Tunable pH-Sensitive 2-Carboxybenzyl Phosphoramidate Cleavable Linkers.

We previously described a pH-sensitive phosphoramidate linker scaffold that can be tuned to release amine-containing drugs at various pH values. In these previous studies it was determined that the tunability of this linker was dependent upon the proximity of an acidic group (e.g., carboxylic acid or pyridinium). In this study, we confirmed that the tunability of pH-triggered amine-release was also dependent upon the pKa of the proximal acidic group. A series of 2-carboxybenzyl phosphoramidates was prepared in which the pKa of the proximal benzoic acid was predictably attenuated by substituents on the benzoate ring consistent with their σ-values.

Determination of Gas-Phase Ion Mobility Coefficients Using Voltage Sweep Multiplexing.

In a standard single averaged, drift tube ion mobility spectrometry (IMS) experiment, typically less than 1% of the ions are utilized, with the rest of the ions neutralizing on a closed ion gate or ion optic element. Though some efforts at lower pressures (e.g., 4 Torr) have been made to address this issue by concentrating ions prior to release into a drift cell, the ion current reaching the detector during an IMS experiment is often diminished due to this lower duty cycle. Additionally, when considering the temporal nature of the drift tube IMS experiment and the trajectory of IMS towards higher resolution separations and lower duty cycles, increased detector sampling rates are another factor also which further necessitates new modes of conducting the IMS experiment. Placing this trend in context with ion mobility-mass spectrometry instruments (IM-MS), there are numerous types of mass spectrometers that are simply incompatible with the single averaged ion mobility spectrometry experiments due to timing incompatibilities (i.e., ion traps are an order of magnitude slower than the IMS experiment). However, by utilizing a dual gate ion mobility spectrometer for ion multiplexing, ion utilization efficiency can be significantly increased while creating a measurement signal that can be recorded at low sampling rates. In this work, we present the fundamental theory and first results from proof-of-concept measurements using a new type of ion multiplexing that relies on changing the electric field within the drift cell during the course of an experiment while simultaneously opening the ion gates at a constant frequency. For brevity, this mode is termed voltage sweep multiplexing (VSM). Key variables for this type of experiment are discussed and verified with measurements from traditional signal averaged experiments. Graphical Abstract .

On the Path to UHC - Global Evidence Must Go Local to Be Useful Comment on "Disease Control Priorities Third Edition Is Published: A Theory of Change Is Needed for Translating Evidence to Health Policy".

The Disease Control Priorities (DCP) publications have pioneered new ways of thinking about investing in health. We agree with Norheim, that a useful first step to advance efforts to translate DCP's global evidence into local health priorities, is to develop a clear Theory of Change (ToC). However, a ToC that aims to define how global evidence (DCP and others) can be used to inform national policy is too narrow an undertaking. We propose efforts should be directed towards developing a ToC to define how to support progressive institutional development to deliver on universal health coverage (UHC), putting the client at the center. Enhancing efforts to meet the new global health imperatives requires a shift in focus of attention to move radically from global to local. In order to achieve this we need to reorganize the nature of technical assistance (TA) along three major lines (1) examine and act to clarify the mandates and roles to be played by multilateral normative and convening agencies, (2) ensure detailed understanding of local institutions, their needs and their demands, and (3) provide TA over time and in trust with local counterparts. This last requirement implies the need for long-term local presence as well as an international network of expertise centers, to share scarce technical capabilities as well as to learn together across country engagements. Financing will need to be reorganized to incentivize and support demand-led capacity strengthening.

Optimized Reconstruction Techniques for Multiplexed Dual-Gate Ion Mobility Mass Spectrometry Experiments.

