Based on the experimental data of scanning tunneling microscopy (STM), models of three-stranded braid-like DNAs composed by three kinds of base triplets AAA, TAT and GCA were constructed. We investigated the braid-like DNAs and their comparative triplex DNAs using a molecular mechanics method. The three strands of braid-like DNAs are proven equivalent, while those of triplex DNAs are not. The conformational energies for braid-like DNAs were found to be higher than that for triplex DNAs. Each period in one strand of braid-like DNA has 18 nucleotides, half of which are right-handed, while the other half are left-handed. Additional discussions concerning sugar puckering modes and the H-bonds are also included. q1999 Elsevier Science B.V. All rights reserved.

The interactions between fibrinogen ligands and platelet receptor aIIbb3 were studied under physiological conditions by atomic force microscopy (AFM). Two linear peptide sequences in fibrinogen, RGD and HHLGGAKQAGDV, play central roles in the regulation of hemostasis and thrombosis by facilitating adhesion and aggregation of platelets. In order to measure the interactions (i.e., debonding force), oligopeptides, GSSSGaaa, where aaa is -RGDSPA or -HHLGGAKQAGDV, were synthesized and grafted on to the surface of AFM probe tips. The interaction forces between a peptide-modified AFM probe tip and platelet surface were determined from pN to nN levels using AFM force measurements. Our results show that the zero kinetic off-rate, Koffo

Platinum nanoparticles with a narrow size distribution were prepared on highly orientated pyrolytic graphite (HOPG) surfaces by electrochemical deposition. The surfaces were characterized by atomic force microscopy operated in air in the tapping mode. Particle sizes between 20 and 100nm can be prepared by using dierent deposition times and overpotentials. The deposition appears to be controlled by interfacial electron transfer and diusion. Adding a supporting electrolyte will reduce non-faradiac charging resistance and the apparent deposition time scale. While isolated particles are formed at short deposition times, connected clusters of various morphologies can be observed at long deposition times. 1998 Elsevier Science B.V. All rights reserved.

Platinum crystal growth by electrochemical deposition on highly orientated pyrolytic graphite HOPG.surfaces was studied by atomic force microscopy AFM.operated in the tapping mode. In the absence of a supporting electrolyte, 2D Pt nanoparticles aggregated. After reaching a critical mobile particle size, subsequent growth of platinum morphology appeared to be dominated by surface diffusion of mobile Pt particles. In the presence of HClO4, 3D growth of deposited platinum appeared to be the dominant mechanism. Various morphologies of Pt electrodeposition on HOPG are the consequence of competing 3D growth and 2D particle growth. Anions specifically adsorbed on platinum may also play an important role in affecting 2D versus 3D crystal growth.

The conformational transitions (helix-coil transitions) of three hairpin triple helices, models 5’-(A-G), + 5’-(T-C),-T,-(hrC-T), [CY]. S-&G), + 5'-(T-h'C),-T,-(C-T), [YC] and 5'.(A-G), +5'-(T-h'C),-T,-(h'C-T), [YY], are characterized in this work by UV spectroscopy. Melting of these triplexes is biphasic. and the profiles are used to obtain the thermodynamic parameters. The thermodynamic properties of the hairpin triplex are T=19.45"C and i! H=293.I2 kJ molt'for CY, q=22.85"C and AH.,=256.63 kJ mol-for YC and 7; =28.47" C and AH,=234.68 kJ molt for YY at pH 4.4. Those of the duplex are 7=30.5O"C and AH,=427.09 kJ molt'for CY, T=32.96"C and AH,,=374.47 kJ molt'for YC and 7= 33.24"C and 1 H,=329.67 kJ mol-for YY at pH 4.4. The distinct transitions of triplex to duplex and duplex to single strands are analyzed win g the nearest-neighbor Ising model. Electrostatic effects on each conformation are also analyzed. 0.1997 Elsevier Science B.V.