Secondary Amine Sites Research Articles

Measurement of total amine site concentrations on bacterial cell surfaces using selective site-blocking and potentiometric titrations

Bacterial cell surface amine binding sites can form strong complexes with both toxic metal cations and anionic contaminants, thereby affecting the behavior of these contaminants in both natural and engineered systems. In this study, a novel approach was developed to measure the concentration of total amine sites on bacterial cell surfaces by combining selective site-blocking, potentiometric titrations and surface complexation modeling. Our controls show that the amine blocker sulfo-N-hydroxysulfosuccinimide acetate (SNHS) selectively reacts with primary and secondary amine sites but does not react with other binding sites on the bacterial cell surface. Amine site concentrations on bacterial cell surfaces, therefore, can be measured as the difference between the total site concentrations of un-blocked and SNHS-blocked bacterial samples. We measured amine site concentrations on Bacillus subtilis and Pseudomonas putida of 52 ± 5 and 78 ± 6 μmol/g, respectively, which account for 24% and 32% of the total binding sites on each bacterial surface. Our results suggest that amine sites can be present in relatively high concentrations on bacterial surfaces, and further studies that are focused on the role of cell surface amine sites on the transport and bioavailability of toxic metal cations and anionic contaminants are crucial.

Metal-Organic Frameworks as Versatile Heterogeneous Solid Catalysts for Henry Reactions.

Metal–organic frameworks (MOFs) have become one of the versatile solid materials used for a wide range of applications, such as gas storage, gas separation, proton conductivity, sensors and catalysis. Among these fields, one of the more well-studied areas is the use of MOFs as heterogeneous catalysts for a broad range of organic reactions. In the present review, the employment of MOFs as solid catalysts for the Henry reaction is discussed, and the available literature data from the last decade are grouped. The review is organized with a brief introduction of the importance of Henry reactions and structural properties of MOFs that are suitable for catalysis. The second part of the review discusses the use of MOFs as solid catalysts for the Henry reaction involving metal nodes as active sites, while the third section provides data utilizing basic sites (primary amine, secondary amine, amides and urea-donating sites). While commenting on the catalytic results in these two sections, the advantage of MOFs over other solid catalysts is compared in terms of activity by providing turnover number (TON) values and the structural stability of MOFs during the course of the reaction. The final section provides our views on further directions in this field.

Clay-Based Nanocomposites as Recyclable Adsorbent toward Hg(II) Capture: Experimental and Theoretical Understanding.

Here, we report the development of inorganic–organic hybrid nanocomposites through selective modification of the negative outer surfaces of halloysite nanoclays with two different organosilanes having primary or secondary amine sites to be explored them as novel and cost-effective adsorbents for the extraction of toxic inorganic contaminants from aqueous solution. They possess excellent selectivity for the adsorption of mercury, which shows monolayer molecular adsorption over the nanocomposites. The adsorption kinetics of Hg(II) is very fast and follows pseudo-second-order model compared to pseudo-first-order model. A combined experimental and theoretical study demonstrated that Hg(II) uptake by these nanocomposites is highly favorable and spontaneous up to 40 °C, and beyond this temperature, the uptake capacity gradually reduced. Temperature-dependent adsorption study exhibits endothermicity at low temperature (≤40 °C) and exothermicity beyond 40 °C. pH-dependent adsorption study showed their high uptake capacity until pH 7, which reduced at alkaline pH. All of the nanocomposites hold excellent adsorption capacity even at low concentration of adsorbate, along with multicycle sorption capability. The outstanding adsorption capacity as well as the easy synthetic route to achieve these nanocomposites may attract researchers to develop low-cost adsorbents to capture toxic metals, which in turn regulate the permissible limit of these toxic metals in drinking water.

