Benzenehexapyrrole‐α,ω‐dialdehyde, composed of a pair of formyltripyrrole units with a 1,3‐phenylene linker, was metallated to give dinuclear single‐stranded helicates. X‐ray studies of the bis‐nickel(II) complex showed a helical C2 form with a pair of helical–metal coordination planes of a 3N+O donor set. The terminal aldehyde was readily converted into the imine by optically active amines, whereby helix‐sense bias was induced. Bis‐nickel(II) and bis‐palladium(II) complexes of the benzenehexapyrrole‐α,ω‐diimines were studied to show that an enantiomer pair of the helical C2 form are interchanged by slow flipping of each coordination plane and fast rotation around the C(benzene)?C(pyrrole) bond. The helical screw in the bis‐nickel(II) complexes was biased to one side in more than 95 % diastereoselectivity, which was achieved by using a variety of optically active amines, such as (R)‐1‐cyclohexylethylamine, (S)‐1‐ phenylethylamine, L ‐Phe(OEt) (Phe=phenylalanine), and (R)‐valinol. The nickel complexes showed much better diastereoselectivity than the corresponding palladium complexes. 相似文献
Summary: A diastereomeric pair of novel N‐propargylphosphonamidates, HCCCH2NHP(O)(CH3)O‐L ‐menthyl was synthesized by the successive condensations of methylphosphonic dichloride with L ‐menthol and propargylamine. The (R)‐P‐isomer ( 1a ) was isolated, and the absolute configuration was determined by XRD. Polymerization of 1a , and a mixture of 1a and (S)‐P‐isomer ( 1b ) was carried out with a zwitterionic Rh complex as a catalyst. cis‐Stereoregular polymers with number‐average molecular weights of 5 600–9 800 were obtained in good yields. Poly( 1a ) and poly( 1a 29‐co‐ 1b 71) exhibited large specific rotations (+408 and −146°), and intense Cotton effects ([θ] = +2.25 and −0.9 × 104 deg · cm2 · dmol−1) based on the conjugated polyacetylene backbone around 325 nm in CHCl3, indicating that these polymers have helical structures, whose predominant helical senses are opposite.
Polymerization of N‐propargylphosphonamidate. 相似文献
This communication reports the first gold nanoparticles (NPs) chirally functionalized with optically active helical substituted polyacetylene (the resulting hybrid particles are defined as Au@PPA NPs). The novel nanoparticles consist of gold as core and optically active helical poly(N‐propargylamide) as shell and show considerable optical activity derived from helical poly(N‐propargylamide) chains with predominantly one‐handed screw sense. The Au@PPA NPs are prepared by a three‐step approach: i) a thiol‐containing N‐propargylamide monomer [Mth, HC≡CCH2NHCO(CH2)10SH] is synthesized and characterized with FTIR and1HNMR spectroscopy and elemental analysis; ii) a copolymer (poly(Mth‐co‐Mch)) was prepared by starting from monomer Mth and another chiral N‐propargylamide monomer (Mch); poly(Mth‐co‐Mch) formed helical conformations and showed optical activities; and, iii) Au@PPA NPs are prepared from hydrogen tetrachloroaurate (III) and poly(Mth‐co‐Mch) through a one‐spot procedure by using LiBH4 as reducing agent. The as‐obtained hybrid nanoparticles are characterized by FTIR spectroscopy, TEM, UV‐vis absorption and circular dichroism (CD) techniques. UV‐vis and CD measurements demonstrated the remarkable optical activity of the Au@PPA NPs. More interestingly, the Au@PPA NPs show much stronger UV‐vis and CD sigals when compared to the corresponding orginal helical copolymer, poly(Mth‐co‐Mch). The chiral hybrid nanoparticles demonstrate different absorption toward (R)‐(+)‐ and (S)‐(−)‐1‐phenylethylamines, preferentially adsorbing the (S)‐isomer.
On crystallization from CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2, 6‐chloro‐5‐hydroxy‐2‐pyridone, C5H4ClNO2, (I), undergoes a tautomeric rearrangement to 6‐chloro‐2,5‐dihydroxypyridine, (II). The resulting crystals, viz. 6‐chloro‐2,5‐dihydroxypyridine chloroform 0.125‐solvate, C5H4ClNO2·0.125CHCl3, (IIa), 6‐chloro‐2,5‐dihydroxypyridine carbon tetrachloride 0.125‐solvate, C5H4ClNO2.·0.125CCl4, (IIb), 6‐chloro‐2,5‐dihydroxypyridine 1,2‐dichloroethane solvate, C5H4ClNO2·C2H4Cl2, (IIc), and 6‐chloro‐2,5‐dihydroxypyridine 1,1,2,2‐tetrachloroethane solvate, C5H4ClNO2·C2H2Cl4, (IId), have I41/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent‐free crystals with P21/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion‐related molecules form R22(8) dimers via pairs of N—H...O hydrogen bonds. The dimers are linked by O—H...O hydrogen bonds into R46(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel‐containing pyridine solvate crystals, viz. (IIa)–(IId), two independent host molecules form an R22(8) dimer via a pair of O—H...N hydrogen bonds. One molecule is further linked by O—H...O hydrogen bonds to two 41 screw‐related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O—H...O hydrogen bonded to two related equivalents to form tetrameric R44(28) rings. The dimers are π–π stacked with inversion‐related dimers, which in turn stack the R44(28) rings along c to form continuous solvent‐accessible channels. CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2 solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels. 相似文献
