Resulting Complexes (resulting + complex)

Distribution by Scientific Domains


Selected Abstracts


Characterization of an unusual folding pattern in a catalytically active guanine quadruplex structure

BIOPOLYMERS, Issue 6 2006
Pinaki R. Majhi
Abstract In the presence of certain metal ions, DNA and RNA can form guanine quadruplex structures, which have been proposed to play a functional role in a variety of biological processes. An 18-nucleotide DNA oligomer, PS2.M, d(GTG3TAG3CG3T2G2), was previously reported to bind hemin and the resulting complex exhibited peroxidase activity. It was proposed that PS2.M folds unimolecularly into an antiparallel quadruplex with unusual, single-base loops and terminal guanines positioned in adjacent quartets. Here we describe structural and stability properties of PS2.M alone in different buffers and metal ions, using gel electrophoresis, circular dichroism (CD), ultraviolet (UV)-visible spectroscopies, and one-dimensional 1H nuclear magnetic resonance (NMR). Native gel behavior of PS2.M in the presence of either Na+ or Pb2+ suggests the formation of unimolecular structures but, in the presence of K+, both unimolecular and multistranded structures are observed. In the presence of Pb2+ ions, PS2.M forms a unimolecular quadruplex containing three guanine quartets. CD titrations reveal that binding of Pb2+ ions to PS2.M is stoichiometric, and a single lead cation suffices to fully fold PS2.M. The PS2.M,Na+ system also forms a similar unimolecular quadruplex. In the presence of K+, the PS2.M,K+ system forms mixed species. With increasing time and PS2.M concentration, the contribution of unimolecular species decreases while that of multimolecular species increases, and this behavior is independent of buffer media. These results suggest that the catalytically active form, studied in the presence of K+, may be a parallel, multistranded quadruplex rather than an antiparallel, unimolecular quadruplex. © 2006 Wiley Periodicals, Inc. Biopolymers 82:558,569, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]


Effective Manipulation of the Electronic Effects and Its Influence on the Emission of 5-Substituted Tris(8-quinolinolate) Aluminum(III) Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2006
Victor A. Montes
Abstract The unique electron-transport and emissive properties of tris(8-quinolinolate) aluminum(III) (Alq3) have resulted in extensive use of this material for small molecular organic light-emitting diode (OLED) fabrication. So far, efforts to prepare stable and easy-to-process red/green/blue (RGB)-emitting Alq3 derivatives have met with only a limited success. In this paper, we describe how the electronic nature of various substituents, projected via an arylethynyl or aryl spacer to the position of the highest HOMO density (C5), may be used for effective emission tuning to obtain blue-, green-, and red-emitting materials. The synthetic strategy consists of four different pathways for the attachment of electron-donating and electron-withdrawing aryl or arylethynyl substituents to the 5-position of the quinolinolate ring. Successful tuning of the emission color covering the whole visible spectrum (,=450,800 nm) was achieved. In addition, the photophysical properties of the luminophores were found to correlate with the Hammett constant of the respective substituents, providing a powerful strategy with which to predict the optical properties of new materials. We also demonstrate that the electronic nature of the substituent affects the emission properties of the resulting complex through effective modification of the HOMO levels of the quinolinolate ligand. [source]


Synthesis, Solution-State and Solid-State Structural Characterization of Monocationic Nitrido Heterocomplexes [M(N)(DTC)(PNP)]+ (M = 99Tc, Re; DTC = Dithiocarbamate; PNP = Heterodiphosphane)

