Thermodynamic Studies of Two Different Inclusion Compounds with the Same Guest:  Toward a General Understanding of Melting Behavior in Binary Compounds

White, Mary Anne; Harnish, R. S.

doi:10.1021/cm970578g

Cited by 7 publications

(4 citation statements)

References 53 publications

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“…The two solid-phase samples also yielded similar thermograms ( Fig. 2) that shared common trends with previously published DSC data for UIC containing FFA or hexadecane guests (9,11). Upon an increase of temperature during the first cycle, a first peak appeared at ca.…”

Section: Resultssupporting

confidence: 86%

“…Slow rates of crystallization are known to yield long needle-like hexagonal crystalline UIC of nearly 30 µm diameter, as depicted in Figure 1B. The geometry and size of the UIC match those provided in the literature (8,9). In contrast, a rapid cooling process yields crystals of significantly smaller size but of fundamentally the same geometry ( Fig.…”

Section: Resultssupporting

confidence: 68%

“…The dissociation temperature for UIC formed using rapid cooling, 120.0°C, is slightly higher in comparison, perhaps suggesting a minor difference of physicochemical behavior for UIC formed from rapid cooling, in agreement with the difference in appearance suggested in Figure 1. However, the specific heats of UIC formation, calculated from the UIC dissociation peak of the thermograms contained in Figure 2 (9,11), with the slightly lower values for the heat of fusion reported herein perhaps due to the small loss of mass that occurred between 122 and 130°C, as detected by thermogravimetric analysis (Hayes, D.G., unpublished data). In summary, the DSC results demonstrate that the UIC formed using rapid and slow-temperature cooling had nearly the same thermodynamic properties and shared similar properties with previously published values for UIC.…”

Section: Resultsmentioning

confidence: 54%

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Effect of temperature programming on the performance of urea inclusion compound‐based free fatty acid fractionation

Hayes

2006

J Americ Oil Chem Soc

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The effect of cooling rate on the degree of removal of saturated acyl groups from FFA derived from canola oil and the isolation of di-and polyunsaturated acyl groups from FFA derived from vegetable and fish oil, respectively, during urea inclusion compound (UIC)-based fractionation was investigated. Traditionally, slow cooling has been used (ca. −1°C min −1 ). A more rapid cooling rate (−47°C min −1 ) produced UIC crystals of similar morphology and thermodynamic properties, but of a size an order of magnitude smaller than the UIC formed during slow cooling. Fractionations used only renewable materials (urea, FFA, and 95% ethanol as solvent) and benign operating conditions (ambient pressure, 25-75°C, and neutral pH). When the recovery of FFA (in the solvent-rich phase) was relatively high (>60%), the selectivity of UIC-based fractionation toward the inclusion of saturated FFA and against polyunsaturated FFA was not affected by the cooling rate. In contrast, when the FFA recovery was low, representing cases in which an increase of the PUFA purity is a more important economic goal, a slower cooling rate resulted in a significantly greater discrimination against PUFA groups, hence to a FFA product with a measurably greater purity. Paper no. J11191 in JAOCS 82, 253-259 (March 2006). KEY WORDS: Canola oil, DHA (docosahexaenoic acid), DSC, EPA (eicosapentaenoic acid), FFA (fractionation of), fish oil, PUFA, urea inclusion compounds, vegetable oil.Urea inclusion compounds (UIC), hexagonal clanthrate materials consisting of hydrogen-bonded networks of urea that form a series of linear, parallel, narrow channels of diameter 0.55-0.58 nm, are well-known vehicles for fractionating or purifying FFA or FAME (reviewed in Ref. 1). For a given mixture of FFA or FAME, UIC will selectively remove long-chain saturated acyl groups, while acyl groups with branching and polyunsaturation do not partition as strongly to the UIC solid phase. Thus, UIC have been used to isolate PUFA from FFA derived from fish, linseed, and borage oils and to remove saturated acyl groups from FFA derived from edible oils such as low erucic acid rapeseed (LEAR) (reviewed in Refs. 2-4). UIC-based fractionation has potential value as a large-scale and robust prefractionation step because of its low temperature and environmentally friendly operating conditions, and its use of inexpensive renewable materials (urea and ethanol or methanol as solvent). To be a viable choice, a process that uses UIC-based fractionation must occur within a short time period. In contrast, a typical UIC-based fractionation procedure consists of slowly cooling a homogeneous solution of urea, FFA, and solvent for several hours. Recently, however, a rapid cooling process effectively fractionated FFA in a highly reproducible fashion, resulting in a simple and scalable purification process (5,6). But, as suggested recently by Lee (7), the use of a slower-temperature cooling program improves the selectivity by reducing the amount of tetragonal crystals of pure urea that form. The purpose of...

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Section: Resultssupporting

confidence: 86%

Section: Resultssupporting

confidence: 68%

Section: Resultsmentioning

confidence: 54%

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Effect of temperature programming on the performance of urea inclusion compound‐based free fatty acid fractionation

Hayes

2006

J Americ Oil Chem Soc

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“…A different melting behavior is shown for urea/ n -alkane ICs . A direct comparison of the PHTP and urea ICs with the same guest (C 16 ) was recently published . In that report the factors influencing congruent/incongruent melting in binary compounds are summarized.…”

Section: Resultsmentioning

confidence: 99%

Isolated Linear Alkanes in Aromatic Nanochannels

et al. 1999

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Novel channel-like inclusion compounds were formed by tris(o-phenylenedioxy)spirocyclotriphosphazene (TPP) with linear hydrocarbons. The molecular characterization was performed by 13 C and 31 P solid-state NMR under magic angle spinning conditions. The hexagonal symmetry of the host was verified in the 31 P and 13 C MAS spectra and by X-ray powder diffraction patterns. The new inclusion compounds present congruent meltings, and the temperatures increase with chain length. These compounds provide the opportunity to observe hydrocarbons confined as isolated chains in the solid state at temperatures 200 K above their melting points. Furthermore, the aliphatic chains are in the unusual state of being surrounded by aromatic rings displaced parallel to the channel. This geometry was proved by a through-space 1.4 ppm upfield shift on the 13 C resonances of the guests, due to the aromatic ring current. The mobility at the chain ends and the propagation of the conformational defects within the guest molecules is discussed and a comparison made with alkanes in different inclusion compounds and bulk alkanes in the high-temperature modification. The formation of the inclusion compounds was also highlighted by throughspace transferring of magnetization from the hydrogens of the host matrix to the chain carbons of a deuterated guest under Hartmann-Hahn conditions.

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Stability and phase behavior of the poly(ethylene oxide)–urea complexes prepared by electrospinning

Liu

Pellerin

2009

Polymer

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Thermodynamic Studies of Two Different Inclusion Compounds with the Same Guest: Toward a General Understanding of Melting Behavior in Binary Compounds

Cited by 7 publications

References 53 publications

Effect of temperature programming on the performance of urea inclusion compound‐based free fatty acid fractionation

Effect of temperature programming on the performance of urea inclusion compound‐based free fatty acid fractionation

Isolated Linear Alkanes in Aromatic Nanochannels

Stability and phase behavior of the poly(ethylene oxide)–urea complexes prepared by electrospinning

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