Fe(III)-polyuronic acid photochemistry: radical chemistry in natural polysaccharide.

The photochemistry of Fe(III) coordinated to natural uronate-containing polysaccharides has been investigated quantitatively in aqueous solution. It is demonstrated that the photoreduction of the coordinated Fe(III) to Fe(II) and oxidative decarboxylation occurs in a variety of uronate-containing polysaccharides. The photochemistry of the Fe(III)-polyuronic acid system generated a radical species during the reaction which was studied using the spin trapping technique. The identity of the radical species from this reaction was confirmed as CO2•- indicating that both bond cleavage of the carboxylate and oxidative decarboxylation after ligand to metal charge transfer radical reactions may be taking place upon irradiation. Degradation of the polyuronic acid chain was investigated with dynamic light scattering, showing a decrease in the hydrodynamic radius of the polymer assemblies in solution after light irradiation that correlates with the Fe(II) generation. A decrease in viscosity of Fe(IIII)-alginate after light irradiation was also observed. Additionally, the photochemical reaction was investigated in plant root tissue (parsnip) demonstrating that Fe(III) coordination in these natural materials leads to photoreactivity that degrades the pectin component. These results highlight that this Fe(III)-polyuronic acid can occur in many natural systems and may play a role in biogeochemical cycling of iron and ferrous iron generation in plants with significant polyuronic acid content.

The role of primary sequence in helical control compared across short α- and ß(3)-peptides.

α-helices are the most common form of secondary structure found in proteins. In order to study controlled protein folding, as well as manipulate the interface of helical peptides with targets in protein-protein interactions, many techniques have been developed to induce and stabilize α-helical structure in short synthetic peptides. Furthermore, short, non-natural ß-peptides have been established that fold into predictable 14-helices that mimic α-helical structure. We created a panel of short 6-8 residue α- and ß-peptides that used confirmed primary sequence design features which influence helical control and directly compared the helicity across peptides with the most minimal epitopes. Using CD spectroscopy, we found that both α- and ß-peptides abided by their respective design principles, with no significant "cross-helicity" inducing an α- or a ß-peptide to fold into the oppositely controlled helix. Generally, the ß-peptide of the most optimal sequence displayed the largest percent of 14-helicity, whereas the two α-peptides of most favorable design showed some α-helicity and a marked 310-helical contribution. Overall, the results can inform future peptidomimetic designs, especially in the development of short, structured peptides with biological function.

Microwave-accelerated surface modification of plasmonic gold thin films with self-assembled monolayers of alkanethiols.

A rapid surface modification technique for the formation of self-assembled monolayers (SAMs) of alkanethiols on gold thin films using microwave heating in <10 min is reported. In this regard, SAMs of two model alkanethiols, 11-mercaptoundecanoic acid (11-MUDA, to generate a hydrophilic surface) and undecanethiol (UDET, a hydrophobic surface), were successfully formed on gold thin films using selective microwave heating in (1) a semicontinuous fashion and (2) a continuous fashion at room temperature (24 h, control experiment, no microwave heating). The formation of SAMs of 11-MUDA and UDET was confirmed by contact angle measurements, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The contact angles for water on SAMs formed by the selective microwave heating and conventional room temperature incubation technique (24 h) were measured to be similar for 11-MUDA and UDET. FT-IR spectroscopy results confirmed that the internal structures of SAMs prepared using both microwave heating and room temperature were similar. XPS results revealed that the organic and sulfate contaminants found on bare gold thin films were replaced by SAMs after the surface modification process had been conducted using both microwave heating and room temperature.

Crystallization of Amino Acids on a 21-well Circular PMMA Platform using Metal-Assisted and Microwave-Accelerated Evaporative Crystallization.

