Mixed-valence organo-triiron complexes as strongly cytotoxic and highly selective anticancer agents

Cancer is a major health issue worldwide, and the development of innovative and effective drugs is an ultimate demand for research. Iron compounds have aroused a great interest in the search for new metal based chemotherapics, on account of their relatively low toxicity and their redox chemistry, exportable to physiological media.

Some ferrocene derivatives have shown a promising anticancer potential, with a strong activity mostly associated with FeII to FeIII oxidation, leading to alteration of the cellular redox balance and subsequent production of toxic substances (reactive oxygen species, ROS). However, they provide a limited variability of the metal coordination set, and they need to be carefully formulated for in vivo applications due to a generally insufficient water solubility.

Since 2019, a series of cationic [FeIFeI] complexes based on the [Fe2Cp2(CO)2] core and comprising a vinyliminium bridging ligand have emerged as a novel class of potential chemotherapeutic agents. Thanks to the unique features of the bimetallic core, these complexes are easily prepared up to gram scale from a commercial precursor in a few synthetic steps. Remarkably, they are amphiphilic and appreciably water-soluble, and exhibit an antiproliferative activity against cancer cell lines which depends on the ligand substituents. The choice of the latter is virtually limitless, thanks to the generality of the synthetic procedure, and this feature allows to optimise physico-chemical properties for biological purposes. Different mechanisms, mainly ROS production but also protein interaction and weak DNA binding, may contribute to the mode of action of these dinuclear structures.

Recently, the group of Fabio Marchetti and co-workers have reported, for the first time, the conjugation of a ferrocenyl moiety with a diiron framework, as a strategy to obtain robust mixed-valence triiron compounds featured by a potent cytotoxicity and excellent selectivity towards cancer cell lines (i.e., IC50 values in the low micromolar/nanomolar range on the cancer cell lines, and up to 35 times higher values on the nontumoral cells).

Figure 1. General structure of the novel triiron complexes derived from the tethering of a ferrocenyl unit and a di-organoiron core. R=Me, aryl, Bz, allyl; R’=Me, Bz; X=CF3SO3, NO3.

A combination of stability studies, electrochemical experiments, iron cellular uptake and targeted biological studies indicate that the cationic triiron complexes synergistically combine the redox behaviour of the ferrocenyl moiety with the amphiphilicity and the versatility of the diiron vinyliminium structure, and that their powerful activity arises from the ability to disrupt the redox homeostasis of tumour cells, through the overproduction of intracellular ROS and the alteration of the thioredoxin reductase, assessed on a synthetic dodecapeptide as a simplified model of the enzyme.

Corresponding Author:

Fabio Marchetti
University of Pisa

Fabio Marchetti received his Degree in Industrial Chemistry from the University of Bologna in 1999 (summa cum laude), and the PhD in Chemistry from the same University in 2003. In 2006 he obtained a researcher position at the University of Pisa, and since October 2018 he has been Full Professor in the same University. FM has co-authored over 200 scientific publications on international journals, 2 book chapters and 2 international patents. His research interests regard the synthesis, the characterization and the properties of new transition metal compounds, and the metal-mediated activation of small organic molecules.

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Emerging Investigator: Lingling Mao from Southern University of Science and Technology, China

Emerging Investigator: Lingling Mao

Position              Associate Professor

Postdoc             2018–2021  UC Santa Barbara

Education          2014–2018  Northwestern University (USA)      Ph.D.

                          2010–2014  Sun Yat-sen University (China)      B.Sc.

Group website    https://faculty.sustech.edu.cn/maoll/en/

ORCID                0000-0003-3166-8559

Read Lingling Mao’s Emerging Investigator Series article on Inorganic Chemistry Frontiers and learn more about her.

     
  “Breathing” organic cation to stabilize multiple structures in low-dimensional Ge-, Sn-, and Pb-based hybrid iodide perovskites  
Congcong Chen, Emily E. Morgan, Yang Liu, Jian Chen, Ram Seshadri and Lingling Mao*

 

By using S-(2-aminoethyl)isothiouronium (ETU) as the templating cation, five new metal iodide hybrids, (ETU)GeI4, (ETU)4Ge5I18, (ETU)PbI4 and (ETU)3Pb2I10 are reported with varied C–S–C angles in the organic cation.

