Chemometric Combination of Ultrahigh Resolving Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy for a Structural Characterization of Lignin Compounds.

In recent years, the potential of lignins as a resource for material-based applications has been highlighted in many scientific and nonscientific publications. But still, to date, a lack of detailed structural knowledge about this ultracomplex biopolymer undermines its great potential. The chemical complexity of lignin demands a combination of different, powerful analytical methods, in order to obtain these necessary information. In this paper, we demonstrate a multispectroscopic approach using liquid-state and solid-state Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and nuclear magnetic resonance (NMR) spectroscopy to characterize a fractionated LignoBoost lignin. Individual FT-ICR-MS, tandem MS, and NMR results helped to determine relevant information about the different lignin fractions, such as molecular weight distributions, oligomer sizes, linkage types, and presence of specific functional groups. In addition, a hetero spectroscopic correlation approach was applied to chemometrically combine MS, MS/MS, and NMR data sets. From these correlation analyses, it became obvious that a combination of tandem MS and NMR data sets gives the opportunity to comprehensively study and describe the general structure of complex biopolymer samples. Compound-specific structural information are obtainable, if this correlation approach is extended to 1D-MS and NMR data, as specific functional groups or linkages are verifiable for a defined molecular formula. This enables structural characterization of individual lignin compounds without the necessity for tandem MS experiments. Hence, these correlation results significantly improve the depth of information of each individual analysis and will hopefully help to structurally elucidate entire lignin structures in the near future.

Nonequilibrium Colloids: Temperature-Induced Bouquet Formation of Flower-like Micelles as a Time-Domain-Shifting Macromolecular Heat Alert.

Climate change requires enhanced autonomous temperature monitoring during logistics/transport. A cheap approach comprises the use of temperature-sensitive copolymers that undergo temperature-induced irreversible coagulation. The synthesis/characterization of pentablock copolymers (PBCP) starting from poloxamer PEO130-b-PPO44-b-PEO130 (poly(ethylene oxide)130-b-poly(propylene oxide)44-b-poly(ethylene oxide)130) and adding two terminal qPDMAEMA85 (quaternized poly[(2-dimethylamino)ethyl methacrylate]85) blocks is presented. Mixing of PBCP solutions with hexacyanoferrate(III)/ferricyanide solutions leads to a reduction of the decane/water interfacial tension accompanied by a co/self-assembly toward flower-like micelles in cold water because of the formation of an insoluble/hydrophobic qPDMAEMA/ferricyanide complex. In cold water, the PEO/PPO blocks provide colloidal stability over months. In hot water, the temperature-responsive PPO block is dehydrated, leading to a pronounced temperature dependence of the oil-water interfacial tension. In solution, the sticky PPO segments exposed at the micellar corona cause a colloidal clustering above a certain threshold temperature, which follows Smoluchowski-type kinetics. This coagulation remains for months even after cooling, indicating the presence of a kinetically trapped nonequilibrium state for at least one of the observed micellar structures. Therefore, the system memorizes a previous suffering of heat. This phenomenon is linked to an exchange of qPDMAEMA-blocks bridging the micellar cores after PPO-induced clustering. The addition of ferrous ions hampers the exchange, leading to the reversible coagulation of Prussian blue loaded micelles. Hence, the Fe2+ addition causes a shift from history monitoring to the sensing of the present temperature. Presumably, the system can be adapted for different temperatures in order to monitor transport and storage in a simple way. Hence, these polymeric "flowers" could contribute to preventing waste and sustaining the quality of goods (e.g., food) by temperature-induced bouquet formation, where an irreversible exchange of "tentacles" between the flowers stabilizes the bouquet at other temperatures as well.

A Non-Hydrolytic Sol-Gel Route to Organic-Inorganic Hybrid Polymers: Linearly Expanded Silica and Silsesquioxanes.