We describe the design and the use of a circular poly(methyl methacrylate) (PMMA) crystallization platform capable of processing 21 samples in Metal-Assisted and Microwave-Accelerated Evaporative Crystallization (MA-MAEC). The PMMA platforms were modified with silver nanoparticle films (SNFs) to generate a microwave-induced temperature gradient between the solvent and the SNFs due to the marked differences in their physical properties. Since amino acids only chemisorb on to silver on the PMMA platform, SNFs served as selective and heterogeneous nucleation sites for amino acids. Theoretical simulations for electric field and temperature distributions inside a microwave cavity equipped with a PMMA platform were carried out to determine the optimum experimental conditions, i.e., temperature variations and placement of the PMMA platform inside a microwave cavity. In addition, the actual temperature profiles of the amino acid solutions were monitored for the duration of the crystallization experiments carried out at room temperature and during microwave heating. The crystallization of five amino acids (L-threonine, L-histidine, L-leucine, L-serine and L-valine HCl) at room temperature (control experiment) and using MA-MAEC were followed by optical microscopy. The induction time and crystal growth rates for all amino acids were determined. Using MA-MAEC, for all amino acids the induction times were significantly reduced (up to ~8-fold) and the crystal growth rates were increased (up to ~50-fold) as compared to room temperature crystallization, respectively. All crystals were characterized by Raman spectroscopy and powder x-ray diffraction, which demonstrated that the crystal structures of all amino acids grown at room temperature and using MA-MAEC were similar.

Rapid Crystallization of L-Alanine on Engineered Surfaces using Metal-Assisted and Microwave-Accelerated Evaporative Crystallization.

This study demonstrates the application of metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique to rapid crystallization of L-alanine on surface engineered silver nanostructures. In this regard, silver island films (SIFs) were modified with hexamethylenediamine (HMA), 1-undecanethiol (UDET), and 11-mercaptoundecanoic acid (MUDA), which introduced -NH(2), -CH(3) and -COOH functional groups to SIFs, respectively. L-Alanine was crystallized on these engineered surfaces and blank SIFs at room temperature and using MA-MAEC technique. Significant improvements in crystal size, shape, and quality were observed on HMA-, MUDA- and UDET-modified SIFs at room temperature (crystallization time = 144, 40 and 147 min, respectively) as compared to those crystals grown on blank SIFs. Using the MA-MAEC technique, the crystallization time of L-alanine on engineered surfaces were reduced to 17 sec for microwave power level 10 (i.e., duty cycle 100%) and 7 min for microwave power level 1 (duty cycle 10%). Raman spectroscopy and powder x-ray diffraction (XRD) measurements showed that L-Alanine crystals grown on engineered surfaces using MA-MAEC technique had identical characteristic peaks of L-alanine crystals grown using traditional evaporative crystallization.

Crystallization of l-alanine in the presence of additives on a circular PMMA platform designed for metal-assisted and microwave-accelerated evaporative crystallization.

Crystallization of l-alanine in the presence of l-valine and l-tryptophan additives on a circular poly(methyl) methacrylate (PMMA) platform designed for Metal-Assisted and Microwave-Accelerated Evaporative Crystallization (MA-MAEC) technique was investigated. Theoretical simulations predicted homogeneous temperature and electric field distributions across the circular PMMA platforms during microwave heating. Crystallization of l-alanine with and without additives on the blank and silver nanoparticle films (SNFs) modified sides of the circular PMMA platform occurred within 32-50 min using MA-MAEC technique, while the identical solutions crystallized within 161-194 min at room temperature. Optical microscopy studies revealed that l-alanine crystals without additives were found to be smaller in size and had several well-developed faces, whereas l-alanine crystals grown with additives appeared to be larger and had only one dominant highly-developed face. Raman spectroscopy and powder X-ray diffraction (XRD) measurements showed that all l-alanine crystals had identical peaks, despite the morphological differences between the l-alanine crystals with and without additives observed by optical microscope images.

Metal-Assisted and Microwave-Accelerated Evaporative Crystallization: Application to L-Alanine.

L-Alanine is an important amino acid that plays a key role in the molecular structure of many proteins. Crystallized forms of this molecule are currently in high demand in chemical, pharmaceutics, and food industries. However, the traditional evaporative crystallization method takes up to several hours to complete and does not always consistently yield usable crystals. Using the metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique, larger and better-organized L-alanine crystals were formed in a fraction of the time using room temperature crystallization. This technique may be applicable to organic molecules other than amino acids and thus will be able to produce the large amount of molecular crystals desired by industries today.