Herbert H. Hooper

Swelling equilibria for ionized temperature‐sensitive gels in water and in aqueous salt solutions

Swelling equilibrium data in water and in aqueous NaCl solutions are presented for thermally sensitive N‐isopropylacrylamide (NIPA) hydrogels containing 0–4 mol % quaternized amine (positively ionizable) comonomer. We report the effect of gel charge and solution ionic strength on the temperature‐induced collapse of NIPA gels. Experimental swelling equilibria are compared with predictions based on a recently proposed oriented‐quasichemical model. This model has been shown previously to describe lower critical solution behavior in uncharged aqueous polymer solutions and gels (i.e., aqueous NIPA gel). We apply the model here to ionized NIPA gel. Semiquantative predictions are obtained for the effects of gel charge and solution ionic strength on temperature‐dependent swelling behavior.

Rapid, parallel separations of d1S80 alleles in a plastic microchannel chip.

We have performed fast, parallel separations of alleles of the D1S80 locus in a plastic, multi-channel chip, replicated from a microfabricated master and laminated with a plastic film. The array of 16 channels was filled with a replaceable sieving polymer, and a size-dependent, electrophoretic separation of the DNA fragments was performed in all channels in less than 10 min, representing a 30-fold increase in throughput compared to that on a single-capillary instrument. To detect the fragments in all 16 channels in parallel during the run, we designed and built a scanning, confocal, laser-induced fluorescence system. The electropherograms were then used to determine the sample genotype. To demonstrate the use of multiplexed, microchannel arrays for real-life samples, we amplified D1S80 alleles from genomic DNA extracted from whole blood and separated these alleles by electrophoresis in the plastic chip. Evaluation of the electrophoretic data showed that, using a 300- and a 1,000-base pair fragment as internal mobility markers, 83% of the alleles were assigned correctly, using the allele identification from a single capillary instrument as a reference. This work demonstrates that, with improvements in the microchannel electrophoresis system, it is feasible to perform rapid, parallel genotyping in mass-produced, inexpensive, disposable plastic devices for large-scale applications in medicine and the life sciences.

Mutual solubilities of water and hydrocarbons from an equation of state. Need for an unconventional mixing rule

Abstract For calculating mutual solubilities of water and hydrocarbons with an equation of state, none of the conventional mixing rules are satisfactory for engineering calculations. Based on recent experimental data, an unconventional modification is introduced into the usual quadratic mixing rule for attractive-energy parameter a ; this modification represents the well-studied hydrophobic effect. For the temperature range 20–200° C, quantitative description of mutual solubilities in binary systems is obtained with three binary parameters. Attempts to correlate these parameters with molecular properties were only partially successful.

Monte Carlo simulations of hydrophobic weak polyelectrolytes: Titration properties and pH‐induced structural transitions for polymers containing weak electrolytes

Monte Carlo simulation has been used to study titration and configurational properties of an isolated hydrophobic polymer containing weakly‐ionizable groups. Using a cubic lattice, simulations were performed in the grand canonical ensemble to include the effect of the local charge environment on the ionization of weak electrolyte segments. Properties were studied as a function of polymer hydrophobicity, fraction of ionizable segments, solution ionic strength, and pH. The polymer segments experienced three types of competing interaction: excluded volume, attractive nearest‐neighbor forces which account for the net balance of segment–segment, segment–solvent, and solvent–solvent interactions, and long‐range electrostatic forces between ionized segments, calculated with a screened Debye–Huckel potential. Simulations show that the model chain expands with chain ionization, which depends on solution pH. As the chain becomes increasingly charged, the ionization process becomes more difficult because of rising l...

Monte Carlo simulations of hydrophobic polyelectrolytes. Evidence for a structural transition in response to increasing chain ionization

Monte Carlo simulation has been used to study the configurational properties of a lattice‐model isolated polyelectrolyte with attractive segment–segment interaction potentials. This model provides a simple representation of a hydrophobic polyelectrolyte. Configurational properties were investigated as a function of chain ionization, Debye screening length, and segment–segment potential. For chains with highly attractive segment–segment potentials (i.e., hydrophobic chains), large, global changes in polymer dimensions were observed with increasing ionization. The transformation from a collapsed chain at low ionization to an expanded chain at high ionization becomes increasingly sharp (i.e., occurs over a smaller range of ionization) with increasing chain hydrophobicity. The ionization‐induced structural transitions for this model hydrophobic polyelectrolyte are analogous to pH‐induced transitions seen in real polyelectrolytes and gels. These studies suggest a simple explanation for such transitions based o...

Integrated capillary electrophoresis using glass and plastic chips for multiplexed DNA analysis

Micromachined devices made of plastic have been used for fast electrophoretic separations using short separation distances and high electric field strengths. Unlike their glass counterparts, plastic chips can be manufactured economically and in high volume. Analysis can be performed in single channels, as shown for DNA sequencing mixtures, or in channel arrays as demonstrated for the analysis of ds DNA fragments. Compared to slab gel electrophoresis and capillary electrophoresis, separations are extremely fast with a time-scale under 20 minutes for a sequence analysis and under 2 minutes for fragment analysis. Confocal laser- induced fluorescence provides a sensitive means of detection.

