Dipicolinic Acids Research Articles

Yellow and green-emissive N‑containing carbon dots-integrated bio-MOF: A highly sensitive sensing platform for anthrax biomarkers-picolinic and dipicolinic acids

The intentional release of Bacillus anthracis spores through aerosols or contaminated materials poses a serious threat to both individuals and populations. Therefore, it is of utmost importance to develop highly sensitive and rapid techniques for detecting Bacillus anthracis or its biomarkers, picolinic acid (PA) and dipicolinic acid (DPA), to effectively prevent and control potential outbreaks. In this study, we present a promising new approach where green and yellow emissive N‑doped carbon dots (NCDs) are integrated into bio-MOFs enriched with functional groups based on adenine (Ad) and 1,3,5-benzene tricarboxylic acid (BTC) linkers. This integrated system exhibits remarkable stability, high sensitivity, and selectivity, making it an exceptional fluorescent biosensor capable of detecting PA and DPA in a linear range of 5.0 to 140.0 µM and 0.5 to 75.0 µM, respectively. The unprecedentedly low detection limits of 1.65 and 0.16 µM for PA and DPA showcase the sensor's remarkable performance. Through the successful practical application of the sensor, we have been able to rapidly and accurately analyze spiked samples of DPA and PA in urine and water, yielding excellent results and demonstrating the feasibility of this approach. Moreover, our low-cost and user-friendly visual fluorescent sensor enables preliminary qualitative analysis of DPA and PA using the naked eye. The potential of this sensor as a diagnostic system for Anthrax monitoring is highly promising and warrants further exploration for its significant contribution to disease surveillance and control.

Speciation of the Ternary Cobalt(II) Picolinic and Dipicolinic Acid Complexes with Small Bioligands

This study reports on the determination of stability constants for ternary cobalt(II) complexes using primary ligands, pyridine carboxylic acids (picolinic (HPic) and dipicolinic (H2Dipic) acids), along with secondary ligands: lactic acid (HLac, HL), oxalic acid (H2Ox, H2L), citric acid (H3Cit, H3L), and phosphoric acid (H3PO4, H3L). Potentiometric data for binary cobalt(II) bioligand complexes and ternary cobalt(II) pyridine carboxylic acid and bioligand complexes were analyzed using the computational program LETAGROP. The experiments were conducted in an ionic medium of 1.0 mol dm–3 NaNO3 at 25 °C. Species distribution diagrams were generated, and relative stability parameters Δlog10 K, log10 X, and % R.S. were calculated. These findings may have important implications for the design of new cobalt(II) complexes for various applications.

Zwitterionic or Not? Fast and Reliable Structure Determination by Combining Crystal Structure Prediction and Solid-State NMR.

When it comes to crystal structure determination, computational approaches such as Crystal Structure Prediction (CSP) have gained more and more attention since they offer some insight on how atoms and molecules are packed in the solid state, starting from only very basic information without diffraction data. Furthermore, it is well known that the coupling of CSP with solid-state NMR (SSNMR) greatly enhances the performance and the accuracy of the predictive method, leading to the so-called CSP-NMR crystallography (CSP-NMRX). In this paper, we present the successful application of CSP-NMRX to determine the crystal structure of three structural isomers of pyridine dicarboxylic acid, namely quinolinic, dipicolinic and dinicotinic acids, which can be in a zwitterionic form, or not, in the solid state. In a first step, mono- and bidimensional SSNMR spectra, i.e., 1H Magic-Angle Spinning (MAS), 13C and 15N Cross Polarisation Magic-Angle Spinning (CPMAS), 1H Double Quantum (DQ) MAS, 1H-13C HETeronuclear CORrelation (HETCOR), were used to determine the correct molecular structure (i.e., zwitterionic or not) and the local molecular arrangement; at the end, the RMSEs between experimental and computed 1H and 13C chemical shifts allowed the selection of the correct predicted structure for each system. Interestingly, while quinolinic and dipicolinic acids are zwitterionic and non-zwitterionic, respectively, in the solid state, dinicotinic acid exhibits in its crystal structure a "zwitterionic-non-zwitterionic continuum state" in which the proton is shared between the carboxylic moiety and the pyridinic nitrogen. Very refined SSNMR experiments were carried out, i.e., 14N-1H Phase-Modulated (PM) pulse and Rotational-Echo Saturation-Pulse Double-Resonance (RESPDOR), to provide an accurate N-H distance value confirming the hybrid nature of the molecule. The CSP-NMRX method showed a remarkable match between the selected structures and the experimental ones. The correct molecular input provided by SSNMR reduced the number of CSP calculations to be performed, leading to different predicted structures, while RMSEs provided an independent parameter with respect to the computed energy for the selection of the best candidate.

