Using hybrid atomic force microscopy and infrared spectroscopy (AFM-IR) to identify chemical components of the hair medulla on the nanoscale.

Atomic force microscopy integrated with infrared spectroscopy (AFM-IR) has been used to topographically and chemically examine the medulla of human hair fibres with nanometre scale lateral resolution. The mapping of cross-sections of the medulla showed two distinct structural components which were subsequently characterised spectroscopically. One of these components was shown to be closely similar to cortical cell species, consistent with the fibrillar structures found in previous electron microscope (EM) investigations. The other component showed large chemical differences from cortical cells and was assigned to globular vacuole species, also confirming EM observations. Further characterisation of the two components was achieved through spectral deconvolution of the protein Amide-I and -II bands. This showed that the vacuoles have a greater proportion of the most thermodynamically stable conformation, namely the antiparallel ß-sheet structures. This chimes with the observed lower cysteine concentration, indicating a lower proportion of restrictive disulphide cross-link bonding. Furthermore, the large α-helix presence within the vacuoles points to a loss of matrix-like material as well as significant intermolecular stabilisation of the protein structures. By analysing the carbonyl stretching region, it was established that the fibrillar, cortical cell-like components showed considerable stabilisation from H-bonding interactions, similar to the cortex, involving amino acid side chains whereas, in contrast, the vacuoles were found to only be stabilised significantly by structural lipids.

Nanoscale Molecular Characterization of Hair Cuticle Cells Using Integrated Atomic Force Microscopy-Infrared Laser Spectroscopy.

The hair cuticle provides significant protection from external sources, as well as giving rise to many of its bulk properties, e.g., friction, shine, etc. that are important in many industries. In this work, atomic force microscopy-infrared spectroscopy (AFM-IR) has been used to investigate the nanometer-scale topography and chemical structure of human hair cuticles in two spectral regions. AFM-IR combines atomic force microscopy with a tunable infrared laser and circumvents the diffraction limit that has impaired traditional infrared spectroscopy, facilitating surface-selective spectroscopy at ultra-spatial resolution. This high resolution was exploited to probe the protein secondary structures and lipid content, as well as specific amino acid residues, e.g., cystine, within individual cuticle cells. Characterization across the top of individual cells showed large inhomogeneity in protein and lipid contributions that suggested significant changes to physical properties on approaching the hair edge. Additionally, the exposed layered sub-structure of individual cuticle cells allowed their chemical compositions to be assessed. The variation of protein, lipid, and cystine composition in the observed layers, as well as the measured dimensions of each, correspond closely to that of the epicuticle, A-layer, exocuticle, and endocuticle layers of the cuticle cell sub-structure, confirming previous findings, and demonstrate the potential of AFM-IR for nanoscale chemical characterization within biological substrates.

Adsorption of 1- and 2-butylimidazoles at the copper/air and steel/air interfaces studied by sum frequency generation vibrational spectroscopy.

The structure of thin films of 1- and 2-butylimidazoles adsorbed on copper and steel surfaces under air was examined using sum frequency generation (SFG) vibrational spectroscopy in the ppp and ssp polarizations. Additionally, the SFG spectra of both isomers were recorded at 55 °C at the liquid imidazole/air interface for reference. Complementary bulk infrared, reflection-absorption infrared spectroscopy (RAIRS), and Raman spectra of both imidazoles were recorded for assignment purposes. The SFG spectra in the C-H stretching region at the liquid/air interface are dominated by resonances from the methyl end group of the butyl side chain of the imidazoles, indicating that they are aligned parallel or closely parallel to the surface normal. These are also the most prominent features in the SFG spectra on copper and steel. In addition, both the ppp and ssp spectra on copper show resonances from the C-H stretching modes of the imidazole ring for both isomers. The ring C-H resonances are completely absent from the spectra on steel and at the liquid/air interface. The relative intensities of the SFG spectra can be interpreted as showing that, on copper, under air, both butylimidazoles are adsorbed with their butyl side chains perpendicular to the interface and with the ring significantly inclined away from the surface plane and toward the surface normal. The SFG spectra of both imidazoles on steel indicate an orientation where the imidazole rings are parallel or nearly parallel to the surface. The weak C-H resonances from the ring at the liquid/air interface suggest that the tilt angle of the ring from the surface normal at this interface is significantly greater than it is on copper.

Using density functional theory to interpret the infrared spectra of flexible cyclic phosphazenes.

