From high-spin organic molecules to organic polymers with magnetic ordering

This concept paper outlines the design of the first pi-conjugated organic polymer with magnetic ordering. This rational, "bottom-up" macromolecular design is based on synthesis and study of polyarylmethyl polyradicals with increasing number of exchange-coupled unpaired electron spins. The prospects for attaining organic polymer magnets with stability at ambient temperature and/or higher magnetic ordering temperatures will be discussed.     

Layer-by-layer growth of oriented metal organic polymers on a functionalized organic surface

A metal-organic coordination polymer based on benzenetricarboxylic acid ligands and Zn(II) ions was grown on a COOH-terminated organic surface in a stepwise fashion. The deposited films were characterized using a number of surface analysis techniques, including X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. IR measurements show that the metal-organic coordination polymer grows in a layer-by-layer fashion and can be reversibly loaded with NH3. The deposition is very selective and occurs only on COOH-terminated regions of an organic surface, as demonstrated by AFM measurements.     

The pyrolytic identification of organic molecules: I. The pyrolytic behavior of organic molecules

Results of a study on the pyrolysis of about 70 organic compounds of varied composition are presented and discussed. Identification of the volatile products formed was accomplished by mass spectrometry. It is shown how the pyrolytic patterns may be employed to distinguish one molecule from another. Some attention has been given to isomeric compounds and to aromatic structures containing one or more functional groups.     

NMR determination of smectic ordering of probe molecules

The NMR spectra of the three solutes ortho-, meta-, and para-dichlorobenzene in the nematic and smectic A phases of the liquid crystals 8CB and 8OCB are analyzed to yield two orientational order parameters for each solute. Extrapolation of the asymmetry in the energy parameters that describe the orientational ordering in the nematic phase are used to provide estimates of the strength of the nematic potential in the smectic A phase. The experimentally determined asymmetry of the orientational order parameters in the smectic A phase is then used in conjunction with Kobayashi-McMillan theory applied to solutes to give information about the smectic A layering and the nematic/smectic A coupling. In both smectic A solvents, the solute smectic coupling constant, tau, is negative (with the origin fixed at the center of the smectic layer) for all solutes. The signs and relative values of tau indicate that the ortho and para solutes favor the interlayer region while the meta solute is more evenly distributed throughout the layers.     

Palladium assisted organic reactions-II: Ortho-aminomethylstilbene derivatives

Di-μ-chlorobis(N,N-dimethyl-3,4-dimethoxybenzylamine-6-C,N)dipalladium (1b) reacts readily with a variety of styrenes to give good yields of the corresponding o-aminomethylstilbene derivatives.     

Conformational ordering of chain molecules in liquid crystals

Deuterium NMR studies have been performed to elucidate orientational characteristics of some ether-type main-chain liquid crystals. Spacers used are of the type -O(CH₂)_nO- with n = 9 and 10. Dimers, homopolymers as well as copolymers in which spacers n = 9 and 10 are arranged in an alternative fashion were investigated. The quadrupolar splitting data obtained from the deuterium-labeled mesogenic core and spacer have been studied within the rotational isomeric state (RIS) approximation. The ordering characteristics thus estimated were found to be consistent with the magnetic susceptibility data obtained by using superconducting quantum interference device (SQUID) for the same polymers.     

On minimal energy ordering of acyclic conjugated molecules

The energy of a graph is defined as the sum of the absolute values of all the eigenvalues of the graph. Gutman (Acyclic conjugated molecules, trees and their energies, J. Math. Chem. 1 (1987) 123–143) proposes two conjectures about the minimum of the energy of conjugated trees (trees with a perfect matching), which are verified by Zhang and Li (On acyclic conjugated molecules with minimal energies, Discrete Appl. Math. 92 (1999) 71–84). This paper focuses on the trees of conjugated hydrocarbon /EquationSource> trees in the class in the increasing order of their energies.     

