Comparison between the isocratic and gradient retention behaviour of polypeptides in reversed-phase liquid chromatographic environments.

The isocratic and gradient elution behaviour of beta-endorphin and glucagon, two polypeptides known to exist in amphipathic alpha-helical conformations in lipophilic environments, have been examined under reversed-phase high-performance liquid chromatographic (RP-HPLC) conditions with low pH, aquo-acetonitrile mobile phases. The effects of changes in the volume fraction, psi, of the organic solvent modifier and temperature, T, on the magnitudes of the S and log k(o) values of these two polypeptides, obtained from the plots of logarithmic capacity factor (log k') vs. psi using isocratic elution conditions have been determined. These data have then been compared to the corresponding S and log k(o) values, obtained from the plots of logarithmic median capacity factor (log k) versus the median volume fraction of the organic solvent modifier (psi) derived from the linear gradient elution data, using the same n-butyl silica sorbent and related aquo-acetonitrile mobile phase conditions. As apparent from these studies, substantial differences occur in the temperature-dependent trends and magnitudes of the corresponding S and S values, or the log k(o) and log k(o) values, when these parameters are derived from experimental data acquired by these two different elution methods. Moreover, when gradient elution data for beta-endorphin and glucagon are utilised, the extrapolated values of the intercept and slope of the plots of log k vs. 1/T (corresponding to an apparent change in the median enthalpy of association, deltaH(o)assoc, or an apparent change in the median entropy of association, deltaS(o)assoc) substantially deviated from the values obtained for the thermodynamic parameters, deltaH(o)assoc and deltaS(o)assoc, derived from the log k' vs. 1/T plots using the corresponding isocratic data. These findings thus have important implications for biophysical and thermodynamic investigations when gradient elution data are employed to assess the molecular basis of the interaction of polypeptides with non-polar ligates.     

Electrostatic docking of a supramolecular host-guest assembly to cytochrome c probed by bidirectional photoinduced electron transfer

A water-soluble octacarboxyhemicarcerand was used as a shuttle to transport redox-active substrates across the aqueous medium and deliver them to the target protein. The results show that weak multivalent interactions and conformational flexibility can be exploited to reversibly bind complex supramolecular assemblies to biological molecules. Hydrophobic electron donors and acceptors were encapsulated within the hemicarcerand, and photoinduced electron transfer (ET) between the Zn-substituted cytochrome c (MW = 12.3 kD) and the host-guest complexes (MW = 2.2 kD) was used to probe the association between the negatively charged hemicarceplex and the positively charged protein. The behavior of the resulting ternary protein-hemicarcerand-guest assembly was investigated in two binding limits: (1) when K(encaps) ? K(assoc), the hemicarcerand transports the ligand to the protein while protecting it from the aqueous medium; and (2) when K(assoc) > K(encaps), the hemicarcerand-protein complex is formed first, and the hemicarcerand acts as an artificial receptor site that intercepts ligands from solution and positions them close to the active site of the metalloenzyme. In both cases, ET mediated by the protein-bound hemicarcerand is much faster than that due to diffusional encounters with the respective free donor or acceptor in solution. The measured ET rates suggest that the dominant binding region of the host-guest complex on the surface of the protein is consistent with the docking area of the native redox partner of cytochrome c. The strong association with the protein is attributed to the flexible conformation and adaptable charge distribution of the hemicarcerand, which allow for surface-matching with the cytochrome.     

Effect of toluene in the dipolar interaction of some aliphatic alcohols

Sound velocity, density and viscosity values have been measured at 303 K in the three binary systems of toluene + methanol, ethanol, 1-propanol. From these data, acoustical parameters such as adiabatic compressibility, free length, free volume and internal pressure have been estimated using the standard relations. The results are interpreted in terms of molecular interaction between the components of the mixtures. Observed excess value in all the mixture indicates that the molecular symmetry existing in the system is highly disturbed by the non-polar toluene molecules and dipole–dipole type interactions exist in the systems.     

