CH Bands Research Articles

Optical emission spectra analysis of thermal plasma treatment of poly(vinyl chloride)

Abstract Decomposition of poly(vinyl chloride) (PVC) was investigated in radiofrequency thermal plasma in neutral, oxidative and reductive conditions. Optical emission spectroscopy (OES) was applied for the characterization of the plasma column. OES was used to identify active plasma components such as excited atoms, ions, radicals and molecules. The spectra were dominated by molecular C2, CN, OH, and CH bands, and atomic H, Ar, C, Cl and O lines. Emission intensities of main species were monitored versus various experimental parameters. The rotational-vibrational temperatures determined from different bimolecular species were considered in the range of 2000–6400 K. Solid soot samples were collected and purified to investigate the possibility of graphene formation as a by-product of the decomposition process.

Tailoring the 4I9/2 → 4I13/2 emission in Er3+ ions in different hosts media

The 4I9/2–4I13/2 emission band of Er3+ is potentially interesting for CH4 detection because it can overlap with the optical absorption band of CH4. GaLaS and GeGaS glasses doped with Er3+ ions show the desirable emission under 808nm excitation. An attempt of spectrally shifting 4I9/2–4I13/2 emission band by substituting S by O or Se to obtain a perfect match to the absorption band of CH4 leads to the weakening and disappearance of the 4I9/2–4I13/2 band. This phenomenon is tentatively related to the acceleration of non-radiative relaxation in the case of oxygen addition and to the suppression of up-conversion in the selenium substitution case. The relative intensity of the 4I9/2–4I13/2 band (with respect to the 4I13/2–4I15/2 band) varies significantly in powdered and bulk materials. This effect is discussed in terms of the radiation diffusion (i.e. radiation trapping) model and is confirmed by Monte-Carlo simulations.

Design of cavity-enhanced absorption cell for reducing transit-time broadening.

To reduce the linewidth of Lamb dips, we introduce a cavity-enhanced absorption cell (CEAC) coupled with a Gaussian beam with a 1.9-mm 1/e(2) radius at the beam waist for the reduction of transit-time broadening. We state that transit-time broadening depends only on the beam radius at the beam waist. This fact is useful for the design of the CEAC, and a pair of concave and convex mirrors is thereby employed. We have carried out sub-Doppler resolution spectroscopy of the ν(3) band of CH(4) and the ν(1) band of CH(3)D using a difference-frequency-generation source and the CEAC, and the recorded Lamb dips narrow to 80 kHz (HWHM).

Organic molecules in translucent interstellar clouds.

Absorption spectra of translucent interstellar clouds contain many known molecular bands of CN, CH+, CH, OH, OH+, NH, C2 and C3. Moreover, one can observe more than 400 unidentified absorption features, known as diffuse interstellar bands (DIBs), commonly believed to be carried by complex, carbon-bearing molecules. DIBs have been observed in extragalactic sources as well. High S/N spectra allow to determine precisely the corresponding column densities of the identified molecules, rotational temperatures which differ significantly from object to object in cases of centrosymmetric molecular species, and even the 12C/13C abundance ratio. Despite many laboratory based studies of possible DIB carriers, it has not been possible to unambiguously link these bands to specific species. An identification of DIBs would substantially contribute to our understanding of chemical processes in the diffuse interstellar medium. The presence of substructures inside DIB profiles supports the idea that DIBs are very likely features of gas phase molecules. So far only three out of more than 400 DIBs have been linked to specific molecules but none of these links was confirmed beyond doubt. A DIB identification clearly requires a close cooperation between observers and experimentalists. The review presents the state-of-the-art of the investigations of the chemistry of interstellar translucent clouds i.e. how far our observations are sufficient to allow some hints concerning the chemistry of, the most common in the Galaxy, translucent interstellar clouds, likely situated quite far from the sources of radiation (stars).

Investigating skin barrier function utilizing reflectance NIR spectroscopy.

