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Archaea have histone homologues and chromatin proteins to organize their DNA into a compact form. This allows them to survive in extreme climates. Cren7 is one such chromatin protein conserved in Crenarchaeota. When Cren7 binds to model natural DNA, calf thymus DNA (CTD, 58% AT content) and polynucleotides under adverse solution conditions (high temperature, ionic strength), CD bands at 275-290 nm shift to higher wavelengths indicating structural changes in DNA. It formed a strong complex with CTD and poly(dA-dT)·poly(dA-dT)

Gas-phase cationic ternary complexes of group 10 metals of the formula [(phen)M(X)]+, where phen = 1,10-phenanthroline (M = Ni, Pd, or Pt; and X = H or CH3), react with cyclohexane via C–H activation, forming the respective cyclohexyl species [(phen)M(c-C6H11)]+. Upon collisional activation, these species undergo two key competing processes: (i) ring opening followed by "cracking" of the hydrocarbon chain leading to extrusion of propylene and ethylene as major products among other hydrocarbons; and (ii) dehydrogenation of the cyclohexyl ring leading to the loss of one, two, or three hydrogen molecules, with subsequent loss of cyclohexenes or benzene. The relative prevalence of these two pathways strongly depends on the metal ion, with Pt preferring dehydrogenation over ring opening. The multiple catalytic cycles operating within both pathways are described. Density functional theory (DFT) calculations are used to shed light on mechanistic aspects associated with the experimental results.

Palladium-catalyzed cross-coupling protocols have become a cornerstone in organic synthesis. Here, a gas-phase model of the Hiyama cross-coupling reaction was designed to shed light on the roles of coordinated anions (fluoride versus chloride) in transmetalation from Si to Pd. A combination of mass spectrometry experiments and DFT calculations was used. The ligated palladium fluoride and chloride cationic complexes, [(phen)Pd(X)]+ (X = F and Cl), readily react with vinyltrimethylsilane, Me3Si(CH═CH2), via transmetalation to give [(phen)Pd(CH═CH2)]+ as the major product. DFT calculations reveal that this transmetalation reaction is concerted and proceeds via a four-centered transition state, illustrating the role of coordinated halide in this gas-phase system. Two minor side products are observed corresponding to transmetalation to give [(phen)Pd(CH3)]+ and [(phen)Pd(SiMe2X)]+. DFT calculations suggest that these arise from the same initial Si to Pd methyl transmetalation pathway to give the [(phen)Pd(CH3) + Me2(CH═CH2)SiX]+ intermediate, which either then loses Me2(CH═CH2)SiX or reacts via C–C bond coupling to ultimately yield propene and [(phen)Pd(SiMe2X)]+. [(phen)Pd(CH═CH2)]+ undergoes a reaction with a second molecule of vinyltrimethylsilane to form an adduct, which upon collision-induced dissociation liberates 1,3-butadiene to form [(phen)Pd(SiMe3)]+. DFT calculations suggest a mechanism in which C–C bond formation is followed by migration of SiMe3 from C to Pd. Links between the observed gas-phase chemistry and solution-phase Pd-mediated homocoupling reactions of vinyltrimethylsilanes are explored.

The ternary Pd complexes [(phen)Pd(H)]+ (1-Pd) and [(phen)Pd(CH3)]+ (5-Pd) (where phen = 1,10-phenanthroline) both react with hexane in a linear ion trap mass spectrometer, forming the C–H activation product [(phen)Pd(C6H11)]+ (3-Pd) and releasing H2 and CH4, respectively. Density functional theory (DFT) calculations agree well with the experiments in predicting low barriers for these reactions proceeding via a metathesis mechanism. Species 3-Pd undergoes extensive fragmentation, or "cracking", of the hydrocarbon chain when sufficient energy is supplied via collision-induced dissociation (CID), resulting in the extrusion of a mixture of alkenes, methane, and hydrogen. DFT calculations show that Pd "chain-walking" from α (terminal carbon) to β and from β to γ positions can proceed with barriers sufficiently below those required for chain "cracking". The fragmentation reactions can be made catalytic if 1-Pd and 5-Pd produced by CID of 3-Pd are allowed to react with hexane again. Ni complexes largely mirrored the chemistry observed for Pd. Both 1-Ni and 5-Ni reacted with hexane, forming 3-Ni, which fragmented under CID conditions in a fashion similar to 3-Pd. In contrast, only 5-Pt reacted with hexane to form 3-Pt, which fragmented predominantly via sequential losses of H2.

