Cyclopenta[b]annulation of Heteroarenes by Organocatalytic γ′[C(sp3)−H] Functionalization of Ynones

A new approach for the cyclopenta[b]annulation of heteroarenes through metal‐free and directing‐group‐free γ′[C(sp³)?H] functionalization and intramolecular hydroalkylation of ynones has been developed. In an unprecedented event, nucleophilic addition of an organophosphine to the designed ynones triggers γ′[C(sp³)?H] functionalization, leading to the formation of heteroaryl‐based ortho‐quinodimethane (oQDM) intermediates that undergo carbocyclization to provide cyclopentannulated heteroarenes in good yields and excellent stereoselectivities. Deuterium‐labeling experiments substantiated the proposed reaction mechanism as well as the speculated epimerization.     

Ester‐Mediated Amide Bond Formation Driven by Wet–Dry Cycles: A Possible Path to Polypeptides on the Prebiotic Earth

Although it is generally accepted that amino acids were present on the prebiotic Earth, the mechanism by which α‐amino acids were condensed into polypeptides before the emergence of enzymes remains unsolved. Here, we demonstrate a prebiotically plausible mechanism for peptide (amide) bond formation that is enabled by α‐hydroxy acids, which were likely present along with amino acids on the early Earth. Together, α‐hydroxy acids and α‐amino acids form depsipeptides—oligomers with a combination of ester and amide linkages—in model prebiotic reactions that are driven by wet–cool/dry–hot cycles. Through a combination of ester–amide bond exchange and ester bond hydrolysis, depsipeptides are enriched with amino acids over time. These results support a long‐standing hypothesis that peptides might have arisen from ester‐based precursors.     

Mathematical modelling and analysis of bulk waves in rotating generalized thermoelastic media with voids

The present paper deals with the propagation of body waves in a homogenous isotropic, rotating, generalized thermoelastic solid with voids. The complex quartic secular equation has been solved by employing Descartes’ algorithm and perturbation method to obtain phase velocities, attenuations and specific loss factors of four attenuating and dispersive waves, which are possible to exist in such media. These wave characteristics have been computed numerically for magnesium crystal and presented graphically. Statistical analysis has been performed to compare the obtained computer simulated result in order to have estimate on the suitability of the method to compute various characteristics of the waves. This work may find applications in geophysics and gyroscopic sensors.     

Multicolored and white-light phosphors based on doped GdF3 nanoparticles and their potential bio-applications

Rare-earth-doped gadolinium fluoride nanocrystals were synthesized by a single step synthesis employing ethylene glycol as solvent. Based on X-ray diffraction studies, stabilization of hexagonal modification of GdF(3) has been inferred. The microscopic studies show formation of uniformly distributed nanocrystals (~15 nm). The nanoparticles are readily dispersible in water and show bright luminescence in colloidal solution. The luminescence properties have been investigated as a function of activator concentrations, and enhanced optical properties have been attributed to efficient energy transfer from the Gd(3+) to the activator RE(3+) ions, which has further been confirmed by steady-state and time-resolved optical studies. It has been demonstrated that on doping appropriate amount of activators in host GdF(3), a novel white-light-emitting phosphor is obtained with CIE co-ordinates and correlated color temperature (CCT) very close to broad daylight. This can have promising applications as phosphor for white-light ultraviolet-light-emitting diodes (UV-LEDs). Our experiments showed efficient labeling of human breast carcinoma cells (MCF-7) by Tb(3+)-doped GdF(3) nanoparticles. The fluorescence intensity was found to be dependent on the surface modifying/coating agent, and the results were validated using confocal microscopy in terms of localization of these functionalized nanoparticles.     

Some Characterizations of VNL Rings

A ring R is said to be von Newmann local (VNL) if for any a ∈ R, either a or 1 ?a is (von Neumann) regular. The class of VNL rings lies properly between exchange rings and (von Neumann) regular rings. We characterize abelian VNL rings. We also characterize and classify arbitrary VNL rings without an infinite set of orthogonal idempotents; and also the VNL rings having a primitive idempotent e such that eRe is not a division ring. We prove that a semiperfect ring R is VNL if and only if for any right uni-modular row (a ₁, a ₂) ∈ R ², one of the a _i 's is regular in R. Formal triangular matrix rings that are VNL are also characterized. As a corollary, it is shown that an upper triangular matrix ring T _n (R) is VNL if and only if n = 2 or 3 and R is a division ring.     

