Hydrocarbon Chain Conformation Research Articles

Correlations between bulk and surface properties of meibomian lipids with alteration of wax-to-sterol esters content

In a recent study (Ewurum et al., 2021), wax (WE) and sterol esters (CE) from human meibum secretions (MGS) were separated and reconstituted with controlled WE/CE ratios (0%, 20%, 30%, 40%, 50%, 75% and 100% CE weight fractions). It was found that the alterations in the CE content of WE/CE mixtures modified the hydrocarbon chain conformation and packing of the mixture. A major question that emerges is whether the spectroscopic packing parameters determined for bulk meibum translate to a change in the performance of meibomian layers at the air/water interface, as it is the surface film functionality that is crucial for the performance of MGS at the ocular surface. The study of human meibum films with Langmuir surface balance was performed to access the surface properties at blink-like deformations of the film area. Surface pressure (π)-area (A) isocycles and stress relaxations were used to assess the layer’s reorganization during area cycling and dilatational elasticity, respectively. The morphology of the films was monitored by Brewster angle microscopy. It was found that the increased order and chain melting temperature of the bulk samples correlated with a raise in the maximum surface pressure attained at minimal surface area and in the transient dilatational modulus of the meibomian layers. Such correlations may allow for development of an improved understanding between the bulk and surface properties of human meibum and of other natural and synthetic tear lipid films.

Conformationally Controlled Linear and Helical Hydrocarbons Bearing Extended Side Chains.

Conformationally controlled flexible molecules are ideal for applications in medicine and materials, where shape matters but an ability to adapt to multiple and changing environments is often required. The conformation of flexible hydrocarbon chains bearing contiguous methyl substituents is controlled through the avoidance of syn-pentane interactions: alternating syn-anti isomers adopt a linear conformation while all-syn isomers adopt a helical conformation. From a simple diamond lattice analysis, larger substituents, which would be required for most potential applications, result in significant and unavoidable syn-pentane interactions, suggesting substantially reduced conformational control. Through a combination of computation, synthesis, and NMR analysis, we have identified a selection of substitution patterns that allow large groups to be incorporated on conformationally controlled linear and helical hydrocarbon chains. Surprisingly, when the methyl substituents of alternating syn-anti hydrocarbons are replaced with acetoxyethyl groups, the main chain of almost 95% of the population of molecules adopt a linear conformation. Here, the side chains adopt nonideal eclipsed conformations with the main chain, thus minimizing syn-pentane interactions. In the case of all-syn hydrocarbons, concurrent removal of some methyl groups on the main chain adjacent to the large substituents is required to maintain a high population of molecules adopting a helical conformation. This information can now be used to design flexible hydrocarbon chains displaying functional groups in a defined relative orientation for multivalent binding or cooperative reactivity, for example, in targeting the interfaces defined by disease-relevant protein-protein interactions.

A spectroscopic approach to measuring meibum lipid composition and conformation in donors with Sjӧgren's syndrome

Patients with Sjӧgren's syndrome (SS) have dry eye associated with meibomian gland dysfunction (MGD). The meibum from donors with dry eye due to MGD but without SS (MMGD) presents with lower levels of cholesteryl ester, less straight chains, and more ordered hydrocarbon chains compared with meibum from donors without MGD (Mn). The aim of the current study was to compare the composition and hydrocarbon chain conformation of meibum from donors with Sjögren's syndrome (Mss) to Mn and MMGD. Meibum was expressed from patients with SS using an ILUX instrument (Alcon Inc., Fort Worth TX). All of the nine meibum donors with SS were female. Meibum composition was characterized using 1H-NMR and meibum hydrocarbon chain conformation was measured using fourier transform infrared spectroscopy. Meibum from every donor with SS measured contained a significantly (P < 0.01) higher cholesteryl ester/wax ester ratio and more straight chains compared with donors without SS or dry eye. None of the nine phase transitional parameters were significantly different, P > 0.05, for Mss compared with Mn. Nor was the CH3/CH2 band height ratio used to estimate the number of hydrocarbon CH3 and CH2 moieties different, P = 0.22, for Mss compared with Mn.In conclusion, the compositional differences between Mss compared with Mn did not result in differences in any of the nine meibum lipid phase transitional parameters measured. The compositional differences observed between Mss and Mn could be markers for or contribute to SS as the differences could lead to tear film lipid packing differences other than conformational differences.