 

  From the themed collection: Frontiers Emerging Investigator Series  
  The article was first published on 06 Aug 2022  
  Inorg. Chem. Front., 2022, Advance Article  
  https://doi.org/10.1039/D2QI01247B  
     

My research interest

Key words: Inorganic Chemistry; Materials Chemistry; Solid-state Chemistry
Materials chemistry: designing functional hybrid materials for optoelectronic applications

Establishing structure-property relationship in hybrid materials

10 Facts about me

I am most passionate about my work in discovering new materials. Solving a new crystal structure is the highlight of the day.

My passion besides work is enjoying great food with my friends.

I love skiing, but I have been stuck for two years without skiing due to COVID19.  

One of my hidden talents is sketching. I find it very relaxing.

One thing I cannot live without is music. I play music all the time when I’m driving or in the office.

Great papers depend not only on good results, but also on great writing. The writing reflects your thought process and whether you can deliver the essence.

A recent epiphany: work does not define who you are. Work is work.

I advise my students to take charge of their lives, have fun and do good science.

The most important quality of a mentor is to take a back seat when needed, and always be there for your mentees.

I have a cat named Schrödinger. He is an one-year-old blue/white British shorthair.

Click to find out our Emerging Investigators and their work

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Emerging Investigator: Yuanbin Zhang from Zhejiang Normal University, China

Emerging Investigator: Yuanbin Zhang

Position              Professor

Education           2013-2018  Zhejiang University                        Ph.D.

                           2009-2013  Nanjing University of Sci & Tech   B. Eng.

Group website    https://www.x-mol.com/groups/zhang_yuanbin

ORCID                0000-0002-8268-384X            Google Scholar

Read Yuanbin Zhang’s Emerging Investigator Series article on Inorganic Chemistry Frontiers and learn more about him.

     
  A new boron cluster anion pillared metal organic framework with ligand inclusion and its selective acetylene capture properties  

 

A novel microporous boron cluster pillared metal–organic framework BSF-10 was synthesized with ligand inclusion for efficient C2H2/CO2 and C2H2/C2H4 adsorption separation.

 

  From the themed collection: Frontiers Emerging Investigator Series  
  The article was first published on 19 Jul 2022  
  Inorg. Chem. Front., 2022, Advance Article  
  https://doi.org/10.1039/D2QI00890D
 
     

My research interest

Key words: metal-organic frameworks, supramolecular organic frameworks, gas separation, porous materials, boron cluster chemistry
My research interests mainly focus on the design of new porous materials for selective gas separation (light hydrocarbon splitting, carbon dioxide capture, etc). The gas separation based on traditional distillation method is highly energy-intensive. My work is to design suitable porous adsorbent to realize energy-efficient adsorptive separation of gas mixtures and investigate the structure-property relationship by experiments and theoretical calculation. Metal-organic frameworks (MOFs) and supramolecular organic frameworks (SOFs) are two main materials that I focus on. For different gas mixtures, I design materials with customized properties to recognize the difference. The ultimate target is to achieve efficient gas separation with both high adsorption capacity and high selectivity. Boron cluster anion hybrid supramolecular metal organic frameworks (BSFs) are a new series of crystalline porous materials developed in my group, which have shown benchmark separation performance for C3H8/C2H6/CH4, C2H2/C2H4 and C2H2/CO2 separation. For gas molecules with high polarity, I introduce electronegative elements (F/O) into MOFs’s pore surface to enhance the host-guest interaction. By this strategy, our group have developed a novel MOF termed as ZNU-2 (ZNU = Zhejiang Normal University) for benchmark C3H4/C3H6 separation.

10 Facts about me

I published my first academic article in European Journal of Inorganic Chemistry in 2015. It is also the first paper of my PhD research group. I spent nearly two years to finish the work but a Germany group reported a similar results before me.

I chose chemistry as a career because I want to be a scientist since very young and my middle school science teacher piqued my interest in chemistry.

