Deprotonated Carboxyl Groups Research Articles

A 2D Metal-Organic Framework with a Flexible Cyclohexane-1,2,5,6-tetracarboxylic Acid Ligand: Synthesis, Characterization and Photoluminescent Property.

A novel metal-organic framework, [Zn(2)(OH)(Hcht)(4,4'-bpy)](n).4nH(2)O (1) (H(4)cht = cyclohexane-1,2,4,5-tetracarboxylic acid and 4,4'-bpy = 4,4'-bipyridine), was synthesized by the hydrothermal reaction of Zn(NO(3))(2).6H(2)O, 4,4'-bipyridine, and cyclohexane-1,2,4,5-tetracarboxylic acid in the presence of sodium carbonate. The complex was obtained by controlling the ratio of the starting materials and a reaction temperature at 120 degrees C and was characterized by IR, X-ray powder diffraction, thermogravimetric analysis, fluorescent spectrum, and single crystal X-ray diffraction. Single-crystal X-ray investigation reveals that the structure features a two-dimensional framework with novel coordination mode of Hcht ligand and all Hcht ligands exclusively convert to a sole conformation in the complex. IR spectrum reveals the characteristic absorption peaks of asymmetric stretching vibrations that result from the protonated and deprotonated carboxyl groups,. Thermogravimetric analysis shows four clear courses of weight loss, which corresponds to the decomposition of different ligands. Fluorescent spectrum displays that complex 1 is a potential blue-luminescent material.

Guanidinium 3-carb-oxy-2,3-dihydroxy-propanoate monohydrate.

In the title hydrated salt, CH6N3 +·C4H5O6 −·H2O, the deprotonated carboxyl group is disordered over two positions with a site-occupancy ratio of 0.945 (3):0.055 (3). The bond lengths in the guanidinium cation are inter­mediate between normal C—N and C=N bond lengths, indicating significant delocalization in this species. In the crystal structure, anions and water mol­ecules are linked into sheets parallel to the ab plane by inter­molecular O—H⋯O hydrogen bonds. The linking of the anions and water mol­ecules with the cations by inter­molecular N—H⋯O hydrogen bonds creates a three-dimensional network.

PH-Responsive Self-assembled Nanoparticles of Simulated P(AA-co-SA)-g-PEG for Drug Release

Simulated graft copolymer of poly(acrylic acid-co-stearyl acylate) [P(AA-co-SA)] and poly(ethylene glycol) (PEG) was synthesized, where acrylic acid, stearyl acylate and PEG was employed as the pH-sensitive, hydrophobic and hydrophilic segment, respectively. Polymeric nanoparticles prepared by the dialysis of simulated graft copolymer solution in dimethylformamide against citrate buffer solution with different pH values were characterized by transmission electron microscopy (TEM), fluorescence technique and laser light scattering (LLS). TEM image revealed the spherical shape of the self-aggregates, which was further confirmed by LLS measurements. The critical aggregation concentration increased markedly (10 to 150 mg/L) with increasing pH (4.6 to 7.0), consistent with the de-protonation of carboxylic groups at higher pH. The hydrodynamic radius of polymeric nanoparticles decreased from 118 nm at pH 3.4 to 90 nm at pH 7.0. The controlled release of indomethacin from those nanoparticles was investigated, and the self-assembled nanoparticles exhibited improved performance in controlled drug release.

Tetraaquabis(3-carboxylatopyridineN-oxide-κO3)cadmium(II)

In the title complex, [Cd(C6H4NO3)2(H2O)4], the CdII atom is situated on a crystallographic centre of inversion. The CdII atom shows a slightly distorted octa­hedral geometry and is coordinated by four O atoms from water mol­ecules and two O atoms from deprotonated carboxyl groups of nicotinic acid N-oxide ligands. The mononuclear complex mol­ecules are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network structure.

