Addition of o-aminobenzoic acid during Fmoc solid phase synthesis of a fluorogenic substrate containing 3-nitrotyrosine

Summary Following the Fmoc-tBu synthesis of an intramolecularly quenched substrate with the sequence NH₂-Abz-Gly-Ala-Ala-Pro-Phe-Tyr(3-NO₂)-Asp-OH, in addition to the target peptide a side product accounted for more than 50% of the crude product as measured by the integrated peak area by RP-HPLC analysis.¹H NMR and ESI-MS analysis confirmed the presence of two Abz residues in this side product. The enzymatic and chemical methods revealed the position of this modification to be the hydroxyl function of Tyr(3-NO₂). The side reaction was entirely prevented upon treatment of the resin bound peptide with piperidine prior to final TFA cleavage.     

Synthesis and structural characterization of bis- and tris(3,5-dimethylpyrazolyl)methane complexes of Ni(NO3)2

The complexes (tpm*)Ni(η²-NO₃)(η¹-NO₃) (1), [(bpm*)₂Ni(η²-NO₃)]NO₃ (2), and [(tpm*)(bpm*)Ni(η¹-NO₃)]NO₃ (3) (tpm* = tris(3,5-dimethylpyrazolyl)methane; bpm* = bis(3,5-dimethylpyrazolyl)methane) have been prepared and characterized by IR and UV-Vis spectroscopy and X-ray diffraction studies. These d⁸ complexes all adopt variously distorted octahedral structures in the solid state and their magnetic moments are consistent with a paramagnetic state with two unpaired electrons. The solution ¹H NMR data show that the paramagnetism is maintained in solution.     

Novel internally quenched substrate of the trypsin-like subunit of 20S eukaryotic proteasome

This article describes the synthesis, using combinatorial chemistry, of internally quenched substrates of the trypsin-like subunit of human 20S proteasome. Such substrates were optimized in both the nonprime and prime regions of the peptide chain. Two were selected as the most susceptible for proteasomal proteolysis with excellent kinetic parameters: (i) ABZ-Val-Val-Ser-Arg-Ser-Leu-Gly-Tyr(3-NO₂)-NH₂ (k_cat/K_M = 934,000 M⁻¹ s⁻¹) and (ii) ABZ-Val-Val-Ser-GNF-Ala-Met-Gly-Tyr(3-NO₂)-NH₂ (k_cat/K_M = 1,980,000 M⁻¹ s⁻¹). Both compounds were efficiently hydrolyzed by the 20S proteasome at picomolar concentrations, demonstrating significant selectivity over other proteasome entities.     

Kinetics of reaction of square-planar complexes of nitrosubstituted aromatic di-imines with methoxide and aliphatic amines in dipolar aprotic solvents

The square-planar complexes [Pt(5-NO₂phen)Cl₂], [Pd(5-NO₂phen)₂](ClO₄)₂ and [Pd(5-NO₂phen)X₂] (X = N₃, Cl) give a colour forming reaction with OH⁻ or alkoxides in dipolar aprotic solvents. The process occurs in one observable step and the rate law is k_obs = k₂ [alkoxide]. The second order rate constant k₂ is independent of the nature of the metal and of the coordinated ligands other than 5-NO₂-phen and this is taken as evidence that the nucleophilic attack does not occur at the central atom but rather at the coordinated phenanthroline to give presumably σ-adducts at the carbon. Conductivity stopped-flow shows that the colour forming reaction between neutral substrates and amines is associated with the formation of a 1:1 electrolyte. In dipolar aprotic solvents a colour forming reaction occurs also between [Pd(4-NO₂bipy)Cl₂] and bases.     

DNA-Binding and Photocleavage Properties of Ru(II) Polypyridyl Complexes with DNA and Their Toxicity Studies on Eukaryotic Microorganisms

Four Ru(II) polypyridyl complexes, [Ru(bpy)₂(7-NO₂-dppz)]²⁺, [Ru(bpy)₂(7-CH₃-dppz)]²⁺, [Ru(phen)₂(7-NO₂-dppz)]²⁺, and [Ru(phen)₂(7-CH₃-dppz)]²⁺ (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), (7-Nitro-dppz = 7-Nitro dipyrido[3,2-a:2′-3′-c]phenazine, 7-CH₃-dppz = 7-Methyl dipyrido[3,2-a:2′-3′-c]phenazine), have been synthesized and characterized by IR, UV, elemental analysis, ¹H NMR, ¹³C-NMR, and mass spectroscopy. The DNA-binding properties of the four complexes were investigated by spectroscopic and viscosity measurements. The results suggest that all four complexes bind to DNA via an intercalative mode. Under irradiation at 365 nm, all four complexes were found to promote the photocleavage of plasmid pBR 322 DNA. Toxicological effects of the selected complexes were performed on industrially important yeasts (eukaryotic microorganisms).     

