Large Number Of Organic Molecules Research Articles

On the nature of band splitting in Shpol’skii matrices

This paper includes the results of the analysis of the multiplet structure in the low-temperature luminescence spectra of a large number of organic molecules in n-paraffin solutions, as well as a number of impurity aromatic molecular crystals. A new approach to the interpretation of the Shpol’skii effect is proposed, which is based on taking into account the symmetry properties of the impurity molecule and the matrix crystal. Calculated data are compared with experimental results.

Crystal Plane-Dependent Gas-Sensing Properties of Cu2o Particles Nanostructures: Experimental and Theoretical Studies

Introduction Recently, the study on selective exposure of high-energy facets at the surface of metal-oxide semiconductors nanomaterials (MOSs) have been of great concern. Usually, different facets of a single crystal exhibit distinctive chemical and physical properties, for example, gas-sensing ability, chemical reactivity, and adsorption capacity. In principle, gas-sensing by the MOSs is based on the oxidation–reduction reaction of the detected gases occurring on the semiconductor surface, which leads to an abrupt change in conductance of the sensor. For this reason, the gas-sensing ability of the MOSs is in theory very sensitive to the crystal facets of the sensing materials the applications of MOSs with high-energy facets have been concentrated on the surface-reacted processes. Kaneti et al. [1] and Wang et al. [2] studied on the relation between the sensitivity of metal oxide gas sensor and the nature of the crystal surface exposed to the gas species. They demonstrated that semiconductor metal oxidation with high energy surface has the highest gas sensitivity.But by the method we synthesized, the six Cu2O nanocrystals with different energy facets were achieved by simply adjusting the added PVP. At the optimal working temperature, Cube Cu2O nanocrystal with (100) facet exhibited the best sensitivity to n-propanol gases. The reason for possibility is that the Cu2O nanocrystal with high-energy facets also adsorbed a large number of organic molecules. Method The chemiresistive gas sensor is mainly composed of four parts: 1. A 4 mm long ceramic tube (internal diameter: 0.8 mm, external diameter: 1.2 mm), where a pair of gold electrodes with four Pt wires have been installed originally. 2. Sensing material layer (thickness: ~ 42 um) on the surface of ceramic tube. Taking the material based sensor as an example here. Mix the obtained powder with deionized water to form a slurry and coat the slurry uniformly on the whole surface of the ceramic tube. Then put the well-coated tube in the muffle furnace heating at 100 °C for 2 h in air. 3. A Ni-Cr alloy coil heater, it was inserted through the well-coated and sintered ceramic tube, controlling the working temperature via the flowing current. 4. A hexagon base, which supported the well-coated and sintered ceramic tube through welding. After ageing, the as-prepared sensors were tested through the static test system at a laboratory conditions. Results and Conclusions In this work, A variety of Cu2O architectures with an interesting morphological evolution (from cube, cubooctahedrons, truncated octahedral to octahedral) were realized by simply adjusting the added PVP. The test results demonstrated that Octahedral Cu2O particles exposing the (111) facets exhibit a surprisingly competitive sensing activity to n-propanol gases at the optimal working temperature compared with truncated octahedral Cu2O with (100) and (111) facets. But we found the sensing activity of the cube Cu2O with (100) facet exhibit much better than the octahedral Cu2O particles with (111) facet. The phenomenon could be explained from the PVP organic macromolecular. It can be concluded that PVP had acted as a capping agent and that preferential adsorption occurred on the (111) planes of the Cu2O crystals with large percentage of unsaturated copper atoms. Hence, the adsorbed PVP will also reduce the surface reactivity of the octahedral Cu2O particles with (111) facet. Our findings may provide the mechanism to explore a simple, efficient and promising sensing/catalysis activity materials in gas sensors.