Examination of the binding behaviour of several proteins with the immobilized copper(II) complexes of o-, m- and p-xylylene bridged bis(1,4,7-triazacyclononane) macrocycles

Three new IMAC chelating systems, incorporating immobilised xylenyl-bridged bis(1,4,7-triaza-cyclonane) ligands, complexed with Cu(2+) ions to form binuclear species, have been prepared. Their binding properties have been investigated with three small globular proteins (hen egg white lysozyme, horse skeletal muscle myoglobin and horse heart cytochrome c). The effects of buffer pH, ionic strength and composition on the binding behaviour of these proteins to these new IMAC sorbents have been examined and compared with those found for the corresponding immobilized mononuclear copper complex of 1,4,7-triazacyclononane (tacn). Higher protein binding affinities were observed with the Cu(2+)-bis(tacn) sorbents compared to the Cu(2+)-tacn system, consistent with the immobilized binuclear copper(II) species undergoing enhanced coordinative interaction with the surface-exposed histidine residues of these proteins. Moreover, the protein binding characteristics of these IMAC sorbents at higher ionic strengths, such as 1M NaCl, also reflect the presence of the aromatic ring in the bis(tacn) ligands, whereby hydrophobic pi/pi stacking interactions can occur with the proteins.     

Effects of pH on protein association: modification of the proton-linkage model and experimental verification of the modified model in the case of cytochrome c and plastocyanin.

Effects of pH on protein association are not well understood. To understand them better, we combine kinetic experiments, calculations of electrostatic properties, and a new theoretical treatment of pH effects. The familiar proton-linkage model, when used to analyze the dependence of the association constant K on pH, reveals little about the individual proteins. We modified this model to allow determination not only of the numbers of the H+ ions involved in the association but also of the pK(a) values, in both the separate and the associated proteins, of the side chains that are responsible for the dependence of K on pH. Some of these side chains have very similar pK(a) values, and we treat them as a group having a composite pK(a) value. Use of these composite pK(a) values greatly reduces the number of parameters and allows meaningful interpretation of the experimental results. We experimentally determined the variation of K in the interval 5.4 < or = pH < or = 9.0 for four diprotein complexes, those that the wild-type cytochrome c forms with the wild-type plastocyanin and its mutants Asp42Asn, Glu59Gln, and Glu60Gln. The excellent fittings of the experimental results to the modified model verified this model and revealed some unexpected and important properties of these prototypical redox metalloproteins. Protein association causes a decrease in the pK(a) values of the acidic side chains and an increase in the pK(a) values of the basic side chains. Upon association, three carboxylic side chains in wild-type plastocyanin each release a H+ ion. These side chains in free plastocyanin have an anomalously high composite pK(a) value, approximately 6.3. Upon association, five or six side chains in cytochrome c, likely those of lysine, each take up a H+ ion. Some of these side chains have anomalously low pK(a) values, less than 7.0. The unusual pK(a) values of the residues in the recognition patches of plastocyanin and cytochrome c may be significant for the biological functions of these proteins. Although each mutation in plastocyanin markedly, and differently, changed the dependence of K on pH, the model consistently gave excellent fittings. They showed decreased numbers of H+ ions released or taken up upon protein association and altered composite pK(a) values of the relevant side chains. Comparisons of the fitted composite pK(a) values with the theoretically calculated pK(a) values for plastocyanin indicated that Glu59 and Asp61 in the wild-type plastocyanin each release a H+ ion upon association with cytochrome c. Information of this kind cannot readily be obtained by spectroscopic methods. Our modification of the proton-linkage model is a general one, applicable also to ligands other than H+ ion and to processes other than association.     

反气相色谱法表征漆酚钛螯合高聚物的表面性质

漆酚钛螯合高聚物(UTP)具有优异的耐强酸、耐强碱、耐盐类溶液、耐多种有机溶剂和耐热性能。为进一步扩大其应用领域提供理论和实验依据,采用反气相色谱法(IGC)测定了UTP在70、80、90、100和110 ℃下的表面色散自由能和表面Lewis酸碱常数。以正戊烷(C5)作为标定色谱死时间的探针分子,正己烷、正庚烷、正辛烷和正壬烷作为非极性探针分子,计算了不同温度下UTP的色散表面自由能;以四氢呋喃、丙酮和三氯甲烷作为极性探针分子,计算得到了UTP表面的酸碱作用吸附自由能和吸附焓。实验结果表明: 在70、80、90、100和110 ℃时UTP的色散表面自由能分别为37.68、33.53、35.92、24.01和31.32 mJ/m2; UTP为弱的Lewis碱,Lewis酸常数Ka为0.1853,碱常数Kb为0.9662。这一结果对研究漆酚金属螯合高聚物的表面性质与应用具有指导作用。     

