Discrete Complex Research Articles

Structural Effect of N-7 Alkylation in 6-Chloropurine on Cu (II) Binding: Effect of Anions and Magnetic Studies.

This study investigates the anion-directed assembly of discrete copper (II) complexes. The ligands of choice are two N7-alkyl-purine-based neutral ligands. These ligands facilitate the exclusive coordination through the N3 and N9 positions, preventing polymeric chain formation. Perchlorate ions promoted the formation of discrete paddlewheel-like complexes with the general formula [Cu2(μ-Pur)4(CH3CN)2]4+, while chloride ions yielded chloride-bridged dimers of the form [Cu2(Pur)2(μ-Cl)2Cl2]. Copper-copper bond distances within these complexes ranged from 2.92 to 2.98 Å. Magnetic susceptibility measurement of chloride-bridged complexes exhibited antiferromagnetic coupling, whereas paddlewheel complexes displayed more complex alternating ferromagnetic and antiferromagnetic interactions. Chloride-bridged compounds exhibited strong near-infrared absorption.

Assembling a new generation of radiopharmaceuticals with supramolecular theranostics.

Supramolecular chemistry has been used to tackle some of the major challenges in modern science, including cancer therapy and diagnosis. Supramolecular platforms provide synthetic flexibility, rapid generation through self-assembly, facile labelling, unique topologies, tunable reversibility of the enabling noncovalent interactions, and opportunities for host-guest chemistry and mechanical bonding. In this Review, we summarize recent advances in the design and radiopharmaceutical application of discrete self-assembled coordination complexes and mechanically interlocked molecules - namely, metallacages and rotaxanes, respectively - as well as in situ-forming supramolecular aggregates, specifically pinpointing their potential as next-generation radiotheranostic agents. The outlook of suchsupramolecular constructs for potential applications in the clinic is discussed.

Bottom-up construction of chiral metal-peptide assemblies from metal cluster motifs.

The exploration of artificial metal-peptide assemblies (MPAs) is one of the most exciting fields because of their great potential for simulating the dynamics and functionality of natural proteins. However, unfavorable enthalpy changes make forming discrete complexes with large and adaptable cavities from flexible peptide ligands challenging. Here, we present a strategy integrating metal-cluster building blocks and peptides to create chiral metal-peptide assemblies and get a family of enantiopure [R-/S-Ni3L2]n (n = 2, 3, 6) MPAs, including the R-/S-Ni6L4 capsule, the S-Ni9L6 trigonal prism, and the R-/S-Ni18L12 octahedron cage. X-ray crystallography shows MPA formation reactions are highly solvent-condition-dependent, resulting in significant changes in ligand conformation and discrete cavity sizes. Moreover, we demonstrate that a structure transformation from Ni18L12 to Ni9L6 in the presence of benzopyrone molecules depends on the peptide conformational selection in crystallization. This work reveals that a metal-cluster building block approach enables facile bottom-up construction of artificial metal-peptide assemblies.

High dynamic range land wavefield reconstruction from randomized acquisition

Compressive sensing (CS) is an alternative to regular Shannon sampling that captures similar information from reduced measurements. It relies on randomized sampling patterns and a sparse data representation to reconstruct the regularly sampled object. CS is an important ingredient in affordable seismic acquisition, which can lead to improvements in the near-surface mapping and noise suppression for land data. However, the near surface traps most of the source-generated energy, resulting in data that are rich in high-wavenumber content and have amplitudes spanning several orders of magnitude. When dealing with such high dynamic range nonstationary data, the Fourier domain is not optimal for providing a sparse representation — a necessary condition for successful application of CS. In contrast, a discrete complex wavelet transform can localize high-energy features, has good directional selectivity, and is near-shift invariant. Combined, these properties allow complex wavelets to represent detail-rich wavefields in a compact form. To leverage these features and achieve good CS reconstructions, we develop a scale- and orientation-dependent iterative soft thresholding (IST) scheme for reconstructing high dynamic range wavefields. Our approach requires little parameterization, is easy to implement, and is robust to reconstructed wavefield sampling grid and dynamic range. We test IST on different wavefields with randomly missing traces and compare the data reconstructions with the spectral projected gradient solver and projection onto convex sets. We quantify the reconstructions by a direct comparison of Fourier coefficients between fully sampled and reconstructed wavefields. Taking log10 of Fourier coefficients prior to computing the quality metric deemphasizes the importance of magnitude match while highlighting Fourier coefficient support accuracy, which usually translates into good structural fidelity of reconstructed data. We find that IST performs consistently among all examples, yielding good phase match while performing gentle denoising.

