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Acid Complexes (acid + complex)
Selected AbstractsUse of Highly Reactive, Versatile and Air-Stable Palladium,Phosphinous Acid Complex [(t-Bu)2P(OH)]2PdCl2 (POPd) as a Catalyst for the Optimized Suzuki,Miyaura Cross-Coupling of Less Reactive Heteroaryl Chlorides and Arylboronic Acids.CHEMINFORM, Issue 41 2004Subhash P. Khanapure Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Catalytic Asymmetric Oxidation of Sulfide with Titanium,Mandelic Acid Complex: Practical Synthesis of (S)-3-[1-(2-Methylphenyl)imidazol-2-ylsulfinyl]propan-1-ol, the Key Intermediate of OPC-29030.CHEMINFORM, Issue 31 2001Masato Matsugi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] An Unprecedented 2D 4f-3d-5d Multimetal-Isonicotinic Acid Complex: Synthesis, Structural Characterization and Magnetic PropertiesCHINESE JOURNAL OF CHEMISTRY, Issue 9 2008Wen-Tong CHEN Abstract A novel heterometallic metal-isonicotinic acid inorganic-organic hybrid complex [Zn0.5(H2O)]{(Hg2Cl5)- [Er(C6NO2H4)3(H2O)2]}(HgCl2)·0.5CH3OH·0.5H2O (1) has been successfully synthesized via a hydrothermal reaction and structurally characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in the space group C2/c of the monoclinic system with eight formula units in a cell: a=34.165(4) Ĺ, b=9.4692(8) Ĺ, c=24.575(3) Ĺ, , =115.090(5)°, V=7200(1) Ĺ3, C18.50H21Cl7ErHg3N3O10Zn0.50, Mr=1495.25, Dc=2.759 g/cm3, T=293(2) K, µ(Mo K,) =15.954 mm,1, F(000) =5400 and R1/wR2=0.0561/0.0909 for 3157 observed reflections [I>2,(I)] and 6468 unique reflections. Complex 1 is characteristic of a novel 2D {(Hg2Cl5)[Er(C6NO2H4)3(H2O)2]} layered structure constructed from the [Er(C6NO2H4)3(H2O)2] chains interconnected by the Hg2Cl5, linkers. The 2D {(Hg2Cl5)[Er(C6NO2H4)3(H2O)2]} layers, mercury chloride and the lattice water molecules are held together via hydrogen bonds to form a three-dimensional framework with the methanol molecules and the hydrated zinc ions located in the cavities. The magnetic properties show that complex 1 exhibits antiferromagnetic-like interactions. [source] Electrophilic Reaction of N-Lewis Acid and N-Oxide Lewis Acid Complexes of 4-Methylpyridines and Their N-Oxides Through Base-Induced Deprotonation.CHEMINFORM, Issue 19 2005Yoshinobu Tagawa No abstract is available for this article. [source] NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine,Acid ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Hans-Heinrich Limbach Prof. Abstract In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine,acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine,acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. [source] Catalytic Asymmetric Ring-Opening Reaction of meso -Epoxides with Aryl Selenols and Thiols Catalyzed by a Heterobimetallic Gallium-Titanium-Salen ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Jiangtao Sun Abstract A chiral heterobimetallic Lewis acid complex has been developed as an efficient catalyst. The enantioselective desymmetrization of meso -epoxides with aryl selenols and thiols catalyzed by the heterobimetallic complex has been optimized. The optically active , -arylseleno alcohols and ,- hydroxy sulfides were obtained in good yields and high enantioselectivities (up to 97% ee and 92% ee, respectively). A strong synergistic effect between different Lewis acids was exhibited in the catalytic process. [source] Supplementation of diets for lactating sows with zinc amino acid complex and gastric nutriment-intubation of suckling pigs with zinc methionine on mineral status, intestinal morphology and bacterial translocation in lipopolysaccharide-challenged weaned pigsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 2 2010B. U. Metzler-Zebeli Summary Sixty-four pigs from 16 sows were used to evaluate addition of zinc amino acid complex (ZnAA) to lactating sows and gastric nutriment-intubation of zinc methionine (ZnMet) to suckling pigs on mineral status, intestinal morphology and bacterial translocation after weaning. Sows were fed a barley-based diet supplying 120 ppm zinc (Zn; control) or the control diet supplemented with 240 ppm Zn from ZnAA. At birth, day-10 and day-21 (weaning) of age, pigs from each litter were nutriment-intubated with 5 ml of an electrolyte solution without or with 40 mg Zn from ZnMet. At weaning, 24 h prior to the collection of small and large intestinal lymph nodes and sections of the duodenum, jejunum and ileum, the pigs received an intramuscular injection of saline without or with 150 ,g/kg body weight of Escherichia coli O26:B6 lipopolysaccharide (LPS). With the exception of a tendency (p = 0.09) for lower serum concentration of copper in pigs at weaning from ZnAA-supplemented sows, there were no differences (p > 0.1) than for pigs from control-fed sows for mineral status or intestinal