Biomedical subjects

Abuzar Kabir

Publications and source records attributed to Abuzar Kabir.

7 recordsLinked to original sources

PubMed2005

Capillary electrophoresis and fluorescence anisotropy for quantitative analysis of peptide-protein interactions using JAK2 and SH2-Bbeta as a model system.

Fluorescence anisotropy capillary electrophoresis (FACE) and affinity probe capillary electrophoresis (APCE) with laser-induced fluorescence detection were evaluated for analysis of peptide-protein interactions with rapid binding kinetics. The Src homology 2 domain of protein SH2-Bbeta (SH2-Bbeta (525-670)) and a tyrosine-phosphorylated peptide corresponding to the binding sequence of JAK2 were used as a model system. For peptide labeled with fluorescein, the K(d) = 82 +/- 7 nM as measured by fluorescence anisotropy (FA). APCE assays had a limit of detection (LOD) of 100 nM or 12 amol injected for SH2-Bbeta (525-670). The separation time of 4 s, achieved using an electric field of 2860 V/cm on 7-cm-long capillaries, was on the same time scale as complex dissociation allowing K(d) (101 +/- 12 nM in good agreement with FA measurements) and dissociation rate (k(off) = 0.95 +/- 0.02 s(-)(1) corresponding to a half-life of 0.73 s) to be determined. This measurement represents a 30-fold higher rate of complex dissociation than what had previously been measurable by nonequilibrium CE analysis of equilibrium mixtures. Using FACE, the protein was detected with an LOD of 300 nM or 7.5 fmol injected. FACE was not used for determining K(d) or k(off); however, this method provided better separation resolution for multiple forms of the protein than APCE. Both methods were found suitable for analysis of cell lysate. These results demonstrate that FACE and APCE may be useful complements to existing techniques for exploring binding interactions with rapid kinetics.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Sol-gel approach to in situ creation of high pH-resistant surface-bonded organic-inorganic hybrid zirconia coating for capillary microextraction (in-tube SPME).

A novel zirconia-based hybrid organic-inorganic sol-gel coating was developed for capillary microextraction (CME) (in-tube SPME). High degree of chemical inertness inherent in zirconia makes it very difficult to covalently bind a suitable organic ligand to its surface. In the present work, this problem was addressed from a sol-gel chemistry point of view. Principles of sol-gel chemistry were employed to chemically bind a hydroxy-terminated silicone polymer (polydimethyldiphenylsiloxane, PDMDPS) to a sol-gel zirconia network in the course of its evolution from a highly reactive alkoxide precursor undergoing controlled hydrolytic polycondensation reactions. A fused silica capillary was filled with a properly designed sol solution to allow for the sol-gel reactions to take place within the capillary for a predetermined period of time (typically 15-30 min). In the course of this process, a layer of the evolving hybrid organic-inorganic sol-gel polymer got chemically anchored to the silanol groups on the capillary inner walls via condensation reaction. At the end of this in-capillary residence time, the unbonded part of the sol solution was expelled from the capillary under helium pressure, leaving behind a chemically bonded sol-gel zirconia-PDMDPS coating on the inner walls. Polycyclic aromatic hydrocarbons, ketones, and aldehydes were efficiently extracted and preconcentrated from dilute aqueous samples using sol-gel zirconia-PDMDPS coated capillaries followed by thermal desorption and GC analysis of the extracted solutes. The newly developed sol-gel hybrid zirconia coatings demonstrated excellent pH stability, and retained the extraction characteristics intact even after continuous rinsing with a 0.1 M NaOH solution for 24 h. To our knowledge, this is the first report on the use of a sol-gel zirconia-based hybrid organic-inorganic coating as an extraction medium in solid phase microextraction (SPME).

Chromatography, Gas↗

PubMed2004

High pH-resistant, surface-bonded sol-gel titania hybrid organic-inorganic coating for effective on-line hyphenation of capillary microextraction (in-tube solid-phase microextraction) with high-performance liquid chromatography.

