Assays using a NIMS chip: loosely bound but highly selective.

A fluorous-affinity nanostructure initiator mass spectrometry (NIMS) chip has been developed as an enzyme activity assay. As a proof-of-principle, an assay for detecting cysteine-containing peptide phosphorylation by protein kinase A (PKA) was designed using NIMS technology. The efficacy for an enzyme inhibition assay was characterized by deriving an IC50 value from the ratio of the substrate-to-product mass spectral signal intensities, using known inhibitors of PKA and Abl kinase activity. Lastly, the potential use of a NIMS chip as a multiple screening enzyme inhibition platform was explored.

On-chip enrichment and analysis of peptide subsets using a maleimide-functionalized fluorous affinity biochip and nanostructure initiator mass spectrometry.

A new nanostructure initiator mass spectrometry (NIMS) methodology is presented that uses the strategy of fluorous-phase immobilization and capture by a maleimide-functionalized affinity tag to selectively enrich peptide subsets containing cysteine residues. This surface-based approach allows complex protein digests to be analyzed. The proposed platform makes use of a chemically unmodified porous silicon (pSi)-based NIMS chip. Unlike matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS), the approach described in this paper does not require analytes to be incorporated or cocrystallized with an initiator. The mass spectra generated by the approach in this work are characterized by low background noise and, therefore, high analyte detection sensitivity. Experiments were also conducted that show the potential the approach described in this work has for generating simplified mass spectra for MS/MS analyses.

A fragmentation study of the Rhodamine 610 cation using visible-laser desorption ionization.

The fragmentation of a potential visible matrix-assisted laser desorption ionization: Rhodamine 610 was studied under 532 nm visible irradiation, as a function of anion counter ion. It was found that at a fixed fluence, the chloride salt produced fewer fragments than those formed with ClO(4)(-) or BF(4)(-). Evidence presented suggests that the degree of fragmentation is inversely proportional to the strength of the contact ion pair in the solid state; that is, more energy is deposited into the radical cation which can lead to fragmentation when less energy is required to separate the ion pair. Similar results were found for salts of Rhodamine 6G.

Prediction of the size distributions of methanol-ethanol clusters detected in VUV laser/time-of-flight mass spectrometry.

The size distributions and geometries of vapor clusters equilibrated with methanol-ethanol (Me-Et) liquid mixtures were recently studied by vacuum ultraviolet (VUV) laser time-of-flight (TOF) mass spectrometry and density functional theory (DFT) calculations (Liu, Y.; Consta, S.; Ogeer, F.; Shi, Y. J.; Lipson, R. H. Can. J. Chem. 2007, 85, 843-852). On the basis of the mass spectra recorded, it was concluded that the formation of neutral tetramers is particularly prominent. Here we develop grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) frameworks to compute cluster size distributions in vapor mixtures that allow a direct comparison with experimental mass spectra. Using the all-atom optimized potential for liquid simulations (OPLS-AA) force field, we systematically examined the neutral cluster size distributions as functions of pressure and temperature. These neutral cluster distributions were then used to derive ionized cluster distributions to compare directly with the experiments. The simulations suggest that supersaturation at 12 to 16 times the equilibrium vapor pressure at 298 K or supercooling at temperature 240 to 260 K at the equilibrium vapor pressure can lead to the relatively abundant tetramer population observed in the experiments. Our simulations capture the most distinct features observed in the experimental TOF mass spectra: Et(3)H(+) at m/z = 139 in the vapor corresponding to 10:90% Me-Et liquid mixture and Me(3)H(+) at m/z = 97 in the vapors corresponding to 50:50% and 90:10% Me-Et liquid mixtures. The hybrid GCMC scheme developed in this work extends the capability of studying the size distributions of neat clusters to mixed species and provides a useful tool for studying environmentally important systems such as atmospheric aerosols.

Photodissociation of the geometric isomers of 1,2-dibromoethylene.

