Photochemistry of molecules relevant to the atmosphere: photodissociation of nitric acid in the gas phase.

This Minireview gives an account of the photochemical decay of nitric acid HNO3 in the gas phase, which has been well investigated under bulk and molecular-beam conditions. Due to the importance of this molecule in atmospheric chemistry, attention was paid to the irradiation regions around 300 and 200 nm, where solar photolysis of HNO3 is expected to be particularly efficient. While the low-energy region is characterized by the products OH and NO2, the high-energy region gives rise to a variety of photochemical decay pathways, dominated by channels which lead to the products HONO + O in different electronic states.     

Design,synthesis, and evaluation of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-ribitylaminolumazines as inhibitors of riboflavin synthase and lumazine synthase

A series of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-D-ribityllumazine were synthesized as inhibitors of both Escherichia coli riboflavin synthase and Bacillus subtilis lumazine synthase. The compounds were designed to bind to both the ribitylpurine binding site and the phosphate binding site of lumazine synthase. In the carboxyalkyl series, maximum activity against both enzymes was observed with the 3'-carboxypropyl compound 22. Lengthening or shortening the chain linking the carboxyl group to the lumazine by one carbon resulted in decreased activity. In the phosphonoxyalkyl series, the 3'-phosphonoxypropyl compound 33 was more potent than the 4'-phosphonoxybutyl derivative 39 against lumazine synthase, but it was less potent against riboflavin synthase. Molecular modeling suggested that the terminal carboxyl group of 6-(3'-carboxypropyl)-7-oxo-8-D-ribityllumazine (22) may bind to the side chains of Arg127 and Lys135 of the enzyme. A hypothetical molecular model was also constructed for the binding of 6-(2'-carboxyethyl)-7-oxolumazine (15) in the active site of E. coli riboflavin synthase, which demonstrated that the active site could readily accommodate two molecules of the inhibitor.     

Darstellung von Acetatoblei(IV)- und Acetatozinn(IV)- manganpentacarbonylen durch Acidolyse von (C6H5)4–n−M[Mn(CO)5]n (M  Sn,Pb; n = 1, 2) mit Essigsäure

Preparation of Acetatolead(1V) and Acetatotin(1V) Manganese Pentacarbonyls by Acidolysis of (C₆H₅)_4?n M[Mn(CO)₅]_n (M ? Sn, Pb; n = 1, 2) with Acetic Acid By acidolysis of (C₆H₅)_4?nM[Mn(CO)₅]_n (M ? Sn, Pb; n = 1, 2) with acetic acid no M? Mn bonds are broken, but M? C bonds. In this reaction (CH₃COO)₂M[Mn(CO)₅]₂ is formed from (C₆H₅)₂M[Mn(CO)₅]₂, and (CH₃COO)₃SnMn(CO)₅ and (CH₃COO)₂C₆H₅PbMn(CO)₅ from (C₆H₅)₃MMn-(CO)₅. (CH₃COO)₂C₆H₅SnMn(CO)₅ is prepared from Cl₂C₆H₅SnMn(CO)₅ and AgCH₃COO. According to IR spectroscopic data the acetato ligands of the diacetato complexes are bidentate, while in (CH₃COO)₃SnMn(CO)₅ bi- and monodentate carboxylate groups are present. For the central atoms Sn and Pb octahedral coordination is proposed.     

Optically detected magnetic resonance study of the lowest excited triplet state of aromatic thioketones: Xanthione

The aromatic thioketone xanthione has been investigated by means of the optically detected magnetic resonance (ODMR) technique in a n-hexane matrix at ≈ 1.1 K. It was established that the short-lived red emission, which is characteristic for many thione molecules, is phosphorescence. At high temperatures (77 K) this phosphorescence originates mainly (>80%) from the T₁^z (n, π*) sublevel (k_z^(r) >k_x^(r), k_y^(r). At low temperature (1.1 K) the intersystem crossing following S₂ (π, π*) ← S₀ excitation is a highly spin-sublevel selective process which populates predominantly the T₁^x and T₁^y, levels. Hence, the slow spin—lattice relaxation phosphorescence at low temperature originates from these sublevels. A value of 0.0611 cm^?1 was obtained for the zero-field parameter |E|/hc. A lower limit of 0.66 cm^?1 has been found for the zero-field parameter |D|/hc. This value is considerably larger than those observed for ketones, and it is shown that spin—orbit coupling contributes strongly to the zero-field splitting.     

Amperometry of thiols in a flow-injection system with a nickel oxide electrode

The electrochemical oxidation of a series of thils on the surface of a nickel oxide electrode is investigated in a flow-injection system. The background electrolyte is 0.1 M NaOH containing 5 × 10^?65 M NiSO₄ and the injected sample volume is 25 μl. The net peak current is observed at +0.46 V vs. SCE for thiols dissolved in pH 3.0 phthalate buffer. The upper limit of linearity extends to 10^?3 M. The relative standard deviation for ten replicate measurements on 10^?4 M ethanethiol is 1.6%. The lower limits of detection are between 3 × 10^?5 and 2 × 10^?4 M for a series of thiols. Peak shapes indicate that thiolate oxidation mediated by a higher oxide layer on the electrode rather than mass transport or adsorption / rearrangement is the rate-determining step.     