Identification of New Fusarium sulawense Strains Causing Soybean Pod Blight in China and Their Control Using Carbendazim, Dipicolinic Acid and Kojic Acid.

Soybean plants are highly susceptible to Fusarium species, which significantly reduce soybean production and quality. Several Fusarium species have been reported to synthesize mycotoxins, such as trichothecene, which have been related to major human diseases. In November 2021, soybean pods in Nantong municipality, China, showed black necrotic lesions during the harvest stage. The disease incidence reached 69%. The pathogen was identified as Fusarium sulawense via morphological analysis and sequencing of ITS, EF1-α and RPB2 genes. A PCR assay with primers targeting the trichothecene biosynthesis genes suggested that the three isolates could synthesize trichothecenes. The effectiveness of fungicide carbendazim and natural metabolites dipicolinic acid and kojic acid was screened for the management of F. sulawense on postharvest soybean pods. The highest efficacy was obtained when combining 3.8 mg/mL carbendazim and 0.84 mg/mL dipicolinic acid (curative efficacy: 49.1% lesion length inhibition; preventive efficacy: 82.7% lesion length inhibition), or 1.9 mg/mL carbendazim and 0.71 mg/mL kojic acid (preventive efficacy: 84.9% lesion length inhibition). Collectively, this report will lead to a better understanding of the safety hazards found in soybean products in China and reveals the application of dipicolinic and kojic acids to reduce the use of carbendazim.

Detection of Cr(III), prometryn, and ibuprofen by hybrid Eu(III)–dipicolinate kaolinite luminescent sensor

Europium (III) was complexed on solids prepared by kaolinite functionalization with pyridine 2–carboxylic and pyridine 2,6–dicarboxylic acids; the luminescent properties of the obtained solids were analyzed for evaluating their application as luminescent sensors of prometryn, ibuprofen and chromium (III). The luminescent hybrid materials were characterized through powder X–ray diffraction, infrared absorption spectroscopy, thermal analysis, scanning electron microscopy, ultraviolet/visible absorption spectroscopy, energy dispersion and photoluminescence spectroscopy (excitation and emission) and lifetime measurements of the excited state. The materials proved to be promising, with quantum efficiencies of 31.16% and 45.18% for the samples functionalized with picolinic and dipicolinic acids, respectively. For the contaminant adsorption tests, the solid with picolinic acid showed better detection efficiency in a lower concentration range for chromium (III) than solids with dipicolinic acid, while both showed similar ranges for the organic contaminants.

Sublimation thermodynamics of pyrazinoic, dipicolinic and quinolinic acids: Experiment and theoretical prediction

The thermophysical characteristics and decomposition of pyrazinoic (POA), dipicolinic (DPA), and quinolinic (QNA) acids have been studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and mass-spectrometry. The transpiration method has been used to measure the vapour pressures as a function of the POA, DPA or QNA temperature. It has been found that QNA remains thermally stable in the solid form up to the temperature of 367.15 K, and further heating causes its decarboxylation and irreversible conversion to nicotinic acid. The standard molar enthalpies, entropies, and Gibbs energies of sublimation for POA, DPA and QNA have been calculated. A comparative study of five calculation schemes for sublimation enthalpy estimation (periodic Density Functional Theory computations (DFT-D3), Quantum Theory of Atoms in Molecules (QTAIM), Gavezzotti’s Coulomb-London-Pauli model (CLP and PIXEL) and CrystalExplorer CE-B3LYP) has been conducted. The sublimation thermodynamic functions of the compounds studied by the correlation method have been estimated. When applied to the objects of this study, the method proved to be a quick, convenient and inexpensive way to evaluate the sublimation thermodynamic functions of molecular crystals using only the melting temperature of the compound.

