The X-ray diffraction of molecular compounds of 2-aminopyridine with long chain saturated and unsaturated fatty acids

X-Ray diffraction measurements of long and short spacings are reported for the crystalline 1:1 and 4:1 molecular compounds of 2-aminopyridine with the C₁₀ to C₁₈ saturated fatty acids and the 1:1 and 2:1 compounds of oleic, elaidic, alpha-eleostearic and beta-eleostearic acids. Data are also reported for 2-aminopyridine, α-eleostearic acid and β-eleostearic acid. The angle of tilt of the 1:1 saturated compounds is 42°15′. The long spacings of the 4:1 compounds indicate a unit cell length of four molecules of fatty acid and one molecule of 2-aminopyridine with an angle of tilt of 62°15′. The contribution of the 2-aminopyridine to the length of a molecule of the 1:1 compounds is ca. 6 Å, the distance between the NH₂ and the CH₂ in the para position. In the 4:1 and 2:1 compounds it is ca. 3 Å, the distance between the NH₂ and the ring nitrogen.     

Wide-line NMR spectra of some saturated and unsaturated long chain fatty acids

Wide-line NMR spectra were obtained on a series of homologous normal long chain fatty acids: decanoic, lauric, myristic, palmitic, stearic and behenic as well as three isostructural unsaturated acids: elaidic,trans-5-eicosenoic and brassidic. Also included are NMR spectra of metastable forms of both the saturated and unsaturated acids. NMR parameters are correlated with carbon chain length, crystal long spacing and density. Polymorphic forms are distinguished on the basis of line width and second moment differences. Presented in part at the Meeting of the Society for Applied Spectroscopy, October, 1970, New Orleans, La. So. Market. Nutr. Res. Div., ARS, USDA.     

Aliphatic poly(propylene dicarboxylate)s: Effect of chain length on thermal properties and crystallization kinetics

Polyesters based on 1,3-propanediol glycol and aliphatic dicarboxylic acids with different chain length were synthesized by melt polycondensation, obtaining samples characterized by high and comparable M_n. The polymers were subjected to molecular and thermal characterization. All polymers showed a good thermal stability, even though depending on the chain length. At room temperature all the polymers appeared as semicrystalline materials; the effect of the chain length was a lowering in the T_g value, an odd-even fluctuation for T_m and an increase of the crystallization rate. A comparison of the X-ray data revealed that the polymers with odd carbon number per repeat unit, show similar patterns, different from those of samples with even carbon atoms number. Multiple endotherms were evidenced in melt isothermally crystallized samples, due to melting and recrystallization processes. By applying the Hoffman-Weeks' method, the of the samples was derived. Lastly, the presence of an interphase was not evidenced.     

Thermotropic homopolyesters: 5. Investigation of the smectic phase of polyesters based on p,p′-bibenzoic acid

We report a study of the mesophases of the homologous series of polymers prepared from p,p′-bibenzoic acid and the tetra-, hexa-, octa-, and decamethylene glycols. These polymers are designated BBn, where n is the number of methylene units in the diol. The BB4 and BB6 polymers form a thermotropic smectic phase which was independently identified as S_A by mutual miscibility studies with a known low molecular weight mesogen, TBBA, and by X-ray diffraction studies of oriented samples. The enthalpy change for the smectic-isotropic transition is only 1.4 Kcal mol^?1 a value consistent with a smectic phase of low order. The smectic layer spacing is shorter than the fully extended length of the repeating unit for both BB4 and BB6. Low molecular weight samples of BB6 exhibit three crystal modifications. The two higher temperature forms have the same c-axis spacing as the smectic layer spacing, 18.7 Å, while the polymorph stable at room temperature has a fibre repeat of 32 Å, indicating a still smaller distance per repeating unit, 16 Å. All of these values are smaller than the 20 Å length of the fully extended repeating unit. Shearing the smectic hase of BB6 polymers having η_inh < 0.45 dL/g produces a highly oriented sample in which the repeating units are perpendicular to the direction of flow. Shear of the smectic phases of polymers having higher intrinsic viscosities breaks up the smectic structure, and leads to less perfect orientation of the molecules parallel to the shear direction.     

