Biomedical subjects

Frantisek Svec

Publications and source records attributed to Frantisek Svec.

10 recordsLinked to original sources

PubMed2003

Flow control valves for analytical microfluidic chips without mechanical parts based on thermally responsive monolithic polymers.

Monolithic plugs of poly(N-isopropylacrylamide) cross-linked with 5% methylenebisacrylamide have been prepared by photoinitiated polymerization within the channel of a microfluidic device. The volume change associated with the polymer phase transition at its lower critical solution temperature of 32 degrees C allows both the rapid swelling and the deswelling of the monoliths enabling the polymer to close or open the channel as it functions as a nonmechanical valve. Thermoelectric elements capable of changing the temperature of the system between 17 and 57 degrees C were used to actuate the valve. Flow through the device was monitored by fluorescence measurements via the laser-triggered photobleaching of a dye contained in the liquid phase. Photobleaching occurs quickly once the flow is stopped, and the time required to open and close the valve was 3.5 and 5.0 s, respectively. No changes in function were observed even after 120 open-close cycles. Although the 2-mm-long valve was prepared from a polymerization mixture consisting of only a 5% aqueous solution of monomers, it resists pressures of up to 1.38 MPa (200 psi) without observable structural damage.

Acrylic Resins↗

PubMed2003

Polar polymeric stationary phases for normal-phase HPLC based on monodisperse macroporous poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads.

The effect of variables such as shape template size, porogen composition and percentage, content of cross-linking monomer, and polymerization temperature on the properties of uniformly sized 3-microm porous poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads prepared by the staged templated suspension polymerization technique has been studied. The porous properties of the beads including surface morphology, pore size distribution, and specific surface area have been optimized to obtain highly efficient stationary phases for normal-phase HPLC. A column packed with diol stationary phase obtained by hydrolysis of poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads affords an efficiency of 67,000 plates/m for toluene using THF as the mobile phase. The retention properties and selectivity of the diol beads are easily modulated by changes in the composition of the mobile phase. The performance of these beads is demonstrated with the separations of a variety of polar compounds including positional isomers, aniline derivatives, and basic tricyclic antidepressant drugs.

Aniline Compounds↗

PubMed2003

Macroporous monolithic chiral stationary phases for capillary electrochromatography: New chiral monomer derived from cinchona alkaloid with enhanced enantioselectivity.

A new chiral monomer derived from cinchona alkaloid, namely O-9-(tert-butylcarbamoyl)-11-[2-(methacryloyloxy)ethylthio]-10,11-dihydroquinine 1, was employed for the preparation of enantioselective monolithic capillary columns by an in situ copolymerization with 2-hydroxyethyl methacrylate 2 (HEMA), ethylene dimethacrylate 3 (EDMA) in the presence of cyclohexanol and 1-dodecanol as porogens (UV or thermal initiation of azobisisobutyronitrile (AIBN) as radical initiator). The porous properties and the electrochromatographic behavior of the new chiral monoliths were comparatively evaluated with previously described analogs obtained from O-9-[2-(methacryloyloxy)ethylcarbamoyl]-10,11-dihydroquinidine 4 as chiral monomer. Despite close structural and physicochemical similarities of the both chiral monomers, the pore distribution profiles of the resulting monoliths were shifted typically towards larger pore diameters with the new monomer 1. Once more, it was confirmed that a low cross-linking (10 wt% related to total monomers) and a pore diameter of about 1 microm in the dry state provides the best electrochromatographic efficiency as a result of lower resistance to mass transfer (smaller C-term contribution to peak broadening) and more homogeneous flow profile (smaller A-term). Most importantly, as expected the new poly(1-co-HEMA-co-EDMA) monoliths showed enhanced enantioselectivities and in addition faster separations as compared to poly(4-co-HEMA-co-EDMA) analogs, which represents a significant improvement. Further, the elution order was reversed owing to the pseudoenantiomeric behavior of quinine- and quinidine-derived monomers. Fluorescence-labeled 9-fluorenylmethoxycarbonyl (FMOC), dansyl (DNS), 7-dimethylaminosulfonyl-1,3,2-benzoxadiazol-4-yl (DBD), carbazole-9-carbonyl (CC) amino acids could be separated with resolution values between 2 and 4 (with efficiencies typically between 100,000 and 200,000 plates/m) and fluorescence detection (variable wavelength fluorescence detector in-line with UV) yielding routinely a gain in detection sensitivities up to two orders of magnitude without specific optimization of the conditions with regards to fluorescence efficiency.

Amino Acids↗

PubMed2002

Enzymatic microreactor-on-a-chip: protein mapping using trypsin immobilized on porous polymer monoliths molded in channels of microfluidic devices.

Enzymatic microreactors have been prepared in capillaries and on microfluidic chips by immobilizing trypsin on porous polymer monoliths consisting of 2-vinyl-4,4-dimethylazlactone, ethylene dimethacrylate, and acrylamide or 2-hydroxyethyl methacrylate. The azlactone functionalities react readily with amine and thiol groups of the enzyme to form stable covalent bonds. The optimized porous properties of the monoliths lead to very low back pressures enabling the use of simple mechanical pumping to carry out both the immobilization of the enzyme from its solution and the subsequent analyses of substrate solutions. The Michealis-Menten kinetic characteristics of the reactors were probed using a low molecular weight substrate: N-alpha-benzoyl-L-arginine ethyl ester. The effects of immobilization variables such as the concentration of trypsin in solution and percentage of azlactone functionalities in the monolith, as well as the effect of reaction time on the enzymatic activity, and of process variables such as substrate flow velocity and residence time in the reactor, were studied in detail. The proteolytic activity of the enzymatic microreactor on chip was demonstrated at different flow rates with the cleavage of fluorescently labeled casein used as a substrate. The excellent performance of the monolithic microreactor was also demonstrated with the digestion of myoglobin at the fast flow rate of 0.5 microL/min, which affords a residence time of only 11.7 s. The digest was then characterized using MALDI-TOF MS, and 102 out of 153 possible peptide fragments were identified giving a sequence coverage of 67%.

