Large Ring Structures Research Articles

Solvent Effect for the Structural Control of Molecular Architectures Consisting of Trinuclear Ruthenium Clusters and Ligands at the HOPG Surface.

The molecular architecture of a triruthenium complex and 1,4-di(4-pyridyl)benzene on highly oriented pyrolytic graphite was investigated by drop-casting mixed tetrahydrofuran and methanol solutions. Atomic force microscopy revealed the formation of one-dimensional molecular wires on highly oriented pyrolytic graphite after heating the mixed tetrahydrofuran solution, whereas large ring structures were formed in the methanolic solution. It was found that the molecular architectures composed of triruthenium complexes and 1,4-di(4-pyridyl)benzene strongly depend not only on the temperature of the solution but also on the organic solvents. The formation of the molecular architecture was supported by the ultraviolet-visible absorption spectra of the mixed solution and the electrochemical responses of the deposited film.

Co-pyrolysis of low-rank coal and rice stalk: A comprehensive study on product distributions, product properties, and synergistic effects

Co-pyrolysis of low-rank coal and rice stalk is an important way to achieve hierarchical and efficient utilization of energy. This work explored how blend ratios (0–100 wt%) and temperatures (773–1073 K) affect pyrolysis product distribution and characteristics. The results showed that a higher rice straw ratio (80 wt%) significantly reduced the yield of char (22.38–26.9 wt%) compared with 20 wt% of rice straw at different temperatures. The yield and physicochemical properties of target products were closely related to process parameters, which can provide a promising opportunity to acquire desired products by reaction conditions optimization. Co-pyrolysis was able to inhibit the production of large aromatic ring structures in char. High temperature promoted the generation of cross-linked structures, which was influenced by the blend ratio. The synergistic effects of BET surface area and pore volume were most pronounced when the J content was 40 wt% at 873 K, and their increments were 59.6 m2/g and 0.027 cm3/g, respectively. For the char derived from lower rice straw proportions (0, 20, and 40 wt%), the main combustion range and the maximum combustion rate temperature showed a progressive shift towards higher values with temperature increasing. The research is valuable of guiding high-value utilization of agricultural residues and energy transitions.

Copine C plays a role in adhesion and streaming in Dictyostelium

ABSTRACT Copines are a family of calcium-dependent membrane-binding proteins. To study these proteins, anull mutant for cpnC was created in Dictyostelium, which has six copines genes (cpnA-cpnF). During development, cpnC− cells were able to aggregate, but did not form streams. Once aggregated into mounds, they formed large ring structures. cpnC− cells were less adherent to plastic substrates, but more adherent to other cells. These phenotypes correlated with changes in adhesion protein expression with decreased expression of SibA and increased expression of CsaA in developing cpnC− cells. We also measured the expression of RegA, a cAMP phosphodiesterase, and found that cpnC− cells have reduced RegA expression. The reduced RegA expression in cpnC− cells is most likely responsible for the observed phenotypes.

Structural changes and product distribution of typical Xinjiang coals and chars during pyrolysis

AbstractThis study used micro‐Raman spectroscopy, gas chromatography–mass spectrometry (GC–MS), and gas chromatography–flame ionization detector/thermal conductivity detector (GC–FID/TCD) to analyze the structure and pyrolysis reactions of nine typical coals and chars from Xinjiang. The study fitted 10 Gaussian bands of typical Xinjiang coal and investigated the changes in coal structure during coalification and pyrolysis. The results indicated that the reduction degree of CO structures in coal during coalification had a rough linear relationship with the Vdaf (dry ash‐free volatile matter) content. During coalification, the condensation of aromatic rings is accompanied by a continuous decrease of CO structures, while the contents of cross‐linking and substitution structures decrease persistently relative to the large aromatic ring structures. The influence of coal type on char yield for typical Xinjiang coal is within 15 wt.%; the influence on tar yield is within 8.5%, with a greater impact on the yield of alkanes and phenols in tar; the influence on CO yield in pyrolysis gas is within 6.3%. The relative content of large aromatic ring structures in coal is relatively stable during pyrolysis, while the relative content of small aromatic ring structures declines as coal transforms into char. The study inferred that small aromatic rings might decompose and transform into tar after pyrolysis reaction, which also resulted in a high selectivity of phenolic products in tar from most coal pyrolysis above 40%. This study revealed the structural changes and pyrolysis product distribution of nine typical coals and chars from Xinjiang, providing useful information for their utilization.

