Powder Pattern Spectra Research Articles

Mononuclear coordination compounds containing a pyrazole-based ligand: Syntheses, magnetism and acetylcholinesterase inhibition assays

A series of three pseudo-octahedral coordination compounds with general formula cis-[M(L)2(OH2)4], where M stands for FeII (1), CoII (2) or NiII (3), and HL is 5-amino-1-(benzo[d]thiazol-2-yl)-1H-pyrazole-4-carboxylic acid proligand was synthesized by slow diffusion methodology and thoroughly characterized by spectroscopic techniques, magnetic measurements and ab initio calculations. Single crystal X-ray diffraction data obtained for 1 and 2 revealed that the crystal packing is stabilized by a hydrogen bond network while X-ray powder pattern, Raman and IR spectra indicated that compounds 1 and 3 are isomorphic. Mössbauer spectra recorded at 3 and 300 K for 1 showed that the FeII ion is in its high spin state. Magnetic studies carried out for complexes 1–2 showed the key role played by the zero-field splitting and the experimental fit data were correlated and supported by CASSCF calculations. The activity of acetylcholinesterase enzyme was investigated towards L and 1–3 by using Elman’s methodology, affording inhibition rates of 20%, 56%, 35% and 36%, respectively.

Synthesis, characterisation, XRD, molecular modelling and potential antibacterial studies of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes with bidentate azodye ligand

Six monomeric complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with one O N donor bidentate azodye ligand, 3 – (p-tolylazo) – 4 – hydroxyl – 5 – methoxybenzaldehyde (LH) (TAHMB) have been prepared. The complexes have been characterised by analytical, conductance, magnetic susceptibility, IR, electronic spectra, ESR, NMR, X-ray diffraction (Powder pattern) spectra and molecular modelling studies. The Co (II) and Ni (II) complexes are found to be octahedral, Cu(II) complex is distorted octahedral and a tetrahedral stereochemistry has been assigned to Zn(II), Cd(II) and Hg(II) complexes. The energy optimised structures Figs. 3–5 are proposed using the semi empirical ZINDO/1 quantum mechanical calculations. The Ni(II) complex is found to possess an orthorhombic crystal system. The potential antibacterial studies of the ligand and some metal complexes with gram positive and gram negative bacteria have given encouraging results.

Lineshape-based polarimetry of dynamically-polarized [formula omitted] in solid-state mixtures

Dynamic nuclear polarization (DNP) of 15N2O, known for its long-lived singlet-state order at low magnetic field, is demonstrated in organic solvent/trityl mixtures at ∼1.5K and 5T. Both 15N polarization and intermolecular dipolar broadening are strongly affected by the sample’s thermal history, indicating spontaneous formation of N2O clusters. In situ 15N NMR reveals four distinct powder-pattern spectra, attributed to the chemical-shift anisotropy (CSA) tensors of the two 15N nuclei, further split by the intramolecular dipolar coupling between their magnetic moments. 15N polarization is estimated by fitting the free-induction decay (FID) signals to the analytical model of four single-quantum transitions. This analysis implies (10.2±2.2)% polarization after 37h of DNP, and provides a direct, instantaneous probe of the absolute 15N polarization, without a need for time-consuming referencing to a thermal-equilibrium NMR signal.

Synthesis, Spectral, Thermogravimetric, XRD, Molecular Modelling and Potential Antibacterial Studies of Dimeric Complexes with Bis Bidentate ON–NO Donor Azo Dye Ligands

The dimeric complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) with two new symmetrical ON–NO donor bis bidentate (tetradentate) azo dye ligands, LH2 = 4,4′‐bis(4′‐hydroxyquinolinolinylazo)diphenylsulphone, and L′H2 = 4,4′‐bis(acetoacetanilideazo)diphenylsulphone have been synthesized. The metal complexes have been characterised by elemental analytical, conductance, magnetic susceptibility, IR, electronic spectra, ESR, NMR, thermogravimetry, X‐ray diffraction (powder pattern) spectra, and molecular modelling studies. The Co(II) and Ni(II) complexes are found to be octahedral, Cu(II) complexes are distorted octahedral, and a tetrahedral stereochemistry has been assigned to Zn(II), Cd(II), and Hg(II) complexes. The thermogravimetric study indicates that compounds are quite stable. The energy optimized structures are proposed using the semiempirical ZINDO/1 quantum mechanical calculations. The potential antibacterial study of the ligands and some metal complexes has been made with one gram positive bacteria Staphylococcus aureus and one gram negative bacteria E. coli which gives encouraging results. Both the Co(II) complexes are found to possess monoclinic crystal system.

