Fibre guiding scaffolds for periodontal tissue engineering

The periodontium is a highly hierarchically organized organ composed of gingiva, alveolar bone, periodontal ligament and cementum. Periodontitis leads to the destruction of hard and soft tissues ultimately leading to a loss of the teeth supporting apparatus. Current treatments are capable of limiting the disease progression; however, true regeneration, characterized by perpendicularly oriented periodontal ligament fibre attachment to cementum on the root surface remains challenging. Tissue engineering approaches have been developed to enhance regeneration via micro-engineered topographical features, purposely designed to guide the insertion of the regenerated ligament to the root surface. This review reports on the recent advancements in scaffold manufacturing methodologies for generating fibre guiding properties and provides a critical insight in the current limitations of these techniques for the formation of functional periodontal attachment.

Tandem chain extension-aldol reaction: syn selectivity with a zinc enolate

A tandem chain extension-aldol reaction was developed in which beta-keto esters are transformed to alpha-substituted-gamma-keto esters in an efficient zinc-mediated, one-pot reaction. The diastereoselectivity of the reaction ranged from good to excellent with syn stereochemistry observed for beta-keto ester and amide substrates and anti-stereochemistry observed for a beta-keto imide. [reaction: see text]

Mono- and di-nickellaazaphosphiranes of mono- and bis-(amido)cyclodiphosph(III)azanes

The syntheses and solid-state structures of the first three-membered nickel-phosphorus-nitrogen ring compounds, having anionic four-electron P=N moieties are reported.

Influence of extrinsic factors on electron transfer in a mixed-valence Fe(2+)/Fe(3+) complex: experimental results and theoretical considerations

The crystal structure of the mixed-valence complex (NEt(4))[Fe(2)(salmp)(2)].xMeCN(crystal) (x = 2,3) [1].xMeCN(crystal) was determined at temperatures between 153 and 293 K. The complex shows distinct Fe(2+) and Fe(3+) sites over this temperature interval. Variable temperature Mössbauer spectra confirm the valence-localized character of the complex. In contrast, spectroscopic investigation of powder samples generated from [1].xMeCN(crystal) indicate the presence of a valence-averaged component at temperatures above 150 K. To elucidate this apparent contradiction we have conducted a variable-temperature Mössbauer investigation of different forms of 1, including [1].xMeCN(crystal), [1].2DMF(crystal), [1].yMeCN(powder), and solution samples of 1 in acetonitrile. The low-temperature Mössbauer spectra of all forms are virtually identical and confirm the valence-localized nature of the S = (9)/(2) ground state. The high-temperature spectra reveal a subtle control of electron hopping by the environment of the complexes. Thus, [1].xMeCN(crystal) has valence-localized spectra at all explored temperatures, [1].2DMF(crystal) exhibits a complete collapse into a valence-averaged spectrum over a narrow temperature range, the powder exhibits partial valence averaging over a broad temperature interval, and the solution sample shows at 210 K the presence of a valence-averaged component in a minor proportion. The spectral transformations are characterized by a coexistence of valence-localized and valence-averaged spectral components. This phenomenon cannot be explained by intramolecular electron hopping between the valence-localized states Fe(A)(2+)Fe(B)(3+) and Fe(A)(3+)Fe(B)(2+) in a homogeneous ensemble of complexes, but requires relaxation processes involving at least three distinguishable states of the molecular anion. Hopping rates for [1].2DMF(crystal) and [1].yMeCN(powder) have been determined from spectral simulations, based on stochastic line shape theory. Analysis of the temperature dependences of the transfer rates reveals the existence of thermally activated processes between (quasi) degenerate excited states in both forms. The preexponential factors in the rate law for the hopping processes in the [1].yMeCN(powder) and [1].2DMF(crystal) differ dramatically and suggest an important influence of the asymmetry of the complex environment (crystal) on intramolecular electron hopping. The differences between the spectra for the crystalline sample [1].xMeCN and those for powders generated under vacuum from these crystals indicate that solvate depletion has a profound effect on the dynamic behavior. Finally, two interpretations for the three states involved in the relaxation processes in 1 are given and critically discussed (salmp = bis(salicyledeneamino)-2-methylphenolate(3-)).