A Brief Review: Microwave Chemistry and its Applications

Microwave assisted synthesis has revolutionized chemical synthesis. Small molecules can be built in a fraction of the time required by conventional methods. Green chemistry holds the promise of reducing health and environmental damage. In the past we have focused on cleaning up toxic messes, is a movement to design chemicals that are safer for the environment and human. Microwave assisted reactions in organic chemistry achieve the same by ensuring facilitation of faster reactions under bulk conditions as well as promoting reduction of reaction time. In conventional heating methods oil bath or hot plate are used as a source of heat to a chemical reaction. Microwave irradiation is widely used as a source of heating in chemical synthesis. This article has discussed the different applications of Microwave assisted synthesis of organic compounds most thoroughly by focusing on aspects of speed, reproducibility and scalability. From this review it is clearly identified that independent on the type of organic material, data consistently points out to MW as a novel and powerful tool which has enable synthesis of a number of new compounds and presents the need for future research in this area. The basic mechanisms observed in microwave assisted synthesis are dipolar polarization and conduction. Microwave-assisted synthesis provides clean synthesis with the advantage of enhanced reaction rates, higher yields, greater selectivity, and economic for the synthesis of a large number of organic molecules, have provided the momentum for many chemists to switch from conventional heating method to microwave assisted chemistry.

Synthesis and Evaluation of Anionic Schiff Bases As Pitting Corrosion Inhibitor for Stainless Steel 304 in NaCl Solution

The high corrosion resistance of austenitic stainless steel (SS) arises from the formation of a thin, adherent and protective passive film that forms instantaneously on the surface. Unfortunately, in the presence of aggressive ions like chloride anion, the corrosion resistance of passivated stainless steel is limited by local breakdown and pit nucleation [1]. An efficient and economical method to decrease the metal dissolution in aggressive media is the use of corrosion inhibitors. A large number of organic molecules containing electronegative functional groups, such as π-electron systems or heteroatoms have been proposed for the inhibition of general metallic corrosion, although the use of organic compounds as pitting corrosion inhibitors in neutral solutions is still rather limited. On the other hand, inorganic-based compounds such as chromates and nitrates are also used as pitting corrosion inhibitors for SS in aggressive media; however the application of these inorganics, especially chromates and phosphates, is not recommended because of their biological toxicity. More recently, Schiff bases have been described as cost effective inhibitors due to their robust and convenient synthesis from inexpensive precursors. They are organic compounds containing the imine (-C=N-) functional group in their structure. Schiff base derivatives with additional heteroatoms, such as N and O, and aryl groups have been used as corrosion inhibitors [2,3], but their application as pitting corrosion inhibitors has not been described. In the present study, three new anionic Schiff bases were synthesized through by reacting para-amino benzoic acid with several aromatic aldehydes containing different functional groups in their para- site. They were designed to improve water solubility, to enhance coordination with Fe atoms by including N and O heteroatoms, two benzene rings and the imine group in their chemical structure, and to be large enough to create heavy hydrophobic complex with Fe+3. The inhibitor efficiency of these compounds as pitting corrosion inhibitor for 304 SS in neutral 0.1 M NaCl was examined using potentiodynamic polarization measurements, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) . Polarization data show the shift of the pitting potential to more positive values with increasing inhibitor concentration. Surface analysis shows chromium enrichment at the metal surface under anodic polarization in the passive region of the metal when the inhibitor compound is present in the test solution, whereas no effect occurs under open circuit conditions. XPS data show that the inhibitor molecules do not adsorb on the clean metal, but on the passive layer instead. [1] G.T. Burstein, C. Liu, R.M. Souto, S.P. Vines, Corros. Eng. Sci. Technol. 39 (2004) 25. [2] M.A. Hegazy, Corros. Sci. 51 (2009) 2610. [3] R. Sadeghi Erami, M. Amirnasr, K. Raeissi, M.M. Momeni, S. Meghdadi, J. Iran. Chem. Soc. 12 (2015) 2185.

