Generation of alkoxide anions from a series of aliphatic diols and alcohols and their ion-molecule reactions with carbon dioxide in the gas phase

Alkoxide anions, [M-H](-) from a series of aliphatic diols and alcohols are generated in the source under negative ion electrospray ionisation conditions by cone-voltage fragmentation of the corresponding [M + F](-) ions. The collision-induced dissociation (CID) spectra of [M-H](-) ions consist of [M-H-2H](-) ions, in addition to the other characteristic fragment ions, and the relative abundance of [M-H-2H(-) ions among the series of diols varies as a function of chain length that could be explained based on their stabilities through intramolecular hydrogen bonding. The reactivity of alkoxide anions is studied through ion-molecule reactions with CO(2) in the collision cell of a triple quadrupole mass spectrometer. All the alkoxide anions reacted with CO(2) and formed corresponding carbonate anions, [M-H + CO(2)](-) ions. The reactivity of alkoxide anions within the series of diols also reflected the stability of their [M-H](-) ions.     

Comparison of amperometric and UV-spectrophotometric monitoring in the HPLC analysis of pesticides

Summary Studies have been carried out to compare different detection techniques including amperometric detection in the reductive and oxidative mode and UV detection following the HPLC separation of pesticides. By the example of 4,6-dinitro-o-cresol (DNOC), 2-sec-butyl-4,6-dinitrophenol (Dinoseb) and 2-tert-butyl-4,6-dinitrophenol (Dinoterb), it is shown that the electrochemical detection exhibits higher sensitivities than the UV-technique. The detection limits are in case of the oxidative amperometric technique 0.1 ng for all pesticides, in the reductive mode 0.3 ng for DNOC and 1 ng for Dinoseb and Dinoterb. By UV-monitoring the detection limits were found to be 2 ng for DNOC and 24 ng for Dinoseb and Dinoterb.     

Characterization of alpha- and gamma-glutamyl dipeptides by negative ion collision-induced dissociation

The low-energy CID mass spectra of the [M-H](-) ions of a variety of dipeptides containing glutamic acid have been obtained using cone-voltage collisional activation. Dipeptides with the gamma-linkage, H-Glu(Xxx-OH)-OH, are readily distinguished from those with the alpha-linkage, H-Glu-Xxx-OH, by the much more prominent elimination of H-Xxx-OH from the [M-H](-) ions of the former isomers, resulting in formation of m/z 128, presumably deprotonated pyroglutamic acid. Dipeptides with the reverse linkage, H-Xxx-Glu-OH, show distinctive fragmentation reactions of the [M-H](-) ions including enhanced elimination of CO(2) and formation of deprotonated glutamic acid. Exchange of the labile hydrogens for deuterium has shown that there is considerable interchange of C-bonded hydrogens with labile (N- and O-bonded) hydrogens prior to most fragmentation reactions. All dipeptides show loss of H(2)O from [M-H](-). MS(3) studies show that the [M-H-H(2)O](-) ion derived from H-Glu-Gly-OH has the structure of deprotonated pyroglutamylglycine while the [M-H-H(2)O](-) ions derived from H-Glu(Gly-OH)-OH and H-Gly-Glu-OH show a different fragmentation behaviour indicating distinct structures for the fragment ions.     

Amide bond cleavage in deprotonated tripeptides: a newly discovered pathway to "b2 ions

The fragmentation reactions of the [M-H](-) ions of the tripeptides H-Gly-Leu-Sar-OH, H-Leu-Gly-Pro-OH and H-Gly-Leu-Gly-OH have been investigated in detail using energy-resolved mass spectrometry, isotopic labelling and MS(3) experiments. It is shown that the major route to the "b(2) ions involves loss of a neutral amine from the a(3) ([M-H-CO(2)](-)) ion rather than being formed directly by fragmentation of the [M-H](-) ion. When there is no C-terminal amidic hydrogen (Sar, Pro), loss of a neutral amine is the dominant primary fragmentation reaction of the a(3) ion. However, when there is a C-terminal amidic hydrogen (Gly), elimination of the N-terminal amino acid residue is the major fragmentation reaction of the a(3) ion and formation of the "b(2) ion is greatly reduced in importance. It is proposed that the "b(2) ions are deprotonated oxazolones.     

