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Research was conducted to examine the trend in the activation energies of the recombination reactions with molecular oxygen. The third-order recombination reaction Sr(1S) + O2 + He -> SrO2 + He experiment was performed in a fast-flow reactor in the temperature and pressure range of 303-968 K and 6-12 Torr, respectively. Results show the occurrence of activation energies using ab initio calculations.

Investigates the kinetics of the silicon dioxide growth process in afterglows of microwave-induced plasmas. Information on the technological application of silicon dioxide layers; List of alternative thermal oxidation techniques; Advantages of the flowing afterglow technique in thermal oxidation.

Hafnium aluminates have been investigated as highκ dielectrics for implementation in sub45 nm nonvolatile memory technologies. The growth behavior and quality of these dielectrics strongly depend on the applied deposition technique. We examine the surface reactions that occur during the atomic layer deposition (ALD) of hafnium aluminates from HfCl4, Al(CH3)3, and H2O. When grown in the ALD sequence (HfCl4/H2O)a[Al(CH3)3/H2O]5, HfCI4 chemisorption is enhanced while that of Al(CH3)3 is inhibited compared to the reaction during ALD of the respective binary oxides. Density functional theory simulations suggest that this observation is related to the more efficient hydrolysis of the AlC bond compared to HfCl. However, earlier works on ALD of HfCl4/H2O suggest that the low growth per cycle of this process is not caused by a limited hydrolysis of the HfCl bond but by dehydroxylation of the generated HfOH surface sites into less reactive Hf-O-Hf surface sites. Hence, we propose that the enhanced HfCl4 and inhibited Al(CH3)3 chemisorption during ALD of hafnium aluminates results from a difference in dehydroxy lation behavior between both binary oxides. [ABSTRACT FROM AUTHOR]

The growth behavior and film quality of HfO2 deposited by atomic layer deposition (ALD) using HfCl4/H2O depends on the hydroxylation of the exposed surface. In this work, we investigate the dependence of the first HfCl4 chemisorption reaction at 300°C on the OH density of the silicon surface. We observe that the hydroxyl density, and hence the Hf deposition, on O3/H2O wet oxides depends on the initial preparation as well as on the stabilization time in the ALD reactor. A good understanding of the initial nucleation behavior is necessary because wet oxides are used in complementary metal-oxide-semiconductor transistors as surface pretreatment for aggressively scaled HfO2 gate dielectrics. Moreover, the HfCl4 chemisorption reaction is used to estimate the hydroxylated fraction of these surfaces by means of theoretical models. Finally, the temperature dependence of the OH density, as available in the literature, is applied to gain insight into the stoichiometry of the HfCl4 chemisorption reaction. [ABSTRACT FROM AUTHOR]

To obtain an idea of the magnitudes of the ozone loss rates rO3 in practical applications of ozone, an overall determination of the ozone decay profiles and rate constants was carried out in four different systems. These systems resemble different conditions for industrial application of ozone and the peroxone process, such as in the field of micro electronics, drinking water purification, disinfection, etc. Therefore, the behavior of ozone was monitored in the pH range from 4.5 to 9.0, in pure water and phosphate buffered systems in absence and presence of small amounts of hydrogen peroxide (10-7 M to 10-5 M H2O2). First the reproducibility of the ozone decay profiles was checked and from the various kinetic formalism tests, the reaction order 1.5 for the ozone decay rate has been selected. As expected, hydrogen peroxide increases the decay rates. In pure systems, added concentrations of 10-7M H2O2 already cause a remarkable acceleration of the ozone decay in the acidic and neutral pH range compared to the pure systems. However for alkaline pH conditions almost no effect of the low hydrogen peroxide concentrations was noticed. Contradictory to literature data, in the absence of hydrogen peroxide, ozone displays faster decays in the buffered systems of low ionic strength of 0.02 compared to pure water. This acceleration is more pronounced for acidic pH conditions. Low concentrations of phosphate may indeed accelerate the ozone decay in the presence of organic matter. Adding H2O2 concentrations below 10-5M to phosphate buffered solutions has a negligible effect on the ozone decay rate compared with pure water systems, except for pH 7. It appears that phosphate masks the effect of hydrogen peroxide below 10-5 M as tested here. Thus the application of AOP's by adding low concentrations of hydrogen peroxide is not well feasible in the presence of phosphate buffers in pure water systems. [ABSTRACT FROM AUTHOR]