The Unique N-Terminal Domain of Chlamydial Bactofilin Mediates Its Membrane Localization and Ring-Forming Properties.

Chlamydia trachomatis is an obligate intracellular bacterial pathogen. In evolving to the intracellular niche, Chlamydia has reduced its genome size compared to other bacteria and, as a consequence, has a number of unique features. For example, Chlamydia engages the actin-like protein MreB, rather than the tubulin-like protein FtsZ, to direct peptidoglycan (PG) synthesis exclusively at the septum of cells undergoing polarized cell division. Interestingly, Chlamydia possesses another cytoskeletal element-a bactofilin ortholog, BacA. Recently, we reported BacA is a cell size-determining protein that forms dynamic membrane-associated ring structures in Chlamydia that have not been observed in other bacteria with bactofilins. Chlamydial BacA possesses a unique N-terminal domain, and we hypothesized this domain imparts the membrane-binding and ring-forming properties of BacA. We show that different truncations of the N terminus result in distinct phenotypes: removal of the first 50 amino acids (ΔN50) results in large ring structures at the membrane whereas removal of the first 81 amino acids (ΔN81) results in an inability to form filaments and rings and a loss of membrane association. Overexpression of the ΔN50 isoform altered cell size, similar to loss of BacA, suggesting that the dynamic properties of BacA are essential for the regulation of cell size. We further show that the region from amino acid 51 to 81 imparts membrane association as appending it to green fluorescent protein (GFP) resulted in the relocalization of GFP from the cytosol to the membrane. Overall, our findings suggest two important functions for the unique N-terminal domain of BacA and help explain its role as a cell size determinant. IMPORTANCE Bacteria use a variety of filament-forming cytoskeletal proteins to regulate and control various aspects of their physiology. For example, the tubulin-like FtsZ recruits division proteins to the septum whereas the actin-like MreB recruits peptidoglycan (PG) synthases to generate the cell wall in rod-shaped bacteria. Recently, a third class of cytoskeletal protein has been identified in bacteria-bactofilins. These proteins have been primarily linked to spatially localized PG synthesis. Interestingly, Chlamydia, an obligate intracellular bacterium, does not have PG in its cell wall and yet possesses a bactofilin ortholog. In this study, we characterize a unique N-terminal domain of chlamydial bactofilin and show that this domain controls two important functions that affect cell size: its ring-forming and membrane-associating properties.

Experimental study of the catalytic effect of iron on low-rank coal gasification

Acid-washing low-rank coal samples were loaded with different content of iron catalyst and then pyrolyzed. FT-IR, Raman spectra, and temperature-programmed experiments were used to investigate the influence of iron on the coal char. The FT-IR results revealed that iron catalyst rises the number of –OH, –CH3, and –CH2 functional groups. The Raman spectra results showed that partial large polyaromatic ring structures transform into small polyaromatic ring structures after the addition of iron. The results of temperature-programmed desorption indicated that the number of surface active sites is increased due to the addition of iron. For low-rank coal char with 3% Fe, the number of active sites increased with the increase of adsorption temperature until 800 °C and then start to decrease. At 750 °C, the adsorption capacity of CO2 increased with the increase of time and reached saturation state after 45 min. The results of the char-steam isothermal gasification experiment suggested that the iron catalyst enhances the gasification reactivity of low-rank coal. It is verified that iron catalysts can improve the gasification reactivity of low-rank coal by increasing the number of surface active sites.

Binding and/or hydrolysis of purine-based nucleotides is not required for IM30 ring formation.

