12/10- and 11/13-mixed helices in alpha/gamma- and beta/gamma-hybrid peptides containing C-linked carbo-gamma-amino acids with alternating alpha- and beta-amino acids

New classes of alpha/gamma- and beta/gamma-hybrid peptides have been synthesized with novel 12/10- and 11/13-mixed helical patterns, respectively. The alpha/gamma-peptides were derived from the dipeptide repeats with alternating arrays of l-Ala and gamma-Caa((l)) (C-linked carbo-gamma-amino acid from d-mannose), which generated a new 12/10-mixed helix, for the first time, without a beta-amino acid. The beta/gamma-peptides made from an alternating arrangement of beta-Caa((x)) (C-linked carbo-beta-amino acid) and gamma-Caa((x)) (C-linked carbo-gamma-amino acid from d-xylose), on the other hand, resulted in an unprecedented 11/13-helix. The secondary structures in these peptides have been ascertained from detailed NMR studies, and CD spectroscopy and molecular dynamics investigations provided additional support for the structures derived.     

Design and synthesis of trans-3-aminopyran-2-carboxylic acid (APyC) and α/β-peptides with 9/11-helix

A new β-amino acid, trans-3-aminopyran-2-carboxylic acid (APyC), was designed and synthesized from (R)-glyceraldehyde derivative and used in the synthesis of α/β-peptides in a 1 : 1 alternating pattern with d-Ala. The presence of oxygen atom at the Cβ(2)-position in APyC was envisaged to provide opportunity for additional interaction. These hybrid peptides have shown the presence of 9/11-helix through extensive NMR and MD studies. The amide protons of d-Ala, in addition to participating in 9-mr H-bonding with CO of succeeding β-residue, were also involved in additional electrostatic interaction with pyran ring oxygen of preceding β-residue, which facilitated further stabilization to the 9/11-mixed helix. The study thus results in a new 'motif' for a 9/11-helix, and the first example from a cyclic β-amino acid.     

Design of a "new motif" with beta-amino acids and alpha-aminoxy acids: synthesis of hybrid peptides with 12/10-helix

Hybrid peptides are prepared from a C-linked carbo-beta-amino acid ester (R-beta-Caa) and an alpha-aminoxy acid (R-Ama) derived from S-lactic acid. Extensive NMR (in CDCl 3 solution), CD, and MD studies on the tetra- and hexapeptides led to identification of robust 12/10-mixed helices. The dipeptide repeat having an R-beta-Caa and an R-Ama thus provides a "new motif" to realize a 12/10-mixed helix, for the first time, in oligomers containing R-Ama. To understand the impact of side chains in the mixed helix formation, R-beta-Caa/Ama (with no substitution in Ama) and S-beta-hAla/R-Ama oligomers were investigated. NMR studies revealed the existence of 12/10-helices in these hybrid peptides, and the side chains of monomers were found to have a profound influence on their stabilities. These observations imply that the propensity of beta-amino acid to prefer a mixed 12/10-helix governs the structural behavior in these peptides. The structural consequences of the lone-pair repulsion between nitrogen and oxygen atoms result in a new and interesting structural motif which behaves like "pseudo" beta (3),beta(2)-peptides in generating 12/10-mixed helices.     

Der chemische Transport von Ni3Ge,Ni5Ge3, Ni(Ge)-Mischkristall,CoSn, Co3Sn2, Cu41Sn11 (δ-Phase), Cu10Sn3 (ζ-Phase) und Cu(Sn)-Mischkristall

Chemical Vapour Transport of Intermetallic Systems. 7. Chemical Transport of Ni₃Ge, Ni₅Ge₃, Ni(Ge)-mixed Crystal, CoSn, Co₃Sn₂, Cu₄₁Sn₁₁ (δ-phase), Cu₁₀Sn₃ (ζ-phase), and Cu(Sn)-mixed Crystals By means of GaI₃ as transport agent some intermetallics in the Ni/Ge- and Co/Sn-system can be prepared by CVT-methods. Using Iodine Cu–Sn-compounds can be deposited in a similiar way.     

