N-Heterocyclic Carbenes in Late Transition Metal Catalysis

Stimuli-reponsive polymers and their bioconjugates

Thermosensitive sol-gel reversible hydrogels.

Interest in thermoresponsive polymers has steadily grown over many decades, and a great deal of work has been dedicated to developing temperature sensitive macromolecules that can be crafted into new smart materials. However, the overwhelming majority of previously reported temperature-responsive polymers are based on poly(N-isopropylacrylamide) (PNIPAM), despite the fact that a wide range of other thermoresponsive polymers have demonstrated similar promise for the preparation of adaptive materials. Herein, we aim to highlight recent results that involve thermoresponsive systems that have not yet been as fully considered. Many of these (co)polymers represent clear opportunities for advancements in emerging biomedical and materials fields due to their increased biocompatibility and tuneable response. By highlighting recent examples of newly developed thermoresponsive polymer systems, we hope to promote the development of new generations of smart materials.

New directions in thermoresponsive polymers.

Intracellular temperature mapping has not previously been achieved. Now, a fluorescent polymeric thermometer has been developed that can be used in combination with fluorescence-lifetime imaging microscopy to allow thermometry with spatial and temperature resolutions of 200 nm and 0.18–0.58 ° C.

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Intracellular temperature mapping with a fluorescent polymeric thermometer and fluorescence lifetime imaging microscopy

Coil−globule transition of poly(N-isopropylacrylamide) (PIPA), followed by intermolecular association in H2O and D2O, was investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of the solutions were measured as a function of temperature, and spectral changes induced by the transition were observed. The intensities of the difference IR bands due to the vibrational modes of isopropyl and amide groups critically increased at the lower critical solution temperature (LCST). Heating of the PIPA solutions above the LCST led shifts of the amide II, C−H-stretching, and C−H-bending bands to lower wavenumbers during a shift of the amide I band to a higher wavenumber. The amide I band of the PIPA observed below the LCST could be fitted with a single component centered at 1625 cm-1, whereas two components (1625 and 1650 cm-1) were necessary to fit the band above the LCST. These components may be assigned to the CO group which is bound to water molecules as the solvent (1625 cm-1) and to the N−H in ...

Change in Hydration State during the Coil−Globule Transition of Aqueous Solutions of Poly(N-isopropylacrylamide) as Evidenced by FTIR Spectroscopy†

Phase transitions of poly(N-n-propylacrylamide) (PnPA), poly(N-isopropylacrylamide) (PiPA), and poly(N-cyclopropylacrylamide) (PcPA) in H2O and D2O were investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of these solutions were measured as a function of temperature (T) both in the heating and cooling processes. Subtraction of a spectrum at starting temperature (T0) from a spectrum at T gives an IR difference spectrum (ΔAT-T0). The magnitudes of ΔAT-T0 for IR absorption bands attributable to the alkyl and amide groups of these polymers critically increased at their lower critical solution temperatures (LCSTs). Redshifts of the amide II, C−H stretching, and C−H deformation bands were observed during the coil-to-globule transitions of these polymers. The amide I‘ bands of N-deuterated amide groups (−COND−) in PnPA and PiPA measured below their LCSTs could be fitted with single Gaussian components centered at 1630 and 1625 cm-1, respectively. In contrast, two components were observed i...

Changes in the Hydration States of Poly(N-alkylacrylamide)s during Their Phase Transitions in Water Observed by FTIR Spectroscopy†

Phase transitions of poly(N-vinylcaprolactam) (PVCL) and poly(N-vinylpyrrolidone) (PVPy) in H2O and D2O were investigated by turbidimetry, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy The phase diagram of PVCL solution is binodal with a lower critical solution temperature (LCST) of 325 °C and a critical concentration of about 5 wt % PVPy also undergoes a phase separation around 30 °C in aqueous 15 M KF solution The IR spectra of PVCL and PVPy in water critically change at the phase transition temperature (Tp) Above Tp the C−H stretching and the C−H bending bands shift to lower wavenumbers The amide I band of PVCL is divided into four components, and the intensities of the 1565, 1588, and 1625 cm-1 components increase and that of the 1610 cm-1 component decreases while the phase transition proceeds Addition of KCl and KF lower Tp of PVCL, whereas KI and KBr raise Tp Addition of methanol gradually raises Tp up to ca 40 vol % and steeply raises Tp at >

Hydration and Phase Behavior of Poly(N-vinylcaprolactam) and Poly(N-vinylpyrrolidone) in Water

The phase transitions of poly(vinyl methyl ether) (PVME) in H2O and D2O have been investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of PVME solution are measured as a function of temperature, and changes in the spectra induced by the phase transition are observed. The IR bands attributable to the vibration modes of backbone and methoxy side group exhibit critical changes at a lower critical solution temperature (LCST). Heating of the solution above the LCST leads shifts of C−H stretching bands toward lower wavenumber during a high-wavenumber shift of C−O stretching band (ν(C−O)). Among the C−H stretching bands, symmetric and antisymmetric C−H stretching bands due to the methyl group (νs(CH3) and νas(CH3)) shift to the largest extent (20 cm-1). The νs(CH3) band is composed of two components centered at 2839 and 2820 cm-1, which are assignable to hydrated and dehydrated methyl species, respectively. The molar fraction of the hydrated methyl species is close to 1 below 36 °C and is n...

IR Spectroscopic Study on the Hydration and the Phase Transition of Poly(vinyl methyl ether) in Water

Phase transitions of poly(N,N-dimethylacrylamide) (PdEA) in water and methanol/water mixture were investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of the solutions measured as a function of temperature exhibited critical changes upon the phase transition. The amide I band of PdEA consists of three components centered at 1638, 1619, and 1599 cm-1, which can be assigned to free carbonyl groups and those connected to one and two water molecules through hydrogen bonds, respectively. The relative areas of the 1619 and 1599 cm-1 components decrease and that of the 1638 cm-1 component increases above the phase transition temperature (Tp), but the change is relatively small and most of the amide CO groups remain hydrated even above Tp. The C−H stretching bands shift toward lower wavenumbers that are close to those measured in the neat solid state, indicating that the alkyl groups are almost fully dehydrated above Tp. In the methanol/water mixture, Tp is almost independent of methanol con...

Yasushi Maeda

Papers

Change in Hydration State during the Coil−Globule Transition of Aqueous Solutions of Poly(N-isopropylacrylamide) as Evidenced by FTIR Spectroscopy†

Changes in the Hydration States of Poly(N-alkylacrylamide)s during Their Phase Transitions in Water Observed by FTIR Spectroscopy†

Hydration and Phase Behavior of Poly(N-vinylcaprolactam) and Poly(N-vinylpyrrolidone) in Water

IR Spectroscopic Study on the Hydration and the Phase Transition of Poly(vinyl methyl ether) in Water

Change in Solvation of Poly(N,N-diethylacrylamide) during Phase Transition in Aqueous Solutions As Observed by IR Spectroscopy