Methyl Resonances Research Articles

Strongly Blue Luminescent Cationic Iridium(III) Complexes with an Electron‐Rich Ancillary Ligand: Evaluation of Their Optoelectronic and Electrochemiluminescence Properties

AbstractTwo strongly blue luminescent cationic heteroleptic iridium complexes 1b and 2b bearing a 4,4′‐bis(dimethylamino)‐2,2′‐bipyridine (dmabpy) ancillary ligand and either 1‐benzyl‐4‐(2,4‐difluorophenyl)‐1H‐1,2,3‐triazole (dFphtl) or 2‐(2,4‐difluorophenyl)‐5‐methylpyridine (dFMeppyH), respectively, have been synthesized and fully characterized. In comparison with other analogues, the interplay of the triazole unit with the dmabpy unit and methylation of the pyridine ring are discussed with respect to the photophysical, electrochemical, and electrochemiluminescent (ECL) properties of the complexes. The two complexes, 1b and 2b, are blue emitters with λmax = 495 and 494 nm, respectively. The nature of the excited states was established by various photophysical and photochemical experiments as well as DFT calculations. Both complexes emit from a ligand‐centered state, however, the emission of 1b possesses significant charge‐transfer character, which is absent in 2b. The presence of the methyl group on the cyclometalating ligand leads only to a modest increase in the radiative rate constant, kr, but otherwise does not appreciably influence the optoelectronic properties of the complex compared with the non‐methylated analogue. In contrast, the efficacy of the ECL emission when scanning to 2.50 V is strongly influenced by the presence of the methyl group. ECL emission is also enhanced in complexes bearing dmabpy ancillary ligands compared with those containing dtBubpy ligands. The two complexes exhibit similar electrochemical behavior. Incorporation of the dmabpy ligand shifts both the oxidation and reduction cathodically. The combination of the dmabpy and dFphtl groups increases the redox potential difference and thus the HOMO–LUMO gap but the emission is not further blueshifted. Thus, the structural modification of the cyclometalating ligand, although only modestly tuning the emission energy, modulates the nature of the excited state and the efficiency of the ECL process.

Toxic effects of imidazolium-based ionic liquids on Caenorhabditis elegans: The role of reactive oxygen species

By using Caenorhabditis elegans (C. elegans) as a model animal, the present work is aimed to evaluate the acute toxicity of imidazolium-based bromide Ionic Liquids (ILs), and to elucidate the underlying mechanisms involved. Firstly, 24-h median lethal concentration (LC50) for eight ILs with different alkyl chain lengths and one or two methyl groups in the imidazolium ring were determined to be in a range of 0.09–6.64mgmL−1. Four ILs were selected to investigate the toxic mechanisms. Mortality, levels of reactive oxygen species (ROS), lipofuscin accumulation and expression of superoxide dismutase 3 in C. elegans were determined after exposed to ILs at sub-lethal concentrations for 12h. A significant increase in the levels of these biomarkers was observed in accordance with the results of 12-h lethality assay. The addition of 0.5% dimethyl sulfoxide, which acts as a radical scavenger, remarkably rescued the lethality of C. elegans and significantly decreased the ROS level in C. elegans. Our results suggest that ROS play an important role in IL-induced toxicity in C. elegans.

Properties of columns with several pyridinium and imidazolium ionic liquid stationary phases

Recent advances in the development of new liquid phases (ILs) made it possible to use some classes of ILs as polar stationary liquid phases (SLP). In our days only alkylimidazolium- and alkylphosphonium-based ILs are widely used as polar SLP. In present work some other types of ILs – pyridinium and cyanopropyl/hydroxypropyl imidazolium were investigated as SLP. Columns with efficiencies 2000–2500 plates/m by high-pressure static method were prepared. Polarity and selectivity of these phases were measured. Selectivity was described in terms of intermolecular interactions by using Abraham solvatation parameter model. The set of the regularities between cation structure of ionic liquid and selectivity has been shown. The number and position of methyl groups in ionic liquid pyridinium ring were shown to have the sufficient influence on all type of molecular interactions. Finally the resolutions of test mixture for the several ionic liquid SLP were obtained. For columns with some ionic liquids the dependencies of the height equivalent to a theoretical plate (HETP) and sample loading capacity were obtained and compared with the conventional phases. It was found that the optimal efficiency for the IL columns is attained at lower carrier gas velocities in comparison with traditional phases. Nevetheless sample loading capacity of IL phases is comparable to those of conventional GC phases.

