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PubMed2001

Synthesis, structure, and redox and catalytic properties of a new family of ruthenium complexes containing the tridentate bpea ligand.

We have prepared a new family of ruthenium complexes containing the bpea ligand (where bpea stands for N,N-bis(2-pyridyl)ethylamine), with general formula [Ru(bpea)(bpy)(X)](n+) (2, X = Cl(-); 3, X = H(2)O; 4, X = OH(-)), and the trisaqua complex [Ru(bpea)(H2O)(3)](2+), 6. The complexes have been characterized through elemental analyses, UV-vis and (1)H NMR spectroscopy, and electrochemical studies. For complex 3, the X-ray diffraction structure has also been solved. The compound belongs to the monoclinic P2(1)/m space group, with Z = 2, a = 7.9298(6) A, b = 18.0226(19) A, c = 10.6911(8) A, and beta = 107.549(8) degrees. The Ru metal center has a distorted octahedral geometry, with the O atom of the aquo ligand placed in a trans position with regard to the aliphatic N atom of the bpea ligand so that the molecule possesses a symmetry plane. NMR spectra show that the complex maintains its structure in aqueous solution, and that the corresponding chloro complex also has a similar structural arrangement. The pH dependence of the redox potential for the complex [Ru(bpea)(bpy)(H2O)](PF(6))(2) is reported, as well as the ability of the corresponding oxo complex to catalyze the oxidation of benzylic alcohol to benzaldehyde in both chemical and electrochemical manners.

Journal Article↗
PubMed2002

A dinuclear manganese(II) complex with the [Mn(2)(mu-O(2)CCH(3))(3)](+) core: synthesis, structure, characterization, electroinduced transformation, and catalase-like activity.

Reactions of Mn(II)(PF(6))(2) and Mn(II)(O(2)CCH(3))(2).4H(2)O with the tridentate facially capping ligand N,N-bis(2-pyridylmethyl)ethylamine (bpea) in ethanol solutions afforded the mononuclear [Mn(II)(bpea)](PF(6))(2) (1) and the new binuclear [Mn(2)(II,II)(mu-O(2)CCH(3))(3)(bpea)(2)](PF(6)) (2) manganese(II) compounds, respectively. Both 1 and 2 were characterized by X-ray crystallographic studies. Complex 1 crystallizes in the monoclinic system, space group P2(1)/n, with a = 11.9288(7) A, b = 22.5424(13) A, c =13.0773(7) A, alpha = 90 degrees, beta = 100.5780(10 degrees ), gamma = 90 degrees, and Z = 4. Crystals of complex 2 are orthorhombic, space group C222(1), with a = 12.5686(16) A, b = 14.4059(16) A, c = 22.515(3) A, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, and Z = 4. The three acetates bridge the two Mn(II) centers in a mu(1,3) syn-syn mode, with a Mn-Mn separation of 3.915 A. A detailed study of the electrochemical behavior of 1 and 2 in CH(3)CN medium has been made. Successive controlled potential oxidations at 0.6 and 0.9 V vs Ag/Ag(+) for a 10 mM solution of 2 allowed the selective and nearly quantitative formation of [Mn(III)(2)(mu-O)(mu-O(2)CCH(3))(2)(bpea)(2)](2+) (3) and [Mn(IV)(2)(mu-O)(2)(mu-O(2)CCH(3))(bpea)(2)](3+) (4), respectively. These results have shown that each substitution of an acetate group by an oxo group is induced by a two-electron oxidation of the corresponding dimanganese complexes. Similar transformations have been obtained if 2 is formed in situ either by direct mixing of Mn(2+) cations, bpea ligand, and CH(3)COO(-) anions with a 1:1:3 stoichiometry or by mixing of 1 and CH(3)COO(-) with a 1:1.5 stoichiometry. Associated electrochemical back-transformations were investigated. 2, 3, and the dimanganese [Mn(III)Mn(IV)(mu-O)(2)(mu-O(2)CCH(3))(bpea)(2)](2+) analogue (5) were also studied for their ability to disproportionate hydrogen peroxide. 2 is far more active compared to 3 and 5. The EPR monitoring of the catalase-like activity has shown that the same species are present in the reaction mixture albeit in slightly different proportions. 2 operates probably along a mechanism different from that of 3 and 5, and the formation of 3 competes with the disproportionation reaction catalyzed by 2. Indeed a solution of 2 exhibits the same activity as 3 for the disproportionation reaction of a second batch of H(2)O(2) indicating that 3 is formed in the course of the reaction.

