RESUMO
We present here the high-resolution structure of an antiparallel DNA triplex in which a monomer of para-twisted intercalating nucleic acid (para-TINA: (R)-1-O-[4-(1-pyrenylethynyl)phenylmethyl]glycerol) is covalently inserted as a bulge in the third strand of the triplex. TINA is a potent modulator of the hybridization properties of DNA sequences with extremely useful properties when conjugated in G-rich oligonucleotides. The insertion of para-TINA between two guanines of the triplex imparts a high thermal stabilization (ΔTM = 9ºC) to the structure and enhances the quality of NMR spectra by increasing the chemical shift dispersion of proton signals near the TINA location. The structural determination reveals that TINA intercalates between two consecutive triads, causing only local distortions in the structure. The two aromatic moieties of TINA are nearly coplanar, with the phenyl ring intercalating between the flanking guanine bases in the sequence, and the pyrene moiety situated between the Watson-Crick base pair of the two first strands. The precise position of TINA within the triplex structure reveals key TINA-DNA interactions, which explains the high stabilization observed and will aid in the design of new and more efficient binders to DNA.
Assuntos
DNA , Glicerol , Conformação de Ácido Nucleico , Pirenos , DNA/química , Guanina , Hibridização de Ácido Nucleico , Oligonucleotídeos/química , Pirenos/química , Glicerol/análogos & derivados , Glicerol/químicaRESUMO
Glycocin F (GccF), a ribosomally synthesized, post-translationally modified peptide secreted by Lactobacillus plantarum KW30, rapidly inhibits the growth of susceptible bacteria at nanomolar concentrations. Previous studies have highlighted structural features important for its activity and have shown the absolute requirement for the Ser18 O-linked GlcNAc on the eight-residue loop linking the two short helices of the (C-X6-C)2 structure. Here, we show that an ostensibly very small chemical modification to Ser18, the substitution of the Cα proton with a methyl group, reduces the antimicrobial activity of GccF 1000-fold (IC50 1.5 µM cf. 1.5 nM). A comparison of the GccFα-methylSer18 NMR structure (PDB 8DFZ) with that of the native protein (PDB 2KUY) showed a marked difference in the orientation and mobility of the loop, as well as a markedly different positioning of the GlcNAc, suggesting that loop conformation, dynamics, and glycan presentation play an important role in the interaction of GccF with as yet unknown but essential physiological target molecules.
Assuntos
Anti-Infecciosos , Peptídeos , Peptídeos/química , Espectroscopia de Ressonância Magnética , Imageamento por Ressonância Magnética , Estrutura Secundária de Proteína , Anti-Infecciosos/farmacologiaRESUMO
Integrated service delivery, providing coordinated services in a convenient manner, is important in HIV prevention and treatment for adolescents as they have interconnected health care needs related to HIV care, sexual and reproductive health and disease prevention. This review aimed to (1) identify key components of adolescent-responsive integrated service delivery in low and middle-income countries, (2) describe projects that have implemented integrated models of HIV care for adolescents, and (3) develop action steps to support the implementation of sustainable integrated models. We developed an implementation science-informed conceptual framework for integrated delivery of HIV care to adolescents and applied the framework to summarize key data elements in ten studies or programs across seven countries. Key pillars of the framework included (1) the socioecological perspective, (2) community and health care system linkages, and (3) components of adolescent-focused care. The conceptual framework and action steps outlined can catalyze design, implementation, and optimization of HIV care for adolescents.
