₁-modification. Moreover, the eight γ₃- to γ₁₀-modifications of the various alcohols were detected. Unit cell parameters and the chain tilt were determined for all crystal structures. By X-ray diffraction, stearic acid was shown to exhibit five β_n-(n = 2, 4, 5, 8) and seven γ₂- to γ₈-forms. The β_n-forms consist of molecules tilted over the short subcell a_s-axis, whereas in γ_n-forms the molecular chains are tilted over the b_s-axis. All the modifications of alcohols and fatty acids studied have an orthorhombic subcell, while the neighbouring molecules in monomolecular layers are turned to each other at an angle of about 90°.     

Sperm whale oil analysis by gas chromatography and mass spectrometry

Gas liquid chromatography of winterized sperm oil showed that its wax esters with even carbon numbers range from C₂₄ to C₄₂ and are present in quantities resembling a normal distribution curve with C₃₄ as the mean. Between these even-numbered wax esters, ones with odd chain lengths were eluted. Triglycerides, similarly present in a normal distribution pattern, ranged from C₄₂ to C₅₈ and also included traces of odd chain species. The component acids and alcohols were analyzed by gas chromatography-mass spectrometry, and double bond positions in the monoenoid components were established. Branched chain and odd chain constituents, both saturated and unsaturated, were detected among both alcohols and acids. These moieties, when combined with those having even chains, are responsible for the wax esters and triglycerides with odd carbon numbers. ARS, USDA.     

Dry Fractionation of Cupuassu (Theobroma grandiflorum) Fat: Physical–Chemical Properties and Polymorphic Behavior

Physical chemical properties of cupuassu fat were modified by dry fractionation. Stearin and olein fractions were obtained at 29, 26, and 24 °C. Polymorphic behavior of unfractionated cupuassu fat (UCF) and its fractions were studied in situ by small-angle (SAXS) and wide-angle (WAXS) X-ray scattering using synchrotron light. Polymorphic transitions were followed in real time tempering samples with a thermal cycle. For UCF, the main polymorphic form crystallized under selected conditions was the β’₂. α and β’₁-forms appeared in trace amounts. β₂-form was obtained after storage at 25 °C for 3 months. Stearins obtained at 26 (S-26) and 24 °C (S-24) showed a similar polymorphic behavior. However, S-26 with improved physical properties might be more suitable for chocolate production or as a trans-fat alternative than UCF. Stearin fraction obtained at 29 °C (S-29) had a complex polymorphic behavior. The α-form was the first polymorphic form detected followed by β’₂-form. There was a polymorphic transition from α to β’₁-form but no transition between β’-forms. They were independent to each other showing fractionation in two different solid solutions. Increased contents of the triacylglycerols (TAG) SOA and SOB together with lower contents of SOO compared to UCF led to co-crystallization because there was no complete compatibility among all TAG present in S-29. β₁-form crystallized after storage forming crystals with a double-layer arrangement and a characteristic morphology. This form could be useful for accelerating crystallization process in melted liquid systems.     

Study of the Polymorphism of Saturated Monoacid Triglycerides II: Polymorphic Behaviour of a 50/50 Mixture of Tripalmitin and Tristearin

The polymorphic behaviour of a 50/50 blend of tripalmitin and tristearin has been investigated in detail using differential scanning calorimetry and X-ray diffraction. The blend is characterized by a greater tendency to β'-crystallization as compared to the pure triglycerides. Tripalmitin and tristearin, when mixed in a 1:1 ratio, are miscible in both the α-form and the β-form. In the β-form, however, demixing occurs, resulting in a 2-phase solid state. The characteristics of the α-form are considerably affected by the crystallization conditions, due to the formation of concentration gradients during crystallization. The β'-form can be obtained from the melt as well as via recrystallization of the α-form, and is characterized by a much higher stability as compared to the pure triglycerides. The X-ray diffraction data of the β'-form of the blend reveal a β₁-crystal structure. The β'-form of the pure triglycerides, however, is characterized by a β'₂-crystal structure. On the basis of the present data, however, no clear structural distinction can be made between β'₂ and β'₁.     

