Peptide amphiphiles comprising a class of conjugates of peptide nucleic acid (PNA), natural amino acids, and n-alkanes were synthesized and studied. These PNA amphiphiles (PNAA) self-assemble at concentrations between 10 and 50 muM and exhibit water solubilities above 500 muM. The highly specific, stable DNA binding properties of PNAs are preserved by these modifications, with no significant differences between the thermodynamics of DNA binding of the PNA peptide and the PNA amphiphile. Proper solubilization of the PNAA required the attachment of (Lys)(2) and (Glu)(4) peptides to PNAs, which affected the PNAA-DNA duplex stability by electrostatic interactions between these charged amino acids and the negatively charged DNA backbone. These electrostatic effects did not affect the specificity of DNA binding, however. Electrostatic effects are screened with added salt, in a manner consistent with previous studies of PNA-DNA duplex stability and predictions from a charged-cylinder model for the duplex.
The majority of active pharmaceutical ingredients (APIs) and intermediates are isolated as solid products through crystallization, filtration, and drying. In some cases, filtration of APIs and intermediates exhibit long cycle times and may potentially become the bottleneck of the entire process train. Thus, early assessment of the cake properties is typically required to evaluate filtration performance prior to scale-up. This work presents two approaches to rapidly estimate the specific cake resistance through lab studies. Using the first approach, a first-order approximation of the specific cake resistance is estimated from data collected during a simple Buchner funnel filtration. The second approach provides a more accurate estimate from a more extensive filtration study incorporating dynamic pressure modulation (DPM, a single filtration with ascending pressures), improving the fidelity of filtration predictions. Results from several case studies demonstrate how a workflow combining these two approaches can be appropriately employed to assess the cake properties from laboratory filtrations for predictions of the pilot/manufacturing plant filtration performance.
We present a methodology to perform sequence-specific separations of oligonucleotides using peptide nucleic acids covalently linked to alkane chains, or "PNA amphiphiles (PNAAs)". The PNAA/DNA duplexes are discriminated from unbound DNA using hydrophobic interaction chromatography on a phenyl-substituted Sepharose column. Nearly quantitative recovery is achieved at concentrations of 50 microM after incubation of oligomers with a stoichiometric amount of PNAA for 1 min or so. The method exhibits high sequence specificity, selectivity, and resolution when applied to mixtures of various oligomers up to 60 base pairs in length.
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