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PubMed1996

High frequency (139.5 GHz) electron paramagnetic resonance spectroscopy of the GTP form of p21 ras with selective 17O labeling of threonine.

Electron paramagnetic resonance spectroscopy at 139.5 GHz has been used to study p21 ras complexed with Mn(II) and guanosine 5'-(beta, gamma-imidotriphosphate), an analog of GTP. The p21 sample studied was selectively labeled with [17O gamma]threonine to a final enrichment of 30%. A Mn(II)-17O hyperfine interaction was observed, but the value of the coupling constant, 0.11 +/- 0.04 mT, is the smallest such value yet reported. Ab initio calculations indicate that this value is consistent with direct coordination of the threonine hydroxyl group and provide an estimate for the Mn(II)-17O bond length of 2.7 A. The measured hyperfine coupling constant and associated bond length starkly contrast with typical values for Mn(II)-17O coordination complexes, namely, approximately 0.25 mT and approximately 2.2 A, respectively. This contrast underscores the peculiar weakness of this Mn(II)-O interaction in p21 and persuasively argues that the nucleotide-induced conformational change, which is known to encompass the region of p21 involving Thr35, is not driven by Mn(II) coordination of the Thr35 hydroxyl group.

Binding Sites↗

PubMed1993

A heme c-peptide model system for the resonance Raman study of c-type cytochromes: characterization of the solvent-dependence of peptide-histidine-heme interactions.

The visible absorption and Soret-excited resonance Raman spectra of ferrous microperoxidase-8 [MP8(II)], an octapeptide containing a heme c, are reported. These spectroscopies indicate that MP8(II), dissolved in aqueous buffered solutions, forms low-spin six-coordinated complexes in the 7-14 pH range. Intermolecular bonding interactions of MP8(II) in water account for this behavior. On the contrary, when the hemopeptide is dispersed in aqueous solutions containing detergent or an alcohol, the spectroscopic data show that the iron atom of MP8(II) is essentially high-spin five-coordinated in accordance with a monomeric structure of MP8(II). In addition to a high-spin signature to the heme skeletal modes, the high-frequency regions of resonance Raman spectra characterize an electronic influence of the thioether bridges on the frequency of stretching modes of C beta-C beta bonds (nu 2, nu 11, and nu 29). On the other hand, the low-frequency Raman spectra of monomeric MP8(II) at pH 7.5 present significant differences in the 150-250-cm-1 regions depending upon the solvent composition (pH, presence or absence of detergent, alcohol). These effects are attributed to frequency variations of the Fe-N(His)-involving mode which indicate changes in the H-bonding interactions of the axial His and therefore solvent-dependent changes of the octapeptide conformation. Our resonance Raman data further show that the axial His of monomeric MP8(II) could be totally deprotonated in aqueous cetyltrimethylammonium bromide solution at very alkaline pH (pKa = 13.3). The vibrational data (100-1700 cm-1) obtained for the various monomeric forms of MP8(II) are expected to be useful for determining the heme structure and environment in reduced c'-type cytochromes. Comparisons of resonance Raman data with X-ray crystallographic data available for different hemoproteins allow us to evaluate the ionization and H-bonding states of the His bound to the high-spin five-coordinated hemes. These data are discussed in terms of proximal influence of protein-His-heme interactions on the determination and the regulation of a particular biological function.

Amino Acid Sequence↗

PubMed1975

Cobalt(III) labeled aspartokinase-homoserine dehydrogenase of Escherichia coli.

The kinase activity of the threonine-sensitive aspartokinase-homoserine dehydrogenase enzyme complex of Escherichia coli was selectively inactivated by Co(III) incorporation. Incubation of the enzyme with Co(II) in the presence of oxygen or H2O2 resulted in incorporation of one Co(III) per subunit. The cobalt(III) bound to the enzyme was not removable by dialysis and presumably results from formation of "inert" coordination complexes with ligands contributed by the enzyme. Cobalt was released from the enzyme by incubation with dithiothreitol but not by metal chelating agents. The Co(III)-labeled enzyme was aspartokinase inactive but still retained 60% of its original homoserine dehydrogenase activity. Studies of the time course of inactivation showed aspartokinase inactivation paralleled Co(III) incorporation. The residual dehydrogenase activity of aspartokinase inactive enzyme was still inhibited by threonine Thus, Co(III) incorporation seems to result in a specific inactivation of kinase activity which permits enumeration of the number of aspartokinase sites. Limited alpha-chymotrypsin digestion of Co(III)-enzyme produced homoserine dehydrogenase-active fragments devoid of Co(III), further confirming the specificity of the labeling procedure. Aspartokinase inactivation obtained without concomitant desensitization of homoserine dehydrogenase to threonine inhibition suggests that kinase active site integrity is not required for threonine binding and inhibition of homoserine dehydrogenase.

