Solid-state Circular Dichroism Spectroscopy Research Articles

Crystallization Behavior of Heterotrinuclear ZnII–LnIII–ZnII Complexes Bearing Two Tripodal Nonadentate Ligands: Possibility for Absolute Spontaneous Resolution

Crystal structures and crystallization behaviors of a series of heterotrinuclear ZnII–LnIII–ZnII complexes, [(L)ZnLnZn(L)]NO3 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y; H3L = 1,1,1-tris[(3-methoxysalicylideneamino)methyl]ethane), were examined. Because the trinuclear complex cation has two asymmetric centers (Δ and Λ) at the ZnII sites resulting from the twist of the tripodal ligand arms, it was confirmed from the single-crystal X-ray diffraction (SC-XRD) analysis that these complexes have homochiral structures (i.e., Λ,Λ- or Δ,Δ-enantiomer) in the solid state. Among the series of compounds, various types of spontaneous resolution were observed, which were classified by the SC-XRD analysis (using the Flack parameter) or solid-state circular dichroism spectroscopy. The latter technique was used to determine the chirality of every single crystal and that of an entire bulk mixture of microcrystals obtained in a particular crystallization process. It was found that the TbIII complex, [(L)ZnTbZn(L)]NO3·2MeOH (Zn–Tb–Zn), exclusively deposited the left-handed Λ-conglomerate in every crystallization experiment. This phenomenon may be termed “absolute spontaneous resolution.” It was also notable that only the lanthanoid(III) ions with an even number of 4f electrons (Eu, Tb, Ho, and Lu) exhibited this unusual phenomenon. It was also attempted to deposit the opposite-handed Zn–Tb–Zn Δ-conglomerate, which could not be isolated from the ambient crystallization. Seeding of a crashed single-crystal Δ-conglomerate of [(L)ZnYZn(L)]NO3·2MeOH (Zn–Y–Zn), which was isomorphic to Zn–Tb–Zn, into a saturated methanolic solution of Zn–Tb–Zn gave, for the first time, crystals of the corresponding Δ-conglomerate.

Coordination Patterns of the Diphosphate in IDP Coordination Complexes: Crystal Structure and Chirality

The knowledge of accurate geometrical parameters from X-ray diffraction studies in the solid state of metal nucleotide is very important for understanding the relationship between structures and properties, including biochemical processes and even enzyme-metal-substrate interactions. The research is also very necessary to precisely and controllably design the functional materials. Here, seven types of coordination polymers of inosine 5'-diphosphate nucleotide (IDP) with transition metals, {[Zn(HIDP)(azpy)(H2O)2]·4H2O}n (1), {[Cd2(IDP)2(bpda)2]·[Cd(H2O)6]·11H2O}n (2), {[Cd3(IDP)2(4,4'-bipy)2(H2O)3]·6H2O}n (3), {[Cd2(IDP)2(bpe)2(H2O)2]·(H2bpe)·26H2O}n (4), {[Cu3(IDP)2(azpy)2(H2O)5]·5H2O}n (5), {[Cu3(IDP)2(bpe)2(H2O)5]·9H2O}n (6), and {[Co(HIDP)(azpy)(H2O)2]·7H2O}n (7) [4,4'-bipy = 4,4'-bipyridine, azpy = 4,4'-azopyridine, bpe = 1,2-bis(4-pyridyl)ethene, and bpda = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene], were designed, synthesized, and firmly characterized using single-crystal X-ray diffraction. The coordination patterns of the diphosphate group of IDP in these complexes were studied by crystallographic analysis, namely, open, close, and open-close hybrid types. We have investigated the diverse coordination patterns of the diphosphate group and its spatial relationship relative to the pentose ring on the basis of two conformational parameters, the pseudorotation phase angle and the degree of puckering. Crystallographic studies clearly reveal the correlation between the backbone torsion angle (ω' and φ) of the sugar-diphosphate and the conformational preference of the pentose ring, i.e., the signs of the backbone torsion angles ω' and φ are both plus (+) or minus (-), the conformation of the pentose ring is envelope form (E), while when one of the two signs is plus (+) and the other is minus (-), the pentose ring is in the twist form (T). This is the first time elucidation of the coordination pattern of diphosphate relative to the conformation of the pentose ring in nucleotide metal complexes, which are different from the other inorganic or organic diphosphate compounds. The chirality of these coordination polymers was examined by combining solid-state circular dichroism spectroscopy measurements with the explanation of their crystal structures. The results presented in this paper are very important for understanding their nucleotide coordination chemistry, their supramolecular chemistry, and even their biochemistry.

