Structure Of Adduct Research Articles

Unveiling the atomistic and electronic structure of NiII-NO adduct in a MOF-based catalyst by EPR spectroscopy and quantum chemical modelling.

The nature of the chemical bonding between NO and open-shell NiII ions docked in a metal-organic framework is fully characterized by EPR spectroscopy and computational methods. High-frequency EPR experiments reveal the presence of unsaturated NiII ions displaying five-fold coordination. Upon NO adsorption, in conjunction with advanced EPR methodologies and DFT/CASSCF modelling, the covalency of the metal-NO and metal-framework bonds is directly quantified. This enables unravelling the complex electronic structure of NiII-NO species and retrieving their microscopic structure.

Mechanochemical reaction of ninhydrin with aromatics, enols and amines: Synthesis, crystal structure and supramolecular self-assembly of cyclic and acyclic adducts

Ninhydrin and related indanone scaffolds are employed as effective synthon in organic and bioorganic chemistry. In the present work, the reactivity of ninhydrin is exploited to synthesize various cyclic and acyclic compounds using mortar and pestle grinding method. The reaction of ninhydrin with various naphthols, phenols, acetylacetone/ethylacetoacetate under grinding condition led to fused/spirocyclic products. On the other hand, 2-methoxynaphthalene, 4-hydroxycoumarin, 1,3-indanedione, indole reacted with ninhydrin to afford simple C-2 arylated acyclic adducts. Single crystal X-ray diffraction study revealed that, ninhydrin-o-cresol adduct, which preferentially remains in the cyclic hemiketal form 6, self-assembled to adopt zipper architecture. However, ninhydrin-2-methoxynaphthalene adduct 7 was found to display corrugated sheet like arrangement. Scanning electron microscopy (SEM) study reveals that cyclic adducts 6, 8, 10 exhibit fibrillar morphology, whereas acyclic adducts 7, 12, 15 disclose sheet morphology.

Structure and Conformation of Novel BODIPY Ugi Adducts.

Two novel BODIPY‐Ugi (boron dipyrromethene) adducts exhibit peculiar room temperature (T=20 °C) H‐1 NMR spectra in that several protons located at the aromatic aniline‐type ring are lost in the baseline. This observation revealed the existence of a dynamic conformational process where rotation around the C−N bond is hindered. Variable‐temperature H‐1 and C‐13 NMR spectroscopic analysis confirmed this conclusion; that is, low‐temperature spectra show distinct signals for all four aromatic protons below coalescence, whereas average signals are recorded above coalescence (T=+120 °C). Particularly interesting was the rather large difference in chemical shifts for the ortho protons below coalescence, Δδ=1.45 ppm, which was explained based on DFT computational analysis. Indeed, the calculated lowest‐energy gas‐phase conformation of the BODIPY Ugi adducts locates one half of the aniline‐type ring in the shielding anisotropic cone of the bridge phenyl ring in the BODIPY segment. This is in contrast to the solid‐state conformation established by X‐ray diffraction analysis that shows a nearly parallel arrangement of the aromatic rings, probably induced by crystal packing forces.

Atom-economic Michael reaction between hydroacridines and arylmaleimides without catalyst/additive

Previously unknown spiroderivatives of 3,1-benzoxazines were synthesized by the reaction of anthranilic acid with cyclic ketones. The interaction of 3,1-spirobenzoxazines with Vilsmeier-Haack reagent (POCl3 (PBr3)/DMF), depending on the amount of formulation agent, leads to the formation of hydroacridones or hydroacridines. Under catalyst- and additive-free conditions, N-arylmaleimides, like Michael's acceptors, are added to the hydroacridines in DMSO to form the corresponding adducts. The reaction proceeds stereoselectively with the formation of a mirror pair of diastereomers, if the products have only two chiral centers. In the presence of three chiral centers in the structure of Michael's adducts, the reaction is not stereoselective. The reaction proceeds by the sp3 hybrid carbon atom under non-catalytic conditions due to the imin-enamine tautomerism of chloro(bromo)hydroacridines. The presented reaction can also be considered as an effective atom-economical aza-ene reaction, which fully meets today's requirements for eco-friendly reaction. The synthesized compounds are potential biologically active substances and can also be used as "building-blocks" for organic synthesis.

