Evaluation of photoinduced changes in stability constants for metal-ion complexes of crowned spirobenzopyran derivatives by electrospray ionization mass spectrometry

The photoinduced changes of metal-ion complexing ability of crowned spirobenzopyran derivatives were studied by using electrospray ionization mass spectrometry (ESI-MS). Stability constants for the complexation with various metal ions in methanol under visible-irradiation conditions were determined for the first time by ESI-MS. It was found that the stability constants of crowned bis(spirobenzopyran) derivatives with metal ions are decreased dramatically by visible irradiation due to the disappearance of powerful ionic interaction between phenolate anion(s) of the merocyanine form of their spirobenzopyran moiety and a metal ion bound to their crown ether moiety, and the decrease in the stability constants is more pronounced for the multivalent metal-ion complexes. A theoretical consideration was also made to attain reliable values of stability complexes for metal-ion complexes of crown compounds.     

Study of non-covalent complexation between catechin derivatives and peptides by electrospray ionization mass spectrometry

The recent development of electrospray ionization mass spectrometry (ESI-MS) has allowed its use to study molecular interactions driven by non-covalent forces. ESI-MS has been used to detect non-covalent complexes between proteins and metals, ligands and peptides and interactions involving DNA, RNA, oligonucleotides and drugs. Surprisingly, the study of the interaction between polyphenolic molecules and peptides/proteins is still an area where ESI-MS has not benefited. With regard to the important influence of these interactions in the biological and food domains, ESI-MS was applied to the detection and the characterization of soluble polyphenol-peptide complexes formed in model solution. The ability to observe and monitor the weak interactions involved in such macromolecular complexation phenomena was demonstrated for monomeric and dimeric flavonoid molecules (catechin-derived compounds) largely encountered in plants and plant derived products. Intact non-covalent polyphenol-peptide complexes were observed by ESI-MS using different experimental conditions. Utilizing mild ESI interface conditions allowed the detection of 1 : 1 polyphenol-peptide complexes in all tested solutions and 2 : 1 complexes for the dimers and galloylated polyphenols (flavanols). These results show that there is a preferential interaction between polymerized and/or galloylated polyphenols and peptide compared with that between monomeric polyphenols and peptides. Thus, ESI-MS shows potential for the study of small polyphenolic molecule-peptide interactions and determination of stoichiometry.     

“Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

The effect of electrostatic interactions on the complexation of ionic guests by charged β-cyclodextrin (βCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of βCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino βCD derivatives is also presented.     

A study of C-F...M(+) interaction: metal complexes of fluorine-containing cage compounds

The C-F...M(+) interaction was investigated by observation of the NMR spectroscopic changes and complexation studies between metal cations and the cage compounds 1 and 2 which have fluorobenzene units as donor atoms. As a result, the interaction was detected with all of the metal cations which form complexes with 1 and 2. The stability of the complexes of 1 and 2 was determined by the properties of the metal cations (ionic radii and degree of hydrolysis), not by the hard-soft nature of the cations. Crystallographic analyses of Tl(+) subset 1 and La(3+) subset 2 provided structural information (interatomic distances and bond angles), and the bond strengths, C-F...M(+), O...M(+), and N...M(+), were estimated by Brown's equation based on the structural data. Short C-F...Tl(+) (2.952-3.048 A) distances were observed in the complex Tl(+) subset 1. The C-F bond lengths in the complexes, Tl(+) subset 1 and La(3+) subset 2, are elongated compared to those of the metal-free compounds. Interestingly, no solvent molecules including water molecules were coordinated to La(3+) in the La(3+) subset 2. The stabilization energy of cation-dipole interaction was calculated on the basis of the data from X-ray crystallographic analysis, and it is roughly consistent with the (-)Delta H values estimated in solution. Thus, the C-F...M(+) interaction can be expressed by the cation-dipole interaction. This result explains the fact that compound 1 which has fluorine atom as hard donor strongly binds soft metals such as Ag(+) and Tl(+). Furthermore, it was concluded that the fluorobenzene unit has a poor electron-donating ability compared to that of ether oxygen or amine nitrogen, and thus the ratio of the coordination bond in C-F...M(+) is small. The specific and remarkable changes in the (1)H, (13)C, and (19)F NMR spectra were observed accompanied by the complexation between M(+) and the hosts 1 and 2. These spectral features are important tools for the investigation of the C-F...M(+) interaction. Furthermore, F.Tl(+) spin couplings were observed at room temperature in the Tl(+) subset 1, 2 (J(F-Tl) = 2914 Hz for Tl(+) subset 1 and 4558 Hz for Tl(+) subset 2), and these are clear and definitive evidence of the interaction.     

