Validation of a Multi-Sensor-Based Kiosk for Short Physical Performance Battery.

OBJECTIVES: We aimed to validate a multi-sensor-based kiosk (automatically measured Short Physical Performance Battery [eSPPB] kiosk) that can perform automated measurement of the SPPB. DESIGN: Prospective, cross-sectional study. SETTING: Rehabilitation clinic of a tertiary-care hospital. PARTICIPANTS: Ambulatory outpatients, aged 65 years or older (N = 40). MEASUREMENTS: The eSPPB kiosk was developed to measure the three components of the SPPB: standing balance, gait speed, and chair stand test with embedded sensors and algorithms. Correlations between the total and component-specific scores of the eSPPB and manually measured SPPB (mSPPB), assessed by a physical therapist, were assessed. Further, correlations between SPPB parameters and geriatric functional measures were also evaluated. RESULTS: This study included 40 participants with a mean age of 74.4 ± 6.5 years, a mean total eSPPB score of 10.1 ± 2.1, and a mean total mSPPB score of 10.2 ± 2.1. The intraclass correlation coefficient between the eSPPB and mSPPB total score was 0.97 (P < .001), and the κ agreement was 0.79 (P < .001). The intraclass coefficients between the components of eSPPB and mSPPB were 0.77 (P < .001), 0.88 (P < .001), and 0.99 (P < .001) for standing balance, gait speed, and chair stand test, respectively. CONCLUSION: The newly developed kiosk might be a viable and efficient method for performing the SPPB in older adults. J Am Geriatr Soc 67:2605-2609, 2019.

Degree of ionization in MALDI of peptides: thermal explanation for the gas-phase ion formation.

Degree of ionization (DI) in matrix-assisted laser desorption ionization (MALDI) was measured for five peptides using α-cyano-4-hydroxycinnanmic acid (CHCA) as the matrix. DIs were low 10(-4) for peptides and 10(-7) for CHCA. Total number of ions (i.e., peptide plus matrix) was the same regardless of peptides and their concentration, setting the number of gas-phase ions generated from a pure matrix as the upper limit to that of peptide ions. Positively charged cluster ions were too weak to support the ion formation via such ions. The total number of gas-phase ions generated by MALDI, and that from pure CHCA, was unaffected by the laser pulse energy, invalidating laser-induced ionization of matrix molecules as the mechanism for the primary ion formation. Instead, the excitation of matrix by laser is simply a way of supplying thermal energy to the sample. Accepting strong Coulomb attraction felt by cations in a solid sample, we propose three hypotheses for gas-phase peptide ion formation. In Hypothesis 1, they originate from the dielectrically screened peptide ions in the sample. In Hypothesis 2, the preformed peptide ions are released as part of neutral ion pairs, which generate gas-phase peptide ions via reaction with matrix-derived cations. In Hypothesis 3, neutral peptides released by ablation get protonated via reaction with matrix-derived cations.

Ion yields for some salts in MALDI: mechanism for the gas-phase ion formation from preformed ions.

Preformed ion emission is the main assumption in one of the prevailing theories for peptide and protein ion formation in matrix-assisted laser desorption ionization (MALDI). Since salts are in preformed ion forms in the matrix-analyte mixture, they are ideal systems to study the characteristics of preformed ion emission. In this work, a reliable method to measure the ion yield (IY) in MALDI was developed and used for a solid salt benzyltriphenylphosphonium chloride and two room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate. IY for the matrix (α-cyano-4-hydroxycinnamic acid, CHCA) was also measured. Taking 1 pmol salts in 25 nmol CHCA as examples, IYs for three salts were similar, (4-8) × 10(-4), and those for CHCA were (0.8-1.2) × 10(-7). Even though IYs for the salts and CHCA remained virtually constant at low analyte concentration, they decreased as the salt concentrations increased. Two models, Model 1 and Model 2, were proposed to explain low IYs for the salts and the concentration dependences. Both models are based on the fact that the ion-pair formation equilibrium is highly shifted toward the neutral ion pair. In Model 1, the gas-phase analyte cations were proposed to originate from the same cations in the solid that were dielectrically screened from counter anions by matrix neutrals. In Model 2, preformed ions were assumed to be released from the solid sample in the form of neutral ion pairs and the anions in the ion pairs were assumed to be eliminated via reactions with matrix-derived cations.

