Monovalent Copper Ions Research Articles

Cu+ emission in Li2BPO5 material for thermoluminescence dosimetry

In this study, Li2BPO5 doped with Cu and that co-doped with Mg are synthesized by the wet chemical technique and exposed to γ rays of 60Co to determine their thermoluminescence (TL) properties. The X-ray diffraction technique shows the crystalline nature of the prepared material. The photoluminescence (PL) emission spectra of Li2BPO5:Cu phosphor show the strong prominent peak at 368 nm in the violet region of the visible spectrum due to the transition of 3d94s1 ↔ 3d10 of monovalent copper ion. The PL emission of Li2BPO5:Cu is enhanced by the addition of Mg. The TL glow curves of γ-irradiated Li2BPO5:Cu sample show one glow peak at 143°C, indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The trapping parameters associated with the prominent glow peak of Li2BPO5:Cu are calculated using the glow curve shape (Chen's) method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. A linear TL response is observed in Li2BPO5:Cu in a long span of exposures. The sensitivity of Li2BPO5:Cu sample is observed to be 7.8 times that of (TLD-100) LiF:Mg, Ti.

Topological loading of Cu(i) catalysts onto crystalline cellulose nanofibrils for the Huisgen click reaction

Topological loading of monovalent copper ions (Cu(I)) onto the crystal surfaces of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs), which have a large number of sodium (Na) carboxylate groups on their surfaces, was achieved through ion exchange between Na and Cu species. The Cu-loaded TOCNs were fabricated into aerogels by a freeze-dry treatment. The as-prepared Cu–TOCN aerogel demonstrated an excellent catalytic efficiency for the azide–alkyne Huisgen [3 + 2] cycloaddition reaction, indicating that the Cu(I) catalysts are highly dispersed and exposed on the entire surfaces of crystalline TOCNs, allowing effective contact with the reactants. The Cu–TOCN aerogel was recoverable from the reaction system and Cu(I) catalysts were extensively immobilized on TOCNs during the reaction. It is noteworthy that TOCNs can be easily obtained from native cellulose, which is the most abundant and renewable biomass. Thus, the Cu–TOCN aerogel is a high-performance and environment-friendly catalyst, and this novel technique is expected to comprise a promising approach toward green and sustainable development.

Synthesis of novel heterobimetallic copper(i) hydrazone Schiff base complexes: A comparative study on the effect of heterocyclic hydrazides towards interaction with DNA/protein, free radical scavenging and cytotoxicity

Two new copper(I) hydrazone complexes have been synthesised from bivalent copper precursor [CuCl(2)(PPh(3))(2)] and ferrocene containing bidentate hydrazone ligands HL(1) (1) or HL(2) (2). Based on the elemental analyses and spectroscopic data, the complexes are best formulated as [CuL(1)(PPh(3))(2)] (3) and [CuL(2)(PPh(3))(2)] (4) of the monovalent copper ion. Solid state structures of ligand 2 and its corresponding complex 4 were also determined. The DNA/albumin interactions of all the synthesised compounds were investigated using absorption, emission and synchronous fluorescence studies. Further, antioxidant properties of all the compounds have also been checked against ABTS, O(2)(-) and OH radicals. Additionally, the in vitro cytotoxic activity of compounds 1-4 was assessed using tumour (HeLa, A431) and non-tumour (NIH 3T3) cell lines.

Biochemical Characterization of AtHMA6/PAA1, a Chloroplast Envelope Cu(I)-ATPase

Copper is an essential plant micronutrient playing key roles in cellular processes, among them photosynthesis. In Arabidopsis thaliana, copper delivery to chloroplasts, mainly studied by genetic approaches, is thought to involve two P(IB)-type ATPases: AtHMA1 and AtHMA6/PAA1. The lack of biochemical characterization of AtHMA1 and PAA1, and more generally of plant P(IB)-type ATPases, is due to the difficulty of getting high amounts of these membrane proteins in an active form, either from their native environment or after expression in heterologous systems. In this study, we report the first biochemical characterization of PAA1, a plant copper-transporting ATPase. PAA1 produced in Lactococcus lactis is active, forming an aspartyl phosphate intermediate in the presence of ATP and the adequate metal ion. PAA1 can also be phosphorylated using inorganic phosphate in the absence of transition metal. Both phosphorylation types allowed us to demonstrate that PAA1 is activated by monovalent copper ions (and to a lower extent by silver ions) with an apparent affinity in the micromolar range. In agreement with these biochemical data, we also demonstrate that when expressed in yeast, PAA1 induces increased sensitivities to copper and silver. These data provide the first enzymatic characterization of a P(IB-1)-type plant ATPase and clearly identify PAA1 as a high affinity Cu(I) transporter of the chloroplast envelope.

