Infinite dilution viscoelastic properties of poly(gamma-benzyl-L-glutamate) in m-cresol.

The real and imaginary parts of complex viscosity, η′ and η″, are measured for dilute solutions of poly(γ-benzyl-L -glutamate) in m-cresol, a helicogenic solvent. The frequency range is 2.2–525 kHz; the concentration range 0.2–5 g/dl; the temperature 30°C, and the molecular weights M_r are 6.4 × 10⁴–17 × 10⁴. The dispersion curve of extrapolated intrinsic dynamic viscosity [η′] of samples with M_r > 10⁵ is interpreted in terms of three mechanisms appearing from low to high frequencies: end-over-end rotation, flexural deformation, and side-chain motion. For a sample with M_r < 10⁵, the flexural relaxation disappears and a plateau of [η′] is distinctly observed between rotational and side-chain relaxations. Rotational relaxation times of all the samples obey the Kirkwood–Auer theory. The strong concentration dependence of rotational relaxation time is explained by collisions of molecules rather than association. Flexural relaxation times calculated from a theory by assuming the persistence length as 1200 Å are consistent with observed dispersion curves of [η′].     

Dynamic viscoelastic properties of solutions of shear-degraded deoxyribonucleic acid

Calf thymus and salmon sperm deoxyribouncleie acid were degraded by high-shear stirring to molecular weights M in the range of 1.3–3.2 × 10⁶ and purified by chromatography on methylated bovine serum albumin. Dynamic viscoelastic properties of the fragmented products, in aqueous glycerol solutions in the concentration range of c = 0.003–0.01 g./ml., were investigated with the apparatus of Birnboim and Ferry. At values of the product cM higher than 4 × 10³, the frequency dependence of the components of the complex shear modulus, G′ and G″, displayed a plateau region in which G′ > G″ – ων₁η_S, similar to that observed in concentrated solutions of coiling polymers where it is attributed to an entanglement network (ω is radian frequency, ν₁ volume fraction of solvent, and η₈, solvent viscosity). The width of this plateau region on the logarithmic frequency scale is given by Δ = 3.8 (log cM – 3.56). At lower values of cM, the frequency dependence is intermediate between those predicted by the theory of Zimm for flexible coiled macromolecules and by the theory of Kirkwood and Auer for rods. Fitting to the Zimm theory gives highly discrepant values for molecular weights, while fitting the low-frequency end of the dispersion to the Kirkwood-Auer theory gives reasonable agreement for both molecular weight and rotary diffusion coefficient. It is concluded that the helical fragments appear as nearly rigid rods in their behavior at very low frequencies, but at higher frequencies reveal substantial bending flexibility.     

Untersuchungen zur Sauerstoffdiffusion in wäßrigen Xanthanlösungen

The determination of oxygen diffusion coefficients was carried out by a modified chronoamperometric method using a stationary platinum electrode. The determined diffusion coefficients are related to approximated η₀-values. It was shown a relation of D_i and η₀ according to the HAYDUK-CHENG-potential equation. That means a strong relative lowering of oxygen diffusion coefficients already by low viscosities, but a little influence at high viscosities. A simple laboratory thin film reactor is described, in which the oxygen supply is maintained by diffusion. This reactor is suitable very well for fermentations of viscous fluids.     

Relationship between the Rheological Properties of Thickener Solutions and Their Velocity through the Pharynx as Measured by the Ultrasonic Pulse Doppler Method

The dependence of the dynamic viscoelastic parameters of carboxymethylcellulose (CMC), xanthan gum, and guar gum solutions on the angular frequency (ω) was compared with that of their viscosity (μ) on the shear rate (γ). In addition, the effect of these rheological properties on the maximum velocity through the pharynx, V _max, as measured by the ultrasonic pulse Doppler method, was investigated. The CMC and guar gum solutions examined were taken as a dilute solution and a true polymer solution, respectively. The xanthan gum solution was taken as a weak gel above 0.5% and a true polymer solution below 0.2%. The maximum velocity, V _max, of the thickener solutions correlated well with μ, the dynamic viscosity η′, and the complex viscosity η^*, especially those measured at γ or ω of 20–30 s^?1 (or rad/s) and above, suggesting that μ, η′, and η^* are suitable indexes for care foods of the liquid type for dysphagic patients.     

