共查询到20条相似文献,搜索用时 31 毫秒
1.
The enthalpy change for anabolism is needed to model the growth/respiration relation in plants. If all CO 2 production is assigned to catabolism, the anabolic reaction becomes C substrate→C products+ xO 2 with an enthalpy change, Δ Hb. Four methods are proposed for determining Δ Hb: (a) From the difference in the heats of combustion of substrate and anabolic products (i.e. newly grown tissue). (b) From the composition of newly grown tissue and application of Thornton’s rule. (c) From independently measured values of the specific growth rate, RSG, and of the product ( RSG Δ Hb). The product ( RSG Δ Hb) equals (−Δ HCO2RCO2− Rq) where RCO2 is the specific rate of CO 2 production by respiration, Δ HCO2 is the heat of combustion of respiratory substrate per mole of CO 2 and Rq is the specific metabolic heat rate. Δ Hb is then calculated as the ratio ( RSG Δ Hb)/ RSG. (d) From (Δ Hb=−( Rq/ RCO2+Δ HCO2) [(1−)/] where is the substrate carbon conversion efficiency obtained from a total carbon balance. The first three methods have been tested and compared on oat seedlings and the last on corn seedlings. Δ Hb values from all four methods are in reasonable agreement despite the different assumptions involved. 相似文献
2.
The formation (protonation) constants log Ki, of the acid H jL are determined by regression analysis of potentiometric titration data when common parameters (log Ki, i = 1,…, j) and group parameters ( E0′, L0, HT) are refined. The influence of three kinds of error on the protonation constants has been investigated: error from the strategy of minimization, random error, and error from uncertain estimates of group parameters. An analysis of variance of the log Ki, matrix was made for 7 identical titrations and 8 computational strategies, or of 7 identical titrations and 8 different options of group parameters to be refined. The influence of the standard potential E0 of the glass-electrode cell on the systematic error in log K is greater than that of the acid concentration ( L0) or the concentration of titrant used ( HT). The ill-conditioned group parameters should be refined together with the common parameters ( Ki), otherwise the estimates of log Ki, are not accurate enough. Two ways of calibrating the glass electrode cell were compared. Internal calibration (performed during titration) was more accurate than external calibration done separately. Of the programs tested ESAB and ACBA are the most powerful because they permit refinement of group parameters and internal calibration. Citric acid was chosen as model substance. 相似文献
3.
The complexation reactions between murexide and Co 2+, Ni 2+ and Cu 2+ in C 2H 5OH-H 2O mixtures have been investigated spectrophotometrically. The formation constants of the 1:1 complexes formed increase in the order Co 2+ < Ni 2+ < Cu 2+ for all solvent mixtures studied, and log Kf is a linear function of the mole fraction of ethanol. The heat of complexation was determined calorimetrically for the nickel and copper complexes. The values of Δ H° and Δ S° are solvent-dependent, and all three complexes have negative Δ H° and positive Δ S° values. 相似文献
4.
Dimesitylborane dimer has been shown to exist in equilibrium with dimesitylborane monomer in solution. This equilibrium has been investigated by variable concentration and variable temperature multinuclear NMR spectroscopy and values for the dissociation constant, enthalpy and entropy of dissociation were found to be Kdiss=(3.2±0.4)×10 −3 M, Δ H=70 kJ mol −1, and Δ S=212 J K −1mol −1, respectively. Ab initio methods have been used to investigate the gas-phase structures and energies of both monomer and dimer, and calculated 11B-NMR shifts are also presented. The solid-state structure of dimesitylborane dimer has been investigated by single crystal X-ray diffraction at 100 K and the position of the bridging hydrogen atoms (B---H=1.340(2), 1.342(2) Å, H---B---H=92.46(14)°) has been determined accurately, for the first time, by single crystal neutron diffraction at 20 K. 相似文献
5.
The oxygen permeation properties of mixed-conducting ceramics SrFeCo 0.5O 3−δ (SFCO), Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCFO), La 0.2Sr 0.8Co 0.8Fe 0.2O 3−δ (LSCFO) and Ba 0.95Ca 0.05Co 0.8Fe 0.2O 3−δ (BCCFO) were studied by thermogravimetric method in the temperature range 600–900 °C. The results show that the oxygen adsorption rate constants ka of all material are larger than oxygen desorption rate constants kd and both ka and kd are not strongly dependent on temperature in the studied temperature range. The oxygen vacancy contents δ(N 2) and δ(O 2) in nitrogen and oxygen and their difference Δ δ = δ(N 2) − δ(O 2) play an important role in determining the temperature behavior of oxygen permeation flux JO2. 相似文献
6.
