Search

The concept of self-assembled dendrimers is explored for the creation of discrete nanoparticle assemblies. Hybridization of branched DNA trimers and nanoparticle-DNA conjugates results in the synthesis of nanoparticle trimer and tetramer complexes. Multiple tetramer architectures are investigated, utilizing Au-DNA conjugates with varying secondary structural motifs. Hybridization products are analyzed by gel electrophoresis, and discrete bands are observed corresponding to structures with increasing numbers of hybridization events. Samples extracted from each band are analyzed by transmission electron microscopy, and statistics compiled from micrographs are used to compare assembly characteristics for each architecture. Asymmetric structures are also produced in which both 5 and 10 nm Au particles are assembled on branched scaffolds.

Newly developed porous polymer monolithic capillary columns modified with gold nanoparticles coated with exchangeable functionalities allow easy switching of separation modes by a simple ligand exchange process. These columns are prepared from a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith through reaction of its epoxide moieties with cysteamine to 'afford a monolith rich in surface thiol groups. Gold nanoparticles prepared via in situ reduction of chloroauric acid within the column become attached to the surface of the pores of the monolith. Alternatively, a solution of colloidal gold nanoparticles can be pumped through the thiol modified column to achieve their attachment. While the first approach is faster, it affords a lower coverage of nanoparticles than the second method, while both methods preserve the excellent hydrodynamic properties that are typical of the monolithic columns. Functionalization of the surface of the bound gold nanoparticles is then carried out using low molecular weight thiol-containing surface ligands. The dynamic nature of the bond between gold and these surface ligands enables the replacement of one surface ligand by another through a simple solution exchange process. This novel approach expands the application range of monoliths as a single column can now he used in different separations modes. Applications of the columns with exchangeable chemistries are demonstrated with the capillary electrochromatographic separation of peptides and the nano-high-pressure liquid chromatography (HPLC) separation of proteins in both reversed phase and ion exchange modes. 10.1021/ac1015613

A new porous polymer monolithic capillary column modified with gold nanoparticles that enables the selective capture of cysteine-containing peptides has been developed to reduce the complexity of peptide mixtures generated in bottom-up proteomic analysis. The column is prepared from a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith through reaction of some of its epoxide moieties with cysteamine to afford a monolith rich in surface thiol groups. In situ reduction of chloroauric acid within the column is then used to form gold nanoparticles attached to the surface of the pores of the monolith. This process preserves the excellent hydrodynamic properties of the monolithic column while providing a means to selectively retain cysteine-containing peptides from an analyte due to their high affinity for gold. Release of the retained peptides is subsequently achieved with an excess of 2-mercaptoethanol. The loading capacity determined for L-cysteine using frontal elution is 2.58 [micro]mol/m. Since the gold--thiol link is less stable at elevated temperatures, the adsorption capacity is recovered by washing the column at 80[degrees]C for 2 h. While regeneration is easy, the multiplicity of bonds between the monolithic support and the gold nanoparticles prevents their elution even under harsh conditions such as treatment with pure 2-mercaptoethanol or treatment with boiling water for 5 h. Application of the gold modified monolith in tandem with a packed C18 capillary column is demonstrated with baseline separation of a peptide mixture achieved in a two step process. The first involves retention of cysteine-containing peptides in monolith with reversed phase separation of all other peptides, while the retained peptides are released from monolith and separated in the second step. 10.1021/ac1002646

