The static absorption and ultrafast solvation dynamics of a tricarbocyanine dye IR144 at the silica/acetonitrile and the silica/butanol interfaces were investigated by using steady-state second harmonic generation (SHG) spectroscopy and pump-probe time-resolved SHG (TRSHG) experiments. At both interfaces, the peak wavelength for the S 0 f S 1 transition of adsorbed IR144 is significantly red-shifted with respect to the maximum absorption wavelength in the corresponding bulk solvent. Because IR144 is negatively solvatochromic, this shift is indicative of a smaller polarity at the interface. A theoretical model of TRSHG is discussed which allows extraction of the solvation dynamics correlation function from the time dependence of the TRSHG signal measured in the pump-probe experiment at a chosen probe wavelength. The time constant for the diffusive component of solvation at the silica/acetonitrile interface was found to be 1.05 ( 0.14 ps. It is somewhat shorter, although of the same order of magnitude, than the time constant for the diffusive solvation in bulk acetonitrile, 2.23 ps. At the silica/butanol interface, a time constant of 1.20 ( 0.15 ps was extracted, whereas in the bulk butanol, the corresponding diffusive solvation is biexponential with times of 3.5 and 33 ps. † Part of the special issue "Howard Reiss Festschrift".
The attachment of cells onto solid supports is fundamental in the development of advanced biosensors or biochips. In this work, we characterize cortical neuron adhesion, growth, and distribution of an adhesive layer, depending on the molecular structure and composition . Neuronal networks are successfully grown on amino-terminated alkanethiol self-assembled monolayer (SAM) on a gold substrate without adhesion protein interfaces. Neuron adhesion efficiency was studied for amino-terminated, carboxy-terminated, and 1:1 mixed alkanethiol SAMs deposited on gold substrates. Atomic force microscopy and X-ray photoelectron spectroscopy were used to measure the roughness of gold substrate and thickness of SAM monolayers. Conformational ordering and ionic content of SAMs were characterized by vibrational sum frequency generation (VSFG) spectroscopy. Only pure amino-terminated SAMs provide efficient neuronal cell attachment. Ordering of the terminal amino groups does not affect efficiency of neuron adhesion. VSFG analysis shows that ordering of the terminal groups improves with decreasing surface roughness; however the number of gauche defects in alkane chains is independent of surface roughness. We monitor partial dissociation of carboxy groups in mixed SAMs that implies formation of NH3+ neighbors and appearance of catanionic structure. Such catanionic environment proved inefficient for neuron adhesion. Surface roughness of metal within the 0.7-2 nm range has little effect on the efficiency of neuron adhesion. This approach can be used to create new methods that help map structure-property relationships of biohybrid systems.
Solid-state reactions of F atoms with ethene molecules were initiated by UV photolysis of dilute solutions of F 2 and C 2 H 4 in solid Ar. Products stabilized in the matrix were detected by infrared spectroscopy. Experiments were conducted at different temperatures in order to distinguish reactions in matrix-isolated F 2 -C 2 H 4 complexes (at 16 K) from reactions of diffusing thermal F atoms (at 26 K). Comparison with the kinetic EPR data (Benderskii, V. A. et al. MendeleeV Commun. 1995, 6, 245) permitted the identification of the infrared spectrum of the β-fluoroethyl radical, which is the main product of the F + C 2 H 4 reaction. Frequencies and absolute absorption intensities of the eight strongest infrared bands of β-C 2 H 4 F are reported. Photolysis of isolated F 2 -C 2 H 4 complexes forms the closed-shell products C 2 H 3 F-HF and trans-and gauche-1,2-C 2 H 4 F 2 with relative yields 0.6:0.2:0.2. Successive addition of two thermal F atoms to an isolated C 2 H 4 molecule forms only the two conformers of 1,2-C 2 H 4 F 2 . The difference between product branching ratios of the latter reaction and the direct photoinduced reaction of F 2 -C 2 H 4 complexes is qualitatively explained by the difference in size of the reaction cages and excess energies of the vibrationally excited intermediate (C 2 H 4 F 2 )*.
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