A spectroscopic study of the composition and conformation of cholesteryl and wax esters purified from meibum

Elucidating wax ester (WE) and cholesteryl ester (CE) compositional, structural and functional relationships is key to our understanding of how these lipids are involved in natural and pathological processes. Little is known about how CE and WE interact with one another. The focus of the present study is to bridge this gap of knowledge. CE and WE were collected from human meibum as a source of esters with complex hydrocarbon chains. MgO column chromatography was used to separate WE and CE. The esters were characterized using 1H-NMR and Fourier transform infrared spectroscopy. The complexity of the hydrocarbon chains of native WE and CE influenced how changes in the ratio of WE and CE ester influenced some lipid phase transitional parameters but not others. Changes in CE content of WE/CE mixtures undoubtedly modifies the hydrocarbon chain conformation and packing of the mixture. The nature of the change depends on the conformation of the WE and CE. Differences in the complexity of the hydrocarbon chains are likely not to be a major influence on alterations in the order or phase transition temperature when more ordered WE is added to less ordered CE.

Concentration dependent cholesteryl-ester and wax-ester structural relationships and meibomian gland dysfunction

BackgroundWith dry eye, the ratio of cholesteryl ester (CE) to wax ester (WE) decreases substantially in meibum, but the functional and structural consequences of this change are speculative. The aim of this study is to confirm this finding and to bridge this gap in knowledge by investigating the effect of varying CE/WE ratios on lipid structure and thermodynamics. MethodsInfrared spectroscopy was use to quantify CE and WE in human meibum and to measure hydrocarbon chain conformation and thermodynamics in a cholesteryl behenate, stearyl stearate model system. ResultsThe CE/WE molar ratio was 36% lower for meibum from donors with dry eye due to meibomian gland dysfunction compared with meibum from donors without dry eye. CE (5 mol %) dramatically increased the phase transition temperature of pure WE from -0.12 °C to 63 °C in the mixture. Above 5 mol % CB, the phase transition temperature increased linearly, from 68.5 °C to 85 °C. In the ordered state, CE caused an increase in lipid order from about 72% trans rotamers to about 86% trans rotamers. Above 10% CE, the hydrocarbon chains were arranged in a monoclinic geometry. ConclusionsThe CE/WE is lower in meibum from donors with dry eye due to meibomian-gland dysfunction. Major conformational changes in the hydrocarbon chains of wax and cholesteryl ester mixtures begin to occur with just 5% CB and above. General significanceCE-WE interactions may be important for in understanding lipid layer structure and functional relationships on the surface of tears, skin and plants.

Insights into Tear Film Stability from Babies and Young Adults: A Study of Human Meibum Lipid Conformation and Rheology.

Babies have the most stable tears and people with dry eye have the least stable tears. Meibum may contribute to tear film stability, so in this study, the hydrocarbon chain conformation and rheology of meibum from babies was studied for the first time. Infrared spectroscopy was used to measure lipid phase transitions. Rheology was measured using Langmuir film technology. Meibum from 25 donors 1 to 13 years old was compared with meibum from 18 donors 13 to 25 years old. The phase transition temperature and lipid order (stiffness) increased with increasing age from 1 to 25 years. The increase in meibum lipid order from 1 to 25 years of age may contribute to the instability of the tear film with age and contribute to films with a higher reciprocal compressibility modulus that are not as compressible and not as viscoelastic. Changes in the lipid phase transition parameters of meibum lipid with dry eye are an exacerbation of the changes observed with age. The lower reciprocal compressibility moduli of meibum films from children and babies compared with meibum from adults reiterates higher stability in their films which spread better, resist deformation, and facilitates their ability to be quickly restored after blinking.