Sol-gel titania-poly(dimethylsiloxane) (TiO2-PDMS) coating was developed for capillary microextraction (CME) to perform on-line preconcentration and HPLC analysis of trace impurities in aqueous samples. A method is presented describing in situ preparation of the titania-based sol-gel PDMS coating and its immobilization on the inner surface of a fused silica microextraction capillary. To perform CME-HPLC, the sol-gel TiO2-PDMS capillary was installed in the HPLC injection port as an external sampling loop, and a conventional ODS column was used for the liquid chromatographic separation. The target analytes were extracted on-line by passing the aqueous sample through this sampling loop. The sol-gel titania-PDMS coated capillaries were used for on-line extraction and HPLC analysis of polycyclic aromatic hydrocarbons, ketones, and alkylbenzenes. The extracted analytes were then transferred to the HPLC column using an organic-rich mobile phase followed by HPLC separation via gradient elution. To our knowledge, this is the first report on the use of sol-gel titania-based organic-inorganic material as a sorbent in capillary microextraction. The newly developed sol-gel titania-based CME coatings demonstrated excellent pH stability and enhanced extraction capability over the commercial GC coatings that are conventionally used for the same purpose. Extraction characteristics of a sol-gel titania-PDMS capillary remained practically unchanged after continuous rinsing with a 0.1 M NaOH solution (pH 13) for 12h.

Chromatography, High Pressure Liquid↗

PubMed2004

Parts per quadrillion level ultra-trace determination of polar and nonpolar compounds via solvent-free capillary microextraction on surface-bonded sol-gel polytetrahydrofuran coating and gas chromatography-flame ionization detection.

Sol-gel polytetrahydrofuran (poly-THF) coating was developed for high-sensitivity sample preconcentration by capillary microextraction (CME). Parts per quadrillion (ppq) level detection limits were achieved for both polar and nonpolar analytes through sample preconcentration on sol-gel poly-THF coated microextraction capillaries followed by gas chromatography (GC) analysis of the extracted compounds using a flame ionization detector (FID). The sol-gel coating was in situ created on the inner walls of a fused silica capillary using a sol solution containing poly-THF as an organic component, methyltrimethoxysilane (MTMOS) as a sol-gel precursor, trifluoroacetic acid (TFA, 5% water) as a sol-gel catalyst, and hexamethyldisilazane (HMDS) as a deactivating reagent. The sol solution was introduced into a hydrothermally-treated fused silica capillary and the sol-gel reactions were allowed to take place inside the capillary for 60 min. A wall-bonded coating was formed due to the condensation of silanol groups residing on the capillary inner surface with those on the sol-gel network fragments evolving in close vicinity of the capillary walls. Poly-THF is a medium polarity polymer, and was found to be effective in carrying out simultaneous extraction of both polar and nonpolar analytes. Efficient extraction of a wide range of trace analytes from aqueous samples was accomplished using sol-gel poly-THF coated fused silica capillaries for further analysis by GC. The test analytes included polycyclic aromatic hydrocarbons (PAHs), aldehydes, ketones, chlorophenols, and alcohols. To our knowledge, this is the first report on the use of a poly-THF based sol-gel material in analytical microextraction. Sol-gel poly-THF coated CME capillaries showed excellent solvent and thermal stability (>320 degrees C).

Chromatography, Gas↗

PubMed2004

Capillary microextraction on sol-gel dendrimer coatings.

Sol-gel capillary microextraction (CME) is a new direction in the solventless sample preparation for the preconcentration of trace analytes, and presents significant interest in environmental, pharmaceutical, petrochemical, biomedical, agricultural, food, flavor, and a host of other important areas. It utilizes advanced material properties of organic-inorganic hybrid sol-gel polymers to perform efficient extraction and preconcentration of target compounds from a wide variety of matrices. In the present work, a novel benzyl-terminated dendron-based sol-gel coating was developed for CME. A detailed investigation was conducted to evaluate the performance of the newly developed sol-gel dendrimer coatings to perform solventless extraction of a wide range of polar and nonpolar analytes. The characteristic branched architecture of dendrons makes them structurally superior extraction media compared with their traditional linear polymeric counterparts. Sol-gel chemistry was used to chemically immobilize dendritic macromolecules on fused silica capillary inner surface. Due to the strong chemical bonding with the capillary inner walls, sol-gel dendron coatings showed excellent thermal and solvent stability in capillary microextraction in hyphenation with chromatographic analysis. Efficient extraction of a wide range of analytes from their aqueous solutions was accomplished using sol-gel dendron coated fused silica capillaries. Low parts per trillion level detection limits were achieved in CME-GC for both polar and nonpolar analytes including polyaromatic hydrocarbons (PAHs), aldehydes, ketones, phenols, and alcohols.

