Variations In Molecular Structure Research Articles

Thermotropic Liquid Crystalline Dimers with Varying Alkoxy Terminal Chain Length

We have design and synthesized of homologous Series I dimers and to study the effect of molecular structure variation and change in alkoxy terminal chain length (n = 6, 7, 8) on mesomorphic properties of liquid crystals. Explore further understanding of the structure-property relationship of liquid crystal homologous Seriesl dimers having varying alkoxy terminal chain length. It was found that the decrease in crystalline phase, smectic C and nematic phase transition temperatures with increasing terminal alkoxy chain length. The molecular structures of the Seriesl dimer were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Their mesomorphic properties were investigated by differential scannning calorimetry (DSC) and on the hot-stage of a polarizing microscope (POM).

Unique reactivity of fluorinated molecules with transition metals.

Organofluorine and organometallic chemistry by themselves constitute two potent areas in organic synthesis. Thus, the combination of both offers many chemical possibilities and represents a powerful tool for the design and development of new synthetic methodologies leading to diverse molecular structures in an efficient manner. Given the importance of the selective introduction of fluorine atoms into organic molecules and the effectiveness of transition metals in C-C and C-heteroatom bond formation, this review represents an interesting read for this aim.

Molecular-structure variation of organic materials irradiated with atmospheric pressure plasma

The effect of atmospheric pressure He plasma on the molecular structure of polyethylene terephthalate (PET) has been investigated. The plasma composition was analyzed using optical emission spectroscopy. In addition to strong He emission lines, lines due to O and N radicals were also detected. The change in the molecular structure of the PET film surface was investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It was found that plasma irradiation led to oxidation and degradation of the surface due to chemical and physical effects of the active species. The results demonstrate the feasibility of observing the interaction of plasma with organic material on a local scale.

Metallo-Folded Single-Chain Nanoparticles with Catalytic Selectivity.

Mimicking the substrate specificity and catalytic activity of enzymes is of great interest for different fields (e.g., chemistry, biology, nanomedicine). Enhanced reaction rates using artificial, enzyme-mimic catalysts based on a variety of molecular structures and nanoentities (e.g., macrocyclic compounds, star and helical polymers, dendrimers) have been previously reported. However, examples of enzyme-sized soft entities displaying substrate specificity are certainly scarce. Herein, we report the synthesis and characterization of single-chain nanoparticles based on metallo-folded polymer chains containing complexed Cu(II) ions showing catalytic specificity during the oxidative coupling of mixtures of chemically related terminal acetylene substrates. This work paves the way for the easy and efficient construction of other Pd-, Ni-, Co-, Fe-, Mn-, or Mo-containing soft nanoentities approaching the substrate specificity of natural enzymes for a variety of organic reactions.

Anion-Based pH Responsive Ionic Liquids: Design, Synthesis, and Reversible Self-Assembling Structural Changes in Aqueous Solution

The creation of pH responsive materials that undergo morphological transitions between micelle and vesicle induced by solution pH change is of great importance for their potential application in drug delivery and biochemical engineering. Here, we have developed a series of 18 pH responsive ionic liquids composed of 1-alkyl-3-methylimidazolium cation, [C(n)mim](+) (n = 4, 6, 8, 10, 12, 14), and different pH responsive anions such as potassium phthalic acid ([C6H4COOKCOO](-)), sodium sulfosalicylic acid ([C6H3OHCOOSO3Na](-)), and sodium m-carboxylbenzenesulfonate ([C6H4COOSO3Na](-)). The aggregation behavior and self-assembly structures of the ILs in aqueous solution have been investigated by surface tension, dynamic light scattering, transmission electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance spectroscopy. It was found for the first time that single tail ionic liquids, [C(n)mim]X (n = 12 and 14, X = [C6H4COOKCOO], [C6H3OHCOOSO3Na], and [C6H4COOSO3Na]) could form vesicles without any additives, and reversible transition was observed between spherical micelles and vesicles with the change of solution pH value. The transition in self-assembly structures is suggested to be driven by the variation in molecular structure and hydrophilicity/hydrophobicity of anions of the ILs.

Influence of Structural Variations in Push–Pull Zinc Porphyrins on Photovoltaic Performance of Dye‐Sensitized Solar Cells

We designed and synthesized two new zinc porphyrin dyes for dye-sensitized solar cells (DSCs). Subtle molecular structural variation in the dyes significantly influenced the performance of the DSC devices. By utilizing these dyes in combination with a cobalt-based redox electrolyte using a photoanode made of mesoporous TiO2 , we achieved a power conversion efficiency (PCE) of up to 12.0 % under AM 1.5 G (100 mW cm(-2)) simulated solar light. Moreover, we obtained a high PCE of 6.4 % for solid-state dye-sensitized solar cells by using 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene as a hole-transporting material.