Dissociation constants of organophosphinic acid compounds

The dissociation equilibria of di(2,4,4-trimethylpentyi) phosphinic acid, mono(2,4,4-trimethylpentyl) phosphinic acid, di(n-octyl)phosphinic acid and mono(n-octyl)phosphinic acid have been studied in ethanol-water mixtures by potentiometric titration at 25 degrees C. These data have been analysed both graphically numerically using the program LETAGROP-ZETA. The obtained pK(a) values have been correlated with the corresponding values in water, determined both indirectly by means of extraction measurements and by estimation using the suitable Hammett equation.     

亚甲蓝修饰电极推动的血红素蛋白质直接电子转移反应

本文研究了几种血红素蛋白质包括牛血红蛋白, 人肌红蛋白和马心细胞色素C在亚甲蓝修饰电极上的非均相电子转移反应, 采用光透薄层光谱电化学法监测了血红素蛋白的直接电化学反应过程, 并进行了动力学研究。     

Determination of the acid/base properties of MgY and NH4Y molecular sieves by inverse gas chromatography

The surface characterization of MgY and NH(4)Y zeolites was performed using inverse gas chromatography (IGC). The adsorption thermodynamic parameters (the standard enthalpy (DeltaH degrees ), standard entropy change (DeltaS degrees ), and free energy change of adsorption (DeltaG degrees ), the dispersive component of the surface free energies (gamma(S)(d)), and the acid-base character of the surface of MgY and NH(4)Y zeolites were estimated using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (DeltaG(sp)), the specific enthalpy of adsorption (DeltaH(sp)), and the specific entropy of adsorption (DeltaS(sp)) of polar probes on MgY and NH(4)Y zeolites were determined. The values of the DeltaH(sp) were correlated with both the donor and acceptor numbers of the probes to quantify the acidic K(A) and the basic K(D) parameters of the zeolite surfaces. The values obtained for the K(A) and K(D) parameters indicated a basic character for the surface of MgY and NH(4)Y zeolites.     

Orientational effect of surface-confined cyclodextrin on the inclusion of bisphenols

The molecular recognition of various kinds of bisphenols (BPs) and a bisphenol A-polymer conjugate (BPA-polymer) by a self-assembled monolayer (SAM) of thiolated beta-cyclodextrin (CD) on a gold electrode was examined using cyclic voltammetry (CV). Based on the inhibitory effect of BPs on the inclusion of hydroquinone (HQ) as a probe by the surface-confined CD, the association constants (K(assoc)) of BPs with the immobilized beta-CD were estimated. The K(assoc) values for BPs with the SAM of 3-dithiobis(undecanoylamido)-3-deoxy-beta-cyclodextrin (DTUA-beta-CD) were smaller than those in the free beta-CD system reported previously. A similar tendency was obtained when 6-(lipoylamido)-6-deoxy-beta-cyclodextrin (LP-beta-CD) was used in place of DTUA-beta-CD. The K(assoc) values for all the BPs except for bisphenol B with the SAM of LP-beta-CD were always larger than those with the SAM of DTUA-beta-CD, due to a difference in the orientation of the beta-CD moiety in the SAMs. Furthermore, adsorption and desorption processes of the BPA-polymer from the surface-confined beta-CD was followed using local surface plasmon resonance spectroscopy.     

Investigation of efflorescence of inorganic aerosols using fluorescence spectroscopy

