Structural Study on Fat Crystallization Process Heterogeneously Induced by Graphite Surfaces.

Some inorganic and organic crystals have been recently found to promote fat crystallization in thermodynamically stable polymorphs, though they lack long hydrocarbon chains. The novel promoters are talc, carbon nanotube, graphite, theobromine, ellagic acid dihydrate, and terephthalic acid, among which graphite surpasses the others in the promotion effect. To elucidate the mechanism, we investigated the influence of graphite surfaces on the crystallization manner of trilaurin in terms of crystal morphology, molecular orientation, and crystallographic features. Polarized optical microscopy, cryo-scanning electron microscopy, synchrotron X-ray diffractometry, and polarized Fourier-transform infrared spectroscopy combined with the attenuated total reflection sampling method were employed for the analyses. All the results suggested that the carbon hexagonal network plane of graphite surfaces have a high potential to facilitate the clustering of fat molecules against high thermal fluctuations in fat melt, the fat molecules form a layer structure parallel to the graphite surface, and the clusters tend to grow into thin plate crystals of the ß phase at the temperatures corresponding to low supercooling. The ß' phase also has a larger chance to grow on the graphite surface as supercooling increases.

Binary Phase Behavior of 1,3-Distearoyl-2-oleoyl-sn-glycerol (SOS) and Trilaurin (LLL).

This paper reports the precise analysis of the eutectic mixing behavior of 1,3-distearoyl-2-oleoyl-sn-glycerol (SOS) and trilaurin (LLL), as a typical model case of the mixture of cocoa butter (CB) and cocoa butter substitute (CBS). SOS was mixed with LLL at several mass fractions of LLL (wLLL); the mixtures obtained were analyzed for polymorphic phase behavior using differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffractometry (SR-XRD). In melt crystallization with constant-rate cooling, SOS and LLL formed eutectics in their metastable polymorphs, allowing the occurrence of a compatible solid solution at wLLL ≥ 0.925. With subsequent heating, the resultant crystals transformed toward more stable polymorphs, then melted in a eutectic manner. For mixtures aged at 25 °C after melt crystallization, eutectics were found in the extended wLLL region, even at wLLL = 0.975. These results indicate that phase separation between SOS and LLL progressed in their solid solution under stabilization. The crystal growth of the separated SOS fraction may cause fat-bloom formation in compound chocolate containing CB and CBS. To solve this problem, the development of retardation techniques against phase separation is expected.

Simultaneous SANS/FTIR measurement system incorporating the ATR sampling method.

Small-angle neutron scattering (SANS) is widely used as a powerful technique to study the higher-order structure of soft matter. To increase the reliability of SANS profile analysis for complex multi-component systems, combining different types of structural information obtained by other methods is desirable. A simultaneous measurement system combining SANS and Fourier transform infrared (FTIR) spectroscopy meets this objective. It is beneficial for targets where matching the timing of structural changes between experiments is difficult, but the issue is that samples suitable for SANS are too thick for the typical transmission FTIR method. To overcome this problem, a new simultaneous measurement system that employs the attenuated total reflectance (ART) sampling method for FTIR spectroscopy has been developed.

Crystalline complex of syndiotactic polystyrene with poly(ethylene glycol) dimethyl ethers.

It has been clarified that syndiotactic polystyrene (sPS) forms co-crystalline structures with polyethylene glycol dimethyl ethers (PEGDMEs) with molecular weights ranging from 178 to 1,000 g·mol(-1) through a guest exchange procedure assisted by a plasticizing agent. The PEGDME molecules are incorporated into the spaces between sPS polymer sheets consisting of (T(2)G(2))(2) helices. The results of X-ray diffraction and gravimetric measurements suggest that one or less molecules are included per unit cell for PEGDME with average molecular weight of 1,000 g·mol(-1), which indicates the possibility that longer polymeric molecules can be introduced into sPS lattices with multiple site occupation.

First In Situ X-ray Scattering Measurements of Insect Body Surface Lipids: American Cockroach.

