Synthesis and characterization of amphiphilic star copolymers of 2-(dimethylamino) ethyl methacrylate and methyl methacrylate: Effects of architecture and composition

Six amphiphilic star copolymers comprising hydrophilic units of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and hydrophobic units of methyl methacrylate (MMA) were prepared by the sequential group transfer polymerization (GTP) of the two comonomers and ethylene glycol dimethacrylate (EGDMA) cross-linker. Four star-block copolymers of different compositions, one miktoarm star, and one statistical copolymer star were synthesized. The molecular weights (MWs) and MW distributions of all the star copolymers and their linear homopolymer and copolymer precursors were characterized by gel permeation chromatography (GPC), while the compositions of the stars were determined by proton nuclear magnetic resonance (H-1 NMR) spectroscopy. Tetrahydrofuran (THF) solutions of all the star copolymers were characterized by static light scattering to determine the absolute weight-average MW ((M) over bar (w)) and the number of arms of the stars. The R, of the stars ranged between 359,000 and 565,000 g mol(-1), while their number of arms ranged between 39 and 120. The star copolymers were soluble in acidic water at pH 4 giving transparent or slightly opaque solutions, with the exception of the very hydrophobic DMAEMA(10)-b-MMA(30)-star, which gave a very opaque solution. Only the random copolymer star was completely dispersed in neutral water, giving a very opaque solution. The effective pKs of the copolymer stars were determined by hydrogen ion titration and were found to be in the range 6.5-7.6. The pHs of precipitation of the star copolymer solutions/dispersions were found to be between 8.8-10.1, except for the most hydrophobic DMA-EMA(10)-b-MMA(30)-Star, which gave a very opaque solution over the whole pH range. (c) 2006 Elsevier Ltd. All rights reserved.

Soluble redox-active polymetallic chains [{Ru-0(CO)(L)(bpy)}(m)](n) (bpy=2,2 '-bipyridine, L = PrCN, Cl-; m=0,-1): electrosynthesis and characterization

Electrochemical and spectroelectrochemical techniques were employed to study in detail the formation and so far unreported spectroscopic properties of soluble electroactive molecular chains with nonbridged metal-metal backbones, namely, [{Ru-0(CO)(PrCN)(bpy)}(m)](n) (m = 0, -1) and [{Ru-0(CO)(bpy)Cl}(m)](n) (m = -1, -2; bpy = 2,2'-bipyridine). The precursors cis-(Cl)-[Ru-II(CO)(MeCN)(bpy)Cl-2] (in PrCN) and mer-[Ru-II(CO)(bpy)Cl-3](-) (in tetrahydrofuran (THF) and PrCN) undergo one-electron reductions to reactive radicals [Ru-II(CO)(MeCN)(bpy(center dot-))Cl-2](-) and [Ru-II(CO)(bpy(center dot-))Cl-3](2-), respectively. Both [bpy(center dot-)]-containing species readily electropolymerize on concomitant dissociation of two chloride ligands and consumption of a second electron. Along this path, mer-to-fac isomerization of the bpy-reduced trichlorido complex (supported by density functional theory calculations) and a concentration-dependent oligomerization process contribute to the complex reactivity pattern. In situ spectroelectrochemistry (IR, UV/vis a has revealed that the charged polymer [{Ru-0(CO)(bpy)Cl}(-)](n) is stable in THF, but in PrCN it converts readily to [Ru-0(CO)(PrCN)(bpy)](n). An excess of chloride ions retards this substitution at low temperatures. Both polymetallic chains are completely soluble in the electrolyte solution and can be reduced reversibly to the corresponding [bpy(center dot-)]-containing species.

New half-sandwich heterobimetallic CpMPt (M=Rh, Ir) dithiolato bridged complexes

Cationic heterobimetallic complexes 5–7 [(PPh3)2Pt(μ-edt)MClCp′)]BF4 (edt=−S(CH2)2S−; 5: M=Rh and Cp′=η5-C5H5; 6: M=Rh and Cp′=η5-C5Me5 and 7: M=Ir and Cp′=η5-C5Me5) were prepared by reaction of [Pt(edt)(PPh3)2] with [Cp′ClM(μ-Cl)2MClCp′] in THF in the presence of two equivalents of AgBF4. The crystalline structure of 5 was determined by X-ray diffraction methods. Cationic heterobimetallic complexes [(PPh3)2Pt(μ-S(CH2)2S)MClCp′)]BF4 (M=Rh, Ir) were prepared. The crystalline structure of [(PPh3)2Pt(μ-edt)RhClCp)]BF4 was determined by X-ray diffraction methods.

