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Eiichi Kimura

Publications and source records attributed to Eiichi Kimura.

16 recordsLinked to original sources
PubMed2006

A new fluorescent probe for zinc(II): an 8-hydroxy-5-N,N-dimethylaminosulfonylquinoline-pendant 1,4,7,10-tetraazacyclododecane.

A new fluorescent probe for Zn2+, namely, 8-hydroxy-5-N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L8), was designed and synthesized (cyclen=1,4,7,10-tetraazacyclododecane). By potentiometric pH, 1H NMR, and UV spectroscopic titrations, the deprotonation constants pKa1-pKa6 of L(8)4 HCl were determined to be <2, <2, <2 (for amino groups of the cyclen and quinoline moieties), 7.19+/-0.05 (for 8-OH of the quinoline moiety), 10.10+/-0.05, and 11.49+/-0.05, respectively, at 25 degrees C with I=0.1 (NaNO3). The results of 1H NMR, potentiometric pH, and UV titrations, as well as single-crystal X-ray diffraction analysis, showed that L8 and Zn2+ form a 1:1 complex [Zn(H-1L8)], in which the 8-OH group of the quinoline ring of L8 is deprotonated and coordinates to Zn2+, in aqueous solution at neutral pH. On addition of one equivalent of Zn2+ and Cd2+, the fluorescence emission of L8 (5 microM) at 512 nm in aqueous solution at pH 7.4 [10 mM HEPES with I=0.1 (NaNO3)] and 25 degrees C increased by factors of 17 and 43, respectively. We found that the cyclen moiety has the unique property of quenching the fluorescence emission of the quinolinol moiety when not complexed with metal cations, but enhancing emission when complexed with Zn2+ or Cd2+. In addition, the Zn2+-L8 complex [Zn(H-1L8)] is much more thermodynamically and kinetically stable (Kd{Zn(H-1L8)}=[Zn2+]free[L8]free/[Zn(H-1L8)]=8 fM at pH 7.4) than the Zn2+ complexes of our previous Zn2+ fluorophores ([Zn(H-1L2)] and [Zn(L3)]). Furthermore, formation of [Zn(H-1L8)] is much faster than those of [Zn(H-1L2)] and [Zn(L3)]. The staining of early-stage apoptotic cells with L8 is also described.

Amines↗
PubMed2005

A luminescence sensor of inositol 1,4,5-triphosphate and its model compound by ruthenium-templated assembly of a bis(Zn2+-cyclen) complex having a 2,2'-bipyridyl linker (cyclen = 1,4,7,10-tetraazacyclododecane).

A new supramolecular complex (Ru(Zn2L4)3) was designed and synthesized as a luminescence sensor for inositol 1,4,5-triphosphate (IP3), which is one of the important second messengers in intracellular signal transduction, and its achiral model compound, cis,cis-1,3,5-cyclohexanetriol triphosphate (CTP3), by a ruthenium(II)-templated assembly of three molecules of a bis(Zn2+-cyclen) complex having a 2,2-bipyridyl linker (Zn2L4). Single-crystal X-ray diffraction analysis of a racemic mixture of Ru(Zn2L4)3 showed that three of the six Zn2+-cyclen units are orientated to face the opposite side of the molecule with three apical ligands (Zn2+-bound HO-) of each of the three Zn2+ located on the same face. 1H NMR and UV titrations of Ru(Zn2L4)3 with CTP3 indicated that Ru(Zn2L4)3 forms a 1:2 complex with CTP3, (Ru(Zn2L4)3)-((CTP3)6-)2, in aqueous solution at neutral pH. In the absence of guest molecules, Ru(Zn2L4)3 (10 microM) has an emission maximum at 610 nm at pH 7.4 (10 mM HEPES with I = 0.1 (NaNO3)) and 25 degrees C (excitation at 300 nm). An addition of 2 equiv of CTP3 induced a 4.2-fold enhancement in the emission of Ru(Zn2L4)3 at 584 nm. In this article, we describe that Ru(Zn2L4)3 is the first chemical sensor that directly responds to CTP3 and IP3 and discriminates these triphosphates from monophosphates and diphosphates. The photodecomposition of Ru(Zn2L4)3, which is inhibited upon complexation with CTP3, and the stereoselective complexation of chiral IP3 by Ru(Zn2L4)3 are also described.