Conformation Locking of the Pentose Ring in Nucleotide Monophosphate Coordination Polymers via π-π Stacking and Metal-Ion Coordination.

The conformation of the pentose ring in nucleotides is extremely important and a basic problem in biochemistry and pharmaceutical chemistry. In this study, we used a strategy to regulate the conformation of pentose rings of nucleotides via the synergistic effect of metal-ion coordination and π-π stacking. Seven types of coordination complexes were developed and characterized using Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, ultraviolet-visible spectroscopy, 1H nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction. On the basis of two conformational parameters obtained from single-crystal structure analysis, i.e., the pseudorotation phase angle and degree of puckering, the exact conformation of the furanose ring in these coordination polymers was unequivocally determined. Crystallographic studies demonstrate that a short bridging ligand (4,4'-bipyridine) is conducive to the formation of a twist form, and long auxiliary ligands [1,2-bis(4-pyridyl)ethene and 4,4'-azopyridine] induce the formation of an envelope conformation. However, the longest auxiliary ligands [1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene] cannot limit the flexibility of a nucleotide. Our results demonstrated that the proposed strategy is universal and controllable. Moreover, the chirality of these coordination polymers was examined by combining the explanation of their crystal structures with solid-state circular dichroism spectroscopy measurements.

The recent development of multilevel chirality research based on nucleotide coordination complexes

Chirality is a kind of special symmetry that is prevalent in nature. Organisms exhibit the function of multiple-level transformation of chirality. The transfer, induction and amplification of multi-level chirality are fundamental problems and vital to chemistry, biology, physics and materials science. Generally, there are four levels for chirality transformation from molecular chirality to macroscopic chirality, including configuration (molecular) chirality (first level), conformational chirality (second level), phase chirality (third level) and macroscopic chirality (fourth level). Based on the coordination supramolecular assemblies of nucleotides, the combination of X ray single crystal diffraction technique and solid-state circular dichroism spectrum is an effective way to study multiple-level chirality. The comprehensive understanding of the multi-level chirality transfer mechanism can provide guidelines for us not only to cognize the relationship between the structure and function of organisms, but also to design and synthesis of chiral functional materials and artificial molecular machines rationally. In this review, an effective method to study conformational chirality and phase chirality has been described based on the research results of nucleotide chiral coordination supramolecular assemblies, which is a combination of X-ray single crystal diffraction technique and solid-state circular dichroism spectroscopy. It is the first time to develop the concept of “Extending Axial Chirality” creatively based on axial chirality in organic chemistry to 1D coordination polymer. According to the accurate analysis of crystal structures, the roles of metal-ligand coordination bonding, hydrogen bonding, π-π stacking in chirality inducing, chirality assembly and chirality transfer were revealed. Also, the expectant research areas of chiral research in the future were prospected.

Selective chiral symmetry breaking and luminescence sensing of a Zn(ii) metal-organic framework.

The chiral Zn(ii) metal-organic framework [(CH3)2NH2]5[Zn1.5(Zn3O)(TATAT)2]·9DMF·17H2O (1) has been prepared from achiral precursors Zn(NO3)2·6H2O and 5,5',5''-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H6TATAT) in a solvent mixture of DMF/MeOH/H2O/HCOOH without any chiral sources. In particular, the non-random handedness excess (1P ≫ 1M) was generated and was verified by single-crystal X-ray diffraction and solid-state circular dichroism spectroscopy. Furthermore, complex 1 displays high selectivity and sensitivity for detecting Fe3+ and is found to be an excellent chemical sensor for detecting nitro explosives especially 3-nitrophenol.

Cytosine-Cytosine Base-Pair Mismatch and Chirality in Nucleotide Supramolecular Coordination Complexes.

The base-pair sequences are the foundation for the biological processes of DNA or RNA, and base-pair mismatch is very important to reveal genetic diseases and DNA rearrangements. However, the lack of well-defined structural information about base-pair mismatch is obstructing the investigation of this issue. The challenge is to crystallize the materials containing the base-pair mismatch. Engineering the small-molecule mimics or model is an effective strategy to solve this issue. Here, six cytidine-5'-monophosphate (CMP) and 2'-deoxycytidine-5'-monophosphate (dCMP) coordination polymers were reported containing cytosine-cytosine base-pair mismatch (i-motif), and their single-crystal structures and chiralities were studied. The precise control over the formation of the i-motif was demonstrated, in which the regulating of supramolecular interactions was achieved based on molecular design. In addition, the chiralities of these coordination polymers were investigated according to their crystal structures and solution- and solid-state circular dichroism spectroscopy.

