Terminal Azido Group Research Articles

Construction and Assembly of Branched Y-Shaped DNA: “Click” Chemistry Performed on Dendronized 8-Aza-7-deazaguanine Oligonucleotides

Branched DNA was synthesized from tripropargylated oligonucleotides by the Huisgen-Meldal-Sharpless cycloaddition using "stepwise and double click" chemistry. Dendronized oligonucleotides decorated with 7-tripropargylamine side chains carrying two terminal triple bonds were further functionalized with bis-azides to give derivatives with two terminal azido groups. Then, the branched side chains with two azido groups or two triple bonds were combined with DNA-fragments providing the corresponding clickable function. Both concepts afforded branched (Y-shaped) three-armed DNA. Annealing of branched DNA with complementary oligonucleotides yielded supramolecular assemblies. The concept of "stepwise and double click" chemistry combined with selective hybridization represents a flexible tool to generate DNA nanostructures useful for various purposes in DNA diagnostics, delivery, and material science applications.

Thermoresponsive Self-Assemblies of Cyclic and Branched Oligosaccharide-block-poly(N-isopropylacrylamide) Diblock Copolymers into Nanoparticles

This paper discusses the thermoresponsive nanoparticles obtained by self-assemblies of nonlinear oligosaccharide-based diblock copolymer systems. These diblock copolymers were synthesized by Cu(I)-catalyzed 1,3-dipolar azide/alkyne cycloaddition ("click" reaction) of propargyl-functionalized β-cyclodextrin (βCyD) and xyloglucooligosaccharide (XGO) with poly(N-isopropylacrylamide) (PNIPAM) having a terminal azido group prepared by atom transfer radical polymerization (ATRP). Elastic and quasi-elastic light scattering analysis of the dibock copolymers in H(2)O indicated that thermodynamic phase transitions of the PNIPAM blocks at their cloud points (T(cp)s ≈ 34 °C), around lower critical solution temperatures (LCSTs), triggered their self-assemblies into the nanoparticles. These nanoparticles had narrow size distributions and small interphases (i.e., sharp boundaries). The mean hydrodynamic radii (R(h)s) of the βCyD and XGO-based nanoparticles were determined to be around 150 and 250 nm upon slow heating (i.e., step-by-step heating), and 364 and 91.5 nm upon fast heating, respectively, depending on a predominance of the interchain association or the intrachain contraction. Transmission electron microscope (TEM) and field emission gun-scanning electron microscopy (FEG-SEM) images of the nanoparticles clearly showed compact spherical nanoparticles whose cores are mainly made with the PNIPAM blocks, whereas the rough shells consist in the oligosaccharidic blocks.

Synthesis of highly substituted amide hyaluronan derivatives with tailored degree of substitution and their crosslinking via click chemistry

Hyaluronan (HA) based hydrogels with well defined 3D-molecular architecture have been synthesized combining chemical modification of hyaluronic acid and ‘click chemistry’. The high degree of substitution of HA was obtained after activation of the carboxyl group with ethyl chloroformate and subsequent functionalization of the carboxylic group with primary amine containing either a terminal azido or alkynyl groups. The degree of amide substitution could be controlled by reaction conditions. The chemical modification probed to be highly chemo-selective providing only amide modified HA derivates. The prepared derivates showed higher resistance towards thermal degradation than starting hyaluronan material. The crosslinking reaction of azido- and alkynyl-amide derivates of HA led to the formation of highly organized and porous networks, which due to their high stability against degradation are potential candidates for application as drug delivery systems, or scaffolds in tissue engineering.

