Efficient Direct Nitrosylation of α-Diimine Rhenium Tricarbonyl Complexes to Structurally Nearly Identical Higher Charge Congeners Activable towards Photo-CO Release

The reaction of rhenium α-diimine (N-N) tricarbonyl complexes with nitrosonium tetrafluoroborate yields the corresponding dicarbonyl-nitrosyl [Re(CO)₂(NO)(N-N)X]⁺ species (where X = halide). The complexes, accessible in a single step in good yield, are structurally nearly identical higher charge congeners of the tricarbonyl molecules. Substitution chemistry aimed at the realization of equivalent dicationic species (intended for applications as potential antimicrobial agents), revealed that the reactivity of metal ion in [Re(CO)₂(NO)(N-N)X]⁺ is that of a hard Re acid, probably due to the stronger π-acceptor properties of NO⁺ as compared to those of CO. The metal ion thus shows great affinity for π-basic ligands, which are consequently difficult to replace by, e.g., σ-donor or weak π-acids like pyridine. Attempts of direct nitrosylation of α-diimine fac-[Re(CO)₃]⁺ complexes bearing π-basic OR-type ligands gave the [Re(CO)₂(NO)(N-N)(BF₄)][BF₄] salt as the only product in good yield, featuring a stable Re-FBF₃ bond. The solid state crystal structure of nearly all molecules presented could be elucidated. A fundamental consequence of the chemistry of [Re(CO)₂(NO)(N-N)X]⁺ complexes, it that the same can be photo-activated towards CO release and represent an entirely new class of photoCORMs.     

Nitric oxide and singlet oxygen photo-generation by light irradiation in the phototherapeutic window of a nitrosyl ruthenium conjugated with a phthalocyanine rare earth complex

The photochemical, photophysical and photobiological studies of a mixture containing cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] (H₂-dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and Na₄[Tb(TsPc)(acac)] (TsPc = tetrasulfonated phthalocyanines; acac = acetylacetone), a system capable of improving photodynamic therapy (PDT), were accomplished. cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] was obtained from cis-[Ru(H₂-dcbpy)₂Cl₂]·2H₂O, whereas Na₄[Tb(TsPc)(acac)] was obtained by reacting phthalocyanine with terbium acetylacetonate. The UV–Vis spectrum of cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] displays a band in the region of 305 nm (λ_max in 0.1 mol L⁻¹ HCl)(π–π*) and a shoulder at 323 nm (MLCT), while the UV–Vis spectrum of Na₄[Tb(TsPc)(acac)] presents the typical phthalocyanine bands at 342 nm (Soret λ_max in H₂O) and 642, 682 (Q bands). The cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] FTIR spectrum displays a band at 1932 cm⁻¹ (Ru–NO⁺). The cyclic voltammogram of the cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] complex in aqueous solution presented peaks at E = 0.10 V (NO^+/0) and E = −0.50 V (NO^0/−) versus Ag/AgCl. The NO concentration and ¹O₂ quantum yield for light irradiation in the λ > 550 nm region were measured as [NO] = 1.21 ± 0.14 μmol L⁻¹ and ø_OS = 0.41, respectively. The amount of released NO seems to be dependent on oxygen concentration, once the NO concentration measured in aerated condition was 1.51 ± 0.11 μmol L⁻¹ The photochemical pathway of the cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)]/Na₄[Tb(TsPc)(acac)] mixture could be attributed to a photoinduced electron transfer process. The cytotoxic assays of cis-[Ru(H-dcbpy^-)₂(Cl)(NO)] and of the mixture carried out with B16F10 cells show a decrease in cell viability to 80% in the dark and to 20% under light irradiation. Our results document that the simultaneous production of NO and ¹O₂ could improve PDT and be useful in cancer treatment.     

FTIR-ATR-spectroscopic investigation of the silanization of germanium surfaces with 3-aminopropyltriethoxysilane

Summary The adsorption of 3-aminopropyltriethoxysilane (3-APTS) on germanium crystals was investigated using Attenuated Total Reflection (ATR) spectroscopy. Ethanol, which is produced by the hydrolysis of 3-APTS in water, adsorbs on germanium prior to 3-APTS. This can be checked by the CH₃-modes at 1150 cm^–1 and 2975 cm^–1. The structure differences between chemisorbed and physisorbed 3-APTS can be observed by the shift of the Si-O-Si bands of the silane molecules. The asymmetric and symmetric stretch bands for chemisorbed 3-APTS occurs at 1096 cm^–1 and 1022 cm^–1, whereas, the bands for physisorbed 3-APTS are found at 1115 cm^–1 and 1038 cm^–1. The amino groups of physisorbed 3-APTS display two strong bands at 1566 cm^–1 and 1485 cm^–1 which result from amino groups strongly hydrogen bonded to free silanols. The deformation modes of the amino groups in chemisorbed layers can be found at 1609 cm^–1 and 1512 cm^–1, which is due to the deformation modes of the free amino groups. A controlled chemisorption is important for the development of chemical IR-sensors [15].

