Designing Glass and Crystalline Phases of Metal-Bis(acetamide) Networks to Promote High Optical Contrast.

Owing to their high tunability and predictable structures, metal-organic materials offer a powerful platform to study glass formation and crystallization processes and to design glasses with unique properties. Here, we report a novel series of glass-forming metal-ethylenebis(acetamide) networks that undergo reversible glass and crystallization transitions below 200 °C. The glass-transition temperatures, crystallization kinetics, and glass stability of these materials are readily tunable, either by synthetic modification or by liquid-phase blending, to form binary glasses. Pair distribution function (PDF) analysis reveals extended structural correlations in both single and binary metal-bis(acetamide) glasses and highlights the important role of metal-metal correlations during structural evolution across glass-crystal transitions. Notably, the glass and crystalline phases of a Co-ethylenebis(acetamide) binary network feature a large reflectivity contrast ratio of 4.8 that results from changes in the local coordination environment around Co centers. These results provide new insights into glass-crystal transitions in metal-organic materials and have exciting implications for optical switching, rewritable data storage, and functional glass ceramics.

Liquid and Glass Phases of an Alkylguanidinium Sulfonate Hydrogen-Bonded Organic Framework.

Glassy phases of framework materials feature unique and tunable properties that are advantageous for gas separation membranes, solid electrolytes, and phase-change memory applications. Here, we report a new guanidinium organosulfonate hydrogen-bonded organic framework (HOF) that melts and vitrifies below 100 °C. In this low-temperature regime, non-covalent interactions between guest molecules and the porous framework become a dominant contributor to the overall stability of the structure, resulting in guest-dependent melting, glass, and recrystallization transitions. Through simulations and X-ray scattering, we show that the local structures of the amorphous liquid and glass phases resemble those of the parent crystalline framework.

Polymerization and isomerization cyclic amplification for nucleic acid detection with attomolar sensitivity.

DNA amplification is one of the most valuable tools for the clinical diagnosis of nucleic acid-related diseases, but current techniques for DNA amplification are based on intermolecular polymerization reactions, resulting in the risk of errors in the intermolecular reaction pattern. In this article, we introduce the concept of intramolecular polymerization and isomerization cyclic amplification (PICA), which extends a short DNA strand to a long strand containing periodic repeats of a sequence through cyclic alternating polymerization and isomerization. To the best of our knowledge, this is the first time that a real ssDNA self-extension method without any additional auxiliary oligonucleotides has been reported. By interfacing PICA with external molecular elements, it can be programmed to respond to different targets. Herein, we designed two distinct types of amplified nucleic acid detection platforms that can be implemented with PICA, including cyclic reverse transcription (CRT) and cyclic replication (CR). We experimentally demonstrate the mechanisms of CRT-PICA and CR-PICA using mammalian miRNA and virus DNA. The results showed that this proposed detection platform has excellent sensitivity, selectivity, and reliability. The detection level could reach the aM level, that is, several copies of target molecules can be detected if a small volume is taken into account.

Nitrogen removal through oyster cultivation: Integration with artificial fertilization makes it more efficient.

The use of bivalve aquaculture to mitigate eutrophication in coastal waters has been proposed for years. As nitrogen overenrichment is usually accompanied by comparative shortages in silicate and phosphate, bivalve cultivation integrated with artificial fertilization may exhibit better nitrogen removal performance than bivalve cultivation alone. During a 15-day mesocosm experiment in a nitrogen-eutrophicated, phosphate-limited coastal pond, the nitrogen fixation in oyster tissue under rice husk ash (RHA)1 fertilized conditions was 10 times higher than that in the oyster-only treatments with the same density. Meanwhile, the concentrations of dissolved inorganic nitrogen (DIN) and particulate nitrogen (PN) in the combined oyster-fertilization treatments decreased by 87.0% and 57.2%, respectively. Compared with the RHA fertilization treatments, the net DIN consumption was significantly lower and decreased with the oyster density in the oyster-only treatments. The dissolved N/Si ratio decreased from 1.44 to 1.01 and 0.93 in the control and fertilization treatments, respectively, whereas in the oyster-only treatments, it increased to 3.74 at low density and 29.15 at high density. Our results indicate that oyster cultivation can stimulate the regeneration of nitrogen in dissolved forms and intensify relative silicate shortages. The integration of RHA fertilization mediated silicate shortage and helped maintain a balanced dissolved N/Si ratio. Moreover, the combined oyster-RHA fertilization enhanced nitrogen removal efficiency and biomass accumulation and increased the feasibility of oyster cultivation as a cost-effective nitrogen reduction measure.

