Carboxylic Units Research Articles

Incorporation of conformationally constrained beta-amino acids into peptides.

The use of norbornene units to induce the formation of beta-sheet and beta-turn type structures in peptides is discussed. The norbornene unit is readily prepared by a desymmetrization reaction and is easily incorporated into a peptide chain. Depending upon the exact nature of the norbornene unit, it is possible to form structures which resemble parallel beta-sheets, antiparallel beta-sheets or beta-turns. Similar peptide analogues incorporating a cis-2-amino-cyclopropane carboxylic acid unit can also be prepared. As an illustration of the application of this chemistry, a short, asymmetric synthesis of conformationally constrained metalloprotease inhibitors is presented.

Micelle-like particles formed by carboxylic acid-terminated polystyrene and poly(4-vinyl pyridine) in chloroform/methanol mixed solution

Preparation and characterization of isolated particles and clusters of carboxylic acid-terminated polystyrene (CPS) and poly(4-vinyl pyridine) (P4VP) blends in chloroform/methanol (9/1, v/v) solution are reported. In chloroform CPS–P4VP blends form graft-like structure due to the interaction between terminal carboxylic acid and 4VP units. Upon addition of methanol, isolated particles and clusters with micelle-like structure were prepared. Dynamic light scattering (DLS) results and transmission electron microscopy (TEM) images both suggest the existence of isolated particles and clusters with micelle-like structure in the mixed solution. The effects of weight ratio of CPS to P4VP and addition of copper ion on the size of isolated particles and clusters were also investigated.

Lead selective lipophilic acyclic diionizable polyethers

A structural series of acyclic polyether dicarboxylic acids with n-butyl and n-tetradecyl alkyl side chains at the α-position of the carboxylic acid units, as well as varying lengths of the ethylene glycol ether linkage connecting two benzo units were prepared. In terms of stability constants, competitive solvent extraction and cation transport experiment by bulk liquid membrane toward transition metal ions, ligand 3 with a monoethylene glycol unit and n-butyl side chains provide the best selectivity for the lead ion.

Enantioselective Total Synthesis of Reveromycin B

The reveromycins A (1) and B (2) belong to a new family of natural products that have been isolated from a soil actinomycete of the genus Streptomyces.1 Both compounds inhibit eukaryotic cell growth presumably by interfering with an element associated with the epidermal growth factor receptor pathway.2,3 The molecular structures of 1 and 2 are characterized by a [6,6] or [5,6] spiroketal core respectively, decorated with two highly unsaturated side-chains ending in carboxylic acid units. The relative and absolute configuration of 1 was determined by chemical degradation and spectroscopic analysis, while the structure of 2 was proposed by analogy to 1.4 Herein, we would like to disclose a route to the chemical synthesis of 2, which may also be amenable to the synthesis of other members of this family.5 This reaction sequence constitutes the first total synthesis of a member of the reveromycin family and unambiguously confirms the proposed structures for 2 and 1.

Studies on Complexation of Alkaline Earth Metal Cations with Acyclic Polyether Dicarboxylic Acids

Acyclic polyether dicarboxylic acids having butyl and tetradecyl side alkyl chains at the α-position of the carboxylic acid sidearm unit were prepared by the reaction of bisphenol and 2-bromoalkanoic acid in the presence of sodium hydride with quantitative yields. Complexation studies and solvent extraction on complexes of these ethers with alkaline earth metal ions indicate that 1,2-bis((2-2‘-carboxybutyloxy)phenoxy)ethane (2) shows an excellent selectivity for the calcium ion.

Calcium Complexes of Carboxylate-Containing Polyamide with Sterically Disposed NH···O Hydrogen Bond: Detection of the Polyamide in Calcium Carbonate by 13C Cross-Polarization/Magic Angle Spinning Spectra

Carboxylate-containing polyamides were synthesized from 2,6-di(amino)benzoic acid and dimethylmalonyl dichloride, isophthaloyl dichloride, and fumaryl dichloride. These polymers, {NHC6H3(COO)NHCOC(CH3)2CO}n, {NHC6H3(COO)NHCO-m-C6H4CO}n, and {NHC6H3(COO)NHCO-trans-CHCHCO}n, have seven to eight carboxylate units in a polymer chain, and their Ca(II) complexes possess NH···O hydrogen bonds, which prevents the Ca−O dissociation by hydrolysis. CaCO3 was obtained from aqueous Ca2+ and CO32- in the presence of the polyamide or the Na salt of these polyamides ([Ca2+]/[monomer unit] = 100) to give calcite, vaterite, and/or their mixture. We were able to observe polymers in CaCO3 utilizing the 13C cross-polarization/magic angle spinning solid-state NMR. The binding of Ca(II) by carboxylate appears to be an important factor in these studies and may be relevant to biomineralization of CaCO3.