Superhydrophobic monolithic porous polymer layers with a photopatterned hydrophilic channel have been prepared. These layers were used for two-dimensional thin layer chromatography of peptides. The 50 [micro]m thin poly(butyl methacrylate-co-ethylene dimethacrylate) layers supported onto 4.0 x 3.3 cm glass plates were prepared using UV-initiated polymerization in a simple glass mold. Photografting of a mixture of 2-acrylamido-2-methyl-1-propanesulfonic acid and 2-hydroxyethyl methacrylate carried out through a mask afforded a 600 [micro]m wide virtual channel along one side of the layer. This channel, which contains ionizable functionalities, enabled the first dimension separation in ion exchange mode. The aqueous mobile phase migrates only through the channel due to the large difference in surface tension at the interface of the hydrophilic channel and the superhydrophobic monolith. The unmodified part of the layer featuring hydrophobic chemistry was then used for the reversed phase separation in the orthngonal second dimension. Practical application of our technique was demonstrated with a rapid 2D separation of a mixture of model peptides differing in hydrophobicity and isoelectric point using a combination of ion-exchange and reversed phase modes. In the former mode, the peptides migrated 11 mm in less than 1 min. Detection of fluorescently labeled peptides was achieved through UV light visualization. Separation of the native peptides was monitored directly using a desorption electrospray ionization (DESI) source coupled to a mass spectrometer. Unidirectional surface scanning with the DESI source was found suitable to determine both the location of each separated peptide and its molecular mass. 10.1021/ac100010h

Monolithic poly(butyl methacrylate-co-ethylene dimethacrylate) columns have been prepared in capillaries ranging in inner diameter from 5 to 75 [micro]m using thermally initiated free-radical polymerization of a mixture of butyl methacrylate, ethylene dimethacrylate, and porogens at different temperatures. Scanning electron microscopy and the measurement of hydrodynamic properties reveal that the downward scalability of the monolithic columns is greatly affected by the confinement effect of the capillary wall resulting from the decreased volume-to-surface ratio as the capillary diameter is decreased. The downscaling process is affected most by the polymerization temperature, the diffusion of the propagating radicals, and the density of coverage of polymerizable groups on the inner walls of the capillary. Optimization of all these factors enables the preparation of monolithic structures in capillaries with inner diameters as low as 5 [micro]m while retaining the desirable properties of monoliths prepared in much larger capillaries. Under these conditions, formation of undesired dense polymer layers attached to the capillary wall was minimized. The chromatographic performance of 10, 25, and 50 [micro]m capillaries evaluated in the reversed phase gradient separation of three proteins showed no change in elution times at identical flow velocities and gradient times, while peak elution width was the smallest with the narrowest capillary.

A biodegradable positron-emitting dendritic nanoprobe targeted at [[alpha].sub.v][[beta].sub.3] integrin, a biological marker known to modulate angiogenesis, was developed for the noninvasive imaging of angiogenesis. The nanoprobe has a modular multivalent core-shell architecture consisting of a biodegradable heterobifunctional dendritic core chemoselectively functionalized with heterobifunctional polyethylene oxide (PEO) chains that form a protective shell, which imparts biological stealth and dictates the pharmacokinetics. Each of the 8 branches of the dendritic core was functionalized for labeling with radiohalogens. Placement of radioactive moieties at the core was designed to prevent in vivo dehalogenation, a potential problem for radiohalogens in imaging and therapy. Targeting peptides of cyclic arginine-glycine-aspartic acid (RGD) motifs were installed at the terminal ends of the PEO chains to enhance their accessibility to [[alpha].sub.v][[beta].sub.3] integrin receptors. This nanoscale design enabled a 50-fold enhancement of the binding affinity to [[alpha].sub.v][[beta].sub.3] integrin receptors with respect to the monovalent RGD peptide alone, from 10.40 nM to 0.18 nM [IC.sub.50]. Cell-based assays of the [sup.125]I-labeled dendritic nanoprobes using [[alpha].sub.v][[beta].sub.3]-positive cells showed a 6-fold increase in [[alpha].sub.v][[beta].sub.3] receptor-mediated endocytosis of the targeted nanoprobe compared with the nontargeted nanoprobe, whereas [[alpha].sub.v][[beta].sub.3]-negative cells showed no enhancement of cell uptake over time. In vivo biodistribution studies of [sup.76]Br-labeled dendritic nanoprobes showed excellent bioavailability for the targeted and nontargeted nanoprobes. In vivo studies in a murine hindlimb ischemia model for angiogenesis revealed high specific accumulation of [sup.76]Br-labeled dendritic nanoprobes targeted at [[alpha].sub.v][[beta].sub.3] integrins in angiogenic muscles, allowing highly selective imaging of this critically important process. dendrimer | molecular imaging

