Theoretical studies on the heats of formation, densities, and detonation properties of substituted s-tetrazine compounds

Substituted s-tetrazine compounds were designed and investigated in order to find comprehensive relationships between the structures and performances of high-nitrogen energetic compounds. Density functional theory (DFT) was used to predict the optimized geometries, electronic structures, heats of formation and densities, and the detonation properties were evaluated by using the VLW equation of state (EOS). Calculation results show that there are good linear relationships between heats of formation, densities, detonation properties and the number of N atom in all designed high-nitrogen compounds. Furthermore, several designed high-nitrogen compounds show good detonation velocities and pressures compared with octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), making them potential candidates for high-energy-density materials (HEDM).     

Theoretical investigation on the heats of formation and detonation performance in polydinitroaminocubanes

A series of polydinitroaminocubanes have been designed computationally. We calculated the heats of formation, the detonation velocity (D) and detonation pressure (P) of the title compounds by density function theory (DFT) with 6-311?G** basis set. The relationship between the heats of formation and the molecular structures is discussed. The result shows that all cubane derivatives have high and positive heats of formation, which increase with increasing number of dinitroamino groups. The detonation performances of the title compound were estimated by Kamlet-Jacobs equation, and the result indicated that most cubane derivatives have good detonation performance over RDX (hexahydro-1,3,5-trinitro-1,3,5-trizine) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane). In addition, we also found that the heat of detonation (Q) is another very important impact in increasing detonation performance except density. The relative stabilities of the title compound are discussed in the terms of the calculated heats of formation, and the energy gaps between the frontier orbitals. The results have not only shown that these compounds may be used as high energy density compounds (HEDCs), but also provide some useful information for further investigation.     

Fluorescence properties,thermal duplex stability,and kinetics of formation of cyanin platinum DNAs

Fluorescent and haptenized, monofunctionally binding platinum compounds are increasingly used for chemically labeling nucleic acids for hybridization detection purposes. Here we analyze in detail the effect of labeling density of the cyanin-3 and -5 platinum DNA adducts on fluorescence and thermal stability. We also analyzed the kinetics of the reaction of the cyanin platinum compounds with DNA. The data provided are important for the design of optimal platinum DNA labeling and hybridization conditions for fluorescence hybridization applications.     

Theoretical studies on the thermodynamic properties, densities, detonation properties, and pyrolysis mechanisms of trinitromethyl-substituted aminotetrazole compounds

Trinitromethyl-substituted aminotetrazoles with –NH₂, –NO₂, –N₃, and –NHC(NO₂)₃ groups were investigated at the B3LYP/6-31G(d) level of density functional theory. Their sublimation enthalpies, thermodynamic properties, and heats of formation were calculated. The thermodynamic properties of these compounds increase with temperature as well as with the number of nitro groups attached to the tetrazole ring. In addition, the detonation velocities and detonation pressures of these compounds were successfully predicted using the Kamlet–Jacobs equations. It was found that these compounds exhibit good detonation properties, and that compound G (D = 9.2 km/s, P = 38.8 GPa) has the most powerful detonation properties, which are similar to those of the well-known explosive HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Finally, the electronic structures and bond dissociation energies of these compounds were calculated. The BDEs of their C–NO₂ bonds were found to range from 101.9 to 125.8 kJ/mol^-1. All of these results should provide useful fundamental information for the design of novel HEDMs.     

Theoretical studies on the crystal structure, thermodynamic properties, detonation performance and thermal stability of cage-tetranitrotetraazabicyclooctane as a novel high energy density compound

The B3LYP/6-31G (d) method of density functional theory (DFT) was used to study molecular geometry, electronic structure, infrared spectrum (IR) and thermodynamic properties. The heat of formation (HOF) and calculated density were estimated to evaluate the detonation properties using Kamlet–Jacobs equations. Thermal stability of 3,5,7,10,12,14,15,16-octanitro- 3,5,7,10,12,14,15,16-octaaza-heptacyclo[7.5.1.1^2,8.0^1,11.0^2,6.0^4,13.0^6,11]hexadecane (cage-tetranitrotetraazabicyclooctane) was investigated by calculating the bond dissociation energy (BDE) at unrestricted B3LYP/6-31G (d) level. The calculated results show that the N–NO₂ bond is a trigger bond during thermolysis initiation process. The crystal structure obtained by molecular mechanics (MM) methods belongs to Pna2₁ space group, with cell parameters a?=?12.840 Å, b?=?9.129 Å, c?=?14.346 Å, Z?=?6 and ρ?=?2.292 g·cm^?3. Both the detonation velocity of 9.96 km·s^?1 and the detonation pressure of 47.47 GPa are better than those of CL-20. According to the quantitative standard of energetics and stability, as a high energy density compound (HEDC), cage-tetranitrotetraazabicyclooctane essentially satisfies this requirement.     

