Implications of comparative spectral doublets observed for neon-isolated and gaseous tropolone(OH) and tropolone(OD)

Spectral doublet separations reported for gas phase and neon matrix-isolated samples of tropolone(OH) and tropolone(OD) are found to support recent work suggesting the possibility that tropolone has a slightly nonplanar geometry in the S1 (A 1B2) (pi*-pi) electronic state. Tautomerizations of gaseous tropolones in the S0 and S1 states are governed by equal double-minimum potential energy functions (PEFs), but interactions in the neon matrix environment transform the tautomerization PEFs of the slightly nonplanar S1 tropolones into unequal double-minimum PEFs. The spectral doublets reported for the zero-point S1-S0 transitions imply energy minima for the nonplanar S1 state in a neon matrix are offset by about 7 cm-1, and tunneling splittings in the symmetric double minimum PEFs of the gaseous molecules are damped about 2 cm-1 by the matrix environment. This means gas phase tunneling splittings smaller than 2 cm-1 are fully quenched in the neon matrix, and gas phase tunneling splittings near 20 cm-1 are damped by only 10%.     

Oxidation of naphthalene by radiolytically produced OH radicals

Radiolytically produced OH radicals react with naphthalene in aqueous solution in the presence of ferricyanide mainly to yield 1- and 2-naphthol in a ratio of 2.1:1. Reaction takes place via addition of OH to the naphthalene with a rate constant of 1.2 x 10¹⁰M^-1S^-1. Because of the low solubility of naphthalene (∼ 2 x 10^-4M) γ-radiolysis studies were carried out at doses of ∼ 10³ rad, where the naphthols were produced at micromolar concentrations. Analysis was by high-performance liquid chromatography. The initial yields of naphthols from solutions saturated with N₂O and naphthalene total 4.7 molec/100 eV, indicating near to quantitative conversion of the OH adducts to the naphthols by the ferricyanide. The observed product ratio is taken to reflect a two-fold preference for attack of OH at the 1-position as compared with that at the 2-position of naphthalene with only little (<10%) reaction at the 9-position.     

Sorbitol can be produced not only chemically but also biotechnologically

Sorbitol, a polyol found in many fruits, is attracting increasing industrial interest as a sweetener, humectant, texturizer, and softener. It is principally produced by chemical means. The bacterium Zymomonas mobilis is able to produce sorbitol together with gluconic acid from fructose and glucose, respectively. This is possible in a one-step reaction via the enzyme glucose-fructose oxidoreductase, so far only known from Z. mobilis. The possibilities for the production of sorbitol by Z. mobilis are discussed also under the aspect of an industrial process and compared with the current chemical as well as other microbiologic processes. The production process by Z. mobilis shows economic possibilities for certain countries, such as Brazil, considering only the products sorbitol and ethanol as an important byproduct. For the other byproduct, gluconic acid, further studies for its partial substitution must be conducted.     

Fabrication of colloidal doublets by a salting out-quenching-fusing technique

It is well-known that high ionic strength promotes colloid aggregation. Here we show that, by controlling this aggregation process, we can produce high yields of homodoublet and heterodoublet polymer colloids. The aggregation process is started by increasing the ionic strength to roughly 250 mM KCl. After approximately the rapid flocculation time, we quench the "reaction" by mixing in a large quantity of deionized water, which dilutes the ionic strength and prevents further aggregation. At this point, the suspension consists primarily of singlet and doublet particles. Through heating above the glass transition temperature of the polymers, the doublets are fused together and remain intact even after sonication. It is also shown that heterodoublets can include a silica particle together with a polymer colloid. The salting out-quenching-fusing technique is a rapid, easy-to-perform, repeatable process for fabricating colloidal doublets from polymers and other materials.     

Novel electronic transitions within excited doublets of dimers

We consider the electronic transition between the split components of the excited electronic doublet of a dimer species when the monomer species have permanent dipole moments. We show that the transition moment is given in terms of the permanent dipole moments of the ground and excited states of the monomers. Extension to ionic dimers and transitions between exciton bands in molecular crystals are suggested.     

Simple fabrication of metallic colloidal doublets having electrical connectivity

A method is described for fabricating metallic colloidal doublets of gold-gold, silver-silver, and gold-silver. Individual gold and silver spheres of micrometer diameter were synthesized by the aggregation of nanoparticles. Then, by controlling aggregation using ionic strength, yields of doublets above 20% were obtained by the salting-quenching technique. The gold-gold and silver-silver homodoublets were very stable mechanically, even in sonication; the gold-silver heterodoublets were slightly less stable than the homodoublets in sonication. Electrical connectivity between the gold-silver heterodoublets was verified by observing the autoelectrophoresis of gold-silver doublets in 3% hydrogen peroxide solution. The generality of the salting out and quenching technique is demonstrated here, and the finding that the particles are electrically connected will be of great significance in a number of applications.     

