The RPA-RNF20-SNF2H cascade promotes proper chromosome segregation and homologous recombination repair.

The human tumor suppressor Ring finger protein 20 (RNF20)-mediated histone H2B monoubiquitination (H2Bub) is essential for proper chromosome segregation and DNA repair. However, what is the precise function and mechanism of RNF20-H2Bub in chromosome segregation and how this pathway is activated to preserve genome stability remain unknown. Here, we show that the single-strand DNA-binding factor Replication protein A (RPA) interacts with RNF20 mainly in the S and G2/M phases and recruits RNF20 to mitotic centromeres in a centromeric R-loop-dependent manner. In parallel, RPA recruits RNF20 to chromosomal breaks upon DNA damage. Disruption of the RPA-RNF20 interaction or depletion of RNF20 increases mitotic lagging chromosomes and chromosome bridges and impairs BRCA1 and RAD51 loading and homologous recombination repair, leading to elevated chromosome breaks, genome instability, and sensitivities to DNA-damaging agents. Mechanistically, the RPA-RNF20 pathway promotes local H2Bub, H3K4 dimethylation, and subsequent SNF2H recruitment, ensuring proper Aurora B kinase activation at centromeres and efficient loading of repair proteins at DNA breaks. Thus, the RPA-RNF20-SNF2H cascade plays a broad role in preserving genome stability by coupling H2Bub to chromosome segregation and DNA repair.

Proper RPA acetylation promotes accurate DNA replication and repair.

The single-stranded DNA (ssDNA) binding protein complex RPA plays a critical role in promoting DNA replication and multiple DNA repair pathways. However, how RPA is regulated to achieve its functions precisely in these processes remains elusive. Here, we found that proper acetylation and deacetylation of RPA are required to regulate RPA function in promoting high-fidelity DNA replication and repair. We show that yeast RPA is acetylated on multiple conserved lysines by the acetyltransferase NuA4 upon DNA damage. Mimicking constitutive RPA acetylation or blocking its acetylation causes spontaneous mutations with the signature of micro-homology-mediated large deletions or insertions. In parallel, improper RPA acetylation/deacetylation impairs DNA double-strand break (DSB) repair by the accurate gene conversion or break-induced replication while increasing the error-prone repair by single-strand annealing or alternative end joining. Mechanistically, we show that proper acetylation and deacetylation of RPA ensure its normal nuclear localization and ssDNA binding ability. Importantly, mutation of the equivalent residues in human RPA1 also impairs RPA binding on ssDNA, leading to attenuated RAD51 loading and homologous recombination repair. Thus, timely RPA acetylation and deacetylation likely represent a conserved mechanism promoting high-fidelity replication and repair while discriminating the error-prone repair mechanisms in eukaryotes.

A thermophilic 8-oxoguanine DNA glycosylase from Thermococcus barophilus Ch5 is a new member of AGOG DNA glycosylase family

8-Oxoguanine (8oxoG) in DNA is a major oxidized base that poses a severe threat to genome stability. To counteract the mutagenic effect generated by 8oxoG in DNA, cells have evolved 8oxoG DNA glycosylase (OGG) that can excise this oxidized base from DNA. Currently, OGG enzymes have been divided into three families: OGG1, OGG2 and AGOG (archaeal 8oxoG DNA glycosylase). Due to the limited reports, our understanding on AGOG enzymes remains incomplete. Herein, we present evidence that an AGOG from the hyperthermophilic euryarchaeon Ch5 (Tb-AGOG) excises 8oxoG from DNA at high temperature. The enzyme displays maximum efficiency at 75°C-95°C and at pH 9.0. As expected, Tb-AGOG is a bifunctional glycosylase that harbors glycosylase activity and AP (apurinic/apyrimidinic) lyase activity. Importantly, we reveal for the first time that residue D41 in Tb-AGOG is essential for 8oxoG excision and intermediate formation, but not essential for DNA binding or AP cleavage. Furthermore, residue E79 in Tb-AGOG is essential for 8oxoG excision and intermediate formation, and is partially involved in DNA binding and AP cleavage, which has not been described among the reported AGOG members to date. Overall, our work provides new insights into catalytic mechanism of AGOG enzymes.

