α,β,γ,δ,ε,η-Bi2O3电子结构和光学性质的第一性原理研究

基于密度泛函理论的CASTEP模块研究了α, β, γ, δ, ε和η-Bi₂O₃晶型, 计算分析了其几何结构、 能带结构、 电子态密度和光学性质. 结果表明, α, ε和η相均为层状结构, 其中, α和ε相为单层—Bi—O—结构, 而η相为双层—Bi—O—结构; β, γ和δ相为—Bi_m—O_n—交错结构, 其中δ相交错尤为密集, 呈现导体特性. 各晶相的导带均由Bi 6p态构成, 价带由O_2p态起主导作用. 电势电位分析结果表明, 6种晶相价带电位均在H₂O/O₂之下, 具有强氧化能力, 与实验报道的光催化氧化能力大小顺序γ-Bi₂O₃>β-Bi₂O₃>α-Bi₂O₃>δ-Bi₂O₃一致, 而导带还原电位低于H₂/H₂O, 预测纯Bi₂O₃很难具备催化产氢能力. 光学性质分析发现, γ和δ相的起始响应波长较大, 说明其应具备红外激发的性质. 这些结果可为获得偏红外激发和较宽光谱响应的Bi₂O₃材料研究提供理论基础, 为研发和应用Bi₂O₃及其复合物提供重要的指导.     

新型咪唑[2,1-b][1,3,4]噻二唑衍生物的合成及生物活性

合成了18个新型含苯并噁/噻唑啉酮结构的2,6-二取代咪唑[2,1-b][1,3,4]噻二唑衍生物5a~5i', 即2-[(2-苯并噁/噻唑啉酮-3-基)甲基]-6-芳基-咪唑[2,1-b][1,3,4]噻二唑. 利用红外光谱、 核磁共振和元素分析对化合物的结构进行了表征. β2-肾上腺素受体(β2-AR)拮抗剂钙流筛选结果表明, 部分目标化合物对β2-AR具有明显的拮抗作用, 其中化合物5c'的拮抗效果最高, 为70%. 这些化合物可作为潜在的β2-AR拮抗剂.     

A density functional study of N NQR parameters of imidazole derivatives and extrapolation to PfHRP2–Fe-PPIX complex

In this paper, density functional theory (DFT) was used to calculate ¹⁴N nuclear quadrupole coupling constants (NQCC), χ, and asymmetry parameters, η, for a series of imidazole derivatives: imidazole, 5-methylimidazole and histidine. These calculations were carried out with the PW91P86 method via the Gaussian 98 package. A systematic theoretical investigation of the different environmental effects on (χ, η) values of amino ¹⁴N1 and imino ¹⁴N2 of imidazole ring of these compounds, reveals that the local surrounding of nitrogen atoms play an important role in determining their χ and η values. Our calculations in solution show that adding explicit solvent molecules to the polarizable continuum model (PCM) has a strong effect on (χ, η) values, thereby indicating that for long-range effects, PCM, is not sufficient to describe the whole solvent effects. We also evaluate the influence of [Fe³⁺ (S = 1/2)] on the (χ, η) values of proximal and remote nitrogens of an axial ligand and compare with those of free ligands. The results show that Fe³⁺ has a strong effect on the (χ, η) values of proximal nitrogen unlike remote nitrogen. Finally, our results predict (χ = 1.56 MHz, η = 0.690) for proximal nitrogen and (χ = 2.75 MHz, η = 0.169) for remote nitrogen in PfHRP2–Fe³⁺-PPIX complex.     

