Real-time observation of ultrafast electron injection at graphene-Zn porphyrin interfaces

We report on the ultrafast interfacial electron transfer (ET) between zinc(II) porphyrin (ZnTMPyP) and negatively charged graphene carboxylate (GC) using state-of-the-art femtosecond laser spectroscopy with broadband capabilities. The steady-state interaction between GC and ZnTMPyP results in a red-shifted absorption spectrum, providing a clear indication for the binding affinity between ZnTMPyP and GC via electrostatic and π-π stacking interactions. Ultrafast transient absorption (TA) spectra in the absence and presence of three different GC concentrations reveal (i) the ultrafast formation of singlet excited ZnTMPyP*, which partially relaxes into a long-lived triplet state, and (ii) ET from the singlet excited ZnTMPyP* to GC, forming ZnTMPyP˙(+) and GC˙(-), as indicated by a spectral feature at 650-750 nm, which is attributed to a ZnTMPyP radical cation resulting from the ET process.

A layer-by-layer ZnO nanoparticle-PbS quantum dot self-assembly platform for ultrafast interfacial electron injection

Absorbent layers of semiconductor quantum dots (QDs) are now used as material platforms for low-cost, high-performance solar cells. The semiconductor metal oxide nanoparticles as an acceptor layer have become an integral part of the next generation solar cell. To achieve sufficient electron transfer and subsequently high conversion efficiency in these solar cells, however, energy-level alignment and interfacial contact between the donor and the acceptor units are needed. Here, the layer-by-layer (LbL) technique is used to assemble ZnO nanoparticles (NPs), providing adequate PbS QD uptake to achieve greater interfacial contact compared with traditional sputtering methods. Electron injection at the PbS QD and ZnO NP interface is investigated using broadband transient absorption spectroscopy with 120 femtosecond temporal resolution. The results indicate that electron injection from photoexcited PbS QDs to ZnO NPs occurs on a time scale of a few hundred femtoseconds. This observation is supported by the interfacial electronic-energy alignment between the donor and acceptor moieties. Finally, due to the combination of large interfacial contact and ultrafast electron injection, this proposed platform of assembled thin films holds promise for a variety of solar cell architectures and other settings that principally rely on interfacial contact, such as photocatalysis.

Quantum confinement-tunable intersystem crossing and the triplet state lifetime of cationic porphyrin–CdTe quantum dot nano-assemblies

We show the possibility of modulating the triplet-state lifetime of cationic porphyrins on the surface of CdTe quantum dots.

Generation of Multiple Excitons in Ag2S Quantum Dots: Single High-Energy versus Multiple-Photon Excitation

We explored biexciton generation via carrier multiplication (or multiple-exciton generation) by high-energy photons and by multiple-photon absorption in Ag2S quantum dots (QDs) using femtosecond broad-band transient absorption spectroscopy. Irrespective of the size of the QDs and how the multiple excitons are generated in the Ag2S QDs, two distinct characteristic time constants of 9.6-10.2 and 135-175 ps are obtained for the nonradiative Auger recombination of the multiple excitons, indicating the existence of two binding excitons, namely, tightly bound and weakly bound excitons. More importantly, the lifetimes of multiple excitons in Ag2S QDs were about 1 and 2 orders of magnitude longer than those of comparable size PbS QDs and single-walled carbon nanotubes, respectively. This result is significant because it suggests that by utilizing an appropriate electron acceptor, there is a higher possibility to extract multiple electron-hole pairs in Ag2S QDs, which should improve the performance of QD-based solar cell devices.

