Control of thermoresponsive property of urea end‐functionalized poly(N‐isopropylacrylamide) based on the hydrogen bond‐assisted self‐assembly in water

The precise synthesis and variation in the thermoresponsive property based on the supramolecular assembly of a novel urea end‐functionalized poly(N‐isopropylacrylamide) (PNIPAM) were studied. A series of PNIPAMs with different diphenylurea groups at the chain end (X? Ph? NH? CO? NH? Ph? trz? PNIPAM: X = H, OCH₃, CH₃, NO₂, Cl, and CF₃) were synthesized by using a combination of the atom transfer radical polymerization and the copper(I)‐catalyzed azide‐alkyne cycloaddition. The cloud point of the obtained polymers depended on the hydrogen‐bonding ability of the introduced urea group. The ¹H NMR measurement suggested that the obtained PNIPAM assembled in water via the intermolecular hydrogen bonding by the terminal urea group. From the dynamic light scattering and transmission electron microscopy measurements, the aggregated nanoparticles of the resulting polymer were directly observed in water at a temperature below its cloud point. The hydrogen‐bonding property of the chain end urea group was concluded to be involved in the aggregation of the PNIPAM in water, leading to the variation in its cloud point. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6259–6268, 2009     

Systematization method for distinguishing plastic groups by using NIR spectroscopy.

A systematic classification method for polymers is not yet available in case of using near infrared spectra (NIR). That is why we have been searching for a systematic method. Because raw NIR spectra usually have few obvious peaks, NIR spectra have been pretreated by 2nd derivation for taking well modulated spectra. After the pretreatment, we applied classification and regression trees (CART) to the discrimination between the spectra and the species of polymers. As a result, we obtained a relatively simple classification tree. Judging from the obtained splitting conditions and the classified polymers, we concluded that obtained knowledge on the chemical function groups estimated by the important wavelength regions is not always applicable to this classification tree. However, we clarified the splitting rules for polymer species from the NIR spectral point of view.     

Visualization of dynamic conformational switching of the G-quadruplex in a DNA nanostructure

We herein report the real-time observation of G-quadruplex formation by monitoring the G-quadruplex-induced global change of two duplexes incorporated in a DNA nanoscaffold. The introduced G-rich strands formed an interstrand (3 + 1) G-quadruplex structure in the presence of K(+), and the formed four-stranded structure was disrupted by removal of K(+). These conformational changes were visualized in a nanoscaffold in real-time with fast-scanning atomic force microscopy.     

Flow injection determination of trace amounts of copper based on its catalytic effect on the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine by cumene hydroperoxide

A sensitive and selective flow-injection method has been developed for the catalytic determination of copper(II). The method is based on the oxidation of 3,3′,5,5′-tetramethylbenzidine by cumene hydroperoxide as an organic oxidant in an acidic medium. A highly sensitivity has been achieved by adding 2,9-dimethyl-1,10-phenanthroline as an activator and benzyldimethyltetradecylammonium chloride (zephiramine) as a surfactant. The reaction was spectrophotometrically monitored by measuring the increase in absorbance of oxidation product of 3,3′,5,5′-tetramethylbenzidine at 650 nm. The calibration curve was linear over the range of 0.5–3.0 ng mL^?1 at a rate of 30 samples h^?1. Most of the diverse ions did not interfere with the determination of copper up to at least 50-fold excess. The serious interference by iron(III) was eliminated by addition of fluoride. The method was successfully applied to the determination of copper in water samples.     

Synthesis of Naphtho[1,8‐bc]pyran Derivatives and Related Compounds through Hydroxy Group Directed C?H Bond Cleavage under Rhodium Catalysis

The straightforward and efficient synthesis of naphtho[1,8‐bc]pyran derivatives and related polycyclic compounds is achieved by the rhodium‐catalyzed oxidative coupling of 1‐naphthols or other phenolic and alcoholic substrates with alkynes. In these annulation reactions, the hydroxy groups effectively act as the key function for the regioselective C? H bond cleavage.     

Design,Synthesis, and Biological Evaluation of Artificial Macrosphelides in the Search for New Apoptosis‐Inducing Agents

A drug of two halves : New artificial compounds composed of a macrosphelide core skeleton and an epothilone side chain were designed and synthesized. These compounds were more potent inducers of apoptosis than the parent natural‐type macrosphelides.

     

Asymmetric synthesis of cyclic α-amino acid derivatives by the intramolecular reaction of magnesium carbenoid with an N-magnesio arylamine

The synthesis of pipecolic acid and homopipecolic acid derivatives was developed from ω-(2-aminophenyl)-1-chloroalkyl p-tolyl sulfoxides by treatment with i-PrMgCl. An intramolecular nucleophilic substitution reaction of a magnesium carbenoid with an N-magnesio arylamine is the key step of this reaction. Proline and pipecolic acid derivatives were also synthesized from ω-(arylamino)-1-chloroalkyl p-tolyl sulfoxides by the same chemistry. Starting from enantiomerically pure (1S,R_S)-1-chloro-3-[2-(N-methylamino)phenyl]propyl p-tolyl sulfoxide, enantiomerically pure (R)-pipecolic acid derivative was obtained. The intramolecular nucleophilic substitution reaction of the magnesium carbenoid with N-magnesio arylamine was proven to take place with inversion of the carbenoid carbon. The stereochemistry of these reactions is also discussed.     

Improvement of separation efficiencies of anion-exchange chromatography using monolithic silica capillary columns modified with polyacrylates and polymethacrylates containing tertiary amino or quaternary ammonium groups

Anion-exchange (AEX) columns were prepared by on-column polymerization of acrylates and methacrylates containing tertiary amino or quaternary ammonium groups on monolithic silica in a fused silica capillary modified with anchor groups. The columns provided a plate height (H) of less than 10 μm at optimum linear velocity (u) with keeping their high permeability (K = 9–12 × 10⁻¹⁴ m²). Among seven kinds of AEX columns, a monolithic silica column modified with poly(2-hydroxy-3-(4-methylpiperazin-1-yl)propyl methacrylates) (HMPMA) showed larger retentions and better selectivities for nucleotides and inorganic anions than the others. The HMPMA column of 410 mm length produced 42 000–55 000 theoretical plates (N) at a linear velocity of 0.97 mm/s with a backpressure of 3.8 MPa. The same column could be employed for a fast separation of inorganic anions in 1.8 min at a linear velocity of 5.3 mm/s with a backpressure of 20 MPa. In terms of van Deemter plot and separation impedance, the HMPMA column showed higher performance than a conventional particle-packed AEX column. The HMPMA column showed good recovery of a protein, trypsin inhibitor, and it was applied to the separation of proteins and tryptic digest of bovine serum albumin (BSA) in a gradient elution, to provide better separation compared to a conventional particle-packed AEX column.     

Click Chemistry for the Identification of G‐Quadruplex Structures: Discovery of a DNA–RNA G‐Quadruplex

A trap that closes with a “click” : The copper‐catalyzed azide–alkyne cycloaddition can occur in different G‐quadruplex structures (see scheme). The species trapped by the click reaction can then be separated and analyzed. By using this approach, a DNA–RNA hybrid‐type G‐quadruplex structure formed by human telomeric DNA and RNA sequences was detected.