Hydrothermal Synthesis to Water-stable Luminescent Carbon Dots from Acerola Fruit for Photoluminescent Composites Preparation and its Application as Sensors

Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good water solubility, simple synthetic routes as well as size and excitation-dependent photoluminescence (PL).The aim of this work was to synthesize photoluminescent C-dots by hydrothermal method using acerola fruit (Malpighiaemarginata) as a row material, since this fruit contains large number of organic molecules. Studies about the optimal synthesis conditions were performed, where these organic molecules were converted into C-dots by hydrothermal carbonization at 180 ºC for 18 h. The C-dots exhibited a green emission light at 459 nm when excited under UV-light ( λ ex= 370 nm). These nanomaterials were also successfully used to prepare C-dots/poly (vinyl alcohol) luminescent composites (C-dots/PVA). Both C-dots and C-dots/PVA composite films were investigated by using colorimetric visual sensor for Fe3+ metal ions detection. The results show that the prepared C-dots and C-dots/poly presented strong green emission light. The emission spectra of above materials were quenched in the presence of Fe3+ ions. Thus, highly specific “turn off” fluorescence sensing of Fe3+ was achieved using fluorescent C-dots. Regarding, this work describe that the polymeric films as sensors of metallic ions in aqueous solution appears as a new perspectives to design new composite materials.

Toxicity assessment of chlorinated wastewater effluents by using transcriptome-based bioassays and Fourier transform mass spectrometry (FT-MS) analysis

Effects of chlorination on the toxicity of wastewater effluents treated by activated sludge (AS) and submerged membrane bioreactor (S-MBRB) systems to HepG2 human hepatoblastoma cells were investigated. In addition to the cytotoxicity and genotoxicity assays, the DNA microarray-based transcriptome analysis was performed to evaluate the change in types of biological impacts on HepG2 cells of the effluents by chlorination. Effluent organic matter (EfOM) and disinfection by-products (DBPs) were also characterized by using Fourier transform mass spectrometry (FT-MS). Although no significant induction of genotoxicity was observed by chlorination for both effluents, the chlorination elevated the cytotoxicity of AS effluent but reduced that of S-MBRB effluent. The FT-MS analyses revealed that more DBPs including nitrogenated DBPs (N-DBPs) were formed in the AS effluent than in the S-MBRB effluent by chlorination, supporting the increased cytotoxicity of AS effluent. The lower O/C ratio of S-MBRB EfOM suggests that a large number of organic molecules were detoxified by chlorination, which consequently decreased the cytotoxicity of S-MBRB effluent. Integration of all the results highlights that both cytotoxicity and biological impacts of chlorinated wastewater effluents were clearly dependent on the EfOM characteristics such as DBPs and O/C ratio, namely, on types of treatment systems.

Experimental study of the rydberg orbitals of large molecules

Using photoelectron and optical spectroscopy, the ionization potentials of a large number of organic molecules in their Rydberg excited states were determined. In the limit of large alkyl substituents surrounding a central chromophoric group, it was found that the ionization potential of 3s, 3p, and 3d MO's are independent of the central group in direct contrast to the situation in the ground state. This is interpreted as showing that in the excited states of the limiting molecules, the Rydberg orbitals are completely n = 3 orbitals on the alkyl groups rather than on the central atoms as in the corresponding hydrides.

N-METHYLOL POLYACRYLAMIDE CYCLODEXTRIN COMPOSITE AS A STIFFENING AGENT FOR COTTON FABRICS

To chemically attach β- Cyclodextrin molecules to cotton cellulose, N-methylol-acrylamide was used to synthesize a cyclodextrin containing monomer ,which was then grafted onto cellulose fibers .Cyclodextrin are cyclic oligosaccharides cable of forming inclusion complex with large number of organic molecules .The aim of this work is the preparation of activated Cyclodextrin and applied it as finishing agent on cotton fabrics to improve stiffness properties, tensile strength and Crease Recovery Angle .