Water Enhancement in CO2 Capture by Amines: An Insight into CO2–H2O Interactions on Amine Films and Sorbents

Water, a component in flue gas, plays a significant role in CO2 capture through a complex interaction between water molecules and adsorbed CO2 on amine sorbents. To determine how the H2O–CO2–amine interactions affect amine efficiency and the binding energy of adsorbed CO2, we used in situ infrared spectroscopy (IR) to determine the structure of adsorbed CO2 and H2O as well as their relations to adsorption/desorption kinetics and CO2 capture capacity on tetraethylenepentamine (TEPA) films and Class I amine (i.e., impregnated) sorbents. H2O enhanced amine efficiency of TEPA films and sorbents by increasing the accessibility of secondary amine sites to CO2 and promoting the formation of hydronium carbamate and carbamic acid. CO2 adsorbed on the surface of the TEPA film as a weakly adsorbed CO2 in the form of hydronium and ammonium–carbamate with a low IR intensity of hydrogen bonding (−OH···–OOC or −NH···–OOC) between hydronium/ammonium ions and carbamate ions. CO2 adsorbed on the middle layers (i.e., 0.2–0....

Nitric Oxide Releasing Polymeric Coatings for the Prevention of Biofilm Formation.

The ability of nitric oxide (NO)-releasing polymer coatings to prevent biofilm formation is described. NO-releasing coatings on (poly(ethylene terephthalate) (PET) and silicone elastomer (SE)) were fabricated using aminosilane precursors. Pristine PET and SE were oxygen plasma treated, followed by immobilisation of two aminosilane molecules: N-(3-(trimethoxysilyl)propyl)diethylenetriamine (DET3) and N-(3-trimethoxysilyl)propyl)aniline (PTMSPA). N-diazeniumdiolate nitric oxide donors were formed at the secondary amine sites on the aminosilane molecules producing NO-releasing polymeric coatings. The NO payload and release were controlled by the aminosilane precursor, as DET3 has two secondary amine sites and PTMSPA only one. The antibacterial efficacy of these coatings was tested using a clinical isolate of Pseudomonas aeruginosa (PA14). All NO-releasing coatings in this study were shown to significantly reduce P. aeruginosa adhesion over 24 h with the efficacy being a function of the aminosilane modification and the underlying substrate. These NO-releasing polymers demonstrate the potential and utility of this facile coating technique for preventing biofilms for indwelling medical devices.

The Role of Water in CO2 Capture by Amine

An in situ IR study unraveled that adsorption of CO2 on 20 μm TEPA film at 50 °C followed a zwitterion-intermediate pathway: zwitterion → ammonium carbamate. H2O in the mixed TEPA/H2O (5:1) film decreased the rate of CO2 adsorption but increased the amine efficiency. CO2 preferentially adsorbs on primary amine sites and H2O on secondary amine sites. The presence of H2O promotes the formation of carbamic acid and produces a broad IR band centered at 2535 cm–1, which can be assigned to the ν(O–H) of hydronium carbamate, −NCOO–···H–OH2+. The broadness of this 2535 cm–1 band ranging from 2100 to 2800 cm–1 persists at 120 °C. These broad components of the band can be ascribed to ν(N–H) in hydrogen-bonded ammonium carbamate, a R–NH3+/R1R2–NH2+···–NCOO– moiety. The binding strength of adsorbed species on the TEPA film increases in the order adsorbed H2O < carbamic acid < ammonium carbamate < hydrogen-bonded water/ammonium carbamate.

The Nature of Adsorbed Carbon Dioxide on Immobilized Amines during Carbon Dioxide Capture from Air and Simulated Flue Gas

AbstractThe structure and nature of adsorbed species on solid amine sorbent under various CO2 concentrations from ambient air (0.04 vol %) to an CO2/air stream (15 vol %) have been studied by using in situ IR spectroscopy. The in situ IR study (i) provided evidence to support the zwitterion pathway for CO2 adsorption/desorption and (ii) allowed the determination of the nature of the adsorbed species. The IR‐observable zwitterion was deprotonated to ammonium carbamate and carbamic acid reversibly. CO2 adsorbs on the primary amine site as a strongly adsorbed species in the form of ammonium carbamate and on the secondary amine site as a weakly adsorbed species in the form of carbamic acid. Another form of weakly adsorbed species could be ammonium carbamate on the secondary amine. An increase of the concentration of CO2 in the stream increased the CO2 capture capacity, the fraction of strongly adsorbed CO2, and the binding energy of adsorbed species. A concentration of 400 ppm CO2 in air competes over 0.5 % of water vapor for adsorption on Class I amine sorbents.