Cyclohexanes↗
PubMed2004

Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions.

Two fluorescent ligands, N-(2-(5-cyanopyridyl))cyclen (L5) and N-(2-pyridyl)cyclen (L6) (cyclen = 1,4,7,10-tetraazacyclododecane), were designed and synthesized to control twisted intramolecular charge transfer (TICT) by metal chelation in aqueous solution. By complexation with Zn(2+), L6 exhibited TICT emissions at 430 nm (excitation at 270 nm) in 10 mM HEPES (pH 7.0) with I = 0.1 (NaNO(3)) at 25 degrees C due to the perpendicular conformation of a pyridine ring with respect to a dialkylamino group, which was fixed by Zn(2+)-N(pyridine) coordination, as proven by potentiometric pH, UV, and fluorescence titrations and X-ray crystal structure analysis. We further describe that the 1:1 complexation of ZnL6 with guests such as succinimide, phosphates, thiolates, and dicarboxylates, which compete with a nitrogen in the pyridine ring for Zn(2+) in ZnL6, induces considerable emission shift from TICT emissions (at 430 nm) to locally excited emissions (at ca. 350 nm) in neutral aqueous solution at 25 degrees C.

Journal Article↗
PubMed2004

Monitoring apoptosis with fluorescent Zn2+-indicators.

Apoptosis, a mechanism of programmed cell death that removes superfluous and harmful cells, is important both during development and in tissue homeostasis. Although Zn2+ is believed to be critical in apoptosis, the precise details of its role have yet to be elucidated. The macrocyclic Zn2+ ligand dansylamidoethylcyclen [L1*(HCl)4*(H2O)2], which is found primarily in a diprotonated form (H2L1), is cell-permeable and forms a strongly fluorescent 1:1 Zn2+ complex when Zn2+ entry into cells is facilitated by the Zn2+ ionophore pyrithione. H2L1 can be used to readily identify HeLa cells undergoing the early stages of etoposide-induced apoptosis because of the increased level of free Zn2+ that occurs at this time. The selectivity of H2L1 for the detection of apoptotic cells was verified by a conventional probe for apoptosis, annexin V-Cy3. Here, we describe methods for detecting apoptotic cells with H2L1 and for comparing detection of apoptosis with H2L1 to detection with annexin V-Cy3 and Zinquin.

Annexin A5↗
PubMed2003

A macrocyclic zinc(II) fluorophore as a detector of apoptosis.

Our originally designed dansylamidoethylcyclen 4 as a biomimetic Zn(2+)-selective fluorophore has been demonstrated to be a good detector of the apoptosis (induced by an anticancer agent, etoposide, and H(2)O(2)) in cancer cells such as HeLa and HL60 cells. The macrocyclic Zn(2+) ligand 4 (mostly as a deprotonated form) is cell-permeable to show weak fluorescence (emission at 550 nm), which forms a strong fluorescent 1:1 Zn(2+) complex 5 (emission at 530 nm) when Zn(2+) is incorporated into the cells by a zinc(II) ionophore pyrithione. Thus formed, Zn(2+) complex 5 is cell-impermeable and remains intact over a few hours. When apoptosis in HeLa or HL60 cells is artificially induced, 4 selectively and strongly stains apoptotic cells only at early stages, which was verified by using the conventional apoptosis detection probe annexin V-Cy3. Detection of the apoptotic cells by 4 was perhaps due to significantly increased free Zn(2+) flux at early stages of apoptosis. Apoptotic detection by 4 has been compared with a presently available Zn(2+) fluorophore, Zinquin 1. We present that 4 has advantages in detection of apoptosis over annexin V-Cy3 and Zinquin 1.

Apoptosis↗
PubMed2003

A new zinc(II) fluorophore 2-(9-anthrylmethylamino)ethyl-appended 1,4,7,10-tetraazacyclododecane.