Luminescence of (H 3O)Al 3(SO 4) 2(OH) 6:Cu synthesized under hydrothermal condition

Copper doped hydronium alunite; (H 3O)Al 3(SO 4) 2(OH) 6:Cu was successfully synthesized under hydrothermal conditions. The blue cathodoluminescence (peak at about 414 nm) was observed from the (H 3O)Al 3(SO 4) 2(OH) 6:Cu when the copper ratio x was 1 and above, where x was the molar ratio of Cu:Al:S = x:3:2 (0 ≤ x ≤ 15) in the starting materials. The luminescence intensity increased with increasing x up to 3, and then decreased. The monovalent copper ion (Cu +) was detected by XPS measurements for all the doped samples. In addition, the divalent copper (Cu 2+) was detected for the samples with x ≥ 6. Therefore, the origin of the blue luminescence is considered to be monovalent Cu + ion. Excess doping of Cu + ( x ≥ 6) is thought to cause a concentration quenching of the luminescence. The obtained (H 3O)Al 3(SO 4) 2(OH) 6:Cu is expected to find use in the blue luminescent phosphor under electron beam irradiation.

Topologically novel copper molybdate phases based on 3,4′-dipyridylketone: Hydrothermal synthesis, structural characterization, and magnetic properties

Hydrothermal treatment of CuCl 2·2H 2O, MoO 3, and 3,4′-dipyridylketone (3,4′-dpk) in 1:1:2 mole ratio afforded the new mixed metal oxide phases [Cu 2(MoO 4) 2(3,4′-dpk)(H 2O)] ( 1) or [Cu 4(3,4′-dpk) 4(Mo 8O 26)] ( 2), depending on the pH of the initial reaction mixture. Compound 1 possesses unique one-dimensional (1-D) [Cu 2(MoO 4) 2(H 2O)] n ribbons constructed from the linkage of {Cu II 4O 6} tetrameric units through isolated [MoO 4] 2– tetrahedra. These ribbons in turn are connected into a two-dimensional (2–D) coordination polymer structure by tethering 3,4′-dpk ligands. Compound 2, containing monovalent copper ions, manifests an unprecedented “X-rail” 1-D extended structure with (6 28) 4(6 6) topology formed from the bracketing of discrete [ β–Mo 8O 26] 4– anions by four [ Cu I ( 3 , 4 ′ ‐ dpk ) ] n n + chains. The variable temperature magnetic susceptibility behavior of 1 was fit to a linear tetramer model, with g=2.03(3), J 1=25.8(7) cm –1 and J 2=−46(1) cm –1. Antiferromagnetic inter-tetramer interactions ( zJ′=−0.21(3) cm –1) were also evident. Crystallographic data: 1 monoclinic, P2 1/ c, a=10.3911(11) Å, b=6.9502(6) Å, c=22.958(2) Å, β=100.658(7)°, V=1629.5(3) Å 3, R 1=0.1256, and w R 2=0.2038; 2 triclinic, P 1 ¯ , a=10.9000(3) Å, b=11.7912(4) Å, c=13.5584(4) Å, α=102.482(2)°, β=102.482(2)°, γ=117.481(2)°, V=1450.98(8) Å 3, R 1=0.0428, and w R 2=0.0630.