Biochemical and functional characterization of an endonuclease III from Thermococcus barophilus Ch5.

Endonuclease III (EndoIII) is a bifunctional DNA glycosylase that is essential to excise thymine glycol (Tg) from DNA. Although EndoIII is widespread in bacteria, eukarya and Archaea, our understanding on archaeal EndoIII function remains relatively incomplete due to the limited reports. Herein, we characterized an EndoIII from the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5 (Tba-EndoIII) biochemically, demonstrating that the enzyme can excise Tg from dsDNA and display maximum activity at 50 ~ 70 °C and at pH 6.0 ~ 9.0 without the requirement of a divalent metal ion. Importantly, Tba-EndoIII differs from other reported archaeal EndoIII homologues in thermostability and salt requirement. As observed in other EndoIII homologues, the conserved residues D155 and H157 in Helix-hairpin-Helix motif of Tba-EndoIII are essential for Tg excision. Intriguingly, we first dissected that the conserved residues C215 and C221 in the Fe-S cluster loop in Tba-EndoIII are involved in intermediate formation and Tg excision. Additionally, we first revealed that the conserved residue L48 is flexible for intermediate formation and AP cleavage, but plays no detectable role in Tg excision. Overall, our work has revealed additional archaeal EndoIII function and catalytic mechanism.

Discovery of novel chromone derivatives containing a sulfonamide moiety as potential anti-TSWV agents.

A number of chromone derivatives containing sulfonamide structure were designed and synthesized. Firstly, the target compounds were evaluated for anti-TSWV activities in vivo by the half-leaf method. We found that most of the compounds had good anti-TSWV activities. Among them, compound 12B had excellent anti-TSWV inactivating activity with an EC50 of 80.5 µg/mL, which was significantly better than xiangcaoliusuobingmi (765.7 µg/mL). Secondly, TSWV nucleocapsid protein (N) was expressed and purified, and the affinity between the compounds and TSWV N was tested by microscale thermophoresis (MST). Compound 12B had a good affinity for TSWV N with a Kd value of 5.02 µM, which was superior to xiangcaoliusuobingmi (29.83 µM). Finally, in order to study the mode of interaction between the compound 12B and TSWV N, we carried out molecular docking. The results indicated that compound 12B might inactivate the virus by destroying the TSWV N oligomer structure. These results lay a solid foundation for the further discovery of chromone derivatives containing sulfonamide structure with high anti-TSWV activities.

Identification of a novel bifunctional uracil DNA glycosylase from Thermococcus barophilus Ch5.

Genomes of hyperthermophiles are facing a severe challenge due to increased deamination rates of cytosine induced by high temperature, which could be counteracted by base excision repair mediated by uracil DNA glycosylase (UDG) or other repair pathways. Our previous work has shown that the two UDGs (Tba UDG247 and Tba UDG194) encoded by the genome of the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5 can remove uracil from DNA at high temperature. Herein, we provide evidence that Tba UDG247 is a novel bifunctional glycosylase which can excise uracil from DNA and further cleave the phosphodiester bo nd of the generated apurinic/apyrimidinic (AP) site, which has never been described to date. In addition to cleaving uracil-containing DNA, Tba UDG247 can also cleave AP-containing ssDNA although at lower efficiency, thereby suggesting that the enzyme might be involved in repair of AP site in DNA. Kinetic analyses showed that Tba UDG247 displays a faster rate for uracil excision than for AP cleavage, thus suggesting that cleaving AP site by the enzyme is a rate-limiting step for its bifunctionality. Phylogenetic analysis showed that Tba UDG247 is clustered on a separate branch distant from all the reported UDGs. Overall, we designated Tba UDG247 as the prototype of a novel family of bifunctional UDGs. KEY POINTS: We first reported a novel DNA glycosylase with bifunctionality. Tba UDG247 possesses an AP lyase activity.

