Terminal Azido Group Research Articles

Freeze-Dryable, Stable, and Click-Reactive Nanoparticles Composed of Cello-oligosaccharides for Biomolecular Sensing.

Nanoparticles have been widely used as platforms for biomolecular sensing because of their high specific surface area and attractive properties depending on their constituents and structures. Nevertheless, it remains challenging to develop nanoparticulate sensing platforms that are easily storable without aggregation and conjugatable with various ligands in a simple manner. Herein, we demonstrate that nanoparticulate assemblies of cello-oligosaccharides with terminal azido groups are promising candidates. Azidated cello-oligosaccharides can be readily synthesized via the enzyme-catalyzed oligomerization reaction. This study characterized the assembled structures of azidated cello-oligosaccharides produced during the enzymatic synthesis and revealed that the terminal azidated cello-oligosaccharides formed rectangular nanosheet-shaped lamellar crystals. The azido groups located on the nanosheet surfaces were successfully exploited for antigen conjugation via the click chemistry. The resultant antigen-conjugated nanosheets allowed for the quantitative and specific detection of a corresponding antibody, even in 10% serum, owing to the antifouling properties of cello-oligosaccharide assemblies against proteins. It was found that the functionalized nanosheets were redispersible in water after freeze-drying. This remarkable characteristic is attributed to the well-hydrated saccharide residues on the nanosheet surfaces. Moreover, the antibody detection capability did not decline after the thermal treatment of the functionalized nanosheets in a freeze-dried state. Our findings contribute to developing convenient nanoparticulate biomolecular sensing platforms.

Surface-mediated self-assembly of click-reactive cello-oligosaccharides for fabricating functional nonwoven fabrics

ABSTRACT Polymer fabrics are versatile materials used in various fields. Surface modification methods for hydrophobic polymer fibers have been developed to endow the materials with water wettability and functionality. Nevertheless, it remains a challenge to freely introduce functional groups to polymer fiber surfaces in a simple manner. Herein, we report the decoration of nonwoven fabric surfaces with azidated cello-oligosaccharide assemblies via molecular self-assembly. Cello-oligosaccharides with a terminal azido group were enzymatically synthesized and allowed to self-assemble in polyolefin, polyester, and vinylon nonwoven fabrics. It was found that the functional oligosaccharides formed bark-like assemblies on the nonwoven fiber surfaces, probably through heterogeneous nucleation. The hydrophilic oligosaccharide assemblies made the hydrophobic nonwoven surfaces water-wettable. Moreover, the azido group at oligosaccharide terminal was available for the post-functionalization of the modified nonwovens. In fact, an antigen was successfully conjugated to the modified nonwovens via the click chemistry. The antigen-conjugated nonwovens were useful for the specific and quantitative detection of a corresponding antibody. Our findings demonstrate the great potential of cello-oligosaccharide assembly for the functionalization of fabrics and other polymeric materials.

Gold Nanoparticles Modification with Liquid Crystalline Polybenzylic Dendrons via 1,3-Dipolar Cycloaddition.

A series of six polybenzylic dendrons with an alkynyl focal point were synthesized for their incorporation to gold nanoparticles. Five of these compounds showed columnar mesomorphism in a wide range of temperatures. These dendrons were reacted with gold nanoparticles stabilized with a combination of a dodecanethiol and 11-azidoundecane-1-thiol. The azido group of the last compound allowed the functionalization of the nanoparticles with the six polybenzylic dendrons by 1,3-dipolar cycloaddition between their alkynyl groups and the terminal azido groups of the thiols. A high efficiency of the cycloaddition process (47-69%) was confirmed by several experimental techniques and no decomposition or aggregation phenomena were detected in the dendron-coated nanoparticles. The involved mechanism and the resulting percentage composition of the final materials are discussed. The results of the ulterior growth of the nanoparticles by thermal treatment are influenced by the size and the shape of the dendron and the temperature of the process. The structures of the final nanoparticles were investigated by TEM, DSC, TGA, NMR and UV-Vis spectroscopy. These nanoparticles do not show liquid crystal properties. However, a melting process between a crystalline and a fluid phase is observed. In the solid phase, the nanomaterials prepared show a short-range interaction between nanoparticles with a 2D local hexagonal order. A near-field effect was observed in the UV-vis spectra by coupling of different surface plasmon resonance bands (SPR) probably due to the short-range interactions. The main novelty of this work lies in the scarcity of previous studies of gold nanoparticles coated with dendrons forming themselves columnar mesophases. Most of the studies reported in the literature deal with gold nanoparticles coated with calamitic mesogens. Additionally, the effect of the thermal treatment, which in a previous paper was shown to increase the mean size of the nanoparticles without increasing their size polydispersity, has been studied in these materials.

