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1.
Hossein Amani Mohammad Reza Mehrnia Mohammad Hossein Sarrafzadeh Manouchehr Haghighi Mohammad Reza Soudi 《Applied biochemistry and biotechnology》2010,162(2):510-523
There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology
of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector
was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass (Y
p/x), biosurfactant on sucrose (Y
p/s), and the volumetric production rate (Y) for shake flask were obtained about 0.45 g g−1, 0.18 g g−1, and 0.03 g l−1 h−1, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y
x/s, Y
p/x, Y
p/s, and Y of 0.42 g g−1, 0.595 g g−1, 0.25 g g−1, and 0.057 g l−1 h−1, respectively. The biosurfactant maximum production, 2.5 g l−1, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient
(K
L
a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s−1, respectively. Comparison of K
L
a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with
K
L
a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water
flooding in the sand pack. 相似文献
2.
N. Hattori H. Hirata H. Okabayashi M. Furusaka C. J. O'Connor R. Zana 《Colloid and polymer science》1999,277(1):95-100
The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br−(CH3)2N+(C
m
H2
m
+1)-(CH2)
S
-(C
m
H2
m
+1)N+(CH3)2Br−, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for
micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants
with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation
of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12).
Received: 15 June 1998 Accepted: 22 July 1998 相似文献
3.
The conformations of poly(l-glutamic acid) [P(Glu)] in solutions of the bipolar amphiphile 1,20-icosanediylbis(alkylammonium chloride) [C20(RA)2], where RA includes trimethylammonium (TMA), dimethylammonium (DMA), or methylammonium (MA), were investigated with measurements
of the circular dichroism spectra at 10–35 °C. All C20(RA)2 induced an α-helix of P(Glu) in the aqueous solutions. The residue molar ellipticity at 222 nm showed a similar dependence
on the amphiphile concentration (C
s) below 0.5 of the ratio of 2C
s to the residue concentration (C
p) of P(Glu), but it separated into three directions at 2C
s/C
p>0.5. C20(MA)2 induced an α-helix of P(Glu) at 2C
s/C
p<0.5 followed by a helix aggregate at 2C
s/C
p>0.5. C20(DMA)2 and C20(TMA)2 also induced an α-helix, but a helix aggregate. C20(TMA)2 indicated a strong temperature dependence and did not induce a complete α-helix at 35 °C.
Received: 20 June 2001 Accepted: 6 September 2001 相似文献
4.
Ab initio HF/6-31G* and MP2/6-31G*//HF/6-31G* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C 4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C s) and twist (C 2h) conformers and requires about 22.3 kJ · mol−1. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol−1. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods. 相似文献
5.
Krzysztof Miecznikowski James A. Cox Adam Lewera Pawel J. Kulesza 《Journal of Solid State Electrochemistry》2000,4(4):199-204
We describe a sol-gel approach by which iron hexacyanoferrate is immobilized in silica in a manner suited to investigation
by electrochemistry in the absence of a contacting liquid phase. Such physicochemical parameters as concentration of redox
sites (C
o) and apparent (effective) diffusion coefficient (D
app) are estimated by performing cyclic voltammetric and potential step experiments in two time regimes, which are characterized
by linear and spherical diffusional patterns, respectively. Values of D
app and C
o thereby obtained are 2.0 × 10−6 cm2 s−1 and 1.4 × 10−2 mol dm−3. The D
app value is larger than expected for a typical solid redox-conducting material. Analogous measurements done in iron(III) hexacyanoferrate(III)
solutions of comparable concentrations, 1.0 × 10−2 and 5.0 × 10−3 mol dm−3, yield D
app on the level of 5–6 × 10−6 cm2 s−1. Thus, the dynamics of charge propagation in this sol-gel material is almost as high as in the liquid phase. The residual
water in the silica, along with the pore structure, are important to the overall mechanism of charge transport, which apparently
is limited by physical diffusion rather than electron self-exchange. Under conditions of a solid state voltammetric experiment
which utilizes an ultramicroelectrode, encapsulated iron hexacyanoferrate redox centers seem to be in the dispersed colloidal
state rather than in a form of the rigid polymeric film.
Received: 8 April 1999 / Accepted: 13 August 1999 相似文献
6.
Mingqi Ao Peipei Huang Guiying Xu Xiaodeng Yang Yajing Wang 《Colloid and polymer science》2009,287(4):395-402
The aggregation behavior and thermodynamic properties of micellization for the ionic liquid-type gemini imidazolium surfactants
with different spacer length ([C12–s–C12im]Br2, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence
measurements. The values of cmc, γ
cmc, Γ
max, A
min, π
cmc, pc20 and cmc/pc20 suggest that the shorter the spacer, the higher the surface activity of [C12–s–C12im]Br2 is. The cmc and γ
cmc values are decreased significantly in the presence of sodium halides, and the values decrease in the order NaCl < NaBr < NaI.