Binding Sites↗
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

The effect of ligand scaffold size on the stability of tripodal hydroxypyridonate gadolinium complexes.

The variation of the size of the capping scaffold which connects the hydroxypyridonate (HOPO) binding units in a series of tripodal chelators for gadolinium (Gd) complexes has been investigated. A new analogue of TREN-1-Me-3,2-HOPO (1) (TREN = tri(ethylamine)amine) was synthesized: TREN-Gly-1-Me-3,2-HOPO (2) features a glycine spacer between the TREN cap and HOPO binding unit. TRPN-1-Me-3,2-HOPO (3) has a propylene-bridged cap, as compared to the ethylene bridges within the TREN cap of the parent complex. Thermodynamic equilibrium constants for the acid-base properties of 2 and the Gd(3+) complexation strength of 2 and 3 were measured and are compared with that of the parent ligand. The most basic ligand is 2 while 3 is the most acidic. Both 2 and 3 form Gd(3+) complexes of similar stability (pGd = 16.7 and 15.6, respectively) and are less stable than the parent complex Gd-1 (pGd = 19.2). Two of the three complexes are more stable than the bis(methylamide)diethylenetriamine pentaacetate complex Gd(DTPA-BMA) (pGd = 15.7) while the other is of comparable stability. Enlargement of the ligand scaffold decreases the stability of the Gd(3+) complexes and indicates that the TREN scaffold is superior to the TRPN and TREN-Gly scaffolds. The proton relaxivity of Gd-2 is 6.6 mM(-)(1) s(-)(1) (20 MHz, 25 degrees C, pH 7.3), somewhat lower than the parent Gd-1 but higher than that of the MRI contrast agents in clinical practice. The pH-independent relaxivity of Gd-2 is uncharacteristic of this family of complexes and is discussed.

Contrast Media↗
PubMed2003

A rational approach to the design and synthesis of chiral organopalladium-amine complexes.

A new chiral auxiliary, (+/-)-N,N-dimethyl-1-(2,5-dimethylphenyl)ethylamine, was designed and synthesized in two steps from 1-acetyl-2,5-dimethylbenzene. Its cyclopalladated dimeric complex could be efficiently resolved via the formation of (S)-prolinate derivatives. Both hand forms of the complex could be obtained in similar yields. Despite the enormous inter-chelate steric constraints, the bulky monodentate ligand 3,4-dimethyl-1-phenylphosphole (DMPP) is able to coordinate regiospecifically to the orthopalladated 2,5-dimethylbenzylamine unit trans to the NMe(2) group. Compared to its naphthylamine analogue, the orthopalladated 2,5-dimethylbenzylamine complex exhibits a significantly higher stereoselectivity in the chiral template promoted asymmetric cycloaddition reaction between DMPP and ethyl vinyl ketone.

Journal Article↗
PubMed2003

Investigations into the interactions between DNA and conformationally constrained pyridylamineplatinum(II) analogues of AMD473.

The syntheses of [PtCl(2)(amp)] (amp = 2-pyridylmethylamine) and enantiomerically pure [PtCl(2)(R-pea)] and [PtCl(2)(S-pea)] (pea = 1-(2-pyridyl)ethylamine) and the crystal structure of [PtCl(2)(R-pea)] are reported. The reactions of [PtCl(2)(amp)] and of the enantiomers of [PtCl(2)(pea)] with d(GpG) and with a 52-base-pair oligonucleotide were investigated. Each of the reactions with d(GpG) resulted in the formation of three platinated bifunctional d(GpG) species in a ratio of 1:2:1. These species were shown to be a pair of isomers, one of which exists as a pair of slowly interconverting rotamers that can be separated by HPLC but reequilibrate after 5 days at 37 degrees C. The pyridyl moieties of the pyridylalkylamine ligands are constrained to lie in the coordination plane, and as a consequence, the rotation about the Pt-N7 bond of the adjacent guanine is highly restricted. 2D NMR investigations were carried out on the isomer of [Ptd(GpG)(amp)] that did not form separable rotamers and identified it as the isomer having the pyridine adjacent to the 5'-guanine of the d(GpG). The reaction of each of the three [PtCl(2)(py-R)] complexes (py-R = amp or pea) with a 52-base-pair oligonucleotide resulted in the formation of the same three bifunctional d(GpG) adducts in approximately the same ratios as the reactions with d(GpG), indicating that negligible stereoselectivity results from interactions between the complexes and duplex DNA.

