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Introduction Sigma receptors are appropriate targets for tumor imaging because they are highly expressed in a variety of human tumors. Previously, we synthesized a vesamicol analog, (+)-2-[4-(4-iodophenyl)piperidino]cyclohexanol ((+)- p IV), with high affinity for sigma receptors, and prepared radioiodinated (+)- p IV. In this study, to develop a radiobromine-labeled vesamicol analog as a sigma receptor imaging agent for PET, nonradioactive and radiobromine-labeled (+)-2-[4-(4-bromophenyl)piperidino]cyclohexanol ((+)- p BrV) was prepared and evaluated in vitro and in vivo . In these initial studies, 77 Br was used because of its longer half-life. Methods (+)-[ 77 Br] p BrV was prepared by a bromodestannylation reaction with radiochemical purity of 98.8% after HPLC purification. The partition coefficient of (+)-[ 77 Br] p BrV was measured. In vitro binding characteristics of (+)- p BrV to sigma receptors were assayed. Biodistribution experiments were performed by intravenous administration of a mixed solution of (+)-[ 77 Br] p BrV and (+)-[ 125 I] p IV into DU-145 tumor-bearing mice. Results The lipophilicity of (+)-[ 77 Br] p BrV was lower than that of (+)-[ 125 I] p IV. As a result of in vitro binding assay to sigma receptors, the affinities of (+)- p BrV to sigma receptors were competitive to those of (+)- p IV. In biodistribution experiments, (+)-[ 77 Br] p BrV and (+)-[ 125 I] p IV showed high uptake in tumor via sigma receptors. The biodistributions of both radiotracers showed similar patterns. However, the accumulation of radioactivity in liver after injection of (+)-[ 77 Br] p BrV was significantly lower compared to that of (+)-[ 125 I] p IV. Conclusion These results indicate that radiobromine-labeled p BrV possesses great potential as a sigma receptor imaging agent for PET.

To develop a water-soluble and tumor-targeted photosensitizer for photodynamic therapy (PDT), a porphyrin framework containing the metal ion gallium(III) was combined with platinum(II)-based groups to produce two new pentacationic metalloporphyrinates, Ga-4cisPtTPyP (5,10,15,20-tetrakis{cis-diammine-chloro-platinum(II)}(4-pyridyl)-porphyrinato gallium(III) hydroxide tetranitrate) and Ga-4transPtTPyP (5,10,15,20-tetrakis{trans-diammine-chloro-platinum(II)} (4-pyridyl)-porphyrinato gallium(III) hydroxide tetranitrate). Both complexes exhibited high singlet oxygen quantum yields (Φ∆) and remarkable photocytotoxicity with appreciable phototoxic indexes (PIs). In particular, Ga-4cisPtTPyP showed a low IC50 value (Colon 26: 0.12 μM; Sarcoma 180: 0.08 μM) under illumination and its PI up to 1000. With outstanding tumor accumulation (tumor/muscle ratio > 9), Ga-4cisPtTPyP almost completely inhibited tumor growth over two weeks in an in vivo PDT assay. These results imply that Ga-4cisPtTPyP could be a promising anticancer agent for use in PDT.

金沢大学新学術創成研究機構, Background Release of radionuclides, such as 137Cs and 90Sr, into the atmosphere and the ocean presents an important problem because internal exposure to 137Cs and 90Sr could be very harmful to humans. Chlorella has been reported to be effective in enhancing the excretion of heavy metals; thus, we hypothesized that Chlorella could also enhance the elimination of 137Cs or 90Sr from the body. We evaluated the potential of Chlorella as a decorporation agent in vitro and in vivo, using 85Sr instead of 90Sr. Methods In vitro experiments of adsorption of 137Cs and 85Sr to Chlorella were performed under wide pH conditions. The maximum sorption capacity of Chlorella to strontium was estimated using the Langmuir model. A 85Sr solution was orally administrated to mice pretreated with Chlorella. At 48 h after 85Sr administration, the biodistribution of radioactivity was determined. Results In the in vitro experiments, although 85Sr barely adsorbed to Chlorella at low pH, the 85Sr adsorption ratio to Chlorella increased with increasing pH. The maximum sorption capacity of Chlorella to strontium was 9.06 mg / g. 137Cs barely adsorbed to Chlorella under any pH conditions. In the biodistribution experiments, bone accumulation of radioactivity after 85Sr administration was significantly decreased in the Chlorella pretreatment group compared with the non-treatment control group. Conclusions In conclusion, these results indicated that Chlorella could inhibit the absorption of 90Sr into the blood and enhance the elimination of 90Sr from the body through adsorption in intestine. Further studies are required to elucidate the mechanism and the components of Chlorella needed for adsorption to strontium and could promote the development of more effective decorporation agents. © 2016 Ogawa et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

β-Citryl-L-glutamate (β-CG) is a unique compound initially isolated from developing brains, which also appears in high concentrations during the period characterized by growth and differentiation of neurons in developing animals, and then decreases with maturation. However, its functional roles remain unclear. The stability constant obtained in our previous pH titration studies showed that β-CG forms relatively strong complexes with copper. Reactive oxygen species (ROS) and nitric oxide (NO) have been suggested to act as mediators of the cell death that occurs in neurons during development of the nervous system. However, regulation of ROS and NO formation by Cu in the developing brain remains poorly understood. The activity of superoxide dismutase (SOD), a key superoxide scavenging enzyme, is low in the developing brain. Furthermore, xanthine oxidase (XO) has been implicated in diverse pathological situations due to its capability of generating both ROS and NO. Therefore, we examined the effects of β-CG and its Cu-complex on SOD and XO activities. We found that the [Cu(II)(β-CG)] complex had SOD activity and a strong competitive inhibition of XO, while reduced glutathione caused concentration-dependent decreases of the XO inhibitory activities in the [Cu(II)(β-CG)] complex.

The compound beta-citryl-L-glutamate (beta-CG) was initially isolated from developing brains, while it has also been found in high concentrations in testes and eyes. However, its functional roles are unclear. To evaluate its coordination with metal ions, we performed pH titration experiments. The stability constant, logbeta(pqr) for M(p)(beta-CG)(q)H(r) was calculated from pH titration data, which showed that beta-CG forms relatively strong complexes with Fe(III), Cu(II), Fe(II) and Zn(II). beta-CG was also found able to solubilize Fe more effectively from Fe(OH)(2) than from Fe(OH)(3). Therefore, we examined the effects of beta-CG on Fe-dependent reactive oxygen species (ROS)-generating systems, as well as the potential ROS-scavenging activities of beta-CG and metal ion-(beta-CG) complexes. beta-CG inhibited the Fe-dependent degradation of deoxyribose and Fe-dependent damage to DNA or plasmid DNA in a dose-dependent manner, whereas it had no effect on Cu-mediated DNA damage. In addition, thermodynamic data showed that beta-CG in a physiological pH solution is an Fe(II) chelator rather than an Fe(III) chelator. Taken together, these findings suggest that beta-CG is an endogenous low molecular weight Fe chelator.