A1.45 Hyperglycosylation of ACPA-IGG variable domains modulates reactivity to citrullinated antigens

Background and ObjectivesAutoantibodies specific for citrullinated antigens are highly relevant diagnostic and prognostic biomarkers in rheumatoid arthritis and have been considered to be involved in disease pathogenesis. Previous studies have...

Study on the Coupling Behaviour of Microwave Absorption for Sulphide Concentrate

Abstract. The microwave energy absorption of solid mineral in microwave field is the key problem of the microwave metallurgy application. For the calculation formula of absorbing microwave energy (P=2πfε0ε"E2) the fundamental data is necessary, including dielectric constant and electric field strength etc. But these basic data varies in practice due to the variation of molecular structure, overall dimension, and electromagnetic parameter of the mineral. Therefore, the theoretical calculation formula is difficult to predict the microwave absorbing ability of solid mineral [1-3]. In this paper the ability of four kinds of sulphide concentrate and their mixture coupling in absorbing microwave was investigated by intermediate medium calorimetry. The results show that the microwave-absorbing ability of chalcopyrite concentrate is the strongest, sphalerite concentrate is the weakest, and sphalerite concentrate is stronger than silica, the mixture minerals still keep their own microwave absorbing characteristics. The mass percent of strong absorbent of microwave decide the microwave-absorbing ability of mixture, and affect energy transfer between microwave and mineral.

Barley genotype expressing “stay-green”-like characteristics maintains starch quality of the grain during water stress condition

The identification of “stay-green” in sorghum and its positive correlation with yield increases has encouraged attempts to incorporate “stay-green”-like traits into the genomes of other commercially important cereal crops. However, knowledge on the effects of “stay-green” expression on grain quality under extreme physiological stress is limited. This study examines impacts of “stay-green”-like expression on starch biosynthesis in barley (Hordeum vulgare L.) grain under mild, severe, and acute water stress conditions induced at anthesis. The proportions of long amylopectin branches and amylose branches in the grain of Flagship (a cultivar without “stay-green”-like characteristics) were higher at low water stress, suggesting that water stress affects starch biosynthesis in grain, probably due to early termination of grain fill. The changes in long branches can affect starch properties, such as the rates of enzymatic degradation, and hence its nutritional value. By contrast, grain from the “stay-green”-like cultivar (ND24260) did not show variation in starch molecular structure under the different water stress levels. The results indicate that the cultivar with “stay-green”-like traits has a greater potential to maintain starch biosynthesis and quality in grain during drought conditions, making the “stay-green”-like traits potentially useful in ensuring food security.

Tuning the Temperature Dependence for Switching in Dithienylethene Photochromic Switches

Diarylethene photochromic switches use light to drive structural changes through reversible electrocyclization reactions. High efficiency in dynamic photoswitching is a prerequisite for applications, as is thermal stability and the selective addressability of both isomers ring-opened and -closed diarylethenes. These properties can be optimized readily through rational variation in molecular structure. The efficiency with regard to switching as a function of structural variation is much less understood, with the exception of geometric requirements placed on the reacting atoms. Ultimately, increasing the quantum efficiency of photochemical switching in diarylethenes requires a detailed understanding of the excited-state potential energy surface(s) and the mechanisms involved in switching. Through studies of the temperature dependence, photoswitching and theoretical studies demonstrate the occurrence or absence of thermal activation barriers in three constitutional isomers that bear distinct π-conjugated systems. We found that a decrease in the thermal barriers correlates with an increase in switching efficiency. The origin of the barriers is assigned to the decrease in π-conjugation that is concomitant with the progress of the photoreaction. Furthermore, we show that balanced molecular design can minimize the change in the extent of π-conjugation during switching and lead to optimal bidirectional switching efficiencies. Our findings hold implications for future structural design of diarylethene photochromic switches.

Prediction of Milk/Plasma Concentration Ratios of Drugs and Environmental Pollutants Using In Silico Tools: Classification and Regression Based QSARs and Pharmacophore Mapping.