IM30, the inner membrane-associated protein of 30kDa, is conserved in cyanobacteria and chloroplasts. Although its exact physiological function is still mysterious, IM30 is clearly essential for thylakoid membrane biogenesis and/or dynamics. Recently, a cryptic IM30 GTPase activity has been reported, albeit thus far no physiological function has been attributed to this. Yet, it is still possible that GTP binding/hydrolysis affects formation of the prototypical large homo-oligomeric IM30 ring and rod structures. Here, we show that the Synechocystis sp. PCC 6803 IM30 protein in fact is an NTPase that hydrolyzes GTP and ATP, but not CTP or UTP, with about identical rates. While IM30 forms large oligomeric ring complexes, nucleotide binding and/or hydrolysis are clearly not required for ring formation.

Structural evolution of rubber-wood char under different pyrolysis conditions

In order to explore the effect of different pyrolysis conditio ns on the structural characteristics of rubber wood biomass pyrolysis, rubber wood char was prepared under fast pyrolysis and slow pyrolysis conditions. The char was analyzed by BET, SEM, FT-IR and Raman spectroscopy to explore the effects of different pyrolysis conditions on pore characteristics, surface structure and chemical structure. The results showed that the nitrogen isothermal adsorption/desorption curves of slow pyrolysis at 900°C are obviously different, and the char structure has a certain amount of mesopores and macropores. With the pyrolysis temperature increased, the alkane side chain of rubber wood char broke, and formeda large number of active sites, which promoted the condensation of small aromatic rings into large aromatic ring structures, and deepened the aromatization of char structures. The rapid pyrolysis method causes the content of the small aromatic ring structure to be greater than that of the large aromatic ring structure at low temperature. The slow pyrolysis method causes the increase of the large aromatic ring structure to be greater than that of the small aromatic ring at a lower temperature contrarily.

Understanding thermal expansion of pressurized silica glass using topological pruning of ring structures

AbstractWe investigate the structural origin of the large thermal expansion coefficient of hot‐compressed silica glass upon heating to a threshold temperature using molecular dynamics (MD) simulations. While the simulated thermal expansion at low temperature correlates well with the elongation of the average interatomic separation distance of the Si–O or Si–Si pair, the excess thermal expansion due to hot compression mainly results from change in medium range order, including a decrease in the population of large rings upon heating, without significant modification of the small ring population and without changing the short range ordering, such as the Si‐O coordination number. The reduction in the characteristic ring size can be connected to the high thermal expansion through the topological pruning mechanism. Such large thermal expansion is suppressed when the silica glasses are held at their respective quench pressures. The suppression of this excess thermal expansion is consistent with the pressure stabilization of the large ring structures.

Susceptibility Pattern of Enteric Bacteria Isolated During Raining Season in Some Areas of Ado-Ekiti to Macrolide Antibiotics

Background: Macrolides are considered one of the oldest classes of antibiotics which have been regarded among the best-tolerated antibiotic for almost several years. They are characterized by their large lactone ring structures and by their growth-inhibiting (bacteriostatic) effects on bacteria. Aim: The potency of macrolide antibiotics were determined against enteric bacteria (E. coli, Shigella spp. and Salmonella spp.) isolated during the raining season between June to September in the year 2018 from locations in Ado Ekiti metropolis. The consequences of the presence of these bacteria can be fatal hence the need to investigate their susceptibility to macrolide antibiotics. Methodology: The bacteria were isolated from well water, soil and drainage samples obtained at Erifun, Omisanjana, Fiyinfoluwa, Ajilosun areas using serial dilution method. Results: It was observed that the bacteria were susceptible to 250 µg/mL and 500 µg/mL concentration of Azithromycin, Erythromycin, and Clarithromycin though with varying degrees of susceptibility. Azithromycin showed the highest potency.Conclusion: The present study indicated samples of the well water, soil and drainage at Erifun, Omisanjana, Ajilosun and Fiyinfoluwa areas of Ado-Ekiti were severely contaminated with E. coli, Salmonella spp., and Shigella spp. this is due to the lack of adequate sanitary measures. However, unhygienic behaviour like indiscriminate disposal of waste and open defecation should be discouraged.