morphology. Nutriment-intubation of ZnMet increased serum (p = 0.001) and liver (p = 0.003) Zn concentrations, number of goblet cells per 250 ,m length of jejunal villous epithelium (p = 0.001) and tended (p = 0.06) to enhance jejunum mucosa thickness. Interactive effects (p < 0.05) for higher jejunal villi height and villi:crypt ratio and increased ileal goblet cell counts were apparent for pigs from ZnAA-supplemented sows that also received nutriment-intubation of ZnMet. Challenge with LPS increased (p = 0.05) ileal villous width. Nutriment-intubation of ZnMet decreased (p = 0.05) anaerobic bacteria colony forming unit counts in the large intestinal mesenteric lymph nodes. In conclusion, nutriment-intubation of ZnMet increased serum and liver tissue concentrations of Zn and resulted in limited improvement to intestinal morphology of weaned pigs. [source] Factors affecting the sensitivity to acid inhibition in novel acrylates characterized by secondary functionalitiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2007Harini Kilambi Abstract Here we demonstrate that acrylates exhibit significant rate reductions in the presence of small concentrations of protic acids (0.1,0.5 wt %) compared with the bulk monomer concentration. Dramatically different sensitivities to acid inhibition, differing by up to 2 orders of magnitude, are exhibited for various acrylates. This study examines the various factors that cause enhanced sensitivity toward acid inhibition in novel acrylates characterized by carbamate and cyclic carbonate secondary functionalities. Acid inhibition studies conducted in the presence of a highly polar solvent, such as propylene carbonate, have been performed to determine the impact of overall medium polarity and the extent of acid dissociation on the sensitivity to acid inhibition. The studies depict only a twofold increase in the parameters associated with acid inhibition, upon the addition of 70 wt % propylene carbonate, in comparison with an increase of 2 orders of magnitude for the novel acrylates. These studies indicate that the susceptibility to acid inhibition is primarily determined by the stability of the hypothesized radical,acid complex as well as its propensity to terminate with other species in the system and not by the extent of acid dissociation in the system. Furthermore, it is implied that the stability of the radical,acid complex and its propensity to terminate with other species in the system are dominated by intramolecular interactions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1287,1295, 2007 [source] Preparation and Fluorescent and Magnetic Properties of Polyurethane/Eu(MA)3 FilmsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2007Shuxue Zhou Abstract Europium(III) (Eu3+)-doped polyurethane films were prepared by mixing Eu-methacrylic acid complex (Eu(MA)3) with aliphatic polyurethane oligomer and subsequently curing under UV irradiation. Transmission electron microscopy photos and the appearance of the resulting hybrid films showed that phase separation occurred only at an Eu(MA)3 content above 20 wt.-%. Fluorescence spectra indicated that the fluorescence of Eu3+ was barely influenced by the polyurethane matrix and its intensity increased with an Eu(MA)3 content in the range of approximately 0 to 10 wt.-%. An obvious applied external-field-dependent magnetization (M) of polyurethane/Eu(MA)3 films, namely, an increasing M at low field and a decreasing M at high field, was observed at room temperature from the hysteresis loops, which was influenced by both the Eu(MA)3 content and the ultrasonication imposed on the coatings before curing. It seems that ultrasonication leads to a thermodynamically-unstable structure of Eu3+ in hybrid films, which can be fixed by UV curing but gradually rearranges to its original form during the thermal-curing process, and enhances the diamagnetic part of the hybrid film. Thus, the magnetic property of Eu3+ -doped polyurethane film at room temperature can be adjusted by simply changing the preparation method and the Eu(MA)3 content instead of the type of Eu3+ -organic complex. [source] Toward mechanistic elucidation of iron acquisition in barley: efficient synthesis of mugineic acids and their transport activitiesTHE CHEMICAL RECORD, Issue 2 2010Kosuke Namba Iron acquisition of graminaceous plants is characterized by the synthesis and secretion of iron-chelating compounds, mugineic acids (MAs), and by a specific uptake system for MAs-iron(III) complexes. We identified a transporter, HvYS1 (Hordeum vulgare L. yellow stripe 1), that is highly specific for MAs-iron(III) in barley roots. In this article we outline the characterization of HvYS1, and our recent work on the practical syntheses of MAs and investigations into the molecular basis of the specific transport of their iron(III) complexes by HvYS1. 