A large set of 185 compounds with diverse molecular structures and different mechanisms of therapeutic actions was used to develop and validate statistically significant classification and regression based QSTR models for predicting partitioning of drugs/chemicals into breast milk. Pharmacophore mapping was also carried out which showed four important features required for lower risk of secretion into milk: (i) hydrophobic group (HYD), (ii) ring aromatic group (RA), (iii) negative ionizable (NegIon) and (iv) hydrogen bond donor (HBA). QSTR and pharmacophore models were rigorously validated internally as well as externally to check the possibilities of any chance correlation and judge the predictive potential of the models. Pharmacological distribution diagrams (PDDs) were used for the classification model as a visualizing technique for the identification and selection of chemicals with lower partitioning into milk. Our in silico models enable to identify the essential structural attributes and quantify the prime molecular pre-requisites which were chiefly responsible for secretion into milk. The developed models were also implemented to screen milk/plasma partitioning potential for a huge number DrugBank database (http://www.drugbank.ca/) compounds.

Nanocrystal Preparation: Low-Energy Precipitation Method Revisited

Nanocrystals have the potential to address the challenges of delivering drugs with low aqueous solubility. In this study, the use of low energy anti-solvent precipitation for producing nanocrystals has been investigated. Stable nanocrystals with uniform particle size were prepared for the three model compounds, glyburide, ibuprofen, and artemisinin, which are all practically insoluble in water and have diverse molecular structures and crystal packings. The choice of crystal growth inhibitors/stabilizers was found to be critical and specific for each drug. The effect of the process variables, temperature, stirring rate, and the solute solution infusion rate into the antisolvent, was rationalized in terms of how these factors influence the local supersaturation attained at the earliest stages of precipitation. The dissolution of the nanocrystals in aqueous media under physiological conditions was shown in all cases to occur almost instantaneously, being markedly more rapid than that observed for micronized suspensions of the model drugs and their marketed tablet formulations. Rationalization of the choice of optimum stabilizers in terms of molecular interaction with the exposed crystal surfaces proved to be difficult. The study demonstrates that standard crystallization technology is effective in producing nanocrystals with the primary challenge being physicochemical (rather than mechanical), involving the identification of molecule-specific crystal growth inhibitors and/or stabilizers.

THU0177 Structural Differences Between Anti-TNF Agents are Associated with Dissimilar Rates of Secondary Loss of Effectiveness and Drug Adjustments

BackgroundDifferences in drug survival between anti-TNF agents (aTNF) have been attributed to variations in molecular structure leading to increased immunogenicity, in particular between chimeric and fully human monoclonal antibodies (MABs)...

Branching the auxin signaling; Multiple players and diverse interactions

In contrast to its short signaling pathway, auxin plays a wide spectrum of biological roles during plant growth and development. The nuclear auxin signaling pathway can be described in a single step; auxin/receptor-mediated ubiquitination/degradation of transcriptional repressors that affect the auxin responsive genes. However, this simple signaling step generates not only diverse but also seemingly contrary signaling outputs, such as activation/repression of gene expression and promotion/inhibition of cell growth. This diversity of the nuclear auxin signaling is likely to derive from multiple and diverse players of the signaling components. The major nuclear auxin signaling components are receptors, repressors, DNA-binding transcription factors, and co-repressors. In most land plants, each component of the auxin signaling consists of multiple isoforms with somewhat diversified structures; and thus with diverse molecular functions. The diversity of members of each signaling component is anticipated to contribute to the diverse auxin responses. This study reviews the recent results regarding the diverse molecular structures and interactions among the nuclear auxin signaling players.

Linear discriminant analysis for skin sensitisation potential of diverse organic chemicals

Skin sensitisation is one of the emerging toxicological endpoints posing a significant concern for human health. Stimulation index (SI) and murine local lymph node assay (LLNA) are used to estimate quantitatively the skin sensitisation potential to classify chemicals as skin sensitising or non-skin sensitising. To obviate these time-consuming and expensive approaches, development of in silico predictive models has gained considerable attention over the last few decades. In this background, we have developed a linear discriminant analysis (LDA) model for LLNA based on the skin sensitisation potential of 147 chemicals with wide diversity of molecular structures. The developed LDA model is rigorously validated using various classification metrics, which show that the model is able to discriminate the skin-sensitising and non-skin-sensitising compounds. The developed model and contribution plot suggested that rotatable bond or molecular flexibility gives negative contribution, whereas dragon branching index gives positive contribution towards both skin-sensitising and non-skin-sensitising compounds. The descriptors such as number of sulphonate fragments (thio-/dithio-), number of triple bonds, number of nitrogen atoms and quadric index have equal contributions on the skin-sensitising and non-skin-sensitising property. Finally, the model was applied to screen DrugBank database compounds to identify the compounds that are likely to have skin sensitisation.