Unusual Metal–organic Multicomponent Ni(II) and Mononuclear Zn(II) Compounds Involving Pyridine dicarboxylates: Supramolecular Assemblies and Theoretical Studies

In the present work, we reported the synthesis and characterization [single crystal X-ray diffraction technique, spectroscopic, etc.] of two new Ni(II) and Zn(II) coordination compounds, viz. [Ni(2,6-PDC)2]2[Ni(en)2(H2O)2]2[Ni(en)(H2O)4]·4H2O (1) and [Zn(2,6-PDC)(Hdmpz)2] (2) (where 2,6-PDC = 2,6-pyridinedicarboxylate, en = ethylene-1,2-diamine, and Hdmpz = 3,5-dimethyl pyrazole). Compound 1 is found to crystallize as a multicomponent Ni(II) compound with five discrete complex moieties, whereas compound 2 is isolated as a mononuclear Zn(II) compound. A deep analysis of the crystal structure of 1 unfolds unusual dual enclathration of guest complex cationic moieties within the supramolecular host cavity stabilized by anion–π, π-stacking, N–H⋯O, C–H⋯O, and O–H⋯O hydrogen bonding interactions. Again, the crystal structure of compound 2 is stabilized by the presence of unconventional C–H⋯π(chelate ring) interactions along with C–H⋯O, C–H⋯N hydrogen bonding, π-stacking, and C–H⋯π(pyridyl) interactions. These non-covalent interactions were further studied theoretically using density functional theory (DFT) calculations, molecular electrostatic potential (MEP) surfaces, non-covalent interaction (NCI) plot index, and quantum theory of atoms in molecules (QTAIM) computational tools. The computational study displays that π-stacking or H bonds greatly tune the directionality of compound 1, although non-directional electrostatic forces dominate energetically. For compound 2, a combined QTAIM/NCI plot analysis confirms the presence of unconventional C–H⋯π(chelate ring) interactions along with other weak interactions obtained from the crystal structure analysis. Further, the individual energy contributions of these weak yet significant non-covalent interactions have also been determined computationally.

Estimation of the surface impedance based on the discrete complex image source method and array processing

This paper introduces a method for estimating the sound absorption coefficient of a large panel of absorbing material from measurements using a microphone array. The method relies upon describing the pressure field as the set of monopoles obtained when the reflection coefficient is represented as the Laplace Transform of an image source distribution. This formulation results in a well-behaved integral equation, which is discretized using Gaussian quadrature to yield an inverse problem. It is possible to determine the regularized solution to the inverse problem and reconstruct the surface impedance of the sample by conducting measurements of the sound pressure at multiple points of observation. This sound field representation is adequate for sound sources in the close range of the material and the array. The paper presents simulated and experimental investigations to delineate the efficacy of the proposed measurement technique against the well-known image source method, thereby highlighting its significant potential to advance acoustic characterization methodologies.

Supramolecular Hybrids of Proteins from Habu Snake Venom with Discrete [Pt(CN)4]2- Complex.

The venom of the Habu snake Protobothrops flavoviridis (P. flavoviridis) is known to contain a diverse array of proteins and peptides, with a notable presence of phospholipase A2 (PLA2) enzymes. These PLA2 enzymes have been extensively studied for their function and molecular evolution. Nevertheless, several aspects, such as the physical properties and the self-assembly mechanism of hierarchical structure from the nanoscale to the microscale with different chemical compounds, remain poorly understood. This study aims to fill this knowledge gap by investigating the behavior of enzyme components purified from P. flavoviridis venom in the presence of anionic [Pt(CN)4]2- complexes, which have the potential for soft metallophilic interactions and interesting optical properties. The purified PLA2 isozymes were diluted in Dulbecco's phosphate buffered saline (D-PBS (-)) and combined with the anionic metal complex, resulting in the formation of microstructures several micrometers in size, which further grew to form fibrous structures. This novel approach of combining PLA2 enzymes with discrete functional metal complexes opens up exciting possibilities for designing flexible and functional supramolecular and biomolecular hybrid systems in aqueous environments. These findings shed light on the potential applications of snake venom enzymes in nanotechnology and bioengineering.

