Amphiphilic and magnetic properties of a new class of cluster-bearing [L2Cu4(mu4-O)(mu2-carboxylato)4] soft materials

A general approach toward amphiphilic systems bearing multimetallic clusters and their ability to form Langmuir-Blodgett films is presented. The synthetic strategy to stabilize these clusters involves the use of a ligand (HL) containing an N(2)O-donor set and long octadecanoic chains to obtain the carboxylate-supported [L(2)Cu(4)(mu(4)-O)(mu(2)-OAc)(4)]EtOH (1) and [L(2)Cu(4)(mu(4)-O)(mu(2)-OBz)(4)] (2) in which OAc(-) and OBz(-) represent acetate (1) and benzoate (2) co-ligands. These species were thoroughly characterized and had their structures solved by X-ray crystallography. We observed that the mu-oxo Cu(4) cluster is antiferromagnetically coupled and used broken-symmetry density functional theory (DFT) calculations to describe the main superexchange pathways of the tetracopper core. We also describe the amphiphilic properties of the ligand and the cluster-containing systems by means of area versus pressure isotherms and show that these cluster-bearing species can be transferred onto solid substrates yielding homogeneous Langmuir-Blodgett films, as characterized by atomic force microscopy and contact angle measurements.     

Room-temperature copper-catalyzed alpha-arylation of malonates

An effective method in targeting alpha-aryl malonates is reported. In the presence of a catalytic amount of 2-picolinic acid and CuI, the coupling of aryl iodides with diethyl malonate proceeds smoothly even at room temperature. The high levels of functional group compatibility and exceptionally mild reaction conditions offer this an attractive protocol in accessing a variety of arylated malonates.     

Contributions of the nanovoid structure to the kinetics of moisture transport in epoxy resins

Absorbed moisture can degrade the physical properties of an epoxy resin, jeopardizing the performance of an epoxy‐based component. Although specific water–epoxy interactions are known to be very important in determining transport behavior, the role of network topology is not clear. In this article, a series of epoxies in which the topology is systematically varied (and the polarity held constant) is used to explore how topology influences the kinetics of moisture transport. The topology is quantified via the positron annihilation lifetime spectroscopy technique in terms of the size and volume fraction of electron density heterogeneities 5–6 Å in diameter, a dimension comparable to the 3‐Å kinetic diameter of a water molecule. Surprisingly, the volume fraction of such nanopores does not affect the diffusion coefficient (D) of water in any of the resins studied. For temperatures at and below 35 °C, there is a mild exponential dependence of D on the average nanopore size observed. Otherwise, the kinetics of moisture transport do not appear to depend on the nanopores. However, the initial flux of moisture into the epoxy does appear to correlate with the intrinsic hole volume fraction. That this correlation persists only in the initial stages of absorption is partially understood in terms of the ability of the water to alter the nanopore structure; only in the initial stages of uptake are the nanopores, as quantified in the dry state, relevant to transport. The role of specific epoxy–water interactions are also discussed in terms of transport kinetics. The lack of a correlation between the topology and transport suggests that polar interactions, and not topology, provide the rate‐limiting step of transport. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 776–791, 2000     

Lipid lateral mobility and membrane phase structure modulation by protein binding

Using a combination of fluorescence correlation and infrared absorption spectroscopies, we characterize lipid lateral diffusion and membrane phase structure as a function of protein binding to the membrane surface. In a supported membrane configuration, cholera toxin binding to the pentasaccharaide headgroup of membrane-incorporated GM1 lipid alters the long-range lateral diffusion of fluorescently labeled probe lipids, which are not involved in the binding interaction. This effect is prominently amplified near the gel-fluid transition temperature, Tm, of the majority lipid component. At temperatures near Tm, large changes in probe lipid diffusion are measured at average protein coverage densities as low as 0.02 area fraction. Spectral shifts of the methylene symmetric and asymmetric stretching modes in the lipid acyl chain confirm that protein binding alters the fraction of lipid in the gel phase.     

