Exploring the length scales, timescales and chemistry of challenging materials (Part 2).

This themed issue explores the different length and timescales that determine the physics and chemistry of a variety of key of materials, explored from the perspective of a wide range of disciplines, including physics, chemistry materials science, Earth science and biochemistry. The topics discussed include catalysis, chemistry under extreme conditions, energy materials, amorphous and liquid structure, hybrid organic materials and biological materials. The issue is in two parts, with this second set of contributions exploring hybrid organic materials, catalysis low-dimensional and graphitic materials, biological materials and naturally occurring, super-hard material as well as dynamic high pressure and new developments in imaging techniques pressure. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Exploring the length scales, timescales and chemistry of challenging materials (Part 1).

This themed issue explores the different length scales and timescales that determine the physics and chemistry of a variety of key materials, explored from the perspective of a wide range of disciplines, including physics, chemistry, materials science, Earth science and biochemistry. The topics discussed include catalysis, chemistry under extreme conditions, energy materials, amorphous and liquid structure, hybrid organic materials and biological materials. The issue is in two parts, with the present part exploring glassy and amorphous systems and materials at high pressure. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Effect of water on the glass transition of a potassium-magnesium carbonate melt.

Calorimetric measurements of the glass transition temperatures (Tg) of hydrous carbonate melts are reported on a near-eutectic composition of 55 mol% K2CO3 - 45 mol% MgCO3 with up to 42 mol% bulk H2O dissolved in the carbonate melt. Hydrous melts were quenched from 750°C to transparent and crystal-free glasses and were subsequently analysed for water content before and after measuring Tg by high-sensitivity differential scanning calorimetry. The glass transition and limited fictive temperatures as a function of the water content were determined at 10 K/min cooling/heating rates resulting in Tg ranging from 245°C at nominally anhydrous conditions to 83°C in the presence of 42 mol% H2O in the glass. Through a generalized Gordon-Taylor analysis, the factors k (7.27), k0 (3.2) and the interaction parameter Ax (0.49) were derived. The limited fictive temperature of a hypothetically, zero water containing 55 mol% K2CO3 - 45 mol% MgCO3 glass is 232 ± 5°C (505 K). The high value of the interaction parameter A indicates strong specific molecular interactions between water and the carbonates in the glassy state and a large decrease in the excess enthalpy of mixing during the conversion of the glassy into the liquid state at the glass transition. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

The local ordering of polar solvents around crystalline carbon nitride nanosheets in solution.

The crystalline graphitic carbon nitride, poly-triazine imide (PTI) is highly unusual among layered materials since it is spontaneously soluble in aprotic, polar solvents including dimethylformamide (DMF). The PTI material consists of layers of carbon nitride intercalated with LiBr. When dissolved, the resulting solutions consist of dissolved, luminescent single to multilayer nanosheets of around 60-125 nm in diameter and Li+ and Br- ions originating from the intercalating salt. To understand this unique solubility, the structure of these solutions has been investigated by high-energy X-ray and neutron diffraction. Although the diffraction patterns are dominated by inter-solvent correlations there are clear differences between the X-ray diffraction data of the PTI solution and the solvent in the 4-6 Å-1 range, with real space differences persisting to at least 10 Å. Structural modelling using both neutron and X-ray datasets as a constraint reveal the formation of distinct, dense solvation shells surrounding the nanoparticles with a layer of Br-close to the PTI-solvent interface. This solvent ordering provides a configuration that is energetically favourable underpinning thermodynamically driven PTI dissolution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Glass transition temperatures and crystallization kinetics of a synthetic, anhydrous, amorphous calcium-magnesium carbonate.

