Helical Ligand Research Articles

The NMR structure of the Orf63 lytic developmental protein from lambda bacteriophage

The orf63 gene resides in a region of the lambda bacteriophage genome between the exo and xis genes and is among the earliest genes transcribed during infection. In lambda phage and Shiga toxin (Stx) producing phages found in enterohemorrhagic Escherichia coli (EHEC) associated with food poisoning, Orf63 expression reduces the host survival and hastens the period between infection and lysis thereby giving it pro-lytic qualities. The NMR structure of dimeric Orf63 reveals a fold consisting of two helices and one strand that all make extensive intermolecular contacts. Structure-based data mining failed to identify any Orf63 homolog beyond the family of temperate bacteriophages. A machine learning approach was used to design an amphipathic helical ligand that bound a hydrophobic cleft on Orf63 with micromolar affinity. This approach may open a new path towards designing therapeutics that antagonize the contributions of Stx phages in EHEC outbreaks.

Alkaline earth metal Atom-Doped Aza-Single-Strand pyridine Helix M@SP-Helix (M = Be, Mg, and Ca) as high-performance candidates for Single-Molecular redox SPDT NLO molecular switches

Redox molecular switch is undoubted to be a good choice for the requirement of terminal molecular device. By doping an alkaline earth metal atom into the aza-single-strand pyridine helical ligand to form M@SP-Helix (M = Be, Mg, and Ca), the alkaline earth metal atom not only act the role of providing two electrons but also the type of them can significantly affect the distribution region of every two electrons on SP-Helix in the in the redox process. Our results found that the electronic and vibrational static first hyperpolarizabilities as well as the frequency-dependent first hyperpolarizability exhibit high-performance single-pole double-throw (SPDT) nonlinear optics (NLO) switching effects from its oxidized state (off form) to neutral (on form) and to reduced states (on form) as obtaining four electrons by twice. Notably, the electronic first hyperpolarizability is increased approximately 1003- and 1.34 × 106-fold from 35 to 3.51 × 104 and 4.69 × 107 au for Ca@SP-Helix. Therefore, this work can provide a theoretical reference that the alkaline earth atom doping is an important method to design high-performance NLO molecular switch material.

Iron(II) complexes of 2,6-bis(imidazo[1,2-a]pyridin-2-yl)pyridine and related ligands with annelated distal heterocyclic donors.

Following a published synthesis of 2,6-bis(imidazo[1,2-a]pyridin-2-yl)pyridine (L1), treatment of α,α'-dibromo-2,6-diacetylpyridine with 2 equiv. 2-aminopyrimidine or 2-aminoquinoline in refluxing acetonitrile respectively gives 2,6-bis(imidazo[1,2-a]pyrimidin-2-yl)pyridine (L2) and 2,6-bis(imidazo[1,2-a]quinolin-2-yl)pyridine (L3). Solvated crystals of [Fe(L1)2][BF4]2 (1[BF4]2) and [Fe(L2)2][BF4]2 (2[BF4]2) are mostly high-spin, although one solvate of 1[BF4]2 undergoes thermal spin-crossover on cooling. The iron coordination geometry is consistently distorted in crystals of 2[BF4]2 which may reflect the influence of intramolecular, inter-ligand N⋯π interactions on the molecular conformation. Only 1 : 1 Fe : L3 complexes were observed in solution, or isolated in the solid state; a crystal structure of [FeBr(py)2L3]Br·0.5H2O (py = pyridine) is presented. A solvate crystal structure of high-spin [Fe(L4)2][BF4]2 (L4 = 2,6-di{quinolin-2-yl}pyridine; 4[BF4]2) is also described, which exhibits a highly distorted six-coordinate geometry with a helical ligand conformation. The iron(II) complexes are high-spin in solution at room temperature, but 1[BF4]2 and 2[BF4]2 undergo thermal spin-crossover equilibria on cooling. All the compounds exhibit a ligand-based emission in solution at room temperature. Gas phase DFT calculations mostly reproduce the spin state properties of the complexes, but show small anomalies attributed to intramolecular, inter-ligand dispersion interactions in the sterically crowded molecules.