Correlation of Solution and Gas Phase Complexation Assessed by Electrospray Ionization Mass Spectrometry: Application to One-, Two-, and Three-Ring Macrocycles

Electrospray ionization mass spectrometry (ESI-MS) was used to probe multiple cation complexation by C(12)H(25)(CH(2))(12)(CH(2))(12)C(12)H(25), 2, and <18N>CH(2)C(6)H(4)CH(2), 3. Complexation of two cations (2Na(+), 2 K(+), or Na(+) and K(+)) by 3 and three cations by 2 (3 Na(+), 3 K(+), and mixtures) as well as mixed proton-metallic cation complexes of both were observed. The K(+)/Na(+) cation-binding selectivity of 18-crown-6 was studied by ESI-MS of a methanol solution, and the selectivity profile was favorably compared with data obtained previously by ion-selective electrode techniques in the same solvent.     

Equilibrium studies on chromium(III) complexes of salicylic acid and salicylic acid derivatives in aqueous solution

The complexes of chromium(III) ion formed by salicylic acid, SA(H(2)L), and its derivatives (H(2)L): 5-nitrosalicylic acid (5-NSA), 5-sulphosalicylic acid (5-SSA) were investigated by means of potentiometry and spectroscopy, at 25 degrees C and in ionic strength of 0.1 M KNO(3) and 0.1 M KCl, respectively. Over the acidic pH range, the coordination of Cr(III) ion to SA and its derivatives in 1 : 1 mole ratio occurs, CrL(+) type complex is formed. In the excess of ligand, the coordination of the second ligand molecule is somewhat hindered; as a result CrL(HL) type complex occurs. Their existences were verified and their formation constants were determined. At near neutral pH, CrL(OH) and CrL(HL)(OH)(-) type hydroxo complexes formed by hydrolytic equilibria and their formation constants were also defined. The stabilities of Cr(III) complexes of SA and its derivatives decrease in the following order: SA>5-SSA>5-NSA. The formation constants of Cr(III) complexes of SA and its derivatives are in comparable ranges with the corresponding complexes of the 2,x-dihydroxybenzoic acid (2,x-DHBA) of Cr(III) ion. The stabilities of SA complexes for V(IV), Cr(III) and Fe(III) ions that have similar ionic radii, increase in the order VOL相似文献   

The significance of the alkene size and the nature of the metal ion in metal-alkene complexes: a theoretical study

Cation interactions with π-systems are a problem of outstanding contemporary interest and the nature of these interactions seems to be quite different for transition and main group metal ions. In this paper, we have systematically analyzed the contrast in the bonding of Cu(+) and main group metal ions. The molecular structures and energetics of the complexes formed by various alkenes (A = C(n)H(2n), n = 2-6; C(n)H(2n- 2), n = 3-8 and C(n)H(2n + 2), n = 5-10) and metal ions (M = Li(+), Na(+), K(+), Ca(2+), Mg(2+), Cu(+) and Zn(2+)) are investigated by employing ab initio post Hartree-Fock (MP2/6-311++G**) calculations and are reported in the current study. The study, which also aims to evaluate the effect of the size of the alkyl portion attached to the π-system on the complexation energy, indicates a linear relationship between the two. The decreasing order of complexation energy with various metal ion-alkene complexes follows the order Zn(2+)-A > Mg(2+)-A > Ca(2+)-A > Cu(+)-A > Li(+)-A > Na(+)-A > K(+)-A. The increased charge transfer and the electron density at (3,-1) intermolecular bond critical point corroborates well with the size of the π-system and the complexation energy. The observed deviation from the linear dependency of the Cu(+)-A complexes is attributed to the dπ→π* back bonding interaction. An energy decomposition analysis via the reduced variational space (RVS) procedure was also carried out to analyze which component among polarization, charge transfer, coulomb and exchange repulsion contributes to the increase in the complexation energy. The RVS results suggest that the polarization component significantly contributes to the increase in the complexation energy when the alkene size increases.     