Synthesis and structure of dimeric anthracene-9-carboxylato bridged dinuclear erbium(III) complex, [Er 2(9-AC) 6(DMF) 2(H 2O) 2

We study the influence of the bulky aromatic rings, e.g. anthracence-9-carboxylic acid (9-ACA) with a large conjugated π-system on the structure and spectroscopic properties of [Er 2(9-AC) 6(DMF) 2(H 2O) 2] complex where 9-AC = anthracence-9-carboxylato and DMF = N, N′-dimethylformamide. The complex has been prepared from the erbium chloride and 9-ACA in the mixture of H 2O:DMF solution (4:1, v/v) followed by pH adjustment to 6. The complex is crystallized in a monoclinic system with space group P2 1/ n. The two Er(III) ions are double bridged by the deprotonated carboxyl groups of two 9-AC anions (O1 and O1A), forming an eight-coordination number. The chelating bidentate ( O, O), chelating–bridging tridentate ( O, O, O′) and monodentate of 9-AC anions are observed in the dinuclear [Er 2(9-AC) 6(DMF) 2(H 2O) 2] complex. The Er–Er distance is 4.015 Å in the dimeric unit. Intramolecular O–H⋯O and C–H⋯O hydrogen bonds as well as numerous of intermolecular C–H⋯π interactions between the anthracene rings by edge-to-face interactions linked the dinuclear dimeric units into two-dimensional supramolecular network in a propeller-arrangement. Electronic absorption spectra of the Er(III) complex and its salt were measured. The emission spectrum of the complex is composed of a broad band due to the emission of intraligand π* → π transition from the 9-AC anions and a shoulder peak originating from the 4f–4f emission transition of the Er(III) ions. The complex has a high thermal stability which can be attributed to the effectively increase the rigidity of the 9-AC anions.

Uranium sequestration by a marine cyanobacterium, Synechococcus elongatus strain BDU/75042

A marine, unicellular cyanobacterium, Synechococcus elongatus strain BDU/75042 was found to sequester uranium from aqueous systems at pH 7.8. The organism could remove 72% (53.5 mg U g −1 dry weight) of uranium from test solutions containing 100 μM uranyl carbonate within 1 h. The equilibrium data fitted well in the Langmuir isotherm thus suggesting a monolayer adsorption of uranium on the cyanobacterial biomass and predicted the maximum adsorption capacity of 124 mg U g −1 dry weight. Light and scanning electron microscopy coupled with energy dispersive X-ray fluorescence (EDXRF) spectroscopy confirmed the uranyl adsorption by this organism. Most of the bound uranium was found to be associated with the extracellular polysaccharides (EPS) suggesting its interaction with the surface active ligands. Fourier transform infrared (FT-IR) spectroscopy suggested the amide groups and the deprotonated carboxyl groups on the cyanobacterial cell surface were likely to be involved in uranyl adsorption. The cell bound uranium could be released by washing with ethylene diamine tetraacetic acid (EDTA) or 0.1 N HCl. The X-ray diffraction (XRD) analyses revealed the identity of uranium deposits associated with the cell biomass as uranyl carbonate hydrate. The study revealed the potential of this cyanobacterium for harvesting uranium from natural aquatic environments.

2-Ammonio-3-(4-nitrophenyl)propanoate monohydrate

The title compound, C9H10N2O4·H2O, exists as a zwitterion with a deprotonated carboxyl group and a protonated amine group. The crystal packing is stabilized by inter­molecular N—H⋯O and O—H⋯O hydrogen bonds, building sheets parallel to the (001) plane.

