Preparation of a Zinc Monocysteine Compound

Both zinc and the amino acid cysteine play important roles in biological function, including antioxidant protection and tissue repair. We attempted to prepare a (1:l) zinc‐cysteine complex using L‐cysteine and zinc metal. Zinc metal was added to a solution of L‐cysteine and refluxed with constant stirring. The product was selected by filtration and, after evaporation precipitation, was subjected to elemental analysis, ¹H NMR, and mass spectroscopy. The novel compound has one molecule of zinc conjugated to one molecule of cysteine.     

Shaping Antiaromatic π‐Systems by Metalation: Synthesis of a Bowl‐Shaped Antiaromatic Palladium Norcorrole

The synthesis of a bowl‐shaped antiaromatic molecule was achieved through the deformation of a planar antiaromatic porphyrinic π‐conjugation system by insertion of palladium into the small cavity of a metal‐free norcorrole. The bowl‐to‐bowl inversion dynamics of the antiaromatic Pd‐coordinated norcorrole was determined by variable‐temperature ¹H NMR spectroscopy. The metal‐free norcorrole was prepared from acid‐induced demetalation of a copper norcorrole, which was obtained from the intramolecular coupling of a bis(diiododipyrrin) copper complex with copper thiophenecarboxylate.     

Direct Estimation of the Surface Location of Immobilized Functional Groups for Concerted Catalysis Using a Probe Molecule

The location of active sites during concerted catalysis by a metal complex and tertiary amine on a SiO₂ surface is discussed based on the interaction between the functionalized SiO₂ surface and a probe molecule, p‐formyl phenylboronic acid. The interactions of the probe molecule with the surface functionalities, diamine ligand, and tertiary amine, were analyzed by FT‐IR and solid‐state ¹³C and ¹¹B MAS NMR. For the catalyst exhibiting high 1,4‐addition activity, the diamine ligand and tertiary amine base exist in closer proximity than in the catalyst with low activity.     

Synthesis and Structural Characterization of Cadmium(II) and Mercury(II) Complexes Derived from 3‐Aminoquinoline

Two novel metal complexes derived from interactions of Cd²⁺ and Hg²⁺ ions with 3‐aminoquinoline in the molar ratio 1 : 2 are reported. The synthesized and isolated metal complexes were characterized by UV/VIS, FT‐IR, ¹H‐ and ¹³C‐NMR, and ESI‐MS spectroscopic studies, and elemental analyses. FT‐IR and NMR studies confirmed that the NH₂ group remains uncoordinated in both synthesized complexes. The molecular structure of the Cd^II complex was additionally determined by X‐ray single‐crystal analysis. The Cd complex crystallizes in the triclinic centrosymmetric P$\bar 1$ space group. Moreover, the Cd^II complex exists as neutral discrete molecule and was found to show tetrahedral geometry.     

Crystal Structure and Spectroscopic Characterization of Zinc(II) and Mercury(II) Complexes of N‐(Pyridin‐2‐ylmethylene)benzene‐1,4‐diamine

The behavior of N,N′‐bis(pyridin‐2‐ylmethylene)benzene‐1,4‐diamine (L) towards zinc(II), cadmium(II), and mercury(II) chlorides was studied in methanol solutions. In the presence of metal ions, the organic molecule was decomposed to N‐(pyridin‐2‐ylmethylene)benzene‐1,4‐diamine (L′), and complexes of general formula M(L′)Cl₂ were isolated from the mixture. The complexes were identified by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectra, and their structures were further confirmed by single‐crystal X‐ray diffraction analysis of Zn(L′)Cl₂ and Hg(L′)Cl₂. In the solid state of both complexes, the molecules are stabilized by N–H ··· Cl hydrogen bonds and aromatic π–π stacking interactions.     