Aspartokinase Homoserine Dehydrogenase↗

PubMed2001

A monomeric three-coordinate magnesium bis(amide).

The metallation reaction between dibutylmagnesium and 2,6-diisopropyl-N-(trimethylsilyl)aniline gives the unusual monomeric three-coordinate complex (diethyl ether-kappa O)bis[2,6-diisopropyl-N-(trimethylsilyl)anilido-kappa N]magnesium(II), [Mg(C(15)H(26)NSi)(2)(C(4)H(10)O)] or [Mg[(Me(3)Si)(2,6-(i)Pr(2)C(6)H(3))N](2)(Et(2)O)]. This low-coordinate species has a distorted trigonal-planar coordination environment, with an additional short Mg-C(ipso) contact of 2.799 (2) A.

Journal Article↗

PubMed2001

Stabilization of active-site loops in NH3-dependent NAD+ synthetase from Bacillus subtilis.

The NH(3)-dependent NAD(+) synthetase (NADS) participates in the biosynthesis of nicotinamide adenine dinucleotide (NAD(+)) by transforming nicotinic acid adenine dinucleotide (NaAD) to NAD(+). The structural behavior of the active site, including stabilization of flexible loops 82-87 and 204-225, has been studied by determination of the crystal structures of complexes of NADS with natural substrates and a substrate analog. Both loops are stabilized independently of NaAD and solely from the ATP-binding site. Analysis of the binding contacts suggests that the minor loop 82-87 is stabilized primarily by a hydrogen bond with the adenine base of ATP. Formation of a coordination complex with Mg(2+) in the ATP-binding site may contribute to the stabilization of the major loop 204-225. The major loop has a role in substrate recognition and stabilization, in addition to the protection of the reaction intermediate described previously. A second and novel Mg(2+) position has been observed closer to the NaAD-binding site in the structure crystallized at pH 7.5, where the enzyme is active. This could therefore be the catalytically active Mg(2+).

Amide Synthases↗

PubMed2002

Nickel(II)-molybdenum(III)-cyanide clusters: synthesis and magnetic behavior of species incorporating [(Me(3)tacn)Mo(CN)(3)].