Resistance to pyrethroids (PY) and organophosphate (OP) insecticides is widespread among populations of Culex quinquefasciatus, the major vector of lymphatic filariasis (LF). The present study was designed to detect the L1014F kdr (knockdown resistant) mutation among Cx. quinquefasciatus populations in the filarial belt of Sri Lanka. Mosquitoes were reared from field-caught larvae from seven localities where LF is endemic. Susceptibility status of Cx. quinquefasciatus to adulticides, 0.05% deltamethrin, 0.75% permethrin, 5% malathion, and the larvicide temephos was determined using the standard WHO susceptibility tests. A fragment of vgsc gene was amplified and sequenced to identify the responsible kdr mutations. The susceptibility test results revealed less than 90% mortalities for 0.05% deltamethrin, and 0.75% permethrin and temephos. For 5% malathion, all study sites except Maharagama revealed greater than 90% mortality. The L1014F kdr mutation was observed in all studied populations. Although the overall microfilaria rate is less than 1% in the country, there is a high risk of re-emergence of LF in Sri Lanka due to abundant Cx. quinquefasciatus mosquitoes, increased resistant status to currently used insecticides, imported LF cases, higher rates of microfilaria among neighboring countries, and the advancement of tourism.

Acceptorless dehydrogenation of ethane was achieved in the gas phase via a two-step catalytic cycle involving ternary cationic metal hydrides, [(phen)M(H)]+, 1, and metal ethides, [(phen)M(CH2CH3)]+, 2, (where M = Ni, Pd, or Pt, and phen = 1,10-phenanthroline). Species 1 and 2 were generated and their reactivity studied in a quadrupole ion trap mass spectrometer. It was found that 1 readily reacted with ethane releasing H2 and forming 2, with the relative reactivity being Pt > Ni ≫ Pd. Density functional theory (DFT) calculations for this metathesis reaction agree with the experimental reactivity order. Species 2 can in turn be converted into 1 and release ethylene when sufficient energy is supplied via collision-induced dissociation. DFT calculations also provided insight into competing side reactions (e.g., dehydrogenation of 2 and formation of protonated phen ligand) that become competitive during this endothermic step. The catalytic cycle can be repeated in the mass spectrometer several times. Multiple entry points into the cycle have been identified and discussed.

Although back-surface passivation plays an important role in high-efficiency photovoltaics, it has not yet been definitively demonstrated for CdTe. Here, we present a solution-based process, which achieves passivation and improved electrical performance when very small amounts of oxidized Al3+ species are deposited at the back surface of CdTe devices. The open circuit voltage (Voc) is increased and the fill factor (FF) and photoconversion efficiency (PCE) are optimized when the total amount added corresponds to ∼1 monolayer, suggesting that the passivation is surface specific. Addition of further Al3+ species, present in a sparse alumina-like layer, causes the FF and PCE to drop as the interface layer becomes blocking to current flow. The optimized deposit increases the average baseline PCE for both Cu-free devices and devices where Cu is present as a dopant. The greatest improvement is found when the Al3+ species are deposited prior to the CdCl2 activation step and Cu is employed. In this case, the best-cell efficiency was improved from 12.6 to 14.4%. Time-resolved photoluminescence measurements at the back surface and quantum efficiency measurements performed at the maximum power point indicate that the performance enhancement is due to a reduction in the interface recombination current at the back surface.