The Continuous downscaling of complementary metal oxide semiconductor devices demands the introduction of dielectric layers with a high permittivity κ. Three-dimensional (3D) transistor structures, such as FinFET devices, require excellent step coverage by the high-κ material as provided by atomic layer deposition (ALD). In addition, because of the 3D structure, surfaces with different crystallographic orientation need to be covered. Because the initial HfO2 deposition using ALD HfCI4/H2O is governed by the OH surface density, we investigated its dependence on the crystallographic orientation of the silicon substrate. For oxidations in O3/H2O, a (110) orientated substrate oxidizes faster than silicon (100) up to a thickness of ~0.7 nm as measured by X-ray photoelectron spectroscopy. Also, irrespective of the substrate Orientation, the HfO2 deposition is found to increase with increasing SiO2 thickness and thus OH coverage of the surface. This implies that, for oxide thicknesses below 0 .7 nm, the oxidation of silicon (100) results in a thinner oxide and, hence, less HfO2 deposition in comparison to silicon (110). However, these differences are marginal after implementation in transistor devices as is shown by their capacitance and mobility. As a result, for FinFET applications, a conformally deposited HfO2 layer will be independent of the crystallographic substrate orientation. [ABSTRACT FROM AUTHOR]

In this paper, a number of case studies on the analysis of novel metallic contaminants on conventional and alternative substrates using the technique of total reflection X-ray fluorescence spectrometry (TXRF) is presented. Investigated materials include Si and Ge substrates, high-κ dielectric contaminants, and layers, and Si wafers contaminated with elements from metal gates and Cu interconnects. One focus is on the application and optimization of detection limits in direct TXRF. For the TXRF analysis of contaminants on Si wafers, a general conclusion is that a combination of three excitation sources is needed to cover the whole range of interest: a low-energy excitation (about 5 keV, e.g., WMα, Cr Kα) for the low Z elements such as Na, Mg, and Al, a moderate-energy excitation (10-20 keV, e.g., WLβ, MoKα) for the 3d-transition elements, and a high-energy excitation (25-35 keV, e.g., W, continuum) for the analysis of elements such as Zr, Ru, Mo, and Pd. Also, for the analysis of novel substrates using direct TXRF, a careful selection of the excitation source results in better detection limits. In this way, detection limits at 1010-1011 at/cm2 can be achieved, even for novel contaminants and substrates. As the International Technology Roadmap for Semiconductors (ITRS) requires control below 5×109 at/cm2, the application of a preconcentration procedure such as vapor phase decomposition-droplet collection TXRF (VPD-DC-TXRF) is required. Proper use of this procedure allows the improvement of the detection limits by two to three orders of magnitude, depending on wafer size and chemical collection efficiency. The usability of this preconcentration procedure in combination with TXRF will be demonstrated for noble elements and germanium substrates. [ABSTRACT FROM PUBLISHER]

Ozone is considered an environmentally friendly alternative for currently applied H[sub 2]SO[sub 4]-based mixtures in the cleaning of semiconductor devices. In order to implement ozone/water cleaning processes in practical systems, fundamental research is needed to understand the underlying chemical processes. Related to the removal of organic contamination from silicon surfaces, one needs to know whether ozone or radical species are the most efficient. A kinetic modeling study is performed to solve this problem whereby the pH is varied and different additives are checked. Theoretical concepts as Dominant Oxidation Pathway (DOP) and Radical Pool (RP) will be introduced for the evaluation of the various reaction pathways. Key Words Ozone; Organics, Semiconductors; Advanced Oxidation Processes; Radicals; Dominant Oxidant Pathway; Radical Pool [ABSTRACT FROM AUTHOR]

Mainly because of cost-saving and environmental concerns, ozone has been introduced as a cleaning agent in semiconductor manufacturing in recent years. This work reports the determination of the most important degradation products formed after the stripping of two different types of photoresist (PR) (I-Line and DUV resist) by ozone processing. Six low molecular weight carboxylic acids could be identified for the I-line PIL five for the DUV PR. The behavior of these degradation products under continuous ozonation as well as their stability in water was also investigated. Despite the chemical similarity of these carboxylic acids, their behavior appears to be quite different. [ABSTRACT FROM AUTHOR]