Assuntos
Prestação Integrada de Cuidados de Saúde , Infecções por HIV , Serviços de Saúde Reprodutiva , Humanos , Adolescente , Infecções por HIV/prevenção & controle , Comportamento Sexual , Saúde ReprodutivaRESUMO
BACKGROUND: The high prevalence of HIV among adolescent girls and young women aged 15-24 in Eastern and Southern Africa indicates a substantial need for accessible HIV prevention and treatment services in this population. Amidst this need, Zambia has yet to meet global testing and treatment targets among adolescent girls and young women living with HIV. Increasing access to timely, high-quality HIV services in this population requires addressing the intensified anticipated and experienced stigma that adolescent girls and young women often face when seeking HIV care, particularly stigma in the health facility setting. To better understand the multi-level drivers and manifestations of health facility stigma, we explored health workers' perceptions of clinic- and community-level stigma against adolescent girls and young women seeking sexual and reproductive health, including HIV, services in Lusaka, Zambia. METHODS: We conducted 18 in-depth interviews in August 2020 with clinical and non-clinical health workers across six health facilities in urban and peri-urban Lusaka. Data were coded in Dedoose and thematically analyzed. RESULTS: Health workers reported observing manifestations of stigma driven by attitudes, awareness, and institutional environment. Clinic-level stigma often mirrored community-level stigma. Health workers clearly described the negative impacts of stigma for adolescent girls and young women and seemed to generally express a desire to avoid stigmatization. Despite this lack of intent to stigmatize, results suggest that community influence perpetuates a lingering presence of stigma, although often unrecognized and unintended, in health workers and clinics. CONCLUSIONS: These findings demonstrate the overlap in health workers' clinic and community roles and suggest the need for multi-level stigma-reduction approaches that address the influence of community norms on health facility stigma. Stigma-reduction interventions should aim to move beyond fostering basic knowledge about stigma to encouraging critical thinking about internal beliefs and community influence and how these may manifest, often unconsciously, in service delivery to adolescent girls and young women.
Assuntos
Infecções por HIV , Adolescente , Feminino , Infecções por HIV/epidemiologia , Infecções por HIV/prevenção & controle , Humanos , Pesquisa Qualitativa , Comportamento Sexual , Estigma Social , Zâmbia/epidemiologiaRESUMO
The effect on secondary structure and antimicrobial activity of introducing different cyclic constraints in linear ß-hairpin antimicrobial peptides has been investigated with the intention of generating cyclic ß sheets as promising antimicrobials with improved therapeutic potential. The linear peptides were cyclized head to tail either directly or after the addition of either a second turn motif or a disulfide bridge. The propensity of these peptides to adopt a cyclic ß-sheet structure has been correlated to their antibacterial activity. All cyclic peptides showed enhanced activity, compared with their linear counterparts against methicillin-resistant Staphylococcus aureus. Scanning electron microscopy and transmission electron microscopy studies showed that this family kills bacteria through membrane lysis. The peptide that showed the best efficacy against all strains (exhibiting nanomolar activity), while retaining low haemolysis, bears two symmetrical, homochiral d-phe-2-Abz-d-ala turns and adopted a flexible structure. Its twin peptide that bears heterochiral turns (one with d-ala and one with L-Ala) showed reduced antibacterial activity and higher percentage of haemolysis. Circular dichroism and nuclear magnetic resonance spectroscopy indicate that heterochirality in the two turns leads to oligomerization of the peptide at higher concentrations, stabilizing the ß-sheet secondary structure. More rigid secondary structure is associated with lower activity against bacteria and loss of selectivity.