Design, synthesis and anti-TMV activities of novel chromone derivatives containing dithioacetal moiety.

Thirty-five novel chromone derivatives containing dithioacetal moiety were designed, synthesized, and their anti-TMV activities were evaluated through half-leaf method. The results showed compound c23 illustrates highly curative, protective and inactivating activities against TMV at 500 mg/L, with the values of 68.8%, 58.8%, 86.0% respectively, which were superior to that of Ribavirin (42.3%, 49.8%, 68.4%, respectively) and similar to that of Ningnanmycin (59.4%, 52.4%, 88.4%, respectively). The EC50 value of inactivating activities of compound c23 is 9.3 mg/L, which was better than that of Ribavirin (135.2 mg/L), and equivalent to that of Ningnanmycin (8.8 mg/L). Furthermore, compound c23 can destroy the integrity of TMV-CP, resulting in reduced infectivity of TMV. Meanwhile, compound c23 can combine with TMV protein coat and hydrolyze TMV protein coat to impact the process of self-assembling of TMV, with the association constant (Kd) 4.5 mg/L. This finding suggests that chromone derivatives containing dithioacetal moiety can be used as new antiviral agent.

Biochemical characterization and mutational analysis of a novel flap endonuclease 1 from Thermococcus barophilus Ch5.

Flap endonuclease 1 (FEN1) plays important roles in DNA replication, repair and recombination. Herein, we report biochemical characteristics and catalytic mechanism of a novel FEN1 from the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5 (Tb-FEN1). As expected, the recombinant Tb-FEN1 can cleave 5'-flap DNA. However, the enzyme has no activity on cleaving pseudo Y DNA, which sharply contrasts with other archaeal and eukaryotic FEN1 homologs. Tb-FEN1 retains 24% relative activity after heating at 100 °C for 20 min, demonstrating that it is the most thermostable among all reported FEN1 proteins. The enzyme displays maximal activity in a wide range of pH from 7.0 to 9.5. The Tb-FEN1 activity is dependent on a divalent metal ion, among which Mg2+ and Mn2+ are optimal. Enzyme activity is inhibited by NaCl. Kinetic analyzes estimated that an activation energy for removal of 5'-flap from DNA by Tb-FEN1 was 35.7 ± 4.3 kcal/mol, which is the first report on energy barrier for excising 5'-flap from DNA by a FEN1 enzyme. Mutational studies demonstrate that the K87A, R94A and E154A amino acid substitutions abolish cleavage activity and reduce 5'-flap DNA binding efficiencies, suggesting that residues K87, R94, and E154 in Tb-FEN1 are essential for catalysis and DNA binding as well. Overall, Tb-FEN1 is an extremely thermostable endonuclease with unusual features.

Biochemical characterization and mutational studies of a novel 3-methlyadenine DNA glycosylase II from the hyperthermophilic Thermococcus gammatolerans.

The hyperthermophilic and radioresistant euryarchaeon Thermococcus gammatolerans encodes a putative 3-methlyadenine DNA glycosylase II (Tg-AlkA). Herein, we report biochemical characterization and catalytic mechanism of Tg-AlkA. The recombinant Tg-AlkA can excise hypoxanthine (Hx) and 1-methlyadenine (1-meA) from dsDNA with varied efficiencies at high temperature. Notably, Tg-AlkA is a bi-functional glycosylase, which is sharply distinct from all the reported AlkAs. Biochemical data show that the optimal temperature and pH of Tg-AlkA for removing Hx from dsDNA are ca.70 °C and ca.7.0-8.0, respectively. Furthermore, the Tg-AlkA activity is independent of a divalent metal ion, and Mg2+ stimulates the Tg-AlkA activity whereas other divalent ions inhibit the enzyme activity with varied degrees. Mutational studies show that the Tg-AlkA W204A and D223A mutants abolish completely the excision activity, thereby suggesting that residues W204 and D223 are involved in catalysis. Surprisingly, the mutations of W204, D223, Y139 and W256 to alanine in Tg-AlkA lead to the increased affinity for binding DNA substrate with varied degrees, suggesting that these residues are flexible for conformational change of the enzyme. Therefore, Tg-AlkA is a novel AlkA that can remove Hx and 1-meA from dsDNA, thus providing insights into repair of deaminated and alkylated bases in DNA from hyperthermophilic Thermococcus.