The phase transition is one of the most fundamental phenomena affecting the physical and chemical properties of atmospheric aerosols. Efflorescence, in particular, is not well understood, partly because the molecular interactions between the solute and water molecules of saturated or supersaturated solution droplets have not been well characterized. Recently, we developed a technique that combines the use of an electrodynamic balance and a fluorescence dye, 8-hydroxyl-1,3,6-pyrenetrisulfonate (pyranine), to study the distributions of solvated and free water in aqueous droplets (Choi, M. Y.; Chan, C. K.; Zhang, Y. H. J. Phys. Chem. A 2004, 108, 1133). We found that the equality of the amounts of solvated and free water is a necessary but not sufficient condition for efflorescence. For efflorescing compounds such as Na2SO4, (NH4)2SO4, and a mixture of NaCl and Na2SO4, the amount of free water decreases, while that of solvated water is roughly constant in bulk measurements and decreases less dramatically than that of free water in single-particle measurements as the relative humidity (RH) decreases. Efflorescence of the supersaturated droplets of these solutions occurs when the amounts of free and solvated water are equal, which is consistent with our previous observation for NaCl. For nonefflorescing compounds in single-particle levitation experiments such as MgSO4 and Mg(NO3)2, the amounts of free and solvated water are equal at a water-to-solute molar ratio of about 6, at which spectral changes due to the formation of contact ion pairs between magnesium and the anions occur as shown by Raman spectroscopy. Fluorescence imaging shows that the droplets of diluted Mg(NO3)2 (at 80% RH) and MgSO4 are homogeneous but those of NaCl, Na2SO4, (NH4)2SO4, and supersaturated Mg(NO3)2 (at 10% RH) are heterogeneous in terms of the solvated-to-free water distribution. The solvated-to-free water ratios in NaCl, Na2SO4, and (NH4)2SO4 droplets are higher in the outer regions by about half a radius deep than at the center of the droplets.     

Providing a chemical basis toward understanding the histidine base-on motif of methylcobalamin-dependent methionine synthase: an improved purification of methylcobinamide,plus thermodynamic studies of methylcobinamide binding exogenous imidazole and pyridine bases

Reported herein are the synthesis and improved purification of MeCbi(+).BF(4)(-) leading to 95% pure product. The availability of this higher purity MeCbi(+).BF(4)(-) has, in turn, allowed a study of the K(assoc), DeltaH, and DeltaS for exogenous imidazole and pyridine bases binding to MeCbi(+) in ethylene glycol and buffered aqueous solution. The results show that (1) the bases studied have larger K(assoc) values (where measurable) when binding to MeCbi(+) than when binding to AdoCbi(+) under analogous conditions; (2) comparison of the thermodynamic binding parameters for py and N-MeIm show that these bases bind similarly, within experimental error to MeCbi(+), contrary to what was seen earlier with AdoCbi(+); (3) the bases follow the expected trend, with the base with the highest pK(a) of those studied, 4-Me(2)Npy, exhibiting the highest K(assoc) value (K(assoc)(25 degrees C) = 18.0 +/- 0.3 M(-1)) and the base of lowest pK(a), py, exhibiting the lowest detectable K(assoc) value (K(assoc) (25 degrees C) = 6.2 +/- 0.4 M(-1)); (4) there is no detectable binding (K(assoc) = 0.07 M(-1)) for 2-Mepy or 2,6-Me(2)py with MeCbi(+); and (5) the base that is closest to the biologically relevant axial His759 residue in methionine synthase, N-MeIm, exhibits an unusual DeltaH value for the formation of MeCbi(+).N-MeIm, results interpreted as offering further support for the presence of sigma plus pi effects when imidazole bases bind to alkylcobinamides. The results of these studies allow the percentage of base-on methylcobinamide, MeCbi(+).base, to be calculated as a function of temperature and added base. As such, they provide necessary background information for RS(-) + MeCbi(+).base and other methionine synthase chemical precedent studies.     

Dielectric investigation of the tetrahydrofuran+caprylic acid system

Dielectric studies have been carried out for the binary mixture of tetrahydrofuran (THF) with caprylic acid at temperatures 303, 308, 313 and 318?K. The Kirkwood correlation factors, excess permittivity and excess free energy of the mixture were found through dielectric measurements for different concentrations of the system. Analysis of these parameters reveals the existence of H-bonded heterogeneous molecular aggregates in the mixture. Parallel alignment of dipoles of the complex in THF region has been identified.     

Single ion activities in aqueous sulfuric acid solutions: A new extra-thermodynamic assumption

Single ion activities in aqueous H₂SO₄ have been calculated from the mean ionic activity coefficients of H₂SO₄, the solubilities of PbSO₄ and the degrees of the second dissociation of H₂SO₄ in these solutions by employing a new extra-thermodynamic assumption. The hydrogen ion activities thus obtained are compared with the corresponding acidity function values based on different classes of acid-base indicators.     