A new 2-(9-anthrylmethylamino)ethyl-appended cyclen, L(3) (1-(2-(9-anthrylmethylamino)ethyl)-1,4,7,10-tetraazacyclododecane) (cyclen = 1,4,7,10-tetraazacyclododecane), was synthesized and characterized for a new Zn(2+) chelation-enhanced fluorophore, in comparison with previously reported 9-anthrylmethylcyclen L(1) (1-(9-anthrylmethyl)-1,4,7,10-tetraazacyclododecane) and dansylamide cyclen L(2). L(3) showed protonation constants log K(a)(i)() of 10.57 +/- 0.02, 9.10 +/- 0.02, 7.15 +/- 0.02, <2, and <2. The log K(a3) value of 7.15 was assigned to the pendant 2-(9-anthrylmethylamino)ethyl on the basis of the pH-dependent (1)H NMR and fluorescence spectroscopic measurements. The potentiometric pH titration study indicated extremely stable 1:1 Zn(2+)-L(3) complexation with a stability constant log K(s)(ZnL(3)) (where K(s)(ZnL(3)) = [ZnL(3)]/[Zn(2+)][L(3)] (M(-)(1))) of 17.6 at 25 degrees C with I = 0.1 (NaNO(3)), which is translated into the much smaller apparent dissociation constant K(d) (=[Zn(2+)](free)[L(3)](free)/[ZnL(3)]) of 2 x 10(-)(11) M with respect to 5 x 10(-)(8) M for L(1) at pH 7.4. The quantum yield (Phi = 0.14) in the fluorescent emission of L(3) increased to Phi = 0.44 upon complexation with zinc(II) ion at pH 7.4 (excitation at 368 nm). The fluorescence of 5 microM L(3) at pH 7.4 linearly increased with a 0.1-5 microM concentration of zinc(II). By comparison, the fluorescent emission of the free ligand L(1) decreased upon binding to Zn(2+) (from Phi = 0.27 to Phi = 0.19) at pH 7.4 (excitation at 368 nm). The Zn(2+) complexation with L(3) occurred more rapidly (the second-order rate constant k(2) is 4.6 x 10(2) M(-)(1) s(-)(1)) at pH 7.4 than that with L(1) (k(2) = 5.6 x 10 M(-)(1) s(-)(1)) and L(2) (k(2) = 1.4 x 10(2) M(-)(1) s(-)(1)). With an additionally inserted ethylamine in the pendant group, the macrocyclic ligand L(3) is a more effective and practical zinc(II) fluorophore than L(1).

Algorithms↗
PubMed2003

Heterogeneous nuclear ribonucleoprotein K interacts with and is proteolyzed by calpain in vivo.

Calpain is a cytosolic "modulator protease" that modulates cellular functions in response to Ca2+. To identify in vivo substrates of calpain, yeast two-hybrid screening was done using the 5-EF-hand (penta-EF-hand; PEF) domain of the micro-calpain large subunit (domain IV), since several possible in vivo substrates for calpain have been previously reported to bind to the 5-EF-hand domains. Other than the regulatory subunit of calpain, which binds to the domain IV, heterogeneous nuclear ribonucleoproteins (hnRNP) K and R were identified, and shown to be proteolyzed by micro-calpain in vitro. When expressed in COS7 cells, hnRNP K and micro-calpain co-localized in the cytosol, and Ca2+-ionophore stimulation of the cells resulted in proteolysis of hnRNP K, indicating that hnRNP K is an in vivo substrate for calpain. Now, hnRNP K is considered to function as a scaffold protein for its binding proteins, such as PKCdelta and C/EBPbeta, which were reported to be calpain substrates, suggesting that hnRNP-K is a scaffold for calpain to proteolyze these proteins.

Animals↗
PubMed2002

Study of pH-dependent zinc(II)-carboxamide interactions by zinc(II)-carboxamide-appended cyclen complexes (cyclen = 1,4,7,10-tetraazacyclododecane).