The substitution of Mo(III) for Cr(III) in metal-cyanide clusters is demonstrated as an effective means of increasing the strength of the magnetic exchange coupling and introducing magnetic anisotropy. Synthesis of the octahedral complex [(Me(3)tacn)Mo(CN)(3)] (Me(3)tacn = N,N',N"-trimethyl-1,4,7-triazacyclononane) is accomplished with the addition of precisely 3 equiv of LiCN to a solution of [(Me(3)tacn)Mo(CF(3)SO(3))(3)] in DMF. An excess of LiCN prompts formation of a seven-coordinate complex, [(Me(3)tacn)Mo(CN)(4)](1)(-), whereas less LiCN produces multinuclear species such as [(Me(3)tacn)(2)Mo(2)(CN)(5)](1+). In close parallel to reactions previously performed with [(Me(3)tacn)Cr(CN)(3)], assembly reactions between [(Me(3)tacn)Mo(CN)(3)] and [Ni(H(2)O)(6)](2+) or [(cyclam)Ni(H(2)O)(2)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) afford face-centered cubic [(Me(3)tacn)(8)Mo(8)Ni(6)(CN)(24)](12+) and linear [(Me(3)tacn)(2)(cyclam)NiMo(2)(CN)(6)](2+) clusters, respectively. Generation of the former involves a thermally induced cyanide linkage isomerization, which rapidly leads to a low-spin form of the cluster containing diamagnetic Ni(II) centers. The cyclic voltammagram of this species in DMF reveals a sequence of six successive reduction waves spaced approximately 130 mV apart, suggesting class II mixed-valence behavior upon reduction. The magnetic properties of the aforementioned linear cluster are consistent with the expected ferromagnetic coupling and an S = 4 ground state, but otherwise vary slightly with the specific conformation adopted (as influenced by the packing of associated counteranions and solvate molecules in the crystal). Magnetization data indicate an axial zero-field splitting parameter with a magnitude falling in the range [D] = 0.44-0.72 cm(-1), and fits to the magnetic susceptibility data yield exchange coupling constants in the range J = 17.0-17.6 cm(-1). These values represent significant increases over those displayed by the analogous Cr(III)-containing cluster. When perchlorate is used as a counteranion, [(Me(3)tacn)(2)(cyclam)NiMo(2)(CN)(6)](2+) crystallizes from water in a dimeric form with pairs of the linear clusters directly linked via hydrogen bonding. In this case, fitting the magnetic susceptibility data requires use of two coupling constants: one intramolecular with J = 14.9 cm(-1) and another intermolecular with J' = -1.9 cm(-1). Reacting [(Me(3)tacn)Mo(CN)(3)] with a large excess of [(cyclam)Ni(H(2)O)(2)](2+) produces a [(Me(3)tacn)(2)(cyclam)(3)(H(2)O)(2)Ni(3)Mo(2)(CN)(6)](6+) cluster possessing a zigzag structure that is a simple extension of the linear cluster geometry. Its magnetic behavior is consistent with weaker ferromagnetic coupling and an S = 6 ground state. Similar reactions employing an equimolar ratio of reactants afford related one-dimensional chains of formula [(Me(3)tacn)(cyclam)NiMo(CN)(3)](2+). Once again, the ensuing structure depends on the associated counteranions, and the magnetic behavior indicates ferromagnetic coupling. It is hoped that substitutions of the type exemplified here will be of utility in the design of new single-molecule magnets.

Journal Article↗

PubMed2006

Trimanganese complexes bearing bidentate nitrogen ligands as a highly efficient catalyst precursor in the epoxidation of alkenes.

A series of trinuclear manganese complexes coordinated with neutral bidentate nitrogen ligands, [Mn3L2(OAc)6], were prepared from manganese acetate and the corresponding ligands. Using peracetic acid as the oxidant, the air- and moisture-stable manganese clusters exhibited excellent catalytic activity and selectivity in the epoxidation of olefins under mild conditions. The highest activity was observed with a trinuclear complex containing a 2-pyridylimino ligand, [Mn3(ppei)2(OAc)6] (ppei = 2-pyridinal-1-phenylethylimine). With this system, the substrate scope was extremely wide to include terminal and electron-deficient double bonds of both aliphatic and aromatic alkenes. The high activity was undiminished under the reaction conditions even directly using a mixture of the pyridylimino ligands and manganese acetates, making this process more convenient. It was also observed that analogous trinuclear complexes, such as [Mn3(bipy)2(OAc)6] and [Mn3(phen)2(OAc)6], displayed excellent activities. While radical intermediacy was inferred from the product distribution, kinetic data revealed that the epoxidation is roughly first-order in manganese cluster precursor and oxidant, respectively, and zero-order in olefin. These results led us to propose that the trinuclear complexes [Mn3L2(OAc)6] serve as catalyst precursors that dissociate into monomeric species with the formulation of [MnL2(OAc)2] under the reaction conditions.

Alkenes↗

PubMed2001

Bis(O,O'-di-p-tolyldithiophosphato-S,S')(1,10-phenanthroline-N,N')nickel(II).

The title coordination complex, [Ni(C14H14O2PS2)2(C12H8N2)] or [Ni(pMePh-dtp)2(phen)] (phen is 1,10-phenanthroline; dtp is diaryldithiophosphate), has a non-crystallographic twofold axis of symmetry through the Ni atom and the phen moiety. Two O,O-di-p-tolyldithiophosphate (dtp) ions act as bidentate ligands. The central metal atom is coordinated by four S atoms from two dtp groups and two N atoms from the phen ligand. The title compound displays distorted octahedral geometry around the central Ni atom.