2,-Deoxymugineic acid (DMA) was synthesized in a good overall yield from commercially available Boc-l-allylglycine using a minimal number of short simple operations with minimal protecting groups and work-up/purification procedures. The same strategy was also successfully applied to , -hydroxy-l-allylglycine, which was obtained by an allylic oxidation of l-allylglycine derivatives, to give MA and 2,-epi-MA efficiently. HvYS1 transported the iron(III) complexes of all three synthetic specimens with efficiency similar to that of a natural mugineic acid complex. With sufficient quantities of MAs in hand, we analyzed the function of HvYS1 and revealed by preparing chimeric transporters that the sixth outer membrane loop of the transporter plays a vital role in substrate specificity. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 10: 140,150; 2010: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.200900028 [source] An X-ray diffraction study of partially ordered electron density in clathrates of Dianin's compound that include simple carboxylic acidsACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2003Ronald W. H. Small The nature of the inclusions in ten clathrate complexes of Dianin's compound have been investigated by the use of electron-density difference maps. The guest species are the first eight straight-chain carboxylic acids, formic to octanoic, a branched-chain acid (dimethylacetic acid) and trifluoroacetic acid. The point-group symmetry of the clathrate cavity, , is satisfied by partial occupation of symmetry-related sites by two included molecules in the case of formic, acetic and trifluoroacetic acids and by a single molecule in the remainder. Hydrogen-bonding requirements in the case of formic and acetic acids are satisfied by dimer formation; in the trifluoroacetic acid complex the two acid molecules form hydrogen bonds to framework O atoms at either end of the cavity. The adoption of gauche conformations in heptanoic and octanoic acid chains shortens them sufficiently that they fit the cavity with only slight distortion. [source] Efficient Heterogeneous Asymmetric Catalysis of the Mukaiyama Aldol Reaction by Silica- and Ionic Liquid-Supported Lewis Acid Copper(II) Complexes of Bis(oxazolines)ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2 2008S. Doherty Abstract Lewis acid complexes based on copper(II) and an imidazolium-tagged bis(oxazoline) have been used to catalyse the asymmetric Mukaiyama aldol reaction between methyl pyruvate and 1-methoxy-1-trimethylsilyloxypropene under homogeneous and heterogeneous conditions. Although the ees obtained in ionic liquid were similar to those found in dichloromethane, there was a significant rate enhancement in the ionic liquid with reactions typically reaching completion within 2,min compared with only 55,% conversion after 60,min in dichloromethane. However, this rate enhancement was offset by lower chemoselectivity in ionic liquids due to the formation of 3-hydroxy-1,3-diphenylbutan-1-one as a by-product. Supporting the catalyst on silica or an imidazolium-modified silica using the ionic liquid or in an ionic liquid-diethyl ether system completely suppressed the formation of this by-product without reducing the enantioselectivity. Although the heterogeneous systems were characterised by a drop in catalytic activity the system could be recycled up to five times without any loss in conversion or ee. [source] Comparison of iron chelates and complexes supplied as foliar sprays and in nutrient solution to correct iron chlorosis of soybeanJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2010Patricia Rodríguez-Lucena Abstract The application of synthetic chelates is the most efficient remedy for correcting iron (Fe) chlorosis. However, chelates are usually expensive and nondegradable products. Recently, new degradable chelates have been proposed for their use as Fe fertilizers. Also, Fe complexes cheaper than synthetic chelates and derived from natural products are also used to correct Fe deficiencies. Fifteen products, including five different synthetic chelates (Fe-EDDS, Fe-IDHA, and three Fe-EDTA formulations) and ten natural complexes (humates, lignosulfonates, amino acids, glycoproteins, polyamines, citrate, and gluconate), have been compared when applied at low concentration to soybean (Glycine max L.) chlorotic plants grown in hydroponics under controlled conditions. In the first experiment, Fe compounds were applied to the nutrient solution, while in the second trial, Fe was foliar-supplied. Dry matter, Fe concentration in shoots and roots, and SPAD values were used to evaluate the effectiveness of the Fe in the different products. In the nutrient-solution experiment, synthetic chelates provided better plant growth, Fe