Using fatty acids as renewable sources of biofuels requires deoxygenation. While a number of promising catalysts have been developed to achieve this, their operating mechanisms are poorly understood. Here, model molecular systems are studied in the gas phase using mass spectrometry experiments and DFT calculations. The coordinated metal complexes [(phen)M(O2CR)]+ (where phen=1,10‐phenanthroline; M=Ni or Pd; R=CnH2n+1, n≥2) are formed via electrospray ionization. Their collision‐induced dissociation (CID) initiates deoxygenation via loss of CO2 and [C,H2,O2]. The CID spectrum of the stearate complexes (R=C17H35) also shows a series of cations [(phen)M(R’)]+ (where R’ 17) separated by 14 Da (CH2) corresponding to losses of C2H4‐C16H32 (cracking products). Sequential CID of [(phen)M(R’)]+ ultimately leads to [(phen)M(H)]+ and [(phen)M(CH3)]+, both of which react with volatile carboxylic acids, RCO2H, (acetic, propionic, and butyric) to reform the coordinated carboxylate complexes [(phen)M(O2CR)]+. In contrast, cracking products with longer carbon chains, [(phen)M(R)]+ (R>C2), were unreactive towards these carboxylic acids. DFT calculations are consistent with these results and reveal that the approach of the carboxylic acid to the “free” coordination site is blocked by agostic interactions for R > CH3.

Because bifacial solar cells increase the power generated per area, their market share is projected to increase over the next decade. While silicon technologies have implemented bifacial technology...

Herein we report the photophysical and photochemical properties of palladacycle complexes derived from 8-aminoquinoline ligands, commonly used auxiliaries in C–H activation. Spectroscopic, electrochemical and computational studies reveal that visible light irradiation induces a mixed LLCT/MLCT charge transfer providing access to synthetically relevant Pd(iii)/Pd(iv) redox couples. The Pd(ii) complex undergoes photoinduced electron transfer with alkyl halides generating C(sp3)–H halogenation products rather than C–C bond adducts. Online photochemical ESI-MS analysis implicates participation of a mononuclear Pd(iii) species which promotes C–X bond formation via a distinct Pd(iii)/Pd(iv) pathway. To demonstrate the synthetic utility, we developed a general method for inert C(sp3)–H bond bromination, chlorination and iodination with alkyl halides. This new strategy in auxiliary-directed C–H activation provides predictable and controllable access to distinct reactivity pathways proceeding via Pd(iii)/Pd(iv) redox couples induced by visible light irradiation., Visible light irradiation of 8-aminoquinoline Pd(ii) complexes initiates photoinduced electron transfer with alkyl halides, affording C–H halogenation over C–C bond adducts. A method for inert C(sp3)–H bond halogenation (Br, Cl and I) is reported.

Heat shock proteins (Hsps) stabilize the newly synthesized polypeptide chains preventing them from aggregation. They contribute to systemic response under stress and thus behave as signaling molecules. Hsp70 has been detected on the surface of stressed cells. It translocates to the extracellular environment through the plasma membrane without causing cell death. But the interaction of the protein with the membrane leading to the export process remains elusive. Hsp70 has a tendency to generate channels within lipid bilayers, and this has been a driving force for studying protein-lipid interactions. Transport of these proteins across the membrane paves their pathways for performing the desired function. We have attempted to characterize how the interaction of Hsp70 with negatively charged phospholipids affects the structure of lipids. This study will help in explaining the transport mechanism of proteins that are devoid of defined signaling pathways. The interaction of amino acids of Hsp70 with the head and tail group leads to the rearrangement of the hydration layer in contact with the bilayers. Critical analysis of the results obtained from small-angle X-ray scattering along with QCM-D provides valuable insights to analyze the effect of Hsp70 adsorption on an anionic POPS lipid bilayer.

Motivated by their utility in CdTe-based thin film photovoltaics (PV) devices, an investigation of thin films of the magnesium-zinc oxide (MgxZn1−xO or MZO) alloy system was undertaken applying spectroscopic ellipsometry (SE). Dominant wurtzite phase MZO thin films with Mg contents in the range 0 ≤ x ≤ 0.42 were deposited on room temperature soda lime glass (SLG) substrates by magnetron co-sputtering of MgO and ZnO targets followed by annealing. The complex dielectric functions ε of these films were determined and parameterized over the photon energy range from 0.73 to 6.5 eV using an analytical model consisting of two critical point (CP) oscillators. The CP parameters in this model are expressed as polynomial functions of the best fitting lowest CP energy or bandgap E0 = Eg, which in turn is a quadratic function of x. As functions of x, both the lowest energy CP broadening and the Urbach parameter show minima for x ~ 0.3, which corresponds to a bandgap of 3.65 eV. As a result, it is concluded that for this composition and bandgap, the MZO exhibits either a minimum concentration of defects in the bulk of the crystallites or a maximum in the grain size, an observation consistent with measured X-ray diffraction line broadenings. The parametric expression for ε developed here is expected to be useful in future mapping and through-the-glass SE analyses of partial and complete PV device structures incorporating MZO.