The molecular structure and one-pot synthesis of [Li(thf)3·Sn(SiMe3)3]

The molecular structure of [Li(thf)3 · Sn(SiMe3)3], prepared by a new, one-pot synthesis in 44% yield, has been determined by a single crystal X-ray diffraction study using synchrotron radiation and a CCD detector. The +Li(thf)3 and −Sn(SiMe3)3 moieties are joined by a Li–Sn bond, 2.865(5) Å in length. [Li(thf)3 · Sn(SiMe3)3] is isomorphous with its germanium analogue.

Synthesis and X-ray crystal and molecular structure of tetrakis(2,2-dimethyl-1-phenylethenyl)chromium(IV), the first structurally-characterised homoleptic alkenyl compound of a transition metal

The title compound, the first homoleptic Group 6A metal alkenyl, has been prepared from CrCl3·3(thf), and its properties, including X-ray crystal structure determination, are reported.

Solvent-Dependent Formation of Os(0) Complexes by Electrochemical Reduction of [Os(CO)(2,2′-bipyridine)(L)Cl2]; L = Cl−,PrCN

Cyclic voltammetry and ultraviolet−visible/infrared (UV−vis/IR) spectroelectrochemistry were used to study the cathodic electrochemical behavior of the osmium complexes mer-[OsIII(CO) (bpy)Cl3] (bpy = 2,2′-bipyridine) and trans(Cl)-[OsII(CO) (PrCN)(bpy)Cl2] at variable temperature in different solvents (tetrahydrofuran (THF), butyronitrile (PrCN), acetonitrile (MeCN)) and electrolytes (Bu4NPF6, Bu4NCl). The precursors can be reduced to mer-[OsII(CO) (bpy•−)Cl3]2− and trans(Cl)-[OsII(CO)(PrCN) (bpy•−)Cl2]−, respectively, which react rapidly at room temperature, losing the chloride ligands and forming Os(0) species. mer-[OsIII(CO) (bpy)Cl3] is reduced in THF to give ultimately an Os−Os-bonded polymer, probably [Os0(CO) (THF)-(bpy)]n, whereas in PrCN the well-soluble, probably mononuclear [Os0(CO) (PrCN)(bpy)], species is formed. The same products were observed for the 2 electron reduction of trans(Cl)-[OsII(CO)(PrCN) (bpy)Cl2] in both solvents. In MeCN, similar to THF, the[Os0(CO) (MeCN)(bpy)]n polymer is produced. It is noteworthy that the bpy ligand in mononuclear [Os0(CO) (PrCN)(bpy)] is reduced to the corresponding radical anion at a significantly less negative potential than it is in polymeric [Os0(CO) (THF)(bpy)]n: ΔE1/2 = 0.67 V. Major differences also exist in the IR spectra of the Os(0) species: the polymer shows a broad ν(CO) band at much smaller wavenumbers compared to the soluble Os(0) monomer that exhibits a characteristic ν(Pr-CN) band below 2200 cm−1 in addition to the intense and narrow ν(CO) absorption band. For the first time, in this work the M0-bpy(M = Ru, Os) mono- and dicarbonyl species soluble in PrCN have been formulated as a mononuclear complex. Density functional theory (DFT) and time-dependent-DFT calculations confirm the Os(0) oxidation state and suggest that [Os0(CO)(PrCN)(bpy)] is a square planar moiety. The reversible bpy-based reduction of [Os0(CO) (PrCN)(bpy)] triggers catalytic reduction of CO2 to CO and HCOO−.

Spectroelectrochemical study of complexes [Mo(CO)2(h3-allyl)(adiimine)(NCS)] (a-diimine ¼ bis(2,6-dimethylphenyl)- acenaphthenequinonediimine and 2,20-bipyridine) exhibiting different molecular structure and redox reactivity

