Applications of thermal analysis in some solid-state reactions

TG-DTG-DTA has been used to characterize various isomers of CoCl₂·2(CH₃C₆H₄NH₂). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.Thanks are due to Drs. Keshav Chander, K. Kaur, Rajinder Singh and G. S. Chopra for helpful discussions and experimental work.     

Excitation decay pathways of Lhca proteins: a time-resolved fluorescence study

Light-harvesting complex I (LHCI), which serves as a peripheral antenna for photosystem I (PSI) in green plants, consists mainly of four polypeptides, Lhca1-4. We report room temperature emission properties of individual reconstituted monomeric Lhca proteins (Lhca1, -2, -3, and -4) and dimeric Lhca1/4, performed by steady-state and time-resolved fluorescence techniques. The emission quantum yields of the samples are approximately 0.12, 0.085, 0.081, 0.041, and 0.063 for Lhca1, -2, -3, -4, and the -1/4 dimer, respectively, which is considerably lower than the value of 0.22 found for light-harvesting complex II (LHCII), the main peripheral antenna complex of photosystem II in green plants. The decay components of LHCI proteins can be divided in two categories: Lhca1 and Lhca3 have decay times of 1.1-1.6 ns and 3.3-3.6 ns, and Lhca2 and Lhca4 have decay times of 0.7-0.9 ns and 3.1-3.2 ns. These categories seem to correlate with the pigment composition of the samples. All decay times are faster than that observed previously for LHCII. When the absolute emission yields and the lifetimes of the Lhca samples are combined, the overall emission properties of the individual Lhca proteins are expressed in terms of their emitting dipole moment strength. In the samples without extreme red states, that is, Lhca1 and Lhca2, the emitting dipole moment has a value close to unity (relative to monomeric chlorophyll in acetone), which is similar to that for LHCII, whereas, in the samples with the red-most state (F-730), that is, Lhca3, -4, and the -1/4 dimer, the emitting dipole moment has a value less than unity (0.6-0.8), which can be explained by mixing the red-most (exciton) state with a dark charge-transfer state, as suggested in previous PSI red pigment studies. In addition, we find a lifetime component of approximately 50-150 ps in all red-pigment-containing samples, which cannot be due to "slow" energy transfer, but is instead assigned to an unrelaxed state of the pigment-protein, which, on this time-scale, is converted into the final emitting state.     

Thermal decomposition of Cu(II) Malonate

The isothermal decomposition of anhydrous Cu(II) malonate of uniform particle size has been studied at 170, 180 and 190°. Decomposition to cupric oxide takes place via the intermediate formation of 2CuCO₃.Cu(OH)₂. X-ray diffraction has been employed to identify the decomposition products. The experimental kinetic data for Cu(II) malonate decomposition are best fitted by two stages: (i) a linear process and (ii) a first-order expression. The activation energies for the two kinetic stages have been found to be 45.7 and 57.2 kcal/mole, respectively. A DTA study of Cu(II) malonate decomposition has also been made. Activation energies have been determined via analysis of the DTA curve using the Borchardt and Piloyan equations.

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Zusammenfassung Die isotherme Zersetzung von wasserfreiem Cu(II)-malonat einheitlicher Partikelgröße wurde bei Temperaturen von 170°, 180° und 190° untersucht. Die Zersetzung von Cu(II)-malonat zu Kupfer(II)-oxid erfolgt über die intermediäre Bildung von 2CuCO₃.Cu(OH)₂. Die Röntgendiffraktionstechnik wurde zur Identifizierung der Zersetzungsprodukte eingesetzt. Die Versuchsergebnisse von Cu(II)-malonat können am besten zwei kinetischen Zuständen angepaßt werden: (1) einem linearen Prozeß und (2) einem Ausdruck erster Ordnung. Die entsprechenden Aktivierungsenergien für die zwei kinetischen Zustände waren 45.7 Kcal/Mol bzw. 57.2 Kcal/Mol. Eine DTA-Untersuchung von Cu(II)-malonat wurde ebenfalls durchgeführt. Die Aktivierungsenergien wurden aus der Analyse der DTA-Kurve mittels der Gleichungen von Borchardt und Piloyan bestimmt.

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Résumé On a étudié la décomposition thermique du malonate de cuivre(II) anhydre à 170, 180 et 190°. La décomposition du malonate en CuO se produit avec formation intermédiaire de 2CuCO₃.Cu(OH)₂. Les produits de décomposition ont été identifiés par diffraction des rayons X. Les données expérimentales correspondent à deux étapes de cinétique différente: (i) un processus linéaire et (ii) une expression du premier ordre. Les énergies d'activation respectives des deux étapes cinétiques s'élèvent à 45.7 et 57.2 kcal.mol^/s-1. Le malonate de cuivre(II) a aussi été étudié par ATD. Les énergies d'activation ont été déterminées à partir de la courbe ATD en appliquant les équations de Borchardt et de Piloyan.