Pre-association of polynuclear platinum anticancer agents on a protein, human serum albumin. Implications for drug design

The interactions of polynuclear platinum complexes with human serum albumin were studied. The compounds examined were the "non-covalent" analogs of the trinuclear BBR3464 as well as the dinuclear spermidine-bridged compounds differing in only the presence or absence of a central -NH(2)-(+) (BBR3571 and analogs). Thus, closely-related compounds could be compared. Evidence for pre-association, presumably through electrostatic and hydrogen-bonding, was obtained from fluorescence and circular dichroism spectroscopy and Electrospray Ionization Mass Spectrometry (ESI-MS). In the case of those compounds containing Pt-Cl bonds, further reaction took place presumably through displacement by sulfur nucleophiles. The implications for protein pre-association and plasma stability of polynuclear platinum compounds are discussed.     

Characterization of noncovalent complexes of antimalarial agents of the artemisinin-type and Fe(III)-heme by electrospray mass spectrometry and collisional activation tandem mass spectrometry

In this study, we demonstrate, using electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation tandem mass spectrometry (ESI-MS/CID/MS), that stable noncovalent complexes can be formed between Fe(III)-heme and antimalarial agents, i.e., quinine, artemisinin, and the artemisinin derivatives, dihydroartemisinin, alpha- and beta-artemether, and beta-arteether. Differences in the binding behavior of the examined drugs with Fe(III)-heme and the stability of the drug-heme complexes are demonstrated. The results show that all tested antimalarial agents form a drug-heme complex with a 1:1 stoichiometry but that quinine also results in a second complex with the heme dimer. ESI-MS performed on mixtures of pairs of various antimalarial agents with heme indicate that quinine binds preferentially to Fe(III)-heme, while ESI-MS/CID/MS shows that the quinine-heme complex is nearly two times more stable than the complexes formed between heme and artemisinin or its derivatives. Moreover, it is found that dihydroartemisinin, the active metabolite of the artemisinin-type drugs in vivo, results in a Na(+)-containing heme-drug complex, which is as stable as the heme-quinine complex. The efficiency of drug-heme binding of artemisinin derivatives is generally lower and the decomposition under CID higher compared with quinine, but these parameters are within the same order of magnitude. These results suggest that the efficiency of antimalarial agents of the artemisinin-type to form noncovalent complexes with Fe(III)-heme is comparable with that of the traditional antimalarial agent, quinine. Our study illustrates that electrospray ionization mass spectrometry and collision-induced dissociation tandem mass spectrometry are suitable tools to probe noncovalent interactions between heme and antimalarial agents. The results obtained provide insights into the underlying molecular modes of action of the traditional antimalarial agent quinine and of the antimalarials of the artemisinin-type which are currently used to treat severe or multidrug-resistant malaria.     

Comparison of cyclodextrin-barbiturate noncovalent complexes using electrospray ionization mass spectrometry and capillary electrophoresis

Various noncovalent complexes between native and derivatized cyclodextrins (CDs) and barbiturates were studied using capillary electrophoresis (CE) and electrospray ionization mass spectrometry (ESI-MS). This paper involves the study of four aspects of CD-barbiturate noncovalent inclusion complexes. The first study focused on determining the formation of CD-barbiturate inclusion complexes in ESI-MS. This determination was accomplished by the comparison of migration data from CE with ESI-MS inclusion complex peak abundances, which were found to be complementary. The second study found the possibility of predicting native beta-CD mediated CE elution orders for barbiturates using data from ESI-MS. A third study focused on the formation of barbiturate inclusion complexes with derivatized beta-CD and gamma-CD. As part of this study, the effect of the extent of side chain substitution on native CD complexation behavior was investigated. The results indicated that the number of side chains on the CD does not affect the formation of barbiturate complexes with the hydrophobic CD cavity. Finally, a comparison of the hydroxypropyl-beta-CD-barbiturate and hydroxypropyl-gamma-CD-barbiturate complexes in CE and ESI-MS was made to study the relationship between strength of drug-CD binding and enantioresolution. The results from the above studies indicated that the gas phase and the solution state complexes showed comparable behavior indicating that similar interactions played a role in stabilizing these complexes. While it was possible to use the ESI-MS data to determine drug binding to the CDs, it was not possible to predict whether a separation of the enantiomers of a chiral barbiturate would occur. However, the ESI-MS data could be used to eliminate certain CDs from consideration as chiral selectors.     

