Ligand Chain Length Research Articles

Flexiblemeso-Bis(sulfinyl) Ligands as Building Blocks for Copper(II) Coordination Polymers: Cavity Control by Varying the Chain Length of Ligands

Füllungen und Hohlräume: Die drei neuartigen metallorganischen Pseudooktaedergerüste 1–3 wurden aus CuII-Zentren und R,S-Bis(sulfinyl)-Liganden verschiedener Größe aufgebaut. Die Gerüste bestehen aus metallacyclischen Netzwerken ohne Durchdringung und zeigen schwache antiferromagnetische Wechselwirkungen. Die Größe der Hohlräume innerhalb des Netzwerkes lässt sich durch Variation der Kettenlänge des Liganden steuern.

Involvement of CD14 and beta2-integrins in activating cells with soluble and particulate lipopolysaccharides and mannuronic acid polymers.

Lipopolysaccharide (LPS) and related bacterial products can be recognized by host inflammatory cells in a particulate, bacterium-bound form, as well as in various soluble, released forms. In the present study we have compared the mechanisms used by LPS, detoxified LPS (DLPS), and mannuronic acid polymers (M-polymers), in solution or covalently linked to particles, in stimulating monocytes to tumor necrosis factor (TNF) production. The addition of recombinant LPS binding protein (LBP) and/or soluble CD14 (sCD14) enhanced the production of TNF from monocytes stimulated with soluble LPS, DLPS, or M-polymer, but did not affect the response to M-polymer or DLPS attached to particles. Treatment of monocytes with antibody to CD14, CD18, or CD11b showed that CD14, but not CR3 (CD11b/CD18), mediated monocyte TNF production in response to the soluble antigens. In contrast, anti-CD14, anti-CD11b and anti-CD18 monoclonal antibodies all inhibited the response to the particulate stimuli. On the other hand, B975, a synthetic analog of Rhodobacter capsulatus lipid A, completely abrogated the monocyte TNF response induced by LPS but did not affect the TNF induction by DLPS or M-polymer, either in soluble or particulate forms. These data demonstrate that the engagement of immune receptors by bacterial products such as LPS, DLPS, and M-polymer is dependent upon the presentation form of their constituent carbohydrates, and that factors such as aggregation state, acylation, carbohydrate chain length, and solid versus liquid phase of bacterial ligands influence the mechanisms used by cells in mediating proinflammatory responses.

Dependence of cyano bonded phase hydrolytic stability on ligand structure and solution pH

As part of our program to develop more stable cyano (CN) high-performance liquid chromatography (HPLC) column packings, we have evaluated hydrolytic stability as a function of ligand connectivity, chain length, and side group steric protection and the pH of the mobile phase. Three accelerated tests were used to evaluate stability: (1) A non-HPLC screening test measuring carbon loss in refluxing MeOH-100 m M KH 2PO 4 pH 4.5 (1:1, v/v) solution; (2) a continuous flow HPLC test measuring capacity factor maintenance in 1% trifluoroacetic acid in water (pH 1.02) at 80°C; and (3) a continuous flow HPLC test measuring column efficiency maintenance in 50 m M triethylamine in water (pH 10.00) at 50°C. The stability of the CN phases was found to be dependent on both ligand chemical structure and the pH of the test conditions. The starting screen test of intermediate pH was least able to differentiate the CN phases based on structure, because two different degradation mechanisms appear to offset each other (acid induced siloxane bond cleavage vs. base induced silica dissolution). A trifunctional and a sterically protected CN phase were notably stable under the acidic test conditions, but had poor stability under basic conditions. Conversely, chain extension afforded poor stability under acidic conditions, but did afford improved stability at higher pH. In total, the data indicate that good CN column stability can be achieved by using a trifunctional or a sterically protected phase in acidic mobile phases. However, as mobile phases of intermediate or higher pH are employed, shorter column lifetimes can be expected due to an accelerated dissolution of the underlying silica substrate. Materials were also compared chromatographically using a mixture of non-polar, polar, and basic analytes under reversed-phase conditions.

