Synthesis of well‐designed polymers carrying saccharide moieties via RAFT miniemulsion polymerization

Two hydrophobic vinyl saccharide monomers based on D ‐glucose and D ‐fructose were polymerized by employing the reversible addition‐fragmentation transfer (RAFT) miniemulsion polymerization technique to prepare well‐designed glycopolymers. Three dithiobenzoate‐RAFT agents [S?C(Ph)S? R], 1‐phenylethyl dithiobenzoate (PED), 2‐phenylprop‐2‐yl dithiobenzoate (PPD), and 2‐cyanoprop‐2‐yl dithiobenzoate (CPD), were used to control the growth of polymer chains. The best results were obtained in the presence of the PPD‐RAFT agent and the formed polymers have polydispersity index's (PDI) lower than 1.15. Under adequate miniemulsion polymerization conditions, a glycopolymer with PDI of 1.1 and molecular weight of 5 × 10⁴ g/mol has been successfully synthesized in a short reaction time of 100 min. Furthermore, some block copolymers containing saccharide segment with butyl or methyl methacrylate were prepared. Copyright © 2007 John Wiley & Sons, Ltd.     

Zinc(II) and Cadmium(II) Complexes of the 3‐(2‐Pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDPT) Ligand,Structural Studies of [Zn(PDPT)2Cl(ClO4)] and [Cd(PDPT)2(NO3)(ClO4)]

Two new mixed‐anion zinc(II) and cadmium(II) complexes of 3‐(2‐pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDPT) ligand, [Zn(PDPT)₂Cl(ClO₄)] and [Cd(PDPT)₂(NO₃)(ClO₄)], have been synthesized and characterized by elemental analysis, IR‐ and ¹H NMR spectroscopy. The single crystal X‐ray analyses show that the coordination number in these complexes is six with four N‐donor atoms from two “PDPT” ligand and two of the anionic ligands, ZnN₄ClO_perchlorate, CdN₄O_nitrateO_perchlorate. Self‐assembly of these compounds in the solid state via π–π‐stacking interactions is discussed.     

The absolute stereochemistry of grenadamide

3-(2S-Heptylcycloprop-1S-yl)propanoic acid 2-phenylethanamide was synthesised from cis-cyclopropan-1,2-dimethanol via enzymatic desymmetrisation of the dibutyrate; it gave identical NMR spectroscopic data to those reported for grenadamide but had an equal and opposite absolute rotation, indicating that the latter is the 2R,1R-enantiomer.     

Synergic effect of triphenylphosphine oxide (TPPO) on the extraction of Hg(II), Se(IV), Co(II) and Mn(II) with fluorinated pyrazolone (HPMTFP)

Extraction of Hg(II), Se(IV), Mn(II) and Co(II) has been carried out with 1-phenyl-3-methyl-4-trifluoroacetyl-2-pyrazolin-5-one (HPMTFP) and triphenylphosphine oxide (TPPO) into chloroform from pH 1–10. Quantitative extraction of Hg(II), Mn(II) and Co(II) at pH 4 with equimolar 0.05M (PMTFP+TPPO) in chloroform was observed. Se(IV) remains unextracted at this pH range. The stoichiometric composition of the extracted complexes M(PMTFP)₂·nH₂O (M=Mn, Hg), M(PMTFP)₂·2TPPO (M=Mn and Co) and Co(PMTFP)₂·TPPO·H₂O at less than 0.1M TPPO has been established. The formation constantsK _m,0 andK _m,n and stability constants _m,n have been computed. The analytical method developed was applied to the IAEA standard reference material (SRM) potato fluor V-4 for the determination of these elements using NAA technique.     

2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol as a reagent for the spectrophotometric determination of La(III), Y(III), and Ce(III)

The complexes of the reagent 5-Br-PADAP with the metal ions La(III), Ce(III), and Y(III) have been studied.The composition and stability of these complexes have been determined. A sensitive spectrophotometric procedure for the determination of the metal ions La(III), Ce(III), and Y(III) has been proposed. The limitations of this procedure and the effect of other ions have been studied.     

The reaction of (N-isocyanimino)triphenylphosphorane with benzoic acid derivatives: a novel synthesis of 2-aryl-1,3,4-oxadiazole derivatives

The reactions of benzoic acid derivatives with (N-isocyanimino)triphenylphosphorane proceed smoothly at room temperature to afford 2-aryl-1,3,4-oxadiazoles in high yields.     