Thermoresponsive Vesicular Morphologies Obtained by Self-Assemblies of Hybrid Oligosaccharide-block-poly(N-isopropylacrylamide) Copolymer Systems

This work discusses the self-assembly properties of thermoresponsive hybrid oligosaccharide-block-poly(N-isopropylacrylamide) copolymer systems: maltoheptaose-block-poly(N-isopropylacrylamide) (Mal(7)-b-PNIPAM(n)) copolymers. Those systems at different molar masses and volume fractions were synthesized using Cu(I)-catalyzed 1,3-dipolar azide/alkyne cycloaddition, so-called "click" chemistry, between an alkynyl-functionalized maltoheptaose (1) and poly(N-isopropylacrylamide) having a terminal azido group (N(3)-PNIPAM(n)) prepared by atom transfer radical polymerization (ATRP). While the cloud point (T(cp)) of the N(3)-PNIPAM(n) ranged from 36.4 to 51.5 degrees C depending on the degree of polymerization, those obtained of the diblock copolymers ranged from 39.4 to 73.9 degrees C. The self-assembly of such systems is favored due to the hydrophobicity of the PNIPAM in water above the T(cp). While the N(3)-PNIPAM(n) present polydisperse globular shape with a mean diameter of 500 nm, well-defined vesicular morphologies with an approximate diameter of 300 nm are obtained in diblock copolymer systems. These results were obtained and confirmed using static and dynamic light scattering as well as imaging techniques such as transmission electron microscope experiments.

Influence of dialkyne structure on the properties of new click-gels based on hyaluronic acid

Hydrogels have been widely used in tissue engineering as a support for tissue formation and/or to deliver drug locally. A novel procedure for the in situ rapid chemical gelation of aqueous solutions of hyaluronan (HA) was employed. HA was functionalised with an arm bearing a terminal azido group (HAAA). When HAAA was mixed with a series of dialkyne reagents of different length, a 1,3-dipolar cycloaddition (“click-chemistry”) reaction took place in the presence of catalytic amount of Cu(I) resulting in fast gelation at room temperature. The resulting gels were characterised in terms of degree of cross-linking by 1H HR-MAS NMR. The kinetic of gelation and the determination of elastic moduli as well as the degree of swelling and the controlled release of a model drug, were studied as a function of chemical nature of the dialkyne group, catalyst concentration, HAAA concentration and temperature. All these variables allowed the swelling ratio and the extent of release of a drug, doxorubicin, entrapped within the gel, to be modulated. In all cases the kinetic of release reached the stationary state within 150 h. The height of the plateau was dependent on the overall (chemical and topological) degree of cross-linking.

The Mn(II)-2,2′-dipyridylamine-pseudohalide system: Synthesis, crystal structure and luminescence behaviour of [Mn(dpa) 2(X) 2] · H 2O and [Mn(dpa) 2(X)(OH 2)]ClO 4 (dpa = 2,2′-dipyridylamine; [formula omitted], NCO −)

Four complexes of the type [Mn(dpa) 2(X) 2] · H 2O (dpa = 2,2′-dipyridylamine; X = N 3 - , 1 ; X = NCO −, 2) and [Mn(dpa) 2(X)(OH 2)]ClO 4 ( X = N 3 - , 3 ; X = NCO −, 4) have been synthesized using single-pot reactions of manganese(II) salt, dpa and X in 1:2:2 and 1:2:1 molar ratios, respectively. The compounds have been characterized by microanalytical, physicochemical, spectroscopic and magnetic results. Room temperature magnetic moments ( μ eff) are in the range 5.88–5.97 BM and are typical of high-spin manganese(II) complexes ( t 2 g 5 idealized, S = 5/2). The complexes display a Mn(III)–Mn(II) couple at ∼0.6 V versus SCE in DMF solutions. X-ray structure determinations show that in 1– 4 the manganese(II) centres are in a distorted octahedral environment. Compounds 1 and 2 contain the MnN 6 chromophore, completed by two bidentate dpa units and two terminal azido groups in 1 or N-coordinated cyanato ligands in 2, along with a water of crystallization. In 3 and 4, one water molecule acts as a coordinating ligand replacing one of the terminal pseudohalides in 1 and 2, respectively, resulting in a MnN 5O chromophore. The amine H, terminal azido N or cyanato O, O and H’s of the water molecule are engaged in extensive hydrogen bonding of the type N–H⋯N, O–H⋯N and N–H⋯O in 1 and 2. Additionally O–H⋯O bonding is observed in 3 and 4. Supramolecular 2D sheet structures are obtained arising from such weak intermolecular forces. All the complexes display high-energy intraligand 1(π–π*) fluroscence and intraligand 3(π–π*) phosphorescence in glassy solutions (DMF at 77 K).