Ascorbylation of a Reactive Cysteine in the Major Apple Allergen Mal d 1.

The protein Mal d 1 is responsible for most allergic reactions to apples (Malus domestica) in the northern hemisphere. Mal d 1 contains a cysteine residue on its surface, with its reactive side chain thiol exposed to the surrounding food matrix. We show that, in vitro, this cysteine residue is prone to spontaneous chemical modification by ascorbic acid (vitamin C). Using NMR spectroscopy and mass spectrometry, we characterize the chemical structure of the cysteine adduct and provide a three-dimensional structural model of the modified apple allergen. The S-ascorbylated cysteine partially masks a major IgE antibody binding site on the surface of Mal d 1, which attenuates IgE binding in sera of apple-allergic patients. Our results illustrate, from a structural perspective, the role that chemical modifications of allergens with components of the natural food matrix can play.

Abstract 2257: DNA adductome analysis in human colorectal tissues

Abstract Due to recent advancement of DNA sequencing technologies, cancer genome analysis has shown that somatic mutations have different trends in various tissues and individuals. Some of trends has been associated with exposure of chemically reactive compounds derived from exogenous or endogenous sources and genetic deficiencies in DNA repair and DNA replication as mutational signatures. Accumulation of these information will ultimately expect to identify carcinogenic etiologies in an individual case. However, what types of DNA damage caused the mutational signatures and how extent they contribute to human carcinogenesis has not yet fully explained.To directly evaluate the chemical types of DNA damage in human colorectal tissues, we performed comprehensive identification of DNA adducts by a liquid chromatography coupled with mass spectrometry. In this DNA adductome methodology, genome DNA was enzymatically hydrolyzed into mononucleoside and separated using a reversed-phase chromatography. Chemical structure of DNA adducts including products of epigenetic modification in genome DNA was identified using column retention time and m/z of chemical standard library of DNA adducts. Peak areas of DNA adducts were normalized by that of naturally-occurring isotopologues of canonical DNA nucleoside and compared with clinicopathological information. We identified several DNA adducts in human colorectal tissue. These included DNA adducts of alkylation, oxidation, and lipid peroxidation. C5-methyl-2’-deoxycytidine was most abundant atypical DNA in human colorectal tissue and prevalent in all cases. C5-hydroxymethyl-2’-deoxycytdine was decreased in colorectal cancer cases compared with non-colorectal cancer cases. Other DNA adducts like 1,N6-etheno-2’-deoxyadenosine were present with group- or individual-specificity. Compared with our previous results of DNA adductome analysis in human stomach mucosae and kidney tissues, DNA adducts observed in human colorectal tissue showed some tissue specificity. We will discuss whether profiles of DNA adducts are based on similar contexts of chemical exposure among individuals. DNA adducts observed in our study potentially indicated chemical causes of DNA mutation in human colorectal tissue. We propose that the integration of DNA adductomics using mass spectrometric profiling with other genetic analysis such as mutational signature analysis leverage the exploration of chemical and genetic etiology in an individual carcinogenic context and evaluate gene-environment interaction in human carcinogenesis. Citation Format: Yuji Iwashita, Shunsuke Ohtsuka, Ippei Ohnishi, Yuto Matsushita, Takashi Yamashita, Keisuke Inaba, Atsuko Fukazawa, Hideto Ochiai, Keigo Matsumoto, Nobuhito Kurono, Yoshitaka Matsushima, Hiroki Mori, Shioto Suzuki, Shohachi Suzuki, Fumihiko Tanioka, Haruhiko Sugimura. DNA adductome analysis in human colorectal tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2257.

Lewis Adduct-Dissociating Hydrolysis of Boratrane for Water-Triggered Dehydration of Copolymers with a Hydrophobic Moiety.