Near Infrared Spectroscopy is seen as a potentially valuable technique for skin analysis, and has been employed by many previous studies to measure skin hydration, since it is competent of providing information regarding various functional groups including OH, CH and NH bands. The aim of this study was to investigate the capability of further utilizing this method by attempting to analyze skin barrier function as well as water content, through the evaluation of skin water uptake on two test sites, one untreated, and another treated with a high lipid moisturizer for a period of 7 days. Reflectance NIRS measurements were supported by capacitance readings obtained using the Corneometer® CM 825. Baseline recordings taken on the first day following treatment showed that more differences were observed between the treated and untreated sites in the regions belonging to, or are influenced by CH and NH groups rather than purely on the water bands. On the hand, moisture levels measured after placing a wet patch on the skin remained nearly equal for both sites but second derivative spectra showed that a clear contrast existed between absorbance heights at the water bands of the treated and untreated, suggesting that moisturizer use could have limited water uptake to a more superficial layer of the skin, whereas for the untreated site, the opposite would have been true and water was able to penetrate deeper. Overall, results here suggest that NIR spectroscopy can possibly provide valuable information not only on skin water contents but perhaps on other skin parameters such as barrier function.

Remote measurements of concentration of organic solvents in binary mixtures using Raman spectroscopy

Binary mixtures of methanol, ethanol, isoamyl alcohol, and acetic acid with water in various ratios have been studied using Raman spectroscopy. Upon variations in organic solvent concentration, the intensities of stretching vibration bands of CH and OH group change within the spectral range 2600–3800 cm−1. For quantitative characterization of the partial concentrations of a solvent, we have chosen the integral intensity ICH of CH group stretching vibrations normalized to the total intensity of bands of CH and OH groups (ICH + IOH) within the 2600–3800 cm−1 range. With this normalization, the intensity ICH/(ICH + IOH) linearly depends on the volume fraction of the organic solvent throughout the whole range of its concentrations for the spectra of all mixtures. This allows noncontact measurements of concentrations of organic solvents in water solutions, including flammable or toxic ones. The relative concentration accuracy is 0.5, 1.1, and 1.5% for aqueous ethanol, methanol, and acetic acid, respectively.

SOLAR SPECTRAL IRRADIANCE CHANGES DURING CYCLE 24

We use solar spectra obtained by the Ozone Monitoring Instrument (OMI) on board the Aura satellite to detect and follow long-term (years) and short-term (weeks) changes in the solar spectral irradiance (SSI) in the 265-500 nm spectral range. During solar Cycle 24, in the relatively line-free regions the SSI changed by approximately 0.6% +/- 0.2% around 265 nm. These changes gradually diminish to 0.15% +/- 0.20% at 500 nm. All strong spectral lines and blends, with the notable exception of the upper Balmer lines, vary in unison with the solar continuum. Besides the lines with strong chromospheric components, the most involved species include Fe I blends and all prominent CH, NH, and CN spectral bands. Following the general trend seen in the solar continuum, the variability of spectral lines also decreases toward longer wavelengths. The long-term solar cycle SSI changes are closely, to within the quoted 0.1%-0.2% uncertainties, matched by the appropriately adjusted short-term SSI variations derived from the 27 day rotational modulation cycles. This further strengthens and broadens the prevailing notion about the general scalability of the UV SSI variability to the emissivity changes in the Mg II 280 nm doublet on timescales from weeks to years. We also detect subtle deviations from this general rule: the prominent spectral lines and blends at lambda approximately or greater than 350 nm show slightly more pronounced 27 day SSI changes when compared to the long-term (years) trends. We merge the solar data from Cycle 21 with the current Cycle 24 OMI and GOME-2 observations and provide normalized SSI variations for the 170-795 nm spectral region.