Manganese as a calcium probe: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy of intact cells

Summary When Lettree cells are exposed to Mn²⁺, the cation becomes associated with cells in two ways: in a relatively loose and mobile manner that gives a six-line EPR spectrum designated Mn _b ^*, and in an immobile, relatively tight manner that gives no detectable EPR spectrum, designated Mn _b . Mn _b ^* is probably on the surface of cells; most Mn _b is probably inside cells. NMR measurements of Lettree cell suspensions show two water proton relaxation rates and confirm the existence of cell-associated Mn. Human erythrocytes, on the other hand, bind no Mn²⁺ under these conditions, as judged by EPR and NMR measurements.Virally-treated Lettree cells show an increase in Mn _b (but not in Mn _b ^*). They also show a third water proton relaxation rate.     

Flow properties of high-molecular-weight DNA solutions: viscosity, recoil, and longest retardation time

Viscosity η, recoil Γ, and longest retardation time τ_1R were measured for buffered aqueous solution of T2 DNA (M = 1.3 × 10⁸) and cell lysattes of Bacillus subtiles W23 (DNA M = 2 × 10⁹) as a function of concetration, shear stress σ, and time of shear t, using a cartesian-diver-suspended couette flow system. For the T2 solution, η decreased with increasing σ, Γ(t) going through a maximum with t. For the B. subtiles lysates, the preponderant rheological component of which is chromatin DNA, above a critical σ, the η, Γ(t), and τ_1R increased t over 15 to 45 minutes duration to values up to several times larger, indicating the formation of intermolecular aggregates. The onset of such effects and their significance in th e measurement of molecular properties by hydrodynamic means is disscussed.     

Experimental and Simulation Studies of Electro-rheology

Abstract

Electro-rheological fluids are colloidal dispersions that, under the influence of an applied electric field, can show a spectacular increase in yield stress and viscosity. Despite many technological roles for fluids with a viscosity that can be controlled electrically, progress at making them commercially viable products has been slow, partly due to a lack of understanding of this phenomenon at the microscopic level. In this report, simulation and experimental data are combined to provide insights into the microscopic origins of this effect. The simulations produce electric field-induced “strings” of particles that span the electrodes, in agreement with the experimental observation, and are responsible for the major enhancements in the viscosity. The field also causes a strong distortion in the first coordination shell of colloidal particles. The combination of shear and electric field produces a long-range microstructure that is periodically forming and decaying, caused by the competing effects of electric field and shear rate. Comparison with experiment reveals that the Electro-rheological effect is driven by the applied field-induced Stokesian diffusion of the solid particles and relies little on the accompanying Brownian motion.     

The effect of solvent viscosity and temperature on DNA viscoelastic behavior

The effect of solvent viscosity (η_s) and temperature (T) on the shape of the concentration dependence of the principal and total recoils in creep-recovery viscoelastometry experiments has been studied for T4 DNA solutions. The range of DNA concentration (c) was 2 – 40 μg/ml; glycerol, 70–80% v/v, sucrose, 60% v/v; NaCl, 5 mM – 1M; and T, 275 – 323 K. A linear proportionality between recoil and c was obtained at high η_s/T. At low η_s/T, the c-dependence was nonlinear, approaching saturation at higher c. At low c, the slope of both curves was the same. Transition between “linear” and “nonlinear” values occurred over a narrow range of η_s/T (a width of 1–5 K if η_s/T was changed by varying T). (η_s/T)_tr, the midpoint of the transition, was independent of solvent properties other than viscosity. Also, (η_s/T)_tr increased with c. For a given c, η_s/T values above this transitional value yield linear behavior; below this, nonlinear behavior. The ratio of linear to nonlinear recoil values is a linear function of c with K_c, the slope of this dependence, independent of η_s and T. A kinetic model for the observed nonlinearity of recoil with c is presented. It explains the independence of K_c on η_s and T. An attempt has been made to explain the linear–nonlinear transitions by comparison of τ₁ and T_R, the lifetime of the contact points of the polymer network in the de Gennes theory. The nonlinear values are consistent with a pseudogel that exists when τ₁ < T_R. At τ₁ > T_R, the DNA behavior is similar to that in dilute solutions (linear values). Thus, the condition for transition is τ₁ = T_R. However, some unsolved problems remain.     

