The second and third order non-linear optical properties of liquid crystalline polymers

The second and third order non-linear optical susceptibilities of several donoracceptor substituted side chain polymers, some of which exhibit mesophases, will be reported. The susceptibilities were measured by harmonic generation from thin films, typically 0·5 μm thick, at a fundamental wavelength of 1064 nm and 1579 nm. For second harmonic generation, the spin coated films were contact poled on a glass substrate with an interdigited electrode pattern. Typical values obtained were χ⁽²⁾₃₁ = 1 × 10^-9 esu and χ⁽²⁾₃₃ = 3 × 10^-9 esu, the largest value was χ⁽²⁾₃₃ = 6·3 × 10^-9 esu. The difficulty in deriving reliable second order structure-property relations because of the large effect which the contact poling process has on the non-linear optical susceptibility of the films will be highlighted. The highest χ⁽³⁾ value of 5·8 × 10^-12 esu obtained from an amorphous film of a polymer with an asymmetrically substituted azo side group is comparable with the susceptibility of more typical third order non-linear materials such as the main chain polymers polyphenylacetylene and poly-p-phenylenebenzobisthiazole.     

Photoinduced electron transfer in crystal violet (CV)–bovine serum albumin (BSA) system: evaluation of reaction paths and radical intermediates

Photoinduced electron transfer (PET) from excited probes attached to proteins is of considerable current interest. Photochemical processes following 532 nm excitation of triphenyl methane dye, crystal violet (CV⁺) bound to a protein, bovine serum albumin (BSA), have been investigated in picosecond (ps) to microseconds (μs) time scales by flash photolysis technique. The excited singlet state lifetime of CV⁺ is found to be increased to 130 ps as compared to 1–5 ps for the unbound dye in low viscosity solvents. From flash photolysis studies in microsecond region, transient absorption in the region 650 nm is observed which is attributed to the dication radical CV√²⁺ formed by electron transfer from ³CV^+* to BSA, contrary to electron transfer from BSA to the excited dye as proposed in a recent report. Supporting spectral evidence for the electron transfer from ³CV^+* to BSA is obtained from pulse radiolysis studies.     

The lively chemistry of the di-μ-methylene-bis(pentamethylcyclopentadienyl-rhodium) complexes, analogues of surface reactions in heterogeneous catalysis

The chemistry of the di-μ-methylene-bis(pentamethylcyclopentadienyl-rhodium) complexes is reviewed. The complex [{(η⁵-C₅Me₅)RhCl₂}₂] (1a) reacted with MeLi to give, after oxidative work-up, blood-red cis-[{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)₂], 2. This has the two rhodiums in the +4 oxidation state (d⁵), and linked by a metal-metal bond (2.620 Å). Trans-2 was formed on isomerisation of cis-2 in the presence of Lewis acids, or by direct reaction of 1a with Al₂Me₆, followed by dehydrogenation with acetone. The Rh-methyls in [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)₂] were readily replaced under acidic conditions (HX) to give [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(X)₂] (X = Cl, Br or I); these latter complexes reacted with a variety of RMgX to give [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(R)₂] (R = alkyl, Ph, vinyl, etc.). Trans-2 also reacted with HBF₄ in the presence of L to give first [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)(L)]⁺ and then [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(L)₂]²⁺ (L = MeCN, CO, etc.). The {(η⁵-C₅Me₅)Rh(μ-CH₂)}₂ core is rather kinetically inert and also forms a variety of complexes with oxy-ligands, both cis-, e.g. [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(μ-OAc)]⁺ and trans-, such as [(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(H₂O)₂]²⁺. The complexes [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(R)L]⁺ (R = Me or aryl) in the presence of CO, or [{(η⁵-C₄Me₅)Rh(μ-CH₂)}₂(R)₂] (R = Me, Ph or CO₂Me) in the presence of mild oxidants, readily yield the C---C---C coupled products RCH=CH₂. The mechanisms of these couplings have been elucidated by detailed labelling studies: they are more complex than expected, but allow direct analogies to be drawn to C---C couplints that occur during Fischer-Tropsch reactions on rhodium surfaces.     