Theoretical design of energetic nitrogen-rich derivatives of 1,7-diamino-1,7-dinitrimino-2,4,6-trinitro-2,4,6-triazaheptane

The heats of formation (HOFs), energetic properties, and thermal stability of a series of 1,7-diamino-1,7-dinitrimino-2,4,6-trinitro-2,4,6-triazaheptane derivatives with different substituents, different numbers of substituents, and different original chains are found by using the DFT-B3LYP method. The results show that -NO₂ or -NH₂ is an effective substituent for increasing the gas-phase HOFs of the title compounds, especially -NO₂ group. As the numbers of substitutents increase, their HOFs enhance obviously. Increasing the length of original chain is helpful for improving their HOFs. The substitution of -NO₂ is useful for enhancing their detonation performances and the effects of the length of original chains on detonation properties are coupled with those of the substituents. An analysis of the BDE of the weakest bonds indicates that the substitution of the -NH₂ groups and replacing the -NO₂ groups of N-NO₂ by the -NH₂ groups are favorable for improving their thermal stability, while the substitution of -NO₂ and increasing the length of original chain decrease their thermal stability. Considering the detonation performance and thermal stability, seven compounds may be considered as the potential candidates of high energy density compounds.     

Conformations of cyclic peptide/calcium complexes in solution

Synthetic cyclic octapeptides of general structure cyclo[Glu(γOBzl)-Sar-Gly-(N-R)Gly]₂ (R = n-hexyl and cyclohexyl) transport calcium ions selectively across organic phases and phospholipid membranes. We have now used proton nmr spectroscopy (360 MHz) to study the solution conformation(s) of their calcium complexes. When Ca(ClO₄)₂ was added to solutions of these peptides in CDCl₃, nmr spectra of the resulting calcium complexes were characteristic of a single C₂-symmetric conformer. From a Karplus-Bystrov analysis of vicinal coupling constants in both the peptide backbone and Glu side chain (treated as an ABCC′MX spin system), in conjuction with model-building studies, a structure was proposed in which the calcium ion is bound in an octahedral-type complex by the four (coplanar) carbonyl groups of the (all-trans) Glu-Sar and Gly-(N-R)Gly peptide bonds. Occurrence of preferred rotamers about Glu side chain C^α–C^β bonds indicated that restricted rotation in peptide side chains arises upon calcium binding.     

A new proteinase 3 substrate with improved selectivity over human neutrophil elastase

We report the synthesis and enzymatic studies on a new proteinase 3 intermolecular quenched substrate with enhanced selectivity over neutrophil elastase. Using combinatorial chemistry methods, we were able to synthesize the hexapeptide library with the general formula ABZ-Tyr-Tyr-Abu-X₁′-X₂′-X₃′-Tyr(3-NO₂)-NH₂ using the mix and split method. The iterative deconvolution of such a library allowed us to obtain the sequence ABZ-Tyr-Tyr-Abu-Asn-Glu-Pro-Tyr(3-NO₂)-NH₂ with a high specificity constant (k_cat/K_M = 1534 × 10³ M⁻¹ s⁻¹) and superior selectivity over neutrophil elastase and other neutrophil-derived serine proteases. Moreover, using the obtained substrate, we were able to detect a picomolar concentration of proteinase 3 (PR3). Incubation of the above-mentioned substrate with neutrophil lysate resulted in a strong fluorescent signal that was significantly reduced in the presence of a PR3 selective inhibitor.     