Microwave assisted organic synthesis (MAOS) of small molecules as potential HIV-1 integrase inhibitors

Integrase (IN) represents a clinically validated target for the development of antivirals against human immunodeficiency virus (HIV). In recent years our research group has been engaged in the stucture-function study of this enzyme and in the development of some three-dimensional pharmacophore models which have led to the identification of a large series of potent HIV-1 integrase strand-transfer inhibitors (INSTIs) bearing an indole core. To gain a better understanding of the structure-activity relationships (SARs), herein we report the design and microwave-assisted synthesis of a novel series of 1-H-benzylindole derivatives.     

Layer-by-layer surface modification of functional nanoparticles for dispersion in organic solvents

In order to prepare SiO(2) nanoparticles that are dispersible in various organic solvents, an anionic surfactant 1, which branches into a hydrophobic chain and a hydrophilic chain, was adsorbed on to SiO(2) nanoparticles through a layer-by-layer surface modification route using polyethyleneimine (PEI). First, the relationship among the additive content of PEI, adsorbed content of PEI, and the redispersion stability of the SiO(2) nanoparticles in water was investigated. While almost the entire PEI was adsorbed when the additive PEI content was lower than 67 mg/g of SiO(2), the adsorbed content of PEI became saturated when the additive content was increased above 90 mg/g of SiO(2). SiO(2) nanoparticles that were saturated with PEI could be redispersed into water at sizes close to their primary particle size without the large-scale formation of aggregates. Next, the anionic surfactant 1 was adsorbed on the SiO(2) nanoparticles by using a SiO(2) aqueous suspension saturated with adsorbed PEI. It was found that the adsorbed content of 1 increased almost linearly as the additive content was increased when the additive condition was below 1400 mg/g of SiO(2). Furthermore, SiO(2) nanoparticles adsorbed with 80 mg/g of SiO(2) of PEI and 810 mg/g of SiO(2) of 1 could be dispersed into various organic solvents with different polarities. This layer-by-layer modification technique can also be applied to Ag nanoparticles in order to prepare Ag nanoparticles that can be dispersed in various organic solvents.     

Effects of small neutral molecules on phospholipid bicelle ordering

The effects of small neutral molecules on the liquid-crystalline ordering of dimyristoyl-phosphatidylcholine (DMPC)/dihexanoyl-phosphatidylcholine (DHPC) bicelles (q = 3.0 and 3.5) were studied via 2H, 31P, and 13C variable-temperature NMR. The addition of chloroform (up to approximately 90 mM, with a lipid concentration of approximately 120 mM) was observed to reduce the temperature onset of bicelle ordering by up to approximately 10 degrees C, likely resulting from the depression of the DMPC phase transition temperature. The temperature for the collapse of the bicelle phase was also significantly reduced; the observed effects amount to a downward shift in temperature (and reduction in range) of the liquid-crystalline portion of the bicelle phase diagram with increasing dopant concentration. Other model dopants (e.g., tetrahydrofuran and benzene) yielded smaller effects. Additionally, the variable bicelle alignment permitted the characterization of the ordering of chloroform molecules within the lipid phase.     

Layer-by-layer adsorption of water molecules on the surface of a silver iodide crystal

Computer simulations at the molecular level were used to analyze the mechanism of the nucleation of water condensate from the vapor phase on the surface of a silver iodide crystal at 260 K. The initial stage of the condensation process is the sequential growth of monolayers on the substrate surface without formation of a compact microdroplet. The dependence of the equilibrium work of formation of the condensate film on its thickness exhibits oscillations. The formation of layers close to the substrate surface involves the overcoming of a Gibbs energy barrier.     

Layer-by-layer electrostatic assembly with a control over orientation of molecules: anisotropy of electrical conductivity and dielectric properties

While forming layer-by-layer (LbL) electrostatic assembly of a magnetic organic molecule, namely, nickel phthalocyanine (NiPc), we apply a magnetic field. The field orients the magnetic moment of the molecules on a monolayer along the direction of magnetic field. Such an orientation of the molecules is then electrostatically immobilized with a monolayer of a polycation. By repeating the dipping cycle, we form LbL films with planar NiPc molecules facing a particular direction. With NiPc's moment perpendicular to the molecular plane, two types of LbL films were formed: (a) NiPc's molecular plane parallel to the substrate (moment is perpendicular) and (b) molecules perpendicular to the substrate and facing one particular direction, the direction of magnetic field. Such films, with the molecules lying either (a) parallel or (b) perpendicular to the substrate, provide unique systems to study anisotropy of optical, dielectric, and electrical characteristics in these planar organic molecules. The latter film responds to the polarization of incident beam in electronic absorption spectroscopy. Here we show methods to obtain an orientation of molecules in LbL films and study anisotropy of dielectric constant and conductivity of the molecules in ultrathin films.     

