Aliphatic Ligands Research Articles

One- and two-dimensional divalent copper coordination polymers based on kinked organodiimine and long flexible aliphatic dicarboxylate ligands

Hydrothermal synthesis under acidic conditions has afforded a pair of divalent copper coordination polymers containing the kinked dipodal tethering organodiimine 4,4′-dipyridylamine (dpa) and flexible long-chain aliphatic dicarboxylate ligands. The new materials were characterized by single crystal X-ray structure determination, infrared spectroscopy, and thermogravimetric analysis. [CuCl(suberate) 0.5(dpa)] ( 1) manifests 1-D ladder-like motifs aggregated into 3-D through hydrogen bonding and copper-mediated supramolecular interactions. Extension of the aliphatic chain within the dicarboxylate ligand by one methylene unit resulted in {[Cu(azelate)(dpa)(H 2O)] · 3H 2O} ( 2), a (4,4) rhomboid grid 2-D coordination polymer encapsulating acyclic water molecule trimers.

Design, synthesis and spectroscopic studies of resveratrol aliphatic acid ligands of human serum albumin

As one of the natural polyphenols, resveratrol possesses hydroxyl substituted trans-stilbene structure and exerts impact on health by inhibiting multiple human enzymes, such as cyclooxygenase, F1 ATPase, and tyrosinase. Resveratrol has to be bound by human serum albumin (HSA) to keep a high concentration in serum, since its solubility is low in water. To improve water solubility and bioavailability, two resveratrol aliphatic acids and their esters have been designed and synthesized. The solubilities of the resveratrol and its derivatives have been measured using a standard procedure. The two aliphatic acids showed better solubilities in pure water and phosphate buffer (pH 7). The binding affinities of resveratrol derivatives for HSA were also measured, and the drug–protein interaction mechanism was investigated using fluorescence, UV–vis, and NMR spectroscopies. Interestingly, resveratrol hexanoic acid ( 5) was found to be a much better ligand ( K a = (6.70 ± 0.10) × 10 6 M −1) for HSA than resveratrol ( K a = (1.64 ± 0.07) × 10 5 M −1), and there was 41-fold improvement for the binding affinity. It was the first time that the increase of fluorescence of resveratrol moiety was observed during the binding to HSA, suggesting that 5 should be bound tightly by HSA. The UV–vis absorption spectroscopy revealed a maximum absorption shift from 318 to 311 nm with decreasing intensity by 20% upon complexation, suggesting that the π–π conjugation of the stilbene structure was impaired during the binding. Although HSA was reported to have only one binding site for resveratrol, the Job’s and molar ratio plots suggested that HSA should bind two molecules of 5. NMR study suggested that phenyl group (B ring) in the center of the molecule of 5 should be involved in the π–π stacking interactions with HSA aromatic amino acid residues. Molecular geometry calculation of 5 with Spartan software showed that the stilbene structure had two conformers, orthogonal and planar ones. The former ( E = −1.432 KJ/mol) was more stable than the latter ( E = −0.128 KJ/mol), suggesting that the former should be the conformer of 5 in the complexation with HSA.

Solvent‐Dependent Regiochemical Cyclotrimerisation of Phenylacetylene with Cobalt Catalysts Containing Disulfide Ligands: A Case Study

AbstractThe intermolecular cobalt‐catalysed cyclotrimerisation of phenylacetylene as a benchmark alkyne with [1,2‐bis(4‐methoxyphenylthio)ethane]cobalt dibromide gave the symmetrical 1,3,5‐triphenylbenzene as the major product when dichloromethane was used as the solvent, whereas the unsymmetrical 1,2,4‐trisubstituted product was obtained in acetonitrile in quantitative yield. Optimisation of the aromatic and aliphatic disulfide ligands in different solvents is discussed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Preparation and X-ray characterization of two-coordinate Cu(I) complex of aliphatic thiolato ligand: Effect of steric bulk on coordination features