Molecular, Supramolecular Structures Combined with Hirshfeld and DFT Studies of Centrosymmetric M(II)-azido {M=Ni(II), Fe(II) or Zn(II)} Complexes of 4-Benzoylpyridine

The supramolecular structures of the three metal (II) azido complexes [Fe(4bzpy)4(N3)2]; 1, [Ni(4bzpy)4(N3)2]; 2 and [Zn(4bzpy)2(N3)2]n; 3 with 4-benzoylpyridine (4bzpy) were presented. All complexes contain hexa-coordinated divalent metal ions with a slightly distorted octahedral MN6 coordination sphere. Complexes 1 and 2 are monomeric with terminal azido groups while 3 is one-dimensional coordination polymer containing azido groups with μ(1,1) and μ(1,3) bridging modes of bonding. Hirshfeld analysis was used to quantitatively determine the different contacts affecting the molecular packing in the studied complexes. The most common interactions are the polar O…H and N…H interactions and the hydrophobic C…H contacts. The charges at the M(II) sites are calculated to be 1.004, 0.847, and 1.147 e for complexes 1–3, respectively. The degree of asymmetry is the highest in the case of the terminal azide in complexes 1 and 2 while was found the lowest in the μ(1,1) and μ(1,3) azide bonding modes in the Zn(II) complex 3. These facts were further explained in terms of atoms in molecules (AIM) topological parameters.

Synthesis and self-assembly of a penta[60]fullerene bearing benzo[ghi]perylenetriimide units.

A benzo[ghi]perylenetriimide (BPTI) derivative bearing a terminal azido group on the expanded π-conjugated backbone has been synthesized and characterized. This promising photo- and electroactive BPTI motif has been used to obtain an original penta(organo)fullerene as a promising multi-electron acceptor system. Our studies show its self-assembly resulting from aggregation via π–π stacking interaction in solution and in the solid state.

Design of a fluorescent and clickable Ag38(SRN3)24 nanocluster platform: synthesis, modeling and self-assembling.

Fluorescent atomically precise Ag38(11-azido-2-ol-undecane-thiolate)24 nanoclusters are easily prepared using sodium ascorbate as a “green” reducer and are extensively characterized by way of elemental analyses, ATR-FTIR, XRD, SAXS, UV-vis, fluorescence spectroscopies, and theoretical modeling. The fluorescence and the atomically determined stoichiometry and structure, the facile and environmentally green synthesis, together with the novel presence of terminal azido groups in the ligands which opens the way to “click”-binding a wide set of molecular species, make Ag38(11-azido-2-ol-undecane-thiolate)24 nanoclusters uniquely appealing systems for biosensing, recognition and functionalization in biomedicine applications and in catalysis.

Spatial modulation of biomolecules immobilization by fabrication of hierarchically structured PEG-derived brush micropatterns: An versatile cellular microarray platform

