Important applications of photon upconversion through triplet-triplet annihilation require conversion of near-IR photons to visible light. Generally, however, efficiencies in this spectral region lag ...behind bluer analogues. Herein we consider potential benefits from a conformationally well-defined covalent dimer annihilator TIPS-BTX in studies that systematically compare function to a related monomer model TIPS-tetracene (TIPS-Tc). TIPS-BTX exhibits weak electronic coupling between chromophores juxtaposed about a polycyclic bridge. We report an upconversion yield
UC
for TIPS-BTX that is more than 20× larger than TIPS-Tc under comparable conditions (0.16%). While the dimer
UC
is low compared to bluer champion systems, this yield is amongst the largest so-far reported for a tetracenic dimer system and is achieved under unoptimized conditions suggesting a significantly higher ceiling. Further investigation shows the
UC
enhancement for the dimer is due exclusively to the TTA process with an effective yield more that 30× larger for TIPS-BTX compared to TIPS-Tc. The
TTA
enhancement for TIPS-BTX relative to TIPS-Tc is indicative of participation by intramolecular multiexciton states with evidence presented in spin statistical arguments that the
5
TT is involved in productive channels. For TIPS-BTX we report a spin-statistical factor
f
= 0.42 that matches or exceeds values found in champion annihilator systems such as DPA. At the same time, the poor relative efficiency of TIPS-Tc suggests involvement of non-productive bimolecular channels and excimeric states are suspected. Broadly these studies indicate that funneling of photogenerated electronic states into productive pathways, and avoiding parasitic ones, remains central to the development of champion upconversion systems.
We report upconversion for a rigid tetracene dimer that yields 20× that of a monomer model. This is due to a 30× relative enhancement in TTA, indicating participation by intramolecular multiexciton states, including the
5
TT, in productive channels.
A comprehensive investigation of the solution-phase photophysics of tetracene bis-carboxylic acid 5,12-tetracenepropiolic acid (Tc-DA) and its related methyl ester 5,12-tetracenepropynoate (Tc-DE), a ...non-hydrogen-bonding counterpart, reveals the role of the carboxylic acid moiety in driving molecular aggregation and concomitant excited-state behavior. Low-concentration solutions of Tc-DA exhibit similar properties to the popular 5,12-bis((triisopropylsilyl)ethynl)tetracene, but as the concentration increases, evidence for aggregates that form excimers and a new mixed-state species with charge-transfer (CT) and correlated triplet pair (TT) character is revealed by transient absorption and fluorescence experiments. Aggregates of Tc-DA evolve further with concentration toward an additional phase that is dominated by the mixed CT/TT state which is the only state present in Tc-DE aggregates and can be modulated with the solvent polarity. Computational modeling finds that cofacial arrangement of Tc-DA and Tc-DE subunits is the most stable aggregate structure and this agrees with results from 1H NMR spectroscopy. The calculated spectra of these cofacial dimers replicate the observed broadening in ground-state absorption as well as accurately predict the formation of a near-UV transition associated with a CT between molecular subunits that is unique to the specific aggregate structure. Taken together, the results suggest that the hydrogen bonding between Tc-DA molecules and the associated disruption of hydrogen bonding with solvent produce a regime of dimer-like behavior, absent in Tc-DE, that favors excimers rather than CT/TT mixed states. The control of aggregate size and structure using distinct functional groups, solute concentration, and solvent in tetracene promises new avenues for its use in light-harvesting schemes.
Controlling the binding of functional organic molecules on quantum dot (QD) surfaces and the resulting ligand/QD interfacial structure determines the resulting organic–inorganic hybrid behavior. In ...this study, we vary the binding of tetracenedicarboxylate ligands bound to PbS QDs cast in thin films by performing solid-state ligand exchange of as-produced bound oleate ligands. We employ comprehensive Fourier-transform infrared (FTIR) analysis coupled with ultraviolet–visible (UV–vis) spectrophotometric measurements, transient absorption, and Density Functional Theory (DFT) simulations to study the QD/ligand surface structure and resulting optoelectronic properties. We find that there are three primary QD/diacid structures, each with a distinct binding mode dictated by the QD–ligand and ligand–ligand intermolecular and steric interactions. They can be accessed nearly independently of one another via different input ligand concentrations. Low concentrations produce mixed oleate/tetracene ligand structures where the tetracene carboxylates tilt toward QD surfaces. Intermediate concentrations produce mixed oleate/tetracene ligand structures with ligand–ligand interactions through intramolecular hydrogen bonding with the ligands perpendicular to the QD surface and weaker QD/ligand electronic interactions. High concentrations result in full ligand exchange, and the ligands tilt toward the surface while the QD film compacts. When the tetracene ligands tilt or lie flat on the QD surface, the benzene ring π-system interacts strongly with the p-orbitals at the PbS surface and produces strong QD–ligand interactions evidenced through QD/ligand state mixing, with a coupling energy of ≈700 meV.
SV40 induces mesotheliomas in hamsters Cicala, C; Pompetti, F; Carbone, M
The American journal of pathology,
05/1993, Volume:
142, Issue:
5
Journal Article
Peer reviewed
In the course of studies to elucidate the relative contribution of simian virus 40 (SV40) large T and small t proteins during oncogenesis, we observed the appearance of pericardial and pleural tumors ...in 100% of Syrian hamsters injected in the pleural space with wild type SV40. When SV40 was injected via the intracardiac or intraperitoneal routes, more than 50% of hamsters developed mesothelial tumors. Macroscopic, microscopic, ultramicroscopic, and histochemical characteristics identify these neoplasms and derived cell lines as mesotheliomas and mesothelioma-derived cell lines. The SV40 genome was integrated and expressed in the mesotheliomas and derived cell lines. The absence of mesotheliomas in hamsters injected with SV40 small t deletion mutants indicates that the small t protein plays an important role in the development of SV40-induced mesotheliomas. To the best of our knowledge, this is the first definitive report of virus-induced mesotheliomas in mammals.