When coupling drift-tube gas-phase ion mobility separations with ion trapping mass analyzers an integrative, stepped approach to spectral reconstruction is a logical, yet highly inefficient means to determine gas-phase mobility coefficients. This experimental mode is largely predicated on the respective time scales of the two techniques each requiring tens of milliseconds to complete under routine conditions. Multiplexing techniques, such as Fourier and Hadamard based techniques, are a potential solution but still require extended experimental times that are not fully compatible with modern front-end separation schemes. Using a basis pursuit denoising (BPDN) approach to deconvolute Fourier transform ion mobility mass spectrometry (FT-IMMS) drift time spectra, we demonstrate significant time savings while maintaining a high degree of spectral resolution and signal-to-noise ratio. Under ideal conditions, the FT-IMMS operates with increased ion transmission (up to 25%); however, the linear chirp that spans into the kHz range often leads to significant levels of ion gate depletion, which limit both resolving power and ion transmission. The method proposed in this manuscript demonstrates the potential to reduce IMS acquisition time while simultaneously maximizing spectral resolution at longer effective gate pulse widths compared to the traditional set of multiplexing and signal averaging experiments.

Stabilization of gas-phase uranyl complexes enables rapid speciation using electrospray ionization and ion mobility-mass spectrometry.

Significant challenges exist when characterizing f-element complexes in solution using traditional approaches such as electrochemical and spectroscopic techniques as they do not always capture information for lower abundance species. However, provided a metal-complex with sufficient stability, soft ionization techniques such as electrospray offer a means to quantify and probe the characteristics of such systems using mass spectrometry. Unfortunately, the gas-phase species observed in ESI-MS systems do not always reflect the solution phase distributions due to the inherent electrochemical mechanism of the electrospray process, ion transfer from ambient to low pressures conditions, and other factors that are related to droplet evaporation. Even for simple systems (e.g. hydrated cations), it is not always clear whether the distribution observed reflects the solution phase populations or whether it is simply a result of the ionization process. This complexity is further compounded in mixed solvent systems and when multiply charged species are present. Despite these challenges, the benefits of mass spectrometry with respect to speed, sensitivity, and the ability to resolve isotopes continue to drive efforts to develop techniques for the speciation of metal complexes. Using an electrospray ionization atmospheric pressure ion mobility mass spectrometer (ESI-apIMS-MS), we demonstrate an approach to stabilize simple uranyl complexes during the ionization process and mobility separation to aid speciation and isotope profile analysis. Specifically, we outline and demonstrate the capacity of ESI-apIMS-MS methods to measure mobilities of different uranyl species, in simple mixtures, by promoting stable gas phase conformations with the addition of sulfoxides (i.e. dimethyl sulfoxide (DMSO), dibutyl sulfoxide (DBSO), and methyl phenyl sulfoxide (MPSO)). Addition of these sulfoxides, as observed in the mass spectrum and mobility domain, produce stable gas-phase conformations that enable the observation of the counter anion pair while minimizing the range of ligand exchange events as the ionized complex enters the gas-phase. Other enhancements include improved data acquisition times by applying multiplexing approaches to the IMS Bradbury-Nielsen (BN) gate to realize increased ion transmission and improve ion statistics measured at the m/z detector. Analyte identification using this approach is based on a multitude of combined measured gas-phase ion metrics, which include mass measurements, isotope profiling, and experimentally determined reduced mobilities measured at the low-field limit (<2 E/N). Though geared initially towards uranyl complexes, this approach may find application in fields where both chemical speciation and isotopic profiles provide diagnostic information for a given metal.

Acceleration of metal-ligand complexation kinetics by electrospray ionization.

Electrospray ionization mass spectrometry (ESI-MS) is a valuable and frequently used analytical technique across nearly all branches of chemistry, and has recently seen increasing use in the study of metal-ligand solution equilibria. Despite its prevalence, the method by which ESI produces gas-phase ions from solutions containing metal-ligand complexes is not fully understood, with recent reports showing significant changes to solution equilibria during ESI analysis. This study examines perturbations to the formation kinetics of metal-ligand complexes during the ESI process, showing how quickly new equilibria - reflective of the ionization process and not solution - can be established. Electrospray ionization mass spectrometry (ESI-MS) and ion mobility spectrometry (IMS) are used to examine the well studied Lu-DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) complexation reaction, with collision cross section modeling based on density functional theory (DFT) optimized structures used to aid in the interpretation of the ion mobility results. The electrospray process was found to significantly accelerate the formation kinetics, increasing the formation rate constant by more than an order of magnitude over its previously determined solution-phase value.

Ambient Pressure Inverse Ion Mobility Spectrometry Coupled to Mass Spectrometry.