Assuntos
Antibacterianos/farmacologia , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Peptídeos Cíclicos/farmacologia , Antibacterianos/química , Testes de Sensibilidade Microbiana , Peptídeos Cíclicos/química , Estrutura Secundária de ProteínaRESUMO
A quaternary ammonium butylsulfonyl phosphoramidate group (N+) was designed to replace all the phosphates in a G-rich oligodeoxynucleotide d(TG4 T), resulting in a formally charge-neutral zwitterionic N+TG4 T sequence. We evaluated the effects of N+phosphate modifications on the structural, thermodynamic and kinetic properties of the parallel G-quadruplexes (G4) formed by TG4 T and compared them to the properties of the recently published phosphoryl guanidine d(TG4 T) (PG-TG4 T). Using size-exclusion chromatography, we established that, unlike PG-TG4 T, which exists as a mixture of complexes of different molecularity in solution, N+TG4 T forms an individual tetramolecular complex. In contrast to PG modifications that destabilized G4s, the presence of N+ modifications increased thermal stability relative to unmodified [d(TG4 T)]4 . The initial stage of assembly of N+TG4 T proceeded faster in the presence of Na+ than K+ ions and, similarly to PG-TG4 T, was independent of the salt concentration. However, after complex formation exceeded 75 %, N+TG4 T in solution with Na+ showed slower association than with K+ . N+TG4 T could also form G4s in solution with Li+ ions at a very low strand concentration (10â µM); something that has never been reported for the native d(TG4 T). Charge-neutral PG-G4s can invade preformed native G4s, whereas no invasion was observed between N+and native G4s, possibly due to the increased thermal stability of [N+TG4 T]4 . The N+ modification makes d(TG4 T) fully resistant to enzymatic digestion, which could be useful for intracellular application of N+-modified DNA or RNA.
Assuntos
DNA/síntese química , Oligodesoxirribonucleotídeos/química , Fosfatos/química , DNA/química , Quadruplex G , Potássio/química , Sódio/químicaRESUMO
PURPOSE: Breast cancer is the leading cause of cancer-related deaths in women younger than 40 years. We aim to evaluate cost as a barrier to care among female breast cancer patients diagnosed between 18 to 39 years. METHODS: In early 2017, we distributed a survey to women diagnosed with breast cancer between the ages of 18 and 39 years, as identified by the central cancer registries of California, Georgia, North Carolina, and Florida. We used multivariable statistics to explore cost-related barriers to receiving breast cancer care for the 830 women that completed the survey. RESULTS: About half of the women (47.4%) reported spending more on breast cancer care than expected, and almost two-thirds (65.3%) had not discussed costs with their care team. A third of the patients (31.8%) indicated forgoing care due to cost. Factors associated with not receiving anticipated care due to cost included age less than35 years at diagnosis, self-insurance, comorbid conditions, and late-stage diagnosis. CONCLUSION: Previous studies using breast cancer registry data have not included detailed insurance information and care received by young women. Young women with breast cancer frequently forgo breast cancer care due to cost. Our results highlight the potential for policies that facilitate optimal care for young breast cancer patients which could include the provision of comprehensive insurance coverage.
Assuntos
Neoplasias da Mama/diagnóstico , Custos de Cuidados de Saúde/estatística & dados numéricos , Acessibilidade aos Serviços de Saúde , Adolescente , Adulto , Feminino , Humanos , Sistema de Registros , Inquéritos e Questionários , Adulto JovemRESUMO
The thermodynamic stability of a cytosine(C)-rich i-motif tract of DNA, which features pH-sensitive [C..H..C]+ moieties, has been studied as function of both pressure (0.1-200â MPa) and pH (3.7-6.2). Careful attention was paid to correcting citrate buffer pH for known variations that stem from changes in pressure. Once pH-corrected, (i) at pH >4.6 the i-motif becomes less stable as pressure is increased (KD decreases), giving a small negative volume change for dissociation (ΔD V°) of the i-motif - a conclusion opposite to that which would be drawn if the buffer pH was not corrected for the effects of pressure; (ii) the i-motif's melting temperature increases by more than 30â K between pHâ 6.5 and 4.5, the consequence of an enthalpy for dissociation (ΔD H°) of 77(3) and 90(3)â kJ (mol H+ )-1 at 0.1 and 200â MPa, respectively; (iii) below pHâ 4.6 at 0.1â MPa (pHâ 4.3 at 200â MPa) the melting temperature decreases as a result of double protonation of cytosine pairs, and ΔD H° and ΔD V° change signs; and (iv) the combination of ΔD H° and ΔD V° lead to the melting temperature at pHâ 4.3 being 3â K higher at 200â MPa than at 0.1â MPa.