Recently the microelectronics industry is investigating the application of ozonated solutions in the cleaning of semiconductor devices as an alternative for the frequently used H[sub 2]SO[sub 4]-mixtures. The use of ozone would result in more environmentally friendly and cost-saving cleaning concepts. To optimize this new wet chemical cleaning processes, fundamental understanding of the behavior of ozone in ultrapure water is required. The decomposition and the solubility of ozone in ultrapure water were investigated as a function of pH, temperature and various additives. Some applications will also be discussed, namely the oxidation of silicon and the mechanistic aspects of the removal of organic contamination. [ABSTRACT FROM AUTHOR]

Abstract: Ge substrates are recently being reconsidered as a candidate material for the replacement of Si substrates in advanced semiconductor devices. The reintroduction of this material requires reengineering of the standard IC processing steps. In this paper, we present the extension of the methodology of vapor phase decomposition–droplet collection–total reflection X-ray fluorescence spectrometry (VPD–DC–TXRF) for metallic contamination analysis towards Ge substrates. A first step that asked for adaptation was the collection chemistry as the Ge wafers surface is not hydrophobic after the VPD treatment. The contact angle could be significantly increased using a concentrated HCl solution. This chemistry has been proved to perform well in the collection of metals from intentionally contaminated Ge wafers. A second step that needed optimization was the matrix removal method as a sample preparation step prior to the TXRF analysis. First, the upper limits of TXRF on Ge containing solutions have been characterized. The accuracy of TXRF is found to be acceptable for Ge contents lower than 1×1014 atoms (250 ppb in 50 μL) but decreases systematically with higher Ge contents. Fortunately, Ge can be volatilized at low temperatures as GeCl4 by the addition of HCl. The parameters within this method have been investigated with respect to the removal of Ge and the recovery of metal traces. Finally, the full VPD–DC–TXRF method has been applied on intentionally contaminated Ge wafers and proved to be very accurate. [Copyright &y& Elsevier]

The combination of vapor phase decomposition–droplet collection (VPD–DC) with total reflection-X-ray fluorescence spectrometry (TXRF) is a well-established method for metallic contamination analysis of Si wafers. However, the efficiency of the methodology is not fully quantitatively understood. This study aims for the identification of the sources of error in the VPD–DC–TXRF process. From a study of systematic recovery rate (RR) on standard wafers, it is concluded that the VPD–DC method is very efficient in collecting impurities from Si wafers. TXRF saturation effect on the micro-droplet residue limits the accuracy of quantification to the levels below 3×1013 atoms of metallic contamination. This represents a homogenous single element surface contamination of 1×1011 at/cm2 on a 200-mm wafer. Implications of this finding are more serious for multi-element contaminations and for larger wafer dimensions. The origin of this saturation effect is discussed and solutions are evaluated. Further, we suggest a monitoring of the scattered X-rays from VPD–DC residues as an indicator for TXRF accuracy. [Copyright &y& Elsevier]

An analysis methodology for the metallic contamination control of Ge wafer substrates has been developed and evaluated for six elements (K, Ca, Cr, Fe, Ni and Zn). Detection limits (DL) of Direct-total reflection X-ray fluorescence spectrometry (D-TXRF) analysis on Ge wafers have been determined and found to be at the E10 at/cm2 level. The values have been found to be a factor between 1 and 3 higher than on Si wafers, exclusively caused by differences in the background intensity. Additionally, a preconcentration procedure based on the Droplet sandwich etch (DSE) method has been developed. This method relies on the transfer of the surface and subsurface contaminants from the wafer to the liquid phase by wet chemical etching. Application of the DSE method on reference Ge wafers followed by analysis of the etch liquid by TXRF resulted in recovery rates (RR) of 40%. In an optimization study, it was found that the main DSE method parameters had limited influence on the RR. However, a detection efficiency study clearly demonstrated an underestimation by the TXRF analysis. An independent analysis for Ca, Cr, Fe and Zn by GF-AAS resulted in RR varying at approximately 100%. By internal standardization with the element La for the TXRF analysis, recovery rates could be increased to the 60% level. This underestimation by TXRF may find an origin in a matrix effect caused by the Ge etch products. By application of the developed DSE-TXRF method, DL at the E9 at/cm2 level could be realized, with values, which are at least one order of magnitude lower compared to the DL of D-TXRF on Ge wafers. [Copyright &y& Elsevier]