The surface compositions of Pluto and Charon

The surface of Pluto as it is understood on the eve of the encounter of the New Horizons spacecraft (mid-2015) consists of a spatially heterogeneous mix of solid N2, CH4, CO, C2H6, and an additional component that imparts color, and may not be an ice. The known molecular ices are detected by near-infrared spectroscopy. The N2 ice occurs in the hexagonal crystalline β-phase, stable at T>35.6K. Spectroscopic evidence for wavelength shifts in the CH4 bands attests to the complex mixing of CH4 and N2 in the solid state, in accordance with the phase diagram for N2+CH4. Spectra obtained at several aspects of Pluto’s surface as the planet rotates over its 6.4-day period show variability in the distribution of CH4 and N2 ices, with stronger CH4 absorption bands associated with regions of higher albedo, in correlation with the visible rotational light curve. CO and N2 ice absorptions are also strongly modulated by the rotation period; the bands are strongest on the anti-Charon hemisphere of Pluto. Longer term changes in the strengths of Pluto’s absorption bands occur as the viewing geometry changes on seasonal time-scales, although a complete cycle has not been observed. The non-ice component of Pluto’s surface may be a relatively refractory material produced by the UV and cosmic-ray irradiation of the surface ices and gases in the atmosphere, although UV does not generally penetrate the atmospheric CH4 to interact with the surface. Laboratory simulations indicate that a rich chemistry ensues by the irradiation of mixtures of the ices known to occur on Pluto, but specific compounds have not yet been identified in spectra of the planet. Charon’s surface is characterized by spectral bands of crystalline H2O ice, and a band attributed to one or more hydrates of NH3. Amorphous H2O ice may also be present; the balance between the amorphization and crystallization processes on Charon remains to be clarified. The albedo of Charon and its generally spatially uniform neutral color indicate that a component, not yet identified, is mixed in some way with the H2O and NH3·nH2O ices. Among the many known small bodies in the transneptunian region, several share characteristics with Pluto and Charon, including the presence of CH4, N2, C2H6, H2O ices, as well as components that yield a wide variety of surface albedo and color. The New Horizons investigation of the Pluto–Charon system will generate new insight into the physical properties of the broader transneptunian population, and eventually to the corresponding bodies expected in the numerous planetary systems currently being discovered elsewhere in the Galaxy.

Diamondoid synthesis in atmospheric pressure adamantane–argon–methane–hydrogen mixtures using a continuous flow plasma microreactor

Due to their small size, low-power consumption and potential for integration with other devices, microplasmas have been used increasingly for the synthesis of nanomaterials. Here, we have investigated the possibility of using dielectric barrier discharges generated in continuous flow glass microreactors for the synthesis of diamondoids, at temperatures of 300 and 320 K, and applied voltages of 3.2–4.3 kVp–p, at a frequency of 10 kHz. The microplasmas were generated in gas mixtures containing argon, methane, hydrogen and adamantane, which was used as a precursor and seed. The plasmas were monitored by optical emission spectroscopy measurements and the synthesized products were characterized by gas chromatography—mass spectrometry (GC–MS). Depending on the gas composition, the optical emission spectra contained CH and C2 bands of varying intensities. The GC–MS measurements revealed that diamantane can be synthesized by microplasmas generated at atmospheric pressure, and that the yields highly depend on the gas composition and the presence of carbon sources.

Towards understanding the spectroscopic features of enflurane. The fundamental and overtone bands of CH stretching vibrations

The near-IR and the mid-IR spectrum of enflurane dissolved in liquid Xe was studied at T∼170K. Inversion nature of the two CH stretching vibrations were analyzed by comparison of relative intensities of corresponding bands in a range of a first overtone and fundamental transition. The effect was explained by including features of the dipole moment function of enflurane. The analysis of the electro-optic parameters of the stable conformers was done with the help of MP2/6-311++G(df,pd) anharmonic calculations.