Synthesis,characterization and antitumor activity of some metal complexes of 3- and 5-substituted salicylaldehyde o-hydroxybenzoylhydrazones

Complexes of Mn(II), Fe(III), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Pt(II) with 3- and 5-substituted salicylaldehyde o-hydroxybenzoylhydrazones (XSBH, X = H, 3-NO₂, 3-CH₃O, 5-Cl, 5-Br, 5-CH₃ or 5-NO₂) have been prepared and characterized by elemental analysis, conductance measurements, magnetic susceptibilities (from room temperature down to liquid nitrogen temperature) and spectral studies. These studies indicate the following structures: monomeric, high-spin, distorted octahedral for Mn(XSBH)₂; monomeric, high-spin, five-coordinate for Fe(XSBH)SO₄·H₂O; dimeric, high-spin phenoxide bridged, five-coordinate for Fe(XSBH)Cl; dimeric, high-spin five-coordinate for Co(XSBH)Cl·2H₂O; dimeric low-spin, five-coordinate for Ni(XSBH)Cl·2H₂O; dimeric, four-coordinate for Zn(XSBH); and a square-planar structure for M(XSBH)Cl·H₂O (M = Cu(II) or Pt(II).Intermolecular antiferromagnetic exchange interactions are present in Fe(III) complexes, where the exchange parameter (J) is ca. −8.0 cm⁻¹ for these complexes. The Fe(III) complexes exhibit asymmetric quadrupole split doublets in their ⁵⁷Fe Mössbauer spectra. The asymmetry is found to be temperature dependent with relatively symmetrical doublets seen at low temperature. The polycrystalline ESR spectra of Cu(II) complexes are isotropic and indicate a d_x²−y² ground state in square-planar stereo-chemistry. All these metal complexes have been screened for their antitumor activity against the P 388 lymphocytic leukaemia test system in mice and enhanced antitumor activity relative to the free ligand was found but no significant activity at the dosages used.     

Synthesis, structures and properties of dinuclear cadmium(II) complexes based on polybenzimidazole binucleating ligands

Three novel cadmium(II) complexes [Cd₂(tbpo)(O₂CC₆H₄-p-NO₂)₂]ClO₄·3CH₃OH (1) [Cd₂(bbap)(O₂CC₆H₄-p-NO₂)₂]ClO₄·4.5CH₃OH·0.75H₂O (2) and [Cd(ntb)(O₂CC₆H₄-p-NO₂)]ClO₄·4CH₃OH (3) have been synthesized and characterized by IR, elemental analysis, ¹H NMR and X-ray crystallography, where tbpo⁻ and bbap⁻ are anions of N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane and 2,6-bis[bis(2-benzimidazolylmethyl)aminomethyl]-4-methylphenol, respectively; ntb is tris(2-benzimidazolymethyl)amine. Complexes 1 and 2 contain μ-phenolate-bridged and μ-alkoxo-bridged dicadmium(II) cores with the Cd1?Cd2 separation of 3.671 Å for complex 1 and 3.718 Å for 2. One of the 4-nitrobenzoate anions bridged the two cadmium(II) ions in syn-anti mode through its carboxylate group, the other 4-nitrobenzoate is only coordinated with Cd2 in bidentate chelating mode. The two central cadmium(II) atoms are in trigonal bipyramidal and pentagonal bipyramidal geometry. In complex 3, the cadmium(II) atom is coordinated with four nitrogen atoms of ntb and one carboxylate oxygen atom of 4-nitrobenzoate in distorted trigonal bipyramidal geometry. Experiment shows that there is a higher affinity of 4-nitrobenzoate anion as coligand with the dinuclear [Cd₂(tbpo)]³⁺ and [Cd₂(bbap)]³⁺ cores than that with the mononuclear [Cd(ntb)]²⁺ core.     

Enhanced secretion of adhesive recognition sequence containing hirudin III mutein in <Emphasis Type="Italic">E. coli</Emphasis>