Assuntos
DNA/química , Sequência de Bases , Dicroísmo Circular , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Conformação de Ácido Nucleico , Pressão , Termodinâmica , Temperatura de TransiçãoRESUMO
Skin is made up of mainly collagen type I and its structure is stabilised by the formation of covalent immature and mature crosslinks. In this study, collagen immature crosslink hydroxylysinonorleucine (HLNL) was isolated from bovine skin in high purity using two sequential purification steps. These consisted of preparative fibrous cellulose and size exclusion chromatography. The purified crosslink was then analysed using tandem mass spectrometry and high-resolution nuclear magnetic resonance (NMR) spectroscopy. The mass of singly and doubly charged ions of HLNL was 292.1865 and 146.5970 m/z and their optimised fragmentation energy was 17 keV and 5 keV, respectively. The 13C NMR of HLNL showed a doubled-up peak at 67.84 and 67.91 ppm which corroborated a diastereomeric form of collagen immature crosslink HLNL and both are chiroptically indistinguishable. The chemical structure was fully resolved using 1H, 13C and DEPT-135 high-resolution NMR spectroscopy and compared with other previous studies. We also obtained for the first time the 2D NMR spectra COSY and HSQC of HLNL. We therefore suggested that collagen organization into specific fibrils' orientation may be affected by the different configuration of these diastereomers of HLNL.
Assuntos
Colágeno Tipo I/metabolismo , Reagentes de Ligações Cruzadas/química , Reagentes de Ligações Cruzadas/isolamento & purificação , Dipeptídeos/química , Dipeptídeos/isolamento & purificação , Espectroscopia de Ressonância Magnética , Pele/metabolismo , Animais , Bovinos , Reagentes de Ligações Cruzadas/metabolismo , Dipeptídeos/metabolismo , Imageamento por Ressonância MagnéticaRESUMO
Here we demonstrate G-quadruplex formation by oligodeoxynucleotides containing α-2'-deoxyguanosine (α-dG) as a sole source of guanosines in G4T4, G4T4G4 and T(G3Tn)3G3T sequences with various numbers of natural ß-T in the loops (n = 1-4). Based on circular dichroism spectra we observed that all α-dG-containing DNAs formed G-quadruplexes with uniform arrangement of α-dG-tetrads, which implies formation of G-quadruplexes of parallel topology. In several cases, native DNA structures that usually adopt an antiparallel topology were converted to more thermally stable G-quadruplexes of parallel topology. Using 2D ROESY NMR spectra a new 'sequential walk' was established for α-dGs in a tetramolecular, parallel complex formed by the α-G4ß-T4 sequence. Analysis of ROEs in α-dGs indicates that guanines in [α-G4ß-T4]4 adopt anti-glycosidic conformations. These results demonstrate that α-dG can be used for an antiparallel-to-parallel switch of G-quadruplex DNAs producing complexes with higher thermal stability and uniform stacking of α-dG-tetrads.
Assuntos
DNA/química , Desoxiguanosina/química , Quadruplex G , Ressonância Magnética Nuclear BiomolecularRESUMO
APOBEC3 proteins are double-edged swords. They deaminate cytosine to uracil in single-stranded DNA and provide protection, as part of our innate immune system, against viruses and retrotransposons, but they are also involved in cancer evolution and development of drug resistance. We report a solution-state model of APOBEC3A interaction with its single-stranded DNA substrate obtained with the 'method of small changes'. This method compares pairwise the 2D 15N-1H NMR spectra of APOBEC3A bearing a deactivating mutation E72A in the presence of 36 slightly different DNA substrates. From changes in chemical shifts of peptide N-H moieties, the positions of each nucleotide relative to the protein can be identified. This provided distance restraints for molecular-dynamic simulations to derive a 3-D molecular model of the APOBEC3A-ssDNA complex. The model reveals that loops 1 and 7 of APOBEC3A move to accommodate substrate binding, indicating an important role for protein-DNA dynamics. Overall, our method may prove useful to study other DNA-protein complexes where crystallographic techniques or full NMR structure calculations are hindered by weak binding or other problems. Subsequent to submission, an APOBEC3A structure with a bound DNA oligomer was published and coordinates released, which has provided an unbiased validation of the 'method of small changes'.