The emission rates of CH, CD and C2 spectral bands and a re-evaluation of the chemical sputtering yield of the JT-60U carbon divertor plates

The CH photon emission rate, defined as the number of photons over a dissociation and/or ionization event of CH4, has been determined from the ratio of the measured emission intensity of the CH spectral band over the CH4 injection rate into the divertor plasma of JT-60U. Similar photon emission rates of CD for CD4, and CH and C2 for C2H4 and C2H6, have also been determined. Interestingly, the C2 spectral band intensity is found to increase during the CH4 and CD4 injection, suggesting that the injected CH4 reacts with the carbon divertor plates to form heavier hydrocarbons. Previously published chemical sputtering yields (Nakano et al 2002 Nucl. Fusion 42 689) evaluated with the photon efficiencies determined in PISCES-A (Pospieszczyk et al 1989 UCLA Report UCLA-PPG-1251) have been re-evaluated using the measured emission rates. By applying the photon emission data found here and taking into account the C2 emission process originating from CH4, the re-evaluated total chemical sputtering yield becomes lower (∼7%) compared to the original in (Nakano et al 2002 Nucl. Fusion 42 689) (∼8%), and the dependence on the incident ion flux and energy becomes weaker.

Aromatic and aliphatic organic materials on Iapetus: Analysis of Cassini VIMS data

We present a quantitative analysis of the hydrocarbon and other organic molecular inventory as a component of the low-albedo material of Saturn’s satellite Iapetus, based on a revision of the calibration of the Cassini VIMS instrument. Our study uses hyperspectral data from a mosaic of Iapetus’ surface (Pinilla-Alonso, N., Roush, T.L., Marzo, G.A., Cruikshank, D.P., Dalle Ore, C.M. [2011]. Icarus 215, 75–82) constructed from VIMS data on a close fly-by of the satellite. We extracted 2235 individual spectra of the low-albedo regions, and with a clustering analysis tool (Dalle Ore, C.M., Cruikshank, D.P., Clark, R.N. [2012]. Icarus 221, 735–743), separated them into two spectrally distinct groups, one concentrated on the leading hemisphere of Iapetus, and the other group on the trailing. This distribution is broadly consistent with that found from Cassini ISS data analyzed by Denk et al. (Denk, T. et al. [2010]. Science 327, 435–439). We modeled the average spectra of the two geographic regions using the materials and techniques described by Clark et al. (Clark, R.N., Cruikshank, D.P., Jaumann, R., Brown, R.H., Stephan, K., Dalle Ore, C.M., Livio, K.E., Pearson, N., Curchin, J.M., Hoefen, T.M., Buratti, B.J., Filacchione, G., Baines, K.H., Nicholson, P.D. [2012]. Icarus 218, 831–860), and after dividing the Iapetus spectrum by the model for each case, we extracted the resulting spectra in the interval 2.7–4.0μm for analysis of the organic molecular bands. The spectra reveal the CH stretching modes of aromatic hydrocarbons at ∼3.28μm (∼3050cm−1), plus four blended bands of aliphatic CH2 and CH3 in the range ∼3.36–3.52μm (∼2980–2840cm−1). In these data, the aromatic band, probably indicating the presence of polycyclic aromatic hydrocarbons (PAH), is unusually strong in comparison to the aliphatic bands, as was found for Hyperion (Dalton, J.B., Cruikshank, D.P., Clark, R.N. [2012]. Icarus 220, 752–776; Dalle Ore, C.M., Cruikshank, D.P., Clark, R.N. [2012], op. cit.) and Phoebe (Dalle Ore, C.M., Cruikshank, D.P., Clark, R.N. [2012], op. cit.). Our Gaussian decomposition of the organic band region suggests the presence of molecular bands in addition to those noted above, specifically bands attributable to cycloalkanes, olefinic compounds, CH3OH, and N-substituted PAHs, as well as possible Hn-PAHs (PAHs with excess peripheral H atoms). In a minimalist interpretation of the Gaussian band fitting, we find the ratio of aromatic CH to aliphatic CH2+CH3 functional groups for both the leading and trailing hemispheres of Iapetus is ∼10, with no clear difference between them. In the aliphatic component of the surface material, the ratio CH2/CH3 is 4.0 on the leading hemisphere and 3.0 on the trailing; both values are higher than those found in interstellar dust and other Solar System materials and the difference between the two hemispheres may be statistically significant. The superficial layer of low-albedo material on Iapetus originated in the interior of Phoebe and is being transported to and deposited on Iapetus (and Hyperion) in the current epoch via the Phoebe dust ring (Tosi, F., Turrini, D., Coradini, A., Filacchione, G., and the VIMS Team [2010]. Mon. Not. R. Astron. Soc. 403, 1113–1130; Tamayo, D., Burns, J.A., Hamilton, D.P., Hedman, M.M. [2011]. Icarus 215, 260–278). The PAHs on Iapetus exist in a H2O-rich environment, and consequently are subject to UV destruction by hydrogenation on short time-scales. The occurrence of this material is therefore consistent with the assertion that the deposition of the PAH-bearing dust is occurring at the present time. If the organic inventory we observe represents the interior composition of Phoebe, we may be sampling the original material from a region of the solar nebula beyond Neptune where Phoebe formed prior to its capture by Saturn (Johnson, T.V., Lunine, J.I. [2005]. Nature 435, 69–71).

