Polyelectrolyte multilayers on wood fibers: influence of molecular weight on layer properties and mechanical properties of papers from treated fibers

This paper compares the influence of the molecular weight of polylelectrolytes forming polyelectrolyte multilayers (PEM) on wood fibers on adhesion and paper strength. Sheets were made from fibers treated with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) of molecular mass 70,000 and 240,000, respectively, and of poly(dimethyldiallylammonium chloride) (PDADMAC)/poly(styrene sulfonate) (PSS) of molecular mass 30,000 and 80,000, respectively. The results were compared to what has recently been reported for PEM formation on fibers using a low-molecular-mass combination of PAH and PAA and a high-molecular-mass combination of PDADMAC/PSS. There was a less significant improvement in the case of the low-molecular-mass PDADMAC/PSS and the high-molecular-mass PAH/PAA. The adsorbed amounts of PAH and PDADMAC were also determined, showing a lower adsorbed amount of the low-molecular-mass PAH than of the high-molecular-mass PDADMAC. The amount of low-molecular-mass PDADMAC was similar to that found for high-molecular-mass PDADMAC/PSS. Individual fibers were partly treated and studied, showing a less significant decrease in wettability with low-molecular-mass PDADMAC/PSS than with the high-molecular-mass combination. The effect of the molecular weight on the adhesion was discussed in terms of the structure and wettability of the PEMs.     

Electrochemical behaviors of native and thermally denatured fish DNA in the presence of cytosine derivatives and porphyrin by cyclic voltammetry using boron-doped diamond electrode

The electrochemical behaviors of native and thermally denatured fish DNA was investigated using boron-doped diamond (BDD) film electrode by cyclic voltammetry. The BDD electrode afforded us to measure weak current less than muA for the DNA solution in 100 microl. The mixture of acetic acid and sodium acetate solution (0.2 M) was used as a supporting electrolyte. Two oxidation peaks were observed at about +1.1 V and +1.3 V at pH 4.6 for thermally denatured fish DNA. This is due to the oxidation of guanine and adenine in the denatured fish DNA, respectively. In contrast, the native fish DNA showed ill-defined peaks at +1.1 V. Furthermore, the electrochemical behaviors of thermally denatured fish DNA were studied in the presence of cytosine, cytidine, cytidine-5-monophosphate, tetrakis(1-methypyridinium-4-yl)porphyrin (H(2)(TMPyP)(4+)) and Ru(II)(TMPyP)(4+). The oxidation peak intensity at +1.1 V gradually decreased with the increase of the concentrations of the above compounds. Based on the above studies, electrochemical behaviors of the thermally denatured fish DNA at BDD electrode is discussed.     

Electrochemical behavior of DNA at a silver electrode studied by cyclic and elimination voltammetry

Electrochemical characteristics of native and denatured calf thymus DNA have been studied by voltammetry on a silver electrode (AgE). Experimental results obtained from linear sweep or cyclic voltammetry (LSV or CV) have been employed in elimination voltammetry. The elimination voltammetry with linear scan (EVLS), using the linear combination of the total currents measured at different scan rates, enables one or two selected particular currents to be eliminated. The best results have been obtained by using a function eliminating the kinetic and charging currents (I(k),I(c)), and conserving the diffusion current (I(d)). This function makes it possible to increase significantly voltammetric signals of native and denatured DNAs, and to reveal processes not detectable by conventional electrochemical methods. The influence of electrochemical pretreatment of silver electrode surfaces and of starting and switching potentials on DNA voltammetric signals have been discussed. Silver electrodes coupled with elimination voltammetry represent promising tools for developing new nucleic acids biosensors.     