We report the first calorimetric observations of glass transition temperatures and crystallization rates of anhydrous, amorphous calcium-magnesium carbonate using fast scanning differential scanning calorimetry. Hydrous amorphous Ca0.95Mg0.05CO3 · 0.5H2O (ACMC) solid was precipitated from a MgCl2-NaHCO3 buffered solution, separated from the supernatant, and freeze-dried. An aliquot of the freeze-dried samples was additionally dried at 250°C for up to 6 h in a furnace and in a high-purity N2 atmosphere to produce anhydrous ACMC. The glass transition temperature of the anhydrous Ca0.95Mg0.05CO3 was determined by applying different heating rates (1000-6000 K s-1) and correcting for thermal lag to be 376°C and the relaxational heat capacity was determined to be Cp = 0.16 J/(g K). Additionally, the heating rate dependence of the temperature that is associated with the corrected crystallization peaks is used to determine the activation energy of crystallization to be 275 kJ mol-1. A high-resolution transmission electron microscopy study on the hydrous and anhydrous samples provided further constraints on their compositional and structural states. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Cd/Pt Precursor Solution for Solar H2 Production and in situ Photochemical Synthesis of Pt Single-atom Decorated CdS Nanoparticles.

Despite extensive efforts to develop high-performance H2 evolution catalysts, this remains a major challenge. Here, we demonstrate the use of Cd/Pt precursor solutions for significant photocatalytic H2 production (154.7 mmol g-1 h-1 ), removing the need for a pre-synthesized photocatalyst. In addition, we also report simultaneous in situ synthesis of Pt single-atoms anchored CdS nanoparticles (PtSA -CdSIS ) during photoirradiation. The highly dispersed in situ incorporation of extensive Pt single atoms on CdSIS enables the enhancement of active sites and suppresses charge recombination, which results in exceptionally high solar-to-hydrogen conversion efficiency of ≈1 % and an apparent quantum yield of over 91 % (365 nm) for H2 production. Our work not only provides a promising strategy for maximising H2 production efficiency but also provides a green process for H2 production and the synthesis of highly photoactive PtSA -CdSIS nanoparticles.

Structure and Liquid Fragility in Sodium Carbonate.

The relationship between local structure and dynamics is explored for molten sodium carbonate. A flexible fluctuating-charge model, which allows for changes in the shape and charge distribution of the carbonate molecular anion, is developed. The system shows the evolution of highly temperature-dependent complex low-dimensional structures which control the dynamics (and hence the liquid fragility). By varying the molecular anion charge distribution, the key interactions responsible for the formation of these structures can be identified and rationalized. An increase in the mean charge separation within the carbonate ions increases the connectivity of the emerging structures and leads to an increase in the system fragility.

The structure of liquid alkali nitrates and nitrites.

High energy X-ray diffraction has been combined with containerless techniques to determine the structure of a series of alkali and ammonium nitrate and nitrite liquids. The systems have been modelled using molecular dynamics simulation which allows for the flexibility of, and movement of charge within, the molecular anions. The model reproduces the experimentally-determined scattering functions in both the low- and high-Q regimes reflecting the inter- and intra-molecular length-scales. For ammonium nitrate the best fit to the diffraction data is obtained by assuming the NH4+ cation to have a radius closer to that for Cs+ rather than a smaller cation such as Rb+ as often previously assumed. The alkali nitrites show an emergent length scale, attributed to the nitrogen-nitrogen spatial correlations, that depends on both temperature and the identity of the alkali cation. The corresponding nitrates show a more subtle effect in the nitrogen-nitrogen correlations. As a result, the nature of this N-N length-scale appears different for the respective nitrites and nitrates.

High-pressure transformation of SiO2 glass from a tetrahedral to an octahedral network: a joint approach using neutron diffraction and molecular dynamics.

A combination of in situ high-pressure neutron diffraction at pressures up to 17.5(5) GPa and molecular dynamics simulations employing a many-body interatomic potential model is used to investigate the structure of cold-compressed silica glass. The simulations give a good account of the neutron diffraction results and of existing x-ray diffraction results at pressures up to ~60 GPa. On the basis of the molecular dynamics results, an atomistic model for densification is proposed in which rings are "zipped" by a pairing of five- and/or sixfold coordinated Si sites. The model gives an accurate description for the dependence of the mean primitive ring size ⟨n⟩ on the mean Si-O coordination number, thereby linking a parameter that is sensitive to ordering on multiple length scales to a readily measurable parameter that describes the local coordination environment.