Overlapping spectral features and new assignment of 2‐propanol in the C–H stretching region

The vibrational spectra of gaseous and liquid 2‐propanol in the C–H stretching region of 2800 ~ 3100 cm−1 were investigated by polarized photoacoustic Raman spectroscopy and conventional Raman spectroscopy, respectively. Using two deuterated samples, that is, CH3CDOHCH3 and CD3CHOHCD3, the overlapping spectral features between the CH and CH3 groups were identified. With the aid of depolarization ratio measurements and density functional theory calculations, a new spectral assignment was presented. In the gas phase, the band at 2884 cm−1 was assigned to the overlapping of one CH3 Fermi resonance mode and a CH stretching of gauche conformer. The bands at 2917 and 2933 cm−1 were assigned to another two CH3 Fermi resonance modes, but the latter includes weak contribution from CH stretching of trans conformer. The bands at 2950 and 2983 cm−1 were assigned to CH3 symmetric and antisymmetric stretching, respectively. The spectral features of liquid 2‐propanol are similar to those in the gas phase except for the blue shift of CH and the red shift of CH3 band positions, which can be attributed to the intermolecular interaction in the liquid state. The new assignments not only clarify the confusions in previous studies from different spectral methods but also provide the reliable groundwork on spectral application of 2‐propanol in the futures. Copyright © 2014 John Wiley & Sons, Ltd.

CHF3 as a probe for surface basicity

FTIR spectra of adsorbed fluoroform as a test for surface basicity have been studied on a number of oxides and zeolites. CHF3 does not dissociate even on strongest basic sites, and forms H-bond with considerable stretching CH frequency lowering. With weaker basic oxygen atoms it demonstrates the blue-shifting H-bond accompanied by CH band intensity decrease and a high frequency shift of bending vibrations. Dependence of the frequency and integrated absorption coefficient of CH stretching vibration on the strength of H-bond is discussed. The problem of basicity testing can be solved by using two different probe molecules for sites of various strength. While fluoroform is good for stronger sites, weak sites can be tested by pyrrole, acetylene or its derivatives that are more sensitive, but dissociate on the most basic oxygen centers.

CO2-broadening coefficients in the ν4 fundamental band of methane at room temperature and application to CO2-rich planetary atmospheres

Using a tunable diode-laser spectrometer, we have measured the CO2-broadening coefficients of 28 absorption lines in the ν4 band of CH4. Each line was recorded at room temperature (296K) and at 4 different pressures, ranging from 8 to 50mbar. The experimental determination of the CO2-broadening coefficients was performed by fitting a theoretical profile to the experimental profile of each line recorded at each pressure. Voigt, Rautian–Sobel’man and Galatry models were therefore used. The impact of these determinations on atmospheric investigations on CO2-rich planetary atmospheres are addressed.