An accomplishment I’m particularly proud of is the design of the first boron cluster anion pillared supramolecular metal organic framework, which displays a new application of anionic boron clusters. This work was published in Angewandte Chemie in 2019.

One of my hidden talents is cooking. I will be a good cooker if I am not a researcher.

My favourite sport is badminton. I ever obtained 3rd Prize of badminton competition in high school.

A key experience in my education was my visiting time at UCLA. During that stay, I made the decision of changing my research field from organic chemistry to MOFs that I am still insisting on.

The biggest challenge facing me is to get funding as well as to manage the time.

The most important thing I learned from my students is that everyone has their own strengths and weaknesses. It is my job to help them become the best version of themselves.

My most important role models are the advisors Duttwyler, Spokoyny, and Xing during my PhD and postdoc study. They are all great scientists and I learned a lot of things from them.

Guaranteed to make me happy is making progress every day and having new discovery from my lab.

Click to find out our Emerging Investigators and their work

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Heptadentate chelates for 89Zr-radiolabelling of monoclonal antibodies

Zirconium-89 complexation chemistry is an important area of research in the context of developing radiolabelled proteins for applications in diagnostic positron emission tomography (PET) imaging. For this imaging technology, the metalloradionuclide 89Zr4+ ion needs to be sequestered by a ligand to form a coordination complex that is thermodynamically, kinetically, and metabolically stable in biological systems. In this regard, desferrioxamine B (DFO), a natural bacterial siderophore, is one of the outstanding hexadentate linear chelator for zirconium-89, used in clinical trials with 89ZrDFO-radiolabeled antibodies (mAbs). Nevertheless, preclinical studies have demonstrated that 89ZrDFO-mAbs can suffer from dissociation and metal ion release in vivo resulting in partial bone uptake in mice which could be partially due to the incomplete coordination sphere around the metallic cation. Driven by the goal of increasing the stability of the 89Zr4+ coordination complex toward demetallation in vivo, several groups around the world have explored the synthesis and coordination chemistry of novel multidentate chelates with coordination numbers from 6 to 8 but the development of heptadentate remained unexplored.

Recently, a collaborative work between the group of Prof. Dr Jason P. Holland (University of Zurich, Switzerland) and a team from the Institut Plurisdisciplinaire Hubert Curien (IPHC, CNRS, University of Strasbourg, France) have demonstrated that photoactivatable heptadentate chelates could be a new alternative for the ultra-fast, light-induced production of stable 89Zr-mAbs in vivo (Figure 1). The researchers synthesise new chelates, used density functional theory to predict the thermodynamic stability, and studied the in vitro stability of the radiolabelled complexes to find the most promising candidate for in vivo application.

Figure 1. (A) Overview of the light-induced photoradiosynthesis to produce 89Zr-labelled monoclonal antibodies (mAbs) and structure of the ligands (13). (B) Optimised structures of the three model Zr complexes. (C) Bar chart showing the stability of the 89Zr-radiolabelled complexes (formed from chelates 14) under different challenge conditions.

The researchers also selected the most stable complex (Zr-2) and produced 89Zr-radiolabelled onartuzumab (the monoclonal antibody component of MetMAbTM which binds to the human hepatocyte growth-factor receptor c-MET) using photoradiochemical methods. Finally, the pharmacokinetic profile and c-MET targeting was evaluated in vivo and ex vivo by using PET imaging and biodistribution studies in female athymic nude mice bearing subcutaneous MKN-45 human gastric cancer xenografts (Figure 2).

 

Figure 2. (A) Coronal and axial PET images taken through the centre of the tumours showing the spatial distribution of [89Zr]Zr-2-onartuzumab over time after intravenous administration in mice bearing subcutaneous MKN-45 tumours on the right flank. T = Tumour, H = Heart, L = Liver, K = Kidneys. (B) Bar chart showing ex vivo biodistribution data (%ID g-1) for the uptake of [89Zr]Zr-2-onartuzumab (normal group, white; blocking group, blue) and the 6-coordinate control compound [89Zr]Zr-4-onartuzumab (normal group, red; blocking group, green) in mice bearing MKN-45 tumours.

