Effect of aldehyde and methoxy substituents on nucleophilic aromatic substitution by [F]fluoride

For a series of benzaldehydes only with a leaving group or with both a leaving group and a single methoxy substituent ¹⁸F-fluorination via nucleophilic aromatic substitution (S_NAr) was studied in DMF and Me₂SO. In general, the radiochemical yields were clearly higher in DMF than in Me₂SO. In the fluorodehalogenation reaction (leaving group: halogen = Br, Cl), extremely low radiochemical yields were observed in Me₂SO (<1%). By monitoring labeling reactions using HPLC, oxidation of the aldehyde function of the precursor was detected. Especially, 2-bromobenzaldehyde was oxidized fastest in Me₂SO (within 3 min reaction time, 90% of the precursor was consumed; radiochemical yield = 1.0 ± 0.5%); however, in DMF oxidation was always kept at a low level during the entire reaction (<5% of the precursor was oxidized; radiochemical yield = 73.0 ± 0.2%). In DMF, nitrobenzaldehydes with a methoxy substituent (methoxy group in meta-position to the nitro group) were labeled with good radiochemical yields (4-methoxy-2-nitrobenzaldehyde: 87 ± 3%; 2-methoxy-4-nitrobenzaldehyde: 83 ± 3%; 2-methoxy-6-nitrobenzaldehyde: 79 ± 4%) comparable to the non-substituted nitrobenzaldehydes (2-nitrobenzaldehyde: 84 ± 3%; 4-nitrobenzaldehyde: 81 ± 5%). Moreover, for structurally similar compounds, radiochemical yields showed a good correlation with ¹³C-NMR ppm values of the aromatic carbon atom bearing the leaving group.     

C-F?M interaction in anionic α-fluorovinyl rhenium oxycarbene complexes and their β-fluoroenolate analogs

The C-F?M⁺ interaction in anionic σ-(α-fluorovinyl)rhenium oxycarbene complexes, [RCFCFReC(O)R′(CO)₄]M (1-6), M = Na, Li, K is studied by ¹⁹F NMR in THF and Et₂O. The coordination of α-F to M⁺ results in an upfield shift of the corresponding ¹⁹F NMR signal and a decrease of ¹J_CF. The maximum shift is found for the Li salt of complex 4 in Et₂O (Δδ_Fα = 36.4 ppm), in which case a ⁷Li-¹⁹F spin-spin coupling is also observed (J_LiF = 40 Hz). The ΔE of C-F?M⁺ interaction and its effect on ¹⁹F shielding was further studied by DFT calculations using β-fluoroenolates as models, which confirmed a strong impact of CF-bond environment on the coordination ability of fluorine in these F,O-chelates. A compound with a β-fluoroenolate backbone but without rhenium, o-(α-fluorovinyl)phenolate 12, was prepared and studied by ¹⁹F NMR, and similarly showed indications of C-F?M⁺ interaction in THF solution. It is concluded that the donor ability of fluorine in the studied system is enhanced because of the conjugation of α-fluorovinyl group with the enolate π-system and back donation from the transition metal.     

Cs4P2Se10: A new compound discovered with the application of solid-state and high temperature NMR

The new compound Cs₄P₂Se₁₀ was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. ³¹P magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of −52.8 ppm that could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs₄P₂Se₁₀ has the triclinic space group P-1 with a=7.3587(11) Å, b=7.4546(11) Å, c=10.1420(15) Å, α=85.938(2)°, β=88.055(2)°, and γ=85.609(2)° and contains the [P₂Se₁₀]⁴⁻ anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe₄) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs₄P₂Se₁₀ was recovered upon annealing. The static ³¹P NMR spectrum at 350 °C contained a single peak with a −35 ppm chemical shift and a ∼7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature.     