The Structure of Adsorbed Species on Immobilized Amines in CO2 Capture: An in Situ IR Study

The nature and structure of adsorbed CO2 on immobilized amine sorbent in the presence and absence of H2O vapor have been studied by in situ infrared spectroscopy. CO2 adsorbed on the primary amine as ammonium carbamate and on the secondary amine as carbamic acid. Adsorbed H2O mainly on secondary amine enhanced CO2 capture capacity by increasing accessibility of amine sites and promoting the formation of carbamic acid. The binding strength of the adsorbed species increased in the order: carbamic acid < adsorbed H2O < paired carbamic acid; ammonium carbamate < ammonium chloride. Flowing argon over the amine sorbent at 50 °C removed weakly adsorbed H2O and carbamic acid from the secondary amine sites. Raising temperature is required to completely regenerate sorbent by removing strongly adsorbed ammonium carbamate from the primary amine sites and paired carbamic acid. The results of this study clarify the role of H2O vapor in amine-sorbents for CO2 capture and provide a molecular basis for the design of the s...

Assessing Atmospheric CO2 Entrapped in Clay Nanotubes using Residual Gas Analyzer.

A residual gas analyzer (RGA) coupled with a high-vacuum chamber has been explored to measure atmospheric CO2 entrapped in aminosilane-modified clay nanotubes. Ambient CO2 uptake efficacy together with stability of these novel adsorbents composed of both primary and/or secondary amine sites has been demonstrated at standard ambient temperature and pressure. The unprecedented sensitivity and accuracy of the RGA-based mass spectrometry technique toward atmospheric CO2 measurement has been substantiated with a laser-based optical cavity-enhanced integrated cavity output spectroscopy. The adsorption kinetics of atmospheric CO2 on amine-functionalized clay nanotubes followed the fractional-order kinetic model compared to that of the pseudo-first-order or pseudo-second-order rate equations. The efficiency along with stability of these novel adsorbents has also been demonstrated by their repetitive use for CO2 capture in the oxidative environment. Our findings thus point to a fundamental study on the atmospheric CO2 adsorption by amine-loaded adsorbents using an easy handling and low-cost benchtop RGA-based mass spectrometer, opening a new strategy for CO2 capture and sequestering study.

Cucurbit[7]uril-improved recognition by a fluorescent sensor for cadmium and zinc cations

The host–guest interaction of cucurbit[7]uril (Q[7]) with the new fluorescent sensor guest molecule (BIBPAH+), formed by alkylation of the secondary amine site in N,N-bis(2-pyridylmethyl)amine with 2-(bromomethyl)benzimidazole, was investigated by fluorescence and 1H NMR spectroscopy. The results indicate the formation of an inclusion complex in a 1:1 ratio with an association constant of Ka = (2.9 ± 0.7) × 105 L ∙ mol−1. There is minimal difference in the fluorescence intensities upon the introduction of each of Mn2+, Ni2+, Co2+, Cr3+, Ho3+ and Lu3+. However, the emission was slightly quenched on the addition of Cu2+ or Fe3+ whether Q[7] is present or not. Further investigation showed that encapsulation of BIBPAH+ in Q[7] improves Cd2+ and Zn2+ recognition by enhancing the fluorescence intensity, leading to an improvement in the limits of detection. In contrast, comparative parallel experiments in which Cu2+, Mn2+, Ni2+, Co2+, Fe3+, Cr3+, Ho3+ or Lu3+ were substituted for Zn2+ or Cd2+ resulted in minimal changes in the fluorescence that occurs for the corresponding metal-free system. The natures of the encapsulated Zn2+ and Cd2+ complexes have been investigated using fluorescence and 1H NMR spectroscopy as well as by quantum chemistry.