It has been previously shown that Escherichia coli l-asparaginase II (l-ASP) signal peptide is capable of being utilized to direct extracellular secretion of hirudin III (HV3) in shake flask. In this study HV3 muteins R₃₃G₃₄D₃₅(S₃₆)-HV3 were generated by introduction of adhesive recognition sequence RGD(S) into the non-functional region of HV3. The resultant recombinants were cultivated on 30 l bioreactor scale using l-ASP signal peptide expression system and the optimized fed-batch cultivation was well established. After cultivation for approximately 11 h the secreted product accumulated up to ∼1 g l⁻¹, which means 17-fold increase in productivity compared to initial expression in shake flask. N-terminal analysis, pI measurement, and MALDI mass spectral analysis on mutein R₃₃G₃₄D₃₅S₃₆-HV3 confirmed the authenticity of the product. Compared to wild-type HV3 and R₃₃G₃₄D₃₅HV3, the mutein R₃₃G₃₄D₃₅S₃₆-HV3 exhibits the improved pharmacological activity. Collectively, a novel secretion strategy using l-ASP signal peptide for the rapid, efficient and cost-effective production of HV3 mutein possessing improved pharmacological activity on bioreactor scale has been well established. Using this expression system downstream processing becomes very simple because secreted product is mature, soluble, active, and without N-terminal extension of Met, which is quite critical for most therapeutic protein to reduce the side effect in clinic use. Thus, it provides a promising alternative for extracelluar production of other difficult-to-express protein for biopharmaceutical use.     

Preferred side‐chain conformation of arginine residues in a triple‐helical structure

The crystal structure of the triple‐helical peptide (Pro‐Hyp‐Gly)₃‐Pro‐Arg‐Gly‐(Pro‐Hyp‐Gly)₄ (POG3‐PRG‐POG4) was determined at 1.45 Å resolution. POG3‐PRG‐POG4 was designed to permit investigation of the side‐chain conformation of the Arg residues in a triple‐helical structure. Because of the alternative structure of one of three Arg residues, four side‐chain conformations were observed in an asymmetric unit. Among them, three adopt a ttg^?t conformation and the other adopts a tg^?g^?t conformation. A statistical analysis of 80 Arg residues in various triple‐helical peptides showed that, unlike those in globular proteins, they preferentially adopt a tt conformation for χ₁ and χ₂, as observed in POG3‐PRG‐POG4. This conformation permits van der Waals contacts between the side‐chain atoms of Arg and the main‐chain atoms of the adjacent strand in the same molecule. Unlike many other host–guest peptides, in which there is a significant difference between the helical twists in the guest and the host peptides, POG3‐PRG‐POG4 shows a marked difference between the helical twists in the N‐terminal peptide and those in the C‐terminal peptide, separated near the Arg residue. This suggested that the unique side‐chain conformation of the Arg residue affects not only the conformation of the guest peptide, but also the conformation of the peptide away from the Arg residue. © 2014 Wiley Periodicals, Inc. Biopolymers 101: 1000–1009, 2014.     

Synthesis and crystal structures of cobalt(II), cadmium(II), and zinc(II) complexes of 4-nitro phenylcyanamide: enhancing the biological properties through bound to human serum albumin

Metal complexes of the type [Co(phen)₂(4-NO₂pcyd)₂].CH₃OH, 1, [Zn(phen)₂(4-NO₂pcyd)₂].CH₃OH, 2, [Cd(phen)₂(4-NO₂pcyd)₂], and 3, (phen?=?1,10-phenanthroline, 4-NO₂pcyd?=?4-nitro phenylcyanamide) have been studied. The synthesis, characterization, and the biological activities of complexes 1-3 have been investigated. The geometries of complexes 1-3 were confirmed by single-crystal X-ray crystallography. The interactions of complexes 1-3 with human serum albumin (HSA) were studied using fluorescence and circular dichroism spectroscopy. The thermodynamic studies have showed the reaction for the binding of complexes 1-3 with HSA is hydrophobic (ΔH_0???0 and ΔS₀ > 0). The in vitro cytotoxic potential of complexes 1-3 and their complexes with HSA were examined. The complexes 1-3 with HSA enhance about 3-fold cytotoxicity in cancer cells lines.     

A series of oxo-vanadium(IV) complexes containing mixed ligands of poly(pyrazolyl)borate and organic carboxylic acid: Synthesis, structural characterization and primary study of bromination reaction activities