金沢大学新学術創成研究機構 / 金沢大学医薬保健研究域薬学系, Objective: Rhenium is one of the most valuable elements for internal radiotherapy because 186Re and 188Re have favorable physical characteristics. However, there are problems when proteins such as antibodies are used as carriers of 186/188Re. Labeling methods that use bifunctional chelating agents such as MAG3 require the conjugation of the 186/188Re complex to protein after radiolabeling with the bifunctional chelating agent. These processes are complicated. Therefore, we planned the preparation by a simple method and evaluation of a stable 186/188Re-labeled antibody. For this purpose, we selected 186/188Re(I) tricarbonyl complex as a chelating site. In this study, A7 (an IgG1 murine monoclonal antibody) was used as a model protein. 186/188Re-labeled A7 was prepared by directly reacting a 186/188Re(I) tricarbonyl precursor, [186/188Re(CO)3(H2O)3]+, with A7. We then compared the biodistribution of 186/188Re-labeled A7 in tumor-bearing mice with 125I-labeled A7. Methods: For labeling A7, [186/188Re(CO)3(H2O)3]+ was prepared according to a published procedure. 186/188Re-labeled A7 (186/188Re-(CO)3-A7) was prepared by reacting [186/188Re(CO)3(H2O)3]+ with A7 at 43°C for 2 h. Biodistribution experiments were performed by the intravenous administration of 186/188Re-(CO)3-A7 solution into tumor-bearing mice. Results: 186Re-(CO)3-A7 and 188Re-(CO)3-A7 were prepared with radiochemical yields of 23 and 28%, respectively. After purification with a PD-10 column, 186/188Re-(CO)3-A7 showed a radiochemical purity of over 95%. In biodistribution experiments, 13.1 and 13.2% of the injected dose/g of 186Re-(CO)3-A7 and 188Re-(CO)3-A7, respectively, accumulated in the tumor at 24-h postinjection, and the tumor-to-blood ratios were over 2.0 at the same time point. Meanwhile, uptake of 125I-A7 in the tumor was almost the same as that of 186/188Re-(CO)3-A7 at 24-h postinjection. Blood clearances of 186/188Re-(CO)3-A7 were faster than those of 125I-A7. Conclusion: 186/188Re-labeled A7 showed high uptakes in the tumor. However, further modification of the labeling method would be necessary to improve radiochemical yields and their biodistribution. © 2009 The Japanese Society of Nuclear Medicine.

Adduct formation of ternary Pt(II) complexes composed of an amino acid and an aromatic diimine, [Pt(A)(DA)] (A = glycinate (Gly), alaninate (Ala), valinate, or arginine (Arg); DA = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen)), with flavin mononucleotide (FMN) and anthraquinone-2-sulfonate (AQS) were investigated by spectroscopic, X-ray diffraction, and electrochemical methods. The Pt(II) complexes formed 1:1 [Pt(A)(DA)]–FMN adducts by stacking with the aromatic moiety of FMN, and the stability constants, log K, for the systems with [Pt(A)(phen)] (A = Gly, Ala, and Arg) and [Pt(Arg)(bpy)] were determined to be 2.83(8)–3.42(6) from 1H NMR spectra at 25 °C in D2O (I = var.). The structure of the adduct [Pt(Ala)(phen)](AQS) (1) was determined by X-ray analysis to involve a π–π stacking interaction between coordinated phen and AQS with the distance of 3.400(7) A and a hydrogen bond between the sulfonate moiety of AQS and the amino group of coordinated Ala. Cyclic voltammetry of the 1:1 [Pt(A)(DA)]–FMN systems in a phosphate buffer (pH 7.0) showed that the potentials, E1/2, for the two-electron redox process of FMN shifted to higher values by 18–31 mV as compared with the value for free FMN.

医薬保健研究域 薬学系, Cu in blood has been believed to transport into cell via albumin and some amino acids. To shed light on the Cu transport process we studied the reaction of the Cu(II)-peptide with the amino acid by absorption and CD spectra. Albumin mimic peptides GlyGly-l-HisGly (GGHG) and penta-Gly(G5) formed stable 4N coordinated Cu(II) complexes, but in the reaction with histidine (His) and penicillamine (Pes) the ternary Cu(II) complex formations were observed different by the kinetic study. Cu(II)-G5 complexes reacted with Pes to form the ternary complex Cu(H-1G5)(Pes-) which was subsequently transformed to the binary complex Cu(Pes-)2. In the system with GGHG the Cu(II) was also transported from GGHG to Pes, but the ternary Cu(H-1GGHG)(Pes-) complex as the intermediate was detected a trace. The ternary complex would be spontaneously transformed to Cu(Pes-)2 upon forming, because the rate constant of the ternary complex formation k1+ = ∼2 M-1 s-1 was less than k2+ = ∼5 × 102 M-1 s-1 for the Cu(Pes-)2 formation at physiological pH. In the Cu(II)-GGHG-His system the ternary Cu(H-1GGHG)(His) complex was also hardly identified because the formation constant K1 and k1+ were very small and the equilibrium existed between Cu(H-2GGHG) and Cu(His)2 and its overall equilibrium constant β2 for Cu(His)2 was very small to be 1.00 ± 0.05 M-1 at pH 9.0. These results indicated that the ternary complex is formed in the Cu transport process from the albumin to the amino acid, but His imidazole nitrogen in the fourth-binding site of Cu(II) strongly resists the replacement by the incoming ligand. © 2007 Elsevier Inc. All rights reserved.

This paper gives insight into chemical speciation. After a brief introduction, the methods available to study solution state of metal ions and the importance of speciation in biology are discussed ...

金沢大学医薬保健研究域 薬学系, Ternary Cu(ii) complexes containing an aromatic diimine (DA = di(2-pyridylmethyl)amine (dpa), 4,4′-disubstituted 2,2′-bipyridine (Y2bpy; Y = H (bpy), Me, Cl, N(Et)2, CONH2 or COOEt) or 2,2′-bipyrimidine) and an aromatic amino acid (AA = l-phenylalanine (Phe), p-substituted phenylalanine (XPhe; X = NH2, NO2, F, Cl or Br), l-tyrosine (Tyr), l-tryptophan (Trp) or l-alanine (Ala)) were characterized by X-ray diffraction, spectroscopic and potentiometric measurements. The structures of [Cu(dpa)(Trp)]ClO4·2H 2O and [Cu((CONH2)2bpy)(Phe)]ClO 4·H2O in the solid state were revealed to have intramolecular π-π interactions between the Cu(ii)-coordinated aromatic ring moiety, Cu(DA) (Mπ), and the side chain aromatic ring of the AA (Lπ). The intensities of Mπ-Lπ interactions were evaluated by the stability constants of the ternary Cu(ii) complexes determined at 25 °C and I = 0.1 M (KNO3), which revealed that the stability enhancement of the Cu(DA)(AA) systems due to the interactions is in the order (CONH 2)2bpy < bpy < Me2bpy < (Et 2N)2bpy with respect to DA. The results indicate that the electron density of coordinated aromatic diimines influences the intensities of the stacking interactions in the Cu(DA)(AA) systems. The Mπ-Lπ interactions are also influenced by the substituents, X, of Lπ and are in linear relationship with their Hammett σp values with the exception of X = Cl and Br. © The Royal Society of Chemistry

Two methoxy-substituted TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) derivatives, T(MQ)EN (N,N,N',N'-tetrakis(6-methoxy-2-quinolylmethyl)ethylenediamine) and T(TMQ)EN (N,N,N',N'-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)ethylenediamine), have been prepared, and their fluorescence properties with respect to Zn2+ coordination were investigated. Introduction of a methoxy substituent at 6-position of the quinoline ring enhances the fluorescence intensity by 10-fold, and the three methoxy substituents in the 5,6,7-positions afford significant enhancement of the long-wavelength component of the fluorescence of zinc complex. The substituents did not alter the binding affinity of these compounds toward zinc ion significantly. T(MQ)EN was proved to be effective in detection of zinc ion in cells by fluorescent microscopy.

We quantitatively investigated the coordination ability of ATCUN peptides possessing various amino acid residues on the N-terminal side of the third histidine, toward Cu2+. We discovered that the s...