As a new example of intrinsically water-triggered phenomena, we report underwater dehydration of the statistical copolymers synthesized from triethanolamine borate (TEAB) methacrylate and styrene (St) induced by the hydrolysis of the pendant TEAB group. TEAB possesses high polarity owing to its internal Lewis adduct structure, which is lost by hydrolysis to triethanolamine (TEA) with a lower dipole moment. Therefore, the hydration of the copolymers became unfavorable through the hydrolysis of the pendant TEAB to TEA, despite polyol formation, and through a hydrophobic interaction based on St moieties becoming alternatively dominant. The dehydration behavior of the copolymers, along with the hydrolysis of the pendant TEAB group, was systematically investigated. The water solubility of the copolymers was found to be dependent on the gradient of the hydrolysis equilibrium of TEAB on the side chains and was the lowest for the TEA state. These findings offer a novel concept toward designing water-responsive materials.

Spectroscopy, Structure, Biomacromolecular Interactions, and Antiproliferation Activity of a Fe(II) Complex With DPA-Bpy as Pentadentate Ligand.

An Fe(II) complex with DPA-Bpy (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6 -methanamine) as the ligand was synthesized and characterized to mimic bleomycin. The binding constants (K b) of the complex with calf thymus DNA and human serum albumin (HSA) were quantitatively evaluated using fluorescence spectroscopy, with K b as 5.53×105 and 2.40×104 M−1, respectively; the number of the average binding site (n) is close to 1. The thermodynamic analyses suggested that the electrostatic interactions exist between the complex and DNA, and the hydrogen bonding and Van der Waals force exist for the complex and HSA. The Fe complex exhibits cleavage ability toward pBR322 DNA, and the crystal structure of the HSA Fe complex adduct at 2.4 Å resolution clearly shows that His288 serves as the axial ligand of the Fe center complexed with a pentadentate DPA-Bpy ligand. Furthermore, the cytotoxicity of the complex was evaluated against HeLa cells. Both the Fe complex and HSA Fe complex adduct show obvious effect on cell proliferation with an IC50 of 1.18 and 0.82 μM, respectively; they induced cell apoptosis and arrested cell cycles at S phase. This study provides insight into the plausible mechanism underlying their metabolism and pharmacological activity.

Interstrand Crosslinking Involving Guanine: A New Major UVC Laser-Induced Biphotonic Oxidatively Generated DNA Damage.

Several classes of oxidatively generated DNA damage including oxidized purine and pyrimidine bases, interstrand base crosslinks and DNA-protein crosslinks have been previously shown to be generated in both isolated DNA and cellular DNA upon exposure to either 266-nm laser irradiation or one-electron oxidants. In this study, we provide evidence that biphotonic ionization of guanine bases by UVC laser irradiation of double-stranded deoxyoligonucleotides in aerated aqueous solutions induces the formation of interstrand crosslinks (ICLs). This is supported by various experiments including sequencing gel analyses of formed photoproducts and effects of UVC laser intensity on their formation. This constitutes a novel example of the diversity of reactions of guanine radical cation that can be generated by various one-electron oxidants including UVC laser biphotonic ionization, direct effect of ionization radiation and type I photosensitizers. However, the exact structure of the interstrand base adducts that is a challenging analytical issue remains to be further established. Examples of relevant biochemical/structural applications of biphotonic induction of ICLs in DNA samples by high-intensity UVC laser pulses are provided.

Interaction of a 1,3-Dicarbonyl Toxin with Ru(II)-Biimidazole Complexes for Luminescence Sensing: A Spectroscopic and Photochemical Experimental Study Rationalized by Time-Dependent Density Functional Theory Calculations.

A family of ruthenium(II) complexes containing one 2,2′-biimidazole (bim) ligand and two polypyridyl (NN) ligands has been prepared and their photophysical and photochemical features have been tested in the presence of tenuazonic acid (TeA), a widespread food and feed mycotoxin of current concern. While not tested in in vivo studies, TeA and other secondary metabolites of Alternaria fungi are suspected to exert adverse effects on the human health, so sensors and rapid analytical procedures are required. It is well-known that 1,3-dicarbonyl compounds such as TeA are relatively easy to deprotonate (the pKa of TeA is 3.5), yielding an enolate anion stabilized by resonance. The chelating and hydrogen-donor features of bim allow simultaneous binding to the metal core and to the target β-diketonate delocalized anion. Such a binding induces changes in the blue absorption (40 nm bathochromic shift), red luminescence intensity (>75% quenching), and triplet lifetime (0.2 μs decrease) of the Ru(NN)2(bim)2+ luminophore. Moreover, we have computationally rationalized, by time-dependent density functional theory, the structure of the different adducts of Ru–bim complexes with TeA and the electronic nature of the spectral absorption bands and their change upon the addition of TeA.

