Flavin photochemistry in the analysis of electron transfer reactions: role of charged and hydrophobic residues at the carboxyl terminus of ferredoxin-NADP(+) reductase in the interaction with its substrates

The enzyme Ferredoxin-NADP(+) reductase participates in the reductive side of the photosynthetic chain transferring electrons from reduced Ferredoxin (Fd) (or Flavodoxin (Fld)) to NADP(+), a process that yields NADPH that can be used in many biosynthetic dark reactions. The involvement of specific amino acids in the interaction between the two proteins has been studied using site-directed mutagenesis. In the present study, the participation of charged (H299), polar (T302) or hydrophobic (V300) amino acid residues that are in the NADP(+)-binding domain of the reductase have been examined by analyzing its C-terminal region, which is located close to the active site. Stopped-flow and laser flash photolysis results of the reaction in which these mutant proteins participate show very little differences with respect to the wild-type protein. These results suggest that the NADPH-binding domain of the reductase has little effect on the processes of recognition and electron transfer to (and from) Fd or Fld, according to the recently reported crystallographic structure of the FNR/Fd complex.     

Liquid chromatography/time-of-flight mass spectrometric analyses for the elucidation of the photodegradation products of triclosan in wastewater samples

Liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOFMS) was applied for the identification of four new photodegradation products of triclosan, a major antimicrobial agent used in personal care products. Wastewater samples, spiked at 7 microg/mL with triclosan, were irradiated with natural sunlight in order to generate the photodegradation products. Aliquots of the spiked water samples were taken at different times of irradiation and compounds were isolated from the water samples by solid-phase extraction. Separation and detection of the compounds and degradation products were accomplished by LC/TOFMS, which provided highly selective information about elemental compositions. Accurate mass measurements for the four degradation products permitted postulation of proposed empirical formulae in this study. Replacement of chlorine atoms by hydroxyl groups and chlorine losses are the major degradation pathways proposed. The degradation products were formed also under environmental conditions in wastewater matrices, thus suggesting their presence in real wastewater treatment processes.     

Synthesis and Properties of 2‐Phenylbenzoxazole‐Based Luminophores for in situ Photopolymerized Liquid‐Crystal Films

We report the synthesis of a series of blue‐emitting 2‐phenylbenzoxazoles (PBOs) substituted at either the 5‐ or 6‐position of the benzoxazole ring and the para‐position of the phenyl substituent. The thermal and optical properties of the materials can be rationalized in terms of the position of the substituent at the benzoxazole moiety and the electron‐withdrawing or electron‐donating character of the substituents. From the results, we conclude that the combination of an electron‐donating substituent at the benzoxazole fragment and an electron‐withdrawing one at the phenyl fragment has a more marked effect on the electronic properties of the aromatic PBO core than other possibilities. This particular combination gives luminophores that are suitable for optical applications on the basis of their high emission efficiency and photostability. In view of that, oriented films were prepared by in situ polymerization of a mixture of a liquid crystalline direactive matrix containing 5% (w/w) of the luminophore. The films exhibit linearly polarized emission.     

On cyclic <Emphasis Type=Italic>p</Emphasis>-gonal Riemann surfaces with several <Emphasis Type=Italic>p</Emphasis>-gonal morphisms

Let p be a prime number, p > 2. A closed Riemann surface which can be realized as a p-sheeted covering of the Riemann sphere is called p-gonal, and such a covering is called a p-gonal morphism. If the p-gonal morphism is a cyclic regular covering, the Riemann surface is called a cyclic p-gonal Riemann surface. Accola showed that if the genus is greater than (p − 1)² the p-gonal morphism is unique. Using the characterization of p-gonality by means of Fuchsian groups we show that there exists a uniparametric family of cyclic p-gonal Riemann surfaces of genus (p − 1)² which admit two p-gonal morphisms. In this work we show that these uniparametric families are connected spaces and that each of them is the Riemann sphere without three points. We study the Hurwitz space of pairs (X, f), where X is a Riemann surface in one of the above families and f is a p-gonal morphism, and we obtain that each of these Hurwitz spaces is a Riemann sphere without four points.     

