A chiral pinwheel supramolecular network driven by the assembly of PTCDI and melamine

The mixing of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine) at room temperature in a ratio of 3 : 4 on Au(111) leads to the formation of a new chiral "pinwheel" structure.     

Exchange narrowing of the J band of molecular dye aggregates

The exchange narrowing of the J band of certain dye monomers upon aggregation in solution has been known since the 1930s. Here, we analyze the theoretical explanations put forward to account for these narrow absorption bands. Although the theories range from models of identical monomers interacting with vibrations to the opposite of rigid monomers with statistically distributed electronic site energies, all approaches exhibit exchange narrowing. However, we show that the origins of the narrowing are different. A unified theory incorporating the two approaches is presented in which features of both narrowing mechanisms are evident.     

Toward controlled spacing in one-dimensional molecular chains: alkyl-chain-functionalized fullerenes in carbon nanotubes

A range of fullerenes (C60) functionalized with long alkyl chains have been synthesized and inserted into single-walled carbon nanotubes. The impact of the alkyl chain length and of the type of linker between the addend and the fullerene cage on the geometry of molecular arrays in nanotube has been studied by high-resolution transmission electron microscopy. In the presence of functional groups the mean interfullerene separations are significantly increased by 2-8 nm depending on the length of the alkyl chain, but the periodicity of the fullerene arrays is disrupted due to the conformational flexibility of the alkyl groups.     

Single-laboratory validation of the biosense direct competitive enzyme-linked immunosorbent assay (ELISA) for determination of domoic acid toxins in shellfish

Method validation was conducted for an enzyme-linked immunosorbent assay (ELISA) for the determination of domoic acid (DA) toxins, known to give amnesic shellfish poisoning (ASP) symptoms, in shellfish. The calibration curve range of the assay is approximately 10-260 pg/mL, with a dynamic working range for DA toxins in shellfish from 0.01 to at least 250 mg/kg. The ASP ELISA showed no significant cross-reactivity to structural analogs, and proved to be robust to deliberate alterations of the optimal running conditions. The shellfish matrix effects observed with mussels, oysters, and scallops were eliminated by diluting shellfish extracts 1:200 prior to analysis, leading to a limit of detection at 0.003 mg/kg. Thirteen blank shellfish homogenates were spiked with certified mussel material containing DA to levels in the range of 0.1-25 mg DA/kg, and analyzed in quadruplicate on 3 different days. The relative standard deviation (RSD) under intra-assay repeatability conditions ranged from 6.5 to 13.1%, and under interassay repeatability conditions the RSD ranged from 5.7 to 13.4%, with a mean value of 9.3%. The recoveries ranged from 85.5 to 106.6%, with a mean recovery of 102.2%. A method comparison was conducted with liquid chromatography with ultraviolet detection, using naturally contaminated scallop samples (n = 27) with DA levels at 0-244 mg/kg. The overall correlation coefficient was 0.960 and the slope of the regression was 1.218, indicating a good agreement between the methods.     

Configuration-selective spectroscopic studies of Er3+ centers in ErSc2N@C80 and Er2ScN@C80 fullerenes

Low temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of high purity ErSc(2)N@C(80) and Er(2)ScN@C(80) fullerenes reveal at least two metastable configurations of the Er(3+) ion within the cage, consistent with previous observations from x-ray diffraction. Using PLE measurements at a number of different emission wavelengths we have characterized the ground state, (4)I(152), and the first excited state, (4)I(132), of the various Er(3+) configurations and their crystal-field splitting. We present detailed energy level diagrams for the ground and excited states of the two dominant configurations of ErSc(2)N@C(80) and Er(2)ScN@C(80).     

Time dependence in quantum mechanics

It is shown that the time-dependent equations (Schr?dinger and Dirac) for a quantum system can be derived from the time-independent equation for the larger object of the system interacting with its environment, in the limit that the dynamical variables of the environment can be treated semiclassically. The time which describes the quantum evolution is then provided parametrically by the classical evolution of the environment variables. The method used is a generalization of that known for a long time in the field of ion-atom collisions, where it appears as a transition from the full quantum mechanical perturbed stationary states to the impact parameter method in which the projectile ion beam is treated classically. Received 25 October 1999     

Characterisation of cryopreserved cells freshly isolated from human bone marrow

Osteoblast progenitor cells (OBPCs) isolated from bone marrow have the ability to differentiate into osteoblasts and thus potential therapeutic use to tissue-engineer bone. In order for OBPCs to be available for clinical use a means of storing viable cells is necessary. The aim of this study was to determine whether a simple method of cryopreservation had an effect on osteogenic differentiation or growth of OBPCs isolated from fresh human bone marrow. Stro-1 was used to identify the isolated OBPCs. The osteoblastic potential of the marrow cells was confirmed as culture with osteogenic supplements (OS) significantly increased osteoblastic protein production (alkaline phosphatase (ALP), osteopontin and osteocalcin) compared with standard conditions (P less than 0.05). Ten further marrow aspirates were harvested; each was halved for either cryopreservation or control culture. Primary cultures from both populations formed colonies with recognised OBPC morphology. OS stimulated both cryopreserved and control populations to produce significantly more osteoblastic proteins (P less than 0.05) and there was no significant difference between the increase in osteogenic proteins when cultured with OS (P great than 0.2). The proliferation rate after 5 days in culture was not significantly affected by cryopreservation (P greater than 0.05). It has been suggested that OBPCs are immuno-privileged; so allogenic cells could be implanted into patients for tissue engineering bone without causing a hypersensitivity reaction. Our study demonstrates a method of storage, which allows OBPCs to be available for use without affecting osteoblastic potential or viability.     

Probing intramolecular CH-π interactions in o-quinodimethane adducts of [60]fullerene using variable temperature NMR

Several o-quinodimethane adducts of [60]fullerene were synthesized and their intramolecular aryl CH-fullerene π interactions were studied using variable temperature-NMR (VT-NMR). Evaluation of the rate constants associated with the first-order transition states for cyclohexene boat-to-boat inversions enables quantification of ΔG(?) values for each inversion. A comparison between two constitutional isomers, only one of which is capable of intramolecular CH-π interactions, provides a lower limit of 0.95 kcal/mol for each aryl CH-fullerene π interaction.     

Acoustic classification of multiple simultaneous bird species: a multi-instance multi-label approach

Although field-collected recordings typically contain multiple simultaneously vocalizing birds of different species, acoustic species classification in this setting has received little study so far. This work formulates the problem of classifying the set of species present in an audio recording using the multi-instance multi-label (MIML) framework for machine learning, and proposes a MIML bag generator for audio, i.e., an algorithm which transforms an input audio signal into a bag-of-instances representation suitable for use with MIML classifiers. The proposed representation uses a 2D time-frequency segmentation of the audio signal, which can separate bird sounds that overlap in time. Experiments using audio data containing 13 species collected with unattended omnidirectional microphones in the H. J. Andrews Experimental Forest demonstrate that the proposed methods achieve high accuracy (96.1% true positives/negatives). Automated detection of bird species occurrence using MIML has many potential applications, particularly in long-term monitoring of remote sites, species distribution modeling, and conservation planning.