Developing novel strategies for the functionalization of core–shell magnetic nanoparticles with folic acid derivatives

In this work, we explore the development of new synthetic strategies leading to the formation of folic acid di-ester functionalized iron oxide-based magnetic nanoparticles. For this, initially, folic acid di-ester was converted into an acrylamide monomer through amidation of the primary amine site. Interestingly, esterification with a different acid chloride molecule carrying a long alkyl chain terminated with an azide group resulted into amidation of the secondary amine site. In a different set of experiments, magnetite nanoparticles decorated with a polymerization initiator, an acrylamide monomer, or a terminal alkyne group, were prepared. These folic acid and magnetic nanoparticles building blocks could then be combined in different ways to give rise to the targeted materials. In the first scheme, folic acid-based monomer could be polymerized through the initiating sites located at the surface of the magnetic nanoparticles. Alternatively, a random copolymerization between the folic acid-based monomer was carried out with the monomeric sites stabilizing the nanoparticles. Finally, the alkyne functionalities of the nanoparticles were coupled with the azide moieties of the folic acid derivatives. Thus, three different synthetic strategies were established for the formation of folic acid di-ester functionalized core–shell magnetic nanoparticles.

Nitric oxide reactivity of copper(II) complexes of bidentate amine ligands

Two copper(II) complexes, 1 and 2 with L1 and L2 [L1=propane-1,3-diamine; L2=N-isopropylpropane-1,3-diamine], respectively, were synthesized and characterized structurally. In acetonitrile solution of the complexes, the Cu(II) centre was found to reduce in presence of nitric oxide gas. The formation of [CuII–NO] intermediate prior to the reduction of Cu(II) center was evidenced by UV–Vis, solution FT-IR, X-band EPR studies. This reduction led to the ligand transformation through diazotization at primary amine site in complex 1; whereas, N-nitrosation at the secondary amine site of the ligand was observed in 2. The final organic products were isolated and characterized by spectroscopic studies.

Important roles of enthalpic and entropic contributions to CO2 capture from simulated flue gas and ambient air using mesoporous silica grafted amines.

The measurement of isosteric heats of adsorption of silica supported amine materials in the low pressure range (0-0.1 bar) is critical for understanding the interactions between CO2 and amine sites at low coverage and hence to the development of efficient amine adsorbents for CO2 capture from flue gas and ambient air. Heats of adsorption for an array of silica-supported amine materials are experimentally measured at low coverage using a Calvet calorimeter equipped with a customized dosing manifold. In a series of 3-aminopropyl-functionalized silica materials, higher amine densities resulted in higher isosteric heats of adsorption, clearly showing that the density/proximity of amine sites can influence the amine efficiency of adsorbents. In a series of materials with fixed amine loading but different amine types, strongly basic primary and secondary amine materials are shown to have essentially identical heats of adsorption near 90 kJ/mol. However, the adsorption uptakes vary substantially as a function of CO2 partial pressure for different primary and secondary amines, demonstrating that entropic contributions to adsorption may play a key role in adsorption at secondary amine sites, making adsorption at these sites less efficient at the low coverages that are important to the direct capture of CO2 from ambient air. Thus, while primary amines are confirmed to be the most effective amine types for CO2 capture from ambient air, this is not due to enhanced enthalpic contributions associated with primary amines over secondary amines, but may be due to unfavorable entropic factors associated with organization of the second alkyl chain on the secondary amine during CO2 adsorption. Given this hypothesis, favorable entropic factors may be the main reason primary amine based adsorbents are more effective under air capture conditions.

Infrared Study of Strongly and Weakly Adsorbed CO2 on Fresh and Oxidatively Degraded Amine Sorbents

CO2 adsorption on fresh and oxidatively degraded tetraethylenepentamine (TEPA) and polyethylene glycol (PEG-200) supported on amorphous silica (SiO2) was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Fresh TEPA sorbents adsorb CO2 in the form of ammonium ions, carbamates, and carbamic acid of which infrared features and binding strength strongly depend on the type of amine sites (i.e., primary or secondary) and their densities. CO2 adsorbed on the primary amine sites exhibited a strong IR intensity of carbamate in the 1680–1200 cm–1 region, and CO2 adsorbed on the secondary amine sites showed a high IR intensity of ammonium ion in the 2800–2100 cm–1 region. Oxidative degradation of the fresh sorbents in the presence of air at 100 °C for 12 h converted a high fraction of secondary amines in TEPA to amide and imide species, isolating the primary amine sites and decreasing the overall density of amines in the sorbent. The isolated primary amine sites of the degraded sorbent...