Structure and spectroscopy of diorganotin(IV) complexes derived from N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide

Three new diorganotin(IV) complexes of the general formula R₂Sn[3-(OMe)-2-OC₆H₃CHN-NC(O)Ph] (R = Ph, Ia; R = Me, Ib; R = n-Bu, Ic) have been synthesised from the corresponding diorganotin(IV) dichlorides and the ligand, N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide in methanol at room temperature in the presence of trimethylamine. All the complexes have been characterized by elemental analysis, IR and ¹H, ¹³C, ¹⁵N, ¹¹⁹Sn NMR spectra, and their structures have been confirmed by single crystal X-ray diffraction analysis of one representative compound Ia. Complex Ia crystallises in the orthorhombic system, space group Pna2₁ with a = 12.424(5), b = 9.911(5), c = 18.872(5) Å; Z = 4. The ligand N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide (H₂L) coordinates to the metal centre in the enolate form via the phenolic O, imino N and enolic O atoms. In Ia, the central tin atom adopts a distorted trigonal bipyramidal coordination geometry with the oxygen atoms in axial positions, while the imino nitrogen atom of the Schiff base and the two phenyl groups occupy the equatorial sites. The δ(¹¹⁹Sn) values for the complexes Ia, Ib and Ic are −327.3, −151.7 and −187.2 ppm, respectively, thus indicating penta-coordinated Sn centres in solution.     

Synthesis of [F]xenon difluoride as a radiolabeling reagent from [F]fluoride ion in a micro-reactor and at production scale

[¹⁸F]Xenon difluoride ([¹⁸F]XeF₂), was produced by treating xenon difluoride with cyclotron-produced [¹⁸F]fluoride ion to provide a potentially useful agent for labeling novel radiotracers with fluorine-18 (t_1/2 = 109.7 min) for imaging applications with positron emission tomography. Firstly, the effects of various reaction parameters, for example, vessel material, solvent, cation and base on this process were studied at room temperature. Glass vials facilitated the reaction more readily than polypropylene vials. The reaction was less efficient in acetonitrile than in dichloromethane. Cs⁺ or K⁺ with or without the cryptand, K 2.2.2, was acceptable as counter cation. The production of [¹⁸F]XeF₂ was retarded by K₂CO₃, suggesting that generation of hydrogen fluoride in the reaction milieu promoted the incorporation of fluorine-18 into xenon difluoride. Secondly, the effect of temperature was studied using a microfluidic platform in which [¹⁸F]XeF₂ was produced in acetonitrile at elevated temperature (≥85 °C) over 94 s. These results enabled us to develop a method for obtaining [¹⁸F]XeF₂ on a production scale (up to 25 mCi) through reaction of [¹⁸F]fluoride ion with xenon difluoride in acetonitrile at 90 °C for 10 min. [¹⁸F]XeF₂ was separated from the reaction mixture by distillation at 110 °C. Furthermore, [¹⁸F]XeF₂ was shown to be reactive towards substrates, such as 1-((trimethylsilyl)oxy)cyclohexene and fluorene.     

Syntheses, structures and electrochemistry of some 1-(η-allylamino)-1-ferrocenylcarbene complexes of chromium(0), molybdenum(0) and tungsten(0) : Part 13: The chemistry of metallacyclic alkenylcarbene complexes

The metallacyclic complexes (OC)₄MC(η²-NHCH₂CHCHX)Fc (4; X = H) and (5; X = CH₂OH) [M = Cr: a; Mo: b; W: c; Fc = ferrocenyl = CpFe(C₅H₄)] were obtained in good yields upon photo-decarbonylation of the bimetallic allylaminocarbene complexes (OC)₅MC(NHCH₂CHCHX)Fc (2; X = H)/(3; X = CH₂OH). At room temperature complexes 2/3 exist as mixtures of E- and predominantly Z-isomers with regard to the C-N bond. The molecular structures of 4b and 4c were determined by X-ray diffraction analyses. The intermetallic communicative effects and the interplay of Fc and η²-alkene moieties of 4a and 4b were assessed by cyclovoltammetry. All complexes were also characterized in solution by one- and two-dimensional NMR spectroscopy (¹H, ¹³C, ¹H NOE, ¹H/¹H COSY, ¹³C/¹H HETCOR).     

