Nanothermometry: From Microscopy to Thermal Treatments

Measuring temperature in cells and tissues remotely, with sufficient sensitivity, and in real time presents a new paradigm in engineering, chemistry and biology. Traditional sensors, such as contact thermometers, thermocouples, and electrodes, are too large to measure the temperature with subcellular resolution and are too invasive to measure the temperature in deep tissue. The new challenge requires novel approaches in designing biocompatible temperature sensors—nanothermometers—and innovative techniques for their measurements. In the last two decades, a variety of nanothermometers whose response reflected the thermal environment within a physiological temperature range have been identified as potential sensors. This review covers the principles and aspects of nanothermometer design driven by two emerging areas: single‐cell thermogenesis and image guided thermal treatments. The review highlights the current trends in nanothermometry illustrated with recent representative examples.     

Peptide immobilization on amine-terminated boron-doped diamond surfaces

This paper reports on the formation and characterization of semicarbazide termination on aminated boron-doped diamond (BDD) surfaces, and further preparation of peptide microarray through site-specific alpha-oxo semicarbazone ligation. Hydrogen-terminated BDD electrodes were first aminated using NH3 plasma treatment and then reacted with triphosgene and Fmoc-protected hydrazine to yield a protected semicarbazide termination. Subsequent deprotection and chemical reaction with glyoxylyl peptides led to the covalent immobilization of the peptides on the surface through site-specific ligation. The resulting surfaces were characterized using X-ray photoelectron spectroscopy (XPS) and fluorescence measurements.     

Two-dimensional arrays of amphiphilic Zn2+-cyclens for guided molecular recognition at interfaces

The sterically guided molecular recognition of nucleobases, phosphates, adenosine, and uridine nucleotides on Langmuir monolayers and Langmuir-Blodgett monolayers of amphiphilic mono- or bis(Zn2+-cyclen)s assembled on thiolated surfaces was investigated. The stepwise selective binding of metal ions, uracil, or phosphate by dicetyl cyclen monolayers with variously tuned structures at the air/water interface was corroborated by the measurements of the corresponding LB films deposited onto quartz crystals. Two types of recognition surfaces were fabricated from Zn2+-dicetyl cyclen. The surface covered with a complex preformed in the Langmuir monolayer was capable both of imide and of phosphate binding. The similar complex formed directly in an LB film on thiolated gold was inactive with respect to imide. The surface plasmon resonance measurements evidenced the stepwise assembly of complementary nucleotides on SAM/LB templates through consecutive phosphate-Zn2+-cyclen coordination. Base pairing between nucleotides resulted in a formation of A-U bilayers comprising two complementary monolayers. Finally, we report on SAM/LB patterns designed for divalent molecular recognition of uridine phosphate by amphiphilic bis(Zn2+-cyclen).     

Time-domain ab initio study of charge relaxation and recombination in dye-sensitized TiO2

In order to investigate the electron dynamics at the alizarin/I2-/TiO2 interface this study uses a novel state-of-the-art quantum-classical approach that combines time-dependent density functional theory with surface hopping in the Kohn-Sham basis. Representing the dye-sensitized semiconductor Gr?tzel cell with the I-/I3- mediator, the system addresses the problems of an organic/inorganic, molecule/bulk interface that are commonly encountered in molecular electronics, photovoltaics, and photoelectrochemistry. The processes studied include the relaxation of the injected electron inside the TiO2 conduction band (CB), the back electron transfer (ET) from TiO2 to alizarin, the ET from the surface to the electrolyte, and the regeneration of the neutral chromophore by ET from the electrolyte to alizarin. Developing a theoretical understanding of these processes is crucial for improving solar cell design and optimizing photovoltaic current and voltage. The simulations carried out for the entire system that contains many electronic states reproduce the experimental time scales and provide detailed insights into the ET dynamics. In particular, they demonstrate the differences between the optimized geometric and electronic structure of the system at 0 K and the experimentally relevant structure at ambient temperature. The relaxation of the injected electron inside the TiO2 CB, which affects the solar cell voltage, is shown to occur on a 100 fs time scale and occurs simultaneously with the electron delocalization into the semiconductor bulk. The transfer of the electron trapped at the surface to the ground state of alizarin proceeds on a 1 ps time scale and is facilitated by vibrational modes localized on alizarin. If the electrolyte mediator is capable of approaching the semiconductor surface, it can form a stable complex and short-circuit the cell by accepting the photoexcited electron on a subpicosecond time scale. The ET from TiO2 to both alizarin and the electrolyte diminishes the solar cell current. Finally, the simulations show that the electrolyte can efficiently regenerate the neutral chromophore. This is true even though the two species do not form a chemical bond and, therefore, the electronic coupling between them is weaker than in the TiO2-chromophore and TiO2-electrolyte donor-acceptor pairs. The chromophore-electrolyte coupling can occur both directly through space and indirectly through bonding to the semiconductor surface. The ET events involving the electrolyte are promoted primarily by the electrolyte vibrational modes.     