Distribution of chain defects and microstructure of melt crystallized polyethylene

A combined study using wide-angle X-ray diffraction (WAXD) and small-angle X-ray diffraction (SAXD) of a series of mostly low density polyethylenes with a wide range of chain defect concentrations (0.1–7%) crystallized from the melt is reported. The data presented here complement the earlier results obtained by Swan⁷ and Holdsworth and Keller⁸ for copolymers. The concurrent unit cell expansion and long period decrease with increasing chain defect concentration leads to a picture of chain defects (branches, unsaturations) being distributed between the crystalline lamellae and the surface layer. Based on a model which assumes inclusion of defects within the lattice by means of a generation of 2gl kinks, (supported by the parallel increase of paracrystallinity) an estimation of the concentration of chain defects, ?_c, incorporated into the crystal lattice (<1%) is attempted. The density of defects in the non-crystalline regions, ?_a, turns out to be substantially larger than ?_c and supports the view of a clustering of defects, ?_c and ?_a are both increasing functions of ? with a tendency to level off for ? > 6. According to this model, the fraction of defects incorporated into the lattice does not exceed 20% of the total number of defects in any of the samples investigated. The fraction of defects excluded from the lattice (>80%), on the other hand, sets a higher permissable limit to the crystal thickness value achieved.     

Kerogen structure by stepwise oxidation: Use of sodium dichromate in glacial acetic acid

Green River shale kerogen was degraded by a careful five-step oxidation with sodium dichromate in glacial acetic acid. Products isolated from each oxidation step were examined by capillary gas chromatography and combined gas chromatography-mass spectrometry. The analyses revealed the presence of several homologous series. Saturated normal monocarboxylic acids (C₆C₃₅) and saturated normal α,ω-dicarboxylic acids (C₄C₃₃) were the major constituent series, while isoprenoid acids (C₁₄C₂₁, except C₁₈), iso and anteiso acids (C₆C₁₆), branched dicarboxylic acids (C₂₀C₂₉), triterpenoidal acids (C₂₇C₃₃), cyclic, and oxo-acids were the minor constituent series. Moreover, a few aromatic acids, branched ketones, heterocyclic compounds, as well as a series of (C₂₅C₃₀) n-alkanes were identified. The results were discussed in terms of the qualitative and quantitative variations of the products with duration of oxidation. The data corroborate the conclusion of a predominantly open chain crosslinked aliphatic structure for Green River kerogen, and indicate that aromatic structures are mainly in the form of isolated phenyl and tolyl groups. The results further confirm the presence of etioporphyrin as a significant constituent in the kerogen studied.     

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°.     

Microscopically-viewed relationship between the chain conformation and ultimate Young's modulus of a series of arylate polyesters with long methylene segments

Relationship between the chain conformation in the crystal lattice and the ultimate Young's modulus has been discussed on the basis of the crystal structural information revealed by the X-ray diffraction analysis for a series of arylate polyesters with long methylene segments (–[–COC₆H₄CO–O(CH₂)_mO–]_n–). The X-ray structural analysis revealed that the molecular chains take the all-trans-zigzag conformations for all of the even-numbered polyesters and their model compounds as well as the odd-numbered polyesters with the methylene segmental length longer than (CH₂)₁₄. These chain conformations have been correlated well to the ultimate Young's modulus along the chain axis or the crystallite modulus E_c, which has been estimated experimentally by the X-ray diffraction method under a constant stress and also predicted theoretically using the X-ray-analyzed crystal structures on the basis of the molecular mechanics method. The E_c was found to show the minimum at around m = 4–6 and increased gradually with an increment of m and approached the crystallite modulus of polyethylene, 235 GPa (X-ray value) ∼ 316 GPa (calculate) at an infinite m value. This behavior of E_c as a function of the number of methylene segmental units m was reasonably interpreted by developing the theoretical equation of E_c for a simplified zigzag chain model composed of a repetition of two linear rods representing the benzene–ester and methylene segmental parts respectively. These findings may promise that the mechanical property of arylate polyester can be controlled by adjusting the methylene segmental length m.     