Microcalorimetric studies of interactions between proteins and hydrophobic ligands in hydrophobic interaction chromatography: effects of ligand chain length, density and the amount of bound protein

Using isothermal titration calorimetry (ITC), this investigation directly measured the adsorption enthalpies of proteins on various hydrophobic adsorbents. Various amounts of butyl and octyl groups were attached onto CM-Sepharose to form C 4 and C 8, two types of hydrophobic adsorbents. The adsorption enthalpies of both trypsinogen and α-chymotrypsinogen A were measured at 4.0 M NaCl and pH 10.0, in which most ionic interaction was suppressed. The adsorption isotherms of both proteins on various adsorbents were also measured, thus allowing us to calculate the Gibbs free energy and entropy of adsorption. Experimental results indicated that the adsorption of both proteins on butyl-containing adsorbents was exothermic, while their adsorption on octyl ones was endothermic. In addition, binding of both proteins with the butyl ligand is basically an adsorption process, while binding with the octyl ligand is adsorption and partition processes. Moreover, on both butyl or octyl, the adsorption enthalpy became increasingly positive as the ligand density increased, while the adsorption entropy became more positive as the alkyl chain length or density of the adsorbent increased. In addition, ITC was used to measure protein–protein interaction. The adsorption enthalpy of both proteins increased as the amount of bound protein increased, and the enthalpy increase of trypsinogen appeared to be higher than that of α-chymotrypsinogen A. This observation implies that protein–protein repulsion was stronger among trypsinogen molecules in the experiments.

The complex formation of non-cyclic polyethers and crown ethers with Ag+ in acetone and propylene carbonate studied by potentiometric and calorimetric methods

Potentiometric and calorimetric titrations are performed to study the complexation reactions of non-cyclic polyethers and crown ethers with Ag+ in acetone and propylene carbonate. With increasing chain length of the non-cyclic ligands the complex stability increases due to favourable enthalpic contributions. The macrocyclic polyethers already possess a preformed cavity for the complexation of the Ag+ ion. The cavity size and substituents influence the stability constants of the complexes formed. Only the smallest crown ether examined, 12-crown-4, forms 2:1 complexes in acetone and propylene carbonate solutions. The highest values of the stability constants for the reaction of Ag+ with crown ethers are measured if the dimensions of the silver ion and of the cavities are nearly identical. The results clearly demonstrate the entropic origin of the macrocyclic effect in both solvents.

Lattice effects in the Mössbauer spectra of salts of [Fe 4S 4{S(CH 2) nOH} 4] 2−. Crystal structures of [PPh 4] 2[Fe 4S 4{S(CH 2) nOH} 4] ( n=2, 3 and 4)

The synthesis and spectroscopic (NMR, UV–Vis, Mössbauer) characterisation are reported for a series of mercaptoalcohol ligated cluster salts [Q] 2[Fe 4S 4{S(CH 2) n OH} 4] (Q=NMe 4, n=2, 3, 4, 6; Q=PPh 4, n=2, 3, 4), together with the crystal structures of the three [PPh 4] + salts. The variation of the solid state Mössbauer parameters with ligand alkyl chain length, n, is discussed and related to crystallographic properties. In dimethyl sulfoxide frozen solution, all samples, independent of cation and ligand chain length, n, show the same quadrupole splitting in their Mössbauer spectrum.

Small-angle x-ray-scattering study of silver-nanocrystal disorder-order phase transitions