Microarray technology holds enormous promise in the development of various fields ranging from tissue engineering, regenerative medicine to high-throughput screening. Here, based on the digital micromirror device (DMD)-based spatiotemporal regulation of surface-initiated photoinduced atom transfer radical polymerization (Photo-ATRP) process, a flexible and versatile methodology was developed to fabricate a hierarchical microarray structure constituted with a homogeneous hyperbranched polyethylene glycol (PEG)-derived brush layer as anti-fouling background and an extension layer of square-grid poly(2-(2-azido-2-methyl-1-oxopropoxy) ethyl methacrylate) (PAMEMA) brushes micropatterns on the silicon substrate. The terminal azido groups on the side chains of PAMEMA brushes provide abundant reactive sites to realize the covalent immobilization of target biomolecules, including RGD peptide, fibronectin, BSA and streptavidin. The TOF-SIMS and fluorescence characterizations demonstrated the feasibility and efficiency of spatially modulating the density of surface-bound biomolecules through regulating the 3D architecture parameters of the PAMEMA brush micropatterns and consequentially the azido chemical functionality. Moreover, culture experiments of human bone-derived marrow stromal cells (BMSCs) and mouse L929 cells were conducted on the obtained hierarchical microarray structure in a high-throughput manner. The presented hierarchical microarray structure holds excellent potential as a high-throughput screening platform, allowing for the parallel assessment of cell-surface interactions.

Modification of polyhydroxyalkanoates: Evaluation of the effectiveness of novel copper(II) catalysts in click chemistry

Copper(I) catalyzed azide-alkyne cycloadditions, click reactions, are an established synthetic tool to derivatize polymers. Only a few catalytic systems have been explored towards the derivatization of functionalized poly(3‑hydroxyalkanoate)s, PHAs, using click reactions. Here, the performances of three Cu(II)-catalysts supported by tetradentate polypyridyl ligands, [Cu(L1)ClO4]ClO4, [Cu(L2)ClO4]ClO4 and [Cu(L3)ClO4]ClO4, were examined in click reactions on functionalized PHAs carrying either terminal azido or alkyne groups in the side chain and the results were compared to the traditional CuSO4·5H2O/Na ascorbate and the organo-soluble Cu(I) bromotris(triphenylphosphine)copper(I), CuBr(PPh3)3 catalysts. It was determined that the effectiveness of the catalytic systems depended on the molecular architecture of the polymer and the nature of the small molecule reactants to be clicked onto the PHA. Click reactions on PHAs with terminal azido groups were catalyzed with Cu(II)-catalysts, but not with CuBr(PPh3)3. For alkyne-containing polymers CuBr(PPH3)3 effected 65% conversion in contrast to Cu(II) catalysts that were ineffective. While no strong trend was found, differences in the effectiveness were related to dissimilarities in the accessibility of the alkyne moiety for the reactive Cu(I) species. Propargyl benzoate was most effectively clicked onto a azido PHA (100% conversion) when catalyzed by CuSO4·5H2O/Na ascorbate, however the click reaction with a similar reactant, propargyl acetate, was more effectively catalyzed by a Cu(II)-catalyst supported by a tetradentate polypyridyl ligand (44% conversion).

The 4-N-acyl and 4-N-alkyl gemcitabine analogues with silicon-fluoride-acceptor: Application to 18F-Radiolabeling

The coupling of gemcitabine with functionalized carboxylic acids using peptide coupling conditions afforded 4-N-alkanoyl analogues with a terminal alkyne or azido moiety. Reaction of 4-N-tosylgemcitabine with azidoalkyl amine provided 4-N-alkyl gemcitabine with a terminal azido group. Click reaction with silane building blocks afforded 4-N-alkanoyl or 4-N-alkyl gemcitabine analogues suitable for fluorination. RP-HPLC analysis indicated better chemical stability of 4-N-alkyl gemcitabine analogues versus 4-N-alkanoyl analogues in acidic aqueous conditions. The 4-N-alkanoyl gemcitabine analogues showed potent cytostatic activity against L1210 cell line, but cytotoxicity of the 4-N-alkylgemcitabine analogues was low. However, 4-N-alkanoyl and 4-N-alkyl analogues had comparable antiproliferative activities in the HEK293 cells. The 4-N-alkyl analogue with a terminal azide group was shown to be localized inside HEK293 cells by fluorescence microscopy after labelling with Fluor 488-alkyne. The [18F]4-N-alkyl or alkanoyl silane gemcitabine analogues were successfully synthesized using microscale and conventional silane-labeling radiochemical protocols. Preliminary positron-emission tomography (PET) imaging in mice showed the biodistribution of [18F]4-N-alkyl to have initial concentration in the liver, kidneys and GI tract followed by increasing signal in the bone.