Concentrations of bacteria and bacterial and fungal spores calculated from chemical tracers associated with size-segregated aerosol in a composting plant

The lack of information on biological risks in workplaces arises from the difficulty to measure bioaerosol. This study aimed to develop and improve the bioaerosol monitoring technique that uses proper biomarkers as a tool. Muramic and dipicolinic acids, and ergosterol were used as tracers for bacteria cells, bacterial spores, and fungal spores, respectively. Furthermore, 12- and 13-methyltetradecanoic acids (iso- and anteiso- C15:0) were used to study the presence of airborne bacteria and 3-hydroxy fatty acids were used to determine the concentration of peptidoglycan. Airborne particulate matter was sampled in a municipal indoor waste composting facility by multistage impactor samplers, during three main stages of composting process. The microorganism content, in airborne particles with aerodynamic diameter minor then 1 μm and between 1 and 10 μm, was determined starting from the aforementioned biomarker concentrations. For iso- and anteiso- C15:0, a conversion factor to transform its concentration into bacterial content was tentatively proposed. The results show that the chemical method covers some gaps in the information about bioaerosol presence in polluted atmospheres. Differences up to two orders of magnitude are observed, by comparing the results obtained by biomarkers and by cultivation-dependent methods. The microbial content, expressed as a percentage by mass on respect the PM, ranged from 4 to 28% with higher percentages during shredding and mixing stages and lower values during biocell opening operations. Bacterial spores, bacterial cells, and fungal spores detected were high in number, compared with the findings in similar studies elsewhere.

Enthalpies of Anion Exchange of Chloride by Pyridinecarboxylate in AV-17-8 Anionite

Enthalpies of Cl– anion exchange for anions of nicotinic, isonicotinic, dipicolinic, and cinchomeronic acids on the strongly basic anionite AV-17-8 are measured at 298 K by means of microcalorimetry. Partial and standard enthalpies of sorption of pyridinecarboxylic acid anions on the Cl-form of AV-17-8 anionite from aqueous solutions are determined. The values of standard enthalpies lie in the range 3–14 kJ/mol, increasing in the order nicotinate, isonicotinate, dipicolinic acid anions, and cinchomeronic acid anions.

Heats of exchange of chloride with pyridinecarboxylate ions in Dowex-1 anion exchanger

The heats of exchange of chloride with pyridinecarboxylic acids anions in Dowex-1 strongly basic anion exchanger was obtained by the microcalorimetric method at 298 K. Nicotinic acid, isonicotinic acid, dipicolinic and cinchomeronic acids as pyridinecarboxylic acids were selected. It has been revealed that the sorption of pyridinecarboxylic acid anions by Cl form of Dowex-1 anion exchanger from aqueous solutions is the endothermic process. The standard enthalpy values of the exchange of chloride by pyridinecarboxylate ions in Dowex-1 anion exchanger calculated via microcalorimetric experimental data are in the range of 3–14 kJ mol−1. The standard enthalpies of model reaction that simulated the anion exchange process were determined via quantum chemical calculations of the reagent formation enthalpies in vacuum in the framework of the MOPAC2016 program. The enthalpies of both ion exchange of chloride by pyridinecarboxylate and the model reaction increase in the sequence: nicotinate, isonicotinate, anion of dipicolinic acid, anion of cinchomeronic acid.

Anion exchange kinetics with participation of cinchomeronic and dipicolinic acids

The rate of sorption and desorption of cinchomeronic and dipicolinic acids on the AB-17-8 strongly basic anion exchanger is limited by slow diffusion of components in the polymer phase. The diffusion coefficient of the organic anion in the phase of the AB-17-8 anion exchanger is equal to (3.7±0.5)•10–12 m2 s–1. Taking into account high rates of desorption of anions of cinchomeronic and dipicolinic acids from anionite (the half-transformation time is 6 min), the AB-17-8 strongly basic anion exchanger can be recommended for use as a container for development of prolonged drugs based on pyridinedicarboxylic acids.

Study on luminescent ternary EuEDTA complexes with a set of substituted 4-phenylethynyl and 4-aryl pyridine-2,6-dicarboxylic acids

A set of pyridine-2,6-dicarboxylic acids (dipicolinic acids, DPAD, Lx) were prepared to study the photo-physical properties of their ternary complexes with Eu(III) and ethylenediaminetetraacetic acid (EDTA or Y). The stability constant of the formation of EuY-L1 (L1= dipicolinic acid, measured log Kter =5.38) was determined and found to be comparable to the formation constant of Eu(L1)3(logK3 =5.51). All the studied ternary complexes exhibit two predominant luminescence decay times. The origin of the shorter lifetime was shown to be due to the dissociation of carboxylate group(s) and their replacement by water molecules. The presence of the short-lived component decreases the quantum yields compared those reported for complexes of Eu(Lx)3. However, the use of ternary complexes of EuY-Lx offers a simple comparison method between different dipicolinic acids (Lx). Eight of the studied ligands Lx form brighter ternary complexes than the currently used ligand in the duplex PCR assay, with quantum yields over 20%, and the most luminescent one has three times higher signal level compared to the currently used ligand.