A molecular flytrap for the selective binding of citrate and other tricarboxylates in water

The synthesis and binding properties of a new tricationic guanidiniocarbonyl pyrrole receptor 7 are described. Receptor 7 binds citrate 9 and other tricarboxylates such as trimesic acid tricarboxylate 8 with unprecedented high association constants of K(assoc) > 10(5) M(-1) in water as determined by UV and fluorescence tritration studies. According to NOESY experiments and molecular modeling calculations, the tricarboxylates are bound within the inner cavity of receptor 7 by ion pairing between the carboxylate groups and the guanidiniocarbonyl pyrrole moieties, favored by the nonpolar microenvironment of the cavity. Hence, receptor 7 can be regarded as a molecular flytrap. In the case of the aromatic tricarboxylate 8, additional aromatic interactions further strengthen the complex. The complexes with the tricarboxylates are so strong that even the presence of a large excess of competing anions or buffer salts does not significantly affect the association constant. For example, the association constant for citrate changes only from K(assoc) = 1.6 x 10(5) M(-1) in pure water to K(assoc) = 8.6 x 10(4) M(-1) in the presence of a 170-fold excess of bis-tris buffer and a 1000-fold excess of chloride. This makes 7 one of the most efficient receptors for the binding of citrate in aqueous solvents reported thus far.     

Free energy decomposition analysis of bonding and nonbonding interactions in solution

A free energy decomposition analysis algorithm for bonding and nonbonding interactions in various solvated environments, named energy decomposition analysis-polarizable continuum model (EDA-PCM), is implemented based on the localized molecular orbital-energy decomposition analysis (LMO-EDA) method, which is recently developed for interaction analysis in gas phase [P. F. Su and H. Li, J. Chem. Phys. 130, 074109 (2009)]. For single determinant wave functions, the EDA-PCM method divides the interaction energy into electrostatic, exchange, repulsion, polarization, desolvation, and dispersion terms. In the EDA-PCM scheme, the homogeneous solvated environment can be treated by the integral equation formulation of PCM (IEFPCM) or conductor-like polarizable continuum model (CPCM) method, while the heterogeneous solvated environment is handled by the Het-CPCM method. The EDA-PCM is able to obtain physically meaningful interaction analysis in different dielectric environments along the whole potential energy surfaces. Test calculations by MP2 and DFT functionals with homogeneous and heterogeneous solvation, involving hydrogen bonding, vdW interaction, metal-ligand binding, cation-π, and ionic interaction, show the robustness and adaptability of the EDA-PCM method. The computational results stress the importance of solvation effects to the intermolecular interactions in solvated environments.     

Protein-ligand binding free energy estimation using molecular mechanics and continuum electrostatics. Application to HIV-1 protease inhibitors

A method is proposed for the estimation of absolute binding free energy of interaction between proteins and ligands. Conformational sampling of the protein-ligand complex is performed by molecular dynamics (MD) in vacuo and the solvent effect is calculated a posteriori by solving the Poisson or the Poisson-Boltzmann equation for selected frames of the trajectory. The binding free energy is written as a linear combination of the buried surface upon complexation, SASbur, the electrostatic interaction energy between the ligand and the protein, Eelec, and the difference of the solvation free energies of the complex and the isolated ligand and protein, deltaGsolv. The method uses the buried surface upon complexation to account for the non-polar contribution to the binding free energy because it is less sensitive to the details of the structure than the van der Waals interaction energy. The parameters of the method are developed for a training set of 16 HIV-1 protease-inhibitor complexes of known 3D structure. A correlation coefficient of 0.91 was obtained with an unsigned mean error of 0.8 kcal/mol. When applied to a set of 25 HIV-1 protease-inhibitor complexes of unknown 3D structures, the method provides a satisfactory correlation between the calculated binding free energy and the experimental pIC5o without reparametrization.     