白山毛桃根抗脑胶质瘤活性成分及其纳米胶束的制备

采用溶剂提取和萃取方法得到白山毛桃根乙酸乙酯、 正丁醇和水层萃取物. 通过噻唑蓝(MTT)比色法考察了各萃取物对脑胶质瘤细胞U87MG活性的抑制作用. 采用高效液相色谱(HPLC)指纹图谱法比对确认活性部位的主要化学成分为2α,3α,24-三羟基-12-烯-28-乌苏酸. 采用溶剂挥发法制备了2α,3α,24-三羟基-12-烯-28-乌苏酸纳米胶束, 对其包封率、 粒径及ζ电位等进行了表征, 并考察了其抗肿瘤活性. 体外细胞实验结果表明, 白山毛桃根乙酸乙酯萃取物对脑胶质瘤细胞U87MG具有抑制作用, 通过与标准品比对确认2α,3α,24-三羟基-12-烯-28-乌苏酸为乙酸乙酯部位的主要成分, 且该成分对脑胶质瘤细胞活性具有较强抑制作用. 通过溶剂挥发法制备的2α,3α,4-三羟基-12-烯-28-乌苏酸纳米胶束包封率为64.7%, 粒径为20 nm, 粒径分布宽度(PDI)为0.246, ζ电位为-5.7 mV. 细胞实验结果进一步证明, 与单体化合物相比, 2α,3α,24-三羟基-12-烯-28-乌苏酸纳米胶束对脑胶质瘤细胞活性具有更强的抑制作用, 为白山毛桃根在脑胶质瘤治疗中的应用提供了实验依据.     

金属串配合物[MM′M″(dpa)4(Cl)2](M=Co,Ni;M′,M″=Co,Rh)电子输运的理论研究

采用密度泛函理论DFT/BP86方法研究金属串配合物[MM'M″(dpa)₄(Cl)₂] [MM'M″=CoCoCo(1), CoCoRh(2), CoRhRh(3), NiCoRh(4)] 的结构和电子输运性质. 结果表明, 配合物1, 2和4的最稳定自旋态均存在1个(MM'M″)⁶⁺的离域$\sigma_{3}^{3}$键($\sigma^{2}\sigma_{nb}^{1}\sigma^{*0}$); 但配合物3具有1个(MM'M″)⁶⁺的离域$\sigma_{3}^{4}$键($\sigma^{2}\sigma_{nb}^{2}\sigma^{*0}$)和2个$\pi_{3}^{5}$键($\pi^{4}\pi_{nb}^{4}\pi^{*2}$), 故Rh—Rh键和Co—Rh键较强; Rh的引入使M—M键增强, Ni的引入则使M—M键减弱, 键强次序为Rh—Rh>Co—Rh>Co—Co>Ni—Co. 配合物14的传输通道均含有π和σ型轨道. 正偏压下, 配合物2和3的电流大于配合物1和4的. 负偏压下, 配合物4中出现负微分电阻效应. 配合物3中形成传输通道的σ_nbα/β和π^*α/β轨道能级分裂明显, (MM'M″)⁶⁺对β自旋的π^*轨道的贡献(88%)比α自旋(74%)的大, 使β自旋的电子更易传输, 具有较好的自旋过滤效应(70%80%).     

七水合三氯化铈-碘化钠催化氨基苯硫酚与高位阻α, β-不饱和酮的迈克尔加成反应

对七水合三氯化铈-碘化钠(CeCl₃·7H₂O-NaI)化邻氨基苯硫酚、 对氯邻氨基苯硫酚、 间氨基苯硫酚、 对氨基苯硫酚和对甲基苯硫酚与α,β-不饱和酮(1a~1o)的迈克尔加成反应进行了系统研究. 结果表明, CeCl₃·7H₂O-NaI-SiO₂复合催化剂能有效催化邻氨基苯硫酚及对氯邻氨基苯硫酚与α,β-不饱和酮(1a~1o)的迈克尔加成反应. 在优化的反应条件下, 即n(CeCl₃·7H₂O):n(NaI):n(α,β-不饱和酮)=1:2:2, m(CeCl₃·7H₂O):m(SiO₂)=1:1.6, 三氯甲烷作溶剂, 反应温度为回流温度, 反应时间为2 h, 反应可达到中等产率(43.1%~58.8%). 催化剂重复使用4次基本稳定. 此外, 提出了可能的催化机理.     