Fluorescent Cross‐Linked Supramolecular Polymer Constructed by Orthogonal Self‐Assembly of Metal–Ligand Coordination and Host–Guest Interaction

A new host molecule consists of four terpyridine groups as the binding sites with zinc(II) ion and a copillar[5]arene incorporated in the center as a spacer to interact with guest molecule was designed and synthesized. Due to the 120 ° angle of the rigid aromatic segment, a cross‐linked dimeric hexagonal supramolecular polymer was therefore generated as the result of the orthogonal self‐assembly of metal–ligand coordination and host–guest interaction. UV/Vis spectroscopy, ¹H NMR spectroscopy, viscosity and dynamic light‐scattering techniques were employed to characterize and understand the cross‐linking process with the introduction of zinc(II) ion and guest molecule. More importantly, well‐defined morphology of the self‐assembled supramolecular structure can be tuned by altering the adding sequence of the two components, that is, the zinc(II) ion and the guest molecule. In addition, introduction of a competitive ligand suggested the dynamic nature of the supramolecular structure.     

NMR study of localization and mobility of 1‐phenylethanol enantiomers in homochiral metal‐organic sorbent Zn2(bdc)(S‐lac)(dmf)

Structural features of localization of chiral isomers of 1‐phenylethanol (R‐PhEtOH and S‐PhEtOH) and their mobility activation in homochiral metal‐organic [Zn₂(bdc)(S‐lac)(dmf)] sorbent were studied with ¹H and ¹³C NMR methods. ¹³C NMR chemical shifts do not show obvious advantage of selective interaction of molecule guests. But activation molecular mobility of S‐PhEtOH and R‐PhEtOH clearly indicates that stabilization of [Zn₂(bdc)(S‐lac)(dmf)]·S‐PhEtOH structure is more preferable than stabilization of [Zn₂(bdc)(S‐lac)(dmf)]·R‐PhEtOH structure. Copyright © 2015 John Wiley & Sons, Ltd.     

Tautomeric Switching and Metal‐Cation Sensing of Ligand‐Equipped 4‐Hydroxy‐/4‐oxo‐1,4‐dihydroquinolines

Novel 4‐hydroxyquinoline (4HQ) based tautomeric switches are reported. 4HQs equipped with coordinative side arms (8‐arylimino and 3‐piperidin‐1‐ylmethyl groups) were synthesized to access O‐ or N‐selective chelation of Zn²⁺ and Cd²⁺ ions by 4HQ. In the case of the monodentate arylimino group, O chelation of metal ions induces concomitant switching of phenol tautomer to the keto form in nonpolar or aprotic media. This change is accompanied by selective and highly sensitive fluorometric sensing of Zn²⁺ ions. In the case of the bidentate 8‐(quinolin‐8‐ylimino)methyl side arm, NMR studies in CD₃OD indicated that both Cd²⁺ and Zn²⁺ ions afford N chelation for 4HQ, coexisting with tautomeric switching from quinolin‐4(1H)‐one to quinolin‐4‐olate. In corroboration, UV/Vis‐monitored metal‐ion titrations in toluene and methanol implied similar structural changes. Additionally, fluorescence measurements indicated that the metal‐triggered tautomeric switching is associated with compound signaling properties. The results are supported by DFT calculations at the B3LYP 6‐31G* level. Several X‐ray structures of metal‐free and metal‐chelating 4HQ are presented to support the solution studies.     

Complete assignments of NMR data of salens and their cobalt (III) complexes

Salens, derived from 1,2‐ethylenediamine and salicylaldehydes, have been widely used as ligands for metal complexes which have been showing enormous potential in chemical properties of asymmetric catalysts as well as biological properties such as anticancer agents. Almost all of the salen–metal complexes with their corresponding metal (II)‐complexes show the evidences of chelation of two oxygens in salens. However, several metal (II) complexes, especially cobalt (II) complexes, could not show NMR spectra due to their paramagnetism. Recently, it has been reported that one of the cobalt (III) complexes was used for NMR spectroscopy to evaluate its stereoselectivity as a catalyst. Even though many salen ligands are known, their NMR data are not assigned completely. It was possible that modification in northern part of salen with 2‐hydroxyphenyl group afforded another oxygen chelation site in salen ligand. Here we report that synthesis and full NMR assignment of new salen ligands, which form meso 1,2‐bis(2‐hydroxyphenyl)ethylenediamine) and their cobalt (III) complexes. The assignments of ¹H and ¹³C NMR data obtained in this experiment can help us to predict the NMR data of other salen ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