The heats of combustion of 1-nitroadamantane (1), 2-nitroadamantane (2), 2,2-di-nitroadamantane (3) and 2-cyano-2-nitroadamantane (4) were measured by combustion calorimetry, and the heats of sublimation were derived from the temperature dependence of the vapour pressure measured in a flow system. The results for Δ HXXXc(c) and Δ HSub (in kJ mol −1, standard deviation in parentheses) are: 1, −5824.1 (±2.2) and 63.6 (±1.0); 2, −5841.0 (±2.2) and 58.0 (±2.3); 3, −5685.2 (±1.0) and 96.4 (±1.4); 4, −6238.4 (±1.5) and 70.0 (±1.9). A comparison of the resulting heats of formation ΔHXXXf(g) (in kJ mol−1, standard deviation in parentheses) for 1 = −191.1 (± 2.4), 2 = −179.8 (±3.2), 3 = −154.3 (±1.7) and 4 = −21.0 (±2.5) reveals a destabilizing interaction of the geminal substituents in 3 and 4 amounting to 59 kJ mol−1 (nitro/nitro) and 33 kJ mol−1 (nitro/cyano) respectively. 相似文献
7.
Activities of solutes and compositions of solutions may be expressed corretly in terms of molarity ( c), molality ( m) or mole fraction ( x), leading to corresponding equilibrium constants Kc, Km, or Kx. Equations for differences between Δ G° c, Δ G° m, and Δ G° x values are derived. Common errors in calculations involving (dln Kc/d T) and (dln Kc/d P) are identified and remedies for these errors are presented. 相似文献
8.
This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4- R -phenyl 4-(4-octyloxybenzoyloxy)benzoates ( 1 ), 4-octyloxyphenyl 4-(4- R-benzyloxy)benzoates ( 2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates ( 3), and 4- R-phenyl 4-octyloxyphenyl terephthalates ( 4) where R = OCH 3, CH 3, OC 8H 17, C8H17, halogens, CF 3, OCF 3, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis. 相似文献
9.
By applying G1 theory to a potential energy surface of the stoichiometry ClO 3 three equilibrium geometries were found and their zero-point heats of formation calculated. They correspond to the structures ClO·O 2 (Δ Hf,0 K = 41 kcal/mol), OCl·O 2 (Δ Hf,0 K = 58 kcal/mol), and sym-ClO 3 (Δ Hf,0 K = 48 kcal/mol). It is shown that the formation of an adduct by association of O 2 to ClO is endothermic. In the G1 electronic energy calculations the basis set containing additional polarization functions was extended to 6-311G(3df) on chlorine. 相似文献
10.
Anionic surfactants having two polyfluoroalkyl chains per molecule, i.e. the sodium salt of bis(1 H, 1 H, 2 H,2 H-heptadeca-fluorodecyl)-2-sulfosuccinate, CF 3(CF 2) 7(CH 2) 2OCOCH 2CH(SO 3Na)COO(CH 2) 2(CF 2) 7CF 3, the sodium salt of bis(1 H, 1 H, 2 H, 2 H-tridecafluoro-octyl)-2-sulfosuccinate, CF 3(CF 2) 5(CH 2) 2OCOCH 2CH(SO 3Na)COO(CH 2) 2(CF 2) 5CF 3, and the sodium salt of bis(1 H, 1 H, 2 H, 2 H-nonafluorohexyl)-2-sulfosuccinate, CF 3(CF 2) 3(CH 2) 2OCOCH 2CH(SO 3Na)COO(CH 2) 2(CF 2) 3CF 3, have been prepared from maleic anhydride, the corresponding alcohols possessing a polyfluoroalkyl chain and sodium hydrogen sulfite. The flocculation and redispersion abilities of these surfactants for dispersed magnetic particles in water have been examined to investigate the effect of the chain length. It was found that this ability was enhanced by an increase in the chain length. The contact angles for water for pelleted surface-modified magnetite have been measured. In order to compare this ability and the contact angles, data for other fluorinated surfactant have been obtained. The Kraff point, the surface tension and the pNa of the aqueous surfactant solutions have also been measured. 相似文献
11.