Condensation reactions of chlorosilanes (SiCl4 and CH3SiCl3) and bis(trimethylsilyl)ethers of rigid, quasi-linear diols (CH3)3SiO-AR-OSi(CH3)3 (AR = 4,4'-biphenylene (1) and 2,6-naphthylene (2)), with release of (CH3)3SiCl as a volatile byproduct, afforded novel hybrid materials that feature Si-O-C bridges. The precursors 1 and 2 were characterized using FTIR and multinuclear (1H, 13C, 29Si) NMR spectroscopy as well as single-crystal X-ray diffraction analysis in case of 2. Pyridine-catalyzed and non-catalyzed transformations were performed in THF at room temperature and at 60 °C. In most cases, soluble oligomers were obtained. The progress of these transsilylations was monitored in solution with 29Si NMR spectroscopy. Pyridine-catalyzed reactions with CH3SiCl3 proceeded until complete substitution of all chlorine atoms; however, no gelation or precipitation was found. In case of pyridine-catalyzed reactions of 1 and 2 with SiCl4, a Sol-Gel transition was observed. Ageing and syneresis yielded xerogels 1A and 2A, which exhibited large linear shrinkage of 57-59% and consequently low BET surface area of 10 m2⋅g-1. The xerogels were analyzed using powder-XRD, solid state 29Si NMR and FTIR spectroscopy, SEM/EDX, elemental analysis, and thermal gravimetric analysis. The SiCl4-derived amorphous xerogels consist of hydrolytically sensitive three-dimensional networks of SiO4-units linked by the arylene groups. The non-hydrolytic approach to hybrid materials may be applied to other silylated precursors, if the reactivity of the corresponding chlorine compound is sufficient.

P-Ru-Complexes with a Chelate-Bridge-Switch: A Comparison of 2-Picolyl and 2-Pyridyloxy Moieties as Bridging Ligands.

Starting from [Ru(pyO)2(nbd)] 1 and a N,P,N-tridentate ligand (2a: PhP(pic)2, 2b: PhP(pyO)2) (nbd = 2,5-norbornadiene, pic = 2-picolyl = 2-pyridylmethyl, pyO = 2-pyridyloxy = pyridine-2-olate), the compounds [PhP(µ-pic)2(µ-pyO)Ru(κ2-pyO)] (3a) and [PhP(µ-pyO)3Ru(κ2-pyO)] (3b), respectively, were prepared. Reaction of compounds 3 with CO and CNtBu afforded the opening of the Ru(κ2-pyO) chelate motif with the formation of compounds [PhP(µ-pic)2(µ-pyO)Ru(κ-O-pyO)(CO)] (4a), [PhP(µ-pic)2(µ-pyO)2Ru(CNtBu)] (5a), [PhP(µ-pyO)4Ru(CO)] (4b) and [PhP(µ-pyO)4Ru(CNtBu)] (5b). In dichloromethane solution, 4a underwent a reaction with the solvent, i.e., substitution of the dangling pyO ligand by chloride with the formation of [PhP(µ-pic)2(µ-pyO)Ru(Cl)(CO)] (6a). The new complexes 3a, 4a, 5a, 5b and 6a were characterized by single-crystal X-ray diffraction analyses and multi-nuclear (1H, 13C, 31P) NMR spectroscopy. The different coordination behaviors of related pairs of molecules (i.e., pairs of 3, 4 and 5), which depend on the nature of the P-Ru-bridging ligand moieties (µ-pic vs. µ-pyO), were also studied via computational analyses using QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) approaches, as well as the NCI (non-covalent interactions descriptor) for weak intramolecular interactions.

Synthesis and temperature-dependent NMR studies of monomeric and dimeric tris(dialkylamido)alanes.

After an introductory overview of all currently known tris(dialkylamido)alanes with the formula [Al(NR2)3]n (n = 1, 2), a simplified synthetic method based on the usage of is presented. The simplification results from the fact that the ether adduct can already be obtained during the necessary synthesis of the alane moiety and that the use of trimethylamine is no longer required. Current conflicts regarding the experimental data of tris(diethylamido)alane and their interpretation have been resolved by means of single crystal structure analysis. The N-methylpiperazine derivative was described for the first time and characterised by various analytical methods. In temperature-dependent NMR measurements ranging from -35 °C to 90 °C coalescence phenomena of 13C and 1H NMR signals of tris(N-methylpiperazino)alane as well as thermal migration of 1H NMR signals of tris(diethylamido)alane were observed.

Disilanes with Pentacoordinate Si Atoms by Carbon Dioxide Insertion into Aminodisilanes: Syntheses, Molecular Structures, and Dynamic Behavior.

The insertion of carbon dioxide into the Si-N bonds of aminodisilanes ((RR'N) n Me3-n Si)2 affords carbamoyloxydisilanes ((RR'NC(O)O) n Me3-n Si)2. Some of the obtained insertion products feature pentacoordinate silicon atoms in the solid state and in solution, with two carbamoyloxy moieties bridging the Si-Si bond. The aminodisilanes and their insertion products were extensively analyzed, including single-crystal X-ray structure analyses. The temperature dependence of the higher coordination was investigated using variable temperature NMR experiments.