Coordination-Driven Self-Assembly of Complexes Constructed from Two Helical Ligands: Synthesis, Structures, and Selective Gas Adsorption Properties.

Two helical ligands (L1 and L2) were designed and synthesized by a Schiff base condensation reaction. Eight complexes, {[Zn(L1)I2]·H2O}n (1), [Cd2(L1)2I4(CH3OH)2] (2), [Hg2(L1)2I4] (3), [Ag(L1)NO3]n (4), [Ag2(L1)2(NO3)2DMSO]·H2O (5), {[Zn2(L2)2Cl4]·2CHCl3}n (6), {[Ag(L2)]·NO3}n (7), and {[Ag(L2)NO3]·CH3OH}n (8), were synthesized and characterized based on these two ligands. The crystal structures show that both Schiff base compounds exist as racemic ligands with equal amounts of P- and M-helicity, and the assembly of these racemic ligands with metal ions can lead to homochiral or heterochiral complexes via a chiral self-recognition or self-discrimination process. Complexes 2, 3, and 5 exist as heterochiral metallomacrocycles with a figure-eight conformation. Complexes 1, 6, and 8 exist as one-dimensional (1D) homochiral helical chain coordination polymers, while complexes 4 and 7 exist as 1D heterochiral helical chain coordination polymers. Furthermore, gas and vapor adsorption measurements show that all of the synthesized complexes exhibit good selective adsorption capacities toward methanol and ethanol vapor over N2, H2, and O2.

Synthesis, crystal structures, electrochemical and gas adsorption properties of two 1D silver(I) coordination polymers constructed from racemic helical ligands

Two helical ligands (L1 and L2) were designed and synthesized by Schiff base condensation reaction. Two Ag(I) coordination polymers (CPs), namely, {[Ag2(L1)2(NO3)2]·3H2O}n (1) and [AgL2NO3]n (2) were synthesized and characterized via elemental analysis, FT-IR spectra and single-crystal X-ray diffraction techniques. The crystal structures show that both Schiff base compounds exist as racemic ligands with equal amounts of P- and M-helicity. CP 1 exists as a 1D homochiral helical chain polymer via self-recognition process, and CP 2 exists as a 1D looped chain polymer. The cyclic voltammetric properties of the two CPs were investigated. Furthermore, gas and vapor adsorption measurements show that both CPs exhibit good adsorption capacity toward CH3OH over CO2 and N2.

Chiral Self-Assembly, Electrochemical and Gas Adsorption Properties of Two 1d Silver(I) Coordination Polymers Constructed from Racemic Helical Ligands

Chiral Self-Assembly, Electrochemical and Gas Adsorption Properties of Two 1d Silver(I) Coordination Polymers Constructed from Racemic Helical Ligands

Enantioselective Synthesis of Homochiral Au13 Nanoclusters and Their Chiroptical Activities.

A pair of enantiopure Au13 nanoclusters have been enantioselectively synthesized by chiral ligands with stereogenic centers at the phosphorus atoms. Their structures are determined by X-ray crystallography, which are typical models with a high symmetric core and chiral surface ligand arrangement. Correlation between the crystallographic structure, the calculation, and the circular dichroism (CD) study indicates that helical ligand arrangement inducing the core into chiral distortion accounts for the chiroptical activities in the visible region. A rare example of cocrystallization of a mixture of diastereomers has been observed for the first time for gold nanoclusters, reflecting the lack of chiral self-sorting of the ligands.