Cation–anion interactions in triphenyl telluronium salts. The crystal structures of (Ph3Te)2[MCl6] (M=Pt, Ir), (Ph3Te)[AuCl4], and (Ph3Te)(NO3)·HNO3

Triphenyltelluronium hexachloroplatinate (1), hexachloroiridate (2), tetrachloroaurate (3), and tetrachloroplatinate (4) were prepared from Ph₃TeCl and potassium salts of the corresponding anions. Upon recrystallization of 4 from concentrated nitric acid, K₂[PtCl₆] and (Ph₃Te)(NO₃)·HNO₃ (5) were obtained. The crystal structures of 1–3 and 5 are reported. Compounds 1 and 2 are isostructural. They are triclinic, P , Z=2 (the asymmetric unit contains two formula units). Compound 1: a=10.7535(2), b=17.2060(1), c=21.4700(3) Å, =78.9731(7), β=77.8650(4), γ=78.8369(4)°. Compound 2: a=10.7484(2), b=17.1955(2), c=21.4744(2) Å, =78.834(1), β=77.649(1), γ=78.781(1)°. Compound 3 is monoclinic, P2₁/c, Z=4, a=8.432(2), b=14.037(3), c=17.306(3) Å, β=93.70(3)°. Compound 5 is monoclinic. P2₁/n, Z=4, a=9.572(2), b=14.050(3), c=13.556(3) Å, β=90.76(3)°. The primary bonding in the Ph₃Te⁺ cation in each salt is a trigonal AX₃E pyramid with Te---C bond lengths in the range 2.095(8)–2.14(2) Å and the bond angles 94.1(6)–100.9(5)°. The weak TeCl (1–3) and TeO (5) secondary interactions expand the coordination sphere. In 1 and 2 the cation shows a trigonal bipyramidal AX₃YE coordination with one primary Te---C bond and the shortest secondary TeCl contact in axial positions and the two other Te---C bonds and the lone-pair in equatorial positions. The cation in 3 shows a distorted octahedral AX₃Y₃E environment and that in 5 is a more complex AX₃Y₃Y′₂ arrangement. In both latter salts the structure is a complicated three-dimensional network of cations and anions.     

Structure and conformation of 2,3,4-triphenyl-1-oxa-4-azabutadiene

2,3,4-triphenyl-1-oxa-4-azabutadine (C20H15NO) has been studied by X-ray analysis and AM1 molecular orbital methods. It crystallises in the triclinic space group P-1 with a=9.414(3), b=10.479(3), c=8.385(2) Å, =103.31(3)°, β=97.10(3)°, γ=74.09(1)°, V=772.5(4) ų, Z=2, D_c=1.227 gcm⁻³, and μ(MoK)=0.075 mm⁻¹ and F₀₀₀=300. The structure was solved by direct methods and refined to R=0.043 for 2672 reflections [I>2σ(I)]. The conformational analysis of the title compound were investigated by semi-empirical quantum mechanical AM1 calculations. The minimum conformation energies were calculated as a function of the three torsion angles θ₁(O(1)C(7)C(8)N(1)), θ₂(C(8)N(1)C(15)C(16)) and θ₃(C(14)C(9)C(8)N(1)). The results are compared with the X-ray results. C=O and C=N groups are twisted about each other by 95.5(2)°.     

Tautomeric properties, conformations and structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine

The crystal structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine (C₁₃H₁₀NO₂Cl) was determined by X-ray analysis. It crystallizes orthorhombic space group P2₁2₁2₁ with a=12.967(2) Å, b=14.438(3) Å, c=6.231(3) Å, V=1166.5(6) Å³, Z=4, D_c=1.41 g cm⁻³ and μ(MoK)=0.315 mm⁻¹. The title compound is thermochromic and the molecule is nearly planar. Both tautomeric forms (keto and enol forms in 68(3) and 32(3)%, respectively) are present in the solid state. The molecules contain strong intramolecular hydrogen bonds, N1–H1O1/O2 (2.515(1) and 2.581(2) Å) for the keto form and O1–H01N1 for the enol one. There is also strong intermolecular O2–HO1 hydrogen bonding (2.599(2) Å) between neighbouring molecules. Minimum energy conformations AM1 were calculated as a function of the three torsion angles, θ₁(N1–C7–C6–C5), θ₂(C8–N1–C7–C6) and θ₃(C9–C8–N1–C7), varied every 10°. Although the molecule is nearly planar, the AM1 optimized geometry of the title compound is not planar. The non-planar conformation of the title compound corresponding to the optimized X-ray structure is the most stable conformation in all calculations.     