Quantitative analysis of fluid inclusions in evaporites by ion chromatography

Natural salt minerals often contain inclusions of saturated salt solutions with diameters from 1 to> 100 μm. With the quantification of the composition of the fluid inclusions, the origin and metamorphism of the salt rocks can be interpreted. Hence, these data are important concerning the long-term safety of underground repositories in salt rocks [1]. For the extraction of the solutions in fluid inclusions with diameters 300 μm, an optical precision instrument was developed. For the simultaneous determination of Cl⁻, Br⁻, SO₄²⁻, Li⁺, Na⁺, K⁺, Mg²⁺ and Ca²⁺ two ion chromatographic systems with conductivity detection for cations and anions and additional photometric detection for Br⁻ were used. To prevent column overload, the Cl concentration must be less than 50 μg/ml in the measuring solution. The extracted samples (volumes> 0.1 μl) are diluted with demineralized water by a factor of 1 · 10⁴ (20-μl sample loops). The practical limit of determination for the measured elements is 0.01–0.3 μg/ml in the measuring solutions. By calculation of the anion and cation charge balance (molar equivalence), a relative error of <5% for the analysis of fluid inclusions was found.     

Reactivity of tri- and tetra-nuclear ethylidyne cyclopentadienylcobalt clusters towards protonic acids

The bis(μ₃-ethylidyne) tricobalt cluster [(CpCo)₃(μ₃-CCH₃)₂] (1b) is protonated by trifluoroacetic acid to give the dicobalt edge-protonated cation [H(CpCo)₃(μ₃-CCH₃)₂]⁺ [lb + H]⁺. Protonation of the μ₃-ethylidyne tetracobalt cluster hydride [H(CpCo)₄(μ₃-CCH₃)] (3) takes place in two consecutive steps. At low temperature [H₂(CpCo)₄(μ₃-CCH₃)]⁺ [3 + H]⁺ is formed first, and is then slowly converted into [H₃(CpCo)₄(μ₃-CCH₃)]²⁺ [3 + 2H]²⁺ by an excess of acid. As judged by the ¹H NMR data and the crystal structure of [3 + X]⁺[(CF₃COO)₂X]⁻ (X = H or D) the endo hydrogens in [3 + H]⁺ and [3 + 2H]²⁺ occupy μ₃-(Co₃) face capping hydridic positions. The cations [1b + H]⁺ and [3 + H]⁺ show hydride fluxionality in solution, which in the case of [3 + H]⁺ can be frozen out on the NMR timescale at low temperature (ΔG ^≠ (203 K) = 40.8 kJ/mol). The structure of [3 + X]⁺ [(CF₃COO)₂X]⁻ (X = H or D) was determined by X-ray crystallography. One of the hydrides/deuterides is located on the crystallographic mirror plane, capping a tricobalt face of the cluster cation. The other endo hydrogen atom is believed to be disordered between the other two μ₃-(Co₃) sites, which are related by space group symmetry. Deuteronation of 3 shows a strong normal kinetic deuterium isotope effect. From the temperature independence of the ¹H NMR spectrum of [3 + 2D]²⁺ a non-fluxional solution structure can be inferred. In all the systems studied, hydridic (μ₂- or μ₃-) sites are thermodynamically preferred to possible isomeric agostic CoHC or Co₂HC sites for the endo hydrogens. Agostic interactions cannot, however, be ruled out in transient intermediates during the course of the protonations.     

1.54 and 1.75 μm infrared luminescence of Y2O3:Er

A new 1.75 μm infrared emission transition of Y₂O₃:Er³⁺ is assigned to the ⁴S_3/2 → ⁴I_9/2 transition of Er³⁺ ions situated at the C₂ sites of cubic RE₂O₃ (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm ⁴I_15/2–⁴I_13/2 absorption transition due to Er³⁺ at S₆ and C₂ sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er³⁺ at the different sites. The 1.54 μm emission lines are predominantly from Er³⁺ ions at C₂ sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er³⁺ dopant ion concentration, preparation technique, Yb³⁺ co-doping, temperature change and different excitation line are rationalized.     