Molecules and solids in planetary nebulae and proto-planetary nebulae

Recent millimeter-wave and infrared spectroscopic observations have identified a large number of organic molecules through their rotational and vibrational transitions. In particular, the detections of the stretching and bending modes of aliphatic and aromatic compounds have revealed a continuous synthesis of organic materials at the late stages of stellar evolution. High resolution imaging observations in the submillimeter (e.g., SMA) and in the mid-infrared (e.g., Gemini) have made possible the mapping of the distribution of these compounds, allowing us to infer the history of circumstellar chemistry. In this paper, we present some of the recent spectroscopic and imaging observations of the circumstellar envelopes of evolved stars and discuss a scenario of chemical evolution including the possible role of photochemistry in the late stages of stellar evolution.

Photoanodic reactions occurring at nanostructured titanium dioxide films

The reasons of unusually large differences observed in photocurrent efficiencies for the oxidation of various organic and inorganic substrates at nanostructured TiO 2 photoelectrodes are discussed. The “redox cycling”, where a product of the hole transfer acts, in turn, as scavenger for the photogenerated electrons, appears as a frequent cause of weak photocurrents. Such a recombination mechanism operates not only under open-circuit conditions but also in the presence of large anodic bias applied to the conducting support of the TiO 2 electrode. Experiments conducted in the presence of both, an efficient hole scavenger, formate ion, and an electron acceptor, methyl viologen dication, showed that, in a major part of the anodically polarized nanostructured TiO 2 film, the quasi-Fermi level of electrons remains actually close to the conduction band edge potential. Importantly, addition to the solution of an electron acceptor causes large drop of the photocurrent both under weak and intense UV illumination generated by an argon-ion laser. On the other hand, a large number of organic molecules undergoing essentially irreversible photooxidation (e.g., to form CO 2 and H 2O) generate high photocurrents at the nanostructured TiO 2 electrodes. Such reactions, when occurring in the presence of large concentrations of the reactants, may involve direct hole transfer.

Grafting of cotton with β‐cyclodextrin via poly(carboxylic acid)

AbstractCyclodextrins are cyclic oligosaccharides. Cyclodextrin molecules can form inclusion complexes with a large number of organic molecules. The properties of cyclodextrins enable them to be used in a variety of different textile applications. Cyclodextrins can act as auxiliaries in washing and dyeing processes, and they can also be fixed onto different fiber surfaces. Because of the complexing abilities of cyclodextrins, textiles with new functional properties can be prepared. Poly(carboxylic acid)s such as 1,2,3,4‐butane tetracarboxylic acid (BTCA) are well‐known non‐formaldehyde crosslinking reagents. BTCA has four carboxylic acid groups, which can react with hydroxyl groups of cellulose and form stable ester bonds. We crosslinked β‐cyclodextrin molecules on hydroxyl groups of cellulose via BTCA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1323–1328, 2005

Azetidin-2-ones, synthon for biologically important compounds.

Azetidin-2-one, a four-membered cyclic lactam (beta-lactam) skeleton has been recognised as a useful building block for the synthesis of a large number of organic molecules by exploiting the strain energy associated with it, in addition to its use in the synthesis of a variety of beta-lactam antibiotics. Efforts have been made in exploring such new aspects of beta-lactam chemistry using enantiomerically pure beta-lactams as versatile intermediates for the synthesis of aromatic beta-amino acids and their derivatives, peptides, polyamines, polyamino alcohols, amino sugars and polyamino ethers. The development of methodologies based on beta-lactam nucleus is now referred as 'the beta-lactam synthon methods'. The selective bond cleavage of the strained ring coupled with further interesting transformation render this fascinating molecule as a powerful building block. This provides an access to diverse structural type of synthetic target molecules lacking beta-lactam ring structure. This review provides an account of synthesis of organic compounds having biological significance at the same time lacking beta-lactam ring, by using beta-lactam as synthon.

Prediction of the Vapor Pressure Boiling Point, Heat of Vaporization and Diffusion Coefficient of Organic Compounds

AbstractThe prototype computer program SPARC has been under development for several years to estimate physical properties and chemical reactivity parameters of organic compounds strictly from molecular structure. SPARC solute‐solute physical process models have been developed and tested for vapor pressure (at any temperature), heat of vaporization (at 25C and the boiling point), diffusion coefficient (at 25C) and boiling point (at any pressure) for a relatively large number of organic molecules. The RMS deviation error of the predicted the vapor pressures, heats of vaporization (at any temperature) and boiling points (at any pressure) were close to the intralaboratory experimental errors.