Adipocytokines and aging: adiponectin and leptin

Adipose tissue is an active metabolic organ secreting adipocytokines which are involved in the energy homeostasis and regulation of glucose and lipid metabolism. Aging is associated with fat redistribution, which is characterized by loss of peripheral subcutaneous fat and accumulation of visceral fat. Visceral adipose tissue is more involved in the developement of metabolic diseases than subcutaneous adipose tissue. Aging also alters the function, proliferation, size, and number of adipose cells which leads to alterations in the secretion, synthesis and function of the adipocytokines. Adiponectin is an insulin sensitizing, anti-inflammatory, and antiathoregenic adipokine. Centarians have higher adiponectin levels associated with longevity. However, in older individuals ‑ age 65 or more ‑ adiponectin is associated with higher mortality. Dysregulation of adiponectin in older individuals may be due to loss of function of circulating adiponectin or a response to increased inflammatory process. Longitidunal increase in adiponectin levels 5with aging rather than genetically high adiponectin levels may translate to increased mortality in older patients. The adipocytokine leptin is traditionally viewed as a product of adipocytes that can exert endocrine effects. There have been conflicting reports of not only the effects of aging on leptin, but also the effects of leptin on age-related diseases including sarcopenia, Alzheimer's disease and cardiovascular diseases. Aging is also associated with resistance to leptin and/or to a decrease of receptors for this hormone. In this review, we briefly discuss the role of two major adipocytokines adiponectin and leptin in the aging process and age-related diseases.

Polarization and droplet size effects in the laser-trapping-induced reconfiguration in individual nematic liquid crystal microdroplets

We experimentally demonstrate reordering throughout the inside of an individual bipolar nematic liquid-crystalline microdroplet optically trapped by a highly focused laser beam, when the laser powers are above a definite threshold. The threshold depends on the droplet size and laser polarization. A physical interpretation of the results is presented by considering the nonlocal orientations of the nematic liquid-crystal molecules in the droplets with the dimensions on the order of the focal spot diameter or larger. On the basis of the finite size approximation, we show that the dependence of threshold power on the droplet size is calculated to be in qualitative agreement with the experimental data.

Optical trapping of nanoparticles by ultrashort laser pulses

Optical trapping with continuous-wave lasers has been a fascinating field in the optical manipulation. It has become a powerful tool for manipulating micrometer-sized objects, and has been widely applied in physics, chemistry, biology, material, and colloidal science. Replacing the continuous-wave- with pulsed-mode laser in optical trapping has already revealed some novel phenomena, including the stable trap, modifiable trapping positions, and controllable directional optical ejections of particles in nanometer scales. Due to two distinctive features; impulsive peak powers and relaxation time between consecutive pulses, the optical trapping with the laser pulses has been demonstrated to have some advantages over conventional continuous-wave lasers, particularly when the particles are within Rayleigh approximation. This would open unprecedented opportunities in both fundamental science and application. This Review summarizes recent advances in the optical trapping with laser pulses and discusses the electromagnetic formulations and physical interpretations of the new phenomena. Its aim is rather to show how beautiful and promising this field will be, and to encourage the in-depth study of this field.

Pattern of oncologic emergencies seen in adult cancer patients attending the Radiotherapy and Oncology Centre, Ahmadu Bello University Teaching Hospital, Zaria - Nigeria

AIMS AND OBJECTIVES

To evaluate the Pattern of Oncologic Emergencies seen in Adult cancer patients and the treatment modalities used.

MATERIALS AND METHODS

Between January 2004 and December 2008, a total of 1824 (M:F = 1:1.8) new patients were seen. 196 (M:F = 1:1.4) consecutive patients with histologically confirmed malignancies presenting with or having oncologic emergencies were treated and have been reviewed. Patients' folders were reviewed retrospectively with a structured pro forma. Results were analysed using Epi Info soft ware Version 3.4.1; 2007 Edition.

RESULTS

The median age was 49 years and mean age of 42 years (range, 15 - 82 years). M: F = 1:1.4. 162 patients had oncologic emergencies at presentation while 21 during treatments and 13 during follow up. At the time of diagnosis of oncologic emergency, 126 were not on any treatment, 42 patients on hormonal therapy and 28 patients were on diverse chemotherapy. All the patients presented late with 108 patients presenting with metastatic disease and 88 patients with locally advanced disease. Only 35 patients were treated within 1 week of onset of emergency. 59 patients had cervical cancer, 31 patients with breast cancer and 28 patients with prostate cancer. Tumour haemorrhage wass the commonest oncologic emergency seen in 107 patients followed by bone pain with imminent cord compression from bone metastases in 59 patients. Of 107 patients with tumour haemorrhage, 54 patients had cardiovascular collapse with 7 having acute renal failure. Similarly, of the 107 with tumour haemorrhage, 56 patients bled from cervical cancer, 12 patients from breast cancer and 8 patients from urinary bladder. 129 patients were treated with teletherapy, 31 patients had chemotherapy, 27 patients had emergency surgery and 5 patients had chemoradiation. Oncologic emergencies were corrected in 126 patients.

