“…25 It should be noted that CDs similarly functionalized at the C2, C3, and C6 hydroxyl positions have been used as stationary phases in gas chromatography at temperatures ranging up to 200 °C. 34,35 Both AFM and XPS were used to study the thin film coated MCs. Figure 5 shows the AFM images (left) and XPS spectra (right) for three of the surfaces studied.…”
Section: Resultsmentioning
confidence: 99%
“…The reaction scheme to produce the HDATB-β-CD involves several steps and chromatographic isolation of the desired product, but clearly not in the highest purity . It should be noted that CDs similarly functionalized at the C2, C3, and C6 hydroxyl positions have been used as stationary phases in gas chromatography at temperatures ranging up to 200 °C. , 4 IR spectra of HDATB-β-CD before (a) and after (b) vapor deposition onto a gold-coated surface.…”
It is shown that the performance of microcantilver-based chemical sensors in a liquid environment is affected by altering cantilever surface morphology and receptor phase type and thickness. Self-assembled monolayers of thiolated beta-cyclodextrin (HM-beta-CD) and thin films of vapor-deposited heptakis (2,3-O-diacetyl-6-O-tertbutyl-dimethylsilyl)-beta-cyclodextrin (HDATB-beta-CD) were studied on smooth and nanostructured (dealloyed) gold-coated microcantilever surfaces. The dealloyed surface contains nanometer-sized features that enhance the transduction of molecular recognition events into cantilever response, as well as increase film stability for thicker films. Improvements in the limits of detection of the compound 2,3-dihydroxynaphthalene as great as 2 orders of magnitude have been achieved by manipulating surface morphology and film thickness. The observed response factors for the analytes studied varied from 0.02-604 nm/ppm, as determined by cantilever deflection. In general, calibration plots for the analytes were linear up to several hundred nanometers in cantilever deflections.
“…25 It should be noted that CDs similarly functionalized at the C2, C3, and C6 hydroxyl positions have been used as stationary phases in gas chromatography at temperatures ranging up to 200 °C. 34,35 Both AFM and XPS were used to study the thin film coated MCs. Figure 5 shows the AFM images (left) and XPS spectra (right) for three of the surfaces studied.…”
Section: Resultsmentioning
confidence: 99%
“…The reaction scheme to produce the HDATB-β-CD involves several steps and chromatographic isolation of the desired product, but clearly not in the highest purity . It should be noted that CDs similarly functionalized at the C2, C3, and C6 hydroxyl positions have been used as stationary phases in gas chromatography at temperatures ranging up to 200 °C. , 4 IR spectra of HDATB-β-CD before (a) and after (b) vapor deposition onto a gold-coated surface.…”
It is shown that the performance of microcantilver-based chemical sensors in a liquid environment is affected by altering cantilever surface morphology and receptor phase type and thickness. Self-assembled monolayers of thiolated beta-cyclodextrin (HM-beta-CD) and thin films of vapor-deposited heptakis (2,3-O-diacetyl-6-O-tertbutyl-dimethylsilyl)-beta-cyclodextrin (HDATB-beta-CD) were studied on smooth and nanostructured (dealloyed) gold-coated microcantilever surfaces. The dealloyed surface contains nanometer-sized features that enhance the transduction of molecular recognition events into cantilever response, as well as increase film stability for thicker films. Improvements in the limits of detection of the compound 2,3-dihydroxynaphthalene as great as 2 orders of magnitude have been achieved by manipulating surface morphology and film thickness. The observed response factors for the analytes studied varied from 0.02-604 nm/ppm, as determined by cantilever deflection. In general, calibration plots for the analytes were linear up to several hundred nanometers in cantilever deflections.
“…A novel GC CSP containing octakis(2,3-di-O-propionyl-6-O-tert-butyldimethylsilyl)-γ-CD was described, and the separation factors and thermodynamic parameters of several chiral compounds on two columns with different CD content was reported (79). Different di-tert-butyldimethyl-silylated CD CSPs were evaluated for the separation of various chiral analytes, and the separation factors and thermodynamic data were reported (80). It was found that modifying the substitution pattern of the tert-butyldimethylsilyl group in positions 2 and 3 or changing from β-to γ-CD significantly affects the separation properties of the CD derivatives.…”
“… N -trifluoroacetyl n -butyl ester of valine heptakis(2,3,6- O -trimethyl)-β-cyclodextrin 85 Krupcik et al γ-pentalactone octakis(2,6-di- O - tert -butyldimethylsilyl- 3- O -methyl)-γ-cyclodextrin 67 Mosandl et al isomenthone octakis(2,6-di- O -tert-butyldimethylsilyl)- γ-cyclodextrin 63 Mosandl et al …”
Inversion of the elution order of enantiomers caused by enthalpy-entropy compensation at the isoenantioselective temperature (Tiso) was experimentally observed by gas chromatography on the diamide-type chiral stationary phase (CSP), Chirasil-L-Val-C11, with N-ethoxycarbonyl propylamide (ECPA) derivatives of a number of alpha-amino acids. For the first time, a clear visual representation of the increase of the apparent enantioseparation factor alpha app from 1.00 to 1.08 as the temperature is raised from 120 to 170 degrees C is presented. The increase of alpha app is accompanied by a concomitant reduction of the retention factors of the enantiomers. The Tiso values were in the range from 110 to 130 degrees C depending on the nature of the alpha-amino acid. On the contrary, the Tiso values of the N(O)-trifluoroacetyl ethyl ester derivatives (TFA-Et) of the same alpha-amino acids were approximately 80 degrees higher than that of ECPA derivatives. The comprehensive thermodynamic investigation of the enantioseparation of ECPA and TFA-Et derivatives of valine and alanine using the retention increment method showed that the Delta L,D(DeltaH) difference between the diastereomeric selector-selectand associates was almost the same for ECPA and TFA-Et derivatives despite a much stronger bonded selector-selectand association taking place for the ECPA derivatives. On the other hand, the Delta L,D(DeltaS) values were found to be more negative in the case of ECPA derivatives, resulting in the unusually low values of Tiso. A temperature-dependent inversion of the elution order of enantiomers was also observed on the cyclodextrin-type CSP, Chirasil-Dex, with TFA-Et derivatives of several alpha-amino acids. The Tiso values were in the range from 20 to 170 degrees C depending on the nature of the alpha-amino acid. The results obtained demonstrate the necessity to conduct temperature-dependent studies in order to optimize the enantiomeric separation of single racemates isothermally or of mixtures of racemates in temperature-programmed runs using enantioselective GC. It is also shown that consideration of the elution order of enantiomers and the value of the apparent enantioseparation factor alpha app alone, without performing temperature-dependent measurements, can easily lead to wrong conclusions regarding the enantiorecognition mechanism.
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