Ion/molecule reactions provide new evidence for the structure and origin of

Ion/molecule reactions leading to formation of the diagnostically useful [C(3)H(4)N](+) ion (m/z 54), from acetonitrile CI plasma, have been studied using a tandem quadrupole mass spectrometer. Evidence is presented to demonstrate that [C(3)H(4)N](+) is produced from an ion/molecule reaction between [C(2)H(2)N](+) (m/z 40) and neutral acetonitrile, via a [C(4)H(5)N(2)](+) (m/z 81) intermediate. Loss of HCN, where the H atom arises from neutral acetonitrile and the CN group from [C(2)H(2)N](+) (m/z 40), leads to the production of [C(3)H(4)N](+) (m/z 54). These results are consistent with a proposed concerted elimination of HCN, generating m/z 54 as a methylene vinylidene ammonium ion. Copyright 1999 John Wiley & Sons, Ltd.     

The ESI CAD fragmentations of protonated 2,4,6-tris(benzylamino)- and tris(benzyloxy)-1,3,5-triazines involve benzyl-benzyl interactions: a DFT study

The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6-tris(benzylamino)-1,3,5-triazine (1) and 2,4,6-tris(benzyloxy)-1,3,5-triazine (6) show abundant product ion of m/z 181 (C(14) H(13)(+)). The likely structure for C(14) H(13)(+) is α-[2-methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the 'N' analog (1) but low for the 'O' analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M?+?H-toluene](+) and [M?+?H-benzene](+) for compounds 1 and 6, respectively. The protonated 2,4,6-tris(4-methylbenzylamino)-1,3,5-triazine (4) exhibits competitive eliminations of p-xylene and 3,6-dimethylenecyclohexa-1,4-diene. Moreover, protonated 2,4,6-tris(1-phenylethylamino)-1,3,5-triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring 'N'. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H-shift from ring carbon to 'O' generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium-labeling and CAD experiments combined with DFT calculations.     

The bacteriochlorophylla cation radical revisited. An ENDOR and TRIPLE resonance study

The bacteriochlorophyll (BGhl)a cation radical is studied by cw-EPR and multinuclear ENDOR/TRIPLE resonance techniques in liquid solution yielding the hyperfine coupling constants (hfcs) for 12 protons, all 4 nitrogens and the central magnesium nucleus. The H hfcs are assigned to specific molecular positions by various experimental techniques including isotope substitution, H/D exchange experiments and comparison with bacteriochlorophyll derivatives. The determined temperature dependences of the H hfcs are measured and related to dynamical properties of the molecule in solution. The experimental hfcs compare well with those obtained from semiempirical molecular orbital calculations of the RHF-INDO/SP type. The importance of these results for BChl speciesin vivo, i.e., in the protein matrix, is discussed.     

Experimental constraints on the spin and parity of the Lambdac(2880)+

We report the results of several studies of the Lambda(c)(+)pi(+)pi(-)X final state in continuum e(+)e(-) annihilation data collected by the Belle detector. An analysis of angular distributions in Lambda(c)(2880)(+)-->Sigma(c)(2455)(0,++)pi(+,-) decays strongly favors a Lambda(c)(2880)(+) spin assignment of 5/2 over 3/2 or 1/2. We find evidence for Lambda(c)(2880)(+)-->Sigma(c)(2520)(0,++)pi(+,-) decay and measure the ratio of Lambda(c)(2880)(+) partial widths Gamma(Sigma(c)(2520)pi)/Gamma(Sigma(c)(2455)pi)=0.225+/-0.062+/-0.025. This value favors the Lambda(c)(2880)(+) spin-parity assignment of 5/2(+) over 5/2(-). We also report the first observation of Lambda(c)(2940)(+)-->Sigma(c)(2455)(0,++)pi(+,-) decay and measure Lambda(c)(2880)(+) and Lambda(c)(2940)(+) mass and width parameters. These studies are based on a 553 fb(-1) data sample collected at or near the Upsilon(4S) resonance at the KEKB collider.     