---

FTIR-ATR-Spektroskopische Untersuchung der Silanisierung von Germaniumoberflächen mit 3-Aminopropyltriethoxysilan

---

Dedicated to Prof. Dr. G. Tölg at the occasion of his 60. birthday     

Regularities of the trans-Influence of Ligand L on the Energy Characteristics of the Metastable Isomers of trans-[RuX4(NO)L]q (L = H2O, NH3, Pyrazine, Cl?, OH?, CN?, NO2?; X = Cl?, NH3)

The geometric structures of the ground state and metastable isomers of the nitroso complexes trans-[RuCl₄(NO)L]^q (L = H₂O, NH₃, pyrazine (Pz), q = −1; Cl⁻, OH⁻, CN⁻, NO ₂ ⁻ , q = −2) and cis[RuCl₄(NO)L]^q (L = Pz, q = −1) were optimized in terms of the density functional theory. The variation of the trans-ligand L influences the relative energy of the metastable isomer with a side NO coordination. The presence of π-acceptor substituents in the trans-ligand L decreases the energy.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 606–611.Original Russian Text Copyright © 2005 by Lyubimova, Sizova.     

Size-dependent reactivity of cobalt cluster ions with nitrogen monoxide: Competition between chemisorption and decomposition of NO

Reactions of NO molecules on cobalt cluster ions were studied in a beam-gas geometry by using a tandem mass spectrometer. Single-particle collision reactions of Co_mNO⁺ (m = 3–10) with NO were found to proceed in such a manner that NO decomposition dominates at m = 4–6 with the maximum reaction cross section at m = 5 and chemisorption dominates in m ≥ 7. On the other hand, in two-particle collision reactions of Co_n⁺ (n = 2–10) with NO, NO decomposition at n ≥ 5 and chemisorption of two NO molecules with Co atoms loss at n ≥ 8 were found to proceed. These results indicate that the size-dependency of the multiple collision reactions originates from secondary attacking of an NO molecule to primary products of the initial single collision reactions. The DFT calculation supports the scheme that both the decomposition and chemisorption of two-particle collision reactions proceed via a common intermediate, Co_mN₂O₂⁺, in which the two NO molecules are dissociatively chemisorbed on the cobalt cluster ion, and the size-dependency of the two-particle collision reactions is explained in terms of the structure of this reaction intermediate.     

Inducing non-adiabatic effects through coadsorption: CO + NO on iridium

We compare the response of the intramolecular C–O stretch of carbon monoxide alone and coadsorbed with nitric oxide on Ir{1 1 1} following femtosecond laser heating with the help of time-resolved vibrational sum frequency (SF) spectroscopy. The C–O stretch of a pure CO layer couples anharmonically to the CO frustrated translation and its frequency adiabatically follows the temperature of the iridium surface. In a mixed CO/NO layer, the C–O frequency exhibits non-adiabatic coupling to the hot iridium electrons with a friction coefficient that depends on the electron temperature and the CO:NO ratio. Two possible scenarios emerge: NO causes a static tilt of the CO with a tilt angle depending on the relative coverage. This increases the degree of bonding of the CO 2π^* orbital to the iridium surface, which in turn increases the degree of non-adiabatic coupling. Alternatively, the C–O frequency reflects transient changes in the bonding configuration of the neighboring NO. The latter interaction could be the primary step in the direct reduction of NO by CO to form CO₂.     

Study of SO2 adsorption on titanium dioxide by IR spectroscopy and thermal desorption

Conclusions At least two different forms of chemisorbed SO₂ have been identified on the surface of anatase. The weakly bound SO₂ (a low-temperature peak with T_max=405–445 K, H_ads =85.7 kJ/ mole) is characterized by IR bands at 1330 and 1141 cm^– and is stabilized on coordinatively-unsaturated titanium ions. The strongly bound SO₂ (high-temperature peak with T_max=550–615 K) has a band at 1070 cm^–1. The thermal stability of SO₂ chemisorbed on TiO₂ is lower than on -Al₂O₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 503–505, March, 1989.     