Two representatives of a new type of β‐amino acids, carrying two functionalized side chains, one in the 2‐ and one in the 3‐position, have been prepared stereoselectively: a β‐Ser derivative with an additional CH2OH group in the 2‐position (for β‐peptides with better water solubility; Scheme 2) and a β‐HCys derivative with an additional CH2SBn group in the 2‐position (for disulfide formation and metal complexation with the derived β‐peptides; Scheme 3). Also, a simple method for the preparation of α‐methylidene‐β‐amino acids is presented (see Boc‐2‐methylidene‐β‐HLeu‐OH, 8 in Scheme 3). The two amino acids with two serine or two cysteine side chains are incorporated into a β‐hexa‐ and two β‐heptapeptides ( 18 and 23/24 , resp.), which carry up to four CH2OH groups. Disulfide formation with the β‐peptides carrying two CH2SH groups generates very stable 1,2‐dithiane rings in the centre of the β‐heptapeptides, and a cyclohexane analog was also prepared (cf. 27 in Scheme 6). The CD spectra in H2O clearly indicate the presence of 314‐helical structures of those β‐peptides ( 18 , 23 , 24 , 27b ) having the `right' configurations at all stereogenic centers (Fig. 2). NMR Measurements (Tables 1 and 2, and Fig. 4) in aqueous solution of one of the new β‐peptides ( 24 ) are interpreted on the assumption that the predominant secondary structure is the 314‐helix, a conformation that has been found to be typical for β‐peptides in MeOH or pyridine solution, according to our previous NMR investigations. 相似文献
Sequential reaction of a multisite LH4 ligand {2‐[2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylideneamino]‐2‐methylpropane‐1,3‐diol} with appropriate lanthanide salts followed by the addition of Ni(NO3)2 ? 6 H2O in a 4:1:2 stoichiometric ratio in the presence of triethylamine afforded four heterobimetallic trinuclear complexes [Ni2Gd(LH3)4] ? 3 NO3 ? 3 MeOH ? H2O ? CH3CN ( 1 ), [Ni2Tb(LH3)4] ? 3 NO3 ? 3 MeOH ? CH3CN ( 2 ), [Ni2Dy(LH3)4] ? 3 NO3 ? 3 MeOH ? H2O ? CH3CN ( 3 ), and [Ni2Ho(LH3)4] ? 3 NO3 ? 3 MeOH ? H2O ? CH3CN ( 4 ). Complexes 1 – 4 possess linear trimetallic cores with a central lanthanide ion. Magnetic studies revealed a predominant ferromagnetic interaction between the Ni and Ln centers. Alternating current susceptibility measurements of complex 3 showed a small frequency dependence of the out‐of‐phase signal, χ′′M , under zero direct current field, but without achieving a net maximum above 2 K. Magnetic studies on 1 revealed that it has a significant magnetocaloric effect. 相似文献
Crystals of the zwitterionic copper(I) π‐complex [(HC≡CCH2NH3)Cu2Br3] have been synthesized by interaction of CuBr with [HC≡CCH2NH3]Br in aqueous solution (pH < 1) and X‐ray studied. The crystals are monoclinic: space group P21/n, a = 6.722(4), b = 12.818(8), c = 9.907(3) Å, β = 100.25(4)°, V = 840.0(8) Å3, Z = 4, R = 0.0592 for 3015 reflections. The crystal structure of the π‐complex contains isolated [(HC≡CCH2NH3)+(Cu2Br3)?]2 units which are incorporated into a framework by strong hydrogen N–H···Br and C≡C–H···Br bonds. The length of π‐coordinated propargylammonium C≡C bond is equal 1.216(8) Å and Cu(I)–(C≡C) distance equals 1.958(5) Å. 相似文献
The GROMOS96 molecular‐dynamics (MD) program and force field was used to calculate the conformations at 298 K in CHCl3 solution of two hexakis(3‐hydroxyalkanoic acids). One consists of (R)‐3‐hydroxybutanoate (HB) residues only: H−(OCH(Me)−CH2−CO)6−OH ( 1 ). The other one carries the side chains of valine, alanine, and leucine: H−(OCH(CHMe2)CH2−CO−O−CH(Me)−CH2−CO−O−CH(CH2 CHMe2)−CH2−CO)2−OH ( 2 ), with homochiral 3‐hydroxyalkanoate (HA) moieties. In both cases, the conformational equilibria were sampled 2500 times for 25 ns. Other than clusters of arrangements with inter‐residual hydrogen bonding (between the O‐ and C‐terminal OH and COOH groups, and with chain‐bound ester carbonyl O‐atoms; Fig. 6), there are no preferred backbone conformations in which the molecules 1 and 2 spend more than 5% of the time. Specifically, neither the 21‐ nor the 31‐helical conformation of the oligoester backbone (found in stretched fibers, in lamellar crystallites, and in single crystals of polymers PHB and of oligomers OHB) is sampled to any significant extent (Fig. 8 and 9), in spite of the high population, in both oligomers, of the (−)‐synclinal conformation around the C(2)−C(3) bond (angle ϕ2 in Fig. 2). In contrast to β‐oligopeptides, for which strongly preferred secondary structures are found after a few ns, and for which the number of conformations levels off with time, the number of conformational clusters of the corresponding oligoesters found by our force‐field MD calculations increases steadily over the observation time of 25 ns (Fig. 5). Thus, the conclusion from biological and physical‐chemical studies, according to which the PHB chain is extremely flexible, is confirmed by our computational investigation: in CHCl3 solution, the hexakis(3‐hydroxyalkanoate) chain samples its conformational space randomly! 相似文献