Parameters of micellization and hydrophobicity of sodium salts of 7-buthyl (butylidene) and 7-octyl (octylidene) derivatives of the cholic and the deoxycholic acid in a water solution: Pattern recognition — Linear hydrophobic congeneric groups

In this paper the influence of hydrophobicity is analysed (expressed with the reversed phase HPLC capacity factor, k) of the steroid skeleton anion derivatives with next groups placed in a position C7 of the steroid skeleton: octyl, octylidene, butyl, and butylidene group; the influence on their micellization parameters: aggregation number (n) and critical micelle concentration (CMC). If the examined derivative is more hydrophobic (higher values of k), CMC values are lower. Examined molecules have the same length of C7 hydrocarbon chain but different position of a double bond in the ring B (endocyclic between C6 and C7, and exocyclic on the C7) and have a different hydrophobicity as well as different CMC values. This can be explained using conformation analysis according to which conformation of the B ring of the steroid skeleton determines conformation of the C7 hydrocarbon chain, i.e. the degree of their departuring from steroid skeleton mean plane and approaching to convex surface of the molecule. In the plane lnk–n new derivatives with octyl/octylidene i.e. buthyl/butylidene group form two linear congeneric group: GE-LCC and H-LCC. Bile acid anions that form the H-LCC group, due the steric reasons, have a low possibility for formation of hydrogen bonds between different building units of a micelle. In the plane lnk–lnCMC only one linear hydrophobic congeneric group is formed which suggests that in micelles, on CMC, hydrogen bonds between building units are not present. Values of partition coefficients of nitrazepan for analysed derivatives micelles suggest that, in formation of mixed micelles of nitrazepan C7 alkyl chain from twisted conformation switches to elongated conformation and takes part in ecraning of the guest molecule.

Thermal and Structural Properties of Organically Modified Montmorillonite and its Surface Activated with Hydrochloric Acid

This paper presents preliminary results of modified Montmorillonite samples and the surface treatment with hydrochloric acid were investigated. The modification of this Montmorillonite surface, negatively charged and exchanged by organic cations such as alkylammoniums (Trimethylexadecyl C16 and Trimethyloctadecyl C18), yields a modified Montmorillonite (MMt). The resulting organo-mineral material acquires an organophilic character which could be used in several applications. The organically modified MMts were prepared by an ion exchange process in which sodium ions were replaced by alkylammonium ions. This material, used in the present work, is an Algerain montmorillonite obtained from MAGHNIA (West Algeria). Octadecyltrimethylammonium and hexadecyltrimethylammonium chlorides, utilized here as surfactants activators to organophilize the Montmorillonite. The microstructure of this modified Montmorillonite was characterized by XRD-diffraction with which the effects of the intercalation associated to the conformation of the long hydrocarbon chain were investigated. The results obtained showed that the amounts of hydrochloric acid added to these modified materials affect considerably the conformation of the intercalated surfactants. Their physical characteristics were determined by infrared spectrophotometer (FT-IR) and their chemical modification revealed that their thermal properties have been advantageously improved.

Evaporation and Hydrocarbon Chain Conformation of Surface Lipid Films

PurposeThe inhibition of the rate of evaporation (Revap) by surface lipids is relevant to reservoirs and dry eye. Our aim was to test the idea that lipid surface films inhibit Revap. MethodsRevap were determined gravimetrically. Hydrocarbon chain conformation and structure were measured using a Raman microscope. Six 1-hydroxyl hydrocarbons (11-24 carbons in length) and human meibum were studied. Reflex tears were obtained from a 62-year-old male. ResultsThe Raman scattering intensity of the lipid film deviated by about 7 % for hydroxyl lipids and varied by 21 % for meibum films across the entire film at a resolution of 5 μm2. All of the surface lipids were ordered. Revap of the shorter chain hydroxyl lipids were slightly (7%) but significantly lower compared with the longer chain hydroxyl lipids. Revap of both groups was essentially similar to that of buffer. A hydroxyl lipid film did not influence Revap over an estimated average thickness range of 0.69 to >6.9 μm. Revap of human tears and buffer with and without human meibum (34.4 μm thick) was not significantly different. Revap of human tears was not significantly different from buffer. ConclusionsHuman meibum and hydroxyl lipids, regardless of their fluidity, chain length, or thickness did not inhibit Revap of buffer or tears even though they completely covered the surface. It is unlikely that hydroxyl lipids can be used to inhibit Revap of reservoirs. Our data do not support the widely accepted (yet unconfirmed) idea that the tear film lipid layer inhibits Revap of tears.

