High-energy Compounds Research Articles

Memories of Annemarie Weber.

Memories of Annemarie Weber.

A novel assay of DGAT activity based on high temperature GC/MS of triacylglycerol.

Diacylglycerol acyltransferase (DGAT) catalyzes the final step in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG), a high-energy compound composed of three fatty acids esterified to a glycerol backbone. In vitro DGAT assays, which are usually conducted with radiolabeled substrate using microsomal fractions, have been useful in identifying compounds and genetic modifications that affect DGAT activity. Here, we describe a high-temperature gas chromatography (GC)/mass spectrometry (MS)-based method for monitoring molecular species of TAG produced by the catalytic action of microsomal DGAT. This method circumvents the need for radiolabeled or modified substrates, and only requires a simple lipid extraction prior to GC. The utility of the method is demonstrated using a recombinant type-1 Brassica napus DGAT produced in a strain of Saccharomyces cerevisae that is deficient in TAG synthesis. The GC/MS-based assay of DGAT activity was strongly correlated with the typical in vitro assay of the enzyme using [1-(14)C] acyl-CoA as an acyl donor. In addition to determining DGAT activity, the method is also useful for determining substrate specificity and selectivity properties of the enzyme.

A Comparison Between Plant Photosystem I and Photosystem II Architecture and Functioning

Oxygenic photosynthesis is indispensable both for the development and maintenance of life on earth by converting light energy into chemical energy and by producing molecular oxygen and consuming carbon dioxide. This latter process has been responsible for reducing the CO2 from its very high levels in the primitive atmosphere to the present low levels and thus reducing global temperatures to levels conducive to the development of life. Photosystem I and photosystem II are the two multi-protein complexes that contain the pigments necessary to harvest photons and use light energy to catalyse the primary photosynthetic endergonic reactions producing high energy compounds. Both photosystems are highly organised membrane supercomplexes composed of a core complex, containing the reaction centre where electron transport is initiated, and of a peripheral antenna system, which is important for light harvesting and photosynthetic activity regulation. If on the one hand both the chemical reactions catalysed by the two photosystems and their detailed structure are different, on the other hand they share many similarities. In this review we discuss and compare various aspects of the organisation, functioning and regulation of plant photosystems by comparing them for similarities and differences as obtained by structural, biochemical and spectroscopic investigations.

Testing the versatility of the alternating sites of reactivity mechanism in the phosphagen kinases (768.11)

Phosphagen kinases achieve “buffering” of cellular ATP levels by catalyzing the reversible transfer of a phosphoryl group from ATP to a guanidino acceptor to form a high energy compound, phosphagen. Creatine kinase (CK), a PK found mainly in vertebrates, exists as a dimer in muscles; whereas, arginine kinase (AK), found exclusively in invertebrates, exists mainly as a monomer. The physiological functions of different oligomerization states within the PK family are not fully understood. Crystal structures of dimeric CK and AK are consistent with cooperativity in ligand binding between the two subunits. Based on these results, a reciprocating mechanism of catalysis was suggested for dimeric PKs. However, the exact mechanism and the potential effects of negative cooperativity on ligand binding ability of dimeric PKs remains unexplained. In this study, we’ve shown direct functional evidence of negative cooperativity in rabbit muscle CK (rbCK) by measuring the enzymes’ affinity for MgADP using isothermal titration calorimetry. Measurements of rbCK‐ligand interactions, in presence of saturating concentrations of creatine and nitrate, to form the transition‐state analogue quaternary complex, were fitted using a two‐site binding model with Kd1 = 56 ± 32 µM and Kd2 = 2.7 ± 1.4 mM. In the absence of creatine and nitrate, MgADP binding by rbCK fits a one‐site binding model, with Kd = 720 ± 330 µM. These suggest that the presence of creatine enables the conformation necessary to permit cross‐talk between the subunits. Pre‐steady state kinetic assays and the effect of viscosity on kcat show that the rate‐limiting step of reaction catalyzed by PKs is dependent on the oligomerization state of the enzyme, consistent with the alternating site of reactivity mechanism.Grant Funding Source: NSF Grant #0619123

High-energy compounds mobilize intracellular Ca2+ and activate calpain in cultured cells: Is calpain an energy-dependent protease?