Base Sequence↗
PubMed2005

Stereochemical investigations of a novel class of chiral phosphapalladacycle complexes derived from 1-[(2,5-dimethyl)phenyl]ethyldiphenylphosphine.

The phosphapalladacycle derived from 1-(2',5'-dimethylphenyl)ethyldiphenylphosphine has been prepared in the optically active and racemic forms. The phosphine was synthesized as a racemate by the treatment of 1-chloro-1-(2',5'-dimethylphenyl)ethane with sodium diphenylphosphide in THF. The racemic phosphapalladacycle was subsequently obtained as the chloro-bridged dimer by the treatment of the phosphine with palladium(II) acetate followed by anion metathesis with lithium chloride. Alternatively, the phosphine could be optically resolved via metal complexation using (R,R)-bis(mu-chloro)bis{1-[1-(N,N-dimethylamino)ethyl]naphthyl-C(2),N}dipalladium(II) as the resolving agent. An efficient separation of the resulting diastereomeric complexes was achieved by silica gel chromatography. The obtained optically resolved diastereomers were next subject to chemoselective removal of the (R)-N,N-(dimethylamino)-1-(1-naphthyl)ethylaminate auxiliary by treatment with concentrated hydrochloric acid. This process yielded the binuclear dimer complexes containing the resolved eta(1)-P ligand. Cyclopalladation of the coordinated phosphine could next be performed by treatment of its eta(1)-P binuclear dimer with silver(I) hexafluorophosphate(V) in a dichloromethane/water mixture followed by treatment with lithium chloride, giving rise to a pair of optically pure enantiomeric dimers with [alpha](D) -322 and +319 degrees in CH(2)Cl(2). Despite the possibilities of the phosphine to attain a five- membered structure by ortho-palladation or a six-membered ring formation by aliphatic C-H bond activation, only the former was observed. X-ray crystallographic data of the meso dimer and an acetylacetonate derivative indicated that the phosphapalladacycle alpha-C methyl substituent was axially located. The 2-D (1)H-(1)H ROESY spectrum of the acetylacetonate derivative further revealed that the phosphapalladacycle was conformationally rigid in CDCl(3).

Journal Article↗
PubMed2006

Catalytic ability of a cationic Ru(II) monochloro complex for the asymmetric hydrogenation of dimethyl itaconate and enamides.

The synthesis of two Ru chloro complexes, Ru(III)Cl(3)(bpea), 1, and cis-fac-Delta-[Ru(II)Cl{(R)-(bpea)}{(S)-(BINAP)}](BF(4)), cis-fac-Delta-(R)-(S)-2, (bpea = N,N-bis(2-pyridylmethyl)ethylamine; (S)-BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), is described. Complex 2 is characterized in solution through UV-vis, cyclic voltammetry (CV), and 1D and 2D NMR spectroscopy. X-ray diffraction analysis indicates that in the solid state it possesses the same structure as in solution, as expected for a low-spin d(6) Ru(II)-type complex. The molecular structure of cis-fac-Delta-(R)-(S)-2, consists of a nonsymmetric complex, where the Ru metal center has a significantly distorted octahedral-type coordination because of the bulkiness of the (S)-BINAP ligand. cis-fac-Delta-(R)-(S)-2 has a remarkable catalytic performance at P = 6.8 atm of H2 and T = 70 degrees C toward the hydrogenation of prochiral double bonds both from efficiency and from stereoselectivity viewpoints. As an example, prochiral olefins of technological interest such as dimethyl itaconate, methyl 2-acetamidoacrylate or methyl 2-acetamidocinnamate are catalytically hydrogenated by cis-fac-Delta-(R)-(S)-2, with conversions higher than 99.9% and ee > 99. Furthermore, cis-fac-Delta-(R)-(S)-2, also catalyzes the selective hydrogenation of beta-keto esters, although the reaction rates are lower than those found with the former substrates.

Amides↗
PubMed2006

New Ru complexes containing the N-tridentate bpea and phosphine ligands: consequences of meridional vs facial geometry.