Guest-dependent complexation of triptycene-based macrotricyclic host with paraquat derivatives and secondary ammonium salts: a chemically controlled complexation process

The triptycene-based macrotricyclic host containing two dibenzo-[24]-crown-8 moieties has been found to form stable 1:1 or 1:2 complexes in different complexation modes with different functional paraquat derivatives and secondary ammonium salts in solution and in the solid state. Consequently, the alkyl-substituted paraquat derivatives thread the lateral crown cavities of the host to form 1:1 complexes. It was interestingly found that the paraquat derivatives containing two beta-hydroxyethyl or gamma-hydroxypropyl groups form 1:2 complexes, in which two guests thread the central cavity of the host. Other paraquat derivatives containing terminal hydroxy, methoxy, 9-anthracylmethyl, and amide groups were included in the cavity of the host to form 1:1 complexes. Moreover, the host also forms a 1:2 complex with two 9-anthracylmethylbenzylammonium salts, in which the 9-anthracyl groups were selectively positioned outside the lateral crown cavities. The competition complexation process between the host and two different guests (the propyl-substituted paraquat derivative and a dibenzylammonium salt) could be chemically controlled.     

Speciation of M+3-hydroxypyrone chelation complexes by electrospray ionization ion trap and Fourier transform ion cyclotron resonance mass spectrometry

Kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone) is known to have a high affinity for transition metals, and it and its derivatized cogeners are used both analytically and clinically. The interactions between kojic acid (KA) and eleven +3 metals (Al(+3), As(+3), Cr(+3), Ga(+3), Fe(+3), In(+3), Yb(+3), Y(+3), Gd(+3), Nd(+3), La(+3)) were examined by electrospray ionization mass spectrometry (ESI-MS) using an ion trap in an aqueous medium. For a subset of five ions, Fourier transform ion cyclotron resonance (FTICR)-MS was conducted to provide accurate mass confirmation of peak assignments for metals having clustering of abundant isotopes. KA readily formed complexes with all the metal ions tested. The most common complexes observed were ML(3)H(+) and M(2)L(5). Different behavior was seen for small and large ionic radius ions, with a relative cut-off between In(+3) ( approximately 80 pm) and Yb(+3) ( approximately 87 pm); a striking trend in % collision energy vs. cluster complexity was revealed. The KA-Cr(+3)complex shows a high affinity for H(2)O molecules in the gas phase, whilst In(+3) shows a preference for dimetal complexes and Y(+3) a deviant behavior when complexed to two neutrals.     

Electrospray mass spectrometric and DFT study of substituent effects in Ag(+) complexation to polycyclic aromatic hydrocarbons (PAHs)

Complexation of Ag(i) cation to a series of substituted anthracenes (AN), phenanthrenes (PH), pyrenes (PY) and cyclopenta[a]phenanthrenes (CPaPH) was studied in competitive experiments by allowing PAHs to react in pairs with AgOTf. The resulting complexes were examined by electrospray mass spectrometry (ES-MS) to determine relative abundances of the corresponding monomeric and dimeric complexes. Based on this data a sequence of complexation ability rankings was derived for each group. Among the substituents examined, a -COMe group when placed at the meso position in AN and PH, or at the C-1 in PY is most effective in Ag(+) complexation, whereas an -NO(2) group is least efficient. Methyl groups at the meso positions are better than in the terminal rings. For the CPaPH series, bay region substitution (methyl and alkoxy) have limited effect as does carbonyl substitution in the annelated CP ring. In the PY series, a -COPh or a -CH(Me)OH group at C-1 is as efficient as -COMe. Based on extensive potential energy searches, four types of complexation modes were identified by B3LYP/LANL2DZ calculations involving Ag(+) complexation to -NO(2) oxygens, to -COMe or to -OH and a peri-carbon, to just one ring carbon, or by bridging two ring carbons. Among these modes, the first two are most favorable. The energetic preferences were rationalized with charge decomposition analysis (CDA). Effect of Ag(+) complexation on relative aromaticity in various rings was examined by NICS (nucleus independent chemical shift) in two representative cases. Structures and energies of the acetyl pyrene-Ag(+)-pyrene hetero-dimer and acetyl pyrene-Ag(+)-acetyl pyrene homo-dimer complexes were determined with the same model. These complexes have sandwich structures.     

