A spectral investigation of the copper(II) complex of the antitumor compound bleomycin

A thorough spectral investigation of the copper(II) complex of the antitumor compound, bleomycin, has been carried out in solution employing optical, difference optical, electron spin resonance, and circular dichroism techniques. The optical spectrum of a pH = 7 solution of the 1:1 complex between copper(II) and bleomycin is characterized by a broad weak band in the visible region (λ_max = 610 nm) that cannot be resolved and intense ultraviolet bands at 317 (? = 2800), 327 (shoulder), 250 (? = 4700), and 257 nm (shoulder). The circular dichroism spectrum in the visible region shows the broad and weak visible absorption band contains at least three components (558, 675, and 880 nm) that are likely to be “d-d” in origin. The electron spin resonance spectrum is characteristic of a tetragonal d⁹ copper(II) system showing no rhombic distoritions at X-band frequencies (g_x = g_y ± 0.002). The spin Hamiltonian parameters for the pH = 7.0 solution corrected for second order effects are A_∥ = 177 × 10^?4 cm^?1, A_⊥ ? 15 × 10^?4 cm^?1, g_∥ = 2.214, g_⊥ = 2.039. Most interesting was the observation of extra hyperfine splitting due to endogenous nitrogen coordination in a 30% glycerol glass (A^N = 12.0 × 10^?4 cm^?1). That pattern is best interpreted as a seven-line sequence associated with three liganded nitrogens. A dramatic change in all spectral properties occurs when the pH of the copper(II)-bleomycin complex is lowered to 2.5. All these data taken together suggest a CuN₃O coordination complex in solution. Details and justifications as well as a discussion of the limitations of the interpretations are presented.     

An EPR Study of NO Bonding to Erythrocruorin from the Earthworm Octolasium Complanatum

The EPR properties of the nitric oxide derivative of Octolasium complanatum erythrocruorin have been investigated as a function of the concentration of protons and cations which are known to affect the oxygen-linked allosteric equilibrium. The EPR spectrum has a rhombic shape with g_x = 2.08, g_z = 2.005, and g_y = 1.99, and remains unchanged under all the experimental conditions used. A supernyperfine pattern consisting of nine equally spaced lines is present in the g_z region indicating an interaction with two nonequivalent nitrogen atoms, one contributed by the nitric oxide and the other by the proximal histidine. The constancy of the EPR spectrum suggests that changes in the allosteric equilibrium do not involve differences in the strain of the Fe(II)-histidine bond as in tetrameric hemoglobins.     

Analysis of the electron paramagnetic resonance spectrum of the cobalamin intermediate in ribonucleotide reduction

EPR absorption-derivative lineshapes have been computed and least-squares fitted to the spectrum of the intermediate derived from 5'-deoxy-5'-adenosyl-cobalamin in the ribonucleotide reductase reaction. A Gausian-type intrinsic lineshape was assumed and the effects of inhomogenous broadening, rotation of coordinate axes of the A-tensor relative to the g-tensor, angular dependence of transition probability and ligand hyperfine splitting have also been investigated.When the overall spectrum was computed as the sum of the linshapes corresponding to two distinct Co(II) species, A and B, each having rhombic asymmetry, the least squares procedure converged to a much better fit than with a single species, and matched almost all of the features of the experimental spectrum.The magnetic properties of A and B were compared with those of a series of other Co(II) complexes by a plot of g_|?g₆ versus ∥A₆∥?∥A_|∥. The results eliminate cobalt with 5-coordination to nitrogen for A and B, suggest low-spin cobalt complexes having strongly distorted 6-fold coordination. The possibility that the sixth, symmetry-decreasing ligand is the oxygen molecule is excluded by the chemistry of the system and by the EPR properties of previously reported cob(II)alamins. It is suggested that the sixth ligand is carbonyl, amide or sulfhydryl group of an enzyme sidechain which is inserted off-axis into the coordination position so as to exert the observed symmetry-lowering effect.     

