The pH responsiveness of fluorescein loaded in polysaccharide composite films.

Stimuli-responsive materials have been used in biomedical applications. Composite films fabricated using polyion complexes comprising anionic and cationic polysaccharides exhibited loading and release abilities for water-soluble molecules, the release ability of which depended on the solution pH. However, the interactions between polysaccharides and loaded molecules in the film have not been evaluated. In this study, polysaccharide composite films loaded with fluorescein (FL) as a probe molecule were fabricated and the film properties, FL ionization, and release behaviour of FL were investigated. FL loading did not significantly affect the mechanical and morphological properties of the films. The release behaviour of FL was determined by the pH of the solution as well as the electrostatic interaction between polysaccharides and FL ionic structures in FL-loaded films. Furthermore, the ionic structure change of FL that remained in the film was suppressed due to interactions with polysaccharides, such as through hydrogen bonding. Additionally, the pH responsiveness of FL in the film in the dried state was evaluated. The result shows that polysaccharide composite films were swollen because of air moisture and that the diffusion of molecules inside the film accelerated. These findings are useful to understand the properties of the loaded molecules such as ionic state and diffusiveness in the films made of polyion complexes.

Selective Synthesis of Oligosaccharides by Mechanochemical Hydrolysis of Chitin over a Carbon-Based Catalyst.

Oligosaccharides possess fascinating functions that are applicable in a variety of fields, such as agriculture. However, the selective synthesis of oligosaccharides, especially chitin-oligosaccharides, has remained a challenge. Chitin-oligosaccharides activate the plant immune system, enabling crops to withstand pathogens without harmful agrichemicals. Here, we demonstrate the conversion of chitin to chitin-oligosaccharides using a carbon catalyst with weak acid sites and mechanical milling. The catalyst produces chitin-oligosaccharides with up to 94 % selectivity in good yields. Monte-Carlo simulations indicate that our system preferentially hydrolyzes larger chitin molecules over oligomers, thus providing the desired high selectivity. This unique kinetics is in contrast to the fact that typical catalytic systems rapidly hydrolyze oligomers to monomers. Unlike other materials carbons more strongly adsorb large polysaccharides than small oligomers, which is suitable for the selective synthesis of small oligosaccharides.

Impact of tensile and compressive forces on the hydrolysis of cellulose and chitin.

Mechanochemistry enables unique reaction pathways in comparison to conventional thermal reactions. Notably, it can achieve selective hydrolysis of cellulose and chitin, a set of abundant and recalcitrant biomass, by solvent-free ball-milling in the presence of acid catalysts. Although the merits of mechanochemistry for this reaction are known, the reaction mechanism is still unclear. Here, we show how the mechanical forces produced by ball-milling activate the glycosidic bonds of carbohydrate molecules towards hydrolysis. This work uses experimental and theoretical evaluations to clarify the mechanism. The experimental results reveal that the ball-mill accelerates the hydrolysis by mechanical forces rather than local heat. Meanwhile, the classical and quantum mechanics calculations indicate the subnano to nano Newton order of tensile and compressive forces that activate polysaccharide molecules in the ball-milling process. Although previous studies have taken into account only the stretching of the molecules, our results show that compressive forces are stronger and effective for the activation of glycosidic bonds. Accordingly, in addition to stretching, compression is crucial for the mechanocatalytic reaction. Our work connects the classical physics of ball-milling on a macro scale with molecular activation at a quantum level, which would help to understand and control mechanochemical reactions.

Preparation of Ruthenium Dithiolene Complex/Polysiloxane Films and Their Responses to CO Gas.

To develop advanced materials using metal complexes, it is better to prepare metal complexes contained in composite or hybrid films. To achieve this purpose, we synthesized ruthenium complexes with dihalogen-substituted benzendithiolate ligands, [(η6-C6Me6)Ru(S2C6H2X2)] (X = F, 3,6-Cl, Br, 4,5-Cl), 1b-1e. We also investigated preparation of 1c or 1e containing polysiloxane composite films and their reactivity to CO gas. All ruthenium complexes 1b-1e reacted with CO gas, and carbonyl ligand adducts 2b-2e were generated. Ruthenium complexes 1b-1e show two strong absorption peaks around 550 and 420 nm. After exposure to CO gas, these absorption peaks were immediately decreased without a peak shift. A similar trend was observed in 1c or 1e containing polysiloxane composite films. These results indicate that 1c and 1e were easily converted into 2c and 2e, both in the solution and the polysiloxane film during CO gas exposure.

Re-organization of Pacific overturning circulation across the Miocene Climate Optimum.