We have synthesized in a single-step procedure from available copper(I) precursor at RT two Cu(I) thiolato clusters of the formula [Cu 4(μ-SCH(CH 3) 2) 6] 2− and [Cu 5(μ-SC(CH 3) 3) 6] − as revealed by X-ray crystallography, where increased steric bulk leads to a bigger cage with some two-coordinate metal centers. In addition, we identified a mononuclear two coordinate thiolato complex with the bulkier ligand, of the formula NEt 4[Cu(SC(CH 3) 3) 2]. This is only the second example of such a complex of an aliphatic ligand that is structurally characterized. The X-ray structure reveals an S–Cu–S angle of 176.7–179.5°, with Cu–S distances of 2.14 Å.

How Do Copper Enzymes Hydroxylate Aliphatic Substrates? Recent Insights from the Chemistry of Model Systems

Copper at work: The aliphatic ligand hydroxylation by a copper–oxygen center has been observed for the first time on a model system of the enzyme PHM (peptidylglycine-α-hydroxylating monooxygenase). This result is put in the context of the enzymatic mechanism, which presumably involves a high-valent copper oxo unit (violet-red) that hydroxylates the substrate (cyan).

Unique gas and hydrocarbon adsorption in a highly porous metal-organic framework made of extended aliphatic ligands

High and unique gas and hydrocarbon adsorption in a highly stable guest-free microporous metal-organic framework constructed on rigid aliphatic ligands, H(2)bodc and ted, is reported in this work.

Surface Modification of ZrO2 Nanoparticles as Functional Component in Optical Nanocomposite Devices

ABSTRACTWe have recently shown the successful synthesis of zirconia nanoparticles that can be optimized for use in volume phase holography by a post-functionalization surface treatment. Here, we present further investigations on the surface modification treatment with the aim of providing tools to tailor the nanoparticle compatibility to the photocurable organic matrix. Highly crystalline ZrO2 nanoparticles with a mean diameter of 5nm are synthesized in multigram yield through a one-pot solvothermal reaction of zirconium (IV) n-propoxide in benzyl alcohol. It is shown that the yield of the ZrO2 nanoparticles and stability of the nanoparticle dispersions are strongly dependent on the synthesis temperature. Post-synthetic surface modification of ZrO2 nanoparticles using several aliphatic ligands with different surface binding groups such as carboxylate (-COO−), amine (−NH2), phosphate (−PO4) and methoxysilane (−SiOCH3) was performed in order to compare the binding ability of these functional groups to the nanoparticle surface and therefore provide a new rational approach for nanoparticle stabilization with organic ligands.

Crystal structure and magnetic properties of a unique 3D coordination polymer constructed from flexible aliphatic tricarballylic acid ligands featuring linear trimeric Manganese(II)-based, metal carboxylate chains

A novel linear trimeric-based, Mn(II)–carboxylate chain well separated by long-linking flexible aliphatic tricarballylic acid ligands in a 3D coordination polymer [Mn 3(C 6H 5O 6) 2(H 2O) 4] n ( 1, C 6H 5O 6 CH (COO −)(CH 2COO −) 2, TCA) exhibits low-dimensional antiferromagnetic order at 3.0 K. Such magnetic behavior is arises from the alternate Antiferro–Antiferro–Antiferro′ ( J 1 J 1 J 2) repeating interactions sequence, based on the nature of the binding modes of Mn(II)-carboxylate chain and the effect of interchains arrangement of 1. The reported carboxylate-bridged metal chain systems display a new structurally authenticated example of linear homometallic spin arranged antiferromagnet among metal carboxylates.