The cyclic phosphazene trimer P(3)N(3)(OCH(2)CF(3))(6)and the related cyclic tetramer P(4)N(4)(OCH(2)CF(3))(8) have been synthesized, isolated and their vapor-phase absorption spectra recorded at moderate resolution using an FTIR spectrometer. The interpretation of these spectra is achieved primarily by comparison with the results of high-precision density functional calculations, which enable the principal absorption features to be assigned and conclusions to be drawn regarding the geometries and conformations adopted by both molecules. These in turn allow interesting comparisons to be made with analogous cyclic halo-phosphazenes (such as P(3)N(3)Cl(6)) and other related ring compounds. The highly flexible nature of the two cyclic phosphazenes precludes a complete theoretical study of their potential energy hypersurfaces and a novel alternative approach involving the analysis of a carefully selected subset of the possible molecular conformations has been shown to produce satisfactory results. The two cyclic phosphazene oligomers have been proposed as the major low-to-medium temperature pyrolysis products of the parent polyphosphazene (PN(OCH(2)CF(3))(2))(n), and the identification of vibrational absorption features characteristic of each molecule will enable future studies to test the validity of this proposition.

The structure of oleamide films at the aluminum/oil interface and aluminum/air interface studied by Sum Frequency Generation (SFG) vibrational spectroscopy and Reflection Absorption Infrared Spectroscopy (RAIRS).

The structure of oleamide (cis-9-octadecenamide) films on aluminum has been investigated by sum frequency generation vibrational spectroscopy (SFG) and reflection absorption infrared spectroscopy (RAIRS). Three different film deposition strategies were investigated: (i) films formed by equilibrium adsorption from oleamide solutions in oil, (ii) Langmuir-Blodgett films cast at 1 and 25 mN m(-1), (iii) thick spin-cast films. Both L-B and spin-cast films were examined in air and under oil. The adsorbate formed in the 1 mN m(-1) film in air showed little orientational order. For this film, the spectroscopic results and the ellipsometric thickness point to a relatively conformationally disordered monolayer that is oriented principally in the plane of the interface. Direct adsorption to the metal interface from oil results in SFG spectra of oleamide that are comparable to those observed for the 1 mN m(-1) L-B film in air. In contrast, SFG and RAIRS results for the 25 mN m(-1) film in air and SFG spectra of the spin-cast film in air both show strong conformational ordering and orientational alignment normal to the interface. The 25 mN m(-1) film has an ellipsometric thickness almost twice that of the 1 mN m(-1) L-B film. Taken in combination with the spectroscopic results, this is indicative of a well packed monolayer in air in which the hydrocarbon chain is in an essentially defect-free extended conformation with the methyl terminus oriented away from the surface. A similar structure is also deduced for the surface of the spin-cast film in air. Upon immersion of the 25 mN m(-1) L-B film in oil the SFG spectra show that this film rapidly adopts a relatively disordered structure similar to that seen for the 1 mN m(-1) L-B film in air. Immersion of the spin-cast film in oil results in the gradual disordering of the amide film over a period of several days until the observed spectra become essentially identical to those observed for direct adsorption of oleamide from oil.

Adsorption of sodium dodecyl sulfate at the hydrophobic solid/aqueous solution interface in the presence of poly(ethylene glycol): dependence upon polymer molecular weight.

The polar orientation and degree of conformational order of sodium dodecyl sulfate (SDS) adsorbed at the hydrophobic octadecanethiol/aqueous solution interface in the presence of poly(ethylene glycol) (PEG) has been investigated as a function of the surfactant concentration and the molecular weight of the polymer. Sum frequency generation (SFG) vibrational spectroscopy was employed to obtain spectra of interfacial surfactant; weak SFG signals from interfacial polymer were also detected for polymer molecular weights of 900 and above. The phase of the SFG spectra indicated that both the surfactant and polymer had a net orientation of their CH2 and/or CH3 groups toward the hydrophobic surface. Spectra of SDS in the presence of mixed polymer/surfactant solutions showed increasing conformational order as the surfactant concentration was raised. At the lowest surfactant concentrations, the spectra of SDS were weaker in the presence of the polymer than in its absence. All PEG molecular weights investigated, with the exception of PEG 400, gave rise to significant inhibition of ordered surfactant adsorption below the critical micelle concentration. The greatest inhibitory effect was noted for PEG 900. Probing interfacial PEG specifically through the use of perdeuterated SDS revealed that the polymer spectral intensity decreased monotonically as the surfactant concentration was increased for all polymer molecular weights where a PEG spectrum was apparent. These findings are interpreted in terms of the displacement of preadsorbed polymer as the surfactant concentration increases. This result is compatible with observations of adsorption from SDS/PEG solutions at solid/solution and solution/air interfaces made using other techniques.