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Electrospray-assisted laser desorption/ionization (ELDI) combined with mass spectrometry allows chemical and biochemical compounds to be characterized directly from hydrophilic and hydrophobic organic solutions mixed with carbon powders under ambient conditions. Organic and inorganic compounds dissolved in polar or nonpolar solvent such as methanol, tetrahydrofuran, ethyl acetate, toluene, dichloromethane, or hexane can be detected using this ambient ionization technique without prior pretreatment. We have used this technique to monitor the progress in several ongoing reactions: the epoxidation of chalcone in ethanol, the chelation of ethylenediaminetetraacetic acid with copper and nickel ions in aqueous solution, the chelation of 1,l0-phenanthroline with iron(II) in methanol, and the tryptic digestion of cytochrome c in aqueous solution. Liquid-ELDI analyses simply require irradiation of the surface of the sample solution with a pulsed ultraviolet laser; the laser energy is adsorbed by the carbon powder presuspended in the sample solution; the absorbed laser energy is then transferred to the surrounding solvent and to the analyte molecules in the solution, leading to their desorption; the desorbed gaseous analyte molecules are then postionized within an electrospray (ESI) plume to generate ESI-like analyte ions.

Amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethyleneoxide) copolymers, also known as poloxamers, have broad biomembraneactivities. To illustrate the nature of these activities, 1H Overhauser dynamic nuclear polarization NMR spectroscopy was employedto sensitively detect polymer–lipid membrane interactions throughthe modulation of local hydration dynamics in lipid membranes. Ourstudy shows P188, the most hydrophilic poloxamer that is a known membranesealant, weakly adsorbs on the membrane surface, yet effectively retardsmembrane hydration dynamics. Contrarily, P181, the most hydrophobicpoloxamer that is a known membrane permeabilizer, initially embedsat lipid headgroups and enhances intrabilayer water diffusivity. Unprecedentedresolution for differentiating weak surface adsorption versus translocationof polymers to membranes is obtained by probing local water diffusivityin lipid bilayer systems. Our results illustrate that the relativehydrophilic/hydrophobic ratio of the polymer dictates its functions.These findings gleaned from local hydration dynamics are well supportedby a thermodynamics study presented in the accompanying paper (Wang,J.-Y.; Marks, J. M.; Lee, K. Y. C. Biomacromolecules, 2012, DOI: 10.1021/bm300847x). [ABSTRACT FROM AUTHOR]

The synthesis, crystal structure, and antimicrobial efficacy are reported for a novel material comprising a 1:2 ratio of chlorhexidine (CHX) to N-cyclohexylsulfamate ( i.e. , artificial sweetener known as cyclamate). The chemical structure is unambiguously identified by incorporating a combination of single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass spectrometry (ESI-MS), 1 H nuclear magnetic resonance (NMR) spectroscopy, correlation spectroscopy (COSY), and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). The new material: 1) is amongst only several reported structures identified to date incorporating the vital chlorhexidine antimicrobial drug; 2) exhibits broad spectrum antimicrobial activity at concentrations less than 15 μg/mL; and 3) provides a unique delivery method for the essential active pharmaceutical ingredient (API). Furthermore, substitution of inactive gluconate with bioactive cyclamate counterion potentially provides the additional benefit of improving the taste profile of chlorhexidine.

We demonstrate that the effect of protein crowding is critically dependent on the stability of the protein's hydration shell, which can dramatically vary between different proteins. In the human eye lens, γS-crystallin (γS-WT) forms a densely packed transparent hydrogel with a high refractive index, making it an ideal system for studying the effects of protein crowding. A single point mutation generates the cataract-related variant γS-G18V, dramatically altering the optical properties of the eye lens. This system offers an opportunity to explore fundamental questions regarding the effect of protein crowding, using γS-WT and γS-G18V: (i) how do the diffusion dynamics of hydration water change as a function of protein crowding?; and (ii) upon hydrogel formation of γS-WT, has a dynamic transition occurred generating a single population of hydration water, or do populations of bulk and hydration water coexist? Using localized spin probes, we separately probe the local translational diffusivity of both surface hydration and interstitial water of γS-WT and γS-G18V in solution. Surprisingly, we find that under the influence of hydrogel formation at highly crowded γS-WT concentrations up to 500 mg/mL, the protein hydration shell remains remarkably dynamic, slowing by less than a factor of 2, if at all, compared to that in dilute protein solutions of ∼5 mg/mL. Upon self-crowding, the population of this robust surface hydration water increases, while a significant bulk-like water population coexists even at ∼500 mg/mL protein concentrations. In contrast, surface water of γS-G18V irreversibly dehydrates with moderate concentration increases or subtle alterations to the solution conditions, demonstrating that the effect of protein crowding is highly dependent on the stability of the protein-specific hydration shell. The core function of γS-crystallin in the eye lens may be precisely its capacity to preserve a robust hydration shell, whose stability is abolished by a single G18V mutation.

The study of crystals of molecular wheels as nanoporous materials is reported. Hyperpolarized (129)Xe NMR spectroscopy has been used to characterize the mode of molecular diffusion and Xe interactions within the supramolecular nanochannels formed upon crystallization of the molecular wheels [Ga(10)(OMe)(20)(O(2)CMe)(10)] and [Ga(18)(pd)(12)(pdH)(12)(O(2)CMe)(6)(NO(3))(6)](NO(3))(6). In agreement with expectations based on the collision diameter of the Xe atom relative to the differing internal diameters of the two types of gallium wheels, single-file diffusion occurs in the Ga(10) channels, whereas in the Ga(18) system the data are consistent with normal, Fickian diffusion. Information about the electronic environment inside the channels was probed by the Xe chemical shift. The interaction of the gas with the channel walls is found to be substantially stronger than the interaction in organic nanotubes and zeolites. The results establish the ability of crystals of molecular wheel compounds to function as a new class of porous nanotubular materials, and ones of a known and variable diameter, for studying the channel diameter dependence of molecular exchange and unidirectional diffusion on the micrometer length scale.

The kinetics of gas --> channel and channel --> gas exchange of Xe in self-assembled L-alanyl-L-valine (AV) nanotubes was facilitated by continuous flow hyperpolarized xenon-129 two-dimensional exchange NMR spectroscopy. Cross-peaks due to gas atoms entering or exiting were observed at Xe pressures of 92, 1320, and 3300 mbar, corresponding to Xe fractional occupancies ranging from 0.047 to 0.64. At each pressure, the rate of desorption from the channels was determined by fitting the mixing time dependence of the cross-peak and diagonal-peak signals to a magnetization exchange model, assuming steady-state Langmuir adsorption under hyperpolarized gas flow conditions. The observed rate constant for desorption of Xe from AV nanotubes decreased from 4.5 s-1 to 2.0 s-1 over the occupancy range studied, a finding that is consistent with a decrease in the diffusivity in the channels.