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PubMed1998

[New approach to the study of interaction of amino acid side groups with aryl azides].

A new approach to the study of the interaction of amino acid side chains with photoreactive aryl azides was proposed. This approach was based on the drawing together of the reacting groups by the attachment of the reacting compounds to complementary oligonucleotides. Cystamine, histamine, and 1,6-hexamethylenediamine mimicking the cystine, histidine, and lysine residues, respectively, were attached to the 3'-terminal phosphate of the oligonucleotide GGTATCp through a phosphamide bond and used as the targets for photomodification. Derivatives of the oligonucleotide pGATACCAA with the fragment N3C6H4NH- attached directly to its 5'-end by a phosphamide bond or through the spacer -(CH2)nNH- (where n is 2, 4, and 6) were used as photoreagents. Their derivatives containing the same spacer and the N3C6F4CO-NH(CH2)3NH- or 2-N3,5-NO2-C6H3CO-NH(CH2)3NH- residues were also used. The duplexes were photomodified by irradiation with 300-350 nm wavelength light. The maximal yields of the photo-cross-linking were from 22 to 68%. The reagents containing p-azidoaniline residue were found to be the most effective toward the targets. The maximum yields of the photomodification products modeling the side chains of cysteine and lysine were found to vary from 40 to 67% and to depend on the length and the structure of the spacers used. The duplex with the target bearing the imidazole residue (the histidine model) manifested a yield decreased to 25%. This fact was in a good agreement with the data of computer modeling that indicated an unfavorable mutual displacement of the imidazole residue and the photoreactive group.

Amino Acids↗
PubMed2000

Unexpected formal [1+3] cycloadditions between azides and alpha-zirconated phosphanes: a route to unprecedented phosphazide and iminophosphorane complexes.

Polycyclic zwitterionic complexes that incorporate one or two phosphonium unit(s) as cationic center(s) and zirconocene-ate moiety(ies) as the anionic counterpart(s) can be easily prepared by either [1+3] or [1+3] and [2+3] cycloadditions which involve bi- or tricyclic alpha-zirconated phosphanes 3 or 4 and various azides. Some of these species exhibit unprecedented phosphazide chelation with bonding between the zirconium and a nitrogen atom in the alpha position relative to phosphorus. When heated, the phosphazide complexes lose dinitrogen to form stable polycyclic zwitterionic phosphonium mono- or dinuclear complexes. The solid-state structure of the two zwitterionic complexes 5 and 8 was determined by X-ray crystallography.

Journal Article↗
PubMed1999

Stable Polymer-Bound Iodine Azide.

1,2-Azido-iodination of a wide range of alkenes under very mild conditions can be achieved by using a novel iodate(I) reagent, a stable and storable polymer-bound iodine azide, which is available in two steps (see scheme). Simple work-up and convenient use in automated parallel synthesis are important features of this polymer-bound reagent.

Journal Article↗
PubMed2000

Activation and desoxygenation of CO, CO2, and SO2 with sulfur-rich azide and amide.

The azide and amide complexes (NBu4)[Ni(N3)('S3')] (2) and (NBu4)[Ni[N(SiMe3)2]('S3')] (4) were found to react with CO, CO2, and SO2 under very mild conditions at temperatures down to -50 degrees C. Depending on the N oxidation state of the nitrogen ligands, addition or partial to complete desoxygenation of the oxides takes place. The reaction between 2 and CO gives (NBU4)[Ni(NCO)('S3')] (3). The reactions between 4 and CO, CO2, and SO2 afford selectively the cyano, isocyanato, and sulfinylimido complexes (NBu4)[Ni(X)('S3')] with X = CN- (5), NCO- (3), and NSO- (6). The silyl groups act as oxygen acceptors. Mechanisms are suggested which have in common the formation of reactive five-coordinate (NBu4)[Ni(L)(L')('S3')] intermediates. In these reactions, highly activated L and L' react with each other. The complexes were characterized by standard methods, and (NBu4)[Ni(CN)('S3')] (5) was also analyzed by X-ray crystallography.