Antioxidants↗

PubMed2005

A developing view of the origins of urgency: the importance of animal models.

Although caution should be used when applying animal data to human physiology, if care is taken to differentiate between general principles and complications of detail, particular to the species being examined, then experimentation on animal models can reveal basic phenomena in the bladder that offer clues to the origin of urgency. Recent data from the whole isolated bladder of guinea pigs showed unexpected complexities in autonomous activity during the filling phase of the micturition cycle: small, transient increases in intravesical pressure were associated with propagating waves of contractile activity and localized stretches of bladder wall. This complex, coordinated activity suggests that there are mechanisms within the bladder wall devoted specifically to generating phasic activity. Thus, there appear to be two systems controlling detrusor contractions: one associated with overall contractions similar to the micturition contraction and the other generating phasic activity. The mechanisms generating the phasic activity appear to be the point of complex integration of both excitatory and inhibitory inputs. There is evidence that local activity in the bladder wall generates afferent discharge, which probably contributes to bladder sensations. Animal data suggest a novel motor/sensory system incorporating contractile (motor) events, which cause stretches resulting in activation of afferent nerves (sensory). The motor element of this system appears to be controlled in a highly complex fashion such that the amplitude and frequency of the motor activity can be modulated by a variety of inputs. This raises the possibility that the sensitivity of the system informing the central nervous system, and thus awareness of the bladder's state during the micturition cycle, can be manipulated, possibly via novel drugs targeted at areas involved in overactive bladder, including urgency incontinence.

Animals↗

PubMed1999

Synthesis and Characterization of Functionalized N,N'-Diphenylformamidinate Silver(I) Dimers: Solid-State Structures and Solution Properties.

Functionalized N,N'-diphenylformamidines and their deprotonated silver(I) complexes have been synthesized: silver(I) N,N'-di(4-alkyl)phenylformamidinate (alkyl = methyl, ethyl, n-butyl, and n-hexadecyl) 1-4; silver(I) N,N'-di(4-trifluoromethyl)phenylformamidinate 5, silver(I) N,N'-di(3-methoxy)phenylformamidinate 6, silver(I) N,N'-di(3-methylmercapto)phenylformamidinate 7, silver(I) N,N'-di(2-methoxy)phenylformamidinate 8, silver(I) N,N'-di(2-methylmercapto)phenylformamidinate 9. The effects of increasing the coordination number of the silver(I) centers by donor substituents on the phenyl groups have been investigated by solution and solid-state studies. Variable-temperature proton NMR (223-303 K) for 1-4 shows coupling between the proton attached to the amidinate carbon and the (107/109)Ag centers at room temperature which is unaffected by cooling (2). For the four-coordinate complexes, 8 and 9, such coupling is only observed on cooling. Molecular weight measurements recorded in solution by vapor pressure osmometry at 310 K show some aggregation to higher molecular weight species than simple dimers for 1-4 and 6, but 8 and 9 exist as discrete dimeric species. Measurement of thermal stability shows the expected increase in stability with increasing coordination number. Compounds 8 and 9 were structurally characterized by X-ray methods. Both show four-coordinate silver dimers bridged by two amidinate ligands with additional longer interactions with the ether oxygens or thioether sulfurs.

Journal Article↗

PubMed2004

The nature of arsenic-phytochelatin complexes in Holcus lanatus and Pteris cretica.

We have developed a method to extract and separate phytochelatins (PCs)-metal(loid) complexes using parallel metal(loid)-specific (inductively coupled plasma-mass spectrometry) and organic-specific (electrospray ionization-mass spectrometry) detection systems-and use it here to ascertain the nature of arsenic (As)-PC complexes in plant extracts. This study is the first unequivocal report, to our knowledge, of PC complex coordination chemistry in plant extracts for any metal or metalloid ion. The As-tolerant grass Holcus lanatus and the As hyperaccumulator Pteris cretica were used as model plants. In an in vitro experiment using a mixture of reduced glutathione (GS), PC(2), and PC(3), As preferred the formation of the arsenite [As((III))]-PC(3) complex over GS-As((III))-PC(2), As((III))-(GS)(3), As((III))-PC(2), or As((III))-(PC(2))(2) (GS: glutathione bound to arsenic via sulphur of cysteine). In H. lanatus, the As((III))-PC(3) complex was the dominant complex, although reduced glutathione, PC(2), and PC(3) were found in the extract. P. cretica only synthesizes PC(2) and forms dominantly the GS-As((III))-PC(2) complex. This is the first evidence, to our knowledge, for the existence of mixed glutathione-PC-metal(loid) complexes in plant tissues or in vitro. In both plant species, As is dominantly in non-bound inorganic forms, with 13% being present in PC complexes for H. lanatus and 1% in P. cretica.