Establishing Microporosity in Open Metal−Organic Frameworks: Gas Sorption Isotherms for Zn(BDC) (BDC = 1,4-Benzenedicarboxylate)

Construction of microporous metal-organic frameworks by copolymerization of organic molecules with metal ions has received widespread attention in recent years, with significant strides made toward the development of their synthetic and structural design chemistry.1 Cognizant of the fact that access to the pores and understanding the inclusion chemistry of these materials are essential to their ultimate utility, we prepared rigid frameworks that maintain their structural integrity and porosity during anion-exchange and guest sorption from solution and in the absence of guests.2-4 Although gas sorption isotherm measurements are often used to confirm and study microporosity in crystalline zeolites and related molecular sieves,5 such studies have not been established in the chemistry of open metal-organic frameworks6 thus leaving unanswered vital questions regarding the existence of permanent porosity in this class of materials. Herein, we present the synthesis, structural characterization, and gas sorption isotherm measurements for the Zn(BDC) microporous framework of crystalline Zn(BDC)‚(DMF)(H2O) (BDC ) 1,4benzenedicarboxylate and DMF ) N,N′-dimethylformamide). Slow vapor diffusion at room temperature of triethylamine (0.05 mL) and toluene (5 mL) into a DMF solution (2 mL) containing a mixture of Zn(NO3)2‚6H2O (0.073 g, 0.246 mmol) and the acid form of BDC (0.040 g, 0.241 mmol) diluted with toluene (8 mL) yields colorless prism-shaped crystals that were formulated as Zn(BDC)‚(DMF)(H2O). X-ray single-crystal analysis8 on a sample obtained from the reaction product revealed an extended open-framework structure composed of the building unit shown in Figure 1. A total of four carboxylate units of different, but symmetrically equivalent, BDC building blocks are bonded to two zinc atoms in a di-monodentate fashion. Each zinc is also linked to a terminal water ligand to form an overall arrangement that is reminiscent of the carboxylate bridged M-M bonded molecular complexes. Although the Zn-Zn distance (Zn1-Zn1A ) 2.940 (3) A) is indicative of some M-M interaction, it does not represent an actual bond.9 The structure extends into the (011) crystallographic plane by having identical Zn-Zn units linked to remaining carboxylate functionalities of BDC to yield 2-D microporous layers. These layers are held together along the a axis by hydrogen-bonding interactions between water ligands of one layer and carboxylate oxygens of an adjacent layer as illustrated in a. Stacking of the layers in the

Chelation properties of polymer complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide)

The metal-complexing properties of intermolecular complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide) were studied by means of the liquid-phase polymer based retention (LPR) technique. The metal ion retention ability at pH 5 for 400 μg of Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), and Zn(II) was investigated due to their environmental and analytical interest in the presence of 1.1 M of carboxylic acid units and variable amounts of amide groups. The retention profiles of the intermolecular complexes were compared with those of the correspondent homopolymers and copolymers. The retention capacity of poly(acrylic acid) is 100% for all metal ions except for Co(II), Ni(II), and Zn(II) whose values were about 90%, while poly(acrylamide) does not retain any of the metal ion studied. The presence of poly(acrylamide) decreases the retention capacity down to 60% for Co(II) and Ni(II) and to 70% for Zn(II). The decrease on the retention values is dependent on the polymer ratio. A smaller effect is observed by the addition of poly(N,N-dimethylacrylamide) which also decreases the retention capacity down to 80% for Co(II) and Ni(II) for a ratio poly(acrylic acid)/poly(N,N-dimethylacrylamide) = 1/2. The metal ion binding behavior of the interpolymer complexes is very close to that of the copolymers.