High field ESR measurements of S = 1/2 low dimensional antiferromagnet (2,3-dmpyH)2CuBr4

High field ESR measurements of (2,3-dmpyH)2CuBr4 powder sample have been performed in the frequency range from 60 to 315 GHz using the pulsed magnetic field up to 16 T. Observed temperature range is 1.8 to 265 K. ESR spectrum observed at 265 K shows a typical powder pattern spectrum of Cu2+ ion, and obtained g-values are g// = 2.307 and g⊥ = 2.053. Temperature dependence measurements are also performed at 80, 160 and 315 GHz, and almost no temperature dependence of g-value is observed for all frequencies down to 1.8 K. These results are rather unusual for the low dimensional strongly correlated spin system, and possible mechanisms by spin frustration is suggested.

High-Frequency ESR Measurements of S = 1/2 1-D Heisenberg Antiferromagnetic Zig-Zag Chain (VO)(SO4)(2,2-bpy)

High-frequency electron spin resonance (ESR) measurements of S = 1/2 one-dimensional Heisenberg antiferromagnetic zig-zag chain substance (VO)(SO4)(2,2-bpy) were performed in the temperature region from 1.8 to 265 K. ESR measurements at 265 K show typical powder pattern spectra of the V4+ ion and g || = 1.925 ± 0.001 and g ⊥ = 1.976 ± 0.001 were obtained. Although the magnetic susceptibility shows a maximum at 3.1 K suggesting the existence of a short-range order, no g-shift and line width broadening were observed down to 1.8 K. We suggest that these temperature-independent features of ESR can be attributed to the result of frustration in (VO)(SO4)(2,2-bpy).

Phthalocyanine as a Chemically Inert, Redox-Active Ligand: Structural and Electronic Properties of a Nb(IV)-Oxo Complex Incorporating a Highly Reduced Phthalocyanine(4−) Anion

This report describes the reduction of a niobium(V) phthalocyanine complex and investigation of the electronic structure of the resulting products. The reduction of PcNbCl(3) (Pc = phthalocyanine dianion) with 5.5 equiv of potassium graphite in 1,2-dimethoxyethane (DME) resulted in the isolation of K(2)PcNbO.5DME (1a). Addition of 18-crown-6 to 1a gave [K(18-crown-6)](2)(mu-DME)PcNbO (1b). Both 1a and 1b were structurally characterized by single-crystal X-ray diffraction analysis. In both complexes, the niobium center adopts a square pyramidal geometry and is coordinated by four basal Pc nitrogen atoms and an apical oxo ligand. Notably, the Pc ligand in 1a is saddle-shaped, with significant bond length alternation, rather than flat with delocalized bonding. The production of ethylene during the reduction of PcNbCl(3), detected by gas chromatography/mass spectrometry (GC/MS), suggests that the oxo ligand likely results from double C-O bond activation of DME solvent. A combination of spectroscopic techniques and density functional theory (DFT) calculations were used to establish the electronic structure of 1a. The close correspondence of the electronic absorption spectrum of 1a to that of [PcZn](2-) with a di-reduced Pc(4-) ligand, indicates a similar electronic structure for the two complexes. Evaluation of the electronic transitions for 1a and [PcZn](2-) by time-dependent DFT calculations further suggests a similar electronic structure for both complexes, indicating that differences in symmetry between 1a and [PcZn](2-) do not significantly affect the nature of the electronic transitions. Electron paramagnetic resonance (EPR) spectroscopy of 1a in solution at room temperature gave a 10-line spectrum, while frozen-solution X- and Q-band EPR spectra are consistent with powder-pattern spectra defined by uniaxial g and (93)Nb hyperfine tensors: these imply the presence of a d(1) Nb(IV) metal center. EPR and electron nuclear double resonance spectroscopy suggests that the spin density in 1a is centered almost completely on the niobium, in agreement with the DFT calculations. These results illustrate the value of Pc as a chemically inert, redox-active ligand for stabilizing reactive metal centers.

