A new approach to determine soil microbial biomass by calorimetry

A method to determine soil microbial biomass (SMB) by isothermal calorimetry is reported. Soil samples ranging in pH from 6.2 to 9.4 and different textures were used to develop the method. Soil at 60% of its field capacity humidity was amended with a previously determined amount of glucose as to give the maximal response of CO₂ evolution. Then, an aliquot was weighed in the calorimeter ampoule and specific thermal power (p)–time (t) curves were obtained at 25 °C. After 1–2 h, a vial containing a 0.5 M NaOH solution was introduced to determine the specific thermal power due to CO₂ evolution, pCO₂ during 1–2 h. Then, the vial was removed and the experiment continued for 1–2 h. Specific thermal power due to CO₂ evolution was converted to rate (CO₂-C/mm³ g⁻¹ h⁻¹) by using the heat of reaction of CO₂ with NaOH and the molar volume. This value was further converted into SMB/μg g⁻¹ by using a conversion factor of 32.4. A guide to perform the calculations is given. Values of log SMB were linearly related with values of log p giving a similar relation to a previously reported where SMB was determined by conventional methods.     

Purification and Characterization of Chitinase from <Emphasis Type="BoldItalic">Paenibacillus</Emphasis> sp. D1

A 56.56-kDa extracellular chitinase from Paenibacillus sp. D1 was purified to 52.3-fold by ion exchange chromatography using SP Sepharose. Maximum enzyme activity was recorded at pH 5.0 and 50 °C. MALDI-LC-MS/MS analysis identified the purified enzyme as chitinase with 60% similarity to chitinase Chi55 of Paenibacillus ehimensis. The activation energy (E _a) for chitin hydrolysis and temperature quotient (Q ₁₀) at optimum temperature was found to be 19.14 kJ/mol and 1.25, respectively. Determination of kinetic constants k _m, V _max, k _cat, and k _cat/k _m and thermodynamic parameters ΔH*, ΔS*, ΔG*, ΔG*_E–S, and ΔG*_E–T revealed high affinity of the enzyme for chitin. The enzyme exhibited higher stability in presence of commonly used protectant fungicides Captan, Carbendazim, and Mancozeb compared to control as reflected from the t _1/2 values suggesting its applicability in integrated pest management for control of soil-borne fungal phytopathogens. The order of stability of chitinase in presence of fungicides at 80 °C as revealed from t _1/2 values and thermodynamic parameters E _a(d) (activation energy for irreversible deactivation), ΔH*, ΔG*, and ΔS* was: Captan > Carbendazim > Mancozeb > control. The present study is the first report on thermodynamic and kinetic characterization of chitinase from Paenibacillus sp. D1.     

Steric effects on the singlet-triplet energy gaps of five-membered ring R<Subscript>2</Subscript>C<Subscript>4</Subscript>H<Subscript>2</Subscript>M

Thermal internal energy gaps, ΔE _s−t; enthalpy gaps, ΔH _s−t; Gibbs free energy gaps, ΔD _s−t, between singlet (s) and triplet (t) states of R₂C₄H₂M (M = C, Si, and Ge) were calculated at B3LYP/6-311++G** level of theory. The ΔG _s−t of R₂C₄H₂C was increased in the order (in kcal/mol): R = −CH₃ (−10.51) > −H (−9.59) > i-Pr (−9.51) > t-Bu (−8.98). While, the ΔG _s−t of R₂C₄H₂Si and R₂C₄H₂Ge were increased in the order (in kcal/mol): −CH₃ (17.01) > i-Pr (15.30) > −H (15.26) > t-Bu (14.35) and -H (22.79) > −CH₃ (22.69) > i-Pr (21.66) > t-Bu (21.01), respectively.     