Image Contrast in Sum Frequency Generation Microscopy Based on Monolayer Order and Coverage

Sum frequency generation imaging microscopy (SFGIM) was used to study a binary system of self-assembled monolayers (SAMs) on evaporated gold. A two-step process that consists of microcontact printing (μCP) and the solution backfilling method is used to generate a sample surface with two distinct SAMs domains. The high contrast chemical identification and the homogeneity map of the SAMs for two different head groups are revealed by processing the three-dimensional images (xy-surface and infrared wavenumbers) obtained from SFGIM. For conformation order analysis, the amplitude ratios of the methylene and methyl symmetric resonance obtained by a nonlinear curve fit of the spatially and spectrally resolved SFG images are used to reconstruct spatial image maps. The conformation order map shows the distribution of gauche defects in SAMs with improved contrast across monodentate and bidentate alkanethiol monolayer regions. The results show that variation of the head group attached on the surface dominantly influences the conformation disorder and surface coverage of the molecules, while the terminal methyl group in both monodentate and bidentate SAMs shows a similar orientation angle.

The Archaeal Exosome: Identification and Quantification of Site-Specific Motions That Correlate with Cap and RNA Binding

The Archaeal Exosome: Identification and Quantification of Site-Specific Motions That Correlate with Cap and RNA Binding

Evaluating the effect and effectiveness of different constructs with a conserved sequence for silencing of Coffea canephora N-methyltransferases

Caffeine biosynthesis involves sequential methylation of the purine ring by the transfer of methyl group from the methyl donor S-adenosyl methionine. Genes that code for the individual methyl transferase have a high degree of sequence homology. To achieve decaffeination by genetic engineering of coffee, the effect and efficiency of different post-transcriptional gene silencing (PTGS) constructs were evaluated. Sense, antisense and invert repeat constructs were developed using a 339 bp fragment from the conserved region of the coffee N-methyltransferase genes involved in caffeine biosynthesis. The silencing constructs were mobilized into Agrobacterium tumefaciens (EHA101). Sonication assisted Agrobacterium-mediated transformation of the somatic embryos of C.canephora was performed, followed by regeneration of the transformants. Molecular analysis and identification of flanking regions confirmed the stable integration of the transgenes in the transformants and their integration in non coding regions of the genome, respectively. Effectiveness of the silencing constructs was evaluated by transcript analysis of the targeted genes by RT-PCR and northern blotting. The silencing efficiency was further evaluated by estimation of the purine alkaloid content in the transgenic lines using HPLC. The three constructs differed in their silencing efficiencies and specificity. Though the constructs were not specific to a single N-methyltransferase, transformants obtained were mainly affected in one of the N-methyltransferases. Results show that the use of homologous coding sequence in the PTGS constructs results in a much higher efficiency in silencing the caffeine biosynthetic pathway. Further, the lowering of caffeine content should be the preferred over complete decaffeination due to extremely low survival rate of transgenic plants with extremely low levels of caffeine.

Orientation of cholesterol in hybrid bilayer membranes calculated from the phases of methyl resonances in sum frequency generation spectra

The phases of Sum Frequency Generation (SFG) vibrational resonances recorded from thin films on metal surfaces provide information on the orientation and tilt angles of the functional groups of molecules in the film. SFG spectra have been simulated for monolayer films in which the adsorbed molecule has an unequal number of methyl groups oriented in two different directions. The phases, on resonance, of the methyl symmetric (r(+)) and asymmetric (r(-)) resonances are determined as a function of the two methyl group tilt angles and the fraction of groups pointing in that particular direction. The results are first presented as two-dimensional projection plots for the r(+) and r(-) resonances and then combined to show the tilt angles of the methyl groups, and fraction of methyl groups in that orientation, for which both resonances are in phase or out of phase with one another. Mathematical expressions have been calculated to identify the precise boundary conditions for when the phases of the r(+) and r(-) resonances change. The results of these simulations are compared to the phases of the methyl resonances in experimental SFG spectra of d7-cholesterol in a hybrid bilayer membrane.

The influence of methyl groups on the torsion angle and on the energetics of 1-phenylpyrrole derivatives: a thermodynamic and computational study

Calorimetric and effusion techniques, complemented by computational calculations were combined to determine the standard (p o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, $$\Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right)$$ , at T = 298.15 K, of 1-(3,5-dichlorophenyl)-2,5-dimethylpyrrole and 2,5-dimethyl-1-phenyl-3-pyrrolecarboxaldehyde, as (107.2 ± 2.7) and (25.9 ± 3.2) kJ mol−1, respectively. These values were derived from the respective standard molar enthalpies of formation, in the crystalline phase, $${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{cr}} \right)$$ , at T = 298.15 K, obtained from combustion calorimetry measurements, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined by the Knudsen effusion mass-loss method. The gas-phase enthalpies of formation of both experimentally studied compounds were also estimated by G3(MP2)//B3LYP computations, using a set of working reactions; the results obtained are in good agreement with the experimental data. With this computational approach, the enthalpies of formation of 1-(3,5-dichlorophenyl)pyrrole, 1-(3,5-dichlorophenyl)-2-methylpyrrole, 1-phenyl-3-pyrrolecarboxaldehyde and 2-methyl-1-phenyl-3-pyrrolecarboxaldehyde were also estimated and a value for their $${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right)$$ has been defined. Moreover, the molecular structures of the six molecules were established, their geometrical parameters were determined and the influence of methyl groups in the pyrrole ring (2 and 5 positions) on the phenyl/pyrrole torsion angle was analyzed. All the results were also interpreted in terms of enthalpic increments.

ω,ω'-DIHETARYL-SUBSTITUTED 2,5-DIMETHYL-1,4-DIVINYLBENZENES

A series of ω ,ω ' -dihetaryl-substituted 2,5-dimethyl-1,4-divinylbenzenes has been synthesized and these show an increased solubility when compared with analogs not containing methyl groups in the central benzene ring. The dependence of spectral parameters on the chemical structure has been analyzed. Authors: R. A. Minakova, A. I. Bedrik, and V. M. Shershukov. English Translation in Chemistry of Heterocyclic Compounds , 1999, 35 (5), pp 617-620 http://link.springer.com/article/10.1007/BF02324649

3,5-Dimethyl-1-{2-[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]acetyl}-2,6-diphenylpiperidin-4-one

In the title compound, C24H25N3O2S2, the piperidine ring adopts a distorted boat conformation. The phenyl rings subtend angles of 75.6 (1)° and 86.3 (1)° with the mean plane of the piperidine ring. In the crystal, mol­ecules are linked through a network C—H⋯N hydrogen bonds, forming zigzag chains along [100]. The thia­diazol ring methyl group is disordered over two positions with an occupancy ratio of 0.69 (4):0.31 (4).

Ionic Conductivities of Binary Mixtures Containing Pyridinium-Based Ionic Liquids and Alkanols

In this study, we have determined ionic conductivities of six binary systems composed of an ionic liquid (1-butylpyridinium tetrafluoroborate, 1-butyl-3methylpyridinium tetrafluoroborate, or 1-butyl-4methylpyridinium tetrafluoroborate) and a short chain alkanol (methanol or ethanol) at four temperatures, T = (293.15, 303.15, 313.15, and 323.15) K. The ionic conductivity data have been correlated using both an empirical equation and the Vogel–Tamman–Fulcher equation. We also have compared the behavior of different mixtures, paying special attention to the influence of methyl group in the pyridine ring and the effect of both alkanols in the mixtures. Ionic conductivities of all the mixtures are bigger than those of the pure components and present a maximum at small mole fractions of the ionic liquid. Moreover, conductivity values are bigger for the binary mixtures containing methanol instead or ethanol. Finally, the relationship between viscosity and ionic conductivity from Waldeńs rule has provided a measurement of the ionicity of the mixtures.

Backbone and ILV methyl resonance assignments of E. coli thymidylate synthase bound to cofactor and a nucleotide analogue

Thymidylate synthase (TSase) is a 62 kDa homodimeric enzyme required for de novo synthesis of thymidine monophosphate in most organisms. This makes the enzyme an excellent target for anticancer and microbial antibiotic drugs. In addition, TSase has been shown to exhibit negative cooperativity and half-the-sites reactivity. For these collective reasons, TSase is widely studied, and much is known about its kinetics and structure as it progresses through a multi-step catalytic cycle. Recently, nuclear magnetic resonance spin relaxation has been instrumental in demonstrating the critical role of dynamics in enzyme function in small model systems. These studies raise questions about how dynamics affect function in larger enzymes with more complex reaction coordinates. TSase is an ideal candidate given its size, oligomeric state, cooperativity, and status as a drug target. Here, as a pre-requisite to spin relaxation studies, we present the backbone and ILV methyl resonance assignments of TSase from Escherichia coli bound to a substrate analogue and cofactor.

Quantifying functional group interactions that determine urea effects on nucleic acid helix formation.

Urea destabilizes helical and folded conformations of nucleic acids and proteins, as well as protein-nucleic acid complexes. To understand these effects, extend previous characterizations of interactions of urea with protein functional groups, and thereby develop urea as a probe of conformational changes in protein and nucleic acid processes, we obtain chemical potential derivatives (μ23 = dμ2/dm3) quantifying interactions of urea (component 3) with nucleic acid bases, base analogues, nucleosides, and nucleotide monophosphates (component 2) using osmometry and hexanol-water distribution assays. Dissection of these μ23 values yields interaction potentials quantifying interactions of urea with unit surface areas of nucleic acid functional groups (heterocyclic aromatic ring, ring methyl, carbonyl and phosphate O, amino N, sugar (C and O); urea interacts favorably with all these groups, relative to interactions with water. Interactions of urea with heterocyclic aromatic rings and attached methyl groups (as on thymine) are particularly favorable, as previously observed for urea-homocyclic aromatic ring interactions. Urea m-values determined for double helix formation by DNA dodecamers near 25 °C are in the range of 0.72-0.85 kcal mol(-1)m(-1) and exhibit little systematic dependence on nucleobase composition (17-42% GC). Interpretation of these results using the urea interaction potentials indicates that extensive (60-90%) stacking of nucleobases in the separated strands in the transition region is required to explain the m-value. Results for RNA and DNA dodecamers obtained at higher temperatures, and literature data, are consistent with this conclusion. This demonstrates the utility of urea as a quantitative probe of changes in surface area (ΔASA) in nucleic acid processes.

(S)-N-[(4-{(S)-1-[2-(4-Methoxybenzamido)-2-methylpropanoyl]pyrrolidine-2-carboxamido}-3,4,5,6-tetrahydro-2H-pyran-4-yl)carbonyl]proline dimethyl sulfoxide monosolvate (4-MeBz-Aib-Pro-Thp-Pro-OH)

The asymmetric unit of the title compound, C28H38N4O8·C2H6OS, contains one tetra­peptide and one disordered dimethyl sulfoxide (DMSO) mol­ecule. The central five-membered ring (Pro2) of the peptide mol­ecule has a disordered envelope conformation [occupancy ratio 0.879 (2):0.121 (2)] with the envelope flap atom, the central C atom of the three ring methylene groups, lying on alternate sides of the mean ring plane. The terminal five-membered ring (Pro4) also adopts an envelope conformation with the C atom of the methylene group closest to the carboxylic acid function as the envelope flap, and the six-membered tetra­hydro­pyrane ring shows a chair conformation. The tetra­peptide exists in a helical conformation, stabilized by an intra­molecular hydrogen bond between the amide N—H group of the heterocyclic α-amino acid Thp and the amide O atom of the 4-meth­oxy­benzoyl group. This inter­action has a graph set motif of S(10) and serves to maintain a fairly rigid β-turn structure. In the crystal, the terminal hy­droxy group forms a hydrogen bond with the amide O atom of Thp of a neighbouring mol­ecule, and the amide N—H group at the opposite end of the mol­ecule forms a hydrogen bond with the amide O atom of Thp of another neighbouring mol­ecule. The combination of both inter­molecular inter­actions links the mol­ecules into an extended three-dimensional framework.

Bare-Minimum Fluorous Mixture Synthesis of a Stereoisomer Library of 4,8,12-Trimethylnonadecanols and Predictions of NMR Spectra of Saturated Oligoisoprenoid Stereoisomers

All four diastereomers of a typical saturated oligoisoprenoid, 4,8,12-trimethylnonadecanol, are made by an iterative three-step cycle with the aid of traceless thionocarbonate fluorous tags to encode configurations. The tags have a minimum number of total fluorine atoms, starting at zero and increasing in increments of one. With suitable acquisition and data processing, each diastereomer exhibits characteristic chemical shifts of methyl resonances in its (1)H and (13)C NMR spectra. Together, these shifts provide a basis to predict the appearance of the methyl region of the spectrum of every stereoisomer of higher saturated oligoisoprenoids.

MAP-XSII: an improved program for the automatic assignment of methyl resonances in large proteins

NMR studies of large proteins have gathered much interest in recent years, especially after methyl-transverse relaxation optimized spectroscopy was successfully applied to systems as large as ~1 MDa in molecular weight. However, to fully take advantage of these spectra, there is a need for convenient and robust methods for making resonance assignments rapidly. Here, we present an improved version of our program MAP-XS (methyl assignment prediction from X-ray structure) for the automatic assignment of methyl peaks, based on nuclear Overhauser effects (NOE) correlations and chemical shifts together with available structures. No manual analysis of the NOE data is needed in this new version, which helps to further accelerate the assignment process. A refined algorithm as well as more efficient sampling produces results from single runs of MAP-XSII using unanalyzed NOE data are comparable to those achieved by the old version using manually curated data with every NOE peak correctly attributed to the two related methyl peaks; in addition, checking the results from multiple parallel runs against each other provides an effective mechanism for getting rid of the wrong assignments while keeping the correct ones, which significantly improves the reliability of final assignments. The new program is tested against three different proteins and delivers ~95 % correct assignments; positive results are also achieved for tests using different cut-off distances for NOEs, structures of lower resolutions, and ambiguous residue types.

Alkaline polymer electrolytes containing pendant dimethylimidazolium groups for alkaline membrane fuel cells

Novel anion exchange membranes (AEMs), based on poly(phenylene oxide) (PPO) chains linked to pendant 1,2-dimethylimidazolium (DIm) functional groups, have been prepared for evaluation in alkaline polymer electrolyte membrane fuel cells (APEFCs). Successful functionalisation of the PPO chains was confirmed using 1H-NMR and FT-IR spectroscopies. The ionic conductivities of the resulting DIm–PPO AEMs at 30 °C are in the ranges of 10–40 mS cm−1 and 18–75 mS cm−1 at 60 °C. The high ionic conductivities are attributed to the highly developed microstructures of the membranes, which feature well-defined and interconnected ionic channels (confirmed by atomic force microscopy, AFM, measurements). Promisingly, the ion-exchange capacities (IECs) of the DIm–PPO AEM are maintained after immersion in an aqueous KOH solution (2 mol dm−3) for 219 h at 25 °C; a previously developed monomethyl imidazolium PPO analogue AEM (Im–PPO) showed a significant decline in IEC on similar treatment. This reduction in undesirable attack by the OH− conducting anions is ascribed to an increase in steric interference and removal of the acidic C2 proton [in the monomethyl Im-groups] by the methyl group in the DIm cationic ring. Moreover, the maximum power densities produced in simple beginning-of-life single cell H2/O2 fuel cell tests increased from 30 mW cm−2 to 56 mW cm−2 when switching from the Im–PPO AEM (fuel cell temperature = 50 °C) to the DIm–PPO-0.54 AEM (fuel cell temperature = 35 °C) respectively (even with the use of lower temperatures).

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

Solid-state NMR is used to characterise dynamics in the ethanol solvate of the pharmaceutical material formoterol fumarate and its associated desolvate. Jump rates and activation barriers for dynamic processes such as phenyl ring rotation and methyl group rotational diffusion are derived from 1D-EXSY and (13)C spin-lattice relaxation times respectively. (2)H and (13)C spin-lattice relaxation times measured under magic-angle spinning conditions are used to show that the fumarate ion in the desolvate is undergoing small-amplitude motion on a frequency scale of 100s of MHz at ambient temperature with an activation parameter of about 32 kJ mol(-1). Exact calculations of relaxation times under MAS provide a simple and robust means to test motional models in cases where relaxation rate maxima are observed, including for systems where the crystal structure of the material is unknown.

Enhanced deep-blue emission from Pt(ii) complexes bound to 2-pyridyltetrazolate and an ortho-xylene-linked bis(NHC)cyclophane

The coordination of 2-pyridyltetrazolate and ortho-xylene-linked bis(NHC)cyclophane to Pt(II) yielded a novel complex characterised by enhanced pure deep-blue emission, whose intensity can be modulated via methylation of the tetrazole ring.

Facile dimethylarsenic exchange and pyramidal inversion in its cysteine and glutathione adducts

Rapid thiolate exchange of dimethylarsonium, Me2As(+), is observed between two different thiolate species in solution. NMR is used to characterize the equilibrium constants for interthiol transfer as well the rapid intra molecular conformational dynamics which leads to the coalescence of diastereotopic methyl resonances. These rapid exchange kinetics have important consequences of arsenic's toxicity and pharmacology.