Selective screening of tyrosine-nitrated peptides in tryptic mixtures by in-source photodissociation at 355 nm in matrix-assisted laser desorption ionization.

Nitration of tyrosine residues in proteins is an important post-translational modification related to various diseases such as Alzheimer's. In this work, efficient and selective photodissociation (PD) at 355 nm was observed for [M + H](+), [M + H - 16](+), and [M + H - 32](+) generated by matrix-assisted ultraviolet laser desorption ionization (UV-MALDI) of tyrosine-nitrated peptides (nitropeptides). Product ion spectra obtained by post-source PD at this wavelength contained useful information on the amino acid sequence. The spectra for nitropeptides obtained with 355 nm irradiation inside the ion source (MALDI/in-source PD) displayed characteristic triplet patterns due to PD of the above ions. For peptides displaying prominent signal in a MALDI mass map of a tryptic mixture, which are mostly those with arginine at the C-terminus, in-source PD allowed positive identification of their tyrosine-nitrated forms. Identification of such nitropeptides was possible at the 10 fmol level (in tryptic digest of 100 fmol BSA).

Observation of phosphorylation site-specific dissociation of singly protonated phosphopeptides.

In ultraviolet photodissociation of phosphopeptide ions with a basic residue (arginine, lysine, or histidine) at the N-terminus, intense a(n) - 97 peaks were observed. These ions were formed by cleavage at phosphorylated residues only. For multiply phosphorylated peptides, this site-specific cleavage occurred at every phosphorylated residue. H/D exchange studies showed that a(n) - 97 was formed by H(3)PO(4) loss from a(n) + 1 radical cations. The site-specificity of phosphate loss observed here is in contrast to the nonspecific phosphate loss from b(n) and y(n) reported previously. Characteristics of the reaction and its potential utility for phosphopeptide analysis are discussed.

Construction and performance test of a multiplexed multistage (MS(n)) time-of-flight mass spectrometer.

A time-of-flight mass spectrometer equipped with two reflectrons was constructed for multiplexed photodissociation tandem mass spectrometry of peptide ions generated by matrix-assisted laser desorption ionization. A linear reflectron was used for high-resolution selection of a precursor ion while a quadratic reflectron was used for product ion analysis. With the photoexcitation of a precursor ion inside a cell floated at high voltage, information (MS(3)) on intermediate ions generating a particular product ion was obtained. Fully multiplexed detection resulted in good MS(3) signal levels. Use of the quadratic reflectron allowed intermediate ion mass determination within 4 Da. The possibility of further extending the technique and its analytical potential are discussed.

Photodissociation at 193 nm of some singly protonated peptides and proteins with m/z 2000-9000 using a tandem time-of-flight mass spectrometer equipped with a second source for delayed extraction/post-acceleration of product ions.

A tandem time-of-flight mass spectrometer was built for photodissociation (PD) of singly protonated peptides and small proteins generated by matrix-assisted laser desorption/ionization. PD was performed in a second source after deceleration of precursor ions. The delayed extraction/post-acceleration scheme was used for the product ions. For the PD at 193 nm of small singly protonated peptides, the present instrument showed much better sensitivity and resolution for product ions than the previous one (Moon JH, Yoon SH, Kim MS, Bull. Korean Chem. Soc. 2005; 26: 763) even though the overall spectral patterns obtained with the two instruments were similar. The present instrument was inferior in precursor ion selection and background noise level. PD was achieved for precursor ions as large as the singly protonated ubiquitin (m/z 8560.63), indicating that the photoexcitation is capable of supplying a sufficient amount of internal energy to dissociate large singly protonated proteins. As the precursor ion m/z increased, however, product ion signals deteriorated rather rapidly. As in the PD of small peptide ions with m/z around 1000, the types of the product ions generated from singly protonated peptides with m/z in the range 2000-4000 were mostly determined by the positions of arginine residues. Namely, a(n) and d(n) ions dominated when an arginine residue(s) was near the N-terminus while v(n), w(n), x(n) and y(n) dominated when the same residue(s) was near the C-terminus. In addition, d(n), v(n) and w(n) ions were generated according to the correlation rules previously observed in the collisionally activated dissociation. Isoleucine and leucine isomers could be easily distinguished based on the w(n) and d(n) ions.