N,N'-二乙基-N,N'-二(丙氧基苯基)-2,6-吡啶二酰胺对铀酰离子的选择性络合萃取

研究了新型萃取剂 N,N'- 二乙基- N , N' -二(丙氧基苯基)-2,6-吡啶二酰胺( 1 a~ 1 c)对铀酰离子(UO 2 2+ )的络合萃取. 结果表明, 当不加硝酸或硝酸浓度为6 mol/L时, 化合物 1 a对UO 2 2+ 的萃取率分别高达99%和94%. 在6 mol/L HNO 3 的高酸度条件下, 化合物 1 a能实现UO 2 2+ 和镧系元素(La, Eu及Yb)的选择性分离[分离比SF U(Ⅵ)/Ln(Ⅲ) >20]; 而化合物 1 b和 1 c则可以实现UO 2 2+ 和轻镧系元素(La, Eu)之间的分离. 双对数图(lg-lg plot)实验结果表明, 化合物 1 a~ 1 c与UO 2 2+ 的萃合比在1~2之间, 表明同时存在2:1和1:1两种比例的萃合物. 核磁共振波谱和红外光谱数据证明吡啶氮和羰基氧参与了对UO 2 2+ 的配位.

Mixed-ligand complex formation equilibria of vanadium(III) with picolinic and dipicolinic acids with some dicarboxylic acids (oxalic, malonic, and phthalic acids) studied in 3.0 M KCl at 25 °C

The ternary complexes formed between vanadium(III) and picolinic acid (Hpic) and dipicolinic acid (H2dipic) with the dicarboxylic oxalic, malonic, and phthalic acids (H2ox), (H2mal), and (H2phtha) briefly (H2L) were studied in aqueous solution by means of electromotive forces’ measurements emf(H) at 25 °C and 3.0 mol dm−3 KCl as ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, considering the hydrolysis products of the V(III), the acidity constants of the ligands employed, and the formation constants of the binary complexes, obtaining the complexes V(pic)(ox), log β1,1,1,−3 = 5.39(7) and [V(pic)2(ox)]−, log β1,2,1,−4 = 4.3(1); V(pic)(ma), log β1,1,1,−3 = 5.58(5) and [V(pic)2(ox)]−, log β1,2,1,−4 = 5.00(8); V(pic)(phtha), log β1,1,1,−3 = 5.66(6) and [V(pic)2(phtha)]− log β1,2,1,−4 = 4.5(2) in the vanadium(III)-Hpic-H2L system. In the case of the vanadium(III)-H2dipic-H2L system, the complexes [V(dipic)(ox)]−, log1,1,1,−4 β = 9.3(2), [V(dipic)(Hox)(ox)]2−, log β1,1,2,−5 = 11.2(2) and [V(dipic)(ox)2]3−, log β1,1,2,.6 = 5.7 max 7.0; [V(dipic)(ma)]−, log β1,1,1,−4 = 8.7(2), [V(dipic)(Hma)(ma)]2−, log β1,1,2,−5 = 10.3(1) and [V(dipic)(ma)2]3−, log β1,1,2,.6 = 6.9(1); [V(dipic)(phtha)]−, log β1,1,1,−4 = 10.9(1), [V(dipic)(Hphtha)(phtha)]2−, log β1,1,2,−5 = 9.2 max 10.4 and [V(dipic)(phtha)2]3−, log β1,1,2,.6 = 6.9(3) were observed.

Amides of heterocyclic carboxylic acids as novel extractants for high-level waste treatment

Extraction properties of various heterocyclic carboxylic acid amides are considered. The extraction properties of heterocyclic dicarboxylic acid diamides are determined by two major factors: diamide structure and kind of diluent. Among heterocyclic (di)carboxylic acid amides and diamides, the most promising extractants for separating actinides and lanthanides are tri- and tetradentate extractants: diamides of dipicolinic, bipyridinedicarboxylic, and phenanthrolinedicarboxylic acids, which can be used for recovering metals from acid solutions.