concentration, and SPAD values than complexes. Among the Fe complexes, transferrin generally provided good plant responses, similar to those obtained with synthetic chelates. After foliar application, the highest regreening was observed for plants treated with synthetic chelates and amino acid complexes, but the translocation to roots only occurred for Fe lignosulfonate. Fe-EDDS and Fe-EDTA performed in a similar way when applied in nutrient solution or as foliar sprays. [source] Optical properties of polyimines: UV,vis and photoluminescence study of undoped and doped polymers in aprotic and protic solventsPOLYMER ENGINEERING & SCIENCE, Issue 8 2007Agnieszka Iwan The optical properties of polyimines (PAs) with structure containing aliphatic,aromatic and aromatic,aromatic moieties are reported. It is demonstrated that the photoluminescence (PL) spectra can be regulated over a wide range by variation in main chain structure and through protonation or intramolecular hydrogen bonding. By combining these two methods it is possible to precisely tune the emission spectra of PAs in the spectral range of 480,531 nm. Luminescent PA/1,3,5-benzenetricarboxamide sulfonic acid complexes were self-organizated from nonamphiphilic ,-conjugated PAs, in DMA and in m -cresol solution. Solvatochromism is manifested in the PL spectra of the undoped and doped PAs. The emission spectra of doped PAs are blue or red shifted relative to the undoped one. Additionally, absorption (UV,vis) properties of the PAs before and after protonation with 1,3,5-benzenetricarboxamide sulfonic acid ("dopant I") were tested. We propose that the novel self-assembly is driven by the amphiphilicity of 1,3,5-benzenetricarboxamide sulfonic acid activated by protonation of PAs. POLYM. ENG. SCI., 47:1179,1186, 2007. © 2007 Society of Plastics Engineers [source] X-ray studies on crystalline complexes involving amino acids and peptides.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2001XXXVIII. The complexes of glutaric acid with l -arginine and l -histidine (two crystal forms) exhibit different stoichiometries and ionization states. The aggregation patterns in two of the crystals are remarkably similar to those observed earlier in similar structures, while the pattern in the remaining one has not been seen earlier. The variability in the ionization state and stoichiometry observed in amino acid,dicarboxylic acid complexes appears to represent subtle differences in the response of a molecule to the presence in its neighbourhood of another type of molecule. The glutaric acid molecules (or glutarate or semiglutarate ions) in their complexes and in other crystals favour a fully extended conformation, albeit with frequent departures from it. The change in the chirality of the component molecules in the complex could lead to drastic changes in the aggregation pattern; alternatively, the effects of the change are accommodated through small adjustments in essentially the same pattern. [source] Synthesis and structural investigations on R2 Sn(IV)- D -aldonic acid complexes (R = methyl; butyl).APPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2008Liza saliens (Osteichthyes, Mugilidae): a histological study, Their effect on a new toxicity test organism Abstract Eight R2Sn(IV)- D - aldonate complexes [(R = Me, Bu; D - aldonate = D - galactonate2, (Galn), D - Gluconate2, (Glun), D - Gulonate2, (Guln), D - Ribonate2, (Ribn)], five of which are new derivatives, have been synthesized and structurally characterized both in solid and solution state by IR, 119Sn Mössbauer and 1H, 13C, 119Sn NMR spectroscopies, showing that ligands act as dianonic chelating agents. In solution phase, NMR data suggest that the bidentate chelation is attained by the O1 carboxylate and the vicinal O2 alkoxide atoms, which can be dynamically extended to a third binding site (O4) competing with O2. In Me2Sn(IV)- D - gluconate complex the occurrence of a self-association process leading to a dimeric species was also observed. Histopathological studies on different organs of Liza saliens showed that the dibutyltin(IV)- D - aldonate complexes, although preserving the defense immunity system, exhibit a specific toxicity on some target cells and organs. The toxicity of such complexes has been compared with respect to the effects of a previous study with tributyltin(IV) chloride solutions. Copyright © 2008 John Wiley & Sons, Ltd. [source] A crystallization screen based on alternative polymeric precipitantsACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Clemens Grimm Most commercially available crystallization screens are sparse-matrix screens with a predominance of inorganic salts and polyethylene glycols (PEGs) as precipitants. It was noted that commercially available screens are largely unsatisfactory for the purpose of the