Zero-point vibrational effects on proton shieldings: functional-group contributions from ab initio calculations.

We investigate the effects of zero-point vibrational motion on the nuclear magnetic shielding constants of a large number of organic molecules. The vibrational corrections include anharmonic contributions from the potential energy surface and harmonic contributions from the curvature of the property surface. Particular attention is paid to vibrational corrections to hydrogen shielding constants where we show that vibrational corrections may be substantial, ranging from about +0.50 to -0.70 ppm, and thus demonstrating that ignoring these effects may give errors in the chemical shifts by more than 1 ppm in certain extreme cases. These effects can therefore not be neglected when comparing calculated results with experiment, not even for the chemical shifts. However, we also demonstrate that the vibrational corrections to the hydrogen shieldings are to a large extent transferable from one molecule to another. We have tabulated functional vibrational corrections to the hydrogen shieldings, based on results for more than 35 molecules. Unfortunately, no similar transferability has been observed for the vibrational corrections to shielding constants of other nuclei such as carbon, nitrogen, or oxygen.

Estimation of microscopic, zwitterionic ionization constants, isoelectric point and molecular speciation of organic compounds

Mathematical models based on structure–activity relationships and perturbed molecular orbital theory have been developed to calculate the ionization p K as for a large number of organic molecules. These models include resonance, direct and indirect electrostatic field effects, sigma induction, steric effects, differential solvation and hydrogen bonding. The thermodynamic microscopic ionization constants, p k i , of molecules with multiple ionization sites and the corresponding complex speciation as a function of pH have been determined using these chemical reactivity models. For a molecule of interest SPARC (SPARC performs automated reasoning in chemistry) calculates all of the microscopic ionization constants and the fraction of each species as a function pH along with the titration (charge) curve. The system has been tested on several biologically and environmentally important compounds.

The Use of Cyclodextrins in Textile Processes — An Overview

Cyclodextrins are cyclic oligosaccharides. These molecules are able to form inclusion complexes with a large number of organic molecules. The properties of cyclodextrins enable them to be used in a variety of different textile applications. Cyclodextrins may act as auxiliaries in washing and dyeing processes, and they can also be fixed onto different fibre surfaces. Owing to the complexing abilities of cyclodextrins, textiles with new functional properties could be made available.

Multiple human taste receptor sites: a molecular modeling approach.

Numerous experimental data on the human peripheral taste system suggest the existence of multiple low-affinity and low-specificity receptor sites which are responsible for the detection and the complete discrimination of a very large number of organic molecules. According to this hypothesis, a given molecule interacts with numerous taste receptors and vice versa. Statistical analysis of taste intensities estimated by 58 human subjects for various molecules enables the calculation of taste intermolecular distances. For the present modeling study, we hypothesized that a short taste distance (i.e. taste similarity) between two distinct molecules indicates that they bind with similar distributions of affinities to the taste receptors, and hence display similar binding motifs. In order to find common molecular binding motifs among 14 selected organic tastants, hydrogen-bonding and hydrophobic interaction properties were mapped onto their molecular surfaces. The 14 surfaces were then cut in 240 fragments, most of which were made up of 2-4 potentially interacting zones. A correspondence index was defined to measure the analogy between two optimally superimposed fragments. The 75 most representative fragments were all matched pairwise. Twelve distinct clusters of fragments were isolated from the 2775 calculated comparisons. These 12 fragment types were used to calculate structural similarity distances. We then performed a combinatorial analysis to identify which fragment combination best reconciled structural and taste distances. We finally identified an optimal subset of seven fragment types out of the 12, which significantly and best accounted for the 91 pairwise taste distances between all 14 modeled tastants. These seven validated fragment types are therefore presented as good candidates to be recognized by the same number of distinct taste receptor sites. Potential applications of these identified binding motifs to tastant design are suggested.