Effect of Solvent on the Structural Diversity of Quasi-Aromatic Möbius Cadmium(II) Complexes Fabricated from the Bulky N6 Tetradentate Helical Ligand

We present the synthesis and structural and computational characterization of a heteroleptic dinuclear discrete complex [Cd2(μ1,3-NCS)2(NCS)2(LI)2]·4MeOH (1·4MeOH), where LI is the product of hydrolysis of one of the 2-PyC(Ph) groups of the parent ligand 1,2-diphenyl-1,2-bis((phenyl(pyridin-2-yl)methylene)hydrazono)ethane (L), fabricated from a mixture of Cd(NO3)2·4H2O and NH4NCS in methanol. An analogous procedure but in EtOH and iPrOH yielded crystals of the heteroleptic dinuclear discrete complex [Cd2(μ1,3-NCS)2(NCS)2(L)2] (2) and the polymeric complex of the composition [Cd3(NCS)6(L)]n (3). The bulky helical ligand L in the constituting CdII based synthons has been found to exhibit a quasi-aromatic Mobius features as revealed by the electron density of delocalized bonds method as well as the extended transition state coupled with natural orbitals for chemical valence calculations. It means that a transition metal induces π-electron delocalization solely in the ligand’s part; however, the d orbitals of...

Band Structures of Quasi-One-Dimensional Incommensurate Helical Systems: A Case Study of Infinite Chromium Extended Metal Atom Chain.

Extended metal atom chains (EMACs) are promising candidates for molecular wires but their band structures remain to be explored. As a quasi-one-dimensional (Q1D) system, the incommensurate helical nature of EMACs hinders such calculations. In this work, we resolved this issue via explicit implementation of helical symmetry. Moreover, the pattern of metal d bands was rationalized by a systematic investigation on a series of related Q1D helical systems. Two critical factors, helical ligand field and chemically asymmetric ligand field, are proposed and identified. We found that the symmetry and ligand fields of the system dominate the pattern of the metal d bands, instead of specific chemical composition of ligands. The presented method and rationale are applicable to not only EMACs but also related Q1D helical systems.

Redox-switchable structures and NLO property: Li2 doped into the cavity of pyridine helix

Abstract Helical structure was ubiquitous in the nature and many chemists were attracted to synthesize various helicates, to obtain more fantastic functional materials. In this work, we designed pyridine helical ligand with Li2 doped and explored the effects of redox process on its NLO property. All results stressed the control of redox switch on Li2-doped helical complex. In the aspect of geometric structural traits, obtaining or losing electrons made the helix shrank or extended like a coil spring. In the aspect of NLO property, the sharp fluctuation of βtot values with the range of 1.88 × 102 to 7.73 × 106 au indicated that redox process was an effective switch to control the on-off NLO response. According to the two-level formula, the variation of Δμ qualitatively explained the change of βtot. In terms of bonding traits, NBO and AIM analyses showed in the redox process, NBO charge transferred along reversed direction for oxidation and reduction process. The results of E2 and WBIs obtained by population analysis and the properties at Li N BCPs via AIM analysis, including ρ(r), ∇ 2 ρ(r) and H(r) suggested that in the process of obtaining electrons, Li1 N1 bond became weaker while Li1 N3 bond became stronger. All of the results suggested that obtaining or losing electrons was an effective switch to tune the peculiarities of the complex.

Molecular Magnetism of Lanthanides Complexes and Networks

Lanthanides ions allows for the design of remarkable magnetic compounds with unique magnetic properties.[...]

Solvent-dependent dual-luminescence properties of a europium complex with helical π-conjugated ligands.

A europium(iii) complex with a large π-conjugated helical ligand, tris(hexafluoroacetylacetonato)europium(iii)bis((pentahelicenyl)diphenylphosphine oxide) (Eu(hfa)3(HPO)2), exhibits dual luminescence excited at the π-π* transition band. In this study, the solvent-dependent photophysical properties of Eu(hfa)3(HPO)2 are reported. The ground-state properties of the ligand and the Eu(iii) complex are assessed from electronic absorption spectra, magnetic circular dichroism spectra, and density functional theory calculations. The excited-state properties of these compounds are evaluated using luminescence spectra, excitation spectra, luminescence lifetimes, and luminescence quantum yields depending on solvents, which are CHCl3, C2H5Br, C2H5I, CH3COCH3, and CD3COCD3. Under all of the examined conditions, the intensity ratios of dual luminescence originating from the ligand and the Eu(iii) ion were strongly dependent on the properties of the solvent. The solvent dependence of the luminescence ratio is discussed in terms of the external heavy atom effect.