Highly sensitive,stretchable and durable strain sensors based on conductive double-network polymer hydrogels

Hydrogel-based strain sensors have been attracting immense attention for wearable electronic devices owing to their intrinsic soft characteristics and flexibility. However, developing hydrogel sensors with hightensile strength, stretchability, and strain sensitivity remains a great challenge. Herein, we report a technique to synthesize highly sensitive hydrogel-based strain sensors by integrating carbon nanofibers (CNFs) with a double-network (DN) polymer hydrogel matrix comprising of a physically cross-linked agar network and a covalently cross-linked polyacrylamide (PAAm) network. The resultant nanocomposite sensors display superior piezoresistive sensitivity with a hightrue gauge factor (GF_T = 1.78) at an ultrahigh strain of 1,000%, a fast response time and linear correlation of ln(R/R₀) and ln(L/L₀) up to 1,000% strain. Most significantly, these sensors possess highmechanical strength (~0.6 MPa) and superb durability (>1,000 cycles at strain of 100%), stemming from the effective energy dissipation mechanism of the first agar network acting as sacrificial bonds and the CNFs serving as dynamic nanofillers. The combination of highstrain sensitivity and ultrahigh stretchability of hydrogel sensors makes it possible to sense both small mechanical deformations induced by human motions and large strain up to 1,000%.     

The application of size exclusion chromatography to the analysis of biopolymers

High performance size exclusion chromatography (HPSEC), employing microparticulate, hydrophilic, surface-modified silicas or hydrophilic, cross-linked, organic polymers and buffered eluents, is an effective means of separating native and denatured proteins of molecular weights in the 10 000–500 000 range. HPSEC can be further used for molecular weight identification, and the fractionation and isolation of proteins.     

交联聚(N-异丙基丙烯酰胺)/(海藻酸钠/聚(N-异丙基丙烯酰胺))半互穿网络水凝胶的制备及其溶胀性能

将线性聚(N-异丙基丙烯酰胺)(PNIPAAm)和海藻酸钠(SA)分子同时引入到PNIPAAm凝胶中,制备了交联聚(N-异丙基丙烯酰胺)/(海藻酸钠/聚(N-异丙基丙烯酰胺))半互穿网络(Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN)水凝胶。在弱碱性条件下(pH=7.4),改变SA与线性PNIPAAm的质量比对Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN水凝胶的溶胀度没有太大的影响。在酸性条件下(pH=1.0),其溶胀度随着SA与线性PNIPAAm质量比的减小而增大。由于亲水性SA与线性PNIPAAm的协同作用,Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN水凝胶的消溶胀速率得到很大提高。     

Fabrication of poly(ethylene glycol) hydrogel microstructures using photolithography

The fabrication of hydrogel microstructures based upon poly(ethylene glycol) diacrylates, dimethacrylates, and tetraacrylates patterned photolithographically on silicon or glass substrates is described. A silicon/silicon dioxide surface was treated with 3-(trichlorosilyl)propyl methacrylate to form a self-assembled monolayer (SAM) with pendant acrylate groups. The SAM presence on the surface was verified using ellipsometry and time-of-flight secondary ion mass spectrometry. A solution containing an acrylated or methacrylated poly(ethylene glycol) derivative and a photoinitiator (2,2-dimethoxy-2-phenylacetophenone) was spin-coated onto the treated substrate, exposed to 365 nm ultraviolet light through a photomask, and developed with either toluene, water, or supercritical CO2. As a result of this process, three-dimensional, cross-linked PEG hydrogel microstructures were immobilized on the surface. Diameters of cylindrical array members were varied from 600 to 7 micrometers by the use of different photomasks, while height varied from 3 to 12 micrometers, depending on the molecular weight of the PEG macromer. In the case of 7 micrometers diameter elements, as many as 400 elements were reproducibly generated in a 1 mm2 square pattern. The resultant hydrogel patterns were hydrated for as long as 3 weeks without delamination from the substrate. In addition, micropatterning of different molecular weights of PEG was demonstrated. Arrays of hydrogel disks containing an immobilized protein conjugated to a pH sensitive fluorophore were also prepared. The pH sensitivity of the gel-immobilized dye was similar to that in an aqueous buffer, and no leaching of the dye-labeled protein from the hydrogel microstructure was observed over a 1 week period. Changes in fluorescence were also observed for immobilized fluorophore labeled acetylcholine esterase upon the addition of acetyl acholine.     

