Synthesis and structure of some thienopyrimidine derivatives

A series of substituted thieno[2,3-d]pyrimidines was synthesized starting from ethyl-2-amino-4-isopropylthiophene-3-carboxlate. Reaction of 2-hydrazino-5-isopropyl-thieno[2,3-d]pyrimidin-4(3H)-one and its 3-methyl analogue with different reagents afforded thieno[2,3-d]triazolo[4,3-a]pyrimidines and thieno[3,2-e]triazolo[4,3-a]pyrimidines, beside open chain derivatives. Correspondence: Atef A. Hamed, Department of Chemistry, Faculty of Science, Menoufia University, Shebin El Koam, Egypt.     

Anilinolysis of Picryl Benzoate Derivatives in Methanol: Reactivity,Regioselectivity, Kinetics,and Mechanism

The reaction of picryl benzoate derivatives 1a–g with aniline in methanol proceeds through CO? O and Ar? O bond cleavage pathways. Furthermore, the reactivity of these esters toward anilinolysis is correlated to the energy gap between highest occupied molecular orbital aniline and lowest unoccupied molecular orbital of each ester. The regioselectivity of acyl? oxygen versus aryl? oxygen cleavage is also discussed. The overall rate constants k_tot split into k_{CO? O} (the rate constant of acyl‐oxygen cleavage) and k_{Ar? O} (rate constant of aryl‐oxygen cleavage). The CO? O bond cleavage advances through a stepwise mechanism in which the formation of the tetrahedral intermediate is the rate‐determining step. The Ar? O bond cleavage continues through a S_NAr mechanism in which the departure of the leaving group from the Meisenheimer complex occurs rapidly after its formation in the rate‐determining step.     

Iron‐Mediated Cleavage of C?C Bonds in Vicinal Tricarbonyl Compounds in Water

Three of a kind : Vicinal tricarbonyl compounds undergo C? C cleavage mediated by ferric ions (see scheme). The observed cleavage of ninhydrin and dehydroascorbic acid has relevance for amino acid detection and the metabolism of vitamin C.

     

Baked hydrogel from corn starch and chitosan blends cross‐linked by citric acid: Preparation and properties

Citric acid (CA)–modified hydrogels from corn starch and chitosan were synthesized using a semidry condition. This strategy has great benefits of friendly environment because of the absence of organic solvents and compatible with the industrial process. The hydrogel blends were prepared with starch/chitosan ratios of 75/25, 50/50, and 25/75. The thermal stability, morphology, water absorption, weight loss in water, and methylene blue absorption were determined. Multi‐carboxyl structure of CA could result in a chemical cross‐linking reaction between starch, chitosan, and CA. The cross‐linking reaction between free hydroxyl groups of starch, amino groups of chitosan, and carboxyl groups of CA has been confirmed by attenuated total reflectance infrared (ATR‐IR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) analysis. The water absorption properties of CA‐modified hydrogel blends were increased significantly compared with the native starch and chitosan. Moreover, the hydrogel blends modified with CA showed good water resistance and gel content. The morphology study confirmed the complete chemical cross‐linking and porous structure of hydrogel blends. The hydrogel blend with the starch/chitosan ratio of 50/50 presented powerful absorption of methylene blue as well as chemical cross‐linking reaction and dense structure. In sum, the hydrogel blend comprising 50% starch and 50% chitosan has the potential to be applied for water maintaining at large areas, for example, in agriculture.     

Theoretical prediction of proton and electron affinities,gas phase basicities,and ionization energies of sulfinamides

Structural Chemistry - Sulfinamides, as an asymmetric synthesizer, especially in drug synthesis, play critical roles in organic chemistry. In this study, the gas phase ion energetics data including...     

Silica aerogel-filled PMMA by in situ reverse atom transfer radical polymerization: kinetics and thermal studies

Hydrophobically modified silica aerogel nanoparticles (H-SiANp) were used for in situ polymerization of methyl methacrylate by reverse atom transfer radical polymerization to synthesize well-defined PMMA nanocomposites. Inherent characteristics of the prepared H-SiANp were evaluated by nitrogen adsorption/desorption isotherms, SEM, and TEM. Conversion and molecular weight determinations were carried out using GC and SEC, respectively. Addition of 3 mass% of the H-SiANp leads to decrement of conversion from 92 to 74%. Molecular weight of poly (methyl methacrylate) chains also decreases from 19,737 to 15,662 g mol^?1 by addition of only 3 mass% H-SiANp; however, PDI values increase from 1.36 to 1.82. Linear increase of ln(M₀/M) with time for all the samples shows that polymerization proceeds in a living manner. In addition, suitable agreement between theoretical and experimental molecular weight in combination with low PDI values can appropriately demonstrate the living nature of the polymerization. TG results indicate that by increasing H-SiANp content, improvements in thermal stability of the nanocomposites were obtained. DSC results show a decrease in glass transition temperature from 87.4 to 80.9 °C by addition of 3 mass% H-SiANp.