Catalytic and Thermodynamic Characterization of Endoglucanase (CMCase) from <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> cmc-1

Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg⁻¹ protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol⁻¹ at optimum temperature (55 °C), and its temperature quotient (Q ₁₀) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V _max for CMC hydrolysis was 854 U mg⁻¹ protein and K _m was 20 mg CMC ml⁻¹. The turnover (k _cat) was 356 s⁻¹. The pK _a1 and pK _a2 of ionisable groups of active site controlling V _max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol⁻¹, ΔG* = 64.57 kJ mol⁻¹ and ΔS* = −195.05 J mol⁻¹ K⁻¹, respectively. Activation energy for irreversible inactivation ‘E _a(d)’ of the endoglucanase was 378 kJ mol⁻¹, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol⁻¹, 111.36 kJ mol⁻¹ and 833.06 J mol⁻¹ K⁻¹, respectively.     

Water desorption isotherms of cellulose-acetate membranes

 The water desorption isotherms are determined in three cellulose acetate membranes with different acetyl content as a function of p/p ₀ at 10–40 °C. The partition coefficients (adsorbed water over water pressure) show a minimum at p/p ₀=0.5–0.6. This indicates a two energy mechanism. The agreement of our results with the BET adsorption isotherms only till p/p ₀<0.3 shows that a two energy adsorption mechanism is valid only for small water contents, probably one hydrate layer and a second more liquid-like water layer. At large p/p ₀, the adsorbed water becomes more and more liquid like by polarization of the hydrogen bonds. The heat of desorption is larger than the vaporization heat of water ΔH _vap(H₂O). It decreases with increasing water content asymptotically to ΔH _vap(H₂O). The cause may be a larger van der Waals interaction of the hydrate layer due to coordination numbers larger than 4.4 as in liquid water. Additionally, we found a hole adsorption process by sorbing unpolar solvents. The water and methonal adsorption are 100 times larger due to a swelling mechanism depending on the number of acetyl groups in the membranes. The amounts of n-alcohols sorbed decrease with their chain length. Received: 25 April 1997 Accepted: 10 June 1997     

Influence of Cycle Temperatures on the Thermochemical Heat Storage Densities in the Systems Water/Microporous and Water/Mesoporous Adsorbents

The adsorption equilibrium of water on microporous adsorbents (zeolites of NaA-, NaY- and NaX-type as well as their ion exchanged forms) and on mesoporous adsorbents (different silica gels and composite material i.e. silica gel + salt hydrate) has been studied experimentally and theoretically. Using the Dubinin theory of pore filling the characteristic curves of the adsorption systems and other relevant dependences such as isotherms, isobars, isosteres and the curve of the differential heat of adsorption were calculated. For all systems investigated the adsorption were calculated. A_ads and the desorption potential A_des of the closed heat storage system were estimated. These values define the working range of the adsorption/desorption cycle and allow to calculate the specific heat storage density Δ h_sp. On the basis of Δ h_sp the different adsorbents were compared in order to select the optimal porous storage material for a given application. The presented experimental and theoretical investigations show that the adsorption systems water-zeolite and water-composites are promising working pairs for thermochemical heat storage processes for hot tap water supply and space heating of single family dwellings. The advantage of the water-composite system is the low desorption temperature (solar energy) the main shortcoming the low temperature lift. The advantage of the water zeolite system is the high temperature lift, the shortcoming are the relative high desorption temperatures.     

Microcalorimetric investigation of water vapor adsorption on silica gel

In this study, the activities of four ginsenosides Rc, Re, Rd, and Rf on splenic lymphocytes growth were studied by microcalorimetry. Some qualitative and quantitative information, such as the metabolic power–time curves, growth rate constant k, maximum heat-output power of the exponential phase P _max and the corresponding appearance peak time t _max, total heat output Q _t, and promotion rate R _p of splenic lymphocytes growth affected by the four ginsenosides were calculated. In accordance with thermo-kinetic model, the corresponding quantitative relationships of k, P _max, t _max, Q _t, R _p, and c were established, . Also, the median effective concentration (EC₅₀) was obtained by quantitative analysis. Based on both the quantitative quantity–activity relationships (QQAR) and EC₅₀, the sequence of promotion activity was Rc > Re > Rd > Rf. The analysis of structure–activity relationships showed that the number, type, and position of sugar moieties on the gonane steroid nucleus had important influences on the promotion activity of Rc, Re, Rd, and Rf on splenic lymphocytes growth. Microcalorimetry can be used as a useful tool for determining the activity and studying the quantity–activity relationship of drugs on cell.     