Characterization of branched chain fatty acids from subcutaneous triacyglycerols of barley-fed lambs

The fatty acids of subcutaneous triacylglycerols (containing ca. 11% of branched chain components) from lambs fed on barley-rich diets were fractionated by treatment with mercuric acetate and by urea adduct formation to yield concentrates rich in the branched chain components, all of which were saturated. The concentrates were subjected to analysis by high resolution gas liquid chromatography in conjunction with mass spectrometry. The branched chain fatty acids consisted of a complex mixture of mono-, di-, and trimethyl substituted components. The greater part of the mixture comprised monomethyl substituted acids of chain length 10–17 carbon atoms. Within each of these molecular species, a number of positional isomers was identified, notably in respect of methyltetradecanoic acid (methyl substituent on carbon 2, 4, 6, 8, 10, and 12) and methylhexadecanoic acid (methyl substituent on carbon 2, 4, 6, 8, 12, and 14). Homologous series also could be recognized of one of which all eight members from 4-methyldecanoic acid to 4-methylheptadecanoic acid were identified; together they accounted for ca. 39% of the branched chain fatty acids which were sampled for mass spectrometry. The dibranched acids identified consisted of five members of a homologous series, ranging in chain length from 11–15 carbon atoms and with substituent methyl groups at positions 4 and 8. Though the identity of only one tribranched acid (2,6,10-trimethyltetradecanoic acid) was established, others also apparently were present in the mixture. The probable involvement of methylmalonate in the biosynthesis of these branched chain acids is discussed briefly, with particular reference to the availability of vitamin B₁₂ in relation to the activity of methylmalonyl coenzyme A mutase.     

Molecular packing density in the crystalline state of semi-rigid chain polymers. I: Polyimides

Published data on crystal lattice unit cell parameters were used to calculate molecular packing density coefficients (K_c) in the crystalline state for a series of polyimides. The values of K_c were shown to decrease, the larger the chain cross-section thickness, and the lower the ratio of chain persistence length to chain thickness.     

Synthesis,structure and fluorescence properties of a uranyl-2,5-pyridinedicarboxylic acid coordination polymer: The missing member of the UO22+-2,n-pyridinedicarboxylic series

A 3D uranium-pyridinedicarboxylate, compound (1) [UO₂(C₇H₃NO₄)], represents the final member of a series of materials incorporating a series of 2,n-pyridinedicarboxylic (pydc) acids (n = 3,4,5,6). The resulting crystal structure [FW = 419.13, monoclinic, P2₁/n, a = 9.0096(3) Å, b = 8.1371(2) Å, c = 11.6954(4) Å, V = 852.45 ų, Z = 4] was determined by single crystal X-ray diffraction and fluorescent properties were investigated. Additionally, the complete series of uranium-2,n-pydc materials was examined on a basis of fluorescent behaviors and architectural similarities.     

The helical structure of cellulose I

The unit cell dimension along the crystallographic b-axis of cellulose is widely accepted to be 10.3 Å, as against the distance of 10.3912 Å between the terminal oxygen atoms of a cellobiose molecule, estimated from the now well-established crystal structure of cellobiose. Since cellulose is only a polymer of the cellobiose residue, it has been possible to derive the crystal structure of cellulose I from that of cellobiose. The strict application of stereochemical principles to the sucessive residues in the cellulose chain and a consideration of the formal geometric characteristics of a helix suggest a helical form to the cellulose molecule, with seven cellobiose residues per turn, radius r = 1.5830 Å, and angle of helix 7°51′ which is close to the x-ray orientation angle of 8°21′ observed in ramie, the best-oriented native cellulose. An analysis of intensity data both for the equatorial and for the meridional reflections leads to a unit cell with central reversed and corner chains and a relative shift between them of one fourth of the repeat length along the b-axis.     