The thermodynamic parameters of micellization (, , ) indicate that the micellization of [C12–2–C12im]Br2 and [C12–4–C12im]Br2 is entropy-driven, whereas aggregation of [C12–6–C12im]Br2 is enthalpy-driven at lower temperature but entropy-driven at higher temperature. Finally, the fluorescence measurements
show that the micropolarity of micelles increases but the aggregation numbers decrease with increasing the spacer length of
[C12–s–C12im]Br2. 相似文献
7.
Summary. Ab initio HF/6-31G* and MP2/6-31G*//HF/6-31G* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C
4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C
s) and twist (C
2h) conformers and requires about 22.3 kJ · mol−1. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol−1. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries
of the title compound are in good agreement with the results of ab initio methods.
Received July 9, 2001. Accepted September 26, 2001 相似文献
8.
Raman scattering spectra and molecular conformations of bis(quaternaryammonium bromide)-water systems 总被引:1,自引:0,他引:1
The dimeric bis(quaternaryammonium bromide) surfactants, [Br−(CH3)2N+(C
m
H2
m
+1)—(CH2)
s
—(C
m
H2
m
+1)N+(CH3)2Br−, s = 2, 3 and m = 4, 6, 10 and 12, s = 6 and m = 8, 10, 12], have been synthesized and the phase maps of the sm6-8-water, sm6-10-water and sm6-12-water binary systems have
been determined (sm6-8 implies s = 6, m = 8). In order to examine the molecular structures of these solid samples and of their dimeric surfactant-water binary systems,
Raman spectra of the simple dimeric surfactants, sm2-4 and sm3-4, in which crystal structures of the trans- and cis-type conformations
have been determined by single-crystal X-ray diffraction analysis, have been investigated, and Raman bands characteristic
of these skeletal structures were found in the skeletal deformation region. On the basis of these characteristic Raman bands
for the two conformations, it has been concluded that the dimeric surfactants, sm6-8, sm6-10 and sm6-12 also take up a cis-type
conformation in the crystalline state. Furthermore, it has been found that the Raman bands in the C—H stretching, skeletal
stretching and CH2 scissoring regions are sensitive to phase structure.
Received: 21 July 1998 Accepted in revised form: 9 November 1998 相似文献
9.
A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO2) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic
diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol)
(TX). Under static conditions phenol was quantitatively extracted onto TX-SiO2 in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO2 for phenol is 2.4 mg g−1 with distribution coefficients up to 3.4 × 104 mL g−1; corresponding data for 1-naphthol are 1.5 mg g−1 and 3 × 103 mL g−1. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than
0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol
and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A
540) and phenol concentration (C) in water was found according to the equation A
540 = (6 ± 1) × 10−2 + (0.9 ± 0.1)C (μmol L−1) with a detection range from 1 × 10−8 mol L−1 (0.9 μL g−1) to 2 × 10−7 mol L−1 (19 μL g−1), a limit of quantification of 1 μL g−1 (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric
method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical
analysis. The detection limit of 1-naphthol with this method is 6 μL g−1 while the quantification limit is 20 μL g−1. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one
to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g−1. 相似文献
10.
The gallium monohydride (GaH) molecule and its positive ion were theoretically investigated by abinitio molecular orbital
calculations with a flexible basis set including g-type functions on the Ga atom. Electron correlations among not only the valence electrons of Ga 4s4p and H 1s but also the semi-core electrons of Ga 3d were incorporated by a size-consistent scheme of the coupled pair approximation. The contribution of the 3d electron correlation was found to be considerable on spectroscopic constants of both GaH and GaH+, especially on the bond length.
Received: 25 July 1997 / Accepted: 13 November 1997 相似文献
11.
This paper describes the use of an aluminum electrode covered by metallic palladium and modified by Prussian blue prepared
by a simple and rapid electroless method for the electro-oxidation of morphine. Two different pathways for electro-oxidation
of morphine at various pH ranges were suggested. Also, some thermodynamic and kinetic parameters such as the number of electrons
involved in the rate determining step, n
α
, transfer coefficient α, and the total electrons (n) involved in morphine oxidation at the time scale of the cyclic voltammetric technique, the catalytic rate constant of the
electrochemical process k, and diffusion coefficient of morphine D were determined. The mean values obtained are 0.5, 0.5, 1, 26.8 M-1 s-1 and 3.1 × 10−5 cm2 s−1, respectively. 相似文献
12.