Network-Forming Liquids from Metal-Bis(acetamide) Frameworks with Low Melting Temperatures.

Molten phases of metal-organic networks offer exciting opportunities for using coordination chemistry principles to access liquids and glasses with unique and tunable structures and properties. Here, we discuss general thermodynamic strategies to provide an increased enthalpic and entropic driving force for reversible, low-temperature melting transitions in extended coordination solids and illustrate this approach through a systematic study of a series of bis(acetamide)-based networks with record-low melting temperatures. The low melting temperatures of these compounds are the result of weak coordination bonds, conformationally flexible bridging ligands, and weak electrostatic interactions between spatially separated cations and anions, which collectively reduce the enthalpy and increase the entropy of fusion. Through a combination of crystallography, spectroscopy, and calorimetry, enthalpic trends are found to be dictated by the strength of coordination bonds and hydrogen bonds within each compound, while entropic trends are strongly influenced by the degree to which residual motion and positional disorder are restricted in the crystalline state. Extended X-ray absorption fine structure (EXAFS) and pair distribution function (PDF) analysis of Co(bba)3[CoCl4] [bba = N,N'-1,4-butylenebis(acetamide)], which features a record-low melting temperature for a three-dimensional metal-organic network of 124 °C, provide direct evidence of metal-ligand coordination in the liquid phase, as well as intermediate- and extended-range order that support its network-forming nature. In addition, rheological measurements are used to rationalize differences in glass-forming ability and relaxation dynamics. These results provide new insights into the structural and chemical factors that influence the thermodynamics of melting transitions of extended coordination solids, as well as the structure and properties of coordination network-forming liquids.

Pharmaceutically active compounds (PhACs) in surface sediments of the Jiaozhou Bay, north China.

Pharmaceutically active compounds (PhACs) have attracted increasing attention due to their large consumption volumes, high bioactivity and potential ecotoxicity. In this study, a total of 150 commonly used drugs were investigated in sediments of Jiaozhou Bay (JZB). Twenty-five target compounds were detected, of which ten were discovered for the first time in marine sediments. The range of total PhAC content was 3.62-21.4 ng/g dry weight. Ketoprofen (2.49 ng/g), oxytetracycline (1.00 ng/g) and roxithromycin (0.97 ng/g) were the preponderant PhACs. PhACs gradually decreased from east to west, and the distribution of PhACs in the sediment was controlled by the source channel, seawater dynamic process and sediment composition. The diatom, organic matter, and clay proportions in the sediments and the nutrients in the overlying water were the most important environmental factors affecting the distribution of PhACs. PhAC pollution in the sediments of the JZB exhibited an increasing trend. Coprostanol could be used as a chemical indicator of the PhAC concentration in JZB sediments. PhACs were mainly derived from direct pollution due to human fecal excretion in the eastern region. Ofloxacin, tetracycline and oxytetracycline were found to pose high or medium risks to aquatic organisms. It is necessary and urgent to improve the treatment technology of drug residues in sewage treatment plants to decrease the pollution of PhAC residues. With the continuous aging of the global population, the use of PhACs will increase rapidly, which may cause more unpredictable threats to the marine ecosystem. Therefore, the monitoring of PhACs in the marine environment needs to be strengthened, and studies on PhAC occurrence and effects must be considered a priority in global environmental research.