Nitric oxide reactivity of copper(ii) complexes of bidentate amine ligands: effect of chelate ring size on the stability of a [CuII–NO] intermediate

Three copper(II) complexes, 1, 2, and 3 with L(1), L(2) and L(3) [L(1) = 2-(2-aminoethyl)-pyridine; L(2) = 2-(N-ethyl-2-aminoethyl)-pyridine; L(3) = 3,3'-iminobis(N,N-dimethylpropylamine)], respectively, were synthesized and characterized. Addition of nitric oxide gas to the degassed acetonitrile solution of the complexes were found to result in the reduction of the copper(II) center to copper(I). In cases of complexes 1 and 2, the formation of the [Cu(II)-NO] intermediate prior to the reduction of Cu(II) was evidenced by UV-visible, solution FT-IR and X-band EPR spectroscopic studies. However, for complex 3, the formation of [Cu(II)-NO] has not been observed. DFT calculations on the [Cu(II)-NO] intermediate generated from complex 1 suggest a distorted square pyramidal geometry with the NO ligand coordinated to the Cu(II) center at an equatorial site in a bent geometry. In the case of complex 1, the reduction of the copper(II) center by nitric oxide afforded ligand transformation through diazotization at the primary amine site in acetonitrile solution; whereas, in an acetonitrile-water mixture, it resulted in 2-(pyridine-2-yl)ethanol. On the other hand, in cases of complexes 2 and 3, it was found to yield N-nitrosation at the secondary amine site in the ligand frameworks. The final organic products, in each case, were isolated and characterized by various spectroscopic studies.

Nitric oxide reactivity of copper(ii) complexes of bidentate amine ligands: effect of substitution on ligand nitrosation

Three copper(ii) complexes with bidentate ligands L(1), L(2) and L(3) [L(1), N,N(/)-dimethylethylenediamine; L(2), N,N(/)-diethylethylenediamine and L(3), N,N(/)-diisobutylethylenediamine], respectively, were synthesized as their perchlorate salts. The single crystal structures for all the complexes were determined. The nitric oxide reactivity of the complexes was studied in acetonitrile solvent. The formation of thermally unstable [Cu(II)-NO] intermediate on reaction of the complexes with nitric oxide in acetonitrile solution was observed prior to the reduction of copper(II) centres to copper(I). The reduction was found to result with a simultaneous mono- and di-nitrosation at the secondary amine sites of the ligand. All the nitrosation products were isolated and characterized. The ratio of the yield of mono- and di-nitrosation product was found to be dependent on the N-substitution present in the ligand framework.

NONOates–Polyethylenimine Hydrogel for Controlled Nitric Oxide Release and Cell Proliferation Modulation

In recent years, numerous research activities have been devoted to the controlled release of nitric oxide (NO) due to its potential as a restenosis inhibitor which inhibits the proliferation of vascular smooth muscle cells, the apoptosis of vascular endothelial cells, and aggregation of platelets. This work has demonstrated the development of a novel NO-conjugated gel system comprising of thermosensitive Pluronic F127, branched polyethylenimine (BPEI), and diazeniumdiolates (NONOates). Synthesis of conjugated Pluronic-BPEI-NONOates involved coupling of activated F127 to BPEI followed by the installation of NONOates at the secondary amine sites of branched PEI backbone under high pressure. NO-conjugated gel system, F127-BPEI-NONOates, reduced the initial burst of NO release and prolonged NO release. Furthermore, F127-BPEI-NONOates polymer coated on cell culture dish displayed much higher increase of endothelial cell proliferation and reduction of smooth muscle cell proliferation than that exhibited by non-NO releasing control. Such an NO-releasing device can operate locally and has a great potential in several biomedical applications due to high biocompatibility imparted by the conjugated F127.

Interaction of an extended series of N-substituted di(2-picolyl)amine derivatives with copper(II). Synthetic, structural, magnetic and solution studies