Synthesis of electroactive multinuclear dipyrrinato complexes and Fe(III) assisted formation of α-alkoxy substituted 5-ferrocenyldipyrromethenes

The synthesis and characterization of multinuclear complexes [Pd(acac)(fcdpm)] (1), [Pd(fcdpm)(2)] (2), [Co(acac)(fcdpm)(2)] (3), [Co(fcdpm)(3)] (4) and α-alkoxy derivatives [α-OMe-fcdpm] (5), [α-OEt-fcdpm] (6), [α-OPr(n)-fcdpm] (7) and [α-OBu(n)-fcdpm] (8) (fcdpm = 5-ferrocenyldipyrromethene; acac = acetylacetone) have been described. Formation of alkoxy derivatives 5-8 takes place from highly selective Fe(III) mediated alkoxylation of fcdpm in alcohol. It has been established that yield of α-alkoxy derivatives depend on the alcohol chain length. The compounds under study have been characterized by elemental analyses, spectral (IR, (1)H, (13)C NMR, ESI-MS, UV-vis) and electrochemical studies (CV and DPV). Structures of 1, 3 and 5 have been verified by X-ray single crystal analyses. Structural studies revealed distorted square planar and octahedral geometry about Pd(II) and Co(III) centres. All the compounds exhibited oxidation wave due to Fc/Fc(+) redox couple (0.34-0.36, 1-4; 0.24-0.25 V, 5-8).     

Determination of binding selectivities in host-guest complexation by electrospray/quadrupole ion trap mass spectrometry

The quantifiable relationship between the equilibrium solution composition and electrospray (ESI) mass spectral peak intensities of simple host-guest complexes was investigated. Specifically, host-guest complexes of simple crown ethers or glymes with alkali metals and ammonium ions were studied. Comparisons were made between the theoretical concentrations of host-guest complexes derived in solution from known stability constants and the peak intensities for the complexes observed by ESI mass spectrometry (ESI-MS). Two types of complexation experiments were undertaken. First, complexation of a single guest ion, such as an alkali metal, and two crown ethers was studied to evaluate the determination of binding selectivities. Second, complexation of two different guest ions by a single polyether host was also examined. In general, solvation was found to play an integral part in the ability to quantify binding selectivities by ESI-MS. The more similar the solvation energies of the two complexes in the mixture, the more quantifiable their binding selectivities by ESI-MS. In some cases, excellent correlation was obtained between the theoretically predicted selectivity ratios and the ESI mass spectral ratios, in particular when the ESI ratios were adjusted based on evaluation of ESI response factors for the various host-guest complexes.     

Functionalized gold nanoparticles as phosphorescent nanomaterials and sensors

Ligand-capped gold nanoparticles were synthesized by capping monothiol derivatives of 2,2'-dipyridyl onto the surface of Au nanoparticles (Au-BT). The average size of the metal core is around 4 nm, with a shell of approximately 340 bipyridine ligands around the Au nanoparticle. The high local concentration of the chelating ligands ( approximately 5 M) around the Au nanoparticle makes these particles excellent ion sponges, and their complexation with Eu(III)/Tb(III) ions yields phosphorescent nanomaterials. Absorption spectral studies confirm a 1:3 complexation between Eu(III)/Tb(III) ions and bipyridines, functionalized on the surface of Au nanoparticles. The red-emitting Au-BT:Eu(III) complex exhibits a long lifetime of 0.36 ms with six line-like emission peaks, whereas the green-emitting Au-BT:Tb(III) complex exhibits a lifetime of 0.7 ms with four line-like emission peaks. These phosphorescent nanomaterials, designed by linking BT:Eu(III) complexes to Au nanoparticles, were further utilized as sensors for metal cations. A dramatic decrease in the luminescence was observed upon addition of alkaline earth metal ions (Ca(2+), Mg(2+)) and transition metal ions (Cu(2+), Zn(2+), Ni(2+)), resulting from an isomorphous substitution of Eu(III) ions, whereas the luminescence intensity was not influenced by the addition of Na(+) and K(+) ions. Direct interaction of bipyridine-capped Au nanoparticles with Cu(2+) ions brings the nanohybrid systems closer, leading to the formation of three-dimensional superstructures. Strong interparticle plasmon interactions were observed in these closely spaced Au nanoparticles.     