The effect of dielectric polarization of the electrode on anomalous temperature effects in the electrical double layer

Monte Carlo simulations and a modified Poisson–Boltzmann (MPB) theory are used to investigate the temperature dependence of the capacitance (around the potential of zero charge) of an electric double layer in the presence of surface polarization due to a dielectric boundary. Within the context of the restricted primitive model planar double layer, whose solvent dielectric constant is ε₂, the cases when the electrode is an insulator (ε₁ = 1), when the electrode and the electrolyte have the same permittivity (ε₁ = ε₂, no polarization), and when the electrode is a conductor (ε₁ → ∞) are studied for the case where the electrolyte concentration is 0.1 M. The simulations reveal a capacitance anomaly, that is, a positive temperature dependence of the capacitance at low temperatures for the former two situations. The MPB theory also shows this effect for these two situations and is in qualitative or better agreement with the simulation data. In these two cases, both the simulations and theory show a dramatic increase of the diffuse layer potential in the temperature regime where capacitance anomaly occurs. However, in the latter situation, where the electrode is metallic, the capacitance always has a negative temperature derivative for the MPB theory and probably also for the simulation data.     

The Rheology of 6-Propyl Duodecane and 5-Dibutyl Nonane by Non-Equilibrium Molecular Dynamics Simulations

Abstract

In recent papers, we reported non-equilibrium molecular dynamics (NEMD) simulations of planar Couette flow for liquid n- and i-butane, and liquid n-decane and 4-propyl heptane, using two collapsed atom models and an atomistically detailed model. It was found that the collapsed atom models predict the viscosities of the n-butane and n-decane quite well, and that the atomistically detailed model does not yield quantitative agreement with the viscosity of the n-alkanes or the branched alkanes, but it does have the one positive feature that the calculated viscosities of the branched alkanes are higher than these of the n-alkanes. In the present paper, we report results of NEMD simulations of planar Couette flow for liquid 6-propyl duodecane and 5-dibutyl nonane at 296 K and 0.782 g/cc, using an expanded collapsed atom model for simplicity. The strain rate dependent viscosity shows three different regions—two shear thinning ones and a Newtonian one. The slopes of the log-log plot for the branched-chain alkanes at high strain rate are different from those at intermediate strain rate, which is characterized as a rheological behavior of branched-chain alkanes. The Newtonian viscosity of the branched-chain alkanes can be extrapolated from the plateau value of the strain rate dependent viscosity at low strain rate as for straight-chain alkanes [J. Chem. Phys., 105, 1214 (1996)]. The results indicate that more-branched alkanes have a larger viscosity than less-branched C₁₇ alkanes.     

Stress Distortion Restraint to Boost the Sodium Ion Storage Performance of a Novel Binary Hexacyanoferrate

Mn‐based hexacyanoferrate Na_xMnFe(CN)₆ (NMHFC) has been attracting more attention as a promising cathode material for sodium ion storage owing to its low cost, environmental friendliness, and its high voltage plateau of 3.6 V, which comes from the Mn²⁺/Mn³⁺ redox couple. In particular, the Na‐rich NMHFC (x > 1.40) with trigonal phase is considered an attractive candidate due to its large capacity of ≈130 mAh g^?1, delivering high energy density. Its unstable cycle life, however, is holding back its practical application due to the dissolution of Mn²⁺ and the trigonal‐cubic phase transition during the charge–discharge process. Here, a novel hexacyanoferrate (Na_1.60Mn_0.833Fe_0.167[Fe(CN)₆], NMFHFC‐1) with Na‐rich cubic structure and dual‐metal active redox couples is developed for the first time. Through multiple structural modulation, the stress distortion is minimized by restraining Mn²⁺ dissolution and the trigonal‐cubic phase transition, which are common issues in manganese‐based hexacyanoferrate. Moreover, NMFHFC‐1 simultaneously retains an abundance of Na ions in the framework. As a result, Na_1.60Mn_0.833Fe_0.167[Fe(CN)₆] electrode delivers high energy density (436 Wh kg^?1) and excellent cycle life (80.2% capacity retention over 300 cycles), paving the way for the development of novel commercial cathode materials for sodium ion storage.     

Strong effect of the interaction potential cut-off on the crystallinity of films grown by simulations

The paper deals with the methodology of film growth simulations using classical molecular dynamics and an empirical interaction potential. We focus on the effect of the cut-off distance (r_C) of the short-range part of the potential. On the one hand, we find that r_C does not affect the qualitative conclusions of the simulations and that its quantitative effect is in the logical direction (better crystallinity at higher r_C). On the other hand, we show that the aforementioned quantitative effect is very strong, and clearly underestimated in the literature. The film crystallinity is affected by (non-)neglecting of as seemingly low energies as several meV per bond. The results are important for the design of growth simulations of crystalline films and for the correct interpretation of their results.     