Thermodynamic investigation of effect of salt concentrations on denatured α-Amylase adsorbed onto a moderately hydrophobic surface

The displacement adsorption enthalpies (ΔH) of denatured α-Amylase (by 1.8 mol L⁻¹ GuHCl) adsorbed onto a moderately hydrophobic surface (PEG-600, the end-group of polyethylene glycol) from solutions (x mol L⁻¹ (NH₄)₂SO₄, 0.05 mol L⁻¹ KH₂PO₄, pH 7.0) at 298 K are determined by microcalorimeter. Further, entropies (ΔS), Gibbs free energies (ΔG) and the fractions of ΔH, ΔS, and ΔG for net adsorption of protein and net desorption of water are calculated in combination with adsorption isotherms of α-Amylase based on the stoichiometric displacement theory for adsorption (SDT-A) and its thermodynamics. It is found that the displacement adsorptions of denatured α-Amylase onto PEG-600 surface are exothermic and enthalpy driven processes, and the processes of protein adsorption are accompanied with the hydration by which hydrogen bond form between the adsorbed protein molecules favor formation of β-sheet and β-turn structures. The Fourier transformation infrared spectroscopy (FTIR) analysis shows that the contents of ordered secondary structures of adsorbed α-Amylase increase with surface coverages and salt concentrations increment.     

Enthalpic characteristics of solution of amino acids and aliphatic dipeptides in aqueous solutions of KCl

The integral enthalpies of dissolution Δ_sol H ^m of L-α-serine and L-α-asparagine in mixtures of water with KCl were measured in electrolyte concentrations of up to 4 mol/kg at 298.15 K. The standard enthalpies of dissolution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of amino acids from water to aqueous solutions of KCl were calculated. The enthalpic pair interaction coefficients h _xy of biomolecules with KCl were estimated within the McMillan-Mayer theory. The changing nature of the interaction between the components of the solution (depending on the structure of the dissolved biosubstance side substituents) is shown on the basis of data we obtained earlier for amino acids and dipeptides series. Estimates of the contributions from the electrostatic and other interactions of dipolar ions of amino acids and dipeptides with ions of electrolyte KCl in the enthalpic pair interaction coefficients h _xy are obtained using the Kirkwood approach.     

The study of alanine oscillating reaction catalyzed by tetraazamacrocyclic nickel(II) complex

A closed oscillation system comprised of alanine, KBrO₃, H₂SO₄ and acetone catalyzed by tetraazamacrocyclic nickel(II) complex is introduced, and quantitatively characterized with kinetic parameters, namely the rate constant (k _in, k _p), the apparent activation energy (E _in, E _p) and pre-exponential constant (A _in, A _p) and thermodynamic functions (ΔH _in, ΔG _in, ΔS _in and ΔH _p, ΔG _p, ΔS _p), where indexes “in” and “p” mean “induction period” and “oscillation period,” respectively. The results indicate that tetraazamacrocyclic nickel(II) complex can catalyze alanine oscillating reaction and the reaction corresponds exactly to the feature of irreversible thermodynamics as the entropy of system is negative.     

A short review and an empirical method for estimating the absorbed enthalpy of formation and the absolute enthalpy of dried microbial biomass for use in studies on the thermodynamics of microbial growth

Calculations are made using the equations Δ_r G = Δ_r H − TΔ_r S and Δ_r X = Δ_r H − Δ_r Q where Δ_r X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δ_r Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations of thermodynamic properties as (H _T  − H ₀) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δ_r H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change in the absorbed heat of a biochemical growth process system as represented by either Δ_r Q or TΔ_r S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔ_r S and Δ_r Q can be markedly different when compared to one another, these differences are small when compared to the value for Δ_r G or Δ_r X.     

Supplement on applicability of the Kissinger equation in thermal analysis

The relative errors (e%) in the determination of the activation energy from the slope of the Kissinger straight line ln(β/βT _p²) vs. 1/T _p (β is the heating rate) are in-depth discussion. Our work shows that the relative errors is a function containing the factors of x _p and Δx _p, not only x _p (x _p = E/RT _p, E is the activation energy, T _p is the temperature corresponding to maximum process rate, R is the gas constant). The relative error between E _k and E _p will be smaller with the increase of the value of x and/or with the decrease of the value of Δx. For a set of different heating rates in thermal analysis experiments, the low and close heating rates are proposed from the kinetic theory.     

