Dynamics of p-terphenyl crystals at the phase transition temperature: a zero-field EPR study of the photoexcited triplet state of pentacene in p-terphenyl crystals.

Pulsed zero-field electron paramagnetic resonance free induction decay (ZF EPR FID) techniques are employed to study the phase transition of p-terphenyl crystals (Tc = 193 K) by measuring selectively populated photoexcited triplet ZF transitions of dilute pentacene molecules in p-terphenyl single crystals. The sensitivity of ZF spectroscopy to small shifts in local magnetic fields enables the studies of guest-host configuration changes over a wide temperature range. Here we report the observation of guest pentacene (-h(14) and -d(14)) triplet ZF EPR FID spectra that disappear abruptly at Tc and of spectral broadening and shift below Tc. We interpret these spectral changes as evidence for guest couplings to host phenyl rings. Further, these data allow assignments of spectroscopic sites to crystallographic sites that occur in the phase transition.

Orientational anisotropic studies by field rotation technique: near zero-field pulsed EPR experiments of pentacene doped in p-terphenyl.

We report a new technique to map the orientational anisotropy of paramagnetic systems without physically changing the crystal orientations in near zero-field (NZF) pulsed EPR experiments. By implementing three sets of orthogonal coils around the sample, we are ble to create a magnetic vector up to 2 mT in any three-dimensional orientation in space. In NZF region, the hyperfine tensor elements are comparable to the electronic Zeeman interaction energy, thus very rich spectral patterns can be obtained by "dialing" in a magnetic field vector without moving the sample. The technique further allows us to examine the site symmetry of organic crystals and powdered solids doped with chromophores which can be photo-excited to the triplet state by laser light. The technique is exemplified in the study of pentacene in p-terphenyl crystals.

Defining the pHi-hyperthermia sensitivity relationship for the RIF-1 tumor in vivo: a 31P MR spectroscopy study.

This study quantifies the enhancement of the therapeutic efficacy of hyperthermia resulting from an acutely acidified and accurately monitored intracellular pH (pHi) in a mouse tumor model in vivo. Metabolic manipulation of the physiology of RIF-1 tumor (subcutaneous, on the hind flanks of female C3H/HeJ mice) achieved by i.p. bolus injection of glucose (glycolytic tumor acidification) or 3-O-methylglucose (non-glycolytic tumor acidification) was monitored by 31P magnetic resonance (31P MR) prior to, during and up to 1 h after localized hyperthermia. The pre-hyperthermia 31P MR-observable metabolic parameter that correlates most strongly with thermal sensitivity is pHi. Thermal sensitivity increases linearly with decreasing pHi regardless of the mechanism (glycolytic or non-glycolytic) of metabolic manipulation. The quantitative relationship is described by log10(SF)/EQ43=0.0079 pHi,preHT -0.0606 (R=0.63, P<0.0001), where EQ43 is the thermal heat dose delivered to the tumor (in units of equivalent minutes at 42.5 degrees C), pHi,preHT is the intracellular pH immediately prior to hyperthermia, and SF is the surviving fraction. The therapeutic enhancement is not as dramatic as expected based upon previously reported in vitro studies but is generally consistent with other in vivo studies. The method still represents a viable strategy for enhancing the therapeutic efficacy of hyperthermia, especially when used in combination with other therapeutic modalities.