Deficiency in energy metabolisms is perhaps the earliest modifiable defect in brain aging and sporadic Alzheimer's disease (sAD). Several high-energy compounds (HECs) such as ATP, phosphoenolpyruvate, phosphocreatine and acetyl coenzyme A have been shown to exhibit neuroprotective effects. To understand their mechanism of actions, we tested the effects of these HECs on intracellular Ca(2+), a central regulator in brain function. Our data showed that the HECs robustly and dose-dependently mobilized intracellular Ca(2+) in cultured SH-SY5Y cells, and the actions were sensitive to intracellular Ca(2+) chelator BAPTA-AM or energy metabolism blocker rotenone. The Ca(2+) influx triggered by the HECs was from both extracellular medium and intracellular stores and the HECs also induced repetitive Ca(2+) oscillations. As these actions were similar to those of classical Ca(2+) agonists, the HECs may be viewed as a new group of physiological Ca(2+) agonists. We also found that the HECs promoted the intracellular activity of calpain, a Ca(2+)-dependent protease, and the enzyme activity fluctuated in concert with cellular energy levels, suggesting that calpain activity may also be energy-driven or energy-dependent. These findings may add to current knowledge for the regulatory mechanisms of Ca(2+) and calpain. Since Ca(2+) and calpain undergo critical dysfunction in brain aging but the underlying mechanisms remain elusive, our work may provide a new perspective for clarifying some controversies. More importantly, the HECs, as key intermediates in glucose catabolism, the primary source of energy supply in the brain, may be used as potential drugs for rational prevention of sAD.

Activation of the Ano1 (TMEM16A) chloride channel by calcium is not mediated by calmodulin

The Ca(2+)-activated Cl channel anoctamin-1 (Ano1; Tmem16A) plays a variety of physiological roles, including epithelial fluid secretion. Ano1 is activated by increases in intracellular Ca(2+), but there is uncertainty whether Ca(2+) binds directly to Ano1 or whether phosphorylation or additional Ca(2+)-binding subunits like calmodulin (CaM) are required. Here we show that CaM is not necessary for activation of Ano1 by Ca(2+) for the following reasons. (a) Exogenous CaM has no effect on Ano1 currents in inside-out excised patches. (b) Overexpression of Ca(2+)-insensitive mutants of CaM have no effect on Ano1 currents, whereas they eliminate the current mediated by the small-conductance Ca(2+)-activated K(+) (SK2) channel. (c) Ano1 does not coimmunoprecipitate with CaM, whereas SK2 does. Furthermore, Ano1 binds very weakly to CaM in pull-down assays. (d) Ano1 is activated in excised patches by low concentrations of Ba(2+), which does not activate CaM. In addition, we conclude that reversible phosphorylation/dephosphorylation is not required for current activation by Ca(2+) because the current can be repeatedly activated in excised patches in the absence of ATP or other high-energy compounds. Although Ano1 is blocked by the CaM inhibitor trifluoperazine (TFP), we propose that TFP inhibits the channel in a CaM-independent manner because TFP does not inhibit Ano1 when applied to the cytoplasmic side of excised patches. These experiments lead us to conclude that CaM is not required for activation of Ano1 by Ca(2+). Although CaM is not required for channel opening by Ca(2+), work of other investigators suggests that CaM may have effects in modulating the biophysical properties of the channel.

Book review: “Glial physiology and pathophysiology” by Alexei Verkhratsky and Arthur Butt, Wiley-Blackwell, 2013

Book review: “Glial physiology and pathophysiology” by Alexei Verkhratsky and Arthur Butt, Wiley-Blackwell, 2013

In Vivo Evidence for Cerebral Bioenergetic Abnormalities in Schizophrenia Measured Using31P Magnetization Transfer Spectroscopy

Abnormalities in neural activity and cerebral bioenergetics have been observed in schizophrenia (SZ). Further defining energy metabolism anomalies would provide crucial information about molecular mechanisms underlying SZ and may be valuable for developing novel treatment strategies. To investigate cerebral bioenergetics in SZ via measurement of creatine kinase activity using in vivo 31P magnetization transfer spectroscopy. Cross-sectional case-control study in the setting of clinical services and a brain imaging center of an academic psychiatric hospital. Twenty-six participants with chronic SZ (including a subgroup diagnosed as having schizoaffective disorder) and 26 age-matched and sex-matched healthy control subjects (25 usable magnetic resonance spectroscopy data sets from the latter). 31P magnetization transfer spectroscopy. The primary outcome measure was the forward rate constant (k(f)) of the creatine kinase enzyme in the frontal lobe. We also collected independent measures of brain intracellular pH and steady-state metabolite ratios of high-energy phosphate-containing compounds (phosphocreatine and adenosine triphosphate [ATP]), inorganic phosphate, and the 2 membrane phospholipids phosphodiester and phosphomonoester. A substantial (22%) and statistically significant (P = .003) reduction in creatine kinase kf was observed in SZ. In addition, intracellular pH was significantly reduced (7.00 in the SZ group vs 7.03 in the control group, P = .007) in this condition. The phosphocreatine to ATP ratio, inorganic phosphate to ATP ratio, and phosphomonoester to ATP ratio were not substantially altered in SZ, but a significant (P = .02) reduction was found in the phosphodiester to ATP ratio. The abnormalities were similar between SZ and schizoaffective disorder. Using a novel 31P magnetization transfer magnetic resonance spectroscopy approach, we provide direct and compelling evidence for a specific bioenergetic abnormality in SZ. Reduced kf of the creatine kinase enzyme is consistent with an abnormality in storage and use of brain energy. The intracellular pH reduction suggests a relative increase in the contribution of glycolysis to ATP synthesis, providing convergent evidence for bioenergetic abnormalities in SZ. The similar phosphocreatine to ATP ratios in SZ and healthy controls suggest that the underlying bioenergetics abnormality is not associated with change in this metabolite ratio.