Mass spectral fragmentation of the intravenous anesthetic propofol and structurally related phenols

Propofol (2,6-diisopropyl phenol) is a widely used intravenous anesthetic. To define its pharmacokinetics and pharmacodynamics, methods for its quantitation in biological matrixes have been developed, but its pattern of mass spectral fragmentation is unknown. We found that fragmentation of the [M - H](-) ion (m/z 177) of propofol in both APCI MS/MS and ESI MS/MS involves the stepwise loss of a methyl radical and a hydrogen radical from one isopropyl side chain to give the most intense product ion, [M -H - CH(4)](-), at m/z 161. This two-step process is also the preferred mode of fragmentation for similar branched alkyl substituted phenols. This mode of fragmentation of the [M - H](-) ion is supported by three independent lines of evidence: (1) the presence of the intermediary [M - H - CH(3)](-) radical ion under conditions of reduced collision energy, (2) the determination of the mass of the predominant [M - H - CH(4)](-) product ion by high resolution mass spectrometry, and (3) the pattern of product ions resulting from further fragmentation of the [M - H - CH(4)](-) product ion. Phenols with a single straight chain alkyl substituent, in contrast, undergo beta elimination of the alkyl radical irrespective of the length of the alkyl chain, yielding the most intense product ion at m/z 106. This product ion represents a special case of a stable intermediary radical for the two-step process described for branched side chains, because further elimination of a hydrogen radical from the beta carbon is not possible.     

Structural characterization of iridoid glucosides by ultra-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

The mass spectral fragmentation behavior of ten iridoid glucosides (IGs) has been studied using electrospray ionization (ESI), collision-induced dissociation (CID), and quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). In the negative ESI mass spectra, the deprotonated [M-H](-) ion was observed for all of the ten IGs except gardoside methyl ester, while the formate adduct [M+HCOO](-) ion appeared to be favored by the presence of a methyl ester or a lactone group in the C-4 position when formic acid was added to the mobile phase. The CID MS/MS spectra of the [M-H](-) ions have been used for structural elucidation. Ring cleavages of the aglycone moiety have been observed in the MS/MS spectra, corresponding to (1,4)F(-), (2,6)F(-), (2,7)F(-), and (2,7)F(0) (-) ions, based on accurate mass measurements and the elemental compositions of the product ions. These characteristic ions gave valuable information on the basic structural skeletons. Furthermore, on the basis of the relative abundances of the fragment ions (1,4)F(-) and (2,7)F(-), different sub-classes, such as cyclopentane-type and 7,8-cyclopentene-type IGs, can be differentiated. Ring cleavage of the sugar moieties was also observed, yielding useful information for their characterization. In addition, the neutral losses, such as H(2)O, CO(2), CH(3)OH, CH(3)COOH, and glucosidic units, have proved useful for confirming the presence of functional substituents in the structures of the IGs. Based on the fragmentation patterns of these standard IGs, twelve IGs have been characterized in an extract of Hedyotis diffusa Willd. by means of ultra-performance liquid chromatography/Q-TOF MS/MS, of which six have been unambiguously identified and the other six have been tentatively identified.     

Structural characterization of glycoporphyrins by electrospray tandem mass spectrometry

Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES-MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H](+) ions. For the glycoporphyrins with pyridyl substituents and those having a tetrafluorophenyl spacer, the doubly charged ions [M + 2H](2+) were also observed in ES-MS with high relative abundance. The fragmentation of both [M + H](+) and [M + 2H](2+) ions exhibited common fragmentation pathways for porphyrins with the same sugar residue, independently of the porphyrin structural unit and type of linkage. ES-MS/MS of the [M + H](+) ions of the galactose-substituted porphyrins gave the fragment ions [M + H - C(2)H(4)O(2)](+), [M + H - C(3)H(6)O(3)](+), [M + H - C(4)H(8)O(4)](+) and [M + H - galactose residue](+). The fragmentation of the [M + 2H](2+) ions of the porphyrins with galactose shows the common doubly charged fragment ions [porphyrin + H](2+), [M + 2H - C(2)H(4)O(2)](2+), [M + 2H - C(4)H(8)O(4)](2+), [M + 2H - galactose residue](2+) and the singly charged fragment ions [M + H - C(3)H(6)O(3)](+) and [M + H - galactose residue](+). The fragmentation of the [M + H](+) ions of glycoporphyrins with a protected galactosyl residue leads mainly to the ions [M + H - CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2) - CO](+), [M + H - C(10)H(16)O(4)](+) and [M + H - protected galactose](+). The doubly charged ions [M + 2H](2+) fragment to give the doubly charged ions [porphyrin + H](2+) and the singly charged ions [M + H - protected galactose residue](+) and [M + H - CO(CH(3))(2)](+). For the porphyrins where the sugar structural unit is linked by an ester bond, [M + 2H](2+), ES-MS/MS showed a major and typical fragmentation corresponding to combined loss of a sugar structural unit and further loss of water, leading to the ion [M + 2H - sugar residue - H(2)O](2+), independently of the structure of the sugar structural unit. These results show that ES-MS/MS can be a powerful tool for the characterization of the sugar structural unit of glycoporphyrins, without the need for chemical hydrolysis.     

Tools to discover anionic and nonionic polyfluorinated alkyl surfactants by liquid chromatography electrospray ionisation mass spectrometry

A tiered approach is proposed for the discovery of unknown anionic and nonionic polyfluorinated alkyl surfactants (PFASs) by reversed phase ultra high performance liquid chromatography (UHPLC)--negative electrospray ionisation--quadrupole time of flight mass spectrometry (UHPLC-ESI(-)-QTOF-MS). The chromatographic separation, ionisation and detection of PFASs mixtures, was achieved at high pH (pH=9.7) with NH(4)OH as additive. To distinguish PFASs from other chemicals we used the characteristic negative mass defects of PFASs, their specific losses of 20 Da (HF) and the presence of series of chromatographic peaks, belonging to homologues series with m/z of n×50 Da (CF(2)) or n×100 Da (CF(2)CF(2)). The elemental composition of the precursor ions were deducted from the accurate m/z values of the deprotonated molecules [M-H](-). In case of in-source fragmentation, the presence of dimers, e.g. [M(2)-H](-) and adduct ions such as [M-H+solvent](-) and [(M-H)(M-H+Na)(n)](-) were used to confirm the identity of the precursor ions. In relation to quantification of PFASs, we discuss how their surfactancy influence the ESI processes, challenge their handling in solution and choices of precursor-to-product ions for MSMS of e.g., structural PFAS isomers. The method has been used to discover PFASs in industrial blends and in extracts from food contact materials.     

Structural analysis of selected characteristic flavones by electrospray tandem mass spectrometry.

Seven structure analogical flavonoid aglycones have been analyzed using electrospray ionization tandem mass spectrometry (ESI-MSn) in the negative-ion mode. The spectra obtained ESI-MSn allowed us to propose plausible schemes for their fragmentation mechanism. By analyzing the product ions spectra of deprotonated molecule ions [M-H](-), some neutral diagnostic losses and specific retro Diels-Alder fragments were obtained. By using all of these characteristic fragment ions we can specially differentiate the flavone isomer.     

Mass spectrometric characterization of 4-oxopentanoic acid and gas-phase ion fragmentation mechanisms studied using a triple quadrupole and time-of-flight analyzer hybrid system and density functional theory

4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M-H](-) anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M-H](-) anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M-H-H2O](-). Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented.     

Interactions of nucleosides with CrO(4) (2-) and Cr(3+) as studied by electrospray ionization mass spectrometry

The interactions of CrO(4) (2-) and Cr(3+) with nucleosides studied by electrospray ionization mass spectrometry (ESI-MS) are reported. In water, the nucleosides which do not contain the NH(2) group form the unstable [M+HCrO(4)](-) anion. In the presence of a reducing agent, namely methanol, chromate anion forms stable complexes with nucleosides, [M+CH(3)CrO(4)](-) anions. The fragmentation of [M+CH(3)CrO(4)](-) anions involve elimination of the methanol molecule. Chromium cation-nucleoside complexes were not observed in water. In methanol solutions, adenosine and cytidine form [(M-H)+CrOCH(3)](+) and [(M-H)(2)+Cr](+) ions. Most probably, deprotonated imine tautomers form complexes in which a metal cation is simultaneously coordinated by two nitrogen atoms. Complexes containing chloride anions and a few methanol molecules were observed for other nucleosides. Guanosine and inosine form doubly charged ions of the type [M(2)+CrOCH(3)](2+) that probably contain a bond between the oxygen atom and the chromium cation, (HN(1)--C(6)==O)(2) (....)Cr(3+)).     

