Unit resolution mass spectra of 112 kDa molecules with 3 Da accuracy

Previously, the highest molecular weight for a sample yielding a unit resolution mass spectrum was 67 kDa (marginal at 86 kDa), obtained with a 6. 2 T Fourier-transform mass spectrometer with electrospray ionization. Now with a 9. 4 T instrument, resolving power of 170,000 has been achieved for chondroitinase I (997 amino acids) and II (990 amino acids), making possible molecular weight assignments of 112,509 and 111,714, respectively, versus 112,508 and 111,713 calculated. Assisting these assignments was the noise reduction in the resolved isotopic peaks achieved by the time domain data sampling technique introduced by Senko, Marshall, and co-workers.     

Passive synchronization of all-fiber lasers through a common saturable absorber

We present the synchronization of two all-fiber mode-locked lasers, operating at 1.0?μm and 1.54?μm, coupled through the use of a shared single-wall carbon nanotube absorber. Both lasers operate in the soliton-regime, achieving a synchronized repetition rate of 13.08?MHz. The broadband absorption range of the single-wall carbon nanotubes allows the stable mode-locking behavior at 1?μm and 1.5?μm. The nonlinear coupling effects between two energy states of the carbon nanotube absorber result in stable synchronized pulses for hours of operation, with a large cavity mismatch of 1400?μm.     

Comparison of radon (Rn-222) concentration in Portugal and Finland underground waters

Journal of Radioanalytical and Nuclear Chemistry - Intercomparison results of Radon (Rn-222) measurements using two phase liquid scintillation counting (LSC) technique was performed. The results...     

Standard procedures for native CZE-MS of proteins and protein complexes up to 800 kDa

Native mass spectrometry (nMS) is a rapidly growing method for the characterization of large proteins and protein complexes, preserving “native” non-covalent inter- and intramolecular interactions. Direct infusion of purified analytes into a mass spectrometer represents the standard approach for conducting nMS experiments. Alternatively, CZE can be performed under native conditions, providing high separation performance while consuming trace amounts of sample material. Here, we provide standard operating procedures for acquiring high-quality data using CZE in native mode coupled online to various Orbitrap mass spectrometers via a commercial sheathless interface, covering a wide range of analytes from 30–800 kDa. Using a standard protein mix, the influence of various CZE method parameters were evaluated, such as BGE/conductive liquid composition and separation voltage. Additionally, a universal approach for the optimization of fragmentation settings in the context of protein subunit and metalloenzyme characterization is discussed in detail for model analytes. A short section is dedicated to troubleshooting of the nCZE-MS setup. This study is aimed to help normalize nCZE-MS practices to enhance the CE community and provide a resource for the production of reproducible and high-quality data.     

Phasor plots in optical injection experiments

An interferometric method for obtaining phasor plots of an optically injected laser is described. The technique is applied to a quantum well device and corresponding numerical plots are obtained for comparison yielding excellent quantitative agreement. An extension of the technique to obtain 3-D plots by incorporating a measurement of the gain is also described and applied to an injected quantum dot laser.     

The effect of kaolinite intercalation on the structural arrangements of N-methylformamide and 1-methyl-2-pyrrolidone

N-methylformamide (NMF) and 1-methyl-2-pyrrolidone (NMP) were intercalated with kaolinite, characterized, and deintercalated for analysis (the NMP was intercalated after expansion of the kaolinite layers with NMF). The dynamics of guest molecules within the kaolinite lamellae was studied by means of FT-IR and liquid state (1)H and (13)C NMR on the NMF and NMP before intercalation and also on the deintercalated solutions. Both compounds were deintercalated using water. The FT-IR spectra show no significant differences before and after intercalation, for either NMF or NMP, indicating that there is no change in molecular arrangement as a result of intercalation. (1)H and (13)C NMR investigations supported the findings of the FT-IR and indicated that structural arrangement and orientation of the guest species remain the same after deintercalation. This work provides evidence that intercalation is due to weak physical bonding.     

Complete large-molecule high-resolution mass spectra from 50-femtomole microvolume injection

For electrospray ionization in Fourier-transform mass spectrometry, direct injection of 5×10^?14 mol (0.5 µL of 100 nM from a microvolume sample valve) of ubiquitin (8565 Da) into the flowing solvent stream yields a spectrum with 85:1 signal-to-noise ratio, 2-ppm mass accuracy, and isotopic resolution. Gated trapping for 100 µs from a 0.15-µL/min injection of 20-µM ubiquitin consumes 5×10^?18 mol, which produces a spectrum with 23:1 signal-to-noise ratio and τ;3×10⁵ resolving power.     

Incorporation of nonmethyl branches by isoprenoid-like logic: multiple beta-alkylation events in the biosynthesis of myxovirescin A1

Several polyketide secondary metabolites are predicted to undergo isoprenoid-like beta-alkylations during biosynthesis. One such secondary metabolite is myxovirescin A1, produced by Myxococcus xanthus. Myxovirescin is of special interest in that it appears to undergo two distinct beta-alkylations. Additionally, the myxovirescin biosynthetic gene cluster lacks tandem thiolation domains required in the synthesis of other beta-branched secondary metabolites. To probe the origins of the beta-branches in myxovirescin, we heterologously overexpressed the proteins predicted to be responsible for myxovirescin beta-alkylation and reconstituted their activities in vitro on model substrates. Our results confirm that myxovirescin undergoes two isoprenoid-like beta-alkylations during its biosynthesis, including an unprecedented beta-ethylation. The study of its biosynthesis should shed light on the scope and requirements for isoprenoid-like biosynthetic logic in a polyketide context.     

Phase-locked mutually coupled 1.3 microm quantum-dot lasers

Fabry-Perot InAs quantum-dot lasers grown on GaAs substrates are mutually coupled with a delay of several nanoseconds. Stable phase-locked output with narrow linewidth is obtained when the frequency detuning between the two lasers is less than 4 GHz. This simple locking scheme could find application in a variety of photonics applications.