Extension of separation range in capillary isoelectric focusing for resolving highly basic biomolecules

The non-availability of commercial carrier ampholytes in the pH range greater than 11 has contributed to difficulties in focusing and resolving highly basic proteins/peptides using capillary isoelectric focusing (cIEF). Two different approaches, involving the use of N,N,N',N'-tetramethylethylenediamine (TEMED) and ampholyte 9-11, are investigated for their effects on the extension of separation range in cIEF. The addition of TEMED into pharmalyte 3-10 not only prevents the peptides/proteins from focusing in sections of the capillary beyond the detection point, but also extends the separation range to at least isoelectric point (pI) 12. The combination of ampholyte 9-11 with pharmalyte 3-10 surprisingly provides baseline resolution between bradykinin (pI 12) and cytochrome c (pI 10.3). The sample mixture, containing bradykinin, the high-pI protein calibration kit (pI 5.2-10.3), and cytochrome c digest, is employed to demonstrate the cIEF separation of proteins and peptides over a wide pH range of 3.7-12.     

Negative Ion In-Source Decay Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry for Sequencing Acidic Peptides

Matrix-assisted laser desorption/ionization (MALDI) in-source decay was studied in the negative ion mode on deprotonated peptides to determine its usefulness for obtaining extensive sequence information for acidic peptides. Eight biological acidic peptides, ranging in size from 11 to 33 residues, were studied by negative ion mode ISD (nISD). The matrices 2,5-dihydroxybenzoic acid, 2-aminobenzoic acid, 2-aminobenzamide, 1,5-diaminonaphthalene, 5-amino-1-naphthol, 3-aminoquinoline, and 9-aminoacridine were used with each peptide. Optimal fragmentation was produced with 1,5-diaminonphthalene (DAN), and extensive sequence informative fragmentation was observed for every peptide except hirudin(54–65). Cleavage at the N–Cα bond of the peptide backbone, producing c′ and z′ ions, was dominant for all peptides. Cleavage of the N–Cα bond N-terminal to proline residues was not observed. The formation of c and z ions is also found in electron transfer dissociation (ETD), electron capture dissociation (ECD), and positive ion mode ISD, which are considered to be radical-driven techniques. Oxidized insulin chain A, which has four highly acidic oxidized cysteine residues, had less extensive fragmentation. This peptide also exhibited the only charged localized fragmentation, with more pronounced product ion formation adjacent to the highly acidic residues. In addition, spectra were obtained by positive ion mode ISD for each protonated peptide; more sequence informative fragmentation was observed via nISD for all peptides. Three of the peptides studied had no product ion formation in ISD, but extensive sequence informative fragmentation was found in their nISD spectra. The results of this study indicate that nISD can be used to readily obtain sequence information for acidic peptides.

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Reaction route control by microperoxidase-9/CTAB micelle ratios

Microperoxidases (MP) as water-soluble models attract interest to studying the reaction mechanism of peroxidases because these heme peptides are able to form the same enzyme intermediates during the reaction with peroxides. In this work we have demonstrated that the association of Fe(III)MP-9 and Fe(III)MP-11 with CTAB micelles (MP-9/CTAB and MP11/CTAB) provides a microenvironment with an alkaline interface and a hydrophobic core that exhibits peroxidase behavior. This microenvironment shifts positively the redox potential of microperoxidases by approximately 100 mV. tert-Butylhydroperoxide (t-BuOOH) when added to the medium, converted Fe(III)MP-9/CTAB to MP-9/CTAB Compound II, a high valence oxidized intermediate of the heme peptide. Subsequent addition of diphenylacetaldehyde (DPAA) to MP-9/CTAB Compound II regenerated the native form of the enzyme, Fe(III)MP-9/CTAB, what characterizes the occurrence of a peroxidase cycle. Fe(III)MP-9/CTAB regenerated during the peroxidase cycle reacted with residual DPAA in the medium to form Fe(II)MP-9/CTAB, which indicates that both Fe(III)MP-9/CTAB and its oxyferryl form can use aldehydes as reducing agents. According to the determined reduction potential, Fe(III)MP-9 and Fe(III)MP-9/CTAB should be able to oxidize DPAA (reduction potential -630 mV). The reaction of MP-9/CTAB with DPAA produced benzophenone as final product, detected by infrared spectroscopy and mass spectrometry. Interestingly, a significant difference was observed in the benzophenone yield according to the micelle/MP-9 molar ratio.     

