Desorption ionization combined with tandem mass spectrometry: Advantages for investigating complex lipids,disaccharides and organometallic complexes

Combining desorption ionization with tandem mass spectrometry overcomes the disadvantage of limited fragmentation accompanying desorption and permits mixtures of closely related substances to be investigated directly. These features of the combination are illustrated by completing the structure-proof of a minor component of an ornithine-containing lipid mixture isolated from Thiobacillus thiooxidans. The minor component is a homolog of the major constituent and differs from the principal component owing to the presence of a double bond in lieu of a cyclopropyl ring in one of the constituent fatty acids. Another feature of the combined method is the potentially complementary nature of collision-activated dissociation spectra of protonated and cationized biomolecules. This is illustrated by the differences in the collision-activated dissociations of the [M + Na]⁺ of sucrose, desorbed by field desorption, and [M + H]⁺, desorbed by fast atom bombardment. A third illustration is the application of field desorption and tandem mass spectrometry to an organometallic compound. The combined approach allows the ligands to be identified and the relative ligand binding energies to be approximated.     

Beta-delayed two-proton decay of39Ti

The beta-delayed two-proton decay of theT _z =–5/2 nuclide³⁹Ti has been observed. The³⁹Sc isobaric analog state has been calculated to lie at 8.82 MeV using the measured two-proton sum energy of 4750±40 keV for its decay to the³⁷K ground state. Combining this excitation energy with a Coulomb displacement energy calculation has lowered the energy available for ground state two-proton emission of³⁹Ti from 760 to 530 keV.This work was supported by Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U.S. Depeartment of Energy under Contracts DE-AC03-76SF00098 with Lawrence Berkeley Laboratory, DE-AC02-76CH00016 with Brookhaven National Laboratory and DE-AC06-76RL0 1830 with Pacific Northwest Laboratories.     

Construction of a Live‐Attenuated HIV‐1 Vaccine through Genetic Code Expansion

A safe and effective vaccine against human immunodeficiency virus type 1 (HIV‐1) is urgently needed to combat the worldwide AIDS pandemic, but still remains elusive. The fact that uncontrolled replication of an attenuated vaccine can lead to regaining of its virulence creates safety concerns precluding many vaccines from clinical application. We introduce a novel approach to control HIV‐1 replication, which entails the manipulation of essential HIV‐1 protein biosynthesis through unnatural amino acid (UAA*)‐mediated suppression of genome‐encoded blank codon. We successfully demonstrate that HIV‐1 replication can be precisely turned on and off in vitro.     

Fast-atom bombardment and tandem mass spectrometry of macrolide antibiotics

Molecular weights of macrolide antibiotics can be determined from either (M + H)⁺ or (M + Met)⁺, the latter desorbed from alkali metal salt-saturated matrices. The ion chemistry of macrolides, as determined by tandem mass spectrometry (MS/MS), is different for ions produced as metallated than those formed as (M + H)⁺ species. An explanation for these differences is the location of the charge. For protonated species, the charge is most likely situated on a functional group with high proton affinity, such as the dimethylamino group of the ammo sugar. The alkali metal ion, however, is bonded to the highly oxygenated aglycone. As a result, the collision-activated dissociation spectra of protonated macrolides are simple with readily identifiable fragment ions in both the high and low mass regions but no fragments in the middle mass range. In contrast, the cationized species give complex spectra with many abundant ions, most of which are located in the high mass range. The complementary nature of the fragmentation of these two species recommends the study of both by MS/MS when determining the structure or confirming the identity of these biomaterials.     

Omega- and Omega+ production in central Pb + Pb collisions at 40 and 158A GeV

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-) + Omega(+) at 40A GeV and for Omega(-) and Omega(+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models.     

Measurement of excitation functions in the reactions 197Au(11C, xn)208-xAt using a radioactive 11C beam

A light-element radioactive ion-beam capability has been developed at the LBNL 88-Inch Cyclotron. The system is based on the coupled-cyclotrons method and utilizes short-lived species, e.g., 11C, 14O, 13N produced by (p,n) and (p,alpha) reactions at the LBNL Biomedical Isotope Facility Cyclotron. In a first experiment, 197Au(11C,xn)208-xAt excitation functions have been measured for energies ranging from the Coulomb barrier up to 110 MeV using a beam of 11C with intensities up to (1-2)x10(8) ions/sec on target. The results of this experiment are compared to measurements of 197Au(12C, xn)209-xAt excitation functions.     

Measurement of the B(+) production cross section in pp collisions at sqrt[s]=7 TeV

Measurements of the total and differential cross sections dσ/dp(T)(B) and dσ/dy(B) for B(+) mesons produced in pp collisions at sqrt[s]=7 TeV are presented. The data correspond to an integrated luminosity of 5.8 pb(-1) collected by the CMS experiment operating at the LHC. The exclusive decay B(+)→J/ψK(+), with J/ψ→μ(+)μ(-), is used to detect B(+) mesons and to measure the production cross section as a function of p(T)(B) and y(B). The total cross section for p(T)(B)>5 GeV and |y(B)|<2.4 is measured to be 28.1±2.4±2.0±3.1 μb, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement.     

Search for stopped Gluinos in pp collisions at square root s=7 TeV

The results of the first search for long-lived gluinos produced in 7 TeV pp collisions at the CERN Large Hadron Collider are presented. The search looks for evidence of long-lived particles that stop in the CMS detector and decay in the quiescent periods between beam crossings. In a dataset with a peak instantaneous luminosity of 1×10(32) cm-2 s-1, an integrated luminosity of 10 pb-1, and a search interval corresponding to 62 hours of LHC operation, no significant excess above background was observed. Limits at the 95% confidence level on gluino pair production over 13 orders of magnitude of gluino lifetime are set. For a mass difference mg - mχ1(0) >100 GeV/c2, and assuming BR(g→gχ1(0))=100%, mg < 370 GeV/c2 are excluded for lifetimes from 10 μs to 1000 s.