crystallization of multimeric protein and protein,nucleic acid complexes. This was reasoned to be a consequence of the redundancy in screening crystallization parameter space by the predominance of PEG as a precipitant in standard screens and it was suggested that this limitation could be overcome by introducing a variety of other organic polymers. Here, a set of 288 crystallization conditions was devised based on alternative polymeric precipitants and tested against a set of 20 different proteins/complexes; finally, a screen comprising the 96 most promising conditions designed to complement PEG- and salt-based commercial screens was proposed. [source] Near-atomic resolution structures of urate oxidase complexed with its substrate and analogues: the protonation state of the ligandACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Laure Gabison Urate oxidase (uricase; EC 1.7.3.3; UOX) from Aspergillus flavus catalyzes the oxidation of uric acid in the presence of molecular oxygen to 5-hydroxyisourate in the degradation cascade of purines; intriguingly, catalysis proceeds using neither a metal ion (Fe, Cu etc.) nor a redox cofactor. UOX is a tetrameric enzyme with four active sites located at the interface of two subunits; its structure was refined at atomic resolution (1,Ĺ) using new crystal data in the presence of xanthine and at near-atomic resolution (1.3,1.7,Ĺ) in complexes with the natural substrate (urate) and two inhibitors: 8-nitroxanthine and 8-thiouric acid. Three new features of the structural and mechanistic behaviour of the enzyme were addressed. Firstly, the high resolution of the UOX,xanthine structure allowed the solution of an old structural problem at a contact zone within the tetramer; secondly, the protonation state of the substrate was determined from both a halochromic inhibitor complex (UOX,8-nitroxanthine) and from the H-atom distribution in the active site, using the structures of the UOX,xanthine and the UOX,uric acid complexes; and thirdly, it was possible to extend the general base system, characterized by the conserved catalytic triad Thr,Lys,His, to a large water network that is able to buffer and shuttle protons back and forth between the substrate and the peroxo hole along the reaction pathway. [source] P2X7 receptors in rat parotid acinar cells: formation of large poresAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 4 2001Simon J. Gibbons 1 Permeabilization of cells mediated by P2X7 receptors occurs to varied degrees in native and heterologous expression systems. Previous studies on P2X7 receptors in parotid acinar cells suggested that ATP does not permeabilize these cells. 2 Modification of the assay conditions showed that ATP permeabilizes freshly dissociated rat parotid acinar cells to the fluorescent dye YOPRO-1. 3 The pharmacological and physiological properties of this effect indicate that permeabilization is mediated by the P2X7 receptor. Adenosine 5,-triphosphate (ATP) and 3,- O -(4-benzoyl)benzoyl adenosine 5,-triphosphate (BzBzATP) were effective agonists with EC50 values of 49.3 and 0.6 ,M, respectively. 4 Permeabilization was best observed in low divalent cation concentrations and at physiological temperatures. Previous studies failed to detect permeabilization because of the sensitivity of this effect to temperature and divalent cations. 5 An important consideration in understanding the effect of divalent cations is that the fluorescence of YOPRO-1/nucleic acid complexes is directly quenched by addition of divalent cations. This must be considered if quantitative study of the interaction of divalent cations with P2X7 receptors is carried out using fluorescent DNA-binding dyes. 6 In summary, our data show that P2X7 receptors in parotid acinar cells can form large pores in the plasma membrane. This property likely contributes to signalling and may be cytotoxic and have particular significance in damaged or inflamed salivary glands. [source] NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine,Acid ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Hans-Heinrich Limbach Prof. Abstract In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine,acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine,acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. [source] Selenium Derivatization of Nucleic Acids for X-Ray Crystal-Structure and Function StudiesCHEMISTRY & BIODIVERSITY, Issue 4 2010Jia Sheng Abstract It is estimated that over two thirds of all new crystal structures of proteins are determined via the protein selenium derivatization (selenomethionine (Se-Met) strategy). This selenium derivatization strategy via MAD (multi-wavelength anomalous dispersion) phasing has revolutionized protein X-ray crystallography. Through our pioneer research, similarly, Se has also been successfully