Laser ablation synthesis of new gold phosphides using red phosphorus and nanogold as precursors. Laser desorption ionisation time-of-flight mass spectrometry

Gold phosphides show unique optical or semiconductor properties and there are extensive high technology applications, e.g. in laser diodes, etc. In spite of the various AuP structures known, the search for new materials is wide. Laser ablation synthesis is a promising screening and synthetic method. Generation of gold phosphides via laser ablation of red phosphorus and nanogold mixtures was studied using laser desorption ionisation time-of-flight mass spectrometry (LDI TOFMS). Gold clusters Au(m)(+) (m?=?1 to ~35) were observed with a difference of one gold atom and their intensities were in decreasing order with respect to m. For P(n)(+) (n?=?2 to ~111) clusters, the intensities of odd-numbered phosphorus clusters are much higher than those for even-numbered phosphorus clusters. During ablation of P-nanogold mixtures, clusters Au(m)(+) (m?=?1-12), P(n)(+) (n?=?2-7, 9, 11, 13-33, 35-95 (odd numbers)), AuP(n)(+) (n?=?1, 2-88 (even numbers)), Au(2)P(n)(+) (n?=?1-7, 14-16, 21-51 (odd numbers)), Au(3)P(n)(+) (n?=?1-6, 8, 9, 14), Au(4)P(n)(+) (n?=?1-9, 14-16), Au(5)P(n)(+) (n?=?1-6, 14, 16), Au(6)P(n)(+) (n?=?1-6), Au(7)P(n)(+) (n?=?1-7), Au(8)P(n)(+) (n?=?1-6, 8), Au(9)P(n)(+) (n?=?1-10), Au(10)P(n)(+) (n?=?1-8, 15), Au(11)P(n)(+) (n?=?1-6), and Au(12)P(n)(+) (n?=?1, 2, 4) were detected in positive ion mode. In negative ion mode, Au(m)(-) (m?=?1-5), P(n)(-) (n?=?2, 3, 5-11, 13-19, 21-35, 39, 41, 47, 49, 55 (odd numbers)), AuP(n)(-) (n?=?4-6, 8-26, 30-36 (even numbers), 48), Au(2)P(n)(-) (n?=?2-5, 8, 11, 13, 15, 17), A(3) P(n)(-) (n?=?6-11, 32), Au(4)P(n)(-) (n?=?1, 2, 4, 6, 10), Au(6)P(5)(-), and Au(7)P(8)(-) clusters were observed. In both modes, phosphorus-rich Au(m)P(n) clusters prevailed. The first experimental evidence for formation of AuP(60) and gold-covered phosphorus Au(12)P(n) (n?=?1, 2, 4) clusters is given. The new gold phosphides generated might inspire synthesis of new Au-P materials with specific properties.     

Charge and substituent effects on the stability of porphyrin/G-quadruplex adducts

The adduct ions of two tetramolecular G-quadruplexes formed from the d(TGGGGT) and d(TTGGGGGT) single strands with a group of cationic porphyrins, with different charges and substituents, and one neutral porphyrin, were investigated by ESI-MS and ESI-MS/MS in the negative ion mode. Formation of [Q + nNH(4)(+)+P(p+)-(z + n + p)H(+)](z-) adduct ions (where Q = quadruplex, n = number of quartets minus 1, P = porphyrin and p(+) = 0,1,2,3,4) indicates that the porphyrins are bound outside the quadruplexes providing an additional stabilization to those structures. The fragmentation pathways of the [Q + nNH(4)(+)+P(p+)-(z + n + p)H(+)](z-) adduct ions depend on the number of positive charges (p(+)) of the porphyrins and on the overall complex charge (z(-)), but do not show a significant dependence on the type of the substituent groups in the porphyrins. Formation of the 'unfilled' ions [Q + P(p+)-(z + p)H(+)](z-) predominates for porphyrins with a higher number of positive charges. Strand separation with the formation of [T + P(p+)-(z-2 + p)H(+)]((z-2)-) and (SS-2H(+))(2-) ions, where T = [d(TG(4)T)](3) and [d(T(2)G(5)T)](3) and SS = d(TG(4)T) and d(T(2)G(5)T) is only observed for the complexes with a higher overall negative charge. Porphyrin loss with the formation of [Q + nNH(4)(+)-(z + n)H(+)](z-) ions occurs predominantly for the neutral and monocharged porphyrins. The predominant formation of the 'unfilled' ions, [Q + P(p+)-(z + n)H(+)](z-), for porphyrins with a higher number of charges shows that these porphyrins can prevent strand separation and preserve, at least partially, the quadruplex structure.     