Study of Protein Amyloid-Like Aggregates by Solid-State Circular Dichroism Spectroscopy.

Protein aggregation and amyloidogenesis are closely associated with the pathogenesis of neurodegenerative diseases. Elucidating the morphology and structure of the amyloid aggregates or fibrils is important for understanding the molecular mechanisms of these proteinopathies. This review article describes the general principle and establishment of solid-state circular dichroism (ssCD) spectroscopy, and discusses its application for the analysis of secondary structures of proteins or peptides in amyloids and structural transformation of these proteins or peptides during their amyloidogenic aggregation.

Water‐Stable Homochiral Cluster Organic Frameworks Built by Two Kinds of Large Tetrahedral Cluster Units

Compared with metal organic frameworks (MOFs), the proton conductivity of cluster organic frameworks has been less studied. Herein, two supertetrahedral cluster organic frameworks (SCOFs) have been made that show two-fold interpenetrated networks built by trivalent lanthanide tetrahedral clusters and monovalent cuprous T3 -supertetrahedral clusters. The structure analysis, second harmonic generation signals, and solid-state circular dichroism spectroscopy consistently reveal the chirality of these SCOFs. Remarkably, the water-stable SCOFs show a high proton conductivity value of 1.4×10(-3) S cm(-1) at 80 °C and 95 % RH (relative humidity).

Spontaneous Resolution of Evans-Showell-Type Polyoxometalates in Constructing Chiral Inorganic-Organic Hybrid Architectures.

Six new hybrid compounds based on [Co2Mo10H4O38](6-) polyoxoanion, (4-H2pya)6Co2Mo10H4O38·10H2O 1 (4-Hpya =3-(4-pyridyl)acrylic acid) and (4-H2pya)4[M(H2O)6][Co2Mo10H4O38]·5H2O (M = Co 2, Ni 3, Cu 4, Zn 5, Cd 6), were synthesized and characterized by elemental analysis, IR spectroscopy, TG analysis, solid diffuse reflective spectrum, powder X-ray diffraction, and single crystal X-ray diffraction. Compound 1 crystallizes in the centrosymmetric space group P-1, which is built up of protonated 4-H2pya molecules and isolated [Co2Mo10H4O38](6-) polyoxoanions. Isostructural compounds 2-6 crystallize in the chiral space group P1 by spontaneous resolution, as a conglomerate of two enantiomerically pure crystals, which were obtained by adding different metal cations to the reaction system of compound 1. The structures of 2-6 comprise chiral [Co2Mo10H4O38](6-) anions, cationic [M(H2O)6](2+) units, and protonated 4-H2pya ligands. The chiral [Co2Mo10H4O38](6-) polyoxoanions can be connected up together by directional hydrogen-bonding interactions among terminal oxygen atoms of anions, coordinated water molecules and organic ligands to construct a 3D supramolecular chiral framework in 2-6. The absolute configuration of 2-6 was determined from the Flack parameter by X-ray crystallography and solid state circular dichroism spectroscopy. As far as we know, compounds 2-6 represent the first examples of chiral inroganic-organic hybrid species based on Evans-Showell-type polyoxometalates. Furthermore, the second harmonic generation (SHG) activities for 2 and 4 were measured, showing an SHG efficiency of approximately 0.9 × KH2PO4.

Metal Supramolecular Frameworks with Silver and Ditopic Bis(pyrazolyl)methane Ligands: Effect of the Anions and Ligand Substitution

A study of the self-assembly of different silver salts and the potentially ditopic ligands bis(pyrazol-1-yl)(pyridine-4-yl)methane (L1) and bis(3,5-dimethylpyrazol-1-yl)(pyridine-4-yl)methane (L2) was undertaken and species’ with discrete or polymeric structures were obtained. Reactions with L1 always yielded derivatives that had a box-like cyclic dimer structure with two metal centers and two ligands. However, on using ligand L2, the resulting structure strongly depended on the coordination ability of the anion. On using anions that have coordinating ability (X = NO3–, CF3SO3–, PF2O2–), a similar box-like structure was formed. However, the use of anions with lower coordinating ability (X = PF6–, ClO4–) led to coordination polymers with a helical disposition. Spontaneous resolution was observed in the two compounds, and only one enantiomer was present in the crystals studied. Solid-state circular dichroism spectroscopy was applied to bunches of crystals, and the results indicate that growth of single colo...