Laser spectroscopy on organic molecules

Various laser spectrometric methods have been developed until now. Especially, laser fluorometry is most sensitive and is frequently combined with a separation technique such as capillary electrophoresis. For non-fluorescent compounds, photothermal spectrometry may be used instead. A diode laser is potentially useful for practical trace analysis, because of its low cost and long-term trouble-free operation. On the other hand, monochromaticity of the laser is essential in high-resolution spectrometry, e.g. in low temperature spectrometry providing a very sharp spectral feature. Closely-related compounds such as isomers can easily be differentiated, and information for assignment is obtained from the spectrum. Multiphoton ionization mass spectrometry is useful for soft ionization, providing additional information concerned with molecular weight and chemical structure. A short laser pulse with a sufficient energy is suitable for rapid heating of the solid surface. A matrix-assisted laser desorption/ion-ization technique is recently employed for introduction of a large biological molecule into a vacuum for mass analysis. In the future, laser spectrometry will be developed by a combination with state-of-the-art laser technology. In the 21st century, new laser spectrometry will be developed, which may be based on revolutionary ideas or unexpected discoveries. Such studies will open new frontiers in analytical laser spectroscopy.     

Laser spectroscopy on organic molecules

Various laser spectrometric methods have been developed until now. Especially, laser fluorometry is most sensitive and is frequently combined with a separation technique such as capillary electrophoresis. For non-fluorescent compounds, photothermal spectrometry may be used instead. A diode laser is potentially useful for practical trace analysis, because of its low cost and long-term trouble-free operation. On the other hand, monochromaticity of the laser is essential in high-resolution spectrometry, e.g. in low temperature spectrometry providing a very sharp spectral feature. Closely-related compounds such as isomers can easily be differentiated, and information for assignment is obtained from the spectrum. Multiphoton ionization mass spectrometry is useful for soft ionization, providing additional information concerned with molecular weight and chemical structure. A short laser pulse with a sufficient energy is suitable for rapid heating of the solid surface. A matrix-assisted laser desorption/ion-ization technique is recently employed for introduction of a large biological molecule into a vacuum for mass analysis. In the future, laser spectrometry will be developed by a combination with state-of-the-art laser technology. In the 21st century, new laser spectrometry will be developed, which may be based on revolutionary ideas or unexpected discoveries. Such studies will open new frontiers in analytical laser spectroscopy.     

Rotational tunnelling in organic molecules

Experimental investigations of molecular tunnelling in symmetrical molecular groups using the techniques of neutron scattering are reviewed. Particular emphasis is laid upon the tunnelling spectra of methyl groups. The relationship between the dynamics of the rotors and their “static” molecular environment is discussed with examples from published work.     

Calculation of conformations of organic molecules

The most stable conformation of the molecule has a minimum of potential energy that arises due to the competition between the tendency of the valency angles to take ideal values and that of non-bonded atoms to be situated at an equilibrium distance. The equilibrium distance is equal to the sum of intermolecular radii determined by measuring the distances between atoms of adjacent molecules in the crystal. This idea is suggested as underlying a method of computation that enables to solve two problems. Firstly, the structure of the molecule being known, it becomes possible to ascertain the points of the interaction curve of the non-bonded atoms and secondly, with the interaction curve known, one can calculate the optimal configuration of the molecule.

To illustrate the suggested theory the conformation of molecules of some cyclic hydrocarbons has been calculated. It is to be stressed that the investigation of the conformation of strained molecules affords the main means of studying the interaction of non-bonded atoms.