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(II) 170°, 180° 190°. (II) 2CuCO₃. Cu(H)₂. . (II) : (1) (2) . , , , 45,7 / 57,2 /. (II). , , .

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One of the authors (P.C.K.) is grateful to the University Grants Comission, New Delhi, for the award of a junior research fellowship. The authors are grateful to Dr. K. N. Goswami of the Physics Department, University of Jammu, for his help in the X-ray studies of the products.     

Comparative study of solid state reactivity between ferrous oxalate dihydrate and unsubstituted/substituted aniline hydrochlorides

The solid state reactions between ferrous oxalate dihydrate i.e. FeC₂O₄.2H₂O and unsubstituted/ substituted aniline hydrochlorides have been studied. The products [FeCl/oxH/. AN-Cl] have been characterized by elemental analysis, infrared and Mössbauer spectroscopic techniques. The kinetic studies for the reactions have been performed at various temperatures for fixed particle sizes at constant compaction. The following order of reactivity has been observed: unsubstituted > p-substituted > m-substituted o-substituted.     

Synthesis and x-ray crystal structure of the TiMgCl5(OOCCH2Cl) · (ClCH2COOC2H5)3 Adduct

The synthesis of the TiMgCl₅(OOCCH₂Cl) · (ClCH₂COOC₂H₅)₃ adduct, obtained by reacting TiCl₄ with a solution of MgCl₂ in dry ClCH₂COOC₂H₅, is reported together with its molecular and crystal structure as determined by x-ray diffraction. The structure was solved by direct and Fourier methods and refined by least-squares techniques to R = 0.057 for 1318 independent observed reflections. Crystals are monoclinic, space-group P2₁/c, with 4 formula units in a unit-cell of dimensions a = 10.480(4), b = 19.641(9), c = 16.597(6) Å, β = 120.21(5)°. The titanium(IV) atom is octahedrally coordinated by five chlorine atoms and an oxygen atom of a OOCCH₂Cl residue. The magnesium atom is similarly coordinated by two chlorine atoms, the carbonyl oxygen atoms of three ClCH₂COOC₂H₅ molecules and an oxygen atom of the OOCCH₂Cl residue. The two octahedra share an edge by a double chlorine bridge between the magnesium and the titanium atoms and are also connected by the COO group of the OOCCH₂Cl residue. Changes in the configurations and dimensions with respect to the free acceptor and donor molecules are discussed.     

Are Collapse Models Testable via Flavor Oscillations?

Collapse models predict the spontaneous collapse of the wave function, in order to avoid the emergence of macroscopic superpositions. In their mass-dependent formulation, they claim that the collapse of any system’s wave function depends on its mass. Neutral K, D, B mesons are oscillating systems that are given by Nature as superposition of two distinct mass eigenstates. Thus they are unique laboratory for testing collapse models that are sensitive to the mass. In this paper we derive—for the single mesons and bipartite entangled mesons—the effect of the mass-proportional CSL (Continuous Spontaneous Localization) collapse model on the dynamics on neutral mesons. We compare the theoretical prediction with experimental data from different accelerator facilities.     

Screening of Three Transition Metal‐Mediated Reactions Compatible with DNA‐Encoded Chemical Libraries

The construction of DNA‐encoded chemical libraries (DECLs) crucially relies on the availability of chemical reactions, which are DNA‐compatible and which exhibit high conversion rates for a large number of diverse substrates. In this work, we present our optimization and validation procedures for three copper and palladium‐catalyzed reactions (Suzuki cross‐coupling, Sonogashira cross‐coupling, and copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC)), which have been successfully used by our group for the construction of large encoded libraries.     

Driving Organic Nanocrystals Dissolution Through Electrochemistry

We have recently discussed how organic nanocrystal dissolution appears in different morphologies and the role of the solution pH in the crystal detriment process. We also highlighted the role of the local molecular chemistry in porphyrin nanocrystals having comparable structures: in water-based acid solutions, protonation of free-base porphyrin molecules is the driving force for crystal dissolution, whereas metal (Zn^II) porphyrin nanocrystals remain unperturbed. However, all porphyrin types, having an electron rich π-structure, can be electrochemically oxidized. In this scenario, a key question is: does electrochemistry represent a viable strategy to drive the dissolution of both free-base and metal porphyrin nanocrystals? In this work, by exploiting electrochemical atomic force microscopy (EC-AFM), we monitor in situ and in real time the dissolution of both free-base and metal porphyrin nanocrystals, as soon as molecules reach the oxidation potential, showing different regimes according to the applied EC potential.