The kinetic stability of a chelate-ring unit in Cu(H - 1 GlyGly), Cu(H - 1 β-AlaGly), and Cu(EDMA) complexes has been inspected by stopped-flow spectroscopy. Those three Cu(II) complexes reacted with cysteine (CysH) or penicillamine (PesH) to form primarily ternary complexes, formulated as Cu(H - 1 L)(Rs - ); L = GlyGly and β-AlaGly, and Cu(EDMA)(Rs-); where Rs represents the aminothiolates. The chelate-ring units composed of [N-(Gly)]-, [N-(β-Ala)]-, and [N-(2-aminoethyl)]-moieties in Cu(H - 1 GlyGly ), Cu(H - 1 β-AlaGly), and Cu(EDMA) were conserved, respectively, in the corresponding ternary complexes. The rate of the ternary complex formation was very rapid, so much so that the rate constants, k 1 + , could not be determined by the conventional stopped-flow techniques. The ternary complexes upon forming reacted with the RsH to produce the binary Cu(Rs - ) 2 species. Thus, the observables were limited to the rate constants, k 2 + , for the transformation from Cu(H - 1 L)(Rs - ) to Cu(Rs - ) 2 . The kinetic stabilities of those chelate-ring units were compared based on the rate constant, k 2 + , and equilibrium constant, K 2 . The stability was arranged as follows: [N-(Gly)]- > [N-(2-aminoethyl)]- > [N-(β-Ala)]-unit. Though Cu(EDMA) was kinetically stable, the Cu(II) in Cu(EDMA)(Rs - ) was rapidly delivered by a nucleophilic attack of RsH to form Cu(Rs - ) 2 . On the contrary, Cu(H - 1 -GlyGly) was kinetically less stable than Cu(EDMA), but delivery of the Cu(II) from Cu(H - 1 L)(Rs - ), by the proton-assisted mechanism, was comparatively slow.

The transport of Cu(II) complexed with histidine-containing tripeptides (Cu(H−iL), L = HisGlyGly (i = 2), GlyHisGly (i = 1), and GlyGlyHis (i = 2)) to cysteine was examined by a stopped-flow spectrophotometric method. The S → Cu(II) charge transfer (LMCT) bands at 335 nm and 390 nm were used as probes for tracing the reaction. Primarily formed was the ternary Cu(H−1L)(Cys−) complex. The rate of the Cu(H−1L)(Cys−) formation depended on the affinity of Cu(II) for the donor atoms at the fourth binding site of Cu(H−2L). Cu(H−1L)(Cys−) subsequently reacted with free Cys− to yield a binary complex, Cu(Cys−)2. The rate of Cu(H−1L)(Cys−) formation was generally faster than that of conversion from Cu(H−1L)(Cys−) to Cu(Cys−)2. An exception was found in the reaction with Cu(H−2GlyGlyHis), where the relation k1+ < k2+ existed. The ternary complex, Cu(H−1HisGlyGly)(Cys−), was too labile to be detect by the conventional stopped-flow methods. Probably, Cu(H−1HisGlyGly)(Cys−) upon forming changed spontaneously to Cu(HisG...

Cu(II) complexes of glycine-peptides, abbreviated as Cu(H−iL): L = glycylglycine, triglycine, tetraglycine, and pentaglycine (i = 1–3), react with cysteine to form ternary complexes, Cu(H−1L)(Cys−), as first intermediates. The spectral parameters of the ternary complexes, which were similar irrespective of the peptides, were as follows: λmax = 332 ± 1 nm (e = 4250 ± 50 M−1 cm−1), g|| = 2.170 ± 0.005, g⊥ = 2.00 ± 0.05, and A|| = (2.05 ± 0.01) × 10−4 cm−1, indicating that the ternary complexes have identical coordination structures: the Cu(II) coordinates with the peptides via the nitrogens from the terminal amino and the neighboring deprotonated-amide group, and with cysteine via the amino nitrogen and the thiolate sulfur. Based on the absorbance-time curves, the concentrations of each Cu(II) and Cu(I) species during the reaction were calculated. The species distribution curve clearly visualized the pathway of the Cu(II) transport from Cu(H−iL) to Cu(Cys−)2 via Cu(H−1L)(Cys−). The rate of Cu(H−1L)(Cys−) fo...

Adduct formations of Pt(II) complexes containing an aromatic diimine (DA) and an L-amino acid (A) with an aromatic carboxylate (AR) or a mononucleotide (NMP) has been studied by synthetic, structural, spectroscopic, and calorimetric methods. Several adducts between Pt(II) complexes, [Pt(DA)(L-A)] (charges are omitted; DA=2,2'-bipyrimidine (bpm); A=L-arginine (L-Arg), L-alaninate (L-Ala), and AR (=indole-3-acetate (IA), gentisate (GA)) or GMP were isolated as crystals and structurally characterized by the X-ray diffraction method. GMP in [Pt(bpm)(Arg)](GMP).5 H(2)O was revealed to be bound through the pi-pi stacking and guanidinium-phosphate hydrogen bonds. The [Pt(DA)(A)]-AR and -NMP systems in aqueous solution exhibited NMR upfield shifts of the aromatic ring proton signals due to stacking. The stability constants (K) for the adducts were determined by absorption and NMR spectra and calorimetric titrations. The log K values were found to be in the range 1.40-2.29 for AR and 1.8-3.3 for NMP, the order for NMP being GMP>AMP>CMP>UMP. The DeltaH degrees values were negative for all the systems studied, and the values for AR (=IA and GA) were more negative than those for NMP, indicating that ARs are stronger electron donors than NMPs. Comparison of the log K values for [Pt(bpm)(L-Arg)] and [Pt(bpm)(L-Ala)] (Ala=alaninate) indicated that the Arg moiety further stabilized the adducts by the guanidinium-carboxylate or -phosphate hydrogen bonds. The combined effects of weak interactions on the stability of the adducts in solution are discussed on the basis of the thermodynamic parameters and solid state structures.

Structures and stabilities of ternary copper(II) complexes, Cu(DP)(DA), where DP and DA denote dipeptides with an aromatic amino acid residue and bidentate nitrogen donor ligands, respectively, have been studied by synthetic, crystallographic, potentiometric, and spectroscopic methods. The X-ray crystal structure analysis of [Cu(gly· l- tyr)(bzp)] (gly· l- tyr=glycyl- l -tyrosinate, bzp=N-benzyl-N-2-pyridylmethylamine) revealed that the complex has a distorted square-pyramidal structure exhibiting an intramolecular edge-to-face stacking interaction between the pyridine ring of bzp and the phenol ring of gly· l- tyr around the Cu(II) center. [Cu(gly· l- tyr)(bzmp)] (bzmp=N-benzyl-N-6-methyl-2-pyridylmethylamine) was also revealed to have a similar structure and an intramolecular CH-π-type interaction between the methyl group of bzmp and the phenol ring of gly· l- tyr. The absorption spectra of the ternary Cu(II)–DP–DA systems in water showed that the ternary complexes have a shoulder peak near 900 nm, supporting that the Cu(II) center has a square-pyramidal geometry. From the stability constants for the ternary Cu(II) complexes determined by pH titration at 25 °C and I=0.1 M (KNO3), Cu(gly· l- tyr)(DA) and Cu(gly· l- trp)(DA) (DA=ligands with one or two aromatic rings) were found to be stabilized relative to Cu(gly·gly)(DA) (gly·gly=glycylglycinate), which has been concluded to be due to the contribution of the edge-to-face or CH-π interactions within the complexes in solution.