Copper Fixation to Guaiacyl Lignin Units by Nitrogen Donor Ligands

Several new copper(II) complexes with guaiacyl lignin models vanillin (HL1) [Cu(L1)2(nia)2] (1) (nia = nicotinamide) or vanillic acid (HL2) [Cu(L2)2(nia)2] (2) [Cu2(μ-L2)4(nia)2] (3), and [Cu(L2)2(Hetam)2] (4) (Hetam = ethanolamine) were isolated and characterized. The molecular structure of complex 1 reveals bidentate vanillin (HL1) coordination via the methoxy and the deprotonated hydroxy groups. On the other hand, the vanillic acid (HL2) complexes 2 - 4 show a deprotonated carboxylate group with chelating coordination mode in 2, bridging in 3 and monodentate coordination in 4. The mononuclear complexes 1, 2 and 4 show a distorted trans octahedral coordination sphere with pairs of monodentate and chelating ligands. A replacement of the monodentate nicotinamide ligand in 2 with the bidentate ethanolamine ligand in 4 changes the coordination mode of the vanillic acid anion from bidentate (complex 2) to monodentate (complex 4). This shift inside the coordination sphere reveals different O-Cu-O Jahn-Teller axes by the vanillic acid anion in 2 and ethanolamine in 4. Empty channels are present in the crystal structure of the dinuclear complex 3, stabilized by hydrogen bonds and π-π stacking.

Site‐Specific Adsorption of 1,3‐Dinitrobenzene to Bacterial Surfaces: A Mechanism of n–π Electron‐Donor‐Acceptor Interactions

Surface and subsurface contamination with nitroaromatic compounds (NACs) has drawn considerable attention, and biosorption may play an important role in the fate and transport of these compounds in the environment. We studied the sorption of polar 1,3-dinitrobenzene (DNB) as a representative NAC and 2,6-dichlorobenzonitrile and nonpolar phenanthrene and 1,2,4,5-tetrachlorobenzene from the aqueous phase to two common bacteria, gram-negative Escherichia coli and gram-positive Bacillus subtilis. Sorption of DNB is highly nonlinear and is well described by the Langmuir model and shows the highest capacity among all tested solutes (up to 2.4% of E. coli biomass and 7.6% of B. subtilis biomass by weight) despite the lowest solute hydrophobicity. These results indicate that strong specific sorptive interactions exist between DNB and bacterial surfaces. We propose a mechanism of n-pi electron-donor-acceptor interactions between the oxygen electron pairs of deprotonated carboxyl groups (electron donors) of bacterial surfaces and DNB (electron acceptor). Biosorption of DNB increases with deprotonation of functional groups as pH increases, which rules out hydrophobic effects and H-bonding as major sorption driving forces because they are both favored by protonation of functional groups as pH decreases.

Initial evaluation of new 99mTc(CO)3 renal imaging agents having carboxyl-rich thioether ligands and chemical characterization of Re(CO)3 analogues

The first human studies of a characterized radiopharmaceutical containing a {(99m)Tc(CO)(3)}(+) core, Na[(99m)Tc(CO)(3)(LAN)], demonstrated that Na[(99m)Tc(CO)(3)(LAN)] was an excellent renal imaging agent; however, its clearance was less than that of (131)I-orthoiodohippurate ((131)I-OIH), and it did not provide a direct measure of effective renal plasma flow. In order to develop a (99m)Tc renal agent with pharmacokinetic properties equivalent to those of (131)I-OIH, we investigated the (99m)Tc(CO)(3)/Re(CO)(3) complexes formed from carboxymethylmercaptosuccinic acid (CMSAH(3)) and thiodisuccinic acid (TDSAH(4)). Once the ligand is bound to (99m)Tc(CO)(3) through a thioether and two carboxyl groups, the complexes have at least one unbound carboxyl group, essential for the interaction with the renal tubular transporter. X-ray crystal structural analysis of [NMe(4)][Re(CO)(3)(CMSAH)] was performed to interpret the nature of (99m)Tc tracers. CMSAH(3) and TDSAH(4) were radiolabeled by incubating each ligand and the precursor [(99m)Tc(CO)(3)(H(2)O)(3)](+) at 70 degrees C (pH 7) for 30 min. The products were purified by reversed-phase high-performance liquid chromatography, and biodistribution studies were performed in Sprague-Dawley rats, with (131)I-OIH as an internal control at 10 and 60 min. Radiolabeling CMSAH(3) and TDSAH(4) with the [(99m)Tc(CO)(3)(H(2)O)(3)](+) precursor gave products quantitatively. Analysis of the Re(CO)(3) complexes with the CMSAH(3) and TDSAH(4) ligands demonstrates that ligands are bound in (99m)Tc/Re(CO)(3) complexes through a thioether and two deprotonated carboxyl groups (forming tridentate dianionic moieties, generally with two 5-membered chelate rings). Renal excretion at 60 min (activity in the urine as a percentage of (131)I-OIH) was 68+/-1% for Na(3)[(99m)Tc(CO)(3)(TDSA)] but was 98+/-1% for Na(2)[(99m)Tc(CO)(3)(CMSA)]. In rats, Na(2)[(99m)Tc(CO)(3)(CMSA)] is extracted by the kidneys and eliminated in the urine almost as rapidly as (131)I-OIH; consequently, Na(2)[(99m)Tc(CO)(3)(CMSA)] may provide a direct measure of effective renal plasma flow, and further evaluation in humans is warranted.