Mixed Valence Tungsten(IV,V) Compounds with Layered Structures (Part II)): Synthesis and Crystal Structures of Cu1−x[W2O2Cl6] and Cu1−x[W4O4Cl10

AbstractThe reaction of CuCl with WOCl3 at 400 °C leads to a mixture of Cu1−x[W2O2Cl6] (1) and Cu1−x[W4O4Cl10] (2) in form of black lustrous needles. Both compounds crystallize in space group C2/m with a = 12.7832(5) Å, b = 3.7656(2) Å, c = 10.7362(3) Å, β = 119.169(2)° for 1 and a = 12.8367(19) Å, b = 3.7715(7) Å, c = 15.955(3) Å, β = 102.736(5)° for 2. The structures are made up of WO2Cl4 octahedra. In the case of 1 two octahedra are edge‐sharing via chlorine atoms to form pairs which are linked via the trans‐positioned oxygen atoms to form infinite double strands $^{\infty}_{1}\rm [W_{2}O_{4/2}Cl_{2/2}Cl_{4}]$. In the structure of 2 two of these double strands are condensed via terminal chlorine atoms to form quadruple strands $^{\infty}_{1}\rm [W_{4}O_{8/2}Cl_{6/2}Cl_{4}]$. Like for all members of the Mx[W2O2X6] structure family (X = Cl, Br) nonstochiometry with respect to the cations M was observed. The copper content of 1 and 2 was derived from the site occupation factors of the respective structure refinements. For several crystals examined the copper content varied between x = 0.27 and 0.17 for 1 and x = 0.04 for 2. In both structures the oxochlorotungstate strands are negatively charged and connected to layers by the monovalent copper ions, which are tetrahedrally coordinated by the non‐bridging chlorine atoms of the strands. The structure models imply disorder of the Cu+ ions over closely neighboured sites.

Identification of two types of exchangeable sites for monovalent copper ions exchanged in MFI-type zeolite

Three different approaches have been used to characterize the state of exchanged copper ions in copper-ion-exchanged MFI (CuMFI) samples. (1) Two types of an ion-exchangeable site with different adsorption properties for N(2) or CO molecules were identified depending on the pre-treatment temperature (723 or 873 K) of a sample prepared by using an aqueous solution of CuCl(2). (2) The state of the active sites formed by the evacuation of a sample at 873 K that had been prepared using a mixture solution of aqueous NH(4)CH(3)COO and Cu(CH(3)COO)(2) was analysed utilizing both (13)C(18)O and (12)C(16)O to identify the two types of active adsorption sites for CO molecules. (3) CuMFI samples prepared by the ion-exchange method employing anhydrous CuCH(3)COO showed a surprising adsorption feature characterized by a single IR band occurring at 2159 cm(-1) due to the adsorbed CO molecules, but there was no corresponding IR band due to adsorbed N(2) molecules. A successful preparation of CuMFI, in which the monovalent copper ions exclusively occupied another one of the two types of ion-exchangeable sites, was also carried out utilizing the solid-ion exchange method using Cu(CH(3)COO)(2).H(2)O. This site exhibits an IR band occurring at 2151 cm(-1) for CO molecules and also acts as an active site for N(2) molecules. These experimental data correlate, and clearly indicate that there are at least two types of exchangeable sites for copper ions in MFI-type zeolites.

New Information Related to the Adsorption Model of N2 on CuMFI at Room Temperature

The N2 adsorption occurring at temperatures around room temperature is a particularly surprising phenomenon given by the copper ion-exchanged MFI-type zeolite (CuMFI). However, the assignment of the active sites for N2 adsorption on CuMFI at room temperature is controversial: which ones act as the real active center, the dimeric or monomeric Cu+ sites? We have analyzed the real active site for N2 adsorption by studying the adsorption of CO and N2, and also by spectroscopic methods, such as photoluminescence, X-ray absorption fine structure, and IR measurements. Clear evidence was observed for the adsorption of N2 molecules on the monomeric Cu+ ions exchanged in the MFI-type zeolite at temperatures around room temperature, which puts to an end the dispute regarding the dimeric state made up of the monovalent copper ions as being a potential adsorption site.