The response of the ocean overturning circulation to global warming remains controversial. Here, we integrate a multiproxy record from International Ocean Discovery Program Site U1490 in the western equatorial Pacific with published data from the Pacific, Southern and Indian Oceans to investigate the evolution of deep water circulation during the Miocene Climate Optimum (MCO) and Middle Miocene Climate Transition (MMCT). We find that the northward export of southern-sourced deep waters was closely tied to high-latitude climate and Antarctic ice cover variations. Global warming during the MCO drove a progressive decrease in carbonate ion concentration and density stratification, shifting the overturning from intermediate to deeper waters. In the western equatorial Pacific, carbonate dissolution was compensated by increased pelagic productivity, resulting in overall elevated carbonate accumulation rates after ~16 Ma. Stepwise global cooling and Antarctic glacial expansion during the MMCT promoted a gradual improvement in carbonate preservation and the initiation of a near-modern Pacific overturning circulation. We infer that changes in the latitudinal thermal gradient and in Southern Ocean zonal wind stress and upper ocean stratification drove radically different modes of deep water formation and overturning across the MCO and MMCT.

Catalytic conversion of chitin as a nitrogen-containing biomass.

The conversion of chitin enables the utilisation of naturally-fixed nitrogen in addition to carbon toward establishing a sustainable carbon and nitrogen cycle. Chitin is an abundant biomass, 100 Gt per year, but most chitin-containing waste is discarded due to its recalcitrant properties. This feature article summarises the challenges and our work on chitin conversion to N-acetylglucosamine and oligomers with fascinating applications. Afterwards, we introduce recent progress on the chemical transformation of N-acetylglucosamine, followed by a discussion of future perspectives based on current status and findings.

Preparation of Mechanically Anisotropic Polysaccharide Composite Films Using Roll-Press Techniques.

Natural polysaccharides are biocompatible and biodegradable; therefore, they can be used as feedstock for biodegradable structural materials and biomaterials. In this study, anisotropic polysaccharide composite films consisting of chondroitin sulfate C (CS) and chitosan (CHI) were fabricated from their polyion complex (PIC) gels by roll-press techniques. The obtained films (CS/CHI films) were thin and transparent, similar to the composite films prepared by hot-press techniques. The roll-press conditions were optimized, and it was observed that the molecular weight of CHI did not significantly affect the formability of the films, whereas the roll temperature and rolling speed were important. The tensile tests of the roll-pressed films revealed that the mechanical strength of the films in the mechanical direction (MD) was approximately 5 times higher than that in the transverse direction (TD), indicating that the roll-press techniques imparted mechanical anisotropy to the films. Additionally, the films shrank in the MD and expanded in the TD after immersion in aqueous solutions, followed by drying. Such anisotropic shrinking and expanding properties indicate that these films can be used as shape-memory materials.

The FORCIS database: A global census of planktonic Foraminifera from ocean waters.

Planktonic Foraminifera are unique paleo-environmental indicators through their excellent fossil record in ocean sediments. Their distribution and diversity are affected by different environmental factors including anthropogenically forced ocean and climate change. Until now, historical changes in their distribution have not been fully assessed at the global scale. Here we present the FORCIS (Foraminifera Response to Climatic Stress) database on foraminiferal species diversity and distribution in the global ocean from 1910 until 2018 including published and unpublished data. The FORCIS database includes data collected using plankton tows, continuous plankton recorder, sediment traps and plankton pump, and contains ~22,000, ~157,000, ~9,000, ~400 subsamples, respectively (one single plankton aliquot collected within a depth range, time interval, size fraction range, at a single location) from each category. Our database provides a perspective of the distribution patterns of planktonic Foraminifera in the global ocean on large spatial (regional to basin scale, and at the vertical scale), and temporal (seasonal to interdecadal) scales over the past century.

Equatorial Pacific seawater pCO2 variability since the last glacial period.

The ocean may have played a central role in the atmospheric pCO2 rise during the last deglaciation. However, evidence on where carbon was exchanged between the ocean and the atmosphere in this period is still lacking, hampering our understanding of global carbon cycle on glacial-interglacial timescales. Here we report a new surface seawater pCO2 reconstruction for the western equatorial Pacific Ocean based on boron isotope analysis-a seawater pCO2 proxy-using two species of near-surface dwelling foraminifera from the same marine sediment core. The results indicate that the region remained a modest CO2 sink throughout the last deglaciation.

Carbon Monoxide Addition to Ruthenium-Dithiolene Complex and Polysiloxane Hybrid Film Formation.

The addition of carbon monoxide to the ruthenium center of [(η(6) -C6 Me6 )Ru(S2 C6 H4 )] (1) has been investigated. [(η(6) -C6 Me6 )Ru(CO)(S2 C6 H4 )] (2) was obtained by the addition of CO gas to the ruthenium center of 1 in both solution and solid states. 1 was reproduced by treating 2 with an oxidant. A 1/polysiloxane self-standing hybrid film was also prepared and showed a dramatic color change upon transformation of 1 to 2 in polysiloxane hybrid film.