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Template Synthesis (Self-Assembly) of Macrocycles: Theory and Practice

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Structure".

Deadline for manuscript submissions: closed (30 September 2023) | Viewed by 7759

Special Issue Editor

Department of Analytical Chemistry, National Research Technological University, K. Marx Street 68, 420015 Kazan, Russia
Interests: coordination chemistry; quantum chemistry; chemistry of macrocyclic compounds; nanosciences; scientometrics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

More than 60 years in coordination chemistry, and since the beginning of the 21st century, and in molecular nanotechnology there is a very significant interest in template synthesis reactions, in which the design of metal complexes with complex ligands is carried out not according to the classical scheme (metal ion + ligand ® complex), but according to the scheme (metal ion + "building blocks" of the future ligand (so-called ligand synthons or ligsons) ® complex). At the same time, the preparation of such metal heterocyclic compounds by traditional methods is either difficult or even impossible. The metal ion present in the reaction system (the so-called template), which is extremely important, plays the role of a kind of pattern (template) that directs this kind of “self-assembly” in one direction or another; while in its absence it does not occur at all. In a similar way, in a number of cases, the preparation is carried out from simpler starting blocks and very complex organic compounds, which are obtained from the metal chelates formed at the beginning by means of their demetallization. The importance of this “self-assembly”, particularly that which underlies the synthesis of a number of so-called macroheterocyclic compounds, has recently shown an increasing tendency in both fundamental science and in practical terms. It should be noted that “self-assembly” reactions now occupy a dominant position in the synthesis of nitrogen-, nitrogen-oxygen-, and nitrogen-sulfur-containing macrocycles, crown ethers, and other systems with closed loops that include various heteroatoms in their framework. The end products of these reactions, having a complex with non-trivial physical and chemical properties, are due to this extremely diverse application—in addition to chemistry proper, their consumers are metallurgy and medicine, industrial biotechnology and catalysis, microelectronics and agriculture and many other branches of human activity.

Although the number of works on template synthesis currently amounts to many thousands (if not tens of thousands), in this area of chemical synthesis, the structural-chemical design and control of this synthesis, as well as the prediction of the specifics of its products, remain relevant problems. These problems clearly manifest themselves during the self-assembly of the so-called small metallocycles, the results of which in each particular case are difficult to predict, unless any close analogues of such processes are known. Sometimes even ions which are similar in geometric and electronic parameters, being in the role of a template, “organize” this self-assembly in completely different directions. Particularly interesting in the self-assembly reactions are the so-called ambidentate, primarily (N,O,S,P)-donor atomic ligand synthons, which, depending on the starting conditions of complex formation and the nature of the metal ion, are capable of being coordinated to the latter by means of various donor atoms. This circumstance opens new opportunities for the targeted synthesis of a wide variety of metal-macrocyclic compounds on the one hand, and in some cases makes it possible to obtain new, previously unknown metal complexes, which is undoubtedly valuable both for fundamental coordination and supramolecular chemistry, and for molecular nanotechnology. The foregoing is especially important at present, when the efforts of the overwhelming majority of complex chemists all over the world are directed primarily to the development of new methods for the synthesis of metal-macrocyclic and supramolecular compounds.

Considering the above, this Special Issue aims include, first of all, original full articles and brief reports on any processes for the self-assembly (template synthesis) of p-, d-, and f-element macrocyclic compounds. We also welcome papers presenting, along with experimental data, quantum chemical calculations of the molecular/electronic structures of the corresponding macrocyclic compounds, as well as papers presenting purely theoretical calculations related to compounds of this type. Review articles may also be submitted for publication in this Special Issue (including authors’ reviews focusing primarily on their own publications).

Prof. Dr. Oleg V. Mikhailov
Guest Editor

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Keywords

  • macrocyclic compounds
  • template synthesis
  • self-assembly
  • molecular structure
  • thermodynamic characteristics

Published Papers (5 papers)