The polymorphism of odd and even saturated single acid triglycerides,C8–C22

The polymorphism of single fatty acid odd triglycerides, C₁₁ through C₁₇ has been reinvestigated, with extension of the study to C₉, C₁₉ and C₂₁. With study of the even glycerides C₈, C₂₀ and C₂₂ it has been possible to review the whole series (odd and even) C₈ through C₂₂. The odd glycerides resemble the even in showing three distinct melting levels. Lowest melting forms are α. Stable forms are β except for C₉ and C₁₁ which show a different structure type. Intermediate melting β′ forms of odd glycerides are substantially more stable than their even counterparts as well illustrated by differential thermal analysis. There are no vitreous forms. Alternation in mp (between odd and even) is confirmed for stable phases and nonalternation for α and (within experimental error) for β′. Both β′ and β long spacings show alternation but not α. Alternation is evident in the short spacings of β′ and β forms. While short spacings of β′ forms of even triglycerides are much alike especially for C₁₄ through C₂₂, those of odd glycerides show a fortuitous 4-carbon cycle. This appears to involve no significant structural variation as chain length increases but simply an approximate 4-carbon cycle of variation in diffraction details derived from the presumed unvarying 0 ⊥ type subcell structure.     

Lipids of freshwater dolphinSotalia fluviatilis: Comparison of odontocete bioacoustic lipids and habitat

The melon and jaw lipids of the freshwater dolphinSotalia fluviatilis are composed mainly of isovaleroyl wax esters and diisovaleroyl triglycerides. The blubber fat contains only a trace of wax ester and is mostly tri- (long chain) and monoisovaleroyl triglycerides. Detailed gas liquid chromatographic analyses of the intact wax esters and triglycerides and of the derived fatty acids and fatty alcohols indicate common compositional patterns in the wax esters and triglycerides of the respective head lipids. Both odd and even long chain (C₁₂−C₁₆) iso-structures are prominent in the melon and jaw lipids, but only higher odd chain length iso-acids are major components in the blubber.Sotalia fluviatilis (family Delphinidae) andInia geoffrensis (family Platanistidae) share the same freshwater habitat in the upper Amazon River, and both utilize echolocation to navigate and to find food. Comparison of their respective bioacoustical lipid compositions shows distinctive types of head fats,Sotalia being rich in iso-5∶0 andIndia lacking iso-5∶0. This indicates that isovaleric acid per se has no obligatory role in dolphin echolocation.     

Mechanism of the solvent-mediated transformation of taltirelin polymorphs promoted by methanol

Taltirelin, a central nervous system activating agent, has two crystal forms (α- and β-forms). Previously it has been reported that methanol (MeOH) as a co-solvent promoted the solvent-mediated phase transformation from α-form to β-form. In the present study, the mechanism of the promotion was investigated. Of the three processes in the solvent-mediated transformation, namely dissolution of the metastable form, nucleation of the stable form, crystal growth of the stable form, MeOH promoted the latter two processes. In particular, the nucleation was strongly promoted. The nOe (nuclear Overhauser effect) data suggested that MeOH promotes the conformational change from the α-form to the β-form. The solute–MeOH interaction resulted in the formation of pseudo-polymorphs of the β-form (2H₂O·MeOH or H₂O·2MeOH solvate), although these pseudo-polymorphs were exchangeable to the β-form (4H₂O solvate) under a humid atmosphere. Based on these findings, a possible mechanism of the transformation of taltirelin polymorphs in the presence of MeOH was discussed.     

Mineralogical phase analysis of alkali and sulfate bearing belite rich laboratory clinkers

