Electron spin resonance study on chemical‐crosslinking reaction mechanisms of polyethylene using a chemical agent. VI. Effect of α‐methyl styrene dimer

The effect of α‐methyl styrene dimer (AMSD), which is used as a scorch retarder, on the reaction mechanisms of the chemical crosslinking of polyethylene (PE) with dicumyl peroxide (DCP) at high temperatures was investigated using electron spin resonance. When AMSD was added to PE containing DCP, the AMSD radical was observed; however, the PE alkyl radical or allyl radical presence was not detected. At 145 °C, crosslinking was obstructed as a result of the reaction between AMSD and alkyl radicals. As the temperature increased, AMSD fragmented to form 2‐phenyl‐2‐propyl and double bonds in PE. This generation of double bonds, however, accelerated crosslinking at 180 °C and was more effective than when AMSD was not present. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2151–2156, 2001     

Helically Assembled Pyrene Arrays on an RNA Duplex That Exhibit Circularly Polarized Luminescence with Excimer Formation

Circularly polarized luminescence (CPL) was observed in pyrene zipper arrays helically arranged on an RNA duplex. Hybridization of complementary RNA strands having multiple (two to five) 2′‐O‐pyrenylmethyl modified nucleosides affords an RNA duplex with normal thermal stability. The pyrene fluorophores are assembled like a zipper in a well‐defined helical manner along the axis of RNA duplex, which, upon 350 nm UV illumination, resulted in CPL emission with pyrene excimer formation. CPL (g_lum) levels observed for the pyrene arrays in dilute aqueous solution were +2×10^?2–+3.5×10^?2, which are comparable with |g_lum| for chiral organic molecules and related systems. The positive CPL signals are consistent with a right‐handed helical structure. Temperature dependence on CPL emission indicates that the stable rigid RNA structure is responsible for the strong CPL signals. The single pyrene‐modified RNA duplex did not show any CPL signal.     

Syntheses of effectively-shielded N-heterocyclic carbene ligands

A novel type of N-heterocyclic carbene ligand, with a bicyclic motif at the non-carbenic carbons of an imidazolin-2-ylidene core, has been developed. This type of ligand formed an air and moisture stable silver complex even with N,N′-dimethyl NHC. Allylic arylation with a Grignard reagent catalyzed by copper complexes of the NHC ligands proceeded preferentially at the γ-position, indicating the effective steric shielding ability of this framework.     

One‐Pot Synthesis of N,N‐Disubstituted (Z)‐4‐(Halomethylidene)‐4H‐3,1‐benzothiazin‐2‐amines from 2‐(2,2‐Dihaloethenyl)phenyl Isothiocyanates and Secondary Amines

We have developed a one‐pot procedure for the preparation of N,N‐disubstituted (Z)‐4‐(halomethylidene)‐4H‐3,1‐benzothiazin‐2‐amines 3 from 2‐(2,2‐dihaloethenyl)phenyl isothiocyanates 1 , easily accessible from known 2‐(2,2‐dihaloethenyl)benzenamines by a three‐step sequence, and secondary amines. Thus, the isothiocyanates 1 react with secondary amines to afford the corresponding thiourea derivatives, of which the treatment with NaH provides the desired products.     

Magnetite 3D colloidal crystals formed in the early solar system 4.6 billion years ago

Three-dimensional colloidal crystals made of ferromagnetic particles, such as magnetite (Fe(3)O(4)), cannot be synthesized in principle because of the strong attractive magnetic interaction. However, we discovered colloidal crystals composed of polyhedral magnetite nanocrystallites of uniform size in the range of a few hundred nanometers in the Tagish Lake meteorite. Those colloidal crystals were formed 4.6 billion years ago and thus are much older than natural colloidal crystals on earth, such as opals, which formed about 100 million years ago. We found that the size of each individual magnetite particle determines its morphology, which in turn plays an important role in deciding the packing structure of the colloidal crystals. We also hypothesize that each particle has a flux-closed magnetic domain structure, which reduces the interparticle magnetic force significantly.     