Arsenic↗

PubMed2002

Aluminum corrolin, a novel chlorophyll analogue.

A corrole-based chlorophyll analogue has been prepared, based on the notation that the major differences between the prosthetic groups of chlorophylls and hemes are the presence of a non-transition metal (Mg vs. Fe) and one reduced double bond in the porphyrin ligand. As corroles act as tri- rather than dianionic ligands, the analogy requires the insertion of aluminum into the macrocycle and the reduction of one of its double bonds, two reactions that have not been previously reported with any corrole. The aluminum complexes of both the corrole and the corrolin (the dihydrocorrole) display fluorescence quantum yield that are much larger than of chlorophyll and of all other previously reported synthetic analogues. The results suggest that the light metal atom ion is responsible for low intersystem crossing probability to the triplet excited state and the structural rigidity of the hexa-coordinated complexes for reducing the probability of internal conversion.

Aluminum↗

PubMed2000

Kinetics and mechanism of iron(III) dissociation from the dihydroxamate siderophores alcaligin and rhodotorulic acid.

The kinetics and mechanism of siderophore ligand dissociation from their fully chelated Fe(III) complexes is described for the highly preorganized cyclic tetradentate alcaligin and random linear tetradentate rhodotorulic acid in aqueous solution at 25 degrees C (Fe2L3 + 6H+ reversible 2 Fe3+ aq + 3 H2L). At siderophore:Fe(III) ratios where Fe(III) is hexacoordinated, kinetic data for the H(+)-driven ligand dissociation from the Fe2L3 species is consistent with a singly ligand bridged structure for both the alcaligin and rhodotorulic acid complexes. Proton-driven ligand dissociation is found to proceed via parallel reaction paths for rhodotorulic acid, in contrast with the single path previously observed for the linear trihydroxamate siderophore ferrioxamine B. Parallel paths are also available for ligand dissociation from Fe2(alcaligin)3, although the efficiency of one path is greatly diminished and dissociation of the bis coordinated complex Fe(alcaligin)(OH2)2+ is extremely slow (k = 10(-5) M-1 s-1) due to the high degree of preorganization in the alcaligin siderophore. Mechanistic interpretations were further confirmed by investigating the kinetics of ligand dissociation from the ternary complexes Fe(alcaligin)(L) in aqueous acid where L = N-methylacetohydroxamic acid and glycine hydroxamic acid. The existence of multiple ligand dissociation paths is discussed in the context of siderophore mediated microbial iron transport.

Hydroxamic Acids↗

PubMed2000

Divalent samarium compounds with heavier chalcogenolate (EPh; E = Se, Te) ligands.

Crystalline coordination complexes of Sm(EPh)2 (E = Se, Te) are described. The selenolate compound Sm(SePh)2 is unstable in solution, but a divalent selenolate can be prepared and isolated when precisely 1 equiv of Zn(SePh)2 is present to form heterometallic [(THF)3Sm(mu 2-SePh)3Zn(mu 2-SePh)]n (1). This compound is a 1D coordination polymer with alternating Sm(II) and Zn(II) ions connected by an alternating (1,3) number of bridging selenolate ligands and three THF ligands bound to each Sm(II) ion. The tellurolate Sm(TePh)2 forms a stable pyridine coordination compound (py)5Sm(TePh)2 (2) that is isostructural with known Eu and Yb benzenetellurolates. Both compounds were characterized by conventional spectroscopic methods. Polymer 1 was characterized by low-temperature single-crystal X-ray diffraction, and the unit cell of the tellurolate was determined. Crystal data (Mo K alpha, 153(5) (K) are as follows. 1: monoclinic space group P21, a = 10.666(2) A, b = 16.270(3) A, c = 12.002(3) A, beta = 114.81(2) degrees, Z = 2.2: orthorhombic space group Pbca, with a = 13.865(3) A, b = 16.453(5) A, c = 31.952(7) A, Z = 8.

