Terpenoids from the liverwort Chandonanthus hirtellus

A new bicyclogermacrane sesquiterpenoid, two new cembrane diterpenoids and five new dolabellane diterpenoids, along with known terpenoids, have been isolated from the Malaysian liverwort Chandonanthus hirtellus. The structures of the new compounds were established by spectroscopic and chemical methods in addition to X-ray crystallographic studies.     

Cyclization of peptide b9 ions

The product ion mass spectra obtained by CID of the b₉ ions derived by loss of neutral alanine from the MH⁺ ion of the peptides Tyr(Ala)₉, (Ala)₄Tyr(Ala)₅, and (Ala)₈TyrAla are essentially identical, indicative of full cyclization reaction to a common intermediate before fragmentation. This leads to abundant nondirect sequence ions in the product ion mass spectra of the b₉ ions. The product ion mass spectra of the b₈ ions from the first two peptides also are essentially identical. The fragmentation of the MH⁺ ions also leads to low intensity nondirect sequence ions in the product ion mass spectra. N-terminal acetylation blocks the cyclization and eliminates nondirect sequence fragment ions in the product ion mass spectra.     

Determination of the bond-angle distribution in vitreous B2O3 by B double rotation (DOR) NMR spectroscopy

The B–O–B bond angle distributions for both ring and non-ring boron sites in vitreous B₂O₃ have been determined by ¹¹B double rotation (DOR) NMR and multiple-quantum (MQ) DOR NMR. The [B₃O₆] boroxol rings are observed to have a mean internal B–O–B angle of 120.0±0.7° with a small standard deviation, σ_R=3.2±0.4°, indicating that the rings are near-perfect planar, hexagonal structures. The rings are linked predominantly by non-ring [BO₃] units, which share oxygens with the boroxol ring, with a mean B_ring–O–B_non-ring angle of 135.1±0.6° and σ_NR=6.7±0.4°. In addition, the fraction of boron atoms, f, which reside in the boroxol rings has been measured for this sample as f=0.73±0.01.     

Barium azacryptand sodide,the first alkalide with an alkaline Earth cation,also contains a novel dimer, (Na(2))(2-)

The first barium sodide, with stoichiometry Ba(2+)(H(5)Azacryptand[2.2.2](-))Na(-).2MeNH(2), was synthesized by the reaction of Ba, Na, and H(6)Azacryptand[2.2.2] in NH(3)-MeNH(2) solution. It was characterized by X-ray crystallography, (23)Na MAS NMR, hydrogen evolution, DSC, optical spectroscopy, and magnetic susceptibility. This is the first sodide in which the sodium anions form (Na(2))(2)(-) dimers. Previous theoretical predictions were verified by a calculation of the potential energy curve for the dimer in the field of the surrounding charges, whose positions were determined from the crystal structure.     

Effect of the his residue on the cyclization of b ions

The MSⁿ spectra of the [M + H]⁺ and b ₅ peaks derived from the peptides HAAAAA, AHAAAA, AAHAAA, AAAHAA, and AAAAHA have been measured, as have the spectra of the b ₄ ions derived from the first four peptides. The MS² spectra of the [M + H]⁺ ions show a substantial series of b_n ions with enhanced cleavage at the amide bond C-terminal to His and substantial cleavage at the amide bond N-terminal to His (when there are at least two residues N-terminal to the His residue). There is compelling experimental and theoretical evidence for formation of nondirect sequence ions via cyclization/reopening chemistry in the CID spectra of the b tons when the His residue is near the C-terminus. The experimental evidence is less clear for ions when the His residue is near the N-terminus, although this may be due to the use of multiple alanine residues in the peptide making identifying scrambled peaks more difficult. The product ion mass spectra of the b ₄ and b ₅ ions from these isomeric peptides with cyclically permuted amino acid sequences are similar, but also show clear differences. This indicates less active cyclization/reopening followed by fragmentation of common structures for b _n ions containing His than for sequences of solely aliphatic residues. Despite more energetically favorable cyclization barriers for the b ₅ structures, the b ₄ ions experimental data show more clear evidence of cyclization and sequence scrambling before fragmentation. For both b ₄ and b ₅ the energetically most favored structure is a macrocyclic isomer protonated at the His side chain.     

[VO(SeO3)(H2O)2]·0.5H2O

In poly[[diaquaoxido[μ₃‐trioxidoselenato(2−)]vanadium(IV)] hemihydrate], {[VO(SeO₃)(H₂O)₂]·0.5H₂O}_n, the octahedral V(H₂O)₂O₄ and pyramidal SeO₃ building units are linked by V—O—Se bonds to generate ladder‐like chains propagating along the [010] direction. A network of O—H...O hydrogen bonds helps to consolidate the structure. The O atom of the uncoordinated water molecule lies on a crystallographic twofold axis. The title compound has a similar structure to those of the reported phases [VO(OH)(H₂O)(SeO₃)]₄·2H₂O and VO(H₂O)₂(HPO₄)·2H₂O.     