EPR of Cu Prion Protein Constructs at 2 GHz Using the g⊥ Region to Characterize Nitrogen Ligation

A double octarepeat prion protein construct, which has two histidines, mixed with copper sulfate in a 3:2 molar ratio provides at most three imidazole ligands to each copper ion to form a square-planar Cu²⁺ complex. This work is concerned with identification of the fourth ligand. A new (to our knowledge) electron paramagnetic resonance method based on analysis of the intense features of the electron paramagnetic resonance spectrum in the g_⊥ region at 2 GHz is introduced to distinguish between three and four nitrogen ligands. The methodology was established by studies of a model system consisting of histidine imidazole ligation to Cu²⁺. In this spectral region at 2 GHz (S-band), g-strain and broadening from the possible rhombic character of the Zeeman interaction are small. The most intense line is identified with the M_I = +1/2 extra absorption peak. Spectral simulation demonstrated that this peak is insensitive to cupric A_x and A_y hyperfine interaction. The spectral region to the high-field side of this peak is uncluttered and suitable for analysis of nitrogen superhyperfine couplings to determine the number of nitrogens. The spectral region to the low-field side of the intense extra absorption peak in the g_⊥ part of the spectrum is sensitive to the rhombic distortion parameters A_x and A_y. Application of the method to the prion protein system indicates that two species are present and that the dominant species contains four nitrogen ligands. A new loop-gap microwave resonator is described that contains ∼1 mL of frozen sample.     

The structure of the secondary donor of Photosystem II investigated by EPR at 9 and 35 GHz

Signal II of plant photosynthesis, which is generally thought to be connected to the secondary donor complex of Photosystem II, has been investigated with EPR spectroscopy at 9 and 35 GHz. From the spectrum at 35 GHz of deuterated Chlorella vulgaris, the principle values of the g-tensor are determined to be g_xx = 2.0074, g_yy = 2.0044 and g_zz = 2.0023. Proton hyperfine coupling tensor elements and orientations were determined from spectral simulation of random and oriented samples, assuming that Signal II is due to a plastose-miquinone cation having its π-electrons in an antisymmetric orbital as proposed by P.J. O'Malley, G.T. Babcock and R.C. Prince (Biochim. Biophys. Acta 765 (1984) 370–379). In contrast to their work, it is found that most hyperfine interaction is due to the methylene group at ring position 5 and to both hydroxyl groups. One of the hydroxyl groups shows bond bending of 35°. We presume that this is due to hydrogen bonding and that this bond stabilizes the antisymmetric orbital of the π-electrons.     

Heme complexes of rabbit hemopexin,human hemopexin and human serum albumin: Electron spin resonance and Mőssbauer spectroscopic studies

The electron spin resonance (ESR) spectra of human and rabbit ferriheme-hemopexin complexes at 30^oK show an ESR absorption characterized by g_x = 1.60, g_y = 2.25 and g_z = 2.86, characteristic of low-spin ferriheme-proteins. The low-spin nature of the heme-iron in heme-hemopexin is corroborated by the observation of nuclear hyperfine splitting in M?ssbauer spectra at 4.2^oK. The similarity of the ESR spectra of ferriheme-hemopexin with those of low-spin cytochromes which coordinate heme via two histidine residues points to a similar coordination mechanism in hemopexin. In contrast, the ESR spectra of the 1:1 and 2:1 complexes of heme with human serum albumin display signals at g = 6.0 and g = 2.0, characteristic of high-spin ferrihemeproteins.     

Poduction of free radicals from phenol and tocopherol by bleomycin-iron(II) complex.

Oxygen-bubbling of 1:1 bleomycin(BLM)-Fe(II) complex efficiently generates hydroxy radical which is inhibited by catalase. Hydroxy radical produced from BLM-Fe(II)-O₂ system oxidizes 2,6-di-tert-butyl-p-cresol and α-tocopherol to form the corresponding phenoxy and tocopheroxyl radicals, respectively. These free radicals were identified by the ESR hyperfine structures.     

Electron spin resonance spectra of penta- and hexacoordinated nitrosyl iron protoporphyrin IX complexes

Electron spin resonance (ESR) spectra of frozen aqueous solutions of NO · haem · base complexes and NO · haem intercalated into dodecyl sulfate micelles have been measured at 77 K and analyzed for the hyperfine components of ¹⁵NO,¹⁴N-base, ¹⁴N-pyrroles and ⁵⁷Fe which coincide with the principal directions of the g tensor. The influence of the basicity of the nitrogen base on the spin distribution and geometry of the Fe-N-O grouping has been demonstrated by replacing imidazole for pyridine and by comparing the ESR spectra with those obtained for the monomeric insect haemoglobin CTT IV.The comparison of the hyperfine parameters described for the so-called pentacoordinated nitrosyl complex of CTT IV with those of the NO · haem intercalated into detergent micelles has furnished evidence that the ESR spectrum of this conformation state of haemoglobin has to be definitely assigned to a pentacoordinated nitrosyl complex.The a_zz values increase with the following orders: CTT IV (2.98 mT) < imidazole complex (3.04mT) < pyridine complex (3.15mT) for ¹⁵NO, and pyridine complex (0.59 mT) < imidazole complex (0.67 mT) < CTT IV (0.70 mT) for the ¹⁴N-base. This result is in conformity with an increase of the donor and the acceptor strengths of the nitrogen base in trans-position to ¹⁵NO. The a_yy and a_xx components of ¹⁵NO and the ¹⁴N-base are strongly nonequivalent in the nitrosyl haemoglobin CTT IV, and less nonequivalent in the NO · haem · pyridine complex, indicating bending of the Fe-N-O grouping. The hyperfine components of the axial ligands coinciding with the x and y component of the g tensor are nearly equal for the NO · haem · imidazole complex.     

