The contour length of DNA fragments, deposited and imaged on mica under buffer, was measured as a function of deposition temperature. Extended DNA molecules (on Ni-and silane-treated surfaces) contract rapidly with falling temperature, approaching the contour length of A-DNA at 2℃. The contraction is not unique to a specific sequence and does not occur in solution at 2℃ or on a surface at 25℃, indicating that it arises from a combination of low temperature and surface contact. It is probably a consequence of reduced water activity at a cold surface.

Condensation of DNA by multivalent cations can provide useful insights into the physical factors governing the folding and packaging of DNA in vivo. In this work, local ordered structures of spermidine-DNA complexes prepared from different DNA concentrations have been examined by using atomic force microscopy (AFM) and polarizing microscopy (PM). Two types (I and II) of DNA condensates, significantly different in sizes, were observed. It was found that for extremely dilute solutions (DNA concentrations around 1ng/ml or below), the DNA molecules would collapse into toroidal structures with a volume equivalent to a single l-DNA (type I). In relatively dilute solutions (DNA concentrations between 1 and 10ng/ml), a significantly larger structure of multimolecular toroids (circular and elliptical, type II) were formed, which were constructed by many fine particles. Measurements show that the average diameter of these fine particles was similar to the outer diameter of the monomolecular toroids observed in extremely dilute solutions, and the thickness of the multimolecular toroids had a distribution of multi-layers with height increments of 11 nm, indicating that the multimolecular toroidal structures have lamellar characteristics. Moreover, by enriching the DNA-spermidine complexes in very diluted solution, branch-like structures constructed by subunits were observed by using AFM. The analysis of the pellets in polarizing microscopy reveals a liquid-crystal-like pattern. These observations suggest that DNA-spermidine condensation could have multiple stages, which are very sensitive to the DNA and spermidine concentrations.

This article reviews the current and future applications of micro reactors in the field of chemistry, biochemistry and drug discovery. The fabrication and physical characterisation of micro reactors, together with details of their use and operation is described. Liquid and gas phase reactions have been used to illustrate the advantages of performing chemical reactions in micro reactors. A brief evaluation of the possible advantages that micro fabrication could offer in developing biological applications, based on miniaturized devices is also presented.

Rhodamine B-ethylenediamine-cyclodextrins (RhB-βCDen) and rhodamine B-cyclodextrins (RhB-βCD) can form inclusive complexes with many guest molecules, a reaction which can be used as a nucleic acid probe. In this paper, the most stable conformations of RhB-βCDen and RhB-βCD have been determined by fluorescence experiments and analyzed by molecular modeling simulation. The interaction between RhB-βCDen and two guest molecules, 1-borneol and cyclohexanol, has also been investigated. The results showed that RhB-βCDen has a stronger interaction with 1-borneol than with cyclohexanol. Borneol could push the three aromatic-rings of rhodamine B out of the CD cavity, while the cyclohexanol could not. The interactive sites of host andguest are also presented.