Diphenyllead(IV) thiosemicarbazonates and pyrazolonates: Synthesis and characterization

Cyclization of thiosemicarbazones derived from β-keto esters and β-keto amides (HTSC) in the presence of diphenyllead(IV) acetate was explored in methanol solution at room temperature and under reflux. All β-keto ester TSCs underwent cyclization to give the corresponding pyrazolone (HL), which, except in one case, deprotonated and coordinated the PbPh₂²⁺ moiety to form homoleptic [PbPh₂(L)₂] or heteroleptic [PbPh₂(OAc)(L)] derivatives. Cyclization did not occur with β-keto amide TSCs and only [PbPh₂(TSC)₂] or [PbPh₂(OAc)(TSC)] thiosemicarbazonates were isolated. The complexes were characterized by IR spectroscopy in the solid state and by ¹H, ¹³C and ²⁰⁷Pb NMR spectroscopy in DMSO–d₆ solution, in which they evolve and decompose with time. Additionally, crystals of p-acetoacetanisidide thiosemicarbazone (HTSC¹⁰), [PbPh₂(OAc)(L⁵)] · MeOH (HL⁵ = 2,5-dihydro-3,4-dimethyl-5-oxo-1H-pyrazolone-1-carbothioamide), [PbPh₂Cl(L²)] (HL² = 2,5-dihydro-5-oxo-3-phenyl-1H-pyrazolone-1-carbothioamide), [PbPh₂(OAc)(TSC⁸)] · 2MeOH (HTSC⁸ = acetoacetanilide thiosemicarbazone), [PbPh₂(OAc)(TSC¹⁰)] · H₂O and [PbPh₂(OAc)(TSC¹¹)] · 0.75MeOH (HTSC¹¹ = o-acetoacetotoluidide) were studied by X-ray crystallography. The complexes, monomers or dimers with almost linear C–Pb–C moieties, are compared with the corresponding derivatives of Pb(II).     

Nucleophilic substitution of nitro groups by [F]fluoride in methoxy-substituted ortho-nitrobenzaldehydes—A systematic study

As model reactions for the introduction of [¹⁸F]fluorine into aromatic amino acids, the replacement of NO₂ by [¹⁸F]fluoride ion in mono- to tetra-methoxy-substituted ortho-nitrobenzaldehydes was systematically investigated. Unexpectedly, the highly methoxylated precursors 2,3,4-trimethoxy-6-nitrobenzaldehyde and 2,3,4,5-tetramethoxy-6-nitrobenzaldehyde showed high maximum radiochemical yields (82% and 48% respectively). When the electrophilicity of the leaving group substituted carbon atom is expressed by its ¹³C NMR chemical shift a good correlation with the reaction rate at the beginning of the reaction (first min) was found (R² = 0.89), whereas the maximum radiochemical yields correlated much poorer with this electrophilicity parameter. This may be caused by side reactions becoming influencial in the further reaction course. As possible side reactions the demethylation of methoxy groups and intramolecular redox reactions could be detected by HPLC/MS.     

Molecular structure and spectroscopic properties of N-methylmorpholine betaine complex with 4-hydroxybenzoic acid

Crystal structure of the 1:1 complex of N-methylmorpholine betaine (MMB) with 4-hydroxybenzoic acid (4-HBA) has been determined by X-ray diffraction. Crystals are orthorhombic, space group Pna2₁ with a=7.933(2), b=15.336(3), and Z=4, R=0.033. The acid molecule forms two O-H?O hydrogen bonds with two betaine molecules. The COOH group of the acid forms shorter hydrogen bond with betaine (2.587(2) Å), than the hydroxyl group (2.677(2) Å). The carbonyl oxygen atom of the acid also interacts with the methylene hydrogen atom of the betaine through C-H?O hydrogen bond (3.256(2) Å). Thus formed infinite chains parallel to the z axis are connected by other C-H?O hydrogen bonds into layers perpendicular to the x axis. The morpholine ring has a chair conformation with the methyl group in the equatorial position and CH₂COO⁻ group in the axial one. The powder FTIR and Raman spectra and semiempirical calculations of the isolated molecule confirm the structure of the complex investigated. The ¹H and ¹³C spectra indicate that in DMSO-d₆ solution, protons are not transferred from the acid to the betaine molecules.     

Al NMR studies of Ce-Al mixed oxides: origin of 40 ppm peak

CeO₂-γ-Al₂O₃ mixed oxides have been prepared by using both co-precipitation and impregnation methods followed by calcination at 650°C and investigated by ²⁷Al MAS NMR, powder X-ray diffraction and temperature programmed reduction techniques to understand the nature of chemical interaction existing between CeO₂ and γ-Al₂O₃. The ²⁷Al NMR spectra of CeO₂-containing samples showed an additional peak placed at 40 ppm along with the two peaks at 68 and 6 ppm which originate from the tetrahedrally and octahedrally coordinated Al³⁺ ions present in γ-Al₂O₃. As the concentration of CeO₂ in the mixed oxide increased, the intensity of the 40 ppm peak increased and this was the prominent peak for CeO₂-rich mixed oxide samples. The origin of this 40 ppm peak is discussed and it is inferred that this peak is due to Al³⁺ ions, which are present in CeO₂ lattice, forming a solid solution.     

