Effect of Complexes of Zinc, Cobalt and Copper With D-Aminosugars on the Replication of Herpes Simplex Virus Type 1 (HSV-1)

Our previous results show that Zn(pic)(2) and Zn(asp)(2) inhibit key steps of the replication of HSV-1. Anti-HSV effect of complexes of Co(II) with aminoacids Lys and Ser was also found. In the present study we describe the effect of complexes of Zn(II), Co(II) and Cu(II) with D-aminosugars on the replication of HSV-1 and on the infectivity of free virions. The experiments were done using primary rabbit kidney cells (r.k.), diploid human embryonal fibroblasts (F) and Vero cells. No differences in the toxicity of metal complexes on diploid cells- r.k. and F, were found. Neither metal complexes, nor ligands-galactosoxime and glucosoxime, influenced the viral replication. During 1-4h prolonged contact only Cu(Gl.NOH)(2) inactivated HSV-1 virions up to 90%. The results show that D-aminosugars are not suitable ligands for Zn(II), Cu(II) and Co(II) in respect of the inhibition of viral replication. However, only Cu(Gl.NOH)(2) was able to inhibit the infectivity of free virions.     

Zinc(II) Complexes - A New Group of Non-Mutagenic Herpes Simplex Virus Inhibitors

Former studies showed that complexes of Zn(II) with picolinic and with aspartic acids, Zn(pic)(2) and Zn(asp)(2), are able to inhibit HSV infection in cultured cells by affecting key steps of virus replication. As these complexes are candidates for a novel class anti-HSV drugs, further studies on their mutagenicity are of particular interest. In the present paper we present data showing that Zn(pic)(2) and Zn(asp)(2) do not express mutagenic effect in both prokaryotic (Salmonella typhimurium) and eukaryotic (Saccharomices cerevisiae) test systems.     

Effect of Complexes of Cobalt With Aminoacids on the Replication of Herpes Simplex Virus Type 1 (HSV-1)

Cobalt, being essential metal, influences different physiological and enzymatic functions. As cobalt does not accumulate in the body, Co-compounds have relatively low toxicity. The aim of the present study is the effect of complexes of Co(II) with aminoacids - lysine, arginine, histidine and serine on HSV-1 replication. No effect of [O(2)Co(his)(4)].nH(2)O and [O(2)Co(arg)(2)].nH(2)O on HSV-1 infection in vitro was found. Both, [O(2)Co(lys)(2)].nH(2)O and [O(2)Co(ser)(2)].nH(2)O suppress the attachement of HSV-1 particles onto target cells and the viral replication as well. Moreover, the properties of the particular Co-complex (charge, stability, structure) are manifestated by their virucidal effect. Thus, [O(2)Co(ser)(2)].nH(2)O irreversibly inhibits the infectious activity of free HSV-1 virions, while virucidal effect of [O(2)Co(lys)(2)].nH(2)O is completely reversible after the 2h of contact.     

Dissociative pathway of the [Pd(2,2′-bipyridyl)(2-picoline)2]2+ cation

Pyridines of C_s symmetry coordinated to [Pd(bipy)(pyr)₂]²⁺ cations (bipy = 2,2′-bipyridyl; pyr = substituted pyridines) lead to syn and anti isomers due to their perpendicular orientation. Rate constants of syn–anti isomerizations of [Pd(bipy)(2pic)₂]²⁺ (2pic = 2-methyl-pyridine) have been measured by quantitative 2D-EXSY NMR. Results suggest a dissociative (D) pathway involving an unsaturated 14-electrons Pd^II intermediate stabilized by γ-agostic interactions. Kinetic isotope effect, activation parameters, and crystal structure of the anti isomer support the D mechanism.     

Influence of preparation method on performance of Cu(Zn)(Zr)-alumina catalysts for the hydrogen production via steam reforming of methanol

The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260^°C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al₂O₃) and Cu(Zn)(Zr)(Al₂O₃). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al₂O₃) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al₂O₃) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al₂O₃). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al₂O₃) catalyst gave the consistent performance for a long time compared to other catalysts.     