Effects of vesicle components on the electro-permeability of lipid bilayers of vesicles induced by pulsed electric fields (PEF) treatment

In this study, the effects of pulsed electric field (PEF) treatments on the electro-permeability of vesicles made from dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), dioleoyl-sn-glycero-3-phosphocholine (DOPC), Soya phosphatidylcholine (soya PC), cholesterol and a binary mixture of them encapsulated 5(6)-Carboxyfluorescein (5(6)-CF) were investigated, based on the electric field strength of 0–40 kV/cm and treatment time of 0–4.8 ms. Results indicated that the electro-permeability of lipid membrane was directly related to the composition of lipid bilayers membrane of vesicles. As compared to DPPC vesicles, DOPC vesicles were much more sensitive to PEF treatment. For the DOPC vesicles, the 5(6)-CF release percentage (R) was 9.24%, 20.12%, and 30.62% after PEF treatment at 20, 30, and 40 kV/cm for 4.8 ms treatment time, respectively. However, for the DPPC vesicles, it was only 1.84%, 4.02%, and 6.51%, respectively. On the other hand, the electro-permeability of DOPC vesicles was greatly affected by the addition of DPPC. The electro-permeability of DOPC vesicles was decreased sharply with the increase of DPPC molar ratio. Under the PEF treatment with 40 kV/cm and 1.2 ms, it was observed that the R of DOPC vesicles decreased markedly from 27.56% to 9.80% with the molar ratio of DPPC increased from 0 to 40%.For the soya PC vesicles, the R was dropped sharply from 48.13% to 24.11% with the molar ratio of cholesterol increased from 0 to 50%. Raman spectroscopy analysis revealed that the decrease of electro-permeability of soya PC vesicles with the addition of cholesterol was responsible for the incorporating of cholesterol into hydrocarbon partition of lipid bilayers, leading to the order arrangement of hydrocarbon chain of phospholipids, which was resulted an increase in the thickness of bilayers membrane and decrease in the fluidity of bilayers membrane. However, for the mixture of DOPC and DPPC (DOPC/DPPC) vesicles, there has no effect on the conformation of hydrocarbon chain of phospholipids and the fluidity of bilayer membrane of DOPC/DPPC vesicles with the addition of DPPC.

SERS of the Positive Charge Bearing Pyridinium Ring Terminated Self-Assembled Monolayers: Structure and Bonding Spectral Markers

Bifunctional self-assembled monolayers (SAMs) are widely used for construction of surfaces with desirable properties. To predict and control the function of SAMs, molecular level understanding of monolayer architecture is required. In this work, structure and bonding of positive charge bearing SAM of N-(6-mercapto)hexylpyridinium (MHP) on Au and Ag electrodes was probed by SERS, first-principles calculations, isotopic substitution, and reductive desorption voltammetry. Based on analysis of immersion time- and temperature-dependent SERS spectra as well as DFT calculations, the marker bands for MHP structure, bonding, and orientation have been established. The presence of a band around 1083 cm–1 was found to be a reliable SERS marker for the all-trans conformation of hydrocarbon chain. Soft C–H stretching mode near 2832 cm–1 was recognized as a marker for the probing of direct interaction of alkyl chain with the metal. Based on solvent-dependent Raman spectra the pyridinium ring ═C–H band (ν2) was proposed ...

Mechanism of stearic acid adsorption to calcite

Abstract This paper presents the interpretation of binding mechanism of stearic acid for calcite surface in two modification methods. In the “dry” method, a surface dissociation of stearic acid is assumed where H + ion goes to a surface carbonate ion and stearic ion is chemisorbed on primary surface center of − Ca + ion which is only available for chemisorption. The structure of adsorbed layer indicates chemisorption of stearate, but due to steric effects, and the oblique or gauche conformation of hydrocarbon chains. A part of surface − Ca + centers can be blocked, which is explained by the result that physical adsorption dominates over 1.5%. In the “wet” method, by adding stearic acid, at concentration above the critical concentration of micelle formation in base solution, micelles are formed, and on the other side free stearic acid molecules or molecules from developed micelle dissociate. The resulting stearic ions can be chemisorbed on primary centers of − Ca + ions or participate in ion exchange with OH − ions from secondary surface centers. With increasing adsorption density, the adsorbed ions and molecules, due to interactions of hydrocarbon chains, and thickness of double electrical layer, achieve a vertical orientation and keep the trans-conformation of hydrocarbon chains.