A New Strategy for the Improvement of the N2Adsorption Properties of Copper-Ion-Exchanged MFI-Type Zeolites at Room Temperature

A copper-ion-exchanged MFI-type zeolite, CuMFI, which exhibits an extremely efficient adsorption of the dinitrogen (N2) molecule at room temperature, has been successfully prepared by ion exchange in an aqueous solution of Cu(CH3COO)2 containing a component of NH4CH3COO. This ion-exchange method has unique characteristics as follows; first, the copper ion exchange takes place exclusively on the ion-exchangeable site that acts as the active site for N2 adsorption, and second, the extent of the reduction of the divalent copper ion exchanged attains a high value of 88%. In addition, the CuMFI sample thus prepared exhibits a high efficiency for N2 adsorption at 298 K where the monovalent copper ions act as adsorption sites; approximately 86% of them are effective for N2 adsorption. In this case, the heats of adsorption of N2 were large, 87−60 kJ mol-1. These observations were rationalized as showing that the site-selective ion exchange with copper ions occurs, accompanying acetate ligands by which the effect ...

Synthesis and optimization of copper sulfide‐coated electrically conducting poly(acrylonitrile) fibers

AbstractIn this research work, coating of acrylic fibers (fibers spun from poly acrylonitrile) with copper sulfide was investigated. Surface of the acrylic fibers were coated with an insoluble conducting copper sulfide layer. One‐step dipping method was carried out. Acrylic fibers were treated in a bath containing divalent copper ions, a reducing agent, which is capable of reducing the divalent copper ions to a monovalent copper ions and a sulfur‐containing compound. This treatment resulted in a reduction of electrical resistance to 1 × 109that of an almost infinite resistance for the untreated fibers. The influence of some parameters such as concentration of copper (II) sulfate, hydroxylamine sulfate, sodium thiosulfate, and temperature of treatment bath were also investigated. A second reducing material such as sodium dithionite was used to improve the electrical conductivity of the fibers. The amount of reacted copper was measured by atomic absorption technique. The surface properties of the coated‐acrylic fibers were studied using scanning electron microscopy (SEM). Within the experimental conditions, a solution containing 1.2 g/dm3copper (II) sulfate, 1.6 g/dm3hydroxylamine sulfate, 3.6 g/dm3sodium thiosulfate, and 3 g/dm3sodium dithionite was selected as a suitable formulation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Unambiguous evidence supporting the decomposition reaction of NO on two types of monovalent copper-ion in CuZSM-5 zeolite

By combining the methods of calorimetry and spectroscopy using CO as a probe molecule, we obtained the evidence supporting the decomposition reaction of NO on two types of monovalent copper-ion (Cu +) species in CuZSM-5 zeolite. These Cu + species showed the characteristic emission bands at 21,000 and 18,500 cm −1 and, respectively, gave the CO adsorption heats of 122 and 110 kJ mol −1. Taking account of our previous EXAFS data, it was found that the former species take the two-coordinated structure involving lattice oxygen atoms, while the latter ones the three-coordinated structure. In this paper, we also emphasized the validity of our original assignment of active sites on CuZSM-5 for N 2 adsorption at room temperature; three-coordinated Cu + species adsorb N 2 molecules.

Synthesis and Crystal Structure of Ammine Copper(I) Cyanamide, Cu4(NCN)2NH3

AbstractAmmine copper(I) cyanamide, Cu4(NCN)2NH3, was obtained as a white powder from the reaction between CuCl and H2NCN in concentrated ammonia solution. X‐ray and neutron diffraction experiments yield the hexagonal system with space group P63mc (no. 186) and a = 5.7661(1) Å, c = 10.7817(3) Å, and Z = 2. The structure is characterized by layers of monovalent copper ions with an average Cu–Cu distance of 2.89Å, and the layers are connected through two crystallographically independent NCN2− units. While one CuI is linearly bonded to an NCN2− unit and an additional NH3 molecule, the other CuI is also linearly coordinated but by two NCN2− groups; the Cu–N bonds lie between 1.86–1.98Å. The C–N bond lengths and angles evidence both NCN2− groups as essentially linear cyanamides.