Synthesis and conformational studies of peptides from new C-linked carbo-beta-amino acids (beta-Caas) with anomeric methylamino- and difluorophenyl moieties

New C-linked carbo-beta-amino acids (beta-Caas), Cbz-(S)-beta-Caa-(NHBoc)-OMe (1) and Cbz-(R)-beta-Caa-(NHBoc)-OMe (2), with an additional amine group (methylamino group of NHBoc) at the C-1 position of the lyxofuranoside side chain and Boc-(S)-beta-Caa-(diFP)-OMe (3) and Boc-(R)-beta-Caa-(diFP)-OMe (4), with a C-difluorophenyl (diFP) moiety at the anomeric position of the lyxofuranoside side chain were prepared from D-mannose. Beta-peptides [tetra- and hexapeptides] were synthesized from these beta-Caas, 'epimeric' [at the amine stereocentre (C(beta))], using the concept of 'alternating chirality' to carry out their conformational studies [NMR (CDCl(3)), CD and MD]. In the monomer design, it was envisaged that the presence of an additional amine group in 1 or 2 would help in solubilizing the peptides in water, while, the C-difluorophenyl (diFP) moiety of 3 and 4 is expected to enhance the biological activity. The peptides having 1 and 2, though could not retain their 12-10-mixed helices in water, have shown moderate activity against gram positive and gram negative bacterial strains. The peptides prepared from 3 and 4, much against our expectations, did not display any biological activity.     

K3(Nb3Ti2)O11F4: un nouvel oxyfluorure de type ‘bronzes oxygénés de tungstène quadratiques’

A new oxyfluoride K₃(Nb₃Ti₂)O₁₁F₄ with a tetragonal tungsten bronze type structure has been prepared and characterized in the KNbO₃---TiOF₂ system. The room temperature space group (P4/mbm) has been determined on a single crystal. The unit cell parameters are a = 12.453 Å and c = 3.972 Å.

Résumé

L'étude du système KNbO₃---TiOF₂ a permis de mettre en évidence et de caractériser un nouvel oxyfluorure de type ‘bronzes quadratiques de tungstène’: K₃(Nb₃Ti₂)O₁₁F₄. Le groupe spatial à température ambiante (P4/mbm) a été déterminé sur monocristal. Les paramètres de la maille élémentaire sont a = 12,453 Å et c = 3,972 Å.     

New Helical Folds in α‐Peptides with Alternating Chirality

In α‐peptides, the 8/10 helix is theoretically predicted to be energetically unstable and has not been experimentally observed so far. Based on our earlier studies on ‘helical induction’ and ‘hybrid helices’, we have adopted the ‘end‐capping’ strategy to induce the 8/10 helix in α‐peptides by using short α/β‐peptides. Thus, α‐peptides containing a regular string of α‐amino acids with alternating chirality were end capped by α/β‐peptides with 11/9‐helical motifs at the termini. Extensive NMR spectroscopy studies of these peptides revealed the presence of a hitherto unknown 8/10‐helical pattern; the H‐bonds in the shorter pseudorings were rather weak. The approach of using short helical motifs to induce new mixed helices in α‐peptides could provide avenues for more versatile design strategies.     

12/14/14‐Helix Formation in 2:1 α/β‐Hybrid Peptides Containing Bicyclo[2.2.2]octane Ring Constraints

The highly constrained β‐amino acid ABOC induces different types of helices in β urea and 1:1 α/β amide oligomers. The latter can adopt 11/9‐ and 18/16‐helical folds depending on the chain length in solution. Short peptides alternating proteinogenic α‐amino acids and ABOC in a 2:1 α/β repeat pattern adopted an unprecedented and stable 12/14/14‐helix. The structure was established through extensive NMR, molecular dynamics, and IR studies. While the 1:1 α‐AA/ABOC helices diverged from the canonical α‐helix, the helix formed by the 9‐mer 2:1 α/β‐peptide allowed the projection of the α‐amino acid side chains in a spatial arrangement according to the α‐helix. Such a finding constitutes an important step toward the conception of functional tools that use the ABOC residue as a potent helix inducer for biological applications.     

