Evaluation of Structural and Compositional Changes of a Model Monoaromatic Hydrocarbon in a Benchtop Hydrocracker Using GC, FTIR, and NMR Spectroscopy.

Hydrogenation is a catalytic process that has the potential to facilitate sustainable chemical production. In this work, a model monoaromatic hydrocarbon, phenyldodecane (PDD), comprising an aromatic ring with a long aliphatic side chain has been chosen as representative of a typical species involved in hydrogenation and hydrocracked at a high pressure and temperature over a platinum catalyst in a bespoke benchtop mini-reactor. Gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy were employed to analyze the changes that took place after hydrocracking for different time periods.

Investigating Bénard-Marangoni migration at the air-water interface in the time domain using sum frequency generation (SFG) spectroscopy of palmitic acid monolayers.

Sum-frequency generation (SFG) spectroscopy is frequently used to investigate the structure of monolayer films of long-chain fatty acids at the air-water interface. Although labeled a non-invasive technique, introducing intense SFG lasers onto liquid interfaces has the potential to perturb them. In the present work, narrowband picosecond SFG is used to study the structural changes that occur in palmitic acid and per-deuterated palmitic acid monolayers at the air-water interface in response to the high field strengths inherent to SFG spectroscopy.

Probing the Nanoscale Heterogeneous Mixing in a High-Performance Polymer Blend.

The blend of polyetheretherketone (PEEK) and polybenzimidazole (PBI) produces a high-performance blend (PPB) that is a potential replacement material in several industries due to its high temperature stability and desirable tribological properties. Understanding the nanoscale structure and interface of the two domains of the blend is critical for elucidating the origin of these desirable properties. Whilst achieving the physical characterisation of the domain structures is relatively uncomplicated, the elucidation of structures at the interface presents a significant experimental challenge.

Chemically characterizing the cortical cell nano-structure of human hair using atomic force microscopy integrated with infrared spectroscopy (AFM-IR).

Objective: The use of conventional microscopy and vibrational spectroscopy in the optical region to investigate the chemical nature of hair fibres on a nanometre scale is frustrated by the diffraction limit of light, prohibiting the spectral elucidation of nanoscale sub-structures that contribute to the bulk properties of hair. The aim of this work was to overcome this limitation and gain unprecedented chemical resolution of cortical cell nano-structure of hair.

Methods: The hybrid technique of AFM-IR, combining atomic force microscopy with an IR laser, circumvents the diffraction limit of light and achieves nanoscale chemical resolution down to the AFM tip radius.

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.

Nanoscale adhesion profiling and membrane characterisation in sickle cell disease using hybrid atomic force microscopy-IR spectroscopy.

Sickle cell disease (SCD) presents a significant global health problem. At present there is no effective treatment, with most being supportive for its associated complications such as the vaso-occlusive crises that result from increased cell adhesion. Hypoxic sickle cells have previously shown greater phosphatidylserine (PS) exposure and oxidative damage, as well as being notably "stickier" suggesting that increased cell cohesion and adhesion to the blood vessel endothelium is a possible mechanism for vaso-occlusion.

Infrared Nanospectroscopy of Air-Sensitive Biological Substrates Protected by Thin Hydrogel Films.

The air sensitivity of many substrates, and specifically biosurfaces, presents an experimental challenge for their analysis by vibrational spectroscopy and, in particular, infrared microscopy on a nanometer scale. The recent development of atomic-force-microscopy-based infrared spectroscopy (AFM-IR), which circumvents the Abbe diffraction limit, allows nanoscale chemical characterization of surfaces. Additionally, this technique has been shown to work for thin films under aqueous environments but is limited to substrates up to 10 nm thick, thus ruling out application to many biological surfaces.

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.

Spectral Analysis and Deconvolution of the Amide I Band of Proteins Presenting with High-Frequency Noise and Baseline Shifts.

The challenge of deriving quantitative information from the infrared spectra of proteins arises from the large number of secondary structures and amino acid side-chain functional groups that all contribute to the spectral intensity, such as within the amide I band (1600-1700 cm). The band is invariably heavily convoluted from overlapping spectral features, thereby making interpretation difficult such that deconvolution is usually required. This work critically examines the methods available to deconvolute the spectra and assesses the commonly used methods and algorithms applied to vibrational spectra for smoothing and peak identification.

