Tirucallane Triterpenoid Saponins from Munronia delavayi Franch

Four new tirucallane triterpenoid saponins, named munronosides I–IV ( 2 – 5 ), along with three known triterpenoids, sapelin B ( 1 ), melianodiol, and (3β)‐22,23‐epoxytirucall‐7‐ene‐3,24,25‐triol, were isolated from the EtOH extract of the whole plants of Munronia delavayi Franch by chromatographic methods. On the basis of spectroscopic evidences, the structures of 2 – 5 were elucidated as (20S,23R,24S)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐23,24‐dihydroxytirucall‐7‐ene‐3,21‐dione ( 2 ), (3β,20S,23R,24S)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐3,23,24‐trihydroxytirucall‐7‐en‐21‐one ( 3 ), (20S,23R,24S)‐24‐(acetyloxy)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐23‐hydroxytirucall‐7‐ene‐3,21‐dione ( 4 ), and (3β,20S,23R,24S)‐24‐(acetyloxy)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐3,23‐dihydroxytirucall‐7‐en‐21‐one ( 5 ).     

Computer-assisted optimization of selectivity by tuning temperature and carrier gas pressure drop in two GC capillary columns coupled in series

The paper shows a computer-assisted procedure for the optimization of selectivity of two columns coupled in series by tuning the working temperature (using the isothermal mode) and columns coupling-point pressure at constant inlet and outlet carrier gas pressures. The optimization procedure validation was tested by the separation of 32 hydrocarbons in a column series with the aim to resolve the maximum number of components in the shortest possible analysis time.Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday     

N—乙基—N—苄基苯胺合成方法的改进

以苯胺和乙醇为原料，采用ＲａｎｅｙＮｉ为催化剂，合成了Ｎ－乙基苯胺，再在相转移催化剂作用下，经苄基化反应得到标题化合物，第一步合成方法的收率比通常方法的收率提高约３０％。     

Ab initio MO study of potential energy surface of NH2 with CN reaction

An extensive quantum chemical study of the potential energy surfaces (PES) for the association reaction of NH₂ with CN and the subsequent isomerization and dissociation reactions has been carried out using density functional theory (DFT)/B3LYP/6‐311++G(3df,2p) level of theory on both singlet and triplet states. The reaction mechanism on the triplet surface is more complicated than that on the singlet surface. A total of 19 isomers and 46 transition states have been identified and characterized on the triplet PES. Among them, IM2 (IM2a), IM3 (IM3a, IM3b), and IM10 are the lowest‐lying isomers with thermodynamic stability. Twenty available dissociation channels, depending on the different initial isomers, have been identified. On the singlet surface, only 12 isomers and 16 transition states have been found, and among them IM1(S) and IM2(S) are the lowest‐lying isomers. The higher isomerization and dissociation barriers on the singlet surface indicate that the addition and the subsequent reactions of NH₂+CN are most likely to occur on the triplet PES because of the lower barriers. A prediction can be made for the possible mechanism explaining the production of H+HNCN. Besides HNCN, other major products are NH+HCN and NH+HNC, which are produced by direct dissociation reactions from triplet IM2 and IM3, respectively. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

High accuracy mass measurement of peptides with internal calibration using a dual electrospray ionization sprayer system for protein identification

A dual-ESI-sprayer system was constructed and applied to achieve high accuracy of peptide mass measurement for protein identification by means of peptide mapping. Sample was introduced in one sprayer, and reference in the other, thus making internal calibration possible greatly enhancing the mass accuracy. Several samples were utilized to evaluate the reliability of this dual-ESI-sprayer system. The range of mass errors was 0.16-5.37 ppm. The peptide masses of tryptic digests of myoglobin (horse) were measured by the HPLC/dual-ESI-MS system, with mass deviations ranging from 0.01-7.67 ppm, and about 75% mass deviations below 5 ppm with 40% below 1[?]ppm. These peptide masses were utilized to perform database searching for protein identification, and compared to results obtained by external calibration. This comparison showed that the internal calibration provides a more reliable method of protein identification, with a much smaller number of required peptides for matching, and with less CPU time consumed for database searching.     

Europium(II) and ytterbium(II) cyclic organohydroborates with agostic interactions

The divalent lanthanide bis((cyclooctane-1,5-diyl)dihydroborate) complexes {K(THF)4}2{Ln{(mu-H)2BC8H14}4} (Ln = Eu, 3; Yb, 4) were prepared by a metathesis reaction between (THF)(x)LnCl2 and K[H2BC8H14] in THF in a 1:4 molar ratio. Although the reaction ratios were varied between 1:3 and 1:6, complexes 3 and 4 were the only lanthanide 9-BBN hydroborates produced. Because of disorder of THF in crystals of 3 and 4, good single-crystal X-ray structural data could not be obtained. However, when the potassium cation was replaced by the tetramethylammonium cation or when MeTHF (2-methyltetrahydrofuran) was employed in place of THF, good quality crystals were obtained. Complexes [NMe4]2[Ln{(mu-H)2BC8H14}4] (Ln = Eu, 5; Yb, 6) were afforded by metathesis reactions of NMe4Cl with 3 and 4 in situ. On the basis of the single-crystal X-ray diffraction analysis, the four 9-BBN tetrahydroborate ligands are tetrahedrally arranged around the lanthanide cation in 5 and 6. The two structures differ in that one alpha-C-H bond from each of the four {(mu-H)2BC8H14}4 units exhibits an agostic interaction with Eu(II) in 5 but, in complex 6, only two of the alpha-C-H bonds form agostic interactions with Yb(II). Complexes {K(MeTHF)3}2{Ln{(mu-H)2BC8H14}4} (Ln = Eu, 7; Yb, 8) were produced by employing MeTHF in place of THF. The structures of 7 and 8 display connectivity between the anion {Ln{(mu-H)2BC8H14}4}2- and the cation {K(MeTHF)3}+, in which the potassium not only interacts directly with the hydrogens of the Ln-H-B bridged bonds but is also involved in agostic interactions with alpha-C-H bonds. By systematically examining the structures of complexes 3-8 and taking into account the previously reported complexes (THF)4Ln{(mu-H)2BC8H14}2 (Ln = Eu, 1; Yb, 2), it is concluded that Eu(II) appears to have a better ability to form agostic interactions than Yb(II) because of its larger size, even though Yb(II) has a higher positive charge density.     