Cobalt(II) and copper(II) complexes of (2-thiophene)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone

New complexes having the formulae [L2CoX2] and [LCuCl2], [LCuCl] and [LCu](ClO4)2 where L = (2-thiophene)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone TDPTH; X = Cl, OAc or ClO4 have been synthesized and characterized on the basis of elemental analyses, conductance, magnetic moments and infrared, electronic and ESR spectral data. The IR spectra indicate that TDPTH is a neutral bidentate ligand, coordinating via a triazine-N and azomethine-N in [L2CoX2] and [LCuCl2] with the thiophene-S not coordinated but is tridentate in [LCuCl] and [LCu](ClO4)2 through the same two nitrogen atoms and thiophene-S. The magnetic moment and electronic spectral data suggest a distorted octahedral structure for Co(II) complexes, a dimeric square pyramidal geometry for [LCuCl2] through chloride bridges and a dimeric diamagnetic, four-coordinate copper in [LCu](ClO4)2 through thiophene-S bridges. The X-band ESR spectra of Co(II) complexes, in the solid state, are rhombic with three g values consistent with a high-spin distorted octahedral structure. The X-band ESR spectrum of the powdered sample of both [LCuCl2]·2H2O and [LCu](ClO4)2 at room temperature and at 77 K showed only one broad signal due to ΔM s = ± 1 transition and a weak signal due to the forbidden ΔM s = ± 2 transition, indicating an antiferromagnetic interaction between copper(II) centers whereas [LCuCl] is ESR silent, indicating a monovalent copper ion in this complex.

Anomalous valence changes and specific dinitrogen adsorption features of copper ion exchanged in ZSM-5 zeolite prepared from an aqueous solution of [Cu(NH3)2

Direct ion-exchange of monovalent copper ions into a ZSM-5-type zeolite was carried out using an aqueous solution of diammine–copper(I) ions, [Cu(NH3)2]+, to prepare a copper ion-exchanged ZSM-5 zeolite including only monovalent copper ions, and the effect of monovalent copper ions on the zeolite's adsorption properties for dinitrogen (N2) was examined. Strangely enough, the reoxidation of monovalent copper-ion exchanged in ZSM-5 took place in the evacuation process at around 473 K. The changes in valence and structure of the exchanged copper-ions during the evacuation process and the interaction with N2 molecules at room temperature have been investigated by using spectroscopic techniques such as X-ray absorption fine structure (XAFS), IR and photoemission spectroscopy, as well as by measurements of adsorption isotherms and adsorption heats. On the basis of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses, it has become apparent that the Cu+ species exchanged in ZSM-5 zeolite is oxidized by water to form a divalent species having a CuO-like structure through heat-treatment in vacuo at 473 K. Further heat-treatment at temperatures above 673 K caused a reduction of the divalent species to a monovalent one that exhibits a pronounced adsorption feature for N2 even at room temperature. XANES and photoemission data clearly indicated that the Cu+ species in an 873 K-treated CuZSM-5 sample has a three-coordinate structure with lattice oxygen atoms and interacts strongly with an N2 molecule at room temperature. The strong interaction with N2 was also verified through the adsorption heat and IR data: an initial adsorption energy of 85 kJ mol−1 and an absorption band at 2295 cm−1. A prominent feature of this system is that some of the adsorbed species survives after evacuation at 300 K, indicative of a strong interaction between N2 and the three-coordinate copper ion.

On the hydrothermal stability of CuAPSO-34 microporous catalysts for N 2O decomposition: a comparison with CuZSM-5

The hydrothermal stability of CuAPSO-34 microporous silicoaluminophosphates with chabasite structures has been investigated and compared to that of a copper-exchanged ZSM-5 zeolite by a combined XRD, FTIR, and catalytic study. CuAPSO-34 showed a higher hydrothermal structural stability (steaming 80 h at 600 °C), as found by XRD. Spectroscopic FTIR investigation of adsorbed CO revealed that upon this steaming procedure the concentration of monovalent copper ions in CuAPSO-34 was not significantly affected, whereas, even after a less severe steaming (60 h at 550 °C), these species dramatically decreased in CuZSM-5, and extraframework Al 3+ ions were simultaneously formed. Consequently, the high activity in N 2O decomposition shown by fresh CuZSM-5 was essentially lost after steaming, while CuAPSO-34 exhibited a significantly milder deactivation.