Determining a Line Strength in the ν Band of the Silyl Radical Using Quantum Cascade Laser Absorption Spectroscopy.

Silane (SiH) plasmas are widely used for the deposition of hydrogenated amorphous silicon (a-Si:H) films. Nevertheless, the chemical processes governing film deposition are still incompletely understood. Moreover, there is still no general method available to determine the absolute concentration of the silyl radical (SiH), which is the accepted chemical precursor of a-Si:H films.

A time domain study of surfactin penetrating a phospholipid monolayer at the air-water interface investigated using sum frequency generation spectroscopy, infrared reflection absorption spectroscopy, and AFM-nano infrared microscopy.

We have investigated the interaction of surfactin with a monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at the air-water interface as a function of time, following its injection into the sub-phase, using non-linear Sum Frequency Generation (SFG) vibrational spectroscopy and Infrared Reflection Absorption Spectroscopy (IRRAS). SFG resonances from the phospholipid and from the surfactin were distinguished from each other by using selective deuteration. The surface pressure at the interface was measured concurrently for up to 8 h.

Structure of the Fundamental Lipopeptide Surfactin at the Air/Water Interface Investigated by Sum Frequency Generation Spectroscopy.

The lipopeptide surfactin produced by certain strains of Bacillus subtilis is a powerful biosurfactant possessing potentially useful antimicrobial properties. In order to better understand its surface behavior, we have used surface sensitive sum frequency generation (SFG) vibrational spectroscopy in the C-H and C═O stretching regions to determine its structure at the air/water interface. Using surfactin with the leucine groups of the peptide ring perdeuterated, we have shown that a majority of the SFG signals arise from the 4 leucine residues.

A structural and temporal study of the surfactants behenyltrimethylammonium methosulfate and behenyltrimethylammonium chloride adsorbed at air/water and air/glass interfaces using sum frequency generation spectroscopy.

Molecular scale information about the structure of surfactants at interfaces underlies their application in consumer products. In this study the non-linear optical technique of Sum Frequency Generation (SFG) vibrational spectroscopy has been used to investigate the structure and temporal behaviour of two cationic surfactants used frequently in hair conditioners. SFG spectra of films of behenyltrimethylammonium methosulfate (BTMS) and behenyltrimethylammonium chloride (BTAC) were recorded at the air/water interface and on glass slides following Langmuir Blodgett (LB) deposition.

Interfacial structure of soft matter probed by SFG spectroscopy.

Sum frequency generation (SFG) vibrational spectroscopy, an interface-specific technique in contrast to, for example, attenuated total reflectance spectroscopy, which is only interface sensitive, has been employed to investigate the surface and interface structure of soft matter on a molecular scale. The experimental arrangement required to carry out SFG spectroscopy, with particular reference to soft matter, and the analytical methods developed to interpret the spectra are described. The elucidation of the interfacial structure of soft matter systems is an essential prerequisite in order to understand and eventually control the surface properties of these important functional materials.

The structure of lipid bilayers adsorbed on activated carboxy-terminated monolayers investigated by sum frequency generation spectroscopy.

The formation and structure of isotopically asymmetric supported bilayer membranes (SBMs) has been investigated using sum frequency generation (SFG) vibrational spectroscopy supplemented by reflection absorption infrared spectroscopy (RAIRS). The bilayers were composed of a proximal and distal leaflet of the phospholipid dipalmitoyl phosphatidylethanolamine (DPPE) supported on a gold surface. The proximal leaflet was chemically tethered to the gold via an 11-mercapto-undecanoic acid (MUA) self-assembled monolayer (SAM) that had been chemically modified to produce an activated succinimidyl ester headgroup using N-hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC).

Orientation of cholesterol in hybrid bilayer membranes calculated from the phases of methyl resonances in sum frequency generation spectra.

The phases of Sum Frequency Generation (SFG) vibrational resonances recorded from thin films on metal surfaces provide information on the orientation and tilt angles of the functional groups of molecules in the film. SFG spectra have been simulated for monolayer films in which the adsorbed molecule has an unequal number of methyl groups oriented in two different directions. The phases, on resonance, of the methyl symmetric (r(+)) and asymmetric (r(-)) resonances are determined as a function of the two methyl group tilt angles and the fraction of groups pointing in that particular direction.

