Phenylalanine In Solution Research Articles

Photoprotective Steering of Previtamin D3 Photochemistry by Phenylalanine in Solution

Provitamin D3 is the biological precursor to naturally formed vitamin D3 in humans, and its conversion is initiated via photoexcitation by near ultraviolet light. Following an initial photolysis, the primary intermediate, known as previtamin D3, is prone to light-induced isomerization or recyclization, which creates byproducts that limit the desired final thermal conversion to vitamin D3. The branching of the photochemical reaction is highly wavelength-dependent, whereby excitation toward the blue edge of the provitamin D3 absorption spectrum tends to terminate the reaction with the most undesired tachysterol byproduct and the lowest previtamin D3 concentration. In this work, the influence of introducing the natural amino acid phenyalanine as an excitation energy donor to the photochemical reaction is investigated. We find that the incorporation of phenylalanine into provitamin D3 solution results in greater intermediate concentrations and prolonged lifetimes of the desired previtamin D3 while simultaneously reducing the final concentration of tachysterol when exposing the solution to wavelengths at the blue edge of the provitamin D3 spectrum. The results, coupled with quantum chemical analysis, suggest that phenylalanine indeed helps to funnel energy from shorter wavelengths more effectively into the provitamin D3 precursor, while simultaneously screening those wavelengths from direct excitation, which otherwise leads to enhanced concentrations of tachysterol byproduct at the expense of previtamin D3.

Radiolysis of phenylalanine in solution with Bragg-Peak energy protons

Phenylalanine aqueous solutions were irradiated with Bragg-Peak energy protons (0.6–5.6 MeV). An innovative circulation setup has been developed for the irradiation of these solutions with low-energy protons. Every detectable radiolysis product has been identified and quantified after irradiation. While tyrosines are well-known products of phenylalanine radiolysis, 2,5-dihydroxyphenylalanine and dimers were detected in high quantities, for the first time. The track-yields (G'-values) of all products formed under proton irradiation were determined and compared to those obtained with gamma-rays, and 2,5-dopa and dimers production seems to be specific to accelerated ions. A bi-radical mechanism could explain their higher production with a higher density of energy deposition in the track structure.

Quantum chemical simulation of hydration and association of phenylalanine in solution

A quantum chemical simulation of the structure of a hydrated phenylalanine zwitterion, dimers and larger phenylalanine associates in an aqueous solution is performed by the hybrid B3LYP density functional method with the 6-31G++(d,p) basis set. It is shown that the association of the amino acid occurs by the formation of hydrogen bonds between phenylalanine amino carboxyl groups involving water molecules.

Application of a quartz crystal nanobalance to the molecularly imprinted recognition of phenylalanine in solution

A quartz crystal nanobalance (QCN) biosensor was developed for the selective determination of phenylalanine (Phe) in aqueous solutions. A Phe imprinted copolymer was synthesized using polyacrylonitrile and acrylic acid [poly(AN-co-AA)]. The copolymer was then coated on quartz crystal electrode to form complementary structures for the template recognition of Phe. The composite electrode was then used to determine Phe levels in solution. Determinations were based on frequency shifts of molecularly imprinted polymer (MIP) modified quartz crystal electrode caused by Phe adsorption. The frequency shifts were linearly dependent on Phe concentration over the range 50∼500 mgL−1. The results obtained show that the imprinted poly(AN-co-AA) modified biosensor had higher sensitivity (0.5839 Hz/mgL−1) than a non-molecularly imprinted copolymer (0.2724 Hz/mgL−1). Furthermore, good reproducibility, R.S.D. = 1.84% (n = 7) was observed, and the detection limit was 45 mgL−1. The selectivity of the imprinted poly(AN-co-AA) modified biosensor was examined using a number of analytes similar to Phe, i.e., dopamine (DA), ascorbic acid (AscA), vanillylmandelic acid (VMA), uric acid (UA), tryptophan (Trp), and tyrosine (Tyr), and the results obtained showed a size dependent selective effect.

Chemically bound gold nanoparticle arrays on silicon: assembly, properties and SERS study of protein interactions

A highly reproducible and facile method for formation of ordered 2 dimensional arrays of CTAB protected 50 nm gold nanoparticles bonded to silicon wafers is described. The silicon wafers have been chemically modified with long-chain silanes terminated with thiol that penetrate the CTAB bilayer and chemically bind to the underlying gold nanoparticle. The silicon wafer provides a reproducibly smooth, chemically functionalizable and non-fluorescent substrate with a silicon phonon mode which may provide a convenient internal frequency and intensity calibration for vibrational spectroscopy. The CTAB bilayer provides a potentially biomimetic environment for analyte, yet allows a sufficiently small nanoparticle separation to achieve a significant electric field enhancement. The arrays have been characterized using SEM and Raman spectroscopy. These studies reveal that the reproducibility of the arrays is excellent both between batches (<10% RSD) and across a single batch (<5% RSD). The arrays also exhibit good stability, and the effect of temperature on the arrays was also investigated. The interaction of protein and amino acid with the nanoparticle arrays was investigated using Raman microscopy to investigate their potential in bio-SERS spectroscopy. Raman of phenylalanine and the protein bovine pancreatic trypsin inhibitor, BPTI were studied using 785 nm excitation, coincident with the surface plasmon absorbance of the array. The arrays exhibit SERS enhancements of the order of 2.6 x 10(4) for phenylalanine, the standard deviation on the relative intensity of the 1555 cm(-1) mode of phenylalanine is less than 10% for 100 randomly distributed locations across a single substrate and less than 20% between different substrates. Significantly, comparisons of the Raman spectra of the protein and phenylalanine in solution and immobilized on the nanoparticle arrays indicates that the protein is non-randomly orientated on the arrays. Selective SERS enhancements suggest that aromatic residues penetrate through the bilayer inducing conformational changes in the protein.

Non-bonded aromatic–amide attraction in 5-benzyl-3-arylhydantoins

Proton and 13C n.m.r. and X-ray diffraction evidence has been presented for non-bonded aromatic-amide attraction leading to a folded structure for hydantoin derivatives of phenylalanine in solution and in the solid state.