To elucidate intrinsic recognition of carboxamides by zinc(II) in carbonic anhydrase (CA) (as inhibitors) and carboxypeptidase A (CPA) (as substrates), a new series of Zn(2+)-carboxamide-appended cyclen complexes have been synthesized and characterized (cyclen = 1,4,7,10-tetraazacyclododecane). Two types of Zn(2+)-carboxamide interactions have been found. In the first case represented by a zinc(II) complex of carbamoylmethyl-1,4,7,10-tetraazacyclododecane (L(1)), the amide oxygen binds to zinc(II) at slightly acidic pH (to form ZnL(1)), and the deprotonated amide N(-) binds to zinc(II) at alkaline pH (to form ZnH(-1)L(1)) with pK(a) = 8.59 at 25 degrees C and I = 0.1 (NaNO(3)), as determined by potentiometric pH titrations, infrared spectral changes, and (13)C and (1)H NMR titrations. The X-ray crystal structure of ZnH(-1)L(3) (where L(3) = N-(4-nitrophenyl)carbamoylmethyl cyclen, pK(a) = 7.01 for ZnL(3) <==> ZnH(-1)L(3)) proved that the zinc(II) binds to the amidate N(-) (Zn-N(-) distance of 1.974(3) A) along with the four nitrogen atoms of cyclen (average Zn-N distance 2.136 A). Crystal data: monoclinic, space group P2(1)/n (No. 14) with a = 10.838(1) A, b = 17.210(2) A, c = 12.113(2) A, b = 107.38(1) degrees, V = 2156.2(5) A(3), Z = 4, R = 0.042, and R(w) = 0.038. These model studies provide the first chemical support that carboxamides are CA(-) inhibitors by occupying the active Zn(2+) site both in acidic and alkaline pH to prevent the occurrence of the catalytically active Zn(2+)-OH(-) species. In the second case represented by a zinc(II) complex of 1-(N-acetyl)aminoethylcyclen, ZnL(6), the pendant amide oxygen had little interaction with zinc(II) at acidic pH. At alkaline pH, the monodeprotonation yielded a zinc(II)-bound hydroxide species ZnL(6)(OH(-)) (pK(a) = 7.64) with the amide pendant remaining intact. The ZnL(6)(OH(-)) species showed the same nucleophilic activity as Zn(2+)-cyclen-OH(-). The second case may mimic the Zn(2+)-OH(-) mechanism of CPA, where the nucleophilic Zn(2+)-OH(-) species does not act as a base to deprotonate a proximate amide.

Journal Article↗
PubMed2002

Guanidine is a Zn(2+)-binding ligand at neutral pH in aqueous solution.

We have found the first well-characterized coordination of guanidine with Zn(2+) in a 1:1 complex (ZnL(1)) with cyclen (= 1,4,7,10-tetraazacyclododecane) functionalized with guanidinylethyl group (L(1) = (2-guanidinyl)ethyl-cyclen). The X-ray structure analysis of the 1:1 complex crystallized at pH 7.5 revealed an apical coordination of the pendant guanidinyl group to Zn(2+) ion in ZnL(1). By potentiometrtic pH titration, initial formation of a 1:1 Zn(L(1).H(+)) complex was indicated, where only the cyclen N's bind to Zn(2+) with the complexation constant, log K(s) (K(s) = [Zn(L(1).H(+))]/[Zn(2+)][L(1).H(+)] (M(-1))), being 12.4 +/- 0.1. Facile deprotonation of the guanidinium pendant in the Zn(L(1).H(+)) occurred with a pK(a) value of 5.9 +/- 0.1 at 25 degrees C with I = 0.1 (NaNO(3)) to yield the guanidine-coordinating complex ZnL(1). 4-Nitrophenyl phosphate dianion (NPP(2-)) interacted with ZnL(1) through a new Zn(2+)-phosphate coordination, as indicated by (31)P NMR titration and potentiometric pH titration. An apparent complexation constant for this new species, log K(app)(Zn(L(1).H(+))-NPP), was 4.0 +/- 0.1, which is larger than the log K(app)(ZnL(2)-NPP) value of 3.1 for the 1:1 complex of Zn(2+)-cyclen (ZnL(2)) with NPP at the common pH 5.6. The interaction of ZnL(1) with a phosphate dianion was proven by the X-ray crystal structure analysis of the 1:1 ZnL(1)-PP(2-) complex (PP(2-) is a dianion of phenyl phosphate) obtained from an aqueous solution at pH 6.5. At higher pH, the pendant guanidinium cation is deprotonated to displace the phosphate to yield the Zn(2+)-guanidine bond.