UV–visible spectrum of the phenyl radical and kinetics of its reaction with NO in the gas phase

Pulse radiolysis transient UV–visible absorption spectroscopy was used to study the UV–visible absorption spectrum (225–575 nm) of the phenyl radical, C₆H₅(), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225–340 nm. In the presence of NO phenyl radicals are converted into nitrosobenzene. The phenyl radical spectrum was measured relative to that of nitrosobenzene. Based upon σ(C₆H₅NO)_{270 nm}=3.82×10⁻¹⁷ cm² molecule⁻¹ we derive an absorption cross-section for phenyl radicals at 250 nm, σ(C₆H₅())_{250 nm}=(2.75±0.58)×10⁻¹⁷ cm² molecule⁻¹. At 295 K in 200–1000 mbar of Ar diluent k(C₆H₅()+NO)=(2.09±0.15)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

The protocovalent NO bond: Quantum chemical topology (QCT of ELF and ELI-D) study on the bonding in the nitrous acid HONO and its relevancy to the experiment

Topologically challenging, the protocovalent NO bond, which belongs to a distinct class called charge-shift bonds, has been identified in the HONO (cis, trans) molecules on the basis of topological analysis of the ELF and ELI-D functions obtained from the B3LYP and CASSCF(12,10) calculations. The presence of the protocovalent NO bond is associated with energetically possible dissociation channel: HONO(¹A′) → OH(²π) + NO(²π).     

Synthesis,Biomacromolecular Interactions,Photodynamic NO Releasing and Cellular Imaging of Two [RuCl(qn)(Lbpy)(NO)]X Complexes

Two light-activated NO donors [RuCl(qn)(Lbpy)(NO)]X with 8-hydroxyquinoline (qn) and 2,2′-bipyridine derivatives (Lbpy) as co-ligands were synthesized (Lbpy₁ = 4,4′-dicarboxyl-2,2′-dipyridine, X = Cl⁻ and Lbpy₂ = 4,4′-dimethoxycarbonyl-2,2′-dipyridine, X = NO₃⁻), and characterized using ultraviolet–visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (¹H NMR), elemental analysis and electrospray ionization mass spectrometry (ESI-MS) spectra. The [RuCl(qn)(Lbpy₂)(NO)]NO₃ complex was crystallized and exhibited distorted octahedral geometry, in which the Ru–N(O) bond length was 1.752(6) Å and the Ru–N–O angle was 177.6(6)°. Time-resolved FT-IR and electron paramagnetic resonance (EPR) spectra were used to confirm the photoactivated NO release of the complexes. The binding constant (K_b) of two complexes with human serum albumin (HSA) and DNA were quantitatively evaluated using fluorescence spectroscopy, Ru-Lbpy₁ (K_b~10⁶ with HSA and ~10⁴ with DNA) had higher affinity than Ru-Lbpy₂. The interactions between the complexes and HSA were investigated using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) and EPR spectra. HSA can be used as a carrier to facilitate the release of NO from the complexes upon photoirradiation. The confocal imaging of photo-induced NO release in living cells was successfully observed with a fluorescent NO probe. Moreover, the photocleavage of pBR322 DNA for the complexes and the effect of different Lbpy substituted groups in the complexes on their reactivity were analyzed.     

Studies on the stability of four-membered ring chelates Part V. The stability of dialkyl dithiocarbamate chelates

This paper systematically studies the structure and the internal mechanism of the stability of sulphur-coordinated four-membered rings in chelates of dialkyl dithiocarbamate. It was found that the conjugated π electron structure of the free ligand is Π₄⁶, while in the metal chelate it is Π₄⁴. The stable chelates have strong σ- and π-coordinated bonds. The actual strain of the sulphur-coordinated four-membered ring in chelates is not as strong as assumed. It mainly depends on the atomic radius of the metal. The stronger the electronegativity of the metal, the stronger the π-coordinated bond. The stabler the four-membered ring, the weaker the intensity of the C-S vibrational band.     