The activation of laboratory belite clinkers has been carried out by adding variable amounts of alkaline salts (K₂CO₃, Na₂CO₃), and/or SO₃ as gypsum in the raw materials but keeping almost constant the main elements ratios, Ca/Si/Al/Fe. Quantitative phase analyses by the Rietveld method using high resolution synchrotron and strictly monochromatic CuKα₁ laboratory X-ray powder diffraction data has been performed. Quantitative phase analysis results have been compared to validate the protocol using laboratory X-ray data. The agreement in the results is noteworthy, which indicates that good quantitative phase analyses can be obtained from laboratory X-ray powder data. Qualitative studies have confirmed that the addition of alkaline salts to raw mixtures promotes the stabilization, at room temperature, of the highest temperature polymorphs: α′_H-C₂S and α-C₂S. Quantitative studies gave the phase assemblage for ten different laboratory belite clinkers. As an example, an active belite clinker with 1.0 wt.% of K₂O and 1.0 wt.% of Na₂O (amounts added to the raw mixtures) contains 8.5(3) wt.% of β-C₂S, 21.2(3) wt.% of α'_H-C₂S, 24.1(2) wt.% of α-C₂S, 18.9(3) wt.% of total C₃S, 17.3(2) wt.% of C₃A and 10.0(2) wt.% of C₄AF. A belite clinker with 0.8 wt.% SO₃ (nominal loading) contains 60.7(1) wt.% of β-C₂S, 6.7(2) wt.% of α′_H-C₂S, 12.3(7) wt.% of C₃S, 9.1(2) wt.% of C₃A and 11.2(2) wt.% of C₄AF. Overall, quantitative phase analyses have shown that alkaline oxides stabilize α′_H-C₂S and α-C₂S, sulfur stabilizes β-C₂S, with a large unit cell volume, and the joint presence of alkaline oxides and sulfur promotes mainly the stabilization of the α′_H-C₂S polymorph.     

Polymorphie von zweisäurigen Triglyceriden der Stearinsäure- und Behensäure-Reihe

Polymorphism of Diacid Triglycerides of the Stearic Acid and Behenoic Acid Series Short- to medium-chain saturated diacyl derivatives of 1-monostearin and 1-monobehenin were synthesized in highly pure state and tested for their polymorphous behaviour. With the exception of the dicaprylo derivative the triglycerides of the behenoic acid series were strikingly stable in a wax-like plastic and stretchable α- resp. subα-modification which is obviously stable in the stearic acid series. The most stable modification of both series was the β-form, only the dibutyro-1-monobehenin by no manner could be transformed to a β′- or β-form. On heating the chilled samples or vice versa on cooling of the α-form two adjacent reversible phase transitions (subα₂ ? subα₁ ? α) could be observed with most of the triglycerides investigated here whereas in literature in case of the 1-monostearin derivatives the existence of only one subα-form has been described up to now.     

Thermodynamic and structural analyses of the solid phases in multi-alkane mixtures similar to petroleum cuts at ambient temperature

Structural analyses were carried out by X-ray diffraction, at ambient temperature, on multi-alkane samples whose mole fraction distribution shows a shape of the ‘exponential decreasing’ type, as observed in petroleum cuts. Nine samples, whose normal-alkane number varies from 15 to 23, have been studied with mole fraction continuous distributions of normal-alkanes going from C₂₂-C₃₆ to C₁₄-C₃₆: each mixture differs from the previous sample by the addition of a lighter n-alkane. At the solid state, the multi-alkane solid samples C₂₂-C₃₆ and C₂₁-C₃₆ are two-phase, C₂₀-C₃₆ to C₁₅-C₃₆, three-phase, and the broader distribution C₁₄-C₃₆, four-phase. In these polyphase solid systems, whose heaviest n-alkane is always C₃₆, the average composition of the heavy and middle phases are constant and their structure are isostructural to the β′ ordered intermediate solid solution, observed in n-alkane binary or ternary molecular alloys; the mean carbon atom number of the light phase decreases as the global average carbon atom number of the synthetic mixtures in relation to the addition of light n-alkanes and its structure simultaneously evolves from the β′ ordered intermediate solid solution towards the β-RI(Fmmm) and the disordered solid solutions, observed in pure n-alkanes: the light n-alkane added between each distribution intercalates itself into the structure whose molecule stacking period (thickness) is compatible with its own carbon chain length, in order to reduce the molecular gaps.     