CONCLUSION

Tumour haemorrhage is the commonest oncologic emergency in this environment and teletherapy is the commonest therapy used. More radiotherapy centres are needed for prompt treatment and their usefulness in managing emergencies should be made known. Oncologic emergencies are commonly seen in metastatic and locally advanced disease.

Glycine crystallization in solution by CW laser-induced microbubble on gold thin film surface

We have developed a novel laser-induced crystallization method utilizing local heat-induced bubble/water interface. Continuous laser beam of 1064 nm is focused on a gold nanoparticles thin film surface covered with glycine supersaturated aqueous solution. Light absorption of the film due to localized plasmon resonance caused local heating at the focal position and produced a single thermal vapor microbubble, which generated thermal gradient followed by convection flow around the bubble and eventually induced glycine crystallization and growth. The crystallization mechanism is discussed by considering gathering and accumulating molecules around the bubble/water interface assisted by convection flow and temperature jump.

New insights into the ultrafast photophysics of oxidized and reduced FAD in solution

The ultrafast photophysics of oxidized and reduced flavin adenine dinucleotide (FAD) in aqueous solution was studied by broadband UV-vis femtosecond transient absorption spectroscopy. We observed that oxidized FAD (FAD(ox)) in solution readily aggregates at submillimolar concentration. Upon excitation of FAD(ox), three excited-state lifetimes were found and assigned to three different species: the closed (stacked) conformation of the monomer (∼5.4 ps), the open (extended) conformation of the monomer (∼2.8 ns), and the dimer (∼27 ps). In the case of the stacked conformation of the monomer, we show that intramolecular electron transfer from the adenine to the isoalloxazine ring occurs with a time constant of 5.4 ps and is followed by charge recombination on a faster time scale, namely, 390 fs. We additionally demonstrate that deprotonated reduced flavin (FADH(-)) undergoes biphotonic ionization under high excitation fluence and dissociates into a hydrated electron and the neutral semiquinone radical FADH(•).

Characterization of two members of the cryptochrome/photolyase family from Ostreococcus tauri provides insights into the origin and evolution of cryptochromes

Cryptochromes (Crys) are blue light receptors believed to have evolved from the DNA photolyase protein family, implying that light control and light protection share a common ancient origin. In this paper, we report the identification of five genes of the Cry/photolyase family (CPF) in two green algae of the Ostreococcus genus. Phylogenetic analyses were used to confidently assign three of these sequences to cyclobutane pyrimidine dimer (CPD) photolyases, one of them to a DASH-type Cry, and a third CPF gene has high homology with the recently described diatom CPF1 that displays a bifunctional activity. Both purified OtCPF1 and OtCPF2 proteins show non-covalent binding to flavin adenine dinucleotide (FAD), and additionally to 5,10-methenyl-tetrahydrofolate (MTHF) for OtCPF2. Expression analyses revealed that all five CPF members of Ostreococcus tauri are regulated by light. Furthermore, we show that OtCPF1 and OtCPF2 display photolyase activity and that OtCPF1 is able to interact with the CLOCK:BMAL heterodimer, transcription factors regulating circadian clock function in other organisms. Finally, we provide evidence for the involvement of OtCPF1 in the maintenance of the Ostreococcus circadian clock. This work improves our understanding of the evolutionary transition between photolyases and Crys.

Verapamil stimulation test in hyperprolactinemia: loss of prolactin response in anatomic or functional stalk effect

AIM

Verapamil stimulation test was previously investigated as a tool for differential diagnosis of hyperprolactinemia, but with conflicting results. Macroprolactinemia was never considered in those previous studies. Here, we aimed to re-investigate the diagnostic value of verapamil in a population who were all screened for macroprolactinemia. Prolactin responses to verapamil in 65 female patients (age: 29.9 +/- 8.1 years) with hyperprolactinemia were tested in a descriptive, matched case-control study.