Water-soluble lanthanide complexes with a helical ligand modified for strong luminescence in a wide pH region

Luminescent helical lanthanide complexes with hydrophilicity were examined for stability and reversibility in a pH region between 1.9 and 11.9.

Slow Magnetic Relaxation of Lanthanide(III) Complexes with a Helical Ligand

Isostructural Ln(III) mononuclear complexes [Ln(NO3)2L]PF6·MeCN (Ln = Nd, Tb, or Dy; L denotes a helical hexa-dentate ligand) were synthesized, and their slow magnetic relaxation behavior was investigated. In these complexes, oblate-type Ln(III) ions are located in an axially stressed ligand field with two nitrate anions, and can exhibit single-molecule magnet (SMM) behavior. Field-induced SMM behavior was observed for Nd(III) and Dy(III) complexes under an applied bias DC field of 1000 Oe.

Aromaticity of metal acetylacetonates and a Möbius chelate of a cadmium(II) complex of an N4 helical ligand

Interaction of a benzene C–H tip with a metallacycle of various metal acetylacetonates are studied by means of DFT calculations at M062X/LanL2DZ and M062X/6-311++G(2d,p) levels. It is concluded that an angular interaction with a tilt angle θ of the C–H tip is diagnostic of aromaticity of a chelate ring in a metal acetylacetonate. Larger the θ value, the more aromatic is the probed molecule. This finding is supported by the known X-ray crystal structure of bis(acetylacetonato)platinum(II)-benzene. Acetylacetonate anion has 6 π electrons fulfilling Hückel’s 4n+2 rule for aromaticity. A thirteen membered 12 π electron chelate ring in a cadmium(II) complex of a helical N4 ligand is shown to be aromatic by establishing it as a Möbius object.

Novel Chiral C3-Symmetric Monophosphite Ligands: Synthsis and Catalytic Performance in Asymmetric Hydroformylation and 1,4-Conjugate Addition

A family of the novel chiral helical C3-symmetric monophosphite ligands has been synthesized from axially chiral (R)or (S)-H8-BINOL and PCl3. The performance of these ligands in asymmetric catalysis was evaluated by the Rh-catalyzed asymmetric hydroformylation of styrene, and the Cu-catalyzed asymmetric 1,4-conjugate addition of diethylzinc to acyclic enones. The catalytic hydroformylation of styrene gave rather high conversion (93%), high regioselectivity (b/n=95/5) and low enantioselectivity [28% ee (R)] using ligand (R)-2 in tetrahydrofuran at room temperature. Under the optimal 1,4-conjugate addition of ZnEt2 to chalcone 3a conditions, eleven acyclic enones 4a~4k were all converted smoothly to the 1,4-adducts with high enantiomeric excess. Using Cu(OTf)2 as catalyst precursor and Et2O as solvent at -20 °C, the structure of ligand (R)-3 comprising a partially hydrogenated 2,2'-(1,1'-binaphthyl)-phosphite scaffold and an adamantyl moiety was key factor in improving catalytic activity and the enantioselectivity with up to 98% yield and 72% ee (R). The sense of enantiodiscrimination of the reaction was controlled by the configuration of the diaryl phosphite moieties.

Chirality at metal and helical ligand folding in optical isomers of chiral bis(naphthaldiminato)nickel(II) complexes.