As the performance of the front interface and the CdTe absorber are improved, minority carrier recombination at the back of the device will limit the photoconversion efficiency. To determine the li...

Comparing to the traditional CdS buffer layer, zinc magnesium oxide (ZMO) offers the following advantages for CdTe-based thin-film solar cells: it introduces a spike to conduction band offset, whic...

Formation of a low barrier back contact plays a critical role in improving the photoconversion efficiency of the CdTe solar cells. Incorporating a buffer layer to minimize the band bending at the back of the CdTe device can significantly lower the barrier for the hole current, improving open circuit voltage (VOC) and the fill factor. Over the past years, researchers have incorporated the both ZnTe and Te as buffer layers to improve CdTe device performance. Here we compare device performance using these two materials as buffer layers at the back of CdTe devices. We show that using Te in contact to CdTe results in higher performance than using ZnTe in contact to the CdTe. Low temperature current density-voltage measurements show that Te results is a lower barrier with CdTe than ZnTe, indicating that Te has better band alignment, resulting in less downward bending in the CdTe at the back interface, than ZnTe does.

As the efficiency of single junction devices improve, bifacial thin film (BFT) devices are being increasingly investigated as a way to increase energy yield per unit area. At the same time, increasing doping density of thin film devices are also being developed to increase the energy yield per unit area. Here, we investigate how critical parameters to improving backside illuminated devices and increasing the absorber doping density affect backside illuminated device performance. We show that reducing recombination at the back of the device through increasing initial Fermi level offset (IFLO) or decreasing back surface recombination velocity (BSRV) is far more important than increasing absorber doping density. We also show that there is a wide range of the IFLO-BSRV parameter space that can lead to high backside illumination device efficiency for highly doped thin film devices.

We report a new visible light-mediated carbonylative amidation of aryl, heteroaryl and alkyl halides. A tandem catalytic cycle of [Ir(ppy)2(dtb-bpy)]+ generates a potent iridium photoreductant via a second catalytic cycle in the presence of DIPEA which productively engages aryl bromides, iodides and even chlorides as well as primary, secondary and tertiary alkyl iodides. The versatility of the in-situ generated catalyst is illustrated by compatibility with aliphatic and aromatic amines, high functional group tolerance and the late-stage amidation of complex natural products.

Organic–inorganic metal halide perovskites are notoriously unstable in humid environments. While many studies have revealed the morphology and crystal structure changes that accompany exposure to humidity, little is known about changes to the photophysics that accompany the degradation process. By combining in situ steady-state and time-resolved photoluminescence with Hall effect measurements, we examined the changes in the photoexcited carrier dynamics for methylammonium lead iodide (MAPbI3) and bromide (MAPbBr3) films exposed to nitrogen gas containing water vapor at 80% relative humidity. The changes in the photophysics of MAPbI3 interacting with water follow a four-stage process, consisting of surface passivation, free electron doping, interfacial hydration, and bulk hydration. In contrast, MAPbBr3 exhibits only features associated with the first two stages, which occur at a faster rate. Our results elucidate the degradation mechanisms of perovskite films in high humidity from the perspective of the p...

Wide bandgap Cd1-xZnxTe (CZT) and Cd1-xMgxTe (CMT) have drawn attention as top cells in tandem devices. These materials allow tuning of the band gap over a wide range by controlling the Zn or Mg concentration with little alteration to the base CdTe properties. Historically, CdS has been used as a heterojunction partner for CZT or CMT devices. However, these devices show a significant lower open circuit voltage (VOC) than expected for wide bandgap absorbers. Recent modelling work suggests that poor band alignment between the CdS emitter and absorber results in a high concentration of holes at the interface, which increased recombination and limits the VOC. This recombination should be exacerbated for wider bandgap absorbers such as CZT and CMT. In this study, we use numerical simulations with SCAPS-1D software to investigate the band alignment in the front contacts for wider bandgap CdTe based absorbers. Results show that by replacing the CdS with a wide bandgap emitter layer, the VOC can be greatly improved, though under certain conditions, the fill factor remains sensitive to the location of the emitter conduction band. As a result, different transparent front contacts were also investigated to determine a device structure required to produce a high performance CZT or CMT top-cell for tandems devices.