Method development and validation for trifluoroacetic acid determination by capillary electrophoresis in combination with capacitively coupled contactless conductivity detection (CE-C4D)

A method was developed to determine traces of trifluoroacetic acid as impurity in synthetic or semi-synthetic drugs as antibiotics, macropeptides, etc. Capillary electrophoresis in combination with capacitively coupled contactless conductivity detection (CE-C⁴D) was used due to lack of UV absorbance property of trifluoroacetic acid (TFA). The optimized method took less than 1 min with good linearity (R² = 0.9995) for trifluoroacetic acid concentration from 2 to 100 ppm. It also has a good repeatability expressed by the relative standard deviation (% RSD) which is 1.2 and 2.1% for intraday and interday precision, respectively, at 50 ppm TFA, and good sensitivity with 0.34 ppm, 1.2 ppm LOD and LOQ, respectively. In addition, the content of TFA in synthetic drug, was determined using the validated method which gave good linearity (R² = 0.9996) for trifluoroacetic acid spiked into drug in a concentration range of 2-80 ppm, with good intraday repeatability of 2.0%.The analysis is performed in a background electrolyte composed of 20 mM morpholinoethane-sulfonic acid (Mes) and 20 mM l-histidine (l-His) pH 6.1. Cetyltrimethylammonium bromide (CTAB) was added as flow modifier in a concentration (0.2 mM) lower than the critical micellar concentration. Ammonium formate 6 ppm was used as internal standard. The applied voltage was 30 kV in reverse polarity. A fused silica capillary with 75 μm internal diameter and total length 47 cm (31 cm to C⁴D detector and 37 cm to DAD detector) was used.     

The first N,N′-ditosyl-substituted cyclic boron cation, stabilized by neighboring-group participation by two sulfonyl groups, and the alternative, stabilized by polar solvents

When 2-bromo-1,3-ditosyl-1,3,2-diazaborolidine was treated with AgSbF₆, a novel cyclic boron cation was formed in CD₂Cl₂, the ¹¹B NMR chemical shift of which appeared at 8.7 ppm. Ab initio calculations were consistent with the cationic boron center being stabilized by neighboring-group participation of the two sulfonyl functions. The reaction in CD₃NO₂ resulted in an alternate formation of a cyclic boron cation species (16.2 ppm), stabilized by coordination to the basic solvents.     

Be and P NMR analyses on Be complexation with cyclo-tri-μ-imidotriphosphate anions in aqueous solution

Microscopic information on the complexation of Be²⁺ with cyclo-tri-μ-imidotriphosphate anions in aqueous solution has been gained by both ⁹Be and ³¹P NMR techniques at −2.3 °C. Separate NMR signals corresponding to free and complexed species have been observed in both spectra. Based on an empirical additivity rule, i.e., proportionality observed between the ⁹Be NMR chemical shift values and the number of coordinating atoms of ligand molecules, the ⁹Be NMR spectra have been deconvoluted. By precise equilibrium analyses, the formation of [BeX(H₂O)₃]⁺ and [BeX₂(H₂O)₂]⁰ (X = non-bridging oxygen donor as a coordination atom in the phosphate groups) has been verified, and the formation of complexes coordinating with the nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. Instead, the formation of one-to-one (ML) complexes, one-to-two (ML₂), together with two-to-one (M₂L) complexes (L = cP₃O₆(NH)₃) has been disclosed, the stability constants of which have been evaluated as log K_ML = 3.87 ± 0.03 (mol dm⁻³)⁻¹, log K_ML2 = 2.43 ± 0.03 (mol dm⁻³)⁻² and log K_M2L = 1.30 ± 0.02 (mol dm⁻³)⁻², respectively. ³¹P NMR spectra measured concurrently have verified the formation of the complexes estimated by the ⁹Be NMR measurement. Intrinsic ³¹P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be²⁺, together with the ³¹P-³¹P spin-spin coupling constants have been determined.     