Electrochemical and photophysical properties of a chemically modified electrode

A surface extinction coefficient for an inorganic complex, bis(2,3′-bipyridine)(2,2′-bipyridine-4,4′-dicarboxylato) ruthenium(II), immobilised on a transparent electrode has been determined for the first time, and demonstrated to be significnatly larger than that of its analogue in homogeneous solution. The first observation of a formal redox potential, for an immobilised complex, which is sharply dependent upon the extent of surface coverage is also reported.     

Water structure and dynamics at a silica surface: Pake doublets in 1H NMR spectra

Detailed knowledge about the dynamics and structure of liquids in the vicinity of a solid surface is important in several fields of research. In this study a homogeneous model system of colloidal and nonporous silica particles with a narrow particle size distribution was used to examine such properties of adsorbed water and 1-heptanol. Doublet (1)H water resonances ("Pake doublets") indicate a preferred spatial orientation for the water molecules, as well as a lower molecular density in the surface-induced water structures compared to bulk water. These surface-induced structures are found to extend at least 8 nm from the silica surface. T(1) relaxation measurements at several temperatures indicate weaker H-bonding in the adsorbed water compared to bulk water. T(2) relaxation measurements at several temperatures reveal the presence of two water phases and give quantitative information on the mobility of water molecules and proton exchange processes. The presence of 1-heptanol changes the water characteristics, primarily in the water phase closer to the surface, where water molecules experience decreased translational and increased rotational freedom. In the absence of water, adsorbed 1-heptanol forms surface aggregates encompassing several molecular layers, where the first adsorbed layer shows severe restrictions in mobility and subsequent layers are more mobile.     

Design of Expression Cassettes for Inverted Repeat and Intron-Spliced Inverted Repeat of PATE Gene Silencing

Palm oil of Elaeis guineensis Jacq. contains approximately 50% saturated and 50% unsaturated fatty acids. In the composition of saturated fatty acid, palmitic acid is the most abundant which is predominantly around 44% of the total fatty acids. The high level of accumulation of palmitic acid should be reduced in order to get a better dietary fatty acid and a more nutritional value oil in the market.The purpose in reducing palmitic acid content could be carried out by silencing palmitoyl-ACP thioesterase (PATE) gene activities. Primer pairs to amplify partial PATE fragments, intron and 3Untranslated Region (3UTR) were designed from PATE of Elaeis guineensis var tenera (GenBank DQ422858). PATE fragments, intron and 3UTR were constructed in two expression cassettes with inverted repeat (IR) and intron-spliced inverted repeat (ISIR) orientations to generate hair-pin RNAs (hpRNA). Combinations of restriction enzymes (RE) were used to confirm, the size, orientation and location of the inserts.     

The synthesis of a chemically reactive and polymeric luminescent gel

In the past, chemically reactive polymeric interfaces have been considered to be of potential interest for developing functional materials for a wide range of practical applications. Furthermore, the rational incorporation of luminescence properties into such chemically reactive interfaces could provide a basis for extending the horizon of their prospective utility. In this report, a simple catalyst-free chemical approach is introduced to develop a chemically reactive and optically active polymeric gel. Branched-polyethyleneimine (BPEI)-derived, inherently luminescent carbon dots (BPEI-CDs) were covalently crosslinked with pentaacrylate (5Acl) through a 1,4-conjugate addition reaction under ambient conditions. The synthesized polymeric gel was milky white under visible light; however, it displayed fluorescence under UV light. Additionally, the residual acrylate groups in the synthesized fluorescent gel allowed its chemical functionality to be tailored through facile, robust 1,4-conjugate addition reactions with primary-amine-containing small molecules under ambient conditions. The chemical reactivity of the luminescent gel was further employed for a proof-of-concept demonstration of portable and parallel ‘ON’/‘OFF’ toxic chemical sensing (namely, the sensing of nitrite ions as a model analyte). First, the chemically reactive luminescent gel derived from BPEI-CDs was covalently post-modified with aniline for the selective synthesis of a diazo compound in the presence of nitrite ions. During this process, the color of the gel under visible light changed from white to yellow and, thus, the colorimetric mode of the sensor was turned ‘ON’. In parallel, the luminescence of the gel under UV light was quenched, which was denoted as the ‘OFF’ mode of the sensor. This parallel and unambiguous ‘ON’/‘OFF’ sensing of a toxic chemical (nitrite ions, with a detection limit of 3 μM) was also achieved even in presence of other relevant interfering ions and at concentrations well below the permissible limit (65 μM) set by the World Health Organization (WHO). Furthermore, this chemically reactive luminescent gel could be of potential interest in a wide range of basic and applied contexts.

An unprecedented chemically reactive and polymeric luminescent gel is developed, and this material is further employed to develop a portable and rapid sensor for a practically relevant analyte (nitrite ions) with a sensitivity of 3 μM.     