Effect of counter-ion on the thermotropic liquid crystal behaviour of bis(alkyl)-tris(imidazolium salt) compounds

Recently, new thermotropic ionic liquid crystals (LCs) with a hexyl-linked tris(imidazolium bromide) core and two terminal alkyl chains were synthesised and characterised. To explore the effect of different counter-ions on the LC behaviour of this system, derivatives with BF₄^? and Tf₂N^? counter-ions were prepared and analysed. Five of the BF₄^? derivatives were found to exhibit thermotropic LC behaviour. The 12-, 14- and 16-carbon tail BF₄^? compounds form SmA phases. The 18- and 20-carbon tail homologues form what appears to be a smectic phase but are weakly mesogenic and harder to characterise. Only two of the Tf₂N^? derivatives exhibited mesogenic behaviour. The 18-carbon tail Tf₂N^? compound forms an as-yet unidentified, highly periodic smectic phase with positional order while the 20-carbon tail homologue forms a periodic SmA phase. The Tf₂N^? mesogens have much lower clearing points even though their LC phases have more order than the Br^? and BF₄^? mesogens. X-ray diffraction showed that these mesogens have different amounts of tail interdigitation between the smectic layers depending on the counter-ion present. Atomistic molecular dynamics simulations indicated that counter-ion size plays an important role in defining the density of the ionic region, which in turn affects the amount of interdigitation in the smectic phases.     

A new class of arylpiperazine derivatives: the library synthesis on SynPhase lanterns and biological evaluation on serotonin 5-HT(1A) and 5-HT(2A) receptors

An efficient solid-supported method for the synthesis of a new class of arylpiperazine derivatives containing amino acid residues has been developed. A 72-membered library was synthesized on SynPhase Lanterns functionalized by a BAL linker. A one-pot cleavage/cyclization step of aspartic and glutamic acid derivatives yielded succinimide- and pyroglutamyl-containing ligands (chemsets 9 and 10). The library representatives under study showed different levels of affinity for 5-HT(1A) and 5-HT(2A) receptors (estimated K(i) = 24-4000 and 1-2130 nM, respectively). Several dual 5-HT(1A)/5-HT(2A) ligands were found, of which two (9(3,3) and 9(3,5)) displayed high 5-HT(2A) affinity comparable to that of the reference drug ritanserin. A set of individual fragment contributions for the prediction of 5-HT(1A) and 5-HT(2A) affinity of all the library members were defined on the basis of the Free-Wilson analysis of 26 compounds. An alkylarylpiperazine fragment had essentially the same impact on the affinity for both receptors, whereas different terminal amide fragments were preferred by 5-HT(1A) (chemset 17, R(2) = adamantyl) and 5-HT(2A) (chemset 9, R(2) = norborn-2-ylmethyl) binding sites.     

Synthesis and potentiometric analysis of organophosphorus metal complexones and complexonates based on 2-aminothiazole derivatives

Synthesis conditions of 4-phenyl-2-amidothiazolyl acetate and 2-thiourido-4-diethylphosphothiazole were developed, and the complexation capacity of these compounds in formation of mixed-ligand complexes was studied. The optimal conditions and thermodynamic parameters of the complexation process were determined. The potentiometric method was used to find thermodynamic parameters of the reactions of mixed-ligand complexation with copper(II) and lead(II) ions, the composition of the complexes being formed on the basis of 4-phenyl-2-aminothiazole and its phosphorylated derivatives was determined.     

Complexation of transition metals by 3-azidopropionitrile. An electrospray ionization mass spectrometry study

Most complexes of azides and transition metals involve the N(3)(-) azide anion as a ligand other than an organic azide. Complexes of organic azides with metals are involved in biological applications and in the deposition of nitrenes on metal surfaces, producing nitride layers for semi-conductors preparation; this makes the study of these interactions an important issue. This work describes a study of the complexation of nickel and cobalt by 3-azidopropionitrile by means of electrospray ionization mass spectrometry (ESI-MS). Complexes were obtained from solutions of NiCl(2) and CoCl(2) in methanol/water. In the case of nickel, other NiX(2) salts were investigated (where X = Br or NO(3)) and other solvents were also studied (notably ethanol/water). All complexes detected were single positively charged, with various stoichiometries, some resulted from the fragmentation of the ligand, the loss of N(2), and HCN being quite common. The most abundant cations observed were [Ni(II)AzAzX](+), where X = Cl, Br, NO(3). Some of the complexes showed solvation with methanol/ethanol/water. Metal reduction was observed in complexes where a radical was lost, resulting from the homolytic cleavage of a metal-nitrogen bond. Collision induced dissociation (CID) experiments followed by tandem mass spectrometry (MS-MS) analysis were not absolutely conclusive about the coordination site. However, terminal ions observed from the fragmentation routes were explained by a proposed gas-phase mechanism. Density functional theory calculations were carried out and provided structures for some complexes, pointing to the possibility of 3-azidopropionitrile acting as a mono- or a bidentate ligand.