Chemical modification of functionalized polyhydroxyalkanoates via “Click” chemistry: A proof of concept

A novel approach to the post-biosynthetic chemical modification of bromo and alkyne functionalized poly(3-hydroxyalkanoates), (PHAs), via copper-catalyzed azide-alkyne cycloaddition (CuAAC) and strain promoted azide alkyne cycloaddition (SPAAC) is reported. Optimum conditions for the biosynthesis of the PHA copolymers, poly(3-hydroxynonanoate-co-3-hydroxy-11-bromoundecanoate) (PHNUBr) and poly(3-hydroxynonanoate-co-3-hydroxy-10-undecynoate) (PHNUD), using Pseudomonas oleovorans as cell factories were 20h of fermentation time and a total carbon substrate concentration of 40mM. Percent incorporation of brominated repeat units and alkyne repeat units were 38.5% and 50% respectively, as determined by 1H NMR. PHNUBr was converted into an azido-terminated precursor for the polymer analogous “click” reactions via SN2 nucleophilic substitution reaction using sodium azide with a yield of 96.7% and analyzed by FTIR and 1H NMR. CuAAC reactions were used to attach propargyl benzoate and methyl-2-azidoacetate to the PHAs with terminal azido and alkyne functional side groups respectively, with yields of 78.2% and 65.4% respectively. FTIR analysis of the products showed the disappearance of the azide peak at 2093.5cm−1 and the alkynyl CCH stretch at 3292cm−1. 1H NMR analysis confirmed the formation of the expected triazole linkage; showing the expected proton chemical shift corresponding to the triazole proton at 7.73 and 7.47ppm respectively. A strain promoted azide-alkyne reaction was used to attach (1R,8S,9s)-Bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN-OH) to the azido-terminated PHA with an average yield of 94.5%. Products were analyzed by FTIR and 1H NMR.

Covalent Functionalization of Graphene Flakes with Well-Defined Azido-Terminated Poly(ԑ-caprolactone) and Poly(2-oxazoline)

We report on grafting-on method to covalently functionalize exfoliated graphene flakes (GFs) synthesized via ultrasonication of graphite nanoplatelets (GNPs) in N-methylpyrrolidone (NMP). A well-defined poly(ε-caprolactone) (PCL) and poly(2-isopropyl-2-oxazoline) (PIPOZ) with terminal azido group were prepared. The reactions between the azido-terminated PCL or PIPOZ and ultrasonication-assisted exfoliated GFs were carried out through nitrene chemistry to obtain PCL-grafted-GFs (PCL-g-GFs) and PIPOZ-grafted-GFs (PIPOZ-g-GFs). Infrared (IR), thermogravimetry analysis (TGA) and transmission electron microscope (TEM) measurements confirmed the structure of polymer grafted GFs. The results suggested that functionalization might be an effective approach to overcome the restacking issue of graphene. Further, the presence of polymer chains onto GFs provides solubility in a wide variety of organic solvents. This type of material may open up a new opportunity for the synthesis of graphene-based materials and fabrications.

Azide-tagged sphingolipids: new tools for metabolic flux analysis.

Several diseases involve alterations in sphingolipid metabolism, so the development of tools for the analysis of sphingolipid metabolic fluxes is of interest. In this work, ω-azidosphingolipids 1-3 have been synthesized and tested as tracers in live cells. The synthesis starts from (S)-Garner's aldehyde and uses bromide or tosyloxy precursors for the introduction of the azido group into the sphingoid base. Studies in HGC-27 cells showed that probes 1-3 compete with the natural metabolites and are incorporated into sphingolipid pathways without affecting cell viability. The reactivity and bioorthogonality of the terminal azido group have been exploited by means of click reactions with different azadibenzocyclooctyne tags. This allows the mass spectrometric characterization of azidosphingolipidomes in pooled samples from different cell populations after independent treatments, providing proof of concept of the applicability of this technology in sphingolipid metabolic flux analysis.

