No abstract

Electrospinning has been used to successfully create polystyrene (PS) nanofibers containing either of three different types of cyclodextrin (CD); α-CD, β-CD, and γ-CD. These three CDs are chosen because they have different sized cavities that potentially allow for selective inclusion complex (IC) formation with molecules of different size or differences in affinity of IC formation with one type of molecule. The CD containing electrospun PS nanofibers (PS/CD) were initially characterized by scanning electron microscopy (SEM) to determine the uniformity of the fibers and their fiber diameter distributions. X-ray photoelectron spectroscopy (XPS) was used to quantitatively determine the concentration of each CD on the different fiber surfaces. Static time-of-flight secondary ion mass spectrometry (static-ToF-SIMS) showed the presence of each type of CD on the PS nanofibers by the detection of both the CD sodium adduct molecular ions (M + Na+) and lower molecular weight oxygen containing fragment ions. The comparative efficiency of the PS/CD nanofibers/nanoweb for removing phenolphthalein, a model organic compound, from solution was determined by UV-vis spectrometry, and the kinetics of phenolphthalein capture was shown to follow the trend PS/α-CD > PS/β-CD > PS/γ-CD. Direct pyrolysis mass spectrometry (DP-MS) was also performed to ascertain the relative binding strengths of the phenolphthalein for the CD cavities, and the results showed the trend in the interaction strength was β-CD > γ-CD > α-CD. Our results demonstrate that nanofibers produced by electrospinning that incorporate cyclodextrins with different sized cavities can indeed filter organic molecules and can potentially be used for filtration, purification, and/or separation processes.

No abstract

Electrospinning of nanofibers with cyclodextrin inclusion complexes (CD-ICs) is particularly attractive since distinct properties can be obtained by combining the nanofibers with specific functions of the CD-ICs. Here we report on the electrospinning of poly(methyl methacrylate) (PMMA) nanofibers containing cyclodextrin-menthol inclusion complexes (CD-menthol-ICs). These CD-menthol-IC functionalized nanofibers were developed with the purpose of producing functional nanofibers that contain fragrances/flavors with high temperature stability, and menthol was used as a model fragrance/flavor material. The PMMA nanofibers were electrospun with CD-menthol-ICs using three type of CD: alpha-CD, beta-CD, and gamma-CD. Direct pyrolysis mass spectrometry (DP-MS) studies showed that the thermal evaporation of menthol occurred over a very high and a broad temperature range (100-355 degrees C) for PMMA/CDmenthol-IC nanowebs, demonstrating the complexation of menthol with the CD cavity and its high temperature stability. Furthermore, as the size of CD cavity increased in the order alpha-CDbeta-CD>alpha-CD.

Cataloged from PDF version of article.Poly(methyl methacrylate) (PMMA) nanofibers containing the inclusion complex forming beta-cyclodextrin (β-CD) were successfully produced by means of electrospinning in order to develop functional nanofibrous webs for organic vapor waste treatment. Electrospinning of uniform PMMA nanofibers containing different loadings of β-CD (10%, 25% and 50% (w/w)) was achieved. The surface sensitive spectroscopic techniques; X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed that some of the β-CD molecules are present on the surface of the PMMA nanofibers, which is essential for the trapping of organic vapors by inclusion complexation. Direct pyrolysis mass spectrometry (DP-MS) studies showed that PMMA nanowebs containing β-CD can entrap organic vapors such as aniline, styrene and toluene from the surroundings due to inclusion complexation with β-CD that is present on the fiber surface. Our study showed that electrospun nanowebs functionalized with cyclodextrins may have the potential to be used as molecular filters and/or nanofilters for the treatment of organic vapor waste and air filtration purposes

No abstract

No abstract

Rate constants and deuterium kinetic isotope effects (KIEs) are measured for gas-phase nucleophilic substitution (SN2) reactions of solvated fluoride ions of F-(methanol) + CH3X (X = Br, I), F-(isopropyl alcohol) + CH3I, and F-(hydrogen fluoride) + CH3I at 300 K. The isotope effects are determined as the rate constant ratio k H/k D for specifically deuterated reactants, that is, methanol (CH3OH, CD3OH, CH3OD, and CD3OD), isopropyl alcohol (i-C3H7OH and i-C3H7OD), hydrogen fluoride (HF and DF), and methyl halides (CH3X and CD3X). The data reveal identical trends to those previously observed for F-(water) + CH3X (O'Hair, R. A. J.; Davico, G. E.; Hacaloglu, J.; Dang, T. T.; DePuy, C. H.; Bierbaum, V. M. J. Am. Chem. Soc. 1994, 116, 3609). The SN2 reactivities decrease as reaction exothermicity decreases (CH3I > CH3Br > CH3Cl) and as the nucleophile is solvated. Moderate inverse kinetic isotope effects (k H/k D < 1) are observed for the deuteration of the methyl halide, whereas substantial inverse KIEs are measured for the deuteration of the hydroxyl group of the solvent (or the deuteration of hydrogen fluoride). Moderate inverse KIEs are also measured for the deuteration of the methyl group in methanol. The observed trends and magnitudes of the isotope effects are rationalized qualitatively in terms of the SN2 transition-state structure and bonding interactions analogous to those in the F-(H2O) + CH3X system.