Solid‐state NMR spectroscopic studies on the interaction of sorbic acid with phospholipid membranes at different pH levels

2H, 31P, and 1H-magic-angle-spinning (MAS) solid-state NMR spectroscopic methods were used to elucidate the interaction between sorbic acid, a widely used weak acid food preservative, and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers under both acidic and neutral pH conditions. The linewidth broadening observed in the 31P NMR powder pattern spectra and the changes in the 31P longitudinal relaxation time (T1) indicate interaction with the phospholipid headgroup upon titration of sorbic acid or decanoic acid into DMPC bilayers over the pH range from 3.0 to 7.4. The peak intensities of sorbic acid decrease upon addition of paramagnetic Mn2+ ions in DMPC bilayers as recorded in the 1H MAS NMR spectra, suggesting that sorbic acid molecules are in close proximity with the membrane/aqueous surface. No significant 2H quadrupolar splitting (DeltanuQ) changes are observed in the 2H NMR spectra of DMPC-d54 upon titration of sorbic acid, and the change of pH has a slight effect on DeltanuQ, indicating that sorbic acid has weak influence on the orientation order of the DMPC acyl chains in the fluid phase over the pH range from 3.0 to 7.4. This finding is in contrast to the results of the decanoic acid/DMPC-d54 systems, where DeltanuQ increases as the concentration of decanoic acid increases. Thus, in the membrane association process, sorbic acids are most likely interacting with the headgroups and shallowly embedded near the top of the phospholipid headgroups, rather than inserting deep into the acyl chains. Thus, antimicrobial mode of action for sorbic acid may be different from that of long-chain fatty acids.

Inherent paramagnetic defects in layered Si/SiO2 superstructures with Si nanocrystals

An extensive electron spin resonance (ESR) analysis has been carried out on structures comprised of Si nanoparticles (∼2 nm across) embedded in a regular pattern in an amorphous SiO2 matrix, fabricated by the SiO/SiO2 superlattice approach, with the intent to reveal and quantify occurring paramagnetic defects. The as-grown state is found to exhibit only a Si dangling bond (DB) signal, which through combination of first and second harmonic X-, K-, and Q-band observations in combination with computer spectra simulation, could be conclusively disentangled as solely comprised of overlapping powder pattern spectra of Pb(0) and Pb1 defects, the archetypal intrinsic defects of the Si/SiO2 interface, with no evidence for a D line (Si DBs in disordered Si). This indicates a full crystalline system of randomly oriented Si nanocrystals (NCs). The Pb(0)/Pb1 defect system, pertaining to the NC-Si/SiO2 interfaces, is found to be both qualitatively and quantitatively much alike that of standard (high-quality) thermal Si/SiO2. The system is inherent, remaining unaffected by subsequent UV/vacuum UV irradiations. Relying on the known properties of Pb-type defects in standard microscopic Si/SiO2, the data would comply with Si nanocrystallites, in average, predominantly bordered by (111) and (100) facets, perhaps with morphology, schematically, of [100] truncated (111) octahedrons. Based on independent NC particles counting, there appears a Pb-type center at ∼71% of the Si NCs indicating the latter to be comprised of two subsystems–with or without an incorporated strain relaxing interface defect–which in that case will exhibit drastically different defect-sensitive properties, such as, e.g., photoluminescence (PL). Upon additional optical irradiation, two more defects appear, i.e., the SiO2-associated Eγ′ and EX centers, where the observed density of the former, taken as criterion, indicates the SiO2 matrix to be of standard thermal oxide quality. Thus, the properties of the revealed crucial intrinsic point defects bear out a high quality of both the NC-Si/SiO2 interfaces and the embedding SiO2, alike that of standard thermal Si/SiO2. In combination with H passivation/depassivation treatments, the degrading impact of the optical excitation (∼360 nm) itself used during PL measurements has been studied, revealing weak ESR reactivation of Pb(0), Pb1, and Eγ′ defects.

Analysis of 11B NMR Powder Lineshape of MgB2 in the Normal Conductive Phase

11 B nuclear magnetic resonance (NMR) measurements have been performed on MgB 2 powder sample at several magnetic fields ranging from 6.3 to 21.9 T. The isotropic Knight-shift, as well as quadrupole coupling frequency, was accurately determined from magic-angle spinning (MAS) spectra by analyzing its magnetic-field dependence. These NMR parameters were then used to interpret its static powder-pattern spectra observed at various magnetic fields, which reflect both the anisotropic Knight-shift tensor and the second-order quadrupole coupling tensor. We found that the Knight-shift tensor and the quadrupole coupling are both axially symmetric and their relative orientation to the molecular frame was also determined. This is the first experimental determination of the anisotropy of the Knight-shift of MgB 2 in a powder form from an exact analysis of the powder lineshape of the 11 B NMR spectra. The anisotropy was found to be very small (∼4 ppm), being in consistent with previous observations indicating that ani...