Synthesis, characterization, and reactivity of ferrous and ferric oxo/peroxo pivalate complexes in relation to Gif-type oxygenation of substrates

This study examines structural features and aspects of reactivity of Gif-type reagents, which depend on O2/Zn to mediate oxidation of hydrocarbons. The reagents investigated derive from the use of iron complexes with the anion of the weak carboxylic acid Me3CCO2H (pivalic acid (PivH)) in pyridine/PivH. In these solutions, the known compound [Fe3O(O2CCMe3)6(py)3] is reduced by Zn to generate yellow-green [FeII(O2CCMe3)2(py)4], which readily reverts to [Fe3O(O2CCMe3)6(py)3], and eventually to [Fe3O(O2CCMe3)6(py)3]+, upon exposure to dioxygen. All three species are equally well suited to mediate Gif-like oxygenation of substrates supported by O2/Zn. [FeIII3O(O2CCMe3)6(L)3]+ (L = H2O, py) is converted by H2O2 to afford the hexairon(III) peroxo compounds [Fe6(O2)(O)2(O2CCMe3)12(L)2] (L = Me3CCO2H, py), which feature a [Fe6(eta 2-mu 4-O2)(mu 3-O)2] core previously documented in the closely related [Fe6(O2)(O)2(O2CPh)12(H2O)2]. A similar peroxo species, [Fe6(O2)(O)2(O2CCMe3)2(O2CCF3)10(H2O)2], is obtained upon replacing all pivalate ligands by trifluoroacetate groups with the exception of those pivalates that bridge between the two [Fe3O(O2CCF3)5(H2O)]2+ units. The structure of the [Fe6(O2)(O)2] core in these peroxo species is found to range from a recliner to a butterfly-type conformation. Reduction of [Fe6(O2)(O)2(O2CCMe3)12(HO2CCMe3)2] with NaBH4 generates [Na2Fe4(O)2(O2CCMe3)10(L)(L')] (L = CH3CN, L' = Me2CO; L = L' = Me3CCO2H), which feature a [Na2Fe4(O)2] core possessing a bent butterfly conformation of the [Fe4(O)2] unit. Oxidation of the same peroxo complex by CeIV or NOBF4 regenerates the oxo-bridged [Fe3O(O2CCMe3)6(solv)3]+ (solv = EtOH, H2O, thf). Employment of the sterically encumbered 2-Me-5-Etpyridine provides the tetrairon compound [Fe4(O)2(O2CCMe3)8(2-Me-5-Etpy)2], which can be readily transformed upon treatment with H2O2 to the asymmetric peroxo complex [Fe6(O2)(O)2(O2CCMe3)12(2-Me-5-Etpy)2]. The peroxo-containing complexes oxidize both cis-stilbene and adamantane in either benzene or py/PivH, but only under forceful conditions and at very low yields. The low reactivity and high selectivity (tert/sec = 8) obtained in the oxidation of adamantane suggests that the present type of peroxo species is not directly involved in catalytic Gif-type oxygenations of adamantane.

Structural and functional characteristics of rhenium clusters derived from redox chemistry of the triangular [ReIII3(mu-Cl)3] core unit

The present study investigates structural and functional aspects of the redox chemistry of rhenium(III) chloride [Re3Cl9] (1) in aqueous and organic solvents, with emphasis on the dioxygen-activating capabilities of reduced rhenium clusters bearing the Re3(8+) core. Dissolution of 1 in HCl (6 M) generates [Re3(mu-Cl)3Cl9]3- (2a), which can be isolated as the tetraphenylphosphonium salt (2b). Anaerobic one-electron reduction of 1 by Hg in HCl (6-12 M) produces [(C6H5)4P]2[Re3(mu-Cl)3Cl7(H2O)2].H2O (3), the structure of which features a planar [Re3(mu-Cl)3Cl3] framework (Re3(8+) core), involving two water ligands that occupy out-of-plane positions in a trans arrangement. Compound 3 dissociates in the presence of CO, yielding [(C6H5)4P]2[ReIII2Cl8] (4) and an unidentified red carbonyl species. In situ oxidation (O2) of the reduced Re3(8+)-containing cluster in HCl (6 M) produces quantitatively 2a, whereas oxidation of 3 in organic media results in the formation of [(C6H5)4P]4[(Re3(mu-Cl)3Cl7(mu-OH))2].2CH2Cl2 (5). The structure of 5 reveals that two oxygen ligands (hydroxo units) bridge asymmetrically two Re3(9+) triangular clusters. The origin of these hydroxo units derives from the aquo ligands, rather than O2, as shown by 18O2 labeling studies. The hydroxo bridges of 5 can be replaced by chlorides upon treatment with Me3SiCl to afford the analogous [(C6H5)4P]4[(Re3(mu-Cl)3Cl7(mu-Cl))2].10CH2Cl2 (6). The reaction of 5 with Hg in HCl (6 M)/tetrahydrofuran regenerates compound 3. Complexes 1-3 exhibit nitrile hydratase type activity, inducing hydrolysis of CH3CN to acetamide. The reaction of 3 with CH3CN yields [(C6H5)4P]2[Re3(mu-Cl)3Cl6.5(CH3CN)1.5(CH3C(O)NH)0.5] (7), the structure of which is composed of [Re3(mu-Cl)3Cl7(CH3CN)2]2- (7a) and [Re3(mu-Cl)3Cl6(CH3CN)(CH3C(O)NH)]2- (7b) (Re3(8+) cores) as a disordered mixture (1:1). Oxidation of 7 with O2 in CH3CN affords [(C6H5)4P]2[Re3(mu-Cl)3Cl7(CH3C(O)NH)].CH3CN (8) and small amounts of [(C6H5)4P][ReO4] (9). Compound 8 is also independently isolated from the reaction of 2b with wet CH3CN, or by dissolving 5 in CH3CN. In MeOH, 5 dissociates to afford [(C6H5)4P]2[Re3(mu-Cl)3Cl8(MeOH)].MeOH (10).