Background: Cancer navigation programs aim to support, educate, and empower patients and families, addressing barriers to diagnostics, treatment, and care. Navigators engage with people to ensure timely access to services and resources. While promising for older people with cancer, these programs are scarce in Europe, and research on their effectiveness and implementation is limited. We describe the protocol of the EU NAVIGATE randomized controlled trial, aimed to evaluate (1) effectiveness and cost-effectiveness of NavCare-EU, an intervention that aims to support older people with cancer throughout their illness trajectory, spanning the continuum of supportive, palliative, and end-of-life care, and (2) the intervention's implementation processes and feasibility of its integration into different health care systems in Europe, contextual barriers and facilitators for effective and sustainable implementation, and mechanisms involved in reaching the outcomes., Methods: We will conduct a multisite pragmatic fast-track randomized controlled trial with embedded convergent mixed-method process evaluation in Belgium, Ireland, Italy, Netherlands, Poland, and Portugal. The study targets people with cancer and declining health, 70 years or older, and their close family caregivers. The trial compares the NavCare-EU intervention plus standard care with standard care alone. We will perform a baseline measurement prior to randomization and follow-up measurements at 12 weeks, 24 weeks, and 48 weeks in intervention and control group, and an additional measurement at 72 weeks in the control group. Primary outcomes, measured at 24 weeks are (1) the older person's global health status/quality of life, a 2-item subscale from EORTC-QLQ-C30 (revised) measuring health-related quality of life, (2) level of social support measured with Medical Outcomes Study Social Support Survey (MOS-SSS scale). The study will include at least 246 older persons with completed global health status/quality of life at 24 weeks., Discussion: The EU NAVIGATE trial will cross-nationally test the effectiveness and cost-effectiveness of a navigation intervention for older people with cancer and their family caregivers, and its implementation in different health care systems in Europe. As continuity and access to health, social, and community care is a priority for patients and caregivers, the trial is timely and critically needed., Trial Registration: Clinicaltrials.gov: identifier NCT06110312 (2023/10/31)., Competing Interests: Declarations. Ethics approval and consent to participate: Ethics approval from the relevant ethics committees were obtained in all participating countries. Belgium: Commissie Medische Ethiek, 09/08/2023; Ireland: SJH/TUH Joint Research Ethics Committee, 14/11/2023; Italy: Comitato Etico Territoriale Lombardia 4, Istituto Tumori, 31/07/2023; the Netherlands: METC Amsterdam UMC, 22/08/2023; Portugal: Ethics Committee of the Faculty of Medicine of the University of Coimbra and Ethics Committee of the Portuguese Institute of Oncology of Coimbra Francisco Gentil, 25/09/2023; Poland: Komisja Bioetyczna, Uniwersytetu Jagiellońskiego, 14/06/2023. If all eligibility criteria are met, the researcher or research assistant will obtain informed consent from both the older person and the close family caregiver (if there is one). Patients and caregivers will be given the time to consider participation and will be assured that they are free to withdraw their participation without any effect on their care. Written consent will be obtained without any coercion of study participants. The research team will provide all participants with full disclosure about the nature and goal of the study. Consent for publication: Not applicable. Competing interests: The authors declare that they have no competing interests., (© 2024. The Author(s).)

In this paper, we present a method for growing copper-based nanowires. The method is based on the unusual modification of a halogenated copper surface by exposure to a helium plasma. The nanowires have diameters ranging between 50 and 150 nm and lengths up to 50 microm. They are polycrystalline, and large parts of the wires have a pronounced core-shell structure with a dense shell and less material inside. The wires are grown in a plasma environment at room temperature, and large amounts can be grown in a matter of minutes. The critical process parameters for the growth process are the gas flow and pressure settings, and the impact thereof will be discussed in detail. In order to gain insight in a possible growth mechanism, our observations are compared with literature on the growth of silver whiskers from halogenated silver crystallites. Finally, photoluminescence spectra of the wires are discussed in view of the analytical data about the stoichiometry and structure of the nanowires.