The synthesis and isolation of the complex cis,fac-[RuIICl2(bpea)(PPh3)][3; bpea = N,N-bis(2-pyridylmethyl)ethylamine] and three geometrical isomers of the complex [RuIICl(bpea)(dppe)](BF4) [4; dppe = (1,2-diphenylphosphino)ethane], trans,fac (4a), cis,fac (4b), and mer(down) (4c), have been described (see Chart 1 for a drawing of their structures). These complexes have been characterized through analytical, spectroscopic (IR, UV/vis, and 1D and 2D NMR), and electrochemical (cyclic voltammetry) techniques. In addition, complexes 3, 4a, and 4b have been further characterized in the solid state through monocrystal X-ray diffraction analysis. The molecular and electronic structures of isomers 4a, 4b, 4c, and 4d (the mer(up) isomer) have also been studied by means of density functional theory (DFT) calculations. Furthermore, their low-energy electronic transitions have been simulated using time-dependent DFT approaches, which have allowed unraveling of their metal-to-ligand charge-transfer nature. Complexes 3 and 4a-c are capable of catalyzing H-transfer types of reactions between alcohols and aromatic ketones such as acetophenone and 2,2-dimethylpropiophenone (DP). A strong influence of the facial versus meridional geometry in the bpea ligand coordination mode is observed for these catalytic reactions, with the meridional isomer being much more active than the facial one. The meridional isomer is even capable of carrying out the H-transfer reaction of bulky substrates such as DP at room temperature.

Journal Article↗
PubMed2006

Structural and magnetic studies on cyano-bridged rectangular Fe2M2 (M = Cu, Ni) clusters.

Using the tricyano precursor, (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl) hydroborate) (1), four new tetranuclear clusters, [(Tp)Fe(CN)3Cu(Tp)]2.2H2O (2), [(Tp)Fe(CN)3Cu(bpca)]2.4H2O (3) (bpca = bis(2-pyridylcarbonyl)amidate anion), [(Tp)Fe(CN)3Ni(tren)]2(ClO4)2.2H2O (4) (tren = tris(2-amino)ethylamine), and [(Tp)Fe(CN)3Ni(bipy)2]2[(Tp)Fe(CN)3]2.6H2O (5) (bipy = 2,2'-bipyridine), have been synthesized and structurally characterized. The four clusters possess similar square structures, where FeIII and MII (M = CuII or NiII) ions alternate at the rectangle corners. There exist intermolecular - stacking interactions through pyrazolyl groups of Tp- ligands in complexes 2 and 4, which lead to 1D chain structures. Complex 5 shows a 3D network structure through the coexistence of - stacking effects and hydrogen-bonding interactions. Magnetic studies show intramolecular ferromagnetic interactions in all four clusters. The exchange parameters are +11.91 and +1.38 cm(-1) for clusters 2 and 3, respectively, while uniaxial molecular anisotropy can be detected in complex 3 due to the distorted core in its molecular structure. Complex 4 has a ground state of S = 3 and shows SMM behavior with an effective energy barrier of U = 18.9 cm(-1). Unusual spin-glass-like dynamic relaxations are observed for complex 5.

Journal Article↗
PubMed2002

Oxo-transfer reaction from a bis(mu-oxo)dicopper(III) complex to sulfides.

Oxygenation of sulfides to the corresponding sulfoxides by a distinct bis(mu-oxo)dicopper(III) complex has been accomplished for the first time using 2-(2-pyridyl)ethylamine derivative L(Py1Bz) (N-ethyl-N-[2-(2-pyridyl)ethyl]-alpha,alpha-dideuteriobenzylamine) as the supporting ligand. Detailed kinetic analysis has indicated that the reaction consists of two distinct steps, where the first quick process is association of the substrate to the bis(mu-oxo)dicopper(III) complex (k(1)) and the second slow process is intramolecular oxygen atom transfer from the copper-oxo species to the substrate in the associated complex (k(2)). The rate constant k(2) of the second process is rather insensitive to the oxidation potential of the substrates, suggesting that the oxo-transfer reaction proceeds via a mechanism involving direct oxygen atom transfer rather than a mechanism involving electron transfer.

Journal Article↗
PubMed2002

FTIR spectra and normal-mode analysis of a tetranuclear manganese adamantane-like complex in two electrochemically prepared oxidation states: relevance to the oxygen-evolving complex of photosystem II.