Theoretical study on a novel high-energy density material 4,6,10,12-tetranitro-5,11-bis(nitroimino)-2,8-dioxa-4,6,10,12-tetraaza-tricyclo[7,3,0,03,7]dodecane

A novel high-energy density material (HEDM) 4,6,10,12-tetranitro-5,11-bis(nitroimino)-2,8-dioxa-4,6,10,12-tetraaza-tricyclo[7,3,0,03,7]dodecane was designed and studied by a density functional theory (DFT) method. The geometric structure and thermodynamic properties were investigated at the B3LYP/6-31G (d,p) level. The heat of formation (HOF) and detonation properties were predicted by isodesmic reactions and Kamlet–Jacobs equations. The bond dissociation energy (BDE) and impact sensitivity were also studied to give a better understanding of its chemical and physical properties. The calculated results indicate that 4,6,10,12-tetranitro-5,11-bis(nitroimino)-2,8-dioxa-4,6,10,12-tetraaza-tricyclo[7,3,0,03,7]dodecane belongs to the P space group, with cell parameters Z = 2, a = 13.554 Å, b = 8.552 Å, c = 15.575 Å, α = 70.638°, β = 29.515° and γ = 82.702°. In view of the heat of formation (HOF, 530.36 kJ mol−1), detonation velocity (D, 9.72 km s−1), detonation pressure (P, 45.12 GPa), bond dissociation energy (BDE, 109.85 kJ mol−1) and impact sensitivity (h50, 20.79 cm), it is predicted that 4,6,10,12-dinitro-5,11-bis(nitroimino)-2,8-dioxa-4,6,10,12-tetraaza-tricyclo[7,3,0,03,7] dodecane could be considered as a potential candidate high-energy density compound.

Cannulated screw and hexapodal fixator reconstruction for compound upper tibial fractures

Objectives: The aim of the treatment of tibial plateau fractures is to obtain a pain-free and fully functional knee with closed reduction, percutaneous cannulated screw fixation and hexapodal external fixator reconstruction for high energy compound upper tibial fractures. Methods: Patients with comminuted tibial plateau fractures underwent closed reduction, percutaneous fixation with cannulated screws, and reconstruction with hexapodal external fixator. The follow-up period was 24 months. Results: The clinical and radiological results were good or excellent. The average knee flexion was 125°. Conclusion: Our results are successful in the initial stage, however, it should be pointed out that during the long term follow-up osteoarthritis may develop leading to worsening of the condition. Level of Evidence IV, Case Series.

Detection of high-energy compounds using photoluminescent silicon nanocrystal paper based sensors

Luminescent silicon nanocrystals (Si-NCs) surface functionalized with dodecyl groups were exposed to solutions of nitroaromatic compounds including nitrobenzene, nitrotoluene, and dinitrotoluene. It was found that Si-NC luminescence was quenched upon exposure to nitroaromatics via an electron transfer mechanism as indicated by Stern-Volmer analysis. This quenching was exploited and a straightforward paper-based Si-NC sensor was developed. This paper motif was found to be sensitive to solution, vapor, and solid phase nitroaromatics, as well as solution borne RDX and PETN.