Cations, Divalent↗
PubMed2002

New supramolecular trigonal prisms from zinc(II)- 1,4,7,10-tetraazacyclododecane (cyclen) complexes and trithiocyanurate in aqueous solution.

The multiple bonding between multinuclear zinc(II)-1,4,7,10-tetraazacyclododecane (cyclen, a 12-membered tetraamine) complexes and multidentate ligands is an effective method for constructing supramolecular complexes having well defined and distinct structures in aqueous solution. Herein we present examples of supramolecular D(3h) prisms formed by self-assembly of linearly dimeric or trimeric zinc(II)-cyclen complexes with a potentially trianionic C(3) subunit trithiocyanuric acid (TCA(3-)), wherein Zn(2+)-S(-) or Zn(2+)-N(-) coordination bonds and hydrogen bonds are responsible for stability of the multicomponent architectures in aqueous solution at neutral pH.

Crystallography, X-Ray↗
PubMed2002

A cuboctahedral supramolecular capsule by 4:4 self-assembly of Tris(Zn(II)-cyclen) and trianionic trithiocyanurate in aqueous solution at neutral pH (cyclen=1,4,7,10-tetraazacyclododecane).

A 1:1 mixture of a tris(Zn(II)-cyclen) (1: [Zn(3)L(1)], L(1)=1,3,5-tris(1,4,7,10-tetraazacyclododecan-1-ylmethyl)benzene) and trithiocyanuric acid (TCA) yielded a 4:4 self-assembly complex [(Zn(3)L(1))(4)-(TCA(3-))(4)] (6) through the formation of Zn(II)-S(-) coordination bonds and hydrogen bonds between 1,3,5-triazine N and cyclen NH (cyclen=1,4,7,10-tetraazacyclododecane); the supramolecular capsule structure was revealed by X-ray crystal structure analysis. The capsule exterior represents a twisted cuboctahedral framework containing a nanoscale truncated tetrahedral cavity. The crystal data: formula C(144)H(308)N(72)O(58)S(12)Zn(12) (6[NO(3)](12) x 22 H(2)O), M(r)=5145.75, cubic, space group F432 (No. 209), a=39.182(1) A, V=60153(3) A (3), Z=8, R=0.100, R(w)=0.259. Lipophilic organic molecules with the matching sizes, for example, ([D(4)]-2,2,3,3)-3-(trimethylsilyl)propionic acid (TSP), 1-adamantanecarboxylic acid, 2,4-dinitrophenol (2,4-DNP), adamantane (ADM), or the tetra-n-propylammonium (TPA) cation, are encapsulated in the inner cavity, as revealed by remarkable upfield shifts of the (1)H NMR signals of these guest molecules. The encapsulation of ADM was confirmed by X-ray crystal structure analysis. Crystal data of the ADM-encapsulating complex: formula C(154)H(334)N(72)O(63)S(12)Zn(12) (6-ADM[NO(3)](12) x 27 H(2)O), M(r)=5372.06, cubic, space group F432 (No. 209), a=39.061(1) A, V=59599(3) A(3), Z=8, R=0.103, R(w)=0.263. The 4:4 self-assembly was stabilized by incorporation of one of these guest molecules. The apparent 4:4 self-assembly constants for 6 in the presence of an excess amount of a guest TPA, log K(app) (K(app)=[6-TPA]/[1](4)[TCA](4)) (M(-7))), were determined to be 34.0+/-2.0 and 35.5+/-3.0 by potentiometric pH and UV spectrophotometric titrations, respectively. An apparent encapsulation constant for 2,4-DNP, log K(enc) (K(enc)=[6-2,4-DNP]/[6][2,4-DNP] (M(-1))), was 6.0+/-0.1 at pH 7.0 (50 mM HEPES with I=0.1 (NaNO(3))), as determined by UV titrations. The lipophilicity of the inner cavity was close to that of 2-propanol, as a quantum yield (phi) of 0.24+/-0.1 for the fluorescent emission of 7-diethylaminocoumarin-1-carboxylic acid (20 microM) in the capsule was close to the phi of 0.22 found for 2-propanol. Encapsulation properties of the present Zn(II)-containing cage have been compared with those of cyclodextrins and Fujita's Pd(II)-containing supramolecular cage. The exterior chirality of the 4:4 complex was controlled from within by an encapsulated chiral guest molecule, 2,10-camphorsultam, as indicated by Cotton effects in the circular dichroism spectra.

