Cypellogins A, B and C, acylated flavonol glycosides from Eucalyptus cypellocarpa

Three new acylated flavonol glycosides, cypellogins A (1), B (2) and C (3), along with eight known phenolic compounds, were isolated from the dried leaves of Eucalyptus cypellocarpa, and their structures were elucidated using spectroscopic methods, including 2D NMR experiments and chemical evidence.     

Structure formation of PVDF/PMMA blends studied

Conformational formation and crystallization dynamics of miscible PVDF/at-PMMA and PVDF/iso-PMMA polymer blends from the molten state were studied by the simultaneous DSC/FT-IR measurement. Formation of TGTG' conformation occurred before starting crystallization exothermic peak in the PMMA content (_PMMA) range from 0 to 0.4 for both blends. The formation rate of TGTG' conformation, crystal growth rate and surface free energy of PVDF crystal in blends depended linearly on _PMMA for PVDF/at-PMMA, however, those rates for PVDF/iso-PMMA slightly influenced by _PMMA. These results suggested that the former was miscible blend in molecular level, however, the latter was a miscible blend with large concentration fluctuation or a partially segregated system.     

Nucleation kinetics of folded chain crystals of polyethylene on active centers

Kinetic equations describing formation of nuclei of a new phase on active centers from supercooled melt taking into account exhaustion of active centers are solved numerically. Basic characteristics of nucleation process (total number of nuclei and nucleation rate) of folded chain crystals of polyethylene at low supercooling are determined and compared with measured data. Our model gives good coincidence with experimental measurements of the total number density of nuclei. Nucleation rate reaches some quasistationary limit at sufficiently long time, which is approximately 20% of the stationary nucleation rate determined by the standard way.     

Oxidative addition and insertion reactions of cyclic alkyne-platinum(0) complexes

The reactions of various alkyne-platinum(0) complexes with methyl iodide and with iodine have been studied. The 3-hexyne complex Pt(C₂H₅C₂C₂H₅)(PPh₃)₂ gives alkyne-free oxidative addition products PtI(CH₃) (PPh₃)₂ and PtI₂ (PPh₃)₂ exclusively. In contrast, the strained cyclic alkyne complexes Pt(C₆H₈)(PPh₃)₂, Pt(C₇H₁₀)(PPh₃)₂, Pt(C₆H₈) (dppe) and Pt(C₇H₁₀) (dppe)¹ react with methyl iodide to give mainly 2-methylcycloalkenyiplatinum(II) complexes, e.g. PtI(C₆H₈CH₃) (PPh₃)₂, formed by electrophilic attack on the metal-alkyne bond. Iodine reacts similarly with Pt(C₆H₈) (PPh₃)₂ and Pt(C₇H₁₀) (PPh₃)₂ to give 2-iodocycloalkenylplatinum(II) complexes but, in the case of the corresponding dppe complexes, PtI₂(dppe) is the main product. The insertion reaction of methyl iodide with Pt(C₆H₈)(PPh₃)₂ proceeds via an oxidative addition intermediate PtI(CH₃) (C₆H₈) (PPh₃)₂ which can be isolated. Trifluoromethyl iodide reacts with Pt(C₆H₈)(PPh₃)₂ to give a 2-iodocyclohexenyl complex Pt(CF₃) (C₆H₈I) (PPh₃)₂ and with Pt(C₇H₁₀) (PPh₃)₂ to give PtI(CF₃) (PPh₃)₂. ³¹P NMR data are given and discussed.     

Resonance Raman spectra of 15N enriched metallooctaethylorphyrins. Characterization of the oxidation state marker bands of hemoproteins

Resonance Raman spectra of ¹⁵N enriched metallooctaethylporphyrins [M(OEP) ? ¹⁵N₄] [M = Ni²⁺, Fe³⁺ (high spin), and Fe³⁺ (low spin)] were observed. Polarized Raman lines corresponding to the oxidation state marker band of hemoproteins were observed at 1377 (Ni), 1369 (Fe high spin) and 1372^?1 (Fe low spin) which were shifted to lower frequency from those of the ¹⁴N compounds by 6, 5, and 6 cm^?1, respectively. The vibrational mode for this band was shown to include an appreciable contribution of the C_αN symmetric stretching vibration and to be associated with ca. 0.01 Å of in-phase displacement of the four pyrrole nitrogens toward the metal ion.     

Thermoresponsive conductivity of poly(N‐isopropylacrylamide)/potassium chloride gel electrolytes

A series of thermoresponsive polymer gel electrolytes (PGEs) based on poly(N‐isopropylacrylamide) in aqueous potassium chloride was synthesized by radiation‐induced polymerization and gelation using γ rays from a ⁶⁰Co source. The electric conductivity and swelling properties of the PGE were determined as a function of temperature. It was found that the electric conductivity of the PGE depended strongly on the swelling ratio; most notably, it changed drastically near the volume phase‐transition temperature of the PGE. The temperature/conductivity profile of the PGE exhibits a maximum peak at a certain temperature that is defined as the maximum conductivity temperature (T_max). The T_max of all of the PGEs prepared by low‐dose irradiation agreed with the temperature, near the end of the volume phase transition, where the PGE was completely shrunken. Consequently, the conductivity of gels should provide a good method with which the totally shrunken temperature of the thermoresponsive gels can be monitored with good temperature precision. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 134–141, 2002     

Direct catalytic asymmetric Mannich-type reaction of hydroxyketone using a Et2Zn/linked-BINOL complex: synthesis of either anti- or syn-beta-amino alcohols

Full details of a direct catalytic asymmetric Mannich-type reaction of a hydroxyketone using a Et2Zn/(S,S)-linked-BINOL complex are described. By choosing the proper protective groups on imine nitrogen, either anti- or syn-beta-amino alcohol was obtained in good diastereomeric ratio, yield, and excellent enantiomeric excess using the same zinc catalysis. N-Diphenylphosphinoyl (Dpp) imine 3 gave anti-beta-amino alcohols in anti/syn = up to >98/2, up to >99% yield, and up to >99.5% ee, while Boc-imine 4 gave syn-beta-amino alcohols in anti/syn = up to 5/95, up to >99% yield, and up to >99.5% ee. The high catalyst turnover number (TON) is also noteworthy. Catalyst loading was successfully reduced to 0.02 mol % (TON = up to 4920) for the anti-selective reaction and 0.05 mol % (TON = up to 1760) for the syn-selective reaction. The Et2Zn/(S,S)-linked-BINOL complex exhibited far better TON than in previous reports of catalytic asymmetric Mannich-type reactions. Mechanistic studies to clarify the reason for the high catalyst efficiency as well as transformations of Mannich adducts are also described.