NMR Study of YbAl3C3in High Magnetic Field

We have carried out 27 Al nuclear magnetic resonance (NMR) measurements on YbAl 3 C 3 . The obtained NMR line is well decomposed into two powder pattern spectra characterized by the nuclear magnetic resonance (NQR) frequency ν Q =3.55 MHz (Al 2 d -site) and 0.35 MHz (Al 4 f -site). About the transition at exceptionally high temperature T * = 80 K, it was found that the NMR line becomes broadened rapidly just below T * , and T * increases by about 10 K at the field of 30 T. Analogous phenomena are commonly seen in many quadrupolar ordering systems, implying that the transition in YbAl 3 C 3 is associated with the quadrupolar order.

Intensity and mosaic spread analysis from PISEMA tensors in solid-state NMR

The solid-state NMR experiment PISEMA, is a technique for determining structures of proteins, especially membrane proteins, from oriented samples. One method for determining the structure is to find orientations of local molecular frames (peptide planes) with respect to the unit magnetic field direction, B 0. This is done using equations that compute the coordinates of this vector in the frames. This requires an analysis of the PISEMA function and its degeneracies. As a measure of the sensitivity of peptide plane orientations to the data, we use these equations to derive a formula for the intensity function in the powder pattern. With this function and other measures, we investigate the effect of small changes in peptide plane orientations depending on the location of the resonances in the powder pattern spectrum. This gives us an indication of the change in lineshape due to mosaic spread and a way to interpret these in terms of an orientational error bar.

Structure and dynamics of photosynthetic membrane-bound proteins in Rhodobacter Sphaeroides, studied with solid-state NMR spectroscopy.

The photosynthetic purple bacteria such as Rb. sphaeroides possesses an intracytoplasmic membrane (ICM) and a variety of pigment-binding membrane proteins located in the ICM, acting as photoreceptor. Such photosynthetic apparatus is concentrated in the ICM. It is composed of three multimeric membrane-bound proteins; light-harvesting complexes (LH 1, LH 2), a reaction center (RC) and a cytochrome b/c1 complex. We have purified these membranes, which are called chromatophores, and characterized the structure and dynamics of the photosynthetic membrane-bound proteins by means of multi-nuclear solid state NMR. First, the isotropic chemical shift of carbonyl carbons in natural abundance and [1-(13)C] Phe labeled chromatophores indicates that the membrane-bound proteins take mainly the helical conformation. Second, the chemical shifts of side-chain resonances of uniformly (15)N-labeled chromatophores indicate the side-chain histidine residue is mainly hydrogen bonded, whereas structural heterogeneity of arginine and lysine side-chains are probed by those wide distribution of (15)N shifts. Thirdly, the [beta-(2)H(3)]Ala and [epsilon-(2)H(2)]Tyr labeling of the chromatophores are performed and dynamics of the [beta-(2)H]Ala and the [epsilon-(2)H(2)]Tyr labeled chromatophores are studied by means of (2)H solid state NMR. The dynamics of [beta-(2)H(3)]Ala is found to be a 10(8)Hz three-site jump motion with 10 degrees liberation along the Calpha-Cbeta bond axis. The (2)H-NMR powder pattern spectrum of [epsilon-(2)H(2)] Tyr labeled chromatophores was interpreted with an averaged correlation time of 5x10(5) Hz with 180 degrees two-fold flips, the result of the averaging of two kinds of split spectra in terms of motional time scale.

High-Frequency and -Field Electron Paramagnetic Resonance of High-Spin Manganese(III) in Porphyrinic Complexes.