研究快报：锻炼缓解内质网还原应激从而促进健康衰老

目的 锻炼是延缓衰老的有效策略,本工作的目的在于探索锻炼是如何在细胞器水平影响内质网的氧化还原状态,以及内质网氧化还原状态是否影响个体衰老。方法 利用定位于内质网响应过氧化氢的Hyperion探针检测线虫衰老过程中及经过游泳运动后体壁肌肉内质网的氧化还原状态。通过在线虫内质网中特异过表达哺乳动物过氧化氢酶的同源基因ctl-1构建内质网特异的还原应激模型,研究了内质网还原应激对个体衰老的影响。线虫的健康状态以线虫寿命、身体摆动次数及对压力的响应能力为判断指标进行表征。结果 用Hyperion_ER探针检测发现,衰老线虫的内质网中过氧化氢水平相比与年轻线虫显著降低,表明内质网在衰老过程中发生了还原应激。线虫经过短时90 min游泳运动及长时期4 d （3次+3次+2次+2次,90 min/次）的游泳运动都可以增加内质网的氧化力。相比于对照,内质网还原应激的线虫寿命缩短,身体摆动次数降低,应对压力的响应能力下降,表明内质网还原应激加速线虫衰老。进一步研究发现,长时期的锻炼可以提高内质网的氧化力,缓解衰老相关的内质网还原应激,经过锻炼的第8天的线虫运动活力显著高于未锻炼的第...     

Total Relaxivities of Material Content in Various Cysts and Ameloblastoma: Implications for Discriminating Different Fluids

Nuclear magnetic resonance T ₁ and T ₂ relaxivities (r ₁ and r ₂) exhibit efficiency of a material to alter the relaxation rates (1/T ₁ and 1/T ₂), and they are being used for diagnostic purposes. The determination of total relaxivities (r _1t and r _2t) of cystic fluid content and ameloblastoma may therefore be useful for discriminative purposes. In order to determine what makes total relaxivities of hemorrhagic cysts, four sets of tubes containing pooled cyst were doped with increasing concentrations of iron, copper, albumin, and γ-globulins. These sets were replaced in a phantom together with six individual cysts and one ameloblastoma. The relaxation times were measured by magnetic resonance imaging operating at 1.5 T. The relaxivities of individual ions and proteins were determined from the slope of the relation between relaxation rates and concentration, while total relaxivities were determined by using the increases in relaxation rates and material content of cystic fluid (MC). Iron, copper, albumin, and γ-globulins were found to be the sources of r _1t and r _2t. Each of r _1t, r _2t, r _1tMC, r _2tMC, and r _2t/r _1t are distinctive parameters for each cystic category and ameloblastoma. Except for MC, the parameters measured for ameloblastoma are significantly smaller than those of cysts. The similarity of the present results to those used in clinical applications suggests that each of r _1t, r _2t, r _1tMC, r _2tMC, and r _2t/r _1t has an ability to discriminate various fluids and masses. The present work also suggests that r _1tMC, r _2tMC, and r _2t/r _1t can be determined in vivo.     

Relevance of phenylalanine 216 in the affinity of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> phosphoenolpyruvate carboxykinase for Mn(II)

Saccharomyces cerevisiae phosphoenolpyruvate (PEP) carboxykinase catalyzes the reversible formation of oxaloacetate and adenosine triphosphate from PEP, adenosine diphosphate and carbon dioxide, and uses Mn²⁺ as the activating metal ion. Comparison with the crystalline structure of homologous Escherichia coli PEP carboxykinase [Tari et al. (1997) Nature Struct. Biol. 4, 990–994] shows that Lys²¹³ is one of the ligands to Mn²⁺ at the enzyme active site. Coordination of Mn²⁺ to a lysyl residue is not common and suggests a low pK _a value for the ε-NH₂ group of Lys²¹³. In this work, we evaluate the role of neighboring Phe²¹⁶ in contributing to provide a low polarity microenvironment suitable to keep the ε-NH₂ of Lys²¹³ in the unprotonated form. Mutation Phe216Tyr shows that the introduction of a hydroxyl group in the lateral chain of the residue produces a substantial loss in the enzyme affinity for Mn²⁺, suggesting an increase of the pK _a of Lys²¹³. In agreement with this interpretation, theoretical calculations indicate an alkaline shift of 2.8 pH units in the pK _a of the ε-amino group of Lys²¹³ upon Phe216Tyr mutation.     