Characterization of C-glycosyl flavones O-glycosylated by liquid chromatography-tandem mass spectrometry

Fifty three O-glycosyl-C-glycosyl flavones with O-glycosylation on phenolic hydroxyl or on the C-glycosyl residue or combination of both forms have been studied by liquid chromatography-UV diode array detection-electrospray ionisation mass spectrometry ion trap in the negative mode. The study of the relative abundance of the main ions from the MS preferential fragmentation on -MS2 and/or -MS3 events allows the differentiation of the position of the O-glycosylation, either on phenolic hydroxyl or on the sugar moiety of C-glycosylation. In addition, it is possible to discriminate between O-glycosylation at 2' and at 6' positions. The occurrence of an abundant ion Y(0)(-) ([(M-H)-132/-146/-162](-), mono-O-pentosyl/rhamnosyl/hexosyl-C-glycosyl derivatives) after -MS2 fragmentation characterizes the O-glycosylation on phenolic hydroxyls. The preferential fragmentation leading to a relevant Z(1)(-) ([Y(1)-18](-)) fragment is characteristic of 2'-O-glycosyl-C-glycosyl derivatives. The 6'-O-glycosyl-C-glycosyl derivatives are characterized by (0,2)X(0)(-), which is generated by a global loss of the sugar moiety from the O-glycosylation at 6' and the glycosidic fraction that involves the carbons 6'-3' of the C-glycosyl residue ([(M-H)-162-120](-), in the case of 6'-O-hexosyl-C-hexosyl derivatives). Regarding the combined O-glycosylated compounds (both on phenolic hydroxyl and on sugar moiety at C-glycosylation), the main fragmentation on -MS2 events produces a Y(0)(-) characterizing the O-glycosylation on the phenolic hydroxyl, and the -MS3[(M-H)-->Y(0)](-) fragmentation of the O-glycosylation on the C-glycosyl residue.     

Electrospray ionization mass spectrometry of tribenzyltin substituted-phenoxyacetate compounds

Hydrolysis products of organotin compounds RC(6)H(4)OCH(2)COOSn(CH(2)ph)(3) (R = o-NO(2), 1; m-NO(2), 2; p-NO(2), 3; o-CH(3), 4; o-OCH(3), 5; o-Cl, 6; o-Br, 7) and RC(6)H(3)OCH(2)COOSn(CH(2)ph)(3) (R = o,o-2CH(3), 8, o-OCH(3), p-CHO, 9; o,p-2Cl, 10), produced in aqueous acetonitrile solution, have been investigated by electrospray mass spectrometry (MS) and MS(n) techniques. The complexes [Y(2)SnXR'](-), [Y(3)SnXR'](-), [Y(3)SnX(2)R'](-), [Y(2)SnX(3)R'](-), and fragment ions of [Y(3)SnR'](-), plus abundant RC(6)H(4)(or RC(6)H(3))OCH(2)COO(-) and RC(6)H(4)(or RC(6)H(3))O(-) ions are observed in negative mode, whereas the protonated molecular ion [M + H](+), complexes [Y(2)SnXR'](+), [Y(3)SnXR'](+), [Y(2)SnX(2)R'](+), [Y(3)SnX(2)R'](+), [Y(2)SnX(3)R'](+), [Y(3)SnX(3)R'](+), as well as [YSnXR'](+), [M - CH(2)ph](+), XSn(+), (phCH(2))(3)Sn(+), phCH(2)Sn(+) (Y = &bond;CH(2)ph, X = &bond;OOCCH(2)OC(6)H(4)R(or C(6)H(3)R)) are detected in the positive mode. Water adduct ions are seen in both modes. The assignments are facilitated by agreement between observed and calculated isotopic patterns and tandem mass spectrometry studies.     