Evidence for a new early acceptor in Photosystem I of plants. An ESR investigation of reaction center triplet yield and of the reduced intermediary acceptors

The yield of the triplet state of the primary electron donor of Photosystem I of photosynthesis (P^T-700) and the characteristic parameters (g value, line shape, saturation behavior) of the ESR signal of the photoaccumulated intermediary acceptor A have been measured for two types of Photosystem I subchloroplast particles: Triton particles (TSF 1, about 100 chlorophyll molecules per P-700) that contain the iron-sulfur acceptors F_X, F_B and F_A, and lithium dodecyl sulfate (LDS) particles (about 40 chlorophyll molecules per P-700) that lack these iron-sulfur acceptors. The results are: (i) In Triton particles the yield of P^T-700 upon illumination is independent of the redox state of A and of F_X,B,A and is maximally about 5% of the active reaction centers at 5 K. The molecular sublevel decay rates are k_x = 1100 s^?1 ± 10%, k_y = 1300 s^?1 ± 10% and k_z = 83 s^?1 ± 20%. In LDS particles the triplet yield decreases linearly with concentration of reduced intermediary acceptors, the maximal yield being about 4% at 5 K assuming full P-700 activity. (ii) In Triton particles the acceptor complex A consists of two acceptors A₀ and A₁, with A₀ preceding A₁. In LDS particles at temperatures below ?30°C only A₀ is photoactive. (iii) The spin-polarized ESR signal found in the time-resolved ESR experiments with Triton particles is attributed to a polarized P-700-A^?₁ spectrum. The decay kinetics are complex and are influenced by transient nutation effects, even at low microwave power. It is concluded that the lifetime at 5 K of P-700A₀A^?₁ must exceed 5 ms. We conclude that P^T-700 originates from charge recombination of P-700A^?₀, and that in Triton particles A₀ and A₁ are both photoaccumulated upon cooling at low redox potential in the light. Since the state P-700AF^?_X does not give rise to triplet formation the 5% triplet yield in Triton particles is probably due to centers with damaged electron transport.     

Epr detection of endogenous nitric oxide in postischemic heart using lipid and aqueous-soluble dithiocarbamate-iron complexes

Spin-trapping techniques combined with electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (·NO) production were compared in the ischemic-reperfused myocardium for the first time, using both aqueous-soluble and lipophilic complexes of reduced iron (Fe) with dithiocarbamate derivatives. The aqueous-soluble complex of Fe and N-methyl-D-glucamine dithiocarbamate (MGD) formed MGD2-Fe-NO complex with a characteristic triplet EPR signal (a_N12.5 G and g_iso = 2.04) at room temperature, in native isolated rat hearts following 40 min global ischemia and 15 min reperfusion. Diethyldithiocarbamate (DETC) and Fe formed in ischemic-reperfused myocardium the lipophilic DETC2-Fe-NO complex exhibiting an EPR signal (g = 2.04 and g = 2.02 at 77K) with a triplet hyperfine structure at g. Dithiocarbamate-Fe-NO complexes detected by both trapping agents were abolished by the ·NO synthase inhibitor, N^G-nitro-L-arginine methyl ester. Quantitatively, both trapping procedures provi ded similar values for tissue ·NO production, which were observed primarily during ischemia. Postischemic hemodynamic recovery of the heart was not affected by the trapping procedure. (Mol Cell Biochem 175: 91–97, 1997)     

Oxidation-Reduction Reactions of Iron Bleomycin in the Absence and Presence of DNA