On the molecular origins of volumetric data

We use a statistical thermodynamic approach and a simple thermodynamic model of hydration to examine the molecular origins of the volumetric properties of solutes. In this model, solute-solvent interactions are treated as a binding reaction. The free energy of hydration of the noninteracting solute species coincides with the free energy of cavity formation, while the free energy of solute-solvent interactions is given by the binding polynomial. By differentiating the relationship for the free energy of hydration with respect to temperature and pressure, one obtains the complete set of equations describing the thermodynamic profile of hydration, including enthalpy, entropy, volume, compressibility, expansibility, and so forth. The model enables one to rigorously define in thermodynamic terms the hydration number and the related concept of hydration shell, which are both widely used as operational definitions in experimental studies. Hydration number, nh, is the effective number of water molecules solvating the solute and represents the derivative of the free energy of hydration with respect to the logarithm of water activity. One traditional way of studying hydration relies on the use of volumetric measurements. However, microscopic interpretation of macroscopic volumetric data is complicated and currently relies on empirical models that are not backed by theory. We use our derived model to link the microscopic determinants of the volumetric properties of a solute and its statistical thermodynamic parameters. In this treatment, the partial molar volume, V degrees, of a solute depends on the cavity volume, hydration number, and the properties of waters of hydration. In contrast, the partial molar isothermal compressibility, K degrees T, and expansibility, E degrees, observables, in addition to the intrinsic compressibility and expansibility of the cavity enclosing the solute, hydration number, and the properties of waters of hydration, contain previously unappreciated relaxation terms that originate from pressure- and temperature-induced perturbation of the equilibrium between the solvated solute species. If significant, the relaxation terms may bring about a new level of nonadditivity to compressibility and expansibility group contributions that goes beyond the overlap of the hydration shells of adjacent groups. We apply our theoretical results to numerical analyses of the volume and compressibility responses to changes in the distribution of solvated species of polar compounds.     

Standard free energy of releasing a localized water molecule from the binding pockets of proteins: double-decoupling method

Localized water molecules in the binding pockets of proteins play an important role in noncovalent association of proteins and small drug compounds. At times, the dominant contribution to the binding free energy comes from the release of localized water molecules in the binding pockets of biomolecules. Therefore, to quantify the energetic importance of these water molecules for drug design purposes, we have used the double-decoupling approach to calculate the standard free energy of tying up a water molecule in the binding pockets of two protein complexes. The double-decoupling approach is based on the underlying principle of statistical thermodynamics. We have calculated the standard free energies of tying up the water molecule in the binding pockets of these complexes to be favorable. These water molecules stabilize the protein-drug complexes by interacting with the ligands and binding pockets. Our results offer ideas that could be used in optimizing protein-drug interactions, by designing ligands that are capable of targeting localized water molecules in protein binding sites. The resulting free energy of ligand binding could benefit from the potential free energy gain accompanying the release of these water molecules. Furthermore, we have examined the theoretical background of the double-decoupling method and its connection to the molecular dynamics thermodynamic integration techniques.     

New types of the flexible self-assembled metal-organic coordination polymers constructed by aliphatic dicarboxylates and rigid bidentate nitrogen ligands

The reaction of metal ions, flexible aliphatic dicarboxylates and rigid bidentate linear ligands under mild conditions in water afford four novel metal-organic coordination polymers, [Cd(mu-mal)(mu-pyz)(0.5)(H(2)O)](n) 1 (mal = malonate dianion, pyz = pyrazine), [Cd(2)(mu-suc)(2)(mu-pyz)(H(2)O)(2)](n) 2 (suc = succinate dianion), and ([M(mu-bipy)(H(2)O)4][suc].4H(2)O)(n)(M = Co, 3, M = Zn, 4, bipy = 4,4'-bipyridine). The molecular structures of 1-4 have been established by single-crystal X-ray crystallography. 1 is a 3D network being composed of layers of octahedrally coordinated Cd atoms bridged by malonate anions in syn-anti configurations within the layers and pyz molecules between layers. Unlike that in 1, each Cd atom in 2 displays uncommon pentagonal-bipyramidal geometry to form 2D infinite grid sheets with square grid dimensions of ca. 7.936 x 7.936 [Angstrom]. Both 3 and 4 exhibit 1D linear -M-bipy-M-bipy- chain polymers, and these chains were packed as ...ABCABC... layered structures. The bridging succinate ligands in 2 adopt the syn-anti mode with a torsion angle of 60.8(7) degrees, while the solvated succinate ligands in 3 and 4 adopt the anti-anti mode with a torsion angle of 180.0 degrees. To our knowledge, compound 2 represents the first example of flexible self-assembled succinate-pyrazine mixed bridging ligand coordination network. 3 and 4 are the first two cases of succinate-bipy polymers with non-coordinated succinate. The magnetic behavior for 3 was studied in the temperature range of 5-300 K. The result indicates the occurrence of a weak antiferromagnetic coupling between the cobalt(II) ions.