In situ X-ray scattering measurements of insect body surface lipids were successfully attempted by using a synchrotron X-ray source. The temperature-dependent structural changes of the cuticular hydrocarbons covering the forewing of an American cockroach were able to be followed, which showed that the majority of the hydrocarbons were in a liquid state even far below the critical temperature of water transpiration through the body surface. The results clearly demonstrated that synchrotron radiation X-ray scattering has the potential to obtain the detailed information about the intact lipid structure and physical properties on insect body surfaces.

Cuticular Lipid Topology on Insect Body Surfaces Studied by Synchrotron Radiation FTIR ATR Microspectroscopy.

The cuticular lipid covering the integument of insects is exposed to the environment and involved in a variety of functions offered by insect body surfaces, ranging from protection against the environment, such as the control of water transpiration, the reduction of abrasive damage, and the prevention of pathogen intrusion, to the communication between insects from intraspecific to interspecific interactions. In comparison with the importance of their physiological functions, there is remarkably little information on the structure and physical property of cuticular lipids on insect body surfaces. The lipid layer on the outer exoskeleton is very thin, estimated on the order of 0.01-1 µm or less, and this has led to a lack of practical methodologies for detailed structural analyses. To fill this devoid, we have exploited the characteristics of Fourier transform infrared (FTIR) attenuated total reflection (ATR) spectroscopy, which allows us to conduct a chemical analysis on insect body surfaces and also to investigate depth-dependent structural changes. We have applied a combination of FTIR ATR microspectroscopy with IR radiation provided by a synchrotron facility to obtain in situ two-dimensional (2D) information of the cuticular lipid layer on the surface of the integument. The 2D FTIR spectra measured on the two-spotted cricket and the American cockroach show that the IR bands due to the cuticular lipid, such as CH2 symmetric and antisymmetric stretch, νa(CH2) and νs(CH2), change in intensity significantly, depending on the location of measurements. As if to keep pace with this, the bands of the amide group for the underlying cuticular layer also change in intensity significantly, although the changes are in the opposite direction; as the lipid bands increase in intensity, the amide band decreases, and vice versa. The ATR spectral analysis, which takes into account the characteristics of the evanescent wave, points out that the lipid layer would vary tens of times in the range of 0.01-1 µm significantly. The νa(CH2) and νs(CH2) bands show frequency shifts, which correlate to some extent with their intensity changes, suggesting that the drastic uneven distribution of the cuticular lipid would be related to the solid-liquid phase separation and also the coarsening of the solid phase domains. The formation of such topological features, significant heterogeneity in the lipid layer thickness, and solid-liquid phase ratios would be accompanied by the partitioning of lipid components according to molecular structures and physicochemical properties. Considering that each lipid component in insect body surface lipids is involved in various physiological roles, the segregation of lipid components during the formation of such heterogeneous structures is thought to have a significant impact on the functionality of the insect body surface.

Complexation of syndiotactic polystyrene with 12-crown-4.

Solid-state complexation of syndiotactic polystyrene (sPS) with a crown ether compound, 1,4,7,10-tetraoxa-cyclododecane (12-crown-4), took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted with a plasticizing agent. The new guest 12-crown-4 molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of host sPS helices. X-ray diffraction and thermogravimetric investigations showed that sPS/12-crown-4 complex had a clathrate complex structure which contained four 12-crown-4 molecules per unit cell. IR and Raman data suggested that 12-crown-4 took a C(i) -type conformation in the sPS complex phase.

Photoacoustic Experimental System To Confirm Infrared Absorption Due to Greenhouse Gases.