Computational screening of several silicon-based high-energy hexanitrohexaazaisowurtzitane-like derivatives

Silicon-based hexanitrohexaazaisowurtzitane (CL-20) derivatives, including nitro (NO2) and difluoramino (NF2) group containing derivatives, may become important high-energy compounds. Density Functional Theory Becke exchange plus Perdew correlation (BP) with triple numerical set plus polarization functions (TNP) and homodesmotic reactions were employed to calculate cage strain energies, gaseous phase formation enthalpies of several silicon-based CL-20 derivatives. Comparative studies were carried out between silicon-based CL-20 nitro and difluoramine derivatives. The structural stability of these silicon-based CL-20 derivatives were evaluated in terms of NNO2 or NNF2 bond dissociation energies and Mulliken charges of NO2 or NF2 groups by means of density functional theory revised versions of the Perdew–Burke–Ernzerhof (RPBE) with TNP functions, and the exchange component of Perdew and Wang's 1991 functional (PW91) with TNP functions, two theoretical methods were chosen according to experimental data. The theoretical studies show that their performances are better than CL-20 in terms of detonation velocities, detonation pressures and explosion temperatures. Structural stability of these silicon-based CL-20 derivatives is higher than CL-20 according to NNO2 or NNF2 bond dissociation energies and cage strain energies. This work will lay some foundations for the future explorations of novel high-energy silicon-based compounds.

An Investigation into the Effects of Additives on Crystal Characteristics and Impact Sensitivity of RDX

Additives are one of the most important factors that greatly affect the crystal characteristics of the high energy compound hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX, C3H6N6O6) and they have an influence on impact sensitivity. In this article, a growth morphology method was applied to obtain the crystal habit of RDX in a vacuum as well as the morphologically important faces, and molecular dynamics simulations were applied to calculate the interaction energy between these crystal faces and additive molecules for prediction of the additive-effect crystal habits of RDX. On this basis, crystal characteristics including crystal morphology, aspect ratio, and total surface charge were investigated. Then the particle size and surface electrostatic voltage of the samples from recrystallization were analyzed experimentally. The impact sensitivity test indicated that acrylamide, which could enhance the regularity and degree of sphericity of RDX crystals and effectively reduce the surface static electricity of RDX, was successful in reducing the impact sensitivity of RDX as an additive for crystallization. The above experimental results were in good agreement with the conclusions based on the theoretical calculations.

Addressing the challenges for sustainable production of algal biofuels: I. Algal strains and nutrient supply

Microalgae hold promise for the production of sustainable replacement of fossil fuels due to their high growth rates, ability to grow on non-arable land and their high content, under the proper conditions, of high energy compounds that can be relatively easily chemically converted to fuels using existing technology. However, projected large-scale algal production raises a number of sustainability concerns concerning land use, net energy return, water use and nutrient supply. The state-of-the-art of algal production of biofuels is presented with emphasis on some possible avenues to provide answers to the sustainability questions that have been raised. Here, issues concerning algal strains and supply of nutrients for large-scale production are discussed. Since sustainability concerns necessitate the use of wastewaters for supply of bulk nutrients, emphasis is placed on the composition and suitability of different wastewater streams. At the same time, algal cultivation has proven useful in waste treatment processes, and thus this aspect is also treated in some detail.

Condensed‐phase laser ionization time‐of‐flight mass spectrometry of highly energetic nitro‐aromatic compounds

Analysis of explosive compounds represents an interesting field of work due to the obvious social relevance of these compounds. Direct laser ionization allows the analysis of these high internal energy compounds without sampling or preparation procedures. We have studied nitro-aromatic compounds to understand their mass spectra when directly ionized in the condensed phase, different from the gas-phase studies commonly conducted. Direct condensed-phase laser ionization time-of-flight mass spectrometry of high energy density materials has been performed using a 5 ns width quadrupled Nd:YAG laser. No matrix assistance was used. Fine control of the laser energy allowed the study of the fragmentation processes from values close to the ionization threshold to ones where atomic-only mass spectra were recorded. The influence of the variation of extraction conditions on the recorded mass spectra was investigated. For low extraction width pulses, ions with low m/z values were mainly observed, whereas, at higher widths, higher mass fragment ions were also detected while the total ion current was maintained. Therefore, the mass spectra can be modulated to obtain mass spectra containing molecular or atomic information. The onset of ion generation for the different fragment ions was also studied, yielding information that can help to understand the processes involved in the fragmentation pathways of the molecule and in the dissociation mechanisms. Two sampling procedures allowed the prospective use of LIMS as a screening technique for nitro-aromatic-based highly energetic explosives. Direct analysis of explosive compounds has been performed by laser ionization. A large dependence of the resultant spectra on the laser energy was observed that might be useful for studies of fragmentation pathways. For forensic applications, two sampling procedures might allow the use of LIMS as a screening technique.