Predicted radiolysis yield in a Fricke solution irradiated with various heavy ions

Experimental data on the spatial distribution of the energy deposited around an energetic heavy ion, from 1 MeV proton to 5.9 MeV/n uranium ion, which have been reported in the literature were documented to obtain a scaled radial dose distribution; (β/Z*)² D(Z*, β,t)=200 (for t=0–1), 200/t² (for t=1t_c), and 200 t_c/t³ (for t>t_c) where Z* and β are the effective charge and velocity relative to c, the velocity of light, of the incident ion, respectively, D the dose in unit of Gy, t the radial distance in unit of nm, t_c the critical distance empirically determined.

Then, if we know the yield of any chemical reaction as a function of dose from the results of experiments using γ-radiations or fast electrons or theoretical calculations, we can calculate the probability for the yield of the chemical reaction in the system bombarded with a heavy ion of the effective charge Z* and velocity β. The results of the present calculation of the LET-values and of G(Fe³⁺) in the ferrous sulfate acidic solution are presented and compared with reported experimental results.     

Interfacial characteristics of β-casein spread films at the air–water interface

Casein is well known to be a good protein emulsifier and β-casein is the major component of casein and commercial sodium caseinate. This work studies the behaviour of β-casein at the interface. The interfacial characteristics (structure and stability) of β-casein spread films have been examined at the air–water interface in a Langmuir-type film balance, as a function of temperature (5–40°C) and aqueous phase pH (pH 5 and 7). From surface pressure–area isotherms (π–A isotherms) as a function of temperature we can draw a phase diagram. β-Casein spread films present two structures and the collapse phase. That is, there is a critical surface pressure and a surface concentration at which the film properties change significantly. This transition depends on the temperature and the aqueous phase pH. The film structure was observed to be more condensed and β-casein interfacial density was higher at pH 5. β-Casein films were stable at surface pressures lower than equilibrium surface pressure. In fact, no hysteresis was observed in π–A isotherms after continuous compression-expansion cycles or over time. The relative area relaxation at constant surface pressure (10 or 20 mN m⁻¹) and the surface pressure relaxation at constant area near the monolayer collapse, can be fitted by two exponential equations. The characteristic relaxation times in β-casein films can be associated with conformation–organization changes, hydrophilic group hydration and/or surface rheology, as a function of pH.     

改性钛基PbO2电极的制备及其对COD的快速检测

通过制备Ti/α/β-PbO₂、Ti/Ag/β-PbO₂这两种含有不同中间层的钛基二氧化铅电极来探究电催化氧化技术快速测定葡萄糖模拟废水中有机物(COD)含量的可行性。为了评估两种电极的各项性能,首先采用扫描电镜(SEM)、X射线衍射(XRD)对电极进行形貌表征,其次进行电化学性能测试包括线性伏安曲线(LSV)、塔菲尔曲线(Tafel)、循环伏安曲线(CV)以及交流阻抗测量分析。结果表明,Ti/α/β-PbO₂电极表面晶体结构更加均匀,晶粒尺寸偏小,具有更大的电活性表面积。Ti/α/β-PbO₂电极的析氧电位为1.77 V,为·OH的产生提供良好条件。在Tafel、CV测试中,Ti/α/β-PbO₂电极的交换电流密度i₀及比电容C_p分别为0.0995 A·cm^-1、0.004098 F·cm^-1均高于Ti/Ag/β-PbO₂电极,说明Ti/α/β-PbO₂电极的耐腐蚀性以及释放电子的能力优异。最终选用Ti/α/β-PbO₂电极为工作电极。Ti/α/β-PbO₂电极检测COD的最佳条件为：氧化电位1.30 V、电解时间150 s、电解液浓度0.03 mol·L^-1 硝酸钠(NaNO₃)。电化学法与比色消解法测定COD的相关系数可达0.9909,同时具有良好的重现性与相关性,COD的检测范围为0 mg·L^-1 ~ 500 mg·L^-1。在误差允许的范围内可以替代标准的重铬酸钾法,为实现COD的在线快速检测提供参考价值。     

Kinetic analysis of thermogravimetric data obtained under linear temperature programming—a method based on calculations of the temperature integral by interpolation