Kinetics of dissociation of molecular oxygen from a superoxorhodium(III) complex and reactivity of a macrocyclic rhodium(II) ion

The kinetics of disappearance of the superoxorhodium complex L2(H2O)RhOO2+ (L2 = meso-hexamethylcyclam) were determined in the presence of several oxidants (H2O2, (NH3)5CoBr2+, and IrCl62-) in both air-free and air-saturated aqueous solutions. Under air-free conditions, the reaction obeyed first-order kinetics. After the correction for the appropriate stoichiometric factors, the value of the rate constant kh was the same irrespective of the oxidant, kh = 2.18 (+/-0.37) x 10(-4) s(-1) at 25.0 degrees C in acidic solutions. The disappearance of L2(H2O)RhOO2+ was slower in the presence of O2. All the data suggest a sequence of reactions beginning with homolytic dissociation of O2 from L2(H2O)RhOO2+, followed by capture of the newly generated L2(H2O)Rh2+ by added oxidants in competition with O2. The equilibrium constant for O2 binding by L2(H2O)Rh2+ is 109-fold greater than that for the cobalt analogue. This difference is attributed to the lower reduction potential of the rhodium complex.     

Silver(I) and thallium(I) complexes of a PNP ligand and their utility as PNP transfer reagents

Silver(I) and thallium(I) complexes of a diarylamido-based PNP pincer ligand have been prepared and characterized. The silver complex [(PNP)Ag]2 exists as a dimer both in solution and in the solid state and is stable under an ambient atmosphere. Thallium complex (PNP)Tl is, however, monomeric and acutely sensitive to moisture and air. Both reagents serve to transfer PNP into the coordination sphere of divalent nickel, palladium, and platinum. [(PNP)Ag]2 is able to effect PNP transfer in air, but the transfer to nickel(II) is less efficient than that with the thallium(I) analogue.     

Density functionals that are one- and two- are not always many-electron self-interaction-free, as shown for H2+, He2+, LiH+, and Ne2+

The common density functionals for the exchange-correlation energy make serious self-interaction errors in the molecular dissociation limit when real or spurious noninteger electron numbers N are found on the dissociation products. An "M-electron self-interaction-free" functional for positive integer M is one that produces a realistic linear variation of total energy with N in the range of M-12. Thus all these SIC's produce an exact binding energy curve for H2+, and an accurate one for He2+, but only the unscaled Perdew-Zunger SIC produces an accurate one for Ne2+, where there are more than two electrons on each fragment Ne+0.5. We also discuss LiH+, which is relatively free from self-interaction errors. We suggest that the ability of the original and unscaled Perdew-Zunger SIC to be nearly M-electron self-interaction-free for atoms of all M stems in part from its formal resemblance to the Hartree-Fock theory, with which it shares a sum rule on the exchange-correlation hole of an open system.     

Conformational dependence of intramolecular vibrational redistribution in methanol

Previous state-selected spectra of methanol in the 5nu(1) OH stretch overtone region [O. V. Boyarkin, T. R. Rizzo, and D. S. Perry, J. Chem. Phys. 110, 11346 (1999)] revealed a structure indicating an intramolecular vibrational redistribution on three time scales. Whereas in that work, methanol in the 5nu(1) bright state was prepared close to the staggered conformation, methanol in the "partially eclipsed" conformation is prepared here by double resonance excitation through a torsionally excited intermediate state. The excited molecules are detected by infrared laser assisted photofragment spectroscopy. In partially eclipsed methanol, the strong coupling of the nu(1) OH stretch to the nu(2) CH stretch becomes weaker, but the coupling responsible for the widths of the narrowest features becomes stronger.