Overall, the researchers proved that [89Zr]Zr-2-onartuzumab provides specific tumour targeting and high tumour-to-organ contrast on the PET pictures and from the biodisitribution analysis. The results obtained in the study confirm that heptadentate complexes of 89Zr display improved stability in vivo compared with hexadentate analogs and are promising candidates for future 89Zr-radiotracer design.

About the corresponding author

Jason P. Holland is from Yorkshire in the UK and is currently an SNSF Professor for Medicinal Radiochemistry at the University of Zurich. Research activities in the Holland group focus on advancing radiolabelling methods through novel bioconjugation approaches for labelling bioactive molecules with various radionuclides (18F, 64Cu, 67/68Ga, 86/90Y, 99mTc, 111In, 177Lu, 188Re, etc).

E-mail: jason.holland@chem.uzh; Twitter: @HollandLab_

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Best Inorganic Chemistry Frontiers Covers of 2021

We are delighted to announce the Best Inorganic Chemistry Frontiers Covers of 2021!

Read below the scientific papers.

A red-light-chargeable near infrared MgGeO3:Mn2+,Yb3+ persistent phosphor for bioimaging and optical information storage applications

Inorg. Chem. Front., 2021,8, 5149-5157
https://doi.org/10.1039/D1QI01158H

Issue 24 Volume 8 Outside Front Cover

Binuclear metal complexes with a novel hexadentate imidazole derivative for the cleavage of phosphate diesters and biomolecules: distinguishable mechanisms

Inorg. Chem. Front., 2021,8, 2684-2696
https://doi.org/10.1039/D1QI00108F

Issue 11 Volume 8 Inside Front Cover

Designing lanthanide coordination nanoframeworks as X-ray responsive radiosensitizers for efficient cancer therapy

Inorg. Chem. Front., 2021,8, 3433-3439
https://doi.org/10.1039/D1QI00442E

Issue 14 Volume 8 Inside Front Cover

Congratulations to the winners of Best Inorganic Chemistry Frontiers Covers of 2021!

We expressed our sincere appreciation for all the support and contributions from our authors, reviewers, and readers in the past 2021.

Looking forward to receiving your high-quality work in 2022.

Happy Chinese New Year!

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A highly active and E-selective Co catalyst for transfer-semihydrogenation of alkynes

The efficient semihydrogenation of internal alkynes to selectively produce either E– or Z-alkenes is one of the main challenges in homogeneous catalysis. Numerous systems were reported in the past, however, such reactions typically require either the use of gaseous hydrogen at high pressure, noble metal catalysts, or rather high catalyst loading at long reaction times, the latter resulting in alkene isomerisation or overreduction to produce alkanes. Amine boranes such as ammonia borane (H3B·NH3) are known to be well-suited for transfer hydrogenation reactions, providing stoichiometric amounts of H2 either by dehydrogenation (i.e. H2 production), followed by hydrogenation, or by stepwise hydride and proton transfer to an organic substrate. Homogeneous precatalysts based on the Co(II) oxidation state have been reported in the past, however, mechanistic insights into such systems were rather limited to date.

Recently, the groups of Jiao and Beweries at LIKAT Rostock have demonstrated that PNN(H) Co(II) complexes serve as very efficient precatalysts for the selective formation of E-alkenes at very mild conditions, suing MeOH and H3B·NH3 as the hydrogen source. This reaction is suggested to take place exclusively via the Co(II) oxidation state, which was corroborated though a combination of control experiments, EPR spectroscopy, and DFT analysis. Key feature for the high activity of this Co system is the proton responsive PNN(H) ligand, possessing a pyrazole fragment that undergoes deprotonation during catalyst activation. The results presented herein could be relevant for the design of other proton responsive ligands for non-noble metal free transfer hydrogenation reactions.