A new technique, called interpolation method, with general application in the kinetic analysis of processes studied by thermogravimetry (TG) under linear temperature programming is developed. It is based on the linear relationship, with slope 1, between log g() and log I(γ, θ) for the appropriate kinetic function, where I(γ, θ) is the normalized temperature integral, θ the normalized temperature (θ=T/T₀) and γ a dimensionless activation energy (γ=E/RT₀). Values of log I(γ, θ) are calculated by linear interpolations in a pre-built table. This method can easily be programmed and implemented in a personal computer, where the results (kinetic parameters and quality of regressions for the kinetic functions considered) are typically obtained in a very short time. The method is validated by analyzing different simulated thermogravimetric curves and comparing the results with those determined with some classic methods taken from the literature. In addition, the results are compared with the values obtained by a similar method, also developed and explained in this paper, which involves the evaluation of all the values of the temperature integral by numerical integration, therefore, demanding a much larger calculation time. The interpolation method is found to be more accurate than other published methods, particularly in the case of thermogravimetric curves corresponding to processes with low activation energies. The results obtained are always similar to those determined by the integration method, which is taken as reference. Application of the technique to experimental data for various types of reactions shows that the results are in agreement with the published parameters and kinetic laws.     

Effect of salts on the electrical conductance of a fluorine-containing poly(carboxylic acid), PPFNA

Electrical conductance and other solution properties of aqueous solutions of a fluorine-containing poly(carboxylic acid), (poly(9H,9H-perfluoro-2,5-dimethyl-3,6-dioxa-8-nonenoic acid), PPFNA) were studied with special attention to the salt effect. This polymer dissociated strongly resulting in a low pH value in unneutralized state (β = 0, β: degree of neutralization). The specific conductance was the highest at β = 0 and decreased as β increased. A considerable increase in conductance was observed by titrating NaCl at low β, because large amounts of bound protons were released by addition of NaCl. The amounts of released protons exceeded those originally dissociated at β = 0. Such an anomalous proton liberation suggests that this polymer is a fairly strong polyacid but not a typical one such as poly(styrene sulfonic acid). Under fully neutralized state (β = 1), however, the solution conductance was lower than the sum of the polymer and NaCl added, due to polyion–salt ion interaction.     

Effect of pH on the electrophoretic mobility of a particle with a charge-regulated membrane in a general electrolyte solution

The electrophoretic motion of an entity comprised of a rigid, uncharged core covered by a charge-regulated membrane which simulates a biological cell, in a general a:b electrolyte solution is analyzed. The membrane carries a fixed charge which arises from the dissociation of the acidic functional group HA. We show that the higher the concentration of cations in the bulk liquid phase, the lower the absolute Donnan potential, _D, and the lower the concentration of functional group, N₀, the lower the _D. Also, the higher the pH, the higher the absolute electrical potential, and the greater the N₀, the lower the pH. The absolute mobility of a cell, μ, increases with pH, but decreases with the increase in the friction coefficient of the membrane phase, γ. For a fixed total number of HA, if γ is large, μ/μ_s is less than unity, μ_s being the mobility of the corresponding rigid particle, and it decreases with the thickness of membrane d, and the inverse is true if γ is small. For a medium γ, the variation of μ/μ_s as a function of d has a local maximum, and depending upon d, it can be either greater or less than unity.     

亚磷酸锌无机-有机杂化化合物的合成与结构表征

在水热条件下, 以1,6-己二胺为模板剂合成了一个三维(3D)亚磷酸锌无机-有机杂化化合物(C₆N₂H₁₆)_0.5ZnHPO₃(ZnHPO-CJ15), 并对其单晶结构进行了解析. 结果表明, ZnHPO-CJ15晶体属单斜晶系, P2₁/c空间群, a=1.19587(7) nm, b=0.82766(5) nm, c=0.77756(5) nm, α=90.00°, β=95.8370(10)°, γ=90.00°, V=0.76562(8) nm³, Z=1. ZnHPO-CJ15具有层柱状结构, 其骨架结构是由ZnO₃N四面体和HPO₃假四面体连接构成的二维4×8元环网层结构, 层与层之间由1,6-己二胺分子与Zn配位柱撑连接形成三维结构.     