Synthesis and anion recognition studies of new ureylbenzamide-based receptors

A new group of ureylbenzamide-based receptors (1–4) has been synthesized; its binding affinity and capacity to form supramolecular complexes in solution with different anions have been investigated. For designing these receptors, it was considered a combination of the positions of the urea and amide groups (ortho and meta), and the chromophore groups naphthyl and nitrophenyl, yielding four receptors. The position and chromophore structure affected the acidity of the urea and amide hydrogens in the order 4>3>2>1. All the spectroscopic studies showed a significant change of 1 and 2 compared with 3 and 4 in the presence of different TBAX salts in acetonitrile. The ¹H-NMR spectra show a preferential interaction of the anions with the urea group in receptors 1 and 2 due to the less steric hindrance, while there is a cooperative interaction of amide group in receptors 3 and 4 due to the closeness of both groups.     

Cold crystallization and multiple melting behavior of poly(l-lactide) in homogeneous and in multiphasic epoxy blends

Cold crystallization and melting of poly(l-lactide) (PLLA) blended with an uncured or with an amino-cured epoxy resin (diglycidyl ether of bisphenol-A [DGEBA]) were investigated. It was found that the uncured PLLA/DGEBA blends were miscible, as they exhibited a single composition-dependent glass transition temperature (T _g). Melting point depression measurements indicated the existence of some type of interaction between the blend components, which was confirmed by Fourier transform infrared spectroscopy. Depending on the crystallization conditions and on the blend composition, a mixture of α and α′ crystals have been detected in PLLA and in uncured DGEBA/PLLA blends when crystallized from the glassy state. At high DGEBA contents, preferably imperfect α crystals are formed. On the contrary, at low DGEBA contents, the α′ form predominates and an exotherm associated to the α′–α transformation appears on the differential scanning calorimetry (DSC) scan before the main melting peak. Upon curing, the system transforms from a homogeneous mixture with a single refractive index into an opaque multiphasic one, as revealed by the existence of two T _gs in the DSC scans. These cross-linked immiscible blends displayed a single crystallization exotherm which scarcely changed with composition, and PLLA cold crystallized mainly into the α′ form from an almost pure PLLA phase; subsequently, the α′ crystals transform into the α form just before melting during the DSC scan.     

Tri-[Pt2Tl]3- and polynuclear chain [Pt-Tl]infinity- complexes based on nonbridged Pt(II)-Tl(I) bonds: solid state and frozen solution photophysical properties

Treatment of (NBu4)2[PtR4] (R = C6F5) with 1 or 0.5 equiv of TlNO3 in EtOH/H(2)O produces colorless crystals of trinuclear complex (NBu4)3[Tl{PtR4}2], 1, in which the Tl+ center is complexed by two [PtR4]2- fragments (Pt-Tl = 2.9777(4) and 3.0434(4) A). The expected mixed complex with a Pt/Tl composition of 1:1, 2, is generated as an orange microcrystalline solid by treating [PtR4]2- with a large excess of TlNO3 (approximately 8 equiv). Crystallographic analysis of 2 reveals the formation of a novel one-dimensional (1D) heterometallic linear chain (NBu4)(infinity)[Tl{PtR4}](infinity), 2, formed by alternating a [PtR4]2- fragment and a Tl+ center with a uniform Pt-Tl bond separation along the chain of 3.0321(2) A. Surprisingly, treatment of (NBu4)2[PtR4] with 1 equiv of TlPF6 in EtOH yields pale greenish-yellow needles of an unusual adduct, 2.{(NBu4)(PF6)}(infinity) (3), which was found to form a similar extended linear chain, {TlPtR4}(infinity), constructed by two alternating Pt-Tl separations, a shorter (3.1028(6) A) one and a longer (3.2306(6) A) one. The solid state and solution photophysical properties have been examined. While complex 1 shows a high-energy MM'CT blue phosphorescence (450 nm), the extended chain in 2 exhibits a lower-energy emission (582 nm) than that in adduct 3 (505 nm). For products 2 and 3, interesting luminescence thermochromism is observed in frozen solutions. The emissions are found to be strongly dependent on the solvent, concentration, and excitation wavelength.