Synthesis and first use of pyridine-2,6-diylbis(pyrazine-2-ylmethanone) in metal cluster chemistry: a {Mn(III)3Na2} complex with an ideal trigonal bipyramidal geometry.

The successful organic synthesis of a new dipyrazole/pyridine-dicarbonyl organic molecule, namely pyridine-2,6-diylbis(pyrazine-2-ylmethanone) [(pz)CO(py)CO(pz)], followed by its employment in Mn coordination chemistry has yielded the neutral cluster compound [Mn3Na2O(N3)3(L)3] (1), where L(2-) is the (pz)C(CH2COCH3)(O(-))(py)C(CH2COCH3)(O(-))(pz) dianion. The latter group was formed in situ, presumably by the nucleophilic attack of the carbanion (-)CH2COCH3 to the carbonyl carbon atoms of (pz)CO(py)CO(pz), in the presence of Mn(n+) ions under basic conditions and in solvent Me2CO. Complex 1 possesses an almost ideal trigonal bipyramidal topology, with the two Na(I) ions occupying the apical positions and the three Mn(III) ions residing in the equatorial trigonal plane. The bridging ligation about the metal ions is provided by a μ3-O(2-) ion and six μ-OR(-) groups from the L(2-) ligand, while peripheral ligation is completed by three terminal azido groups and the pyridine N and carbonyl O atoms of L(2-). Magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the paramagnetic Mn(III) centres; the use of an anisotropic, equilateral Mn(III)3 triangle model allowed us to fit the magnetic data and obtain the best-fit parameters: J = -10.8 cm(-1), D = -5.3 cm(-1), and g = 1.99. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting architectures.

Solubilization of graphene flakes through covalent modification with well‐defined azido‐terminated poly(ε‐caprolactone)

ABSTRACTA well‐defined poly(ε‐caprolactone) (PCL) with terminal azido group was prepared. Grafting‐on reaction between the azido‐terminated PCL (N3PCL) and ultrasonication‐assisted exfoliated graphene flakes (GF) was carried out to obtain PCL‐grafted‐GF (PCL‐g‐GF) which showed good dispersibility in a wide variety of organic solvents. Gel permeation chromatography, 1H NMR, IR, Raman, UV‐vis, and TEM measurements indicated that PCL macromolecules were covalently introduced on the surface of GF without disrupting the structure of GF. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41569.

Structural and theoretical investigation on two dinuclear Fe(III) complexes of tridentate NNO-donor Schiff base ligands

Two new Fe(III) complexes of formulas [FeL1(N3)(OMe)]2 (1) and [FeL2(N3)(OH)]2·H2O (2) have been synthesized by using two tridentate NNO-donor Schiff base ligands HL1{(2-[(3-methylaminoethylimino)-methyl]-phenol)} and HL2 {(2-[1-(2-dimethylaminoethylimino)methyl]-phenol)}, respectively. Substitution of the –CH3 group on the secondary amine group of the N,N-dimethyldiamine fragment of the Schiff base by a H-atom leads to a structural change from a methoxido-bridged dimer (1) to a single hydroxido-bridged dimer (2). Both complexes have been characterized by single-crystal X-ray analyses, IR and UV–Vis spectroscopy and DFT studies. Both dimers are centrosymmetric containing two FeIII atoms which are bridged by two methoxido ions in compound 1 and by two hydroxido ions in compound 2. The chelating tridentate Schiff base and a terminal azido group complete the distorted octahedral environment around each iron center in both complexes. To explain the preferential bridging ability of methoxido and hydroxido groups in complexes 1 and 2, we have carried out theoretical calculations based on DFT to compare their formation energies and dimerization energies. In the case of complex 2, it is noticed that the close proximity of the azido group from the iron centers allow the hydroxido bridged complex to gain extra stability through H-bonds, whereas due to the steric crowding of the azido group and the methyl moiety of adjacent molecules, complex 1 disfavors the formation of hydrogen bonds as well as hydroxido bridging.