Animals↗

PubMed2002

Effect of multivalency on the performance of enantioselective separation media for chiral HPLC prepared by linking multiple selectors to a porous polymer support via aliphatic dendrons.

Chiral stationary phases (CSPs) containing L-proline indananilide chiral selectors attached through a multivalent dendritic linker to monodisperse macroporous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads have been prepared using two different approaches. The convergent method involves the preparation of ligands in solution and their subsequent attachment to the support. The divergent approach is based on the stepwise "on-bead" formation of the linker using methods that are typical of solid-phase synthesis. While the convergent CSPs feature well-defined ligands, their loading is relatively low. In contrast, the divergent technique affords CSPs with higher loading but with more limited control over precise ligand architecture. Excellent enantioselectivities characterized by separation factors of up to 31 were achieved for the separation of racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkyl amides with these new CSPs under normal-phase HPLC conditions.

Alanine↗

PubMed2002

Polymeric monolithic stationary phases for capillary electrochromatography.

This review summarizes the contributions of a number of groups working in the rapidly growing area of monolithic columns for capillary electrochromatography (CEC), with a focus on those prepared from synthetic polymers. Monoliths have quickly become a well-established stationary phase format in the field of CEC. The simplicity of their in situ preparation method as well as the good control over their porous properties and surface chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. A wide variety of approaches as well as materials used for the preparation of the monolithic stationary phases are detailed. Their excellent chromatographic performance is demonstrated by numerous separations of different analytes.

Chromatography↗

PubMed2002

Capillary electrochromatography: a rapidly emerging separation method.

This overview concerns the new chromatographic method--capillary electrochromatography (CEC)--that is recently receiving remarkable attention. The principles of this method based on a combination of electroosmotic flow and analyte-stationary phase interactions, CEC instrumentation, capillary column technology, separation conditions, and examples of a variety of applications are discussed in detail.

Buffers↗

PubMed2002

Porous polymer monoliths: an alternative to classical beads.

Porous polymer monoliths are a new category of materials developed during the last decade. These materials are prepared using a simple molding process carried out within the confines of a closed mold. Polymerization of a mixture that typically contains monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable flow-through applications. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. The porous properties of the monolith can be controlled over a broad range. These, in turn, determine the hydrodynamic properties of the devices that contain the molded media. Since all the mobile phase must flow through the monolith, the mass transport within the molded material is dominated very much by convection, and the monolithic devices perform well even at very high flow rates. The applications of monolithic materials are demonstrated on the chromatographic separation of biological compounds and synthetic polymers, electrochromatography, gas chromatography, enzyme immobilization, molecular recognition, and in advanced detection systems. Grafting of the pore walls with selected polymers leads to materials with completely changed surface chemistries.

Chromatography↗

PubMedDate not supplied

Chiral recognition: design and preparation of chiral stationary phases using selectors derived from ugi multicomponent condensation reactions and a combinatorial approach.

Combinatorial approaches together with high-throughput screening have been used to develop highly selective stationary phases for chiral recognition. Libraries of potential chiral selectors have been prepared by the Ugi multicomponent condensation reactions and screened for their enantioselectivity using the reciprocal approach involving a chiral stationary phase with immobilized model target compound N-(3,5-dinitrobenzoyl)-alpha-l-leucine. The best candidates were identified from the library of phenyl amides of 2-oxo-azetidineacetic acid derivatives. This screening also enabled specification of the functionalities of the selector desired to achieve the highest level of chiral recognition. The substituents of the phenyl ring adjacent to the chiral center of the selector candidates exhibited the most profound effect on the chiral recognition. The best candidate was then synthesized on a larger scale, resolved into single enantiomers using preparative enantioselective HPLC, and attached to porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads via an ester linkage to afford the desired stationary phase. Selectivities alpha as high as 3.2 were found for the separation of a variety of amino acid derivatives.

Acetates↗

PubMedDate not supplied

High-throughput peptide mass mapping using a microdevice containing trypsin immobilized on a porous polymer monolith coupled to MALDI TOF and ESI TOF mass spectrometers.

An enzymatic microreactor with a volume of 470 nL has been prepared by immobilizing trypsin on a 10 cm long reactive porous polymer monolith located in a 100 microm i.d. fused silica capillary. This reactor affords suitable degrees of digestion of proteins even after very short residence times of less than 1 min. The performance is demonstrated with the digestion of eight proteins ranging in molecular mass from 2848 to 77 754. The digests were analyzed using mass spectrometry in two modes: off-line MALDI and in-line nanoelectrospray ionization. The large numbers of identified peptides enable a high degree of sequence coverage and positive identification of the proteins. The extent of sequence coverage decreases as the molecular mass of the digested protein increases.

Peptide Mapping↗