Trithioarsenites [(RS)3As], dithioarsonites [R-As(SR′)2] and thioarsinites [R2As-SR′]: Preparations, chemical, biochemical and biological properties

Contrary to P(V) compounds, As(V) compounds can very easily reduced by thiols to As(III) thiolates that are deemed to play a central role in the metabolism of arsenic and therefore a review on the preparation and properties of the title thiolates can be of interest. The preparation of trithioarsenites, dithioarsonites and thioarsinites involves reactions of a thiol with a proper As(V) or As(III) precursor via 4-centered transition states or a thiolate by SN2 mechanisms. Convenient precursors are the solids As2O3, arsonic and arsinic acids, although for the latter two acids the separation of the product from the co-produced disulfides can be problematic. Only a few crystal structures have been reported and involve only trithioarsenites. From their chemical properties, the hydrolyses, transthiolations and air oxidations are of particular interest from mechanistic and biochemical/biological points of view. Their nucleophilicity towards alkyl halides and acyl derivatives revealed unexpected behavior. Although these molecules have many free electron pairs only three reports were found pertaining to their reaction with metal cations (Hg2+) and metal carbonyls; the mercuric complexes being not characterized. Only a few studies appeared for the action of the title compounds towards enzymes, while the patent literature revealed that they have bactericidal, fungicidal and insecticidal activities for agricultural applications, some have antiparasitic activity on animals and a few are carcinostatic.

Triazole-Anil and Triazol-Azo Reagents (Creation, Spectral Categorization, Scanning Microscopy, Thermal Analysis)

The last decades of this century witnessed a wide interest in three heterogeneous compounds, especially nitrogen atoms, which were represented by triazole rings and their derivatives, whose effects were studied in the widest medical and pharmaceutical journals and as anti-cancer agents and other groups that are characterized by the presence of electronic pairs, which have given greater importance for this reason. In order to increase the effectiveness of any compound, it must include in its composition active groups, donor groups, or electron pairs, and this has been proven by researchers in biochemistry, coordination research, reagent chemistry, reagents, analytical chemistry, estimation of elements and ions in river water and environmental models. Extensive studies have been conducted for the reagents under study to determine their chemical structures through microscopic technical examinations, spectroscopic techniques (Uv-Vis, FT.IR, H.NMR, Mass)–spectra, also Analytical studies like: {Thermal study, TLC–Technique, Scanning Electron Microscopy (FESEM)} and other physico-chemical measurements.

The Nature of Zeolite Catalytic Sites

<p>The nature of zeolite catalytic sites was studied by observing their interactions with sorbants. In situ FTIR studies of a range of sorbants on H+ZSM-5, H+mordenite and H+Y showed that the zeolite Bronsted proton was transferred towards the sorbant. Sorbants could be placed in three classes depending on the type of hydrogen bond formed. "Class A" sorbants were alcohols, alkanes, ammonia, amines and carboxylic acids and showed a single v0-H band shifted from the vO-H of the zeolite. The shift in vO-H increased with increasing proton affinity of the sorbant. "Class B" sorbants were alkenes and aromatics and showed a resultant broad, flat vO-H due to bonding through the t electrons of the double bond or aromatic ring. "Class C" sorbants included water, ethers, ketenes, aldehydes, nitriles and carboxylic acids (also Class A). They showed extremely broad hydroxyl bands from -3700 to -1200 cm-1 with several maxima. Bonding was through oxygen or nitrogen lone electron pairs. A novel, low temperature (-400 [degrees] C), reaction of acetic acid to ketene was observed over alkali-exchanged zeolites. Thermal desorption/mass spectrometry, mini-reactor mass spectrometry and in situ FTIR techniques were used to investigate the products obtained by varying the carboxylic acid and the catalyst, and the reaction mechanism.</p>

The Nature of Zeolite Catalytic Sites

<p>The nature of zeolite catalytic sites was studied by observing their interactions with sorbants. In situ FTIR studies of a range of sorbants on H+ZSM-5, H+mordenite and H+Y showed that the zeolite Bronsted proton was transferred towards the sorbant. Sorbants could be placed in three classes depending on the type of hydrogen bond formed. "Class A" sorbants were alcohols, alkanes, ammonia, amines and carboxylic acids and showed a single v0-H band shifted from the vO-H of the zeolite. The shift in vO-H increased with increasing proton affinity of the sorbant. "Class B" sorbants were alkenes and aromatics and showed a resultant broad, flat vO-H due to bonding through the t electrons of the double bond or aromatic ring. "Class C" sorbants included water, ethers, ketenes, aldehydes, nitriles and carboxylic acids (also Class A). They showed extremely broad hydroxyl bands from -3700 to -1200 cm-1 with several maxima. Bonding was through oxygen or nitrogen lone electron pairs. A novel, low temperature (-400 [degrees] C), reaction of acetic acid to ketene was observed over alkali-exchanged zeolites. Thermal desorption/mass spectrometry, mini-reactor mass spectrometry and in situ FTIR techniques were used to investigate the products obtained by varying the carboxylic acid and the catalyst, and the reaction mechanism.</p>