Does the electron ionization induced fragmentation of partly saturated stereoisomeric pyrrolo‐ and isoindoloquinazolinones show stereospecificity?

The electron ionization mass spectrometric behavior of pyrroloquinazolinones (1-6) and isoindoloquinazolinones (7-14) was studied. These compounds were further classified as partly saturated pyrroloquinazolinones (1-3), benzologues (7-11), methylene-bridged derivatives (4-6, 12, 13) and a bisacyl compound (14). The mass spectra of the pyrrolo- and isoindoloquinazolinones did not exhibit stereospecific retro-Diels-Alder (RDA) fragmentations. The cyclohexane-fused compounds 7 (cis annelated) and 8 (trans annelated) did display some other ions differing in their abundances that could be used to differentiate this pair of stereoisomers. Also the cyclohexene-fused compounds 2, 3, 9 and 10 exhibited somewhat different ion abundances pairwise that could be utilized for isomeric differentiation. Earlier hypothesis of pyrrolo ring cleavage via the loss of C(3)H(5)O(.) was strengthened by the fragmentation of compounds 1-4. RDA(+/-H) fragmentation is more favorable than the formation of [M-R](+) ions (R=H, C(6)H(4)CH(3), or C(6)H(4)Cl) when an unsaturated bicyclic group is present but both RDA fragmentation and [M-R](+) formation occur for cyclohexene-fused compounds, possibly because of the lower ring strain than with norbornene-fused compounds. The [M-H](+) ion was abundant for compounds 7 and 8 as was [M-Ar](+) for 1-4 and 11. Although the compounds studied might participate in amide-imidol tautomerism, no indication of such tautomerism was detected.     

Tandem mass spectra of transition-metal ion adducts of glycosyl dithioacetals; distinction among stereoisomers

Electrospray ionization mass spectra of some glycosyl dithioacetals recorded in the presence of transition-metal chlorides, XCl2 (where X = Co, Mn and Zn), give abundant adduct ions such as [M+XCl]+ and [2M-H+X]+ and minor ions such as [M-H+X]+ and [2M+XCl]+. The tandem mass spectra of these adducts show characteristic elimination of neutral molecules such as H2O, HCl, EtSH, CH2O, C2H4O2/C2H4O. [M+XCl]+ ions fragment readily and the fragmentation appears to be stereochemically controlled as the relative abundances of the fragments are different for three stereoisomers. The added metal is lost as neutral molecules in the form of XCl(OH) and XCl(SEt). This is a predominant pathway in the ZnCl+ adducts. [2M+XCl]+ ions fragment preferentially by elimination of HCl, indicating strong metal interactions in the resulting dimeric [2M-H+X]+ ion. As there are several electron-rich centers in the molecule, the dimeric complex [2M-H+X]+ can have several structures and the observed fragmentations may reflect the sum of those of all these structures. The dimeric complexes fragment by elimination of neutral molecules leaving the dimeric interactions intact. The extent of fragmentation varies for the stereoisomers, leading to stereochemical differentiation.     

Self-assembly of D-penicillaminato M6M'8 (M = Ni(II), Pd(II), Pt(II); M' = Cu(I), Ag(I)) clusters and their organization into extended La(III)M6M'8 supramolecular structures

