Effects of the rate of supersaturation generation on polymorphic crystallization of m-hydroxybenzoic acid and o-aminobenzoic acid

Effects of the rate of supersaturation generation on polymorphic crystallization have been investigated through evaporation and cooling crystallization experiments of m-hydroxybenzoic acid (m-HBA) in methanol, acetone and ethyl acetate, and o-aminobenzoic acid (o-ABA) in ethanol. The rate of supersaturation generation has been altered by systematically changing either the cooling rate or the evaporation rate of solvent using a jacketed crystallizer and a microfluidic evaporation device, respectively. The results have revealed that the rate of supersaturation generation and the tendency of the formation of the less stable polymorph are positively correlated. Kinetic effects are dominant when the rate of supersaturation generation is high, thereby producing the metastable polymorphs (orthorhombic m-HBA; Form II of o-ABA); on the contrary, more stable polymorphs (monoclinic m-HBA; Forms III and I of o-ABA) are formed when the rate of supersaturation generation is low and the thermodynamic effects are prevailing.     

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Self-Referential Noise and the Synthesis of Three-Dimensional Space

Generalising results from Gödel and Chaitin in mathematics suggest that self-referential systems contain intrinsic randomness. We argue that this is relevant to modelling the universe and show how three-dimensional space may arise from a non-geometric order-disorder model driven by self-referential noise.     

A 3000 K laboratory emission spectrum of water

An emission spectrum of hot water with a temperature of about 3000 K is obtained using an oxy-acetylene torch. This spectrum contains a very large number of transitions. The spectrum, along with previous cooler laboratory emission spectra and an absorption spectrum recorded from a sunspot, is analyzed in the 500-2000 cm(-1) region. Use of a calculated variational linelist for water allows significant progress to be made on assigning transitions involving highly excited vibrational and rotational states. In particular emission from rotationally excited states up to J=42 and vibrational levels with up to eight quanta of bending motion are assigned.     

The effect of addition of fluorescent moieties to dihydropyrenes: enhancing photochromicity and fluorescence monitoring

A series of dihydropyrenes with appending fluorescent moieties were synthesized with the objective of increasing the photochromic efficiency for this class of compounds and to establish how suitable fluorescence would be to follow their photochromic behavior. The ring opening quantum yields of dihydropyrenes with aroyl substituents at the 4-position showed increased ring opening quantum yields without a decrease of the half-life for the thermal reversion of the less stable open isomer, the metacyclophanediene to the dihydropyrene. The fluorescence of the appending naphthoyl or pyrenoyl moieties was not suitable to follow the photochromic cycling of the dihydropyrenes. However, the emission detected above 600 nm of the closed isomer of the dihydropyrene moiety was shown to be a good monitoring method for the photochromic cycling.     

Importance of Debye and Keesom interactions in separating m-xylene and p-xylene in GC-MS analysis utilizing PEG stationary phase

In electron impact gas chromatography (GC)-mass spectrometry analysis of a complex mixture, such as gasoline, two coeluting solutes can be distinguished if each has a unique major ion. The boiling-point difference between m-xylene and p-xylene, which also has identical major ions (mz-1: 91 and 106 Da), is 0.77 degrees C. These cannot be separated even on a crossed-linked polydimethylsiloxane capillary column, which has a minimum of 5000 plates/m. They are separated on a crossed-linked polar polyethylene glycol (PEG) capillary column. GC separation on a stationary phase depends on the relative strengths of solute-solute, stationary phase-stationary phase, and solute-stationary phase interactions. Although the calculated molar electronic polarization and refractivity factor of Lorenz-Lorentz equation for m-xylene and p-xylene are nearly equal because of its greater dipole moment difference (0.30 and 0.02), the calculated orientation polarization of m-xylene is 80 times greater than p-xylene. This implies the dipole reinforcement through inductive polarization by the hydroxyl of PEG stationary phase molecules is greater on m-xylene than p-xylene. In addition, as the permanent dipole moment of m-xylene is 15 times greater than p-xylene, m-xylene has a stronger Keesom interaction with PEG. In order for m-xylene and p-xylene to solvate in PEG, analytes must overcome the PEG-PEG Keesom/hydrogen bonding interaction forces. Physical and chemical parameters indicate that compared with p-xylene, m-xylene has a greater Debye-Keesom interaction tendency with PEG molecules. This is supported by the 0.12-min. retention-time difference between them.     

Polyunsaturated alkyl amides from Echinacea: synthesis of diynes, enynes, and dienes

The synthesis of 20 alkyl amides, including 15 naturally occurring polyunsaturated alkyl amides previously identified from Echinacea spp. (1-13 and 62) or from Achilla sp. (55) and five previously unknown geometric isomers (23, 28, 67, 73, and 80), is described. Importantly, these amides include all of the major alkyl amides present in commercially used Echinacea extracts. The syntheses demonstrate methodology used for constructing alkyl amides containing conjugated diyne and isomerically pure enyne and diene moieties and may be adapted easily for the preparation of other alkyl amides present in Echinacea spp. Terminal-conjugated diynes were prepared by a Cadiot-Chodkiewitz coupling/deprotection sequence utilizing a protected bromoacetylene, and methyl-substituted diynes were made via a base-catalyzed rearrangement of terminal-skipped diynes. Conjugated dienes were prepared conveniently and with high stereoselectivity by the reduction of enynes or diynes with Rieke zinc. With the exception of 1-2 and 11-12, the alkyl amides are synthesized here for the first time, and their NMR data are consistent with that of the reported isolated natural compounds.     

Ring fiber resonators based on fused-fiber grating add-drop filters:application to resonator coupling

We introduce a fiber ring optical resonator based on adiabatic fused-fiber grating couplers. The coupling of a through fiber to the resonator is controlled by the strength of the fiber Bragg gratings. By using two of these couplers and incorporating erbium-doped (ED) fiber in the ring, we control the internal loss of the ring by pumping the ED fiber. The transmission spectra of the through port and the drop port of a four-port configuration, a ring coupled to two waveguides, are measured. We show that the loss/coupling ratio of the ring-fiber system can be changed and thus that the transmission properties of the fiber can be controlled.     

Right on time: measuring Kuramoto model coupling from a survey of wrist-watches

Using a survey of wrist-watch synchronization from a randomly selected group of independent volunteers, we model the system as a Kuramoto-type coupled oscillator network. Based on the phase data both the order parameter and likely size of the coupling are derived and the possibilities for similar research to deduce topology from dynamics are discussed.