The redox properties and reactivity of [Mo(CO)2(η3-allyl)(α-diimine)(NCS)] (α-diimine = bis(2,6-dimethylphenyl)-acenaphthenequinonediimine (2,6-xylyl-BIAN) and 2,2′-bipyridine (bpy)) were studied using cyclic voltammetry and IR/UV–Vis spectroelectrochemistry. [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN)(NCS)] was shown by X-ray crystallography to have an asymmetric (B-type) conformation. The extended aromatic system of the strong π-acceptor 2,6-xylyl-BIAN ligand stabilises the primary 1e−-reduced radical anion, [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN•−)(NCS)]−, that can be reduced further to give the solvento anion [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN)(THF)]−. The initial reduction of [Mo(CO)2(η3-allyl)(bpy)(NCS)] in THF at ambient temperature results in the formation of [Mo(CO)2(η3-allyl)(bpy)]2 by reaction of the remaining parent complex with [Mo(CO)2(η3-allyl)(bpy)]− produced by dissociation of NCS− from [Mo(CO)2(η3-allyl)(bpy•−)(NCS)]−. Further reduction of the dimer [Mo(CO)2(η3-allyl)(bpy)]2 restores [Mo(CO)2(η3-allyl)(bpy)]−. In PrCN at 183 K, [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN•−)(NCS)]− converts slowly to 2e−-reduced [Mo(CO)2(η3-allyl)(2,6-xylyl-BIAN)(PrCN)]− and free NCS−. At room temperature, the reduction path in PrCN involves mainly the dimer [Mo(CO)2(η3-allyl)(bpy)]2; however, the detailed course of the reduction within the spectroelectrochemical cell is complicated and involves a mixture of several unassigned products. Finally, it has been shown that the five-coordinate anion [Mo(CO)2(η3-allyl)(bpy)]− promotes in THF reduction of CO2 to CO and formate via the formation of the intermediate [Mo(CO)2(η3-allyl)(bpy)(O2CH)] and its subsequent reduction.

Incorporation of group 14 elements into siloxane-bridged paracyclophanes cyclo-[p,p´-Me2SiC6H4EMe2C6H4SiMe2O]2 (E = C, Si, Ge, Sn)§

The bis(arylene silanes) p,p'-HMe₂SiC₆H₄EMe₂C₆H₄SiMe₂H (E = C (10), Si (11), Ge (12), Sn(13)) were prepared by the in situ Grignard reaction of p,p'-BrC₆H₄CMe₂C₆H₄Br, Mg turnings, and HSiMe₂Cl (for 10) and the Grignard reaction using p-HMe₂SiC₆H₄Br, Mg turnings, and Me₂ECl₂ (E = Si for 11, Ge for 12, Sn for 13). The oxidation of 10-13 using Pearlman's catalyst, Pd(OH)₂/C, in aqueous THF provided the bis(arylene silanols) p,p'-HOMe₂SiC₆H₄EMe₂C₆H₄SiMe₂OH (E = C (14), Si (15), Ge (16), Sn(17)). The HCl-catalyzed condensation of 14-17 in highly diluted solutions of acetone/water afforded the siloxane-bridged paracyclophanes cyclo-[p,p'-Me₂SiC₆H₄EMe₂C₆H₄SiMe₂O]₂ (6-9) that incorporate the group 14 elements E = C, Si, Ge, and Sn. Compounds 6-17 were investigated by multinuclear solution and solid-state NMR spectroscopy and 6 and 9 also by X-ray crystallography.

Self-assembled complexes of poly(4-vinylphenol) and poly(ε-caprolactone)-block-poly(2-vinylpyridine) via competitive hydrogen bonding

Nanostructured complexes were prepared from poly(ε-caprolactone)-block-poly(2-vinylpyridine) (PCL-b-P2VP) and poly(4-vinylphenol) (PVPh) in tetrahydrofuran (THF). The phase behavior, specific interactions, and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). In this A-b-B/C type block copolymer/homopolymer system, both blocks of the PCL-b-P2VP block copolymer have favorable intermolecular interaction toward PVPh via hydrogen bonding, but the interaction between P2VP block and PVPh is significantly stronger than that between PCL block and PVPh. It was found that the disparity in competitive intermolecular interactions, specifically PVPh and P2VP block interact strongly whereas PVPh and PCL block interact weakly, leads to the formation of a variety of nanostructures depending on PVPh concentration. Spherical micelles of 30−40 nm in diameter were obtained in the complex with 10 wt % PVPh, followed by wormlike micelles with size in the order of 40−50 nm in the complexes with 30−60 wt % PVPh. At low PVPh concentrations, PCL interacts weakly with PVPh, whereas in the complexes containing more than 20 wt % PVPh, the PCL block began to interact considerably with PVPh, leading to the formation of composition-dependent nanostructures. The complex becomes homogeneous with PVPh content beyond 60 wt %, since a sufficient amount of PVPh is available to form hydrogen bonds with both PCL and P2VP. Finally, a model was proposed to explain the self-assembly and microphase morphology of these complexes based on the experimental results obtained. The competitive hydrogen-bonding interactions cause the self-assembly and formation of different microphase morphologies.