Assuntos
Citidina Desaminase/metabolismo , DNA de Cadeia Simples/metabolismo , Espectroscopia de Ressonância Magnética , Mutação/genética , Proteínas/metabolismo , Fluorescência , Humanos , Simulação de Dinâmica Molecular , Oligonucleotídeos/metabolismo , Especificidade por Substrato , TermodinâmicaRESUMO
The relatively low chemical stability of cytosine compared with other nucleobases is a key concern in origin-of-life scenarios, but the effect of pressure on the rate of hydrolysis of cytosine to uracil remains unknown. Through in situ NMR spectroscopy measurements, it has been determined that the half-life of cytosine at 373.15â K decreases from (18.0±0.7)â days at ambient pressure (0.1â MPa) to (8.64±0.18)â days at high pressure (200â MPa). This yields an activation volume for hydrolysis of (-11.8±0.5)â cm3 mol-1 ; a decrease that is similar to the molar volume of water (18.0â cm3 mol-1 ) and consistent with a tetrahedral 3,3-hydroxyamine transition-state/intermediate species. Similar behaviour was also observed for cytidine. At both ambient and high pressures, the half-life of cytosine decreases significantly as the pH decreases from 7.0 to 6.0. These results provide scant support for the notion that RNA-based life forms originated in high-temperature, high-pressure, acidic environments.
Assuntos
Citosina/química , Uracila/química , Concentração de Íons de Hidrogênio , Hidrólise , Ressonância Magnética Nuclear Biomolecular , PressãoRESUMO
Three linear peptides incorporating d-Phe-2-Abz as the turn motif are reported. Peptide 1, a hydrophobic ß-hairpin, served as a proof of principle for the design strategy with both NMR and CD spectra strongly suggesting a ß-hairpin conformation. Peptides 2 and 3, designed as amphipathic antimicrobials, exhibited broad spectrum antimicrobial activity, with potency in the nanomolar range against Staphylococcus aureus. Both compounds possess a high degree of selectivity, proving non-haemolytic at concentrations 500 to 800 times higher than their respective minimal inhibitory concentrations (MICs) against S. aureus. Peptide 2 induced cell membrane and cell wall disintegration in both S. aureus and Pseudomonas aeruginosa as observed by transmission electron microscopy. Peptide 2 also demonstrated moderate antifungal activity against Candida albicans with an MIC of 50 µM. Synergism was observed with sub-MIC levels of amphotericin B (AmB), leading to nanomolar MICs against C. albicans for peptide 2. Based on circular dichroism spectra, both peptides 2 and 3 appear to exist as a mixture of conformers with the ß-hairpin as a minor conformer in aqueous solution, and a slight increase in hairpin population in 50% trifluoroethanol, which was more pronounced for peptide 3. NMR spectra of peptide 2 in a 1:1 CD3 CN/H2 O mixture and 30 mM deuterated sodium dodecyl sulfate showed evidence of an extended backbone conformation of the ß-strand residues. However, inter-strand rotating frame Overhauser effects (ROE) could not be detected and a loosely defined divergent hairpin structure resulted from ROE structure calculation in CD3 CN/H2 O. The loosely defined hairpin conformation is most likely a result of the electrostatic repulsions between cationic strand residues which also probably contribute towards maintaining low haemolytic activity.