A series of chiral M(6)M'(8) cluster compounds having twelve free carboxylate groups, [M(6)M'(8)(D-pen-N,S)(12)X](5-) (M/M'/X = Pd(II)/Ag(I)/Cl(-) ([1](5-)), Pd(II)/Ag(I)/Br(-) ([2](5-)), Pd(II)/Ag(I)/I(-) ([3](5-)), Ni(II)/Ag(I)/Cl(-) ([4](5-)), Pt(II)/Ag(I)/Cl(-) ([5](5-)), Pd(II)/Cu(I)/Cl(-) ([6](5-)); D-H(2)pen = D-penicillamine), in which six cis-[M(D-pen-N,S)(2)](2-) square-planar units are bound to a [M'(8)X](7+) cubic core through sulfur-bridges, was synthesized by the reactions of cis-[M(D-pen-N,S)(2)](2-) with M' in water in the presence of halide ions. These M(6)M'(8) clusters readily reacted with La(3+) in aqueous buffer to form La(III)(2)M(6)M'(8) heterotrimetallic compounds, La(2)[1](CH(3)COO), La(2)[2](CH(3)COO), La(2)[3](CH(3)COO), La(2)[4](CH(3)COO), La(2)[5](CH(3)COO) and La(2)[6]Cl, in which the M(6)M'(8) cluster units are linked by La(3+) ions through carboxylate groups in a 1?:?2 ratio. While the La(III)(2)M(6)Ag(I)(8) compounds derived from [1](5-), [2](5-), [3](5-), [4](5-) and [5](5-) have a 1D helix supramolecular structure with a right-handedness, the La(III)(2)Pd(II)(6)Cu(I)(8) compound derived from [6](5-) has a 2D sheet-like structure with a triangular grid of the Pd(II)(6)Cu(I)(8) cluster units. When aqueous HCl was added to the reaction solution of [6](5-) and La(3+), another La(III)(2)Pd(II)(6)Cu(I)(8) heterotrimetallic compound, La(2)[6]Cl·HCl, in which the Pd(II)(6)Cu(I)(8) cluster units are linked by La(3+) ions to form a 2D structure with a rectangular grid, was produced. The solid-state structures of these La(III)(2)M(6)M'(8) compounds, determined by single-crystal X-ray crystallography, along with the spectroscopic properties of the M(6)M'(8) cluster compounds in solution, are described.     

Liquid chromatography/tandem mass spectrometry analysis of long-chain oxidation products of cardiolipin induced by the hydroxyl radical

The anionic phospholipid cardiolipin (CL) is found almost exclusively in the inner membrane of mitochondria, playing an important role in energy metabolism. Oxidation of CL has been associated with apoptotic events and various pathologies. In this study, electrospray ionization mass spectrometry coupled with liquid chromatography (LC/ESI-MS) was used to identify tetralinoleoyl-cardiolipin (TLCL) modifications induced by the OH(·) radical generated under Fenton reaction conditions (H(2)O(2) and Fe(2+)). The identified oxidation products of TLCL contained 2, 4, 6 and 8 additional oxygen atoms. These long-chain oxidation products were characterized by LC/ESI-MS/MS as doubly [M-2H](2-) and singly charged [M-H](-) ions. A detailed analysis of the fragmentation pathways of these precursor ions allowed the identification of hydroperoxy derivatives of CL. MS/MS analysis indicated that CL oxidation products with 4, 6 and 8 oxygen atoms have one fatty acyl chain bearing 4 oxygen atoms ([RCOO+4O](-)). Even when the TLCL molecule was oxidized by the addition of eight oxygen atoms, one of the acyl chains remained non-modified and one fatty acyl chain contained three or four oxygen atoms. This led us to conclude that under oxidative conditions by the OH(·) radical, the distribution of oxygens/peroxy groups in the CL molecule is not random, even when CL has the same fatty acyl chains in all the positions. Using mass spectrometry, the oxidation products have been unequivocally assigned, which may be useful for their detection in biological samples.     

Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic ester polymerisation

The reactions of the bulky amino-bis(phenol) ligand Me(2)NCH(2)CH(2)N[CH(2)-3,5-Bu(t)(2)-C(6)H(2)OH-2](2)(1-H(2)) with Zn[N(SiMe(3))(2)](2)(4), [Mg[N(SiMe(3))(2)](2)](2)(5) and Ca[N(SiMe(3))(2)](2)(THF)(2)(6) yield the complexes 1-Zn, 1-Mg and 1-Ca in good yields. The X-ray structure of 1-Ca showed the complex to be dimeric, with calcium in a distorted octahedral coordination geometry. Five of the positions are occupied by an N(2)O(3) donor set, while the sixth is taken up by an intramolecular close contact to an o-Bu(t) substituent, a rare case of a Ca...H-C agostic interaction (Ca...H distances of 2.37 and 2.41 Angstroms). Another sterically hindered calcium complex, Ca[2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)O](2)(THF)(2).(C(7)H(8))(2/3)(7), was prepared by reaction of 6 with the iminophenol 2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)OH (3-H). According to the crystal structure 7 is monomeric and octahedral, with trans THF ligands. The complex Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2)(2-Ti) was prepared by treatment of Ti(OPr(i)(4)) with the new amino-bis(phenol) Me(2)NCH(2)CH(2)N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)OH-2](2)(2-H(2)). The reduction of 2-Ti with sodium amalgam gave the titanium(III) salt Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2).Na(THF)(2)(8). A comparison of the X-ray structures of 2-Ti and 8 showed that the additional electron in 8 significantly reduced the intensity of the pi-bonding from the oxygen atoms of the isopropoxide groups to titanium. 1-Ca and 8 were active initiators for the ring-opening polymerisation of epsilon-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and yielded polymers with narrow molecular weight distributions.     