Phenylarsonic acid-DMPS redox reaction and conjugation investigated by NMR spectroscopy and X-ray diffraction.

The reaction between 2,3-dimercaptopropane-1-sulfonate (DMPS, unithiol) and four phenylarsonic(V) acids, i.e. phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), 2-aminophenylarsonic acid (o-APAA) and 4-aminophenylarsonic acid (p-APAA), is investigated in aqueous solution. The pentavalent arsenic compounds are reduced by DMPS to their trivalent analogs and instantly chelated by the vicinal dithiol, forming covalent As-S bonds within a five-membered chelate ring. The different types and positions of polar substituents at the aromatic ring of the arsonic acids influence the reaction rates in the same way as observed for reaction with glutathione (GSH), as well as the syn/anti molar ratio of the diastereomeric products, which was analyzed using time- and temperature-dependent nuclear magnetic resonance (NMR) spectroscopy. Addition of DMPS to the conjugate formed by a phenylarsonic(V) acid and the biologically relevant tripeptide GSH showed the immediate replacement of GSH by chelating DMPS, underlining the importance of dithiols as detoxifying agent.

Bis-(triphenylphosphane) Aluminum Hydride: A Simple Way to Provide, Store, and Use Non-Polymerized Alane for Synthesis.

AlH3 (PPh3 )2 was synthesized as a stable solid being the first known 1 : 2 alane arylphosphane adduct. Although only weakly intra-molecularly coordinated, it displays as a molecular crystal significant inertness against atmospheric humidity and oxygen due to strong steric screening of the alane unit. The compound readily dissociates PPh3 in solution allowing for its use as a Lewis acidic reducing agent. These features lead to an easy to store, easy to use reducing agent that may enable the quantitative investigation of aluminum hydride chemistry including reduction, complexation and hydroalumination reactions. The structure contains two non-equivalent penta-coordinated aluminum centers that despite long Al-P distances of ca. 2.7 Šdisplay unusually high quadrupolar coupling constants CQ of 25.1 and 26.5 in 27 Al solid state NMR measurements. The product was also tested as a reducing agent on a small set of selected compounds with various functional groups.

Electrochemical Stimulation of Water-Oil Interfaces by Nonionic-Cationic Block Copolymer Systems.

Variable interfacial tension could be desirable for many applications. Beyond classical stimuli like temperature, we introduce an electrochemical approach employing polymers. Hence, aqueous solutions of the nonionic-cationic block copolymer poly(ethylene oxide)114-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}171 (i.e., PEO114-b-PDPAEMA171 with a quaternized poly(diisopropylaminoethyl methacrylate) block) were investigated by emerging drop measurements and dynamic light scattering, analyzing the PEO114-b-qPDPAEMA171 impact on the interfacial tension between water and n-decane and its micellar formation in the aqueous bulk phase. Potassium hexacyanoferrates (HCFs) were used as electroactive complexants for the charged block, which convert the bishydrophilic copolymer into amphiphilic species. Interestingly, ferricyanides ([Fe(CN)6]3-) act as stronger complexants than ferrocyanides ([Fe(CN)6]4-), leading to an insoluble qPDPAEMA block in the presence of ferricyanides. Hence, bulk micellization was demonstrated by light scattering. Due to their addressability, in situ redox experiments were performed to trace the interfacial tension under electrochemical control, directly utilizing a drop shape analyzer. Here, the open-circuit potential (OCP) was changed by electrolysis to vary the ratio between ferricyanides and ferrocyanides in the aqueous solution. While a chemical oxidation/reduction is feasible, also an electrochemical oxidation leads to a significant change in the interfacial tension properties. In contrast, a corresponding electrochemical reduction showed only a slight response after converting ferricyanides to ferrocyanides. Atomic force microscopy (AFM) images of the liquid/liquid interface transferred to a solid substrate showed particles that are in accordance with the diameter from light scattering experiments of the bulk phase. In conclusion, the present results could be an important step toward economic switching of interfaces suitable, e.g., for emulsion breakage.

The direct and reversible hydrogenation of activated aluminium supported by piperidine.