A series of oxo-vanadium(IV) complexes: Tp^∗VO(pzH^∗)(CH₃COO) (1), Tp^∗VO(pzH^∗)(CCl₃COO) (2), Tp^∗VO(pzH^∗)(C₆H₅COO) (3), Tp^∗VO(pzH^∗)(m-NO₂-C₆H₄COO)·CH₃CN (4) and [Tp^∗VO(pzH^∗)(H₂O)]⁺[m-NO₂-C₆H₄-SO₃]⁻·CH₃OH (5) (Tp^∗ = hydrotris(3,5-dimethylpyrazolyl)borate; pzH^∗ = 3,5-dimethylpyrazole) are synthesized in methanol solution under physiological conditions. They are characterized by elemental analysis, IR, UV-Vis and X-ray crystallography. Structural analyses show that the vanadium atoms in complexes 1-5 are all in a distorted-octahedral environment with the N₄O₂ donor set, and intra- or inter-hydrogen bonding linkages have been also observed in each complex. Bromination reaction activity of the complexes has been evaluated by the method with phenol red as organic substrate in the presence of H₂O₂, Br⁻ and phosphate buffer, indicating that they can be considered as potential functional model vanadium-dependent haloperoxidases. In addition, thermal analysis and quantum chemistry calculations were also performed and discussed in detail.     

Synthesis and evaluation of a class of 1,4,7-triazacyclononane derivatives as iron depletion antitumor agents

Iron depletion has been confirmed as an efficient strategy for cancer treatment. In the current study, a series of 1,4,7-triazacyclononane derivatives HE-NO2A, HP-NO2A and NE2P2A, as well as the bifunctional chelators p-NO₂-PhPr-NE3TA and p-NH₂-PhPr-NE3TA were synthesized and evaluated as iron-depleting agents for the potential anti-cancer therapy against human hepatocellular carcinoma. The cytotoxicity of these chelators was measured using hepatocellular cancer cells and compared with the clinically available iron depletion agent DFO and the universal metal chelator DTPA. All these 1,4,7-triazacyclononane-based chelators exhibited much stronger antiproliferative activity than DFO and DTPA. Among them, chelators with phenylpropyl side chains, represented by p-NO₂-PhPr-NE3TA and p-NH₂-PhPr-NE3TA, displayed the highest antiproliferative activity against HepG2 cells. Hence, these compounds are attractive candidates for the advanced study as iron depletion agents for the potential anti-cancer therapy, and could be further in conjugation with a targeting moiety for the future development in targeted iron depletion therapy.     

Proton NMR study of the conformation of bradykinin: pH titration.

pH titration by ¹H-NMR spectroscopy of the peptide hormone bradykinin was carried out in ²H₂O. Assignment of all α-proton signals and of most of the other resonances permitted the extraction of vicinal coupling constants ³J_αβ,β′ from which side chain conformation of all residues could be followed and analyzed as a function of pH. It is shown that the ionization of the terminal COOH group affects simultaneously the Arg-9 and Phe-8 chemical shifts and side chain orientation, and the non-equivalence of the Gly-4 methylene protons. Cooperative effects along the peptide backbone or a folded structure of the C-terminal part of bradykinin could explain this effect.     

Determination of Key Metabolites during Biodegradation of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine with Rhodococcus sp. Strain DN22

Rhodococcus sp. strain DN22 can convert hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to nitrite, but information on degradation products or the fate of carbon is not known. The present study describes aerobic biodegradation of RDX (175 μM) when used as an N source for strain DN22. RDX was converted to nitrite (NO₂⁻) (30%), nitrous oxide (N₂O) (3.2%), ammonia (10%), and formaldehyde (HCHO) (27%), which later converted to carbon dioxide. In experiments with ring-labeled [¹⁵N]-RDX, gas chromatographic/mass spectrophotometric (GC/MS) analysis revealed N₂O with two molecular mass ions: one at 44 Da, corresponding to ¹⁴N¹⁴NO, and the second at 45 Da, corresponding to ¹⁵N¹⁴NO. The nonlabeled N₂O could be formed only from -NO₂, whereas the ¹⁵N-labeled one was presumed to originate from a nitramine group (¹⁵N-¹⁴NO₂) in RDX. Liquid chromatographic (LC)-MS electrospray analyses indicated the formation of a dead end product with a deprotonated molecular mass ion [M-H] at 118 Da. High-resolution MS indicated a molecular formula of C₂H₅N₃O₃. When the experiment was repeated with ring-labeled [¹⁵N]-RDX, the [M-H] appeared at 120 Da, indicating that two of the three N atoms in the metabolite originated from the ring in RDX. When [U-¹⁴C]-RDX was used in the experiment, 64% of the original radioactivity in RDX incorporated into the metabolite with a molecular weight (MW) of 119 (high-pressure LC/radioactivity) and 30% in ¹⁴CO₂ (mineralization) after 4 days of incubation, suggesting that one of the carbon atoms in RDX was converted to CO₂ and the other two were incorporated in the ring cleavage product with an MW of 119. Based on the above stoichiometry, we propose a degradation pathway for RDX based on initial denitration followed by ring cleavage to formaldehyde and the dead end product with an MW of 119.     