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Editorial

Jump to: Research

7 pages, 1891 KiB  
Editorial
Template Synthesis (Self-Assembly) of Macrocycles: Theory and Practice
by Oleg V. Mikhailov
Molecules 2022, 27(15), 4829; https://doi.org/10.3390/molecules27154829 - 28 Jul 2022
Cited by 1 | Viewed by 1408
Abstract
For more than 60 years, in coordination chemistry (and since the beginning of the 21st century, in molecular nanotechnology, too), there has been very significant interest in template synthesis reactions, in which the design of coordination compounds (metal complexes) with complex ligands is [...] Read more.
For more than 60 years, in coordination chemistry (and since the beginning of the 21st century, in molecular nanotechnology, too), there has been very significant interest in template synthesis reactions, in which the design of coordination compounds (metal complexes) with complex ligands is carried out not according to the classical scheme [metal ion + ligand → complex], but according to scheme [metal ion + “building blocks” of the future ligand (the so-called ligand synthons or ligsons) → complex] [...] Full article
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Research

Jump to: Editorial

13 pages, 1990 KiB  
Article
Molecular and Electronic Structures of Macrocyclic Compounds Formed at Template Synthesis in the M(II)—Thiocarbohydrazide—Diacetyl Triple Systems: A Quantum-Chemical Analysis by DFT Methods
by Oleg V. Mikhailov and Denis V. Chachkov
Molecules 2023, 28(11), 4383; https://doi.org/10.3390/molecules28114383 - 27 May 2023
Viewed by 795
Abstract
Using density functional theory (DFT) B3PW91/TZVP, M06/TZVP, and OPBE/TZVP chemistry models and the Gaussian09 program, a quantum-chemical calculation of geometric and thermodynamic parameters of Ni(II), Cu(II), and Zn(II) macrotetracyclic chelates, with (NNNN)-coordination of ligand donor centers arising during template synthesis between the indicated [...] Read more.
Using density functional theory (DFT) B3PW91/TZVP, M06/TZVP, and OPBE/TZVP chemistry models and the Gaussian09 program, a quantum-chemical calculation of geometric and thermodynamic parameters of Ni(II), Cu(II), and Zn(II) macrotetracyclic chelates, with (NNNN)-coordination of ligand donor centers arising during template synthesis between the indicated ions of 3d elements, thiocarbohydrazide H2N–HN–C(=S)–NH–NH2 and diacetyl Me–C(=O)–C(=O)–Me, in gelatin-immobilized matrix implants was performed. The key bond lengths and bond angles in these coordination compounds are provided, and it is noted that in all these complexes the MN4 chelate sites, the grouping of N4 atoms bonded to the M atom, and the five-membered and six-membered metal chelate rings are practically coplanar. NBO analysis of these compounds was carried out, on the basis of which it was shown that all these complexes, in full accordance with theoretical expectations, are low-spin complexes. The standard thermodynamic characteristics of the template reactions for the formation of the above complexes are also presented. Good agreement between the data obtained using the above DFT levels is noted. Full article
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11 pages, 3001 KiB  
Article
Computational and Experimental Evidence for Templated Macrocyclization: The Role of a Hydrogen Bond Network in the Quantitative Dimerization of 24-Atom Macrocycles
by Alexander J. Menke, Nicholas C. Henderson, Lola C. Kouretas, Anne N. Estenson, Benjamin G. Janesko and Eric E. Simanek
Molecules 2023, 28(3), 1144; https://doi.org/10.3390/molecules28031144 - 23 Jan 2023
Cited by 4 | Viewed by 1552
Abstract
In the absence of preorganization, macrocyclization reactions are often plagued by oligomeric and polymeric side products. Here, a network of hydrogen bonds was identified as the basis for quantitative yields of macrocycles derived from the dimerization of monomers. Oligomers and polymers were not [...] Read more.
In the absence of preorganization, macrocyclization reactions are often plagued by oligomeric and polymeric side products. Here, a network of hydrogen bonds was identified as the basis for quantitative yields of macrocycles derived from the dimerization of monomers. Oligomers and polymers were not observed. Macrocyclization, the result of the formation of two hydrazones, was hypothesized to proceed in two steps. After condensation to yield the monohydrazone, a network of hydrogen bonds formed to preorganize the terminal acetal and hydrazine groups for cyclization. Experimental evidence for preorganization derived from macrocycles and acyclic models. Solution NMR spectroscopy and single-crystal X-ray diffraction revealed that the macrocycles isolated from the cyclization reaction were protonated twice. These protons contributed to an intramolecular network of hydrogen bonds