Chelation properties of polymer complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide)

The metal-complexing properties of intermolecular complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide) were studied by means of the liquid-phase polymer based retention (LPR) technique. The metal ion retention ability at pH 5 for 400 μg of Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), and Zn(II) was investigated due to their environmental and analytical interest in the presence of 1.1 M of carboxylic acid units and variable amounts of amide groups. The retention profiles of the intermolecular complexes were compared with those of the correspondent homopolymers and copolymers. The retention capacity of poly(acrylic acid) is 100% for all metal ions except for Co(II), Ni(II), and Zn(II) whose values were about 90%, while poly(acrylamide) does not retain any of the metal ion studied. The presence of poly(acrylamide) decreases the retention capacity down to 60% for Co(II) and Ni(II) and to 70% for Zn(II). The decrease on the retention values is dependent on the polymer ratio. A smaller effect is observed by the addition of poly(N,N-dimethylacrylamide) which also decreases the retention capacity down to 80% for Co(II) and Ni(II) for a ratio poly(acrylic acid)/poly(N,N-dimethylacrylamide) = 1/2. The metal ion binding behavior of the interpolymer complexes is very close to that of the copolymers.

Chelation properties of polymer complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide)

The metal-complexing properties of intermolecular complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide) were studied by means of the liquid-phase polymer based retention (LPR) technique. The metal ion retention ability at pH 5 for 400 μg of Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), and Zn(II) was investigated due to their environmental and analytical interest in the presence of 1.1 M of carboxylic acid units and variable amounts of amide groups. The retention profiles of the intermolecular complexes were compared with those of the correspondent homopolymers and copolymers. The retention capacity of poly(acrylic acid) is 100% for all metal ions except for Co(II), Ni(II), and Zn(II) whose values were about 90%, while poly(acrylamide) does not retain any of the metal ion studied. The presence of poly(acrylamide) decreases the retention capacity down to 60% for Co(II) and Ni(II) and to 70% for Zn(II). The decrease on the retention values is dependent on the polymer ratio. A smaller effect is observed by the addition of poly(N,N-dimethylacrylamide) which also decreases the retention capacity down to 80% for Co(II) and Ni(II) for a ratio poly(acrylic acid)/poly(N,N-dimethylacrylamide) = 1/2. The metal ion binding behavior of the interpolymer complexes is very close to that of the copolymers.

Diruthenium and diosmium tetracarboxylates: synthesis, physical properties and applications

Dimetal tetracarboxylates, [M 2(O 2CR) 4] n , have received much coverage in the literature. The metals include Cr, Mo, W, Tc, Re, Ru, Os, Co, Rh, Ir, Ni and Cu with n ranging from −2 to +4 (0 to +2 being most common). Diruthenium and diosmium tetracarboxylates form two of the younger families of these ubiquitous compounds and are known to exist as homovalent Ru 2(II,II) and Os 2(III,III) and mixed-valent Ru 2(II,III) and Os 2(II,III) species. This paper will provide a comprehensive review of these complexes and include such things as their discovery, synthesis and crystal structures; electronic, vibrational (IR and Raman), ESR and photoelectron spectroscopy; magnetic susceptibility; electrochemistry; kinetics; calorimetry; theoretical calculations such as SCF-Xα-SW and CASSCF; and more recent studies of their mesomorphic behaviour and biological and catalytic applications. The ruthenium compounds, in particular, have shown a potential application as liquid crystals. Current work (including this author's) is also focused on the development of linear chains involving these metal carboxylate units and bidentate bridges with the view to developing ferromagnetic materials and conductive polymers. There have been no previous reviews on ruthenium (and osmium) carboxylates per se. Cotton and Walton give them some coverage in the context of metal–metal bonds in Multiple Bonds Between Metal Atoms (2nd ed., 1993) however the direct coverage of Ru 2(O 2CR) 4 and Os 2(O 2CR) 4 type complexes is cursory and dispersed throughout the book. As well, the coverage is only comprehensive through December 1990 with some references from 1991. The current review will be complete through to mid-1997.

Three-phase transport studies of benzimidazole ligands bearing hydrophobic N-alkyl substituents: transport of metal(II) ions (Ni, Cu, Zn, Cd) in single- and multiple-ion experiments †

New ligands having two benzimidazole units, or one benzimidazole and one carboxylic acid unit, the two functions linked by a chain, and bearing hydrophobic N-alkyl substituents have been tested as transfer agents for metal(II) ions (Ni, Cu, Zn, Cd) using three-phase transport techniques. The transport was pH-dependent, so all comparisons were made with buffered feed and receiving phases at fixed pH. Variations in the nature and number [single and double N-alkyl-substituted bis(benzimidazole) ligands] of N-alkyl substituents, linker chain and its donor atoms were explored and resultant transport trends are discussed. While single-ion transport results were ambivalent (singly alkylated 2-oxapropane derivatives being the best extractants for copper, and the analogous 2-thiapropane ligands for zinc), in multiple-ion experiments copper was always transported in preference to zinc. Even for ligands with a longer linking chain (based on 2,5-dioxaoctane) the order for extraction of metal(II) ions was always Cu > Zn > Cd and the transport of Ni was negligible. From the benzimidazole ligands screened, those having a carboxylic acid moiety reveal the highest metal-ion selectivity.