Journal Article↗
PubMed2006

(NHC)Copper(I)-catalyzed [3+2] cycloaddition of azides and mono- or disubstituted alkynes.

A versatile and highly efficient catalyst for the Huisgen cycloaddition reaction has been developed. Previously isolated or in situ generated azides yielded 1,2,3-triazoles with differently substituted alkynes in the presence of a [(NHC)CuBr] complex (NHC = N-heterocyclic carbene). Extremely high reaction rates and excellent yields were obtained in all cases. This catalytic system fulfils the requirements of "click chemistry" with its mild and convenient conditions, notably in water or solvent free reactions and simple isolation with no purification step. Furthermore, for the first time, an internal alkyne was successfully used in this copper-catalyzed cycloaddition reaction. DFT calculations on this particular system allowed for the proposition of a new mechanistic pathway for disubstituted alkynes.

Journal Article↗
PubMed2001

Reactivity of anomeric 1alpha- and 1beta-pentofuranosyl azide derivatives in ammonia chemical ionization.

Electron impact (EI), fast atom bombardment (FAB) and ammonia chemical ionization [CI(NH3)] mass spectrometry were applied with the aim of differentiating between the anomeric 1alpha- and 1beta-azidopentofuranosyl derivatives. Calculated ammonium affinities [AA(M)] and proton affinities [PA(M)] show that beta-anomers have higher affinities for H+ and NH4+ ions than alpha-azides. Protonated molecules, obtained by CI(NH3) of azidofuranosyl derivatives, lose HN3 giving abundant furanosyl (S+) ions. Ammonia solvation of MH+ ions competes with the previous reaction producing the [SNHN2NH3]+ ion, a competitive product to the ammonium-attached [SN3NH4]+ ion. The fragmentation pathways of the stable and metastable [MNH4]+, MH+ ions, and several other important fragment ions, were determined using mass analyzed ion kinetic energy spectrometry (MIKES). The abundance of the [SN3NH4]+ and/or [SNHN2NH3]+ ions was found to correlate inversely with the exothermicity of ammonia solvation of the MH+ ion. The abundance of the fragment ions [SNHNH3]+, [SNH3]+ and SNH+ in some examples correlates with the exothermicity of the corresponding [MNH4]+ and MH+ parent ion formation. The fragment ions SNH3+ and SNHNH3+ can be formed, at least in part, in the ammonia solvation reaction of the S+ and SNH+ ions taking place within the high-pressure region of the CI ion source.

Journal Article↗
PubMed2002

Electrospray ionization mass spectrometric investigation of ammonium ion complexes with anomeric 2,3-O-isopropylidene-1alpha- and -1beta-D-ribofuranosyl azides: anomeric and kinetic isotope effects in ammonium affinities.