混合型甘氨酸-N，N-双亚甲基膦酸-磷酸锆：合成、表征及插层

采用氢氟酸络合法,在nP/nZr=2.0条件下,以甘氨酸-N,N-双亚甲基膦酸(DMPG)和H3PO4为原料,按不同投料物质的量的比制备了2个α、γ-混合型甘氨酸-N,N-双亚甲基膦酸-磷酸锆层状主体化合物Zr(PO4)0.41(HPO4)0.043[(O3PCH2)2NCH2COOH]0.67.H2O(1)和Zr(PO4)0.21(HPO4)0.038[(O3PCH2)2NCH2COOH]0.82.2H2O(2),用元素分析、X射线衍射、红外光谱、热分析、固体核磁磷谱等对化合物进行了表征,同时研究了与正丁胺客体分子的插层组装性能。     

In vacuo isotope coded alkylation technique (IVICAT); an N-terminal stable isotopic label for quantitative liquid chromatography/mass spectrometry proteomics

We present a new isotopic labeling strategy to modify the N-terminal amino group of peptides in a quantifiable reaction without the use of expensive reagents or solvents. The In Vacuo Isotope Coded Alkylation Technique (IVICAT) is a methylation reaction, carried out at low pressure (<100 mTorr), that results in a stable quaternary trimethylammonium group, thus adding a permanent positive charge at the N-terminus of peptides without modifying the epsilon-amino groups of lysine. The methylation reaction increases the signal intensity of modified peptides in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and liquid chromatography (LC)/MS and the isotopic peak pair differs by 9 mass units which can be easily resolved by either instrument. N-terminally trimethylated peptides exhibit collision-induced dissociation (CID) mass spectra that differ from their unmodified analogues by an enhanced b-ion series in MS2 spectra due to the fixed positive charge. Using LC/MS/MS with an LTQ mass analyzer for quantification, the experimentally determined ratios of H9- to D9-trimethyl-labeled peptides of beta-casein provided accurate estimates of the actual ratios with low % error. IVICAT labeling also accurately quantified proteins in rat kidney inner medullary collecting duct cell types, as judged by comparison with relative quantification by subsequent immunoblotting experiments. IVICAT labeling, when used in conjunction with the new proteomics software QUIL, can accurately report relative protein abundances and increase the sequence coverage of proteins of tissue proteomes.     

Macropolyhedral boron-containing cluster chemistry. Aspects of the S2B16H16 system. Preparation, structure, NMR spectroscopy and isomerism

Thermolysis of [arachno-4-SB₈H₁₂] (1) in boiling cyclohexane gives two isomers 2 and 3 of 18-vertex [S₂B₁₆H₁₆], together with known 12-vertex [closo-1-SB₁₁H₁₁] (4) and known 11-vertex [nido-7-SB₁₀H₁₂] (5). Compounds 2 and 3 are characterised by single-crystal X-ray diffraction analyses and single- and double-resonance ¹¹B- and ¹H-NMR spectroscopy. The [n-S₂B₁₆H₁₆] isomer 2 takes the form of nido ten-vertex: nido ten-vertex [anti-B₁₈H₂₂] with the 9 and 9′ positions occupied by S vertices, whereas the [iso-S₂B₁₆H₁₆] isomer 3 takes the form of a nido 11-vertex {SB₁₀} subcluster fused via a common two-boron edge to a nido-type {B₈} subcluster that is additionally linked exo to the {SB₁₀} subcluster by a bridging S atom that is held endo to the {B₈} unit. Isomer 2 is readily deprotonated and its monoanion 6 is characterised by NMR spectroscopy and by a single-crystal X-ray diffraction analysis of its [tmndH]⁺[n-S₂B₁₆H₁₅] salt 6b; deprotonation has occurred from an open-face B---H---B bridging site.     