     

Simulation-based design of thermally-driven actuators using liquid crystal elastomers

Liquid crystal elastomers (LCEs) are a class of soft functional materials which exhibit complex mechanical responses to external stimuli. Their promise for technological applications is difficult to realise in practice due to the complexity of design, fabrication and performance quantification of these materials. In order to address these issues, simulation-based methods are necessary to both enhance and accelerate the design process, compared to traditional experimentation alone. This work presents such an approach using a hyperelastic solid mechanics model and experimental measurement of material parameters for a thermotropic LCE. The simulation method is validated using existing experimental data of the thermomechanical response of an LCE-based cantilever resulting from a hybrid-aligned nematic texture imposed during crosslinking. The validated method is then used to perform a proof-of-concept design process of an LCE multilegged gripper in order to determine optimal design parameters for gripper performance. The simulation method and results presented in this work represent a significant step towards simulation-based design of LCE materials, which has the potential to overcome the complexity and cost of the LCE design process.     

Role of protein structure and the role of individual fingers in zinc finger protein–DNA recognition: a molecular dynamics simulation study and free energy calculations

Molecular dynamics and MM_GBSA energy calculations on various zinc finger proteins containing three and four fingers bound to their target DNA gave insights into the role of each finger in the DNA binding process as part of the protein structure. The wild type Zif 268 (PDB code: 1AAY) gave a ΔG value of ??76.1 (14) kcal/mol. Zinc fingers ZF1, ZF2 and ZF3 were mutated in one experiment and in another experiment one finger was cut and the rest of the protein was studied for binding. The ΔΔG values for the Zinc Finger protein with both ZF1 and ZF2 mutated was +?80 kcal/mol, while mutating only ZF1 the ΔΔG value was +?52 kcal/mol (relative to the wild type). Cutting ZF3 and studying the protein consisting only of ZF1 linked to ZF2 gave a ΔΔG value of +?68 kcal/mol. Upon cutting ZF1, the resulting ZF2 linked to ZF3 protein gave a ΔΔG value of +?41 kcal/mol. The above results shed light on the importance of each finger in the binding process, especially the role of ZF1 as the anchoring finger followed in importance by ZF2 and ZF3. The energy difference between the binding of the wild type protein Zif268 (1AAY) and that for individual finger binding to DNA according to the formula: ΔΔG_{linkers, otherstructuralfactors}?=?ΔG_zif268???(ΔG_F1+F2+F3) gave a value?=???44.5 kcal/mol. This stabilization can be attributed to the contribution of linkers and other structural factors in the intact protein in the DNA binding process. DNA binding energies of variant proteins of the wild type Zif268 which differ in their ZF1 amino acid sequence gave evidence of a good relationship between binding energy and recognition and specificity, this finding confirms the reported vital role of ZF1 in the ZF protein scanning and anchoring to the target DNA sequence. The role of hydrogen bonds in both specific and nonspecific amino acid-DNA contacts is discussed in relation to mutations. The binding energies of variant Zinc Finger proteins confirmed the role of ZF1 in the recognition, specificity and anchoring of the zinc finger protein to DNA.     

Specific heat and phase transition of (Li1−xKx)2SO4 single crystals

A specific heat study of (Li_1–xK_x)₂SO₄ — LKS — mixed crystals has been made in a wide concentration rangex covering the temperature range 300–800 K. The phase diagram was determined. It is shown that a variation of the Li⁺:K⁺ concentration changes the critical behaviour of the specific heat. The results are discussed in terms of scattering mechanisms of energy carriers.

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Zusammenfassung Bei Temperaturen zwischen 300 und 800 K wurde für einen breiten Konzentrationsbereich für x die spezifische Wärme von (Li_1–xK_x)₂SO₄-Mischkristallen untersucht und das entsprechende Phasendiagramm erstellt. Es wurde gezeigt, daß eine Änderung des Verhältnisses Li⁺:K⁺ auch das kritische Verhalten der spezifischen Wärme verändert. Die Ergebnisse werden hinsichtlich von Sreuungsmechanismen der Energieträger diskutiert.