Synthesis and Luminescence Spectral Properties of New 2,7-Dihydroxy-9H-fluoren-9-one Derivatives

A number of new 2,7-dihydroxyfluorenone derivatives containing side-chain oligoethylene glycol fragments with terminal hydroxy, p-tolylsulfonyl, azido, and amino groups were synthesized. When the side chain has a certain length, an interaction between the terminal group and the fluorenone fragment becomes possible, which considerably changes photoluminescence properties of the molecule.

Oxalato‐Bridged [CuIICrIII] and [MnIICrIII] Binuclear Complexes: Synthesis, Crystal Structures, Magnetic and EPR Investigations

AbstractTwo new heterobinuclear complexes, [(bipy)(C2O4)Cr(μ‐C2O4)Cu(Hfsaaep)(H2O)]·2H2O (1) and [(phen)(C2O4)Cr(μ‐C2O4)Mn(phen)2(N3)]·H2O (2) have been obtained by using bis(oxalato)chromium(III) anions, [Cr(AA)(C2O4)2]−, as building blocks [AA = 2,2′‐bipyridine (bipy); 1,10‐phenanthroline (phen)]. The crystal structures of the two complexes have been solved. These complexes comprise neutral oxalato‐bridged CrIII−CuII and CrIII−MnII units. The [Cr(AA)(C2O4)2]− anion acts as a bidentate ligand toward CuII in compound 1 and as a monodentate ligand toward MnII in compound 2. The copper(II) ion in 1 exhibits a slightly distorted square bipyramidal stereochemistry, with the aqua ligand and one of the bridging oxalato oxygen atoms disposed in the apical positions [Cu(1)−O(1w) = 2.360(3) Å and Cu(1)−O(4) = 2.504(2) Å]. The second bridging oxalato oxygen atom [Cu(1)−O(2) = 2.0747(18) Å] and the N,N,O‐type Hfsaaep ligand are located in the basal plane. The distance between the CrIII and CuII ions across the bridging oxalate unit is 5.506 Å. The MnII ion in compound 2 is hexacoordinate (two chelating phen ligands, one oxalato bridging oxygen, and one terminal azido group). The intermolecular CrIII···MnII distance is 5.257 Å. The magnetic properties of the two complexes have been investigated. The magnetic coupling between CrIII and CuII in 1 was found to be ferromagnetic (J = +1.4 cm−1). The nature of the ground state (S = 2) has been further confirmed by plotting the magnetization‐versus‐field curve. An antiferromagnetic interaction was found between CrIII and MnII in compound 2 (J = −1.9 cm−1). The magnetization‐versus‐field curve indicates the occurrence of a crossover between the Zeeman components: MS = −1 (ground state S = 1), MS = −2, from the first excited state (S = 2), and MS = −3, from the second excited state. The EPR spectra of the two compounds are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Crystal structures and magnetic properties of uniform and alternating azido-bridged (2,2′-bipyridyl)copper(II) chains