A conceptually unique approach was developed to study the interparticle interactions between organized alkanethiol-capped silver nanocrystals. Dense nanocrystal fluids were formed by evaporating the solvent from a ``size-polydisperse'' $(\ensuremath{\sigma}\ifmmode\pm\else\textpm\fi{}12%)$ nanocrystal dispersion on a substrate. The sample polydispersity prevented the disorder-order phase transition (i.e., superlattice formation) from occurring. Small-angle x-ray scattering was then used to measure the static structure factors $S(q),$ of these disordered nanocrystal films as a function of the ratio $〈L〉/R$ between the capping ligand chain length to the core nanocrystal radius. The pair-distribution and direct correlation functions were then calculated from Fourier transformations of $S(q).$ This enabled the use of the hypernetted chain approximation to calculate the pair interparticle potential $u(r).$ The 6-12 Lennard-Jones potential provided reasonable fits to all experimentally determined values of $u(r),$ indicating the predominance of relatively short-range repulsion between nanocrystals. Monodisperse dodecanethiol- and octanethiol-capped silver nanocrystals were then condensed into ordered arrays. Face-centered-cubic (fcc) packing was favored for $〈L〉/Rl0.60,$ and body-centered-cubic (bcc) packing was favored when $〈L〉/Rg0.60.$ Lower-symmetry body-centered-tetragonal packing was observed for octanethiol-capped silver nanocrystals with $〈L〉/Rg0.66.$ A simple model employing the experimentally determined values for $u(r),$ predicts that the $\mathrm{fc}\stackrel{\ensuremath{\rightarrow}}{c}\mathrm{bcc}$ superlattice phase transition occurs when $〈L〉/R0.65.$

Crystal structures of nitridotechnetium(V) complexes of amine oximes differing in carbon chain lengths

Structures of nitridotechnetium(V) amine oxime complexes, [TcN(pnao)(H2O)][BPh4] 1, [TcN(bnao)(H2O)][BPh4] 2 and [TcN(pentao)(H2O)][BPh4] 3 [Hpnao = HONCMeCMe2NH(CH2)3NHCMe2CMeNOH; Hbnao = HONCMeCMe2NH(CH2)4NHCMe2CMeNOH; Hpentao = HONCMeCMe2NH(CH2)5NHCMe2CMeNOH], differing in carbon chain length of the amine oxime ligands, were characterized by X-ray crystallography. These complexes are six-co-ordinated and distorted octahedral. Four nitrogen atoms of the amine oxime ligands are in the equatorial plane and both the nitrido and H2O ligands in the apical positions. These complexes have an asymmetrical intramolecular hydrogen bond between the two oxime oxygen atoms. Their intramolecular O· · ·O distances are 2.720 A in 1, 2.512 A in 2 and 2.531 A in 3. The longest O· · ·O distance in 1 is ascribed to a steric effect of the carbon chain length between the amine nitrogens. Namely, the shorter carbon chain of the pnao ligand causes strain on the co-ordinated pnao moiety, and the O· · ·O distance in 1 is longer than that in 2 and 3 with longer carbon chains.

Effects of Ligand Chain Length and Terminal N‐Alkylation on the Protonation Constants and Stability Constants of Some Transition Metal Complexes of Linear Tetraaza and Pentaaza Ligands

AbstractA number of terminal N‐alkylated linear tetraaza and pentaaza ligands were prepared. Their ligand protonation constants and some transition and post‐transition metal (Ni2+, Cu2+, Zn2+, and Cd2+) complex stability constants were determined by potentiometric titration methods. In general, methylation and ethylation at the terminal nitrogen atoms caused the corresponding ligand nitrogen basicity to increase; however, the corresponding metal complex stabilities were decreased compared to the non‐alkylated structural analogs, presumably due to a steric effect.

Synthesis, photophysics, photochemistry, electrochemistry and structural studies of luminescent rhenium(I) surfactant complexes; non-linear optical properties in Langmuir–Blodgett films

A series of structurally related rhenium(i) tricarbonyl diimine surfactant-active complexes, [Re(CO)3(diimine){py(CH2)nCH3 }]+ and [Re(CO)3(diimine){pyCO(Chol)}]+ have been synthesized (n=0, 1, 4, 12, 14, 16, 18; py=pyridyl, Chol=cholesteryl), and their photophysical, photochemical and electrochemical properties studied. A systematic study on the dependence of their photophysical properties in different environments has also been presented. In general, there is no apparent change in the photophysical behavior of these complexes as a function of the chain length of the surfactant type pyridyl ligands, the mechanism of which has been discussed. Langmuir–Blodgett films of the complexes have been prepared, and their π–A isotherms, together with their electronic absorption and emission properties studied. The second harmonic generation (SHG) properties of the LB films have also been investigated. The X-ray crystal structure of a surfactant rhenium(i) complex, [Re(bpy)(CO)3(pyC17H35)]ClO4 has been determined.