An experimental system for detecting infrared absorption using the photoacoustic (PA) effect is described. It is aimed for use at high-school level to illustrate the difference in infrared (IR) absorption among the gases contained in the atmosphere in connection with the greenhouse effect. The experimental system can be built with readily available components and is suitable for small-group experiments. The PA signal from a greenhouse gas (GHG), such as CO(2), H(2)O, and CH(4), can be detected down to a concentration of 0.1%. Since the basic theory of the PA effect in gases due to IR absorption is straightforward, the experiments with this PA system are accessible to students. It can be shown that there is a significant difference in IR absorption between GHGs and the major components of the atmosphere, N(2), O(2), and Ar, which helps students understand that the minor components, that is, the GHGs, determine the IR absorptivity of the atmosphere.

A new simultaneous measurement system of wide Q-range small angle neutron scattering combined with polarized Fourier transform infrared spectroscopy.

Small angle neutron scattering (SANS) is a versatile and convenient method to investigate the higher order structure of molecular assembly systems. However, the more complicated a system of interest, the more difficult the interpretation in the SANS profile. In order to increase the reliability of structural analysis on a complicated system, it is desirable to obtain different kinds of structural information from the same sample simultaneously. Polarized infrared spectroscopy is able to provide information about the molecular structure, concentration, and orientation of each chemical species in a system. In order to utilize these advantages of polarized infrared spectroscopy, a simultaneous measurement system was built by incorporating a Fourier transform infrared (FTIR) spectrometer into a time-of-flight small angle neutron scattering instrument covering a wide Q range. Using this system, simultaneous measurements of wide- and small-angle neutron scattering and polarized FTIR spectroscopy was realized for the first time.

ATR FTIR Spectroscopic Study on Insect Body Surface Lipids Rich in Methylene-Interrupted Diene.

To protect themselves, insects cover their bodies with what is called cuticular lipid. The cuticular lipid of an American cockroach has a unique lipid content; the most abundant is a cis-alkadiene, cis, cis-6,9-heptacosadiene, amounting to about 70%, which is followed by a branched alkane 3-methylpentacosane. In order to clarify the structural features of the unique lipid composition below the critical temperature, the cuticular lipid was studied by Fourier transform infrared (FTIR) spectroscopy in combination with an attenuated total reflection (ATR) sampling technique. The infrared spectra measured on an extracted lipid sample at 20 °C suggested that the lipid keeps an appreciable level of conformational and lateral packing regularity, in spite of a high cis-unsaturated lipid content, and also a highly disordered condition around the methyl terminals and cis-olefin groups. The CH2 scissoring and the CH2 rocking regions showed the characteristics of the O⊥ subcell. The same characteristics were observed also by in situ measurements on a forewing of the American cockroach. Combining the spectral features of these bands and the physicochemical properties of each component, it can be inferred that saturated lipids form highly ordered domains within the liquid containing the cis, cis-diene as the main component. For comparison, the cuticular lipid of a male cricket, which consisted of many different hydrocarbons, including 15% of unsaturated hydrocarbons, showed a lower regularity both in the conformation and in the lateral packing of hydrocarbon chains. These results imply that not only the degree of cis-unsaturation but also the chemical structure diversity of hydrocarbons are the important factors to determine the physicochemical properties of cuticular lipid.

Adsorption-induced conformational changes of antifreeze glycoproteins at the ice/water interface.

The conformation of antifreeze glycoprotein (AFGP) molecules adsorbed at the ice/water interface was studied by attenuated total reflection (ATR)-FTIR spectroscopy. Measurements were carried out for AFGP/D2O solution films formed on the surface of an ATR prism as a function of temperature. Using the FTIR spectrum from the O-D stretching band of D2O molecules, we monitored the supercooled and frozen states of the film and measured the thickness of the quasi-liquid layer (QLL) at the ice/prism interfaces. The AFGP structure was determined for the liquid, supercooled, and frozen states of the solution film using the amide I band spectra. No noticeable differences in conformation were observed in the solution conformation from room temperature down to the 15 K supercooling studied, whereas the alpha-helical content of AFGP suddenly increased when the supercooled solution film froze at -15 degrees C. This change in conformation can increase the overall interaction between the AFGP molecules and ice surface and allow a stronger adsorption. In contrast, the alpha-helical content of AFGP in the frozen film gradually decreased with increasing temperature and finally returned to its solution-state level at the melting point of D2O ice. This gradual decrease in the alpha-helix content directly correlates with the measured increase in QLL thickness. Finally, we conclude that the differences in the alpha-helix signals between the frozen and supercooled states indicate the conformational change of AFGP molecules upon adsorption at the ice/water interface, emphasizing the importance of the structure-function relationship, even for this highly flexible antifreeze.

