Interaction of water with the regenerated cellulose membrane studied by DSC

One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation processes. A large amount of non-freezable strongly bounded water was also detected. Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected during the first, the second and the third heating. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calculations of D‐wave bound states and resonance states of the screened helium atom using correlated exponential wave functions

We have investigated the effects of screened Coulomb (Yukawa) potentials on the bound ^1,3D states and the doubly excited ^1,3 D^e resonance states of helium atom using highly correlated exponential basis functions. The Density of resonance states are calculated using stabilization method. Highly correlated exponential basis functions are used to consider the correlation effect between the charged particles. A total of 18 resonances (nine each for ¹ D^e and ³ D^e states) below the n = 2 He ⁺ threshold has been calculated. For each spin states, this includes four members in the 2pnp series, three members in the 2snd series, and two members in 2pnf series. The resonance energies and widths for various screening parameters ranging from infinity to a small value for these ^1,3 D^e resonance states are reported along with the bound‐excited 1s3d ^1,3 D state energies. Overall behavior of the spectral profile of 1s3d ¹D state of helium atom due to electron‐electron and electron‐nucleus screening are also presented. Accurate resonance energies and widths are also reported for He in vacuum. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

气相色谱-质谱法检测沉积物中自由态与束缚态多溴联苯醚和四溴双酚-A

建立了一种同时测定沉积物中不同赋存形态的多溴联苯醚(PBDEs)和四溴双酚A(TBBPA)的分析方法.样品由等体积的丙酮和正己烷混合溶剂抽提得到自由态目标物,再通过碱性水解反应释放束缚态目标化合物.通过调节酸度(pH值)实现PBDEs和TBBPA的分离和提取.PBDEs由复合硅胶柱净化,运用气相色谱-质谱(负离子化学源)-分时段选择离子监测技术测定;TBBPA经重氮甲烷衍生化反应后由酸性硅胶柱预纯化,运用气相色谱-质谱(电子轰击源)-分时段选择离子监测技术测定.8种低溴联苯醚(BDE28,-47,-66,-100,-99,-154,-153,-183),十溴联苯醚(BDE209)和TBBPA的检出限分别为0.6～12.5 pg/g,172 pg/g,4 2 pg/g.方法具有良好的准确度和精确度,回收率均在74%～106%之间,RSD≤10%.对东江沉积物样品的分析表明,本方法能够实现不同形态的PBDEs 和TBBPA的有效检测.     

Calorimetric approach to tetronic/water interactions

Tetronic^®comprises X-shaped copolymers formed by four poly(propylene oxide) (PPO) andpoly(ethylene oxide) (PEO) block chains bonded to an ethylene diamine centralgroup. Micellization behaviour of three representative Tetronics (T304, T904and T1307) was characterized to gain an insight into the interactions betweenthe copolymer unimers and the state of water in their solutions. The enthalpyof demicellization, recorded at 37°C in an isoperibol microcalorimeter,indicated that the process was in all cases exothermic and the enthalpy rankedin the order T1307≥T904>>T304. Micellization is entropy-driven owing tohydrophobic interactions between the PPO chains.DSC analysisshowed that the crystallization and melting peaks of the free water remainingin T304 and T904 solutions were progressively shifted toward lower temperaturesas the surfactant proportion increased, owing to a colligative effect. Boundwater corresponded to 3 water molecules per EO repeating unit. In the caseof T1307, which has longer PEO chains, a splitting of the melting peak wasobserved, one peak appearing around 0°C due to free water and anotherat –15°C due to interfacial water. As T1307 proportion raised, theenthalpy of the former decreased, whilst the enthalpy of the latter increased.In 40% T1307 solutions, interfacial water overcame the proportion of freewater; there being 1 interfacial and 3 bound water molecules per EO repeatingunit. Gaussian deconvolution of FTIR spectra also enabled to characterizethe evolution of free water as a function of Tetronic proportion. The dependenceof micellization and water interaction behaviour on Tetronics structure shouldbe taken into account to use these copolymers as drug solubilizers and micellarcarriers.     

NANOMECHANICAL MAPPING OF CARBON BLACK REINFORCED NATURAL RUBBER BY ATOMIC FORCE MICROSCOPY

Atomic force microscopy （AFM） has the advantage of obtaining mechanical properties as well as topographic information at the same time. By analyzing force-distance curves measured over two-dimensional area using Hertzian contact mechanics, Young＇s modulus mapping was obtained with nanometer-scale resolution. Furthermore, the sample deformation by the force exerted was also estimated from the force-distance curve analyses. We could thus reconstruct a real topographic image by incorporating apparent topographic image with deformation image. We applied this method to carbon black reinforced natural rubber to obtain Young＇s modulus distribution image together with reconstructed real topographic image. Then we were able to recognize three regions; rubber matrix, carbon black （or bound rubber） and intermediate regions. Though the existence of these regions had been investigated by pulsed nuclear magnetic resonance, this paper would be the first to report on the quantitative evaluation of the interfacial region in real space.     