MALDI-Q-TOF mass spectrometric determination of gold and platinum in tissues using their diethyldithiocarbamate chelate complexes

A rapid determination method is presented for gold (Au³⁺) and platinum (Pt⁴⁺) in tissues using matrix-assisted laser desorption ionization quadrupole time-of-flight mass spectrometry (MALDI-Q-TOF-MS). Au and Pt ions in wet-ashed tissue solution were reacted with diethyldithiocarbamate (DDC), and the resulting chelate complex ions Au(DDC)₂ ⁺ and Pt(DDC)₃ ⁺ were detected by MALDI-Q-TOF-MS using α-cyano-4-hydroxycinnamic acid as a matrix. The limit of detection (LOD) was 0.8 ng/g tissue and the quantification range was 2–400 ng/g for Au, and the LOD was 6 ng/g tissue and the quantification range was 20–4,000 ng/g for Pt. The Pt levels detected by MALDI-Q-TOF-MS in several tissues of a patient overdosed with cisplatin were nearly the same as those detected by flow-injection electrospray ionization mass spectrometry. The LODs of Au and Pt were 0.04 pg per well (sample spot) and 0.3 pg per well, respectively. To our knowledge, this is the first attempt to quantify Au³⁺ and Pt⁴⁺ ions in tissues by MALDI-Q-TOF-MS.

Diketopyrrolopyrrole J‐Aggregates Formed by Self‐Organization with DNA

Bis(2‐thienyl)diketopyrrolopyrrole with two Zn^II‐cyclens (ZnCyc‐DPP) was designed and synthesized to evaluate the selective binding of Zn^II‐cyclen with thymine base in single‐strand DNA as a tool for the construction of a highly ordered multichromophore system on DNAs. Through UV/Vis titrations, gel filtration chromatography, and circular dichroism spectroscopy, ZnCyc‐DPP formed J‐type DPP aggregates with oligo‐dT_n DNAs. The DPP aggregates absorbed on a gold electrode exhibited good photocurrent responses. The present results show that binding Zn^II‐cyclen–chromophore conjugates and thymine bases together is a powerful tool for preparing DNA‐templated multichromophoric systems with specific functions.     

Flow injection analysis for oxidation state speciation of vanadium(IV) and vanadium(V) in natural water.

A sensitive and simultaneous spectrophotometric flow injection method for the determination of vanadium(IV) and vanadium(V) is proposed. The method is based on the effect of ligands such as 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) and diphosphate on the conditional redox potential of iron(III)/iron(II) system. A four-channel flow system is assembled. In this flow system, diluted hydrochloric acid (1.0 x 10(-2) mol dm(-3)) as a carrier for standard/sample, acetate buffer (pH 5.5) as a carrier for diphosphate solution, an equimolar mixed solution of iron(III) and iron(II) and a TPTZ solution are delivered, so that the baseline absorbance can be established by forming a constant amount of iron(II)-TPTZ complex (lambda(max) = 593 nm). Vanadium(IV) and/or vanadium(V) (400 microL) and diphosphate (200 microL) solutions are simultaneously introduced into the flow system; in this system the diphosphate solution passes through a delay coil. The potential of the iron(III)/iron(II) system increases in the presence of TPTZ, and therefore vanadium(IV) is easily oxidized by iron(III) to vanadium(V) to produce an iron(II)-TPTZ complex (a positive peak for vanadium(IV) appears). On the other hand, the potential of the redox system decreases in the presence of diphosphate, so that vanadium(V) can be easily reduced by iron(II) to vanadium(IV). In this case, the amount of iron(II) decreases according to the amount of vanadium(V). As a result, the produced iron(II)-TPTZ complex decreases (a negative peak for vanadium(V) appears). In this manner, two peaks for vanadium(IV) and vanadium(V) can be alternately obtained. The limits of detection (S/N = 3) are 1.98 x 10(-7) and 2.97 x 10(-7) mol dm(-3) for vanadium(IV) and vanadium(V), respectively. The method is applied to the simultaneous determination of vanadium(IV) and vanadium(V) in commercial bottled mineral water samples.     

Confirmation of the structure of ceriperol and its related sesterterpenes by the total synthesis

The dl-synthesis of the revised formula of ceriferol and ceriferol-I was achieved, leaving no doubt that the revised structure has been correctly formulated.