The reversible hydrogenation of aminoalanes employing activated aluminium and piperidine has been explored. A selection of transition metal (TM) compounds have been investigated as additives for producing TM-activated aluminium (TM = Ti, Zr, Hf and Y). The effect of these additives on the activation of aluminium with respect to hydrogenation of an aluminium/piperidinoalane system has been studied. It has been shown that Ti, Zr and Hf can efficiently promote the activation of aluminium for its hydrogenation. The experiments performed showed that the TM activity for the piperidinoalane formation decreases in the order Zr > Hf > Ti > Y. Using multinuclear NMR spectroscopy, the reversibility of this piperidinoalane-based hydrogenation system has been evidenced, demonstrating a potential pathway for hydrogen storage in aminoalanes. The syntheses of piperidinoalanes as well as their structural and spectroscopic characterisation are described. Single-crystal X-ray diffraction analyses of [pip2AlH]2 and [pip3Al]2 (pip = 1-piperidinyl, C5H10N) revealed dimers containing a central [AlN]2 unit.

Convenient two step synthesis of 29Si labelled tetraalkoxysilanes.

29Si enrichment would be advantageous for many NMR studies of the structural properties of sol-gel derived materials. The required starting materials (29Si enriched alkoxysilanes), however, are expensive and difficult to provide. Here we present a scalable, reliable synthesis of 29Si enriched tetraethoxysilane starting from silicon dioxide or elemental silicon with a total yield up to 75%.

Ionic Dissociation of SiCl4 : Formation of [SiL6 ]Cl4 with L=Dimethylphosphinic Acid.

Reactions of SiCl4 with R2 PO(OH) (R=Me, Cl) yield compounds with six-fold coordinated silicon atoms. Whereas R=Me afforded the hexacoordinated tetra-cationic silicon complex [Si(Me2 PO(OH))6 ]4+ with chloride counter-ions, R=Cl caused release of HCl with formation of a cyclic dimeric silicon complex [Si(Cl2 PO(OH))(Cl2 PO2 )3 (µ-Cl2 PO2 )]2 with bridging bidentate dichlorophosphates.

Spider Chitin: An Ultrafast Microwave-Assisted Method for Chitin Isolation from Caribena versicolor Spider Molt Cuticle.

Chitin, as a fundamental polysaccharide in invertebrate skeletons, continues to be actively investigated, especially with respect to new sources and the development of effective methods for its extraction. Recent attention has been focused on marine crustaceans and sponges; however, the potential of spiders (order Araneae) as an alternative source of tubular chitin has been overlooked. In this work, we focused our attention on chitin from up to 12 cm-large Theraphosidae spiders, popularly known as tarantulas or bird-eating spiders. These organisms "lose" large quantities of cuticles during their molting cycle. Here, we present for the first time a highly effective method for the isolation of chitin from Caribena versicolor spider molt cuticle, as well as its identification and characterization using modern analytical methods. We suggest that the tube-like molt cuticle of this spider can serve as a naturally prefabricated and renewable source of tubular chitin with high potential for application in technology and biomedicine.

Extreme biomimetics: Preservation of molecular detail in centimeter-scale samples of biological meshes laid down by sponges.

Fabrication of biomimetic materials and scaffolds is usually a micro- or even nanoscale process; however, most testing and all manufacturing require larger-scale synthesis of nanoscale features. Here, we propose the utilization of naturally prefabricated three-dimensional (3D) spongin scaffolds that preserve molecular detail across centimeter-scale samples. The fine-scale structure of this collagenous resource is stable at temperatures of up to 1200°C and can produce up to 4 × 10-cm-large 3D microfibrous and nanoporous turbostratic graphite. Our findings highlight the fact that this turbostratic graphite is exceptional at preserving the nanostructural features typical for triple-helix collagen. The resulting carbon sponge resembles the shape and unique microarchitecture of the original spongin scaffold. Copper electroplating of the obtained composite leads to a hybrid material with excellent catalytic performance with respect to the reduction of p-nitrophenol in both freshwater and marine environments.

Effect of Charge Transfer upon Li- and Na-Ion Insertion in Fine-Grained Graphitic Material as Probed by NMR.