Synthesis, structure and hydrogenation catalytic activity of [Ru3(μ3,η-ampy)(μ,η:η-PhC=CHPh)(CO)6(PPh3) (Hampy = 2-amino-6-methylpyridine)

The compound [RU₃(μ₃,η²- -ampy)(μ₃η¹:η²-PhC=CHPh)(CO)₆(PPh₃)₂] (1) (ampy = 2-amino-6-methylpyridinate) has been prepared by reaction of [RU₃(η-H)(μ₃,η²- ampy) (μ,η¹:η²-PhC=CHPh)(CO)₇(PPh₃)] with triphenylphosphine at room temperature. However, the reaction of [RU₃(μ-H)(μ₃, η² -ampy)(CO)₇(PPh₃)₂] with diphenylacetylene requires a higher temperature (110°C) and does not give complex 1 but the phenyl derivative [RU₃(μ₃,η²-ampy)(μ,η ¹:η² -PhC=CHPh)(μ,-PPh₂)(Ph)(CO)₅(PPh₃)] (2). The thermolysis of complex 1 (110°C) also gives complex 2 quantitatively. Both 1 and 2 have been characterized by0 X-ray diffraction methods. Complex 1 is a catalyst precursor for the homogeneous hydrogenation of diphenylacetylene to a mixture of cis- and trans -stilbene under mild conditions (80°C, 1 atm. of H₂), although progressive deactivation of the catalytic species is observed. The dihydride [RU₃(μ-H)₂(μ ₃,η²-ampy)(μ,η¹:η²- PhC=CHPh)(CO)₅(PPh₃)₂] (3), which has been characterized spectroscopically, is an intermediate in the catalytic hydrogenation reaction.     

Silane-induced ring-opening polymerization of 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclopentane catalyzed by a triruthenium cluster

The silane-induced ring-opening polymerization of a cyclic siloxane, 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclopentane (2), is catalyzed by a ruthenium cluster, (μ₃,η²:η³:η⁵-acenapthylene)Ru₃(CO)₇ (1), to give poly(tetramethylsilethylenesiloxane) with M_n=6300–780,000 and M_w/M_n=1.5–3.0. The molecular weight of the polymer can be controlled by changing the concentration of the monomer solution. Addition of acetone results in formation of the polymer with M_n=4400, spectroscopic analysis of which reveals existence of a siloxy and an isopropoxy moieties at the end group.     

Application of a synchrotron microprobe to the analytical characterization of ion-implanted material

A synchrotron microprobe has been used to characterize ion implantations of nickel and cobalt in silicon (100) or (111) wafers. The synchrotron radiation is collimated by means of a rigid cylindrical glass capillary of 110 mm length, 5 mm outer and 30 μm or 10 μm inner diameter. The beam is pointed at the wafer sample and the emitted radiation of X-rays is detected by an energy dispersive spectrometer. Line scans are recorded step by step over the implantation areas and across their borders. The sharpness of the borders is characterized at a lateral resolution of 13 μm and the edge lengths ranging from 0.6 to 8 mm are determined with an accuracy better than ± 20 μm. The signal intensity and implantation dose of cobalt ranging from 1 × 10¹⁵ to 1 × 10¹⁷ ions cm⁻² show a linear relationship as is to be expected for the micrometre thin implanted layers.     

Reactions of the cationic diruthenium carbonyl complex [Ru2(μ-dppm)2(CO)4(μ,η-O2CMe)] with bidentate ligands; intramolecularly assisted stereospecific synthesis via the second-sphere face-to-face π–π stacking interactions

The reactions of the diruthenium carbonyl complexes [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]X (X=BF₄⁻ (1a) or PF₆⁻ (1b)) with neutral or anionic bidentate ligands (L,L) afford a series of the diruthenium bridging carbonyl complexes [Ru₂(μ-dppm)₂(μ-CO)₂(η²-(L,L))₂]X_n ((L,L)=acetate (O₂CMe), 2,2′-bipyridine (bpy), acetylacetonate (acac), 8-quinolinolate (quin); n=0, 1, 2). Apparently with coordination of the bidentate ligands, the bound acetate ligand of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ either migrates within the same complex or into a different one, or is simply replaced. The reaction of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ (1) with 2,2′-bipyridine produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)₂] (2), [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-bpy)]⁺ (3), and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-bpy)₂]²⁺ (4). Alternatively compound 2 can be prepared from the reaction of 1a with MeCO₂H–Et₃N, while compound 4 can be obtained from the reaction of 3 with bpy. The reaction of 1b with acetylacetone–Et₃N produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-acac)] (5) and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-acac)₂] (6). Compound 2 can also react with acetylacetone–Et₃N to produce 6. Surprisingly [Ru₂(μ-dppm)₂(μ-CO)₂(η²-quin)₂] (7) was obtained stereospecifically as the only one product from the reaction of 1b with 8-quinolinol–Et₃N. The structure of 7 has been established by X-ray crystallography and found to adopt a cis geometry. Further, the stereospecific reaction is probably caused by the second-sphere π–π face-to-face stacking interactions between the phenyl rings of dppm and the electron-deficient six-membered ring moiety of the bound quinolinate (i.e. the N-included six-membered ring) in 7. The presence of such interactions is indeed supported by an observed charge-transfer band in a UV–vis spectrum.     