Benzoghiperylene monoimides (BPIs) have recently been employed as organic photocatalysts for challenging reductions. In probing their function, we identify a thermal degradation product involving ...imide ring opening, and this in turn motivates the development and synthesis of a high-symmetry model systema benzoghiperylene diester (BPDE)whose structural simplicity is useful for mechanistic exploration relevant to the broader photocatalyst class. Using electrochemical and spectroscopic tools, we probe both the singly and doubly reduced states of BPDE and report the generation of BP-H – , a two-electron, one-proton activated closed-shell super-reductant. This catalytically active species, after visible photon absorption, operates from its singlet excited state, where the motions of the added proton are coupled to an electron transfer event, which enables direct reduction of inert substrates like benzene and fluorobenzene. Traditional Birch chemistry on benzene has been previously realized only by solvated electrons or electrochemistry. The function of this model system uncovered in these mechanistic explorations suggests modes of operation for this photocatalyst class that will enable future optimizations.
Duane syndrome (MIM126800) is an autosomal dominant disease responsible for 1% of all strabismus cases and has been related to a 8q12-13 contiguous gene syndrome. We report on an insertion of ...chromosome region 8q13-q21.2 on to band 6q25 in a patient presenting with Duane syndrome, mental retardation, and other dysmorphisms. FISH analysis using chromosome 8 radiation hybrid LIA2L indicated a concurrent deletion within the 8q rearranged region. These results were corroborated by STR-PCR analysis and FISH using YAC contig WC8.8 disclosed a deletion in 8q13. Comparison of the two known patients with Duane syndrome associated with deletion of 8q identifies a small region of overlap (SRO) of < 3 cM extending from D8S533 and D8S1767 in which a Duane syndrome locus is assigned. In addition YAC analysis in our patient showed that 8q rearrangement was rather complex since 8q deletion and insertion occurred in two distinct segments separated by a region which maintained its location on 8q.
Y chromosome molecular analysis was performed using the STS-PCR technique in 50 patients with oligozoospermia. Microdeletions of interval 6 of the Y chromosome were detected in seven patients, in six ...of whom subinterval E was affected. All patients retained the RBM1 and DAZ genes, while in one deletion involved the SPGY gene. The size of the deletion was not apparently related to the severity of the disease. These results suggest the presence of an oligozoospermia critical region on the Y chromosome within subinterval E of interval 6.
The c-myc and c-fos proto-oncogenes have several putative functions, including regulation of cell growth. In many neoplasms c-myc overexpression has been linked to poor prognosis. In order to study ...the role of c-myc and c-fos expression on the tumorigenesis, and the metastatic spread of osteosarcoma, frozen and paraffin-embedded tissue 38 primary osteosarcoma and 10 lung metastases were analyzed. The mRNA analysis was performed by quantitative reverse transcription-polymerase chain reaction and in situ hybridization. The protein expression was studied by Western blot analysis and immunohistochemistry. C-myc and c-fos were found overexpressed in a high percentage of the relapsed tumors and of the metastases, and overexpression of both oncogenes in the same tumor was strongly correlated to the development of metastases (p < 0.05), as 6 of the 7 primary tumors overexpressing both the oncogenes gave metastases. In conclusion, both c-myc and c-fos are involved in the growth and spread of osteosarcoma and a synchronous overexpression of both oncogenes is highly significant for a metastatic potential of a primary tumor.
Simian virus 40 (SV40) is a monkey virus that induces ependymomas, choroid plexus tumors, mesotheliomas, osteosarcomas, sarcomas and true histiocytic lymphomas when injected in hamsters. Recently, ...approximately 60% of human ependymomas, choroid plexus tumors and mesotheliomas were reported to contain and express SV40-like sequences (N. Engl. J. Med., 1992, 36, 988-993; Oncogene, 1994, 9, 1781-1790). In this study the presence of SV40-like sequences was investigated in additional types of human tumors. Initially, 200 tumor and normal tissue DNA samples were analysed by polymerase chain reaction (PCR) with primers that amplify a 574 base pair region of SV40 large T antigen (Tag), which includes the Rb-pocket binding domain and the intron of Tag. PCR amplification and Southern blot hybridization with a probe specific for SV40 Tag revealed that 18/200 samples contained SV40-like sequences and, unexpectedly, 11/18 were from patients with osteosarcomas. Additional DNA samples from bone tumors were then analysed. In 40/126 osteosarcomas, and 14/34 other bone-related tumors, Tag sequences could be amplified. Sequence analysis of the DNA amplified from seven different tumors confirmed that the amplified sequences corresponded to SV40 Tag, with some demonstrating deletions in the intron region but not in the Rb-pocket binding domain. The extent of SV40 genome sequences present in the DNA samples was further analysed in two osteosarcomas. PCR amplification, Southern blot hybridization, and sequence analysis revealed that these samples also contained sequences for the carboxy-terminal domain of Tag, the viral regulatory region, and the VP1 capsid protein. These results indicate that SV40-like sequences are present in human bone tumors.
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