Removal of Paramagnetic Ions Prior to Analysis of Organic Reactions in Aqueous Solutions by NMR Spectroscopy.

This article describes a method for improving H NMR spectra of aqueous samples containing paramagnetic metals by precipitation of metal cations with a variety of counteranions. The addition of hydroxide, phosphate, carbonate, and arsenate to solutions of transition metals such as Fe and Mn can reduce line broadening and improve the ability of a spectrometer to lock on the signal of deuterium. The method is most effective under strongly alkaline conditions, and care must be taken to observe whether the organic substrates undergo side reactions or are themselves removed from solution upon addition of the precipitating salts.

Design of Hydrolytically Degradable Polyethylene Glycol Crosslinkers for Facile Control of Hydrogel Degradation.

Hydrogels, whose degradability can be controlled while also preserving cell viability or biomolecule stability, are in demand. Degradable polyethylene glycol crosslinkers are hydrolytically designed for use in hydrogels. Degradation is controlled by crosslinker chemical structure, such as introducing local hydrophobicity, steric hindrance, or electron-withdrawing moieties near a degradable ester moiety.

The Prebiotic Provenance of Semi-Aqueous Solvents.

The numerous and varied roles of phosphorylated organic molecules in biochemistry suggest they may have been important to the origin of life. The prominence of phosphorylated molecules presents a conundrum given that phosphorylation is a thermodynamically unfavorable, endergonic process in water, and most natural sources of phosphate are poorly soluble. We recently demonstrated that a semi-aqueous solvent consisting of urea, ammonium formate, and water (UAFW) supports the dissolution of phosphate and the phosphorylation of nucleosides.

Prebiotic condensation through wet-dry cycling regulated by deliquescence.

Wet-dry cycling is widely regarded as a means of driving condensation reactions under prebiotic conditions to generate mixtures of prospective biopolymers. A criticism of this model is its reliance on unpredictable rehydration events, like rainstorms. Here, we report the ability of deliquescent minerals to mediate the oligomerization of glycine during iterative wet-dry cycles.

Quantitative Analysis of Glycine Oligomerization by Ion-Pair Chromatography.

This paper describes a method for the quantitative analysis of mixtures of glycine and its oligomers by ion-pair high-performance liquid chromatography (IP-HPLC), with a particular focus on applications in origins-of-life research. We demonstrate the identification of glycine oligomers (Gly ) up to 14 residues long-the approximate detectable limit of their solubility in water-and measurement of the concentration of these species in the product mixture of an oligomerization reaction. The molar response factors for higher oligomers of glycine-which are impractical to obtain as pure samples-are extrapolated from direct analysis of pure standards of = 3-6, which established a clear linear trend.

The drive to life on wet and icy worlds.

This paper presents a reformulation of the submarine alkaline hydrothermal theory for the emergence of life in response to recent experimental findings. The theory views life, like other self-organizing systems in the Universe, as an inevitable outcome of particular disequilibria. In this case, the disequilibria were two: (1) in redox potential, between hydrogen plus methane with the circuit-completing electron acceptors such as nitrite, nitrate, ferric iron, and carbon dioxide, and (2) in pH gradient between an acidulous external ocean and an alkaline hydrothermal fluid.

Thermodynamic analysis to assist in the design of recombinant antibodies.

This critical review examines the thermodynamics of binding of bivalent antibodies (IgG and IgE) to soluble ligands with two or more binding moieties joined covalently (multivalent ligands) and to surfaces functionalized with multiple identical ligands. Given the prevalence of antibodies in nature, the goal of this paper is to begin to understand what aspects of bivalent antibodies are important relative to their monovalent counterparts (Fab). We provide a brief introduction to the thermodynamic parameters of importance to bivalent binding, guidance as to which of these parameters are most useful for the comparison of disparate systems, and a re-examination of binding studies of bivalent antibodies from the literature.

The relative rates of thiol-thioester exchange and hydrolysis for alkyl and aryl thioalkanoates in water.

This article reports rate constants for thiol-thioester exchange (k (ex)), and for acid-mediated (k (a)), base-mediated (k (b)), and pH-independent (k (w)) hydrolysis of S-methyl thioacetate and S-phenyl 5-dimethylamino-5-oxo-thiopentanoate-model alkyl and aryl thioalkanoates, respectively-in water. Reactions such as thiol-thioester exchange or aminolysis could have generated molecular complexity on early Earth, but for thioesters to have played important roles in the origin of life, constructive reactions would have needed to compete effectively with hydrolysis under prebiotic conditions. Knowledge of the kinetics of competition between exchange and hydrolysis is also useful in the optimization of systems where exchange is used in applications such as self-assembly or reversible binding.

Patterned paper as a template for the delivery of reactants in the fabrication of planar materials.

This account reviews the use of templates, fabricated by patterning paper, for the delivery of aqueous solutions of reactants (predominantly, ions) in the preparation of structured, thin materials (e.g., films of ionotropic hydrogels).

Heterogeneous films of ionotropic hydrogels fabricated from delivery templates of patterned paper.

The use of delivery templates makes it possible to fabricate shaped, millimeter-thick heterogeneously patterned films of ionotropic hydrogels. These structures include two-dimensional (2-D) patterns of a polymer cross-linked by different ions (e.g.

Electrically addressable parallel nanowires with 30 nm spacing from micromolding and nanoskiving.

This paper describes the fabrication of arrays of parallel, electrically addressable metallic nanowires by depositing alternating layers of thin films of metal and polymer-both planar and topographically patterned-and sectioning the laminated structures with an ultramicrotome (nanoskiving). The structures that resulted from this process had two distinct regions: one in which parallel Au nanowires were separated by a minimum distance of 30 nm, and one in which the nanowires diverged such that the distal ends were individually addressable by low-resolution (> or =10 microm) photolithography. Conductive polyaniline (PANI) was electrochemically deposited across the nanowire electrodes to demonstrate their electrical addressability, continuity, and physical separation.

Fabrication and Manipulation of Ionotropic Hydrogels Crosslinked by Paramagnetic Ions.

This manuscript describes the fabrication and manipulation of millimeter-scale spheres fabricated from ionotropic hydrogels that are crosslinked with paramagnetic metal ions (e.g., Ho(3+)).

Dependence of effective molarity on linker length for an intramolecular protein-ligand system.

This paper reports dissociation constants and "effective molarities" (M(eff)) for the intramolecular binding of a ligand covalently attached to the surface of a protein by oligo(ethylene glycol) (EG(n)) linkers of different lengths (n = 0, 2, 5, 10, and 20) and compares these experimental values with theoretical estimates from polymer theory. As expected, the value of M(eff) is lowest when the linker is too short (n = 0) to allow the ligand to bind noncovalently at the active site of the protein without strain, is highest when the linker is the optimal length (n = 2) to allow such binding to occur, and decreases monotonically as the length increases past this optimal value (but only by a factor of approximately 8 from n = 2 to n = 20). These experimental results are not compatible with a model in which the single bonds of the linker are completely restricted when the ligand has bound noncovalently to the active site of the protein, but they are quantitatively compatible with a model that treats the linker as a random-coil polymer.

[60]fullerene-stoppered porphyrinorotaxanes: pronounced elongation of charge-separated-state lifetimes.

A series of Sauvage-type porphyrinorotaxanes containing [60]fullerene stoppers have been synthesized by a convergent route. Photoinduced energy transfer and electron-transfer reactions in these rotaxanes yield long-distance charge-separated radical-pair states, whose lifetimes in solution at ambient temperatures are as high as 32 mus, depending on the distance between the fullerene and zinc porphyrin chromophores.