Putting ammonia into a chemically opened fullerene

We put ammonia into an open-cage fullerene with a 20-membered ring ( 1) as the orifice and examined the properties of the complex using NMR and MALDI-TOF mass spectroscopy. The proton NMR shows a broad resonance corresponding to endohedral NH 3 at delta H = -12.3 ppm relative to TMS. This resonance was seen to narrow when a (14)N decoupling frequency was applied. MALDI spectroscopy confirmed the presence of both 1 ( m/ z = 1172) and 1 + NH 3 ( m/ z = 1189), and integrated intensities of MALDI peak trains and NMR resonances indicate an incorporation fraction of 35-50% under our experimental conditions. NMR observations showed a diminished incorporation fraction after 6 months of storage at -10 degrees C, which indicates that ammonia slowly escapes from the open-cage fullerene.     

Laser-induced fluorescence detection of OH produced by reaction of hot H atoms with CO2

Laser-induced fluorescence (LIF) detection of OH radicals is used to examine the reaction of CO₂ molecules with translationally hot H atoms generated by ArF laser photolysis of HBr. Prompt formation of rotationally excited OH X ²Πi(υ″ = 0,1,2), has been observed.     

Electrophoretic rotation of doublets composed of two spheres almost in contact

Colloidal doublets formed from spheres with different zeta potentials rotate as dipoles into alignment with an applied electric field. The rate of rotation is proportional to the difference in the electrophoretic mobilities of the isolated spheres times a dimensionless rotation coefficient (N). The coefficient N, which describes the interaction effects between the particles, has been previously calculated numerically under the assumptions of infinitesimal double layers and uniform zeta potentials on each sphere. These numerical values have been used to interpret experiments which probe the tangential forces between two particles almost in contact. But since these assumptions might not hold for the small gaps in actual experiments, it is important to know how N is affected when the double layers of two spheres overlap or when the charge is nonuniformly distributed on the sphere surfaces (especially in the gap region). Using an extension of the Lorentz reciprocal theorem for Stokes flow, we have developed a semi-analytical solution for N which is valid in the asymptotic limit of small (but finite) gaps of fluid between the spheres. For infinitesimal double layers and uniform zeta potentials, this result shows that N is weakly singular in the gap between the spheres. Our method also enables us to examine the effects of overlapping double layers and nonuniform zeta potentials in the gap region, and an important result of this paper is that even when these effects are considered, the result for infinitesimal double layers and uniform zeta potentials remains a very good approximation.     

Collective behavior of a population of chemically coupled oscillators

Experiments are performed in which a large number (approximately 10(4)) of relaxation oscillators are globally coupled through the concentration of chemicals in the surrounding solution. Each oscillator consists of a microscopic catalyst-loaded particle that displays oscillations in the concentrations of chemical species when suspended in catalyst-free Belousov-Zhabotinsky (BZ) reaction solution. In the absence of stirring, the uncoupled particles display a range of oscillatory frequencies. In the well-stirred system, oscillations appear in the surrounding solution for greater than a critical number density of particles (n(crit)). There is a growth in the amplitude of oscillations with increasing n, accompanied by a slight increase or no change in frequency. A model is proposed to account for the behavior, in which the transfer of activator and inhibitor to and from the bulk medium is considered for each particle. We demonstrate that the appearance and subsequent growth in the amplitude of oscillations may be associated with partial synchronization of the oscillators.     

Helium entry and escape through a chemically opened window in a fullerene

(3)He has been inserted into the cavity of an open-cage fullerene derivative close to room temperature, reaching an incorporation fraction of 0.1%. The rate of escape of (3)He from this fullerene was monitored by (3)He NMR to yield the activation barrier and to compare the size of the orifice to those of other open-cage fullerenes. The equilibrium constant was also measured.     

Marine-derived fungi: a chemically and biologically diverse group of microorganisms

A diverse array of secondary metabolites have been isolated and characterized from marine-derived fungi. The structures and biological activities of these metabolites are presented. Additionally, some basic principles of mycology are covered. Overall, 273 structures are presented and the review contains 162 references     

Characterizing the rovibrational distribution of CD2CD2OH radicals produced via the photodissociation of 2-bromoethanol-d4

This work characterizes the internal energy distribution of the CD(2)CD(2)OH radical formed via photodissociation of 2-bromoethanol-d(4). The CD(2)CD(2)OH radical is the first radical adduct in the addition of the hydroxyl radical to C(2)D(4) and the product branching of the OH + C(2)D(4) reaction is dependent on the total internal energy of this adduct and how that energy is partitioned between rotation and vibration. Using a combination of a velocity map imaging apparatus and a crossed laser-molecular beam scattering apparatus, we photodissociate the BrCD(2)CD(2)OH precursor at 193 nm and measure the velocity distributions of the Br atoms, resolving the Br((2)P(1/2)) and Br((2)P(3/2)) states with [2 + 1] resonance enhanced multiphoton ionization (REMPI) on the imaging apparatus. We also detect the velocity distribution of the subset of the nascent momentum-matched CD(2)CD(2)OH cofragments that are formed stable to subsequent dissociation. Invoking conservation of momentum and conservation of energy and a recently developed impulsive model, we determine the vibrational energy distribution of the nascent CD(2)CD(2)OH radicals from the measured velocity distributions.