Two Histidines in an α‐Helix: A Rigid Co2+‐Binding Motif for PCS Measurements by NMR Spectroscopy

Pseudocontact shifts (PCS) generated by paramagnetic metal ions present valuable long‐range information in the study of protein structural biology by nuclear magnetic resonance (NMR) spectroscopy. Faithful interpretation of PCSs, however, requires complete immobilization of the metal ion relative to the protein, which is difficult to achieve with synthetic metal tags. We show that two histidine residues in sequential turns of an α‐helix provide a binding site for a Co²⁺ ion, which positions the metal ion in a uniquely well‐defined and predictable location. Exchange between the bound and free cobalt is slow on the timescale defined by chemical shifts, but the NMR resonance assignments are nonetheless readily transferred from the diamagnetic to the paramagnetic NMR spectrum by an I_zS_z‐exchange experiment. The double‐histidine‐Co²⁺ motif offers a straightforward, inexpensive, and convenient way of generating precision PCSs in proteins.     

Siamese‐Twin Porphyrin: A Pyrazole‐Based Expanded Porphyrin of Persistent Helical Conformation

The 3+3‐type synthesis of a pyrazole‐based expanded porphyrin 22 H₄ , a hexaphyrin analogue named Siamese‐twin porphyrin, and its homobimetallic diamagnetic nickel(II) and paramagnetic copper(II) complexes, 22 Ni₂ and 22 Cu₂ , are described. The structure of the macrocycle composed of four pyrroles and two pyrazoles all linked by single carbon atoms, can be interpreted as two conjoined porphyrin‐like subunits, with the two opposing pyrazoles acting as the fusion points. Variable‐temperature 1D and 2D NMR spectroscopic analyses suggested a conformationally flexible structure for 22 H₄ . NMR and UV/Vis spectroscopic evidence as well as structural parameters proved the macrocycle to be non‐aromatic, though each half of the molecule is fully conjugated. UV/Vis and NMR spectroscopic titrations of the free base macrocycle with acid showed it to be dibasic. In the complexes, each metal ion is coordinated in a square‐planar fashion by a dianionic, porphyrin‐like {N₄} binding pocket. The solid‐state structures of the dication and both metal complexes were elucidated by single‐crystal diffractometry. The conformations of the three structures are all similar to each other and strongly twisted, rendering the molecules chiral. The persistent helical twist in the protonated form of the free base and in both metal complexes permitted resolution of these enantiomeric helimers by HPLC on a chiral phase. The absolute stereostructures of 22 H₆ ²⁺, 22 Ni₂ , and 22 Cu₂ were assigned by a combination of experimental electronic circular dichroism (ECD) investigations and quantum‐chemical ECD calculations. The synthesis of the first member of this long‐sought class of expanded porphyrin‐like macrocycles lays the foundation for the study of the interactions of the metal centers within their bimetallic complexes.     

NMR analysis of 6‐(2′,3′‐dihydro‐1′H‐inden‐1′‐yl)‐1H‐indene

¹H, ¹³C and two‐dimensional NMR analyses were applied to determine the NMR parameters of 6‐(2′,3′‐dihydro‐1′H‐inden‐1′‐yl)‐1H‐indene. The measurements were accomplished with 0.5 mg of the substance, this quantity being sufficient to determine the chemical shifts of all the H and C atoms, and also the appropriate coupling constants and to give the complete NMR resonance assignments of the molecule. The predicted patterns of the four different H atoms of the methylene groups of the indane structural element coincided completely with the complex patterns in the NMR spectra. Copyright © 2002 John Wiley & Sons, Ltd.     