Incoherent quasielastic neutron scattering study on the polymorphism of tristearin: dynamical properties of hydrocarbon chains.

Dynamical properties of acyl chains in the three polymorphic phases alpha, beta', and beta of tristearin [C(3)H(5)(OCOC(17)H(35))3] have been studied by means of incoherent quasielastic neutron scattering (IQNS) using selectively deuterated samples. The mean square displacement of hydrogen atoms, , was estimated from the scattering vector Q dependence of the elastic scattering component under the harmonic approximation. It was shown that the temperature dependence of was significantly different between the three phases. There was no marked difference in between these phases up to 193 K, and the value increased linearly with temperature. Although the beta phase remained linear up to 293 K, the alpha and beta' phases started to show a nonlinear increase around 200 K, suggesting an anharmonic nature of molecular motions. The alpha phase exhibited the most conspicuous temperature dependence. These characteristics were ascribable to the difference in the lateral packing of acyl chains. Compared with the beta phase which has a tightly packed T// subcell, the beta' and alpha phases have looser O perpendicular and H subcells, respectively. The molecular motion in the alpha phase was analyzed using the model of uniaxial rotational diffusion in a onefold cosine potential. It has been clarified that the rotational fluctuation about the chain axis in the alpha phase is rather restricted compared with that in the rotator phase of n-alkanes.

Structural study on polymorphism of cis-unsaturated triacylglycerol: triolein.

To clarify the influence of cis-unsaturation on solid-state structures of triacylglycerols (TAGs), the crystal structures of three crystalline phases (alpha, beta' and beta) of triolein [C3H5(OCOC17H33)3] were investigated by powder X-ray diffractometry and IR and Raman spectroscopy. The influence on the structural change of the alpha phase in the course of cooling was also studied. With respect to the subcell structure and conformational order of hydrocarbon chains in the beta and beta' phases, triolein resembles saturated TAGs; trans-zigzag hydrocarbon chains are adopted in the T(parallel) subcell for the beta phase and in the O(perpendicular) subcell for the beta' phase. The influence of cis-unsaturation was most obvious in the structure of the alpha phase and its temperature dependence. The alpha phase of triolein does not form the ordinary hexagonal subcell but a rather loose distorted subcell, which hardly changes in cooling, forming a striking contrast to the hexagonal-->pseudohexagonal subcell transformation found in the alpha phase of saturated TAGs.

Simultaneous small-angle neutron scattering and Fourier transform infrared spectroscopic measurements on cocrystals of syndiotactic polystyrene with polyethylene glycol dimethyl ethers.

Syndiotactic polystyrene (sPS) is a crystalline polymer which has a unique property; it is able to form cocrystals with a wide range of chemical compounds, in which the guest molecules are confined in the vacancies of the host sPS crystalline region. Recently, it has been found that even polyethylene glycol oligomers with a molecular weight of more than several hundreds can be introduced into the sPS crystalline region. It is quite important to know how such a long-chain molecule is stored in the host sPS lattice. To tackle this issue, a new simultaneous measurement method combing small-angle neutron scattering and Fourier transform infrared spectroscopy (SANS/FTIR), which has been recently developed by the authors, was applied to an sPS cocrystal with polyethylene glycol dimethyl ether with a molecular weight of 500 (PEGDME500). The temperature-dependent changes of the SANS profile and FTIR spectrum were followed from room temperature up to 413 K for a one-dimensionally oriented SANS/PEGDME500 cocrystal sample. The intensity of the reflections due to the stacking of crystalline lamellae showed a significant temperature dependence. The two-dimensional pattern in the high Q region of SANS also changed depending on temperature. The combined information obtained by SANS and FTIR suggested that PEGDME500 molecules are distributed in both the crystalline and amorphous regions in the low-temperature region close to room temperature, but they are predominantly included in the amorphous region in the high-temperature region. It was also suggested by the two-dimensional SANS profile that PEGDME500 molecules in the crystalline region have an elongated structure along the thickness direction of the crystalline lamellae.