Nanostructure and hydrogen bonding in interpolyelectrolyte complexes of poly(ε-caprolactone)-block-poly(2-vinyl pyridine) and poly(acrylic acid)

Nanostructured poly(ε-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP)/poly(acrylic acid) (PAA) interpolyelectrolyte complexes (IPECs) were prepared by casting from THF/ethanol solution. The morphological behaviour of this amphiphilic block copolymer/polyelectrolyte complexes with respect to the composition was investigated in a solvent mixture. The phase behaviour, specific interactions and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy (OM), dynamic light scattering (DLS) and atomic force microscopy (AFM). Micelle formation occurred due to the aggregation of hydrogen bonded P2VP block and polyelectrolyte (PAA) from non-interacted PCL blocks. It was observed that the hydrodynamic diameter (D_h) of the micelles in solution decreased with increasing PAA content up to 40 wt%. After 50 wt% PAA content, D_h again increased. The micelle formation in PCL-b-P2VP/PAA IPECs was due to the strong intermolecular hydrogen bonding between PAA homopolymer units and P2VP blocks of the block copolymer. The penetration of PAA homopolymers into the shell of the PCL-b-P2VP block copolymer micelles resulted in the folding of the P2VP chains, which in turn reduced the hydrodynamic size of the micelles. After the saturation of the shell with PAA homopolymers, the size of the micelles increased due to the absorption of added PAA onto the surface of the micelles.

7,7-dimetoxi-1,4,5,6-tetraclorobiciclo[2.2.1]heptan-5-en-2-endo-ol : um versátil reagente na síntese de 1,3-aminoálcoois e de ciclopentanóides quirais altamente funcionalizados

Este trabalho relata a síntese de uma série de novos ligantes quirais (+) e (-)-syn-1,3-aminoálcoois derivados do norbornano. Através da reação de transesterificação enzimática com a lípase da Candida rugosa em acetato de vinila do álcool racêmico 7,7-dimetoxi-1,4,5,6-tetraclorobiciclo[2.2.1]heptan-5-en-2-ol, (±)-3, foram obtidos os álcoois quirais (+)-3 e (-)-3 (Esquema 1). Através da reação de redução e descloração destes álcoois com Na0/NH3/etanol foram obtidos os respectivos álcoois (+)-4 e (-)-4 (Esquema 2). Os álcoois quirais (+)-4 e (-)-4 foram utilizados como produtos de partida para a síntese dos 1,3-aminoálcoois quirais (+)-9 e (-)-9 em 5 etapas. Deste modo, a partir destes aminoálcoois (9), foi possível sintetizar 12 novos compostos (Esquema 2), todos inétidos na literatura. Os 1,3-aminoálcoois 10, 11, 13, 14 e 15 foram empregados como catalisadores quirais na adição enantiosseletiva de ZnEt2 ao benzaldeído. Excelentes rendimentos e excessos enantioméricos (até 91%) foram obtidos. A relação entre a configuração absoluta do 1-fenilpropanol com a configuração do carbono ligado ao grupo hidroxila dos ligantes foi estudada e, de acordo, com a enantiosseletividade observada foi sugerido um mecanismo para a reação Os produtos com esqueleto ciclopentila são importantes compostos com potencial atividade biológica, fazendo parte da estrutura de prostaglandinas, agentes antitumorais e inibidores da glicosidase. Portanto, nós decidimos usar o acetato clorado quiral 2 para preparar ciclopentanóides quirais altamente funcionalizados. Para isso, o acetato clorado quiral 2 foi submetido à oxidação usando uma quantidade catalítica de RuCl3 anidro na presença de NaIO4 obtendo-se a dicetona 16 (Esquema 3). A dicetona 16 foi clivada com H2O2 em meio alcalino fornecendo os diácidos 17a e 17b, que foram esterificados in situ com excesso de CH2N2 para fornecer uma mistura do hidroxi e acetoxi diéster 18 e 19, respectivamente. A redução da mistura 18 e 19 ou da mistura 17a e 17b com BH3.THF fornece a lactona 20 com excelentes rendimentos.

