Spacer molecule molecular interactions

Tunnelling electrons from a STM have also been used to excite photon emission from individual molecules, as has been demonstrated for Zn(II)-etioporphyrin I, adsorbed on an ultrathin alumina film (about 0.5 nm thick) grown on a NiAl(l 10) surface (Qiu et al, 2003). Such experiments have demonstrated the feasibility of fluorescence spectroscopy with submolecular precision, since hght emission is very sensitive to tip position inside the molecule. As mentioned before the oxide spacer serves to reduce the interaction between the molecule and the metal. The weakness of the molecule-substrate interaction is essential for the observation of STM-excited molecular fluorescence. 

Class 3 fluorophores linked, via a spacer or not, to a receptor. The design of such sensors, which are based on molecule or ion recognition by a receptor, requires special care in order to fulfil the criteria of affinity and selectivity. These aspects are relevant to the field of supramolecular chemistry. The changes in photophysical properties of the fluorophore upon interaction with the bound analyte are due to the perturbation by the latter of photoinduced processes such as electron transfer, charge transfer, energy transfer, excimer or exciplex formation or disappearance, etc. These aspects are relevant to the field of photophysics. In the case of ion recognition, the receptor is called an ionophore, and the whole molecular sensor is... 

Many experiments have been carried out by using this setup the stretching of single DNA molecules, the unfolding of RNA molecules or proteins, and the translocation of molecular motors (Fig. 2). Here we focus our attention on force experiments where mechanical work can be exerted on the molecule and nonequilibrium fluctuations are measured. The most successful studies along this line of research are the stretching of small domain molecules such as RNA [83] or protein motifs [84]. Small RNA domains consist of a few tens of nucleotides folded into a secondary structure that is further stabilized by tertiary interactions. Because an RNA molecule is too small to be manipulated with micron-sized beads, it has to be inserted between molecular handles. These act as polymer spacers that avoid nonspecific interactions between the bead and the molecule as well as the contact between the two beads. 

---