The effect of polarization on multiple hydrogen-bond formation in models of self-assembling materials.

We report density functional theory calculations at the B3LYP/D95(d,p) level on several different cyclic H-bonding dimers, where the monomers of each are connected by a pair of N-H···O=C H-bonding interactions, and the H-bonding donors and acceptors on each monomer are separated by polarizable spacers. Depending on the structures, the individual H-bonds vary in strength (enthalpy) by over a factor of four, from 2.41 to 10.99 kcal/mol. We attribute most of the variation in interaction energies to differences in the extent of polarization due to each of the H-bonds, which can either combine constructively or destructively. The dipole-dipole interactions between the pair of H-bonds also contribute somewhat to the relative stabilities. The relevance of these results to the design of self-assembling materials is discussed.

Through hydrogen-bond vibrational coupling in hydrogen-bonding chains of 4-pyridones with implications for peptide amide I absorptions: density functional theory compared with transition dipole coupling.

We present B3LYP/D95** calculations on the C=O and N-H couplings in H-bonded chains of 4-pyridones. 14C-substitutions are used to decouple various vibrations for purposes of illustration. The coupled C=O vibrations bear analogy to the amide I bands of proteins and peptides. The coupling of the C=O's occurs primarily via the cooperative H-bonds rather than transition dipole coupling (TDC), as demonstrated by the fact that (1) the couplings are greater than previously reported for similar studies on formamides despite the larger distance between the C=O's in the pyridone chains (TDC coupling decreases with distance) and (2) the red shifts (also greater than for formamides) can be attributed to the changes in the geometries (particularly the C=O bond lengths) of the individual 4-pyridones in the H-bonding chains induced by the H-bonds and resulting polarization of the monomers.

Cooperative 4-pyridone H-bonds with extraordinary stability. A DFT molecular orbital study.

The N-H...O H-bonding enthalpy between 4-pyridones connected in a chain of H-bonds can achieve 23 kcal/mol for the most central H-bonds, while that between two 4-pyridones is 9.90 kcal/mol based upon DFT calculations on the counterpoise-corrected potential energy surfaces. That the range of enthalpies for N-H...O H-bonds can vary from as little as 2 to as much 23 kcal/mol depends primarily upon the polarizability of whatever internally connects the N-H and C=O within the H-bonding molecule, which are two parallel -C=C- entities in 4-pyridone. The contribution of covalent or charge-transfer interactions between the pi-systems of adjacent 4-pyridones is small.

Au nanocrystal growth on nanotubes controlled by conformations and charges of sequenced peptide templates.

A new biological approach to fabricate Au nanowires was examined by using sequenced peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled on nanotubes, and the biological recognition of the sequenced peptide selectively trapped Au ions for the nucleation of Au nanocrystals. After Au ions were reduced, highly monodisperse Au nanocrystals were grown on nanotubes. The conformations and the charge distributions of the histidine-rich peptide, determined by pH and Au ion concentration in the growth solution, control the size and the packing density of Au nanocrystals. The diameter of Au nanocrystal was limited by the spacing between the neighboring histidine-rich peptides on nanotubes. A series of TEM images of Au nanocrystals on nanotubes in the shorter Au ion incubation time periods reveal that Au nanocrystals grow inside the nanotubes first and then cover the outer surfaces of nanotubes. Therefore, multiple materials will be coated inside and outside the nanotubes respectively by controlling doping ion concentrations and their deposition sequences. It should be noted that metallic nanocrystals in diameter around 6 nm are in the size domain to observe a significant conductivity change by changing the packing density, and therefore this system may be developed into a conductivity-tunable building block.

Au nanowire fabrication from sequenced histidine-rich peptide.

A new biological approach to fabricate Au nanowires was examined by using sequenced histidine-rich peptide nanowires as templates. The sequenced histidine-rich peptide molecules were assembled as nanowires, and the biological recognition of the sequenced peptide toward Au lead to efficient Au coating on the nanowires. Monodisperse Au nanocrystals were uniformly coated on the histidine peptide nanowires with the high-density coverage, and the crystalline phases of the Au nanocrystals were observed as (111) and (220). The uniformity of the Au coating on the nanowires without contamination of precipitated Au aggregates is advantageous for the fabrication of electronics and sensor devices when the nanowires are used as the building blocks. We believe this simple metal nanowire fabrication method can be applied to various metals and semiconductors with peptides whose sequences are known to mineralize specific ions.

Attachment of ferrocene nanotubes on beta-cyclodextrin self-assembled monolayers with molecular recognitions.

Ferrocene nanotubes were fabricated by binding carboxylic acid-derivatized ferrocenes onto template peptide nanotubes via hydrogen bonding. When these ferrocene-functionalized nanotubes were incubated with beta-cyclodextrin (beta-CD) self-assembled monolayers (SAMs) coated on patterned Au substrates in solution, the ferrocene nanotubes recognized and attached onto the beta-CD SAMs via host-guest molecular recognition. The ferrocene nanotubes were also observed to recognize the certain cavity size of CD. The attachment/detachment of nanotubes on the beta-CD SAMs was controlled electrochemically by tuning the redox states of ferrocene nanotubes. This electric field-responsive building block may be applied to build nanometer-sized switching components in electronics and sensors.