Rh Complexes with Pincer Carbene CNC Lutidine-Based Ligands: Reactivity Studies toward H2Addition

Lutidine-based NHCs pincer precursors CNCMe and CNCMes were combined with [Rh(acac)(nbd)] (acac = acetylacetonate; nbd = 2,5-norbornadiene) in the presence of Cs2CO3 to yield complexes [(CNC)MeRh(nbd)]PF6 (3) and [(CNC)MesRh(NCMe)]PF6 (4), respectively. While in 3, the nbd diolefin remains coordinated, in 4, the voluminous mesityl ligands induce nbd decoordination, so acetonitrile stabilizes Rh(I) adduct 4, which in turn undergoes substitution reactions with a number of neutral ligands to produce cationic complexes [(CNC)MesRh(L)]PF6 (L = CO (5), PMe2Ph (6), PEt3 (7), C2H4 (8)). These complexes have been studied through VT NMR measurements and the molecular structures by X-ray crystallography in the case of adducts 4–7. Deprotonation reactions on cationic complexes 3–6 with hard bases yielded the corresponding neutral complexes [(CNC)*MeRh(nbd)] (9) and mesityl derivatives [(CNC)*MesRh(L)] (L = NCCH3 (10), CO (11), PMe2Ph (12)), all of which are dearomatized complexes due to the deprotonation of one of the methylene arms, a situation confirmed by the X-ray molecular structure of carbonyl adduct 5. We studied the reactivity toward dihydrogen with neutral adducts 11 and 12. The electron rich phosphane 12 adds H2 through oxidative addition, affording the bis(hydrido) Rh(III) complex [(CNC)*MesRh(PMe2Ph)H2] (14). However, the carbonyl adduct 11 reacts with H2 in a different way, so that the central pyridinic ring becomes hydrogenated, breaking the aromaticity and leading to complex [(CNC-H2)*MesRh(CO)] (13), isolated as a mixture of two isomers. DFT studies were carried out in order to establish the mechanisms followed on these hydrogenations, finding that, while the phosphane adduct reacts following an oxidative addition mechanism, the carbonyl complex follows a more complex base-induced profile due to the instability of hydride carbonyl species.

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts*.

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction. The electronic properties are estimated in the liquid state; for example, via the 77 Se liquid state NMR of Se-NHC adducts. We demonstrate that 77 Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via 77 Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state 77 Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the 13 C isotropic chemical shift from the liquid state NMR and the 13 C tensor components are also discussed, and compared with their 77 Se counterparts. 77 Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state 77 Se NMR can provide an in-depth outlook on the properties of NHC ligands.

Lone pair Halogen (X2)…π Interactions Stabilizes Molecular Halogens (X2=I2, Br2, Cl2, and F2) on Reduced Graphene Oxide surface: Structural, Solvent Effect and optical properties

In this work, we investigate the lone pair (lp)…π interaction for the halogens (X2=I2, Br2, Cl2, and F2) binding to the rGO surface. Electronic and optical properties of rGO significantly tuned upon adsorption of halogen molecules, although the weak nature of (lp)…π forces. The structure and optical properties of rGO, rGOI2, rGOBr2, rGOCl2 and rGOF2 adducts were investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT) method. Halogen molecules (X2) stable structures were planer on rGO surface and stabilized by the lone pair X2(lp)…π(C) interactions. The surface oxygen atoms contributed to the stability by the O(lp)… π(X2) charge transfer process. Bader analysis reveals significant charge transfer and bond length elongation for X2 on rGO monolayer sheet in the order I2 > Br2 > Cl2 > F2. Surface adsorption of X2 molecules on rGO surface tunes both band gap energy and optical properties. The TDOS and PDOS reveal that X2 adsorption on rGO surface forms an intermediate states in band gap region, which decrease the energy values. These results are beneficial for photocatalysis and light harvesting applications.

