Highly active catalyst for the heterogeneous Suzuki-Miyaura reaction: assembled complex of palladium and non-cross-linked amphiphilic polymer

An assembled insoluble catalyst, PdAS, prepared from palladium ((NH4)2PdCl4 (1)) and non-cross-linked amphiphilic copolymer poly(N-isopropylacrylamide-co-4-diphenylstyrylphosphine) (2) was developed. It was found that PdAS is an excellent catalyst for the Suzuki-Miyaura reaction on three points: (1) The use of 8 x 10(-7) to 5 x 10(-4) mol equiv of PdAS afforded the coupling products efficiently after easy workup, with the turnover number reaching up to 1,250,000. (2) The catalyst was reusable many times without loss of catalytic activity. (3) PdAS showed good stability in any reaction medium (i.e., water or aqueous or anhydrous organic solvents). Analytical study of PdAS indicates that the phosphines in 2 coordinate to palladium to form PdCl2(PPh2Ar)2 species.     

Atropisomeric properties of the dibenzo[b,d]azepin-6-one nucleus

Dibenzo[b,d]azepin-6-ones (2a,b) were separated by chiral HPLC into the aR- and aS-atropisomers with high stereochemical stability, and methylation at C7 of 2a stereoselectively gave the (aR*,7R*) isomer (4a), which converted to the thermodynamically stable (aS*,7R*) atropisomer (5a) after heating.     

Effect of ultrasonic exposure on Ca2+-ATPase activity in plasma membrane from Aloe arborescens callus cells

We investigated the effect of ultrasound on plasma membrane (PM) Ca2+-ATPase activity of Aloe arborescens callus cells in solid culture. The calluses were exposed by a 20 kHz digital sonifier at the powers of 2 and 10 W from the effective exposure times of 2-10 s. PM Ca2+-ATPase activity was almost significantly higher at 2 W both in continuous wave and 10% duty cycle than that of the control (no ultrasound) at effective exposure times of 5 and 10 s. However, its activity decreased at 10 W in continuous wave exposure. It is possible that the PM Ca2+-ATPase configuration or structure may be partly damaged by high-energy ultrasound at 10 W. Our results showed that low-energy ultrasound exposure was a useful physical field to stimulate A. arborescens callus cells to adapt environmental stress through PM Ca2+-ATPase activity increase.     

Divergent synthesis of L-sugars and L-iminosugars from D-sugars

An efficient divergent synthesis of L-sugars and L-iminosugars from D-sugars is described. The important intermediate, delta-hydroxyalkoxamate, prepared from D-glucono-/galactono-1,5-lactone, was cyclized under Mitsunobu conditions to give the O-cyclized oxime compound and the N-cyclized lactam compound as mixtures. A more detailed investigation revealed that the appropriate protecting groups and solvents controlled the specificity for the O-/N-cyclization of the delta-hydroxyalkoxamate. Suitable protection at the 6-position of delta-hydroxyalkoxamate, derived from D-glucono-1,5-lactone, afforded the corresponding O-alkylation product alone. Thus we succeeded in applying this to the total synthesis of L-iduronic acid. In contrast, with both TBDMS as the protecting group and RCN as the solvent the efficient conversion of D-glucono/galactono-1,5-lactone into the corresponding L-iminosugars (L-idonolactam and L-altronolactam) was achieved.     

Desorption of Tributyltin,Dibutyltin and Zinc from Resuspended Sediment

Adsorption–desorption equilibrium and de- sorption kinetic studies were conducted in order to assess desorption of tributyltin (TBT), dibutyltin (DBT) and zinc from resuspended sediment. Equilibria were described in terms of linear adsorption. Desorption kinetics were represented by a two-site model which assumed that desorption consisted of rapid desorption and first-order kinetic desorption. TBT desorbed the most easily. Desorption kinetic parameters were related to adsorption mechanisms. Some experimental results did not correspond with the theoretical model. This was thought to be caused by natural organic ligands originally held in the sediment. Zinc deviated the most, because it was affected by the natural organic ligands more strongly than butylins. For example the partition coefficient of zinc varied by up to 1000-fold, and re-adsorption to sediment of the zinc that had been discharged to the water took place. Release of chemicals induced by remedial dredging was assessed. Desorbed TBT may pose a high risk. Among remediation alternatives, capping or leaving the sediment to stand prior to in situ degradation are preferred. © 1997 by John Wiley & Sons, Ltd.     