Pyrroles from ketoximes and acetylene

The reaction between ketoximes CH₃(RCH₂)C = NOH and acetylene in the presence of KOH and dimethyl sulfoxide at 120°C leads exclusively to 1-vinyl-2-methyl-3-R-pyrroles in 73–87% yields. The regiospecificity of the reaction is disrupted when the temperature is raised, and the fraction of a second isomer (1-vinyl-2-RCH₂-pyrrole) reaches 20–50% at 140°C. Regioselectivity is not observed for R¹CH₂(R²CH₂)C = NOH (R¹ and R² = n-alkyl). The relative shifts of the signals of the ring protons and the vinyl group for a number of 2-alkyl-1-vinyl- and 2,3-dialkyl-1-vinylpyrroles were measured. Alkyl substituents have a distinct effect on the chemical shifts of the protons of the 4–5 bonds. As the volume of the 2-alkyl substituent increases the protons of the N-vinyl group are deshielded by 0.10–0.13 ppm, and the 4-H ring proton is shielded by 0.05–0.16 ppm; this is explained by steric inhibition of the p- conjugation in the N-vinyl group during an s-trans(anti)-gauche conformational transition.This is actually communication XVI. The first publications (for example, see [1–3] and the literature cited in them) were not numbered.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 54–59, January, 1978.     

Advantages of the Ns group in the reactions of N-SO2R inosines with benzylamine and with NH3

The reactivity of N¹-alkylsulfonyl- and N¹-arylsulfonyl-2′,3′,5′-tri-O-acetylinosine with benzylamine and with ¹⁵NH₃, regarding the attack on C2, has been shown to be in the order CF₃SO₂ (Tf) > 2,4-(NO₂)₂C₆H₃SO₂ (DNs) ? 4-NO₂C₆H₄SO₂ (pNs) ≈ C₆F₅SO₂ (PFBs) > 2-NO₂C₆H₄SO₂ (Ns) ? CH₃SO₂ (Ms) > 4-CH₃C₆H₄SO₂ (Ts) > 2,4,6-(CH₃)₃C₆H₂SO₂ (Mts). In spite of its intermediate reactivity, the Ns group is the most appropriate, since in this case the formation of by-products is minimised during the ring-opening and ring-closing steps of the process. Another advantage of the Ns group is thus disclosed.     

Electronic effects of Me3SiOCR2 substituents in acetylene derivatives

The σR⁰ and σ_p parameters of Me₃SiOCR₂ and HOCR₂ substituents at the triple bond were determined using the IR spectra of individual acetylene derivatives and their H-complexes. These parameters vary as the effective charge on the atoms of the C≡C fragment of terminal acetylenic alcohols and their trimethylsilyl ethers changes due to intermolecular interaction. The most reliable values of σR⁰ and σ_p parameters (−0.02 and −0.03, respectively) for the Me₃SiOCH₂ substituent were established; they indicate a sharp decrease in σ,π-conjugation of the Me₃SiOCH₂ substituent with the triple bond as compared to the Me₃SiCH₂ substituent. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1759–1762, September, 1998.     

Synthesis,structure and characterization of [Mg7(μ3-OCH2CH2OMe)6(μ-OCH2CH2OMe)6][Al(n-Bu)4]2 – A cationic heptanuclear magnesium complex consisting of discrete cations and tetrabutylaluminate anions

Dibutylmagnesium (contaminated with Al(n-Bu)₃; n_Mg:n_Al ca. 1:0.2) was found to react with MeOCH₂CH₂OH followed by the addition of PhSCH(Me)Ph in the presence of 0.2 equiv n-butyllithium yielding [Mg₇(μ₃-OCH₂CH₂OMe)₆(μ-OCH₂CH₂OMe)₆][Al(n-Bu)₄]₂ (1) as the principal product (yield 40–45% referred to MeOCH₂CH₂OH). The single-crystal X-ray diffraction analysis revealed that the centrosymmetric cationic heptamagnesium complex is built up from seven edge-shared MgO₆ octahedra. The [Al(n-Bu)₄]⁻ anions adopt approximately a tetrahedral AlC₄ symmetry. ¹H, ¹³C and ²⁷Al NMR spectroscopic measurements showed that in THF solution the structures both of the heptamagnesium complex and the tetrabutylaluminate anion are preserved and that there are no cation–anion interactions reducing the symmetry. The ²⁷Al resonance (151.6 ppm) was found to be very sharp (w_1/2 = 5 Hz), the coupling constant ¹J(²⁷Al,¹³C) amounts to 72.3 Hz.     