Using the pulse radiolysis technique, we have demonstrated that bleomycin-Fe(III) is stoichiometrically reduced by CO₂^? to bleomycin-Fe(II) with a rate of (1.9 ± 0.2) × 10⁸M^?1s^?1. In the presence of calf thymus DNA, the reduction proceeds through free bleomycin-Fe(III) and the binding constant of bleomycin-Fe(III) to DNA has been determined to be (3.8 ± 0.5) x 10⁴ M^?1. It has also been demonstrated that in the absence of DNA O₂^?1 reacts with bleomycin-Fe(III) to yield bleomycin-Fe(II)O₂, which is in rapid equilibrium with molecular oxygen, and decomposes at room temperature with a rate of (700 ± 200) s^?1. The resulting product of the decomposition reaction is Fe(III) which is bound to a modified bleomycin molecule. We have demonstrated that during the reaction of bleomycin-Fe(II) with O₂, modification or self-destruction of the drug occurs, while in the presence of DNA no destruction occurs, possibly because the reaction causes degradation of DNA.     

Electron Spin Resonance Analysis of the Nitroxide Spin Label 2,2,6,6-Tetramethylpiperidone-N-Oxyl (Tempone) in Single Crystals of the Reduced Tempone Matrix

The nitroxide spin label Tempone (2,2,6,6-tetramethylpiperidone-N-oxyl) can be reduced with ascorbic acid to give a nonparamagnetic species. Single crystals of reduced Tempone serve as a suitable host matrix to orient trace quantities of Tempone for ESR analysis. In these crystals the majority of the Tempone molecules are well-oriented, but a smaller fraction of the molecules tumble freely to give an isotropic electron spin resonance (ESR) spectrum. ESR transitions for the oriented molecules are saturated at much lower microwave power levels than for the tumbling molecules. For the oriented molecules, an analysis of the anisotropy of the spectroscopic splitting factor (g) gives principal values of g₁ = 2.0094, g₂ = 2.0061, g₃ = 2.0021. The hyperfine coupling tensor is nearly axially symmetric, with principal values (in gauss) of A₁ = 6.5, A₂ = 6.7, A₃ = 33.0. Within experimental error, the principal axis systems for the g tensor and the hyperfine tensor are identical. Comparison of the average values of g and A with the isotropic values of these parameters for Tempone in solvents of different polarity suggests a method for choosing the most appropriate tensor elements to be used for spin label experiments in various solvent systems.     

On the nature of the g = 6 EPR signal in isolated cytochrome b6f complex from spinach chloroplasts

Cytochrome b₆ in freshly prepared, active cytochrome t₆f complex from spinach chloroplasts shows a broad, low-spin EPR signal around g_z = 3.6. Maximally half of the hemes of cytochrome b₆ can be changed to high spin with a signal at g = 6 by inactivating treatments, or by isolating cytochrome b₆. In this state the heme reacts with NO. Reduction rates suggest that it is the low-potential heme which changes. The change is accompanied by the loss of the shift in the g_y signal of the Rieske FeS-center by quinone analogs.     

Copper complexes with new oxaaza-pendant-armed macrocyclic ligands: X-ray crystal structure of a macrocyclic copper(II) complex

The synthesis of new oxaaza macrocyclic ligands (2-4) derived from O¹,O⁷-bis(2-formylphenyl)-1,4,7-trioxaheptane and functionalized tris(2-aminoethyl)amine are described. Mononuclear copper(II) complexes were isolated in the reaction of the corresponding macrocyclic ligand and copper(II) perchlorate. The structure of the [Cu(2)](ClO₄)₂ complex was determined by X-ray diffraction analysis. The copper(II) ion is five-coordinated by all N₅ donor atoms, efficiently encapsulated by the amine terminal pendant-arm, with a trigonal-bipyramidal geometry. The complexes are further characterized by UV-Vis, IR and EPR studies. The electronic reflectance spectra evidence that the coordination geometry for the Cu(II) complexes is trigonal-bipyramidal with the ligands 1 and 2 or distorted square-pyramidal with the ligands 3 and 4. The electronic spectra in MeCN solutions are different from those in the solid state, which suggest that some structural modification may occur in solution. The EPR spectrum of powder samples of the copper complex with 2 presents axial symmetry with hyperfine split at g_// with the copper nuclei (I = 3/2), which is characteristic of weakly exchange coupled extended systems. The EPR parameters (g_// = 2.230, A_// = 156 × 10⁻⁴ cm⁻¹ and g_⊥ = 2.085) indicate a d_x²-y² ground state. The EPR spectra of the complexes with ligands 3 and 4 show EPR spectra with a poorly resolved hyperfine structure at g_//. In contrast, the complex with ligand 2 shows no hyperfine split and a line shape which was simulated assuming rhombic g-tensor (g₁ = 2.030, g₂ = 2.115 and g₃ = 2.190).     