Structure-activity relationship of unsaturated fatty acids as mosquito ovipositional repellents

Various straight-chain unsaturated fatty acids from C₁₄ to C₂₄ were evaluated for their ovipositional repellency against gravid females of the southern house mosquitoCulex quinquefasciatus Say, and the relationship between the structures of the fatty acids and their ovipositional repellency was determined. A double bond withZ configuration was prerequisite for an unsaturated fatty acid to be highly repellent;E isomers were less active or even inactive. No relationship was found between the repellency and the number of double bonds in the unsaturated fatty acids. In C₁₈ monounsaturated fatty acids, (Z)-9 acid was more active than (Z)-11 and (Z)-6 acids, indicating that a double bond at the 9 position rendered an acid highly repellent. Among (Z)-9-alkenoic acids of different chain lengths, the most repellent was C₁₈ acid which was also more active than (Z)-11-C₂₀, (Z)-13-C₂₂, and (Z)-15-C₂₄ acids. Oleic[(Z)-9-octadecenoic]acid, which met all these criteria, was the most ovipositionally repellent among the unsaturated fatty acids tested.Diptera: Culicidae.     

The influence of stem conformation on the crystallization of isotactic polypropylene

The influence of stem conformation on the crystallization of i-PP is studied by growing α-form lamellae in melts of β-form lamellae at different temperatures. The melting of β-form lamellae and the crystallization of α-form lamellae is observed in situ at the interface of α- and β-form spherulites by AFM. The growth rate of α-form lamellae in the melt of β-form lamellae is much lower than that in the isotropic melt due to the stem conformation barrier, which originates from the difference in the α and β unit cell packing models.     

Distribution modes and possible origins of sheep wool hydrocarbons

An unusual mode of distribution of low-molecular-weight n-alkanes (C₁₁-C₁₅) with a slight even carbon-number predominance has been observed in the gas Chromatographic analysis of the paraffin fraction which was extracted from the wool of live sheep. This is in addition to the other two modes of medium-, C₁₅-C₂₄, and high-, C₂₄-C₃₃, molecular-weight alkanes usually present in wool wax which have also been found in sheep’s manure. The high-molecular-weight hydrocarbons (predominantly odd carbon-numbered) are presumed to be derived from the diet (pasture plants) whereas the other two hydrocarbon distributions probably result from the combined action of animal and microbial metabolism.     

Higher order structures and mechanical properties of bacterial homo poly(3-hydroxybutyrate) fibers prepared by cold-drawing and annealing processes

Pure bacterial homo poly(3-hydroxybutyrate) (PHB) fibers were prepared by melt spinning, followed by cold-drawing in an amorphous state at a temperature just above its glass transition temperature. Cold drawn fibers obtained were further drawn at higher temperatures, followed by annealing at various temperatures under tension. Relations among the processing conditions, higher order structures and mechanical properties were investigated using wide- and small-angle X-ray diffractions (WAXD and SAXD, respectively), birefringence, differential scanning calorimetry (DSC), and tensile measurements. PHB has two different crystalline forms, 2₁ helix conformation (α-form) and planar zigzag conformation (β-form). A single broad reflection of β-form was detected even in a PHB fiber drawn once at a temperature just above its T_g immediately after quenching and it tended to be stronger after 2nd drawing at higher temperatures. Annealing under low temperature and high tension facilitates the occurrence of β-form. It is suggested that the β-form crystal is formed not only from the tie chains between α-form lamella, but also from completely free amorphous chains. Changes in the amount of two types of crystals were analyzed using the WAXD integrated intensity. Birefringence of these fibers shows negative and positive values, depending on process conditions. Changes in higher order structure on the mechanical properties are also discussed.     

Hydration of B2O3-stabilized α′-and β-modifications of dicalcium silicate

Paste hydration of B₂O₃-stabilized α′- and β-C₂S was studied at reaction times between 5 hours and 28 days. Data on the degree of hydration determined by X-ray diffraction at different ages were used to evaluate hydration rate constants. The higher rate of α′-C₂S hydration resulted in the higher compressive strengths of the α′-C₂S-alite paste as compared with the β-C₂S-alite paste. Differences in crystal imperfections of the two C₂S-polymorphs were determined using electron microscopy and electron diffraction.     

On the Crystal Structure of the β′1-Form of Triglycerides and the Mechanism behind the β′1 → β Transition of Fats

Based on earlier single crystal studies ^1,2 new interpretation of the crystal structure of the stable β′-form (β′₁) is proposed. This new interpretation gives the possibility to discuss the β′₁-form of various triglycerides. A mechanism behind the β′₁ → β transition is proposed. This mechanism is based on differences in the methyl end group region and supported by X-ray diffraction studies.