We investigated the insertion-extraction behaviors of Li and Na ions in graphitic materials using solid-state NMR. A unique advantage of high-degree 13C-isotope enrichment of graphitic material allowed sensitive and metastable graphite intercalation compounds to be measured in a short time. Ex situ 13C magic-angle spinning NMR spectra of 13C fine-grained graphite are presented as a function of state-of-charge. The observations are discussed with respect to graphite intercalation phenomena, which include the effects of charge transfer and the demagnetizing field. Dramatic narrowing of the 13C NMR signal in metal-intercalated graphite evidences quasi-complete charge transfer occurring between lithium and graphite host material and resulting in reducing the macroscopic field effects. Upon Na insertion, incomplete charge transfer is observed and explained by inaccessibility of graphitic interlayer space for Na ions in our study. In addition, critical issues of reversibility of Li- and Na-ion electrochemical cells and solid electrolyte interphase formation are considered on the atomic scale. The knowledge gained in the present work can be applied to advanced high-power-density electrode materials for safe and fast-charging metal-ion batteries or for novel spintronic concepts with controlled spin-polarized charge carrier injection and transport combined with the possibility to manipulate magnetic anisotropy.

Tin(IV) Compounds with 2-C6F4PPh2 Substituents and Their Reactivity toward Palladium(0): Formation of Tin-Palladium Complexes via Oxidative Addition.

The tin(IV) compounds MexSn(2-C6F4PPh2)4-x (1, x = 1; 2, x = 2) and ClSn(2-C6F4PPh2)3 (3) were obtained from the reactions of 2-LiC6F4PPh2 with MeSnCl3 (3:1), Me2SnCl2 (2:1), or SnCl4 (3:1), respectively. The reactions of 2-LiC6F4PPh2 with SnCl4 in different stoichiometric ratios (4:1-1:1) gave 3 as the main product. Compound Cl2Sn(2-C6F4PPh2)2 (4) was formed in the transmetalation reaction of 3 and [AuCl(tht)] but could not be isolated. 1 and 2 react with palladium(0) sources {[Pd(PPh3)4] and [Pd(allyl)Cp]} by the oxidative addition of one of their Sn-CAryl bonds to palladium(0) with formation of the heterobimetallic complexes [MeSn(µ-2-C6F4PPh2)2Pd(κC-2-C6F4PPh2)] (5) and [Me2Sn(µ-2-C6F4PPh2)Pd(κ2-2-C6F4PPh2)] (6) featuring Sn-Pd bonds. The reaction of 3 with palladium(0) proceeds via the oxidative addition of the Sn-Cl bond to palladium(0), thus furnishing the complex [Sn(µ-2-C6F4PPh2)3PdCl] (7) featuring a Sn-Pd bond and a pentacoordinate Pd atom. Transmetalation of MexSn(2-C6F4PPh2)4-x (x = 1-3) with [Pd(allyl)Cl]2 gave MexClSn(2-C6F4PPh2)3-x and [Pd(allyl)(µ-2-C6F4PPh2)]2. For x = 1, the compound MeClSn(2-C6F4PPh2)2 (generated in situ) reacted with another 1 equiv of [Pd(allyl)Cl]2 by the oxidative addition of the Sn-Cl bond to palladium(0) and the reductive elimination of allyl chloride, thus leading to [MeSn(µ-2-C6F4PPh2)2PdCl] (8). The reductive elimination of allyl chloride was also observed in the reaction of 3 with [Pd(allyl)Cl]2, giving [Sn(µ-2-C6F4PPh2)3PdCl] (7). All compounds have been characterized by means of multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and selected compounds by 119Sn Mössbauer spectroscopy. Computational analyses (natural localized molecular orbital calculations) have provided insight into the Sn-Pd bonding of 5-8.

Impact of pre-treatments on properties of lignocelluloses and their accessibility for a subsequent carboxymethylation.

In this issue, different chemical (alkaline and sulfite pulping, ozonolysis) and mechanical (vibratory ball milling) pre-treatments were utilized for activating wheat straw and beech sawdust prior to carboxymethylation. Detailed analysis by a range of methods, including Klason-lignin, cellulose and hemicellulose quantification, Powder-X-ray diffraction (PXRD) and attenuated total reflection (ATR) IR spectroscopy, enabled the investigation of material alterations. Subsequently, carboxymethylation was carried out with both untreated and activated materials, allowing the evaluation of activation steps by determining degrees of substitution with carboxymethyl groups (DSCM). Moreover, carboxymethylation conditions were optimized, realizing high DSCM of up to 1.05. Results further revealed that ball milling enhanced the subsequent conversion; whereas chemical pre-treatments did not effectively increase material accessibilities. Further studies on chemically untreated materials emphasized that a highly reactive surface was already generated in the course of the carboxymethylation, inter alia through the concomitant dissolution of matrix components.

