Search

The anion-induced folding of tripodal imidazolium receptors has been investigated by NMR spectroscopy, electrospray ionization ion mobility mass spectrometry and DFT calculations. Such folding can be switched by anion release upon collision induced dissociation. [ABSTRACT FROM AUTHOR]

Abstract: An approach for the detection and characterization of SA derivatives in plant samples is presented based on liquid chromatography coupled to electrospray ionization (ESI) tandem mass spectrometric techniques. Precursor ion scan methods using an ESI triple quadrupole spectrometer for samples from plants challenged with the virulent Pseudomonas syringae pv tomato DC3000 allowed us to detect two potential SA derivatives. The criterion used to consider a potential SA derivative is based on the detection of analytes in the precursor ion scan chromatogram upon selecting m/z 137 and m/z 93 that correspond to the salicylate and its main product ion, respectively. Product ion spectra of the newly-detected analytes as well as accurate m/z determinations using an ESI Q-time-of-flight instrument were registered as means of characterization and strongly suggest that glucosylated forms of SA at the carboxylic and at the phenol functional groups are present in plant samples. The specific synthesis and subsequent chromatography of salicylic glucosyl ester (SGE) and glucosyl salicylate (SAG) standards confirmed the chemical identity of both peaks that were obtained applying different tandem mass spectrometric techniques and accurate m/z determinations. A multiple reaction monitoring method has been developed and applied to plant samples. The advantages of this LC–ESI–MS/MS methods with respect to the traditional analysis of glucosyl conjugates are also discussed. Preliminary results revealed that SA and the glucosyl conjugates are accumulated in Arabidopsis thaliana in a time dependent manner, accordingly to the up-regulation of SA-dependent defenses following P. syringae infection. This technique applied to plant hormones or fragment ions may be useful to obtain chemical family members of plant metabolites and help identify their contribution in the signaling of plant defenses. [Copyright &y& Elsevier]

The use of electrospray ionization mass spectrometry (ESI-MS) in parallel with 29Si and 1H NMR to elucidate the aqueous speciation and temporal evolution of the organosilane methyldiethoxysilane (MDES) through hydrolysis and condensation processes is reported here. A suitable methodological approach for the monitoring of the oligomerization of MDES under different pH conditions has been developed revealing details on the particular oligomerization mechanism of this organosilane. [ABSTRACT FROM AUTHOR]

Abstract: Reactions of triangular telluride-bridged Mo and W clusters [M3(μ3-Te)(μ2-Te2)3(dtp)3]+ (M=Mo, W; dtp=(EtO)2PS2) with S2Cl2 or Br2 lead to Te/S exchange in the Te2 ligands, with the formation of complexes with a novel TeS2− ligand. Reaction of [W3(μ3-Te)(μ2-Te2)3(dtp)3]+ with Br2 or S2Cl2 gives a mixture of complexes formulated as [W3Te4.25S2.75(dtp)3]+ and [W3Te4.30S2.70(dtp)3]+, respectively, on the basis of X-ray structural analysis. Reaction of the Mo homolog, namely [Mo3(μ3-Te)(μ2-Te2)3(dtp)3]+, with S2Cl2 gives rise to [Мо3Te4.74S2.26((EtO)2PS2)3]+. Electrospray ionization mass spectrometry (ESI-MS) complements the information gathered from X-ray analysis regarding the degree of Te by S substitution; moreover, detailed insights on the regioselectivity of such replacement are also obtained from ESI-MS analysis. These experimental evidences indicate that Te by S replacement in W complexes display high regioselectivity (as evidenced by the exclusive formation of a W3Te4S3 4+ core), the equatorial Te ligands being preferentially replaced over the Teax and μ3-Te ligands. Conversely, for the Mo homologs, a broad distribution of Mo3Te7− x S x 4+ cluster species ranging from x =0 to 6 is observed. Bond distance analysis as well as crystal packing trends as a function of the cluster core M3Te7− x S x 4+ (M=Mo, W; x =0–6) composition are also reported. [Copyright &y& Elsevier]