Molecular self-assembling of chiral and racemic butan-2-ol in carbon tetrachloride solutions

The self-association of (R)-, (S)- and (RS)-butan-2-ol in their carbon tetrachloride solutions was studied through the mid-infrared (mid-IR) and near-infrared (NIR) spectroscopic observations. The mid-IR and NIR spectra for each chiral butan-2-ol were compared with those for the racemic (RS)-butan-2-ol. Although it has been reported that the hydrogen bonding among the chiral butan-2-ol molecules was stronger than that among the racemic ones, any distinguishable differences between the chiral and the racemic butan-2-ol in CCl₄ solution or even in their pure liquid state were not observed both in their mid-IR and NIR spectra. A superior analytical method, assuming a successive association process for the alcohol molecules, was applied to the analysis of the sharp band at 3630 cm⁻¹ (the OH-stretching vibration mode attributed to free OH-monomer) for the (R)-, (S)- or (RS)-butan-2-ol in CCl₄. The mean association number N for each alcohol increased with increasing in concentration until 0.12 mol dm⁻³ and then becomes constant (about four). On the other hand, Zanker's plotting method, assuming an equilibrium between monomers and only one kind of polymer species, was also applied to the analysis of the above spectroscopic results; the association number n evaluated from the Zanker's method fairly agreed with the N value in the concentration region of 0.12–0.60 mol dm⁻³.     

The lowest metal-to-bipyridine charge-transfer excited state of [Cr(2,2′-bipyridine)(CO)4]

The DV-Xα molecular-orbital calculations have been carried out on [Crbpy(CO)₄](bpy,2,2′-bipyridine) and its electron attachment and detachment products. The one-electron attachment of [Crbpy(CO)₄] yields a complex of bipyridine anion radical, while the one-electron detachment results in ionization of the central metal atom. The lowest excited state of [Crbpy(CO)₄] is the metal-to-ligand charge-transfer (MLCT) excited state which consists of the bipyridine anion radical and the central metal ionized. The transition-state calculation predicts the lowest MLCT excited states at around 23～30×10³ cm^?1 and the lowest bipyridine (π,π^*) excitations at 36×10³ cm^?1 and 42～45×10³ cm^?1. The calculation also concludes that the MLCT excitation induces a counter migration of the other electrons not directly involved in the charge-transfer excitation. The configuration-interaction calculations predict the lowest MLCT excited singlet states at around 21～35×10³ cm^?1 and the lowest bipyridine (π, π^*) excited singlet states at 42～62×10³ cm^?1, while the emissive lowest MLCT triplet state is at 17×10³ cm^?1. The transition moments evaluated with the transition-state wavefunctions can reproduce qualitatively the observed absorption spectral profile. The intensity of the MLCT transitions is obtained from the allowed (π, π^*) transitions of coordinated bipyridine but is not due to the intrinsic transition moments of MLCT excitations.     

Tetrathiafulvalenylallene: a new class of donor molecules having strong chiroptical properties in neutral and doped states

A chiral tetrathiafulvalene (TTF) dimer bridged by an allene framework (1) was synthesized. An X-ray analysis of 1 revealed an effective conjugation between TTF and the allene backbone. Allene 1 was resolved into both enantiomers, which showed strong chiroptical electrochromic properties. Absolute configuration of the allene was validated by theoretical study of the electronic circular dichroism (ECD) spectrum. ECD spectra of cationic species 1(2+) and 1(4+) exhibited intense Cotton Effects over the visible region.     

Reduction of n‐type diamond contact resistance by graphite electrode

The contact resistance between heavily phosphorus doped n‐type (n⁺‐type) diamond (111) layers and graphite electrodes was investigated. To analyze the contact resistance properties in detail in the low‐voltage region, the transfer length method including nonlinear terms with a constant current was analyzed based on the double Schottky contact configuration. Using this method, we have revaluated the metal contact resistance reported previously. Using the graphite electrodes, the linearity of current‐voltage characteristics was improved. The contact resistance was reduced by a factor of ten compared to that of conventional Ti/Pt/Au electrodes. The graphite electrodes were formed directly by thermal annealing at 1300 °C for 10 min from an n⁺‐type diamond surface. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)