Dao-Lai Fang Bing-Cai Wu Yong Yan Ai-Qin Mao Cui-Hong Zheng 《Journal of Solid State Electrochemistry》2012,16(1):135-142
Mesoporous Mn–Ni oxides with the chemical compositions of Mn1-x
Ni
x
O
δ
(x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium
hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO2, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn1–x
Ni
x
O
δ
was 42.8, 59.6, and 84.5 m2 g−1 for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge
in 6 mol L−1 KOH electrolyte. Specific capacitances of Mn1-x
Ni
x
O
δ
were 343, 528, and 411 F g−1 at a scan rate of 2 mV s−1 for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g−1 with increasing scan rate to 100 mV s−1, respectively. After 500 cycles at a current density of 1.24 A g−1, the symmetrical Mn1–x
Ni
x
O
δ
capacitors delivered specific capacitances of 160, 250, and 132 F g−1 for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn0.8Ni0.2O
δ
material showed better supercapacitive performance, which was promising for supercapacitor applications. 相似文献
13.
Praher B Rössler R Arenholz E Heitz J Pedarnig JD 《Analytical and bioanalytical chemistry》2011,400(10):3367-3375
Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) method is employed for quantitative determination of oxide
concentrations in multi-component materials. Industrial oxide materials from steel industry are laser ablated in air, and
the optical plasma emission is collected by spectrometers and gated detectors. The temperature and electron number density
of laser-induced plasma are determined from measured LIBS spectra. Emission lines of aluminium (Al), calcium (Ca), iron (Fe),
manganese (Mn), magnesium (Mg), silicon (Si), titanium (Ti), and chromium (Cr) of low self-absorption are selected, and the
concentration of oxides CaO, Al2O3, MgO, SiO2, FeO, MnO, TiO2, and Cr2O3 is calculated by CF-LIBS analysis. For all sample materials investigated, we find good match of calculated concentration
values (C
CF) with nominal concentration values (C
N). The relative error in oxide concentration, e
r = |C
CF − C
N|/C
N, decreases with increasing concentration and it is e
r ≤ 100% for concentration C
N ≥ 1 wt.%. The CF-LIBS results are stable against fluctuations of experimental parameters. The variation of laser pulse energy
over a large range changes the error by less than 10% for major oxides (C
N ≥ 10 wt.%). The results indicate that CF-LIBS method can be employed for fast and stable quantitative compositional analysis
of multi-component materials. 相似文献
14.
Several zerovalent lanthanide bis(arene)-sandwich complexes, Ln(η6-C6H6)2, Ln = La, Ce, Eu, Gd and Lu, have been studied by means of density functional theory. The calculated geometries are in good
agreement with experiment. The calculated dissociation energies of the bond Ln-(η6-C6H6) may be considerably underestimated, but they correctly reveal the variation regularity. The bonding in these molecules can
be described in terms of a relatively weak π-electron donation from benzene to Ln and a stronger electron back-donation from
Ln 5d to the benzene π* orbitals. During bond formation, there is electron promotion from Ln 6s to 5d instead of from 4f to 5d, in opposition to the proposal of Anderson et al. The relativistic effect only slightly influences the molecular geometry,
but decreases the bonding energy considerably through lowering the Ln 6s level and raising the 5d level. It enhances the trend of the bonding energy to decrease along the lanthanide series.
Received: 22 June 1998 / Accepted: 9 September 1998 / Published online: 17 December 1998 相似文献
15.
Milivoj Lovrić Michael Hermes Fritz Scholz 《Journal of Solid State Electrochemistry》1998,2(6):401-404
A solid-state redox reaction involving an insertion of ions is analyzed with respect to the influence of the concentration
of inserting ions in the solution phase. The voltammetric response is independent of the mass transfer in the solution provided
that z = (D
ss/D
aq)1/2
ρ/[C+]* is smaller than 0.1 (D
ss: diffusion coefficient of the cation C+ in the crystal; D
aq: diffusion coefficient of the cation C+ in the solution; ρ: density of the solid compound; [C+]*: concentration of cations in the bulk of the solution). In real cases this condition will be satisfied at solution concentrations
above 1 mol/l.
Received: 15 December 1997 / Accepted: 5 March 1998 相似文献
16.
A number of configurations of NLi
n
Na2 (n = 1–4) species were optimized using the B3LYP–density functional theory method; the 6-31G* basis set was used in this calculation. In order to study all possible dissociation energies, some related species such as
NLi2Na, NLi
n
(n = 1–4), Li
n
(n = 1, 2) and Na
n
(n = 1, 2) were also considered. Optimizations of these species were followed by fundamental frequency calculations at the same
level. Global minima of these species were shown to adopt C
2
v
(NLi4Na2, NLi2Na2), D
3
h
(NLi3Na2) and C
s
(NLiNa2 and NLi2Na) configurations. All possible dissociation energies were obtained.