Assuntos
Aminobenzoatos/química , Aminobenzoatos/farmacologia , Antibacterianos/química , Antibacterianos/farmacologia , Antifúngicos/química , Antifúngicos/farmacologia , Candida albicans/efeitos dos fármacos , Oligopeptídeos/farmacologia , Staphylococcus aureus/efeitos dos fármacos , Aminobenzoatos/síntese química , Antibacterianos/síntese química , Antifúngicos/síntese química , Testes de Sensibilidade Microbiana , Oligopeptídeos/química , Oligopeptídeos/isolamento & purificação , Conformação ProteicaRESUMO
Controlling the arrangement of organic chromophores in supramolecular architectures is of primary importance for the development of novel functional molecules. Insertion of a twisted intercalating nucleic acid (TINA) moiety, containing phenylethynylpyren-1-yl derivatives, into a G-rich DNA sequence alters G-quadruplex folding, resulting in supramolecular structures with defined pyrene arrangements. Based on CD, NMR and ESI-mass-spectra, as well as TINA excited dimer (excimer) fluorescence emission we propose that insertion of the TINA monomer in the middle of a dTG4T sequence (i.e. dTGGXGGT, where X is TINA) converts a parallel tetramolecular G-quadruplex into an assembly composed of two identical antiparallel G-quadruplex subunits stacked via TINA-TINA interface. Kinetic analysis showed that TINA-TINA association controls complex formation in the presence of Na(+) but barely competes with guanine-mediated association in K(+) or in the sequence with the longer G-run (dTGGGXGGGT). These results demonstrate new perspectives in the design of molecular entities that can kinetically control G-quadruplex formation and show how tetramolecular G-quadruplexes can be used as a tuneable scaffold to control the arrangement of organic chromophores.
Assuntos
DNA/química , Quadruplex G , Pirenos/química , Sequência de Bases , Dicroísmo Circular , Eletroforese em Gel de Poliacrilamida , Ligação de Hidrogênio , Substâncias Intercalantes/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Espectrometria de Massas por Ionização por ElectrosprayRESUMO
To investigate the assimilation and production of juice metabolites by Saccharomyces cerevisiae during winemaking, we compared the metabolite profiles of 63 Sauvignon blanc (SB) grape juices collected over five harvesting seasons from different locations of New Zealand before and after fermentation by the commercial wine yeast strain EC1118 at 15 °C. Metabolite profiles were obtained using gas chromatography-mass spectrometry and nuclear magnetic resonance and the oenological parameters were determined by Fourier transform infrared spectroscopy. Our results revealed that the amino acids threonine and serine were the most consumed organic nitrogen sources, while proline and gamma-aminobutyric acid were the least consumed amino acids during SB juice fermentation. Saccharomyces cerevisiae metabolised some uncommon nitrogen sources (e.g. norleucine, norvaline and pyroglutamic acid) and several organic acids, including some fatty acids, most likely after fermenting the main juice sugars (glucose, fructose and mannose). However, consumption showed large variation between juices and in some cases between seasons. Our study clearly shows that preferred nitrogen and carbon sources were consumed by S. cerevisiae EC1118 independent of the juice fine composition, whilst the consumption of other nutrient sources mainly depended on the concentration of other juice metabolites, which explains the uniqueness of each barrel of wine.
Assuntos
Carbono/metabolismo , Nitrogênio/metabolismo , Saccharomyces cerevisiae/metabolismo , Vitis/microbiologia , Vinho/microbiologia , Fermentação , Cromatografia Gasosa-Espectrometria de Massas , Espectroscopia de Ressonância Magnética , Metaboloma , Nova Zelândia , TemperaturaRESUMO
A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of -4)-ß-D-GlcpA-(1 â 2)-α-D-Manp-(1â, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > ηs-Stage 2 > ηs-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.
RESUMO
Single-molecule studies continue to grow in popularity. In cases where biopolymer samples of interest exhibit variations in fine-structure between individual chains such single-molecule studies uniquely offer the promise of revealing deep structure-function relationships. Polysaccharides are typically studied in bulk and, as such, their study could greatly benefit from the application of single-molecule techniques. However, while for example single-molecule optical tweezers (OT) studies have become commonplace for DNA, studies of polysaccharides have lagged behind somewhat, complicated by the difficulty of studying molecules that amongst other things have more complex end-group chemistry. Recently, divalent streptavidin linkers have been shown to be capable of concatenating two pieces of biotin-terminated DNA to produce robust composite strings that run intact through conventional gels, and can be used in single-molecule OT experiments (Mohandas, Kent, Raudsepp, Jameson, & Williams, 2022). By using two such streptavidin linkers, biotin-terminated polymers could be inserted between two sections of DNA in order to facilitate single-molecule experiments on biopolymers that are currently difficult to address by other means. Here, we describe a generic approach for placing the required biotin moieties at both ends of polysaccharide chains, producing plug-and-play polysaccharide inserts that can be incorporated into composite polymer strings using streptavidin linking hubs.