The application of ozone-stable pyrrolidinium based ionic liquids as safe reaction media resulted in selective hydroxy ester formation upon ozonation of cyclic acetals without using low temperatures or acetylating reagents.

The decomposition reaction mechanism of the anions generated by atmospheric pressure chemical ionization (APCI) mass spectrometry, in the negative mode, of nitroanilines and 2,4-dinitroanilines has been probed using quantum chemical calculations. The same process has been analyzed for the neutral counterparts and the simpler neutral and anionic nitrobenzenes. Our computations using density functional theory at the B3LYP/6-311++G(3df,2p) level demonstrate that the decomposition of the anion occurs in a two-stage process, involving an initial nitro-nitrite rearrangement followed by a NO-elimination leading to formation of a phenoxy radical anion derivative. The former is by far the rate-determining step. Calculations using the MP2 and CCSD(T)/6-311++G(d,p) levels also pointed out the same energy landscape. A similar mechanism has also been emphasized for the neutral counterparts. The effects of the amino and nitro groups as well as that of the negative charge on the nitro-nitrite interconversion are rather small and do not qualitatively modify the landscape of the pertinent energy surface and thereby the NO-loss mechanism.

The electronic structure aspects of the M (1S,3P) + N2O(X 1sigma+) (M = Be, Mg, Ca) reactions are investigated using the CASSCF/MRMP2 (complete active space SCF and the multireference Møller-Plesset perturbation theory of the second order) computational methodology. The lowest adiabatic 1 1A' and 1 3A' potential energy surfaces (PESs) favor the bending dissociation mechanism of N2O in all studied cases. The rate-limiting channels are determined by the classical barriers that decrease in the series Be (8.9) > Mg (7.0) > Ca (1.2) kcal/mol, whereas the spin-forbidden reaction channels are found to be less important. A comparison with elaborated kinetic results (Plane et al. J. Phys. Chem. 1990, 94, 5255; Gas-Phase Metal Reactions; Elsevier: Amsterdam, 1992; Vinckier et al. J. Phys. Chem. A 1999, 103, 5328) on the Ca (1S) + N2O(X 1sigma+) reaction is presented, and the differences in the kinetic behavior of the title reactions are discussed. Our results also indicate that the techniques based on the multiconfigurational wave functions are unavoidable if a correct topology of the PESs governing these reactions is needed.

In future microelectronic devices, SiO2 as a gate dielectric material will be replaced by materials with a higher dielectric constant. One such candidate material is HfO2. Thin layers are typically deposited from ligand-containing precursors in chemical vapor deposition (CVD) processes. In the atomic layer deposition (ALD) of HfO2, these precursors are often HfCl4 and H2O. Obviously, the material properties of the deposited films will be affected by residual ligands from the precursors. In this paper, we evaluate the use of grazing incidence--and total reflection-X-ray fluorescence spectrometry (GI-XRF and TXRF) for Cl trace analysis in nanometer-thin HfO2 films deposited using ALD. First, the results from different X-ray analysis approaches for the determination of Hf coverage are compared with the results from Rutherford backscattering spectrometry (RBS). Next, we discuss the selection of an appropriate X-ray excitation source for the analysis of traces within the high-kappa: layers. Finally, we combine both in a study on the accuracy of Cl determinations in HfO2 layers.

The oxidation of the terpenes alpha- and beta-pinene, limonene and Delta(3)-carene by hydroxyl radicals has been investigated in a fast-flow reactor coupled to a liquid nitrogen trap for collecting the carbonyl compounds. Identification of the products was performed via 2,4-dinitrophenylhydrazone (DNPH) derivatization of the carbonyls to form the mono- and di-DNPH derivatives, which were analysed by high-performance liquid chromatographic (HPLC)-DAD (diode array detector) and HPLC-mass spectrometry (HPLC-MS). Both electrospray ionization [ESI(-)] and atmospheric pressure chemical ionization [APCI(-)] were suitable for the detection of the DNPH derivatives of formaldehyde, acetaldehyde, myrtanal, campholene aldehyde, perillaldehyde, acetone, nopinone, trans-4-hydroxynopinone and 4-acetyl-1-methylcyclohexene. Also the mono-DNPH derivatives of the dicarbonyl compounds pinonaldehyde, endolim and caronaldehyde could be identified. The MS(2) spectra generated in the ion trap of the mass spectrometer allowed us to distinguish between aldehydes and ketones on the basis of the characteristic fragment ion m/ z 163 for the aldehydes. For the quantitative analysis of the mono-DNPH derivatives, ESI(-) in combination with single ion monitoring (SIM) detection showed the lowest detection limits. For the quantification of the dicarbonyl compounds, the acid-sensitive di-DNPH derivatives had to be formed by keeping the acidity in the acid-catalysed derivatization reaction at about 1.7 mM H(2)SO(4). Detection of these dicarbonyl compounds can only be performed by APCI(-) with somewhat lesser sensitivity than by HPLC-DAD.