Corresponding author:

PD Dr. Torsten Beweries (Leibniz Institute for Catalysis, Rostock)

Torsten Beweries is head of the department Coordination Chemistry and Catalysis at the Leibniz Institute for Catalysis in Rostock (Germany). He received his PhD in Chemistry at LIKAT in 2008, working on the coordination chemistry of hafnocenes. He then moved to the University of York (UK) for a postdoctoral stay with Prof. Robin N. Perutz in 2009, working on late transition metal complexes for halogen bonding. He returned to LIKAT in 2010, where he established an independent research group. The research field of PD Dr. Torsten Beweries is organometallic chemistry and homogeneous catalysis with focus on new pincer ligands and complexes, main group polymers, and unusual metalacyclic systems. He is the author of 91 articles indexed by SCI and cited more than 1600 times with an index H = 23.

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Unprecedented Organometallic Rare Earth Complexes Containing a Large, Flexible Salophen Ligand

Organometallic chemistry of the rare earth and actinide elements has been a driving force for the development of novel functional materials and catalysts for decades, giving rise to impressive advances in the fields of single-molecule magnetism, luminescence, and polymer sciences. Excitingly, organometallic approaches have always been on the forefront of fundamental chemistry and allowed breakthroughs in the field, not only with the lighter metals but also some of the heaviest actinide candidates. The inherent reactivity of organometallic compounds owing to the apparent labile and reactive metal-carbon bonds renders the isolation and characterization of such molecules exceptionally challenging, especially when aiming at polymetallic rare earth complexes, and is therefore underdeveloped to this date. Consequently, the exploration of suitable synthetic routes to access bridged organometallic metallocene complexes is of great interest for the rare earth and more general inorganic chemistry community.  

Recently, the group of Selvan Demir at Michigan State University has demonstrated that two rare earth metallocene fragments are able to capture the tetradentate salophen ligand, giving rise to the first series of dinuclear salophen-bridged rare earth metallocene complexes with the metals yttrium, gadolinium and dysprosium, Figure 1. These molecules also constitute the first metallocene salophen complexes for any metal ion. Remarkably, the flexibility of the salophen bridge allows the binding pockets to face outwards upon complexation to the metal ions which is a rare, yet intriguing, coordination mode. Consequently, a substantial separation of the metal centers (7.858 – 7.895 Å) occurs leading to weak electronic or magnetic communication between the rare earths. Since the magnitude of magnetic exchange coupling between paramagnetic metal centers and/or organic radical is crucial for the generation of better-performing multinuclear single-molecule magnets,  the magnetic communication in these salophen complexes was explored. 

Figure 1. (A) Schematic view of the salophen-bridged rare earth metallocene complexes. (B) Structure of the rare earth molecules as obtained through single-crystal X-ray diffraction. (C) Arial view of the calculated highest occupied molecular orbital.

The dynamic magnetic properties of the paramagnetic dysprosium complex revealed characteristics of single-molecule magnet behavior, while the static magnetic susceptibility data collected for the paramagnetic gadolinium complex allowed quantification of the magnetic exchange, Figure 2. The determined coupling is of similar magnitude to other polynuclear rare earth complexes containing diamagnetic bridging ligands. DFT calculations on the diamagnetic yttrium conger revealed negligible orbital overlap between the metal center and the salophen ligand in the highest occupied molecular orbital, Figure 1, which may account for the weak magnetic coupling in the paramagnetic variants.

Notably, the lowest unoccupied molecular orbital might be able to be populated with an unpaired electron. Radicals, innate to unpaired electrons, promote strong exchange coupling when placed between rare earth magnetic moments and are, thus, extremely sought-after in the fields of single-molecule magnetism and spintronics. Excitingly, cyclic voltammetry measurements of the salophen

Figure 2. (A) Electron uptake of the dysprosium molecule via electrochemistry. (B) Single-molecule magnet features of the dysprosium complex.

complexes revealed a quasi-reversible feature attributed to the reduction and oxidation of the salophen bridge on the timescale of the electrochemical experiment, Figure 2. This paves the way for chemical reductions of these molecules to generate coveted metal-radical compounds in the future. Noteworthy, chemical functionalization of the salophen backbone may readily be attained which serves as an additional path to augment magnetic coupling and as such highlights the enormous potential of the salophen ligand in organometallic chemistry.