An imidazole-copper(I) metallacycle complex exhibiting thermochromic fluorescence.

In this paper, we firstly report the synthesis and structural characterization of a discrete coordination metallacycle complex, [CuI (bipy)]2 (1). The x-ray diffraction structure, temperature-dependent electronic absorption, and photoluminescence spectra have been investigated. The solid-state fluorescence at variable temperatures shows that complex 1 exhibits an obvious thermochromic fluorescence. At low temperature, the dual fluorescence with peaks at 590 and 694 nm was observed. The emission color significantly changes from red at 77 K to yellow at 200 K and blue-green at 330 K. The thermochromic fluorescent molecular materials show great potential as temperature sensing.

Anion-pairing effect in Cd(II) coordination with a tetrabenzotetraza-crown macrocyclic ligand

Three new complexes of a tetrabenzotetraza-crown ether macrocyclic ligand (L) with Cd(II) chloride (1), iodide (2), and acetate (3) salts were synthesized and characterized by FT-IR, 1H NMR spectroscopy, elemental microanalysis, and single crystal X-ray diffraction. Complex 1 has the formula [Cd(L)Cl]2 [CdCl4] with two square pyramidal [Cd(L)Cl]+ subunits interconnected through the CdCl42− counter anion. Meanwhile, the reaction with CdI2 produces the discrete complex [Cd(L)I]I (2) with an octahedral geometry about the Cd(II) center. A distorted six-coordinated asymmetric unit was observed for [Cd(L)OAc]2(OAc·H2O)2 (3), wherein two [Cd(L)OAc]+ subunits are held together by a flat (OAc·H2O)2 acetate-water cluster. Hirshfeld Surface calculations were applied to confirm the dominant interactions in 1–3, namely π–π, and X⋯H/H⋯X (X-H, C, O, and halogen) interactions as the main factors for their structural differences. At the same time, the structure of [Cd(L)L′]+ (L′ = Cl, I, and OAc) core remained almost unchanged. The Cd(II) coordination with L in the presence of different Cd(II) salts was followed by 1H NMR spectroscopy. All three Cd(II) salt displays 1:1 stoichiometry, with binding constants in the order CdCl2 < CdI2 < Cd(OAc)2.

In-silico antibacterial activity of piperazinyl-based copper(II) metallo-organic pharmacophores

The piperazinyl-based Cu(II)-Schiff base complex {[Cu(HL1′)(N3)]2∙(ClO4)2·4H2O} (1) [HL1′ is the Zwitter ionic form of (E)-2-((2-piperazin-1-ylethylimino)methyl)phenol] was synthesized and characterized by spectroscopic and single crystal X-ray diffraction studies. The X-ray single crystal structure analysis shows that the asymmetric unit of 1 contains a four-coordinate discrete complex cation, [Cu(HL1′)(N3)]+ (1a), with a perchlorate anion and a lattice water molecule. Two square planar units of 1a are dimerized by weak Cu···N intermolecular interaction, forming [Cu(HL1′)(N3)]2 2+ (1′a). DFT and TD-DFT calculations of the monomeric cationic unit, [Cu(HL1′)(N3)]+ (1a) were performed. In-silico antibacterial activities of HL1 as well as monomeric and dimeric cationic units 1a and 1'a, respectively, were performed and study shows that 1a (EC50 0.30 μM) and 1′a (EC50 0.06 μM) may be treated as antibacterial drugs after in-vivo analysis and clinical testing.

Crystal structures, phase transition, and Hirshfeld surface analyses of the bromide and chloride congeners of aqua[2,4,6-tris(pyridin-4-yl)-1,3,5-triazine]zinc(II) halide.

During the course of exploring crystallization conditions in generating metal-organic frameworks (MOFs) for use in the crystalline sponge method, two discrete metal-organic complexes, namely, aqua[2,4,6-tris(pyridin-4-yl)-1,3,5-triazine]zinc(II) bromide, [Zn(C18H12N6)(H2O)]Br2, and aqua[2,4,6-tris(pyridin-4-yl)-1,3,5-triazine]zinc(II) chloride, [Zn(C18H12N6)(H2O)]Cl2, were encountered. Structures in the orthorhombic space group Pnma (No. 62) for the bromide congener at 299 K and the chloride congener at 100 K were obtained. A phase transition for the bromide congener occurred upon cooling from 299 to 100 K, yielding a crystal polymorph with four domains that exhibits monoclinic P21/m space-group symmetry (No. 11), which arises from conformational changes. The main intramolecular contacts that contribute to the crystal packing in all observed structures are H...H, Halide...H/H...Halide, C...H/H...C, and N...H/H...N. Intramolecular hydrogen bonding between the Zn-bound water and non-Zn-bound pyridyl N atoms is a prominent feature within the three-dimensional networks. Aromatic π-stacking between the non-Zn-bound pyridine rings and contacts involving the halide ligands further stabilize the crystal packing.