Combined Fluorescence and NMR Studies of Reversed HPLC Stationary Phases with Different Ligand Chain Lengths

Alkyl chain bonded “reversed” HPLC phases consisting of 6 to 30 carbon atoms are investigated by fluorescence spectroscopy, steady-state and time-resolved fluorescence anisotropy, and solid-state NMR spectroscopy. The structure and dynamics of the interphase formed by alkyl chains and liquid phase penetrating each other are studied as a function of alkyl chain length. Increasing alkyl chain lengths lead to enhanced partitioning of the fluorescent probe diphenylhexatriene (DPH) into the interphase, as monitored by fluorescence decay curves. The concomitant spectral red shift of DPH fluorescence excitation maxima is evidence of increased interphase polarizability. Time-resolved fluorescence anisotropy measurements reveal that the motion of the probe molecule in the interphase is “wobble in cone”-like. Cone angles θ and rotational correlation times τR change from θ = 63° and τR = 0.75 ns in C6 phases to θ = 42° and τR = 1.50 ns in C30 phases, thus indicating decreasing probe mobility with increasing ligand length. This interpretation is supported by 13C CP/MAS NMR spectra, which show reduced contributions of alkyl chain gauche conformations, i.e., enhanced interphase order, in phases with long alkyl chains and high surface coverage. A concomitant increase in the line-widths of 1H MAS NMR peaks indicates reduced mobility of the longer chains. The spectroscopic observations are consistent with the results of HPLC separations, where enhanced shape selectivity is found with increasing ligand length, rod-shaped molecules like DPH showing the greatest increase in retention time.

Physicochemical Basis of Amino Acid Hydrophobicity Scales: Evaluation of Four New Scales of Amino Acid Hydrophobicity Coefficients Derived from RP-HPLC of Peptides

The physicochemical relationships of four new scales of amino acid hydrophobicity coefficients, derived from the reversed-phase high-performance liquid chromatographic (RP-HPLC) retention data of 1738 peptides, have been compared with 12 previously published scales of amino acid hydrobicities. Four different reversed-phase chromatographic systems were used to obtain the experimental data, including three well-characterized hydrophobic adsorbents of different n-alkyl ligand chain length (n-octadecyl (C18), n-octyl (C8), and n-butyl (C4) ligands) and two different aquo-organic eluents, namely a binary water-acetronitrile and a ternary water-acetonitrile-2-propanol elution system, both containing 0.1% trifluoroacetc acid. Significant correlations were observated from the RP-HPLC data of these peptides separated with the C18- and C8-silica absorbents and the water-acetonitrile elution system and the hydrophobicity scales based on the transter free energies of an amino acid entity from a polar to a nonpolar solvent or the statistical degree of exposure to the surrounding solvent or the statistical degree of exposure to the surrrounding solvent of an amino acid side chain within a protein structure. Conversly, lower levels of correlation were observed between the previously calculated hydrophobicity scales for the common α-amino acids and the amino acid hydrophobicity coefficient values derived from this peptide structure-retention data base with the C4 ligand or the C18 ligand in combination with the water-acetonitrile-2-propanol solvent system. The results confirm that the relative ranking and magnitude of the hydrophobicities of amino acid side chains within polypeptides are dependent upon the chemical microenvironment of the interface established between the solute, the solvent and the immunobilized hydrocarbonaceous ligands. The availability of this extensive data base of peptide structure-chromatographic retention behavior has also permitted differences in peptide- nonpolar ligand interactions to be quantified in physicochemical terms, including the propenity of amino acid side chains in environments from aqueous solutions of different hydrogen-bonding of dipolar characteristics

The Effects of Pore Diameter and Ligand Chain Length on Fast Liquid Chromatography of Proteins and Peptides

Abstract Fast flow separations of proteins and peptides were successfully carried out on microbore columns containing reversed phase supports of three pore diameters. Increasing flowrates from 0.25 to 3 ml/min (1.2 mm/s–14.4 mm/s) did not show any adverse effects on the separations when SynChropak RPP-1000 and RPP-4000, which have 1000A and 4000A pore diameters, were used. At 3 ml/min, the 1000A and 4000A pore diameters yielded narrower peaks for proteins than the 300A support, whereas the latter exhibited better resolution for peptides. Analyses in less than five minutes were achieved. A series of ligand chains (C-4, C-8 and C-18) showed few differences in retention or resolution for either protein or peptide standards. Longterm stability of the 300A and 4000A supports was in excess of 25,000 column volumes when run at 3 ml/min with 0.1% trifluoroacetic acid.