Interactions of thorium isotopes with colloidal organic matter in oceanic environments

The phase speciation of thorium and consequences for the residence times of colloids have been examined in seawater of the Middle Atlantic Bight (MAB) and the Gulf of Mexico. Two fractions of colloidal organic matter (COM), 0.2 μm > COM₁ > 1 kD and 0.2 μm > COM₁₀ > 10 kD, were sampled using cross-flow ultrafiltration techniques and measured for their ²³⁴Th activity and organic carbon concentration. The ratios of mass concentrations of COM₁ to those of suspended particulate matter were as high as 10 in the MAB and 6–34 in the Gulf of Mexico. Higher concentrations of colloids may be of great importance in the biogeochemical cycling of many particle-reactive nuclides or trace elements owing to their high specific surface area and complexation capacity. A significant fraction of ²³⁴Th in the traditionally defined “dissolved” pool was found to be associated with colloids. On average, about 10% of “dissolved” ²³⁴Th was in the colloidal fraction of sizes between 10 kDa and 0.2 μm, and 50% was in the 1 kDa-0.2 μm fraction. Values of the partition coefficients [K_c: (0.5−4) × 10⁶ ml g⁻¹ for K_c1 and (0.5−7) × 10⁶ ml g⁻¹ for K_c10] of ²³⁴Th between truly dissolved (<1 kDa) and colloidal fractions approximated those for Th-particle interactions [K_p: (0.3−10) × 10⁶ ml g⁻¹], indicating that colloid and suspended particle surface sites are similar. The distribution of ²³⁴Th between dissolved, colloidal, and particulate phases was broadly similar to that of organic carbon in these oceanic environments. Thus, thorium isotopes might be used as tracers of marine organic carbon cycling. Residence times of colloids derived from ²³⁴Th:²³⁸U disequilibria were consistently short, ranging from 1 to 14 days for COM₁₀ and from 5 to 65 days for COM₁, suggesting that marine colloids are highly reactive in marine biogeochemical processes. The discrepancy between apparent turnover times of colloids (1 kDa) derived from Th scavenging and ¹⁴C measurements suggest that ²³⁴Th and ¹⁴C may trace different geochemical pathways of colloids in the ocean.     

Iron carbonyl complexes from 2-[2,3-diaza-4-(2-thienyl)buta-1,3-dienyl]thiophene: N---N bond cleavage and cyclometalation

When thienyl Schiff base 1, derived from 2-formylthiophene and hydrazine, reacted with Fe₂(CO)₉ in n-hexane, three major complexes were obtained: (1) a diironhexacarbonyl complex with two 2-thienylmethylideneamido bridging ligands 2, which resulted from the =N---N= bond cleavage of ligand 1; (2) a doubly cyclometalated di-μ-di-(η¹:η²-thienyl; η¹:η¹(N))bis(hexacarbonyldiiron) complex (3); and (3) a cyclometalated (μ-η¹:η²-thienyl; η¹:η¹(N))hexacarbonyldiiron complex (4). Molecular structures of compounds 1a, 1c, and 2a have been determined by single-crystal X-ray diffraction.     

