Intramolecular bonding in a statistical associating fluid theory of ring aggregates

The first-order thermodynamic perturbation theory of Wertheim (TPT1) is extended to treat ring aggregates, formed by inter- and intramolecular association. The expression for the residual association contribution to the Helmholtz free energy for ring aggregates, incorporating the appropriate terms in Wertheim's fundamental graph sum of the TPT1 density expansion, is derived to calculate the distribution of the molecular bonding states. This requires the introduction of two new parameters to characterise each possible ring type: the ring size τ, which is equal to one in the case of intramolecular association, and a parameter W that captures the likelihood of two ring-forming sites bonding. The resulting framework can be incorporated in equations of state that account for the residual association contribution to the free energy, such as the statistical associating fluid theory (SAFT) family, or the cubic plus association (CPA) equation of state. This extends the applicability of these equations of state to mixtures with an arbitrary number of association sites capable of hydrogen bonding to form intramolecular and intermolecular rings. The formalism is implemented within SAFT-VR Mie to calculate the fluid-phase equilibria of model chain-like molecules containing two associating sites A and B, allowing for the formation of open-chain aggregates and intramolecular bonds. The effect of adding a second component that competes for the association sites that mediate intramolecular association in the chain is also examined. Accounting for intramolecular bonding is shown to have a significant impact on the phase equilibria of such systems.     

A study of the headgroup motion of sphingomyelin using 31P NMR and an analytically soluble model

A 31P NMR investigation has been carried out of the headgroup dynamics of sphingomyelin molecules in bilayers for the L alpha and L beta' phases. The resulting line shapes have been analysed in terms of a reduced-parameter model, using van Faassen's method for obtaining an analytic solution to first-order stochastic differential equations to simulate the line shapes of oriented and non-oriented samples. Our treatment results in good fits to measured data but using fewer parameters than traditional methods. Angles and correlation times (tau parallel and tau perpendicular) describing the geometry and dynamics of the headgroup are obtained by optimising the agreement between simulated and experimental data. The results are contrasted with those obtained for the lecithins DMPC and DPPC using a similar analysis. Not only are tau parallel and tau perpendicular now equal in value for the L alpha phase, but this value is also found to be nearly four times larger than the longest correlation time for the lecithins. We interpret this as evidence of inter- and intramolecular hydrogen bonding in the L(alpha) phase of sphingomyelin. In the L beta' phase of sphingomyelin, however, although tau(parallel) and tau(perpendicular) remain equal their value is now 32% smaller than that of the lecithins in the same phase. This indicates less difference between the fluidities in the headgroup region of the two phases of sphingomyelin as compared to that of the lecithins. Another significant difference between the L beta' phases is that the tilt angle for sphingomyelin is found to be nearly twice as large as for the lecithins. We argue that these combined observations point to the existence of hydrogen bonding in this phase also. Again in contrast to our previous work on lecithins, our results provide evidence of a negative diamagnetic anisotropy in sphingomyelin molecules, even in the L beta' phase. This is provided for in our model by the assumption that our unoriented samples consist of prolate ellipsoidal liposomes whose major axes are oriented parallel to the static magnetic field. The apparently different diamagnetic behaviour of sphingomyelin in the present work is due to the higher static field used rather than any intrinsic difference in this respect between sphingomyelin and the lecithins DMPC and DPPC.     

Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

Thermoelectric materials have attracted significant research interest in recent decades due to their promising application potential in interconverting heat and electricity. Unfortunately, the strong coupling between the material parameters that determine thermoelectric efficiency, i.e., the Seebeck coefficient, electrical conductivity, and thermal conductivity, complicates the optimization of thermoelectric energy converters. Main‐group chalcogenides provide a rich playground to alleviate the interdependence of these parameters. Interestingly, only a subgroup of octahedrally coordinated chalcogenides possesses good thermoelectric properties. This subgroup is also characterized by other outstanding characteristics suggestive of an exceptional bonding mechanism, which has been coined metavalent bonding. This conclusion is further supported by a map that separates different bonding mechanisms. In this map, all octahedrally coordinated chalcogenides with good performance as thermoelectrics are located in a well‐defined region, implying that the map can be utilized to identify novel thermoelectrics. To unravel the correlation between chemical bonding mechanism and good thermoelectric properties, the consequences of this unusual bonding mechanism on the band structure are analyzed. It is shown that features such as band degeneracy and band anisotropy are typical for this bonding mechanism, as is the low lattice thermal conductivity. This fundamental understanding, in turn, guides the rational materials design for improved thermoelectric performance by tailoring the chemical bonding mechanism.     