Sum frequency generation vibrational spectroscopy of cholesterol in hybrid bilayer membranes.

The assignment of the vibrational spectrum of cholesterol is surprisingly incomplete for such a fundamental molecule. To improve our understanding, a new investigation of the spectra of cholesterol in the C-H stretching region has been undertaken using the surface specific technique of Sum Frequency Generation (SFG) vibrational spectroscopy and the complementary technique of Reflection Absorption Infrared Spectroscopy (RAIRS). They were used to record the spectra of monolayers of cholesterol in hybrid bilayer membranes (HBMs).

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.

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.

Structure of mixed phosphatidylethanolamine and cholesterol monolayers in a supported hybrid bilayer membrane studied by sum frequency generation vibrational spectroscopy.

The structure of hybrid bilayer membranes (HBMs) containing either a pure cholesterol or mixed cholesterol/dipalmitoylphosphatidylethanolamine (DPPE) proximal layer adsorbed onto an octadecanethiol (ODT) self-assembled monolayer (SAM) on a gold substrate have been investigated by sum frequency generation (SFG) spectroscopy. The HBMs were formed by the adsorption of either a pure cholesterol or mixed DPPE/cholesterol monolayer from the air/water interface of a Langmuir-Blodgett trough at surface pressures of 1, 20, or 40 mN·m(-1). SFG spectra were also recorded of HBMs where cholesterol was replaced by cholesterol-d(7), in which the terminal isopropyl group of the alkyl chain of cholesterol was isotopically labeled.

Interference effects in the sum frequency generation spectra of thin organic films. II: Applications to different thin-film systems.

In this paper, the results of the modeling calculations carried out for predicting the interference effects expected in the sum frequency generation (SFG) spectra of a specific thin-layer system, described in the accompanying paper, are tested by comparing them with the experimental spectra obtained for a real thin-layer film comprising an organic monolayer/variable thickness dielectric layer/gold substrate. In this system, two contributions to the SFG spectra arise, a resonant contribution from the organic film and a nonresonant contribution from the gold substrate. The modeling calculations are in excellent agreement with the experimental spectra over a wide range of thicknesses and for different polarization combinations.

Interference effects in the sum frequency generation spectra of thin organic films. I. Theoretical modeling and simulation.

A general theoretical calculation is described for predicting the interference effect in the sum frequency generation (SFG) spectra from a model thin-film system as a function of film thickness. The calculations were carried out for a three-layer thin film consisting of an organic monolayer, a dielectric thin film of variable thickness, and a gold substrate. This system comprises two sources of SFG, namely, a resonant contribution from the monolayer/dielectric film interface and a nonresonant contribution from the dielectric film/gold interface.

Sum frequency generation (SFG) vibrational spectroscopy of planar phosphatidylethanolamine hybrid bilayer membranes under water.

Sum frequency generation (SFG) spectroscopy has been used to study the structure of phosphatidylethanolamine hybrid bilayer membranes (HBMs) under water at ambient temperatures. The HBMs were formed using a modified Langmuir-Schaefer technique and consisted of a layer of dipalmitoyl phosphatidylethanolamine (DPPE) physisorbed onto an octadecanethiol (ODT) self-assembled monolayer (SAM) at a series of surface pressures from 1 to 40 mN m(-1). The DPPE and ODT were selectively deuterated so that the contributions to the SFG spectra from the two layers could be determined separately.

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.

Quantum cascade laser absorption spectroscopy as a plasma diagnostic tool: an overview.

The recent availability of thermoelectrically cooled pulsed and continuous wave quantum and inter-band cascade lasers in the mid-infrared spectral region has led to significant improvements and new developments in chemical sensing techniques using in-situ laser absorption spectroscopy for plasma diagnostic purposes. The aim of this article is therefore two-fold: (i) to summarize the challenges which arise in the application of quantum cascade lasers in such environments, and, (ii) to provide an overview of recent spectroscopic results (encompassing cavity enhanced methods) obtained in different kinds of plasma used in both research and industry.