Ligand and Counterion Control of Ag(I) Architectures: Assembly of a {Ag8} Ring Cluster Mediated by Hydrophobic and Ag···Ag Interactions

A strategy combining ligand design and counterion variation has been used to investigate the assembly of silver(I) complexes. As a result, dinuclear, octanuclear, and polymeric silver(I) species have been synthesized by complexation of the rigid aliphatic amino ligands cis-3,5-diamino-trans-hydroxycyclohexane (DAHC), cis-3,5-diamino-trans-methoxycyclohexane (DAMC), and cis-3,5-diamino-trans-tert-butyldimethylsilylanyloxycyclohexane (DATC) with silver(I) triflate, nitrate, and perchlorate. The compositions of these aggregates, established by X-ray crystallography and elemental analysis, are [{Ag(DAHC)}2](CF3SO3)2 (1), [{Ag(DAMC)}2](CF3SO3)2 (2), [{Ag(DAMC)}2](NO3)2 (3), [{Ag(DATC)}6{Ag(DAHC)}2](NO3)8 (4), and [{Ag(DATC}n](NO3)n (5), where the DAHC present in 4 is formed by in situ hydrolysis of the acid labile silyl ether group. The type of aggregate formed depends both upon the noncoordinating O-substituent of the ligand and the (also noncoordinating) counterion, with the normal preference of the ligand topology for forming Ag2L2 structures being broken by introduction of the bulky, lipophilic O-tert-butyldimethylsilyl (TBDMS) group. Of particular note is the octanuclear silver ring structure 4, which is isolated only when both the O-TBDMS group and the nitrate counteranion are present and is formed from four Ag2L2 dimers connected by Ag...Ag and hydrogen-bonding interactions. Diffusion rate measurement of this {Ag8} complex by 1H NMR (DOSY) indicates dissociation in CD3OD and CD3CN, showing that this supramolecular ring structure is formed upon crystallization, and establishing a qualitative limit to the strength of Ag...Ag interactions in solution. When solutions of the {Ag8} cluster in methanol are kept for several days though, a new UV-vis absorption is observed at around 430 nm, consistent with the formation of silver nanoparticles.

N-Substituted indole-3-thiolate [4Fe–4S] clusters with a unique and tunable combination of spectral and redox properties

A series of N-substituted indole-3-thiols, synthesized by sequential alkylation, thiouronium salt formation, and hydrolysis, are used to generate a novel family of [4Fe–4S] clusters. The redox transitions of the clusters deviate from those of other [4Fe–4S] cluster families, with half-wave potentials lying in a range midway between those of [4Fe–4S] clusters bound by aliphatic thiolate ligands and those bound by thiophenolate-based ligands. In UV–vis spectroscopy, the new cluster family shows absorption maxima that are among the most red-shifted reported thus far in [4Fe–4S] cluster chemistry. The indole-3-thiolate ligand thus leads to a highly specific and uncommon combination of [4Fe–4S] cluster properties, which can be fine-tuned by facile derivatization at the indole nitrogen atom.

On the search of new I 2-IBS aliphatic ligands: Bis-guanidino carbonyl derivatives

Continuing with our search of aliphatic dicationic derivatives as I2-IBS ligands and looking at Amiloride, a known ligand of I2-IBS, we have incorporated the guanidinocarbonyl moiety into our aliphatic compounds with the intention of improving the binding to I2-IBS. Thus, we present the different approaches to the preparation and pharmacological evaluation (in human brain tissue) as I2-IBS ligands of a new series of aliphatic derivatives incorporating the guanidinocarbonyl group and with different chain length ( n = 8–12, and 14 methylene groups).

Diverse Entangled Metal−Organic Framework Materials Incorporating Kinked Organodiimine and Flexible Aliphatic Dicarboxylate Ligands: Synthesis, Structure, Physical Properties, and Reversible Structural Reorganization