Effect of Zn2+ Ions on Upconversion Emission of Er3+ in Zn/Er:LiNbO3 Crystal

The effect of Zn2+ ions codoped on the upconversion emission of Er3+ ions in Er:LiNbO3 crystal under different excitation wavelength was reported.The upconversion emission spectra of Zn/Er:LiNbO3 follo...     

Microwave spectrum of the hydroxyl radical in the ν= 1 Π3/2 state

The J = 7/2, 9/2, 11/2, 13/2 and 15/2 Λ doubling main lines of OH in the ν = 1, ² Π3/2 state have been measured. They are used with the UV and IR data to predict the low J frequencies with an accuracy sufficient for radioastronomical search.     

Methyl group migration during the fragmentation of singly charged ions of trimethyllysine-containing peptides: Precaution of using MS/MS of singly charged ions for interrogating peptide methylation

Core histones are susceptible to a range of post-translational modifications (PTMs), including acetylation, phosphorylation, methylation, and ubiquitination, which play important roles in the epigenetic control of gene expression. Here, we observed an unusual discrepancy between MALDI-MS/MS and ESI-MS/MS on the methylation of trimethyllysine-containing peptides with residues 9–17 from human histone H3 and residues 73–83 from yeast histone H3. It turned out that the discrepancy could be attributed to an unusual methyl group migration from the side chain of trimethyllysine to the C-terminal arginine residue during peptide fragmentation, and this methyl group transfer only occurred for singly charged ions, but not for doubly charged ions. The methyl group transfer argument received its support from the results on the studies of the fragmentation of the ESI- or MALDI-produced singly charged ions of several synthetic trimethyllysine-bearing peptides. The results presented in this study highlighted that caution should be exerted while MS/MS of singly charged ions is employed to interrogate the PTMs of trimethyllysine-containing peptides.     

Chemical derivatization of peptides containing phosphorylated serine/threonine for efficient ionization and quantification in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We describe a useful method for the efficient ionization and relative quantification of peptides containing serine/threonine phosphorylation sites. This method is based on beta-elimination of the phosphate group from serine/threonine phosphorylation sites under alkaline conditions, followed by Michael addition reaction with N-(2-mercaptoethyl)-6-methylnicotinamide (MEMN). As a result of the derivatization reaction, the negatively charged phosphate group is substituted with the nicotinoyl moiety to improve the ionization efficiency of the derivatized peptide. The combination of d(3)-labeled MEMN (d(3)-MEMN) and MEMN (d(0)-MEMN) generates a 3 Da mass difference between d(3)-MEMN-labeled and d(0)-MEMN-labeled peptides, which is a useful signature for the identification of peptides containing serine/threonine phosphorylation sites in the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum. Moreover, the mass difference is useful for the quantitative analysis of serine/threonine phosphorylation in proteins. In this paper, we describe the synthesis of d(0)/d(3)-labeled MEMN and an application of our approach to model peptides and proteins.     

New hedgehog/GLI-signaling inhibitors from Adenium obesum

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. We recently constructed a cell-based screening system to search for Hh/GLI signaling inhibitors from natural resources. Using our screening system, Adenium obesum was found to include Hh/GLI signaling inhibitors from our tropical plant extract libraries. Bioassay-guided fractionation of this plant extract led to the isolation of 17 cardiac glycosides (1-17), including 3 new compounds (4, 9, 16). These compounds showed strong inhibitory activities, especially the IC(50) of 17 is 0.11 μM. The inhibition of GLI-related protein expression with 3, 9, 11, 15 and 17 was observed in human pancreatic cancer cells (PANC1), which express Hh/GLI components aberrantly. The expressions of GLI-related proteins PTCH and BCL2 were clearly inhibited. These compounds also showed selective cytotoxicity against two cancer cell lines, with less effect against normal cells (C3H10T1/2). RT-PCT examinations showed that Ptch mRNA expression by 3, 11, 15 and 17 was inhibited.