A method for photopatterning multiple enzymes on porous polymer monoliths within microfluidic devices has been developed and used to perform spatially separated multienzymatic reactions. To reduce nonspecific adsorption of enzymes on the monolith, its pore surface was modified by grafting poly(ethylene glycol), followed by surface photoactivation and enzyme immobilization in the presence of a nonionic surfactant. Characterization of bound horseradish peroxidase (HRP) was carded out using a reaction in which the steady-state profiles of the fluorescent reaction product could be measured in situ and then analyzed using a plug-flow bioreactor model to determine the observed maximum reaction rate and Michaelis constant. The Michaelis constant of 1.9 [micro]mol/L agrees with previously published values. Mass-transfer limitations were evident at relatively low flow rates but were absent at higher flow rates. Sequential multienzymatic reactions were demonstrated using the patternwise assembly of two- and three-enzyme systems. Glucose oxidase (GOX) and HRP were patterned in separate regions of a single channel, and product formation was analyzed as a function of flow direction. Significant product formation occurred only in the GOX to HRP direction. A three-enzyme sequential reaction was performed using invertase, GOX, and HRP. All possible arrangements of the three enzymes were tested, but significant product formation was only observed when the enzymes were in the correct sequential order. Photopatterning enzymes on polymer monoliths provides a simple technique for preparing spatially localized multiple-enzyme microreactors capable of directional synthesis.

A generic method for the rapid, reproducible, and robust bonding of microfluidic chips fabricated from plastics has been developed and optimized. One of the bonding surfaces is exposed to solvent vapor prior to bringing the mating parts into contact and applying a load. Nanoindentation measurements performed by atomic force microscopy show that a reversible material softening occurs upon exposure to solvent vapor. Subsequent exposure of the bonded chip to UV light then strengthens the bond between mating parts and increases the burst pressure by 50% due to partial cross-linking and chain scission reactions as measured by size exclusion chromatography-multiangle light scattering (SEC-MALS). Performing all steps of this procedure at room temperature eliminates channel distortion observed during thermal bonding and affords channels with highly uniform cross-sectional dimensions. Our technique enables chips resistant to pressures as high as 34.6 MPa.

The development of organic semiconductors, specifically small molecule or oligomeric materials is presented. Synthetic approaches to produce organic semiconductors with a wide variety of functional groups and physical properties and the resulting structure-property relationships are discussed.

The antitumor effect of doxorubicin (DOX) conjugated to a biodegradable dendrimer was evaluated in mice bearing C-26 colon carcinomas. An asymmetric biodegradable polyester dendrimer containing 8-10 wt % DOX was prepared. The design of the dendrimer carrier optimized blood circulation time through size and molecular architecture, drug loading through multiple attachment sites, solubility through PEGylation, and drug release through the use of pH-sensitive hydrazone linkages. In culture, dendrimer-DOX was >10 times less toxic than free DOX toward C-26 colon carcinoma cells after exposure for 72 h. Upon i.v. administration to BALB/c mice with s.c. C-26 tumors, dendrimer-DOX was eliminated from the serum with a half-life of 16 [+ or -] 1 h, and its tumor uptake was ninefold higher than i.v. administered free DOX at 48 h. In efficacy studies performed with BALB/c mice bearing s.c. C-26 tumors, a single i.v. injection of dendrimer-DOX at 20 mg/kg DOX equivalents 8 days after tumor implantation caused complete tumor regression and 100% survival of the mice over the 60-day experiment. No cures were achieved in tumor-implanted mice treated with free DOX at its maximum tolerated dose (6 mg/kg), drug-free dendrimer, or dendrimer-DOX in which the DOX was attached by means of a stable carbamate bond. The antitumor effect of dendrimer-DOX was similar to that of an equimolar dose of liposomal DOX (Doxil). The remarkable antitumor activity of dendrimer-DOX results from the ability of the dendrimer to favorably modulate the pharmacokinetics of attached DOX. antitumor | molecular architecture | therapeutic effect | nanomedicine | dendrimer prodrug