Hydrothermal synthesis has afforded a family of divalent metal adipate (adp) coordination polymers incorporating the kinked dipodal organodiimine 4,4'-dipyridylamine (dpa). As revealed by single-crystal X-ray diffraction, the structures of these materials are critically dependent on the metal coordination geometry, the carboxylate binding modes, and the conformations of the flexible adipate moieties. In all cases, hydrogen-bonding interactions imparted by the dpa tethers also play a structure-directing role. All materials were further characterized via infrared spectroscopy and elemental and thermogravimetric analysis. [Co(adp)(dpa)] (1) displays doubly interpenetrated three-dimensional (3-D) networks with a decorated alpha-Po-type (pcu) topology. In contrast, [Ni(adp)(dpa)(H2O)] (2) possesses a triply interpenetrated binodal cooperite-type (pts) framework, the highest level of interpenetration yet reported for this structure type. [Zn(adp)(dpa)].H2O (3) presents mutually inclined polycatenated 2-D graphitic layers consisting of neutral dimeric [Zn2(mu2-adp)2] kernels conjoined by dipodal dpa ligands. Compound 1 exhibited weak antiferromagnetic coupling between its carboxylate-bridged Co atoms, following Curie-Weiss behavior with Theta=-3.3 K. Compound 3 manifested blue light emission under ultraviolet excitation, as well as a reversible structural reorganization upon dehydration/rehydration.

Synthesis and characterization of polymeric resins with aliphatic and aromatic amino ligands and their sorption behavior towards gold from ammonium hydroxide solutions

The functional resins with amino ligands are synthesized by the modification of lightly crosslinked poly(vinylbenzyl chloride–divinylbenzene) matrix with the following amines: 1-methylpiperazine, ethylenediamine, dipropylamine, 1-methylimidazole, 2-mercapto-1-methylimidazole, 1,2-dimethylimidazole and 1-(3-aminopropyl) imidazole. Two methods of the modification reactions were employed, the first one is the traditional heating of the polymer with either neat amine or amine solution in an appropriate solvent, the second method is heating of the reaction mixture in a microwave reactor. The resultant resins show different degrees of modification depending on the applied method and contain 1.61–3.68 mmol of ligand/g. The 1-methylimidazole resin displays the highest affinity towards gold from ammonium buffer (100 g/dm 3 NH 3 · H 2O, 50 g/dm 3 (NH 4) 2SO 4). For this resin, the sorption is as high as 15.5 mg/g and log K d (distribution coefficient) value is 2.94. All resins are highly selective and they do not sorb copper amino complexes. These polymeric materials were characterized using nitrogen, sulfur and chlorine elemental analysis and FTIR spectroscopy.

Adducts of rhodium(II) tetraacetate with some nitrogenous organic ligands: Application of natural abundance 15N and 13C CPMAS NMR spectroscopy

Adducts of rhodium(II) tetraacetate with some nitrogenous organic ligands: 1-azabicyclo[2,2,2]octane 1, 1,2-diazabicyclo[2,2,2]octane 2, pyrazine 3, pyrimidine 4, [1,3,5]triazine 5 and 1,3,5,7-tetraazatricyclo[3,3,1,1 3,7]decane 6 have been investigated by means of natural abundance 13C and 15N CPMAS nuclear magnetic resonance (NMR) spectroscopy. 1-Azabicyclo[2,2,2]octane 1 having one nitrogen atom in the molecule produces either the 1:1 or 1:2-adduct depending on the reagent molar ratio; some features of its 13C CPMAS NMR spectra suggest the dimeric structure of the 1:1-adduct. Multifunctional ligands having more than one nitrogen atom in a molecule yield the adducts insoluble in common organic solvents. Elemental analysis and NMR experiments have revealed that 1,2-diazabicyclo[2,2,2]octane, pyrazine, pyrimidine and [1,3,5]triazine produced adducts in the form of 1:1 polymeric chains. 1,3,5,7-tetraazatricyclo[3,3,1,1 3,7]decane yields the adduct containing ligand and metal salt in the molar ratio of 3:4. The 15N chemical shift change caused by the Rh–N bond formation (Δ δ parameter) varies from ca. −9 ppm for aliphatic ligands to ca. −40 ppm for heteroaromatic species. The NMR findings have been supported by theoretical calculation (density functional calculation (DFT), LanLD2Z//B3LYB level) of molecular geometry, energy and chemical shieldings.

