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PubMed2006

Mapping the dimer interface in the C-terminal domains of the yeast MLH1-PMS1 heterodimer.

Yeast MutLalpha is a heterodimer of MLH1 and PMS1 that participates in a variety of DNA transactions, including DNA mismatch repair. Formation of the MutLalpha heterodimer requires that the C-terminal domains of MLH1 and PMS1 interact in a manner that is not yet fully understood. Here we investigate the interactions involved in heterodimerization. Using protein surface modification and mass spectrometry, we identify numerous lysine residues that are exposed to solvent in monomeric MLH1. A corresponding analysis of the MLH1-PMS1 heterodimer reveals that three of these exposed residues, K665, K675, and K704, are no longer solvent accessible in the heterodimer, suggesting that they are within the dimer interface. We refine secondary structure predictions and sequence alignments of C-terminal residues of seven eukaryotic MutL homologues and then develop homology models for the N- and C-terminal domains of MLH1. On the basis of this information, we present a model for interaction of the C-terminal domains of MLH1 and PMS1.

Adaptor Proteins, Signal Transducing↗

PubMedDate not supplied

Biomacromolecules electrostatic self-assembly on 3-dimensional tissue engineering scaffold.

A poly(ethylenimine) (PEI) was employed to obtain a stable positively charged surface on a poly(D,L-lactide) (PDL-LA) tissue engineering scaffold. An extracellular matrix (ECM)-like biomacromolecule, gelatin, was selected as polyelectrolyte and deposit alternately with PEI on the activated PDL-LA scaffold via ESA technique. The zeta-potential result showed alternating charge of polyelectrolytes (PEI/gelatin) layering on PDL-LA microspheres. Quartz crystal microbalance (QCM) measurement further verified the gradual deposition of PEI/gelatin on the PDL-LA thin film. The combination of PEI aminolysis and the layer-by-layer technique was then explored to construct gelatin coating onto the 3-D porous PDL-LA scaffold. Scanning electronic microscopy showed that there is no notable difference between modified and unmodified PLA scaffolds, with regard to the porosity, pore diameter, and scaffold integration. The dual-tunnel confocal laser scanning microscopy indicated uniform gelatin distribution on the inner surface of the 3-D porous scaffold. The gradual build-up of protein layer on scaffold was investigated by radioiodination technique. Chondrocyte was chosen to test the cell behavior on modified and unmodified PDL-LA scaffolds. The results of the cell viability, total intracellular protein content, and cell morphology on the PEI/gelatin multilayers modified PDL-LA scaffold showed to promote chondrocyte growth. Comparing conventional coating methods, polyelectrolyte multilayers are easy and stable to prepare. It may be a promising choice for the surface modification of complex biomedical devices. These very flexible systems allow broad medical applications for drug delivery and tissue engineering.

Animals↗

PubMedDate not supplied

Ultrathin functional star PEG coatings for DNA microarrays.

In this study, star PEG coatings on glass substrates have been used as support material for oligonucleotide microarrays. These coatings are prepared from solutions of six armed star shaped prepolymers that carry reactive isocyanate endgroups. As described earlier, such films prevent the adsorption of proteins and the adhesion of cells but can easily be functionalized for specific biological recognition. Here we used the high functionality of these coatings for the covalent immobilization of amino terminated 20mer oligonucleotides, both by microcontact printing and spotting techniques. The permanent immobilization of fluorescently labeled DNA as well as hybridization of 20mer oligonucleotides have been monitored by fluorescence microscopy. The hybridization efficiency as determined by fluorescence intensity varied from 30% to 80% depending on the way of layer preparation. The direct spotting without additional activation and blocking steps of the surface demonstrates the potential of star PEG coatings as ultrathin surface modification for microarrays.

Base Sequence↗

PubMedDate not supplied

An assessment of the effects of shell cross-linked nanoparticle size, core composition, and surface PEGylation on in vivo biodistribution.