Generalized counting rule for hard exclusive processes

We derive a generalized counting rule for hard exclusive processes involving parton orbital angular momentum and hadron helicity flip. We start with a systematic way to enumerate the Fock components of a hadronic light-cone wave function with n partons and orbital angular momentum projection l(z). We show that the wave-function amplitude psi(n)(x(i),k(i perpendicular ),l(zi)) has a leading behavior 1/(k(2)( perpendicular ))[n(+|l(z)|+min(n(')+|l(')(z)|)]/2-1) when all parton transverse momenta are uniformly large, where n(') and l(')(z) are the number of partons and orbital angular momentum projection, respectively, of an amplitude that mixes under renormalization. Besides the generalized counting rule, the result can be used as a constraint in modeling the hadronic light-cone wave functions.     

1，3-二甲基尿嘧啶二聚体的飞行时间质谱裂解规律研究

采用不同进样方式、不同电子轰击能量和不同反应气压力测定了1,3 二甲基尿嘧啶二聚体(DMUD) 的4个立体异构体A、B、C、D的化学电离(CI)和电子轰击电离(EI)飞行时间质谱.不同方式所测得的CI谱结 果一致,4个异构体出现了强度不同的准分子离子峰(m/z=281),由此推断它们结构之间的相对稳定性次序为: B(trans syn)>D(cis syn)>A(trans anti)>C(cis anti).这一结论被低能量(25eV)电子轰击的EI谱所证实, 并且与合成产物的比例相吻合.EI谱用任何方式测谱均不出现分子离子峰(m/z=280),而出现其单体离子(m/z =140)且为基峰。给出了DMUD的飞行时间质谱裂解途径,同时对CI谱的裂解碎片进行了细致的讨论.     

Observing in-phase single-quantum 15N multiplets for NH2/NH3+ groups with two-dimensional heteronuclear correlation spectroscopy

Two-dimensional (2D) F1-(1)H-coupled HSQC experiments provide 3:1:1:3 and 1:0:1 multiplets for AX(3) and AX(2) spin systems, respectively. These multiplets occur because, in addition to the 2S(y)H(z)(a)-->2S(y)H(z)(a) process, the coherence transfers such as 2S(y)H(z)(a)-->2S(y)H(z)(b) occurring in t(1) period provide detectable magnetization during the t(2) period. Here, we present a 2D F1-(1)H-coupled (1)H-(15)N heteronuclear correlation experiment that provides a 1:3:3:1 quartet for AX(3) spin system and a 1:2:1 triplet for AX(2). The experiment is a derivative of 2D HISQC experiment [J. Iwahara, Y.S. Jung, G.M. Clore, Heteronuclear NMR spectroscopy for lysine NH(3) groups in proteins: unique effect of water exchange on (15)N transverse relaxation. J. Am. Chem. Soc. 129 (2007) 2971-2980] and contains a scheme that kills anti-phase single-quantum terms generated in the t(1) period. The purge scheme is essential to observe in-phase single-quantum multiplets. Applications to the NH(2) and NH(3)(+) groups in proteins are demonstrated.     

Spin density distribution of the conduction electrons in diperylene hexafluorophosphate analysed by high-resolution NMR

High-resolution ¹³C nuclear magnetic resonance with ¹H cross polarization and ¹H decoupling under magic angle spinning is measured for the quasi-one dimensional organic conductor diperylene hexafluorophosphate (including tetrahydrofurane solvent molecules) at temperatures between 160 K and 270 K. Ab initio molecular orbital calculations are used for chemical shift analysis and for assignment of Knight shifted lines and individual carbon positions. The coexistence of neutral perylene molecules and perylene radicals in the same radical cation salt is revealed. From Knight and chemical shifts we were able to distinguish two inequivalent perylene radicals within the conducting stack. The spin density distribution of the molecular electronic wave function is determined quantitatively for these radicals. Received 29 June 1999 and Received in final form 4 November 1999     

Testing the stability of fundamental constants with the 199Hg+ single-ion optical clock

Over a two-year duration, we have compared the frequency of the 199Hg+ 5d(10)6s (2)S(1/2)(F=0)<-->5d(9)6s(2) (2)D(5/2)(F=2) electric-quadrupole transition at 282 nm with the frequency of the ground-state hyperfine splitting in neutral 133Cs. These measurements show that any fractional time variation of the ratio nu(Cs)/nu(Hg) between the two frequencies is smaller than +/-7 x 10(-15) yr(-1) (1sigma uncertainty). According to recent atomic structure calculations, this sets an upper limit to a possible fractional time variation of g(Cs)(m(e)/m(p))alpha(6.0) at the same level.     