Three‐dimensional structure of cyclic antibiotic teicoplanin aglycone using NMR distance and dihedral angle restraints in a DMSO solvation model

The three‐dimensional solution conformation of teicoplanin aglycone was determined using NMR spectroscopy. A combination of NOE and dihedral angle restraints in a DMSO solvation model was used to calculate an ensemble of structures having a root mean square deviation of 0.17 Å. The structures were generated using systematic searches of conformational space for optimal satisfaction of distance and dihedral angle restraints. Comparison of the NMR‐derived structure of teicoplanin aglycone with the X‐ray structure of a teicoplanin aglycone analog revealed a common backbone conformation with deviation of two aromatic side chain substituents. Experimentally determined backbone ¹³C chemical shifts showed good agreement with those computed at the density functional level of theory, providing a cross validation of the backbone conformation. The flexible portion of the molecule was consistent with the region that changes conformation to accommodate protein binding. The results showed that a hydrogen‐bonded DMSO molecule in combination with NMR‐derived restraints together enabled calculation of structures that satisfied experimental data. Copyright © 2015 John Wiley & Sons, Ltd.     

Photochromism and Metal Complexation of a Macrocyclic Styryl Naphthopyran

A macrocyclic benzo‐15‐crown‐5 ether unit tethered to a photochromic naphthopyran by a styryl spacer ( MEN ) is shown to form a 1:1 complex with magnesium(II). The structure and dynamics of the specific host–metal interactions were investigated by PFG‐NMR analysis. A combination of UV/Vis and variable temperature multi‐dimensional ¹H NMR photokinetic analysis of the crown‐containing styryl naphthopyran and its metal complex was used to probe the effect of metal complexation on the photochromism.     

Synthesis,characterization, fluorescence imaging,and cytotoxicity studies of a uracil‐based azo derivative and its metal complexes

A uracil‐based heterocyclic azo derivative was prepared by coupling diazotized 5‐aminouracil with 2‐naphthol. This ligand, viz., 1‐(2,4‐dioxopyrimidine‐5‐yl)‐azo‐naphth‐2‐ol (HNAP), was used as a precursor for the synthesis of a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) ions. Various physicochemical measurements UV–Visible, Infrared (IR), ¹H NMR, ¹³C Nuclear Magnetic Resonance (NMR), and electron spin resonance (ESR) spectral studies were employed to characterize the ligand and the metal complexes. The ligand showed good selectivity toward Mn²⁺ over the other metal ions with a detection limit of 1.36 μM. This probe was used for the confocal fluorescence imaging of Mn²⁺ ions in Michigan Cancer Foundation‐7 (MCF‐7) cells. The ligand and the metal complexes were tested for their cytotoxicity on the MCF‐7 cell line. It was observed that complexation of HNAP with the metal ions exhibited a promising cytotoxicity.     

Insights into Intramolecular Trp and His Side‐Chain Orientation and Stereospecific π Interactions Surrounding Metal Centers: An Investigation Using Protein Metal‐Site Mimicry in Solution

