A novel method for measuring initial-burst chemiluminescence in a liquid scintillation counter using the myeloperoxidase-H20Cl− reaction

These studies show that there is an initial quantifiable burst of luminol-enhanced CL associated with the interaction of MPO with H₂O₂ and Cl^?. They also confirm that the reaction is H₂O₂-concentration dependent (2). The novel method for quantifying initial-burst CL in a liquid scintillation counter introduced in this study provides many advantages over previous CL studies using the same counter, as noted above. This method provides for more efficient representation of CL associated with the MPO reaction, and allows for valid conclusions concerning the drug effects on this reaction. The ability to “see” the initial part of the reaction may also allow kinetic analysis of this (and other) enzyme CL reactions.     

Functionalized Templates for the Convergent Assembly of Polyethers: Synthesis of the HIJK Rings of Gymnocin A

Extension ladder : The successful application of epoxide‐opening strategies towards the synthesis of ladder‐type polyethers is contingent upon further elaboration of the product. By employing two different functionalized templates, a fragment of gymnocin A that bears four sites for subsequent fragment coupling has been prepared (see scheme; Bn=benzyl).

     

Wave packet interferometry and quantum state reconstruction by acousto-optic phase modulation

Studies of wave packet dynamics often involve phase-selective measurements of coherent optical signals generated from sequences of ultrashort laser pulses. In wave packet interferometry (WPI), the separation between the temporal envelopes of the pulses must be precisely monitored or maintained. Here we introduce a new (and easy to implement) experimental scheme for phase-selective measurements that combines acousto-optic phase modulation with ultrashort laser excitation to produce an intensity-modulated fluorescence signal. Synchronous detection, with respect to an appropriately constructed reference, allows the signal to be simultaneously measured at two phases differing by 90 degrees. Our method effectively decouples the relative temporal phase from the pulse envelopes of a collinear train of optical pulse pairs. We thus achieve a robust and high signal-to-noise scheme for WPI applications, such as quantum state reconstruction and electronic spectroscopy. The validity of the method is demonstrated, and state reconstruction is performed, on a model quantum system--atomic Rb vapor. Moreover, we show that our measurements recover the correct separation between the absorptive and dispersive contributions to the system susceptibility.     

A combined ab initio/Franck-Condon study of the A-X single-vibronic-level emission spectrum of CCl2 and the photodetachment spectrum of CCl2 -.

State-of-the-art ab initio calculations have been carried out on the X1A1, ?3B1 and A1B1 states of CCl2 and the X2B1 state of CCl2-. Franck-Condon factors including anharmonicity have been calculated, between the CCl2 states, and between the CCl2- X2B1 state and the CCl2 states. They are used to simulate the A-X single-vibronic-level (SVL) emission spectra of CCl2 determined by M.-L. Lui et al. [PCCP 2003, 5, 352] and the 364 nm laser photodetachment spectrum of CCl2- obtained by R. L. Schwartz et al. [J. Phys. Chem. A 1999, 103, 8213]. Comparison between simulated and observed spectra confirms the vibrational assignments of the X2B1 SVL emission spectra and the T0 position of the A1B1 state of CCl2. For the photodetachment spectrum of CCl2-, spectral simulation shows that the higher binding energy ?3B1(CCl2) <-- X2B1(CCl2-) band is well separated from the X1A1(CCl2) <-- X2B1(CCl2-) band. It is concluded that the observed second band, which overlaps heavily with the X1A1(CCl2) <-- X2B1(CCl2-) band in the photodetachment spectrum of CCl2- cannot be assigned to the CCl2(?3B1) + e --> CCl2-(X2B1) detachment process. Further ab initio calculations carried out in the present investigation support the suggestion that the second band in the 364 nm photodetachment spectrum of CCl2- is due to detachment from an excited state of CCl2-, a linear quartet state, to a triplet state of CCl2. These calculations identify the anionic state to be the lowest 4Sigmag- (4Sigma-) state, which photodetaches vertically to the 3Sigmag- (3Sigma-; adiabatically ?3B1) and/or 3Pi(u) (3Pi) states of CCl2 to give the second band observed in the 364 nm photodetachment spectrum of CCl2-.     