Characterization of Langmuir-Blodgett films of rhodopsin: thermal stability studies.

Two-dimensional close packing of purified bovine rhodopsin, made by the Langmuir-Blodgett technique, was characterized by small angle x-ray scattering and nanogravimetric measurements. The area occupied by a molecule of rhodopsin in the film was approximately 1100 Angstrum2 and the periodicity of the layers resulted in 59 Angstrum. The circular dichroism measurements showed that bleached rhodopsin in Langmuir-Blodgett film had high thermal stability, in fact, reaching a temperature of 150 degrees C without a loss of the secondary structure. Moreover, when the film was made up in the dark, rhodopsin maintained its stability up to at least 200 degrees C and its characteristic absorbance peak at 500 nm up to about 90 degrees C.     

Characterization of PINK1 processing, stability, and subcellular localization

Mutations found in PTEN-induced putative kinase 1 (PINK1), a putative mitochondrial serine/threonine kinase of unknown function, have been linked to autosomal recessive Parkinson's disease. It is suggested that mutations can cause a loss of PINK1 kinase activity and eventually lead to mitochondrial dysfunction. In this report, we examined the subcellular localization of PINK1 and the dynamic kinetics of PINK1 processing and degradation. We also identified cytosolic chaperone heat-shock protein 90 (Hsp90) as an interacting protein of PINK1 by PINK1 co-immunoprecipitation. Immunofluorescence of PINK1 protein and mitochondrial isolation show that the precursor form of PINK1 translocates to the mitochondria and is processed into two cleaved forms of PINK1, which in turn localize more to the cytosolic than mitochondrial fraction. The cleavage does not occur and the uncleaved precursor stays associated with the mitochondria when the mitochondrial membrane potential is disrupted. Metabolic labeling analyses show that the PINK1 processing is rapid and the levels of cleaved forms are tightly regulated. Furthermore, cleaved forms of PINK1 are stabilized by Hsp90 interaction as the loss of Hsp90 activity decreases PINK1 level after mitochondrial processing. Lastly, we also find that cleaved forms of PINK1 are degraded by the proteasome, which is uncommon for mitochondrial proteins. Our findings support a dual subcellular localization, implying that PINK1 can reside in the mitochondria and the cytosol. This raises intriguing functional roles that bridge these two cellular compartments.     

An azomethin-zinc complex for organic electroluminescence: Crystal structure, thermal stability and optoelectronic properties

An azomethin-zinc complex, bis[salicylidene(4-dimethylamino)aniline]zinc(II) (Zn(sada)₂) was synthesized and structurally characterized by single-crystal X-ray crystallography. Crystal data for Zn(C₁₅H₁₅N₂O)₂ was determined as follows: space group, triclinic, ; a = 10.2791(9) Å, b = 16.5008(14) Å, c = 17.5984(15) Å, α = 114.830(2)°, β = 96.579(2)°, γ = 97.674(2)°, Z = 4. Through thermal analysis characterization and FT-IR spectra, this complex was proved to have good thermal stability. The vapor-deposited films exhibited uniform and environment-stable morphology. The light emission and charge transporting performance of Zn(sada)₂ in organic light emitting diodes (OLEDs) were investigated preliminarily, and the results indicated the superior electron transporting property of this complex. Compared with the typical bilayer device of N,N′-diphenyl-N,N′-bis(1-naphthyl)-benzidine (NPB)/tris-(8-hydroxyquinoline)aluminum (Alq₃), the device with Zn(sada)₂ as the electron transporting layer exhibited a much lower turn-on voltage of 2.5 V (it is usually 3.5 V for an NPB/Alq₃ device).     