Measurement of dipole-dipole cross-correlated relaxation in fast rotating CH2D groups

Studies of protein dynamics are key to understanding their biological function. NMR relaxation studies of proteins to date have focused primarily on characterizing backbone dynamics. In this paper, we focus on the aliphatic side-chains (Ala, Thr, Val, Leu, and Ile) with the goal of deriving dynamical information on the motion of terminal methyl groups. Dipole-dipole cross-correlated cross-relaxation is analyzed in a fast rotating CH(2)D group, as found in partially deuteriated proteins. In comparison with previous studies on AMX spin systems (methylene C(beta)H(2) groups), the fast rotation of the methyl group makes a number of relaxation pathways efficient, through the coherence C(+)H(1)(+)H(2)(-)+C(+)H(1)(-)H (2)(+). Several pulse schemes were designed to evaluate these relaxation rates: the measured values are small and well predicted by taking into account the complete relaxation network, but they remain strongly influenced by 1H-1H relaxation with all protons in the neighborhood of the CH(2)D moiety. The prospects and limitations of this method are discussed in comparison with 2H relaxation measurements.     

The 4d, 5s,and 5p Orbitals of Rhodium

The 4d, 5s, and 5p orbitals of rhodium have been studied by semiempirical molecular orbital calculations for a Rh2 molecule. Overlap populations, overlap energy, and orbital energies were computed as functions of the orbital exponents of Slater type atomic orbitals. This study was prompted by extremely unsatisfactory results obtained attempting to predict electronic spectra, structure, and bonding in a number of rhodium complexes using analytic atomic orbitals deduced1 from accurate Hartree-Pock(HF) atomic calculations. “These reference calculations considered only the atomic configuration (4d)⁷(5s)² for rhodium.     

Search for strange-pentaquark production in e+e- annihilation at sqrt[s] = 10.58 GeV

We search for strange-pentaquark states that have been previously reported by other experiments--the Theta (1540)(+), Xi(5)(1860)(--), and Xi(5)(1860)(0)--in 123 fb(-1) of data recorded with the BABAR detector at the PEP-II e(+)e(-) storage ring. We find no evidence for these states and set 95% confidence level upper limits on the number of Theta(1540)(+) and Xi(5)(1860)(--) pentaquarks produced per e(+)e(-) annihilation into qq and Gamma(4S) decay. For qq events the Theta(1540)(+) [Xi(5)(1860)(--)] limit is about 8 [4] times lower than the rates measured for ordinary baryons of similar mass.     

直接键链13C-1H的核自旋偶合常数的理论研究

用一种计算直接键链原子核自旋偶合常数¹J_A-B的统一的半经验关系式，研究了各种代表性的环状分子及非环状分子的¹J_C-H的核自旋偶合常数，计算值与实验值吻合的较好, 说明该统一的半经验关系式既可适用于非环状分子又可适用于环状分子化合物体系的直接键链原子的核自旋偶合常数¹J_C-H计算.     

Evidence for the decay sigma+ --> pmu+ mu-

We report the first evidence for the decay Sigma(+)-->pmu(+)mu(-) from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Sigma(+)-->pmu(+)mu(-))=[8.6(+6.6)(-5.4)(stat)+/-5.5(syst)]x10(-8). The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma(+)-->pP(0),P0-->mu(+)mu(-) with a P0 mass of 214.3+/-0.5 MeV/c(2) and branching ratio B(Sigma(+)-->pP(0),P0-->mu(+)mu(-))=[3.1(+2.4)(-1.9)(stat)+/-1.5(syst)]x10(-8).     