Influence of preparation method on performance of Cu(Zn)(Zr)-alumina catalysts for the hydrogen production via steam reforming of methanol

The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260^∘C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al₂O₃) and Cu(Zn)(Zr)(Al₂O₃). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al₂O₃) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al₂O₃) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al₂O₃). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al₂O₃) catalyst gave the consistent performance for a long time compared to other catalysts.     

A [meso-tetrakis(4-sulfonatophenyl)porphyrinato]zinc(ii) complex as an oral therapeutic for the treatment of type 2 diabetic KKA(y) mice

We prepared and characterized [meso-tetrakis(4-sulfonatophenyl)porphyrinato]zinc(II) ([Zn(tpps)]), and investigated its in vitro insulin-mimetic activity and in vivo hypoglycemic effect in type 2 diabetic KKA(y) mice. The results were compared with those of previously proposed insulin-mimetic zinc(II) complexes and zinc sulfate (ZnSO(4)). The in vitro insulin-mimetic activity of [Zn(tpps)] was considerably better than that of bis(allixinato)zinc(II) ([Zn(alx)(2)]), bis(maltolato)zinc(II) ([Zn(mal)(2)]), bis(2-aminomethylpyridinato)zinc(II) ([Zn(2-ampy)(2)](2+)), and ZnSO(4). In particular, the order of in vitro insulin-mimetic activity of the complexes was determined to be: [Zn(tpps)]>[Zn(alx)(2)]>[Zn(mal)(2)]>[Zn(2-ampy)](2+)>ZnSO(4). [Zn(tpps)] normalized the hyperglycemia of KKA(y) mice within 21 days when administered orally at doses of 10-20 mg (0.15-0.31 mmol) Zn per kg body mass for 28 days. In addition, metabolic syndromes such as insulin resistance, the degree of renal disturbance, and the degree of liver disturbance were significantly improved in [Zn(tpps)]-treated KKA(y) mice relative to those administered with saline and ZnSO(4). The improvement in diabetes was validated by the results of oral glucose-tolerance tests and the decrease in the HbA(1c) level observed. In contrast, ZnSO(4) and the ligand H(2)tpps did not lower the elevated blood glucose level under the same experimental conditions. Based on these observations, [Zn(tpps)] is proposed to be the first orally active zinc(II)-porphyrin complex for the efficacious treatment of not only type 2 diabetes but also metabolic syndromes in animals.     

Human C1q Regulates Influenza A Virus Infection and Inflammatory Response via Its Globular Domain

The Influenza A virus (IAV) is a severe respiratory pathogen. C1q is the first subcomponent of the complement system’s classical pathway. C1q is composed of 18 polypeptide chains. Each of these chains contains a collagen-like region located at the N terminus, and a C-terminal globular head region organized as a heterotrimeric structure (ghA, ghB and ghC). This study was aimed at investigating the complement activation-independent modulation by C1q and its individual recombinant globular heads against IAV infection. The interaction of C1q and its recombinant globular heads with IAV and its purified glycoproteins was examined using direct ELISA and far-Western blotting analysis. The effect of the complement proteins on IAV replication kinetics and immune modulation was assessed by qPCR. The IAV entry inhibitory properties of C1q and its recombinant globular heads were confirmed using cell binding and luciferase reporter assays. C1q bound IAV virions via HA, NA and M1 IAV proteins, and suppressed replication in H1N1, while promoting replication in H3N2-infected A549 cells. C1q treatment further triggered an anti-inflammatory response in H1N1 and pro-inflammatory response in H3N2-infected cells as evident from differential expression of TNF-α, NF-κB, IFN-α, IFN-β, IL-6, IL-12 and RANTES. Furthermore, C1q treatment was found to reduce luciferase reporter activity of MDCK cells transfected with H1N1 pseudotyped lentiviral particles, indicative of an entry inhibitory role of C1q against infectivity of IAV. These data appear to demonstrate the complement-independent subtype specific modulation of IAV infection by locally produced C1q.     