Impact of Particulate Antigens, Such as Bacillus anthracis, on the Uniformity of Response across a Biosensor Flow Cell As Determined by GC-SPR

Biosensors are desired for the detection of a wide range of analytes in various scenarios, for example environmental monitoring for biological threats, from toxins to viruses and bacteria. Ideally a single sensor will be capable of simultaneous multianalyte detection. The varying nature, and in particular disparate size, of such a variety of analytes poses a significant challenge in the development of effective high-confidence instruments. Many existing biosensors employ functionalized flow cells in which spatially defined arrays of surface-immobilized recognition elements, such as antibodies, specifically capture their analyte of interest. To function optimally, arrays should provide equivalent responses for equivalent events across their active area. Experimental data obtained using a grating coupled surface plasmon resonance (GC-SPR) instrument, the BIAcore Flexchip, have revealed differences in response behaviors between proteinaceous and particulate analytes. In particular, the magnitude of responses seen with Bacillus anthracis spores appears to be influenced by shear and gravitational effects while those from soluble proteins are more uniform. We have explored this dependence to understand its fundamental impact on the successful implementation of multianalyte environmental biological detection systems.     

Using Gas-Phase Guest–Host Chemistry to Probe the Structures of b Ions of Peptides

Middle-sized b _n (n????5) fragments of protonated peptides undergo selective complex formation with ammonia under experimental conditions typically used to probe hydrogen?Cdeuterium exchange in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Other usual peptide fragments like y, a, a*, etc., and small b _n (n????4) fragments do not form stable ammonia adducts. We propose that complex formation of b _n ions with ammonia is characteristic to macrocyclic isomers of these fragments. Experiments on a protonated cyclic peptide and N-terminal acetylated peptides fully support this hypothesis; the protonated cyclic peptide does form ammonia adducts while linear b _n ions of acetylated peptides do not undergo complexation. Density functional theory (DFT) calculations on the proton-bound dimers of all-Ala b ₄ , b ₅ , and b ₇ ions and ammonia indicate that the ionizing proton initially located on the peptide fragment transfers to ammonia upon adduct formation. The ammonium ion is then solvated by N⁺-H??O H-bonds; this stabilization is much stronger for macrocyclic b _n isomers due to the stable cage-like structure formed and entropy effects. The present study demonstrates that gas-phase guest?Chost chemistry can be used to selectively probe structural features (i.e., macrocyclic or linear) of fragments of protonated peptides. Stable ammonia adducts of b ₉ , b ₉ -A, and b ₉ -2A of A₈YA, and b ₁₃ of A₂₀YVFL are observed indicating that even these large b-type ions form macrocyclic structures.     

Analysis of oxidized glycerophosphocholine lipids using electrospray ionization mass spectrometry and microderivatization techniques

Oxidized low-density lipoprotein (LDL) is thought to play an important role in atherogenesis and cardiovascular disease in humans. Oxidized LDL is a complex mixture of many oxidized species, including numerous oxidized glycerophospholipids. Electrospray ionization and tandem mass spectrometry as well as microchemical derivatization of high-performance liquid chromatographically purified fractions derived from oxidized LDL were investigated as means to determine the structure of individual components present in oxidized LDL. One major oxidized phosphocholine lipid had an [M + H](+) ion at m/z 650. Derivatization to the trimethylsilyl ether and methoxime caused shifts in mass which, along with negative ion collision-induced dissociation mass spectra, were consistent with the presence of three species, 1-palmitoyl-2-(9-oxononanoyl)glycerophosphocholine and two isomeric 1-octadecanoyl-2-(hydroxyheptenoyl)glycerophosphocholines. These species were chemically synthesized. Trimethylsilylation of free hydroxyl groups increased the mass of the phospholipid acyl chains containing hydroxyl groups by 72 u. Conversion of carbonyl groups to the methoxylamine derivative increased the mass by 29 u. Ozonolysis of those products which contained double bonds proved to be a facile technique to determine the position and number of double bonds present. The use of these techniques was illustrated in the structural characterization of one major component (m/z 650, positive ions) in oxidized LDL as 1-octadecanoyl-2-(7-hydroxyhepta-5-enoyl)glycerophosphocholi ne. A possible mechanism for the formation of this unique chain-shortened glycerophospholipid is proposed.     

Metal complex-substituted polysiloxanes as novel coatings for capillary electrophoresis and capillary electrochromatography

Two novel polysiloxane-based polymers, which contain metal complexes, have been prepared. To prepare the Co(TACN)3+(2) (TACN= 1,4,7-triazacyclononane) based polymers, an orthoamide derivative of TACN was added to bromobutane-substituted methylpolysiloxane and hydrolyzed with base. Co(II) was then coordinated to the TACN, followed by cobalt oxidation to make polymer A or followed by N-octyl TACN coordination and cobalt oxidation to make polymer B. In both materials, TACN forms thermodynamically and kinetically stable Co(TACN)3+(2) complexes in which the six coordination sites of the Co(III) are occupied by nitrogens from the TACN. The polymers were coated on fused-silica capillary columns and spherical silica particles, which were used for capillary electrophoresis and capillary electrochromatography, respectively. The open and packed columns showed strong and pH-independent reversed electroosmotic flow.