The IR spectra and normal-mode analysis of the adamantane-like compound [Mn(4)O(6)(bpea)(4)](n+) (bpea = N,N-bis(2-pyridylmethyl)ethylamine) in two oxidation states, Mn(IV)(4) and Mn(III)Mn(IV)(3), that are relevant to the oxygen-evolving complex of photosystem II are presented. Mn-O vibrational modes are identified with isotopic exchange, (16)O-->(18)O, of the mono-micro-oxo bridging atoms in the complex. IR spectra of the Mn(III)Mn(IV)(3) species are obtained by electrochemical reduction of the Mn(IV)(4) species using a spectroelectrochemical cell, based on attenuated total reflection [Visser, H.; et al. Anal. Chem. 2001, 73, 4374-4378]. A novel method of subtraction is used to reduce background contributions from solvent and ligand modes, and the difference and double-difference spectra are used in identifying Mn-O bridging modes that are sensitive to oxidation state change. Two strong IR bands are observed for the Mn(IV)(4) species at 745 and 707 cm(-1), and a weaker band is observed at 510 cm(-1). Upon reduction, the Mn(III)Mn(IV)(3) species exhibits two strong IR bands at 745 and 680 cm(-1), and several weaker bands are observed in the 510-425 cm(-1) range. A normal-mode analysis is performed to assign all the relevant bridging modes in the oxidized Mn(IV)(4) and reduced Mn(III)Mn(IV)(3) species. The calculated force constants for the Mn(IV)(4) species are f(r)(IV)= 3.15 mdyn/A, f(rOr) = 0.55 mdyn/A, and f(rMnr) = 0.20 mdyn/A. The force constants for the Mn(III)Mn(IV)(3) species are f(r)(IV)= 3.10 mdyn/A, f(r)(III)= 2.45 mdyn/A, f(rOr) = 0.40 mdyn/A, and f(rMnr) = 0.15 mdyn/A. This study provides insights for the identification of Mn-O modes in the IR spectra of the photosynthetic oxygen-evolving complex during its catalytic cycle.

Adamantane↗
PubMed2003

Oxidation mechanism of phenols by dicopper-dioxygen (Cu(2)/O(2)) complexes.

The first systematic studies on the oxidation of neutral phenols (ArOH) by the mu-eta(2):eta(2)-peroxo)dicopper(II) complex (A) and the bis(mu-oxo)dicopper(III) complex (B) supported by the 2-(2-pyridyl)ethylamine tridentate and didentate ligands L(Py2) and L(Py1), respectively, have been carried out in order to get insight into the phenolic O-H bond activation mechanism by metal-oxo species. In both cases (A and B), the C-C coupling dimer was obtained as a solely isolable product in approximately 50% yield base on the dicopper-dioxygen (Cu(2)/O(2)) complexes, suggesting that both A and B act as electron-transfer oxidants for the phenol oxidation. The rate-dependence in the oxidation of phenols by the Cu(2)/O(2) complexes on the one-electron oxidation potentials of the phenol substrates as well as the kinetic deuterium isotope effects obtained using ArOD have indicated that the reaction involves a proton-coupled electron transfer (PCET) mechanism. The reactivity of phenols for net hydrogen atom transfer reactions to cumylperoxyl radical (C) has also been investigated to demonstrate that the rate-dependence of the reaction on the one-electron oxidation potentials of the phenols is significantly smaller than that of the reaction with the Cu(2)O(2) complexes, indicative of the direct hydrogen atom transfer mechanism (HAT). Thus, the results unambiguously confirmed that the oxidation of phenols by the Cu(2)O(2) complex proceeds via the PCET mechanism rather than the HAT mechanism involved in the cumylperoxyl radical system. The reactivity difference between A and B has also been discussed by taking account of the existed fast equilibrium between A and B.

Biomimetic Materials↗
PubMed2003

A high-frequency and high-field EPR study of new azide and fluoride mononuclear Mn(III) complexes.

The isolation, structural characterization and electronic properties of three new six-coordinated Mn(III) complexes, [Mn(bpea)(F)(3)] (1), [Mn(bpea)(N(3))(3)] (2), and [Mn(terpy)(F)(3)] (3) are reported (bpea = N,N-bis(2-pyridylmethyl)-ethylamine; terpy = 2,2':6',2' '-terpyridine). As for [Mn(terpy)(N(3))(3)] (4) (previously described by Limburg J.; Vrettos J. S.; Crabtree R. H.; Brudvig G. W.; de Paula J. C.; Hassan A.; Barra A-L.; Duboc-Toia C.; Collomb M-N. Inorg. Chem. 2001, 40, 1698), all these complexes exhibit a Jahn-Teller distortion of the octahedron characteristic of high-spin Mn(III) (S = 2). The analysis of the crystallographic data shows an elongation along the tetragonal axis of the octahedron for complexes 1 and 3, while complex 2 presents an unexpected compression. The electronic properties were investigated using a high-field and high-frequency EPR study performed between 5 and 15 K (190-575 GHz). The spin Hamiltonian parameters determined in solid state are in agreement with the geometry of the complexes observed in the crystal structures. A negative D value found for 1 and 3 is related to the elongated tetragonal distortion, whereas the positive D value determined for 2 is in accordance with a compressed octahedron. The high E/D values, in the range of 0.103 to 0.230 for all complexes, are correlated with the highly distorted geometry present around the Mn(III) ion. HF-EPR experiments were also performed on complex 1 in solution and show that the D value is the only spin Hamiltonian parameter which is slightly modified compared to the solid state (D = -3.67 cm(-1) in solid state; D = -3.95 cm(-1) in solution).