Scattering interference signature of a pair density wave state in the cuprate pseudogap phase

An unidentified quantum fluid designated the pseudogap (PG) phase is produced by electron-density depletion in the CuO2 antiferromagnetic insulator. Current theories suggest that the PG phase may be a pair density wave (PDW) state characterized by a spatially modulating density of electron pairs. Such a state should exhibit a periodically modulating energy gap $${\Delta }_{{{{{{\rm{P}}}}}}}({{{{{\boldsymbol{r}}}}}})$$ Δ P ( r ) in real-space, and a characteristic quasiparticle scattering interference (QPI) signature $${\Lambda }_{{{{{{\rm{P}}}}}}}({{{{{\boldsymbol{q}}}}}})$$ Λ P ( q ) in wavevector space. By studying strongly underdoped Bi2Sr2CaDyCu2O8 at hole-density ~0.08 in the superconductive phase, we detect the 8a0-periodic $${\Delta }_{{{{{{\rm{P}}}}}}}({{{{{\boldsymbol{r}}}}}})$$ Δ P ( r ) modulations signifying a PDW coexisting with superconductivity. Then, by visualizing the temperature dependence of this electronic structure from the superconducting into the pseudogap phase, we find the evolution of the scattering interference signature $$\Lambda ({{{{{\boldsymbol{q}}}}}})$$ Λ ( q ) that is predicted specifically for the temperature dependence of an 8a0-periodic PDW. These observations are consistent with theory for the transition from a PDW state coexisting with d-wave superconductivity to a pure PDW state in the Bi2Sr2CaDyCu2O8 pseudogap phase.

Superconductivity in the doped quantum spin liquid on the triangular lattice

Broad interest in quantum spin liquid (QSL) phases was triggered by the notion that they can be viewed as insulating phases with preexisting electron pairs, such that upon light doping they might automatically yield high temperature superconductivity. Yet despite intense experimental and numerical efforts, definitive evidence showing that doping QSLs leads to superconductivity has been lacking. We address the problem of a lightly doped QSL through a large-scale density-matrix renormalization group study of the t-J model on finite-circumference triangular cylinders with a small but nonzero concentration of doped holes. We provide direct evidences that doping QSL can naturally give rise to d-wave superconductivity. Specifically, we find power-law superconducting correlations with a Luttinger exponent, Ksc ≈ 1, which is consistent with a strongly diverging superconducting susceptibility, $${\chi }_{sc} \,\sim\, {T}^{-(2\,-\,{K}_{sc})}$$ χ s c ~ T − ( 2 − K s c ) as the temperature T → 0. The spin–spin correlations—as in the undoped QSL state—fall exponentially which suggests that the superconducting pair-pair correlations evolve smoothly from the insulating parent state.

Polysaccharide as Green Corrosion Inhibitor

The carbohydrates associated with polysaccharide glycosidic bonds are tightly chained, usually linear and highly branched complex molecules. Their structure mainly consists of hydroxyl groups in the form of functional groups, in which an oxygen heterogeneous atom is present. Some polysaccharides have hetero atoms. Nitrogen and Sulfur in addition to oxygen, which have unshared electron pairs. Hetero atoms easily share their electron pair to the vacant d orbitals of the metal ion and prevent the metal from corrosion. Polysaccharides are biodegradable, renewable, inexpensive and environment friendly due to which they are easily used as corrosion inhibitors. The present study mentions some major research work in which polysaccharides are used as corrosion inhibitors. Their mixed type nature has been reported in most research papers, and in the case of steel metal, they mainly follow the Langmuir adsorption isotherm. Chemical (gravimetric analysis) and electrochemical (EIS & PDP) studies are frequently used for the corrosion inhibition study. Some of the current research papers have also used computational or theoretical studies such as quantum chemical study and MD simulation. At the end of this book chapter, a discussion is also given regarding further research and direction related to the topic.

Field-induced quantum breakdown of superconductivity in magnesium diboride

The quantum breakdown of superconductivity (QBS) is the reverse, comprehensive approach to the appearance of superconductivity. A quantum phase transition from superconducting to insulating states tuned by using nonthermal parameters is of fundamental importance to understanding the superconducting (SC) phase but also to practical applications of SC materials. However, the mechanism of the transition to a nonzero resistive state deep in the SC state is still under debate. Here, we report a systematic study of MgB2 bilayers with different thickness ratios for undamaged and damaged layers fabricated by low-energy iron-ion irradiation. The field-induced QBS is discovered at a critical field of 3.2 Tesla (=Hc), where the quantum percolation model best explains the scaling of the magnetoresistance near Hc. As the thickness of the undamaged layer is increased, strikingly, superconductivity is recovered from the insulating state associated with the QBS, showing that destruction of quantum phase coherence among Cooper electron pairs is the origin of the QBS.