This paper describes two methods to synthesize bottlebrush polymers with molecular weights from 1 million to over 60 million g mol-1 using Grubbs' first and second generation catalysts. In the first method, macromonomers of poly(l-lactide) were synthesized using tin(II) 2-ethylhexanoate and terminated on one end with a norbornyl group. Grubbs' first generation catalyst polymerized macromonomers with one poly(l-lactide) chain per norbornene, and Grubbs' second generation catalyst polymerized macromonomers with two poly(l-lactide) chains per norbornene. The predicted and measured molecular weights closely matched each other, and the polydispersities of the bottlebrush polymers were between 1.05 and 1.39. These examples are the first where Grubbs' second generation catalyst can be considered living for ROMP. In the second method, the backbone was polymerized first, and polylactide arms with molecular weights from 15 000 to 50 000 g mol-1 were polymerized from the backbone. Polymers that were shaped as spheres or rigid rods were synthesized. The polymers were analyzed by GPC, MALLS, QELS, and 1H NMR.

Nanoparticles, including multiwalled carbon nanotubes (MWNTs), strongly absorb near-infrared (nIR) radiation and efficiently convert absorbed energy to released heat which can be used for localized hyperthermia applications. We demonstrate for the first time that DNA-encasement increases heat emission following nIR irradiation of MWNTs, and DNA-encased MWNTs can be used to safely eradicate a tumor mass in vivo. Upon irradiation of DNA-encased MWNTs, heat is generated with a linear dependence on irradiation time and laser power. DNA-encasement resulted in a 3-fold reduction in the concentration of MWNTs required to impart a 10 °C temperature increase in bulk solution temperature. A single treatment consisting of intratumoral injection of MWNTs (100 μL of a 500 μg/mL solution) followed by laser irradiation at 1064 nm, 2.5 W/cm2 completely eradicated PC3 xenograft tumors in 8/8 (100%) of nude mice. Tumors that received only MWNT injection or laser irradiation showed growth rates indistinguishable from nontreated control tumors. Nonmalignant tissues displayed no long-term damage from treatment. The results demonstrate that DNA-encased MWNTs are more efficient at converting nIR irradiation into heat compared to nonencased MWNTs and that DNA-encased MWNTs can be used safely and effectively for the selective thermal ablation of malignant tissue in vivo.

This article reports the synthesis of comb block copolymers with backbones from exo-norbornene esters via ring-opening metathesis polymerizations (ROMP) and arms composed of polystyrene and polylactide. These polymers represent an exciting new architecture of polymers that have applications in the fabrication of photonic materials and nanofluidic systems. The living polymerization of block copolymers by ROMP with degrees of polymerization up to 2000 units and polydispersities less than 1.2 are described. This result is important as it extends the range of block copolymers that can be synthesized by ROMP to include those with high molecular weights. Comb block copolymers were grown from these block copolymers as they displayed initiators for the ring-opening polymerization of lactide and the atom transfer radical polymerization of styrene. Comb block copolymers with polystyrene and polylactide arms were synthesized with molecular weights up to 63 000 000 g mol -1 . The polystyrene arms had narrow polydispersities and molecular weights in excess of 10 000 g mol -1 ; this result showed that the polymerization of styrene was well controlled. The sizes and shapes of these comb polymers were characterized by multiangle laser light scattering and scanning probe microscopy and demonstrated that some of these polymers were shaped as rigid rods with lengths in excess of 300 nm. To demonstrate their potential as photonic materials, an example of a comb block copolymer was assembled in the solid state with domain sizes exceeding 100 nm and characterized by scanning electron microscopy.

The CO2ν3 asymmetric stretching mode is established as a vibrational chromophore for ultrafast two-dimensional infrared (2D-IR) spectroscopic studies of local structure and dynamics in ionic liquids, which are of interest for carbon capture applications. CO2 is dissolved in a series of 1-butyl-3-methylimidazolium-based ionic liquids ([C4C1im][X], where [X](-) is the anion from the series hexafluorophosphate (PF6 (-)), tetrafluoroborate (BF4 (-)), bis-(trifluoromethyl)sulfonylimide (Tf2N(-)), triflate (TfO(-)), trifluoroacetate (TFA(-)), dicyanamide (DCA(-)), and thiocyanate (SCN(-))). In the ionic liquids studied, the ν3 center frequency is sensitive to the local solvation environment and reports on the timescales for local structural relaxation. Density functional theory calculations predict charge transfer from the anion to the CO2 and from CO2 to the cation. The charge transfer drives geometrical distortion of CO2, which in turn changes the ν3 frequency. The observed structural relaxation timescales vary by up to an order of magnitude between ionic liquids. Shoulders in the 2D-IR spectra arise from anharmonic coupling of the ν2 and ν3 normal modes of CO2. Thermal fluctuations in the ν2 population stochastically modulate the ν3 frequency and generate dynamic cross-peaks. These timescales are attributed to the breakup of ion cages that create a well-defined local environment for CO2. The results suggest that the picosecond dynamics of CO2 are gated by local diffusion of anions and cations.

The potential for femtosecond to picosecond time-scale motions to influence the rate of the intrinsic chemical step in enzymecatalyzed reactions is a source of significant controversy. Among the central challenges in resolving this controversy is the difficulty of experimentally characterizing thermally activated motions at this time scale in functionally relevant enzyme complexes. We report a series of measurements to address this problem using twodimensional infrared spectroscopy to characterize the time scales of active-site motions in complexes of formate dehydrogenase with the transition-state-analog inhibitor azide (N − 3 ). We observe that the frequency-frequency time correlation functions (FFCF) for the ternary complexes with NAD þ and NADH decay completely with slow time constants of 3.2 ps and 4.6 ps, respectively. This result suggests that in the vicinity of the transition state, the active-site enzyme structure samples a narrow and relatively rigid conformational distribution indicating that the transition-state structure is well organized for the reaction. In contrast, for the binary complex, we observe a significant static contribution to the FFCF similar to what is seen in other enzymes, indicating the presence of the slow motions that occur on time scales longer than our measurement window. 2D IR spectroscopy | enzyme dynamicsT he functional role of protein motions at the femtosecond to picosecond time scale is a hotly debated topic in enzymology. Although such a role could be general in nature, many experimental (1-10) and theoretical (11-23) studies of enzymecatalyzed hydrogen transfers have invoked protein motions at this time scale to explain anomalous kinetic isotope effects (KIE) and their temperature dependence. These studies result in the development of theoretical models, often referred to as Marcus-like models, in which the environmental reorganization that precedes the hydrogen-tunneling event has evolved to optimize the conformation of the transition state for tunneling (1,7,24). Fig. 1 illustrates the physical picture underlying such models. Heavy atom motions along the reorganization coordinate carry the system to a point where the donor and acceptor wells in the double-well hydrogen atom potential are degenerate and tunneling can proceed. At this position, the donor-acceptor distance and its fluctuations determine the tunneling probability. Mathematically, the rate constant for hydrogen transfer in these models is given by expressions of the form where C is the fraction of reactive complexes, the first exponential, in analogy with the Marcus theory for electron transfer, reflects the reorganization of the heavy atoms that modulates the relative energies of the reactants and the products to minimize the energy defect between the zero-point levels of the donor and acceptor wells. ΔG°is the driving force for the reaction, and λ is the reorganization energy. The second exponential gives the overlap between the donor and acceptor wave functions as a function of the donor-acceptor distan...