The role of humic acid aggregation on the kinetics of photosensitized singlet oxygen production and decay

The effect of humic acid (HA) aggregate formation on the photosensitized generation and subsequent quenching of singlet molecular oxygen O2(a1Δg) was investigated. Time-resolved O2(a1Δg) phosphorescence traces were obtained from (a) bulk samples of HA dispersions and (b) microscope-based experiments performed upon irradiation of a single HA aggregate. In the bulk experiments, the dependence of the O2(a1Δg) lifetime on the HA concentration yields a critical concentration for the formation of micrometric HA aggregates of 0.58 g L−1. This value is consistent with that obtained using pyrene as a fluorescent probe (0.38 g L−1). Microscope-based experiments were also performed with HA samples containing added singlet oxygen sensitizers; either the hydrophobic meso-tetraphenylporphyrin (TPP) or the hydrophilic 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-21H,23H-porphine (TMPyP). Singlet oxygen phosphorescence could only be detected upon irradiation of TMPyP, a molecule which localizes on the exterior part of the HA aggregates. The inability to detect O2(a1Δg) phosphorescence from HA samples containing TPP is consistent with the model that the O2(a1Δg) produced in the interior of the aggregate was completely quenched by the high local concentration of HA reactive groups in this environment.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Phylogeny and Taxonomy of the Round-Eared Sengis or Elephant-Shrews, Genus Macroscelides (Mammalia, Afrotheria, Macroscelidea)

The round-eared sengis or elephant-shrews (genus Macroscelides) exhibit striking pelage variation throughout their ranges. Over ten taxonomic names have been proposed to describe this variation, but currently only two taxa are recognized (M. proboscideus proboscideus and M. p. flavicaudatus). Here, we review the taxonomic history of Macroscelides, and we use data on the geographic distribution, morphology, and mitochondrial DNA sequence to evaluate the current taxonomy. Our data support only two taxa that correspond to the currently recognized subspecies M. p. proboscideus and M. p. flavicaudatus. Mitochondrial haplotypes of these two taxa are reciprocally monophyletic with over 13% uncorrected sequence divergence between them. PCA analysis of 14 morphological characters (mostly cranial) grouped the two taxa into non-overlapping clusters, and body mass alone is a relatively reliable distinguishing character throughout much of Macroscelides range. Although fieldworkers were unable to find sympatric populations, the two taxa were found within 50 km of each other, and genetic analysis showed no evidence of gene flow. Based upon corroborating genetic data, morphological data, near sympatry with no evidence of gene flow, and differences in habitat use, we elevate these two forms to full species

Photosensitizer Drug Delivery via an Optical Fiber

: An optical fiber has been developed with a maneuverable miniprobe tip that sparges O2 gas and photodetaches pheophorbide (sensitizer) molecules. Singlet oxygen is produced at the probe tip surface which reacts with an alkene spacer group releasing sensitizer upon fragmentation of a dioxetane intermediate. Optimal sensitizer photorelease occurred when the probe tip was loaded with 60 nmol sensitizer, where crowding of the pheophorbide molecules and self-quenching were kept to a minimum. The fiber optic tip delivered pheophorbide molecules and singlet oxygen to discrete locations. The 60 nmol sensitizer was delivered into petrolatum; however, sensitizer release was less efficient in toluene-d8 (3.6 nmol) where most had remained adsorbed on the probe tip, even after the covalent alkene spacer bond had been broken. The results open the door to a new area of fiber optic-guided sensitizer delivery for the potential photodynamic therapy of hypoxic structures requiring cytotoxic control

Factors influencing engineering students’ decisions to cheat by type of assessment

Academic dishonesty (cheating) has been prevalent on college campuses for decades, and the percentage of students reporting cheating varies by college major. This study, based on a survey of 643 undergraduate engineering majors at 11 institutions, used two parallel hierarchical multiple regression analyses to predict the frequency of cheating on exams and the frequency of cheating on homework based on eight blocks of independent variables: demographics, pre-college cheating behavior, co-curricular participation, plus five blocks organized around Ajzen’s Theory of Planned Behavior (moral obligation not to cheat, attitudes about cheating, evaluation of the costs and benefits of cheating, perceived social pressures to cheat or not to cheat, and perceived effectiveness of academic dishonesty policies). The final models significantly predict 36% of the variance in “frequency of cheating on exams” and 14% of the variance in “frequency of cheating on homework”. Students don’t see cheating as a single construct and their decisions to cheat or not to cheat are influenced differently depending on the type of assessment. Secondary findings are that a student’s conviction that cheating is wrong no matter what the circumstances is a strong deterrent to cheating across types of assessment and that a student who agrees that he/she would cheat in order to alleviate stressful situations is more likely to cheat on both exams and homework.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42694/1/11162_2006_Article_9010.pd