Mechanochemical metathesis synthesis and characterization of nano-structured MnV2O6·xH2O (x=2, 4)

A solid-state metathesis approach for the synthesis of hydrated MnV₂O₆·xH₂O (x=2, 4) materials driven by mechanochemical activation energy has been demonstrated. The metathesis pathway of forming the desired product is confirmed by the presence of high lattice energy by-product such as NaCl. The structural, optical, and chemical properties of the synthesized materials are examined by powder X-ray diffraction, X-ray photoelectron spectroscopy, thermo gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and diffused reflectance measurements in the UV–vis range. The valence state of Mn and V was determined to be +2 and +5, respectively, for the title compounds and the bandgap values determined showed these materials are likely to be semiconductors.     

Aromatic amines and their derivatives,Part 2. Synthesis,spectroscopic properties,and molecular and crystal structure ofN-acetyl-4,N-dimethyl-6-(N-acetyl-p-toluidinomethyl)aniline

The synthesis and selected aspects of the UV, IR, and¹H NMR spectra of the title compound are described. The crystals of the title compound are triclinic witha=12.999(9),b=8.911(4),c=9.199(5) Å;=105.56(3),=113.50(4), =92.53(3)°;Z=2; space groupP¯1. Its X-ray crystal structure analysis provides information regarding the conformational features of the amide linkage when no intermolecular hydrogen bonding involving this group is present. The X-ray study shows that the C-N bond is longer [1.363(4) Å] than that found normally in peptide molecules. The compound shows a peculiar disorder involving one of the two amide groups present in the molecule. The conformation of theN-methyl acetanilide moiety and its relation to the¹H NMR spectrum of the compound are discussed.     

Synthesis of unsymmetrical substituted 1,4-dihydropyridines through thermal and microwave assisted [4+2] cycloadditions of 1-azadienes and allenic esters

Thermal and microwave assisted [4+2] cycloadditions of 1,4-diaryl-1-aza-1,3-butadienes with allenic esters lead to cycloadducts, which after a 1,3-H shift afford variedly substituted unsymmetrical 2-alkyl-1,4-diaryl-3-ethoxycarbonyl-1,4-dihydropyridines in high yields. Reactions carried out under microwave irradiation are cleaner and give higher yields with much shortened reaction times. Density functional theory (DFT) at the B3LYP/6-31G* level has been used to calculate geometric features of the reactants, barrier for s-trans to s-cis and reverse isomerization of azadienes (5a-d, 10a-e), dihedral angles between N(1), C(2), C(3), and C(4) atoms of azadienes along with various indices such as chemical hardness (eta), chemical potential (micro), global electrophilicity (omega), and the difference in global electrophilicity (Deltaomega) between the reacting pairs and Fukui functions (f (+) and f(-)). The results revealed that s-trans is the predominant conformation of azadienes at ambient temperature and the barrier for conversion of the s-trans rotamer of 1-azadienes to s-cis may be the major factor influencing the chemoselectivity, i.e., [4+2] verses [2+2] cycloaddition. The regiochemistry of the observed cycloadditions is collated with the obtained local electrophilicity indices (Fukui functions). Transition states for the formation of both [4+2] and [2+2] cycloadducts as located at the PM3 level indicate that the transition state for the formation of [4+2] cycloadducts has lower energy, again supporting the earlier conclusion that preferred formation of [4+2] cycloaaducts at higher temperature may be a consequence of barrier for s-trans to s-cis transformation of 1-azadienes.     

Quencher-free molecular beacons: a new strategy in fluorescence based nucleic acid analysis

Molecular beacons (MBs) have been used as viable fluorescent probes in nucleic acid analysis. Many researchers around the world continue to modify the MBs to suit their needs. As a result, a number of nucleic acid probing systems with close resemblance to the MBs are being reported from time to time. Quencher-free molecular beacons (QF-MBs) are a significant modification of the conventional MB; in QF-MBs the quencher part has been eliminated. Despite the absence of the quencher, the QF-MBs can identify specific target DNA. They can also be used in SNP typing and in real-time PCR analysis for quantification of DNAs. The design, factors behind functioning and applications of different types of QF-MBs and closely related quencher-free nucleic acid probing systems (QF-NAPs) have been described in this tutorial review.     