Resonance-enhanced multiphoton ionization (REMPI) spectra of 1,2-dibromoethylene (C(2)H(2)Br(2)) obtained using ultraviolet fundamental wavelengths between 280 and 312.5 nm and monitoring Br(+) fragments in a time-of-flight mass spectrometer are found to differ dramatically from those reported in the literature by detecting C(2)H(2)(+). Laser power plots suggest that the initial excitation process is (2+1) REMPI, which accesses parent excited states between 156.25 and 140.84 nm. Unlike the spectra obtained by monitoring C(2)H(2)(+), the spectra obtained by monitoring Br(+) appear to be identical regardless of which parent isomer (cis or trans) is excited. Based on energetics, it is proposed that Br(+) ions are formed by excitation and fragmentation of a ground-state 2-bromovinyl radical intermediate (CHBr=CH.) generated by the rapid excited-state dissociation of the parent molecules. Density-functional theory calculations using the hybrid Perdew-Burke-Ernzerhof (PBE1PBE) functional and the 6-311++G(3df,3pd) basis set confirm that the barrier to isomerization for the 2-bromovinyl radicals formed from the cis- and trans-1,2-dibromoethylenes is low, which explains why the resultant REMPI spectra cannot be distinguished based on their isomeric origin. Electronic spectra calculated for the 2-bromovinyl radical using the long-range-corrected hybrid PBE functional (LC-omegaPBE) are in qualitative agreement with experimental results.

Rydberg spectra of trans-1,2-dibromoethylene.

(2+1) resonance-enhanced multiphoton ionization spectra of jet-cooled trans-1,2-dibromoethylene are reported for the first time. The two-photon spectral region between 149.7 and 141.2 nm was examined. A 4p(z)<--pi Rydberg transition between 66,800 and 68,000 cm(-1) with A(g) excited state symmetry was analyzed, as well as two 4f<--pi Rydberg transitions with B(g) excited state symmetry and one 4f<--pi Rydberg transition with A(g) excited state symmetry between 68,000 and 70,800 cm(-1). All Rydberg transitions observed in this work belong to series that converge to the first ionization potential of the molecule. The short vibrational progressions observed involve two totally symmetric in-plane normal modes: C=C-H bending (nu(3)) and C=C-Br bending (nu(5)) with average excited state frequencies of 829 and 226 cm(-1), respectively.

Controlling large-scale film morphology by phase manipulation in interference lithography.

An experimental arrangement is described where a Babinet-Soleil compensator is inserted into the path of one of the three beams used for noncoplanar beam interference lithography. This birefringent element can change the phase of the beam so that either a positive two-dimensional pattern or an inverselike structure is generated in a photoresist without disturbing the mechanical geometry of the setup. Simulations are presented that confirm the validity of this approach. Large defect-free sample areas (>1 cm(2)) with submicrometer periodic patterns were obtained by expanding the laser beams used in the lithography experiment.

Mechanism for the formation of gas-phase protonated alcohol-ether adducts by VUV laser ionization and density-functional calculations.

The neutral vapors above liquid alcohol/ether mixtures, (diethyl ether/methanol, diethyl ether/ethanol, tetrahydrofuran/methanol, and tetrahydrofuran/ethanol) were co-expanded with He in a supersonic jet, ionized with a 118-nm vacuum ultraviolet laser, and detected in a time-of-flight mass spectrometer. In each case, features attributed to protonated alcohol-ether dimers and protonated ether monomers were observed, as well as those ions obtained by ionizing neat alcohol or ether samples alone. Theoretical calculations, carried out to establish the energetics of the various possible reactions leading to the formation of the observed binary adducts, indicate that the most thermodynamically favorable pathway corresponds to the addition of a protonated alcohol monomer to neutral ether.

Quantitative elemental analysis for rhodium and palladium in minerals by time-of-flight resonance ionization mass spectrometry.

Results are presented for the trace analysis of Pd and Rh by time-of-flight-resonance ionization mass spectrometry (TOF-RIMS). The spectrometer, developed at the Advanced Mineral Technology Laboratory (Ontario, Canada), is based on a commercial laser-induced mass analyzer with upgrades that include independent laser ablation and ionization sources and pulsed ion optics to minimize noise caused by primary ion formation. The schemes presented for Rh and particularly for Pd detection are simpler than others reported in the literature. The experimental laser fluences were found to be in reasonable agreement with theoretical estimates. The TOF-RIMS measurements were quantified on the basis of calibration curves derived using reference samples covering 3 orders of magnitude in concentration. Minimum detection limits of ~15 parts per billion were found for both metals, with a precision of ~ +/-15%. Samples from sulfide, iron oxide, and silicate minerals were also examined. The results are in excellent agreement with those obtained using dynamics secondary ion mass spectrometry.