Multiplexed, Disposable, Plastic Microfluidic Systems for High-Throughput Applications

Low-cost, mass-produced, plastic microfluidic devices are being developed for a variety of microfluidic applications including DNA analysis, drug discovery, and clinical diagnostics. Plastic substrates with complex patterns of 10–100μm-sized channels are reproducibly formed against mold tools fabricated by micromachining techniques. These substrates are used to produce plastic devices on which reactions and high-efficiency electrophoretic separations of biomolecules have been achieved in timescales of seconds to minutes.

Plastic Microfluidic Systems for High-Throughput Genomic Analysis and Drug Screening

Genomic analysis and drug discovery depend increasingly on rapid, accurate analysis of large sets of sample and extensive compound collections at relatively low cost. By capitalizing on advances in microfabrication, genomics, combinatorial chemistry, and assay technologies, new analytical systems are expected to provide order-of-magnitude increases in analysis throughput along with comparable decreases in per-sample analysis costs. ACLARA’s single-use, plastic LabCard systems, which transport fluids between reservoirs and through interconnected microchannels using electrokinetic mechanisms, are intended to address these analytical needs. These devices take advantage of recent developments in microfluidic and microfabrication technologies to permit their application to DNA sequencing; genotyping and DNA fragment analysis, as well as pharmaceutical candidate screening, and preparing biological samples for analysis. In a parallel effort, ACLARA has developed a new class of reporter molecules that are particularly well suited to capillary electrophoretic analysis. These electrophoretic mobility tags, called eTag reporters, can be used to uniquely label multiplexed sets of oligonucleotide recognition probes or proteins, thereby permitting traditionally homogeneous biochemical reporter assays to be multiplexed for CE analysis. Biochemical multiplexing is key to achieving new thresholds in analytical throughput while maintaining economically viable formats in many application areas. ACLARA’s microfluidic, lab-on-a-chip concept promises to revolutionize chemical analysis, similar to the way miniaturization revolutionized computing, making tools continually smaller, more integrated, less expensive, and higher performing. Microfluidic devices are made up of interconnected networks of microchannels and tiny volume reservoirs in which all the processes required for single analyses may be miniaturized, integrated, and automated within a single substrate the size of a human hand or smaller. However, LabCard devices are more than tiny replicates of existing equipment. They are characterized by high speed, parallel analysis using designs devised to eliminate sample cross contamination while automating processes that are otherwise undesirably cumbersome at the macro laboratory scale. Electrophoresis is one of the most widely used analytical separation methodologies for life science research. Electrophoresis refers to the movement of a charged molecule under the influence of an electric field. Electrophoresis can be used to separate molecules that have different charge-to-mass ratios such as proteins; or, molecules that have similar charge-to-mass ratios but different masses such as DNA fragments. In recent years, the development of capillary electrophoresis (CE), which is performed in a fused silica capillary filled with a buffer or polymer solution, has increased the speed of analytical separations. Planar, microchannel devices offer further improvements over capillary electrophoresis. In general, both electrophoresis and electroosmosis occur when a high electric field is applied along a microchannel (Figure 1). In practice, these effects can be comparable in magnitude, in which case ions of one charge move rapidlyat velocities of millimeters per second-while those of opposite charge move backward or slowly forward, depending upon which of the two effects dominates. The amount of fixed charge on the inner surface of a channel can be controlled by pH, specific adsorption of charged species onto the surface, or surface chemical modification. Therefore, the contribution of electroosmosis (the pumping mechanism) can be tuned relative to electrophoresis (the separating mechanism). The capability to transport and separate exceptionally small liquid volumes with precise electrical control is a powerful tool, which is complemented by an additional benefit of using microchannels with micrometer cross-sections. While electrophoresis channels are of similar cross section in both capillaries and microchannel devices, the planar format of the microchannel devices enables structures more complex than a single, non-intersecting channel to be used. Two or more channels can intersect to

Molecular Thermodynamics of Aqueous Polymers and Gels

SUMMARY The phase behavior of aqueous polymer solutions and gels is often sensitive to prevailing conditions such as temperature, pH, ionic strength or solvent composition. For crosslinked polymer gels, this solution-sensitivity is indicated by large changes in gel volume in response to small changes in solution conditions. This chapter reviews recent work directed at developing a molecular-thermodynamic description of phase behavior in aqueous polymer systems. A theoretical description of phase equilibria correlates systematic experimental data obtained for model systems. Novel molecular-simulation studies of isolated polyelectrolytes provide detailed information on the relationship between expansion of polyelectrolytes in solution and pertinent parameters that characterize polymer and solution properties.