With the use of the copper(I)-catalyzed (3 + 2) azide--alkyne cycloaddition, an element of 'click chemistry,' stationary phases carrying long alkyl chains or soybean trypsin inhibitor have been prepared for use in HPLC separations in the reversed-phase and affinity modes, respectively. The ligands were attached via a triazole ring to size monodisperse porous beads containing either alkyne or azide pendant functionalities. Alkyne-containing beads prepared by direct copolymerization of propargyl acrylate with ethylene dimethacrylate were allowed to react with azidooctadecane to give a reversed-phase sorbent. Azide-functionalized beads were prepared by chemical modification of glycidyl methacrylate particles. Subsequent reaction with a terminal aliphatic alkyne produced a reversed-phase sorbent similar to that obtained from the alkyne beads. Soybean trypsin inhibitor was functionalized with N-(4-pentynoyloxy)succinimide to carry alkyne groups and then allowed to react with the azide-containing beads to produce an affinity sorbent for trypsin. The performance of these stationary phases was demonstrated with the HPLC separations of a variety of peptides and proteins.

The near edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to characterize the microstructure development of convertible oligothiophenes and it is found that the bulky, branched end groups of the precursors strongly affect the packing of the conjugated core, whereas the small allyl end groups of the products do not. The dependence on core length of the precursors might be caused by interplay between the packing forces of pi affinity and phase segregation.

Crystalline monolayer films of a novel organic semi-conducting material were deposited as the active layer for organic thin-film transistors (OTFTs) through inkjet printing. The printed monolayer devices exhibited superior subthreshold characteristics with less hysteresis, and defect and trap densities were improved over thicker film analogs, showing that solution deposition techniques like inkjet printing result in thin films requisite for near-ideal electrostatics in OTFTs.

Activating the immune system to trigger a specific response is a major challenge in vaccine development. In particular, activating sufficient cytotoxic T lymphocyte-mediated cellular immunity, which is crucial for the treatment of many diseases including cancer and AIDS, has proven to be especially challenging. In this study, antigens were encapsulated in acid-degradable polymeric particle carriers to cascade cytotoxic T lymphocyte activation. To target dendritic cells, the most potent antigen-presenting cells, the particle carriers, were further conjugated with monoclonal antibodies. A series of ex vivo and in vivo studies have shown increased receptor-mediated uptake of antibody-conjugated particles by dendritic cells as well as migration of particle-carrying dendritic cells to lymph nodes and stimulation of naive T cells leading to enhanced cellular immune response as confirmed by specific cell lysis and IFNW secretion. acid-degradable particle | drug delivery | targeted vaccine

A novel stationary phase for capillary electrochromatography has been prepared via photoinitiated grafting of two layers of polymer chains onto the pore surface of a porous polymer monolith. To achieve the desired retention, the original monolith with optimized porous properties was grafted with an 'interior' layer consisting of the ionizable monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid, followed by a 'covering' layer of hydrophobic polymer chains. This technique affords monolithic CEC columns that facilitate electroosmotic flow (EOF) while preventing ionized analytes from interacting with the charged surface functionalities. Grafiing of the second layer does not adversely affect the EOF. Grafting times of 30 and 60 s for AMPS and butyl acrylate, respectively, enabled the preparation of a monolith with full shielding of the analytes from the ionizable functionalities and excellent chromatographic performance. This approach allows for the first time the independent optimization of both electroosmotic flow and retention properties in CEC columns. The efficient isocratic separations of mixtures of peptides, including some that are highly basic and would be affected by unshielded charges, were routinely achieved in 40-90 s using a simple MS compatible mobile phase consisting of 20 mmol/L ammonium acetate in a 1:1 water-acetonitrile mixture.