Boron-Doped Polycyclic π-Electron Systems with an Antiaromatic Borole Substructure That Forms Photoresponsive B-P Lewis Adducts.

Heteroatom doping is a powerful strategy to alter the electronic structure of polycyclic aromatic hydrocarbons (PAHs). Especially boron doping endows PAH scaffolds with electron-accepting character and Lewis acidic centers. Herein, we report that embedding a five-membered borole ring into a polycyclic skeleton imparts the π-system with antiaromatic character and thereby induces unique properties and behavior. A series of borole-embedded π-conjugated compounds were synthesized from teraryl precursors via a borylation/intramolecular electrophilic C-H borylation sequence. The obtained compounds exhibit planar structures with distorted geometries around the boron center and form columnar slipped face-to-face π-stacked structures. Among these compounds, a pyrene-fused derivative shows an intense emission with a high quantum yield in solution. This compound also exhibits high Lewis acidity, which reflects the antiaromatic character and strained structure of the borole substructure. This compound forms a Lewis acid-base adduct even with weakly Lewis basic phosphorus-containing polycyclic π-systems. Analyzing the crystal structure of the thus-obtained adduct revealed a complex between the boron- and phosphorus-embedded π-systems with a direct B-P dative bond. This complex undergoes photodissociation in the excited state and exhibits an emission exclusively from the base-free borole-embedded π-system.

Examining the Potential Formation of Ternary Chromium-Histidine-DNA Complexes and Implications for Their Carcinogenicity.

The mutagenic and carcinogenic properties of chromium(VI) complexes have been ascribed to the formation of ternary Cr(III)-small molecule-DNA complexes. As part of these laboratories efforts to establish the structure and properties of discrete binary and ternary adducts of Cr(III) and DNA at a molecular level, the properties of Cr(III)-histidine-DNA complexes formed from Cr(III) were examined. These studies determined the composition of previously described "prereacted" chromium histidinate and reveal the reaction of "prereacted" chromium histidinate with DNA does not form ternary complexes as previously proposed. The products instead are chromium histidinate complexes weakly bound, probably in the minor groove, to DNA. These weakly bound adducts cannot be responsible for the mutagenic and carcinogenic properties ascribed to ternary Cr(III)-histidine-DNA adducts. The results of biological studies where "ternary adducts" of Cr(III), histidine, and DNA were made from "prereacted" chromium histidinate must, therefore, be interpreted with caution.

Electronic structure and spectroscopy of C60 nitroaryl radical adducts

In this study, density functional theory (DFT) calculations were applied to study electronic structure and spectroscopy of C60 nitroaryl radical adducts with 2-nitrophenyl, 4-nitrophenyl, 2,4-dinitrophenyl and up to six 2,4,6-trinitrophenyl substituents. The structural parameters for optimized geometries were measured, and polarity of molecules was compared to nitrobenzene derivatives. The atomic charges and charge distribution map of these compounds were calculated based on electrostatic potential (ESP) and natural population analysis (NPA). The distribution of unpaired electron in opened shell molecules was visualized by spin density profiles. The calculated thermochemical constants for reactions of nitroaryl radicals with C60 were reported. The wave function analysis was performed to study molecular orbital (MO) and density of states (DOS) diagrams. The aromaticity index of molecules was estimated by nucleus-independent chemical shift (NICS) method. The infrared (IR) and carbon-13 nuclear magnetic resonance (13C NMR) spectra of these compounds were also investigated. It was found that addition of nitroaryl radicals to C60 is exothermic and occurs with decreasing entropy and Gibbs free energy. These compounds exhibit higher aromatic character and smaller band gap compared to C60.

L-Tryptophan Interactions with the Horseradish Peroxidase-Catalyzed Generation of Triplet Acetone.