QTLs for the elongation of axile and lateral roots of maize in response to low water potential

Changes in root architecture and the maintenance of root growth in drying soil are key traits for the adaptation of maize (Zea mays L.) to drought environments. The goal of this study was to map quantitative trait loci (QTLs) for root growth and its response to dehydration in a population of 208 recombinant inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). The parents, Ac7643 and Ac7729/TZSRW, are known to be drought-tolerant and drought-sensitive, respectively. Roots were grown in pouches under well-watered conditions or at low water potential induced by the osmolyte polyethylene glycol (PEG 8000). Axile root length (L _Ax) increased linearly, while lateral root length (L _Lat) increased exponentially over time. Thirteen QTLs were identified for six seedling traits: elongation rates of axile roots (ER_Ax), the rate constant of lateral root elongation (k _Lat), the final respective lengths (L _Ax and L _Lat), and the ratios k _Lat/ER_Ax and L _Lat/L _Ax. While QTLs for lateral root traits were constitutively expressed, most QTLs for axile root traits responded to water stress. For axile roots, common QTLs existed for ER_Ax and L _Ax. Quantitative trait loci for the elongation rates of axile roots responded more clearly to water stress compared to root length. Two major QTLs were detected: a QTL for general vigor in bin 2.02, affecting most of the traits, and a QTL for the constitutive increase in k _Lat and k _Lat/ER_Ax in bins 6.04–6.05. The latter co-located with a major QTL for the anthesis-silking interval (ASI) reported in published field experiments, suggesting an involvement of root morphology in drought tolerance. Rapid seedling tests are feasible for elucidating the genetic response of root growth to low water potential. Some loci may even have pleiotropic effects on yield-related traits under drought stress.     

高原鼠兔干扰对高寒草甸植物多样性与土壤养分间关系的影响

高原鼠兔干扰虽然能够改变高寒草甸植物多样性与土壤养分含量,但植物多样性与土壤养分间的关系对高原鼠兔干扰的响应尚不清晰。利用高原鼠兔有效洞口密度将高原鼠兔干扰程度划分为T_1(7个/625 m~2)、T_2(12个/625 m~2)、T_3(22个/625m~2)、T_4(38个/625 m~2)4个水平,运用RDA冗余分析法研究了高原鼠兔不同干扰程度下高寒草甸植物多样性与土壤养分间的关系。结果表明:随着高原鼠兔干扰水平的增加,优势种高山嵩草(Kobresia pygmaea)的重要值先增加后降低,而伴生种小花草玉梅(Anemone rivularis var.flore-minors)和莓叶委陵菜(Potentilla fragarioides)的重要值先降低后增加;当高原鼠兔干扰水平从T_1到T_2时植物多样性指数变化不显著,而高原鼠兔干扰程度超过T_2时则植物多样性指数具有降低趋势;土壤全氮和硝态氮含量随高原鼠兔干扰水平增加而降低,而土壤铵态氮含量则降低后增加,土壤有机碳和全磷先增加后降低;多样性指数与0—10cm土壤深度硝态氮、10—20cm土壤深度全钾间的相关性从T_1到T_3时为正相关,而到T_4时则变为负相关,而与0—10cm土壤深度全氮的相关性则表现T_1到T_3时为负相关,T_4时为正相关,与铵态氮间相关性只有T_1时为负相关,这说明高原鼠兔干扰改变了植物多样性与土壤养分间的关系,其变化阈值介于T_2和T_3。     

Inhibition of autophagy stimulate molecular iodine-induced apoptosis in hormone independent breast tumors

Estrogen receptor negative (ER^−ve) and p53 mutant breast tumors are highly aggressive and have fewer treatment options. Previously, we showed that molecular Iodine (I₂) induces apoptosis in hormone responsive MCF-7 breast cancer cells, and non-apoptotic cell death in ER^−ve–p53 mutant MDA-MB231 cells (Shrivastava, 2006). Here we show that I₂ (3 μM) treatment enhanced the features of autophagy in MDA-MB231 cells. Since autophagy is a cell survival response to most anti-cancer therapies, we used both in vitro and in vivo systems to determine whether ER^−ve mammary tumors could be sensitized to I₂-induced apoptosis by inhibiting autophagy. Autophagy inhibition with chloroquine (CQ) and inhibitors for PI3K (3MA, LY294002) and H+/ATPase (baflomycin) resulted in enhanced cell death in I₂ treated MDA-MB231 cells. Further, CQ (20 μM) in combination with I₂, showed apoptotic features such as increased sub-G1 fraction (∼5-fold), expression of cleaved caspase-9 and -3 compared to I₂ treatment alone. Flowcytometry of I₂ and CQ co-treated cells revealed increase in mitochondrial membrane permeability (p < 0.01) and translocation of cathepsin D activity to cytosol relative to I₂ treatment. For in vivo studies ICRC mice were transplanted subcutaneously with MMTV-induced mammary tumors. A significant reduction in tumor volumes, as measured by MRI, was found in I₂ and CQ co-treated mice relative to I₂ or vehicle treated mice. These data indicate that inhibition of autophagy renders ER^−ve breast tumor cells more sensitive to I₂ induced apoptosis. Thus, I₂ together with autophagy inhibitor could have a potential tumorostatic role in ER^−ve aggressive breast tumors that may be evaluated in future studies.     