Reactivity of tungsten(0) and molybdenum(0) pentacarbonyl thiobenzoate anions: thiobenzoate as a cis-CO labilizing ligand

The [Et₄N][M(CO)₅SCOPh] complexes (1a, M = Mo; 2a, M = W) have been prepared at ambient temperatures by reacting the photogenerated M(CO)₅ THF intermediate with [Et₄N][SCOPh] in THF. Kinetic studies of the reactions of the anions [M(CO)₅SCOPh]^– with the tri(iso-propyl)phosphite (L) ligand under pseudo-first-order conditions indicate that these reactions are first-order in substrate and are independent of the P(OPr-i)₃ concentration. It is thus envisaged that these CO substitutions proceed via a mechanism which involves initial cis-M—CO bond-breaking, followed by fast attack of the incoming nucleophile on the resulting intermediate to give [cis-M(CO)₄{P(O-Pri)₃}SCOPh]^–. This facile displacement of cis-CO indicates the labilizing nature of the thiobenzoate ligand, most probably by virtue of distal oxygen atom participation. Activation parameters for the reactions are: [M(CO)₅SCOPh]^– + L cis-[M(CO)₄(L)SCOPh]^– + CO M = Mo, H = 24.6(2) kcal mol^–1, S = 8.2(6) eu; M = W, H = 28.4(2) kcal mol^–1, S = 11.3(5) eu. Kinetic data and the mechanism of these ligand-substitutions are discussed.     

Vibrational dynamics of hydrogen‐bonded HCN complexes with OH and NH acids: Computational DFT systematic study

Vibrational properties (band position, infrared [IR], and Raman intensities) of C?N stretching mode were studied in 65 gas phase hydrogen‐bonded 1:1 complexes of HCN with OH acids and NH acids using density functional theory (DFT) calculations at the B3LYP‐6‐311++G(d,p) level. Furthermore, general characteristics of the hydrogen bonds and vibrational changes in acids OH/NH stretching bands were also considered. Experimentally observed blue shift of the C?N stretching band promoted by hydrogen bonding, which shortens the triple bond length, is very well reproduced and quantitatively depends on the hydrogen bond length. Both IR and Raman ν(C?N) band intensities are enhanced, also in good agreement with the experimental results. IR intensity increase is a direct function of the hydrogen bond energy. However, the predicted Raman intensity raise is a more complex function, depending simultaneously on characteristics of both the hydrogen bond (C?N bond length) and the H‐donating acid (polarizability). With these two parameters, ν (C?N) Raman intensities of the complexes are explained with a mean error of ±2.4%. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Enantioselective total syntheses of manzamine a and related alkaloids

As a prelude to undertaking the total syntheses of the complex manzamine alkaloids, a series of model studies were conducted to establish the scope and limitations of intramolecular [4 + 2] cycloadditions of N-acylated vinylogous ureas with the trienic substrates 17a,b, 28a,b, and 34. These experiments clearly demonstrated that the geometry of the internal double bond and the presence of an electron-withdrawing group on the diene moiety were essential for the facile and stereoselective formation of the desired cycloadducts. The enantioselective syntheses of the manzamine alkaloids ircinol A (75), ircinal A (5), and manzamine A (1) were then completed by employing a convergent strategy that featured a novel domino Stille/Diels-Alder reaction to construct the tricyclic ABC ring core embodied in these alkaloids. Thus, the readily accessible chiral dihydropyrrole 58 was first converted in a single chemical operation into the key tricyclic intermediate 60. Two ring-closing metathesis reactions were then used to form the 13- and 8-membered rings leading to Z-72 and 74, the latter of which was quickly elaborated into ircinal A (5) via ircinol A (75). The synthetic 5 thus obtained was converted into manzamine A (1) following literature precedent. This concise synthesis of ircinal A required a total of 24 operations from commercially available starting materials with the longest linear sequence being 21 steps.     

Simultaneous Kinetic‐Spectrophotometric Determination of Hydrazine and its Derivatives by Partial Least Squares and Principle Component Regression Methods

Simultaneous kinetic‐spectrophotometric determination of a ternary mixture of hydrazine (HZ) and its derivatives by principal component regression (PCR) and partial least squares (PLS) calibration is described. The methods were based on the difference observed in the reduction rate of iron(III) with HZ, thiosemicarbazide (TSCZ) and phenylhydrazine (PHZ) in the presence of 2,2′‐bipyridine (Bpy). The colored complex of [Fe(Bpy)₃]²⁺ was formed in sodium dodecyl sulfate (SDS) as micellar media, and then monitored at 520 nm. The results showed that simultaneous determination of HZ, TSCZ and PHZ could be performed in their concentration ranges of 1.0–70.0, 0.2–6.0 and 0.1–10.0 μg mL^?1, respectively. The root mean squares errors of prediction (RMSEP) of HZ, TSCZ and PHZ were 0.719, 0.164 and 0.105 (for PLS) 0.788, 0.166 and 0.993 (for PCR), respectively. Both methods (PCR and PLS) were validated using a set of synthetic sample mixtures and then applied for simultaneous determination of HZ, TSCZ and PHZ in water samples.