Hokkaido University

About: Hokkaido University is a education organization based out in Sapporo, Hokkaidô, Japan. It is known for research contribution in the topics: Population & Catalysis. The organization has 53925 authors who have published 115403 publications receiving 2651647 citations. The organization is also known as: Hokudai & Hokkaidō daigaku.

Diphenyl Phosphate as an Efficient Cationic Organocatalyst for Controlled/Living Ring-Opening Polymerization of δ-Valerolactone and ε-Caprolactone

Abstract: The ring-opening polymerization of δ-valerolactone (δ-VL) and e-caprolactone (e-CL) using 3-phenyl-1-propanol (PPA) as the initiator and diphenyl phosphate (DPP) as the catalyst in toluene at room temperature with the [δ-VL or e-CL]0/[PPA]0/[DPP] ratio of 50/1/1 homogeneously proceeded to afford poly(δ-valerolactone) (PVL) and poly(e-caprolactone) (PCL) with narrow polydispersity indices. The molecular weights determined from a 1H NMR analysis (PVL, Mn,NMR = 5170 g mol−1 and PCL, Mn,NMR = 5920 g mol−1) showed good agreement with those estimated from the initial ratio of [δ-VL or e-CL]0/[PPA]0 and monomer conversions (PVL, Mn,theo = 4890 g mol−1 and PCL, Mn,theo = 5680 g mol−1). The 1H NMR, SEC, and MALDI-TOF MS measurements of the obtained PVL and PCL clearly indicated the presence of the initiator residue at the chain end, confirming that the DPP-catalyzed ROP of lactones proceeded through an activated monomer mechanism. The kinetic and chain extension experiments confirmed the controlled/living nature f...

Two distinct classes of muscarinic action on hippocampal inhibitory synapses: M2-mediated direct suppression and M1/M3-mediated indirect suppression through endocannabinoid signalling.

Abstract: The cholinergic system in the CNS plays important roles in higher brain functions, primarily through muscarinic acetylcholine receptors. At cellular levels, muscarinic activation produces various effects including modulation of synaptic transmission. Here we report that muscarinic activation suppresses hippocampal inhibitory transmission through two distinct mechanisms, namely a cannabinoid-dependent and cannabinoid-independent mechanism. We made paired whole-cell recordings from cultured hippocampal neurons of rats and mice, and monitored inhibitory postsynaptic currents (IPSCs). When cannabinoid receptor type 1 (CB1) was blocked, oxotremorine M (oxo-M), a muscarinic agonist, suppressed IPSCs in a subset of neuron pairs. This suppression was associated with an increase in paired-pulse ratio, blocked by the M(2)-preferring antagonist gallamine, and was totally absent in neuron pairs from M(2)-knockout mice. When CB1 receptors were not blocked, oxo-M suppressed IPSCs in a gallamine-resistant manner in cannabinoid-sensitive pairs. This suppression was associated with an increase in paired-pulse ratio, blocked by the CB1 antagonist AM281, and was completely eliminated in neuron pairs from M(1)/M(3)-compound-knockout mice. Our immunohistochemical examination showed that M(2) and CB1 receptors were present at inhibitory presynaptic terminals of mostly different origins. These results indicate that two distinct mechanisms mediate the muscarinic suppression. In a subset of synapses, activation of M(2) receptors at presynaptic terminals suppresses GABA release directly. In contrast, in a different subset of synapses, activation of M(1)/M(3) receptors causes endocannabinoid production and subsequent suppression of GABA release by activating presynaptic CB1 receptors. Thus, the muscarinic system can influence hippocampal functions by controlling different subsets of inhibitory synapses through the two distinct mechanisms.

Tropical tropospheric ozone and biomass burning.

Abstract: New methods for retrieving tropospheric ozone column depth and absorbing aerosol (smoke and dust) from the Earth Probe–Total Ozone Mapping Spectrometer (EP/TOMS) are used to follow pollution and to determine interannual variability and trends. During intense fires over Indonesia (August to November 1997), ozone plumes, decoupled from the smoke below, extended as far as India. This ozone overlay a regional ozone increase triggered by atmospheric responses to the El Nino and Indian Ocean Dipole. Tropospheric ozone and smoke aerosol measurements from the Nimbus 7 TOMS instrument show El Nino signals but no tropospheric ozone trend in the 1980s. Offsets between smoke and ozone seasonal maxima point to multiple factors determining tropical tropospheric ozone variability.

Archaea of the Miscellaneous Crenarchaeotal Group are abundant, diverse and widespread in marine sediments

Abstract: Members of the highly diverse Miscellaneous Crenarchaeotal Group (MCG) are globally distributed in various marine and continental habitats In this study, we applied a polyphasic approach (rRNA slot blot hybridization, quantitative PCR (qPCR) and catalyzed reporter deposition FISH) using newly developed probes and primers for the in situ detection and quantification of MCG crenarchaeota in diverse types of marine sediments and microbial mats In general, abundance of MCG (cocci, 04 μm) relative to other archaea was highest (12–100%) in anoxic, low-energy environments characterized by deeper sulfate depletion and lower microbial respiration rates (P=006 for slot blot and P=005 for qPCR) When studied in high depth resolution in the White Oak River estuary and Hydrate Ridge methane seeps, changes in MCG abundance relative to total archaea and MCG phylogenetic composition did not correlate with changes in sulfate reduction or methane oxidation with depth In addition, MCG abundance did not vary significantly (P>01) between seep sites (with high rates of methanotrophy) and non-seep sites (with low rates of methanotrophy) This suggests that MCG are likely not methanotrophs MCG crenarchaeota are highly diverse and contain 17 subgroups, with a range of intragroup similarity of 82 to 94% This high diversity and widespread distribution in subsurface sediments indicates that this group is globally important in sedimentary processes