The path to life’s origins. Remaining hurdles

Recent progress in abiotic syntheses, especially self-catalytic syntheses, as well as theoretical breakthroughs such as reconstruction of events of early molecular evolution and tracing repeat expansions in contemporary genomes, converge to a rather simple possible scenario of origin of life, notwithstanding the enormity of the problem. The scenario includes self-replicating RNA duplexes, supplemented by monomers and high-energy compounds that, as demonstrated or assumed, can all be synthesized abiotically. The self-replication would proceed with occasional mutational changes, propagated in later cycles. This audacious, as it may seem, walk toward the life origin already involves many laboratories, each exploring its own scenario. The one suggested in this outline seems to the authors well justified to engage in, while bypassing few steps to deal with later.

Bone Remodeling and Energy Metabolism: New Perspectives.

Bone mineral, adipose tissue and energy metabolism are interconnected by a complex and multilevel series of networks. Calcium and phosphorus are utilized for insulin secretion and synthesis of high energy compounds. Adipose tissue store lipids and cholecalciferol, which, in turn, can influence calcium balance and energy expenditure. Hormones long-thought to solely modulate energy and mineral homeostasis may influence adipocytic function. Osteoblasts are a target of insulin action in bone. Moreover, endocrine mediators, such as osteocalcin, are synthesized in the skeleton but regulate carbohydrate disposal and insulin secretion. Finally, osteoblasts and adipocytes originate from the same mesenchymal progenitor. The mutual crosstalk between osteoblasts and adipocytes within the bone marrow microenvironment plays a crucial role in bone remodeling. In the present review we provide an overview of the reciprocal control between bone and energy metabolism and its clinical implications.

Molecular design of trinitromethyl-substituted nitrogen-rich heterocycle derivatives with good oxygen balance as high-energy density compounds

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and pyrolysis mechanism of a series of trinitromethyl-substituted heterocycle (including triazole, tetrazole, furazan, tetrazine, and fused heterocycles) derivatives. It is found that the fused ring, tetrazine, and tetrazole are effective structural units for increasing the HOFs of the derivatives. The substitution of the combination of nitro and trinitromethyl is very useful for improving their HOFs. The calculated energetic properties indicate that the combination of the nitro and trinitromethyl is very helpful for improving their detonation properties and oxygen balances (OB). Most of the title compounds have a good OB over zero. The OB of six compounds are very high and over 22. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the N–O bond in the ring is a trigger bond for BIII-1, CI-3, and CI-4, and the ring–NO2 and (NO2)2C–NO2 bond cleavage is likely to happen in thermal decomposition for the remaining compounds. Considering the detonation performance and thermal stability, seven compounds could be regarded as potential candidates for high-energy compounds. Four compounds may be used as the novel high-energy oxidizers.

Theoretic design of 1,2,3,4-tetrazine-1,3-dioxide-based high-energy density compounds with oxygen balance close to zero

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of 1,2,3,4-tetrazine-1,3-dioxide derivatives with different substituents and bridge groups. It is found that the groups –NO2, –C(NO2)3, and –N=N– play a very important role in increasing the HOFs of the derivatives. The effects of the substituents on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and HOMO–LUMO gaps are coupled to those of different substituents and bridges. The calculated detonation velocities and pressures indicate that the group –NO2, –NF2, –ONO2, –C(NO2)3, or –NH– is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds indicates that incorporating the groups –NO2, –NF2, –ONO2, –C(NO2)3, and –N=N– into parent ring decreases their thermal stability. Considering the detonation performance and thermal stability, 18 compounds may be considered as the target compounds holding the greatest potential for synthesis and use as high-energy density compounds. Among them, the oxygen balances of four compounds are equal to zero. These results provide basic information for the molecular design of the novel high-energy compounds.

Laser-induced plasma spectroscopy of organic compounds. Understanding fragmentation processes using ion–photon coincidence measurements

Coincidence detection is of interest to get as much information as possible about transient events occurring in laser induced plasmas. The present work is focused on coincidence ion–photon detection of laser plasmas of high-energy organic compounds (TNT and DNT) in a condensed phase irradiated with UV laser pulses using an advanced instrument for simultaneous monitoring of both types of chemical species generated. The optical emission spectrum is acquired from atoms, atomic ions and diatomic molecules, whereas the mass spectrum derives from fragment ions of the molecule. These fragments result from direct ionization or may be formed through indirect pathways. Fluence-resolved experiments showed the evolution of the main optical-mass signals in the acquired spectra for a limited energetic range, showing the different stages of lifetime of plasma: the rising thresholds and extinction of the different atomic and molecular studied species, besides the breakage of the aromatic ring and the later excitation of ionic species at a higher fluence level.