Wax-tear and meibum protein, wax–β-carotene interactions in vitro using infrared spectroscopy

Protein–meibum and terpenoids–meibum lipid interactions could be important in the etiology of meibomian gland dysfunction (MGD) and dry eye symptoms. In the current model studies, attenuated total reflectance (ATR) infrared (IR) spectroscopy was used to determine if the terpenoid β-carotene and the major proteins in tears and meibum affect the hydrocarbon chain conformation and carbonyl environment of wax, an abundant component of meibum. The main finding of these studies is that mucin binding to wax disordered slightly the conformation of the hydrocarbon chains of wax and caused the wax carbonyls to become hydrogen bonded or experience a more hydrophilic environment. Lysozyme and lactoglobulin, two proteins shown to bind to monolayers of meibum, did not have such an effect. Keratin and β-carotene did not affect the fluidity (viscosity) or environment of the carbonyl moieties of wax. Based on these results, tetraterpenoids are not likely to influence the structure of meibum in the meibomian glands. In addition, these findings suggest that it is unlikely that keratin blocks meibomian glands by causing the meibum to become more viscous. Among the tear fluid proteins studied, mucin is the most likely to influence the conformation and carbonyl environment of meibum at the tear film surface.

Human Meibum Lipid Conformation and Thermodynamic Changes with Meibomian-Gland Dysfunction

Instability of the tear film with rapid tear break-up time is a common feature of aqueous-deficient and evaporative dry eye diseases, suggesting that there may be a shared structural abnormality of the tear film that is responsible for the instability. It may be that a change in the normal meibum lipid composition and conformation causes this abnormality. Principle component analyses of infrared spectra of human meibum indicate that human meibum collected from normal donors (Mn) is less ordered than meibum from donors with meibomian gland dysfunction (Md). In this study the conformation of Md was quantified to test this finding. Changes in lipid conformation with temperature were measured by infrared spectroscopy. There were two phases to our study. In phase 1, the phase transitions of human samples, Mn and Md, were measured. In phase 2, the phase transitions of model lipid standards composed of different waxes and cholesterol esters were measured. The phase-transition temperature was significantly higher (4°C) for the Md compared with the Mn of age-matched donors with no history of dry-eye symptoms. Most (82%) of the phase-transition temperatures measured for Md were above the values for Mn. The small change in the transition temperature was amplified in the average lipid order (stiffness) at 33.4°C. The average lipid order at 33.4°C for Md was significantly higher (30%, P = 0.004) than for Mn. The strength of lipid-lipid interactions was 72% higher for Md than for Mn. The ability of one lipid to influence the melting of adjacent lipids is termed cooperativity. There were no significant differences between Mn and Md in phase-transition cooperativity, nor was there a difference between Mn and Md in the minimum order or maximum order that Mn and Md achieved at very low and very high temperatures, respectively. The model wax studies showed that the phase transition of complex mixtures of natural lipids was set by the level of unsaturation. A double bond decreased the phase-transition temperature by approximately 40°C. The addition of a second CH CH moiety decreased the phase-transition temperature by approximately 19°C. Unsaturated waxes were miscible with saturated waxes. When a saturated wax was mixed with an unsaturated one, the saturated wax disproportionately increased the phase transition of the mixture by approximately 30°C compared with the saturated wax alone. Cholesterol ester had little effect on the phase-transition temperature of the waxes. Model studies indicated that changes in the amount of lipid saturation, rather than the amount of cholesterol esters, could be a factor in the observed conformational changes. Meibum lipid compositional changes with meibomian gland dysfunction reflect changes in hydrocarbon chain conformation and lipid-lipid interaction strength. Spectroscopic techniques are useful in studying the lipid-lipid interactions and conformation of lipid from individual patients. (ClinicalTrials.gov number, NCT00803452.).

