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X‐ray photoelectron spectroscopy (XPS) is a surface sensitive analytical technique that measures the binding energy of electrons in atoms and molecules on the surface of a material. XPS was used to determine the distribution of the oligosaccharide side chains in the glycoprotein, MUC1 mucin. Low‐resolution XPS spectra provided elemental composition of MUC1 mucin (fully glycosylated), mucin polypeptide (nonglycosylated), and carbohydrates found in mucin. The nitrogen content of MUC1 mucin was determined to be intermediate between the mucin polypeptide and the carbohydrates. Assuming a uniform distribution of carbohydrate on MUC1 mucin, the average thickness of the carbohydrate layer was calculated to be 4.9 nm using the low‐resolution N 1s signals. High‐resolution XPS spectra give detailed information about the chemical bonding of the surface molecules. Calculations based on the high‐resolution O 1s spectra showed a carbohydrate thickness of 6.6 nm. These experimentally determined values agree reasonably well with an estimated 5 nm of carbohydrate thickness from a simple model which assume that the core protein is a rodlike molecule approximately 5 nm in diameter. Although the carbohydrate coating on the MUC1 mucin appears to be thick enough to cover the core protein entirely, fully glycosylated breast milk MUC1 mucin is susceptible to proteolytic digestion without removal of any oligosaccharide side chain, suggesting areas of exposed core protein. A possible explanation is that the oligosaccharide side chains may form patches of carbohydrate along the core protein with regions of exposed core protein. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 257–266, 1998

The reaction of an isomeric mixture of the methyl perfluoroalkyl ether, C 4 F 9 OCH 3 (Novec-7100), in the presence of isopropyl alcohol (IPA) and/or water has been studied by measuring the rate of product formation using an ion-selective electrode (ISE) for fluoride ion, Karl Fisher coulometric titrations for water, and 1 H and 19 F NMR spectroscopy for product identification and rate studies. The results showed the methyl perfluoroalkyl ether to be very stable with products forming at the rate of ∼1 ppm per year at a laboratory temperature of 20 °C. Measurements over the temperature range of 6°to 100 °C were made on samples aged for periods up to 1.8 years. Density functional theory calculations (DFT, B3LYP/6-31+G(d)) were employed to investigate different reaction pathways and formulate the probable reaction mechanism. The experimental enthalpy (ΔH ⧧ ) and entropy (ΔS ⧧ ) of activation were determined based on several different kinetic measurements. The ΔH ⧧ values are in the range of 20−25 kcal/mol and the corresponding ΔS ⧧ values range from −32 to −15 cal/(mol K). These are in good agreement with the theoretical values. While the range of ΔH ⧧ values does not change appreciatively, the ΔS ⧧ values are dependent on the proportion of vapor to liquid involved in the reaction of C 4 F 9 OCH 3 with IPA so that the more vapor the more negative the ΔS ⧧ value.

The 3M Company product Novec™ 71IPA DL, a mixture of methoxyperfluorobutane, methoxyperfluoroisobutane and 4.5 wt.% isopropyl alcohol, has been found to be very stable at ambient temperature, producing fluoride at the rate of ~1 ppm/year. Our earlier kinetic and theoretical studies have identified the reaction mechanism. This paper identifies the (1)H and (19)F NMR chemical shifts, multiplicities, and coupling constants of reactants and the major products that result from aging the mixture in sealed Pyrex NMR tubes for periods up to 1.8 years at temperatures from 26 °C to 102 °C. Chemical shifts and coupling constants of fluorine and hydrogen atoms on the hydrofluoroethers and isopropyl alcohol are traced through the reactions to their values in the products--esters, isopropylmethyl ether, and HF. These spectral positions, multiplicities, and coupling constants are presented in table format and as figures to clarify the transformations observed as the samples age.

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