Characterization of a novel type III alcohol dehydrogenase from Thermococcus barophilus Ch5.

The genome of the hyperthermophilic and piezophilic euryarchaeaon Thermococcus barophilus Ch5 encodes three putative alcohol dehydrogenases (Tba ADHs). Herein, we characterized Tba ADH547 biochemically and probed its catalytic mechanism by mutational studies. Our data demonstrate that Tba ADH547 can oxidize ethanol and reduce acetaldehyde at high temperature with the same optimal temperature (75 °C) and exhibit similar thermostability for oxidization and reduction reactions. However, Tba ADH547 has different optimal pH for oxidation and reduction: 8.5 for oxidation and 7.0 for reduction. Tba ADH547 is dependent on a divalent ion for its oxidation activity, among which Mn2+ is optimal. However, Tba ADH547 displays about 20% reduction activity without a divalent ion, and the maximal activity with Fe2+. Furthermore, Tba ADH547 showcases a strong substrate preference for 1-butanol and 1-hexanol over ethanol and other alcohols. Similarly, Tba ADH547 prefers butylaldehyde to acetaldehyde as its reduction substrate. Mutational studies showed that the mutations of residues D195, H199, H262 and H274 to Ala result in the significant activity loss of Tba ADH547, suggesting that residues D195, H199, H262 and H274 are responsible for catalysis. Overall, Tba ADH547 is a thermoactive ADH with novel biochemical characteristics, thereby allowing this enzyme to be a potential biocatalyst.

Discovery of Novel Chromone Derivatives Containing a Sulfonamide Moiety as Anti-ToCV Agents through the Tomato Chlorosis Virus Coat Protein-Oriented Screening Method.

A number of novel chromone derivatives containing sulfonamide moieties were designed and synthesized, and the activity of compounds against tomato chlorosis virus (ToCV) was assessed using the ToCVCP-oriented screening method. Comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) models were established based on the dissociation constant (Kd) values of the target compounds, and compound 35 was designed and synthesized with the aid of CoMFA and CoMSIA models. The study of affinity interaction indicated that compound 35 exhibited excellent affinity with ToCVCP with a Kd value of 0.11 µM, which was better than that of the positive control agents xiangcaoliusuobingmi (0.44 µM) and ningnanmycin (0.79 µM). In addition, the in vivo inhibitory effect of compound 35 on the ToCVCP gene was evaluated by the quantitative real-time polymerase chain reaction. ToCVCP gene expression levels of the compound 35 treatment group were reduced by 67.2%, which was better than that of the positive control agent ningnanmycin (59.5%). Therefore, compound 35 can be used as a potential anti-ToCV drug in the future.

Repair of Hypoxanthine in DNA Revealed by DNA Glycosylases and Endonucleases From Hyperthermophilic Archaea.