Synthetic, structural, and spectroscopic studies were performed on the copper(II) and palladium(II) complexes of various 2N1O-donor tripod-like ligands containing a pyridine or a dimethylamine nitrogen, a tertiary amine nitrogen, and a phenolate oxygen as donor atoms and a pendent indole ring. [Pd(impp)Cl]·3H2O·CH3CN (impp=N-2-pyridylmethyl-N-2-hydroxybenzyl-3-aminomethylindole) and two other Pd(II) complexes and a Cu(II) complex were isolated as crystals and structurally characterized by the X-ray diffraction method. The indole moiety of the Pd(II) complexes was found to be located close to the pyridine ring or the dimethylamino group and away from the phenolate moiety. 1H NMR spectra of the Pd(II) complexes in CD3CN exhibited large upfield shifts of the pyridine and dimethylamino proton signals due to the pendent indole ring, supporting that the complexes in solution have a stacked structure similar to that found in the solid state. These findings indicated that the aromatic ring stacking interactions or CH–π interactions exist between the indole and the pyridine rings or the methyl groups, respectively. [Cu2(impp)2](ClO4)2·H2O was revealed to have a dimeric structure with the indole moiety close to both the Cu(II) center and the pyridine ring, which suggests the possibility that the Cu(II) ion may undergo metal–aromatic ring interactions.

金沢大学新学術創成研究機構, 67Ga-DOTA-(L-Asp)11 and 67Ga-DOTA-(L-Asp)14, which have been developed as bone imaging agents, showed a high accumulation in bone and a rapid blood clearance in mice. However, peptides composed of D-amino acids are more stable in vivo than those composed of their L-equivalents. In this study, 67Ga-DOTA-(D-Asp)n (n = 2, 5, 8, 11, or 14) were synthesized using the Fmoc-based solid-phase methodology and evaluated. In hydroxyapatite binding assay, binding of 67Ga-DOTA-(D-Asp)n tended to increase with increasing length of the amino acid chain. 67Ga-DOTA-(D-Asp)11 and 67Ga-DOTA-(D-Asp)14 caused a high accumulation of radioactivity in the bones of the mice. However, the results for 67Ga-DOTA-(D-Asp)n and 67Ga-DOTA-(L-Asp)n were comparable. In urine analyses, the proportion of intact complex after injection of 67Ga-DOTA-(D-Asp)14 was significantly higher than that of 67Ga-DOTA-(L-Asp)14. Although 67Ga-DOTA-(D-Asp)14 was more stable than 67Ga-DOTA-(L-Asp)14, the properties of 67Ga-DOTA-(D-Asp)n and 67Ga-DOTA-(L-Asp)n as bone imaging agents may be comparable. © 2017 The Author(s).

α-Amino acids are highly functional small molecules whose side chain groups are like prototypes of metal coordination and weak interactions in proteins. This perspective focuses on non-covalent or weak interactions of the side chain groups of amino acids, such as the charged groups of arginine and aspartic acid and the aromatic rings of tyrosine and tryptophan, in metal complexes in solution and in the solid state. The structure and function of small complexes exhibiting weak interactions and their biological relevance are described.

Radiolabeled monoclonal antibodies (mAbs) are very useful molecular probes for nuclear imaging technique due to their high-target specificity and high-stability in the bloodstream. MAbs are generally labeled by indirect method using the combination of relatively long-lived metallic radionuclides (including (64)Cu, (89)Zr, and (111)In) and bifunctional chelating agents which are capable of binding both antibodies and radio metals. The indirect radiolabeling method has some advantages such as high labeling efficiency and long-term retention ability within their target cells. However, this conventional labeling method can potentially lead to low-target affinity of the mAb probes, because of the non-site-specific introduction of the bifunctional chelators into the active site of the mAbs. To overcome the shortcoming, we proposed a new direct labeling method utilizing fusion proteins comprising mAbs linked to metal binding peptides at the N- or C-terminus. In this study, we synthesized new peptide derivatives possessing an N-terminal tripeptide sequence (Xaa-Yaa-His) called the amino terminal Cu(2+)- and Ni(2+)-binding (ATCUN) motif as (64)Cu binding peptides for the proposed labeling method. Moreover, we studied the stability constants of Cu(2+)-ATCUN peptide complexes by pH titration. From these studies, we found that a low basicity of the N-terminal amine in the peptide resulted in a high stability constant of the complex. This finding may provide valuable guidelines in designing the ATCUN peptide with high-binding affinity toward (64)Cu.

Noncovalent or weak interactions play important roles in molecular recognition and structual organization in chemical and biological systems. Hydrogen bonding and aromatic ring stacking are widely recognized for biomolecules, and these and other types of weak interactions are recently attracting much attention as a clue to understanding the efficiency and specificity of biological reactions. We studied weak interactions around the metal center as factors for mixed ligand (ternary) metal complex formation, molecular recognition, and construction of self-organized structures by potentiometric, spectroscopic, and crystallographic methods. We concluded the electrostatic ligand–ligand interactions within Cu(II) and Pd(II) complexes containing an acidic and a basic amino acid and aromatic ring stacking interactions between the aromatic rings of an aromatic amino acid and a coordinated aromatic ligand such as 2,2′-bipyridine. Selective adduct formation between Pt(II) complexes and uncoordinated mononucleotides w...

New dinucleating ligands having two metal-binding sites bridged by an imidazolate moiety, Hbdpi and HMe4bdpi (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole, HMe4bdpi = 4,5-bis(di(6-methyl-2-pyridylmethyl)aminomethyl)imidazole), have been designed and synthesized as model ligands for copper−zinc superoxide dismutase (Cu,Zn-SOD). The corresponding mononucleating ligand, MeIm(Py)2 (MeIm(Py)2 = ((1-methyl-4-imidazolyl)methyl)bis(2-pyridylmethyl)amine), has also been synthesized for comparison. The imidazolate-bridged Cu(II)−Cu(II) homodinuclear complexes represented as [Cu2(bdpi)(CH3CN)2](ClO4)3·CH3CN·3H2O (1), [Cu2(Me4bdpi)(H2O)2](ClO4)3·4H2O (2), a Cu(II)−Zn(II) heterodinuclear complex of the type of [CuZn(bdpi)(CH3CN)2](ClO4)3·2CH3CN (3), and a Cu(II) mononuclear complex of [Cu(MeIm(Py)2(CH3CN)](ClO4)2·CH3CN (4) have been synthesized, and the structures of complexes 1−4 were determined by X-ray crystallography. The Cu(II)−Zn(II) distance of 6.197(2) A in 3 agrees well with that of native Cu,Zn-S...

The superoxide dismutase (SOD) activity of iron(II) tetrakis-N,N,N',N'(2-pyridylmethyl)ethylenediamine complex (Fe-TPEN) was reexamined using a pulse radiolysis method. In our previous study (J. Biol. Chem., 264, 9243-9249 (1989)), we reported that this complex has a potent SOD activity in a cyt. c (cytochrome c)-based system (IC 50 =0.8 μM) and protects E. coli cells against paraquat toxicity. The present pulse radiolysis experiment revealed that Fe(II)TPEN reacts stoichiometrically with superoxide to form Fe(III)TPEN with a second-order rate constant of 3.9×10 6 M -1 S -1 at pH 7.1, but superoxide did not reduce Fe(III)TPEN to Fe(II)TPEN. The reaction of Fe(III)TPEN and superoxide was biphasic. In the fast reaction, an adduct (Fe(III)TPEN-superoxide complex) was formed at the second-order rate constant of 8.5 ×10 5 M -1 s -1 at pH 7.4. In the slow one, the adduct reacted with another molecule of the adduct, regenerating Fe(III)TPEN. In the cyt. c method with catalase, this Fe(III)TPEN-superoxide complex showed cyt. c oxidation activity, which had led to overestimation of its SOD activity. Based on the titration data, the main species of complex in aqueous media at neutral pH was indicated to be Fe(III)TPEN(OH - ). A spectral change after the reduction with hydrated electron indicates that the OH - ion coordinates directly to Fe(III) by displacing one of the pyridine rings. The X-ray analysis of [Fe(II)TPEN]SO 4 supported this structure. From the above results we propose a novel reaction mechanism of FeTPEN and superoxide which resembles a proton catalyzed dismuting process, involving Fe(III)TPEN-superoxide complex.