(2,2′-Dicarboxy-4,4′-carbonyldibenzoato)bis(1,10-phenanthroline)copper(II) dihydrate

In the title compound, [Cu(C17H8O9)(C12H8N2)2]·2H2O, the CuII cation is hexa­coordinated by two carboxyl­ate O atoms from one of the two deprotonated carboxyl groups in the 3,3,4,4-benzophenone tetra­carboxyl­ate, and four N atoms from two 1,10-phenanthrolines, showing a slightly distorted octa­hedral geometry. A network of hydrogen bonds links the units into a three-dimensional structure.

Possible Mechanism of Proton Transfer through Peptide Groups in the H-Pathway of the Bovine Cytochrome c Oxidase

The peptide group connecting Tyr440 and Ser441 of the bovine cytochrome c oxidase is involved in a recently proposed proton-transfer path (H-path) where, at variance with other pathways (D- and K-paths), a usual hydrogen-bond network is interrupted, thus making this proton propagation rather unconventional. Our density-functional based molecular dynamics simulations show that, despite this anomaly and provided that a proton can reach a nearby water, a multistep proton-transfer pathway can become a viable pathway for such a reaction: a proton is initially transferred to the carbonyl oxygen of a keto form of the Tyr440-Ser441 peptide group [-CO-NH-], producing an imidic acid [-C(OH)-NH-] as a metastable state; the amide proton of the imidic acid is then transferred, spontaneously to the deprotonated carboxyl group of the Asp51 side chain, leading to the formation of an enol form [-C(OH)=N-] of the Tyr440-Ser441 peptide group. Then a subsequent enol-to-keto tautomerization occurs via a double proton-transfer path realized in the two adjacent Tyr440-Ser441 and Ser441-Asp442 peptide groups. An analysis of this multistep proton-transfer pathway shows that each elementary process occurs through the shortest distance, no permanent conformational changes are induced, thus preserving the X-ray crystal structure, and the reaction path is characterized by a reasonable activation barrier.

3-Ammonio-3-(4-pyridyl)propanoate dihydrate

The title compound, C8H10N2O2·2H2O, exists as a zwitterion with a deprotonated carboxyl group and a protonated amino group. The crystal packing is stabilized by N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds.

Synthesis, structure and antimicrobial activity of manganese(II) and cobalt(II) complexes of the polyether ionophore antibiotic Sodium Monensin A

Mononuclear neutral manganese(II) and cobalt(II) complexes with the antibiotic Sodium Monensin A (Mon-Na, 1b) were synthesized and characterized. The crystal structures of M(Mon-Na) 2Cl 2 · H 2O (M = Mn, 2; M = Co, 3) were determined by X-ray crystallography. The complexes crystallize in monoclinic space group C2 with a tetrahedrally coordinated transition metal attached to oxygen atoms of deprotonated carboxyl groups of two Sodium Monensin molecules and two chloride ions. The sodium ion remains in the cavity of the ligand and cannot be replaced by Mn(II) or Co(II). The complexes were additionally characterized by different spectroscopic techniques (UV–Visible, EPR, FAB-MS). A preferable octahedral environment around the transition metal centers is observed in polar solvents while the complexes retain their tetrahedral structure in non-polar media. The antimicrobial activity of 1b, 2 and 3 was tested against Gram(+) and Gram(−) bacteria.