Novel Generation of Crosslinkers allows Single Molecule Force Spectroscopy on Oligomeric Receptors

Single molecule force spectroscopy allows for measurement of the unbinding forces between a tip-tethered ligand and a cognate receptor molecule which is immobilized on the sample surface. Conventionally, the atomic force microscope (AFM) tip is aminofunctionalized and the ligand is coupled via a linear heterobifunctional poly(ethylene glycol) (PEG) linker. This approach restricts the use of force microscopy to the investigation of single ligand-receptor pairs. For extension of the technique to the analysis of dimeric or oligomeric receptors, new crosslinkers carrying two or four terminal coupling groups for ligand-attachment were synthesized.The syntheses are based on tri- and pentavalent core units. Heterobivalent PEGs serve as elongations to create the optimal ligand-to-ligand distance for each ligand-receptor system. In case of the bivalent linker, lysine was chosen as branching element and the biotin-streptavidin couple served as test system. The probability density function (histogram) of the unbinding forces showed two peaks, reflecting mono- and bivalent binding of the tip-bound bis-biotin linker to one support-bound streptavidin molecule. The tetravalent linker was prepared from three copies of a symmetric trifunctional subunit formed from lysine which carries a β-alanine on its α-amino group. In a multistep reaction, a 2∗2 “fork” with four terminal amino groups was synthesized. Fortunately it was possible to elongate each prong of the 2∗2 fork with a PEG chain of the same length, using HATU and HOAt for in-situ coupling of amine and carboxyl groups. Terminal azido-groups provide for coupling of alkyne-functionalized ligands directly on the tip. In conclusion, branched crosslinkers permit single molecule force spectroscopy on oligomeric receptors; their modular structure can easily be adapted for different ligand-receptor-system in terms of coupling functions and ligand-to-ligand distance.

Tuning the apparent formal potential of covalently attached ferrocene using SAM bearing ionizable [sbnd]COOH groups

A method of tuning the apparent formal potential at the interface between the electrode surface covered with carboxylate thiol self assembled monolayer (SAM) and the solution containing electrolytes is reported. Redox active ferrocene moiety has been covalently attached to the terminal azido groups in the SAM using “click” chemistry. Cyclic voltammetry experiments show that the reduction potential of this ferrocene moiety can be tuned easily from 0.345V to 0.200V, i.e. by 145mV by varying the chain length of the thiol carboxylic acid diluents, changing the pH of the electrolytic solution and by changing the coverage of the surface. Using the (applying the theory of interfacial potential distribution by Smith and White and including the Stern layer effect on the potential of the redox species at the interface proposed by Fawcett) modified Nernst equation the shift of apparent formal potential of redox species at the interface has been analyzed when the chain length of the diluents, pH of the solution and coverage of the surface are changed. The data indicate that the phenomenon is governed by the ionizable polar head groups SAM, i.e. COOH which changes the interfacial microenvironment around the redox active ferrocene centre.

Incorporation Efficiency of 5'-Azido-5'-Deoxyguanosine into 5'-Terminus of RNA for Preparation of Azido-Functionalized RNA