ChemInform Abstract: Activating Group Recycling: A Fresh Approach to Arene Functionalization

AbstractReview: ca. 50 refs.

Theoretical modeling of sensitivity factors of Bayard-Alpert ionization gauges

Measuring the relative sensitivity factors (Sr) in Bayard-Alpert ion gauge is technically demanding and time-consuming. Moreover, the accuracy deterioration in the low pressure range (high vacuum) becomes problematic. Experimental Sr values are reported for 91 molecules of diverse molecular structures. A three-descriptor QSPR model based on experimental data is established. The model obtained, which explains more than 93% of the data variance, has a good statistical validity and stability. The three selected molecular descriptors, Kier & Hall index, charge difference on the molecular surface, and count of H donor sites appropriately describe the physicochemical background of the relative sensitivity factors. The model developed in this work is freely accessible through the web: http://www.ut.ee/qsar.

High-Pressure Characterization of Nitrogen-Rich Bis-triaminoguanidinium Azotetrazolate (TAGzT) by In Situ Raman Spectroscopy

Compounds rich in nitrogen are attracting significant interest not only because of their high energy content but also because they are potentially more environmentally benign in comparison to conventional energetic materials. Given this interest, it is desirable to understand their molecular composition and structural variations with pressure to derive their stability and determine the conditions in which they transform physically or chemically. In this study, we examine the room-temperature isothermal compression behavior of bis-triaminoguanidinium azotetrazolate (TAGzT) by in situ Raman spectroscopy to pressures near 17 GPa. We assign the characteristic vibrational bands and report the effects of pressure on band intensity, line width, and frequency shift. Two prominent peaks near 1370 and 1470 cm(-1) arise from the C-N and N═N symmetric stretches, respectively. Overall, the intensity of these bands and others diminishes with pressure, and their spectral linewidths increase monotonically upon compression. The vibrational frequency modes blue shift linearly upon compression, indicating a generalized stiffening of the bonds as the pressure increases. These results, together with micro Raman spectroscopic analyses of the recovered, decompressed samples, suggest that TAGzT does not undergo any phase transitions within this pressure range. We estimate and report the C-N and N═N intermolecular bond lengths under compression.

The Inhibitory Substrate Binding Site of Human Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase (IDO) is a heme-containing enzyme that inserts dioxygen into L-Trp to generate N-formylkynurenine. It is involved in a variety of immune related physiological and pathophysiological conditions, such as fetal tolerance and cancer immune escape. Recently, IDO has attracted a great deal of attention owing to its potential as a therapeutic target for cancer. Our previous studies indicated that the activity of human isoform of IDO (hIDO) exhibits substrate-inhibition behavior due to the presence of two substrate binding sites: an active substrate binding site and an inhibitory substrate binding site (Lu C, Lin Y and Yeh SR, JACS, 131, 12866-7, 2009). We showed that, in addition to the substrate L-Trp, the inhibitory substrate binding site is able to accommodate uncompetitive inhibitors with a variety of molecular structures, making it an ideal target for the design of hIDO-selective inhibitors. Despite its importance, the structure of the inhibitory substrate binding site remains elusive. We hypothesize that the long and flexible Loop-JK in the distal heme pocket of hIDO is a critical structural element of the inhibitory substrate binding site. To test this hypothesis, we sought to examine three mutants of hIDO, in which the Loop-JK was systematically truncated. We found that the mutations only slightly perturbed the efficiency of the enzyme, but they significantly reduced the affinity of L-Trp towards the inhibitory substrate binding site, confirming that the Loop-JK is an integral part of the inhibitory substrate binding site. The data will be discussed in the context of the structural and functional relationships of the enzyme.

Thermoresponsive copolymer microgels.

Colloidal aqueous microgels have attracted notable attention due to their possible applications in both polymer chemistry and the (bio)material sector. Due to their soft internal network structure and their response to different external stimuli, they are suitable as carrier systems for different kinds of molecules (e.g. nanoparticles, drugs, diagnostic agents, and enzymes), as optically active materials or even as model systems for fundamental research on soft condensed matter. Within the class of microgels, a variety of molecular structures is possible. The aim of this manuscript is to review recent progress in the domain of copolymer microgels with different architectures. Although most of the work is based on microgels with poly(N-isopropyl acrylamide) (NIPAM) as one component, non-NIPAM based copolymer systems are also presented and discussed.