An ab initio study of electronic spectra and excited-state properties of 7-azaindole in vapour phase and aqueous solution

The geometries of 7-azaindole (7AI), its tautomer (7AT), and 7AI–H₂O and 7AT–H₂O complexes were optimised in the ground state and some low-lying singlet excited states using the 3-21G basis set. Differences of total energies of the optimised ground and excited states and the vertical excitation energies of these systems were used to explain the observed electronic spectra. Effect of solvation of these systems in bulk water was studied using the polarized continuum model (PCM). The mode of binding of a water molecule in the S₂(n–π^*) excited state of 7AI was found to be quite different from those in its ground and π–π^* excited states. It is shown that crossing of the lowest two singlet excited-state potential surfaces S₁(π–π^*) and S₂(n–π^*) of 7AI occurs in the vapour phase under geometry relaxation while on interaction with water, the S₂(n–π^*) excited state is raised up appreciably going even above the S₃(π–π^*) excited state. Ground- and excited-state molecular electrostatic potential mapping was carried out, which led to valuable information regarding the nature of excited states of the above-mentioned systems.     

New books

Summary Micromolar analyses of the nitrogen species NH₃, NO ₂ ^– , and NO ₃ ^– in soil and other samples are usually accomplished by extracting several samples and testing each for a different species. This procedure is not viable when the quantity of the initial sample is limited. An improved method of separating and analysing for ammonia NH₃(aq), nitrite NO ₂ ^– (aq), and nitrate NO ₃ ^– (aq) from a single small sample with concentrations of 0–50 mol/l is reported. No interferences or carryovers among the three nitrogen containing species were found. Uncertainties were ±2–5 mol/l and accuracies with respect to standards were ±3 mol/l.     

Effects of alkali-metal cations on nitrate-ion N-O bond force constants in ionic melts

Measured frequencies from pure nitrate liquids have been used to calculate the force constants for the nitrate ion and the M⁺-NO₃ ^– systems (M⁺ = Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) by a matrix successive-approximation method based on perturbation theory in dependent coordinates. The valency force constants K_q for the N-O bonds are increased by comparison with free NO ₃ ^– . The N-O bond strengthening is not adequately explained by cation-anion interaction because there is electron-density transfer mainly by the mechanism within the NO ₃ ^– . Correction for the vibrational parameters of the interacting particles confirms the previously demonstrated acid-base mechanism for the cation-anion interaction in liquids containing nitrate.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 230–234, March–April, 1989.     

Palladium species in Pd/H-ZSM-5 zeolite catalysts for CH4-SCR

The active state of palladium for NO reduction with methane (CH₄-SCR) was investigated by comparing the catalytic activity of Pd/H-ZSM-5 with that of PdO/SiO₂. High catalytic activity for CH₄-SCR was given by Pd/H-ZSM-5 in the temperature range of 300–500 °C. PdO/SiO₂ catalyzed the reaction between NO₂ and CH₄ in the absence of oxygen, which retarded the reaction by consuming CH₄ in combustion. CH₄ combustion occurred on either zeolite-supported or silica-supported catalyst, while NO preferentially retarded the combustion on Pd/H-ZSM-5. NO was found to be chemisorbed on the palladium sites in zeolite, while it was hardly chemisorbed on PdO/SiO₂. NaCl titration showed that the palladium species in zeolite are Pd²⁺ cations content, on which NO is strongly chemisorbed resulting in high selectivity for CH₄-SCR.     

Bonding and reactivity in π-allyl—metal compounds

The π-allyl group of π-C₃H₅Co(CO)₃ has two angles of tilt, one of which (from semi-empirical molecular orbital calculations) is stabilised principally by the influence of the C(p_v) orbitals of the terminal carbon atoms, which form part of the σ-framework of the π-allyl group, and the other of which is stabilised by a balance between bonding orbital components of the central and terminal carbon atoms. The Co(CO)₃ moiety has asymmetric bonding, with one CO group more weakly bonded to the metal atom. The asymmetric bonding of the Co(CO)₃ moiety is primarily caused by the electronic character of the π-allyl group, but is significantly influenced by the magnitude of the τ-tilt angle of the π-allyl group. The relatively high reactivity of π-C₃H₅Co(CO)₃, compared with the reactivity of π-C₃H₅Fe(CO)₂NO, Co(NO)(CO)₃, or Ni(CO)₄, is explained by the relatively weak bonding of a CO group to the metal atom and a possible explanation of the anomalous relative rates of the reactions of π-C₃H₄RCo(CO)₃ (R = H, 1-CH₃, 2-CH₃, 1-Cl, 2-Cl) with P(C₆H₅)₃ is indicated.The angles of tilt of the π-allyl group and the asymmetric bonding of the π-cyclopentadienyl moiety in [π-C₃H₄Ni(π-C₅H₅)]₂ are caused by factors similar to those in π-C₃H₅Co(CO)₃.     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

