Feng H. Tay

High-pressure carbon dioxide uptake for porous organic cages: comparison of spectroscopic and manometric measurement techniques

A chemoselective spectroscopic method for measuring CO2 sorption isotherms at pressures up to 14 MPa (140 bar) is validated against manometric measurements and molecular simulations, giving insights into the preferred sorption sites in various crystalline porous organic cages.

Effect of dense gas CO2 on the coacervation of elastin.

In this study for the first time the effect of high-pressure CO2 on the coacervation of alpha-elastin was investigated using analytical techniques including light spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging and circular dichroism (CD) spectroscopy. The coacervation behavior of alpha-elastin, a protein biopolymer, was determined at temperatures below 40 degrees C and pressures lower than 180 bar. At these conditions elevated pressures did not disrupt the ability of alpha-elastin to coacervate. It was feasible to monitor the presence of amide I, II, and III bands for alpha-elastin at high-pressure CO2 using ATR-FTIR imaging. At a constant temperature the peak absorption was substantially enhanced by increasing the pressure of the system. CD analysis demonstrated the preservation of secondary structure attributes of alpha-elastin exposed to dense gas CO2 at the pressure range investigated in this study. The lower critical solution temperature of alpha-elastin was dramatically decreased from 37 to 16 degrees C when the CO2 pressure increased from 1 to 50 bar, without a significant change after that. Carbon dioxide at high pressures also impeded the reversible coacervation of alpha-elastin solution. These effects were predominantly associated with the lowered pH of the aqueous solution and maybe the interaction between CO2 and hydrophobic domains of alpha-elastin.

Chemical Imaging with Variable Angles of Incidence Using a Diamond Attenuated Total Reflection Accessory

A new development in Fourier transform infrared (FT-IR) imaging using a diamond attenuated total reflection (ATR) imaging accessory in a novel manner that allows the angle of incidence to be varied in order to obtain images from subsurface layers of different thickness is introduced. Chemical images of samples from the same area but with different depths of penetration are obtained by changing the angle of incidence as well as using different spectral bands at different wavenumbers. Changes in the angle of incidence with this accessory were made possible by taking advantage of the relatively large numerical aperture employed by the original imaging optics. This arrangement allowed us to introduce an additional movable aperture in the optical design to restrict the angle of incidence to certain values. Two samples have been studied, one for the calibration of the angle of incidence while the other demonstrates the capability of obtaining three-dimensional (3D) information using this approach. Advantages of this new approach include the relatively high spatial resolution (it can spatially resolve features as small as 12 μm without a microscope) and no change in the imaging area and sampling area during manipulation of the angle of incidence.

Application of attenuated total reflection Fourier transform infrared imaging and tape-stripping to investigate the three-dimensional distribution of exogenous chemicals and the molecular organization in Stratum corneum

Attenuated total reflection Fourier transform infrared spectroscopic imaging combined with tape-stripping is an advantageous approach to map the depth penetration and lateral distribution of topically applied chemicals in Stratum corneum (SC) and the conformational order of SC lipids. Tape-stripping progressively removes layers of SC, and chemical imaging provides spatially resolved information on the chemical composition of both the newly exposed SC surface and of the tapes used for stripping. The procedure is rapid, minimally invasive, and does not necessitate cross-sectioning of the skin. This approach offers a simple and direct way to determine the distribution of exogenous volatile and non-volatile chemicals in SC as a function of the chemical composition of the formulation and time, and the conformational order of SC lipids in native and topically treated skin. The procedure described here is well suited to address questions of relevance for the areas of drug delivery, dermatology, and skin care.

A novel approach for study of in situ diffusion in human hair using Fourier transform infrared spectroscopic imaging.

Diffusion of chemicals into human hair fibers has been of interest to the cosmetic industry due to the process of various hair treatments and hair damage assessments, which often involve the diffusion of active compounds into the hair fibers. Various approaches have been applied to study the diffusion of substances into the hair fibers, such as electron microscopy and fluorescence microscopy. Complementary to these approaches is vibrational spectroscopy, which provides chemical information about the sample based on its molecular vibrations. Photoacoustic and confocal Raman has been applied to obtain the depth profile of hair and has been used to study the diffusion of chemicals into hair fibers. The advantage of this method is that depth profiles can be readily obtained without any physical damage (cross-sectioning) to the hair fiber. However, the color of the hair fiber that can be studied is limited to very pale colored or white due to fluorescence of the pigment of colored hair. Despite little differences between the physical properties of gray and black hair, previous studies have shown that the color of hair fibers could be an important factor in studying of the sorption of explosives and incorporation of some drugs into hair. Furthermore, depth profile spectra are measured non-simultaneously in these types of measurements, requiring a relatively long time to collect (up to one hour per depth profile). This limits study to essentially static systems. Infrared spectroscopic imaging using a focal plane array (FPA) detector, on the other hand, provides a means by which to measure all spectra simultaneously in less than one minute (depending on the size of the array detector and the number of scans used), permitting the study of dynamic systems in situ. Fourier transform infrared (FT-IR) imaging has been applied to study the diffusion of solvents in polymer films. Previous studies have shown that FT-IR imaging measurement can be applied both in the micro-attenuated total reflection (ATR) and transmission modes to study hair samples. Despite the necessity of cross-sectioning the samples, the advantages of having in situ measurements with FT-IR imaging could outweigh this disadvantage. This work demonstrates the opportunity to measure the diffusion of different chemicals in cross-sections of hair fibers using FT-IR imaging. The diffusion of four substances, acetonitrile, 4cyanobenzoic acid, 4-cyanophenol, and 1-pentanenitrile, into the cross-sectioned hair fiber were imaged as a function of time. The study of these chemical compounds allows the comparison of the diffusion phenomenon in human hair with molecules of different sizes and functional groups.

Deposit Characterization and Measurements

Abstract The analysis of the structure and chemistry of deposits formed by the crude oil fouling process is paramount in gaining an understanding of the underlying causes and mechanisms. Chapter 4 begins with a review of industrial practice and findings in this context and suggests recommended practice for the collection, preparation, and analysis of refinery samples. The second part of this chapter discusses more advanced techniques for the determination of the chemical structure and molecular weight of deposits and the third part of Chapter 4 introduces a novel technique (chemical imaging) by which the location of various chemical species in a surface layer can be established. The final part of Chapter 4 gives a description of a fluid dynamic gauging technique developed for measuring the thickness and strength of deposits in situ, in real time, and in a liquid environment.