Photochemistry of bis(2,2′-bipyridyl)(methylene-linked diamine)ruthenium(II) complexes, [Ru(bipy) 2(L)] 2+ (L = H 2N-(CH 2) n-NH 2; n = 2 and 3)

The photophysical processes and photochemical reactions of bis(2,2′-bipyridyl)(methylene-linked diamine)-ruthenium(II) complexes, [Ru(bipy) 2L] 2+ (bipy = 2,2′-bipyridyl; L = H 2N-(CH 2) n-NH 2; n = 2, 3) have been examined in order to study the effect of the chain length of the diamine ligands on photosubstitution reactions. The low temperature (77 K) emission properties, luminescent lifetimes and the temperature dependence of the emission intensities were similar for both complexes but much reduced compared with tris(2,2′-bipyridyl)ruthenium(II). Low values of quantum yields for the replacement of the diamine ligand by Cl − anions in CH 3CN and CH 2Cl 2 solutions were found for both n =2 and n =3 complexes although the photosubstitution reactions have low apparent activation energies. Bis(2,2′-bipyridyl)(ethylenediamine)ruthenium(II) showed a lower quantum yield than bis(2,2′-bipyridyl)(1,3-propylenediamine)ruthenium(II) reflecting the fact that the complex with larger chelate ring has a less efficient ring reclosure process. Extended photolysis afforded oxidation of the methylene linked ligand, such that, in pure CH 3CN and H 2O, bis(2,2′-bypyridyl)(ethylenediamine)ruthenium(II) underwent a photooxidation process which transformed the ethylenediamine ligand into a coordinated 1,2-ethylenediimine ligand.

Instant ligands. Part 1. Preparation of some bidentate fluorophosphine ligands derived from straight chain organic substrates, and their reactions to form molybdenum complexes

The compounds (F2P)S(CH2)nS(PF2)(n= 2–6) and (F2P)O(CH2)nO(PF2)(n= 3–6) have been prepared by reactions of S(PF2)2 with the appropriate dithiols and diols, and have been characterised by n.m.r. and i.r. spectroscopy. N.m.r. parameters for oxygen compounds with n= 7–10 and 12 have also been obtained. The compounds react with N-methylpyridinium pentacarbonyliodomolybdate to give compounds with two Mo(CO)5 units linked by the ligands. With tetracarbonyl(norbornadiene)molybdenum two types of products can be formed, depending on ligand chain length. The predominant products for n= 3–6 have two bidentate ligands bridging between two cis-Mo(CO)4 units. For n= 2, 3, or 4 monomeric species with a single chelating ligand on a cis-Mo(CO)4 unit are also generated, and their abundance depends on the concentrations of reactants. The metal complexes have been characterised by n.m.r., i.r., and mass spectroscopy.

Influence of electrolytic dissociation upon rates of reactions. Part 10. Acid-catalysed aquations of some penta-ammine(carboxylato)cobalt(III) ions in aqueous solutions