[Methanol + ammonium acetate] solutions of anomeric 2,3-O-isopropylidene-1alpha- and 1beta-ribofuranosyl azides were investigated by electrospray ionization mass spectrometry (ESI-MS). The compounds included d6-labeled and/or unlabeled isopropylidene groups that enable the identification of peaks characteristic of the ammonium-attached monomeric (MNH4(+)), ammonium-bound homodimeric ([M]2NH4(+)) and heterodimeric ([MNH4M1](+)) complex ions in ESI mass spectra of solutions of a pair of compounds. The intensities of the product ion peaks obtained by the collisionally activated ammonium-bound dimeric ions are related to the secondary isotope effect k(alpha)/k(alphad6) = 0.88 and k(beta)/k(betad6) = 1.25 or to isotope plus anomeric effects k(alpha)/k(betad6) = 1.43 and k(beta)/k(alphad6) = 0.59 in the ammonium affinities of these compounds. The calculations of solely anomeric effects in the ammonium affinities of alpha and beta anomeric compounds obtained from the data presented previously give two series of values: k(alpha)/k(beta) = (k(alpha)/k(alphad6))(k(alphad6)/k(beta)) = 1.49 and k(alphad6)/k(betad6) = (k(alphad6)/k(beta))(k(beta)/k(betad6)) = 2.12 or k(alpha)/k(beta) = (k(alpha)/k(betad6))(k(betad6)/k(beta)) = 1.14 and k(alphad6)/k(betad6) = (k(alphad6)/k(alpha))(k(alpha)/k(betad6)) = 1.63. The disparities of these results indicate the different structures of hydrogen bonding in ammonium-bound dimeric complexes which decompose to monomeric ions with different rate constants. Comparison of experimental results obtained by the qualitative approach of the kinetic method and ammonium affinities of these compounds calculated by the semi-empirical molecular orbital method (AM1) show that the [MNH4M1](+) dimeric complex ions dissociate to the most stable MNH4(+) and M1NH4(+) monomeric ions. The obtained relative order of ammonium affinities of these compounds is: alphad6 > alpha > beta > betad6.

Journal Article↗
PubMed2005

Use of a stopped-flow technique for investigation and determination of thiourea and its N-methyl derivatives as inducers of the iodine-azide reaction.

A stopped-flow technique has been used to investigate the behaviour of 2-thiourea, 1-methyl-2-thiourea, 1,3-dimethyl-2-thiourea, and 1,1,3,3-tetramethyl-2-thiourea in the induced iodine-azide reaction. This technique enables the progress of the reaction to be followed by monitoring the decrease in the absorbance of the iodine-starch complex at 595 nm. The effect of the concentration of the reagents on the rate of the reaction was investigated and a kinetic method for determination of the compounds is proposed. 2-Thiourea, 1-methyl-2-thiourea, and 1,3-dimethyl-2-thiourea can be determined in the range 3-75 micromol L(-1) and 1,1,3,3-tetramethyl-2-thiourea in the range 2-200 micromol L(-1).

Journal Article↗
PubMed1998

Azide accelerates the decay of M-intermediate of pharaonis phoborhodopsin.

Natronobacterium pharaonis has retinal proteins, one of which is pharaonis phoborhodopsin, abbreviated as ppR (or called pharaonis sensory rhodopsin II, psR-II). This pigment protein functions as a photoreceptor of the negative phototaxis of this bacterium. On photoexcitation ppR undergoes photocycling; the photoexcited state relaxes in the dark and returns to the original state via several intermediates. The photocycle of ppR resembles that of bR except in wavelengths and rate. The cycle of bR is completed in 10 ms while that of ppR takes seconds. The Arrhenius analysis of M-intermediate (ppR(M)) decay which is rate-limiting revealed that the slow decay is due to the large negative activation entropy of ppR. The addition of azide increases the decay rate 300-fold (at pH 7); Arrhenius analysis revealed decreases in the activation energy (activation enthalpy) and a further decrease in the activation entropy.

Journal Article↗
PubMed2001

Addition of small molecules by Zn(II) and Cu(II) dinuclear complexes obtained by an amino-phenolic ligand. Crystal structures of the dinuclear zinc complex assembling butanolate and azide anions.