We present the defect analysis by photoluminescence (PL) spectroscopy of CdSexTe1-x thin films, grown with varying Se content by a co-sputtered deposition method. We observe a peak at 1.203 eV in the CdSexTe1-x film for x = 0.21, which shifts towards higher energies with increase in laser power. This peak was assigned to a donor-to-acceptor (DAP) transition, with a measured j-shift of ~4.7 meV/decade. Temperature dependent PL intensity measurements confirm that the observed DAP peak involves a shallow defect state of binding energy ~34.7 meV. In contrast, a free-to-bound (FB) peak at 1.294 eV involving a shallow defect of binding energy ~18.3 meV was observed in the CdSexTe1-x film for x = 0.14. Additionally, we observe band edge emission at 1.452 eV and 1.448 eV in CdSexTe1-x films for x = 0.14 and x = 0.21 respectively. Our analysis shows that the Se concentration not only changes the band gap energy of the resulting CdSexTe1-x alloy thin film, but also modifies the nature of the dominant observed defect emission.

Increasing the band gap of cadmium telluride (CdTe) from 1.48 eV to > 2 eV can be achieved by alloying CdTe with ZnTe. Like CdTe, the alloyed films are expected to allow for low cost production, suggesting that Cd1-xZnxTe could be an ideal top cell for mass produced tandem devices. However, the CdCl2 activation of the alloyed films results in a significant loss of Zn, thereby reducing the bandgap. In this study, we demonstrate a novel CdCl2 activation method that does not result in significant Zn loss. By performing the activation step in a closed, inert environment we are able to avoid oxidation of the Zn in the Cd1-xZnxTe film; furthermore, by including sacrificial Zn in the container, an overpressure of ZnCl2 forms limiting the amount of ZnCl2 formed in the film. Both x-ray diffraction, optical measurements, and Auger spectroscopy show that the CdCl2 treatment with no flowing gas minimizes the loss of Zn from the CZT alloy.

The presence of a Te-rich surface or an elemental Te layer is beneficial for the formation of a low-barrier back contact for high-efficiency CdTe solar cells. Etching processes are widely used to form Te-rich CdTe surfaces, while deposition processes such as evaporation are used to form elemental Te layers. Here, we show that a reaction between methylammonium iodide (CH3NH3I, MAI) and CdTe can be used to simply and controllably produce elemental Te over a wide processing window. Both X-ray diffraction and Raman spectroscopy confirmed the formation of a Te layer. The MAI-produced Te layer reduces the Schottky barrier height, improves the open-circuit voltage ( V OC) and fill factor, and outperforms contacts formed with the evaporated Te. We examined the effect of MAI reaction temperature and the amount of Cu needed to optimize the device. CdS/CdTe stacks that were treated with a 125 mM MAI solution and heated to 125 °C for 10 min showed the best power conversion efficiency (PCE) of 14.1%, while the best efficiency of a standard device without treatment was 13.0%, and the best PCE of an evaporated Te layer was 13.8%. Notably, the improved efficiency for the MAI-treated devices was achieved with less Cu than was required for the standard device. With an indium tin oxide back electrode, the PCE was also improved from 11.0% to 12.2% with MAI treatment, providing a potential route for fabricating high-efficiency transparent or bifacial CdTe solar cells.

The general catalytic synthesis of aryl and vinyl thioethers from readily available halides remains a challenge. Herein we report a unified method for the thiolation of aryl and vinyl iodides with dialkyl disulfides using visible light photoredox catalysis. A range of thioether products bearing diverse functional groups can be accessed in high yield and with excellent chemoselectivity. We demonstrate the versatility of this method through the expedient synthesis of a family of thioether-rich natural products. A detailed investigation of the photocatalytic mechanism is presented from both steady-state and time-resolved luminescent quenching as well as transient absorption spectroscopy experiments.