Low frequency vibrational dynamics and polyamorphism in Y2O3-Al2O3 glasses.

Glass formation, and associated potential polyamorphism are investigated for the key ceramic Y2O3-Al2O3 using a combination of experimental and theoretical techniques. Liquid samples are rapidly cooled by drop quenching and high and low density amorphous regions (LDA and HDA respectively) are identified using reflected light microscopy. Raman spectra are obtained to low frequency focussed on regions identified as pure LDA or HDA. The respective compositions of these regions are confirmed by electron microprobe analysis. These spectra are used to extract the vibrational densities of states and these are compared with those generated for the liquid oxide using polarizable-ion molecular dynamics simulations. The experimental and simulated spectra are used to determine the low temperature heat capacities. The low frequency regions of the spectra display an excess of states (boson peaks) which are different for the two glasses. Thermodynamic modelling is used to demonstrate how samples of the same composition my vitrify or not depending upon the quench rate.

Maternal non-Mendelian inheritance of a reduced lifespan? A hypothesis.

PURPOSE: A negative correlation exists between advanced maternal age and reproduction. Current data suggest that this correlation is due to a decline in oocyte quality with respect to female age. Since a new individual is derived from the fusion of a single sperm and egg, we tested whether the quality of this material could influence the long-term physiological health of offspring, by examining whether a link between parental age and lifespan of offspring exists. METHODS: We requested a search from the Swedish demographic database POPUM 3 maintained by the University of Umeå, Sweden between years 1700 and 1900. Parameters requested included mothers' and fathers' age at gestation, the lifespan of the children, cause of death of children and the region of birth. RESULTS: Complete data was obtained for 30,512 children born to 12,725 mothers and fathers. Kaplan-Meier estimators demonstrated a strong relationship between mother's age at gestation and the longevity of offspring. Extrinsic factors such as century of birth also had an effect on the data. The forward stepwise procedure on Cox's model of proportional hazards suggested that most significant intrinsic factors were mother's lifespan and mother's age at gestation. CONCLUSIONS: These data demonstrate that intrinsic and extrinsic factors influence the lifespan of children. Among intrinsic factors, mother's lifespan and age at gestation had a significant influence on the data. The influence of intrinsic factors remained significant despite a strong extrinsic influence. We suggest that the influence of the mother on the lifespan of offspring is due to extra-genomic factors.

Atomically dispersed asymmetric cobalt electrocatalyst for efficient hydrogen peroxide production in neutral media.

Electrochemical hydrogen peroxide (H2O2) production (EHPP) via a two-electron oxygen reduction reaction (2e- ORR) provides a promising alternative to replace the energy-intensive anthraquinone process. M-N-C electrocatalysts, which consist of atomically dispersed transition metals and nitrogen-doped carbon, have demonstrated considerable EHPP efficiency. However, their full potential, particularly regarding the correlation between structural configurations and performances in neutral media, remains underexplored. Herein, a series of ultralow metal-loading M-N-C electrocatalysts are synthesized and investigated for the EHPP process in the neutral electrolyte. CoNCB material with the asymmetric Co-C/N/O configuration exhibits the highest EHPP activity and selectivity among various as-prepared M-N-C electrocatalyst, with an outstanding mass activity (6.1 × 105 A gCo-1 at 0.5 V vs. RHE), and a high practical H2O2 production rate (4.72 mol gcatalyst-1 h-1 cm-2). Compared with the popularly recognized square-planar symmetric Co-N4 configuration, the superiority of asymmetric Co-C/N/O configurations is elucidated by X-ray absorption fine structure spectroscopy analysis and computational studies.

Structural changes in supercooled Al2O3-Y2O3 liquids.