Selective Sensitization of Eu(III) and Tb(III) Emission with Triarylboron-Functionalized Dipicolinic Acids

Three triarylboron- (Mes2BAr-) functionalized dipicolinic acids, namely, 4-(4-(dimesitylboranyl)-2,3,5,6-tetramethylphenyl)pyridine-2,6-dicarboxylic acid (H2L1), 4-(4-(4-dimesitylboranyl)-2,3,5,6-tetramethylphenyl)-1H-1,2,3-triazol-1-yl)pyridine-2,6-dicarboxylic acid (H2L2), and 4-(4-(4-dimesitylboranyl) phenyl)-1H-1,2,3-triazol-1-yl)pyridine-2,6-dicarboxylic acid (H2L3), have been designed and synthesized. Lanthanide(III) complexes with the general formula of [NBu4]3[LnL3] (Ln = Eu or Tb; L = L1, L2, or L3) were obtained. The new triarylboron-functionalized ligands were found to be effective in the selective sensitization of the emissions of Eu(III) and Tb(III) ions with a high quantum efficiency (e.g., 0.54 for [NBu4]3[TbL13] in the solid state) upon excitation at ∼330 nm. An intraligand charge-transfer (ILCT) transition from the mesityl or aryl group to the boron or boron-aryl unit was found to play a key role in the activation of the Eu(III) and Tb(III) emissions, based on TD-DFT computational data and luminescence titration experiments performed using fluoride and cyanide ions.

Synthetic Ion Channels: From Pores to Biological Applications

In this Account, we describe the development of several diverse families of synthetic, membrane-active amphiphiles that form pores and facilitate transport within membrane bilayers. For the most part, the compounds are amphiphiles that insert into the bilayer and form pores either on their own or by self-assembly. The first family of synthetic ion channels prepared in our lab, the hydraphiles, used crown ethers as head groups and as a polar central element. In a range of biophysical studies, we showed that the hydraphiles formed unimolecular pores that spanned the bilayer. They mediated the transport of Na(+) and K(+) but were blocked by Ag(+). The hydraphiles are nonrectifying and disrupt ion homeostasis. As a result, these synthetic ion channels are toxic to various bacteria and yeast, a feature that has been used therapeutically in direct injection chemotherapy. We also developed a family of amphiphilic heptapeptide ion transporters that selected Cl(-) >10-fold over K(+) and showed voltage dependent gating. The formed pores were approximately dimeric, and variations in the N- and C-terminal anchor chains and the acids affected transport rates. Surprisingly, the longer N-terminal anchor chains led to less transport but greater Cl(-) selectivity. A proline residue, which is present in the ClC protein channel's conductance pore, proved to be critical for Cl(-) transport selectivity. Pyrogallol[4]arenes are macrocycles formed by acid-catalyzed condensation of four 1,2,3- trihydroxybenzenes with four aldehydes. The combination of 12 hydroxyl groups on one face of the macrocycle and four pendant alkyl chains conferred considerable amphiphilicity to these compounds. The pyrogallol[4]arenes inserted into bilayer membranes and conducted ions. Based on our experimental evidence, the ions passed through a self-assembled pore comprising four or five amphiphiles rather than passing through the central opening of a single macrocycle. Pyrogallol[4]arenes constructed with branched chains are also amphiphilic and active in membranes. The pyrogallol[4]arene with 3-pentyl sidechains formed a unique nanotube assembly and functioned as an ion channel in bilayer membranes. Finally, we showed that dianilides of either isophthalic or dipicolinic acids, compounds which have been extensively studied as anion binders, can self-assemble to form pores within bilayers. We called these dianilides tris-arenes and have shown that they readily bind to phosphate anions. These structures also mediated the transport of DNA plasmids through vital bilayer membranes in the bacterium Escherichia coli and in the yeast Saccharomyces cerevisiae . This transformation or transfection process occurred readily and without any apparent toxicity or mutagenicity.

Green and selective oxidation reactions catalyzed by kaolinite covalently grafted with Fe(III) pyridine-carboxylate complexes

The immobilization of Fe(III) picolinate and Fe(III) dipicolinate complexes on kaolinite furnished heterogeneous catalysts, whose catalytic activity was evaluated. The precursor materials were kaolinite grafted with picolinic (Ka-pa) and dipicolinic (Ka-dpa) acids obtained by melting of the pyridine carboxylic acids. To obtain the catalysts Fe(Ka-pa)-n and Fe(Ka-dpa)-n (n=1, 2, or 3 is the ligand/Fe ratio), the precursors were suspended in Fe3+ solutions with cation/ligand ratios of 1:1, 1:2, or 1:3. The resulting materials were characterized by thermal analyses (simultaneous TG/DTA), X-ray diffraction, UV/vis and infrared spectroscopies, and transmission electron microscopy. The grafted complexes were employed as heterogeneous catalysts in the epoxidation of cis-cyclooctene to cis-cyclooctenoxide and in the oxidation of cyclohexane to cyclohexanol and cyclohexanone at ambient temperature and pressure. Hydrogen peroxide was used as oxygen donor at a catalyst/oxidant/substrate molar ratio of 1:300:100. Fe(Ka-pa)-n catalysts were very efficient for cis-cyclooctene epoxidation (38% conversion). For cyclohexane oxidation, Fe(Ka-dpa)-n was 100% selective for cyclohexanone formation, with substrate conversion of 14%. This last series of catalysts was also very effective in the Baeyer–Villiger reaction, with 60% substrate conversion and 100% selectivity for ξ-caprolactone. After reuse (5 times), the catalysts still led to high substrate conversion.

