Stable Molecular Structures Research Articles

Proteinlike molecular architecture: Biomaterial applications for inducing cellular receptor binding and signal transduction

The development of biomaterials with desirable biocompatibility has presented a difficult challenge for tissue engineering researchers. First and foremost, materials themselves tend to be hydrophobic and/or thrombogenic in nature, and face compatibility problems upon implantation. To mediate this problem, researchers have attempted to graft proteins or protein fragments onto biomaterial surfaces to promote endothelial cell attachment and minimize thrombosis. We envisioned a novel approach, based on the capability of biomolecules to self-assemble into well-defined and intricate structures, for creating biomimetic biomaterials that promote cell adhesion and proliferation. One of the most intriguing self-assembly processes is the folding of peptide chains into native protein structures. We have developed a method for building proteinlike structural motifs that incorporate sequences of biological interest. A lipophilic moiety is attached onto an Nα-amino group of a peptide chain, resulting in a “peptide-amphiphile.” The alignment of amphiphilic compounds at the lipid-solvent interface is used to facilitate peptide alignment and structure initiation and propagation, while the lipophilic region adsorbs to hydrophobic surfaces. Peptide-amphiphiles containing potentially triple-helical or α-helical structural motifs have been synthesized. The resultant head group structures have been characterized by CD spectroscopy and found to be thermally stable over physiological temperature ranges. Triple-helical peptide-amphiphiles have been applied to studies of surface modification and cell receptor binding. Cell adhesion and spreading was promoted by triple-helical peptide-amphiphiles. Cellular interaction with the type IV collagen sequence α1(IV) 1263–1277 increased signal transduction, with both the time and level of induction dependent upon triple-helical conformation. Collectively, these results suggest that peptide-amphiphiles may be used to form stable molecular structures on biomaterial surfaces that promote cellular activities and improve biocompatibility. © 1998 John Wiley & Sons, Inc. Biopoly 47: 143–151, 1998

Ab Initio Characterization of Gaseous (HnP< >C)+ Species

Accurate ab initio G1 and G2 protocols have been used to characterize 14 (HnP< >C)+, with n = 1−4, species. We have predicted that the C-site protonation of the earlier characterized P< >C (2B1) species is preferred over the P-site by 1.73 eV at the G2 level. For the (H2P< >C)+ system, five stable molecular structures have been found for each of the singlet and triplet spin multiplicities. In particular, the (HP< >CH)+ singlet isomers do not present either biradicaloid character or P−C cross bonding, while both the (H2P< >C)+ and (P< >CH2)+ singlet molecules are almost pure biradical species with no P−C cross bonding. For every case the singlet state has been found to be more stable than the triplet. Finally, vibrational spectra of these species, which may help in their detection, are discussed.

Structural and vibrational study of 3-hydroxyflavone and 3-methoxyflavone

Abstract Most stable molecular structures of 3-hydroxyflavone and 3-methoxyflavone have been investigated by semiempirical calculations (AMI method) at the state of isolated molecule. For 3OHF, the comparison between X-ray diffraction data and calculated structural parameters shows a major modification in the inter-ring linkage with a rotation of the phenyl ring with regard to the rest of the molecule. This rotation of the B-ring is not observed in the 3OMeF but the orientation of the methoxy group changes with the physical state. The predictions about the conformational modifications with the physical state of these molecules have been confirmed by vibrational spectroscopy. For the 3OHF molecule, the comparison between the solid and solution Raman spectra shows that the 1200–1400 cm−1 spectral range is particularly affected, seeing that the inter-ring stretching vibration contributes to a great number of normal modes. 3OMeF Raman spectra are less perturbed by the change of physical state, only two small frequencies shifts are observed. In order to assign the most important perturbation in the spectra of the two molecules, the vibrational frequencies have been computed to determine the atoms and groups involved in each normal mode.

The Three-Center, Boron-Hydrogen-Metal, Coordinate Bond. Factors Influencing Bond Strength

Abstract The bridge bond is responsible for the formation of stable molecular structures such as that seen in Cl2Zn{B2H4 · 2P(CH3)3} and many related species. Factors involved in the stability of linkages are examined using the premise that the bond is a perturbed (polarized) sigma bond. The analysis relates the existence of these coordination compounds to the “agostic hydrogens” of organic chemistry.

Maximum hardness in P6 isomers

AbstractParr and Chattaraj proposed a principle of maximum hardness for stable molecular structures. Pearson and Palke used ab initio SCF MO calculations for ammonia and ethane to demonstrate the operation of the principle. In this paper, we present ab initio SCF MO results for five isomeric forms of the homoatomic P6 cluster as further support for the principle of maximum hardness. © 1994 John Wiley &amp; Sons, Inc.

Viewing the energy optimization of chemical models with computer animation

Computer animation is applied to a chemical situation which involves the energy optimization of molecular models. This technique has been used in conjunction with a large interactive chemical modelling system (AIMS) which performs the energy optimizations. The goal of energy optimization is to find more stable molecular structures by methodically altering the geometry to conform to a lower internal energy. Three types of optimizations are studied with this technique, each method employing its own assumptions, geometry manipulations and energy calculations. In each case the process is viewed after the display frames were computed in advance as the model geometry changed.