Metal−Organic Frameworks from Copper Dimers withcis- andtrans-1,4-Cyclohexanedicarboxylate andcis,cis-1,3,5-Cyclohexanetricarboxylate

Single crystals of three coordination networks containing the Cu(2)(COO)(4) core bridged by cyclohexane have been hydrothermally prepared by the reaction of 1,4-cyclohexanedicarboxylic (1,4-H(2)chdc) or 1,3,5-cyclohexanetricarboxylic (1,3,5-H(3)chtc) acid and Cu(NO(3))(2) x 6H(2)O. We report their characterizations by single-crystal X-ray structure determinations, IR spectroscopy, thermal analyses, and their magnetic properties. [Cu(2)(trans-1,4-chdc)(2)] (1) consists of 4 x 4 grids with the dimeric nodes connected by the trans-1,4-chdc, and these grids are then connected to each other by Cu-O bonds, resulting in a porous network (void volume of 130 Angstrom(3) per cell or 25%) with no solvent in its cavities. [Cu(2)(cis-1,4-chdc)(2)(H(2)O)(2)] (2) consists of two-legged ladders where the dimer nodes are bridged by pairs of cis-1,4-chdc and the water molecules cap the ends of the Cu dimers. [Cu(2)(1,3,5-Hchtc)(2)] (3) displays 4 x 4 grids, but each dimeric node is connected to its neighbors within the same grid by Cu-O bonds to form a layered network which further makes hydrogen-bond interactions with its neighbors. 2 and 3 have compact structures without any space for solvents. IR and DT-TGA confirm the absence of water in the empty channels of 1, while IR shows the presence of both protonated and deprotonated carboxyl groups for 3. The magnetic properties of all three compounds are dominated by the strong Cu-Cu antiferromagnetic interaction resulting in singlet-triplet gaps of 450-500 K.

Amino acid and peptides on Cu(1 1 0) surfaces: Chemical and structural analyses of l-lysine

Adsorption of l-lysine on a Cu(1 1 0) surface has been carried out under UHV condition from sublimation of a crystalline phase. The adsorption was characterised by FT-RAIRS, LEED and STM. At room temperature, the adsorption geometry of the lysine molecules varies as a function of the exposure. The low coverage phase sees the molecules adsorbed via the oxygen atoms of the deprotonated carboxylate group and the nitrogen atom of the amino group. Close to saturation monolayer regime, the molecules reorient to be anchored to the surface via one oxygen of a side way tilted carboxylate moiety and the interaction of the N atom of the amino group. When this high coverage phase is annealed up to 425 K, the chemical nature and the adsorption geometry stay similar. However, the study of each of these phases by LEED and STM has shown three different two-dimensional adlayers. At room temperature, the low coverage phase exhibits paired chains of molecules growing symmetrically at ±19° of the [0 0 1] direction, while the high coverage phase presents a chiral (−2, −2; 5, −1) chiral phase with an overall growth direction parallel to the [−1 1 2] direction. Finally, the high coverage phase warmed up to 425 K leads to a (3 × n) structure, which seems to be a stable intermediate overlayer at this temperature, that gives rise to a (3 × 2) structure when annealed to 450 K. A number of schematic adsorption geometry models are proposed for each phase.

Guanidinium benzoate

In the title compound, C7H5O2−·CH6N3+, the cation and anion lie on crystallographic mirror planes. The bond length in the deprotonated carboxyl group is intermediate between normal single and double Csp2=O bond lengths, indicating delocalization of the charge over both O atoms of the COO− group. Hydrogen bonds assemble the ions into layers in the bc plane.