High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study two complexes of high-spin manganese(III), d(4), S = 2. The complexes studied were (tetraphenylporphyrinato)manganese(III) chloride and (phthalocyanato)manganese(III) chloride. Our previous HFEPR study (Goldberg, D. P.; Telser, J.; Krzystek, J.; Montalban, A. G.; Brunel, L.-C.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1997, 119, 8722-8723) included results on the porphyrin complex; however, we were unable to obtain true powder pattern HFEPR spectra, as the crystallites oriented in the intense external magnetic field. In this work we are now able to immobilize the powder, either in an n-eicosane mull or KBr pellet and obtain true powder pattern spectra. These spectra have been fully analyzed using spectral simulation software, and a complete set of spin Hamiltonian parameters has been determined for each complex. Both complexes are rigorously axial systems, with relatively low magnitude zero-field splitting: D approximately -2.3 cm(-)(1) and g values quite close to 2.00. Prior to this work, no experimental nor theoretical data exist for the metal-based electronic energy levels in Mn(III) complexes of porphyrinic ligands. This lack of information is in contrast to other transition metal complexes and is likely due to the dominance of ligand-based transitions in the absorption spectra of Mn(III) complexes of this type. We have therefore made use of theoretical values for the electronic energy levels of (phthalocyanato)copper(II), which electronically resembles these Mn(III) complexes. This analogy works surprisingly well in terms of the agreement between the calculated and experimentally determined EPR parameters. These results show a significant mixing of the triplet (S = 1) excited state with the quintet (S = 2) ground state in Mn(III) complexes with porphyrinic ligands. This is in agreement with the experimental observation of lower spin ground states in other metalloporphyrinic complexes, such as those of Fe(II) with S = 1.

Magnitudes and Orientations of the 15N Chemical Shift Tensor of [1-15N]-2′-Deoxyguanosine Determined on a Polycrystalline Sample by Two-Dimensional Solid-State NMR Spectroscopy

The magnitudes and orientations of the 15N chemical shift tensor of [1-15N]-2′-deoxyguanosine were determined from a polycrystalline sample using the two-dimensional PISEMA experiment. The magnitudes of the principal values of the 15N chemical shift tensor of the N1 nitrogen of [1-15N]-2′-deoxyguanosine were found to be ς11 = 54 ppm, ς22 = 148 ppm, and ς33 = 201 ppm with respect to (15NH4)2SO4 in aqueous solution. Comparisons of experimental and simulated two-dimensional powder pattern spectra show that ς33N is approximately collinear with the N–H bond. The tensor orientation of ς33N for N1 of [1-15N]-2′-deoxyguanosine is similar to the values obtained for the side chain residues of 15Nϵ1-tryptophan and 15Nπ-histidine even though the magnitudes differ significantly.

Structure of Bombyx mori Silk Fibroin Based on Solid-State NMR Orientational Constraints and Fiber Diffraction Unit Cell Parameters

Isotopic labeling of Bombyx mori silk fibroin was achieved biosynthetically using two approaches. First, labeled fibroin was achieved by feeding silk worms [13C1]Gly and [13C1]Ala along with an artificial diet. Second, in vitro production of [15N]Gly and [15N]Ala labeled B. mori silk fibroin was accomplished by culturing the posterior silk glands isolated from five-day-old silkworm larvae in the fifth instar stage. Orientation-dependent 15N and 13C solid-state NMR spectra of these isotope-labeled silk fibroin fibers were observed when the fiber axis was arranged at various angles between 0° and 90° to the magnetic field direction. Such data from the silk II structure was simulated on the basis of the chemical shift anisotropy to determine the Euler angles that relate the principal axis system (PAS) to the fiber axis coordinate system. The dipolar modulated 15N and 13C chemical shift powder pattern spectra of 13C−15N double-labeled silk fibroin model peptides were observed and simulated to determine the Eu...

15N chemical shift tensors and conformation of solid polypeptides containing 15N-labeled glycine residue by 15N NMR