Theoretical study of the cosolvent effect on the partial molar volume change of staphylococcal nuclease associated with pressure denaturation

We explain the molecular mechanism of the effect of urea and glycerol cosolvents on the partial molar volume (PMV) change associated with the pressure denaturation of staphylococcal nuclease (SNase) protein recently observed in experiments. Native and denatured conformations of SNase are produced by using molecular dynamics simulations in water, and the PMV is obtained from the integral equation theory of molecular liquids called 3D-RISM, which is based on statistical mechanics. The PMV of the native SNase in water predicted by 3D-RISM theory is in good agreement with experiment. The PMV changes associated with pressure denaturation in water and in water-urea and water-glycerol mixtures are qualitatively reproduced. By analyzing the results obtained, we found two interesting cosolvent effects on the PMV: (1) both urea and glycerol cosolvents increase the PMVs of both native and denatured SNase compared to those in water and (2) both urea and glycerol cosolvents increase the PMV of denatured SNase more than that of native SNase. We also showed that these two observations can be explained in terms of the thermal volume, which is related to the packing effect of solvent molecules.     

Analysis of cross-linked human hemoglobin by conventional isoelectric focusing, immobilized pH gradients, capillary electrophoresis, and mass spectrometry.

Diaspirin cross-linked hemoglobin (DCLHb), a hemoglobin-based oxygen carrier exhibiting near physiological oxygen binding capability and devoid of nephrotoxic side effects, was previously found, by gel permeation, reversed-phase high performance liquid chromatography (RP-HPLC) and mass spectrometry, to consist of ca. 94% cross-linked product (reacted on the Lys 99 of two alpha-chains), accompanied by ca. 6% cross-linked Hb, which also reacted on the Lys 132 and/or Lys-144 of the beta-chains and a small amount of intermolecularly cross-linked dimers. However, conventional isoelectric focusing in carrier ampholyte buffers (CA-IEF) gave an unexpected spectrum of four major, almost equally represented, pI species in the pH range of 6.82-7.01, a band of mid-intensity with a pI of 7.11, and two minor components with pls of 6.73 and 6.77. This extraordinary polydispersity was reevaluated by other surface charge probes, such as immobilized pH gradients (IPG) and capillary zone electrophoresis (CZE) of native and denatured globin chains. IPGs of DCLHb gave the expected spectrum of bands, consisting of a main component (92%) with pl 7.337 and three additional minor bands, with lower pIs, representing ca. 8% of the total. These data were in agreement with CZE profiles of native DCLHb, which resolved, in addition to the main DCLHb peak, 3-4 minor components representing ca. 10% of the total. Also, CZE of denatured, heme-free globin chains gave the expected pattern with only traces of minor, extrareacted species. The latter technique, in addition to resolving alpha- and beta-globin chains in a 1:1 ratio in control Hb, resolved a free beta- and the alpha-alpha-dimer in DCLHb. In a 1:1 mixture of control and DCLHb, three peaks were observed, eluting in the order alpha-, alpha-alpha- and beta-globin chains. The identity of the major DCLHb and of the minor species was ascertained by mass spectrometry.     