Metal‐binding scaffolds incorporating a Trp/His‐paired epitope are instrumental in giving novel insights into the physicochemical basis of functional and mechanistic versatility conferred by the Trp–His interplay at a metal site. Herein, by coupling biometal site mimicry and ¹H and ¹³C NMR spectroscopy experiments, modular constructs EDTA‐(L ‐Trp, L ‐His) (EWH; EDTA=ethylenediamino tetraacetic acid) and DTPA‐(L ‐Trp, L ‐His) (DWH; DTPA=diethylenetriamino pentaacetic acid) were employed to dissect the static and transient physicochemical properties of hydrophobic/hydrophilic aromatic interactive modes surrounding biometal centers. The binding feature and identities of the stoichiometric metal‐bound complexes in solution were investigated by using ¹H and ¹³C NMR spectroscopy, which facilitated a cross‐validation of the carboxylate, amide oxygen, and tertiary amino groups as the primary ligands and indole as the secondary ligand, with the imidazole (Im) N3 nitrogen being weakly bound to metals such as Ca²⁺ owing to a multivalency effect. Surrounding the metal centers, the stereospecific orientation of aromatic rings in the diastereoisomerism is interpreted with the Ca²⁺–EWH complex. With respect to perturbed Trp side‐chain rotamer heterogeneity, drastically restricted Trp side‐chain flexibility and thus a dynamically constrained rotamer interconversion due to π interactions is evident from the site‐selective ¹³C NMR spectroscopic signal broadening of the Trp indolyl C3 atom. Furthermore, effects of Trp side‐chain fluctuation on indole/Im orientation were the subject of a 2D NMR spectroscopy study by using the Ca²⁺‐bound state; a C? H2(indolyl)/C? H5(Im⁺) connectivity observed in the NOESY spectra captured direct evidence that the N? H1 of the Ca²⁺–Im⁺ unit interacted with the pyrrole ring of the indole unit in Ca²⁺‐bound EWH but not in DWH, which is assignable to a moderately static, anomalous, T‐shaped, interplanar π⁺–π stacking alignment. Nevertheless, a comparative ¹³C NMR spectroscopy study of the two homologous scaffolds revealed that the overall response of the indole unit arises predominantly from global attractions between the indole ring and the entire positively charged first coordination sphere. The study thus demonstrates the coordination‐sphere/geometry dependence of the Trp/His side‐chain interplay, and established that π interactions allow ¹³C NMR spectroscopy to offer a new window for investigating Trp rotamer heterogeneity near metal‐binding centers.     

Organophosphine/phosphite‐stabilized silver(I) complexes bearing N‐hydroxysuccinimide ligand: synthesis,solid state structure and their potential use as MOCVD precursors

Six organophosphine/phosphite‐stabilized silver(I) N‐hydroxysuccinimide complexes of type [C₄H₄NO₃Ag?L_n] (L = PPh₃; n = 1, 2a; n = 2, 2b; L = P(OEt)₃; n = 1, 2c; n = 2, 2 d; L = P(OMe)₃; n = 1, 2e; n = 2, 2f) were prepared. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³ C{¹H} NMR and IR spectroscopy, respectively. The molecular structure of 2b has been determined by X‐ray single‐crystal analysis in which the silver atom is in a distorted tetrahedral geometry. An interstitial methanol solvent molecule is hydrogen bonded to the oxygen atom of N‐hydroxysuccinimide molecule. Complex 2f was used to deposit silver films by metal‐organic chemical vapor deposition (MOCVD) for the first time. The silver film obtained at 480 °C is dense and homogeneous, which is composed of many well‐isolated, granular particulates spreading all over the substrate surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Chelating properties of poly(N‐acryloyl piperazine) by liquid‐phase polymer‐based retention (LPR) technique

The synthesis of poly(N‐acryloylpiperazine) was carried out by radical polymerization giving a yield of 90%. The polymer was soluble in water and was characterized by FTIR, ¹H NMR, ¹³C NMR spectroscopy, and TGA. The metal ability binding properties for the Ag(I), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Cr(III) metal ions in the aqueous phase were investigated using the liquid‐phase polymer‐based retention (LPR) method. The metal ion interactions with the hydrophilic polymers were determined as a function of pH and filtration factor.     

Synergic Effect of Active Sites in Zinc‐Modified ZSM‐5 Zeolites as Revealed by High‐Field Solid‐State NMR Spectroscopy

Understanding the nature of active sites in metal‐supported catalysts is of great importance towards establishing their structure–property relationships. The outstanding catalytic performance of metal‐supported catalysts is frequently ascribed to the synergic effect of different active sites, which is however not well spectroscopically characterized. Herein, we report the direct detection of surface Zn species and ¹H–⁶⁷Zn internuclear interaction between Zn²⁺ ions and Brønsted acid sites on Zn‐modified ZSM‐5 zeolites by high‐field solid‐state NMR spectroscopy. The observed promotion of C?H bond activation of methane is rationalized by the enhanced Brønsted acidity generated by synergic effects arising from the spatial proximity/interaction between Zn²⁺ ions and Brønsted acidic protons. The concentration of synergic active sites is determined by ¹H–⁶⁷Zn double‐resonance solid‐state NMR spectroscopy.