Halide Ions Complex and Deprotonate Dipicolinamides and Isophthalamides: Assessment by Mass Spectrometry and UV−Visible Spectroscopy

The F(-), Cl(-), and Br(-) binding selectivity of bis(p-nitroanilide)s of dipicolinic and isophthalic acids was studied by using competitive electrospray mass spectrometry and UV-Visible spectroscopy. Both hosts prefer binding Cl(-) over either F(-) or Br(-). Host deprotonation was observed to some extent in all experiments in which the host was exposed to halide ions. When F(-) was present, host deprotonation was often the major process, whereas little deprotonation was observed by Cl(-) or Br(-), which preferred complexation. A solution of either host changed color when mixed with a F(-), H(2)PO(4)(-), di- or triphenylacetate solution.

Complexation of NpO2+ with N-methyl-iminodiacetic acid: a comparison with iminodiacetic and dipicolinic acids

Complexation of Np(v) with N-methyl-iminodiacetic acid (MIDA) in 1 M NaClO(4) solution was studied with multiple techniques including potentiometry, spectrophotometry, and microcalorimetry. The 1 : 2 complex, NpO(2)(MIDA)(2)(3-) was identified for the first time in aqueous solution. The correlation between its optical absorption properties and symmetry was discussed, in comparison with Np(v) complexes with two structurally related nitrilo-dicarboxylic acids, iminodiacetic acid (IDA) and dipicolinic acid (DPA). The order of the binding strength (DPA > MIDA > IDA) is explained by the difference in the structural and electronic properties of the ligands. In general, the nitrilo-dicarboxylates form stronger complexes with Np(v) than oxy-dicarboxylates due to a much more favorable enthalpy of complexation.

Ternary Complexes of Zinc(II), Cyclen and Pyridinecarboxylic Acids

AbstractBinary and ternary systems containing Zn2+, cyclen and/or pyridinecarboxylic acids and amides [picolinic (HL1), nicotinic (HL2) and dipicolinic (H2L3) acids and nicotinamide (L4)] have been investigated in solution and in the solid state. Dissociation and stability constants for the ligands and binary systems, respectively, are in accordance with literature results. Both picolinic and dipicolinic acids form stable ternary complexes with the [Zn(cyclen)]2+species; a weak interaction is observed for nicotinic acid and nicotinamide. The formation of ternary complexes stabilizes the products of protonation at the cyclen nitrogen atom, and these protonated complexes are found even up to pH = 7. The structures of the complexes in solution correlate well with those found in the solid state and by molecular modelling calculations. The solid‐state structures of several complexes are determined. The zinc atom in the [Zn(cyclen)(NO3)]+complex is bound in an N4O tetragonal‐pyramidal environment. The nicotinic acid anion forms a bridge in the [{Zn(cyclen)}2(μ‐L2‐N,O)]3+cation, and both [Zn(cyclen)]2+units exhibit tetragonal‐pyramidal arrangements. An unusual coordination mode is found in the [{Zn(cyclen)}2(μ‐L1‐O:N,O′)]3+cation, where the picolinic acid anion also bridges two [Zn(cyclen)]2+units but is coordinated monodentately through one oxygen atom to one unit (N4O tetragonal pyramid) and chelates through the other pyridine nitrogen and carboxylate oxygen atoms. Nicotinamide in the [Zn(cyclen)(L4‐N)]2+cation is bound to the [Zn(cyclen)]2+unit through the pyridine nitrogen atom in the axial position of the tetragonal pyramid. This is the first fully quantitative assessment of Zn2+‐cyclen‐ligand ternary systems, and the results, namely the presence of protonated cyclen in the ternary species even at high pH, are relevant for evaluation of the [Zn(cyclen)]2+unit as a model complex for zinc‐containing enzymes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)