Metal‐based antibacterial and antifungal amino acid derived Schiff bases: their synthesis, characterization and in vitro biological activity

AbstractA new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements. The spectral data indicated the Schiff base ligands (L1–L5) derived by condensation of salicylaldehyde with glycine, alanine, phenylalanine, methionine and cysteine, to act as tridentate towards divalent metal ions (cobalt, copper, nickel and zinc) via the azomethine‐N, deprotonated carboxyl group of the respective amino acid and deprotonated oxygen atom of salicylaldehyde by a stoichiometric reaction of M:L (1:2) to form complexes of the type K2[M(L)2] [where M = Co(II), Cu(II), Ni(II) and Zn(II)]. The magnetic moments and electronic spectral data suggested that all complexes have an octahedral geometry. Elemental analyses and NMR spectral data of the ligands and their Zn (II) complexes agree with their proposed structures. The synthesized ligands, along with their metal complexes, were screened for their in‐vitro antibacterial activity against four Gram‐negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa and Salmonella typhi) and two Gram‐positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in‐vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against one or more species as compared with the uncomplexed Schiff base ligands. The brine shrimp bioassay was also carried out to study their in‐vitro cytotoxic properties. Only three compounds (2, 11 and 17) displayed potent cytotoxic activity as LD50 = 8.196 × 10−4, 7.315 × 10−4 and 5.599 × 10−4 M/ml respectively, against Artemia salina. Copyright © 2007 John Wiley & Sons, Ltd.

Adsorption and self-assembly of aromatic carboxylic acids on Au/electrolyte interfaces

The adsorption and self-assembly of benzoic acid (BA), isophthalic acid (IA), and trimesic acid (TMA) on Au(111) single crystals and on Au(111-25 nm) quasi-single crystalline film electrodes have been investigated in 0.1 M HClO4 by combining in situ surface-enhanced infrared reflection absorption spectroscopy (SEIRAS) and scanning tunneling microscopy (STM) with cyclic voltammetry. All three acids are physisorbed on the electrode surface in a planar orientation at negative charge densities. Excursion to positive charge densities (or more positive potentials) causes an orientation change from planar to perpendicular. Chemisorbed structures are formed through the coordination of a deprotonated carboxyl group to the positively charged electrode surface. The three acid molecules assemble in different ordered patterns, which are controlled by pi-stacking (BA) or intermolecular hydrogen bonds between COOH groups (IA, TMA). A detailed analysis of the potential and time dependencies of the nu(C=O), nus(OCO), and nu(C-OH) vibration modes shows that the strength of lateral interactions increases upon chemisorption with an increasing number of COOH groups in the sequence of BA<IA<TMA. The vibration bands shift to higher wavenumbers due to dipole-dipole coupling, Stark tuning, and electron back donation from the electrode to COO-. In addition, an "indirect" electron donation to the COOH groups takes place via the conjugated molecular skeleton superimposed on the intermolecular hydrogen bonding.

A Series of Cadmium(II) Coordination Polymers Synthesized at different pH Values

AbstractA new family of cadmium(II) coordination polymers, {[Cd(Hbic)2·(H2O)2]·2H2O}n (1), [Cd(Hbic)2]n (2), [Cd(Hbic)2·(H2O)]n (3), H2bic = 1H‐benzimidazole‐5‐carboxylic acid, has been hydrothermally prepared by the assembly of CdII with H2bic. A change in the pH values resulted in a series of compounds with different compositions and dimensionalities. Formed at the lowest pH, compound 1 has a two‐dimensional supramolecular structure, which contains 1D chains extended by hydrogen bonds. At a slightly higher pH, compound 2 is synthesized with a higher number of deprotonated carboxylate groups per cadmium atom. A further increase in the pH leads to 3D dinuclear compound 3 with yellow‐green emitting fluorescence. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)