Analysis of phase stability,elastic, electronic,thermal, and optical properties of Sc1-xYxN via ab initio methods

Journal of Molecular Modeling - The recent advances in the application of machine learning to drug discovery have made it a ‘hot topic’ for research, with hundreds of academic groups...     

The two-domain NK1 fragment of plasminogen: folding, ligand binding, and thermal stability profile

The two-domain fragment N+K1 (rNK1) [Glu(1)-Glu(163)] of human plasminogen was expressed in E. coli as a hexahistidine-tagged fusion protein and chromatographically purified. The (1)H NMR spectrum supports proper folding of the K1 component within the refolded rNK1 construct (rNK1/K1). The functional properties of rNK1/K1 were investigated via intrinsic fluorescence titration with kringle-specific omega-aminocarboxylic acid ligands. The affinities closely match those previously measured for the isolated K1, which indicates that the N-domain does not significantly affect the interaction of ligands with the lysine binding site of K1. Far-UV CD spectra recorded for the N-domain suggest conformational plasticity and flexibility for the module. Two classes of spectra, referred to as types A and B, were identified with the type A spectrum reflecting a higher secondary structure content than that estimated for the type B spectrum. Subtracting the CD spectrum of rK1 from that of rNK1 yields a spectrum (Delta) which reflects the conformation of the N-domain within the rNK1 construct (rNK1/N). Delta resembles the type A spectrum, suggesting that rNK1/N adopts a relatively more ordered conformation, stabilized by the adjacent rNK1/K1 domain. In contrast, thermal unfolding curves determined via CD indicate that the rNK1/N slightly lowers the melting temperature (T(m)) of rNK1/K1. Independence of the two domains within rNK1 was tested by monitoring the thermal unfolding of rNK1/K1 when in the presence of the kringle-specific ligand AMCHA, which left the rNK1/N T(m) essentially unaffected, while increasing that of the rNK1/K1 by approximately 10 degrees C.     

A totally synthetic histidine-2 ferredoxin: thermal stability and redox properties.

The entire polypeptide of Clostridium pasteurianum ferredoxin (Fd) with a site-substituted tyrosine-2----histidine-2 was synthesized using standard t-Boc procedures, reconstituted to the 2[4Fe-4S] holoprotein, and compared to synthetic C. pasteurianum and native Fds. Although histidine-2 is commonly found in thermostable clostridial Fds, the histidine-2 substitution into synthetic C. pasteurianum Fd did not significantly increase its thermostability. The reduction potential of synthetic histidine-2 Fd was -343 and -394 mV at pH 6.4 and 8.7, respectively, versus standard hydrogen electrode. Similarly, Clostridium thermosaccharolyticum Fd which naturally contains histidine-2 was previously determined to have a pH-dependent reduction potential [Smith, E.T., & Feinberg, B.A. (1990) J. Biol. Chem. 265, 14371-14376]. An electrostatic model was used to calculate the observed change in reduction potential with pH for a homologous ferredoxin with a known X-ray crystal structure containing a hypothetical histidine-2. In contrast, the reduction potential of both native C. pasteurianum Fd and synthetic Fd with the C. pasteurianum sequence was -400 mV versus standard hydrogen electrode and was pH-independent [Smith, E.T., Feinberg, B.A., Richards, J.H., & Tomich, J.M. (1991) J. Am. Chem. Soc. 113, 688-689]. On the basis of the above results, we conclude that the observed pH-dependent reduction potential for both synthetic and native ferredoxins that contain histidine-2 is attributable to the electrostatic interaction between histidine-2 and iron-sulfur cluster II which is approximately 6 A away.     

Characterization of antagonistic and acid formation properties of Lactobacillus casei

Cultural, morphologic, and biochemical characteristics of Lactobacillus casei were studied as well as their acid-forming and antagonistic activity and resistance to antibiotics. 60 cultures identified as L. caseiwere isolated from 250 samples of sour-milk products and clinical specimens. All isolated strains had respectively high antagonistic activity regardless of their source. Dependence between antagonistic activity and acid formation was not detected. Conclusion about promise for using these lactobacilli for manufacturing of probiotics has been done.     