Journal Article↗
PubMed2002

New potent agents binding to a poly(dT) sequence in double-stranded DNA: bis(Zn(2+)-cyclen) and tris(Zn(2+)-cyclen) complexes.

In an effort to search for mechanistically new and more potent agents than conventional drugs that target AT-rich sequences in double-stranded DNA, we have tested multi(Zn(2+)-cyclen) complexes. Indeed, they selectively bound to poly(dT) sequences to melt the A-T hydrogen bonds; only 2.5 microM or 4 microM of the p-tris(Zn(2+)-cyclen) complex were required to completely melt a 50 microM nucleobase of double-stranded poly(dA) x poly(dT) or poly(dA-dT)(2) at 25 degrees C. The region with seven consecutive T's in native DNA (150 bp) was protected from micrococcal nuclease hydrolysis, as revealed by footprinting assays, with IC(50) values of 2 microM for p-bis(Zn(2+)-cyclen) and 0.5 microM for p-tris(Zn(2+)-cyclen). The high affinity to AT-rich sequences of these Zn(2+)-cyclen complexes matches or surpasses those of the conventional AT-binding drugs distamycin A (IC(50)=2 microM) and DAPI (5 microM). Moreover, the p-tris(Zn(2+)-cyclen) complex selectively binds to the TATA box sequence of the SV40 early promoter to inhibit the binding of the TATA binding protein as effectively as distamycin A, with an IC(50) value of 0.4 microM. In vitro transcription of poly(dA) x poly(dT) using Escherichia coli RNA polymerase was effectively inhibited by p-tris(Zn(2+)-cyclen). The [(3)H]-ATP incorporation into RNA was more strongly blocked (IC(50)=0.8 microM) than the [(3)H]-UTP incorporation (IC(50)=40 microM), a fact indicating that the p-tris(Zn(2+)-cyclen) complex interacts only with the poly(dT) strand in the double-stranded DNA template.

Base Sequence↗
PubMed2002

Recent progress in artificial receptors for phosphate anions in aqueous solution.

Phosphate esters exist ubiquitously in nature in the form of nucleoside phosphates (nucleotides) as components of RNA (or DNA), sugar nucleotides for glycosylation of oligosaccharides or proteins, activated form of proteins responding to extracellular signals, and chemical mediators playing central roles in intracellular signaling signals. Phosphorylation of anti-viral nucleoside analogues by intracellular kinases yields nucleoside phosphates (nucleotide) as biologically active forms as anti-viral agents. Development of artificial phosphate receptors would afford new methodologies for detection, separation, or transport of biologically important phosphates. Herein, a recent progress of artificial phosphate receptors is reviewed with special focus on macrocyclic polyamines and their metal complexes as a new prototype. In comparison to most of the previous artificial receptors (most of them are organic molecules), our system characteristically works in aqueous solution at neutral pH with extremely strong affinities with phosphate anions. Moreover, zinc(II)-macrocyclic tetraamine (cyclen) complexes were discovered to selectively bind thymine and uracil, so that nucleotides of these bases are specifically recognized by the bis(Zn2+-cyclen) complexes.

Anions↗
PubMed2002

[From new molecular science to new supramolecular science with macrocyclic polyamines].

Exploitation of saturated macrocyclic polyamines has led to the discovery of numerous novel functions and new molecules such as 1) unique proton sponge properties; 2) uptake of biological polyanions; 3) peptide-like metal uptake properties; 4) stabilization of unusual oxidation states of metal ions (e.g., CuIII, NiIII); 5) novel uptake and activation of O2 by new NiII-macrocyclic complexes; 6) a new synthetic pathway to functionalize macrocyclic polyamines; 7) the first gold(III) complex that is a new candidate for gold-plating agents; 8) intrinsic zinc(II) properties pertinent to zinc enzymes; 9) selective recognition of thymine by ZnII complexes; and 10) new cage supermolecules. These newly discovered molecules and properties have opened up a new field of supramolecular science.