A fast-flow reactor technique is described by which Fe atoms can be produced in the gas phase in the afterglow of microwave-induced plasmas in hydrogen/argon and hydrogen/helium mixtures. When the iron salt FeCl3(s) was brought into the gas phase by thermal sublimation at temperatures between 360 and 405 K, it was partly converted to Fe atoms by reaction of the gaseous compounds FexCl3x(g) with hydrogen atoms. The Fe atoms were detected by atomic absorption spectroscopy (AAS). It was shown that sublimation of the salt is the rate-determining step of the overall plasma-afterglow atomisation process. Experimental conditions for the generation of Fe atoms suited to kinetic studies start at a temperature of 303 K. In the downstream region the concentration of Fe atoms decays due to diffusion to the reactor wall. Binary diffusion coefficients DFe/Ar and DFe/He of 231.5 +/- 6.6 and 370.0 +/- 15.5 cm2 s-1 Torr at 303 K, respectively, were determined.

In this paper a method is described for determining and quantifying the degradation products of the reaction of alpha-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semi-volatile products are collected on a liquid nitrogen trap (LN2 trap) coated with a 2,4-dinitrophenylhydrazine (2,4-DNPH) solution and the batch samples are subsequently analyzed by HPLC. In order to perform quantitative measurements the batch samples contained two internal standards: benzaldehyde-2,4-DNPH and tolualdehyde-2,4-DNPH. In the experiments carried out at 50 Torr and 100 Torr, HPLC measurements showed that the semi-volatile products formaldehyde, acetaldehyde, acetone, campholenealdehyde and pinonaldehyde could be quantified as oxidation products for the alpha-pinene/OH reaction, with pinonaldehyde being the main product. Assuming that all these five oxidation products have the same collection efficiency on the LN2 trap, one arrives at the following relative product yields (expressed in mol %) at 50 and 100 Torr, respectively: 9.7+/-0.7 and 6+/-5 for formaldehyde; 1.1+/-0.1 and 0.9+/-0.5 for acetaldehyde; 16+/-1 and 6+/-2 for acetone; 11+/-2 and 5.5+/-0.7 for campholenealdehyde; 63+/-3 and 82+/-7 for pinonaldehyde.

In this paper an identification method is described for determining the degradation products of the reaction of alpha-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semivolatile products are collected on a liquid nitrogen trap (LN2 trap) and the batch samples are subsequently analysed by GC-MS and HPLC-MS. Some samples were also collected directly on a LpDNPH-cartridge, followed by HPLC-MS analysis. When experiments were carried out at 50 Torr both GC-MS and HPLC-MS measurements showed that campholenealdehyde and pinonaldehyde were identified as condensable oxidation products for the alpha-pinene/OH reaction, with pinonaldehyde being the main product. Furthermore, the LN2 trap collection method based on the in situ conversion of aldehydes and ketones to their 2,4-dinitrophenylhydrazone derivatives allowed the determination of formaldehyde, acetaldehyde and acetone. Although formaldehyde and acetone are present in small amounts in blank samples it could be established that formaldehyde and acetone are also formed in the alpha-pinene/OH reaction.