Thermal behavior and thermal safety on 3,3-dinitroazetidinium salt of perchloric acid

3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO₄) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior and decomposition reaction kinetics of DNAZ·HClO₄ were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition process of DNAZ·HClO₄ has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO₄ are f(α) = (1 − α)⁻¹/2, 156.47 kJ mol⁻¹, and 10^15.12 s⁻¹, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠of this reaction are 42.26 J mol⁻¹ K⁻¹, 154.44 kJ mol⁻¹, and 135.42 kJ mol⁻¹, respectively. The specific heat capacity of DNAZ·HClO₄ was determined with a continuous C _p mode of microcalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was evaluated as 14.2 s.     

Optimizing conditions to study seed germination by calorimetry using soybean (Glycine max [L.] Merr.) seeds

To establish the best conditions for germination, calorimetric experiments were conducted with individual soybean seeds (Glycine max [L.] Merr.) under different conditions of imbibition at 24.7 °C. The calorimetric curves were analysed for imbibition and metabolic processes and compared with imbibition curves to establish a general methodology that could be used to evaluate inter- and intra-species physical and physiological variability. Measurements of pH were performed during the determination of the imbibition curves. The best experimental method for calorimetric investigations of seed germination is to insert the seed in 1% agar instead of placing the seed over wetted filter paper disks. Correlation of imbibition experiments and pH results with mass specific enthalpy of imbibition (determined in a KCN solution) or mass specific enthalpy of germination when seeds were germinated in 1% agar allowed determination of the water content needed for soybean seeds of the cultivar studied (A7636 RG) to activate their metabolic machinery (74–80% or 2.5–3 h) and the moment in which they are ready for root protrusion (122% or 9 h). The method presented here should be useful for evaluating soybean coat permeability to water and other factors related to seed damage before and during harvest and storage.     

The Dissolution Properties of 2-(1,1-Dinitromethylene)-1,3-diazepentane in N-methyl Pyrrolidone

The dissolution properties of 2-(1,1-dinitromethylene)-1,3-diazepentane in N-methyl pyrrolidone(NMP) were studied with a RD496-2000 Calvet microcalorimeter at three different temperatures. The measured molar enthalpies (Δ_sol H) for 2-(1,1-dinitromethylene)-1,3-diazepentane in NMP at T=(298.15,306.15,311.15) K are (5.02, 5.59, 6.67) kJ⋅mol⁻¹, respectively. The differential molar enthalpies (Δ_dif H), the specific enthalpies (Δ_sol h), and the standard heat effect (Q ^Θ) for 2-(1,1-dinitromethylene)-1,3-diazepentane in NMP were obtained at the same time. The kinetic parameters of activation energy E and pre-exponential factor A are 2.26×10⁴ J⋅mol⁻¹ and 10^2.06 s⁻¹, which indicate that NMP is a good solvent for the title compound.     

Synthesis,crystal structure,and thermal decomposition kinetics of complex [Nd(BA)<Subscript>3</Subscript>bipy]<Subscript>2</Subscript>

The complex of [Nd(BA)₃bipy]₂ (BA = benzoic acid; bipy = 2,2′-bipyridine) has been synthesized and characterized by elemental analysis, IR spectra, single crystal X-ray diffraction, and TG/DTG techniques. The crystal is monoclinic with space group P2(1)/n. The two–eight coordinated Nd³⁺ ions are linked together by four bridged BA ligands and each Nd³⁺ ion is further bonded to one chelated bidentate BA ligand and one 2,2′-bipyridine molecule. The thermal decomposition process of the title complex was discussed by TG/DTG and IR techniques. The non-isothermal kinetics was investigated by using double equal-double step method. The kinetic equation for the first stage can be expressed as dα/dt = A exp(−E/RT)(1 − α). The thermodynamic parameters (ΔH ^≠, ΔG ^≠, and ΔS ^≠) and kinetic parameters (activation energy E and pre-exponential factor A) were also calculated.     