Stabilities and coordination modes of the Cu(II) complexes of tripeptides, glycylglycyl–X (GlyGly–X), where X denotes Gly, β-alaninate, γ-aminobutyrate, δ-aminovalerate, e-aminocaproate, and sarcosinate, have been studied by pH-titration and electronic absorption and electron spin resonance (ESR) spectroscopies. On the basis of the stability constants and spectral data, the structure–stability relationship was determined, and the complexation pathways have been proposed. The stability constants determined at 25°C and I=0.1 M(KNO3) indicated that Cu(II) reacted with tripeptides (L) to form CuL and deprotonated species CuH−1L, CuH−2L, and CuH−3L (charges are omitted). The stability constants for CuH−2L were found to be primarily in the order of the deprotonation from the C-terminal peptide bond and thus to be determined by the accessibility of the carboxylate group to Cu(II). The coordination mode of CuH−2L depended on the size of the chelate ring formed by X with different lengths of the chain –NH(CH2)nCOO−. CuH−2L with n≤3 formed 5-5-5- – 5-5-7-membered fused rings with an amino nitrogen, two deprotonated peptide nitrogens, and a carboxylate oxygen, exhibiting the d–d transition band centered at 550–560 nm. The same species with n≥3 showed the absorption peak at ∼650 nm and was concluded to be Cu(H−1L)(OH−) having a 5-5-membered fused ring with an amino nitrogen, a deprotonated peptide nitrogen, a peptide carbonyl oxygen, and a hydroxide ion as donors. The structures for CuH−3L were also discussed.

The structures and stability constants of the copper(II) complexes of dipeptides (L) composed of N-terminal arginine (Arg), lysine (Lys) or glycinate (Gly), and C-terminal aspartate (Asp), glutamate (Glu) or Gly have been investigated by X-ray crystallographic, potentiometric and spectroscopic methods. The molecular structures of Cu(II)-arginylaspartate and -arginylglutamate both with the deprotonated peptide nitrogen, [Cu(ArgAspH −1 )]·H 2 O ( 1 ) and [Cu(ArgGluH −1 )]·4H 2 O ( 2 ), respectively, were determined to have the dipeptides coordinated in the equatorial positions through the two nitrogen atoms and an oxygen atom from the β-carboxylate group in 1 and the α-carboxylate group in 2 . The α- and γ-carboxylate oxygen atoms in 1 and 2 , respectively, bind with neighboring complex molecules to form a bridge and complete the Cu(II) coordination plane. The bridge formation was supported by the concentration dependence of the electron spin resonance (ESR) spectra. The stability constants for proton–L and 1:1 Cu(II)–L systems were determined at 5, 25 and 37°C ( I =0.1 M KNO 3 ), and the relevant thermodynamic parameters were calculated by using the van't Hoff equation. The stabilities of CuL and Cu(LH −1 ) were found to be in the order XAsp≥XGlu>XGly (X=Arg, Lys or Gly), indicating that the C-terminal Asp residue enhances the stability. From the thermodynamic parameters obtained, the interactions between the oppositely charged side chains in Cu(II)-coordinated XY (X=Arg, Lys; Y=Asp, Glu) have been discussed.

Electrostatic ligand-ligand interactions in ternary copper(II) complexes, Cu(AA)(PA), where AA refers to an aromatic amino acid (AA = 3, 5-diiodo- l -tyrosinate ( l -I 2 tyr), l -tyrosinate ( l -Tyr), or l -phenylalaninate ( l -Phe)) and PA refers to an amino acid with a polar or charged side-chain (PA = l -argininate ( l -Arg), ω-protonated l -lysinate ( l -LysH), l -asparaginate ( l -Asn), l -glutaminate ( l -Gln), or l -alaninate ( l -Ala)), have been studied by potentiometric and spectroscopic methods. The stability constants for Cu(AA)(PA) were determined by pH titrations at 25°C and I = 0.1M (KNO 3 ). The stability enhancement due to electrostatic interactions in Cu(AA)(PA) has been evaluated by several methods including the constant K for the following hypothetical equilibrium calculated from the determined overall stability constants of the relevant ternary complexes: Cu(AA)( l -Ala) + Cu( l -Phe)(PA) ⇄ Cu(AA)(PA) + Cu( l -Phe)( l -Ala) While the log K values were small or negative for Cu( l -I 2 tyr)( l -Asn), Cu( l -I 2 tyr)( l -Gln), and Cu( l -Tyr)(PA) with the protonated phenol OH group, large positive log K values were obtained for Cu( l -I 2 tyrO − )( l -Arg) (0.40) and Cu( l -I 2 tyrO − )( l -LysH) (0.41) with the deprotonated phenol moiety, which indicates that they are stabilized by intramolecular electrostatic interactions between the oppositely charged side groups of the coordinated ligands. Comparison of the 1 H NMR spectra of Pd( l -I 2 tyrO − )( l -LysH) and Pd( l -Ala)( l -LysH) in D 2 O indicated the interaction between the diiodophenolate moiety of I 2 tyrO − and the protonated ω-amino group of LysH. The circular dichroism spectra observed in the d-d region for these complexes exhibited an anomalously large negative maximum near 600 nm, supporting the existence of such interactions in the complexes in solution. Contribution of the iodo groups to the interactions was discussed.

Structures and spectroscopic studies have been carried out on ternary copper(II) complexes, Cu(DA)(AA), with aromatic amino acids (AA = 3,5-diiodo-L-tyrosinate (L-I(2)tyr), 3-iodo-L-tyrosinate (L-Ityr), L-tyrosinate) and diamines (DA = 1,10-phenanthroline, 2,2'-bipyridine (bpy), 2-(aminomethyl)pyridine, histamine (hista), or ethylenediamine). The charge transfer (CT) absorption bands observed in the near UV region and the CD spectral magnitude anomaly observed in the d-d region indicated an effective aromatic ring stacking interaction between the side-chain phenol ring of AA and the aromatic diamine DA in the complexes in solution. Two complexes, [Cu(bpy)(L-Ityr)(H(2)O)].NO(3).CH(3)OH.H(2)O (1) and [Cu(hista)(L-I(2)tyrO(-))(H(2)O)](2).2H(2)O (2), where O(-) represents the deprotonated form of the phenol hydroxyl group, were isolated as single crystals, and their structures were determined by X-ray analysis. Both 1 and 2 crystallized in the monoclinic space group P2(1), with a = 7.549(1) Å, b = 11.431(1) Å, c = 14.292(2) Å, beta = 100.08(1) degrees, and Z = 2 for 1 and a = 9.9642(9) Å, b = 15.825(1) Å, c = 12.451(1) Å, beta = 91.565(7) degrees, and Z = 2 for 2. The molecular structures of 1 and 2 revealed the intramolecular aromatic ring stacking between DA and the iodinated phenol ring of Ityr and I(2)tyrO(-), respectively, in correspondence with the solution spectral observations. The stacking with hista was found to be weaker than that with bpy from the interplanar distances in 1 and 2 and the CT band intensities in solution. The molecular and crystal structures revealed some intermolecular iodine-aromatic ring and iodine-oxygen interactions as well as some hydrogen bonds involving the phenol hydroxyl group.