A Series of Chiral Metal–Organic Frameworks Based on Oxalyl Retro-Peptides: Synthesis, Characterization, Dichroism Spectra, and Gas Adsorption

By synergistic involvement of enantiopure oxalyl retro-peptide ligands and the conformationally flexible ligand 4,4′-bi-3,5-dimethylpyrazole (H2mbpz), four new three-dimensional (3-D) homochiral metal–organic frameworks (MOFs), Cu2(l-OBAla)(H2mbpz)·2H2O (1), Cu2(l-OBVal)(H2mbpz) (2), Cu2(l-OBPhe)(H2mbpz) (3), and [Cu6(l-OBLeu)3(H2mbpz)3 (H2O)2]·7H2O (4) (l-OBAla = N,N′-oxalylbis(l-alanine); l-OBVal = N,N′-oxalylbis(l-valine); l-OBPhe = N,N′-oxalylbis(l-phenylalanine); l-OBLeu = N,N′-oxalylbis(l-leucine)), have been prepared under solothermal conditions. All of these structures contain binuclear subunits in which two copper atoms are coordinated by a single retro-peptide to produce a unique tetracyclic planar rigid moiety. Compounds 1–3 are isostructural. The self-assembly of the binuclear subunits generates two-dimensional (2-D) networks which are further pillared by H2mbpz ligands to give three-dimensional (3-D) frameworks with one-dimensional (1-D) channels. In compound 4, the interaction of the binuclear copper subunits forms an unexpected U-shaped secondary building unit containing six copper atoms, and further linked by H2mbpz ligands to furnish a 3-D architecture. The chiral nature of all compounds was confirmed by solid-state circular dichroism spectroscopy. Gas adsorption experiments indicate the microporous property of compounds 1 and 2. Compound 1 exhibits the highest capability of gas adsorption among the four compounds due to its largest pore volume. Compound 2 reveals selectively adsorption of H2 over N2 as a result of the limited window size.

The Functional Curli Amyloid Is Not Based on In-register Parallel β-Sheet Structure

The extracellular curli proteins of Enterobacteriaceae form fibrous structures that are involved in biofilm formation and adhesion to host cells. These curli fibrils are considered a functional amyloid because they are not a consequence of misfolding, but they have many of the properties of protein amyloid. We confirm that fibrils formed by CsgA and CsgB, the primary curli proteins of Escherichia coli, possess many of the hallmarks typical of amyloid. Moreover we demonstrate that curli fibrils possess the cross-beta structure that distinguishes protein amyloid. However, solid state NMR experiments indicate that curli structure is not based on an in-register parallel beta-sheet architecture, which is common to many human disease-associated amyloids and the yeast prion amyloids. Solid state NMR and electron microscopy data are consistent with a beta-helix-like structure but are not sufficient to establish such a structure definitively.

Racemic twin crystals containing left- and right-handed polyoxometalate chains induced by the asymmetric coordination of metal–organic units

Two racemic twin crystals containing left- and right-handed polyoxometalates (POMs) chains [Cu(en) 2][Cu(en) 2(H 2O)] 2 [SiW 11CuO 39] · 5H 2O ( D-1 and L-1; en = ethylenediamine) have been synthesized and structurally characterized. Both chiral compounds ( D-1 and L-1) were constructed from the achiral building blocks [SiW 11CuO 39] 6− and [Cu(en) 2(H 2O) n ] 2+ ( n = 0 or 1). The structural chirality is induced by the [Cu(en) 2(H 2O) n ] 2+ units asymmetrically coordinated on the chainlike [SiW 11CuO 39] n 6 n − polyoxoanions, leading to the whole molecules crystallized in the chiral P1 space group. The chiroptical activities of D-1 and L-1 were confirmed by the solid-state circular dichroism spectroscopy. Their electrochemical and electrocatalytic properties were also investigated.

Mechanism of Absolute Asymmetric Synthesis and Solid-State CD Spectroscopy of BPOB

1,3-bis(3-phenyl-3-oxopropanoyl)benzene (BPOB) was prepared by Claisen condensation of aceto-phenone and dimethyl isophthalate and characterized by elemental analysis, MS, 1H NMR, UV absorption spectrum, solid-state circular dichroism (CD) spectra, and X-ray single-crystal diffraction. The X-ray crystallographic data indicated that BPOB crystallized in a Sohncke group P212121, UV and 1H NMR showed that the enol tautomer was the most dominant form in solution, and the solid-state CD spectra and repeated recrytallization revealed that the formation of chiral BPOB crystals could be regarded as crystallization-induced asymmetric synthesis.

Breaking Symmetry: Spontaneous Resolution of a Polyoxometalate

A chiral polyoxometalate [Hf(PW11O39)2]10- (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P2(1)2(1)2, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39]7- units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate HfIV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantiomers were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems.