Generalized analytical expressions for the burning velocity in a combustion model with non-constant transport coefficients and several specific heats

We derive new expressions to estimate the burning velocity of a laminar gas flame in a simplified combustion model based on a one-step single reaction with transport coefficients (mass and heat) depending on temperature, and species with different specific heats. These new expressions generalize the bounds and approximations previously derived by Williams, von Karman, Zeldovich and Frank-Kamenetskii, Benguria and Depassier, and the matching asymptotic expansion method in a two zone model. The comparison of the flame speed predicted by these new analytical expressions with that numerically simulated by the full combustion model for a large variety of cases allows us to determine their range of validity. The upper bound based on the Benguria and Depassier method provides very good approximations for the actual propagation speed of combustion flames, being substantially better than the asymptotic method used in the recent papers.     

Synthesis and optoelectronic properties of transition metal complexes incorporating dithieno[3,2-b:2',3'-d]phosphole ligands

A series of dithieno[3,2-b:2',3'-d]phosphole-based transition metal complexes, including Au, Fe, Pt, Rh and W as central metals have been synthesised and characterised. Structural investigations by X-ray single crystal crystallography supported the high degree of pi-conjugation in the dithienophosphole ligands. This essential requirement for potential applications in molecular electronics and optoelectronics provides small band gaps for the materials. Investigations toward the optoelectronic properties of the respective complexes by fluorescence spectroscopy indicated that systematic alterations of the electronic structure are connected to different variables such as transition metal employed, functionalisation of the dithienophosphole ligands as well as complex geometries. The investigated Pt-based complexes exhibit only poor photoluminescence whereas Rh-, W- and Fe-based species with silyl functionalised dithienophosphole ligands show appreciable photophysical properties. The Au complexes investigated exhibit strong photoluminescence properties with very intriguing features in terms of excitation and emission wavelengths, intensity as well as selectivity.     

Position‐Dependent Effects of Fluorinated Amino Acids on the Hydrophobic Core Formation of a Heterodimeric Coiled Coil

Systematic model investigations of the molecular interactions of fluorinated amino acids within native protein environments substantially improve our understanding of the unique properties of these building blocks. A rationally designed heterodimeric coiled coil peptide (VPE/VPK) and nine variants containing amino acids with variable fluorine content in either position a16 or d19 within the hydrophobic core were synthesized and used to evaluate the impact of fluorinated amino acid substitutions within different hydrophobic protein microenvironments. The structural and thermodynamic stability of the dimers were examined by applying both experimental (CD spectroscopy, FRET, and analytical ultracentrifugation) and theoretical (MD simulations and MM‐PBSA free energy calculations) methods. The coiled coil environment imposes position‐dependent conformations onto the fluorinated side chains and thus affects their packing and relative orientation towards their native interaction partners. We find evidence that such packing effects exert a significant influence on the contribution of fluorine‐induced polarity to coiled coil folding.     

Solvatomorphism of Moxidectin

The solvatomorphism of the anthelmintic drug moxidectin is investigated, and a new solvatomorph with nitromethane is reported. Moreover, the hitherto unknown crystal structures of the solvatomorphs with ethanol and 2-propanol are reported and discussed. The thermal characterization of these solvatomorphs through variable-temperature powder X-ray diffraction analysis (VT-PXRD) is also described, providing new insights into the crystallochemistry of this active pharmaceutical ingredient.     

Orthogonally Positioned Diamino Pyrrole- and Imidazole-Containing Polyamides: Synthesis of 1-(3-Substituted-propyl)-4-nitropyrrole-2-carboxylic Acid and 1-(3-Chloropropyl)-4-nitroimidazole-2-carboxylic Acid

Pyrrole- and imidazole-containing polyamides can be tailored to recognize the DNA 6–8 base pair sequence. We found that adding a second amino group via the N1-position of pyrrole or imidazole in polyamides could enhance their DNA binding affinity and water solubility while retaining sequence specificity. Synthesis of the key 1-substituted-4-nitropyrrole (and imidazole)-2-carboxylic acid building blocks are described.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Directing the secondary structure of polypeptides at will: from helices to amyloids and back again?

An ageing society faces an increasing number of neurodegenerative diseases such as Alzheimer's, Parkinson's, and Creutzfeld-Jacob disease. The deposition of amyloid fibrils is a pathogenic factor causing the destruction of neuronal tissue. Amyloid-forming proteins are mainly alpha-helical in their native conformation, but undergo an alpha-helix to beta-strand conversion before or during fibril formation. Partially unfolded or misfolded beta-sheet fragments are discussed as direct precursors of amyloids. To potentially cure neurodegenerative diseases we need to understand the complex folding mechanisms that shift the equilibrium from the functional to the pathological isoform of the proteins involved. This paper describes a novel approach that allows us to study the interplay between peptide primary structure and environmental conditions for peptide and protein folding in its whole complexity on a molecular level. This de novo designed peptide system may achieve selective inhibition of fibril formation.     

Validation of a simplified procedure for convenient and rapid quantification of reduced and oxidized glutathione in human plasma by liquid chromatography tandem mass spectrometry analysis

Endogenous glutathione (GSH) and glutathione disulfide (GSSG) status is highly sensitive to oxidative conditions and have broad application as a surrogate indicator of redox status in vivo. Established methods for GSH and GSSG quantification in whole blood display limited utility in human plasma, where GSH and GSSG levels are ~3–4 orders of magnitude below those observed in whole blood. This study presents simplified sample processing and analytical LC–MS/MS approaches exhibiting the sensitivity and accuracy required to measure GSH and GSSG concentrations in human plasma samples, which after 5-fold dilution to suppress matrix interferences range from 200 to 500 nm (GSH) and 5–30 nm (GSSG). The utility of the methods reported herein is demonstrated by assay performance and validation parameters which indicate good sensitivity [lower limits of quantitation of 4.99 nm (GSH) and 3.65 nm (GSSG), and high assay precision (intra-assay CVs 3.6 and 1.9%, and inter-assay CVs of 7.0 and 2.8% for GSH and GSSG, respectively). These methods also exhibited exceptional recovery of analyte-spiked plasma samples (98.0 ± 7.64% for GSH and 98.5 ± 12.7% for GSSG). Good sample stability at −80°C was evident for GSH for up to 55 weeks and GSSG for up to 46 weeks, with average CVs <15 and <10%, respectively.     

Fast and Tunable Phosphorescence from Organic Ionic Crystals

Crystalline diphosphonium iodides [MeR₂P-spacer-R₂Me]I with phenylene ( 1 , 2 ), naphthalene ( 3 , 4 ), biphenyl ( 5 ) and anthracene ( 6 ) as aromatic spacers, are photoemissive under ambient conditions. The emission colors (λ_em values from 550 to 880 nm) and intensities (Φ_em reaching 0.75) are defined by the composition and substitution geometry of the central conjugated chromophore motif, and the anion-π interactions. Time-resolved and variable-temperature luminescence studies suggest phosphorescence for all the titled compounds, which demonstrate observed lifetimes of 0.46–92.23 μs at 297 K. Radiative rate constants k_r as high as 2.8×10⁵ s⁻¹ deduced for salts 1 – 3 were assigned to strong spin-orbit coupling enhanced by an external heavy atom effect arising from the anion-π charge-transfer character of the triplet excited state. These rates of anomalously fast metal-free phosphorescence are comparable to those of transition metal complexes and organic luminophores that utilize triplet excitons via a thermally activated delayed fluorescence mechanism, making such ionic luminophores a new paradigm for the design of photofunctional and responsive molecular materials.     

Examining Elementary Teachers’ Engineering Self‐Efficacy and Engineering Teacher Efficacy

Research indicates that teacher efficacy influences student achievement and is situation specific. With the Next Generation Science Standards calling for the incorporation of engineering practices into K–12 classrooms, it is important to identify teachers’ engineering teaching efficacy. A study of K–5 teachers’ engineering self‐efficacy and engineering teaching efficacy revealed that that they have low engineering self‐efficacy and low teacher efficacy related to engineering pedagogical content knowledge. Additionally, significant differences existed in self‐efficacy levels based on gender, ethnicity, Title I school status, and grade level taught.