Structures and stabilization due to stacking of ternary copper(II) complexes containing an aromatic amino acid (AA) and an aromatic diamine (DA), Cu(AA)(DA), have been investigated by potentiometric, spectroscopic, and X-ray diffraction methods. For the systems with AA = para-X-substituted l-phenylalanine (l-XPhe; X = H, NO2, OH, NH2) and DA = 2,2‘-bipyridine (bpy) or 1,10-phenanthroline (phen), the difference absorption spectra in the region 320−400 nm exhibited a peak assignable to the charge transfer interaction between the aromatic rings of DA and l-XPhe, the intensity being in the order NH2 > OH > H ≫ NO2 with respect to X. The stability constants of Cu(AA)(DA) determined for AA = dl-XPhe (X = F, Cl, Br) and l-XPhe (X = NH2, NO2, I) at 25 °C and I = 0.1 M (KNO3) indicated that stabilization of Cu(l-XPhe)(DA) relative to Cu(l-Ala)(en) (Ala = alanine; en = ethylenediamine) is in the order Br > OH > Cl ≈ NH2 > NO2 ≥ H ≥ F. The structures of [Cu(l-NH2Phe)(bpy)]NO3·H2O (1), [Cu(l-Tyr)(phen)]ClO4·2.5H2O (2...

金沢大学疾患モデル総合研究センター, 68Ga (T1/2 = 68 min, a generator-produced nuclide) has great potential as a radionuclide for clinical positron emission tomography (PET). Because poly-glutamic and poly-aspartic acids have high affinity for hydroxyapatite, to develop new bone targeting 68Ga-labeled bone imaging agents for PET, we used 1,4,7,10-tetraazacyclododecane-1,4,7,10- tetraacetic acid (DOTA) as a chelating site and conjugated aspartic acid peptides of varying lengths. Subsequently, we compared Ga complexes, Ga-DOTA-(Asp)n (n = 2, 5, 8, 11, or 14) with easy-to-handle 67Ga, with the previously described 67Ga-DOTA complex conjugated bisphosphonate, 67Ga-DOTA-Bn-SCN-HBP. After synthesizing DOTA-(Asp)n by a Fmoc-based solid-phase method, complexes were formed with 67Ga, resulting in 67Ga-DOTA-(Asp)n with a radiochemical purity of over 95% after HPLC purification. In hydroxyapatite binding assays, the binding rate of 67Ga-DOTA-(Asp)n increased with the increase in the length of the conjugated aspartate peptide. Moreover, in biodistribution experiments, 67Ga-DOTA-(Asp) 8, 67Ga-DOTA-(Asp)11, and 67Ga-DOTA- (Asp)14 showed high accumulation in bone (10.5±1.5, 15.1±2.6, and 12.8±1.7% ID/g, respectively) but were barely observed in other tissues at 60 min after injection. Although bone accumulation of 67Ga-DOTA-(Asp)n was lower than that of 67Ga-DOTA-Bn-SCN-HBP, blood clearance of 67Ga-DOTA-(Asp)n was more rapid. Accordingly, the bone/blood ratios of 67Ga-DOTA-(Asp) 11 and 67Ga-DOTA-(Asp)14 were comparable with those of 67Ga-DOTA-Bn-SCN-HBP. In conclusion, these data provide useful insights into the drug design of 68Ga-PET tracers for the diagnosis of bone disorders, such as bone metastases. © 2013 Ogawa et al., CC-BY 4.0

The site-directed mutants of negative patches on silene plastocyanin (PC) were used to investigate the change of interactions between photosystem I (PSI) and PC during the course of evolution from cyanobacteria to plants. The net charges of two highly conserved negative patches (#42-45 and #59-61) on silene PC were systematically modified from -4 to +1. PSI complexes from cucumber and Chlamydomonas reinhardtii were efficient electron acceptors for silene PC. The increase of net charge on the negative patch (#42-45) of silene PC decreased the reduction rates of PSI from cucumber and Chlamydomonas, while the modification of the other negative patch (#59-61) had no effect. Though the addition of MgCl2 decreased the reduction rate of cucumber PSI, the decrease was severely diminished in the case of Chlamydomonas PSI, and the reduction rate increased with increasing concentration of MgCl2 when the net charge of the negative patch (#42-45) was modified to +1. The PSI complexes from Anabaena variabilis and Synechosystis sp. PCC 6803 were inefficient electron acceptors for silene PC and their rates were almost independent of the net charge of the negative patches, as well as the ionic strength of the reaction mixtures. Silene PC specifically cross-linked to the PsaF subunit of PSI complexes from cucumber, Chlamydomonas, Anabaena, and Synechosystis sp. PCC 6803. Modification of the negative patch (#42-45) inhibited the formation of cross-linked adducts in all the cases examined, whereas modification of the other negative patch (#59-61) had essentially no effect. Based on these results, the changes of electrostatic interactions between PC and PSI during the course of evolution from cyanobacteria to plants are discussed.

Structures and stabilities of the ternary copper(II) complexes Cu(DA)(AA), where AA refers to 3,5-diiodo-L-tyrosinate (I(2)tyr) or L-tyrosinate (Tyr) and DA refers to 1,10-phenanthroline (phen), 2,2'-bipyridine (bpy), 2-(aminomethyl)pyridine (ampy), histamine (hista), or ethylenediamine (en), have been investigated by potentiometric, spectroscopic, and X-ray diffraction methods. The stability constants have been determined by potentiometric titrations at 25 degrees C and ionic strength I = 0.1 M (KNO(3)). The equilibrium constants K for a hypothetical equilibrium, Cu(DA)(Ala) + Cu(en)(AA) Cu(DA)(AA) + Cu(en)(Ala) where Ala refers to L-alanine, have been calculated from the determined overall stability constants of the ternary complexes for estimating the stability enhancement due to the stacking interaction between the aromatic rings in Cu(DA)(AA). Large positive log K values have been obtained for the Cu(DA)(I(2)tyrOH) and Cu(DA)(I(2)tyrO(-)) systems (DA = phen or bpy, OH and O(-) refer to the protonated and deprotonated forms of the phenol moiety, respectively), indicating that the complexes are stabilized by effective stacking. Differences between the log K values for Cu(DA)(I(2)tyr) and Cu(DA)(Tyr) systems indicate that the iodine substituents greatly contribute to the stability enhancement. A distinct circular dichroism (CD) magnitude anomaly was also observed for the systems with large log K value, supporting the existence of the stacking interaction in Cu(DA)(AA). Two complexes, [Cu(bpy)(I(2)tyrO(-))(H(2)O)].2H(2)O (1) and [Cu(bpy)(I(2)tyrOH)(NO(3))].CH(3)OH (2), have been isolated as crystals and analyzed by the X-ray diffraction method. Both 1 and 2 crystallized in the orthorhombic space group P2(1)2(1)2(1) with four molecules in a unit cell of dimensions a = 9.2339(4), b = 16.9230(8), and c = 14.8584(5) Å for complex 1, and a = 11.2240(8), b = 11.715(1), and c = 17.966(2) Å for complex 2. The central Cu(II) ion for both complexes has a similar distorted five-coordinate square-pyramidal geometry with the equatorial positions occupied by the two nitrogen atoms of bpy and the nitrogen and oxygen atoms of I(2)tyr, and the apical position is occupied by a water molecule (for 1) or a nitrate ion (for 2). The opposite site to the axial water or nitrate oxygen atom is intramolecularly occupied by the side chain aromatic ring, which is approximately parallel to the copper coordination plane with the average spacing of 3.31 or 3.30 Å for complex 1 or 2, respectively, directly exhibiting the effective stacking interaction between the aromatic rings in the solid state. Distances between the iodine and one of the pyridine rings of bpy (3.79 Å for 1 and 3.56 Å for 2) are shorter than the van der Waals distance (3.85 Å), implying that the iodine substituent may be involved in a weak bonding interaction with the pyridine ring. Effects of the iodine substituents on the stacking interactions between the diiodophenol side ring and the coordinated aromatic diamine and their possible biological relevance have been discussed.