Structural study on polymorphism of long-chain dicarboxylic acids using oblique transmission method for micro FT-IR spectrometers.

Polymorphism and higher-order structures of even-number dicarboxylic acids from hexadecanedioic acid to eicosanedioic acid have been studied by micro-FTIR spectroscopy and microscopic observation. In order to obtain the three-dimensional structural information, the oblique transmission method was incorporated into a micro-FTIR spectrometer equipped with a couple of Cassegrain lenses. The IR spectra showed that the solid states of dicarboxylic acid bore a marked structural similarity to those of n-saturated fatty acids. It was found that a solution-grown single crystal of dicarboxylic acids was an aggregate of lamellae whose thickness exceeded by far their molecular length. The surfaces of lamellae were covered with hydrocarbon segments taking a hairpin structure, and the linkage of hydrogen-bonded dicarboxylic acids formed a folded chain structure. The result of oblique transmission measurements showed that the stacking mode of lamellae varied depending on crystallization conditions.

X-ray diffraction and vibrational spectroscopic study of the influence of cis- and trans-unsaturation on the α-phase of triacylglycerols.

In order to clarify how cis- and trans-unsaturation of acyl chains influences the structure and properties of the metastable α-phase of triacylglycerols (TAGs), the conformation and packing of acyl chains and their temperature dependence were investigated by means of vibrational spectroscopy (IR and Raman) and powder X-ray diffractometry for typical saturated and cis- and trans-unsaturated TAGs, namely, tristearin, triolein, and trielaidin, which have clarified the following characteristics of each TAG. In the high-temperature range close to the melting point, the acyl chains form the hexagonal subcell for tristearin and trielaidin but they build the pseudohexagonal subcell for triolein. On the other hand, both cis- and trans-double bonds have a significant influence on the conformation of acyl chains. In triolein and trielaidin where the acyl chains are divided into two parts by a C═C bond, namely, the methyl-sided and the glycerol-sided chains, the glycerol-sided chain exhibits selective conformational disordering in the α-phase of these TAGs. The structural changes of acyl chains caused by cooling are also significantly affected by cis- and trans-unsaturation. For tristearin, the greater part of hydrocarbon segments change their packing from the hexagonal subcell to the pseudohexagonal subcell by cooling, while the greater part of hydrocarbon segments keep the hexagonal subcell structure and only the smaller part of them transform to the pseudohexagonal subcell for trielaidin. On the other hand, triolein does not exhibit any major changes with respect to subcell structure on cooling.

Dielectric relaxation of guest molecules in a clathrate structure of syndiotactic polystyrene.

Structure and dynamics of semicrystalline polymer films composed of syndiotactic polystyrene (sPS) and 2-butanone were examined through X-ray diffraction, polarized FTIR, and dielectric relaxation measurements. The X-ray and FTIR measurements revealed its crystal structure to be δ-clathrate containing 2-butanone molecules inside. The carbonyl group of 2-butanone in the crystal was found to orient preferentially parallel to the ac plane of the crystal through the polarized ATR FTIR measurements. Dielectric measurements were also conducted on these film samples to see only the relaxation dynamics of 2-butanone thanks to the high dielectric intensity of 2-butanone compared to sPS. Two relaxation modes denoted by slow and fast modes appeared. The former was assigned to the motion of 2-butanone molecules entrapped in the cavities of the crystalline (δ-form) and the latter to those in the amorphous region. We focused on the slow mode in order to elucidate the specific dynamics of the guest molecule confined in the crystalline region. The relaxation time of the slow mode was about 4 orders of magnitude longer than that of liquid 2-butanone. This suggests that the dynamics of guest molecules is highly restricted due to the high barrier to conformational and/or orientational change of the guest molecule in the cavity of δ-crystal. Furthermore, the dielectric intensity Δε of the slow mode was much smaller than the one calculated from that of bulk liquid 2-butanone and the guest concentration in the crystalline region (the intensity was only 10% of the estimated value from the bulk liquid data). This result also indicates that the free rotational motion of 2-butanone molecules is restricted inside the crystal. This will be consistently related to the weak uniplanar orientation of the carbonyl group of 2-butanone parallel to the ac plane revealed by the X-ray and polarized ATR FTIR measurements.