Ultrafast Photogenerated Hole Extraction/Transport Behavior in a CH3NH3PbI3/Carbon Nanocomposite and Its Application in a Metal‐Electrode‐Free Solar Cell

Aligned and flexible electrospun carbon nanomaterials are used to synthesize carbon/perovskite nanocomposites. The free‐electron diffusion length in the CH₃NH₃PbI₃ phase of the CH₃NH₃PbI₃/carbon nanocomposite is almost twice that of bare CH₃NH₃PbI₃, and nearly 95 % of the photogenerated free holes can be injected from the CH₃NH₃PbI₃ phase into the carbon nanomaterial. The exciton binding energy of the composite is estimated to be 23 meV by utilizing temperature‐dependent optical absorption spectroscopy. The calculated free carriers increase with increasing total photoexcitation density, and this broadens the potential of this material for a broad range of optoelectronics applications. A metal‐electrode‐free perovskite solar cell (power conversion efficiency: 13.0 %) is fabricated with this perovskite/carbon composite, which shows great potential for the fabrication of efficient, large‐scale, low‐cost, and metal‐electrode‐free perovskite solar cells.     

Explicit subspace designs

A subspace design is a collection {H ₁, H ₂, ...,H _M } of subspaces of \(\mathbb{F}_q^m\) with the property that no low-dimensional subspace W of \(\mathbb{F}_q^m\) intersects too many subspaces of the collection. Subspace designs were introduced by Guruswami and Xing (STOC 2013) who used them to give a randomized construction of optimal rate list-decodable codes over constant-sized large alphabets and sub-logarithmic (and even smaller) list size. Subspace designs are the only non-explicit part of their construction. In this paper, we give explicit constructions of subspace designs with parameters close to the probabilistic construction, and this implies the first deterministic polynomial time construction of list-decodable codes achieving the above parameters.Our constructions of subspace designs are natural and easily described, and are based on univariate polynomials over finite fields. Curiously, the constructions are very closely related to certain good list-decodable codes (folded RS codes and univariate multiplicity codes). The proof of the subspace design property uses the polynomial method (with multiplicities): Given a target low-dimensional subspace W, we construct a nonzero low-degree polynomial P _W that has several roots for each H _i that non-trivially intersects W. The construction of P _W is based on the classical Wronskian determinant and the folded Wronskian determinant, the latter being a recently studied notion that we make explicit in this paper. Our analysis reveals some new phenomena about the zeroes of univariate polynomials, namely that polynomials with many structured roots or many high multiplicity roots tend to be linearly independent.     

Host Lattice Effect on Paramagnetic Impurity: Single Crystal EPR Study of VO(II)‐Doped Biomineral Cadmium Ammonium Phosphate Hexahydrate

Single crystal electron paramagnetic resonance studies on VO(II) doped cadmium ammonium phosphate hexahydrate were carried out at room temperature. The paramagnetic impurity VO(II) was found to enter the host lattice both substitutionally and interstitially. The spin Hamiltonian parameter values calculated from crystal rotations for both the locations are; Site1: g_∥ = 1.939, g_⟂ = 1.992, A_∥ = 16.3mT, A_⟂ = 7.7mT and site2: g_∥ = 1.933, g_⟂ = 1.998, A_∥ = 16.2mT, A_⟂ = 7.7mT. The powder spectra values agree well with the single crystal data. The two sites have been identified as at right angles to each other. The admixture coefficients and other parameter values (κ and P) were evaluated from the spin Hamiltonian parameters. The complex was found to be fairly covalent in nature.     

Syntheses and photophysical properties of luminescent mono-cyclometalated gold(III) cis-dialkynyl complexes

A series of novel luminescent neutral cyclometalated gold(III) complexes of the type cis-[(N^C)Au(C≡CR)(2)] (R = aryl, silyl groups) having different cyclometalating cores (N^C) have been synthesized by CuI promoted halide to alkynyl metathesis with NEt(3) as in situ deprotonating agent. Along with spectroscopic characterizations (nuclear magnetic resonance and infrared spectroscopies and electrospray ionization mass spectrometry) and elemental analysis, the molecular structures of some of the complexes have been established by single-crystal X-ray diffraction studies. Photophysical studies reveal that the complexes exhibit room-temperature phosphorescence (RTP). Experimental observations and density functional theory calculations qualitatively suggest limited participation of the metal and alkynyl ligands in the lowest energy emitting state. The nature of the emission is mainly governed by metal-perturbed (3)IL(π-π*) transitions originating from the cyclometalate part of the molecule, and its variation readily leads to the tuning of the emission wavelengths. Cyclic voltammetry measurements of selected complexes showed irreversible redox behavior with near-equivalent cathodic peak potential (E(p,c)) assigned to the C^N core.     

Stereospecific solid-state NaBH4-promoted reduction of 1-methylpentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione

NaBH₄ reduction of a cage dione proceeds in a stereospecific fashion to give theendo,endo-diol. This reactivity is related to the crystal structure.