Single molecules detected through the phosphorescence emission of their triplet states, and the emission of the triplet state of single molecules of PtOBCP and Ru(dpp)3Cl(sub 2) are reported. Each molecule was found to have its own characteristic quenching rate by oxygen, and the distribution of the rates was measured for Ru(dpp)3Cl(sub 2) on a quartz surface.

Three alkali metal atoms (sodium, potassium, and cesium) are examined to investigate the effects of varying the electron donor in an electron transfer with CF3Br. Results indicate that the sigma*(sub CBr) LUMO is most accessible to the incoming electron at the Br end of the molecule, rather than inside the CF3 umbrella.

The use of dendrons to site isolate chromophores capable of electronic 'communication' is explored, through their use in organic light emitting diodes. The novel design of the peripheral moieties of the dendrons allowed tuning of properties for the casting of films that did not show a tendency to crystallize

The photochemistry of 4-haloanilines and 4-halo-N,N-dimethylanilines is examined in apolar, polar aprotic, and protic solvents. Photophysical and flash photolysis experiments show that the reaction proceeds in any case from the triplet state.

The synthesis of large dendrons and dendrimers with site-isolated dyes at their core is investigated. coumarin 343 and pentathiophene were the dyes selected as energy transfer processes prevail when the two dyes are intimately mixed, but each should behave independently of the other if site-isolation is achieved.

Microfluidic devices with a dual function containing both a solid-phase extractor and an enzymatic microreactor have been prepared, and their operation has been demonstrated. The devices were fabricated from a 25-mm-long porous poly(butyl methacrylate-co-ethylene dimethacrylate) monolith prepared within a 50-[micro]m-i.d. capillary. This capillary with a pulled 9-12-[micro]m needle tip was used as a nanoelectrospray emitter coupling the device to a mass spectrometer. Photografting with irradiation through a mask was then used to selectively functionalize a 20-mm-long portion of the monolith, introducing reactive poly(2-vinyl-4,4-dimethylazlactone) chains to enable the subsequent attachment of trypsin, thereby creating an enzymatic microreactor with high proteolytic activity. The other 5 mm of unmodified hydrophobic monolith served as micro solid-phase extractor ([micro]SPE). The dual-function devices were used in two different flow directions; concentration of myoglobin that was absorbed from its dilute solution, followed by elution and digestion or digestion, followed by concentration. Operations in both directions afforded equal sequence coverage. Different volumes of myoglobin solution ranging from 2 to 20 [micro]L were loaded on the device. Very high sequence coverages of almost 80% were achieved for the highest loading. Despite the very short length of the extractor unit, the device operated in the digest--solid-phase extraction direction also enabled the separation of peaks that mostly contained undigested protein and peptides.

The development of protein-based vaccines remains a major challenge in the fields of immunology and drug delivery. Although numerous protein antigens have been identified that can generate immunity to infectious pathogens, the development of vaccines based on protein antigens has had limited success because of delivery issues. In this article, an acid-sensitive microgel material is synthesized for the development of protein-based vaccines. The chemical design of these microgels is such that they degrade under the mildly acidic conditions found in the phagosomes of antigen-presenting cells (APCs). The rapid cleavage of the microgels leads to phagosomal disruption through a colloid osmotic mechanism, releasing protein antigens into the APC cytoplasm for class I antigen presentation. Ovalbumin was encapsulated in microgel particles, 200-500 nm in diameter, prepared by inverse emulsion polymerization with a synthesized acid-degradable crosslinker. Ovalbumin is released from the acid-degradable microgels in a pH-dependent manner; for example, microgels containing ovalbumin release 80%. of their encapsulated proteins after 5 h at pH 5.0, but release only 10% at pH 7.4. APCs that phagocytosed the acid-degradable microgels containing ovalbumin were capable of activating ovalbumin-specific cytoxic T lymphocytes. The acid-degradable microgels developed in this article should therefore find applications as delivery vehicles for vaccines targeted against viruses and tumors, where the activation of cytoxic T lymphocytes is required for the development of immunity. polymer | crosslinker | encapsulation | vaccination | cytotoxic T lymphocyte

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.