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2004
Cristina Bolzati
Abstract Mono-cationic nitrido heterocomplexes of general formula [M(N)(DTC)(PNP)]+ (where M is 99Tc or Re, DTC is the mono-anionic form of a dithiocarbamate ligand, and PNP is a diphosphane ligand with a tertiary amine-containing five-membered spacer) were prepared by ligand-exchange reactions with the labile precursors [M(N)Cl2(PPh3)2] in dichloromethane/alcohol mixtures. The molecular structure of the representative rhenium complex [Re(N)(dedc)(pnp2)][PF6] (1) displays a distorted, square-pyramidal geometry with the dithiocarbamate sulfur and the diphosphane phosphorus atoms spanning the four coordination positions on the equatorial plane. If the additional interactions between the nitrido nitrogen and the weakly bonded transN -diphosphane heteroatom, the molecular geometry can be viewed as pseudo-octahedral. The structure in solution, as established by multinuclear NMR spectroscopy and ESI spectrometry, is monomeric, and identical to that shown in the solid state. Replacement of the phenyl groups on the phosphorous atoms in complexes 1, 2, 5, and 6 with alkyl groups modified neither the course of the reaction nor the composition of the resulting complexes. These results, together with the observation that no symmetrical complexes containing two identical bidentate ligands were produced in these reactions, strongly supports the conclusion that a mixed coordination sphere, composed by a combination of ,-donor and ,-acceptor atoms around the [M,N]2+ group, constitutes a highly stable system. Compounds containing dangling alkyl-substituted groups in the outer sphere (3, 4, 7, and 8) were fully characterized by multinuclear NMR spectroscopy and ESI mass spectrometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


Self-Assembling Peptide as a Potential Carrier for Hydrophobic Anticancer Drug Ellipticine: Complexation, Release and In Vitro Delivery

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009
Shan Yu Fung
Abstract The self-assembling peptide EAK16-II is capable of stabilizing hydrophobic compounds to form microcrystal suspensions in aqueous solution. Here, the ability of this peptide to stabilize the hydrophobic anticancer agent ellipticine is investigated. The formation of peptide-ellipticine suspensions is monitored with time until equilibrium is reached. The equilibration time is found to be dependent on the peptide concentration. When the peptide concentration is close to its critical aggregation concentration, the equilibration time is minimal at 5,h. With different combinations of EAK16-II and ellipticine concentrations, two molecular states (protonated or cyrstalline) of ellipticine could be stabilized. These different states of ellipticine significantly affect the release kinetics of ellipticine from the peptide-ellipticine complex into the egg phosphatidylcholine vesicles, which are used to mimic cell membranes. The transfer rate of protonated ellipticine from the complex to the vesicles is much faster than that of crystalline ellipticine. This observation may also be related to the size of the resulting complexes as revealed from the scanning electron micrographs. In addition, the complexes with protonated ellipticine are found to have a better anticancer activity against two cancer cell lines, A549 and MCF-7. This work forms the basis for studies of the peptide-ellipticine suspensions in vitro and in vivo leading to future development of self-assembling peptide-based delivery of hydrophobic anticancer drugs. [source]


Mercury Biosensors: Polydiacetylene,Liposome Microarrays for Selective and Sensitive Mercury(II) Detection (Adv. Mater.

ADVANCED MATERIALS, Issue 36 2009
36/2009)
Polydiacetylene (PDA) liposome microarrays have been developed for selective and sensitive mercury detection. The sensors, reported on p. 3674 by Jinsang Kim and co-workers, are designed to produce red fluorescence emission upon binding with Hg2+; when the single-stranded DNA aptamers on the microarray selectively wrap around the mercury ions, the resulting complexes repulse each other. The epoxy-based PDA liposome design is an excellent universal platform that can be readily extended to other sensor designs. [source]