Técnicas FT-IR (PAS, UATR e Objetiva ATR) Aplicadas à Caracterização de EPDM Modificada com Plasma

Tecnicas FT-IR (UATR, PAS e MIC, com objetiva ATR) foram escolhidas para a caracterizacao da superficie da borracha de EPDM vulcanizada, apos tratamento em plasma de Ar/O2 e N2/H2/Ar gerado em micro-ondas. Apos tratamento, grupos oxigenados foram detectados por UATR e MIC/FT-IR, com objetiva ATR para as duas misturas gasosas, e possiveis grupos nitrogenados foram inseridos na superficie das amostras tratadas com plasma de N2/H2/Ar. A analise MIC/FT-IR sugeriu a formacao de grupos em uma camada mais externa, para as amostras tratadas com plasma de N2/H2/Ar, sendo possivel observar a reducao na intensidade das bandas da absorcao do CH2 e CH3, o que pode estar relacionado ao fato de o nitrogenio ser um gas menos permeavel que o oxigenio. Diferentes velocidades, 0,05 cm.s-1 e 0,2 cm.s-1, foram utilizadas na analise PAS para avaliar a superficie apos tratamento, e apenas para a velocidade 0,05 cm.s-1 com plasma de Ar/O2 alteracoes espectroscopicas foram detectadas. A reducao na medida de ângulo de contato e o aumento na resistencia ao descascamento da colagem indicaram melhoras nas propriedades adesivas da superficie. Falhas de adesao foram observadas entre a interface do filme de adesivo de PU e da borracha de EPDM, e confirmados por UATR/FT-IR.

Non-Destructive Determination of Ethylene Vinyl Acetate Cross-Linking in Photovoltaic (PV) Modules by Raman Spectroscopy

Vibrational spectroscopy was found to be a suitable method for the determination of the degree of cross-linking of ethylene vinyl acetate (EVA) polymers. Spectral changes in the Raman spectra of EVA with increasing lamination time (which equals increasing degree of cross-linking) were mainly detected in the CH vibrational regions, namely, in the relative intensities of the characteristic CH3 and CH2 bands. These spectral regions were chosen for a chemometric evaluation where a calibration was performed with the Raman spectra of reference EVA samples and the results obtained from corresponding thermal analysis (differential scanning calorimetry) and Soxhlet extraction data. These datasets were subsequently used to non-destructively determine the progress of cross-linking in EVA foils, embedded in various mini-modules by Raman microscopy. Thus, we could show that Raman spectroscopy is a highly interesting method for quality control in the production of photovoltaic (PV) modules. However, this approach is valid only for a given grade of EVA, meaning a demand for a new calibration when changing the supplier or the type of EVA used. In addition, the applicability of infrared spectroscopy for the determination of the degree of cross-linking was tested. A good correlation of the decrease in intensity of the characteristic cross-linker infrared bands with increasing progress of the cross-linking was found, as determined by reference methods. However, this analytical method requires taking samples of the EVA foils and is, thus, unsuitable for the non-destructive determination of the degree of cross-linking of the EVA encapsulated within a PV module.

