No abstract

Fourier transform IR spectroscopy has been used to investigate the interaction of carbon dioxide with polymers. IR transmission and attenuated total reflectance spectra were obtained for CO 2 impregnated into polymer films. It has been shown that the polymers possessing electron-donating functional groups (e.g., carbonyl groups) exhibit specific interactions with CO 2 , most probably of Lewis acid-base nature. An unusual aspect is the use of the bending mode (ν 2 ) of CO 2 to probe polymer-CO 2 interactions. The evidence of the interaction is the observation of the splitting of the band corresponding to the CO 2 ν 2 mode. This splitting indicates that the double degeneracy of the ν 2 mode is removed due to the interaction of electron lone pairs of the carbonyl oxygen with the carbon atom of the CO 2 molecule. This splitting has not been observed for polymers lacking electron-donating functional groups (e.g., poly(ethylene)). In contrast, the ν 3 mode shows little if any sensitivity to this interaction, which is in accordance with the interaction where CO 2 molecule acts as an electron acceptor. Finally, the chemical and engineering implications of this type of specific interaction of CO 2 with polymers are discussed; perhaps the changes in spectra

An in situ ATR (attenuated total reflectance)-IR study of CO 2 dissolved in two ionic liquids at high pressures has demonstrated the effects of the anionic species of the ionic liquids on the molecular state of the dissolved CO 2 .

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a highly versatile, label free and non-destructive chemical imaging method which can be applied to study a wide range of samples and systems. This review summarises some of the recent advances and applications of this imaging method in the area of biomedical studies, including examples of section of aorta, skin tissue and live cells. Two of the major advantages of measuring in ATR mode are the opportunity to measure samples that absorb strongly in the IR spectrum, such as aqueous systems, without significant sample preparation and the ability to increase the spatial resolution of the measured image. The implications of these advantages as well as some limitations of this imaging approach are discussed and a brief outlook at some of the possible future developments in this area is provided.

New opportunities exist to obtain chemical images using attenuated total reflection infrared (ATR-IR) spectroscopy. This paper shows the feasibility of obtaining FT-IR images with a spatial resolution of at least 3-4 microm using a Ge ATR objective coupled with an infrared microscope. The improved spatial resolution compared to FT-IR images obtained by the transmission method is due to the high refractive index of the ATR crystal, which gives a high numerical aperture and hence, a higher spatial resolution. FT-IR imaging with a conventional diamond ATR accessory has been investigated. This is the first time that FT-IR imaging is reported using such a versatile accessory based on a diamond ATR crystal. These results showed that a spatial resolution up to 13 microm can be achieved without the use of infrared microscope objectives. One advantage of the diamond element is that it allows pressure to be applied and hence, good contact to be obtained over the whole field of view.

Protein crystallization is of strategic and commercial relevance in the post-genomic era, due to its pivotal role in structural proteomics projects. Although protein structures are crucial for understanding the function of proteins and to the success of rational drug design and other biotechnology applications, obtaining high quality crystals is a major bottleneck to progress. The major means of obtaining crystals is by massive-scale screening of a target protein solution with numerous crystallizing agents. However when crystals appear in these screens, one cannot easily know if they are crystals of protein, salt or any other molecule that happens to be present in the trials. We present here a method based on ATR-FTIR imaging that reliably identifies protein crystals through a combination of chemical specificity and the visualising capability of this approach, thus solving a major hurdle in protein crystallization. ATR-FTIR imaging was successfully applied to study the crystallization of thaumatin and lysozyme in a high-throughput manner, simultaneously from six different solutions. This approach is fast as it studies protein crystallization in situ and provides an opportunity to examine many different samples under a range of conditions.

The measurement of key molecules in individual cells with minimal disruption to the biological milieu is the next frontier in single-cell analyses. Nanoscale devices are ideal analytical tools because of their small size and their potential for high spatial and temporal resolution recordings. Here, we report the fabrication of disk-shaped carbon nanoelectrodes whose radius can be precisely tuned within the range 5-200 nm. The functionalization of the nanoelectrode with platinum allowed the monitoring of oxygen consumption outside and inside a brain slice. Furthermore, we show that nanoelectrodes of this type can be used to impale individual cells to perform electrochemical measurements within the cell with minimal disruption to cell function. These nanoelectrodes can be fabricated combined with scanning ion conductance microcopy probes which should allow high resolution electrochemical mapping of species on or in living cells.

Equilibrium constants measured from the ν2 bending mode of CO2 by FTIR spectroscopy are reported for the electron donor−acceptor interactions of CO2 with three Lewis bases:  triethylamine (TEA), pyridine (PYR), and tributyl phosphate (TBP). The average K c values are 0.046 (CO2−TEA), 0.133 (CO2−PYR), and 1.29 (CO2−TBP) L/mol at 25 °C in the solvent pentane. For the CO2−TBP system, the average enthalpy of association, ΔH°, is −4.7 kcal/mol. Ab initio calculations indicate that steric repulsion of the ethyl groups in TEA cause the binding energy of the CO2−TEA complex to be weaker than that of the CO2−PYR complex by 1.34 kcal/mol, a trend that is in agreement with our spectroscopic data. The lattice fluid hydrogen bonding model was used in conjunction with the spectroscopically determined K c values to predict bubble points for the CO2−TEA and CO2−TBP systems and CO2 sorption in a hypothetical polymer. These calculations indicate that these relatively weak specific interactions have a measurable effect on phase behavior and can influence sorption of CO2 in polymers.