Calorimetric Study of the Glass Transition Process in Humid Proteins and DNA

By method of differential scanning calorimetry the absolute values of heat capacity for the systemwater–biopolymer (globular and fibrillar proteins and DNA) were measured in a wide range of temperatures (from -30 up to 130°C) and concentrations of proteins both in native and denatured states. Thermal properties of humid denatured biopolymers demonstrate a characteristic anomaly in the form of the heat capacity jump at temperature depending on the bound water content. It has been shown that in the systems studied a glass transition, where water serves as a native plasticizer, is observed. It has been established that the S-shaped character of all heat capacity curves obtained on dehydration for native and denatured biopolymers is due to the gradual transition to the glassy state of both native and denatured samples. It was found that thermally denatured humid small globular proteins at subsequent dissolving in water at room temperature are able to restore their native structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

阳离子型聚乙烯吡咯烷酮的制备及其负载RNA性能

将二甲基二烯丙基氯化铵（DADMAC）与乙烯吡咯烷酮（VP）共聚得到阳离子型的聚乙烯吡咯烷酮（CPVP）,并分别合成了聚二甲基二烯丙基氯化铵（PDADMAC）和聚乙烯吡咯烷酮（PVP）均聚物,用粘度法测定了三者的粘均相对分子质量,用红外光谱表征了其结构。 将合成的CPVP与核糖核酸（RNA）以不同比例混合,研究CPVP负载RNA的能力,并与PDADMAC及PVP的负载性能做比较。 结果发现,与PDADMAC及PVP相比,当CPVP与RNA按质量比2∶1混合时,形成的复合体纳米粒的平均粒径约为300 nm,分散度指数为0.0966,粒径分布较窄。     

羧甲基纤维素钠/聚(N-异丙基丙烯酰胺)纳米复合水凝胶的制备及结构性能表征

以无机粘土为交联剂制备了具有温度、pH双重敏感特性的羧甲基纤维素钠/聚(N-异丙基丙烯酰胺)/粘土半互穿网络纳米复合水凝胶(CMC/PNIPA/Clay semi-IPN),并通过红外和透射电镜对其结构和形态进行了表征。在酸性(pH=1.2)和20℃条件下,分别研究了温度和不同pH缓冲液对该凝胶溶胀度的影响,测定了复合水凝胶的力学性能。结果表明:水凝胶中的粘土被剥离成单片层,且均匀分散在凝胶网络中,起交联剂的作用,而CMC以线性大分子的形态存在;CMC/PNIPA/Clay具有良好的温度、pH双重敏感特性;凝胶的断裂伸长率>1 000%。     

Polyelectrolyte complexes formed by poly(diallyl-N,N-dimethylammoniumchloride) and oligo(dextransulphate)

Polyelectrolyte complexes of poly(diallyl-N,N-dimethylammoniumchloride) (PDADMAC) and dextransulphate (DexSul) were formed and characterised. The complex stöchiometry found is 2:1. It depends neither on the PDADMAC molar mass nor on the DexSul molar mass. The degree of complexation is smaller than one and depends on the concentration of the added low molecular salt. The complexes behave like salts. In solution we have a solute and a solid phase. This equilibrium can be disturbed by changing the low molecular salt concentration.     

Electrochemical investigation of nucleic acid behaviour: Part I. Native calf thymus DNA

The polarographic behaviour of DNA extracted from the calf thymus has been studied using phase sensitive a.c. polarography. The conditions of adsorption on the dropping mercury electrode have been studied in terms of the conditions of medium (ionic strength, pH) and of the molecular weight of DNA. The ionic strength plays a deciding role in the conditions of adsorption. The adsorption also depends on the form of the macromolecule. When it is in rod form (low molecular weight) the adsorption occurs parallel to the charged surface. When it adopts a wormlike form, loops are formed which extend into the solution. The adsorption does not depend on the nature of the monovalent counterion thus the adsorption is identical in Na⁺ and NH₄⁺ media.The polarograms of native and denatured DNA present an initial rounded peak situated at the limit of the adsorption zone. The native DNA is characterised by a second peak which appears, whatever the medium and the molecular weight of the DNA may be, on the recordings of the in-phase component of the current. This peak is situated at a more positive potential than that which is normally characteristic of the denatured DNA.The characteristics of the peaks of the native DNA have been specified. The first peak corresponds to the desorption of a certain number of adsorbed elements of the macromolecule. The second peak changes its properties according to the pH. In a slightly acid medium, it corresponds to the reduction of the adsorbed bases without desorption of the reduced products. The zones of reduction are the locally destabilized, i.e. the A-T rich regions of the DNA. In alkaline medium it corresponds to the desorption of the macromolecule. A general schema of the behaviour of native DNA on the dropping mercury electrode is proposed.     