UNC-45 assisted myosin folding depends on a conserved FX3HY motif implicated in Freeman Sheldon Syndrome

Myosin motors are critical for diverse motility functions, ranging from cytokinesis and endocytosis to muscle contraction. The UNC-45 chaperone controls myosin function mediating the folding, assembly, and degradation of the muscle protein. Here, we analyze the molecular mechanism of UNC-45 as a hub in myosin quality control. We show that UNC-45 forms discrete complexes with folded and unfolded myosin, forwarding them to downstream chaperones and E3 ligases. Structural analysis of a minimal chaperone:substrate complex reveals that UNC-45 binds to a conserved FX3HY motif in the myosin motor domain. Disrupting the observed interface by mutagenesis prevents myosin maturation leading to protein aggregation in vivo. We also show that a mutation in the FX3HY motif linked to the Freeman Sheldon Syndrome impairs UNC-45 assisted folding, reducing the level of functional myosin. These findings demonstrate that a faulty myosin quality control is a critical yet unexplored cause of human myopathies.

A discrete three-dimensional divdiv complex on polyhedral meshes with application to a mixed formulation of the biharmonic problem

In this work, following the Discrete de Rham (DDR) paradigm, we develop an arbitrary-order discrete divdiv complex on general polyhedral meshes. The construction rests on (1) discrete spaces that are spanned by vectors of polynomials whose components are attached to mesh entities and (2) discrete operators obtained mimicking integration by parts formulas. We provide an in-depth study of the algebraic properties of the local complex, showing that it is exact on mesh elements with trivial topology. The new DDR complex is used to design a numerical scheme for the approximation of biharmonic problems, for which we provide detailed stability and convergence analyses. Numerical experiments complete the theoretical results.

Discrete Symplectic Fermions on Double Dimers and Their Virasoro Representation

AbstractA discrete version of the conformal field theory of symplectic fermions is introduced and discussed. Specifically, discrete symplectic fermions are realised as holomorphic observables in the double-dimer model. Using techniques of discrete complex analysis, the space of local fields of discrete symplectic fermions on the square lattice is proven to carry a representation of the Virasoro algebra with central charge $$-2$$ - 2 .

A Novel Diastolic Doppler Index Less Affected by Aortic Arch Anomalies Co-existing with Coarctation.

Severity assessment for coarctation of the aorta (CoA) is challenging due to concomitant morphological anomalies (complex CoA) and inaccurate Doppler-based indices. Promising diagnostic performance has been reported for the continuous flow pressure gradient (CFPG), but it has not been studied in complex CoA. Our objective was to characterize the effect of complex CoA and associated hemodynamics on CFPG in a clinical cohort. Retrospective analysis identified discrete juxtaductal (n = 25) and complex CoA (n = 43; transverse arch and/or isthmus hypoplasia) patients with arm-leg systolic blood pressure gradients (BPG) within 24 h of echocardiography for comparison to BPG by conventional Doppler indices (simplified Bernoulli equation and modified forms correcting for proximal kinetic energy and/or recovered pressure). Results were interpreted using the current CoA guideline (BPG ≥ 20 mmHg) to compare diagnostic performance indicators including receiver operating characteristic curves, sensitivity, specificity, and diagnostic accuracy, among others. Echocardiography Z-scored aortic diameters were applied with computational simulations from a preclinical CoA model to understand aspects of the CFPG driving performance differences. Diagnostic performance was substantially reduced from discrete to complex CoA for conventional Doppler indices calculated from patient data, and by hypoplasia and/or long segment stenosis in simulations. In contrast, diagnostic indicators for the CFPG only modestly dropped for complex vs discrete CoA. Simulations revealed differences in performance due to inclusion of the Doppler velocity index and diastolic pressure half-time in the CFPG calculation. CFPG is less affected by aortic arch anomalies co-existing with CoA when compared to conventional Doppler indices.