The interaction of Cu(II) with the following secondary N-substituted derivatives of di(2-picolyl)amine () are reported: N-cyclohexylmethyl-di(2-picolyl)amine (), N-benzyl-di(2-picolyl)amine (), N-(4-pyridylmethyl)-di(2-picolyl)amine (), N-(4-carboxymethylbenzyl)-di(2-picolyl)amine (), N-(9-anthracen-8-ylmethyl)-di(2-picolyl)amine (), 1,3-bis[di(2-picolyl)aminomethyl]benzene (), 1,4-bis[di(2-picolyl)aminomethyl]benzene () and 2,4,6-tris[di(2-picolyl)amino]triazine (). The solid complexes [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2), Cu()(ClO(4))(2), Cu()(2)(ClO(4))(2), [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O, Cu(2)()(ClO(4))(4), [Cu(2)()(Cl)(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were isolated and X-ray structures of [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2,) [Cu()(2)(ClO(4))(2)(H(2)O)].0.5H(2)O, [Cu(2)()Cl(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were obtained. The series is characterised by a varied range of coordination geometries and lattice architectures which in the case of [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O includes a chain-like structure formed by unusual intermolecular pi-interactions between metal bound perchlorate anions and the aromatic rings of adjacent anthracenyl groups. Variable temperature magnetic susceptibility measurements have been performed for [Cu()(micro-Cl)](2)(PF(6))(2) and [Cu()(micro-Cl)](2)(PF(6))(2).0.5H(2)O over the range 2-300 K. Both compounds show Curie-Weiss behaviour, with the data indicating weak antiferromagnetic interaction between the pairs of copper ions in each complex. Liquid-liquid (H(2)O/CHCl(3)) extraction experiments involving and as extractants showed that, relative to the parent (unsubstituted) dipic ligand , substitution at the secondary amine site in each case resulted in an increase in extraction efficiency towards Cu(II) (as its perchlorate salt); at least in part, this increase may be attributed to the enhanced lipophilicities of the N-substituted derivatives.

The stability of polyaniline in strongly alkaline or acidic aqueous media

Polyaniline (PANI) base has been suspended in 9 M potassium hydroxide at 20 °C or 90 °C for various time intervals extending to 4 months. The fraction of acetone-soluble material increased from 1.2 wt.% to 4.5 wt.% after exposure to an alkaline medium for 60 days at 20 °C. Gel-permeation chromatography indicates that the aggregation of PANI is reduced, while the chain degradation itself is negligible. FTIR spectroscopy confirms this trend and the absence of hydrolytic changes in the PANI structure. Polyaniline retains the ability to be reprotonated with a 1 M sulfuric acid to a conducting form. No marked changes in the molecular structure have been found, even after suspension of PANI in 9 M KOH at 90 °C for 60 days. Similar immersion of PANI salt in 5 M sulfuric acid at 20 °C was responsible for changes in the protonation, and the mass increased by 11 wt.%. This was explained by the exchange of the original sulfate or chloride counter-ions for hydrogen sulfate anions or by the protonation of secondary amine sites in PANI in addition to imine ones. The changes in the molecular structure are discussed on the basis of FTIR spectra. The conductivity decreased from 1.2 S cm −1 to ∼10 −3 S cm −1 but no time-dependence of conductivity was observed. There was no fraction of PANI soluble in acetone. PANI in the protonated state is thus stable also in the strongly acidic medium. The study is supplemented by the assessment of the thermal stability of PANI base, which is of importance for the processing of PANI. Loss of moisture has been observed after exposure to 250 °C for 10 h in both nitrogen atmosphere and in air. Good stability was found at 350 °C only in the nitrogen atmosphere, while a marked mass loss in weight was registered in air.

Structures of platinum(II) complexes of 2-aminomethylaziridine and S-2-aminomethylazetidine and correlation of anticancer activities of (2-aminomethylazacycloalkane)platinum(II) complexes with the geometry of the chelate rings formed with platinum(II).

The spectroscopic properties of platinum(II) complexes with 2-aminomethyl-derivatives of small-membered 1-aza-cycloalkane, i.e., =2-aminomethylaziridine=azida and S-2-aminomethylazetidine=S-azeda, and the crystal structures of their dichloro complexes demonstrate that the conformation of the fused three- (azida) or four- (S-azeda) and five-membered chelate ring formed by the coordination of S-azida and S-azeda to platinum(II) has an S(N) absolute configuration at the secondary amine site and that the two alkyl groups extend axially from the five-membered chelate ring. The chelate ring of the azida is more planar than the S-azeda or other 2-aminomethyl-1-azacycloalkanes. The anticancer activity reported for azeda and 2-aminomethylpyrrolidine appears to be related to their coordination structure, namely the presence of cis-fused successive rings.