We discuss the use of fluorescence correlation spectroscopy (FCS) to study the diffusion of single dye-labeled polymer chains in organic solvents. Monodisperse batches of polystyrenes labeled with a single Rhodamine B molecule have been synthesized via anionic polymerization of styrene and ethylene oxide end-capping followed by a polymer analogous coupling reaction. MALDI-ToF mass spectrometry is used to characterize the resulting material. A commercial FCS system has been modified to permit FCS measurements in volatile organic solvents. FCS was used to determine the molecular weight dependence of the diffusion coefficient of 10 nM solutions of end-labeled polystyrenes in toluene. The data are utilized to establish a calibration procedure for FCS measurements in organic solvents.

Raman spectra of solid nitrogen were studied from 8 to 54 GPa at room temperature. Between 8 and 16 GPa three out of four possible lattice modes of the δ–N2 phase were observed. Above 16 GPa up to eight lattice modes can be distinguished, seven of which correspond to lattice modes observed at 15 K in the ε–N2 phase. Branching of existing lattice and vibronic modes above 20 GPa and above 40 GPa indicate additional slight structural modifications. The observed pressure shift of vibrons of the 14N–15N isotopic species appears to favor factor group effects instead of bond weakening to be responsible for the downward shift of one vibronic mode at higher pressures.

We report a kinetic and thermodynamic analysis of interactions between ssDNA and replication protein A (RPA) using surface plasmon resonance (SPR) and fluorescence correlation spectroscopy (FCS) at variable temperature. The two methods yield different values for the Gibbs free energy but nearly the same value for the reaction enthalpy of ssDNA-RPA complex formation. The Gibbs free energy was determined by SPR and FCS to be -62.6 and -54.7 kJ/mol, respectively. The values for the reaction enthalpy are -64.4 and -66.5 kJ/mol. It is concluded that the difference in Gibbs free energy measured by the two methods is due to different reaction entropies. The entropic contribution to the free energy at 25 degrees C is -1.8 kJ/mol for SPR and -11.8 kJ/mol for FCS. In SPR, the reaction is restricted to two dimensions because of immobilization of the DNA molecules to the sensor surface. In contrast, FCS is able to follow complex formation without spatial restrictions. In consequence, the reaction entropy determined from SPR experiments is lower than for FCS experiments.

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The molecular crystals naphthalene-d8 and anthracene-d10 have been investigated at pressures in the range of ambient to 0.8 GPa and simultaneously at temperatures from room temperature down to 15 K. The accurate frequency measurement of the lattice modes allowed the determination of a small temperature dependence in some of the mode-Grüneisen parameters. A qualitative comparison of the temperature dependence with theory is made.

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