Journal Article↗

PubMed2004

Antitumor activity of a new platinum(II) complex with low nephrotoxicity and genotoxicity.

Cisplatin is an important antineoplastic agent, but dose-limiting nephrotoxicity and the occurrence of cellular resistance prevent its potential efficacy. Moreover, cisplatin is known to be carcinogenic and genotoxic in mammalian cells and this feature is of a special interest due to the risk of inducing secondary malignancies. There is a great interest in developing new platinum agents that have broad spectrum of antitumor activity and reduced toxicity. We have recently synthesized a novel platinum(II) coordination complex containing a pyridine nucleus and a dithiocarbamate moiety as ligands, [Pt(ESDT)(Py)Cl], in order to obtain an agent with more favorable therapeutic indices than cisplatin. In this study, the new platinum(II) complex was tested for its cytotoxicity, by MTT assay, on various human cancer cell lines also including different cisplatin-resistant cells endowed with different mechanisms of resistance. On human peripheral blood lymphocytes we evaluated the genotoxic potential of [Pt(ESDT)(Py)Cl] via micronuclei and SCE detection. We also performed in vivo experiments with the purpose of investigating the antitumor and nephrotoxic effects of the new platinum(II) complex. The antitumor activity was studied in ascitic or solid Ehrlich carcinoma bearing mice while nephrotoxicity was monitored in male Wistar rats by means of histopathological findings of renal specimens and of biochemical investigation on urinary parameters (GS and NAG activities and of TUP excretion) of urine samples. The results reported here indicate that [Pt(ESDT)(Py)Cl] showed a remarkable in vitro antitumor activity (with IC50 values about twofold as low as those of cisplatin), moreover, it markedly circumvented the acquired cisplatin resistance in selected human cancer cells. The analysis of the cytogenetic damage in normal cells clearly attested that the new dithiocarbamate complex, tested at equitoxic concentrations, is less genotoxic than cisplatin. Chemotherapy in Ehrlich carcinoma bearing mice with [Pt(ESDT)(Py)Cl] was significantly better tolerated than that with cisplatin. Against the ascitic tumor, [Pt(ESDT)(Py)Cl], showed an activity noticeably higher than that of cisplatin in increasing the life span of treated animals (% T/C = 190 and 129, respectively). In solid-tumor-bearing mice, [Pt(ESDT)(Py)Cl] induced a tumor size reduction very close to that observed with the reference compound. Finally, our findings obtained from the nephrotoxicity studies demonstrated [Pt(ESDT)(Py)Cl] was not nephrotoxic, contrary to cisplatin which caused a notorious acute proximal tubular damage. In summary, [Pt(ESDT)(Py)Cl] may be considered as a new platinum(II) complex with remarkable antitumor activity and low nephrotoxicity and genotoxicity compared with cisplatin.

Animals↗

PubMed2004

Cu(II) in liquid ammonia: an approach by hybrid quantum-mechanical/molecular-mechanical molecular dynamics simulation.

To investigate the solvation structure of the Cu(II) ion in liquid ammonia, ab initio quantum-mechanical/molecular-mechanical (QM/MM) molecular dynamics (MD) simulations were carried out at Hartree Fock (HF) and hybrid density functional theory (B3 LYP) levels. A sixfold-coordinated species was found to be predominant in the HF case whereas five- and sixfold-coordinated complexes were obtained in a ratio 2:1 from the B3 LYP simulation. In contrast to hydrated Cu(II), which exhibits a typical Jahn-Teller distortion, the geometrical arrangement of ligand molecules in the case of ammonia can be described as a [2 + 4] ([2 + 3]) configuration with 4 (3) elongated copper-nitrogen bonds. First shell solvent exchange reactions at picosecond rate took place in both HF and B3 LYP simulations, again in contrast to the more stable sixfold-coordinated hydrate. NH3 ligands apparently lead to strongly accelerated dynamics of the Cu(II) solvate due to the "inverse" [2 + 4] structure with its larger number of elongated copper-ligand bonds. Several dynamical properties, such as mean ligand residence times or ion-ligand stretching frequencies, prove the high lability of the solvated complex.