Received: 30 November 1998 / Accepted: 15 October 1999 / Published online: 14 March 2000 相似文献
17.
Peter Botschwina 《Theoretical chemistry accounts》1998,99(6):426-428
On the basis of large-scale coupled cluster calculations including connectedz triple substitutions in a perturbative way,
the geometrical parameters of the D
3
h
saddle point of the Walden inversion reaction Cl− + CH3Cl′→ ClCH3 + Cl′− are predicted to be R
s
(C—Cl) = 2.301 ? and r
s
(C—H) = 1.069 ?. The barrier height with respect to the reactants is recommended to be 11.5 ± 1.0 kJ mol−1. Connected triple substitutions lower the barrier height by almost a factor of 2, but have very little influence on the geometric
structure of the saddle point.
Received: 26 June 1998 / Accepted: 15 July 1998 / Published online: 28 September 1998 相似文献
18.
The effect of fluorine doping on the electrochemical performance of LiFePO4/C cathode material is investigated. The stoichiometric proportion of LiFe(PO4)1−x
F3x
/C (x = 0.01, 0.05, 0.1, 0.2) materials was synthesized by a solid-state carbothermal reduction route at 650 °C using NH4F as dopant. X-ray diffraction, scanning electron microscope, energy-dispersive X-ray, and X-ray photoelectron spectroscopy
analyses demonstrate that fluorine can be incorporated into LiFePO4/C without altering the olivine structure, but slightly changing the lattice parameters and having little effect on the particle
sizes. However, heavy fluorine doping can bring in impurities. Fluorine doping in LiFePO4/C results in good reversible capacity and rate capability. LiFe(PO4)0.95 F0.15/C exhibits highest initial capacity and best rate performance. Its discharge capacities at 0.1 and 5 C rates are 156.1 and
119.1 mAh g−1, respectively. LiFe(PO4)0.95 F0.15/C also presents an obviously better cycle life than the other samples. We attribute the improvement of the electrochemical
performance to the smaller charge transfer resistance (R
ct) and influence of fluorine on the PO43− polyanion in LiFePO4/C. 相似文献
19.
The electrocatalytic oxidation of quinine sulfate (QS) was investigated at a glassy carbon electrode, modified by a gel containing
multiwall carbon nanotubes (MWCNTs) and room-temperature ionic liquid of 1-Butyl-3-methylimidazolium hexafluorophate (BMIMPF6) in 0.10 M of phosphate buffer solution (PBS, pH 6.8). It was found that an irreversible anodic oxidation peak of QS with
E
pa as 0.99 V appeared at MWCNTs-RTIL/glassy carbon electrode (GCE). The electrode reaction process was a diffusion-controlled
one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the
charge-transfer coefficient (α), diffusion coefficient (D), and electrode reaction rate constant (k
f) of QS were found to be 0.87, 7.89 × 10−3 cm2⋅s−1 and 3.43 × 10−2 s−1, respectively. Under optimized conditions, linear calibration curves were obtained over the QS concentration range 3.0 × 10−6 to 1.0 × 10−4 M by square wave voltammetry, and the detection limit was found to be 0.44 μM based on the signal-to-noise ratio of 3. In
addition, the novel MWCNTs-RTIL/GCE was characterized by the electrochemical impedance spectroscopy and the proposed method
has been successfully applied in the electrochemical quantitative determination of quinine content in commercial injection
samples and the determination results could meet the requirement. 相似文献
20.
Coupled-cluster (CC) theory including single (S) and double (D) excitations and carried out with a spin-unrestricted Hartree–Fock
(UHF) reference wave function is free from S + 1 spin contamination as can be confirmed by an analysis of the expectation value of the spin operator, Ŝ
2. Contamination by the S + 2 contaminant can be projected out by an approximate procedure (APCCSD) with a projection operator, P^, represented by the product of the spin annihilation operators ?
s+
1 and ?s+2. The computational cost of such a projection scales with O(M
6) (M is the number of basis functions). The APCCSD energy obtained after annihilation of the S + 2 contaminant can be improved by adding triple (T) excitations in a perturbative way, thus leading to APCCSD(T) energies.
For the 17 examples studied, the deviation of the UHF-CCSD(T) energies from the corresponding full configuaration interaction
values is reduced from 4.0 to 2.3 mhartree on the average as a result of annihilating the S + 2 contaminant in an approximate way. In the case of single-bond cleavage, APCSSD leads to a significant improvement of
the energy in the region where the bonding electrons recouple from a closed shell to an open shell singlet electron pair.
Received: 13 April 2000 / Accepted: 12 July 2000 / Published online: 24 October 2000 相似文献