The Ericksen number and Deborah number cascades in sheared polymeric nematics

Samples of liquid crystalline poly(γ-benzyl-glutamate) solutions are sheared between glass surfaces with gaps, d = 10-500 μ, and shearing velocities, V = 0·05-10 000 μs^-1 so that the Ericksen number E ≡ Vdγ₁/K is varied over a large range, E ≈ 1-10⁷. Here γ₁ is the rotational viscosity and K₁ is the Frank splay constant, with γ₁/K₁ estimated to be approximately 1 s μ^-2 for our samples. We observe by polarizing microscopy a sequence of transitions with increasing Ericksen number analogous to that observed in small molecule tumbling nematics: namely rotation of the director out of the shearing plane and into the vorticity direction at Vd ≈ 25 μ² s^-1, and formation of roll cells at Vd ≈ 50 μ² s^-1. The roll cells become finer with increased Vd in accord with predictions of linear stability theory using the Leslie-Ericksen equations, and at Vd ≳ 500 μ² s^-1, the cells become very irregular, producing director turbulence. The turbulence becomes finer in scale as Vd increases, reaching sub-micron, and possibly molecular scales when Vd ≧ 10⁵ μ² s^-1. At the highest velocities, transitions in orientation and texture are controlled by the Deborah number De≡λV/d, where λ is the molecular relaxation time, and uniform texture-free samples are obtained when De ≳ 5.     

Simulated T ← S spectra of benzaldehydes as a function of the energy gap between the ππ and nπ levels

The T_1,2 ← S₀ spectra of benzaldehydes have been studied as a function of the energy separation between the vibrationless levels. It is shown that the spectra are very complicated in the region of ΔE[T₂⁰(nπ^*)-T₁⁰(ππ^*)] = 250–400 cm⁻¹, reflecting effective vibronic interferences between T₂⁰(0-0) and each of the ν₃₆-ν₃₃ out-of-plane vibrational levels of T₁⁰(ππ^*). The simulated spectra correspond to the observed spectra. In the case of T₁⁰ = ³nπ^* and T₂⁰ = ³ππ^* the spectral change is not so drastic as in the reverse case loc. cit. because the optical intensity generally concentrates in the longest wavelength band, i.e., the origin band of the T₁(nπ^*) ← S₀ transition. The simulation spectra are useful for interpretation of the absorption spectra in similar electronic structure systems of substituted benzaldehydes.     

芳香查尔酮衍生物的合成、理论计算及三阶非线性光学性质

合成了2种新的具有潜在应用价值的非线性光学(NLO)有机材料芳香查尔酮衍生物1-(呋喃-2-基)-3-(4-甲氧基苯基)丙烯酮(1)和1-(噻吩-2-基)-3-(4-甲氧基苯基)丙烯酮(2),并对其进行了NMR、IR和HR-MS结构表征。 采用4f相位相干成像技术测定了化合物1和2的三阶NLO性质并确定了相关参数:脉冲宽度4 nm,激光波长440 nm,化合物1:非线性吸收系数β=5.5×10^-10 m/W,非线性折射系数n₂=-2.1×10^-17 m²/W,三阶非线性极化率χ⁽³⁾=1.58×10^-11 esu;化合物2:β=-2.4×10^-10 m/W,n₂=0.3×10^-17 m²/W,χ⁽³⁾=0.50×10^-11 esu;并测定了紫外光谱和DSC曲线。 采用密度泛函方法计算了化合物1和2的轨道能量和极化率,结果表明电子转移能在分子内部进行,说明比较易于极化,展示了良好的非线性光学性质。     

芘基查尔酮的合成及三阶非线性光学性质

合成了一种新的具有潜在应用价值的非线性光学(NLO)有机材料1-(芘-1-基)-3-(4-二甲氨基苯基)丙烯酮(PMAK),并通过 NMR、IR、MS和元素分析等技术手段进行了表征。 采用溶液Nd:YAG激光技术测定了PMAK的三阶非线性光学性质并确定了相关参数。 纳秒实验结果:折射率n₂=-3.5×10^-17 m²/W,吸收系数β=7.0×10^-10 m/W,极化率χ⁽³⁾=2.54×10^-11 esu,分子超极化率γ=3.44×10^-30 esu;皮秒实验结果:n₂=-2.8×10^-18 m²/W,β=8.3×10^-11 m/W,χ⁽³⁾=2.49×10^-12 esu,γ=3.33×10^-31 esu。     

Electron counting and bonding analysis in triruthenium clusters containing sulfoximido ligands: true or false electron-deficient systems?