Study on the effects of steam on the precipitation characteristics of sodium during coal thermal conversion

The char samples were prepared from the coal impregnated with NaCl under different steam concentrations and temperatures. The mode of occurrence of sodium and the contents of sodium in different chars with the same conversion ratio were analyzed by inductively coupled plasma mass spectrometry. The effects of steam and temperature on the migration and transformation of sodium in the coal during the thermal conversion processes were studied. The results showed that the increase of steam concentration enhanced the release of water-soluble sodium during the thermal conversion of coal and promoted the transformation of water-soluble sodium into ammonium acetate, hydrochloric acid and insoluble sodium. As a result, the release of sodium was suppressed to a certain extent. It was also observed that increasing the reaction temperature could promote the release of water-soluble sodium and promote the transformation of water-soluble sodium to the other soluble forms of sodium. The evolution of char structure was an important influence on the release of sodium. The results revealed that the degrees of char condensation increased with the steam gasification reaction. The formation of large aromatic ring structures from the condensation of the small aromatic rings played the important role in the encapsulation of sodium, which would inhibit the release of sodium.

Geological Position and Structural Control of Ore Mineralization in the Toupugol–Khanmeishor District (the Polar Urals) Based on the Remote Sensing Results

Large ring, arc, and radial structures have been identified by complex processing of the multispectral satellite imagery of the Landsat. These structures control the gold mineralization position in the Toupugol–Khanmeishor ore district (Novogodnenskoe ore cluster, Polar Urals). This area has been compared with the Tur’insk–Auerbakh ore district (Auerbakh ore cluster, Northern Urals). Similar geological features, regularity in the structures, and the location of gold mineralization in the system of morphostructures have been revealed. The formation depth of the magmatic chambers has been determined for the Novogodnenskoe and Auerbakh paleovolcanic structures for the first time. These chambers are located at depths of ~4 and ~20 km, respectively, in the upper and middle parts of the earth’s crust. The Novogodnenskoe structure is a monogenic structure. It was formed under the influence of one leading geological process. The Auerbakh structure is a larger and more complex structure; it is characterized by a long and multistage development. According to the paleovolcanic reconstruction results, the root (focal) part of the Auerbakh structure plunged from the southeast to the northwest during the evolution of the magmatic process. Gold mineralization within the studied areas of the Northern Urals is confined to the intersections of radial faults near the centers of large concentric morphostructures.

Geological position and structural control of ore mineralization of the Toupugol-Khanmeyshorsky district (the Polar Urals) as a result of remote sensing

Large ring, arc and radial structures were identified based on complex processing of the multispectral satellite imagery of the Landsat apparatus. These structures control the position of gold mineralization of the Toupugol-Khanmeyshorsky ore district (Novogodnenskoe ore cluster, the Polar Urals). The comparative characteristic of this territory with the Turinsk-Auerbakh ore district (Auerbach ore cluster, the Northern Urals) was held. Similar geological features, regularity of the structures and location of gold mineralization in the system of morphostructures were revealed. For the first time, the depths of the formation of magmatic chambers were determined for the Novogodnensky and Auerbach paleovolcanic structures. These chambers were located at depths of ~4 km and ~20 km, respectively in the upper and middle parts of the earth's crust. These are sitting. The Novogodnensky structure is a monogenic structure. It formed under the influence of one leading geological process. The Auerbach structure is larger and more complex structure; it is characterized by a long and multi-stage development. The paleovolcanic reconstruction showed that the root (focal) part of the Auerbach structure plunges from the southeast to the northwest during of the magmatic process evolution. Gold mineralization within the studied areas of the Northern Urals is confined to the intersections of radial faults near the centers of large concentric morphostructures.