Temperature-Dependent, Nitrogen-Perturbed Line Shape Measurements in the ν1 + ν3 Band of Acetylene Using a Diode Laser Referenced to a Frequency Comb

The P(11) line of the ν1 + ν3 combination band of C2H2 was studied using an extended cavity diode laser locked to a frequency comb. Line shapes were measured for acetylene and nitrogen gas mixtures at a series of temperatures between 125 and 296 K and total pressures up to 1 atm. The data were fit to two speed-dependent line shape models and the results were compared. Line shape parameters were determined by simultaneously fitting data for all temperatures and pressures in a single multispectrum analysis. Earlier pure acetylene measurements [Cich et al. Appl. Phys. B 2012, 109, 373-38] were incorporated to account for self-perturbation. The resulting parameters reproduce the observed line shapes for the acetylene-nitrogen system over the range of temperatures and pressures studied with average root-mean-square observed-calculated errors of individual line measurement fits of approximately 0.01% of maximum transmission, close to the experimental signal-to-noise ratios. Errors in the pressure measurements constitute the major systematic errors in these measurements, and a statistical method is developed to quantify their effects on the line shape parameters for the present system.

Low-dimensional compounds containing bioactive ligands. V: Synthesis and characterization of novel anticancer Pd(II) ionic compounds with quinolin-8-ol halogen derivatives

Three novel palladium(II) complexes, NH2(CH3)2[PdCl2(CQ)] (1) (CQ=5-chloro-7-iodo-quinolin-8-ol), NH2(CH3)2[PdCl2(dClQ)] (2) (dClQ=5,7-dichloro-quinolin-8-ol) and NH2(CH3)2[PdCl2(dBrQ)] (3) (dBrQ=5,7-dibromo-quinolin-8-ol) have been prepared and characterized. Their structures contain square-planar [PdCl2(XQ)]− complex anions in which deprotonated XQ ligands are coordinated to the Pd atoms via the pyridine nitrogen and the phenolato oxygen atoms, other two cis-positions are occupied by two chlorido ligands. Negative charges of these anions are balanced by uncoordinated dimethylammonium cations. Coordination of the XQ ligands to Pd(II) atom was confirmed by the differences in the stretching ν(OH) and ν(CN) vibrations in the IR spectra of ligands and prepared complexes while bands of aliphatic CH and NH stretching vibrations observed in the spectra of 1–3 confirm the presence of dimethylammonium cations in the complexes. The binding of complexes 1–3 to calf thymus DNA was investigated using UV–visible and fluorescence emission spectrophotometry. The fluorescence spectral results indicate that the complexes can bind to DNA through an intercalative mode. The Stern–Volmer quenching constants obtained from the linear quenching plot are in the 1.04×104 to 4.35×104M−1 range. The complexes exhibit significant anticancer activity tested on A2780 cells and cisplatin resistant cell line A2780/CP.

Mechanistic investigation and reversible effect of 2-isopropyl-5-methylcyclohexyl heptanoate on the in vitro percutaneous absorption of indomethacin

In the present study, the enhancing effect of 2-isopropyl-5-methylcyclohexyl heptanoate (M-HEP) on the percutaneous absorption of indomethacin (IM) was evaluated by the in vitro penetration experiments using the rat abdominal skin as a barrier. Partition experiment, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectrum and transepidermal water loss (TEWL), was employed to investigate the possible mechanisms of the action of M-HEP. Furthermore, the reversible effect of M-HEP on excised rat skin was also evaluated through in vitro permeation as a preliminary indicator of safety. The result of in vitro permeation experiment indicated that, 10% (w/w) M-HEP in combination with isopropyl palmitate (IPP) significantly increased (p < 0.05), the cumulative amount of IM in comparison with the control group (IPP only). The partition coefficient of IM between the stratum corneum (SC) and enhancer solution was also greater than that between the SC and IPP. A blue shift in the ATR-FTIR spectra of SC after treatment with M-HEP solution was observed at the CH2 band, which indicating that M-HEP disrupted the intercellular lipid structure of the SC. In addition, both M-HEP/IPP and L-menthol (MT)/IPP improved the TEWL value of rat abdominal skin. After removal of M-HEP, the skin barrier function would be restored in 8 h. In conclusion, M-HEP could reversibly enhance the percutaneous absorption of IM by increasing the partitioning of IM into the SC from enhancer solution and disturbing the organized structure of SC lipids and the reversibility of M-HEP was better than MT.