Journal Article↗

PubMed1993

Influence of ligand density on the properties of metal-chelate affinity supports.

A new procedure has been developed to immobilize iminodiacetic acid (IDA) onto the surface of silica supports, such as LiChrospher Si-1000 and 1.5-microns nonporous silica, for use in high-performance immobilized metal affinity chromatography (HPIMAC) of proteins. This IDA immobilization method has been achieved through the synthesis of a new silylation reagent, 1-(iminodiacetic acid di-tert-butylester)-3-glycidoxy-propyltrimethoxysilane (IDA-silane). Various modified silicas of different ligand densities have been prepared by using mixtures between 1 and 100% of the IDA-silane diluted with the corresponding 3-glycidoxy-propyltrimethoxysilane (GLYMO-silane). Frontal analysis was used with the IDA-Cu(II)-Concanavalin-A and IDA-Cu(II)-lysozyme systems to evaluate the capacity and the association constants for these HPIMAC sorbents. With these metal chelate sorbents the specific binding capacity per unit area increased continuously with the ligand density for the nonporous sorbents but reached a maximum at about 50% of the maximum ligand coverage for the porous sorbents. The association constant for the chelate-protein complex was highest for both concanavalin-A (Con-A) and lysozyme (HEWL) at the highest ligand density and decreased with lower ligand density. These observations have been evaluated in terms of the accessibility of histidine residues on the surface of the two test proteins and their ability to act as binding sites for the copper ions in the coordination complex. The experimental data indicate that both steric and conformational effects result in multiple classes of binding phenomena with Con-A and HEWL at high ligand concentrations. These experimental results provide a useful guideline for the design of silica-based sorbents for application in the HPIMAC of proteins.

Adsorption↗

PubMed2000

Synthesis and structural characterization of Sm(II) and Yb(II) complexes containing sterically demanding, chelating secondary phosphide ligands.

Metathesis between [(Me3Si)2CH)(C6H4-2-OMe)P]K and SmI2(THF)2 in THF yields [([Me3Si]2CH)(C6H4-2-OMe)P)2Sm(DME)(THF)] (1), after recrystallization. A similar reaction between [(Me3Si)2CH)(C6H3-2-OMe-3-Me)P]K and SmI2(THF)2 yields [([Me3Si]2CH)(C6H3-2-OMe-3-Me)P)2Sm(DME)].Et2O (2), while reaction between [(Me3Si)2CH)(C6H4-2-CH2NMe2)P]K and either SmI2(THF)2 or YbI2 yields the five-coordinate complex [([Me3Si]2CH)(C6H4-2-CH2NMe2)P)2Sm(THF)] (3) or the solvent-free complex [([Me3Si]2CH)(C6H4-2-CH2NMe2)P)2Yb] (4), respectively. X-ray crystallography shows that complex 2 adopts a distorted cis octahedral geometry, while complex 1 adopts a distorted pentagonal bipyramidal geometry (1, triclinic, P1, a = 11.0625(9) A, b = 15.924(6) A, c = 17.2104(14) A, alpha = 72.327(2) degrees, beta = 83.934(2) degrees, gamma = 79.556(2) degrees, Z = 2; 2, monoclinic, P2(1), a = 13.176(4) A, b = 13.080(4) A, c = 14.546(4) A, beta = 95.363(6) degrees, Z = 2). Complex 3 crystallizes as monomers with a square pyramidal geometry at Sm and exhibits short contacts between Sm and the ipso-carbon atoms of the ligands (3, monoclinic, C2/c, a = 14.9880(17) A, b = 13.0528(15) A, c = 24.330(3) A, beta = 104.507(2) degrees, Z = 4). Whereas preliminary X-ray crystallographic data for 4 indicate a monomeric structure in the solid state, variable-temperature 1H, 13C(1H), 31P(1H), and 171Yb NMR spectroscopies suggest that 4 undergoes an unusual dynamic process in solution, which is ascribed to a monomer-dimer equilibrium in which exchange of the bridging and terminal phosphide groups may be frozen out at low temperature.

Journal Article↗