DSC study of the miscibility of poly(methyl acrylate)-polystyrene sequential interpenetrating polymer networks

The phenomenon of forced compatibilization has been studied in poly(methyl acrylate)-polystyrene PMA-i-PS sequential interpenetrating polymer networks, IPNs, using differential scanning calorimetry. Both networks in the IPN were prepared using the same amount of ethylene glycol dimethacrylate, EGDMA, as crosslinking agent. The samples were subjected to thermal treatments which included annealing at different ageing temperatures T _a, for 300 min. From the DSC curves, recorded on heating the enthalpy loss during the isothermal annealing, Δh _a was calculated. The dependence of Dh _a with the annealing temperature was used to define the temperature interval in which the conformational mobility is significant. The comparison of the Δh _a(T _a) curves obtained in an IPN and the results obtained with the pure component homo-networks with the same crosslinking density reveal some details of the miscibility of the IPN. In the case of the IPN crosslinked with 10% EGDMA, two peaks are apparent in the Δh _a(T _a) curve, but the high-temperature peak is shifted towards lower temperatures compared to that of the polystyrene network while the low-temperature one is nearly at the same temperature than the one of the poly(methyl acrylate) homonetwork. This means that compatibilization is not complete and phase separation still exists even at this high crosslinking density. The different behaviour of the high and low temperature transitions can be explained by the dynamic heterogeneity of the sample, i.e. by the different length of cooperativity of the conformational rearrangements of PMA and PS domains at any temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nonaqueous Solution Studies on the Protonation Equilibria of some Phenolic Acids

The protonation equilibria for some phenolic acids in nonaqueous solutions have been studied by pH-potentiometry. The dissociation constants, pK _a, of these phenolic acids and the thermodynamic functions, ΔG ^o,ΔH ^o and ΔS ^o, for the successive and overall protonation processes of these phenolic acids have been derived at different temperatures in three different mixtures of water and dioxane (mole fractions of dioxane were 0.083, 0.174 and 0.33). Titrations were also carried out in (water + dioxane) with ionic strengths of 0.15, 0.20 and 0.25 mol⋅dm⁻³ NaNO₃, and the resulting dissociation constants are reported. A detailed thermodynamic analysis of the effects of organic solvent, dioxane, temperature and ionic strength on the protonation processes of phenolic acids is presented and discussed to determine the factors which control these processes. Ahmed E. Fazary; previous address: Egyptian Organization for Biological Products and Vaccines, 51 Wezaret El-Zeraa Street, Agouza, Giza, Egypt. Tel. +2010-3017357.     

Singlet-triplet splitting of divalent five-membered fused rings C<Subscript>12</Subscript>H<Subscript>8</Subscript>M (M = C,Si, Ge,Sn, and Pb): Application in nanocomplex synthesis

Energy differences, ΔX _s−t (X = E, H, and G) (ΔX _s−t = X(singlet) − X(triplet)) between singlet (s) and triplet (t) states of C₁₂H₈M were calculated at B3LYP/6-311+G*. The DFT calculations indicated that the ΔG _s−t between singlet (s) and triplet (t) states of C₁₂H₈M were increased from M = C to M = Pb. The ΔG _s−t of C₁₂H₈M was compared with its analogue C₄H₄M through replacement of heavy atoms from M = C to M = Pb. Configurations of the electrons in orbitals (σ² or π²) for the singlet state of C₁₂H₈M were discussed.     

The Enthalpies of Solution of L-cysteine, L-serine and L-asparagine in Aqueous Solutions of Some Alcohols at 298.15 K

Heats of solution, Δ_sol H _m , of L-cysteine, L-serine and L-asparagine amino acids have been measured at different concentrations of aqueous ethanol, propanol and 2-propanol at 298.15 K using solvation calorimetry. These data are compared with the results reported earlier for L-alanine in ethanol. The enthalpic coefficients, h _xy , of the solute-organic cosolvent pair interaction in water have been obtained from the McMillan-Mayer approach and the data have been interpreted in terms of various interactions and changes in solvent structure.