Infrared combination and difference bands of the NO dimer

The mid-infrared (1500-3800 cm⁻¹) absorption spectrum of gaseous nitric oxide has been studied at low temperature (99 K) with a long absorption path (160 m) in order to observe weak combination, difference, and overtone bands of the NO dimer. About ten new bands were assigned with greater or lesser certainty. Combined with previous results, they lead to a set of 12 secure and 7 tentative vibrational term values for (NO)₂, essentially doubling our knowledge of NO dimer vibrational states. The strongest non-fundamental bands in this region, other than the ν₁ (symmetric N-O stretch) + ν₅ (asymmetric N-O stretch) overtone, involve combinations of ν₅ with ν₃ (intermolecular stretch). Excitation of ν₅ results in increased frequencies for the intermolecular modes ν₂, ν₃, and ν₄. A new value of 155.5 cm⁻¹ was obtained for ν₄, the elusive infrared-inactive out-of-plane fundamental vibration.     

Insights into dolphin sonar discrimination capabilities from human listening experiments

A variety of dolphin sonar discrimination experiments have been conducted, yet little is known about the cues utilized by dolphins in making fine target discriminations. In order to gain insights on cues available to echolocating dolphins, sonar discrimination experiments were conducted with human subjects using the same targets employed in dolphin experiments. When digital recordings of echoes from targets ensonified with a dolphinlike signal were played back at a slower rate to human subjects, they could also make fine target discriminations under controlled laboratory conditions about as well as dolphins under less controlled conditions. Subjects reported that time-separation-pitch and duration cues were important. They also reported that low-amplitude echo components 32 dB below the maximum echo component were usable. The signal-to-noise ratio had to be greater than 10 dB above the detection threshold for simple discrimination and 30 dB for difficult discrimination. Except for two cases in which spectral cues in the form of "click pitch" were important, subjects indicated that time-domain rather than frequency-domain processing seemed to be more relevant in analyzing the echoes.     

Shear-induced coalescence of emulsified oil drops

Crude oil droplets, when suspended in water, possess negative surface charges which give rise to double-layer repulsive forces between the drops. According to conventional DLVO theory, the magnitude of this repulsion (based on the measured zeta potential) is more than sufficient to prevent coalescence of the droplets. Indeed, when two such droplets were brought together on direct (i.e., "head-on") approach, coalescence was rarely observed. Upon oblique approach, however, the same droplets were seen to coalesce readily. An oblique encounter must necessarily give rise to lateral relative motion-or shearing-between the droplet surfaces. It is speculated that, if the charge distributions at the droplet surfaces were heterogeneous, lateral shearing would facilitate many encounters between surface patches of different zeta potentials across the intervening water film. If the repulsion across any local region were sufficiently weak to allow formation of an oil bridge across the water film, coalescence of the drops would follow inevitably. With the hypothesis of surface heterogeneity, it is not necessary to invoke any additional colloidal interactions (such as "hydrophobic forces") to account for the observed droplet-droplet coalescence. This finding may have important implications for the underlying mechanisms of emulsion stability in general and the commercial extraction of bitumen from oil sands in particular.     

Electronic structures of dihedral (D5h, D5d, D6h, D6d) fullerenes

By means of our proposed method for Hückel theory calculation, we have calculated the electronic structures of dihedral (D_5h, D_5d, D_6h, D_6d) fullerences, which are generated from icosahedral C₂₀, C₆₀, C₈₀, C₁₈₀, C₂₄₀ and C₅₄₀, respectively. From the calculated results of 1224 fullerence molecules, certain rules on the stability and chemical reactivity have been drawn for such types of dihedral fullerenes.     

Elucidating Factors Manipulated the Formation of Multiply Charged Protein Homomultimeric Complexes by Electrospray Ionization

Native non‐covalently bonded protein‐protein and protein‐substrate complexes are of great interest and have been extensively studied by electrospray ionization mass spectrometry (ESI‐MS). Multiply charged protein homomultimeric complexes are shown to form by ESI‐MS. This study addresses factors that can artificially induce the formation of multiply charged protein homomultimeric complexes. Cytochrome c (Cyt c) and ubiquitin, which are monomers in solution, were found to generate (Cyt c)_mⁿ⁺ by electrospray ionization (ESI). The homomultimeric complexes were not limited to dimeric complexes but include also multiply charged trimers, tetramers, and pentamers. The observation of these homomultimeric complexes has never been revealed from a Cyt c solution at the concentration as low as 10 μM. Increasing the concentration of Cyt c enhanced the formation of (Cyt c)_mⁿ⁺ as expected; however, the protein concentration does not affect the relative intensities of monomeric and dimeric complexes. Additionally the enrichment of NH₄OH also promotes the formation of (Cyt c)_mⁿ⁺. Notably, source collision‐induced dissociations (source‐CID) of (Cyt c)_mⁿ⁺ alter the charge state distribution (CSD) and may lead to an incorrect interpretation of Cyt c conformations. Hence, extra care should be taken when using CSD to interpret the conformation of a protein derived from ESI‐MS.     

Detection of DNA fragments separated by capillary electrophoresis based on their native fluorescence inside a sheath flow

A scheme for the separation and detection of native DNA fragments in capillary electrophoresis is presented. A UV laser at 275 nm excites the intrinsic fluorescence of the fragments, which is greatly enhanced at pH 2.8. To provide a compatible system, methylcellulose-based size separation is performed at the identical pH. A sheath-flow arrangement isolates the detection region from the linear polymer for a reduced background level. The performance is an order-of-magnitude enhancement in detectability over absorption detection. We also uncovered a selective degradation/ligation process at these pH conditions that may be useful as additional selectivity for DNA characterization.     

Micellar electrokinetic capillary chromatographic separation and laser-induced fluorescence detection of 2'-deoxynucleoside 5'-monophosphates of normal and modified bases

Micellar electrokinetic chromatography is used to separate dansylated nucleotides, both normal and modified species. The high separation power allows detection of minor components present in less than 1 part per thousand of the major components. Laser-excited fluorescence is used to detect the separated components at the 6 x 10(-18) mol level or 10(-9) M injected material. Combined with high-performance liquid chromatographic enrichment prior to labeling, this technique can be used to assess DNA damage in carcinogenesis studies.     

Resonance enhanced three-photon absorption of molecular iodine

D ← X resonance enhanced three-photon excitation spectrum of iodine was observed by a cw intracavity absorption technique. Vibrational quantum numbers of D ← X transitions are given for every major spectral feature. The corresponding one-photon enhancement from the B state is evident from the one-photon vibrational assignment. The spectroscopic constants for the D state are v₀₀ = 40 998 cm^?1 ω′₀ = 113 cm^?1 and ω′₀χ′₀ = 0.045 cm^?.