Self-Assembly of a Fluorocarbon−Hydrocarbon Hybrid Surfactant: Dependence of Morphology on Surfactant Concentration and Time

The morphologies of aggregates formed from a hybrid surfactant (F6H5OS) whose molecules have a hydrocarbon chain (pentyl group) and a fluorocarbon chain (perfluorohexyl group) were studied along with changes in the morphologies with time. F6H5OS exhibits a micelle-vesicle transition at a concentration of 5.5 mM in water. Cryo-TEM observation of 5 mM aqueous F6H5OS solution reveals the existence of only micelles with a diameter of ca. 6 nm, while the coexistence of micelles and vesicles is observed in 10 mM aqueous F6H5OS solution. When the 10 mM aqueous F6H5OS solution is aged, the micelles are transformed into vesicles. Further, the vesicles have different structures, namely, spherical and tubular structures. (1)H NMR, (1)H-(1)H NOESY, and FT-IR experiments suggest that upon aging, the conformation of hydrocarbon chains in F6H5OS changes, and the hydrocarbon chains are located close to the phenyl group in the surfactant molecules. At concentrations above 5.5 mM, small micelles are formed immediately after the preparation of the F6H5OS solutions; those micelles subsequently transform into vesicles. The hybridity of F6H5OS, i.e., having a fluorocarbon chain and a hydrocarbon chain in its molecule, plays an important role in the transformation of micelles into vesicles upon aging.

Physical Changes in Human Meibum with Age as Measured by Infrared Spectroscopy

Both lipids and mucins contribute to the stability of the tear film and lipids may inhibit tears from evaporating. Younger people have lower lipid viscosity, higher lipid volume, and a lower rate of tear evaporation. Since age-related changes in human meibum composition and conformation have never been investigated, as a basis for the study of lipid-associated changes with meibomian gland dysfunction, we used the power of infrared spectroscopy to characterize hydrocarbon chain conformation and packing in meibum from humans without dry eye symptoms in relation to age and sex. Meibum from normal human donors ranging in age from 3 to 88 years was studied. Meibum phase transitions were quantified by fitting them to a 4-parameter 2-state sigmoidal equation. Human meibum order and phase transition temperatures decrease with age and this trend may be attributed to lipid compositional changes. If meibum has the same thermodynamic properties on the surface of the tears as it does on the lid margin, a decrease in lipid-lipid interaction strength with increasing age could decrease the stability of tears since lipid-lipid interactions on the tear surface must be broken for the tear film to break up. This study also serves as a foundation to examine meibum conformational differences in meibum from people with meibomian gland dysfunction.

Thermal Behavior of J-Aggregates in a Langmuir−Blodgett Film of Pure Merocyanine Dye Investigated by UV−visible and IR Absorption Spectroscopy

We have characterized the structure of J-aggregate in a Langmuir-Blodgett film of pure merocyanine dye (MS18) fabricated under an aqueous subphase containing a cadmium ion (Cd2+) and have investigated its thermal behavior by UV-visible and IR absorption spectroscopy in the range from 25 to 250 degrees C with a continuous scan. The results of both UV-visible and IR absorption spectra indicate that temperature-dependent changes in the MS18 aggregation state in the pure MS18 system are closely and mildly linked with the MS18 intramolecular charge transfer and the behavior of the packing, orientation, conformation, and thermal mobility of MS18 hydrocarbon chain, respectively. The J-aggregate in the pure MS18 system dissociates from 25 to 150 degrees C, and the dissociation temperature at 150 degrees C is higher by 50 degrees C than that in the previous MS18- arachidic acid (C20) binary system. The lower dissociation temperature in the binary system originates from the fact that temperature-dependent structural disorder of cadmium arachidate (CdC20), being phase-separated from MS18, has an influence on the dissociation of J-aggregate. From 160 to 180 degrees C, thermally induced blue-shifted bands, caused by the oligomeric MS18 aggregation, appear at around 520 nm in the pure MS18 system by contraries, regardless of the lack of driving force by the melting phenomenon of CdC20. The temperature at which the 520 nm bands occur is in good agreement with the melting point (160 degrees C) of hydrocarbon chain in MS18 with Cd2+, whereas its chromophore part is clearly observed to melt near 205 degrees C by UV-visible spectra. Therefore, it is suggested that the driving force that induces the 520 nm band in the pure MS18 system arises from the partial melting of hydrocarbon chain in MS18 with Cd2+.