Synthesis and characterization of metal binding pseudotripeptides

JOURNAL OF PEPTIDE SCIENCE, Issue 8 2003
Sebastian Kuenzel
Abstract Metal complexes with peptide or pseudopeptide type ligands can serve as good model compounds for a deeper understanding of enzymatic catalysis, but ligands with a high selectivity for different transition metal cations are hard to find due to the rather flexible nature of peptides. Since such ligands would be the sine qua non condition for the synthesis of heterodinuclear peptide metal complexes with catalytic activity, the search for small, affine and selective metal chelating sequences is of interest. Using four different amino acids (His, Lys, Asp, Glu) a set of 16 pseudotripeptides of the common structure Bz-AS1 -Sar-AS2 -NH2 has been synthesized, purified and characterized by mass spectrometry and 1H-NMR. Their ability to form metal complexes has been investigated leading to short motifs capable of selectively binding only one or two transition metal cations with high affinity. As expected, the complexation of transition metal cations by pseudotripeptides is strongly dependent not only on the amino acid composition, but also on the sequence with regard to the stability of the resulting complexes, as well as the selectivity of the ligands towards Cu2+, Co2+, Ni2+, Zn2+ and Mn2+. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source]


Effect of metal cations on the conformation and inactivation of recombinant human factor VIII

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2004
Tiffany S. Derrick
Abstract Heavy metals have been implicated in the aggregation of proteins and the pathophysiology of several neurodegenerative diseases. Herein, we describe the interaction of recombinant human factor VIII (rhFVIII) with Al+3, Tb+3, Co+2, and Fe+3 using a combination of intrinsic fluorescence, circular dichroism, and high-resolution fourth-derivative absorbance analysis. rhFVIII in solution was titrated with the metal cations and the properties of the resulting complexes were examined. rhFVIII has a tendency to aggregate and inactivate slowly over time under physiological conditions, but this aggregation process is greatly accelerated in the presence of metals with Al+3 being the most efficient. This leads to a complete loss of activity of the protein. Al+3 -induced conformational changes in the protein were small but detectable with limited changes seen in secondary and tertiary structure. Because rhFVIII is a multidomain protein with subunits linked through divalent metal cations, the small intramolecular changes seen may be attributed to rearrangements of the subunits to an aggregation-competent conformer that is very similar to that of the native form. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2549,2557, 2004 [source]


Recognition of protonated aliphatic ,,,-diamines by coproporphyrin I tetraanion in water

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2002
Alejandro Flores-Villalobos
Abstract Interactions of aliphatic ,,,-diamines [H2N(CH2)nNH2, 2,,,n,,,8] with coproporphyrin I tetraanion (CP) were studied by spectrophotometry, fluorimetry and 1H NMR spectroscopy in the pH range 7,10 and ionic strengths 0.01,0.1,M. Diprotonated diammonium cations induce dimerization of CP by forming 1:1 complexes with CP which undergo much stronger self-aggregation than free CP tetraanions. On increasing the number of methylene units n connecting the ammonium groups, the binding constants for the complex formation with monomeric CP (KL) increase but the dimerization constants of the resulting complexes decrease. A hydrophobic contribution to the binding free energy of ,1.6,±,0.2,kJ,mol,1 per methylene unit was obtained from the linear correlation of logKL values extrapolated to zero ionic strength vs the number of methylene units (n,=,2,6). A model for diammonium-induced porphyrin dimerization is proposed, which involves complexation of diammonium cations with CP monomer via a combination of electrostatic and hydrophobic interactions and subsequent formation of porphyrin face-to-face dimers in which diammonium cations serve as the stabilizing bridges via ion pairing to carboxylate groups of two CP monomeric units. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Behavioural dynamics in the biological control of pests: role of silicon complexes

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2008
Savita Belwal
Abstract The complexes of silicon (IV) with Schiff base ligands (L1H and L2H of isatin derivatives) having a sulfur and oxygen donor system were prepared by the reactions in methanol environment. These were isolated and characterized by elemental analysis, molecular weight determinations and conductance measurements. On the basis of electronic, infrared, 1H, 13C and 29Si NMR spectral studies, trigonal bipyramidal geometry was suggested for the resulting complexes. These data support preferential binding of sulfur and oxygen atom to the silicon atom. The disease resistance activities of the ligands and their corresponding complexes were examined successfully in in vitro and in vivo experiments, against pathogenic fungi and bacteria. Results were quite encouraging and these were compared with the standard pesticides Bavistin and Streptomycin. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Intramolecular phenylborane complexes with monobasic bidentate Schiff bases