Synthesis and reactivity in salt metathesis reactions of trivalent [La(Tp(Me2))(2)X] (X = Cl, I) complexes: crystal structures of [La(Tp(Me2))(2)Cl] and [La(Tp(Me2))(2)(kappa(2)-pz(Me2))]

Reaction of LaX3(THF)(n) (X = Cl, 1) with two equiv. of K(Tp(Me2)) gave good yields of the bis-Tp complexes [La(Tp(Me2))(2)X] (X = Cl (1); I (3)). However, the formation of 1 and 3 is always accompanied by significant amounts of La(Tp(Me2))(2)(kappa(2)-pz(Me2)) ([pz(Me2)](-) = 3,5-dimethyl-pyrazolato) (2). The pyrazolato complex 2, which presumably arises from decomposition of the [Tp(Me2)](-) moiety during salt metathesis, was independently prepared in good yield from 1 and in situ generated [pz(Me2)](-). The solid-state structures of 1 and 2 were determined by single-crystal X-ray diffraction studies. Subsequent reactions of halogeno-Tp(Me2) complexes 1 and 3 with various alkali metal salts MR (M = Li, R = CH2SiMe3, Ph, N(SiMe3)(2); M = K, R = OAr) gave M(Tp(Me2)) as the major product. Alternatively, the mono-Tp bis(aryloxide) derivatives [Ln(Tp(Me2))(OC6H2-2,6-'Bu-4-Me)(2)] (Ln = La (4); Nd (5)) were obtained in high yields by salt metathesis of [Ln(OC6H2-2,6-'Bu-4-Me)(3)] with one equiv. of K(Tp(Me2)). (C) 2004 Elsevier Ltd. All rights reserved.

Structural characterization of an etheno-2 '-deoxyguanosine adduct modified by tetrahydrofuran

The reaction of 2'-deoxyguanosine with the alpha,beta-unsaturated aldehydes trans-2-octenal, trans-2-nonenal, trans-2-decenal, trans,trans-2,4-nonadienal, and trans,trans-2,4-decadienal in THF gives rise to three novel adducts: 3-(2'-deoxy-beta-D-erythro-pentafuranosyl)-7-[3-hydroxy-1-(3(2'-deoxy-beta-D-erythro-pentafuranosyl)-3,5-dihydro-imidazo[1,2-alpha]purin-9-one-7-yl)-propyl] -3,5-dihydro-imidazo[1,2-alpha]purin-9-one (M) and 3-(2'-deoxy-beta-D-erythro-pentafuranosyl)-7-(tetrahydrofuran-2-yl)-3,5-dihydro-imidazo[1,2-alpha]purin-9-one (A8 and A9), which are not observed in the absence of THF. These adducts were isolated from in vitro reactions by reversed-phase HPLC and fully characterized on the basis of spectroscopic measurements. Adduct A7 consists of two 1,N-2-etheno-2'-deoxyguanosine (1,N-2-epsilondGuo) residues linked to a hydroxy-carbon side chain; adducts A8 and A9 are interconvertible 1,N-2-epsilondGuo derivatives bearing a THF moiety. The proposed reaction mechanism involves the electrophilic attack on 1,N-2-epsilondGuo by the carbonyl of 4-hydroxy-butanal, generated via ring opening of alpha-hydroxy-THF (THF-OH), yielding adducts A8 and A9. A further combination of these adducts with another 1,N-2-epsilondGuo produces the double adduct A7. These findings demonstrate that reactions of unsaturated aldehydes in the presence of THF produce novel condensation 1,N-2-epsilondGuo-THF adducts. Further studies would indicate the relevance of these adducts in THF toxicity.

Age-dependent decrease in 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) activity in hypertensive patients

BACKGROUND: The prevalence of arterial hypertension lacking a defined underlying cause increases with age. Age-related arterial hypertension is insufficiently understood, yet known characteristics suggest an aldosterone-independent activation of the mineralocorticoid receptor. Therefore, we hypothesized that 11beta-HSD2 activity is age-dependently impaired, resulting in a compromised intracellular inactivation of cortisol (F) with F-mediated mineralocorticoid hypertension. METHODS: Steroid hormone metabolites in 24-h urine samples of 165 consecutive hypertensive patients were analyzed for F and cortisone (E), and their TH-metabolites tetrahydro-F (THF), 5alphaTHF, TH-deoxycortisol (THS), and THE by gas chromatography-mass spectroscopy. Apparent 11beta-HSD2 and 11beta-hydroxylase activity and excretion of F metabolites were assessed. RESULTS: In 72 female and 93 male patients aged 18-84 years, age correlated positively with the ratios of (THF + 5alphaTHF)/THE (P = 0.065) and F/E (P < 0.002) suggesting an age-dependent reduction in the apparent 11beta-HSD2 activity, which persisted (F/E; P = 0.020) after excluding impaired renal function. Excretion of F metabolites remained age-independent most likely as a consequence of an age-dependent diminished apparent 11beta-hydroxylase activity (P = 0.038). CONCLUSION: Reduced 11beta-HSD2 activity emerges as a previously unrecognized risk factor contributing to the rising prevalence of arterial hypertension in elderly. This opens new perspectives for targeted treatment of age-related hypertension.