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Ethynamine - Ketenimine - Acetonitrile - Rearrangements: A computational Study of Flash Vacuum Pyrolysis Processes
No full textThe rearrangements
of ethynamine 3 (H-CºC-NH2) to
ketenimine 4 (CH2=C=NH)
and acetonitrile 5 (CH3CN)
were investigated computationally up to the MP4(SDTQ)/6-31G*//MP2(FU)/6-31G*
level. The calculated barrier for a concerted reaction 3 -> 4 is very high, 74
kcal/mol, the structure of the transition state very unusual, and this path is
discredited. A lower barrier of about 60 kcal/mol via aminovinylidene 2 and imidoylcarbene 15 has been found. The calculated barrier
for a concerted second step 4 -> 5 is 61 kcal/mol, and the transition state structure is again very
unusual with a virtually linear CCN backbone, but this does not appear to correspond
to physical reality. Instead, CASPT2 calculations predict reaction via vinylnitrene
9 and/or homolysis of 4 to the radical pair ·CH2CN + H· (11)
with a barrier of 67-70 kcal/mol in agreement with experimental shock-tube data.
Recombination (maybe via roaming) affords acetonitrile 5. There is strong experimental evidence for homolytic paths in
pas-phase pyrolyses of ketenimines.</p
Fluorous photosensitizers enhance photodynamic therapy with perfluorocarbon nanoemulsions
No full textPhotodynamic therapy (PDT) requires photosensitizer,
light, and oxygen to induce cell death. The majority of efforts to advance PDT focus
only on the first two components. Here, we employ perfluorocarbon nanoemulsions
to simultaneously deliver oxygen and photosensitizer. We find that the
implementation of fluorous soluble photosensitizers enhances the efficacy of
PDT. </p
Transition probability approach for direct calculation of coefficients of Configuration Interaction wave function
No full textTo reduce the computation cost of Configuration Interaction (CI) method, a new technique is used to calculate the coefficients of doubly excited determinants directly from orbital energies, orbital overlap matrix and electron population obtained from Hartree Fock level run. This approach to approximate the coefficients of CI wave function is termed as transition probability approximated CI (TPA-CI). In principle, calculated dynamical electron correlation energy of TPA-CI and Full CI (FCI) are equivalent. It is observed that computed TPA-CI correlation energies of hydrogen, water, ammonia and ozone are very close to FCI values, within 5% error. The potential energy curve of the hydrogen molecule is also studied and it is found that the energy is minimum at its equilibrium bond length.<br /
Co-planar two-dimensional Metal-Insulator-Semiconductor Capacitor: Numerical study of the device electrostatics.
No full textThe two-dimensional(2D) materials are highly promising candidates to realise elegant and e cient transistor. In the present letter, we conjecture a novel co-planar metal-insulator-semiconductor(MIS) device(capacitor) completely based on lateral 2D materials architecture and perform numerical study of the capacitor with a particular emphasis on its di erences with the conventional 3D MIS electrostatics. The space-charge density features a long charge-tail extending into the bulk of the semiconductor as opposed to the rapid decay in 3D capacitor. Equivalently, total space-charge and semiconductor capacitance densities are atleast an order of magnitude more in 2D semiconductor. In contrast to the bulk capacitor, expansion of maximum depletion width in 2D semiconductor is observed with increasing doping concentration due to lower electrostatic screening. The heuristic approach of performance analysis(2D vs 3D) for digital-logic transistor suggest higher ON-OFF current ratio in the long-channel limit even without third dimension and considerable room to maximise the performance of short-channel transistor. The present results could potentially trigger the exploration of new family of co-planar at transistors that could play a signi significant role in the future low-power and/or high performance electronics.<br /
Oxidase Catalysis via Aerobically Generated Hypervalent Iodine Intermediates
No full textDevelopment of sustainable oxidation chemistry
demands strategies to harness O2 as a terminal oxidant. In
particular, oxidase
catalysis, in which O2 serves as a chemical oxidant without
necessitating oxygen incorporation into reaction products, would allow diverse
substrate functionalization chemistry to be coupled to O2 reduction.
Direct O2 utilization must overcome
the intrinsic challenges imposed by the triplet ground state of O2 and
the disparate electron inventories of four-electron O2 reduction and
two-electron substrate oxidation. Here, we generate hypervalent iodine
reagents, a broadly useful class of selective two-electron oxidants, from O2.
Synthesis of these oxidants is achieved by intercepting reactive intermediates
of aldehyde autoxidation. The use of aryl iodides as mediators of aerobic
oxidation underpins an oxidase catalysis platform that couples a broad array of
substrate oxidations to O2 reduction, including olefin
functionalization chemistry, carbonyl a-oxidation, oxidative dearomatization, and
aerobic C–H amination chemistry
Junction potentials bias measurements of ion exchange membrane permselectivity
No full textIon exchange membranes (IEMs) are versatile materials relevant to a variety of water and waste treatment, energy production, and industrial separation processes. The defining characteristic of IEMs is their ability to selectively allow positive or negative ions to permeate, which is referred to as the permselectivity. Measured values of permselectivity that equal unity (corresponding to a perfectly-selective membrane) or exceed unity (theoretically impossible) have been reported for cation exchange membranes (CEMs). Such non-physical results call into question our ability to correctly measure this crucial membrane property. Since weighing errors, temperature, and measurement uncertainty have been shown to not explain these anomalous permselectivity results, we hypothesized that a possible explanation are junction potentials that occur at the tips of reference electrodes. In this work, we tested this hypothesis by comparing permselectivity values obtained from bare Ag/AgCl wire electrodes (which have no junction) to values obtained from single-junction reference electrodes containing two different electrolytes. We show that permselectivity values obtained using reference electrodes with junctions were greater than unity for CEMs. By contrast, electrodes without junctions always produced permselectivities lower than unity. Electrodes with junctions also resulted in artificially low permselectivity values for AEMs compared to electrodes without junctions. Thus, we conclude that junctions in reference electrodes introduce two biases into results in the IEM literature: (i) permselectivity values larger than unity for CEMs, and (ii) lower permselectivity values for AEMs compared to those for CEMs. These biases can be avoided by using electrodes without a junction. </div
The Matter Simulation (R)evolution
No full textTo date, the program for the development of methods and models for atomistic and continuum simulation directed toward chemicals and materials has reached an incredible degree of sophistication and maturity. Currently, one can witness an increasingly rapid emergence of advances in computing, artificial intelligence, and robotics. This drives us to consider the future of computer simulation of matter from the molecular to the human length and time scales in a radical way that deliberately dares to go beyond the foreseeable next steps in any given discipline. This perspective article presents a view on this future development that we believe is likely to become a reality during our lifetime