On the tautological ring of ℳ g

We prove that any product of tautological classes of _g of degreed (in the Chow ring of _g with rational coefficients) vanishes ford>g–2 and is proportional to the class of the hyperelliptic locus in degreeg–2.Oblatum 28-I-1195 & 15-IV-1995In memory of Nicolaas H. Kuiper (1920–1994)     

Ion solvation by channel carbonyls characterized by 17O solid-state NMR at 21 T

Recently available ultrahigh magnetic fields offer new opportunities for studies of quadrupole nuclei in biological solids because of the dramatic enhancement in sensitivity and resolution associated with the reduction of second-order quadrupole interactions. Here, we present a new approach for understanding the function and energetics of ion solvation in channels using solid-state 17O NMR spectroscopy of single-site 17O-labeled gramicidin A. The chemical shift and quadrupole coupling parameters obtained in powder samples of lyophilized material are similar to those shown in the literature for carbonyl oxygens. In lipid bilayers, it is found that the carbonyl 17O anisotropic chemical shift of Leu10, one of the three carbonyl oxygens contributing to the ion binding site in gramicidin A, is altered by 40 ppm when K+ ion binds to the channel, demonstrating a high sensitivity to such interactions. Moreover, considering the large breadth of the carbonyl 17O chemical shift (>500 ppm), the recording of anisotropic 17O chemical shifts in bilayers aligned with respect to magnetic field B0 offers high-quality structural restraints similar to 15N and 13C anisotropic chemical shifts.     

Glycyl C(alpha) chemical shielding in tripeptides: measurement by solid-state NMR and correlation with X-ray structure and theory

We report here (13)C(alpha) chemical shielding parameters for central Gly residues in tripeptides adopting alpha-helix, beta-strand, polyglycine II, and fully extended 2 degrees structures. To assess experimental uncertainties in the shielding parameters and the effects of (14)N-(13)C(alpha) or (15)N-(13)C(alpha) dipolar coupling, stationary and magic angle spinning (MAS) spectra with and without (15)N decoupling were obtained from natural abundance and double-labeled samples containing [2-(13)C, (15)N]Gly. We find that accurate (<1 ppm uncertainty) shielding parameters are measured with good sensitivity and resolution in (15)N decoupled 1D or 2D MAS spectra of double-labeled samples. Compared to variations of isotropic shifts with peptide angles, those of (13)C(alpha) shielding anisotropy and asymmetry are greater. Trends relating shielding parameters to the 2 degrees structure are apparent, and the correlation of the experimental values with unscaled ab initio shielding calculations has an rms error of 3 ppm. Using the experimental data and the ab initio shielding values, the empirical trends relating the 2 degrees structure to shielding are extended to the larger range of torsion angles found in proteins.     

Sensitive LC MS quantitative analysis of carbohydrates by Cs<Superscript>+</Superscript> attachment

The development of a sensitive assay for the quantitative analysis of carbohydrates from human plasma using LC/MS/MS is described in this paper. After sample preparation, carbohydrates were cationized by Cs(+) after their separation by normal phase liquid chromatography on an amino based column. Cesium is capable of forming a quasi-molecular ion [M + Cs](+) with neutral carbohydrate molecules in the positive ion mode of electrospray ionization mass spectrometry. The mass spectrometer was operated in multiple reaction monitoring mode, and transitions [M + 133] --> 133 were monitored (M, carbohydrate molecular weight). The new method is robust, highly sensitive, rapid, and does not require postcolumn addition or derivatization. It is useful in clinical research for measurement of carbohydrate molecules by isotope dilution assay.     