Triplet carbonyls generated by chemiexcitation are involved in typical photobiochemical processes in the absence of light. Due to their biradical nature, ultraweak light emission and long lifetime, electronically excited triplet species display typical radical reactions such as isomerization, fragmentation, cycloaddition and hydrogen abstraction. In this paper, we report chemical reactions in a set of amino acid residues induced by the isobutanal/horseradish peroxidase (IBAL/HRP) system, a well-known source of excited triplet acetone (Ac3* ). Accordingly, quenching of Ac3* by tryptophan (Trp) unveiled parallel enzyme damage and inactivation, likely explained by scavenging of IBAL tertiary radical reaction intermediate and Ac3* -derived 2-hydroxy-i-propyl radical. Quenching constants were calculated from Stern-Volmer plots, and the structure of radical adducts was revealed by mass spectrometry. As expected, a concurrent Schiff-type adduct was found to be one of the reaction by-products. These findings draw attention to potential structural and functional changes in enzymes involved in the electronic chemiexcitation of their products.

Carbon Spacer Strategy: Control the Photoswitching Behavior of Donor-Acceptor Stenhouse Adducts.

Understanding the relationship between chemical structure and photoswitching property of donor-acceptor Stenhouse adducts (DASAs) is necessary for developments and applications of the novel photoresponsive molecule. In the current work, we demonstrated a close relationship between the length of carbon spacer and photoswitching property of DASAs. A series of DASAs with barbituric acid substituted electron-withdrawing part and N-methylaniline substituted electron-donating part were synthesized. With shortening the carbon spacer between the phenyl and amine groups in the electron-donating part, the efficiency and rate of the light-induced linear-to-cyclic isomerization are improved in all the test solvents. The molecular energy variation during the isomerization process was investigated by density functional theory calculation to further understand the mechanism. This work provides a reliable carbon spacer strategy to control the photoswitching behavior of DASAs using chemical methods.

ADDUCTS OF SUBSTITUTED VINYLOXYCYCLOPRFOPANES WITH THIOLS AS THERMOSTABILIZERS OF PVC

The compositions on the basis of PVC, containing dioctyl phthalate as a plasticizer, complex thermal stabilizers – calcium and zinc stearates and adducts of thiophenol and ethanedithiol with gemdiglycidyloxymethylsubstituted cyclopropylvinyl ether as co-stabilizers and biocidal additives were developed. Thermal properties of the developed compositions were investigated and the influence of the synthesized sulfur-containing adducts on the thermal stability and color change of the compositions studied. The tests were carried out to reveal the antifungal activity of adducts in the structure of PVC compositions. It found that the chemical structure of adducts after introduction into the structure of compositions was not essentially changed. The compositions with the participation of adducts as co-stabilizers acquired improved indices on thermal stability, color stability and antifungal activity.

Precise Distance Measurements in DNA G-Quadruplex Dimers and Sandwich Complexes by Pulsed Dipolar EPR Spectroscopy.

DNA G‐quadruplexes show a pronounced tendency to form higher‐order structures, such as π‐stacked dimers and aggregates with aromatic binding partners. Reliable methods for determining the structure of these non‐covalent adducts are scarce. Here, we use artificial square‐planar Cu(pyridine)4 complexes, covalently incorporated into tetramolecular G‐quadruplexes, as rigid spin labels for detecting dimeric structures and measuring intermolecular Cu2+–Cu2+ distances via pulsed dipolar EPR spectroscopy. A series of G‐quadruplex dimers of different spatial dimensions, formed in tail‐to‐tail or head‐to‐head stacking mode, were unambiguously distinguished. Measured distances are in full agreement with results of molecular dynamics simulations. Furthermore, intercalation of two well‐known G‐quadruplex binders, PIPER and telomestatin, into G‐quadruplex dimers resulting in sandwich complexes was investigated, and previously unknown binding modes were discovered. Additionally, we present evidence that free G‐tetrads also intercalate into dimers. Our transition metal labeling approach, combined with pulsed EPR spectroscopy, opens new possibilities for examining structures of non‐covalent DNA aggregates.