Synthesis and characterization of nitroimidazole complexes of platinum and palladium and the crystal and molecular structure of trans-dichlorobis(misonidazole)platinum(II)

The synthesis and properties of some nitroimidazole complexes of platinum and palladium starting from the MCl₄^2- salts are described. Both 5-NO₂-imidazole and metronidazole give cis-[MCl₂L₂] complexes whereas trans-[MCl₂L₂] is obtained for 2-NO₂-imidazole and misonidazole. The crystal structure of trans-dichlorobis(misonidazole)platinum(II) was determined by three-dimensional X-ray methods. The compound crystallized in space group P2₁/c in discrete monomeric units with a = 11.303(5), b = 13.002(5) and c = 8.125(3) Å, B = 91.39(3)°, Z = 2 and the observed and calculated densities are 1.83 and 1.859 respectively. The final full-matrix least-squares refinement gave values of R₁ = 0.037 and R₂ = 0.045 for 142 variables. The complex is square-planar with Pt-Cl and Pt-N distances of 2.294(3) and 2.016(9) Å respectively. The mean plane of the misonidazole ring is twisted 56° with respect to the PtCl₂L₂ square plane and the Cl-Pt-N angles are 89.4(3) and 90.6(3)°; the nitro group also lies out of the plane of the misonidazole ring. The closest nonbonded contact between non-hydrogen atoms in the unit cells is 2.80 Å suggesting hydrogen bonding between the hydroxyl proton and the ether oxygen in the misonidazole side-chain, i.e. O-H?O. Aspects of the chemistry of these species in relation to their biological activity are discussed.     

A novel computer modeling approach to the structures of small bioactive peptides: The structure of gonadotropin releasing hormone

A novel computer modeling approach suitable for the structure analysis of small bioactive peptides has been developed. This approach involves identification of conformational patterns in protein structure data bank based on the sequence homology with the bioactive peptide. The models built on the basis of this homology and having common conformational patterns are analyzed under the structural constraints derived from the activity data of various synthetic analogs of the peptide. Application of this procedure to the gonadotropin releasing hormone (GnRH) resulted in a library of possible structures for GnRH, 9 among which shared a common β-turn. Further analysis of the structures containing the β-turn motif, in the context of the structure–activity data, led to a model for the active conformation of GnRH. The topology of the putative receptor binding site of the hormone is defined by a contiguous surface formed through an appropriate juxtaposition of the N-terminal pGlu¹ the guanidyl group of Arg⁸, aromatic side chain of Trp³, and the Gly¹⁰-NH₂ at the C-terminal end. ©Wiley-Liss, Inc.     

Five manganese(II) complexes with seven- or eight-coordinated Mn(II), revealing different coordination modes for the nitrato ligands

Four seven-coordinated manganese(II) complexes [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (1), [Mn(bpia)(η₁-NO₃)(η₂-NO₃)] (2), [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (3), [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (4), and one octacoordinated manganese(II) complex [Mn(bppza)(η₂-NO₃)₂] (5) have been synthesized and characterized using the tripodal tetradentate ligands tpa, bpia, bipa, ipqa, and bppza (tpa: tris(2-pyridylmethyl)amine, bpia: bis(2-pyridylmethyl)(2-(N-methyl)imidazolylmethyl)amine, bipa: bis-(2-(N-methyl)imidazolylmethyl)(2-pyridylmethyl)amine, ipqa: (2-(N-methyl)imidazolylmethyl)(2-pyridylmethyl)(2-quinolylmethyl)amine, and bppza: bis(2-pyridylmethyl)(2-pyrazylmethyl)amine). The crystal structures for all compounds have been determined. 1, 2 and 3 crystallize in the triclinic space group , 4 crystallizes in the orthorhombic space group Pbca, whereas the eight-coordinated 5 crystallizes in the monoclinic space group P2₁/n. All compounds have one bidentate bound nitrate group in common. The coordination number and its geometry depend on the coordination mode of the second nitrate group. The coordination polyhedron for 1, 2, 3 and 4 is best described as an oblate octahedron and the one for 5 as a doubly oblate octahedron.