No abstract

The sequence and conformational effects on the gas-phase acidities of peptides have been studied by using two pairs of isomeric cysteine-polyglycine peptides, CysGly 3,4 NH 2 and Gly 3,4 CysNH 2 . The extended Cooks kinetic method was employed to determine the gas-phase acidities using a triple quadrupole mass spectrometer with an electrospray ionization source. The ion activation was achieved via collision-induced dissociation experiments. The deprotonation enthalpies (⌬ acid H) were determined to be 323.9 Ϯ 2.5 kcal/mol (CysGly 3 NH 2 ), 319.2 Ϯ 2.3 kcal/mol (CysGly 4 NH 2 ), 333.8 Ϯ 2.1 kcal/mol (Gly 3 CysNH 2 ), and 321.9 Ϯ 2.8 kcal/mol (Gly 4 CysNH 2 ), respectively. The corresponding deprotonation entropies (⌬ acid S) of the peptides were estimated. The gas-phase acidities (⌬ acid G) were derived to be 318.4 Ϯ 2.5 kcal/mol (CysGly 3 NH 2 ), 314.9 Ϯ 2.3 kcal/mol (CysGly 4 NH 2 ), 327.5 Ϯ 2.1 kcal/mol (Gly 3 CysNH 2 ), and 317.4 Ϯ 2.8 kcal/mol (Gly 4 CysNH 2 ), respectively. Conformations and energetic information of the neutral and anionic peptides were calculated through simulated annealing (Tripos), geometry optimization (AM1), and single point energy calculations (B3LYP/6-31ϩG(d)), respectively. Both neutral and deprotonated peptides adopt many possible conformations of similar energies. All neutral peptides are mainly random coils. The two C-cysteine anionic peptides, Gly 3,4 (Cys-H) Ϫ NH 2 , are also random coils. The two N-cysteine anionic peptides, (Cys-H) Ϫ Gly 3,4 NH 2 , may exist in both random coils and stretched helices. The two N-cysteine peptides, CysGly 3 NH 2 and CysGly 4 NH 2 , are significantly more acidic than the corresponding C-terminal cysteine ones, Gly 3 CysNH 2 and Gly 4 CysNH 2 . The stronger acidities of the former may come from the greater stability of the thiolate anion resulting from the interaction with the helix-macrodipole, in addition to the hydrogen bonding interactions. (J Am Soc Mass Spectrom 2010, 21, 603-614)

No abstract

Sequence-specific polymers are the basis of the most promising approaches to bottom-up programmed assembly of nanoscale materials. Examples include artificial peptides and nucleic acids. Another class is oligo(N-functional glycine)s, also known as peptoids, which permit greater sidegroup diversity and conformational control, and can be easier to synthesize and purify. We have developed a set of peptoids that can be used to make inorganic nanoparticles more compatible with biological sequencespecific polymers so that they can be incorporated into nucleic acid or other biologically based nanostructures. Peptoids offer degrees of modularity, versatility, and predictability that equal or exceed other sequence-specific polymers, allowing for rational design of oligomers for a specific purpose. This degree of control will be essential to the development of arbitrarily designed nanoscale structures. 5 ACKNOWLEDGMENTS