Selvan Demir is an Assistant Professor of Chemistry at Michigan State University. She earned her Dr. rer. Nat. at the University of Cologne researching on scandium solid state chemistry with Prof. Gerd Meyer and scandium organometallic chemistry with Prof. William J. Evans at the University of California, Irvine. Subsequently, she focused on lanthanide-based single-molecule magnets and porous aromatic frameworks with Prof. Jeffrey R. Long at the University of California, Berkeley, and worked on transuranics with Dr. David K. Shuh at the Lawrence Berkeley National Laboratory. Afterwards, she took up a junior professorship of inorganic chemistry at the University of Göttingen. Since 2019, she researches with her group at Michigan State University, on various areas surrounding the chemistry of the rare earth elements and actinides. The research group focuses mainly on organometallic chemistry, small molecule activation, single-molecule magnetism, and lanthanide/actinide separations. A particular emphasis is also on heavy p-block element and uranium chemistry.

 

 

 

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Enantioselective chiral sorption of 1-phenylethanol by homochiral 1D coordination polymers

Amongst the myriad uses of metal-organic frameworks (MOFs) and coordination polymers, separation of complex mixtures, either gaseous or in solution, is one of the most promising applications due to the regular array of well-defined pores. Integration of specific points of interaction that are complementary to the targeted guest species can provide highly selective materials. In particular, precise control of the 3D space within pores may provide a mechanism for enantioselective discrimination for which the exact spatial arrangement of multiple sites of interaction is paramount.

The vast majority of research in this area is driven by 3D metal-organic frameworks, often those possessing permanent porosity. However, for solution-based applications this need not be a prerequisite and materials comprising lower dimensionality coordination polymers may be just as effective is they contain solvent-filled pores.

Recently the group of David Turner at Monash University has shown that a 1D coordination polymer, with pores formed by alignment of loops within the 1D chain, is capable of sorbing 1-phenylethanol with a good degree of enantioselectivity (Figure 1). A closely related material shows no such selectivity, and a reduced uptake capacity, highlighting the importance of structural match between the host framework and the analyte. Ground samples showed higher uptake than unground crystals for the active material, suggesting an influence of surface area or ease of permeation into the solid. Both static (soaking) and dynamic (“micro-LC”) methods showed enhanced uptake of one enantiomer from a racemic solution of 1-phenylethanol, albeit not perfect separation. The group was also able to crystallographically determine the binding site of the preferred enantiomer (Figure 2), showing an array of hydrogen bonding interactions that lie behind the enhanced uptake of one enantiomer over the other.

These results highlight the potential of non-3D coordination polymers in chemical separations and demonstrate the array of host-guest interactions that are required for separations of very similar compounds.

Figure 1. The chiral material contains guest-filled pores resulting from the alignment of loops within the 1D coordination polymer.

Figure 2. The preferred enantiomer of the guest is found crystallographically within the binding pocket, highlighting the array of interactions that hold it in place and provide the enantioselectivity.

Corresponding Author:

David Turner is a Senior Lecturer in the School of Chemistry at Monash University, Australia. After receiving his PhD in 2004 from King’s College, London, he held a number of fellowships at Monash University prior to joining as a Faculty member. Research in the Turner group revolves around metallosupramolecular assemblies, exploring both coordination polymers/MOFs and coordination cages with a particular emphasis on chirality. Dr Turner has published over 130 papers, in addition to two books, attracting almost 5000 citations and an h-index of 32.

https://research.monash.edu/en/persons/david-turner

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A New 2D Layered Aluminophosphate |Hada|6[Al6(PO4)8](H2O)11 Supported Highly Uniform Ag Nanoparticles for 4-Nitrophenol Reduction

Since Wilson and Flanigen found the first microporous aluminophosphate (AlPO) in 1982, the synthesis of AlPO materials with novel frameworks and study their potential properties, such as adsorption, catalysis, and separation, has attracted intense interest of researchers. As the main family of AlPO based materials, 2D layered materials show a rich variety of structures and compositions depending on the diverse coordination and connection modes of Al and P atoms. In recent years, 2D materials, possessing highly exposed surfaces and diverse structures, have become a dramatic category of supports. However, 2D molecular sieves are serving as catalyst supports are very few.