Amphiphilic core-shell nanoparticles have drawn considerable interest in biomedical applications. The precise control over their physicochemical parameters and the ability to attach various ligands within specific domains suggest shell cross-linked (SCK) nanoparticles may be used as multi-/polyvalent scaffolds for drug delivery. In this study, the biodistribution of four SCKs, differing in size, core composition, and surface PEGylation, was evaluated. To facilitate in-vivo tracking of the SCKs, the positron-emitting radionuclide copper-64 was used. By using biodistribution and microPET imaging approaches, we found that small diameter (18 nm) SCKs possessing a polystyrene core showed the most favorable biological behavior in terms of prolonged blood retention and low liver accumulation. The data demonstrated that both core composition, which influenced the SCK flexibility and shape adaptability, and hydrodynamic diameter of the nanoparticle play important roles in the respective biodistributions. Surface modification with poly(ethylene glycol) (PEG) had no noticeable effects on SCK behavior.

Analysis of Variance↗

PubMedDate not supplied

Direct measurement of pH profiles in immobilized enzyme carriers during kinetically controlled synthesis using CLSM.

Confocal laser scanning microscopy was applied to measure the pH value in the carrier of immobilized enzymes during the enzyme-catalyzed synthesis. pH profiles with a high resolution are shown, with the pH increasing in the core of the particles. Significant differences occur for different carrier material, particle size, porosity and surface modification. The increased pH value is identified as one of the reasons leading to reduced enzyme selectivity in the penicillin amidase catalyzed synthesis of cephalosporins and penicillins.

Calibration↗

PubMedDate not supplied

Immobilization of Candida bombicola cells on free-standing organic-gold nanoparticle membranes and their use as enzyme sources in biotransformations.

Preparation of chemically functionalized biocompatible surfaces is of current interest, with application in the immobilization of various bioactive species such as DNA, enzymes, whole cells, etc. We report herein the one-step synthesis of a self-supporting gold nanoparticle membrane, its surface modification, and application in the immobilization of Candida bombicola (yeast) cells. The gold nanoparticle membrane is prepared by the spontaneous reduction of aqueous chloroaurate ions by a diamine at a liquid-liquid interface. The gold nanoparticles in the polymeric membrane may be capped with octadecylamine (ODA) molecules, thereby rendering the nanoparticle membrane hydrophobic. Exposure of the hydrophobized organic-gold nanoparticle membrane to C. bombicola yeast cells results in their binding to the membrane, possibly through nonspecific interactions such as hydrophobic interactions between the yeast cell walls and the ODA molecules. The enzyme cytochrome P450 present in the yeast cells immobilized on the organic-gold nanoparticle membrane was then used in the transformation of the arachidonic acid (AA) to sophorolipids followed by acid hydrolysis to form 20-hydroxyeicosatetraneoic acid (20-HETE). The organic-gold nanoparticle membrane-C. bombicola bioconjugate could be easily separated from the reaction medium and reused a number of times.

Arachidonic Acid↗

PubMedDate not supplied

Membrane chromatography: preparation and applications to protein separation.

As a result of the convective flow of solutes through porous membranes, membrane chromatography has a higher capture efficiency and a higher productivity than column chromatography and shows most promising industrial applications for the recovery, isolation, and purification of proteins and enzymes. This paper presents a comprehensive review of the methods for preparation of adsorptive membranes (such as surface modification, in situ copolymerization, direct formation from hydrophilic materials, and functionalized particulate-entrapped membranes) and deals particularly with novel macroporous chitin and chitosan membranes for protein separations developed by the authors.

Carbohydrate Sequence↗

PubMed2002

Determination and tailoring the pore entrance size in ordered silicas with cage-like mesoporous structures.

A practical approach to the determination of the pore entrance size in ordered silicas with cage-like mesoporous structures (OSCMSs) is proposed. A fundamental insight into the OSCMS pore connectivity is gained, including the control of the pore entrance size by post-synthesis surface modification, and by selection of appropriate synthesis temperature. These findings show a new promise for the synthesis of mesoporous solids with molecular size- and shape-selective properties.

Journal Article↗

PubMed2003

One-pot preparation of subnanometer-sized gold clusters via reduction and stabilization by meso-2,3-dimercaptosuccinic acid.

We report herein a simple method to prepare subnanometer-sized gold clusters by the reactions between hydrogen tetrachloroaurate (HAuCl4) and meso-2,3-dimercaptosuccinic acid (DMSA; HO2CCH(SH)CH(SH)CO2H) in water. It is demonstrated that DMSA molecules efficiently reduce the Au(III) species and stabilize the resultant gold clusters. The Au:DMSA clusters, which tend to aggregate into assemblages in water, can be well-isolated from each other by ion-pair formation between the carboxyl groups of DMSA and tetraoctylammonium (TOA) cations. This surface modification enables us to examine the core size distributions of the individual clusters by mass spectrometry and TEM. It is revealed that the gold clusters comprised of 10-13 atoms (ca. 0.8 nm) are the main products of the reactions.