Gasförmige Acetate

Gaseous Acetates Thermoanalytical and mass-spectrometrical observations are undertaken with some acetates and oxiacetates. The volatilization of copper(I) acetate takes place like that of the silver acetate as M₂Ac₂⁺ (besides the deposition of Ag). On the volatilization of the anhydrous compounds Cu₂Ac₄, Cr₂Ac₄, Rh₂Ac₄, and Mo₂Ac₄ in the vacuum of a mass spectrometer is observed that Cu₂Ac₄ vaporizes dissociative as Cu₂Ac₂⁺ (+ 2 “Ac”), while the other compounds vaporize as M₂Ac₄⁺ and simultaneously is formed an oxidic (e.g. Cr₂O₄) or metallic residue. PdAc₂ vaporizes in the mass spectrometer as a trimeric molecule Pd₃Ac₆. M₄OAc₆, which is formed from the dihydrates, vaporizes in a mass spectrometer with M ? Co, Mn as M₄OAc₆⁺. Other complexes of the same type appear as Be₄OAc₅⁺, Mg₄OAc₅⁺, and Zn₄OAc₅⁺.     

Asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by nucleophilic addition of triazolethiols to a NiII complex with a chiral dehydroalanine Schiff base

An efficient method was developed for the asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by the addition of 3,4-disubstituted 1,2,4-triazole-5-thiols at the electrophilic C=C bond in a Ni^II complex of a Schiff base of dehydroalanine with (S)-N-(N-benzylprolyl)aminobenzophenone. The stereoselectivity of the formation of diastereomeric complexes with the (S,R) configuration under conditions of thermodynamic control of the nucleophilic addition exceeds 94%. Acid treatment of the reaction mixtures afforded enantiomerically pure (R)-S-hetarylcysteines (ee >98%).     

Hydrogen‐bonded frameworks of bis(2‐carboxypyridinium) hexafluorosilicate and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate

In bis(2‐carboxypyridinium) hexafluorosilicate, 2C₆H₆NO₂⁺·SiF₆²⁻, (I), and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate, 2C₁₀H₈NO₂⁺·SiF₆²⁻·2H₂O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter‐ion interactions in (I) occur via strong N—H...F and O—H...F hydrogen bonds, generating corrugated layers incorporating [SiF₆]²⁻ anions as four‐connected net nodes and organic cations as simple links in between. In (II), a set of strong N—H...F, O—H...O and O—H...F hydrogen bonds, involving water molecules, gives a three‐dimensional heterocoordinated rutile‐like framework that integrates [SiF₆]²⁻ anions as six‐connected and water molecules as three‐connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) Å], while the N—H group supports direct bonding to the anion [N...F = 2.7061 (12) Å].     

Synthesis of Substituted 2-Methyl-4-quinolyl Isothiocyanates and 4-Mercaptoquinolines

Synthesis was performed of substituted 2-methyl-4-quinoline thiouronium salts by reaction of 2-methyl-4-chloroquinolines with thiourea. The alkaline hydrolysis of these salts afforded the corresponding 2-methyl-4-quinolyl- isothiocyanates and 2-methyl-4-mercaptoquinolines.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 783–785.Original Russian Text Copyright © 2005 by Avetisyan, Aleksanyan, Ambartsumyan.     

Syntheses based on 8-substituted 3-bromoacetyl-3,8-dimethyl-2,7-dioxaspiro[4,4]nonane-1,6-diones

By reaction of 8-substituted 3-bromoacetyl-3,8-dimethyl-2,7-dioxaspiro[4,4]nonane-1,6-diones with thiourea and substituted thioureas under Hansch reaction conditions, we have obtained the novel heterocycles 3-[2′-amino(arylamino)thiazol-4-yl]-3,8-dimethyl-2,7-dioxaspiro[4,4]nonane-1,6-diones. By reacting the above-indicated bromoacetyl spirodilactones with 5-aryl-3-mercapto-1,2,4-triazoles, we obtained 8-substituted 3-(aryl-3,8-dimethyl-1′,2′,4′-triazol-3′-yl)thioacetyl-2,7-dioxaspiro[4,4]nonane-1,6-diones. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 123–129, January, 2006.