Transition metal complexes of a tridentate ligand bearing two pendant pyridine bases: The X-ray crystal structure of pentacoordinate copper(II) complex

The synthesis of a tridentate ligand, N,N′-bis(2-pyridinyl)-2,6-pyridinedicarboxamide [H₂L] is described together with its manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes which were characterized based on elemental analysis, conductivity measurements, spectral, magnetic and thermal studies. The IR spectral studies of all the complexes exhibit a similar feature about the ligating nature of the ligand to the metal ions and revealed that the ligand has coordinated through the nitrogens of the deprotonated amides and the central pyridine. The two pendant pyridine nitrogens in all the complexes are protonated and involved in hydrogen bonding with the oxygens of amide groups. This observation is confirmed by the single-crystal X-ray crystallographic studies of copper(II) complex. The geometry around the copper atom can be viewed as a distorted trigonal bipyramid with τ = 0.74 [structural parameter, τ = (β − α)/60; where α and β are the two basal angles in a five coordinate complex]. The electrochemical study of the copper(II) complex shows single quasi-reversible redox peak [Cu(II) ↔ Cu(I)]. The EPR spectrum of copper(II) complex exhibits rhombic pattern [g₁ = 2.0276, g₂ = 2.0926 and g₃ = 2.18].     

The interaction between heme and protein in cytochrome c1

The optical spectrum of reduced bovine cytochrome c₁ at 77 K shows a fine splitting of the β-band, which is indicative of the native conformation of the protein. At room temperature, this conformation is reflected in an absorbance band at 530 nm. The exposure of the heme of ferrocytochrome c₁, investigated by means of solvent-perturbation spectroscopy, appears to be extremely sensitive to temperature and SH reagents bound to the oxidized protein. Addition of combinations of potential ligands to the isolated tryptic heme peptide of cytochrome c₁ reveals that only a mixture of methionine and cysteine (or their equivalents) generates a β-band at 77 K which is identical in shape to that of native cytochrome c₁. In the EPR spectrum of a complex of ferrocytochrome c₁ and nitric oxide at pH 10.5, no hyperfine splitting derived from a second ligated nitrogen atom could be detected. The results indicate that methionine and cysteine are the axial ligands of heme in cytochrome c₁. The EPR spectrum of isolated ferricytochrome c₁ is that of a low-spin heme iron compound with a g_z value of 3.36 and a g_y value of 2.04.     

ESR Parameters for Cupric Bleomycin in the Mobilized State

Abstract

The configuration of the copper complex of the glycopeptide bleomycin, CuBlm, is presumed to be pyramidal square planar from a previous X-ray structural determination of a fragment of cupric bleomycin. This study presents evidence for a difference in the ESR parameters for cupric bleomycin in the liquid as opposed to the solid state. A decrease in A_iso for CuBlm in the liquid state can be directly surmised from the low frequency S-band spectrum for which three of the four cupric hyperfine lines are partially resolved. Computer simulated spectra infer that the absolute value of A_∥ increases about 100 MHz and the value of A_⊥ may change sign for CuBlm in the liquid state. Simulations using a rotational correlation time of about 250 psec. indicate that CuBLM may not be spherical in the liquid phase. The fastest component for anisotropic motion could dominate and account for the well resolved cupric hyperfine structure. Furthermore, it is argued from an analysis of the cupric hyperfine coupling constants that the CuBlm structure opens up at room temperature and that the cupric ion is displaced from the square plane.

Supported by NIH Grants Ca-22184 and RR-01008 and the University of Wisconsin-Milwaukee.     

Electron-spin resonance of nitrosyl haemoglobins: normal alpha and beta chains and mutants Hb M Iwate and Hb Zürich.