Evaluation of multi-modal high salt binding ion exchange materials

The performance and selectivity of novel cation and anion exchange multi-modal chromatographic materials were evaluated. Desorption profiles of 13 proteins possessing a range of properties (e.g. size, charge and hydrophobicity) were determined on the cation exchange materials. Batch experiments were carried out by loading individual proteins on each resin at low salt, and examining the desorption of the proteins during sequential washes with increasing salt concentrations. While all of the resins exhibited some binding of proteins at elevated salt concentrations, this effect was more pronounced on the resins with aromatic ligands as compared to the materials with aliphatic ligands. As expected, materials with higher ionic capacities exhibited higher binding at elevated salts. In addition, some proteins exhibited high binding at elevated salt concentrations to all of the resins. The combined effect of charge and other secondary interactions with these multi-modal chromatographic materials enables high salt binding of a range of proteins as well as unique selectivities for the recovery of certain classes of proteins. Since the anion exchange materials all exhibited high binding at elevated salt concentrations the work with these materials focused on a study of elution strategies to remove proteins from these aromatic based materials. After evaluating various elution protocols, a combined strategy of pH change and chaotropic salt were shown to minimize electrostatic and hydrophobic interactions and was found to be an effective elution strategy for this class of anion exchange materials using peanut lectin as a model protein.

Synthesis, characterization and in vitro biological activity studies of Cu–M (M = Cu 2+, Co 2+, Ni 2+, Mn 2+, Zn 2+) bimetallic complexes

Six new bimetallic complexes of the type CuCu, CuCo, CuNi, CuZn and CuMn were prepared. The structures of these complexes and the ligand have been proposed on the basis of FAB mass, elemental analysis, UV–vis, IR, EPR and CV studies. All the complexes completely cleave pBS (SK−) DNA at a concentration of 10 μM; however, even at lower concentrations of 2 μM and 0.1 μM, the complexes ( I and Ia) showed partial cleavage. The results of the fluorescence binding studies of the metal complexes with CT-DNA showed that the presence of aliphatic ligands added additional binding effects including electrostatic, hydrogen binding and vander Waals interactions. Complexes ( I, Ia) showed 50% inhibition of COX-1 and COX-2 activities at as low a concentration as 12.5 μM, 13.5 μM, 14 μM and 14.5 μM. Inhibition assay of top I and top II by different complexes in mutant yeast strains (JN394, JN394 t −1 and JN394 t 2–5) with all the complexes showed significant inhibition of topoisomerase at 5 μM concentration. Complexes I and Ia exhibited good anti-microbial activities against all human pathogens tested except Klebsiella pneumoniae. The following studies showed that among the synthesized bimetallic complexes, complexes I and Ia seem to be promising candidates possessing DNA cleavage activities besides anti-microbial and anti-inflammatory properties to serve as chemical nucleases and chemotherapeutic agents.

Catalyst Performance in “Click” Coupling Reactions of Polymers Prepared by ATRP: Ligand and Metal Effects

CuI-catalyzed azide−alkyne cycloadditions were conducted in organic media under various conditions. The effects of several parameters (ligand, solvent, reducing agent, metal) on these reactions were studied using the step-growth click coupling of low-molecular-weight α,ω-diazido-terminated polystyrene prepared by atom transfer radical polymerization (ATRP). These reactions were typically conducted in DMF, monitored by size exclusion chromatography (SEC), and semiquantitatively analyzed by Gaussian multipeak fitting and subsequent peak integration. Both the electronic properties of the ligand and the number of coordinating atoms had significant influence on the rates of the click coupling reactions. Aliphatic amine ligands led to significantly faster rates as compared to pyridine-based ligands. Faster rates were also observed with tridentate vs tetradentate ligands. A further rate enhancement was observed when the reactions were conducted in a noncoordinating solvent (toluene) vs a coordinating solvent (DM...

