Characterization of aliphatic and aromatic polyester hyperbranched dendrimers by AFM imaging

The aggregates of aliphatic (AL-PE) and aromatic polyester (AR-PE) hyperbranched dendrimers were imaged by tapping mode atomic force microscopy (AFM). The second and third generations of AL-PE dendrimers were adsorbed on mica in large aggregates of 150- and 166-nm diameters with little heights (ca. 1–2 nm). The origin of such flattened aggregates is attributed to their favorable adsorption on mica in view of the presence of –OH surface groups. AR-PE did not show such flattened aggregates instead small aggregates of 63 nm were observed in an organized manner beaving a cavity in the center of each aggregate. The organized aggregates of AR-PE with smaller dimension than AL-PE are ascribed to less favorable adsorption of the latter on mica in view of its stronger hydrophobicity.     

Chiral separation of phenylalanine in ultrafiltration through DNA-immobilized chitosan membranes

Ultrafiltration experiments for the chiral separation of racemic phenylalanine were performed with DNA-immobilized chitosan membranes having various pore sizes. Atomic analysis on the membranes showed that the chitosan membranes covalently bound six times more DNA than the cellulose membranes used in our previous study [A. Higuchi, Y. Higuchi, K. Furuta, B.O. Yoon, M. Hara, S. Maniwa, M. Saitoh, K. Sanui, Chiral separation of phenylalanine by ultrafiltration through immobilized DNA membranes, J. Membr. Sci. 221 (2003) 207–218]. d-Phenylalanine preferentially permeated through DNA-immobilized chitosan membranes with a pore size <6.4 nm [molecular weight cut-off (MWCO) <67,000]. The binding affinity of a specific enantiomer due to the pore size of the DNA-immobilized membranes regulated the preferential permeation of the enantiomer through the membranes. l-Phenylalanine was adsorbed on the DNA-immobilized chitosan membranes with a pore size <6.4 nm (MWCO < 67,000), while there was little difference between the adsorption of d-phenylalanine and l-phenylalanine on the membranes with a pore size >6.4 nm (MWCO > 67,000). The DNA-immobilized chitosan membranes were categorized as channel type membranes.     

Rapid spectrophotometric determination of iron in natural waters with 4-(2-thiazolylazo)-6-chlororesorcinol

4-(2-Thiazolylazo)-6-chlororesorcinol reacts sensitively with iron(II) to form a water-soluble brown complex which has a characteristic absorption at 741 nm. By utilizing this absorption, rapid and selective spectrophotometric determination of iron has been developed. The absorbance is constant at pH 8.7 to 10.9 and Beer's law holds up to 1.8 ppm of iron, with a molar absorptivity of 3.13 × 10⁴ liters mol^?1 cm^?1. Many types of ions are tolerable and the method has been applied successfully to the determination of iron in river waters.     

Ring-opening reaction of phosphorus-bridged [1]ferrocenophane via ring slippage from eta(5)- to eta(1)-Cp

A reaction mechanism was investigated for a ring-opening reaction of RP(E)-bridged [1]ferrocenophane, where RP(E) = PhP(S) (3a), PhP (3b), and MesP (3c) (Mes = 2,4,6-trimethylphenyl). Irradiation of UV-vis light in the presence of an excess amount of P(OMe)(3) transformed 3a to [Fe(PhP(S)(eta(5)-C(5)H(4))(eta(1)-C(5)H(4)))(P(OMe)(3))(2)] (4a), in which one of the two cyclopentadienyl (Cp) rings of 3a changed its coordination mode from eta(5) to eta(1) and vacant coordination sites thus formed on the iron center were occupied by two P(OMe)(3) ligands. The molecular structure of 4a was determined by X-ray analysis, in which eta(1)-Cp adopted a 1-Fe-2-P-1,3-cyclopentadiene structure. Under the same reaction conditions, 3b and 3c also gave similar ring-slipped products 4b and 4c, respectively. Photolysis of 3a using more strongly coordinating PMe(3) in place of P(OMe)(3) led to complete dissociation of a Cp ligand from the iron center to form [Fe(PhP(S)(eta(5)-C(5)H(4))(C(5)H(4)))(PMe(3))(3)] (5). The formation of the ring-slipped and -dissociated products on the photolysis of 3 strongly supports the view that photolytic ring-opening polymerization of 3 proceeds via an unprecedented Fe-Cp bond cleavage mechanism.     

Poly(β-Amino acids). VI. Synthesis and conformational properties of poly[(r)-3-pyrrolidinecarboxylic acid]

Racemic and optically active 3-pyrrolidinecarboxylic acids (β-proline) were synthesized, and their polymers, poly[(RS)-β-proline] and poly[(R)-β-proline], were prepared by the polycondensation reaction of the p-nitrophenyl esters. Model compounds, N-cyclopentylcarboxylic acid pyrrolidide and N-cyclopentylcarbonyl-(R)-3-pyrrolidinecarboxylic acid pyrrolidide, were synthesized to elucidate the conformation of the polymer. The solution properties of poly[(R)-β-proline] and the model compounds were investigated by means of circular dichroism (CD) and NMR spectroscopy. The spectral patterns of the polymer and model compounds were similar in various solvents. Poly[(R)-β-proline] and poly[(RS)-β-proline] showed identical NMR spectra. These results suggest that poly[(R)-β-proline] may exist in a random conformation consisting of mixtures of cis and trans amide bonds. The conformational study of cyclopentanecarboxylic acid pyrrolidide by NMR spectroscopy with a shift reagent, Eu(fod)₃, in CDCl₃ implied that the plane containing the amide group bisects the cyclopentane ring. This suggests that each amide plane in the polymer in chloroform may also bisect the pyrrolidine ring.     