Rate coefficients of aquation at constant ionic strength in lithium perchlorate–perchloric acid media of a series of penta-ammine(carboxylato)cobalt(III) complexes [Co(NH3)5L]n+ have been calculated from u.v. absorbance measurements. With most of these, increases in the observed rate coefficients are not proportional to increases in the acid concentrations. The data have been used to calculate association constants of protonated forms of the complexes and the corresponding rate coefficients of aquation. The obtained association constants are 0.64 (L = acetate; I= 2.0, 40 °C), 0.1 (L =o-methoxybenzoate; I= 2.0, 40 °C), 116 (L = oxalate; first association constant, I= 0.5, 60 °C), 0.24 (L = malonate; second association constant, I= 2.0, 40 °C), 0.69 (L = succinate; second association constant, I= 2.0, 40 °C), 0.02 dm3 mol–1(L =o-phthalate; second association constant, I= 2.0 mol dm–3, 40 °C). With the tartrato-complex the observed rate coefficients increased linearly with increasing [HClO4] and this is also so with the oxalato-complex for I > 0.5 mol dm–3 but such increases are small when compared with those of the other d ica rboxylato-complexes of the present studies. U.v. spectral decreases at constant wavelength with increasing [HClO4] under virtually static conditions have also been used to estimate the association constants of the protonated complexes. The exceptions, since no spectral decreases were found, are the o-methoxybenzoato-complex, the oxalato-form at [HClO4] > 0.5 mol dm–3, and the doubly protonated tartrato-complex. The values obtained are 0.68 (L = acetate; I= 2.0, 30 °C), 125 (L = oxalate; first association constant, I= 0.5, 60 °C), 0.37 (L = malonate; second association constant, I= 2.0, 40 °C), 0.67 (L = succinate; second association constant, I= 2.0, 40 °C), 0.1 dm3 mol–1(L =o-phthalate; second association constant, I= 2.0 mol dm–3, 40 °C). These are in reasonable agreement with the above values derived from the kinetic data and from the latter the rate coefficients of aquation of the protonated species have been estimated. There appear to be broad relationships between the rate coefficients of the protonated forms and the association constants (comparing acetate with o-methoxybenzoate and succinate with malonate). This can perhaps account for the oxalate, tartrate, and o-phthalate complexes showing little evidence of double protonation. This feature is also discussed in terms of ligand chain lengths and it is also noted that in contrast to the first association constants of the protonated dicarboxylate complexes which are large but have relatively little catalytic effect, the second association constants are small but have strong influences upon the rates of aquation.

Oxindolealanine-62 lysozyme: equilibrium, calorimetric, and kinetic studies of the reaction with N-acetylglucosamine oligosaccharides.

Oxindolealanine-62 lysozyme, formed by reaction with N-bromosuccinimide and purified by using affinity chromatography, was examined in its binding of homologous oligosaccharides of N-acetylglucosamine and in its catalysis of hydrolysis and of transglycosylation of the hexasaccharide of N-acetylglucosamine. Equilibrium binding constants were determined by changes in absorbance or fluorescence associated with ligand binding. Enthalpies of binding were measured calorimetrically. The pattern of variation of delta Go and delta Ho of binding with ligand chain length and pH was different for oxindolealanine-62 lysozyme compared with native lysozyme. These results indicate that the interactions of the ABC region of the active site with substrates are substantially altered by Trp-62 oxidation, more than expected for loss only of the Trp-62 interactions. The partitioning of the glycosyl enzyme intermediate between reaction with a saccharide acceptor (transglycosylation) and reaction with water is unaffected by oxidation of Trp-62. Similarly, the pattern of cleavage of the hexasaccharide, predominantly to tetra- and disaccharide, is unaffected by oxidation of Trp-62. The 2000-fold slower rate of catalytic reaction (relative to free enzyme and substrate) apparently reflects a sterically hindered fit of the substrate into the active site of the modified enzyme and not a special catalytic importance of Trp-62. The geometry of the transition state for oligosaccharide hydrolysis is inferred to be the same for native and oxidized enzymes.

Dithioether complex of palladium(II): the relationship between ligand chain length and structure about palladium

Dithioether ligands PhS(CH 2) mSPh form cis-chelated complexes of palladium(II) when m = 2 or 3, but form ligand-bridged complexes of trans-geometry when m = 1, 4, 5, 6, or 8. Different forms of the complex [PdCl 2(PhS(CH 2) 2SPh)] exist, the infra-red spectra of which differ significantly. Reaction of equimolar amounts of (PhS) 2CH 2 and K 2[PtCl 4] gives a complex of 2:1 stoicheiometry, in contrast to the reactions of dithioether ligands with m ⩾ 2.