Structural changes in liquids between Al2O3 and Y2O3 are investigated as a function of the composition and during supercooling using high energy X-ray diffraction (HEXRD) techniques combined with containerless aerodynamic levitation. Many-body molecular dynamics simulation techniques utilizing potential models that incorporate anion polarization effects are applied to study the same liquid systems. The X-ray scattering experiments indicate a change in liquid structure during supercooling around a composition 20% Y2O3 (AlY20) that occurs over a narrow temperature interval. We have associated this change in structure with the onset of a liquid-liquid phase transformation. Analysis of the MD simulated structures has allowed the structure changes to be interpreted in terms of Al(3+) and Y(3+) coordination environments and particularly the Y(3+)-Y(3+) structural correlations. We show that the incipient liquid-liquid phase transition behaviour is correlated with local density fluctuations that represent different coordination polyhedra surrounding oxygen ions. The difference in energy and volume associated with this sampling of high and low density basins in the underlying energy landscape is consistent with independent verifications of the volume and enthalpy differences between different amorphous forms. The differences in the high- and low-density configurations match the difference in diffraction patterns observed experimentally.

Understanding the emergence of the boson peak in molecular glasses.

A common feature of glasses is the "boson peak", observed as an excess in the heat capacity over the crystal or as an additional peak in the terahertz vibrational spectrum. The microscopic origins of this peak are not well understood; the emergence of locally ordered structures has been put forward as a possible candidate. Here, we show that depolarised Raman scattering in liquids consisting of highly symmetric molecules can be used to isolate the boson peak, allowing its detailed observation from the liquid into the glass. The boson peak in the vibrational spectrum matches the excess heat capacity. As the boson peak intensifies on cooling, wide-angle x-ray scattering shows the simultaneous appearance of a pre-peak due to molecular clusters consisting of circa 20 molecules. Atomistic molecular dynamics simulations indicate that these are caused by over-coordinated molecules. These findings represent an essential step toward our understanding of the physics of vitrification.

Intracytoplasmic injection of morphologically selected spermatozoa (IMSI) improves outcome after assisted reproduction by deselecting physiologically poor quality spermatozoa.

PURPOSE: We used computer assisted sperm selection (MSOME) during cycles of intracytoplasmic sperm injection to test whether this technique improves results over traditional ICSI protocols. We also used the TUNEL assay to test whether MSOME could deselect physiologically abnormal spermatozoa. METHODS: Individual spermatozoa were examined with MSOME. Normal and abnormal spermatozoa were tested for the level of DNA fragmentation using TUNEL assay. In a prospective, randomized trial, patients were selected for standard ICSI, or IMSI techniques. We tested the two groups for biological and clinical parameters. RESULTS: 64.8% of spermatozoa, otherwise selectable for ICSI, were characterized by abnormalities after computer-assisted sperm analysis. These sperm were also characterized by an increase in the level of DNA fragmentation. We noted an increase in embryo quality, pregnancy and implantation rates after computerized sperm selection during ICSI procedures. CONCLUSIONS: Computerised selection of spermatozoa during ICSI procedures deselects physiological abnormal spermatozoa and improves clinical results.

How do spermatozoa activate oocytes?

Although the spermatozoon is 500,000 times smaller in volume than the oocyte, it induces rapid and dramatic changes in oocyte physiology that lead to meiosis re-initiation. These oocyte activation events are described here, as is the evidence for a soluble activating factor in the spermatozoon. Since changes in plasma membrane conductance, calcium ion release and maturation-promoting factor inactivation are common to all animal oocytes at activation, it is expected that the sperm-borne trigger is also ubiquitous. One likely candidate, phospholipase C (PLC) zeta 1, induces calcium release in mammalian oocytes; however, work on other deuterostomes suggests that the sperm factor is non-specific and multifactorial, regulating several activation events. Human, sea urchin and ascidian gametes are remarkably similar and comparative studies across the deuterostomes may help in elucidating basic principles in fertilization. Questions to be answered include the identification of PLC zeta 1 in invertebrate spermatozoa and the characterization of other targets in mammalian oocytes, such as the adenosine diphosphate ribose/nitric oxide pathway.

Human cleavage-stage embryo vitrification is comparable to slow-rate cryopreservation in cycles of assisted reproduction.