Ethyl 5-methyl-4-(2,5,5-trimethyl-1, 3-dioxan-2-yl)isoxazole-3-carboxylate

The title compound, C(14)H(21)NO(5), possesses an isoxazolyl group in the axial position of the 1,3-dioxanyl ring. The two rings are rotated about the bond joining them such that the two C(methyl)-C(dioxanyl)-C-C torsion angles are 92.1 (2) and -84.1 (2) degrees. In this conformation, neither the methyl nor ethoxycarbonyl substituents on the isoxazole are presented towards the dioxanyl chair.

Luminescent chains formed from neutral, triangular gold complexes sandwiching TlI and AgI. Structures of (Ag([Au(mu-C2,N3-bzim)]3)2)BF4.CH2Cl2, (Tl([Au(mu-C2,N3-bzim)]3)2)PF(6).0.5THF (bzim = 1-benzylimidazolate), and (Tl([Au(mu-C(OEt)=NC6H4CH3)]3)2)PF6.THF, with MAu6 (M = Ag+, Tl+) cluster cores

It has been found that several trinuclear complexes of AuI interact with silver and thallium salts to intercalate Ag+ and Tl+ cations, thereby forming chains. The resulting sandwich clusters center the cations between the planar trinuclear moieties producing structures in which six AuI atoms interact with each cation in a distorted trigonal prismatic coordination. The resultant (B3AB3B3AB3)infinity pattern of metal atoms also shows short (approximately 3.0 A) aurophilic interactions between BAB molecular centers. These compounds display a strong visible luminescence, under UV excitation, which is sensitive to temperature and the metal ion interacting with the gold. X-ray crystal structures are reported for Ag([Au(mu-C2,N3-bzim)]3)2BF4CH2Cl2 (P1, Z = 2, a = 14.4505(1) A; b = 15.098(2)A; c = 15.957(1)A; alpha = 106.189(3) degrees; beta = 103.551(5) degrees; gamma = 101.310(5) degrees); Tl([Au(mu-C2,N3-bzim)]3)2PF(6)05C4H8O (P1, Z = 2, a = 15.2093(1)A; b = 15.3931(4)A; c = 16.1599(4)A; alpha = 106.018(1) degrees; beta = 101.585(2) degrees; gamma = 102.068(2) degrees); and Tl([Au(mu-C(OEt)=NC6H4CH3)]3)2PF6.C4H8O (P2(1)/n, Z = 4, a = 16.4136(3)A; b = 27.6277(4)A; c = 16.7182(1)A; beta = 105.644(1) degrees). Each compound shows that the intercalated cation, Ag+ or Tl+, coordinates to a distorted trigonal prism of six AuI atoms. The counteranions reside well apart from the cations between the cluster chains.

Syntheses and structures of heterobicyclic bis(tert-butylamido)cyclodiphosph(III)azane compounds having phosphorus(III) and arsenic(III) centers

Syntheses and single-crystal X-ray diffraction studies of heterobicyclic cyclodiphosphazanes having central phosphorus(III) and arsenic(III) atoms are described. Interaction of PCl3 or AsCl3 with cis-[(tBuNP)2(tBuNLixTHF)2] produced the isomorphous ([(tBuNP)2(tBuN)2]ECl); E = P(1), As(4), respectively. These Cs-symmetric molecules crystallize with two molecules in the monoclinic space group P2(1)/m. Unit cell dimensions of 1 are (293 K) a = 9.777(1) A, b = 11.745(1) A, c = 9.986(2) A, and beta = 97.44(1) degrees; those of 4 are (213 K) a = 9.688(3) A, b = 11.873(3) A, c = 9.975(3) A, and beta = 97.80(3) degrees. When ([(tBuNP)2(tBuN)2]PCl) was treated with NaN3 or LiN(SiMe3)2, ([(tBuNP)2(tBuN)2]PN3)(2) and ([(tBuNP)2(tBuN)2]PN(SiMe3)2)(3), respectively, were obtained. Compound 2 crystallizes in the monoclinic space group P2(1)/m and has until-cell dimensions (213 K) of a = 9496(7) A, b = 12455(7) A, c = 10043(6) A, and beta = 9723(4) degrees, Z = 2.