Adrenodoxin: structure, stability, and electron transfer properties

Adrenodoxin is an iron-sulfur protein that belongs to the broad family of the [2Fe-2S]-type ferredoxins found in plants, animals and bacteria. Its primary function as a soluble electron carrier between the NADPH-dependent adrenodoxin reductase and several cytochromes P450 makes it an irreplaceable component of the steroid hormones biosynthesis in the adrenal mitochondria of vertebrates. This review intends to summarize current knowledge about structure, function, and biochemical behavior of this electron transferring protein. We discuss the recently solved first crystal structure of the vertebrate-type ferredoxin, the truncated adrenodoxin Adx(4-108), that offers the unique opportunity for better understanding of the structure-function relationships and stabilization of this protein, as well as of the molecular architecture of [2Fe-2S] ferredoxins in general. The aim of this review is also to discuss molecular requirements for the formation of the electron transfer complex. Essential comparison between bacterial putidaredoxin and mammalian adrenodoxin will be provided. These proteins have similar tertiary structure, but show remarkable specificity for interactions only with their own cognate cytochrome P450. The discussion will be largely centered on the protein-protein recognition and kinetics of adrenodoxin dependent reactions.     

Fabrication of curcumin-loaded zein nanoparticles stabilized by sodium caseinate/sodium alginate: Curcumin solubility,thermal properties,rheology, and stability

Curcumin is a polyphenol with multiple biological activities, but its extremely poor water solubility severely limits its application in the food industry. The purposes of this work were to study the effect of nano-encapsulation on the water solubility of curcumin (C), the interaction of curcumin with zein (Z), the thermal properties, rheological properties, and the stability under different environmental pressures of the nanoparticles. The results of particle size, zeta potential, and surface hydrophobicity (H₀) indicated that the combination of coating materials including sodium caseinate (SC) and sodium alginate (SA) with zein nanoparticles by electrostatic interaction led to a gradual increase in the particle size of composite nanoparticles and a decrease in surface hydrophobicity. The nano-encapsulation significantly improved the water solubility of curcumin and causing its crystal structure to change to an amorphous state. Fourier transform infrared spectroscopy confirmed that curcumin bound to zein through hydrogen bonding. Rheological test results showed that the coating materials combined with zein led to an increase in the apparent viscosity of the nanoparticles. The stability analysis results indicated that the composite nanoparticles with a sodium alginate coating have excellent stability of pH, salt solution and storage, and excellent anti-gastrointestinal fluids digestion characteristics when compared to pure protein nanoparticles.     

The effect of drying on the colloidal properties and stability of humic compounds

It is indicated here that organic macro molecules in the soil are aggregated due to bonds, presumably hydrogen bonds, formed in the presence of water. When the soil is dried, this structure is broken and the stability of the organic matter decreases. This process is not an instantaneous process and apparently some relaxation period is needed for a complete dispersion of the organic matrix. An appreciable fraction of the organic molecules is hindered, even from contact with the solution in the aggregated structure, as indicated by the lower acidity in the wet soil. This steric hinderence seems to be one of the important factors contributing to the stability of humic compounds.     

Conjugation of d-glucosamine to bovine trypsin increases thermal stability and alters functional properties

d-glucosamine was conjugated to bovine trypsin by carbodiimide chemistry, involving a water-soluble carbodiimide and a succinimide ester, with the latter being to increase the yield of the conjugation. Mass spectrometric data suggested that several glycoforms were formed, with around 12 d-glucosamine moieties coupled to each trypsin molecule on average. The moieties were probably coupled to eight carboxyl groups (of glutamyl and aspartyl residues) and to four tyrosyl residues on the surface of the enzyme. The glycated trypsin possessed increased thermal stability. When compared with its unmodified counterpart, T_50% was increased by 7 °C, thermal inactivation of the first step was increased 34%, and long-term stability assay revealed 71-times higher residual activity at 25 °C (without stabilizing Ca²⁺ ions in aqueous buffer) after 67 days. Furthermore, resistance against autolysis was increased almost two-fold. Altered functional properties of the glycated trypsin were also observed. The glycated trypsin was found to become increasingly basophilic, and was found to be slightly structurally altered. This was indicated by 1.2 times higher catalytic efficiency (k_cat/K_m) than unmodified trypsin against the substrate N-α-benzoyl-l-arginine-p-nitroanilide. Circular dichroism spectropolarimetry suggested a minor change in spatial arrangement of α-helix/helices, resulting in an increased affinity of the glycated trypsin for this small synthetic substrate.