Selecting parameters and limits for equipment operational qualification

While operational qualification (OQ) is a well-established term within equipment qualification, users of equipment often become unsure when it comes to implementation. The biggest problem is how to select procedures and acceptance criteria. Should these be the vendor's specifications or should the users define their own limits, and, if so, how? Should all instruments of the same type have the same values or should these be optimized for each individual instrument? This article will provide an overall strategy and specific examples for HPLC on how to select procedures and acceptance limits that are based on efficient use of resources, on practicality and on the intended use of the equipment.     

Model Reactions for Photosynthesis—Photoinduced Charge and Energy Transfer between Covalently Linked Porphyrin and Quinone Units

Photosynthesis is one of the fascinating fields of current interdisciplinary research. It seems miraculous that nature, in the process of evolution, has managed to bring about the process of photosynthesis. The first step involves a charge separation at the reaction centers, which proceeds with 100% quantum yield from the photoexcited singlet state of the bacteriochlorophyll donor, despite the fact that the wasteful deactivation of the electron into the ground state should be highly favored. Biomimetic model compounds (that is, those which resemble the pigments nature has developed) have been constructed from porphyrins and quinones. These model systems have allowed the study of the factors contributing to the highly efficient charge separation. This report focuses on recent developments in the study of electron transfer in porphyrinoquinones. Some of the results of these investigations may not be not fully understood and are often the subject of controversial discussions.     

E-Beam—a new transfer system for isolator technology

In every aseptic filling application, the sterile transfer of goods into the aseptic area is a challenge, and there are many different ways to do it.

With isolator technology a higher sterility assurance level (SAL) is achieved. This SAL is only as good as the weakest segment in the chain of manufacturing. The transfer of goods into and out of the isolator is one of these critical segments.

Today different techniques, some already well established, others still very new, are available on the market like: dry heat tunnel, autoclave, pulsed light, rapid transfer systems (RTP), H₂O₂ tunnel, UV light, etc. all these systems are either not applicable for continuous transfer, only good for heat-compatible materials like glass, or do not guarantee a 6 log spore reduction.

E-Beam opens new perspectives in this field. With E-beam technology it is possible to transfer heat-sensitive (plastic), pre-sterilised materials at high speed, continuously into an aseptic area.

E-Beam unifies three different technologies, that result in a very efficient and high-speed decontamination machine designed for the pharmaceutical industry. First, there is the electron beam that decontaminates the goods and an accurate shielding that protects the surrounding from this beam. Second, there is the conveyor system that guarantees the output and the correct exposure time underneath the beam. And third, there is the isolator interface to provide correct differential pressure and clean air inside the tunnel as well as the decontamination of the tunnel with H₂O₂ prior to production.

The E-beam is a low-energy electron beam, capable of decontaminating any kind of surface. It penetrates only a few micrometers into the material and therefore does not deform the packaging media.

Currently, machines are being built to transfer pre-sterilised syringes, packed in plastic tubs with a Tyvek cover into an aseptic filling isolator with the following data: decontamination efficiency of 10⁶ (6 log spore reduction), decontamination speed of 6 tubs (600 syringes) per minute.

This is just one of many applications for this new technology.     

Comparison of direct infusion and on-line liquid chromatography/electrospray ionization mass spectrometry for the analysis of nucleic acids

The applicability of ion-pair reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry (IP-RP-HPLC/ESI-MS) and direct infusion/ESI-MS to the characterization of nucleic acid mixtures was evaluated by the analysis of the reaction products obtained from solid-phase synthesis of a 39-mer oligonucleotide. IP-RP-HPLC/ESI-MS was performed using 200 microm i.d. capillary columns packed with octadecylated, micropellicular poly(styrene-divinylbenzene) particles and applying gradients of acetonitrile in 50 mM triethylammonium bicarbonate (TEAB). Three different solvent systems were utilized for direct infusion/ESI-MS with removal of metal cations by on-line cation exchange: (1) 10 mM triethylamine (TEA) in 50% aqueous acetonitrile, (2) 2.2 mM TEA, 400 mM hexafluoro-2-propanol (HFIP) in 20% aqueous methanol and (3) 50 mM TEAB in 10% aqueous acetonitrile. Owing to its separation capability, the highest selectivity and specificity were achieved with IP-RP-HPLC/ESI-MS, which, apart form the 39-mer target sequence, allowed the identification of two isobutyryl-protected target sequences and a 10-mer and 20-mer failure sequence. Direct infusion/ESI-MS with TEA-acetonitrile or TEA-HFIP-methanol as solvent revealed signals for the 39-mer in the m/z range 700-1600. The presence of derivatives containing one, two, three and four isobutyryl groups indicated that the hydrolysis of the protecting groups after solid-phase synthesis was not complete. Failure sequences could not be identified by direct infusion/ESI-MS under conditions favoring multiple charging of the analytes owing to the high chemical background and coincidental overlapping of m/z signals. However, efficient charge state reduction upon addition of carbonic acid to the electrosprayed solvent shifted the signals of the 39-mer and derivatives to m/z values >2400 and allowed the detection of seven different failure sequences, ranging from the 8-mer to the 23-mer, in the mixture.