Error estimation properties of Gaussian process models in stochastic simulations

The theoretical relationship between the prediction variance of a Gaussian process model (GPM) and its mean square prediction error is well known. This relationship has been studied for the case when deterministic simulations are used in GPM, with application to design of computer experiments and metamodeling optimization. This article analyzes the error estimation of Gaussian process models when the simulated data observations contain measurement noise. In particular, this work focuses on the correlation between the GPM prediction variance and the distribution of prediction errors over multiple experimental designs, as a function of location in the input space. The results show that the error estimation properties of a Gaussian process model using stochastic simulations are preserved when the signal-to-noise ratio in the data is larger than 10, regardless of the number of training points used in the metamodel. Also, this article concludes that the distribution of prediction errors approaches a normal distribution with a variance equal to the GPM prediction variance, even in the presence of significant bias in the GPM predictions.     

Trapping of Thiol Terminated Acrylate Polymers with Divinyl Sulfone to Generate Well-Defined Semi-Telechelic Michael Acceptor Polymers

Herein we report the synthesis of vinyl sulfone end functionalized PEGylated polymers by reversible addition-fragmentation chain transfer (RAFT) polymerization for conjugation to proteins. Poly(ethylene glycol) methyl ether acrylate (PEGA) was polymerized in the presence of 1-phenylethyl dithiobenzoate with 2,2'-azobis(2-methylpropionitrile) as the initiator to generate well-defined polyPEGAs with number-average molecular weights (M(n)) by gel permeation chromatography (GPC) of 6.7 kDa, 11.8 kDa and 16.1 kDa. Post-polymerization, the majority of polymer chains contained the dithioester functional group at the omega chain end, and the polydispersity indexes (PDI) of the polymers ranged from 1.08 to 1.24. The dithioester was subsequently reduced via aminolysis, and the resulting thiol was trapped with a divinyl sulfone in situ to produce semi-telechelic, vinyl sulfone polyPEGAs with efficiencies ranging between 85% and 99%. It was determined that the retention of vinyl sulfone was directly related to reaction time, with the maximum dithioester being transformed into a vinyl sulfone within 30 minutes. Longer reaction times resulted in slow decomposition of the vinyl sulfone end group. The resulting semi-telechelic vinyl sulfone polymers were then conjugated to a protein containing a free cysteine, bovine serum albumin (BSA). Gel electrophoresis demonstrated that the reaction was highly efficient and that conjugates of increasing size were readily prepared. After polymer attachment, the activity of the BSA was 92% of the unmodified biomolecule.     

Multiscale Modeling of Branch Length in Butyl Acrylate Solution Polymerization

Branch lengths resulting from both backbiting and intermolecular chain transfer to polymer are examined for the solution polymerization of butyl acrylate, using a rate‐equation model and ordinary differential equations. Backbiting is allowed to generate branches of varying length, according to a cumulative distribution function obtained from a lattice kinetic Monte Carlo simulation. About 8% of the branches produced by backbiting are 10 mers or longer. In contrast to common assumptions about the origins of short‐chain and long‐chain branches, the model indicates that nearly all of the long‐chain branches may be produced by backbiting, rather than intermolecular chain transfer to polymer.

     

Preserving quantum states using inverting pulses: a super-Zeno effect

We construct an algorithm for suppressing the transitions of a quantum mechanical system, initially prepared in a subspace P of the full Hilbert space of the system, to outside this subspace by subjecting it to a sequence of unequally spaced short-duration pulses. Each pulse multiplies the amplitude of the vectors in the subspace by -1. The number of pulses required by the algorithm to limit the leakage probability to epsilon in time increases as T exp[square root log(T(2)/epsilon)], compared to T(2)epsilon(-1) in the standard quantum Zeno effect.