At 77 K the electron spin resonance (ESR) spectra of the NO derivatives of the mutant haemoglobins Hb M Iwate and Hb Zurich as well as of the isolated chains of normal haemoglobin were studied. Two types of ESR spectra differing in the g-value and the hyperfine splitting at gzz were observed. The type II spectrum is characterized by a hyperfine structure at gzz = 2.005 with a splitting constant of deltaH = 23 G (14NO) or 32 G (15NO), respectively. In the type I spectrum the splitting constant of the hyperfine structure at gzz = 2.009 amounts to deltaH = 18 G (14NO) or 23 G (15NO), respectively. In some cases this hyperfine structure is coincident with another one at gxx = 2.064 with nearly identical splitting constant. In addition, the type I spectrum is characterized by an increased ESR absorption at gxx = 2.064. At neutral pH the NO derivatives of the isolated chains as well as of the mutant haemoglobins give rise to a type II spectrum. In correspondence with previous results gained with normal NO haemoglobin, the ESR spectra of the NO-alpha chains and NO-Hb Zurich show a transition to type I in the acid region. This transition is favoured by binding of 2,3-bisphosphoglycerate. On the other hand, the ESR spectra of the NO-beta chains and NO-Hb M Iwate are of the type II also at acid pH. The NO-beta chains show a transition of the ESR spectrum from type II to type I only at alkaline pH. These results indicate that in the tetrameric NO haemoglobin only the alpha chains are responsible for the transition of the ESR spectrum from type II to type I in the acid region. The two types of ESR spectra are interpreted in terms of two kinds of haem-NO complexes differing in the iron-NO and iron-imidazole distances. The type II spectrum is attributed to a complex with a relatively short iron-imidazole distance which is responsible for a weakened sigma-bond in trans position. The type I spectrum arises then from a complex with a larger iron-imidazole bond leading to an approach of the NO molecule to the iron. The influence of the protein conformation upon the iron-imidazole bond length is discussed with regard to the ESR spectra of the mutant NO haemoglobins and considering the influence of agents modifying the protein structure.     

Spectroscopic studies on bleomycin-iron complexes with carbon monoxide, nitric oxide, isocyanide, azide, and cyanide and comparison with iron-porphyrin complexes

The bleomycin-iron complexes with CO, NO, C2H5NC, OH-, N-3, CN-, and CH3NH2 were characterized by electronic, ESR, 1H-NMR, and M?ssbauer spectroscopies and the findings were compared with the corresponding hemoprotein complexes. The 1H-NMR and M?ssbauer features for the CO and C2H5NC adducts of the bleomycin-Fe(II) complex are consistent with an S = 0 ferrous assignment. The OH-, CH3NH2, and N-3 adducts of the bleomycin-Fe(III) complex show the ESR, 1H-NMR, and M?ssbauer spectra typical of a low-spin Fe(III). The unique M?ssbauer parameters of the bleomycin-Fe(II)-NO complex demonstrate mixing between the NO pi- and the Fe 3d-orbitals. The magnitude of the proton chemical shifts over +/- 50 ppm indicates a high-spin ferric type for the bleomycin-Fe(III)-CN complex. The M?ssbauer parameters (delta EQ = 0.89 and delta = 0.48 mm/s) of the CN- adduct differ substantially from those of typical low-spin hemoprotein-cyanide complexes. Except for the CN- adduct, the M?ssbauer and crystal field parameters of these bleomycin-iron complexes are similar to those of the corresponding hemoprotein complexes.     

A unique Cu(II) bis(chlorido)-bridged linear chain compound with 2-amino-5-nitropyrimidine as a bifunctional axial ligand: Synthesis, characterization, crystal structure and hydrogen-bonding system

The first linear bis(chlorido)-bridged Cu(II) compound with the ligand 2-amino-5-nitropyrimidine (abbreviated as anpyr), [Cu(μ-Cl)₂(anpyr)₂]_n, has been synthesized and fully characterized by spectroscopy, EPR and X-ray structure analysis. The basal plane around the Cu(II) ion is formed by two chloride anions with a Cu-Cl distance of 2.2513(6) Å and two nitrogen atoms of two trans-located anpyr ligands with a Cu-N distance of 2.068(2) Å. The apical positions of the distorted octahedral geometry are formed by two Cl anions of a neighbouring unit with a distance of 2.8690(8) Å. The Cu-Cl-Cu angle is 94.75(3)°, while the Cu-Cu distance is 3.791 Å. The Cu-bis-μ-chlorido-Cu array provides in this way a 2D linear chain.A neighbouring pair of symmetry-related polynuclear chains is linked through hydrogen bonds with a N···N distance 3.027(3) Å, forming into a kind of Watson-Crick-like pair of hydrogen bonds. Another H-bond is formed by the amine nitrogen to one of the chloride anions with a N···Cl distance 3.248(2) Å.The EPR powder spectrum appears as rhombic with g₁ 2.20, g₂ 2.12; g₃ 2.05, with unresolved hyperfine splittings. Analysis of the magnetic susceptibility measurements, recorded from 2 to 300 K, indicates a very weak antiferromagnetic interaction between the metal ions (J = −2 cm⁻¹).