The substitutional lability of Mo-Cl and Cu-Cl bonds in cubane-type Mo[sub3]CuS[sub4] and incomplete cubane-type Mo[sub3]S[sub4] clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo[sub3]S[sub4](CuCN) (dmpe)[sub3]Cl[sub3]]PF[sub6] ([2]PF[sub6]) and [Mo[sub3]S[sub4](dmpe)[sub3](CN)[sub3]]PF[sub6] ([5]PF[sub6]), and to subsequently use them as precursors in low-dimensional linking reactions. Mixed-metal assemblies formulated as [Mo3S4(Cu-μCN⋯Mo(CO)[sub5]) (dmpe)[sub3]Cl[sub3]][sup+] ([3][sup+]) and [Mo[sub3]S[sub4](dmpe)3(μCN⋯Mo(CO)[sub5])[sub3]][sup+] ([6][sup+]) are obtained by reaction of tetrahydrofuran solutions of [2]BPh[sub4] and [5]BPh[sub4] with the complex (THF)Mo(CO)5. The intrinsic stability of the (M'-μCN⋯Mo (CO)[sub5]) linkages (M' = Cu in 3[sup+] and Mo in 6[sup+]) in solution and in the gas phase is investigated through a combination of variable-temperature [sup31]P NMR, IR, UV-vis spectroscopies, and electrospray ionization tandem mass spectrometry. The spectroscopic and electrochemical consequences of CN coordination as well as Mo(CO)[sub5] ligation either at the Cu or the Mo site in Mo[sub3]CuS[sub4] and Mo[sub3]S[sub4] clusters are reported, Replacement of Cl by CN or CN⋯Mo(CO)[sub5] at the Cu site does not affect the redox potentials, whereas analogous substitution at Mo sites exerts a profound anodic shift of 220 and 500 mV upon Cl to CN and Cl to CN⋯Mo(CO)[sub5] replacement, respectively. [ABSTRACT FROM AUTHOR]

Increasing the efficiency of hydrosilylation assisted by visible-light. Catalytic properties and reaction mechanism with the formation of radicals where the platinum complexes play a dual role as harvesting light species and enabling bond breaking/forming transformations. [Display omitted] • Platinum complexes induce alkyne hydrosilylation under photo or thermal conditions. • A single platinum complex plays a dual role as a photosensitizer and a catalyst enabling bond breaking/forming transformations. • Stereodivergent selectivity under photochemical or thermal conditions. • Increased hydrosilylation efficiency under photocatalytic conditions in terms of reduction time, lower temperature and catalyst loadings. • Trapping intermediates by electrospray ionization mass spectrometry evidence the formation of silylradicals as relevant species in the reaction mechanism. In this manuscript we assess the catalytic properties of pincer platinum complexes in alkyne hydrosilylation either under photo or thermal conditions. The visible light-induced hydrosilylation proved to be more efficient. It can be performed at room temperature and required lower catalyst loadings than that operating under thermal conditions. The platinum complexes play a dual role in photohydrosilylation as serve as a photosensitizer and a catalyst enabling species in bond breaking/forming transformations. In addition, alkyne hydrosilylation is achieved with moderate regio- and stereoselectivity but is enhanced under photocatalytic conditions and in the case of terminal alkynes we have observed the formation of β(Z) products not observable under thermal conditions. Such differences in selectivity constitute an example of stereodivergent catalysis dictated under photochemical or thermal conditions. The selectivity differences are ascribed to a distinctive reaction mechanism for the light- vs thermally-induced process that involve radical or organometallic intermediates, respectively. [ABSTRACT FROM AUTHOR]

Reaction of [Nb6O19]8- with H6TeO6 in water gives telluropentaniobate [(OH)TeNb5O18]6- (1) as single product, which was isolated as Na+ and mixed Na+/K+ salts. Crystal structures were determined for Na6[(OH)TeNb5O18]•15H2O (Na6-1) and K6Na[Nb5.5{Te(OH)}0.5O18.5]•26H2O (K6Na-1). Formation of 1 was monitored with electrospray ionization mass spectrometry (ESI-MS) and 125Te NMR techniques. Capillary electrophoresis was used to calculate electrophoretic mobilities and radii of the anionic species in solutions of [(OH)TeNb5O18]6- and [Nb6O19]8- in borate buffer. No condensation or degradation products were detected. Reactions of 1 with {Cp*Rh}2+ sources gives 1:1 and 2:1 hybrid polyoxometalate, which are present in solution as a mixture of isomers, as detected by 125Te NMR. The isomerism is related to various possibilities of coordination of {Cp*Rh}2+ to different {M3O3} faces, relative to the unique Te atom. According to ESI-MS experiments in water and methanol, rapid redistribution of the organometallic fragments between the 1:1 and 2:1 complexes takes place. The 1:1 complexes are more stable in water, while 2:1 complexes dominate in methanol. X-ray structural analysis of the crystals isolated from 2:1 reaction mixture allowed identification of Na3[{Cp*Rh}2TeNb5O19]•24H2O (Cp*2Rh2-1) with two {Cp*Rh}2+ fragments capping the opposing faces of the Lindqvist anion. [ABSTRACT FROM AUTHOR]