The coordination properties of the ligand 2,6-bis-[[bis-(2-aminoethyl)-amino]methyl]-phenol (L) toward the zinc ion were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). L forms mono- and dinuclear complexes with zinc; the stable dinuclear complexes are practically the only existing species using L/Zn(II), molar ratio of 1:2. In these species, each dien subunit binds one zinc ion, while the phenolate moiety bound to both ions allows the two metal centers to be in close proximity with an incomplete coordination environment. The role of this metal-metal distance in binding secondary ligands was investigated for the dinuclear systems 2Zn/L and 2Cu/L by potentiometric (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)) and NMR experiments in aqueous and methanol solution with a series of small guests having nitrogen donor atoms. The coordination sphere of the two metals was completed by adding 1 equiv of only those guests, which showed at least two contiguous donor atoms or two lone pairs on the same atom, to exactly fit the metal-metal distance without modifying the metal cluster. To do this, the imidazole molecule which shows the highest addition constants to the [M(2)H(-1)L](3+) species probably forms a mu-1,1-amino. These results are in agreement with the two crystal structures reported herein [Zn(2)(H(-1)L)(CH(3)CH(2)CH(2)CH(2)O)](ClO(4))(2) (space group P2(1)nb, a = 11.483(5), b = 14.166(5), c = 18.279(5) A, V = 2973(19) A(3), Z = 4, R = = 0.0701, wR2 = 0.1611) and [Zn(2)(H(-1)L)N(3)](ClO(4))(2) (space group C 2/c, a = 14.460(3), b = 12.814(3), c = 14.875(3) A, beta = 105.35(2) degrees, V = 2658(10) A(3), Z = 4, R = 0.0783, wR2 = 0.1806). In fact, these structures display a butanolate or azide guest linked to both Zn(II) ions of the dinuclear complex, resulting in a mu-1,1-oxo and mu-1,1-azido bridge, respectively.

Journal Article↗
PubMed2003

Reactions of tris(amino)phosphines with arylsulfonyl azides: product dependency on tris(amino)phosphine structure.

The Staudinger reaction of N(CH2CH2NR)3P [R = Me (1), Pr (2)] with 1 equiv of N3SO2C6H4Me-4 gave the ionic phosphazides [N(CH2CH2NR)3PN][SO2C6H4Me-4] [R = Me (3), R = Pr (5a)], and the same reaction of 2 with N3SO2C6H2Me3-2,4,6 gave the corresponding aryl sulfinite 5b. On the other hand, the reaction of 1 with 0.5 equiv of N3SO2Ar (Ar = C6H4Me-4) furnished the novel ionic phosphazide [[N(CH2CH2NMe)3P]2(mu-N3)][SO2Ar] (6). Data that shed light on the mechanistic pathway leading to 3 were obtained by low temperature 31P NMR spectroscopy. A crystal and molecular structure analysis of the phosphazide sulfonate [N(CH2CH2NMe)3PN3][SO3C6H4Me-4] (4), obtained by atmospheric oxidation of 3, indicated an ionic structure, the cationic part of which is stabilized by a transannular P-N bond. A crystal and molecular structure analysis of 6 also indicated an ionic structure in which the cation features two untransannulated N(CH2CH2NMe)3P cages bridged by an azido group in an eta 1: mu: eta 1 fashion. The reaction of P(NMe2)3 with N3SO2Ar (Ar = C6H4Me-4) in a 1:0.5 molar ratio furnished [[(Me2N)3P]2(mu-N3)][SO2-Ar] (11) in quantitative yield. On the other hand, the same reaction involving a 1:1 molar ratio of P(NMe2)3 and N3SO2Ar produced a mixture of 11, [(Me2N)3PN3][SO2Ar] (12), and the iminophosphorane (Me2N)3P=NSO2Ar (10). In contrast, the bicyclic tris(amino)phosphines MeC(CH2NMe)3P (7) and O=P(CH2NMe)3P (8) reacted with N3SO2-Ar (Ar = C6H4Me-4) to give the iminophosphorane MeC(CH2NMe)3P=NSO2Ar (14) (structured by X-ray means) and O=P(CH2NMe)3P=NSO2Ar (16) via the intermediate phosphazides MeC(CH2NMe)3PN3SO2Ar (13) and O=P(CH2NMe)3PN3SO2Ar (15), respectively. The variety of products obtained from the reactions of arylsulfonyl azides with proazaphosphatranes (1 and 2), acyclic P(NMe2)3, bicyclic tris(amino)phosphines 7 and 8 are rationalized in terms of steric and basicity variations among the phosphorus reagents.