Combinatorial approaches to polyketide biosynthesis

Polyketides are a large and structurally diverse family of natural products based on chains of carboxylic acid units. The polyketide synthases that make aromatic polyketides have already been used to generate small combinatorial libraries, by expressing individual genes from different biosynthetic pathways together, so that the enzymes they encode can interact to make novel products. Recent work has shown how to choose these individual components to increase the chances of obtaining such hybrid aromatic compounds. In other polyketide synthases which synthesise complex reduced polyketides, the constituent enzymes are actually linked as domains in a giant multienzyme complex along which the growing polyketide chain is passed. A combinatorial approach here therefore requires the fusing together of individual enzymatic domains from several such synthases in as many productive ways as can be devised, so that the enzyme assembly line produces a library of altered products. A key recent advance has been to demonstrate that such genuinely hybrid enzymes do work as predicted, for example a broad-specificity enzyme that recruits the chain starter unit for an antiparasitic compound has been grafted onto a synthase that makes antimicrobial macrolides.

Synthesis of thermoassociative copolymers

The synthesis of thermoassociative water-soluble copolymers, with polyether as pendant chains, was developed by macromonomer copolymerization and grafting techniques. The discussion was specially focused on the coupling reactions, between ω-methyl α-aminopolyethers and carboxylic units borne on the backbone, which provide in quantitative yield well-defined grafted copolymer structures. According to the thermodynamical properties of poly(ethylene oxide) or poly(propylene oxide) side-chains (lower critical solution temperature), aqueous solutions of grafted copolymers exhibit a microphase separation of polyether grafts upon heating and generate, above C ∗ , thermothickening properties of the solutions. The general basis of this behaviour is discussed, and the roles played by structural and external parameters highlighted.

Synthesis of Lipophilic Acyclic Diionizable Polyethers and Selective Transport of Alkaline-Earth Cations in Bulk Liquid Membrane System

Selective transport of alkaline-earth cations in a bulk liquid membrane system by lipophilic acyclic polyether dicarboxylic acids is reported. Introduction of proton-ionizable groups into such polyethers shows a distinct advantage over neutral macrocycles in that transfer of a metal ion into an organic medium does not require concomitant transport of an aqueous phase anion. A new organic ligand 1,5-bis[2-(2′-carboxypentadecyloxy)phenoxy]-3-oxapentane (8) which bears a tetradecyl group as an alkyl chain at the α-position of the carboxylic acid side-arm unit is sufficiently lipophilic to avoid loss of the complexing agent into the aqueous phase during solvent extraction and exhibited a calcium selectivity over other alkaline-earth cations.

Photoluminescent Mn-Doped ZNS Nanoclusters Synthesized within Block Copolymer Nanoreactors

ABSTRACTMn-doped ZnS nanoclusters were synthesized within microphase-separated films of diblock copolymers containing carboxylic acid units on one of the blocks. Zinc was selectively sequestered into the acid-containing domains by treating the films with diethylzinc or an aqueous zinc acetate solution. Manganese was loaded by subsequent treatment of the films with aqueous manganese acetate solutions. The manganese ions displaced a fraction of the zinc ions, and the extent of loading was controlled by varying the loading time, and the concentration of the manganese acetate solution. The extent of loading was tracked using ICP discharge emission spectroscopy. The doped nanoclusters were formed by subsequent treatment with H2S. The size of the doped ZnS nanoclusters could be varied by carrying out the H2S exposure in the presence of a coordinating base. Photoluminescence measurements revealed that the doped nanoclusters were photoluminescent, and showed the characteristic manganese emission. The universal doped cluster synthesis scheme used is quite general and can be easily modified to produce other doped nanocluster clusters, such as Tb-doped ZnS, or Mn-doped CdS.