The mechanism of the dehydrosulfenylation of 2-arylsulfinyl esters was investigated. The reaction was found to follow a homolytic cleavage mechanism as verified by electrospray ionization tandem mass spectrometry and experimental work. Rearranged sulfoxides are obtained as byproduct during the elimination reaction. [ABSTRACT FROM AUTHOR]

The gas phase fragmentation reactions of sulfur-tich [Mo3S7Br6]2- (12-), [Mo3S7(bdt)3]2- (22-), and [Mo3S4(bdt)3]2- (32-) (bdt = benzenedithiolate) complexes have been investigated by electrospray ionization (ESI) tandem mass spectrometry and theoretical calculations at the density functional theory level. Upon collision induced dissociation (CID) conditions, the brominated 12- dianion dissociates through two sequential steps that involves a heterolytic Mo-Br deavage to give [Mo3S7Br5]- plus Br followed by a two-electron redox process that affords [Mo3S5Br5] and diatomic S2 suffur. Dianion [Mo3S7(bdt)3]2- (22-) dissociates through two sequential redox processes evotang diatomic S2 sulfur and neutral bdt to yield [Mo3S5(bdt)3]2- and [Mo3S5(bdt)2]2-, respectively. Conversely, dianion [Mo3S4(bdt)3]2- (32-), with sulfide instead of disulfide S22- bridged ligands, remains intact under identical fragmentation conditions, thus highlighting the importance of disulfide ligands (S22-) as electron reservoirs to trigger redox reactions. Regioselective incorporation of 34S and Se at the equatorial position of the Mo3S7 duster core in 12- and 22- have been used to identity the product ions along the fragmentation pathways. Reaction mechanisms for the gas-phase dissociation pathways have been elucidated by means of B3LYP calculations, and a compatison with the solution reactivrty of Mo3S7 and Mo3S4 dusters as well as dosely related Mo/S/dithiolene systems is also discussed. [ABSTRACT FROM AUTHOR]

A two-step procedure for the preparation of hybrid complexes based on electroactive tetrathiatulvalene (TTF)-functionalized o-P2 diphosphanes (o-P2 = 3,4-dimethyl-3,4-bis(diphenylphosphino)tetrathiatulvalene) and inorganic C3-symmetrized Mo3O4 (Q = S. Se) clusters, namely, [Mo3S4CI3(o-P2)3]PF6 ([1]PF6) and [Mo3Se4CI3(o-P2)3]PF6 ([2]PF6), is reported. Their molecular and electronic structures are also described on the basis of X-ray diffraction experiments and density functional theory (DFT) calculations aimed at understanding the interactions established between both the organic and the inorganic parts. Cyclic voltammograms of compounds [1]PF6 and [2]PF6 display reduction features associated to the Mo3Q4 core and oxidation characteristics due to the TTF skeleton. The oxidation chemistry of [1]PF6 and [2]PF6 in solution is also investigated by means of in situ electrospray ionization (ESI) mass spectrometry, UV-vis, and, electron paramagnetic resonance (EPR) measurements. Upon addition ot increasing amounts of NOPF6 (less than 3 eqsiv), the sequential formation ot 1n+ (n = 1-4) species was observed whereas addition of a 3-fold excess of NOPE6 allows to access the three-electron oxidized [Mo3S4Cl3(o-P2)3]4 (14j and [Mo3Se4Cl3(o-P2)3]4+ (24+) canons. These 14+ and 24+ canons represent still rare examples 01 complexes with oxidized TTF-ligands that are remarkably stable either toward diphosphane dissociation or phosphane oxidation. Polycrystalline samples 01 compound [1](PF6)4 were obtained by oxidation [1] compound [1]PF6 using NOPF6 which were analyzed by solid state absorption, UV-vis, and Roman spectroscopies. [ABSTRACT FROM AUTHOR]

The reaction of (Bu[sub4]N)[sub2][Re[sub2]CI[sub8]] with lacunary Keggin polyoxometalate K[sub7][PW[sub11]O[[sub39]] in water produces a new dumbbell-shaped heteropolyoxometalate anion, [Re[sub2](PW[sub11]O[sub39])[sub2]][sup8-], whose structure contains a central Re[sub2] core with a quadruple bond between Re atoms (Re-Re 2.25 Å), coordinated to two polyoxometalate units. This complex represents the first example of the direct linking of two polyoxometalate units via a metal-metal multiple bond. The compounds were characterized by X-ray analysis, IR, and electrospray ionization mass spectrometry. [ABSTRACT FROM AUTHOR]