Thermal Behavior of H-Aggregate in a Mixed Langmuir−Blodgett Film of Merocyanine Dye, Arachidic Acid, and n-octadecane Ternary System Investigated by UV−visible and IR Absorption Spectroscopy

We have investigated the thermal behavior of H-aggregate in a mixed Langmuir-Blodgett (LB) film of the merocyanine dye (MS18)-arachidic acid (C20)- n-octadecane (AL18) ternary system by means of UV-visible and IR absorption spectroscopy in the range from 25 to 250 degrees C with a continuous scan. The results of both UV-visible and IR spectra indicate that the temperature-dependent variation in MS 18 aggregation state is linked not only with the degree of intramolecular charge transfer and the behavior of packing, orientation, conformation, and thermal mobility of the MS18 hydrocarbon chain but also with the presence and absence of AL18. The H-aggregate dissociates from 25 up to 50 degrees C, which is caused by the AL18 evaporation from the mixed LB film and the increment of thermal mobility of the MS18 hydrocarbon chain. From 110 to 160 degrees C, blue-shifted bands, attributed to the oligomeric MS18 aggregation, appear near 515 nm in the MS18-C 20-AL18 ternary system as well. The temperature at which the 515 nm band occurs is identical for both present ternary system and previously investigated MS18-deuterated arachidic acid (C20- d) binary system, and it is in good agreement with the melting point (110 degrees C) of cadmium arachidate (CdC20). Therefore, it is indicated that the driving force which induces the 515 nm band comes from the melting phenomenon of CdC20 molecules which are phase-separated from MS 18 molecules in as-deposited LB films.

Phase Separation of Poly(vinyl methyl ether) Aqueous Solution: A Near-Infrared Spectroscopic Study

The thermosensitive phase separation of poly(vinyl methyl ether) (PVME) aqueous solutions has been investigated using near-infrared spectroscopy in combination with two-dimensional correlation analysis, and a two-step phase separation mechanism during gradual heating has been established. Two-dimensional near-infrared (2D NIR) analysis results indicate that during this two-step process the dehydration of CH 2 groups occurs earlier than that of CH 3 groups. This result suggests that it is the change of the hydrophobic hydrocarbon chain conformation induced by heating that indirectly leads to the dehydration of the hydrophilic ether oxygen side groups.

Thermal Behavior of J-Aggregates in Mixed Langmuir−Blodgett Films Composed of Merocyanine Dye and Deuterated Arachidic Acid Investigated by UV−visible and Infrared Absorption Spectroscopy

We have investigated the thermal behavior of J-aggregates in the mixed Langmuir-Blodgett (LB) films composed of the merocyanine dye (MS18)-deuterated arachidic acid (C20-d) binary system in the temperature range from 25 to 250 degrees C by means of UV-visible and IR transmission absorption spectroscopy. The temperature-dependent variations in both UV-visible and IR absorption spectra indicate that the MS18 aggregation states are linked with the MS18 intramolecular charge transfer and the behavior of the packing, orientation, conformation, and thermal mobility of the MS18 hydrocarbon chain. The J-aggregate formed at 25 degrees C in the mixed LB films dissociates in the temperature range from 25 to 110 degrees C, which is mainly ascribed to the increase in the thermal mobility of MS18 hydrocarbon chain and the dissociation of the chelation by a cadmium ion to the MS18 keto group. A thermally induced blue-shifted band appears at around 515 nm from 110 to 160 degrees C. This band is attributed to oligomeric aggregation with side-by-side alignment of the MS18 transition dipole moments on the basis of the shift to a higher-energy side, broadening, and temporary increment of the MS18 intramolecular charge transfer of the band. Consequently, the appearance of the thermally induced blue-shifted band indicates the possibility that the MS18 aggregation states can be controlled from the red shift to the blue shift by the annealing method adopted in the present study.