Nearsightedness-related indices of finite systems based on linear response function: one-dimensional cases

ABSTRACT

We have investigated nearsightedness of electronic matter (NEM) of finite systems on the basis of linear response function to examine theoretical foundation of contemporary computational chemistry such as quantum mechanics/molecular mechanics methods. In this study, we introduce several nearsightedness-related indices to assess the magnitude of localisability of responses for one-dimensional finite model systems. We started from two electrons' systems, which are beyond the scope of the original concept of NEM, and increased the number of electrons (N) to a hundred electrons to analyse dependency of such indices on N. In the process of construction of the indices, we analysed the factors, because of which the magnitude of nonlocal parts of linear response functions becomes small, into several ones, and extracted purely the magnitude of propagation of responses.     

NMR study on the quasi one-dimensional quantum spin magnet with ladder structure

The two-legged spin ladder Cu(CO₃)_0.5(ClO₄)(H₂O)_0.5(NH₃)_2.5 consists of a rung formed by two Cu(II)’s and of a spacing molecule CO\(_{3}^{2-}\) between each two rungs. The non-centrosymmetric shape of CO\(_{3}^{2-}\) molecule brings a slight bond alternation along the leg, and hence the system can be considered as an alternating spin chain, which is confirmed so far by the temperature dependence of magnetic susceptibility. In order to investigate its spin state at low temperatures, we have performed experiments of ¹H-NMR, magnetization and specific heat under wide range of magnetic field, and have found the critical diverging of longitudinal relaxation rate 1/T ₁, the spectral broadening and the lambda-type anomaly in specific heat at T _N? 3.4 K, indicating the existence of long range magnetic order. In paramagnetic state well above T _N, 1/T ₁ showed a power-law temperature dependence, suggesting the realization of Tomonaga Luttinger liquid state.     

Highly Selective Phosphinylphosphination of Alkenes with Tetraphenyldiphosphine Monoxide

In sharp contrast to tetraphenyldiphosphine, which does not add to carbon–carbon double bonds efficiently, its monoxide, [Ph₂P(O)PPh₂] can engage in a radical addition to various alkenes, thus affording the corresponding 1‐phosphinyl‐2‐phosphinoalkanes regioselectively, and they can be converted into their sulfides by treatment with elemental sulfur. The phosphinylphosphination proceeds by the homolytic cleavage of the P^V(O)?P^III single bond of Ph₂P(O)PPh₂, followed by selective attack of the phosphinyl radical at the terminal position of the alkenes, and selective trapping of the resulting carbon radical by the phosphino group. Furthermore, the phosphinylphosphination product could be converted directly into its platinum complex with a hemilabile P,O chelation.     

Anomalous Freezing of Nano‐Confined Water in Room‐Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Nitrate

Non‐crystal formation of ice is investigated by simultaneous X‐ray diffraction and differential scanning calorimetry measurements upon cooling to ?100 °C. At room temperature, size‐tunable water confinement (≈20 Å size) in a room‐temperature ionic liquid (RTIL, 1‐butyl‐3‐methylimidazolium nitrate, [C₄mim][NO₃]) exists in a water‐rich region (70–90 mol % D₂O). The confined water (water pocket) is characterized by almost monodispersive size distribution. In [C₄mim][NO₃]‐x mol % D₂O (70<x<94), the absence of sharp Bragg reflections and a distinct exothermal peak indicate that crystallization/cold crystallization both of [C₄mim][NO₃] and D₂O is suppressed, even upon slow cooling and heating.     

Simultaneous detection of eight active components in Radix Tinosporae by ultra high performance liquid chromatography coupled with electrospray tandem mass spectrometry

A rapid and sensitive ultra high performance liquid chromatography with electrospray ionization tandem mass spectrometry method was developed and validated for the simultaneous determination of eight major active components (magnoflorine, menisperine, 20‐hydroxyecdysone, cepharanthine, columbamine, jatrorrhizine, columbin, and palmatine) in Radix Tinosporae. The separation was performed on an InterSustainSwift C₁₈ column (1.9 μm, 2.1 id × 100 mm) at 40 °C with a gradient elution. A mixture of acetonitrile and methanol (v/v = 1:1) and ammonium acetate buffer (25 mmol/L ammonium acetate with 0.2% formic acid) were used as mobile phases, and the flow rate was set at 0.4 mL/min. The recovery was tested in real samples and calculated to be 86.97–111.28%, and all the compounds showed good linearity (r > 0.998) in relatively wide concentration ranges. The developed method was applied to the determination of eight active compounds in real herb samples, which were collected from four different places. It has been demonstrated that the proposed method has great potential for the quality control of the traditional Chinese medicine Radix Tinosporae.