Triruthenium clusters containing a methylphenylsulfoximido cap or bridge, Ru₃(CO)₉(μ₂-H)[μ₃-NS(O)MePh] (1), Ru₃(CO)₁₀(μ₂-H)[μ₃-NS(O)MePh] (2), Ru₃(CO)₈(μ₃-η²-CPhCHBu)[μ₃-NS(O)MePh] (3), Ru₃(CO)₉(μ₃-η²-PhCCCCHPh)[μ₂-NS(O)MePh] (4), and Ru₃(CO)₇(μ₂-CO)(μ₃-η²-PhCCCCHPh)[μ₃-NS(O)MePh] (5) have been examined by EHT and DFT calculations in order to analyze the bonding present in the clusters and to establish the electron counting. They clearly show that a μ₃-sulfoximido group is not a 3e⁻ ligand as one may be led to think at first sight, but rather acts as a three-orbital/5e⁻ system, i.e. should be considered as isolobal to an N---R⁻ ligand. Because of some delocalization of its π-type orbitals on the sulfur and oxygen atoms, it is expected to bind slightly less strongly to metal atoms than classical imido ligands. Once in a μ₂ coordination mode, the sulfoximido ligand retains a lone pair on its pyramidalized N atom and becomes a two-orbital/3e⁻ ligand. It follows that clusters 1, 2, 4 and 5 are electron-precise, whereas cluster 3 is electron deficient with respect to the 18e⁻ rule but obeys the polyhedral skeletal electron pair electron-counting rules. Consistently, all the calculated clusters exhibit large HOMO–LUMO gaps and no trace of electron deficiency can be found in their electronic structures.     

1-(芘-1-基)-3-(4-甲氧基苯基)丙烯酮的合成及三阶非线性光学性质

合成了一种新的有机非线性光学(NLO)材料1-(芘-1-基)-3-(4-甲氧基苯基)丙烯酮(PMPAK),通过¹H NMR、IR、HR-MS和元素分析表征其结构。 以Nd:YAG-Laser System作为光源,激光波长450 nm,脉冲宽度4 ns(FWHM),采用4f相位相干成像技术测定了PMPAK的三阶NLO性质并确定了相关参数:非线性折射率n₂=-1.84×10^-16 m²/W,非线性吸收系数β=2.53×10^-9 m/W,非线性极化率χ⁽³⁾=1.137×10^-10 esu。     

Study of the performance of an optochemical sensor for ammonia

An optical sensor for ammonia based on ion pairing has been investigated. A pH-sensitive dye (bromophenol blue) was immobilized as an ion pair with cetyltrimethylammonium in a silicone matrix. The colour of the dye changes reversibly from yellow to blue with increasing concentration of ammonia in the sample. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength. All measurements were performed with a dual-beam, solid state photometer. The measurement range is from 6 × 10⁻⁷ to 1 × 10⁻³ M (0.01 to 17 μg ml⁻¹) in 0.1 M sodium phosphate buffer, pH 8. The 90% and 100% response times at a flow rate of 2.5 ml min⁻¹ are 4 min and 10 min, respectively, for a change from 41.9 to 82.5 μM ammonia, or 12 min and 48 min, respectively, for change from 160 to 0 μM ammonia. A continuous drift in signal baseline and ammonia sensitivity limited the measurement stability. The sensor was useful over a period of a few days. The storage stability is more than 10 months (dry). No interference due to pH was observed in the range from pH 5 to pH 9. Sensor performance is seriously affected by amines and cationic detergents. The sensor could be sterilized with 3% hydrogen peroxide or dry heat (90 °C).     

Synthesis and electrochemistry of organometallic ethanethiolato bridged complexes of ruthenium(IV)

Reaction of the ruthenium(IV) chloro-bridged dimer [{Ru(η³ : η³-C₁₀H₁₆)Cl(μ-Cl)}₂], 1, with ethanethiol (EtSH) in CH₂Cl₂ gives the bridged-cleaved adduct [Ru(η³ : η³-C₁₀H₁₆)Cl₂(SHEt)], 2. Stirring of two molar equivalents of 2 in methanol with one equivalent of 1 gives the binuclear, mixed chloro/thiolato bridged compound [{Ru(η³ : η³-C₁₀H₁₆)Cl} ₂(μ-SEt)], 3. The related doubly thiolato bridged complex [{Ru(η³ : η³-C₁₀H₁₀)Cl(μ-SEt)}₂], 4, is formed by treatment of 1 with an excess of EtSH, or by prolonged stirring of 2 alone in methanol. Compounds 2–4 have been studied by cyclic voitammetry. Compound 2 undergoes only irreversible oxidation, whereas in the case of both 3 and 4 the observation of significant return waves is consistent with a greater stability of the primary redox products.