Enantiopure bis[{(R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminato-κ(2)N,O}]nickel(ii) complexes {Ar = C6H5 ( or ), p-OMeC6H4 ( or ), and p-BrC6H4 ( or )} are synthesized from the reactions between (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldimine and nickel(ii) acetate. Circular-dichroism spectra and their density-functional theoretical simulation reveal the expected mirror image relationship between the enantiomeric pairs / and / in solution. CD spectra are dominated by the metal-centered Λ- or Δ-chirality of non-planar four-coordinated nickel, this latter being in turn dictated by the ligand chirality. Single crystal structure determination for and shows that there are two symmetry-independent molecules (A and B) in each asymmetric unit that give a Z' = 2 structure. Two asymmetric and chiral bidentate N^O-chelate Schiff base ligands coordinate to the nickel atom in a distorted square planar N2O2-coordination sphere. The conformational difference between the symmetry-independent molecules arises from the "up-or-down" folding of the naphthaldiminato ligand with respect to the coordination plane, which creates right- (P) or left-handed (M) helical conformations. Overall, the combination of ligand chirality, chirality at the metal and ligand folding gives rise to discrete metal helicates of preferred helicity in a selective way. Cyclic voltammograms (CV) show an oxidation wave at ca. 1.30 V for the [Ni(L)2]/[Ni(L)2](+) couple, and a reduction wave at ca. -0.35 V for the [Ni(L)2]/[Ni(L)2](-) couple in acetonitrile.

Coupled Nanomechanical Motions: Metal-Ion-Effected, pH-Modulated, Simultaneous Extension/Contraction Motions of Double-Domain Helical/Linear Molecular Strands

A new class of shape-enforced synthetic polyheterocyclic molecular strands, containing both a helical and a linear domain, has been designed and synthesized. On reaction with Pb(II), under the effect of cation binding to the coordination subunits, the helical section unfolds into a linear shape in the complex and the linear domain folds into a helical ligand wrapped around the bound cations. Such double-domain ligand strands are thus able to undergo a combined unfolding-folding interconversion on binding and release of metal cations. These changes can be modulated through coupling to a competing ligand that reversibly binds and releases metal cations, when respectively unprotonated and protonated, on effecting alternate pH changes. The resulting process thus performs nanomechanical extension/contraction molecular motions of a linear motor type, which is fueled by acid-base neutralization.

Luminescence behaviour in acetonitrile and in the solid state of a series of lanthanide complexes with a single helical ligand

Luminescence properties of EuIII, TbIII, GdIII and NdIII complexes with a hexadentate ligand (abbreviated to EuL, TbL, GdL, and NdL, respectively), which have two bipyridine moieties bridged by an ethylenediamine unit, have been examined in acetonitrile and in the solid state.

Zinc Complexes of Bipyrrolidine‐Based Diamine‐Diphenolato and Diamine‐Diolato Ligands: Predetermination of Helical Chirality Around Tetrahedral Centres

AbstractThe coordination chemistry of chiral tetradentate dianionic ligands of the diamine‐diphenolato and diamine‐diolato families having the (R,R)‐2,2′‐bipyrrolidine core around ZnII was investigated. Reactions with diethylzinc led to complexes of the type [{ONNO}Zn] for most ligands and to bridging dinuclear complexes of the type [μ‐Lig4(ZnEt)2] for one of the diamine‐diolato ligands. Reactions with bis(hexamethyldisilazide)zinc led to complete conversions. Most complexes were obtained as mononuclear complexes. The least bulky Salan ligand, Lig3, led to an equilibrium between mononuclear and dinuclear complexes in noncoordinating solvents. All ligands were found to wrap around the tetrahedral zinc with very high diastereoselectivities supporting predetermined chiral induction from the bipyrrolidine core to the helical ligand wrapping. Molecular structures determined by single‐crystal X‐ray diffraction for two complexes of the type [{ONNO}Zn] substantiated the predicted Δ wrapping of the (R,R)‐based ligands. In contrast, representative Salan and diamine‐diolato ligands assembled around the trans‐1,2‐diaminocyclohexane core led to diastereomer mixtures of the corresponding complexes.