Although higher resolving powers are often achieved using ambient pressure drift tube ion mobility mass spectrometry (DT-IMMS) systems, lower duty cycles are often required which directly impacts sensitivity. Moreover, the mechanism of ion gating using Bradbury-Nielsen or Tyndall-Gate configurations routinely results in ion gate depletion effects which discriminate against low mobility ions. This paper reports a new method of ambient pressure ion mobility operation in which inverse ion mobility spectrometry is coupled to a time-of-flight mass spectrometer to improve sensitivity and minimize the effects of ion gate depletion. In this mode of operation, the duty cycle is improved to approximate 99% from a typical value of less than 1%, improving the signal intensity by over 2 orders of magnitude. Another advantage of inverse ion mobility mass spectrometry is a reduction of the impact of ion gate depletion on low mobility molecules that translates into higher sensitivity for this class of analytes. To demonstrate these benefits afforded by this instrumental mode of operation differences in sensitivity, resolving power, and ion discrimination are compared between the inverse and normal modes of operation using tetraalkylammonium standards. These results show that the ion throughput is significantly increased for analytes with a broad range of mobilities with little impact on resolving power. While the mobility-based discrimination is minimized using the inverse mode of operation, the noise level in the inverse mode is highly dependent upon the stability of ionization source.

Correlation ion mobility spectrometry.

Using a linearly swept chirp function to modulate a Bradbury-Nielsen (BN) ion gate and application of a common signal processing technique (cross-correlation), we outline a method for obtaining high resolution IMS-MS spectra with ion gate duty cycles approaching 50%. Correlation IMS (CIMS) offers advantages over current multiplexing approaches in IMS-MS, which include the Hadamard and Fourier transforms, by minimizing transform artifacts while maintaining high ion throughput. Although cross-correlation techniques have been utilized previously in the field of IMS, to the best of our knowledge, this approach has not been utilized to obtain spectrum that resembles traditional IMS spectrum with resolving powers approaching the theoretical limit. This new approach relies on a linear sweep, which is a swept frequency signal, commonly utilized in different applications because of its compatibility with the fast Fourier transform (FFT). However, unlike spectra derived from Fourier transformation, CIMS yields data sampling rates that are not dependent upon terminal frequency and takes advantage of several factors unique to IMS operation; the non-linear response of ions at relatively low gate pulse widths, fluctuations in intensity, and peak profiles resembling the input gate pulse vector observed especially noted at low gating frequencies.

Second-Generation Tunable pH-Sensitive Phosphoramidate-Based Linkers for Controlled Release.

We developed a second generation of tunable pH-sensitive linkers based on our phosphoramidate scaffold to release amine-containing drugs under acidic conditions. The pH-triggered phosphoramidate-based linkers are responsive to pH and do not require intracellular enzymatic action to initiate drug release. On the basis of the model scaffolds examined, phosphoramidate-based linkers were selected for particular properties for controlled release applications such as amine type, stability under physiological conditions, or release rates at various pH values such as intracellular endosomal conditions. Key to the pH-triggered amine release from these linker is a proximal carboxylic acid to promote hydrolysis of the phosphoramidate P-N bond, presumably through an intramolecular general acid-type mechanism. Phosphoramidate hydrolysis is largely governed by the pKa of the leaving amine. However, the proximity of the neighboring carboxylic acid attenuates the stability of the P-N bond to hydrolysis, thus allowing for control over the release of an amine from the phosphoramidate center. In addition, we observed that the Thorpe-Ingold effect and rigidification of the scaffold could further enhance the rate of release. Esterification of the neighboring carboxylic acid was found to protect the scaffold from rapid release at low pH. This latter observation is particularly noteworthy as it suggests that the phosphoramidate-based drug-conjugate scaffold can be protected as an ester prodrug for oral administration. While the tunability phosphoramidate linkers is attractive for applications in intracellular trafficking studies in which pH changes can trigger release of turn-on dyes, antibody drug conjugates, small-molecule drug conjugates, and drug eluting stents (DES), the promise of oral delivery of drug conjugates is expected to have broad impact in controlled release applications.

Tunable pH-Sensitive Linker for Controlled Release.

