Extended hopane derivatives in sediments: identification by 1H NMR

The sedimentary C₃₂ hopanoic acid $\text{3a}$, one of the most abundant in nature and of probable bacterial origin, has been isolated for the first time as a single component and characterised by ¹H NMR. The 17αH,21βH configuration of the C₃₁ alkane has been similarly confirmed.     

A naturally occurring,chlorophyll b related porphyrin

A C₃₁ alkyl porphyrin, occurring in an oil shale as the V=O complex, has been isolated as the free base acetylated derivative whose structure has been determined by ¹H NMR spectroscopy; the parent compound provides the first circumstantial evidence for a link between sedimentary porphyprins and chlorophyll b.     

Analysis of carotenoids by field desorption mass spectrometry

The mass spectra of a variety of authentic carotenoids covering a range of structural types have been studied using the field desorption technique. All the compounds examined show the molecular ion as the base peak, even where this ion is of very low intensity in the electron-impact spectra. Little fragmentation is observed, but thermal decomposition can be induced in certain cases by using higher emitter currents. Application to a simple mixture of authentic compounds and a more complex mixture of sedimentary origin shows the potential of the method in the rapid qualitative screening of carotenoids in crude extracts.     

A “confinement safe” charge measure for QCD jets

We introduce a charge measure that enables us to determine the charge of the QCD quantum that gives rise to any particular jet of hadrons. The accuracy of the measure increases rapidly with the multiplicity of the jet, and is found to be already good at the higher PETRA energies.     

Anomalous atomic hydrogen shock pattern in a supersonic plasma Jet

A two-photon laser-induced fluorescence study on the transport of ground-state atomic hydrogen in a supersonic plasma jet, generated from an Ar-H (2) mixture, reveals an unexpected shock pattern. Whereas both the axial-velocity profile and the temperature profile of hydrogen atoms along the jet centerline can be interpreted in terms of a supersonic expansion of an Ar-H gas mixture, the H-atom density profiles do not satisfy the well established Rankine-Hugoniot relation leading to a nonconservation of the forward flux. The experimental results show that H atoms escape from the supersonic expansion by a diffusion process due to strong density gradients between the core of the jet and its vicinity.     

Portable, low-cost NMR with laser-lathe lithography produced microcoils

Nuclear Magnetic Resonance (NMR) is unsurpassed in its ability to non-destructively probe chemical identity. Portable, low-cost NMR sensors would enable on-site identification of potentially hazardous substances, as well as the study of samples in a variety of industrial applications. Recent developments in RF microcoil construction (i.e. coils much smaller than the standard 5mm NMR RF coils), have dramatically increased NMR sensitivity and decreased the limits-of-detection (LOD). We are using advances in laser pantographic microfabrication techniques, unique to LLNL, to produce RF microcoils for field deployable, high sensitivity NMR-based detectors. This same fabrication technique can be used to produce imaging coils for MRI as well as for standard hardware shimming or "ex-situ" shimming of field inhomogeneities typically associated with inexpensive magnets. This paper describes a portable NMR system based on the use of a 2 kg hand-held permanent magnet, laser-fabricated microcoils, and a compact spectrometer. The main limitations for such a system are the low resolution and sensitivity associated with the low field values and quality of small permanent magnets, as well as the lack of large amounts of sample of interest in most cases. The focus of the paper is on the setting up of this system, initial results, sensitivity measurements, discussion of the limitations and future plans. The results, even though preliminary, are promising and provide the foundation for developing a portable, inexpensive NMR system for chemical analysis. Such a system will be ideal for chemical identification of trace substances on site.