Chromatography, Gel↗

PubMed2003

Sol-gel poly(ethylene glycol) stationary phase for high-resolution capillary gas chromatography.

A sol-gel chemistry-based method was developed for the preparation of highly stable capillary gas chromatography (GC) columns with surface-bonded poly(ethylene glycol) (PEG) stationary phase. Through a single-step procedure, it concurrently provided column deactivation, stationary-phase coating, and chemical immobilization of the coated film. Sol-gel reactions were carried out within fused-silica capillaries that were filled with properly designed sol solutions containing two sol-gel precursors, two different triethoxysilyl-derivatized poly(ethylene glycol)s, two sol-gel catalysts, and a deactivation reagent. Hydrolytic polycondensation reactions led to the formation of a sol-gel coating chemically bonded to the inner walls of the capillary. A number of sol-gel coated fused-silica capillary columns were prepared using sol-gel-active PEG derivatives. These columns demonstrated many inherent advantages, the main being the strong anchoring of the coating to the capillary wall resulting from chemical bonding with the silanol groups on the fused-silica capillary inner surface. This chemical bonding yielded strongly immobilized PEG coatings with outstanding thermal stability (up to 320 degrees C). To our knowledge, such a high thermal stability has not been achieved so far on conventionally prepared PEG GC columns. Sol-gel PEG columns provided excellent chromatographic performances: high number of theoretical plates, excellent run-to-run and column-to-column reproducibility, and pronounced selectivity for a wide range of test solutes. Using n-octadecane as a test solute (k = 7.14), an efficiency value of 3200 theoretical plates/m was obtained on a 10 m x 0.25 mm i.d. fused-silica capillary column. Five sol-gel PEG columns provided RSD values of 1.09% for column efficiency (solute, n-octadecane), 1.37% for retention factor (solute, n-octadecane), and 0.9% for separation factor (for solute pair o- and p-xylene). In five replicate measurements using the same column, RSD values of less than 0.50% for the retention time and 1.36% for retention factor (k) were obtained.

Journal Article↗

PubMed2002

Sol-gel capillary microextraction.

Sol-gel capillary microextraction (sol-gel CME) is introduced as a viable solventless extraction technique for the preconcentration of trace analytes. To our knowledge, this is the first report on the use of sol-gel-coated capillaries in analytical microextraction. Sol-gel-coated capillaries were employed for the extraction and preconcentration of a wide variety of polar and nonpolar analytes. Two different types of sol-gel coatings were used for extraction: sol-gel poly(dimethylsiloxane) (PDMS) and sol-gel poly(ethylene glycol) (PEG). An in-house-assembled gravity-fed sample dispensing unit was used to perform the extraction. The analysis of the extracted analytes was performed by gas chromatography (GC). The extracted analytes were transferred to the GC column via thermal desorption. For this, the capillary with the extracted analytes was connected to the inlet end of the GC column using a two-way press-fit fused-silica connector housed inside the GC injection port. Desorption of the analytes from the extraction capillary was performed by rapid temperature programming (at 100 degrees C/min) of the GC injection port. The desorbed analytes were transported down the system by the helium flow and further focused at the inlet end of the GC column maintained at 30 degrees C. Sol-gel PDMS capillaries were used for the extraction of nonpolar and moderately polar compounds (polycyclic aromatic hydrocarbons, aldehydes, ketones), while sol-gel PEG capillaries were used for the extraction of polar compounds (alcohols, phenols, amines). The technique is characterized by excellent reproducibility. For both polar and nonpolar analytes, the run-to-run and capillary-to-capillary RSD values for GC peak areas remained under 6% and 4%, respectively. The technique also demonstrated excellent extraction sensitivity. Parts per quadrillion level detection limits were achieved by coupling sol-gel CME with GC-FID. The use of thicker sol-gel coatings and longer capillary segments of larger diameter (or capillaries with sol-gel monolithic beds) should lead to further enhancement of the extraction sensitivity.

Journal Article↗