Since hyperthermophilic Archaea (HA) thrive in high-temperature environments, which accelerate the rates of deamination of base in DNA, their genomic stability is facing a severe challenge. Hypoxanthine (Hx) is one of the common deaminated bases in DNA. Generally, replication of Hx in DNA before repaired causes AT → GC mutation. Biochemical data have demonstrated that 3-methyladenine DNA glycosylase II (AlkA) and Family V uracil DNA glycosylase (UDG) from HA could excise Hx from DNA, thus triggering a base excision repair (BER) process for Hx repair. Besides, three endonucleases have been reported from HA: Endonuclease V (EndoV), Endonuclease Q (EndoQ), and Endonuclease NucS (EndoNucS), capable of cleaving Hx-containing DNA, thereby providing alternative pathways for Hx repair. Both EndoV and EndoQ could cleave one DNA strand with Hx, thus forming a nick and further initiating an alternative excision repair (AER) process for the follow-up repair. By comparison, EndoNucS cleaves both strands of Hx-containing DNA in a restriction endonuclease manner, thus producing a double-stranded break (DSB). This created DSB might be repaired by homologous recombination (HR) or by a combination activity of DNA polymerase (DNA pol), flap endonuclease 1 (FEN1), and DNA ligase (DNA lig). Herein, we reviewed the most recent advances in repair of Hx in DNA triggered by DNA glycosylases and endonucleases from HA, and proposed future research directions.

Biochemical characterization and mutational studies of a thermostable endonuclease III from Sulfolobus islandicus REY15A.

Endonuclease III (EndoIII), which is ubiquitous in bacteria, Archaea and eukaryotes, plays an important role in excising thymine glycol (Tg) from DNA. Herein, we present evidence that an EndoIII from the hyperthermophilic crenarchaeon Sulfolobus islandicus REY15A (Sis-EndoIII) is capable of removing Tg from DNA at high temperature. Biochemical data show that the optimal temperature and pH of Sis-EndoIII are ca.70 °C and ca.7.0-8.0, respectively. Furthermore, the recombinant Sis-EndoIII retains relative weak activity without a divalent metal ion, and displays maximum activity in the presence of Mg2+ or Ca2+. Additionally, we first revealed the activation energy (Ea) of 39.7 ± 4.2 kcal/mol for Sis-EndoIII to remove Tg from dsDNA. As a bifunctional glycosylase, Sis-EndoIII possesses AP lyase activity in addition to glycosylase activity. Additionally, a covalent intermediate is formed between Sis-EndoIII and Tg-containing dsDNA. Mutational studies demonstrate that residues D50, K133 and D151 in Sis-EndoIII are responsible for removal of Tg from dsDNA and K133 and D151 are essential for formation of the covalent intermediate. To our knowledge, it is the first report of Tg excision by crenarchaeal EndoIII, thus augmenting our understanding on archaeal EndoIII function.

Design, Synthesis, Antiviral Bioactivity, and Mechanism of the Ferulic Acid Ester-Containing Sulfonamide Moiety.

Tobacco mosaic virus (TMV) has caused huge economic losses to tobacco, pepper, cucumber, and ornamental crops all over the world. However, few effective antiviral agents were developed and applied to control such plant disease. It is challenging to find an anti-TMV agent which is highly effective, less toxic, and environmentally friendly. In this work, a series of ferulic acid ester-containing sulfonamide moieties were designed and synthesized, and the antiviral activities of these compounds against TMV were evaluated. The anti-TMV biological activity test showed that the target compounds showed excellent anti-TMV activity in vitro and in vivo. In particular, compound 2 has excellent anti-TMV activity at 500 µg/mL, which is higher than that of the control drug ribavirin. The preliminary mechanism research results showed that compound 2 can obviously destroy the morphology of the virions to show excellent activity. The results show that the ferulic acid ester-containing sulfonamide moiety deserves further research and development.

Design, Synthesis, and Anti-ToCV Activity of Novel Pyrimidine Derivatives Bearing a Dithioacetal Moiety that Targets ToCV Coat Protein.

