Gold nanopariticles, formed by a controllable reduction of tetrachlorauric acid (HAuCl4) and subsequently coated by a self-assembled monolayer (SAM) of 3-mercaptopropionc acid (MPA) molecules, were used to investigate lateral single-electron tunneling (L-SET) using an ultrahigh vacuum four probe technique with gold electrodes on SiO2/Si (100) at low temperature 16 k, and were also used to test ultraviolet absorption. X-ray photoelec tron speclroscopy (XPS) has been used to confirm the gold particles coated by a SAM of MPA. Scanning tunneling microscopy (STM) imaging showed that the coated parlicles were dispersed in diameter size and spherical in shape. Experimental data from electrial transport measurements are in well agreement with semi-classical predietions for correlated L-SET and permit estimations of the electrical resistance and capacitance in a multi-tunnel systed composed of various tunnel junctions. Ultraviolet absorption spectra showed a small blue shift for the smaller particle, and the phenomena of blue shift caused by quantum size effect were also discussed.

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) ere performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tipmolecule distances.

Three triple-helical hairpin DNAs with substitution of 5-bromocytosine for cytosine in different strands have been investigated by molecular mechanics and Raman spectroscopy. The stability of the three substituted triplexes were compared with the corresponding unsubstituted triplex DNA by the molecular mechanics method. Base stacking interactions and strand]strand interactions of each triplex were analyzed in detail. Sugar conformations in these triplexes have been determined by both vibrational spectroscopy and molecular dynamics simulation. The hairpin triplexes with substitution occurring in strand I or both in strands I and III have the main sugar conformation of C39-endo, while the triplex with substitution occurring in strand III is the combination of C39-endo and C29-endo sugar conformation. Theoretical results are basically in agreement with experiments. Q 1999 Elsevier Science B.V. All rights reserved.

We describe in this paper the fabrication of two-and one-dimensional nano-structures with organic molecular beam epitaxy (OMBE) principle based on controlled self-assembly by using adsorbate-ubstrate and intermolecular interactions that are important in molecular fabrication. Cu(100) single crystal was used as substrate in fabricating molecular nanostructures. Scanning tunneling microscopy (STM) experiments confirmed that Zn-tetra-[3,5-di-t-butylphenyl]porphyrin molecules can be used to fabricate both monolayer and molecular wire on Cu(100) surface simultaneously, and the latter is arranged on the terrace edges. We herein briefly discuss the selectivity in terms of a mechanism in which the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the molecules interact with the surface.

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 Tm= 19.45°C and Δ Hvh, = 293. I2 kJ molt-’ for CY, Tm= 22.85°C and Δ Hvh, = 256.63 kJ mol- ’ for YC and Tm = 28.47 °Cand ΔHvh, = 234.68 kJ molt ’ for YY at pH 4.4. Those of the duplex are Tm = 30.5O°C and AH,, = 427.09 kJ molt-’ for CY, Tm= 32.96°C and Δ Hvh, = 374.47 kJ molt ’ for YC and Tm = 33.24°C and Δ Hvh, = 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.