Recently, Prof. Jiuxing Jiang at Sun Yat-sen University and Dr. Jiang-Zhen Qiu of Zhongkai University of Agriculture and Engineering synthesized a new 2D layered aluminophosphate compound by adopting rigid and bulky template of 3,5,N,N-tetramethyladamantane-1-amine (ada) through hydrothermal conditions, which is named the Zhongkai University of Agriculture and Engineering NO.1 (ZHKU-1), with the composition |Hada|6[Al6(PO4)8](H2O)11. The structure of ZHKU-1 was constructed from the alternate connection of AlO4 and triply bridged PO4 tetrahedra ([O=PO3]3-) to form a 4, 6, 12-net (Figure 1). The inorganic sheets are linked and separated by protonated amine and H2O molecules by extensive H-bonds, giving a new 2D structure with an interlayer space of 19.6 Å.

Figure 1 Crystal structure figures of ZHKU-1

ZHKU-1, as a 2D material with a more exposed surface, could be adapted for encapsulating metal nanoparticles (NPs). Ag species are immobilized on the supports of ZHKU-1 by UV reduction and deposition, forming the catalyst of Ag@ZHKU-1 with high loading of 4.9 wt%. The HRTEM images reveal the highly uniform Ag clusters with visually observed sizes of 1.9 nm (Figure 2).

Figure 2 The characterizations of Ag@ZHKU-1 for HRTEM and corresponding mapping images

Since 4-nitrophenol (4-NP) is a notorious industrial pollutant, Ag@ZHKU-1 is applied to the model reaction for 4-NP reduction. The catalytic results show that the reduction reaction of 4-NP into 4-aminophenol could be completely performed within 75 s in NaBH4 solution (Figure 3). Moreover, the catalytic activity was almost the same, with almost 99% conversion after eight cycles. The remarkable catalytic activity and recyclability of Ag@ZHKU-1can be attributed to the high dispensability of Ag nanoclusters confined to the 2D support, which provides more accessible Ag active sites to 4-NP.

Figure 3 Catalytic activity and recycling tests for 4-nitrophenol reduction are over Ag@ZHKU-1 catalyst

This work reports a new 2D layered aluminophosphate compound, which expends the aluminophosphates family. Furthermore, the confinement of metal Ag on this new layer structure through photodeposition gives rise to a small size (~1.9 nm) of AgNPs with homogeneous dispersion. The catalyst of Ag@ZHKU-1 shows excellent catalytic activity and high conversion for 4-nitrophenol reduction. This work is significant for designing 2D aluminophosphate materials to confine small metal nanoparticles for catalytic application.

Prof: Jiuxing Jiang (ORCID: 0000-0001-9664-3235). I received Ph.D degree from Jilin University in 2010. Afterward, I spent 5 years for a Post Doc. stay in Instituto Technologia Quimica (UPV-CSIC) in Valencia Spain supervised by Prof: Avelino Corma. After independent work in Sun Yat-sen University (2015-now), I keep my interesting on the topologically new zeolite synthesis (four three letter code, IRR, -IRY, -IFU, -SYT were granted by Structure Committee of Internation Zeolite Association), and zeolite based heterogeneous catalysis, such as: acid-base catalysis, catalytic ammonium synthesis, NH3-SCR for deNOx reaction, porous materials for energy storage, etc. I have published more than 20 high-impact journal articles, such as Science, Angew. Chem. Int, Ed, Chem.Sci, Chem. Mater. etc. Among them, the work on the synthesis and structure of zeolite ITQ-43 was published in Science, 2011, 333, 1131-1134 and was selected as annually breakthrough of 2011 by Science. Currently serve as a member of Zeolite Committee of Chinese Chemical Society and youth editorial member of Journal of Chemical Research in Chinese University.

Jiang-Zhen Qiu: She received her Ph.D. degree in 2019 from Sun Yat-sen University with M.S. Supervisor Prof. Ming-Liang Tong and Ph.D. Supervisor Prof. Jiuxing Jiang. In 2020, she was introduced to Chemical Engineering of Zhongkai University of Agriculture and Engineering as an “Excellent Doctor”. Her interested research fields include synthesizing new topological structures of zeolite and exploring multifunctional materials with novel functionalities such as light, conductivity, magnetism, or catalysis. Currently, she and her collaborators published 10 papers in related fields, such as Chem. Mater., Chem. Sci., Inorg. Chem. Front., Chem. Commun., Chem. Eur. J.