that engaged distant carbonyl groups to realize a long-range order. DFT calculations showed that this network of hydrogen bonds contributed 8.7 kcal/mol to stability. Acyclic models recapitulated this network in solution. Condensation of an acetal and a triazinyl hydrazine, which adopted a number of conformational isomers, yielded a hydrazone that adopted a favored rotamer conformation in solution. The critical hydrogen-bonded proton was also evident. DFT calculations of acyclic models showed that the rotamers were isoenergetic when deprotonated. Upon protonation, however, energies diverged with one low-energy rotamer adopting the conformation observed in the macrocycle. This conformation anchored the network of hydrogen bonds of the intermediate. Computation revealed that the hydrogen-bonded network in the acyclic intermediate contributed up to 14 kcal/mol of stability and preorganized the acetal and hydrazine for cyclization. Full article
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18 pages, 3744 KiB  
Article
Calix[6]arene-Based [3]Rotaxanes as Prototypes for the Template Synthesis of Molecular Capsules
by Federica Cester Bonati, Margherita Bazzoni, Caterina Baccini, Valeria Zanichelli, Guido Orlandini, Arturo Arduini, Gianpiero Cera and Andrea Secchi
Molecules 2023, 28(2), 595; https://doi.org/10.3390/molecules28020595 - 06 Jan 2023
Viewed by 2415
Abstract
In this work, the ability of several bis-viologen axles to thread a series of heteroditopic tris(N-phenylureido)calix[6]arene wheels to give interwoven supramolecular complexes to the [3]pseudorotaxane type was studied. The unidirectionality of the threading process inside these nonsymmetric wheels allows the formation of highly [...] Read more.
In this work, the ability of several bis-viologen axles to thread a series of heteroditopic tris(N-phenylureido)calix[6]arene wheels to give interwoven supramolecular complexes to the [3]pseudorotaxane type was studied. The unidirectionality of the threading process inside these nonsymmetric wheels allows the formation of highly preorganised [3]pseudorotaxane and [3]rotaxane species in which the macrocycles phenylureido moieties, functionalised with either ester, carboxylic, or hydroxymethyl groups, are facing each other. As verified by NMR and semiempirical computational studies, these latter compounds possess the correct spatial arrangement of their subcomponents, which could lead, in principle, upon proper bridging reaction, to the realisation of upper-to-upper molecular capsules that are based on calix[6]arene derivatives. Full article
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9 pages, 1390 KiB  
Article
Preparation of PMMA Electrospun Fibers Bearing Porphyrin Pendants and Photocatalytic Degradation of Organic Dyes
by Er-Jun Sun, Xiao-Yan Bai, Yu Chang, Qin Li, Xin-Ru Hui, Yan-Song Li and Yue Wang
Molecules 2022, 27(23), 8132; https://doi.org/10.3390/molecules27238132 - 22 Nov 2022
Cited by 3 | Viewed by 902
Abstract
Porphyrins have a large π–π conjugation force between molecules, and they are easy to aggregate in solution, which affects the photoelectric properties of porphyrins. Connecting porphyrins to polymer links through covalent bonds not only retains the mechanical properties and thermal stability of polymer [...] Read more.
Porphyrins have a large π–π conjugation force between molecules, and they are easy to aggregate in solution, which affects the photoelectric properties of porphyrins. Connecting porphyrins to polymer links through covalent bonds not only retains the mechanical properties and thermal stability of polymer materials, but also has the photoelectric properties and catalytic properties of porphyrins, which improves the availability of materials. In this study, first, a porphyrin ligand with double bonds in the side chain was designed and the corresponding copper and zinc complexes were synthesized by adjusting the metal ions in the center of the pyrrole ring. Then, the metalloporphyrin complexes were copolymerized with methyl methacrylate (MMA), and two metalloporphyrin/PMMA copolymers were obtained: CPTPPCu/PMMA and CPTPPZn/PMMA. The structure of the compounds was characterized by IR, 1H NMR, MS, and UV-Vis spectra. Metalloporphyrin/PMMA copolymers were prepared into electrospun fiber materials by electrospinning. The morphology of the composites was studied by SEM, and the thermal stability and optical properties of electrospun fibers were studied by TGA and FL. The catalytic activity of electrospun fiber materials for the degradation of organic dyes was studied. The results showed that the efficiency of the metalloporphyrin/PMMA copolymer in photocatalytic degradation of methylene blue (MB) was better than that of the PMMA electrospun fiber blended with metalloporphyrin. Full article
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