Effects of organic ligands on granite dissolution in batch experiments at pH 6

Yosemite granite from the Tuolumne River series was dissolved under oxic and anoxic conditions in the presence (0.001 or 0.01 M) and absence of organic ligands in batch experiments at pH 6. Release of all elements was enhanced considerably in the presence of organic ligands. Citrate (tridentate) and gallate (tetradentate) increased element release to the greatest extent among the aliphatic and aromatic ligands, respectively. The extent of element mobilization observed for the aliphatic ligands decreased in the order citrate > oxalate ≈ malonate and for the aromatic ligands gallate > salicylate ≈ phthalate. The effects of the ligands generally followed trends in cation-ligand stability constants, but aromatic ligands were less effective in element mobilization than aliphatic ligands. This was attributed to protonation of the functional groups of aromatic ligands at pH 6. Rock dissolution was non-stoichiometric regardless of the presence or absence of organic ligands. Release of P and Cu (% of total element content in the unweathered rock) in the presence of organic ligands was considerably greater than that of other elements. Findings of the present study were compared to the findings of our previous study on dissolution of basalt. Differences in the mobility patterns of Y, Fe, Cu, Ti, and Zr during dissolution of granite and basalt were observed. In basalt, release of Y was enhanced considerably in the presence of citrate. In contrast, in the present study, release of Y from granite with and without citrate was at the detection limit. This difference was attributed to the difference in Y-hosting parent minerals: apatite (basalt) and sphene (granite). With and without organic ligands, no significant differences were observed in the extent of Fe released from granite under oxic versus anoxic conditions, while the extent of Fe release from basalt was considerably greater under anoxic versus oxic conditions with and without organic ligands. These differences can be attributed to the difference in major Fe-hosting phases in the rocks: biotite (granite) versus glass and augite (basalt). In the granite, concentrations of Cu released increased considerably in the presence of organic ligands under both oxic and anoxic conditions. In contrast, concentrations of Cu released from basalt were increased considerably only under oxic conditions, especially in the presence of organic ligands. This difference was attributed to the different extent of Fe release from basalt and granite that affected dissolution of Cu/Fe-sulfides. Although both Ti and Zr can be mobilized in the presence of organic ligands, in the rock where zircons hosted Zr (granite), this element was the most immobile, while in the rock where Fe/Ti oxides hosted Zr (basalt), Ti was the most immobile.

N,N′‐Dialkyl‐ and N‐Alkyl‐N‐mesityl‐Substituted N‐Heterocyclic Carbenes as Ligands in Grubbs Catalysts

Various symmetrically and asymmetrically substituted N-heterocyclic carbene (NHC) ligands bearing aliphatic nitrogen-containing side groups have been synthesised. In our attempts to isolate the corresponding second-generation Grubbs catalysts, we were unsuccessful when using the symmetrical aliphatic NHC ligands. For the asymmetrical ligands bearing an aliphatic moiety on one side and an aromatic mesityl group on the other side, substitution of a phosphine ligand was achieved. The performance of a so-formed series of Ru-based metathesis initiators has been evaluated for the ring-opening metathesis polymerisation (ROMP) of cycloocta-1,5-diene and the ring-closing metathesis (RCM) of diethyl diallylmalonate.

Platinum Group Antitumor Chemistry: Design and development of New Anticancer Drugs Complementary to Cisplatin

In the next two decades, the world is expected to see around 20 million cases of cancer. Moreover, the types of cancer will vary considerably from country to other. Therefore, all efforts will be needed to face such a vast diversity of problems. With current annual sales of about $500 millions, the platinum(II) complex known as cisplatin [cis-(NH3)2PtCl2] is still one of the most effective drugs to treat testicular, ovarian, bladder and neck cancers. Since it was launched in 1978 there has been a rapid expansion in research to find new, more effective metal-based anticancer drugs and to study their interactions with biological systems. This study gives an up to date overview of the anticancer chemistry of the platinum group elements platinum, palladium, and nickel with an emphasis on the new strategies used in the development of new antitumor agents. Methodologies for application of bulky aromatic or aliphatic nitrogen ligands, chiral organic moieties, chelates containing other donor atoms than nitrogen, and biologically active ligands in the design of agents analogous to cisplatin are presented. The review also aims to highlight the class of the unconventional complexes that violate the empirical structure-activity rules (SAR) of platinum compounds and the common features and structural differences between the most successful anticancer complexes that are currently in human clinical trials.