Crystallography, X-Ray↗
PubMed1999

New Robust Bleomycin Analogues: Synthesis, Spectroscopy, and Crystal Structures of the Copper(II) Complexes.

Two new bleomycin analogues, 2-[((2-(4-imidazolyl)ethyl)amino)carbonyl]-6-[((2-amino-2-methylpropyl)amino)methyl]pyridine = L(3)() and 2-[((2-(4-imidazolyl)ethyl)amino)carbonyl]-6-[((2-amino-1,1,2-trimethylpropyl)amino)methyl]pyridine = L(4)(), were synthesized in order to create air-stable ligands of their Cu(I) (and Fe(II)) complexes. The protonation constants (log K(n)()) of the ligands at 25 degrees C and I = 0.1 M NaNO(3) were 9.9, 6.9, and 5.2 for L(3)() and 10.0, 6.7, and 3.9 for L(4)(). The complexation of the triprotonated L(3)() and L(4)() with Cu(II) started at pH < 5 to yield 4-coordinate [Cu(II)(H(-)(1)L).H(+)](2+) complexes, 4 and 6, respectively, followed by formation of square-pyramidal [Cu(II)(H(-)(1)L)](+) complexes, 5 and 7, with pK(a) values of 5.6 for 5 and 5.9 for 7. The complexation constants, log K(Cu)()II(H)()-1(L), were 8.9 for [Cu(II)(H(-)(1)L(3))](+), 5, and 8.6 for [Cu(II)(H(-)(1)L(4))](+), 7, respectively. The structures of [Cu(II)(H(-)(1)L(3))]ClO(4) (5.ClO(4)) and [Cu(II)(H(-)(1)L(4))]BF(4) (7.BF(4)) were determined by X-ray crystallography. Crystal data for 5.ClO(4): monoclinic, space group P2(1)/n (No. 14), a = 13.978(6) Å, b = 8.103(3) Å, c = 18.037(5) Å, beta = 98.61(3) degrees, V = 2019(1) Å(3), Z = 4, R = 0.053, and R(w) = 0.044 for 2996 [I > 3sigma(I)] reflections. Crystal data for 7.BF(4): monoclinic, space group P2(1)/n (No. 14), a = 16.092 (4) Å, b = 7.974(4) Å, c = 16.819(2) Å, beta = 99.64(1) degrees, V = 2127(1) Å(3), Z = 4, R = 0.040, and R(w) = 0.025 for 1633 [I > 4sigma(I)] reflections. The coordination geometry around the copper was a distorted square-pyramid in 5, while that of 7 was the intermediate between a trigonal-bipyramid and a square-pyramid. The distortion is influenced strongly by the number of the methyl group. The EPR spectral data for both copper(II) complexes were consistent with the retention of the solid-state structure in frozen DMF/MeOH (1:1) solution at 77 K. The visible absorption spectra of 10% DMF/aqueous solutions (pH 9.5) of 5 and 7 at I = 0.1 M NaNO(3) showed absorption maxima at 646 nm with a shoulder at ca. 900 nm for 5 and at 658 and 888 nm for 7. The red-shift of 7 by ca. 12 nm relative to 5 reflects the distortion toward the trigonal-bipyramidal geometry of 7 in solution. Both complexes displayed irreversible redox behavior in DMF at I = 0.1 M tetra(n-butyl)ammonium tetrafluoroborate. The anodic and cathodic peak potentials obtained by cyclic voltammetry for 5 and 7 were -0.14 and -0.76 V for 5 and -0.17 and -0.80 for 7 vs Ag/AgCl. The cathodic potentials of copper(II) complexes were shifted toward the anodic direction by ca. 20-60 mV compared to the nonsubstituted 5-coordinate, [Cu(II)(H(-)(1)L(1))](+) complex, 16 (-0.82 V vs Ag/AgCl). The Cu(I) complexes (9and 10) are air-oxidized to the corresponding Cu(II) complexes, 5 and 7, respectively.

Journal Article↗