Electrochemical analysis of the self-complementary B-DNA decamer d(CCAGGCCTGG)

The self-complementary decamer d(CCAGGCCTGG), native and denatured calf thymus DNAs were studied by means of differential pulse polarography with the DME and by cyclic voltammetry with the HMDE. The decamer (which represents one turn of the DNA double helix in the B form) produced cathodic and anodic signals similar to those yielded by high-molar mass DNAs. By measuring the anodic peak (due to guanine residues), it was possible to detect the decamer at subnanomolar concentrations by adsorptive stripping cyclic voltammetry at relatively short waiting times. The high sensitivity of the electrochemical analysis for small changes in the DNA double helix observed earlier in high-molar mass DNAs, together with the low requirements for the amount of the analyzed decamer sample, suggest that electrochemical techniques may become useful also in oligonucleotide studies.     

二(2-苯并咪唑亚甲基)胺合铜(II)配合物与DNA作用方式的光谱研究

应用紫外、荧光、黏度等方法, 对二(2-苯并咪唑亚甲基)胺合铜(II)配合物与小牛胸腺DNA作用方式进行了研究. 配合物与DNA作用时, 使紫外吸收明显减色, 荧光降低, 黏度降低; Scatchard图表明配合物对溴化乙锭(EB)与DNA的结合为非竞争性抑制. 实验结果表明, 配合物与DNA作用方式可能为静电结合.     

Polyion interchange reactions of interpolyelectrolyte complexes in aqueous solutions and gels

Cooperative coupling reaction between two opposite charged polyelectrolytes results in formation of polyelectrolyte complexes (IPEC). This reaction is very fast and diffusion controlled. Whether IPECs formed by linear polyions are soluble or limitary swellable in aqueous media is decided by their composition, namely, by a ratio of oppositely charged polyions as well as by a water phase composition (the nature and the concentration of a simple salt, pH, the presence and the concentration of organic additives etc.). The most important intrinsic property of IPECs is their ability to participate in interchange (exchange and substitution) reactions with competing polyions. The kinetics and the position of equilibria in these reactions are controlled by the low molecular salt concentration, the nature of small counterions, DP of interaction polyelectrolytes, as well as by their linear charge density. IPECs can be formed also by interacting linear and opposite charged networks. It is shown that linear polyelectrolytes dissolved in aqueous solution can penetrate unexpectedly fast into oppositely charged cross-linked polyelectrolyte gels to form “snake-in-cage” composites representing IPECs of corresponding polyion segments. It is proved that the mechanism consists in “relay-race” transfer of linear polyion segments from one segment of the polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. The driving force for the fast transport of linear polyions into the gel is produced by coupling reaction between two polyelectrolytes proceeding on solution/gel interface.     

Hydration of thermally denatured lysozyme studied by sorption calorimetry and differential scanning calorimetry

We have studied hydration (and dehydration) of thermally denatured hen egg lysozyme using sorption calorimetry. Two different procedures of thermal denaturation of lysozyme were used. In the first procedure the protein was denatured in an aqueous solution at 90 degrees C, in the other procedure a sample that contained 20% of water was denatured at 150 degrees C. The protein denatured at 90 degrees C showed very similar sorption behavior to that of the native protein. The lysozyme samples denatured at 150 degrees C were studied at several temperatures in the range of 25-60 degrees C. In the beginning of sorption, the sorption isotherms of native and denatured lysozyme are almost identical. At higher water contents, however, the denatured lysozyme can absorb a greater amount of water than the native protein due to the larger number of available sorption sites. Desorption experiments did not reveal a pronounced hysteresis in the sorption isotherm of denatured lysozyme (such hysteresis is typical for native lysozyme). Despite the unfolded structure, the denatured lysozyme binds less water than does the native lysozyme in the desorption experiments at water contents up to 34 wt %. Glass transitions in the denatured lysozyme were observed using both differential scanning calorimetry and sorption calorimetry. Partial molar enthalpy of mixing of water in the glassy state is strongly exothermic, which gives rise to a positive temperature dependence of the water activity. The changes of the free energy of the protein induced by the hydration stabilize the denatured form of lysozyme with respect to the native form.     