Novel pyrimidine sulfide derivatives containing a dithioacetal and strobilurin moiety were designed and synthesized. Their antiviral activities against tomato chlorosis virus (ToCV) were investigated through the tomato chlorosis virus coat protein (ToCVCP)-oriented screening method. Microscale thermophoresis was used to study the interaction between the compound and the ToCVCP. Compounds B13 and B23 interacted better with ToCVCP than the other compounds and had dissociation constant (Kd) values of 0.09 and 0.06 µM, respectively. These values were lower than those of the control agents, ningnanmycin (0.19 µM) and ribavirin (6.54 µM), which indicated that the compounds had a strong binding effect with ToCVCP. Quantitative real-time polymerase chain reaction was used to evaluate the role of compounds B13 and B23 in the gene regulation of ToCVCP. Both compounds significantly reduced the expression level of the ToCVCP gene in Nicotiana benthamiana with reduction values of 88 and 83%, which were better than those of ningnanmycin (65%) and lead compound C14 (73%). Pyrimidine sulfide containing a dithioacetal and strobilurin moiety is significant in the research and development of novel anti-ToCV agents.

New Insights Into DNA Repair Revealed by NucS Endonucleases From Hyperthermophilic Archaea.

Hyperthermophilic Archaea (HA) thrive in high temperature environments and their genome is facing severe stability challenge due to the increased DNA damage levels caused by high temperature. Surprisingly, HA display spontaneous mutation frequencies similar to mesophilic microorganisms, thereby indicating that the former must possess more efficient DNA repair systems than the latter to counteract the potentially enhanced mutation rates under the harsher environment. Although a few repair proteins or enzymes from HA have been biochemically and structurally characterized, the molecular mechanisms of DNA repair of HA remain largely unknown. Genomic analyses of HA revealed that they lack MutS/MutL homologues of the mismatch repair (MMR) pathway and the recognition proteins of the nucleotide excision repair (NER) pathway. Endonucleases play an essential role in DNA repair. NucS endonuclease, a novel endonuclease recently identified in some HA and bacteria, has been shown to act on branched, mismatched, and deaminated DNA, suggesting that this endonuclease is a multifunctional enzyme involved in NER, MMR, and deaminated base repair in a non-canonical manner. However, the catalytic mechanism and the physiological function of NucS endonucleases from HA need to be further clarified to determine how they participate in the different DNA repair pathways in cells from HA. In this review, we focus on recent advances in our understanding of the function of NucS endonucleases from HA in NER, MMR, and deaminated DNA repair, and propose directions for future studies of the NucS family of endonucleases.

Characterization and application of a family B DNA polymerase from the hyperthermophilic and radioresistant euryarchaeon Thermococcus gammatolerans.

Thermococcus gammatolerans is anaerobic euryarchaeon which grows optimally at 88 °C and its genome encodes a family B DNA polymerase (Tga PolB). Herein, we cloned the gene of Tga PolB, expressed and purified the gene product, and characterized the enzyme biochemically. The recombinant Tga PolB can efficiently synthesize DNA at high temperature, and retain 93% activity after heated at 95 °C for 1.0 h, suggesting that the enzyme is thermostable. Furthermore, the optimal pH for the enzyme activity was measured to be 7.0-9.0. Tga PolB activity is dependent on a divalent cation, among which magnesium ion is optimal. NaCl at low concentration stimulates the enzyme activity but at high concentration inhibits enzyme activity. Interestingly, Tga PolB is able to efficiently bypass uracil in DNA, which is distinct from other archaeal family B DNA pols. By contrast, Tga PolB is halted by an AP site in DNA, as observed in other archaeal family B DNA polymerases. Furthermore, Tga PolB extends the mismatched ends with reduced efficiencies. The enzyme possesses 3'-5' exonuclease activity and this activity is inhibited by dNTPs. The DNA binding assays showed that Tga PolB can efficiently bind to ssDNA and primed DNA, and have a marked preference for primed DNA. Last, Tga PolB can be used in routine PCR.

Biochemical characterization and mutational studies of a thermostable uracil DNA glycosylase from the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5.