Structural and spectral studies of 3-(2-hydroxyphenylimino)-1-phenylbutan-1-one and its diorganotin(IV) complexes

Two diorganotin(IV) complexes of the general formula R₂Sn[Ph(O)CCH-C(Me)N-C₆H₄(O)] (R = Ph, 1a; R = Me, 1b) have been synthesized from the corresponding diorganotin(IV) dichlorides and the ligand, 3-(2-hydroxyphenylimino)-1-phenylbutan-1-one (1) in methanol at room temperature in presence of triethylamine. Both compounds have been characterized by elemental analyses, IR and ¹H, ¹³C, ¹⁵N, ¹¹⁹Sn NMR spectra. The structures of the free ligand and the complexes have been confirmed by single crystal X-ray diffraction. There are three independent molecules in the crystal structure of the ligand 1 and in all three the O-bound proton is transferred to the imine nitrogen and makes an intramolecular N-H?O hydrogen bond with the carbonyl oxygen. In turn this makes an intermolecular hydrogen bond with the phenolic H atom. The crystal structure of 1 is trigonal and a new polymorph; triclinic and monoclinic forms have already been published. In 1a, the central tin atom adopts distorted trigonal-bipyramidal coordination geometry whereas in dimeric 1b it is distorted octahedral when including the intermolecular Sn-O(phenolic) bond [2.7998(20) Å]. The δ (¹¹⁹Sn) values for the complexes 1a and 1b are −306.6 and −127.9 ppm, respectively, thus indicating penta-coordinated Sn centres in solution.     

N,N-polymethylene-bisadenine complexes with d metal ions

The reaction of N⁹,N^9′-(tri or tetramethylene)-bisadenines (Ade₂C_x; x = 3 or 4) in HCl 2 M at 50 °C with MCl₂ · 2H₂O [M = Zn(II), Cd(II)] yields outer sphere compounds like the previously described [(H-Ade)₂C₃][ZnCl₄] · H₂O (3) and [(H-Ade)₂C₃]₂[Cd₂Cl₈(H₂O)₂] · 4H₂O (4) for Ade₂C₃ and the new {[(H-Ade)₂C₄][Cd₂Cl₆(H₂O)₂] · 2H₂O}_n (5) for Ade₂C₄. On the other hand, only in case of Zn(II) complexes by changing [HCl] to 0.1 M, the inner sphere compounds [H-(Ade)₂C₃(ZnCl₃)] (6) and [H-(Ade)₂C₄(ZnCl₃)] · 1.5H₂O (7) are obtained. X-ray diffraction study of compound 6, which represents the first inner sphere complex with a N⁹,N^9′-bisadenine, shows a zwitterionic form with one adenine ring protonated at N(1) while the other ring is coordinated via N(7) to a ZnCl₃ moiety as in other alkyl-adenine derivatives. In addition, with Ade₂C₄, is also possible to obtain another inner sphere complex: [(H-Ade)₂C₄(ZnCl₃)₂] · 3H₂O (8).     

A new electrochemiluminescent detection system equipped with an electrically controlled heating cylindrical microelectrode

A new electrochemiluminescent (ECL) detection system equipped with an electrically controlled heating cylindrical microelectrode (HME) was developed in this paper. The cylindrical microelectrode made of platinum wire (25 μm in diameter, 6 mm in long) was used as the working electrode of the ECL detection system, the temperature of the electrode could be controlled electrically. The Ru(bpy)₃²⁺-ECL and Ru(bpy)₃²⁺-C₂O₄²⁻-ECL systems were used to evaluate this ECL detection system. The detection limit for oxalate was found to be 3.0 × 10⁻⁴ mol/L when T_e (temperature of the HME) was 22 °C, and found to be 3.0 × 10⁻⁶ mol/L at 80 °C, which indicates that the detection limit can be improved greatly at higher T_e, based on which, it is possible to establish a more sensitive method for measurement of ECL by using a heated microelectrode.