STUDIES ON THE PHOTO-C4-CYCLO-ADDITION REACTIONS BETWEEN SKIN-PHOTOSENSITIZING FUROCOUMARINS AND NUCLEIC ACIDS*

Abstract— Among the natural or synthetic furocoumarins (psoralens) a group exists which has interesting biological properties, the best known of which is skin-photosensitization. The mechanism of action has remained unclarified for a long time. Furocoumarins lack photooxidative properties; they act by a mechanism that does not require oxygen and are therefore different from photodynamic substances. Photosensitizing furocoumarins when irradiated at 365 nm react with nucleic acids to give a C₄-cyclo-addition to the 5,6-double bond of the pyrimidine bases engaging their 3,4- or 4‵,5‵-double bond. Differences exist in the behaviour of the various furocoumarins; psoralen reacts equally well with native DNA, with denatured DNA and with RNA, whereas bergapten, xanthotoxin and 8-methylpsoralen at room temperature react to a much greater extent with native DNA than with denatured DNA and with RNA. A temperature effect has also been observed. In the case of native DNA an intercalation, occurring in the dark, of furocoumarins between two adjacent base pairs of the double helix is suggested as the first step in the reaction. The photoreaction is not accompanied by breaks in the polynucleotide chain or by conformational modifications of the macromolecule. A parallelism was observed between the order of activity of the substances of this group for photoreaction with native DNA and for skin-photosensitization. Ehrlich ascites tumor cells lose completely their capacity of transmitting the tumor after irradiation in the presence of psoralen, bergapten and xanthotoxin. By hydrolysis of DNA extracted from Ehrlich ascites tumor cells irradiated in the presence of psoralen a photoadduct between psoralen and thymine was isolated.     

Thermoresponsive behavior of poly(n-isopropylacrylamide) hydrogels containing gold nanostructures

We report the changes in the structure and thermoresponsive behavior of poly(N-isopropylacrylamide) (PNIPAm) hydrogels when gold nanostructures are synthesized in situ within the hydrogel matrix. Cross-linked PNIPAm hydrogels were synthesized using NIPAm and 0.00-3.50% (w/w versus NIPAm) of N,N'-methylenebisacrylamide (MBAm) and/or N,N'-cystaminebisacrylamide (CBAm) as cross-linking agents. The hydrogels were soaked in potassium tetrachloroaurate to introduce gold ions. The hydrogels containing Au3+ were then immersed in a sodium borohydride solution to reduce the gold ions. Infrared spectroscopy, UV-visible spectroscopy, and equilibrium swelling were used to examine the structural/physical differences between gels of different compositions; UV-visible spectroscopy and mass measurements were used to observe the kinetics and thermodynamics of the hydrogel volume phase transition. These studies revealed several differences in the physical characteristics and thermoresponsive behavior of hydrogels based on cross-linker identity and the presence or absence of gold nanostructures. Hydrogels with gold nanostructures and high CBAm and low MBAm content have equilibrium swelling masses 3-20 times their native analogues. In comparison, gold-containing hydrogels with high MBAm and low CBAm content have swelling masses that are equal to their native analogues. Additionally, the gold-containing PNIPAm hydrogels cross-linked with only CBAm have a deswelling temperature of approximately 40 degrees C, approximately 8 degrees C above the samples cross-linked with only MBAm. Varying the CBAm content and introducing gold enables tuning of the deswelling temperature.