Upper aerodigestive tract frostbite complicating volatile substance abuse.

Volatile substance abuse has become increasingly popular among today's youth. It has reportedly been used by up to 13% of teenage populations. Physicians need to be aware of the potential complications which may arise from this form of substance abuse. We describe the case of a young male who presented with massive edema affecting his lips, oral cavity, oropharynx and trachea. It was later discovered that his injury was secondary to thermal trauma related to the abuse of a fluorinated hydrocarbon propellant. This presentation may easily be confused with allergic or angioneurotic edema. Denial by the patient can lead to a further delay in diagnosis. This case is especially notable since frostbite injury involving the upper aerodigestive tract is extremely rare. We discuss the differential diagnosis and the management principals required in the care of this patient. We also present a pertinent review of the literature related to both volatile substance abuse and its complications involving the airway.

Analysis of Xanthate Derivatives by Vacuum Ultraviolet Laser-Time-of-Flight Mass Spectrometry.

A series of liquid O,S-dialkyl dithiocarbonates (xanthate esters) have been synthesized, and time-of-flight (TOF) mass spectra were recorded for their vapors using both ultraviolet (UV) and vacuum ultraviolet (VUV) laser excitation. These compounds are chemical derivatives of low vapor pressure xanthate salts which have found important commercial application as collectors in mineral sulfide flotation circuits. Our experiments demonstrate that esters ionized by short-wavelength VUV light can be detected by parent mass with high efficiency and minimal fragmentation. In contrast, the mass spectra of the same compounds obtained by UV light excitation exhibit a large number of low molecular mass peaks. A preliminary quantitative analysis of the composition of a gas-phase mixture of xanthate esters has also been achieved, which indicates possible subfemtomole detection limits.

Vacuum-ultraviolet laser-excited spectra of Xe(2).

Fluorescence excitation of Xe(2) at 149.0 nm has been observed using a pulsed supersonic jet for dimer formation and cooling and using tunable coherent VUV radiation from four-wave mixing in Mg vapor for excitation. The resolved vibronic structure resulting from isotopic Xe(2) molecules has yielded unambiguous vibrational numbering (upsilon'=37-46), giving the following constants for the first O(+)(u) excited state of Xe(2): T(e) = 63 796(6) cm (-1), omega'(e) = 124.86(30) cm(-1), omega(e)X'(e) = 0.937(3) cm(-1), and D(e) = 4446(7) cm(-1).

Vascularized limb transplantation in the rat. I. Results with syngeneic grafts.

A microsurgical model was developed to study the transplantation of large sections of vascularized skeletal tissue in inbred rats. A modified vascularized leg graft, consisting of the distal femur, knee joint, and intact tibia, with the associated musculature, was orthotopically transplanted in Fischer F344 rats. The femoral artery and vein were anastomosed by means of a microsurgical technique. Skin coverage was accomplished with recipient skin. In the studies reported here, syngeneic grafts were followed for up to twelve months by means of clinical examinations, X-rays, bone scans, and histologic studies. The bone and joint tissues not only survived but grew; the joints functioned and appeared to be histologically normal. Nonvascularized control grafts rapidly developed necrosis and osteomyelitis that lead to death of the recipients. Nonvascularized knee joint grafts, which were performed as additional controls, were better tolerated than nonvascularized limb grafts but they developed progressive degenerative changes. Thus, only the vascularized grafts restored optimal limb function. This model will be useful for exploring the feasibility and potential uses of large vascularized grafts of skeletal tissue.

Bone scanning in assessing viability of vascularized skeletal tissue transplants.

One hundred and eight bone scans using 99mTechnetium methylene diphosphonate (MDP) were performed in rats undergoing vascularized and nonvascularized syngeneic and allogeneic transplants of the hind limb, and in control animals. A six-level system of grading the radionuclide uptake in the graft was used to evaluate healing or complications of the transplantation. Bone scanning was superior to other modalities in assessing viability of the graft. Bone scans were able to: (1) immediately confirm vascular patency, thus obviating angiography; (2) demonstrate differences in the rate of repair in syngeneic and allogeneic nonvascularized grafts; (3) sequentially assess vascularized allograft rejection; and (4) document long-term effects, such as bone atrophy due to disuse and early epiphyseal maturity.