Effect of steam concentration on demineralized coal char surface behaviors and structural characteristics during the oxy-steam combustion process

Abstract Oxy-steam combustion, fuel combusts in O2/H2O atmosphere, is treated to be a novel and promising technology for the next generation oxy-fuel combustion. The purpose of this study is to identify the effects of steam concentration on NO emission characteristics, functional group distribution and char NO reducibility during oxy-steam combustion process. A typical bituminous coal (SH) was employed for demineralization, devolatilization, combustion in O2/H2O environment, and investigated by Temperature Programmed Desorption/Reduction (TPD/TPR) methods and Raman spectrometer. The combustion results illustrated that char N/NO conversion during the oxy-steam combustion tests initially decreased with an increasing steam concentration in low range (1.2–8.5 vol.%), while increased apparently in high steam range (8.5–20 vol.%). Decomposition of H2O molecules promoted the formation of C(O) and small aromatic rings on particle surface at the low steam range; the high concentration of steam could promote the condensation of aromatic ring structures in char, leading to significant generation of large aromatic ring structures with a lower reactivity and the reduction of surface active sites (Cf). The TPD results illustrated that the chars oxidized at moderate steam concentration (8.5 vol.%), and the chars with moderate burnout degrees (such as S3, S6 and S11) had the largest amount of C(O). Due to the decomposition of the C(O) into new Cf and massive CO molecules, a rapid acceleration of NO reduction rate occurred in the temperature range of 1000–1400 K during the TPR process of each sample obtained from identical reaction conditions. Thus, variations in char surface behavior and microstructure might be the primary reasons affecting char-N emission.

The excitation mechanisms and evolutionary stages of UWISH2 planetary nebula candidates

We present medium-resolution K-band long-slit spectroscopy of 29 true, likely, possible and candidate Galactic Plane planetary nebulae (PNe) from the UWISH2 survey - many of which have only been recently discovered. These objects are bright in molecular hydrogen (H2) emission, and many have bipolar morphologies. Through the detection of the Br{\gamma} emission line, which traces ionized hydrogen, we find that the majority of the candidate PNe are indeed likely to be PNe, while 2 of the targets are more likely young stellar objects (YSOs) or pre-planetary nebulae (pPNe). We detect Br{\gamma} in 13 objects which have no detection in IPHAS or SHS H{\alpha} surveys. This implies they are potential members of the little-known optically-obscured PN population, hidden from wide-field optical surveys. We use the spatial extent of the H2 1-0 S(1) and Br{\gamma} lines to estimate the evolutionary stage of our targets, and find that W-BPNe (bipolar PNe with pinched waist morphologies) are likely to be younger objects, while R-BPNe (bipolar PNe with large ring structures) are more evolved. We use line ratios to trace the excitation mechanism of the H2, and find the 1-0 S(1) / 2-1 S(1) and 1-0 S(1) / Br{\gamma} ratios are higher for R-BPNe, implying the H2 is thermally excited. However, in W-BPNe, these ratios are lower, and so UV-fluorescence may be contributing to the excitation of H2.

Catalytic mechanism of ion-exchanging alkali and alkaline earth metallic species on biochar reactivity during CO2/H2O gasification

To understand the detailed catalytic mechanism of ion-exchanging AAEM species on biochar structure and its specific reactivity during CO2/H2O gasification, the experiments were carried out in a laboratory fixed-bed reactor at 800 °C, with two kinds of AAEM-loading methods. The migration and precipitation characteristics of AAEM species was evaluated by ICP-AES, while the transformation of biochar structures were analyzed by FTIR and Raman. The specific reactivity of H2O/CO2 gasification biochar was determined by TGA analysis in Air at 370 °C. The results show that the stronger catalytic properties of K and Ca species in H2O atmosphere are obtained than that in CO2. The effect of K is mainly on the formation of O-containing functional groups (e.g. alcohol/phenolic-OH, aldehyde/ester CO and carboxylic COO groups) and the transformation from small ring systems to larger ones, while the catalytic effect of Ca is only to increase the proportion of large aromatic ring structures (≥6 fused benzene rings). The biochar-CO2 reaction took place mainly at the gas-solid interface of biochar, while biochar-H2O one existed throughout the biochar particle. A better distribution of active sites (i.e. surface K/Ca species and O-containing groups) on biochar surface would result in the high specific reactivity of biochar during gasification.