Highly regioselective construction of spirocycles via phosphine-catalyzed [3 + 2]-cycloaddition

A direct entry to spirocycles with low to moderate regioselectivity was achieved by triphenylphosphine-catalyzed [3 + 2]-cycloaddition of active exo-methylenecycles (1) and ethyl 2,3-butadienoate (2). The regioselectivity of the reaction was greatly improved by using the bulky tert-butyl ester of the 2,3-butadienoate (5). The regioselectivity of the reaction was further enhanced by using the tert-butyl 2-butynoate as the substrate. This protocol provided an efficient entry to the skeleton of spirocarbocycles, especially spiro[4.n]alkanes.     

Alkyne coupling at a rhenium-monocarborane substrate: synthesis of Re,B-eta2:sigma-butadienyl complexes

Treatment of 7-NH(2)Bu(t)-nido-7-CB(10)H(12) in tetrahydrofuran (THF) with LiBu(n)(3 equiv) and then [ReBr(CO)(3)(THF)(2)] gives the rhenacarborane dianion [1-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)](2-), isolated as the bis-[N(PPh(3))(2)](+) salt (4). Iodine oxidation of this Re(I) intermediate gives the Re(III) complex [1,2-mu-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)] 6 in which the carborane functions formally as an 8-electron (6pi+ 2sigma) donor. Reaction of with ligands L in the presence of Me(3)NO gives substituted products [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-closo-2,1-ReCB(10)H(10)][L = PPh(3)(7a), CNXyl (7b; Xyl = C(6)H(3)Me(2)-2,6), or Bu(t)C triple bond CH (7c)]. Formation of complex 7c is unexpectedly accompanied by [1,2-mu-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)] 8a, in which an alkyne-derived dienyl group is bound to both the rhenium centre and to an adjacent boron vertex. Complex 8a is also obtained from 7c with Bu(t)C triple bond CH and Me(3)NO. The same reaction of 7c, using PhC triple bond CH or CNXyl instead of Bu(t)C triple bond CH, gives, respectively, [1,2-micro-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHPh}-closo-2,1-ReCB(10)H(9)] 8b and [1,2-micro-NHBu(t)-2-Bu(t)C triple bond CH-2-CO-2-CNXyl-closo-2,1-ReCB(10)H(10)] 9. Addition of donors L to results in displacement from rhenium of the pendant dienyl moiety, yielding [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-3-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)][L = PMe(3)(10a), CNBu(t)(10b)]. Single-crystal X-ray diffraction analyses have confirmed the novel structural features of compounds 6, 7c, 8b and 9.     

Film Formation and Redispersion of Waterborne Latex Coatings

Poly(vinyl acetate-co-ethylene) latex dispersions are prepared and their films investigated with a focus on the effect of composition upon redispersion. Films of dispersions containing sufficient amounts of poly(vinyl alcohol) (PVA) can be redispersed in water. This property is lost in the presence of surfactant, a fact which suggests a procedure to control film formation. It is demonstrated that redispersion is due to a PVA-membrane which separates the particles. Loss of redispersibility in the presence of surfactant proceeds with the breakup of the membranes and a corresponding change of film properties. Experimental data is provided by light microscopy, mechanical testing, and TEM in conjunction with a staining method new to the field. The hypothesis is developed that interaction with surfactant leads to imperfect PVA-membranes that are no longer able to prevent latex polymer interdiffusion. Fluorescence correlation spectroscopy demonstrates the formation of surfactant micelles, as well as the simultaneous adsorption and aggregation of PVA onto the micelles. It is concluded that the competing surface of the surfactant micelles traps enough PVA to cause thinning and fragmentation of the membranes surrounding the particles, which enables interdiffusion of latex polymer. This effect can be used to convert the system from one forming a redispersible coating to one forming a nonredispersible (permanent) film. Copyright 2000 Academic Press.     

Analytic expressions for the partial waves of the off-shell two body coulomb T-matrix

Closed form expressions for all partial waves of the pure Coulomb off-shell T-matrix p¦ T_c,l.(k ²) ¦p are obtained. All singularities appear through simple special functions, which makes it possible to study the analytic properties of p¦ T_c,l(k²) ¦p as a function not only of one of the momentap, p but even of both of them. With use of the renormalization procedure found by Zorbas the transition to half-and on-shell values is performed reproducing known expressions. By the same method simple expressions for the partial waves of the Coulomb wave function in the momentum representation are found.