 

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Optimizing the relaxivity at high fields: systematic variation of the rotational dynamics in polynuclear Gd-complexes based on the AAZTA ligand

Magnetic Resonance Imaging (MRI) is one of the most important and prominent techniques in in clinical diagnostic medicine, in preclinical studies and in biomedical research. As well as many other imaging modalities, MRI also makes extensive use of contrast agents (CAs) that allow achieving remarkable improvements in medical diagnosis in terms of higher specificity, better tissue characterization and functional information. For the vast majority, the clinically used CAs are coordination complexes in which a GdIII ion is encapsulated within octadentate chelators based on polyaminocarboxylate anions and has a directly bound water molecule. Their use is widespread and is estimated to correspond to approximately 40 million administrations per year of GdIII chelates worldwide.

Their effectiveness (relaxivity; the increase in the relaxation rate R1 of the water protons normalized to a 1 mM concentration of the paramagnetic ion) at the magnetic fields of clinical interest is dominated and limited by the fast rotational dynamics and tends to decrease with the increased magnetic field. However, the current trend in MRI development is towards higher magnetic field strengths and most scanners operate at 1.5 or 3 T, while there is increasing use of those at 7 T. Therefore, a different approach for the relaxivity enhancement of Gd-based CAs becomes necessary for the modern high-field systems.

Recently, the group of Mauro Botta and colleagues from the University of Eastern Piedmont in Alessandria (Italy) investigated the optimization of the efficacy of Gd-based CAs, between 1 and 7 T, by systematically modulating the rotational dynamics through the synthesis of polynuclear systems containing between two and eight GdIII chelates (Figure 1).

Figure 1. [Gd(AAZTA)(H2O)2] and polynuclear Gd2-6L2-L6 complexes 

The [Gd(AAZTA)(H2O)2] chelate was used as a building block due to its remarkable properties: a) ease and high-yield synthesis, presence of two inner sphere water molecules in fast exchange with the bulk; b) high thermodynamic stability; c) kinetic inertness in the presence of physiological concentrations of CuII and ZnII higher than that of the clinical agent [Gd(DTPA)]2-; d) negligible tendency to formation of ternary complexes with endogenous anions. The study demonstrates that the strategy for relaxation enhancement varies with the strength of the magnetic field used.

Up to 3 T, efficacy is limited by molecular rotation and therefore increases proportionally with the increase in molecular size. Between 3 and 7 T, the issue of local flexibility or anisotropic rotation, evaluated with NMR techniques and computational models, becomes more and more relevant and medium-sized rigid systems (tri- or tetranuclear) provide the best results. At ultra-high fields (> 7 T), small and compact mono- or binuclear complexes are most effective (Figure 2).

 

Figure 2. Upper: T1-weighted phantom MR-images at 3 and 7 T on selected polynuclear complexes highlighting the effective signal enhancement of the new MRI probes at clinically relevant magnetic field strengths in comparison to the commercial MRI agent ProHance®. Lower: Signal enhancement (298 K) of Gd3L3, Gd4L4 and Gd6L6 compared to Prohance at 1, 3 and 7 T.

The results of this study allow identifying the most effective strategy for optimizing the CAs, each suited to a well-defined range of applied magnetic field strength.

 

Mauro Botta is full professor of Inorganic Chemistry in the Department of Sciences and Technological Innovation at the University of Eastern Piedmont (Italy). He received the “Laurea” cum laude in Chemistry at the University of Turin in 1985. His scientific interests have focused on the use of NMR techniques for the characterization of inorganic systems, starting from organometallic clusters and then moving on the complexes of the f-elements. Recipient of the “Raffaello Nasini” gold medal award for Inorganic Chemistry of the Italian Chemical Society and of the “GIDRM gold medal for magnetic resonance”. He has published over 280 papers (index H = 63; citation: 12800) and several book chapters on these topics and filed 5 patents.

 

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