Vapor Pressures of Substituted and Unsubstituted Monocarboxylic and Dicarboxylic Acids Measured Using an Improved Thermal Desorption Particle Beam Mass Spectrometry Method

A temperature programmed thermal desorption method we developed previously for measuring vapor pressures and enthalpies of sublimation of low-volatility organic aerosol compounds has been improved and applied to a suite of unsubstituted and substituted carboxylic acids. The method employs a thermal desorption particle beam mass spectrometer to monitor the evaporation of a submonolayer of monodisperse, submicron particles in vacuum. The desorption profile is then analyzed using evaporation rate theory to obtain a Clausius-Clapeyron equation. Improvements to the original instrument design include a redesigned vaporizer that provides uniform temperatures (< 1°C spatial variation) and the addition of a low-stick vaporizer coating that significantly reduces adsorption of molecules to the vaporizer surface. Modifications have also been made to the theory previously used to extract vapor pressures from evaporation measurements. The modified instrument and theory were evaluated by analyzing homologous series of monocarboxylic (C₁₃–C₂₂) and dicarboxylic (C₄–C₁₂) acids and comparing with results obtained using other methods. In addition, hydroxymonocarboxylic and oxodicarboxylic acids were analyzed to investigate the effect of a hydroxyl or carbonyl group, its location, and the carbon chain length on carboxylic acid volatility. Measured vapor pressures and enthalpies of sublimation were also compared with values calculated using SPARC, a group contribution computational method.     

Fatty acid polymorph identification by infrared

IR spectra in the 7.5–25.0 μm region are shown to be unique for polymorphic modifications of long chain saturated fatty acids of even carbon number and also for the individual fatty acids. IR spectra are presented for the A-, B-, C- and E-forms of stearic acid and for the C-form of myristic, palmitic, arachidic and behenic acid and the differences discussed. X-ray determined crystal long spacings for the A-, B-, C- and E-forms of a series of homologous even carbon-numbered acids are presented and compared with literature values. The formation of the different polymorphic forms are found to be temperature-concentration related and affected little by polarity of the solvent. Wideline nuclear magnetic resonance second moment values are given for the polymorphic forms of stearic acid. Presented in part at the AOCS Meeting, Houston, May 1971. S. Market. Nutr. Res. Div., ARS, USDA.     

Fermentation of long chain compounds byTorulopsis magnoliae III. Preparation of dicarboxylic acids from hydroxy fatty acid sophorosides

Conversion of hydroxy fatty acids, prepared from the products of fermentation of long chain hydrocarbons or fatty acids withTorulopsis magnoliae, to dicarboxylic acids with 15 to 18 carbon atoms is described. Both nitric acid oxidation and fission in 85% KOH give yields of 60–75%, but the products have different compositions. The nature of the compound fermented determines the composition of the hydroxy acids produced and hence that of the derived dicarboxylic acids. A convenient method is presented for hydrolysis of the hydroxy fatty acid sophorosides obtained by fermentation. Presented at the AOCS Meeting in Toronto, 1962, Issued as NRC No. 8900.     

Direct Access to Medium‐Chain α,ω‐Dicarboxylic Acids by Using a Baeyer–Villiger Monooxygenase of Abnormal Regioselectivity

Baeyer–Villiger monooxygenases (BVMOs) are versatile biocatalysts in organic synthesis that can generate esters or lactones by inserting a single oxygen atom adjacent to a carbonyl moiety. The regioselectivity of BVMOs is essential in determining the ratio of two regioisomers for converting asymmetric ketones. Herein, we report a novel BVMO from Pseudomonas aeruginosa (PaBVMO); this has been exploited for the direct synthesis of medium‐chain α,ω‐dicarboxylic acids through a Baeyer–Villiger oxidation–hydrolysis cascade. PaBVMO displayed the highest abnormal regioselectivity toward a variety of long‐chain aliphatic keto acids (C₁₆–C₂₀) to date, affording dicarboxylic monoesters with a ratio of up to 95 %. Upon chemical hydrolysis, α,ω‐dicarboxylic acids and fatty alcohols are readily obtained without further treatment; this significantly reduces the synthetic steps of α,ω‐dicarboxylic acids from renewable oils and fats.     