若干具有[（PO4）4Mo6^VO15]^12^-簇骼的化合物的光谱研究

Five novel organic-molybdenum phosphates with [(PO4)4Mo6(V)O15]12- cluster, Na x (H4TETA)3 x (H3O)5 x {Zn[(HPO4)2(PO4)2Mo6O15]2} (2), (H2en)7 x (H3O)4 x {Cu[(HPO4)2(PO4)2Mo6O15]2} x H2O (3), (H3DETA)2 x (H3O)3 x {Co0.5[(HPO4)2(PO4)2Mo6O15]} x H2O (4), [Co(H3TETA)]2{Co0.5[(HPO4)(PO4)3Mo6O15] x 3.5H2O (5) and (H3DETA) x (H3O)4 x {Co1.5 [(HPO4)2(PO4)2Mo6O15]} x 0.5H2O (6), have been synthesized. The relationship between their properties and structures was studied by using FTIR, NIR FT-Raman, UV-Vis DRS and fluorescence etc. In these compounds, every two [(PO4)4Mo6O15] clusters are coordinated by a metal atom to form a {M[(PO4)4Mo6O15]2} dimer. In compound 2, 3 and 4, {M[(PO4)4Mo6O15]2} dimers are hydrogen-bonded by the organic molecules and water molecules to form a three-dimensional expended framework, respectively. In compound 5 and 6, {Co[(PO4)4Mo6O15]2} dimers are coordinated by [Co(H3TETA)] groups and [CoO4] tetrahedra to form a network, respectively. These characteristic vibrational frequencies of the molybdenum phosphates are related to the structure of these compounds. Three characteristic bands in UV-Vis DRS spectra of these compounds have to be attributed to the absorptions of O(d) --> Mo, O(mu) --> Mo and O --> M charge transfer, respectively. These compounds exhibit strong fluorescence emission bands at about 410 nm when excited by 240 nm, which are caused by O(mu) --> Mo charge transfer.     

Nondissociative adsorption of H2 molecules in light-element-doped fullerenes

First-principles density functional and quantum Monte Carlo calculations of light-element doped fullerenes reveal significantly enhanced molecular H2 binding for substitutional B and Be. A nonclassical three-center binding mechanism between the dopant and H2 is identified, which is maximized when the empty p(z) orbital of the dopant is highly localized. The calculated binding energies of 0.2-0.6 eV/H2 is suited for reversible hydrogen storage at near standard conditions. The calculated H2 sorption process is barrier-less, which could also significantly simplify the kinetics for the storage.     

5-乙酰(苯甲酰)基-4-芳基-3,4-二氢嘧啶-2(1H)-酮的质谱裂解规律

利用飞行时间质谱仪的高分辨本领和离子阱串联质谱技术研究了5乙酰(苯甲酰)基4芳基3,4二氢嘧啶2(1H)酮(1-5)的电子轰击质谱的裂解规律.将所有质谱离子的精确质量数据经OpenLynx软件导出其分子离子和碎片离子的元素组成.根据质谱裂解规律,主要质谱离子得到了归属,并经离子阱串联质谱技术加以证实.化合物1-3的质谱出现了丰度很强的分子离子峰,其中1和3的分子离子为基峰,证明此类化合物的结构相当稳定.但4和5的分子离子峰却很弱(相对丰度在4%以下),这是由于嘧啶环4位上的苯环分别含有强吸电子基团-NO2(在苯环的间位才有此效应)和-Cl(苯环的2和4位均含有氯)所致.化合物1-5的主要裂解包括:分子离子失去芳基形成丰度很高的阳离子(M-Ar)+;分子离子失去羰基形成中等强度的阳离子(M-RCO)+;分子离子失去氢原子所产生的(M-H)+峰,以及消除中性分子NH=C=X的嘧啶环破裂裂解.此外,所有化合物在低质量区都发现明显的苯基阳离子Ph+(m/z77).并且还提出个别化合物的几个额外裂解过程为:化合物4(分子中苯环的3位上含有硝基)出现的基峰(M-OH)+;化合物5(分子中苯环的2和4位上都含有氯原子)出现了的基峰(M-Cl)+;化合物3和5分别出现了m/z238(16%)和m/z241(29%)的特征离子峰,它们由相应的离子消除中性分子四员内酰胺生成查耳酮离子,该离子具有共轭大Π键而稳定存在.     

Bonding, backbonding, and spin-polarized molecular orbitals: basis for magnetism and semiconducting transport in V[TCNE]x approximately 2

X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the V L{2,3} and C and N K edges reveal bonding and backbonding interactions in films of the 400 K magnetic semiconductor V[TCNE]x approximately 2. In V spectra, d{xy}-like orbitals are modeled assuming V2+ in an octahedral ligand field, while d{z{2}} and d{x{2}-y{2}} orbitals involved in strong covalent sigma bonding cannot be modeled by atomic calculations. C and N MCD, and differences in XAS from neutral TCNE molecules, reveal spin-polarized molecular orbitals in V[TCNE]x approximately 2 associated with weaker pi bonding interactions that yield its novel properties.