Enthalpic effect of polyacrylonitrile on the concentrated solutions in dimethyl sulfoxide: Strong thixotropic behavior and formation of bound solvents

The effect of dipole–dipole interaction by nitrile groups of PAN on the bound state of solvent molecules and the concentrated solution properties in DMSO was investigated. Variation of a solution viscosity exhibited three overlap concentrations, C1*, C2*, and C3*, at 2.7, 8.6, and 16.3 wt%, respectively, representing the transition of concentration regions in the order of dilute, unentangled‐semi dilute, entangled‐semi dilute, and concentrated regions. The two‐dimensional mapping of FT‐IR analysis and dielectric measurement confirmed that the intermolecular interaction of PAN was suddenly enhanced at the C*s, inducing polarization to DMSO. In the ice‐melting process of PAN solutions, two different melting peaks (T_m2 and T_m3) of DMSO newly appeared at each C2* and C3*, suggesting the different types of bound solvents. In the concentrated solutions, the saturated dielectric constant and the strongly delayed evaporation of the solvent even at the boiling point of DMSO along with strong thixotropic behavior were indicative of the stronger confinement state of bound DMSO than in the semidilute solutions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1080–1089     

Thermal behavior of short-range-order in quenched Cu-12 at% Mn assessed by DSC

Summary The ordering behavior of quenched Cu-12 at% Mn was investigated by differential scanning calorimetry (DSC) under increasing temperature conditions. The ordering process can be better explained in terms of a homogeneous short-range-order (SRO) rather than a disperse-short-range-order (DSRO) model as for concentrated Cu-γMn solid solutions. At the employed high quench rates ordering is established in one stage here termed stage 1, assisted by excess vacancies. This stage obeys a first order kinetics law, being the effective activation energy consistent with a weighed average sum of the activation energy for migration of free and bound vacancies. An estimated solute-vacancy binding energy of 15 kJ mol^-1 seems quite reasonable for this alloy together with the assessed activation energy for complex migration of 92.6 kJ mol^-1. By adopting a first SRO order parameter based in quasi-chemical theory in pair approximation and using boundary values calculated from displayed features of DSC traces, the retained degree of quenched-in order at room temperature was calculated. This procedure also enabled to estimate an ordering energy of -2.7 kJ mol^-1. The effect of quenching temperature demonstrate that for smaller vacancy sink densities, the retained degree of order at room temperature goes through a minimum.     

Effects of DNA secondary structure on oligonucleotide probe binding efficiency

Secondary structure motifs in nucleic acid probes generally impair intended hybridization reactions and so efforts to predict and avoid such structures are commonly employed in probe design schemes. Another key facet of probe design that has received much less attention, however, is that secondary structure at targeted probe binding site regions may also impair hybridization. Thus, evaluation of both probe and target site secondary structures together should improve hybridization prediction and design effectiveness. Several challenges confound this goal, including imperfect empirical rules and parameters underlying predictions and the fact that folding algorithms scale poorly with respect to sequence length. Here, we attempt to quantify the consequences of target site structure on predicted hybridization using sequences sampled from the human genome. We also provide a methodology for choosing a reasonable “window size” around target sites that is as small as possible without compromising folding algorithm prediction accuracy.     

Theoretical study of reaction channels for the weakly bound complex systems created with HF,CO2, and various amines

This investigation conducted reaction channels of weakly bound complexes CO₂…HF, CO₂…HF…NH₃, CO₂…HF…NH₂CH₃, CO₂…HF…NH(CH₃)₂, and CO₂…HF…N(CH₃)₃ systems, using the Gaussian 98 package at the B3LYP/6‐311++G(3df,2pd) level. The syn‐fluoroformic acid or syn‐fluoroformic acid plus NH₃ or amine conformers are more stable than the related anti‐fluoroformic acid or anti‐fluoroformic acid plus NH₃ or amine conformers. However, the above‐mentioned weakly bound complexes are more stable than both the related syn‐ and anti‐type fluoroformic acid or acid plus NH₃ or amine conformers and their related decomposed into CO₂ + HF or CO₂ + NHR₃F (R?H, CH₃) combined molecular systems. Five reaction channels of the weakly bound complexes exist. Each channel includes weakly bound complexes and their related above‐mentioned systems. Moreover, each reaction channel contains two transition states. The transition state between the weakly bound complex and anti‐fluoroformic acid type structure (T₁₃) is significantly higher than that of internal rotation (T₂₃) between syn‐ and anti‐FCO₂H (or FCO₂H…NR₃) structures. However, the above‐mentioned T₁₃ can significantly decrease its energy by adding the third molecule NH₃ or NR₃ (R?H or CH₃). The more CH₃ that is substituted in NR₃ of the reaction channel, the lower the activation energy of the transition state in the system is affected. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

吉林某弹药销毁场土壤炸药污染调查及其赋存状态研究

研究吉林某军事弹药销毁场土壤炸药污染程度以及炸药在土壤中的赋存状态,为炸药和重金属污染土壤修复提供针对性策略。采集了某弹药销毁厂焚烧销毁区表层土壤样品,分析了其理化性质和常见重金属元素含量,测试了土壤全样和不同颗粒度土壤样品中炸药污染物的含量,并结合热重-傅里叶变换红外光谱(TGA-FTIR) 对炸药污染土壤样品热力学行为的表征,探讨了炸药污染物的赋存状态,炸药和重金属组合污染特征等。土壤中含有高浓度的TNT、DNT、ADNT、RDX等炸药污染物及其降解产物,并表现出土壤细颗粒富集趋势,其中土壤全样中TNT总浓度达到了1.66×104 mg·kg-1,远远高于EPA推荐的土壤TNT指导限值,RDX超过了以土壤环境为目标的指导限值;销毁活动还造成了土壤中Pb、Cu、Zn重金属浓度的升高,分别为400 mg·kg-1,318 mg·kg-1,1030 mg·kg-1。土壤中受到重金属和有机质等因素的影响,土壤中经过长期老化的炸药污染物的热解行为明显不同于自由态的炸药分子,热解温度升高、过程延长。在销毁区炸药污染土壤的修复中,应加强炸药污染物与重金属相互作用的研究,并在修复治理实践中采取协同修复的策略。