Surface shear viscosity of straight chain (c15 to c20) fatty acids

Experiments were carried out to measure surface shear viscosities of a series of straight chain fatty acids from C₁₅ to C₂₀. The experimental results indicated that members of the series with even-numbered C-atoms were essentially surface-Newtonian in behaviour with viscosity increasing with increasing chain length. However, members of the series with odd-numbered C-atoms were surface pseudoplastic and the degree of pseudo-plasticity decreased with increase in chain length. The experimental results also indicated that aging of surface-active solutions increases their surface shear viscosities.     

Chain conformation of polyethylene in the solid state as studied by 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy

High-resolution ¹³C nuclear magnetic resonance (n.m.r.) spectra of melt-quenched polyethylene and polyethylene single crystals are measured by the cross-polarization/magic angle spinning technique. Melt-quenched polyethylene and polyethylene single crystals have four small upfield peaks, a shoulder on the main peak and three small peaks, respectively. Based on the ¹³C n.m.r. resonance lines of cyclic paraffin C₆₄H₁₂₈ reported previously, it is concluded that the main peak and the three upfield peaks arise from the trans zigzag structure region and the folded structure region, respectively. From these peak intensities, it is estimated that the stem length of polyethylene single crystals is approximately 125 Å. Taking into account an error in the estimation of the small peak intensities, the calculated stem length of 125 Å is consistent with the crystal thickness (120–150 Å) observed directly by electron microscopy. It can be concluded, therefore, that polyethylene single crystals mainly contain sharply folded structure. Melt-quenched polyethylene may contain sharply folded structure to some extent in addition to loose loops.     

微生物发酵生产长链二元酸

以生物工程技术发酵生产长链二元酸的方法,不但开辟了长链二元酸的新来源,而且解决了一些二元酸无法化学合成的难题。目前,规模化工业生产十二碳二元酸及其衍生产品的装置已经建成投产。     

Effects of chain defects on the thermal behaviour of polyethylene

The annealing behaviour and thermodynamics of fusion of mats of solution-grown single crystals of ethylene-propylene and ethylene/1-butene crystallizable random copolymers are examined in comparison with linear polyethylene crystallized from the melt and from dilute solution. Correlation of quantities such as long spacing, annealing temperature, and apparent enthalpy of fusion, leads to the conclusion that the single crystal aggregates are involved in a morphological transformation during the process of annealing. The long spacing and the annealing temperature corresponding to this transformation decrease with the degree of constitutional defects present in the polyethylenic chain (percentage of propylene or 1-butene comonomeric units). Data in the plots of melting temperatures versus the reciprocal of the long spacing can be represented by straight lines. The thermodynamic equilibrium melting temperature T°_m and the surface free energy σ_e have been determined. Both T°_m and σ_e depend upon the number of constitutional defects in the chain. In the case of ethylene-propylene random copolymers σ_e increases drastically with the percentage of CH₃ side groups. A completely opposite effect is observed in the case of ethylene/1-butene random copolymers; here decrease in σ_e with the percentage of CH₃CH₂ side groups is observed. Both classes of polymers show a lowering in T°_m with the number of side groups, though this effect is much more pronounced in the ethylene-propylene copolymers. The apparent enthalpy of fusion of annealed single crystal aggregates is not in linear relation with the reciprocal of the long spacing and with the corresponding melting temperature. Some consideration on the distribution of the defects in the crystals is also reported.