Single crystals of four copper(II) complexes of formula [Cu(bipy)(N 3) 2] n ( 1,2), [Cu(bipy) 2(N 3)(ClO 4)] ( 3) and [Cubipy) 2(N 3)]ClO 4 ( 4) (bipy=2,2′-bipyridine) were obtained from aqueous solutions containing (2,2′-bipyridyl) copper(II) perchlorate and sodium azide, and their crystal structures were determined by X-ray diffraction methods. The structures of compounds 1 and 4 were already known, but the better accuracy of our structural determination of complex 1 led us to reconsider it here. The structures of compounds 1 and 2 are made up of neutral chains of copper(II) ions bridged by two azide groups exhibiting asymmetrical end-on ( 1) and alternating asymmetrical end-on and end-to-end bridging ( 2) modes. The copper atoms in 1 and 2 exhibit a distorted CuN 6 octahedral environment: two bipyridyl nitrogen atoms from a chelating bipy molecule and two azide nitrogens, either from two bridging azide ( 1) or from one bridging azide and a terminal one ( 2), occupy the equatorial positions whereas two azide nitrogens from the two neighbouring neutral [Cu(bipy)(N 3) 2] units fill the axial positions. The intrachain metal-metal separation is 3.516(1) and 3.497(1) Å in 1 and 3.434(1) and 5.378(1) Å in 2. The equatorial CuN bond lengths vary in the ranges 1.953(2)–2.029(2) ( 1) and 1.953(4)–2.029(3) Å ( 2). The axial bonds are significantly longer, 2.683(3) and 2.684(3) Å for 1 and 2.604(3) and 2.849(4) Å for 2. The structure of complex 3 consists of neutral [Cu(bipy) 2(N 3)(ClO 4)] units where the metal atom has a highly distorted CuN 5O octahedral environment: two chelating bipy in cis positions, a terminal azido group and a weakly coordinated percholrate form the coordination polyhedron. The basal plane is composed of four nitrogen atoms, three from two bipy molecules and one from the azido group (the metal to nitrogen bonds varying in the range 1.971(5)–2.030(5) Å, whereas the apical positions are occupied by a bipy nitrogen (2.218(5) Å) and a perchlorate oxygen (2.950(5) Å) atom. The magnetic properties of 1 and 2 have been investigated in the temperature range 2–300 K. Weak intrachain antiferro- ( 1) and alternating antiferro- and ferromagnetic ( 2) interactions have been observed and the efficiency of the out-of-plane exchange pathway through the azido bridge is analyzed and discussed in the light of the available magneto-structural parameters.

Crystal Structure of Nickel- and Cobalt-Diazidotetrapyridinemetal(II)-2(Pyridine) Clathrates

[MPy4(N3)2]⋅2Py (M = Ni, Co) are clathrates where two of six pyridine species are included in the crystal structure of the host complex without chemical bonding. The clathrates are isostructural, orthorhombic, space group Pnna (52), Z = 4. For the Ni compound a = 14.958(5), b = 11.909(5), c = 17.517(7) U, V = 3120(2) U3, µ = 12.25 cm-1, final R = 0.057.The Cocompound is of very similar structure (a = 14.980(3), b =11.980(2), c = 17.350(5) U, V = 3114(1) U3, µ = 46.50 cm-1. The metal cation in the host molecule is surrounded by six donor nitrogens of two terminal azido-groups in trans-positions and four pyridine ligands. The complex molecule lies on a twofold axis parallel to a.

A copper(II) azide compound of pyrazinic acid containing a new dinuclear complex anion [Cu 2(N 3) 6] 2−. Synthesis, spectral and study of KCu 2(pyrazinato) (N 3) 4

A new complex of copper(II) azide with pyrazinic acid, of general formula KCu 2(pyrazinato)(N 3) 4 has been synthesized and characterized by spectroscopic and crystallographic methods. The structure of the complex consists of a new dinuclear complex anion [Cu 3(N 3) 6] 2−, potassium cations and neutral polymeric complex [Cu(pyrazinato)(N 3)]. Each distorted square-planar copper centre [Cu(1)] in the complex anion is coordinated to four nitrogen atoms from two terminal and two μ-(1,1) bridging azido ligands [CuN distances 1.940(6)–2.011(5) Å]. In the polymeric complex, each copper atom, Cu(2), is coordinated to N(41) of a terminal azido group and N(61), N(62) and O(31) from pyrazinato anions to form infinite, “neutral” chains of polyhedra with orientations along [010]. The potassium cations are located in broad channels which are a consequence of stacking of the copper complexes. The IR spectrum confirms the presence of different asymmetric azido ligands. The absorption frequencies of diagnostic values are given and discussed. The electronic spectrum displays three absorption bands associated with N 3 −Cu II charge transfer transitions. The EPR spectrum of the solid complex suggests an axial structure with non-coupled copper(II) atoms.