Laser induced fluorescence and resonant two-photon ionization spectroscopy of jet-cooled 1-hydroxy-9,10-anthraquinone

We carried out laser induced fluorescence and resonance enhanced two-color two-photon ionization spectroscopy of jet-cooled 1-hydroxy-9,10-anthraquinone (1-HAQ). The 0-0 band transition to the lowest electronically excited state was found to be at 461.98 nm (21,646 cm(-1)). A well-resolved vibronic structure was observed up to 1100 cm(-1) above the 0-0 band, followed by a rather broad absorption band in the higher frequency region. Dispersed fluorescence spectra were also obtained. Single vibronic level emissions from the 0-0 band showed Stokes-shifted emission spectra. The peak at 2940 cm(-1) to the red of the origin in the emission spectra was assigned as the OH stretching vibration in the ground state, whose combination bands with the C=O bending and stretching vibrations were also seen in the emission spectra. In contrast to the excitation spectrum, no significant vibronic activity was found for low frequency fundamental vibrations of the ground state in the emission spectrum. The spectral features of the fluorescence excitation and emission spectra indicate that a significant change takes place in the intramolecular hydrogen bonding structure upon transition to the excited state, such as often seen in the excited state proton (or hydrogen) transfer. We suggest that the electronically excited state of interest has a double minimum potential of the 9,10-quinone and the 1,10-quinone forms, the latter of which, the proton-transferred form of 1-HAQ, is lower in energy. On the other hand, ab initio calculations at the B3LYP/6-31G(d,p) level predicted that the electronic ground state has a single minimum potential distorted along the reaction coordinate of tautomerization. The 9,10-quinone form of 1-HAQ is the lowest energy structure in the ground state, with the 1,10-quinone form lying approximately 5000 cm(-1) above it. The intramolecular hydrogen bond of the 9,10-quinone was found to be unusually strong, with an estimated bond energy of approximately 13 kcal/mol (approximately 4500 cm(-1)), probably due to the resonance-assisted nature of the hydrogen bonding involved.     

Liquid chromatographic determination of ethylenethiourea using pulsed amperometric detection.

A liquid chromatographic method was developed using pulsed amperometric detection at a gold working electrode to measure residue levels of ethylenethiourea (ETU) in crops and groundwater. Use of the sequential pulsing program eliminates electrode fouling while preserving the sensitive and selective detection of ETU. Minimum detection limits in crops were 5-10 ppb (1.25-2.5 ng on-column) and 5 ppb (0.5 ng) in groundwater. The commercial availability of the pulsed electrochemical detector and its gold working electrode that remains functional with a minimum of conditioning is an improvement in method simplicity.     

Fast supercritical fluid chromatography of polymers using packed capillary columns

Summary Fast separations of perfluorinated polyethers and polymethylsiloxanes that are composed of 50–80 oligomers were demonstrated in packed capillary column supercritical fluid chromatography (SFC) using a carbon dioxide mobile phase. Separations were accomplished within 10 min using a 13 cm×250 μm i.d. column packed with 2 μm porous octadecyl bonded silica (ODS) particles. Effects of particle diameter of the packing material and pressure programming on separation were investigated, and packed column SFC was compared with open tubular column SFC. Results show that as the particle diameter was decreased from 5 to 3 to 2 μm and the column length was reduced from 85 to 43 to 13 cm, the separation time could be reduced from 70 to 20 to 10 min while still maintaining similar separation (resolution). Short columns packed with small porous particles are very suitable for fast SFC separations of polymers.     

Effects of Annealing on the Properties of Gamma-Irradiated Sago Starch

The increase in health and safety concerns regarding chemical modification in recent years has caused a growing research interest in the modification of starch by physical techniques. There has been a growing trend toward using a combination of treatments in starch modification in producing desirable functional properties to widen the application of a specific starch. In this study, a novel combination of gamma irradiation and annealing (ANN) was used to modify sago starch (Metroxylon sagu). The starch was subjected to gamma irradiation (5, 10, 25, 50 kGy) prior to ANN at 5 °C (T_o-5) and 10 °C (T_o-10) below the gelatinization temperature. Determination of amylose content, pH, carboxyl content, FTIR (Fourier Transform Infrared) intensity ratio (R_1047/1022), swelling power and solubility, thermal behavior, pasting properties, and morphology were carried out. Annealing irradiated starch at T_o-5 promoted more crystalline perfection as compared to T_o-10, particularly when combined with 25 and 50 kGy, whereby a synergistic effect was observed. Dual-modified sago starch exhibited lower swelling power, improved gel firmness, and thermal stability with an intact granular structure. Results suggested the potential of gamma irradiation and annealing to induce some novel characteristics in sago starch for extended applications.     

Generating self-accelerating Airy beams using a digital micromirror device

We report a new approach for generating an Airy beam by using a digital micromirror device (DMD) and a holographic technique where the DMD loads the desired hologram. Unique characteristics of an Airy beam, such as the non-diffraction and self-acceleration properties, were demonstrated to prove the successful construction of this type of waveform. Experimental results showed good agreement with theoretical calculations. This approach can also be used to generate other special beams.