An evaluation of rate constants for radiation induced decomposition of alkali metal nitrates

Radiation induced decomposition of solid alkali metal nitrates at room temperature has been studied up to an absorbed dose of 300 kGy. [NO ₂ ^– ] increases with absorbed dose. From the kinetic scheme and , rate constants have been evaluated for the overall radiolytic decomposition of alkali metal nitrates. This kinetic scheme is applicable in the low dose range. At higher doses, however, the radiation induced reaction, NO ₂ ^– +1/2 O₂NO ₃ ^– may also contribute. The overall rate constants are 0.13×10^–6 (LiNO₃), 1.05×10^–6 (NaNO₃), 10.10×10^–6 (KNO₃), 9.50×10^–6 (RbNO₃) and 25.50×10^–6 (CsNO₃) kGy^–1.     

Bestimmung von NO2? und NO3? in Lebensmitteln mit Hilfe chromatographischer Methoden

Zusammenfassung WÄhrend NO ₂ ^– problemlos nach dem Griess-Verfahren bestimmt werden kann, treten bei der spektralphotometrischen Erfassung von NO ₃ ^– hÄufig Störungen auf.Zum Nachweis geringer NO ₃ ^– -Mengen eignet sich die Nitrierung von p-Kresol zu 4-Methyl-2-nitrophenol, das durch Wasserdampfdestillation aus dem Reaktionsgemisch abgetrennt und nach überführung in Toluol durch HPLC bzw. GC bestimmt wird.Zur schnellen Erfassung von NO ₂ ^– neben NO ₃ ^– kann neben der Ionen-Chromatographie an AnionenaustauschersÄulen vorteilhaft die Ionen-Paar-Chromatographie an RPSÄulen eingesetzt werden. Durch parallele Anwendung verschiedener Methoden gelingt es, NO ₂ ^– - und NO ₃ ^– -Gehalte auch von komplex zusammengesetzten Lebensmitteln über einen weiten Konzentrationsbereich mit gro\er Genauigkeit störungsfrei zu ermitteln.

---

Determination of NO ₂ ^– and NO ₃ ^– in foods by chromatography

Summary The determination of NO ₂ ^– is achieved by the Griess procedure without problems, whereas during the analysis of NO ₃ ^– by spectrophotometric methods disturbances often occur.Small amounts of NO ₃ ^– are detectable after nitration of p-cresol, subsequent separation of 4-methyl-2-nitrophenol by steam distillation and its determination by HPLC or GLC after extraction with toluene. To enable a rapid determination of NO ₂ ^– as well NO ₃ ^– , apart from the ionchromatographic method with anion-exchange columns the comparatively equal ion-pair chromatographic system using RP columns may also be used. By the parallel use of different methods it is possible to determine the NO ₂ ^– and NO ₃ ^– contents, even in complex matrices, over a wide concentration range with a large degree of accuracy and a minimum of disturbances.

---

---

Nach einem Vortrag anlÄ\lich des Deutschen Lebensmittelchemikertages, München 1983     

Planar hexacoordinate gallium

We report the first planar hexacoordinate gallium (phGa) center in the global minimum of the GaBe₆Au₆⁺ cluster which has a star-like D_6h geometry with ¹A_1g electronic state, possessing a central gallium atom encompassed by a Be₆ hexagon and each Be–Be edge is further capped by an Au atom. The electronic delocalization resulting in double aromaticity (both σ and π) provides electronic stability in the planar form of the GaBe₆Au₆⁺ cluster. The high kinetic stability of the title cluster is also understood by Born–Oppenheimer molecular dynamics simulations. The energy decomposition analysis in combination with the ‘natural orbitals for chemical valence’ theory reveals that the bonding in the GaBe₆Au₆⁺ cluster is best expressed as the doublet Ga atom with 4s²4p_⊥¹ electronic configuration forming an electron-sharing π bond with the doublet Be₆Au₆⁺ moiety followed by Ga(s)→[Be₆Au₆⁺] σ-backdonation and two sets of Ga(p_‖)←[Be₆Au₆⁺] σ-donations.

A star-like texture containing a planar hexacoordinate gallium center is reported in the lowest energy isomer of the GaBe6Au₆⁺ cluster. High thermodynamic and kinetic stability of the title cluster makes it suitable candidate for experimental realization.