Proton and phosphorus-31 magnetic relaxation studies on the interaction of polyriboadenylic acid with Mn2+

Proton and phosphorus-31 nuclear spin–lattice relaxation times T₁ and spin–spin relaxation times T₂ have been measured on the single-stranded polyriboadenylic acid [poly(A)]–Mn²⁺ system in a neutral D₂O solution in the temperature range 10°–90°C at 100 and 40.5 MHz, respectively, with the Fourier transform nmr method. Minimum values of T₁ have been found for all these nuclei, which have enabled the exact estimation of apparent distances from Mn²⁺ to H₂, H₈, H_1′, and the phosphorus nucleus to be 4.7, 4.1, 5.2, and 3.0 Å, respectively. The electron spin of Mn²⁺ penetrates into the phosphorus nucleus, giving ³¹P hyperfine coupling of more than 10⁶ Hz. Evidence of penetration of the electron spin into H₈ and H₂ is also obtained, suggesting direct coordination of nitrogen atoms of the adenine ring to the Mn²⁺ Ion. Combined with the result from proton relaxation enhancement of water, it is concluded that every Mn²⁺ ion added is bound directly to two phosphate groups with a Mn²⁺–phosphorus distance of 3.3 Å, while a part of the Mn²⁺ ions are simultaneouly bound to the adenine ring. It is estimated that 39 ± 13% and 13 ± 5% of Mn²⁺ are coordinated by N₇ and N₃ (or N₁), respectively. The motional freedom of poly(A) in the environment of the Mn²⁺ binding site has been found to be quenched to the extent that the rotational motion becomes several times slower than that of the corresponding Mn²⁺–free poly(A). The activation energies for the molecular motion are, however, practically unchanged from those for Mn²⁺–free poly(A), and are found to be 8.3, 8.5, 6.1, and 8.7 kcal/mol for H₈, H₂, H_1′, and phosphorus, respectively. T₂ of phosphorus is determined by the dissociation rate (k_?1) of Mn²⁺ from the phosphate group for the whole temperature range studied with activation enthalpy of 6.5 kcal/mol. The dissociation rates of Mn²⁺ from the adenine ring are also estimated from proton T₂ values below 50°C.     

The chemical composition of throughfall beneath oak, birch and pine canopies in Northwest Germany

The chemical composition of rainwater is altered upon its passage through tree canopies. In order to investigate how rainwater chemistry is affected by canopy-dependent processes in characteristic forest types of Northwest German sandy lowland regions – oak–birch-forests, Betula pubescens Ehrh. swamp forests, and stands of Pinus sylvestris L. – comparative studies on the chemical composition of throughfall were carried out at seven forest sites, situated in close proximity within a nature reserve. Additionally, rainwater was sampled at three heathland sites for analysis of open-field precipitation and at three sites along an oak–birch-forest edge. Throughfall concentrations of most of the parameters analysed were significantly higher than open-field concentrations, especially with regard to electric conductivity, NH₄-N, K⁺, and KMnO₄-index. Ion concentrations in throughfall were the lowest in a 10-year-old stand of Betula pendula Roth. and Pinus sylvestris and in a Betula pubescens swamp forest and were highest beneath a stand of Pinus sylvestris. Except for Na⁺, Cl⁻, and NO₃⁻, ion concentrations in both throughfall and open-field precipitation increased during the growing season (May–October). In throughfall, Ca²⁺, Mg²⁺, K⁺, and Mn²⁺ were strongly correlated. Enrichment ratios between throughfall and open-field deposition varied among sites and elements and were the highest for K^‰+, Mg^2‰+, and Mn^2‰+. Estimates of canopy leaching indicated high leaching rates of K^‰+ and Mn^2‰+ and moderate leaching of Mg^2‰+. The contribution of foliar leaching to throughfall deposition was higher at the deciduous than at the coniferous stands.