Azides↗
PubMed2004

Cyclic amidine sugars as transition-state analogue inhibitors of glycosidases: potent competitive inhibitors of mannosidases.

A series of monocyclic glycoamidines bearing different exocyclic amine, alcohol, or alkyl functionalities and bicyclic amidines derived from D-glucose and D-mannose were synthesized and tested as inhibitors of various glycosidases. All the prepared compounds demonstrated good to excellent inhibition toward glycosidases. In particular, the biscationic D-mannoamidine 9b bearing an exocyclic ethylamine moiety proved to be a selective competitive inhibitor of alpha- and beta-mannosidases (K(i) = 6 nM) making it the most potent inhibitor of these glycosidases reported to date. A favorable B(2,5) boat conformation might explain the selectivity of mannosidase inhibition compared to other glycosidases.

Amidines↗
PubMed2005

Targeting the tumor-associated folate receptor with an 111In-DTPA conjugate of pteroic acid.

The cell membrane folate receptor is a potential molecular target for tumor-selective drug delivery. To probe structural requirements for folate receptor targeting with low molecular weight radiometal chelates, specifically the role of the amino acid fragment of folic acid (pteroylglutamic acid) in mediating targeting selectivity, the amide-linked conjugate pteroyl-NHCH(2)CH(2)OCH(2)CH(2)OCH(2)CH(2)NH-DTPA was prepared by a three-step procedure from pteroic acid, 2,2'-(ethylenedioxy)-bis(ethylamine), and t-Bu-protected DTPA. This conjugate, 1-{2-[2-[(2-(biscarboxymethyl-amino)ethyl)-carboxymethyl-amino]ethyl]-carboxymethyl-amino}-acetylamino-3,6-dioxa-8-pteroylamino-octane (1), was employed for synthesis of the corresponding (111)In(III) radiopharmaceutical. Following intravenous administration to athymic mice, the (111)In complex of 1 was found to selectively localize in folate receptor-positive human KB tumor xenografts and to afford prolonged tumor retention of the (111)In radiolabel (5.4 +/- 0.8, 5.6 +/- 1.1, and 3.6 +/- 0.6% of the injected dose per gram of tumor at 1, 4, and 24 h, respectively). The observed tumor localization was effectively blocked by co-administration of folic acid with the (111)In-1 complex, consistent with a folate receptor-mediated targeting process. In control studies, tumor targeting with this pteroic acid conjugate appears as effective as that seen using (111)In-DTPA-folate, a radiopharmaceutical that has progressed to clinical trials for detection of folate receptor-expressing gynecological tumors.

Animals↗
PubMed2005

Unique toroidal morphology from composition and sequence control of triblock copolymers.

The mechanism by which the unique toroidal supramolecular assemblies were formed for triblock copolymers of acrylic acid (AA), methyl acrylate (MA), and styrene (S), PAA99-b-PMA73-b-PS66, was probed in this study by investigating the influences of the block copolymer compositions and sequences. Two triblock copolymers, PAA99-b-PMA73-b-PS66 and PAA99-b-PS76-b-PMA62, and two diblock copolymers, PAA99-b-PMA155 and PAA99-b-PS133, were studied under experimental solution-state conditions that involved a range of solvent/nonsolvent (tetrahydrofuran/water) compositions, each in the presence of 2,2'-(ethylenedioxy)bis(ethylamine). The resulting morphologies were determined by transmission electron microscopy. The failures to afford toroidal supramolecular assemblies from both diblock copolymers having comparable lengths of the total hydrophobic chain segment, either entirely PMA or entirely PS, and from the triblock copolymer having a reversed connection sequence for the hydrophobic (PMA and PS) segments demonstrate the unique self-assembly behaviors of triblock copolymers and the importance of the block copolymer sequence.

Acrylic Resins↗