Do anions influence the polarity of protic ionic liquids?

Polarity studies in two classes of imidazolium-based protic ionic liquids (PILs) possessing [HSO(4)](-), [HCOO](-), [CH(3)COO](-) and [CH(3)CH(2)COO](-) anions were carried out using a solvatochromic method from 298.15 to 353.15 K. For 1-methylimidazolium class of PILs, E(T)(30) was found to be independent over the entire range of temperature, while E(T)(30) was noted to decrease with a rise in temperature in the case of 1-butylimidazolium class of PILs containing [CH(3)COO](-) and [CH(3)CH(2)COO](-) anions. The E(T)(30) value decreases in both the classes upon varying the anions ([HSO(4)](-), [HCOO](-), [CH(3)COO](-) and [CH(3)CH(2)COO](-)). The E(T)(30) value is controlled by hydrogen bond acceptor basicity, β, and dipolarity/polarizability, π*. The E(T)(30) value for PILs varies inversely to the strength of the coulombic interaction between ions in PILs. Strong interactions between ions lead to lower E(T)(30) values. Unlike the poor thermal effect on E(T)(30), the Kamlet-Taft parameters i.e. α, β and π* have pronounced thermal effect in the imidazolium-based PILs. Variation in the Kamlet-Taft parameters is controlled by the stabilization of ions and the degree of proton transfer from Br?nsted acid to Br?nsted base.     

Characteristic negative ion fragmentations of deprotonated peptides containing post-translational modifications: mono-phosphorylated Ser, Thr and Tyr. A joint experimental and theoretical study

Peptides and proteins may contain post-translationally modified phosphorylated amino acid residues, in particular phosphorylated serine (pSer), threonine (pThr) and tyrosine (pTyr). Following earlier work by Lehmann et al., the [M-H]- anions of peptides containing pSer and pThr functionality show loss of the elements of H3PO4. This process, illustrated for Ser (and using a model system), is CH3CONH-C(CH2OPO3H2)CONHCH(3) --> [CH3CONHC(==CH2)CONHCH3 (-OPO3H2)] (a) --> [CH3CONHC(==CH2)CONHCH3-H]- + H3PO4, a process endothermic by 83 kJ mol(-1) at the MP2/6-31++G(d,p)//HF/6-31++G(d,p) level of theory. In addition, intermediate (a) may decompose to yield CH3CONHC(==CH2)CONHCH3 + H2PO4 - in a process exothermic by 3 kJ mol(-1). The barrier to the transition state for these two processes is 49 kJ mol(-1). Characteristic cleavages of pSer and pThr are more energetically favourable than the negative ion backbone cleavages of peptides described previously. In contrast, loss of HPO3 from [M-H]- is characteristic of pTyr. The cleavage [NH2CH(CH2-C6H4-OPO3H-)CO2H] --> [NH2C(CH2-C6H4-O-)CO2H (HPO3)] (b) --> NH2CH(CH2-C6H4-O-)CO2H + HPO3 is endothermic by 318 kJ mol(-1) at the HF/6-31+G(d)//AM1 level of theory. In addition, intermediate (b) also yields NH2CH(CH2-C6H4-OH)CO2H + PO3 - (reaction endothermic by 137 kJ mol(-1)). The two negative ion cleavages of pTyr have a barrier to the transition state of 198 kJ mol(-1) (at the HF/6-31+G(d)//AM1 level of theory) comparable with those already reported for negative ion backbone cleavages.