Influence of the host on vibronic relaxation: a study of free-base porphin in a series of n-alkanes by photochemical hole-burning

Photochemical hole-burning is used to determine the relaxation times of vibronic bands of the S₁ ← S₀ transition to free-base porphin in different substitutional sites of n-hexane, n-heptane, n-octane and n-decane at 1.6 K. The vibronic relaxation depends strongly on site and host. A correlation between the n-alkane chain length and the vibronic relaxation time is observed.     

Assessment of angiogenesis: implications for ultrasound imaging

In this paper, the fundamentals of tumor angiogenesis and the implications for ultrasound imaging will be described. Twenty-eight athymic nude mice were implanted with the human melanoma cell lines DB-1 or MW-9 (14 mice/group). Ultrasound contrast agents were injected in the tail veins. Power Doppler and pulse inversion harmonic imaging (PI-HI) was performed (in real time and intermittently). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF), and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between percent area stained with COX-2 and with VEGF relative to power Doppler (p<0.05) and intermittent PI-HI (p<0.05) measures of tumor neovascularity in the MW-9 and the DB-1 mice, respectively. Preliminary results from a human trial of the anti-angiogenic drug Angiostatin (Entremed, Rockville, MD) showed tumor volumes increased in two patients, while the vascularity remained virtually unchanged. Conversely, in three patients with diminished tumor volumes vascularity increased by 38%. In conclusion, contrast enhanced ultrasound imaging of tumor neovascularity may provide noninvasive markers of angiogenesis and may become a useful tool for monitoring anti-angiogenic therapies in vivo.     

Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd.     

Torsional Motion in (tert‐Butyl)ammonium Hemispheraplexes: Rotational Barriers and Energy of Binding

The ADPs (ADPs=atomic anisotropic displacement parameters) from the single‐crystal X‐ray studies of nine related TBA⁺ (TBA⁺=(tert‐butyl)ammonium) hemispheraplexes are analyzed, and the results compared to the free energy of binding of this guest by the nine hosts. The lipophilic hosts (Fig. 1) were synthesized over a number of years, with increasing pre‐organization for and specificity of binding. Structural studies for six of the complexes have been published, but the remaining three structures, including those of the strongest binders of TBA⁺, are disordered and have only now been completed. New area‐detector data has been analyzed for the TBA⁺ClO complexes of 5 and of 8 at two temperatures, while the original data for 9 ?TBA⁺SCN^? has been treated with a disorder model. In addition, improved models are presented for the complexes of 6 and 7 . Methods for assessing the precision of the ADP analyses are discussed. Although most of the structures are imprecise, the TBA⁺ groups do demonstrate some of the characteristics of independent motion. The general trend in calculated libration amplitudes for the TBA⁺ group suggests that the guests with the greatest free energy of binding, and the shortest distances from N⁺ to the ligand plane, are those with the highest barriers to internal rotation.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Optical dephasing of the S1 ← S0 transition of free-base porphin in an n-decane host studied by photochemical hole-burning: a case of slow exchange

The homogeneous width and frequency of S₁ ← S₀ 0-0 transitions of free-base porphin in site B of n-decane are studied by photochemical hole-burning (T = 1.2–4.2 K). A localized phonon mode of 7 cm^?1 is identified as a phonon sideband and holes burnt into it yield a lifetime of 115 ± 20 ps. The results are consistent with the exchange model for slow exchange.     

Homogeneous linewidth and optical dephasing of the S1 ← So transition of magnesium porphin in an n-octane crystal: A study by transient and photochemical hole-burning

Transient and photochemical hole-burning is used to determine the homogeneous linewidths of the S_x ← S_o and S_y ← So transitions of a magnesium porphin-pyridine complex in four sites of n-octane (T = 1.2–4.2 K). Thermally induced dephasing of S_x ← S_o is consistent with “exchange” to low-frequency local modes identified in the spectra. The relaxation time of S_y varies front ≈ to 4 ps from site to site.