Calorimetric and spectroscopic investigations have been carried out on the stacking interactions between nucleosides or nucleotides (NMP) and platinum DNA intercalators and other planar platinum(II) complexes with heteroaromatic ligands (L). Pt(L)(diamine) (L = 1,10-phenathroline (phen), its methyl and nitro derivatives, 2,2′-bipyridine; diamine = ethylenediamine (en), L-2,3-diaminopropionate) reacts with NMP (=adenosine 5′-monophosphate (AMP), guanosine 5′-monophosphate (GMP), inosine 5′-monophosphate (IMP), cytidine 5′ -monophosphate (CMP); nicotinamide adenine dinucleotide (NAD), adenosine, cytidine) to give the Pt(L)(diamine)–(NMP)n adducts (n = 1, 2) with log K1 = 1.63—3.00 and log K2 = 1.47—2.51 at 25 °C at ionic strength = 0.1 mol dm−3 (NaCl). The 1 : 1 adduct formation mainly depends on the enthalpy change ΔH1° = −6.5 — −26.2 kJ mol−1, and the entropy change (ΔS1° = −38—20 J mol−1 K−1) makes a negative or small contribution. 1H NMR upfield shifts observed for the Pt(phen)(en)–NMP systems have subs...

NMR and electronic absorption spectral studies have been carried out on complex formation and non-covalent interactions in ternary palladium(II) systems involving spermidine (Spd) and 2,3-diaminopropionate (Dpa) or 2,4-diaminobutyrate (Dba). 13 C NMR spectra indicated that Pd(Spd) and Pd(Spd) 2 with the N3 and N4 coordinations and Pd(AA) 2 with the N4 coordination were predominant species at neutral pH in the binary Pd(II)-Spd and Pd(II)-AA systems (AA = Dpa or Dba), respectively. Pd(Spd) 2 and Pd(AA) 2 were also found to be predominant in the 1:1:1 Pd(II)-AA-Spd systems, and in the l:2: x Pd(II)-AA-Spd systems ( x = 1–10), Pd(AA) 2 was the only complex species present with entire Spd uncomplexed. Circular dichroism (CD) spectral magnitudes as well as the NMR spectral shifts observed for the ternary systems and the CD magnitude dependence on solvent polarity indicated that the side chain carboxylate group of AA is involved in hydrogen bonds or electrostatic interactions with the protonated amino groups of Spd. The apparent stability constants, log K , for the 1:1 adduct Pd(AA) 2 · Spd at pH 7.5 (25 °C and I = variable) have been calculated from the CD magnitudes to be 2.4 and 2.6 for AA = Dpa and Dba, respectively.

Interaction of phytic acid (myo-inositolhexakisphosphoric acid, IP) and polyamines (A = en, tn, Put, dien, 2,3-tri, 3,3-tri, Spd, 3,3,3-tet, spermine(Spm)) have been studied by potentiometric and (31)P-NMR techniques. The non-covalent interactions have led to the formation of stable molecular complexes of (IP)H(n)(A) type at the 1:1 molar ratio of the ligands, but of different numbers of protons. The IP protonation constants, stability constants of the molecular complexes and metal (Mg(2+)) complexes have been determined. The structural and pH dependences of stability constants showed the interactions between IP and A have the acid-base character determining their effectiveness, although the IP structure (5ax1eq, 5eq1ax) in molecular complexes should be also taken into account. (31)P NMR study showed in the presence of Spm (31)P highfield shifts and high pH shift of signal broadening due to chemical exchange between 5ax1eq and 5eq1ax. The preferable binding of Spm to IP over Mg(2+) in neutral pH indicated the importance of polyamine as a stabilizer of phosphate compounds.

The structures and stabilities of metal(II) complexes of tyrosine- (tyr-) containing dipeptides (L), L-tyr-X [X=glycine(gly), L-/D-alanine, -tyr, -tryptophan, and -phenylalanine) and diamines [DA=ethylenedianune (en), 2,2'-bipyridine (bpy), and 1,10-phenanthroline (phen)) have been studied by crystallographic, spectroscopic, and potentiometric methods

Ternary copper(II) complexes containing an acidic amino acid (A) and a basic amino acid (B), Cu(A)(B), where A refers to ethylenediamine-N-monoaceticacid (EDMA) and DL-2,3-diaminopropionic acid (DAP) and B to L-arginine (L-Arg) and L-lysine (L-Lys), have been investigated by absorption and circular dichroism (CD) spectral, solution equilibrium, and X-ray diffraction methods with emphasis on ligand-ligand interactions.

金沢大学新学術創成研究機構 / 金沢大学医薬保健研究域薬学系, Introduction: 68Ga is a radionuclide of great interest as a positron emitter for positron emission tomography (PET). To develop a new bone-imaging agent with radiogallium, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was chosen as a chelating site and Ga-DOTA complex-conjugated bisphosphonate, which has a high affinity for bone, was prepared and evaluated. Although we are interested in developing 68Ga-labeled bone imaging agents for PET, in these initial studies 67Ga was used because of its longer half-life. Methods: DOTA-conjugated bisphosphonate (DOTA-Bn-SCN-HBP) was synthesized by conjugation of 2-(4-isothiocyanatebenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid to 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (alendronate). 67Ga-DOTA-Bn-SCN-HBP was prepared by coordination with 67Ga, and its in vitro and in vivo evaluations were performed. Results: 67Ga-DOTA-Bn-SCN-HBP was prepared with a radiochemical purity of over 95% without purification. 67Ga-DOTA-Bn-SCN-HBP had great affinity for hydroxyapatite in binding assay. In biodistribution experiments, 67Ga-DOTA-Bn-SCN-HBP accumulated in bone rapidly but was hardly observed in tissues other than bone. Pretreatment of an excess amount of alendronate inhibited the bone accumulation of 67Ga-DOTA-Bn-SCN-HBP. Conclusions: 67Ga-DOTA-Bn-SCN-HBP showed ideal biodistribution characteristics as a bone-imaging agent. These findings should provide useful information on the drug design of bone imaging agents for PET with 68Ga. © 2010 Elsevier Inc. All rights reserved.

The 1.7 Å X-ray crystal structure of the B-DNA dodecamer, [d(CGCGAATTCGCG)]₂ (DDD)-bound non-covalently to a platinum(II) complex, [{Pt(NH₃)₃}₂-µ-{trans-Pt(NH₃)₂(NH₂(CH₂)₆NH₂)₂}](NO₃)₆ (1, TriplatinNC-A,) shows the trinuclear cation extended along the phosphate backbone and bridging the minor groove. The square planar tetra-am(m)ine Pt(II) units form bidentate N-O-N complexes with OP atoms, in a Phosphate Clamp motif. The geometry is conserved and the interaction prefers O2P over O1P atoms (frequency of interaction is O2P O1P, base and sugar oxygens N). The binding mode is very similar to that reported for the DDD and [{trans-Pt(NH₃)₂(NH₂(CH₂)₆(NH₃(+))}₂-µ-{trans-Pt(NH₃)₂(NH₂(CH₂)₆NH₂)₂}](NO₃)₈ (3, TriplatinNC), which exhibits in vivo anti-tumour activity. In the present case, only three sets of Phosphate Clamps were found because one of the three Pt(II) coordination spheres was not clearly observed and was characterized as a bare Pt²(+) ion. Based on the electron density, the relative occupancy of DDD and the sum of three Pt(II) atoms in the DDD-1 complex was 1:1.69, whereas the ratio for DDD-2 was 1:2.85, almost the mixing ratio in the crystallization drop. The high repetition and geometric regularity of the motif suggests that it can be developed as a modular nucleic acid binding device with general utility.