At 25°C, I = 1.0 M (CF 3SO 3−Li ++CF 3SO 3H), [H +] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H 2O), 63+ by bromine was found to be: −d/[Br 2] T/d t= kK/[Br 2][Ti III]/[H +]+ K+ kK/[Br 3−][Ti III]/[H ++ K, where k = 9.2 × 10 −3 M −1 s −1 and K = 4.5 × 10 −3 M. At [H +] = 1.0 M, [Br −] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br −] increases. The pH-dependence of the oxidation of TiIII-edta by bromine is interpreted in terms of the change in identity of the TiIII-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k0edta)2 weighting into an equation of the form: k0edta =k1+k2K1[H+]−1+k3K1K2[H+]−2/1+K1[H+[H+−1+K1K2[H+]−2, with K1 and K2 fixed as earlier determined at 9.55 × 10−3 and 2.29 × 10−9 M, respectively, for the oxidation of bromine. k1=k2=(3.1±0.32)×103M−1s−1 k3=(2.3±0.45)×106N−1s−1. It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br2.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for TiIII-edta+TiIV-edta is estimated at 32 M−1 s−1. 相似文献
12.
The molecular structure and conformational properties of O=C(N=S(O)F 2) 2 (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn– syn and 24(12)% syn– anti conformer (Δ H0= H0( syn– anti)− H0( syn– syn)=1.11(32) kcal mol −1) which is in agreement with the interpretation of the IR spectra (68(5)% syn– syn and 32(5)% syn– anti, Δ H0=0.87(11) kcal mol −1). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F 2 groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn– anti structure (Δ E=−0.11 kcal mol −1) and the B3LYP/6-31G* method results in an energy difference (Δ E=1.85 kcal mol −1) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S) 2 skeleton were derived ( ra values with 3 σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°. 相似文献
13.
The e.m.f. of the galvanic cells Pt,C,Te(l),NiTeO 3,NiO/15 YSZ/O 2 ( Po2 = 0.21 atm),Pt and Pt,C,NiTeO 3,Ni 3TeO 6,NiO/15 YSZ/O 2 ( Po2 = 0.21 atm),Pt (where 15 YSZ=15 mass% yttria-stabilized zirconia) was measured over the ranges 833–1104 K and 624–964 K respectively, and could be represented by the least-squares expressions E(1)±1.48 (mV) = 888.72 − 0.504277 (K) and E(II) ±4.21 (mV) = 895.26 − 0.81543 T (K). After correcting for the standard state of oxygen in the air reference electrode, and by combining with the standard Gibbs energies of formation of NiO and TeO2 from the literature, the following expressions could be derived for the ΔG°f of NiTeO3 and Ni3TeO6: ΔGf°(NiTeO3) ± 2.03 (kJ mol−1) = −577.30 + 0.26692T (K) and ΔG°f(Ni3TeO6)±2.54 (kJ mol−1) = −1218.66 + 0.58837T (K). 相似文献
14.
We have tailored some interesting mono- and diporphyrins, viz., 5, 10, 15, 20-tetrakis(octadecyloxyphenyl)-21 H,23 H-porphyrin (TP), 5, 15-bis(3, 5-dioctylphenyl)-2, 8, 12, 18-tetramethyl-3, 7, 13, 17-tetradodecyl-21 H,23 H-porphyrin (AP) and 1, 3-bis(10′,20′-diundecyl-21′ H,23′ H-porphyrin-5′-yl)benzene (DP) as host molecules to study their complexation behavior with C 60 and C 70. Fluorescence spectroscopic measurements showed that emission of TP, AP and DP in toluene was quenched in the presence of C 60 or C 70. Large binding constants ( K) in the magnitude of 1.5 × 10 4 dm 3 mol −1 have been obtained for the 1:1 complexes of C 70 with TP, AP and DP. However, the C 60 complexes have exhibited 8.5 times smaller K compared to C 70 complexes. Ab initio theoretical calculations give a good support in favor of strong complexation between C 70 and porphyrins. 相似文献
15.
The dependence of the Stern potential, ψ 1, of glass samples on the distance between these, H, has been theoretically calculated, while taking into account the Stern isotherm and the electroneutrality equation. Comparison of the theoretical dependences ψ 1( C) H→∞ with those previously experimentally obtained enables one to calculate the energy of adsorption of OH ions on glass and, further, the dependence ψ 1( H). It has been shown that for pH 4–6 and CKCl = 10 -2-10 -5 mol/L, the value of ψ 1 practically does not depend on H. The result obtained was used to calculate theoretically the ionic-electrostatic forces and to compute (from the experimental values of the interaction forces) structural forces Us( H). The dependence thus obtained, Us( H), is of exponential character. 相似文献
16.