Assuntos
Biotina , DNA , Estreptavidina/química , Estreptavidina/metabolismo , Biotina/química , Biotinilação , DNA/química , Polissacarídeos , PolímerosRESUMO
Nanostructured electronic devices, such as those based on graphene, are typically grown on top of the insulator SiO2. Their exposure to a flux of small size-selected silver nanoparticles has revealed remarkably selective adhesion: the graphene channel can be made fully metallized, while the insulating substrate remains coverage-free. This conspicuous contrast derives from the low binding energy between the metal nanoparticles and a contaminant-free passivated silica surface. In addition to providing physical insight into nanoparticle adhesion, this effect may be of value in applications involving deposition of metallic layers on device working surfaces: it eliminates the need for masking the insulating region and the associated extensive and potentially deleterious pre- and postprocessing.
RESUMO
The synthesis and characterization of the fluxional, d(10) cyclotriphosphazene complexes, [MLCl(2)] (M = Zn, Cd, and Hg; L = spiro-[(1,1'-biphenyl)-2,2'-dioxy]tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene), are described. Single-crystal X-ray structures show that the zinc complex has crystallized into two crystal forms: one as a tetrahedral species, with a N(2)Cl(2) donor set in which a geminal pair of the pendant pyridyloxy nitrogen atoms binds to the zinc, and the other as a trigonal-bipyramidal (tbp) one, with an N(3)Cl(2) donor set. The third nitrogen atom comes from the phosphazene ring and the two pyridyl ligands are non-geminal. The asymmetric unit of the cadmium complex contains three structurally distinct molecules. One molecule has a tbp structure similar to that of the zinc complex. The second molecule has a six-coordinate, distorted octahedral geometry around the cadmium center with a N(4)Cl(2) donor set, with three of the nitrogen donor atoms coming from the pendant pyridyloxy arms. The third site contains a tbp complex and a distorted octahedral species with a relative occupancy of 3:1. The identification of these three different forms in the one crystal suggests that the energy difference between the tbp and distorted octahedral isomers is not large. Quantitative analysis of the (1)H NMR and variable-temperature (31)P NMR spectra of the zinc, cadmium, and mercury complexes in a CD(2)Cl(2) solution, coupled with the X-ray structural results, shows that an associative fluxional mechanism (ΔS(++) < -65 J mol(-1) K(-1)) is operating.
RESUMO
BACKGROUND: Proton nuclear magnetic resonance (NMR)-based metabonomics has only recently been applied to nutritional research. The limitation of any analytical technique is its sensitivity in detecting the smallest variation. Alterations in nutrition often produce only subtle metabolic modulations. The objective of this study was to determine if NMR-based metabonomics could detect variations in the metabolic profile of urine from pigs digesting either native casein (NC) or the same casein that had been enzymatically hydrolysed (EHC). NMR permits simultaneous detection of a large number of metabolites, thus allowing detection of unanticipated metabolic fluctuations that may otherwise have gone undetected with the use of only targeted analysis. RESULTS: Partial least squares discriminant analysis identified significantly (P < 0.05) higher urinary excretions of leucine, valine, taurine and glycine by pigs on the EHC-based diet. CONCLUSION: NMR-based metabonomics is a sensitive method that can uncover unanticipated metabolic changes brought about by physicochemical changes to the feedstock (i.e. hydrolysis). The data show a lower efficiency of retention by the kidney of some amino acids following ingestion of a hydrolysed protein.