We have developed a novel pH-sensitive linker based on a phosphoramidate scaffold that can be tuned to release amine-containing drug molecules at various pH values. The pH-triggered phosphoramidate-based linkers are responsive to pH alone and do not require intracellular enzymatic action to initiate drug release. Key to the pH-triggered amine release from these linkers is a proximal acidic group (e.g., pyridinium or carboxylic acid) to promote the hydrolysis of the phosphoramidate P-N bond, presumably through an intramolecular general-acid type mechanism. Phosphoramidate hydrolysis is largely governed by the pKa of the leaving amine (e.g., primary, secondary, aniline). However, the proximity of the neighboring pyridine group attenuates the stability of the P-N bond to hydrolysis, thus allowing for control over the release of an amine from the phosphoramidate center. Based on the model scaffolds examined, phosphoramidate-based linkers could be selected for particular properties for controlled-release applications such as amine type, stability under physiological conditions, or release rates at various pH values such as intracellular endosomal conditions. The tunability of the phosphoramidate scaffold is expected to find broad applicability in various controlled drug-release applications such as antibody or small-molecule drug conjugates, drug-eluting stents, prodrug activation, as well as intracellular trafficking studies in which pH changes can trigger the release of turn-on dyes.

A two-phase approach to Fourier transform ion mobility time-of-flight mass spectrometry.

It is well known that the duty cycle of common drift-tube ion mobility experiments is often below 1%. However, multiplexing approaches such as Fourier and Hadamard pulsing schemes have been shown to independently enhance the throughput of ion mobility spectrometry (IMS) experiments to levels that approach 50%. While challenges remain to their broad scale implementation we describe a new Fourier transform (FT) IMS experiment that is directly compatible with standard drift tube ion mobility mass spectrometers (DT-IMMS). Compared to previous FT-IMS experiments, our new approach requires only a single gate and circumvents the need for signal apodization by combining data from two frequency pulsing sequences 180° out of phase. Assessment of our initial results highlights an increase in signal-to-noise (SNR) relative to both previous implementations FT-IMS experiments and signal averaged (SA) experiments. For select tetraalkylammonium salts SNR improvements of more than one order of magnitude are routinely possible. To explore the performance metrics associated with the technique a number of experimental variables were systematically altered including frequency sweep range, sweep time, and data acquisition time. Using this experimental design we present the key aspects, considerations, and minimum resources necessary for other IMS researchers to incorporate this operational mode into their research. The two-phase FT-IMMS technique offers a tractable mechanism to enhance sensitivity for IMMS measurements and its broad-scale adoption by IMMS researchers promises to enhance the acquisition speed for mobility measurements using hybrid instrumentation.

Rationally designed sulfamides as glutamate carboxypeptidase II inhibitors.

Glutamate carboxypeptidase II (GCPII) is a membrane-bound cell surface peptidase. There is significant interest in the inhibition of GCPII as a means of neuroprotection, while GCPII inhibition as a method to treat prostate cancer remains a topic of further investigation. The key zinc-binding functional group of the well-characterized classes of GCPII inhibitors (phosphonates and phosphoramidates) is tetrahedral and negatively charged at neutral pH, while glutamyl urea class of inhibitors possesses a planar and neutral zinc-binding group. This study explores a new class of GCPII inhibitors, glutamyl sulfamides, which possess a putative net neutral tetrahedral zinc-binding motif. A small library containing six sulfamides was prepared and evaluated for inhibitory potency against purified GCPII in an enzymatic assay. While most inhibitors have potencies in the micromolar range, one showed promising sub-micromolar potency, with the optimal inhibitor in this series being aspartyl-glutamyl sulfamide (2d). Lastly, computational docking was used to develop a tentative binding model on how the most potent inhibitors interact with the ligand-binding site of GCPII.

Refugee Health: An approach to emergency situations

Ce livre est une réalisation collective des différentes sections de Médecins Sans Frontières (MSF), et a été écrit pour consolider la vaste expérience de MSF dans les programmes de réfugiés. Ce document traite des réfugiés et des personnes déplacées, et de ce quÆun organisme de santé peut faire pour soulager leurs souffrances. Il met l'accent sur ​​les politiques plutôt que sur les aspects pratiques, et vise à servir de guide aux décideurs.