Journal Article↗

PubMed2003

Ultrasensitive DNA detection using highly fluorescent bioconjugated nanoparticles.

Sensitive DNA detection is extremely important in clinical diagnostics, gene therapy, and a variety of biomedical studies. We have developed a novel DNA bioanalysis method with a 0.8 fM (0.8 x 10-15 M) detection limit using a bioconjugated fluorescent nanoparticle-based sandwich assay. An organic dye silica nanoparticle is synthesized using a modified reverse microemulsion. The nanoparticles are highly fluorescent, extremely photostable, and easy for bioconjugation for bioanalysis. They exhibit an excellent signaling ability in the presence of trace amounts of DNA targets. With an effective surface modification, nonspecific binding and nanoparticle aggregation are minimized. In addition, the nanoparticle-based DNA bioanalysis assay can effectively discriminate one-base mismatched DNA sequences. We expect this nanoparticle-based assay to be widely useful in a number of biomedical applications where reproducible, selective, and ultrasensitive gene analysis is critical.

Base Sequence↗

PubMed2003

Single-phase and gram-scale routes toward nearly monodisperse Au and other noble metal nanocrystals.

Single-phase approaches are introduced for the synthesis of nearly monodisperse Au and other noble metal nanocrystals. The new approaches possess all the advantages of the popular Brust method. With weak ligands or surfactants for the metal ions, the control of the size and size distribution of the nanocrystals in synthesis in the size range between 1 and 15 nm was achieved via maintaining balanced nucleation and growth by tuning the activities of the metal precursors and reducing reagents. Because only weak ligands are employed in the new synthetic schemes, surface modification and functionalization of the resulting nanocrystals can be readily carried out.

Journal Article↗

PubMed2004

Isothermal titration calorimetry studies on the binding of DNA bases and PNA base monomers to gold nanoparticles.

An isothermal titration calorimetric (ITC) investigation of the interaction of DNA bases and PNA base monomers with gold nanoparticles is described revealing a binding sequence in the order C > G > A > T. Direct measurement of the strength of interaction of ligands with nanogold by ITC has important implications in surface modification strategies for biomedical, catalysis, and nanoarchitecture applications.

Adenine↗

PubMed2005

Comparative study of acetic acid, methanol, and water adsorbed on anatase TiO2 probed by sum frequency generation spectroscopy.

Sum frequency generation (SFG) vibrational spectroscopy is used to investigate the surface adsorption of three probe molecules-acetic acid, methanol, and water--on a film composed of nanoscale anatase TiO(2) particles. On the TiO(2) surface, only one adsorption mode, chemisorption, is observed for acetic acid. This is evidenced by one sharp SFG peak in the C-H region, which is stable with time and robust both to evacuation and to the addition of water. A Langmuir constant of (9.21 +/- 0.71) x 10(3) is determined from the adsorption isotherm. In the case of methanol adsorption, however, there are two adsorption modes, molecular physisorption and dissociative chemisorption. The corresponding SFG signals are stable with time but diminished with addition of water. Changes in the SFG features for methanol and for the methoxy species with addition of water and subsequent evacuation provide the first experimental proof of reversible hydroxylation and dehydroxylation at the TiO(2) surface. For water adsorption, only one mode, physisorption, is observed on the hydroxylated TiO(2) surface. The water adlayer is mobile, as is evidenced by variation of the water H-bonded SFG signal with time. Competitive adsorption among the three molecular probes is clearly resolved by in situ SFG measurements. The adsorption strength follows the order acetic acid (strongest), methanol, water (weakest). The adsorption order as well as the difference in response of methanol versus acetic acid adsorption to addition of water has direct implications for understanding TiO(2) photocatalysis as well as the surface modifications involved in TiO(2) photoelectrochemical solar cells and processes in TiO(2) nanomaterial synthesis and assembly.

Acetic Acid↗

PubMed2005

Loading of hydrophobic materials into polymer particles: implications for fluorescent nanosensors and drug delivery.