Although the modern biological systems are by large based on DNA genomes and protein enzymes, RNA plays important roles in many fundamental processes in cells, including regulation of protein biosynthesis, RNA splicing, and retroviral replication, with remarkable features. From this point of view, site-specific substitution and derivatization of RNA can provide powerful tools for elucidating RNA structures and functions. The modification of either the 3'and 5'-termini or an internal position of the oligonucleotides with a primary alkylamine group is a widely used method for introducing additional functional groups to the RNA. In particular, several 5'-modifications of RNA molecules such as sulfhydryl modification for functionalizing the 5'-terminus of RNA by a transcription or kinase reaction have been shown to have broad applications in studying RNA structures, mapping RNA-protein interactions, and in vitro selection of catalytic RNAs, since a unique functional group incorporated into the RNA can be subsequently conjugated to the desired molecule by a selective chemical reaction. However, there is still a need to develop coupling chemistry with high stability and yield to modify RNA and other biomolecules. In addition, the coupling functional groups are ideally required to be stable under aqueous reaction conditions, and the coupling reaction should be highly chemoselective. In this regard, Cu-catalyzed azide-alkyne cycloaddition (CuAAC or click chemistry) to form the triazole version of Huisgen’s [2+3] cycloaddition family may be the best choice, because this reaction only occurs between alkynyl and azido functional groups with high yield, and because the resulting 1,2,3-triazoles are stable at aqueous conditions and high temperature. Indeed, the azide group is one of the most utilized bioorthogonal chemical tags for biomolecule-conjugate experiments because of its small size and inertness to most components in a biological environment. We recently reported a two-step synthetic method for 5'azido-5'-deoxyguanosine (azido-G) by adapting literature procedures (Scheme 1) and its efficiency for click chemistry using 6-heptynoyl p-nitroaniline, in consideration that the click chemistry with rapid reaction between the azide and alkyne groups to form a covalent triazole linkage without cross reacting with other functional groups could be used in bioconjugation chemistry. In the present study, we sought enzymatic methods to incorporate azido groups in RNA and measured incorporation efficiency of azido-G into the 5'terminus of RNA by in vitro transcription using T7 RNA polymerase that requires guanosine to efficiently initiate transcription. This is important in consideration that a terminal azido group is able to be introduced to the 5'termini of RNA molecules, and that azides are unstable under solid-phase synthesis conditions. A 97-mer single-stranded DNA containing a T7 promoter at the 3'-end (5'CAG GAC TGC TCT CAC TCT CAC GCA CCA AGA AGC TGC CAT TGA TCC CGC TGC

Rhomboidal [Cu 4 ] coordination cluster from self-assembly of two asymmetric phenoxido-bridged Cu 2 units: Role of μ 1,1 -azido clips

The coordination cluster [Cu2(μ-OMe)(μ 1,1-N3)(μ-bcp)(N3)]2 (1; Hbcp = 2,6-bis(2-benzoyl-4-chloro-phenylimino)-methyl)-4-methylphenol, forming a new member within the rapidly growing family of Cu4 cluster complexes, has been synthesized and structurally characterized by X-ray crystallography. The complex crystallizes in the monoclinic system, space group P21/c, with unit cell parameters a = 14.620(7) Å, b = 17.923(8) Å, c = 15.008(7) Å, β = 115.815(14)° and Z = 2. It is the first example of a rhomboidal [Cu4] compound formed from μ 1,1-azido clipping of two methoxido bridged [Cu2] complexes showing asymmetric coordination from benzophenone oxygen atoms and terminal azido groups. In the presence of sodium azide copper(II) nitrate reacts with 2,6-bis(2-benzoyl-4-chloro-phenylimino)-methyl)-4-methylphenol to give a tetranuclear copper(II) complex resulting from incorporation of two solvent derived methoxide anions.

Zinc and manganese complexes with 4-aminoantipyrine

The interaction of 4-aminoantipyrine (aap) with metal(II) pseudohalides [M=Zn and Mn] in aqueous media resulted in three new complexes; [Zn(aap)(N3)2(H2O)]n (1), [Zn(aap)3][Zn(NCS)4]·1/2H2O (2), and [Mn(aap)2(NCS)2] (3). The structure of 1 reveals μ1,3-bridging azido groups connecting zinc centers to form 1D chains of polyhedra oriented along the c-axis of the monoclinic unit cell. The zinc(II) center is octahedrally coordinated by O(1) and N(1) of bidentate N,O chelating aap molecule, by N(11) and N(13) of μ1,3-bridging azido group, N(21) of a terminal azido group, and O(2) of aqua ligand, resulting in a ZnN4O2 geometry. The structure of complex 2 consists of [Zn(aap)3]2+ complex cations, [Zn(NCS)4]2− complex anions and disordered lattice water molecules. The structure of 3 reveals mononuclear complexes, where the Mn(II) centers are ligated by the exocyclic N and O donor atoms of two chelating aap molecules and two N atoms of terminal isothiocyanato ligands. Thermal properties and IR spectra of the complexes were investigated and shown to be consistent with the structures.