Group 10-group 14 metal complexes [E-TM](IV): the role of the group 14 site as an L, X and Z-type ligand.

A series of new complexes of a general motif [R2E(µ-N,S)2TM-L] (E: metalloid group 14 element; TM: group 10 metal; R: Cl, Ph, pyS, OH, (N,N,O)-chelating ligands; N,S: 1-methylimidazole-2-thiolate (methimazolyl, mt(-)), pyridine-2-thiolate (pyS(-)); L: PPh3, PCy3, pyS) was synthesised and characterised by single-crystal X-ray diffraction, multi-nuclear NMR spectroscopy ((1)H, (13)C, (31)P, (119)Sn), (119)Sn Mössbauer spectroscopy and quantum chemical calculations. The E-TM bonding situation in these compounds can be described with various resonance structures which comprise E(ii)→TM(ii), E(iii)-TM(i) and E(iv)←TM(0) features. Thus, in these complexes the atoms of the group 14 based ligand sites reveal L-, X- and Z-type ligand characteristics. A systematic comparison between structural and spectroscopic parameters as well as the results from NLMO analyses of structurally related compounds provided information about the differences in the E-TM bonding situation upon alteration of the metal atoms or ligand patterns. Under investigation are the structurally related compounds [Cl2Sn(µ-pyS)2TM-PPh3] (1: TM = Pd; 2: TM = Ni; 3: TM = Pt), [Cl2Ge(µ-pyS)2Pd-PPh3] (4) and, for in silico analysis, [Cl2Si(µ-pyS)2Pd-PPh3] (5), which indicate a pronounced shift of the E-TM bond electron pair towards TM for TM = Pt. Further complexes serve as representatives of these compounds with different bridging ligands {[Cl2Sn(µ-mt)2Pd-PPh3] (8)}, different trans-E-TM-bound ligands {[Cl2Sn(µ-pyS)2Pd-PCy3] (9), [Cl2Sn(µ-pyS)2Pd]4 (10)} and with different substituents at Sn (including penta- and hexacoordinated tin compounds), i.e., [R2Sn(µ-pyS)2Pd-PPh3] with R = Ph (6) and pyS (7), [(O,N,N)Sn(µ-pyS)2Pd-PPh3] (11) and (12) having two different (O,N,N) tridentate ligands, and [(µ-OH)ClSn(µ-pyS)2Pd-PPh3]2 (13). The latter series indicates a shift of the E-TM (= Sn-Pd) bond electron pair towards Pd upon transition from penta- to hexacoordinated tin compounds.

Tp*Cu(I)-CN-SiL2-NC-Cu(I)Tp*--a hexacoordinate Si-complex as connector for redox active metals via π-conjugated ligands.

Hexacoordinate silicon complexes L2SiX2 (L = a 2-benzoylpyrrol-1-yl derivative, X = CN, NCS) were synthesized from L2SiCl2 by ligand exchange with trimethylsilyl reagents Me3SiX. In the presence of [Tp*CuNCMe] and Me3SiCN the silicon complex L2Si(NC(CuTp*))2 was obtained, which contains a linear Cu-CN-Si-NC-Cu unit (Tp* = hydrotris(3,5-dimethylpyrazolyl)borato).

Kinetics and activation parameters of the reaction of organoarsenic(V) compounds with glutathione.

In this work the kinetics of the reaction of glutathione (GSH) with the organoarsenic(V) compounds phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), p-aminophenylarsonic acid (p-APAA) and o-aminophenylarsonic acid (o-APAA) as well as monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) is investigated. The reaction progress is monitored in real time by (1)H NMR, allowing the determination of rate coefficients and half-lives as well as activation parameters. The reaction consists of two steps: redox reaction and conjugation. In all investigated systems the conjugation is fast compared to the redox reaction and, therefore, rate determining. All investigated phenylarsonic acids follow the same rate law, showing overall reaction orders of 3 and half-lives between 47.7 ± 0.2 and 71.0 ± 3.6 min. The methylated compounds react slower, showing half-lives of 76.6 ± 0.4 and 444 ± 10 min for DMAA and MMAA, respectively. Enthalpies of activation range from 20 to 36 (± 2) kJ mol(-1) and the entropies of activation are within -154 and -97(± 7)J mol(-1)K(-1). The results reveal a correlation of the toxicity of the arsenic compound and the reaction rate with GSH. This may pave the way for the estimation of the toxicity of such compounds by simple kinetic studies.