Divalent Titanium via Reductive N-C Coupling of a TiIV Nitrido with π-Acids.

The nitrido-ate complex [(PN)2Ti(N){μ2-K(OEt2)}]2 (1) (PN-=(N-(2-PiPr2-4-methylphenyl)-2,4,6-Me3C6H2) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate TiII complexes having a linear cumulene motif, [K(L)][(PN)2Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NtBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural TiIII center containing a neutral cumulene, [(PN)2Ti(NCE)] (E=O, (6); E=NAd (7), NtBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e- reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete TiII complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with [Fc*][B(C6F5)4] resulted in a ligand disproportionated TiIV complex having transoid carbodiimides, [(PN)2Ti(NCNAd)2] (9). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as TiII→TiIII→TiIV and increasing order of π-donation as TiII→TiIII→TiIV, thus displaying more covalency in TiIII species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N-atom to CO and CNAd.

Divalent Titanium via Reductive N−C Coupling of a TiIV Nitrido with π‐Acids

AbstractThe nitrido‐ate complex [(PN)2Ti(N){μ2‐K(OEt2)}]2 (1) (PN−=(N‐(2‐PiPr2‐4‐methylphenyl)‐2,4,6‐Me3C6H2) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five‐coordinate TiII complexes having a linear cumulene motif, [K(L)][(PN)2Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NtBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2–5 with [Fc][OTf] afforded an isostructural TiIII center containing a neutral cumulene, [(PN)2Ti(NCE)] (E=O, (6); E=NAd (7), NtBu (8)) and characterization by CW X‐band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e− reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete TiII complexes 2 and 5, which were further characterized by solution magnetization measurements and high‐frequency and ‐field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with [Fc*][B(C6F5)4] resulted in a ligand disproportionated TiIV complex having transoid carbodiimides, [(PN)2Ti(NCNAd)2] (9). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as TiII→TiIII→TiIV and increasing order of π‐donation as TiII→TiIII→TiIV, thus displaying more covalency in TiIII species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N‐atom to CO and CNAd.

Higher analogues of discrete topological complexity

In this paper, we introduce the nth discrete topological complexity and study its properties such as its relation with simplicial Lusternik–Schnirelmann category and how the higher dimensions of discrete topological complexity relate with each other. Moreover, we find a lower bound of n-th discrete topological complexity which is given by the nth usual topological complexity of the geometric realisation of that complex. Furthermore, we give an example for the strict case of that lower bound.

Polyoxometalates: metallodrug agents for combating amyloid aggregation.

Alzheimer's disease (AD) is a devastating neurodegenerative disease that affects ∼50 million people globally. The accumulation of amyloid-β (Aβ) plaques, a predominant pathological feature of AD, plays a crucial role in AD pathogenesis. In this respect, Aβ has been regarded as a highly promising therapeutic target for AD treatment. Polyoxometalates (POMs) are a novel class of metallodrugs being developed as modulators of Aβ aggregation, owing to their negative charge, polarity, and three-dimensional structure. Unlike traditional discrete inorganic complexes, POMs contain tens to hundreds of metal atoms, showcasing remarkable tunability and diversity in nuclearities, sizes, and shapes. The easily adjustable and structurally variable nature of POMs allows for their favorable interactions with Aβ. This mini-review presents a balanced overview of recent progress in using POMs to mitigate amyloidosis. Clear correlations between anti-amyloid activities and structural features of POMs are also elaborated in detail. Finally, we discuss the current challenges and future prospects of POMs in combating AD.

Supramolecular assemblies derived from methyl-substituted cucurbit[5]uril and lanthanide nitrates

Interaction of the lanthanide nitrates M(NO3)3 (M = Gd, Eu) with methylcucurbit[5]uril (Me10Q[5]) in the presence of transition metal chlorides (ZnCl2 and FeCl3) in acidic media resulted in the isolation of the complexes [Me10Q[5]Gd(H2O)2Cl Gd(H2O)6](ZnCl4)2∙Cl∙8.9H2O (1) and [Me10Q[5]Eu(H2O)3Cl(H3O)](FeCl4)3 (2). The molecular structures of 1 and 2 have been determined by single crystal X-ray crystallography, and reveal discrete complexes which are involved in dense stacking with adjacent Me10Q[5]s linked via H-bonding and/or metal anions resulting in a supramolecular assembly.