Photoluminescence of embedded copper nanoclusters in soda-lime glass

Copper clusters embedded in soda-lime glass are formed by ion-exchange method. These ion-exchanged soda-lime glasses showed a broad bluish green emission band due to the monovalent copper ions introduced into the dielectric matrix during ion-exchange. The ion-exchanged glasses were annealed in air for 1 h at different temperatures and their photoluminescence spectra were recorded at room temperature. It is observed that the intensity of emission increased with the increase in heat treatment temperatures with the photoluminescence peak shifting towards the lower wavelength region. Irradiation of ion-exchanged samples with He + ions of energy 100 keV resulted in vanishing of the photoluminescence due to the stabilization of the Cu + ions embedded in the dielectric matrix, into metal copper nanocrystals.

Hydrothermal Synthesis and Characterization of a One‐Dimensional Copper (I) Halide Cluster with 1,10‐Phenanthroline

AbstractThe title compound Cu2Cl2phen (phen = 1,10‐phenanthroline, C12H8N2) 1 was synthesized from CuCl2·2H2O, CuCl and phen by hydrothermal method and its structure was determined by single crystal X‐ray analysis. With phen, CuG forms one‐dimensional chains, which comprise two zigzag chains based on fused Cu‐X units and connected via covalent bonds. The compound contains two crystallographically unique monovalent copper ions, Cu(1) and Cu(2). The Cu(1) atom in the tetrahedral site, is coordinated to two bridging Cl− and two N atoms in phen. The Cu(2) atom with a slightly distorted triangular planar geometry, is coordinated to three Cl−. The compound 1 was crystallized in monoclinic, space group P21/n with a = 0.37338(4), b = 1.9510(2), c = 1.68008(19) nm, β = 95.605 (3)°, R = 0.0458, and was characterized by elemental analysis, IR spectrum and TGA analysis.

Electrochemical behaviour of copper in trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide, an ammonium imide-type room temperature molten salt

The redox behaviour of copper species in an 'ammonium imide' room temperature molten salt was examined to clarify the applicability of the salt to the electroplating media of various metals. Trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf2N), having an electrochemical window of 5.6 V (50 °C), and the corresponding copper(II); salt were used to prepare the solution. In TMHA-Tf2N media the monovalent copper ion, Cu(I), was stable and Cu metal was oxidized, or corroded, in the presence of Cu(II) species as: Cu2+ + Cu → 2Cu+. Cathodic electrodeposition of copper metal and its anodic dissolution were, thus one-electron reactions and their current efficiencies were almost 100%.

A more efficient copper-ion-exchanged ZSM-5 zeolite for N2 adsorption at room temperature: Ion-exchange in an aqueous solution of Cu(CH3COO)2

The copper-ion-exchanged ZSM-5 type zeolite, prepared by ion-exchange in an aqueous solution of Cu(CH3COO)2 and evacuation at 873 K, gives a distinctive IR band at 2151 cm−1 due to the adsorbed CO species. More efficient adsorption of N2 was exhibited by this sample, compared with samples prepared by other methods, implying site-selective ion-exchange in the preparation process. On the basis of X-ray absorption near-edge structure (XANES) spectra the exchanged copper ion was proved to be in a monovalent state; one of the splitting strong bands, due to the 1s–4pz transition of the monovalent copper ion, loses its intensity on N2 adsorption. The extended X-ray absorption fine structure (EXAFS) spectral pattern around the copper ion also changed on N2 adsorption and a shoulder appeared at around 1.5 Å (no phase-shift correction), in addition to the strong band at around 1.65 Å (no phase-shift correction). It was concluded that the monovalent copper-ion-exchanged site giving the 2151 cm−1 band due to the adsorbed CO species is the active site for specific N2 adsorption. A first principles calculation was carried out with the object of finding the most appropriate model for the CO species adsorbed on the exchanged copper ions in ZSM-5. The data obtained suggest that a three-coordinate copper ion bonded to three lattice oxygen atoms adsorbs CO to give the 2151 cm−1 band. A pseudo-planar structure including the monovalent copper ion bound to three oxygen atoms is assumed to change to a pseudo-tetrahedral arrangement on N2 adsorption. Such a site-selectively ion-exchanged substance has potential for the development of materials for N2 separation or fixation and activation catalysts, as well as for the analysis of NO-decomposition sites.