The reaction of nitrite at pH 5.0-7.0 with the deoxyhaemocyanin of a mollusc, the Roman snail (Helix pomatia), yielded nitrosylhaemocyanin (CuIA.NO+ CuIIB), in contrast with the formation of methaemocyanin with the deoxyhaemocyanin of the crustacean Astacus leptodactylus (mud crayfish). With Helix haemocyanin 1 NO was thereby liberated per active site, as shown by m.s., as against 2 NO with Astacus haemocyanin. Helix nitrosylhaemocyanin was characterized in c.d. by the negative extremum at 336 nm (CuIA.NO+) and by the mononuclear e.p.r. signal at g = 2 (CuIIB). Binuclear e.p.r. signals have been observed after the addition of nitrite to methaemocyanins. With Astacus methaemocyanin, no further reaction occurred, whereas with Helix methaemocyanin the mononuclear e.p.r. signal, characteristic for nitrosylhaemocyanin gradually appeared. This formation of Helix nitrosylhaemocyanin implicates the binding, most likely on CuIIA, of a second nitrite besides a bridging nitrite, so that a dismutation into NO and NO2 can occur there. A further dismutation of NO2 yields nitrite and nitrate. The formation of the latter was demonstrated by Raman spectrometry. The reaction rate of Helix methaemocyanin with nitrite decreased with increasing pH according to the Henderson-Hasselbalch equation with a pKa value of 6.77, attributed to a mu-aquo bridging ligand, which can be exchanged for nitrite, in equilibrium with a mu-hydroxo ligand which cannot. These data also favour the formulation of the final reaction product as nitrosylhaemocyanin instead of semi-methaemocyanin, with or without bound nitrite.

The reaction of nitrite at pH 5.7 with deoxyhaemocyanin of Astacus leptodactylus yielded methaemocyanin in two one-electron steps, as nitrite was reduced to NO. This methaemocyanin could be almost fully regenerated by an anaerobic treatment with HONH2, in contrast with the methaemocyanin prepared with H2O2. A destruction of active sites on treating oxyhaemocyanin with HONH2 explains the partial regeneration of methaemocyanin under air, as traces of H2O2 are formed in the autoxidation of HONH2. The reaction rate of nitrite with deoxyhaemocyanin is almost 15 times that with oxyhaemocyanin. The slope of -1.0 for the logarithm of the pseudo-first-order rate constants plotted against pH indicates that HNO2 is the reacting species. Methaemocyanin was e.p.r.-undetectable, but a binuclear signal was observed at g = 2 on binding nitrite to methaemocyanin. This signal disappeared with a pKa of 6.50, suggesting that a mu-aquo bridging ligand, which can be replaced by nitrite, is deprotonated to a mu-hydroxo bridging ligand, which resists substitution by nitrite. The intensity of this triplet e.p.r. signal allowed the determination of the association constant of nitrite to the active site of Astacus methaemocyanin and yielded a value of 237 M-1 at pH 5.7. The interpretation by some authors of nitrosylhaemocyanin as a nitrite derivative of semimethaemocyanin is contradicted by this rapid reaction of nitrite with copper(I) in deoxyhaemocyanin and in semi-methaemocyanin and by the low binding constant of nitrite to the active site of methaemocyanin.

The rate of the reaction of Astacus leptodactylus methaemocyanin with NO follows the Henderson-Hasselbalch equation with a pKa of 5.85, suggesting that one imidazole ligand of Cu was exchanged for NO. The reaction is blocked by F- as a bridging ligand. The same imidazole residue might be responsible for the decomposition of nitrosylhaemocyanin, [Cu1NO+CuII], with an unlocated binding site for NO, into methaemocyanin and NO, as the rate increase with pH. NO could react preferentially with CuA of Helix pomatia methaemocyanin, CuA'IICuBII, as it possibly has only two histidine ligands instead of the three of CuA in Astacus haemocyanin. This difference might explain the higher formation rate and the much greater stability of Helix nitrosylhaemocyanin. The fast reaction is governed by a pKa of 6.80, probably of a bridging mu-aquo ligand. With F- or a mu-hydroxo bridging ligand a low reaction rate was still observed, in contrast with Astacus methaemocyanin. Helix nitrosylhaemocyanin was transformed by N3- into methaemocyanin with the liberation of N2 and N2O. This methaemocyanin could almost quantitatively be regenerated with H2O2. Helix nitrosylhaemocyanin was only partially regenerated by a direct treatment with H2O2 and almost quantitatively by HONH2 in a similar fairly fast reaction, followed by a much slower one.