Soil organic matter composition in urbic anthrosols in the city of Kiel, NW-Germany, as revealed by wet chemistry and CPMAS 13C-NMR spectroscopy of whole soil samples

In urban environment soil organic matter (SOM) has manifold functions and a tremendous ecological significance. However, little is known about SOM in urbic soils. In six top layers of soils with different age in the city of Kiel at the Baltic Sea, Northwest Germany, the SOM composition was investigated by means of wet chemistry and CPMAS 13C—NMR spectroscopy and compared to data of natural soils. In the urbic forest soils a low level of the recalcitrant lipid fraction and of the mobile fulvic acid fraction and the high amount of carboxylic units in the humic compounds did not reflect the SOM pattern of natural, acidic forests soils. In peaty soils probably a high heavy metal contamination does not retard litter decomposition. A very high aromaticity of total SOM and of the humic compounds might be typical for soils under horticulture in private gardens. In the young soils litter compounds dominate in the SOM. NMR data suggest, that the extracted humic fractions were chemically ill-defined moieties.

Controlled Formation of Carboxylic Acid Groups at Polyphosphazene Surfaces: Oxidative and Hydrolytic Routes

Two methods have been developed for the controlled formation of carboxylic acid units at the surfaces of aryloxyphosphazene high polymers. The first involves a permanganate-induced oxidation of p-methylphenoxy side groups, with the surface density of carboxylic acid units being controlled by the ratio of p-methylphenoxy to phenoxy groups along the polymer chains. The second approach involves a base-induced hydrolysis of carboxylate ester functions at the para-positions of surface aryloxy side groups. In this method the surface density of carboxyl units is controlled by the reaction conditions, especially by the temperature and the solvent for the base. The same ester functions were converted to alcohol moieties by surface reductions using lithium aluminum hydride in diethyl ether. The surface structures before and after these reactions were studied by a combination of contact angle measurements, X-ray photoelectron spectroscopy, scanning electron microscopy with X-ray microanalysis, and ATR-IR spectroscopy.

Synthesis of PbS Nanoclusters within Block Copolymer Nanoreactors

We have demonstrated the synthesis of PbS nanoclusters within the microphase-separated films of diblock copolymers containing carboxylic acid units on one of the blocks. Lead was selectively sequestered into the acid containing domains by treating the polymer films with tetraethyllead, and PbS was formed by subsequently treating the films with H2S. The PbS nanoclusters were characterized by X-ray diffraction, X-ray fluorescence, electron microscopy, and UV−vis spectroscopy. The cluster size could be controlled by varying processing parameters such as temperature, the presence of coordinating bases, and the H2S exposure time. Increasing the size of the nanoreactors increased the cluster size. The universal cluster synthesis scheme enabled multiple passes through the process, which were used to increase the cluster size and which could in principle be used to passivate the surface of the PbS cluster or to produce mixed semiconductor clusters.

Clusters as Ligands. 4. Synthesis, Structure, and Characterization of the Tungsten(II)-Tungsten(III) Cluster Carboxylate {[Na][W(2){OOCCCo(3)(CO)(9)}(2)(OOCCF(3))(4)(THF)(2)]}(2).

The reaction of W(2)(OOCCF(3))(4) with (CO)(9)Co(3)CCOOH and Na[OOCCF(3)] in a nonpolar solvent mixture leads to the formation of the cluster of clusters {[Na][W(2){OOCCCo(3)(CO)(9)}(2)(OOCCF(3))(4)(THF)(2)]}(2), 1, in 40% yield. The structure of 1.3C(6)H(5)CH(3) in the solid state corresponds to a dimer of W(2) dinuclear complexes (monoclinic P2(1)/c, a = 15.234(6) Å, b = 23.326(11) Å, c = 20.658(7) Å, beta = 102.46(3) degrees; V = 7,168(5) Å(3); Z = 4; R(F)() = 8.39%). Each W(2) unit is bridged by two cis cluster carboxylates, and the remaining four equatorial sites are occupied by monodentate [OOCCF(3)](-) ligands. The axial positions contain coordinated THF. The W(2) carboxylate is opened up (W-W distance of 2.449(2) Å) so that the free ends of the [OOCCF(3)](-) ligands on both W(2) carboxylate units can cooperate in chelating two Na(+) ions thereby forming a dimer of W(2) complexes. A distinctive EPR spectrum with g = 2.08 is consistent with each W(2) carboxylate being a mixed-valent W(II)-W(III) species. The reaction of W(2)(OOCCF(3))(4) with (CO)(9)Co(3)CCOOH in THF in the absence of Na[OOCCF(3)] leads to the expected diamagnetic W(II)-W(II) cluster carboxylate W(2){OOCCCo(3)(CO)(9)}(3)(OOCCF(3))(THF)(2), 3.