(Invited) Electrolytic Macrocyclizations on Scale

Electrochemical oxidation at surfaces can elicit unique reactivity and facilitate transformations that would be difficult, if not impossible, otherwise. This lecture will describe an example wherein complex macrocycle formation was uniquely enabled by anodic oxidation. Adaptations of the method for use on manufacturing scales will be discussed, as will attempts to generalize the technique for constructing other highly functionalized, large ring structures.

Polymerization and cracking during the hydrotreatment of bio-oil and heavy fractions obtained by fractional condensation using Ru/C and NiMo/Al2O3 catalyst

Two-step hydrotreatment experiments were performed using three completely different bio-oil fractions namely: whole bio-oil, heavy bio-oil obtained after fractional condensation of pyrolysis vapours and pyrolytic lignin obtained by cold water precipitation of the bio-oil. The aim is to study the de-oxygenation and in addition SEC and UV-fluorescence analysis was used to identify the importance of cracking, polymerization and hydrogenation reactions of the three different bio-oil feedstocks. In the first step hydrotreatment, Ru/C was used at 250 or 300°C with reaction time of 2h. In the second step hydrotreatment, Ni-Mo/Al2O3 catalyst was used at 375 or 400°C, with reaction time of 2 or 4h. During stabilization in the first step, pyrolytic lignin was hydrogenated to a large extent accompanied by cracking reactions. In the second step, unsulphided Ni-Mo/Al2O3 catalyst was active enough to effectively crack pyrolytic lignin into smaller molecules. High molecular weight compounds including large aromatic ring structures were formed from the reactive sugar rich fraction in both first step stabilization and second step hydrotreatment. The newly formed polymerization products were difficult to crack even at extended reaction times of 4h at 400°C. Importantly, the presence of water (and light oxygenates) could significantly supress the polymerization reactions.

The role of water in coesite crystallization from silica gel

Structural changes in silica gel after compression to 5 GPa and 100 °C for one hour were investigated using Raman and IR spectroscopies and X-ray diffraction measurements. The non-powdered silica gel sample was entirely crystallized to coesite under these experimental conditions, showing that the crystallization of silica gel to coesite can be readily achieved in spite of the low temperature conditions and short duration. This behavior may result because the average structure of silica gel is dominated by four-membered rings of SiO 4 tetrahedra, there is a less-polymerized network structure due to the presence of silanol (Si-OH), and larger ring structures, such as 6- and 8-membered rings, of SiO 4 tetrahedra are disrupted by water molecules under pressure. These properties may lead to successive polymerization and reconstruction of the SiO 4 tetrahedra in the bulk silica-gel sample, enabling the easy formation of the coesite-like network structure. This shows the importance of the contribution of silanol and water molecules for coesite formation.

Numerical investigation on chaos in late boundary layer transition to turbulence

The mechanism of chaos in late boundary layer transition is a key issue of the laminar-turbulent transition process in a flat plate boundary layer. A careful study on the characteristic of chaos is carried out by high order direct numerical simulation (DNS). The process of flow chaos was originally considered as a result of large background noise and non-periodic spanwise boundary conditions. It was addressed that the large ring structures are affected by background noises first, and then the change of large ring structures affect the small scale vortices quickly, which directly lead to chaos and formation of turbulent flow. However, according to our DNS observation, the loss of symmetry starts from the middle level vortex rings while the top and bottom rings are still symmetric. The non-symmetric structure of second level vortex rings will influence the small scale vortices at the boundary layer bottom quickly. The loss of symmetry at the bottom of the boundary layer quickly spreads to upper level through ejections. This will lead to chaos of the whole flow field. Therefore, the internal instability of multiple level ring structures, especially the middle ring cycles, is the main reason for the process of flow chaos, but not the large background noise.