Thermogravimetric study on perovskite-like oxygen permeation ceramic membranes

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 k_a of all material are larger than oxygen desorption rate constants k_d and both k_a and k_d are not strongly dependent on temperature in the studied temperature range. The oxygen vacancy contents δ(N₂) and δ(O₂) in nitrogen and oxygen and their difference Δδ = δ(N₂) − δ(O₂) play an important role in determining the temperature behavior of oxygen permeation flux J_O2.     

A simple method for predicting the frequency of the infrared inactive carbonyl stretching mode in LM(CO)5 molecules with C4V symmetry

The paper presents a new method for predicting the frequency of the b₁ mode, which is infrared-inactive, in complexes of the type LM(CO)₅ belonging to C_4V point group. The method was based on the relation λ₃=λ₄+[(1−δ/δ)](λ₁−λ₂), where δ=(λ₁−λ₂)/(λ₁−λ₂+λ₃−λ₄), λ₁, λ₂, λ₃ and λ₄ are the λ parameters of the , , b₁ and e modes, respectively. For a large numbers of complexes of the type LM(CO)₅ the average value of δ was found to be 0.80, with a standard deviation of 0.02. With the use of average value of δ, the frequencies of b₁ mode were estimated. The result obtained indicated that there exists a rather good fit between observed and calculated frequencies, with a mean error of 2.7 cm⁻¹. In addition, it was shown that the δ parameter can be used as a criterion of the correct band assignment for the complexes understudy.     

Small angle X-ray scattering from lamellar phase for β-3,7-dimethyloctylglucoside/water system: comparison with β-n-alkylglucosides

Small angle X-ray scattering (SAXS) is measured for the lamellar phase in aqueous systems of 1-o-β-3,7-dimethyoctyl-D-glucopyranoside (β-Glc(Ger)), which has recently been prepared by us, 1-o-β-decyl-D-glucopyranoside (β-GlcC₁₀), and 1-o-β-octyl-D-glucopyranoside (β-GlcC₈). The repeat distance d obtained from the position of the diffraction peak does not follow the swelling law d = 2δ_hc/_hc, where δ_hc and _hc are the thickness and the volume fraction of the hydrophobic layer, respectively. This may result from the fact that δ_hc increases and, equivalently, the surface area per surfactant molecule (a_s) decreases with increasing concentration. So we calculate δ_hc and a_s from the observed d value at each concentration using the above swelling law. The half-thickness δ_hc increases in the order β-GlcC₈ < β-Glc(Ger) < β-GlcC₁₀ at a fixed concentration. On the other hand, the data on a_s for β-GlcC₁₀ and β-GlcC₈ lie on the same line and the data for β-Glc(Ger) lies above this line. These results suggest that the cross-sectional area of the geranyl chain is larger than that of the glucose headgroup. Existence of water filled defects in bilayer sheets is also discussed based on the SAXS pattern and the concentration dependence of d.     

Blocking and ripening of colloids in porous media and their implications for bacterial transport

A model accounting for the dynamics of colloid deposition in porous media was developed and applied to systems containing similarly charged particles and collectors. Colloid breakthrough and intracolumn retention data confirmed that blocking reduced overall colloidal adhesion to soil. The surface coverage at which blocking occurred varied for the type of colloid, as shown by changes in the clean-bed collision efficiency, _0, and the excluded area parameter, β. Excluded area parameters were relatively high due to unfavorable interactions between particles and collectors, and ranged from 11.5 for one bacterium (Pseudomonas putida KT2442) to 13.7 and 24.1 for carboxylated latex microspheres with differing degrees of charged groups on their surfaces. Differences in β values for the three colloids were correlated with electrophoretic mobility, with the most negatively charged colloid (carboxylated latex; CL microspheres) having the highest β. No correlation between hydrophobicity and ₀ or β was found. Besides using colloidal particles capable of blocking, the addition of chemical additives to the soil has been suggested as a means for reducing attachment of colloids to porous media. Dextran addition caused an order-of-magnitude reduction in the overall (for carboxylated-modified latex; CMLs). This reduction was not attributed to blocking, but to the sorption of dextran to the soil which lowered ₀. The filtration-based numerical model used to fit the ₀ and β parameters was used to demonstrate that blocking could result in significantly enhanced bacterial transport in field situations.