Guanosine tetra- and pentaphosphate analysis: PEI-cellulose thin-layer purification and luciferin-luciferase liquid scintillation quantitation

A system is presented that can separate and quantitate in picomole amounts various guanosine tetra and penta phosphates namely guanosine 5′ triphosphate, 3′ diphosphate (pppGpp), guanosine 5′ tetraphosphate (ppppG), and diguanosine 5′ tetraphosphate (GppppG). It was found to be inactive with guanosine 5′ diphosphate, 3′ diphosphate (ppGpp), and a synthetic compound pCppG.The analytical detection system uses a crude firefly luciferin-luciferase system in which the various derivatives probably transphosphorylate ADP to produce the ATP necessary to emit light with the luciferin-luciferase system.The system should be useful in quantitating reactions in which guanosine tetraphosphates and pentaphosphates are involved. Their role is apparently one of control at either RNA polymerase or ribosomal levels and should be important in further research in molecular biology.     

Temporal sequence of chemiluminescence and aggregation of human neutrophils and platelets after stimulation by arachidonic acid

Using the instrument known as a lumiaggregometer we have simultaneously measured chemiluminescence (CL) and aggregation (Ag) of neutrophils and platelets. The CL and Ag responses are triggered by the addition of 10^?4M arachidonate. We note that chemiluminescence occurs before aggregation of neutrophils (10 sec) and platelets (16 sec). Arachidonate is known to hasten ⁴⁵Ca transport in cellular membranes which probably triggers cellular metabolism to cause chemiluminescence. Additionally metabolized arachidonate or fatty acids are known to cause CL by cyclooxygenase-peroxidase and lipoxygenase pathways via free radicals. Since free radicals are known to react with luminol the CL is enhanced. These free radicals metabolites must occur before the physical event of aggregation.     

Ab initio calculations on low-lying electronic states of TeO2 and Franck-Condon simulation of the (1)1B2 <-- X1A1 TeO2 absorption spectrum including anharmonicity

Ab initio calculations have been carried out on low-lying singlet and triplet states of TeO2 at different levels of theory with basis sets of up to the augmented-polarized valence-quintuple-zeta quality. Equilibrium geometrical parameters, harmonic vibrational frequencies, and relative electronic energies of the X1A1, 1B1, 1B2, 1A2, 3A1, 3B1, 3B2, and 3A2 states of TeO2 have been calculated. Potential energy functions (PEFs) of the X1A1 and the (1)1B2 states were computed at the complete-active-space self-consistent-field multireference configuration interaction level, with a basis set of augmented-polarized valence-quadruple-zeta quality. Franck-Condon factors (FCFs) for the electronic transition between the X1A1 and (1)1B2 states of TeO2 were calculated with the above-mentioned ab initio PEFs. The (1)1B2 <-- X1A1 absorption spectrum of TeO2 was simulated employing the computed FCFs, which include Duschinsky rotation and anharmonicity, and compared with the recently published laser-induced fluorescence (LIF) spectrum of Hullah and Brown [J. Mol. Spectrosc. 200, 261 (2000)]. The ab initio results and spectral simulation reported here confirm the upper electronic state involved in the LIF spectrum to be the (1)1B2 state of TeO2 and also confirm the vibrational assignments of Hullah and Brown. However, our simulated spectrum suggests that the reported LIF spectrum from 345 to 406 nm represents only a portion of the full (1)1B2 <-- X1A1 absorption spectrum of TeO2, which extends from ca. 406 to 300 nm. Another dye other than the two used by Hullah and Brown is required to cover the 345-300 nm region of the LIF band. Ab initio calculations show strong configuration mixing of the (1)1B2 electronic surface with higher 1B2 states in a region of large TeO bond length (> or = 2.0 A) and OTeO bond angle (> or = 135.0 degrees).     

Quantitative predictions of linear viscoelastic rheological properties of entangled polymers

The “dual constraint” model developed by Mead, Van Dyke et al. is here extended by inclusion of “early-time” contour-length fluctuations and constraint-release Rouse relaxation, and then evaluated by comparing its predictions with literature data for over 50 different linear and star polymers. By combining the reptation model of Doi and Edwards with contour-length fluctuations and constraint release, the model provides a systematic approach to prediction of the rheological properties of polymers. The parameters are taken from the literature and used consistently for linear polymers, star polymers, and their mixtures having the same chemical compositions. In most cases, the predictions of the model appears to agree well with data for monodisperse, bidisperse, and polydisperse linear and star polymers, except at low molecular weights. Received: 23 December 1999 Accepted: 28 March 2000