METHODS

Verapamil 80 mg, p.o. was administered, and then PRL levels were measured at 8th and 16th hours, by immunometric chemiluminescence. Verapamil responsiveness was determined by peak percent change in basal prolactin levels (PRL).

RESULTS

Verapamil significantly increased PRL levels in healthy controls (N. 8, PRL: 183%), macroprolactinoma (N. 8, PRL: 7%), microprolactinoma (N. 19, PRL: 21%), macroprolactinemia (N. 23, PRL: 126%), but not in pseudoprolactinoma (N. 8, PRL: 0.8%), and risperidone-induced hyperprolactinemia (N. 7, PRL: 3%). ROC curve analysis revealed that unresponsiveness to verapamil defined as PRL <7%, discriminated anatomical or functional stalk effect (sensitivity: 74%, specificity: 73%, AUC: 0.855+/-0.04, P <0.001, CI: 0.768-0.942) associated with pseudoprolactinoma or risperidone-induced hyperprolactinemia, respectively.

CONCLUSION

Verapamil responsiveness is not a reliable finding for the differential diagnosis of hyperprolactinemia. However, verapamil unresponsiveness discriminates stalk effect (i.e., anatomically or functionally inhibited dopaminergic tonus) from other causes of hyperprolactinemia with varying degrees of responsiveness.

Qualitative phytochemical screening and in vitro antimicrobial effects of methanol stem bark extract of Ficus thonningii (Moraceae)

The methanolic stem bark extract of Ficus thonningii (Moraceae) was subjected to preliminary phytochemical screening and in vitro antimicrobial tests. The phytochemical tests was carried out using standard methods of analysis and these investigations revealed the presence of alkaloids, anthraquinones, carbohydrates, flavonoids, saponins and tannins. The antimicrobial activity of the plant extract was assayed using the agar plate disc diffusion and nutrient broth dilution techniques. Test micro organisms were: Escherichia coli, Klebsiella spp, Pseudomonas aeruginosa, Salmonella typhi (gram-negative), Staphylococcus aureus and Streptococcus spp. (gram-positive). The extracts inhibited the growth of all the test organisms at different concentrations especially against Pseudomonas aeruginosa and Streptococcus spp. which had mean inhibition zone of 33.33+/-7.33 mm and 32.33+/-2.51 mm respectively. The results showed the MIC of 10 mg ml(-1) against pseudomonas and 1.25 against remaining organisms tested. The MBC against Staphylococcus aureus was 2.5 mg ml(-1) and that of Streptococcus spp. was found to be 0.625 mg ml(-1). The extracts showed varied inhibitory activity against the organisms studied.

Spectroscopic characterization of a (6-4) photolyase from the green alga Ostreococcus tauri

The cofactor content of OtCPF1, a (6-4) photolyase isolated from the green marine alga Ostreococcus tauri, was characterized by steady-state absorption and fluorescence spectroscopy. The heterologously expressed, GST-fused, purified protein (MW: 89kDa) is non-covalently bound to flavin adenine dinucleotide (FAD), with a flavin to apoprotein molecular ratio of 64%. No light-harvesting chromophore was found in this protein. In freshly purified OtCPF1, FAD is present in three different redox states: the fully oxidized form (FAD(ox), 82%), the neutral semiquinone (FADH*, 14%) and the fully reduced anion (FADH-, 4%). Keeping the sample in the dark, at 5 degrees C, yields oxidation of FADH* and FADH-, partial release of FAD to the solution and slow degradation of the protein. Upon steady-state blue-light irradiation of OtCPF1 at 450nm, photoreduction processes leading to an accumulation of stable FADH* and FADH- species are observed. We demonstrate that this accumulation is due to the presence of an external electron donor agent in the purification buffer. Composition changes observed under steady-state photoexcitation are interpreted in terms of photoinduced reductions of FAD(ox) and FADH* states and competitive back reactions. Specific irradiation by red light at 620 nm shows both photoreduction of FADH* to FADH- and irreversible oxidation of FADH* to FAD(ox). The photoinduced oxidation reaction is believed to be indirectly caused by the external donor agent present in the buffer. Photoexcitation is also shown to stabilize the binding of FAD to the protein. We suggest this effect to be due to slight changes in the protein conformation, possibly strengthening the hydrogen-bonding network surrounding FAD.