Uracil DNA glycosylases (UDGs) play an important role in removing uracil from DNA to initiate DNA base excision repair. Here, we characterized biochemically a thermostable UDG from the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5 (Tba UDG), and probed its mechanism by mutational analysis. The recombinant Tba UDG cleaves exclusively uracil-containing ssDNA and dsDNA at 65°C. The enzyme displays an optimal cleavage activity at 70-75°C. Tba UDG cleaves DNA over a wide pH spectrum ranging from 4.0 to 11.0 with an optimal pH of 7.0-9.0. In addition, Tba UDG activity is independent on a divalent metal ion; however, both Zn2+ and Cu2+ completely inhibit the enzyme activity. Tba UDG activity is also inhibited by high NaCl concentration. Tba UDG removes uracil from DNA with the following preference: U≈U/G>U/T≈U/C>U/A. Kinetic results showed that Tba UDG cleaves uracil-containing ssDNA and dsDNA at a similar rate. The mutational studies showed that the E118A, N159A and H216A mutants completely abolish cleavage activity and retain compromised binding activity while the Y127A mutant displays similar cleavage and binding activities with the wild-type protein, suggesting that residues E118, N159 and H216 are essential for uracil removal and necessary for uracil recognition.

A comparative study of C2H2 adsorption properties in five isomeric copper-based MOFs based on naphthalene-derived diisophthalates.

In this work, five positional isomeric ligands consisting of two peripheral isophthalate moieties attached to the central naphthyl core in different ways, namely, 5,5'-(naphthyl-1,3-diyl) diisophthalate (H4L1), 5,5'-(naphthyl-1,4-diyl) diisophthalate (H4L2), 5,5'-(naphthyl-1,5-diyl) diisophthalate (H4L3), 5,5'-(naphthyl-1,6-diyl) diisophthalate (H4L4) and 5,5'-(naphthyl-2,6-diyl) diisophthalate (H4L5), have been used to generate five copper-based MOF isomers. As revealed by single-crystal X-ray diffraction studies, they adopted two different types of topologies depending on the organic ligands: ssa topology for the MOFs ZJNU-71 and ZJNU-74 based on the ligands H4L1 and H4L4, respectively, and nbo topology for the MOFs ZJNU-72, ZJNU-73 and NOTT-103 derived from the ligands H4L2, H4L3 and H4L5, respectively. Furthermore, their C2H2 adsorption properties were systematically investigated, revealing that their different C2H2 uptake capacities can be mainly related to their different pore sizes since they possess the same chemical compositions and gravimetric densities of open metal sites. In particular, among these five MOF compounds investigated, ZJNU-71 exhibits the highest gravimetric C2H2 uptake of 208.1 cm3 (STP) g-1 at 295 K and 1 atm. The value is also among the highest reported for MOF compounds under the same conditions. This work provides a fundamental understanding of the impact of the positional isomerism of the organic ligands on the structures as well as gas adsorption properties of the resulting MOFs.

A porous metal-organic framework based on an asymmetric angular diisophthalate for selective adsorption of C2H2 and CO2 over CH4.

A new copper-based metal-organic framework [Cu2L(H2O)2]·5DMF·2H2O (ZJNU-56) has been solvothermally synthesized using a custom-designed asymmetric rigid bent diisophthalate ligand, 5,5'-(1-amine-naphthyl-2,4-diyl) diisophthalic acid (H4L), and structurally determined by single-crystal X-ray diffraction. ZJNU-56 features a three-dimensional (3D) open framework incorporating three different types of metal-organic cages and two distinct types of one-dimensional channels. With a moderate BET surface area of 1655 m2 g-1, optimized pore structure, and functional sites (open copper sites and Lewis basic amine groups) on the cage surface, ZJNU-56 after desolvation exhibits highly selectively adsorptive separation of C2H2 and CO2 over CH4 under ambient conditions. At 298 K, the predicted IAST selectivities are 35.7-72.9 for an equimolar C2H2/CH4 gas mixture and 6.8-7.0 for an equimolar CO2/CH4 gas mixture at pressures varying from 1 to 109 kPa, respectively, which are among the highest reported to date for copper-based MOFs.