Ternary Cu(II) complexes with the phosphoesters of amino acids (A=O-phosphoserine (Pser) or I=0.1 and 1.0 M(KNO3) and the stability enhancement due to the ligand-ligand interactions was evaluated by calculating the equilibrium constant K for the following hypothetical equilibrium from the overall stability constant of each ternary species: , where A′ refers to serine or tyrosine (Tyr) and B′ to alanine and the interactions are possible only in CU(L-A)(L-B). The ionic strength dependence of the log K values (> 0) indicated that Cu(L-A)(L-B) is stabilized by electrostatic interactions. X-ray crystal structure analysis of [Cu(bpy)(L-Tyr)ClO4]·2H2O (bpy=22′-bipyridine) revealed that the non-phosphorylated complex involves aromatic ring stacking between the Tyr phenol and coordinated bpy rings with the average spacing of 3.35 A in a tetrahedrally distorted square-pyramidal structure with the two nitrogen atoms of bpy and the nitrogen and oxygen atoms of L-Tyr at the equatorial positions and an oxygen atom of the perchlorate ion at the axial position. The results show that the stacked Tyr phenol ring is phosphorylated to be involved in the electrostatic interactions with the positively charged side chain of Arg or Lys which may be a possible mechanism of the conformational change due to Tyr phosphorylation in proteins.

Structures and stabilities of pteridine-containing ternary and quaternary Cu(II) complexes have been studied by synthetic, spectroscopic, potentiometric, and X-ray diffraction methods.

With a view to understanding the factors affecting the chemical properties of the copper sites in proteins, model copper(II) complexes of two multidentate ligands with nitrogen and sulfur atoms, 1,5-bis(2-pyridylmethylamino)-3-thiapentane (pmtp) and 2,6-bis(2,6-dithiaheptyl)pyridine (dthp), have been isolated as [Cu(pmtp)][Cu(pmtp)ClO4](ClO4)3 (1) and [Cu(dthp)(NO3)2] (2), respectively, and studied by X-ray diffraction, spectroscopic, and electrochemical methods. Complex 1 crystallizes in space group P21/a of the monoclinic system with four [Cu(pmtp)]2+ ions and four [Cu(pmtp)(ClO4)]+ ions in a cell of dimensions a = 24.180(7), b = 31.855(7), c = 9.760(3) A, and β = 143.84(1)°. The coordinations around the coppers in the two independent complexes are square-pyramidal and octahedral, respectively, with an amine nitrogen, two pyridine nitrogens, and a thioether sulfur at the equatorial positions (eq) and an amine nitrogen (and a perchlorate oxygen in addition in the octahedral complex) at the axial position...

Adduct formation by aromatic ring stacking and electrostatic interactions has been investigated for solutions containing platinum DNA intercalators Pt(L)(en) 2+ (L=2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (nphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me 4 phen); en=ethylenediamine) and mononucleotides NMP 2− (=AMP, GMP, CMP, UMP) or adenosine by spectroscopic methods. Difference absorption spectra of the Pt(L)(en) 2+ -NMP 2− systems revealed spectral changes in the region 290-350 nm probably due to the stacking interaction between Pt(L)(en) 2+ and NMP 2− , which was supported by the induced circular dichroism (CD) peaks observed in this region. The stacking has been substantiated by 1 H NMR spectra

With a view to understanding the precise binding mode and strength of the stacking interaction in the ternary copper(II) complexes comprising an aromatic diamine such as 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) and an aromatic amino acid such as L -phenylalanine, L -tyrosine and L -tryptophan ( L -trp), the crystal structure of [Cu(bpy)( L -trp)]ClO4 and the circular dichroism (CD) and absorption spectra of [Cu(bpy)( L -trp)]ClO4 and [Cu(phen)( L -trp)]ClO4 have been investigated. The complex [Cu(bpy)( L -trp)]ClO4 crystallizes in the monoclinic space group, P21, with two molecules in a unit cell of dimensions a=13.022(1), b=7.753(1), c=10.533(1) A, and β=91.18(1)°. The Cu(II) ion is five-coordinate square-pyramidal, with the two nitrogen atoms of bpy and the nitrogen and oxygen atoms of the amino acid coordinated at the equatorial positions in a slightly distorted square-planar form and the carboxylate oxygen atom of the neighboring molecule at the axial position. The most interesting structural feature of the complex is the existence of the intramolecular stacking interaction between the aromatic rings of L -trp and bpy with the average spacing of 3.67 A from the vacant axial position. The CD spectra in the d-d region for [Cu(bpy)( L -trp)ClO4 and [Cu(phen)( L -trp)]ClO4 in aqueous solution showed a large negative peak at 587 and 598 nm, respectively, and the magnitudes were greatly reduced in dioxane-water, which indicates that the aromatic ring stacking interaction is weakened in a hydrophobic environment. The absorption bands due to the charge transfer (CT) interaction between the indole ring and the aromatic diamine have been observed in the difference spectra in the near ultraviolet region. The strength of the stacking interactions has been demonstrated by the CT band intensity and the distance between the stacked rings to be in the order [Cu(phen)( L -trp)]ClO4>[Cu(bpy)( L -trp)]ClO4 both in solution and in the solid stare.

Late-onset hypogonadism (LOH) is a male-specific disorder caused by the age-related decline in androgens, such as testosterone (T). A sensitive liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) method for the simultaneous quantification of T and its precursor, dehydroepiandrosterone (DHEA), in human saliva has been developed and validated. The saliva was deprotenized with acetonitrile, purified using a Strata-X cartridge, derivatized with 2-hydrazino-1-methylpyridine, and subjected to LC-MS/MS. The recovery rates of the steroids during the pretreatment were about 90%. Quantification was based on selected reaction monitoring using characteristic transitions, and deuterated T and DHEA were used as internal standards. This method allowed the reproducible (inter- and intra-assay precisions,2.9%) and accurate (accuracy, 98.5-101.8%) quantification of the salivary androgens using a 500-microl sample and the limits of quantification for both androgens were 10 pg/ml. As preliminary steps in the practical application of the developed method in diagnosis and medication for LOH, the diurnal rhythms, inter-day alternations and age differences in the salivary T and DHEA were examined; the method found that the salivary T and DHEA show specific diurnal rhythms, significant alternations in early morning and pronouncedly decline with age. The method also enabled the determination of the changes in the individual T and DHEA levels after the DHEA supplementation, which is expected to be a new and easy medication for LOH. Thus, the developed method has satisfactory applicability in the diagnosis and medication for LOH.

医薬保健研究域 薬学系, Previously published stability constants of several metal ion (M2+) complexes formed with thiouridines and their 5′-monophosphates, together with recently obtained log KM (U)M versus p KUH plots for M2+ complexes of uridinate derivatives (U-) allowed now a quantitative evaluation of the effect that the exchange of a (C)O by a (C)S group has on the stability of the corresponding complexes. For example, the stability of the Ni2+, Cu2+ and Cd2+ complexes of 2-thiouridinate is increased by about 1.6, 2.3, and 1.3 log units, respectively, by the indicated exchange of groups. Similar results were obtained for other thiouridinates, including 4-thiouridinate. The structure of these complexes and the types of chelates formed (involving (N3)- and (C)S) are discussed. A recently advanced method for the quantification of the chelate effect allows now also an evaluation of several complexes of thiouridinate 5′-monophosphates. In most instances the thiouracilate coordination dominates the systems, allowing only the formation of small amounts of phosphate-bound isomers. Among the complexes studied only the one formed by Cu2+ with 2-thiouridinate 5′-monophosphate leads to significant amounts of the macrochelated isomer, which means that in this case Cu2+ is able to force the nucleotide from the anti to the syn conformation, allowing thus metal ion binding to both potential sites and this results in the formation of about 58% of the macrochelated isomer. The remaining 42% are species in which Cu2+ is overwhelmingly coordinated to the thiouracilate residue; Cu2+ binding to the phosphate group occurs in this case only in trace amounts. © 2007 Elsevier Inc. All rights reserved.