A straightforward method for loading hydrophobic materials into commercially available polymer nano- or microparticles is described. PMMA and PS nano/microparticles were swelled by an organic solvent with an ionic surfactant (SDS) to stabilize the particles in aqueous solution. FITC and Ru(dpp)3Cl2 were loaded into those particles based on the principle of "like dissolves like". Further surface modification of the loaded particles was achieved via layer-by-layer (LbL) self-assembly. Culture of fibroblasts with the dye-doped, coated particles showed that the cells internalized the fluorescent particles with no apparent toxic effects. The findings suggest the facile process could be useful in a wide range of applications for fluorescent micro/nanosensors and drug delivery.

Drug Delivery Systems↗

PubMed2005

Ultrastable Au nanocatalyst supported on surface-modified TiO2 nanocrystals.

The surfaces of TiO2 nanocrystals were modified with amorphous aluminum-oxide layers using a surface sol-gel process to control the interaction between supports and metal particles. Ultrastable Au nanocatalysts were prepared by the deposition of Au nanoparticles on the surface-modified TiO2 nanocrystals using a deposition-precipitation (DP) method. The TEM analysis showed that the Au nanoparticles on the surface-modified nanocrystal supports were highly stable with a sinter-resistant capability during high-temperature calcination. The HRTEM analysis revealed that the surface of the TiO2 nanocrystals was covered by an amorphous aluminum-oxide layer and the Au nanoparticles were primarily anchored to this amorphous layer. This amorphous aluminum-oxide layer played an extremely important role in the stabilization of the supported Au nanoparticles without affecting catalytic activities. The surface modification of nanocrystal supports highlights new opportunities in tailoring the stability and activity of supported nanocatalyst systems.

Journal Article↗

PubMed2005

Redox-transmetalation process as a generalized synthetic strategy for core-shell magnetic nanoparticles.

Although multicomponent core-shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox-transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core-shell type bimetallic nanoparticles on the sub-10 nm scale. Various core-shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential reduction strategies, this transmetalation process has several advantages for the fabrication of core-shell type nanoparticles: (i) no additional reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core-shell structures by transferring Co@Au nanoparticles from an organic phase to an aqueous phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core-shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chemical process that promotes the core-shell structure formation.

Journal Article↗

PubMed2006

Monodisperse lanthanide oxysulfide nanocrystals.

Monodisperse lanthanide oxysulfide nanoplates and short nanorods were synthesized by the thermal decomposition of molecular precursors in the presence of oxygen. The nanoplates have uniform thicknesses and further self-organize to nanowires up to micron scale. The Eu2O2S and Eu3+-doped Gd2O2S nanocrystals both show unusual fluorescence properties obviously differing from the bulk powder phosphors, which are related to the surface-modification effects.

Journal Article↗

PubMed2005

Adsorption of atomic hydrogen at a nanostructured electrode of polyacrylate-capped Pt nanoparticles in polyelectrolyte.

Atomic hydrogen electrosorption is reported at crystallite sites of polyacrylate-capped Pt nanoparticles (d = 2.5 +/- 0.6 nm), by assembling nanostructured electrodes of polyacrylate-Pt nanocrystallites layer-by-layer in a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). Cyclic voltammetry in 1 M H2SO4 revealed a strongly adsorbed hydrogen state and a weakly adsorbed hydrogen state assigned to adsorption at (100) and (110) sites of the modified nanocrystallites, respectively. Resolving hydrogen adsorption states signifies that surface capping by the carboxylate groups is not irreversibly blocking hydrogen adsorption sites at the modified Pt nanoparticle surface. Adsorption peak currents increased with increasing the number of layers up to 16 bilayers, indicating the feasibility of nanoparticle charging via interparticle charge hopping and the accessibility of adsorption states within the thickness of the nanoparticle/polyelectrolyte multilayers. Despite similarity in hydrogen adsorption in the cyclic voltammorgrams in 1 M H2SO4, negative shifts in adsorption potentials were measured at the nanocrystallite Pt-polyelectrolyte multilayers relative to a polycrystalline bulk Pt surface. This potential shift is attributed to a kinetic limitation in the reductive hydrogen adsorption as a result of the Pt nanoparticle surface modification and the polyelectrolyte environment.

Absorption↗