Synthesis and structural determination of azidotetrakis-(3-ethyl-4methylpyridine)copper(II) perchlorate and di-μ(1,1)-azido-[diazidotetrakis(3-ethyl-4-methylpyridine)]dicopper(II), [Cu(β-collidine) 4(N 3)](ClO 4) and [Cu(β-collidine) 2(N 3) 2] 2

The preparation and structural characterizations of two new copper(II) azido complexes of 3-ethyl-4-methylpyridine (β-collidine), namely azido tetrakis(β-collidine) copper(II) perchlorate ( 1) and di-μ(l,l)-azido-[diazido-tetrakis(β-collidine)]dicopper(II) ( 2) are described. The spectral results suggest an ionic perchlorate and terminal azido group in complex 1 and different asymmetric azides in 2. The structure of 1 consists of isolated [Cu(β-collidine) 4(N 3)]+ cations and ClO 4 − anions. The copper atom in the cation is in a tetragonal pyramidal environment with four collidine ligands occupying the basal sites [CuN  2.033(4) Å] and a terminal azido ligand at the apical position with a CuN distance of 2.141(6) Å. The centrosymmetric binuclear molecule 2 features monodentate collidine ligands, di-μ(l,l)-azido-bridged Cu 2N 2 rings, terminal azido ligands and distorted square pyramidal copper(II) coordination geometry.

Crystal Structure Investigation of Copper(II) Thiocyanato and Cobalt(III Azido Complexes of Picolinic Acid; [Cu(pic)(SCN)(H2O)2] · 2H2O and [Na2Co(pic)2(N3)2(H2O)6] [Co(pic)2(N3)2] · 2H2O

The structures of [Cu(pic)(NCS)(H2O)2] · 2H2O, complex 1, and [Na2Co(pic)2(N3)2(H2O)6][Co(pic)2(N3)2] · 2H2O, complex 2, were determined by X-ray crystallography. Crystal data: 1, C7H12CuSN2O6, orthorhombic, space group Pbca, a = 8.749(4), b = 10.786(5), c = 26.882(9) Å, Z = 8, Rw =0.046 for 826 observed diffractometer data; 2, C24H32Co2Na2N16O16, triclinic, space group P1̄, a = 7.297(3), b = 8.806(4), c = 15.820(7) Å, a = 105.31(3), β = 95.09(3), γ = 99.86(3)°, Z = 1, and Rw = 0.064 for 1680 observed MoKa data. Complex 1 features six-coordinated copper atoms, N,O-bidentate chelate picolinato anions, and μ(N,S) bridging thiocyanato groups with N at the basal site and S at the apical site of tetragonal bipyramid. The remaining two sites are occupied by aqua molecules, whereas two other water molecules serve as lattice water. The bridging thiocyanato groups link the copper polyhedra to form chains along the b axis of the unit cell. Complex 2 contains two Co(III) atoms located at different inversion centers. Co 1 in the [Na2Co(pic)2(N3)2(H2O)6]+ cation is six-coordinated by two trans picolinato anions (A) via their N 1 and O 1 atoms and by two terminal azido ligands. Two oxygen atoms (O 2 and O 2a) of two picolinate anions (A) act as μ(Ο,Ο) bridging atoms at basal sites to form a four-membered Na2O2 ring. Each sodium atom is further linked to three aqua ligands giving rise to trigonal-bipyramidal coordination environments. Two additional lattice water molecules are located between the dimeric sodium polyhedra. Co 2, in the [Co(pic)2(N3)2]- anion, is also six-coordinated by pairs of trans N,O-picolinate anions (B) and terminal azido groups.