The correlation between the isotropic 15N chemical shift ( δ iso) and 15N chemical shift tensor components ( δ 11, δ 22 and δ 33) and the main-chain conformation such as the polyglycine I (PGI: β-sheet), II (PGII: 3 1-helix), α-helix and β-sheet forms of solid polypeptides [Gly∗,X] n consisting of 15N-labeled glycine (Gly∗) and other amino acids (X: natural abundance of 15N) has been studied by solid-state 15N NMR method. A series of polypeptides [Gly∗,X] n (X = glycine, l-alanine, l-leucine, l-valine, l-isoleucine, β-benzyl l-aspartate, γ-benzyl l-glutamate, ϵ-carbobenzoxy l-lysine, and sarcosine) were synthesized by the α-amino acid N-carboxy anhydride (NCA) method. Conformations of these polypeptides in the solid state were characterized on the basis of conformation-dependent 13C chemical shifts in the 13C cross-polarization-magic angle spinning (CP-MAS) NMR spectra and by the characteristic bands in the IR and far-IR spectra. The δ iso, δ 11, δ 22 and δ 33 of the polypetides were determined from the 15N CP-MAS and 15N CP-static (powder pattern) spectra. It was found that the δ iso, δ 11, δ 22 and δ 33 in the PGI form (δ 83.5, 185, 40.7 and 25 ppm, resp.) are upfield from those in the PGII form (88.5, 194, 42.1 and 29 ppm, resp.), which were reproduced by the calculated 15N shielding constants using the finite perturbation theory (FPT)-INDO method. It was also found that the δ 22 of the Gly∗ of [Gly∗,X] n is closely related to the main-chain conformation and the neighboring amino acid sequence, although the δ iso is almost independent of the glycine content and conformation. Consequently, the δ 22 value of Gly∗ containing copolypeptides is useful for the structural (main-chain conformation and neighboring amino acid sequence) analysis in the solid state by 15N NMR, if the 15N-labeled copolypeptide or natural protein can be provided. In addition, it is shown that the δ iso of the glycine residue is useful for the conformational study of some fibrous proteins such as silk fibroins and collagen fibrils in the solid state.

Rapid deconvolution of NMR powder spectra by weighted fast Fourier transformation

The resolution enhancement conferred by numerical deconvolution of powder pattern spectra to spectra characteristic of a single alignment greatly simplifies solid state NMR spectral analysis. This is especially beneficial when the spectrum is a superposition of signals from multiple environments or sites of labelling. We have developed an innovative method to deconvolute (depake) spectra governed by axially symmetric second rank tensor interactions which possess a P 2(cosθ) dependence upon orientation, where θ is the angle between the symmetry axis and the external magnetic field. Our approach differs substantially from previously published procedures which are iterative or require matrix inversion and, hence, are slow. The new method, instead, utilizes weighting functions in time and frequency domains to facilitate a rapidly executed solution based upon fast Fourier transformation (FFT). Its efficacy is demonstrated with 2H and 31P NMR data for model membranes.

Liquid crystalline behavior of octylcyanobiphenyl confined to submicron-size randomly connected porous glasses

We report a study of the orientational order via deuterium NMR and high resolution ac calorimetry on octylcyanobiphenyl (8CB) confined to randomly oriented and interconnected macroporous (1000 \AA{} mean pore size) and microporous (100 \AA{} mean pore size) glasses. In the macroporous glass, the nematic to isotropic $(N\ensuremath{-}I)$ phase transition retains the bulklike weakly first order nature. The nematic phase is characterized by an NMR powder pattern spectra, as expected for a director distribution with no preferred spatial direction, and it coexists with an isotropiclike component. The orientational order is slightly suppressed from the bulk's and there is no sudden increase in orientational order due to the onset of the smectic phase suggesting a weaker coupling between nematic and smectic order parameters. Further, due to the confining size, the smectic-$A$ to nematic transition is considerably suppressed and broadened. In the microporous glass, the orientational order behavior is reminiscent of that in Vycor glass. No phase transitions are detected, rather, there is a continuous evolution of local orientational order. Interporous and intraporous interactions are important.

Structurally Reinforced Chiral Macrocyclic Polyamine Copper (II) Complexes as Studied by ESR and Squid Measurements

Abstract We have synthesized structurally reinforced chiral pentaaza-fifteen-membered polyamines 1 and 2 with a dibridge for the purposes of studying the size-match selectivity of the macrocyclic cavity. Particularly, an attempt has been made to synthesize copper(II) complexes of 1 and 2 to characterize the size-match selectivity of the polyamines in term of microscopic details of the metal-ion binding site. For this purpose the use of ESR spectroscopy has been invoked before X-ray structural analyses of the complexes are carried out. Powder-pattern ESR spectra of the copper(II) complex of 1 in crystalline solid have revealed a temperature dependence of the copper hyperfine structure. This finding suggests that a vibronic effect features in the hyperfine spectra, showing that the pentaaza-macrocycle under study accommodates copper(II) ion and the macrocycle is flexible to exert “genuine” size-match selectivity.