pH determination on a carbonate buffer by Harned cells of different designs

The carbonate solution is one of seven primary standard buffers set recently by the International Union of Pure and Applied Chemistry (IUPAC) recommendations (Buck et al., Pure Appl Chem 74:2169–2200, 2002). The peculiarity of the pH measurement of this buffer in a traditional Harned cell (classic cell) is due to the loss of carbon dioxide with hydrogen flow and the ensuing change of its chemical composition. This results in a continuous increase of the recorded electromotive force (E) of the cell. Therefore, almost all National Metrology Institutes (NMIs) are now using the extrapolation of measured E data to zero time point in order to find the initial pH. The National Metrology Institute of Japan (NMIJ) has developed a different design of Harned cell (NMIJ cell) with compensation of the lost carbon dioxide from the intermediary saturation vessel. The results of the study of the NMIJ cell are presented, together with those of the trilateral NMIJ–PTB–ZMK (NMI of Japan with the NMI of Germany [Physikalisch-Technische Bundesanstalt, PTB] and the German Centre for Measurements and Calibrations [Zentrum für Messen und Kalibrieren GmbH, ZMK]) comparison of pH values for the carbonate solution in different designs of Harned cell.

Photocatalytic CO2 reduction sensitized by a special-pair mimic porphyrin connected with a rhenium(i) tricarbonyl complex

Zn porphyrins with an imidazolyl group at the meso position generate a highly stable porphyrin dimer by complementary coordination from the imidazolyl to the Zn ion in noncoordinating solvents such as chloroform, which mimics the natural special pair in photosynthesis. In this work, we have synthesized an imidazolyl-substituted Zn porphyrin connected with a Re 2,2-bipyridine tricarbonyl complex as a CO₂ reduction catalyst via a p-phenylene linker, affording a homodimer with two Re complexes on both sides (ReDRe). The dimeric structure is easily dissociated into the corresponding monomers in coordinating solvents. Therefore, we prepared a mixture containing a heterodimer with the Re carbonyl complex on one side (ReD) by simple mixing with an imidazolyl Zn porphyrin and evaporating the solvent. Using the Grubbs catalyst, the subsequent olefin metathesis reaction of the mixture gave covalently linked porphyrin dimers through the allyloxy side chains, enabling the isolation of the stable hetero- (ReD′) and homo-dimers (ReD′Re) with gel permeation chromatography. The Zn porphyrin dimers have intense absorption bands in the visible light region and acted as good photosensitizers in photocatalytic CO₂ reduction in a mixture of N,N-dimethylacetamide and triethanolamine (5 : 1 v/v) containing 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the electron donor, giving CO with high selectivity and durability. Under irradiation with strong light intensity, the reaction rate in ReD′ exceeded that of the previous porphyrin Re complex dyad, ZnP-phen=Re. For instance, after irradiation at 560 nm for 18 h, the turnover number (TON_CO) of ReD′ reached 2800, whereas the TON_CO of ZnP-phen=Re was 170. The high activity in the system using the porphyrin dimer originates from no accumulation of the one-electron reduced species of the porphyrin that inhibit light absorption due to the inner-filter effect.

An artificial special pair was connected with a Re 2,2-bipyridine tricarbonyl complex. The special pair derivative acted as a good photosensitizer in photocatalytic CO₂ reduction, giving CO with high selectivity and durability.     

Solvoluminescence of Cerium(III) Thiocyanate Complex

A cerium(III) thiocyanate complex shows bright-blue emission at approximately 450 nm in acetonitrile, the quantum yield of which reaches more than 40 % at 298 K. Non-coordinating solvents such as acetonitrile give blue emission whereas oxygen-coordinating and nitrogen-coordinating solvents afford near UV and green emissions, respectively.     

Effects of orientation and degree of polymerization on tensile properties in the cellulose sheets using hierarchical structure of wood

Cellulose - Structural control is essential for further development of cellulosic materials. Here, we demonstrated the significance of the orientation and degree of polymerization in the integrated...     

New Japanese certified reference materials for electrolytic conductivity measurements

Accreditation and Quality Assurance - The National Metrology Institute of Japan (NMIJ) has established three certified reference materials (CRMs) in electrolytic conductivity with a primary...     

Construction of giant porphyrin macrorings self-assembled from thiophenylene-linked bisporphyrins for light-harvesting antennae

As a model of bacterial photosynthetic light-harvesting antenna, a large number of porphyrin units were organized into barrel-shaped macrorings. Two imidazolylporphyrinatozinc(II) molecules were linked through either unsubstituted thiophenes or 3,4-dioctylthiophenes 1 a and 1 b, respectively. These structures were spontaneously organized by complementary coordination of the imidazolyl to zinc and produced a series of self-assembled fluorescent polygonal macrorings under high dilution conditions. The ring size increased compared with previous m-phenylene examples. The size distribution was also controlled by the presence of octyl substituents. A wide distribution of macrorings from 7- to >15-mer was obtained from 1 a, whereas macrorings ranging from 7- to 11-mer with a maximum population focused at the 8-mer were formed with 1 b. The size distribution was governed by competition between entropy-favored, smaller-ring formation and the enthalpy-favored, less-strained larger macroring. The UV/Vis spectra showed a gradual redshift for the larger rings reflecting an increase in the transition dipole interactions.     

Polymer-supported oligosaccharide synthesis using ultrafiltration methodology

Polymer-supported oligosaccharide synthesis was carried out using an ultrafiltration technique in which the synthesized polymer-bound oligosaccharides were separated from the other reagents by ultrafiltration though membranes with specifically sized pores.     

Isolation, synthesis, and neurite outgrowth-promoting activity of illicinin A from the flowers of Illicium anisatum

Two new prenylated C₆-C₃ compounds, illicinin A (1) and (4S)-illicinone I (2), were isolated from the flowers of Illicium anisatum. The structures of the new compounds were elucidated by spectroscopic methods. The absolute structure of (4S)-illicinone I was determined by comparing its CD spectrum and specific rotation with those of (4S)-illicinone A (4). Illicinin A (1) and 4-allyl-2,6-dimethoxy-3-(3-methylbut-2-enyl)phenol (3) were found to exhibit neurite outgrowth-promoting activity at concentrations ranging from 0.1 to 10 μM in primary cultured rat cortical neurons. Illicinin A and its derivatives were synthesized for structure-activity relationship studies by employing sequential Stille reactions to introduce a prenyl and an allyl group to the benzene ring, thereby indicating that an allylphenyl moiety in the molecule of 1 is essential for its neurotrophic properties.