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2007
Shweta Gaur
Abstract A series of intramolecular complexes with Schiff base ligands having N,S and N,O donor systems were synthesized in an open vessel under microwave irradiation (MWI) using a domestic microwave oven. The reaction time has been brought down from hours to seconds with improved yield as compared with the conventional heating. The complexes have been characterized on the basis of elemental analysis, conductance measurements and spectroscopic analysis. Based on the IR, 1H NMR, 11B NMR and 13C NMR spectroscopic studies, a tetrahedral geometry has been proposed for the resulting complexes. The compounds have been screened in vitro against bacteria and fungi to test their antimicrobial property and in vivo in male albino rats to test their antifertility property. The testicular sperm density, motility and density of cauda epididymal spermatozoa along with biochemical parameters of reproductive organs have been examined and discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Complexation of the Vulcanization Accelerator Tetramethylthiuram Disulfide and Related Molecules with Zinc Compounds Including Zinc Oxide Clusters (Zn4O4)

CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2008
Ralf Steudel Prof.
Abstract Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn2+, ZnMe2, Zn(OMe)2, Zn(OOCMe)2, and the heterocubane cluster Zn4O4 with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me2NCS2., Me2NCS3., Me2NCS2,, and Me2NCS3, have been studied by quantum chemical methods at the MP2/6-31+G(2df,p)//B3LYP/6-31+G* level of theory. More than 35 zinc complexes have been structurally characterized and the energies of formation from their components calculated for the first time. The binding energy of TMTD as a bidendate ligand increases in the order ZnMe2resulting complexes contain ZnS as well as SO bonds. The Zn4O4 nanocluster serves here as a model for bulk zinc oxide used as an activator in rubber vulcanization by sulfur. The further uptake of sulfur atoms by the various complexes from S8 or TMTD with formation of species derived from the radical Me2NCS3. or the trithiocarbamate anion Me2NCS3, is endothermic for mono- and dinuclear zinc dithiocarbamate (dtc) complexes such as [Zn(dtc)2] and [Zn2(dtc)4], but exothermic in the case of polynuclear zinc oxide species containing bridging ligands as in [Zn4O4(,-S2CNMe2)] and [Zn4O4(,-dtc)]. Therefore, zinc oxide as a polynuclear species is predicted to promote the formation of trisulfido complexes, which are generally assumed to serve as catalysts for the transfer of sulfur atoms during rubber vulcanization. This prediction is in accord with the empirical knowledge that ZnO is a better activator in TMTD-accelerated rubber vulcanization than zinc dithiocarbamate. [source]


Modular Solid-Phase Synthetic Approach To Optimize Structural and Electronic Properties of Oligoboronic Acid Receptors and Sensors for the Aqueous Recognition of Oligosaccharides

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2004
Duane Stones Dr.
Abstract This article describes the design and optimization of the first entirely modular, parallel solid-phase synthetic approach for the generation of well-defined polyamine oligoboronic acid receptors and fluorescence sensors for complex oligosaccharides. The synthetic approach allows an effective building of the receptor polyamine backbone, followed by the controlled diversification of the amine benzylic side chains. This approach enabled the testing, in a modular fashion, of the effect of different arylboronic acid units substituted with unencumbering para electron-withdrawing or electron-donating groups. The feasibility of this approach toward automated synthesis was also investigated with the assembly of a sublibrary of receptors by means of the Irori MiniKan technology. Several sublibraries of anthracene-capped sensors containing two or three arylboronic acids were synthesized, and their binding to a series of model disaccharides was examined in neutral aqueous media. The calculation of association constants by fluorescence titrations confirmed that subtle changes in the structures of the interamine spacers in the polyamine backbone can have a significant effect on the stability of the resulting complexes. Most importantly, this study led to the determination of the preferred electronic characteristics for the arylboronate units, and suggests that a new generation of receptors containing very electron-poor arylboronic acids could lead to a significant improvement of binding affinities. [source]