Complex formation of divalent metal ions with uridine 5'-O-thiomonophosphate or methyl thiophosphate: comparison of complex stabilities with those of the parent phosphate ligands

The stability constants of the 1:1 complexes formed in aqueous solution between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Zn2+, or Cd2+ (M2+) and methyl thiophosphate (MeOPS(2-)) or uridine 5'-O-thiomonophosphate (UMPS(2-)) (PS(2-)=MeOPS(2-) or UMPS(2-)) have been determined (potentiometric pH titrations; 25 degrees C; I = 0.1 M, NaNO(3)). Comparison of these results for M(PS) complexes with those known for the parent M(PO) phosphate species, where PO(2-)=CH(3)OPO(2-)(3) or UMP(2-) (uridine 5'-monophosphate), shows that the alkaline earth metal ions, as well as Mn2+, Co2+, and Ni2+ have a higher affinity for phosphate groups than for their thio analogues. However, based on the linear log K(M)(M(R-PO3)) versus pK(H)(H(R-PO3)) relationships (R-PO(2-)(3) simple phosphate monoester or phosphonate ligands with a non-interacting residue R) it becomes clear that the indicated observation is only the result of the lower basicity of the thiophosphate residue. In contrast, the thio complexes of Zn2+ and Cd2+ are more stable than their parent phosphate ones, and this despite the lower basicity of the PS(2-) ligands. This stability increase is identical for M(MeOPS) and M(UMPS) species and amounts to about 0.6 and 2.4 log units for Zn(PS) and Cd(PS), respectively. Since no other binding site is available in MeOPS(2-), this enhanced stability has to be attributed to the S atom. Indeed, from the mentioned stability differences it follows that Cd2+ in Cd(PS) is coordinated by more than 99% to the thiophosphate S atom; the same value holds for Pb(PS), which was studied earlier. The formation degree of the Sbonded isomer amounts to 76+/-6 % for Zn(PS) and is close to zero for the corresponding Mg2+, Ca2+, and Mn2+ species. It is further shown that Zn(MeOPS)(aq)(2+) releases a proton from a coordinated water molecule with pK(a) approximately 6.9; i.e., this deprotonation occurs at a lower pH value than that for the same reaction in Zn(aq)(2+). Since Mg2+, Ca2+, Mn2+, and Cd2+ have a relatively low tendency for hydroxo complex formation, it was possible, for these M2+, to also quantify the stability of the binuclear complexes, M(2)(UMPS-H)+, where one M2+ is thiophosphate-coordinated and the other is coordinated at (N3)(-) of the uracil residue. The impact of the results presented herein regarding M2+/nucleic acid interactions, including those of ribozymes (rescue experiments), is briefly discussed.     

Could a Lower Toll-like Receptor (TLR) and NF-κB Activation Due to a Changed Charge Distribution in the Spike Protein Be the Reason for the Lower Pathogenicity of Omicron?

The novel SARS-CoV-2 Omicron variant B.1.1.529, which emerged in late 2021, is currently active worldwide, replacing other variants, including the Delta variant, due to an enormously increased infectivity. Multiple substitutions and deletions in the N-terminal domain (NTD) and the receptor binding domain (RBD) in the spike protein collaborate with the observed increased infectivity and evasion from therapeutic monoclonal antibodies and vaccine-induced neutralizing antibodies after primary/secondary immunization. In contrast, although three mutations near the S1/S2 furin cleavage site were predicted to favor cleavage, observed cleavage efficacy is substantially lower than in the Delta variant and also lower compared to the wild-type virus correlating with significantly lower TMPRSS2-dependent replication in the lungs, and lower cellular syncytium formation. In contrast, the Omicron variant shows high TMPRSS2-independent replication in the upper airway organs, but lower pathogenicity in animal studies and clinics. Based on recent data, we present here a hypothesis proposing that the changed charge distribution in the Omicron’s spike protein could lead to lower activation of Toll-like receptors (TLRs) in innate immune cells, resulting in lower NF-κB activation, furin expression, and viral replication in the lungs, and lower immune hyper-activation.     