The enantiomers of the perfluorodiether “compound B” [2-(fluoromethoxy)-3-methoxy-1,1,1,3,3-pentafluoropropane], a decomposition product of the inhalational anesthetic sevoflurane [2-(fluoromethoxy)-1,1,1,3,3,3-hexafluoropropane], were separated by gas chromatography on octakis(3- O-butanoyl-2,6-di- O- n-pentyl)-γ-cyclodextrin (Lipodex E), dissolved in polysiloxane PS 255 (30% w/w), with an unexpectedly high separation factor of =10.6 at 26 °C. Using the concept of the retention increment R′, non-enantioselective and enantioselective contributions to retention were separated and thus reliable thermodynamic parameters of enantioselectivity, i.e. −Δ S,R(Δ G)=5.7 (0.05) kJ/mol at 303 K, −Δ S,R(Δ H)=20.1 (0.64) kJ/mol, Δ S,R(Δ S)=−47.4 (2.0) J/K mol and Tisoenant=424 (30) K or 150 °C, were determined by temperature-dependent measurements. The enantiomeric bias represents the largest values ever measured in enantioselective gas chromatography. An equation is presented which allows calculation of the non-enantioselective contributions to retention from measurements at two arbitrary concentrations of Lipodex E in polysiloxane. Surprisingly, the enantioselectivity is greatly reduced when employing the β-cyclodextrin analogue and breaks down completely with the -cyclodextrin analogue of Lipodex E. 相似文献
17.
A series of E-2-benzylideneindanones (a) -tetralones (b) and -benzosuberones (c) with OCH 3 (2–4), NO 2 (5–7) and F (8–10) substituents in ortho, meta or para position was studied by IR and mass spectrometry. The most important IR bands were assigned and stated correlations between some frequencies and the stereostructure or conjugation feature of the molecules investigated. IR spectra were also analyzed in order to find frequencies characteristic of the size of the alkanone ring. The mass spectrometric investigation aimed at determining fragmentation pathways and finding correlations between them and the ring size of the alkanone ring or the position of the substituents. 相似文献
18.
Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies and Scanning Electron Microscopy (SEM) were used to investigate ionic association, hydrogen bonding and morphology in a family of sol–gel derived lithium triflate (LiCF 3SO 3)-doped di-urethane cross-linked poly( ε-caprolactone) (PCL(530))/siloxane hybrid electrolytes. The materials studied, with compositions ∞ > n 0.5 (where n – composition – expresses the molar ratio of PCL(530) ester repeat units per Li + ion), are non-porous and homogeneous. The Li + ions interact with the urethane and ester carbonyl oxygen atoms within the whole range of salt concentration analyzed, promoting the formation of hydrogen-bonded aggregates. The composition dependence of the relative concentration of “free” anions and coordinated anions (weakly coordinated anions, ion pairs or [Li(CF 3SO 3) 2] − triplets, aggregates I ([Li 2(CF 3SO 3)] +) and aggregates II ([Li 3(CF 3SO 3)] 2+) in all the samples is in perfect agreement with the values of the room temperature ionic conductivity reported previously. 相似文献
19.
Resonance fluorescence spectra of CF 2( 1B 1, 040, K' = 9) excited at 253 7 nm have been observed in the photolysis of C 2F 4 using a low-pressure mercury lamp. At low C 2F 4 pressures, the spectra with a series of doublet hands from 254 to 400 nm were consistent with the transitions from 1B 1, 040, K'=9 to 1A 1, 0 v'20, K' = 8, 10, and also to 1A 1, 1 v'20, K' = 8, 10 The appearance of doublet bands (Δ K = ±1) provides clear evidence that the transition is of the perpendicular type. 相似文献
20.
在水热体系中合成了3个中心金属为镍离子, 以六配位扭曲八面体构型形成的具有螺旋结构的配位聚合物{[Ni 2L 2(bib) 2·2H 2O]·5H 2O} n(1), [Ni 2L 2(bpy)] n(2)和{[Ni 2L 2(bibpip) 2·2H 2O]·6H 2O} n(3)[H 2L=4,4'-三苯胺二甲酸; bib=1,3-二(咪唑基)苯; bpy=4,4-联吡啶; bibpip=1,4-二(4-咪唑苄基)哌嗪]. 通过单晶及粉末X射线衍射、 红外光谱、 元素分析和热重分析对这3种化合物进行了表征. 结果表明, 化合物1属于单斜晶系, C2 /c空间群, 其骨架为具有{4 2·6 5·8}拓扑结构的二维层结构; 化合物2属于斜方晶系, Fdd2空间群, 其骨架为具有{4 8·5 4·6 3}拓扑结构的三维超分子网络; 化合物3属于三斜晶系, P空间群, 为1个五重穿插的三维超分子网络, 其骨架具有{4 4·6 2}拓扑结构. 相似文献
|