OBJECTIVES: To compare embryo survival, pregnancy and implantation rates after cryopreservation of human cleavage-stage embryos with slow-rate cryopreservation or vitrification. STUDY DESIGN: 262 patients, attending for assisted reproduction, were prepared for oocyte retrieval using standard controlled ovarian hyperstimulation protocols. Excess embryos were cryopreserved on day 3 either by vitrification, or slow-rate cryopreservation in a programmable freezer. Cycles of thawing were monitored for thaw efficiency, pregnancy and implantation rates. RESULTS: Clinical pregnancy and implantation rates were highly comparable between cycles in which day 3 embryos were thawed either after slow-rate cryopreservation or vitrification. CONCLUSIONS: These data suggest that vitrification of human embryos during assisted reproduction cycles achieves comparable success rates to fresh cycles and therefore can be applied in the laboratory of assisted reproduction.

Aquaporin-like water transport in nanoporous crystalline layered carbon nitride.

Designing next-generation fuel cell and filtration devices requires the development of nanoporous materials that allow rapid and reversible uptake and directed transport of water molecules. Here, we combine neutron spectroscopy and first-principles calculations to demonstrate rapid transport of molecular H2O through nanometer-sized voids ordered within the layers of crystalline carbon nitride with a polytriazine imide structure. The transport mechanism involves a sequence of molecular orientation reversals directed by hydrogen-bonding interactions as the neutral molecules traverse the interlayer gap and pass through the intralayer voids that show similarities with the transport of water through transmembrane aquaporin channels in biological systems. The results suggest that nanoporous layered carbon nitrides can be useful for developing high-performance membranes.

Mitochondria and human preimplantation embryo development.

Human reproduction, like all biological systems, is characterised by a large level of variability. In this field, the variability is observed as a large difference in implantation potential of human embryos developing in vitro, despite similarities in observable parameters such as rate of development and morphology of these embryos. One of the underlying factors that determines developmental potential in these embryos is the availability of energy in the form of ATP for development. Here, we suggest that, despite the evidence suggesting that mitochondrial metabolism is relatively inactive during preimplantation embryo development, aerobic (mitochondrial) metabolism contributes a major role in the supply of ATP. A second pathway, anaerobic respiration, is also active and the two pathways work in synchrony to supply all the ATP necessary. We discuss the differences in the two forms of energy production and suggest that, although anaerobic respiration can supplement deficiencies in the energy supply in the short term, this is not sufficient to substitute for aerobic respiration over long periods. Therefore, we suggest that deficiencies in the levels of aerobic respiration can explain variability in the implantation potential of apparently equivalent embryos.

CO3+1 network formation in ultra-high pressure carbonate liquids.

Carbonate liquids are an important class of molten salts, not just for industrial applications, but also in geological processes. Carbonates are generally expected to be simple liquids, in terms of ionic interactions between the molecular carbonate anions and metal cations, and therefore relatively structureless compared to more "polymerized" silicate melts. But there is increasing evidence from phase relations, metal solubility, glass spectroscopy and simulations to suggest the emergence of carbonate "networks" at length scales longer than the component molecular anions. The stability of these emergent structures are known to be sensitive to temperature, but are also predicted to be favoured by pressure. This is important as a recent study suggests that subducted surface carbonate may melt near the Earth's transition zone (~44 km), representing a barrier to the deep carbon cycle depending on the buoyancy and viscosity of these liquids. In this study we demonstrate a major advance in our understanding of carbonate liquids by combining simulations and high pressure measurements on a carbonate glass, (K2CO3-MgCO3) to pressures in excess of 40 GPa, far higher than any previous in situ study. We show the clear formation of extended low-dimensional carbonate networks of close CO32- pairs and the emergence of a "three plus one" local coordination environment, producing an unexpected increase in viscosity with pressure. Although carbonate melts may still be buoyant in the lower mantle, an increased viscosity by at least three orders of magnitude will restrict the upward mobility, possibly resulting in entrainment by the down-going slab.