Zinc binding drives the folding and association of the homo-trimeric gamma-carbonic anhydrase from Methanosarcina thermophila

Carbonic anhydrase from the archeon Methanosarcina thermophila (Cam) is a homo-trimeric enzyme, the left-handed beta-helical subunits of which bind three catalytic Zn(2+) ions at symmetry-related subunit interfaces. The observation of activity for holo-Cam at nanomolar concentrations provides a minimal estimated free energy of folding and assembly of the trimeric holo-complex of approximately 70 kcal (mol trimer)(-1) at standard state. Although the direct measurement of stability by chemical denaturation was precluded by the irreversible unfolding of the holo-enzyme, the reversible unfolding of metal-free apo-Cam is well described by a three-state model involving the folded apo-trimer, the folded monomer and the unfolded monomer. The monomer is estimated to have a stability of 4.0 +/- 0.3 kcal (mol monomer)(-1). The association to form apo-trimer contributes 13.2 +/- 0.4 kcal (mol trimer)(-1), a value confirmed by analytical ultracentrifugation measurements. Far- and near-UV circular dichroism data show a progressive increase in secondary and tertiary structure as the apo-monomer is converted to holo-trimer. The literature value for the free energy of binding of one Zn(2+) ion to a canonical active site, 16.4 kcal mol(-1), is consistent with the presumption that the >45 kcal (mol trimer)(-1) generated by the binding of three ions represents the major contribution to the stability of the holo-trimeric Cam.     

An aqua-adenine H-bonding interaction controlling the formation of the rare Zn(II)–N9(adenine) bond in crystal structure of diaqua(adenine)(iminodiacetato)zinc(II)

A novel mixed-ligand zinc(II) complex with iminodiacetato(2-) (IDA) and adenine (AdeH) ligands has been obtained. Its crystal consists of octahedral molecules [Zn(IDA)(AdeH)(H₂O)₂] where the selective Zn–N9(AdeH) bond, involving the most basic N(AdeH) donor atom, occupies the trans position versus the Zn–N(IDA) bond. The Zn(II)–N9(AdeH) binding mode seems to be rare enough in comparison to those previously reported for Zn(II) and AdeH or a variety of related ligands. The chelate-nucleobase recognition process is further accomplished by an O–H(aqua)⋯N3(adenine) inter-ligand H-bonding interaction, without any intra-molecular IDA–nucleobase interaction. This finding is attributed to the polarizing effect of Zn(II) on the aqua ligand and the possibilities of AdeH acting as N-donor for the metal(II) atom and H-acceptor for an intra-molecular inter-ligand H-bonding interaction. There are no aromatic π,π-stacking contributions in the 3D H-bonded network, where all polar N–H (IDA or AdeH) and O–H (aqua) bonds are involved as donors in H-bonding interactions, which include AdeH:AdeH and IDA:AdeH pairing by double inter-molecular bridges.     

Effect of Copper Acyclovir Complexes on Herpes Simplex Virus Type 1 and Type 2 (HSV-1, HSV-2) Infection in Cultured Cells