incorporated into nucleic acids to facilitate the X-ray crystal-structure and function studies of nucleic acids. Currently, Se has been stably introduced into nucleic acids by replacing nucleotide O-atom at the positions 2,, 4,, 5,, and in nucleobases and non-bridging phosphates. The Se derivatization of nucleic acids can be achieved through solid-phase chemical synthesis and enzymatic methods, and the Se-derivatized nucleic acids (SeNA) can be easily purified by HPLC, FPLC, and gel electrophoresis to obtain high purity. It has also been demonstrated that the Se derivatization of nucleic acids facilitates the phase determination via MAD phasing without significant perturbation. A growing number of structures of DNAs, RNAs, and protein,nucleic acid complexes have been determined by the Se derivatization and MAD phasing. Furthermore, it was observed that the Se derivatization can facilitate crystallization, especially when it is introduced to the 2,-position. In addition, this novel derivatization strategy has many advantages over the conventional halogen derivatization, such as more choices of the modification sites via the atom-specific substitution of the nucleotide O-atom, better stability under X-ray radiation, and structure isomorphism. Therefore, our Se-derivatization strategy has great potentials to provide rational solutions for both phase determination and high-quality crystal growth in nucleic-acid crystallography. Moreover, the Se derivatization generates the nucleic acids with many new properties and creates a new paradigm of nucleic acids. This review summarizes the recent developments of the atomic site-specific Se derivatization of nucleic acids for structure determination and function study. Several applications of this Se-derivatization strategy in nucleic acid and protein research are also described in this review. [source] A Flexible Method for the Conjugation of Aminooxy Ligands to Preformed Complexes of Nucleic Acids and LipidsCHEMMEDCHEM, Issue 9 2008James Abstract Attachment of targeted ligands to nonviral DNA or RNA delivery systems is a promising strategy that seeks to overcome the poor target selectivity generally observed in systemic delivery applications. Several methods have been developed for the conjugation of ligands to lipids or polymers, however, direct conjugation of ligands onto lipid, or polymer,nucleic acid complexes is not as straightforward. Here, we examine an oximation approach to directly label a lipoplex formulation. Specifically, we report the synthesis of a cationic diketo lipid DMDK, and its use as a convenient ligation tool for attachment of aminooxy-functionalized reagents after its complexation with DNA. We demonstrate the feasibility of direct lipoplex labeling by attaching an aminooxy-functionalized fluorescent probe onto pre-formed plasmid DNA,DMDK lipoplexes (luciferase, GFP). The results reveal that DMDK protects DNA from degradation on exposure to either DNase or human cerebral spinal fluid, and that simple mixing of DMDK lipoplexes with the aminooxy probe labels the complexes without sacrificing transfection efficiency. The biocompatibility and selectivity of this method, as well as the ease of bioconjugation, make this labeling approach ideal for biological applications. [source] Alcohol- O,O,-dibenzoyl-(2R,3R)-tartaric acid complexesCHIRALITY, Issue S1 2004Zoltán Kovári Abstract Structures of chiral and achiral alcohol- O,O,-dibenzoyl-(2R,3R)-tartaric acid (DBTA) complexes were investigated by single-crystal X-ray diffraction (seven new crystal structures were determined). The complexes contain DBTA and chiral alcohol in 1:1, DBTA and achiral alcohol in 1:2 host,guest stoichiometry. The hydrogen bonding structures of chiral alcohol-DBTA and achiral alcohol-DBTA complexes are different, but within a subclass they are isostructural ones. Chirality 16:S23,S27, 2004. © 2004 Wiley-Liss, Inc. [source] Synthesis and Characterization of Heterotrinuclear Complexes of Nickel and Palladium with Pyridinecarboxylate as Bridging LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005José Ruiz Abstract Heterotrinuclear pyridinecarboxylate complexes of nickel(II) and palladium(II) of the types [Ni(mcN3)(pyridinecarboxylate)]2{,-[Pd(C6F5)2]}(PF6)2 [mcN3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me3 -mcN3) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me4 -mcN3)] have been prepared by two different routes. The corresponding monomeric pyridinecarboxylate complexes of nickel and the monomeric pyridinecarboxylic acid/ester complexes of palladium have also been prepared. The crystal structures of two precursors [Ni(Me4 -mcN3)(NC5H4 -3-COO)]PF6 and cis -[Pd(C6F5)2(NC5H4 -4-CH2COOCH3)2] have been established by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | ||||||||||||||||||||||||||||||||||