Spin gap and resonance at the nesting wave vector in superconducting FeSe_{0.4}Te_{0.6}

Neutron scattering is used to probe magnetic excitations in FeSe_{0.4}Te_{0.6} (T_{c} = 14 K). Low energy spin fluctuations are found with a characteristic wave vector (1/21/2L) that corresponds to Fermi surface nesting and differs from Q_{m} = (delta01/2) for magnetic ordering in Fe_{1+y}Te. A spin resonance with variant Planck's over 2piOmega_{0} = 6.51(4) meV approximately 5.3k_{B}T_{c} and variant Planck's over 2piGamma = 1.25(5) meV develops in the superconducting state from a normal state continuum. We show that the resonance is consistent with a bound state associated with s_{+/-} superconductivity and imperfect quasi-2D Fermi surface nesting.

Tunable (deltapi, deltapi)-type antiferromagnetic order in alpha-Fe(Te,Se) superconductors

The new alpha-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and BaFe(2)As(2) families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector (pi, 0), a completely different magnetic order with a composition tunable propagation vector (deltapi, deltapi) was determined for the parent compound Fe_{1+y}Te in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest T_{C} sample. An alternative to the prevailing nesting Fermi surface mechanism is required to understand the latest family of ferrous superconductors.

Phase II and pharmacogenomics study of enzastaurin plus temozolomide and radiation therapy in patients with glioblastoma multiforme or gliosarcoma

2020

Background: ENZ, an oral serine/threonine kinase inhibitor, suppresses signaling through PKCβ and the PI3K/AKT pathways to induce apoptosis, reduce proliferation, and suppress angiogenesis. The primary endpoint of this single-arm phase II trial was overall survival (OS). Secondary objectives included progression-free survival (PFS), safety, PK/PD, and patient-reported outcomes (PROs). A concurrent PGx project assessed the value of pretreatment molecular profiles as predictive of outcome. Magnetic resonance spectroscopy (MRS) was also evaluated during treatment for its value in predicting OS. Methods: Patients enrolled with newly diagnosed GBM/GS and KPS ≥60. Treatment started <5 weeks after diagnosis with RT 60 Gy given over 6 weeks and TMZ 75 mg/m2 given daily during RT and then at 200 mg/m2 from days 1–5 of a 28-day cycle. ENZ 250 mg/day was given daily during RT and adjuvantly. Planned treatment duration was 1 year. PGx parameters were: MGMT promoter methylation, mismatch repair status, PKC isoforms, pERK, pCREB, EGFR, PTEN, GSK3B, ser9, VEGF, and pS6. MRS was performed at baseline and at scheduled intervals. Changes in molecular signatures and imaging characteristics relative to survival were estimated using Kaplan-Meier and proportional hazards models. Analyses included phase I patients at ENZ 250 mg/day. Results: From September 2007 to November 2008, 60 phase II patients enrolled; 52 completed RT and eight are receiving RT. Of these, seven patients progressed immediately after RT and 17 progressed after one or more adjuvant cycles; five discontinued due to toxicity; four withdrew from trial. Treatment was well tolerated. The only toxicities seen in more than one-third of pateints were grade 1 fatigue, grade 1 nausea, and grade 1–2 lymphopenia. Grade 1 thrombocytopenia was seen in eight patients and grade 3 lymphopenia in five patients. OS, PFS, PROs, PGx, and imaging findings will be reported. Conclusions: The combination of ENZ plus TMZ during and following RT was well tolerated and may be an active regimen in GBM. This study represents the future of neuro-oncology clinical trial design by employing a novel multi-modal therapy while concurrently studying novel imaging and molecular techniques that may predict efficacy.

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Tunnel conductance of Watson-Crick nucleoside-base pairs from telegraph noise

The use of tunneling signals to sequence DNA is presently hampered by the small tunnel conductance of a junction spanning an entire DNA molecule. The design of a readout system that uses a shorter tunneling path requires knowledge of the absolute conductance across base pairs. We have exploited the stochastic switching of hydrogen-bonded DNA base-nucleoside pairs trapped in a tunnel junction to determine the conductance of individual molecular pairs. This conductance is found to be sensitive to the geometry of the junction, but a subset of the data appears to come from unstrained molecular pairs. The conductances determined from these pairs are within a factor of two of the predictions of density functional calculations. The experimental data reproduces the counterintuitive theoretical prediction that guanine-deoxycytidine pairs (3 H-bonds) have a smaller conductance than adenine-thymine pairs (2 H-bonds). A bimodal distribution of switching lifetimes shows that both H-bonds and molecule-metal contacts break.

Tunnelling readout of hydrogen-bonding-based recognition

Hydrogen bonding has a ubiquitous role in electron transport and in molecular recognition, with DNA base pairing being the best-known example. Scanning tunnelling microscope images and measurements of the decay of tunnel current as a molecular junction is pulled apart by the scanning tunnelling microscope tip are sensitive to hydrogen-bonded interactions. Here, we show that these tunnel-decay signals can be used to measure the strength of hydrogen bonding in DNA base pairs. Junctions that are held together by three hydrogen bonds per base pair (for example, guanine-cytosine interactions) are stiffer than junctions held together by two hydrogen bonds per base pair (for example, adenine-thymine interactions). Similar, but less pronounced effects are observed on the approach of the tunnelling probe, implying that attractive forces that depend on hydrogen bonds also have a role in determining the rise of current. These effects provide new mechanisms for making sensors that transduce a molecular recognition event into an electronic signal.

Free swelling and confined smart hydrogels for applications in chemomechanical sensors for physiological monitoring

We investigate thin films of "smart" polymer hydrogels used to convert miniature pressure sensors into novel chemomechanical sensors. In this versatile sensing approach, a smart hydrogel is confined between a porous membrane and the diaphragm of a piezoresistive pressure transducer. An increase in the environmental analyte concentration, as sensed through the pores of the membrane, is detected by measuring the change in pressure exerted by the hydrogel on the pressure transducer diaphragm. We compare the response of such a sensor with the response of a free-swelling hydrogel identical to the one used within the sensor. The sensor and the free hydrogel are observed to have comparable mean response times. However, the time-dependent response curve of the sensor, unlike that of the free hydrogel, is highly asymmetric between swelling and deswelling, with a smaller time constant for deswelling. We also investigate novel methods for increasing sensor sensitivity, such as use of a two-layer membrane with a nanoporous polymer inner layer, and pre-loading of the hydrogel under pressure. In ionic strength response tests, use of an inner membrane increases sensor sensitivity without increasing mean response time, an effect that varies with membrane water fraction.