We have found that when copper, zinc or cobalt is bound to a suitable ligand, the appropriate complex exhibited a significant anti-HSV effect (Varadinova et al., 1993; 1996). Recently published data by Sagripanti et al. (1997) also show that the inhibition of HSV by copper was enhanced by reducing agents and that mechanism of the inactivation is similar as for copper-mediated DNA damage (Aruoma, et al. 1991; Dizdaroglu, et al., 1991; Toyokuni and Sagripanti, 1994). Therefore it was interesting to study the efect of Cu(ll) coordination compounds with acyclovir (ACV) on the replication of HSV in cultured cells. The experiments on cytotoxicity as well as on the activity of three different Cu-ACV complexes [Cu(ACV)(2)Cl(2)(H(2)O)(2)] = (A); [Cu(ACV)(2)(H(2)O)(3)](NO(3))(2).H(2)O = (B) and [Cu(ACV)(2)(H(2)O)(2)](NO(3))(2)] = (C) towards virus replication, with special attention on the growth of ACV-resistant strain R-100 were performed on MDBK cells. ACV was used as a reference compound. The following results were obtained: 1) Increased cell's viability in the presence of 20-40(g/ml ACV and decreased one in the presence of Cu-ACV complexes with relative level (A) > (B) > (C); 2) Cu-ACV complexes are more cytotoxic than the ligand - ACV and the relative level is (C)>(B)>(A); 3) The anti-HSV effect of ACV can be modulated by copper at levels depending on the specificity of the particular virus strain: (i) for the ACV sensitive strain DA (HSV-1) - ACV ((A) > (C) > (B); (ii) for the ACV sensitive strain Bja (HSV-2) (A) > ACV > (C) > (B); (iii) for strain R-100 (ACV(R), TK(a)) - (A) > ACV > (C) > (B). This findings are consistent with previously published data and undoubtedly show that Cu-ACV complexes could be useful in the treatment of HSV infections, especially when the causative agent is a resistant to ACV mutant.     

Clean recycling of zinc from blast furnace dust with ammonium acetate as complexing agents

Blast furnace dust (BFD) from ironmaking and steelmaking process is important secondary sources of zinc and other valuable metals. To realize recycling utilization of zinc secondary resource, a clean zinc production process using NH₃-CH₃COONH₄-H₂O as leaching agent has been developed. It was found that the addition of CH₃COONH₄ to NH₃-H₂O system promotes the zinc extraction, and 77.79% (8.23g/L) of Zn could be dissolved. The leaching process is controlled by the diffusion and interface transfer, and the corresponding activation energy E_a is 22.32 kJ/mol. The results of Fourier transforming infrared spectrum (FT-IR) and Electrospray ionization mass spectrometry (ESI-MS) analysis showed that zinc can combine with the carboxylate anion to form Zn-complexes.     

Molecular Interactions of Tannic Acid with Proteins Associated with SARS-CoV-2 Infectivity

The overall impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on our society is unprecedented. The identification of small natural ligands that could prevent the entry and/or replication of the coronavirus remains a pertinent approach to fight the coronavirus disease (COVID-19) pandemic. Previously, we showed that the phenolic compounds corilagin and 1,3,6-tri-O-galloyl-β-D-glucose (TGG) inhibit the interaction between the SARS-CoV-2 spike protein receptor binding domain (RBD) and angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 target receptor on the cell membrane of the host organism. Building on these promising results, we now assess the effects of these phenolic ligands on two other crucial targets involved in SARS-CoV-2 cell entry and replication, respectively: transmembrane protease serine 2 (TMPRSS2) and 3-chymotrypsin like protease (3CLpro) inhibitors. Since corilagin, TGG, and tannic acid (TA) share many physicochemical and structural properties, we investigate the binding of TA to these targets. In this work, a combination of experimental methods (biochemical inhibition assays, surface plasmon resonance, and quartz crystal microbalance with dissipation monitoring) confirms the potential role of TA in the prevention of SARS-CoV-2 infectivity through the inhibition of extracellular RBD/ACE2 interactions and TMPRSS2 and 3CLpro activity. Moreover, molecular docking prediction followed by dynamic simulation and molecular mechanics Poisson–Boltzmann surface area (MMPBSA) free energy calculation also shows that TA binds to RBD, TMPRSS2, and 3CLpro with higher affinities than TGG and corilagin. Overall, these results suggest that naturally occurring TA is a promising candidate to prevent and inhibit the infectivity of SARS-CoV-2.     