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 [micro]L/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%.

Research conducting operations of photoluminescence on lengthy oligothiophenes in order to obtain spectroscopy measurements is presented. Particular attention is given to identifications of interchain delocalizations of oligothiophene nanoaggregates.

Dendrimers possessing coumarin-2 dyes at the periphery and either a cumarin-343 has been studied by femtosecond transient absorption spectroscopy to elucidate energy transfer rate constants. The measured rate constants for energy transfer correlates extremely well with the theoretical rate constants.

Ring-opening polymerization of epsilon-caprolactone with functional dendritic initiation has been used to construct star polymers.

The synthesis of multichromophoric dendrimers that produces not only the target molecules but all the necessary model compounds is presented. This will assist photophysical studies on multichromophoric macromolecules, since a large number of structures are required.

A library of 36 L-amino acid anilides, which are potential selectors for chiral HPLC, was synthesized in solution and attached to functionalized macroporous polymer beads. The best selector from the library was identified by a deconvolution process using the HPLC separation of several racemic N-(3,5-dinitrobenzoyl)-[Alpha]-amino acid alkylamides as a probe. In each deconvolution step, a series of chiral stationary phases (CSPs) containing a subset of the amino acid anilide selector library was screened for enantioselectivity. After the best CSP was chosen, the library was further deconvoluted until the single best selector was found. The highest selectivity was obtained with a L-proline-1-indananilide that exhibited [Alpha] values up to 23 under normal-phase HPLC conditions. In addition, six CSPs were prepared using individual selectors from the library, and screening results indicate that the deconvolution process indeed led to the most selective receptor.

To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of [Alpha]-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 ° C affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time., The polymerization of [Alpha]-olefins by metallocene-based catalysts is at an exciting juncture. Research into a wide variety of cationic metallocene structures, and attendant weakly coordinating anions, has led to the [...]

Porous size monodisperse methacrylate beads containing amino and hydroxyl groups, which can be used as a platform for the production of chiral separation media, have been prepared using the staged templated suspension polymerization process. The monomers 2-hydroxyethyl methacrylate and several tert-butoxycarbonyl-protected aminoalkyl methacrylates were used for the preparation of both hydroxyl- and amino-functionalized beads. Attachment of a chiral selector based on L-valine-3,5-dimethylanilide through a carbamate and a urea linkage, respectively, provides chiral stationary phases with excellent enantioselectivities in the separation of the enantiomers of 3,5-dinitrobenzamido derivatives of [Alpha]-amino acids. For comparison purposes, a separation medium was also prepared by the direct polymerization of a chiral monomer analogous to the hydroxyethyl methacrylate-based stationary phase. The chiral stationary phases prepared with the N-methyl-2-aminoethyl methacrylate platform exhibit the best selectivity, and separation factors as high as 15 were achieved under normal-phase HPLC conditions.

A novel chiral stationary phase that contains a new chiral selector based on L-valine-3,5-dimethylanilide attached to monodisperse poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads has been prepared. The polymeric separation medium provides greatly enhanced enantiose-lectivities and reduced retention times when compared to the analogous silica-based chiral stationary phase in the separation of the enantiomers of 3,5-dinitrobenzamido derivatives of [Alpha]-amino acids under normal-phase HPLC conditions. Separation factors ([Alpha]) of up to 7 were achieved with the polymeric separation medium, which is also useful for the separation of large samples under overload conditions.

The design of new photoprecursors of organic bases and the steric and electronic factors that regulate their photocleavage to produce free amines were studied. The design procedure required the protection of an amine with novel ((benzoinyl)oxy)carbonyl groups and substituted analogs. The resulting masked amines owed their photosensitivity to the rich photochemistry of the benzoinyl chromophore. The photochemistry of this chromophore permits the clean photogeneration of free amine upon irradiation with UV light below 400 nm in both the solid state and in solution.