Chemical selectivity in the dissociative ionization of organic molecules by low-energy positrons.

The ionization and dissociation, induced by positrons having kinetic energies in the range 0.3--3 eV, of a large number of organic molecules have been studied. The required energies for ionization and dissociation are supplied through the annihilation of electrons by the positrons. Cross sections for these interactions are strong functions of molecular size, molecular structure, and bond type. Fragmentation usually occurs between atoms linked by \ensuremath{\sigma} bonds. Multiple bonds tend to stabilize the molecules against fragmentation. Fragmentation induced under the low-energy process occurs preferably in the linear groups of molecules rather than in ring structures. Ionization and dissociation cross sections of large alkane molecules are higher than those of smaller molecules. A possible explanation of the fragmentation phenomena is that positrons annihilate electrons in energy levels below the highest occupied molecular orbital (HOMO), leaving the molecules in excited states. Multiple bonds in molecules tend to promote higher populations near the HOMO state; annihilation of electrons near the HOMO state does not result in fragmentation.

Toward the detection of pure carbon clusters in the ISM

The questions of how and in what form that carbon is distributed in the Universe are critical ones for understanding the evolution of dust and planets, and for elucidating the origin of life on Earth and the prospects for discovering it elsewhere in the cosmos. While the abundant CI and CII atoms and CO molecule, which together account for a large fraction of the total carbon budget, have been thoroughly studied in many sources, and a large number of organic molecules have been detected in cold dust clouds, two potentially large reservoirs of carbon remain essentially unexplored. These are the PAH’s and pure carbon clusters. The former are strongly suspected to be important components of interstellar dust, while the latter have essentially been ignored. Most probably, this simply reflects the fact that relatively little information exists regarding the structures, properties, and in particular, on the transition freauencies of pure carbon clusters that would permit their study by astrophysical methods. The work described below’is designed to mitigate these deficiencies through the study of pure carbon clusters (C,) in the size range n=3-20 by high resolution infrared (350-3000 cm-‘) and far infrared (lo-350 cm-‘) laser spectroscopy. The specific goal of this work is to provide a precise inventory of laboratory frequencies and physical properties for these carbon clusters, such that a serious effort can be made to detect them in cold interstellar sources by far-IR astronomy.

Reactions of MoO 3 with diethylenetriamine (dien): Syntheses, solid-state characterization and thermal behaviour. Molecular and crystal structure of a second polymorph of (H 3dien) 2[Mo 7O 24]·4H 2O

The reaction of MoO 3 with diethylenetriamine in aqueous solution yields four compounds: two polymorphs of bis(diethylenetriammonium) heptamolybdate(VI) tetrahydrate, (H 3dien) 2[Mo 7O 24·4H 2O ( 1 and 2), bis(3-aza-1,5-pentamethylenediammonium) octamolybdate(VI) hexahydrate, (H 2dien) 2[Mo 8O 26]·6H 2O ( 3), and the oxocomplex diethylenetriaminetrioxomolybdenum(VI), [MoO 3(dien)] ( 4). The compounds were characterized by means of thermal analyses and IR spectroscopy. The crystal structure of 1 was determined by X-ray diffraction. Compounds 1 and 2 are an unprecedented case of polymorphism in discrete polyoxomolybdates and their syntheses experimentally confirm the ability of polyoxometallates to promote the stacking of a large number of organic molecules by means of an extended network of hydrogen contacts. Both structures contain discrete[Mo 7O 24] 6− polyanions, diethylenetriammonium cations and water molecules connected through hydrogen bonding interactions which are responsible for a different crystal packing in both compounds. In 1 the Mo(5)O(17) bond length, 2.675(4) Å, is significantly longer than those observed for other organoammonium heptamolybdates that exhibit photochemical properties and antitumour activity. This long molybdenum—oxygen distance may play an important role in the possible photochromism and anticancer activity of this compound.