Journal Article↗
PubMed2004

Structure of two azide salts of a copper(II) macrocycle and magnetic properties of Cu(14ane)Cu(N3)4.

Synthesis of azide complexes with the copper(II) macrocycle complex Cu(14ane)(2+) (where 14ane = 1,4,8,11-tetraazacyclothetradecane) has yielded two compounds. Cu(14ane)Cu(N(3))(4) contains micro(1,3)-azido bridged chains of Cu(14ane)(2+) cations and Cu(N(3))(4)(2)(-) anions. Magnetic studies reveal the presence of ferromagnetic interactions within the chains with J/k = 0.635(4) K. [Cu(14ane)N(3)]BF(4) contains [Cu(14ane)N(3)]+ cations with elongated square pyramidal geometry. The BF(4)(-) anions are weakly coordinated in the sixth coordination site of the cations.

Journal Article↗
PubMed2004

Unprecedented low Cu-N(azide)-Cu angles in end-on double azido bridged copper(II) complex.

A rare asymmetric end-on double azido-bridged copper(II) complex has been synthesized and characterized structurally and magnetically. The Cu-N(azide)-Cu angle in this complex is calculated to be 89.1 degrees. This is unusually low in comparison to the same angle in other end-on azido-bridged binuclear complexes reported so far. Though a strong ferromagnetic interaction between the metal centers is expected in the complex, the coupling has actually been found to be antiferromagnetic, instead.

Journal Article↗
PubMed2003

The first azide(mu1,1)-bridged binuclear cobalt(II)-imino nitroxide complex with ferromagnetic behavior.

The first azide(mu1,1)-bridged binuclear cobalt(II) complex with a chelated imino nitroxide radical, [Co2(immepy)2(N3)(4)].2EtOH, was structurally and magnetically characterized, where immepy = 4,4,5,5-tetramethyl-2-(6'-methyl-2'-pyridyl) imidazoline-1-oxyl. Five nitrogen atoms complete the coordination sphere of the Co(II) ion, showing a distorted trigonal bipyramid geometry. Two N(3)(-) anions act as bridges between cobalt ions in the mu1,1 coordination mode, resulting in a binuclear structure with an inversion center. Magnetic studies show that ferromagnetic couplings occurred between the adjacent cobalt(II) ions through N3(-)(mu1,1)) bridges, and antiferromagnetic couplings between the cobalt(II) ions and organic radicals.

Journal Article↗
PubMed2004

Reaction of AgN3 with SOCl2: evidence for the formation of thionyl azide, SO(N3)2.

Pure thionyl azide SO(N(3))(2), which is the only gaseous reaction product, has been generated in a vacuum by the heterogeneous reaction of SOCl(2) vapor with AgN(3) at room temperature at a SOCl(2) vapor pressure of 1 x 10(-3) Torr. Evidence for the formation of SO(N(3))(2) is given by on line photoelectron spectroscopy (PES) combined with outer valence Green's function (OVGF) calculations with the 6-311++G(2df) basis set. The good agreement between the PES experiment and the OVGF calculation shows that SO(N(3))(2) has C(1) symmetry. The first ionization energy of SO(N(3))(2) is 10.18 eV.

Journal Article↗
PubMed2005

Novel 3-D framework nickel(II) complex with azide, nicotinic acid, and nicotinate(1-) as coligands: hydrothermal synthesis, structure, and magnetic properties.

The hydrothermal reaction of Ni(NO3)2, NaN3, and nicotinic acid (Hnic) yielded a 3-D supramolecular framework complex, [Ni(1.5)(N3)(nic)2(Hnic)]n (1) with unusual magnetic properties. In 1, Hnic and nic-1 coexist and show different coordination modes (mu2-Hnic-N,O, mu2-nic-N,O, and mu3-nic-N,O,O bridging NiII ions), and azide groups adopt mu-1,1 (EO) bridging mode linking NiII ions with an unusual Ni-N-Ni angle.

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