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Noncovalent interaction of methylene blue dye cation (MB + ) with single walled carbon nanotubes (CNT) is characterized by molecular dynamics (MD) simulation, quantum chemical calculations, and laser desorption/ionization (LDI) mass spectrometry. The MD simulation of the (MB + ) n −CNT (n = 1−10) complexes in water demonstrates that the MB + cations are adsorbed on the nanotube surface in the monomeric form. MD reveals both parallel and perpendicular orientations of the MB + tricyclic plane in relation to the long axis of CNT when placed in the water environment. The interaction energy between the components of the complex in the perpendicular conformation, as determined by quantum chemical calculations at the DFT/M05-2X/6-31++G(d,p) level of theory, explains why the bending of the MB + cation at the sulfur atom weakens the π-system of bonds and allows for the perpendicular orientation to occur. It is also found that the adsorbed MB + induces positive electrostatic potential around the adjacent semicylindrical segment of the nanotube. The mainly monomolecular adsorption of the MB + cations at the CNT surface leads to the absence in the LDI mass spectra of (MB + ) n −CNT of features corresponding to products of the reduction of MB + commonly observed in the LDI mass spectra of crystalline dyes.

Frozen solutions of a cryoprotector, glycerol, in water were studied by low temperature fast-atom bombardment mass spectrometry in the temperature range from -196" to 0 "C. Strong dependence of the mass spectral pattern on the water-glycerol ratio and temperature of the sample was observed. The evolution of mass spectra of the frozen 2000: 1 water-glycerol mixture with increase of the sample temperature is reproducible: in the lower portion of the temperature range (-196" to -120°C) the spectra contain a set of cluster ions, (H20),H+, (n = 1-15), characteristic of pure water; then the spectra show a superposition of peaks due to water clusters and glycerol itself, the latter with characteristic changes with temperature rise: degraded "peak at every mass" pattern in the -120" to -80 "C range followed by a build-up of glycerol clusters, G,,H+, (n = 1-3) in the -80 "C to -55°C range. At approximately -55°C to -50°C a sublimation of water component occurs, detected by [H20]+' ion, and the remainder of the spectral pattern coincides with that of pure glycerol up to ambient temperature. Mixed water-glycerol clusters were never observed. An explanation of such spectral behavior is proposed based on ideas about the morphology of the frozen solutions, characterized by water microcrystallites separated by eutectic channels containing cryoprotector. The independent sputtering of the two substances from different domains of the frozen sample surface is discussed.The freezing of a sample allows one to obtain secondary-emission mass spectra from substances which exist in the gaseous or liquid state at room temperature.'-'' The overwhelming majority of low temperature mass spectrometric studies carried out to date have been devoted to individual substances. Whereas the low temperature technique seemed to open up exciting possibilities for mass spectrometric studies of solutions, especially water solutions of both inorganic and organic compound^,^^-'^ the recent interest in the electrospray method" which provides great scope for studies of different types of solutions under nearly ambient conditions, have diverted the interest from frozen samples. While, in the above-listed papers the freezing of liquids was used simply to produce a suitable sample, one of the specific fields of application of low temperatures is cryobiology, and connected with it the study of the freezing of water-cryoprotector mixtures for the cryopreservation of biological material. It is known that one of the reasons for damage to cells and tissues during freezing is the crystallization of water, and the main purpose of cryoprotectors is to prevent the formation of large water crystals and to change the temperature parameters of the freezing process. Glycerol, widely used as a matrix in fast-atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS), is also a widely used cryoprotector. A large set of mass spectrometric information concerning the properties of glycer01~-~.'~ and over a wide temperature range has already been acquired. In the pr...