Solid-state low temperature→middle temperature phase transition of linoleic acid studied by FTIR spectroscopy.

Temperature-dependent FTIR spectra of linoleic acid were measured over a temperature range of -80 to -30 °C to explore solid-state low-temperature (LT) → middle-temperature (MT) phase transition of linoleic acid. Band assignments were made mainly for the 900-760 cm(-1) region, where the bands due to cis-olefin group's ═C-H out-of-plane mode and the progression bands due to CH(2) rocking-CH(2) twisting modes are expected to appear. The structural evolutions during the LT → MT phase transition of linoleic acid were investigated by analyzing the progression bands with the simple-coupled oscillator model to elucidate the features of acyl chain influenced with two cis-C═C bonds linked through one CH(2) group. Structure changes in the LT → MT transition of linoleic acid were compared with those in the γ → α transition of oleic acid. It has been found that the former is rather localized around the cis-diene group, while the latter occurs in the larger portion between the cis-olefin group to the methyl end. It is also suggested that the conformational change in the cis-olefin group on the LT → MT transition is on a lesser scale than that on the γ → α transition.

Study of thermodynamic stabilities of polytypes of n-C36H74 by solubility measurements and incoherent inelastic neutron scattering.

The thermodynamic properties of the two polytypes of n-hexatriacontane (n-C36H74), single-layered structure Mon and double-layered structure Orth II have been investigated by means of solubility measurements and incoherent inelastic neutron scattering. The solubility measurements reveal that Orth II is more stable than Mon by 1.2 kJ/mol because of the advantage of larger entropy. The neutron scattering measurements show that the vibrational modes of Orth II shift to the lower frequencies compared with those of Mon in the frequency region below 120 cm(-1). The advantage of Orth II in vibrational entropy due to the low-frequency shifts is estimated to be 9.6 J K(-1)/mol at 288 K under the harmonic approximation, which nearly agrees with the entropy difference of 6.8 J K(-1)/mol between Mon and Orth II determined by solubility measurements. These results suggest that the difference in vibrational entropy due to low-frequency modes mainly contributes to the relative thermodynamic stabilities of polytypic structures of long-chain compounds. From the frequency of methyl torsional mode, it is suggested that the cohesive force at the lamellar interface is stronger in Mon than in Orth II.

Infrared spectroscopic study of polytypic effects on the crystal-growth mechanism of n-hexatriacontane (n-C36H74).

The solution-crystallization mechanism was investigated for two polytypes in the M011 modification of n-hexatriacontane (n-C36H74), single-layered structure Mon, and double-layered one Orth II. The crystal growth under controlled supersaturation was followed with a micro- Fourier-transform-infrared spectrometer equipped with an optical system for oblique transmission measurements. Supersaturation dependence of growth behavior was significantly different between Mon and Orth II. Although the Mon crystal continued growing at a supersaturation of 0.27, the overgrowth of Orth II on the (001) face of the Mon crystal was confirmed at supersaturations below 0.21. Such a polytypic transformation was not observed for the Orth II crystal at any supersaturation below 0.30. The growth rate of Mon showed a quadratic dependence on supersaturation, while that of Orth II was approximately linear, suggesting spiral growth and two-dimensional-nucleation mechanisms for Mon and Orth II, respectively.