Two novel Zn(II) helical chain polymers containing both bridging and terminal carboxylato groups

Two novel carboxylato-bridged Zn(II) polymeric complexes [Zn(L)(CCl₃COO)]_n and [Zn(L)(CF₃COO)]_n, where [L=2-N-(2^′-pyridylimine)benzoic acid] have been synthesized and structurally characterized. The structures of the two complexes are similar with the Zn(L)(Cl₃CCO₂) or Zn(L)(F₃CCO₂) units being repeated to form infinite helical chains. In each structure, the neighbouring Zn atoms are bridged sequentially by syn–anti carboxylate groups of the Schiff base.     

Antibacterial and Antifungal Activity of Zinc(II) Carboxylates With/Without N-Donor Organic Ligands

The antibacterial and antifungal activity of zinc(II) carboxylates with composition Zn(RCOO)(2)*nH(2)O(R =H-, CH(3) (-), CH(3)CH(2)CH(2) (-), (CH(3))(2)CH-, XCH(2) (-), X=Cl, Br, I, n=0 or 2), [ZnX(2)(Nia(+)CH(2)COO(-))(2)](Nia=nicotinamide, X=Cl, Br, I) and [Zn(XCH(2)COO)(2)(Caf)(2)]*2H(2)O (Car=caffeine, X=Cl, Br) is studied against bacterial strains Staphylococcus aureus, Escherichia coli and yeast Candida albicans. The structural types are assigned to the prepared compounds and the influence of (i) carboxylate chain length, (ii) substitution of hydrogen atom of carboxylate by halogen and (iii) presence of N-donor organic ligands on the biological activity is discussed.     

Metal-organic fameworks based on multi-carboxylate ligands with threefold symmetries and luminescence properties

Three new metal–organic frameworks, namely, [Cd_1.5(tcpb)(DMF)(H₂O)] (1), [Co_1.5(tcpb)(DMF)₂]·3DMF (2) and [Zn(Htcpb)(4,4′-bpy)_0.5]·1.5H₂O (3) (tcpb = 1.3,5-tris(4-carbonylphenyloxy)benzene) have been synthesized by solvent-thermal method. The single-crystal X-ray diffraction analysis shows that compound 1 is 2D grid layers, with the trinuclear cadmium clusters acting as secondary building units (SBUs), and the tcpb ligand serveing as organic linkers. Compound 1 and Compound 2 are isomorphic structures containning similar connection modes of tcpb ligands with trinuclear metal clusters. Compound 3 is a 3D interpenetrated framework based on dinuclear Zn cluster with dia topology. The fluorescence properties for solid state compound 1 and 3 were examined at room temperature. Compared with free tcpb ligands, both of them display remarkable red-shift.     

Metal ion-binding properties of the diphosphate ester analogue, methylphosphonylphosphate, in aqueous solution

The stability constants of the 1:1 complexes formed between methylphosphonylphosphate (MePP(3-)), CH(3)P(O)(-) (2)-O-PO3(2-), and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) (M(2+)) were determined by potentiometric pH titration in aqueous solution (25 degrees C; l = 0.1 M, NaNO(3)). Monoprotonated M(H;MePP) complexes play only a minor role. Based on previously established correlations for M(2+)-diphosphate monoester complex-stabilities and diphosphate monoester beta-group. basicities, it is shown that the M(Mepp)(-) complexes for Mg(2+) and the ions of the second half of the 3d series, including Zn(2+) and Cd(2+), are on average by about 0.15 log unit more stable than is expected based on the basicity of the terminal phosphate group in MePP(3-). In contrast, Ba(Mepp)(-) and Sr(Mepp)(-) are slightly less stable, whereas the stability for Ca(Mepp)(-) is as expected, based on the mentioned correlation. The indicated increased stabilities are explained by an increased basicity of the phosphonyl group compared to that of a phosphoryl one. For the complexes of the alkaline earth ions, especially for Ba(2+), it is suggested that outersphere complexation occurs to some extent. However, overall the M(Mepp)(-) complexes behave rather as expected for a diphosphate monoester ligand.