LTCC基板金丝热超声楔焊正交试验分析

引线键合是微组装技术中的关键工艺,广泛应用于军品和民品芯片的封装。特殊类型基板的引线键合失效问题是键合工艺研究的重要方向。低温共烧陶瓷(LTCC)电路基板在微波多芯片组件中使用广泛,相对于电镀纯金基板,该基板上金焊盘楔形键合强度对于参数设置非常敏感。文章进行了LTCC基板上金丝热超声楔焊的正交试验,在热台温度、劈刀安装长度等条件不变的情况下,分别设置第一键合点和第二键合点的超声功率、超声时间和键合力三因素水平,试验结果表明第一点超声功率和第二点超声时间对键合强度影响明显。     

硅直接键合(SDB)技术在新型电力电子器件应用中的新进展

综述了硅直接键合（SDB）技术在绝缘栅双极晶体管（IGBT）、静电感应晶闸管（SITH）及MOS控制可关断晶闸管（MTO）等器件中的新应用,说明了SDB技术在新型电力电子器件应用中的新方法和新思路。在此基础上,提出了用SDB技术制作集成门极换流晶闸管（IGCT）和集成门极双晶体管（IGDT）的设想,并给出了相应的工艺方案。     

Cooperative Effect of Noncovalent Interactions on Tetrel Bonding in Halogenated Silanes

Tetrel bond, a weak noncovalent interaction between the σ-hole of a Group IV element (silicon in our case) and the cloud of an electronegative element (oxygen in our case) is the focus of this work. The percentage strengthening of tetrel bond has been investigated by optimizing 16 binary complexes of halogenated silane and water of general formula SiX_nH_4−n−H₂O and 16 ternary complexes, of general formula NaX−SiX_nH_4−n−H₂O, where X=F, Cl, Br and I and n=1, 2, 3 and 4 at various levels of theory defined within the formalism of density functional theory (DFT). With the addition of NaX, tetrel bond between Si and O in SiX_nH_4−n−H₂O gets strengthened up to 49 %, owing to cooperativity effect exerted by hydrogen bonding between X and H in the ternary complex NaX−SiX_nH_4−n−H₂O. In the series of complexes studied here, overall stabilization due to cooperativity lies between 10 kJ/mol to 170 kJ/mol. This large extent of reinforcement due to cooperativity has never been showcased before. The exceptional stabilization and reinforcement owe its genesis to the transformation of the ternary complex into a cluster orchestrated by the H-bonding in most of the cases and covalent bonding in few of the cases.     

Protein environmental effects on iron‐sulfur clusters: A set of rules for constructing computational models for inner and outer coordination spheres

The structural properties and reactivity of iron‐sulfur proteins are greatly affected by interactions between the prosthetic groups and the surrounding amino acid residues. Thus, quantum chemical investigations of the structure and properties of protein‐bound iron‐sulfur clusters can be severely limited by truncation of computational models. The aim of this study was to identify, a priori, significant interactions that must be included in a quantum chemical model. Using the [2Fe‐2S] accessory cluster of the FeFe‐hydrogenase as a demonstrative example with rich electronic structural features, the electrostatic and covalent effects of the surrounding side chains, charged groups, and backbone moieties were systematically mapped through density functional theoretical calculations. Electron affinities, spin density differences, and delocalization indexes from the quantum theory of atoms in molecules were used to evaluate the importance of each interaction. Case studies for hydrogen bonding and charged side‐chain interactions were used to develop selection rules regarding the significance of a given protein environmental effect. A set of general rules is proposed for constructing quantum chemical models for iron‐sulfur active sites that capture all significant interactions from the protein environment. This methodology was applied to our previously used models in galactose oxidase and the 6Fe‐cluster of FeFe‐hydrogenase. © 2016 Wiley Periodicals, Inc.     

Insight into Mechanical Properties of CH3SiO3/2 Film

Young's modulus and stress-optical coefficient of self-sustained gel film of CH₃SiO_3/2 were measured. Young's modulus varied from 1.1 to 1.5 GPa, depending on the structural state of the film. It increased with an increase in the degree of polymerization that was induced by heat treatments, and also increased with subsequent exposure to the ambient condition. The stress-optical coefficient was 6.3 × 10^–12 Pa^–1 for a sample treated at 120°C. The compliance of the film seems to depend mainly on the intermolecular structure of Si–CH₃...CH₃–Si as well as hydrogen bonding due to silanols and adsorbed water.     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

Organometallic Allene [(μ-C)(Fe(CO)4)2]: Bridging Carbon Showing Transformation from Classical Electron-Sharing Bonding to Double σ-Donor and Double π-Acceptor Ligation

Allenes (R₂C=C=CR₂) have been traditionally perceived to feature localized orthogonal π-bonds between the carbon centres. We have carried out quantum-mechanical studies of the organometallic allenes envisioned by the isolobal replacement of the terminal CH₂ groups by the d⁸ Fe(CO)₄ fragment. Our studies have identified two organometallic allenes viz. D_2d symmetric [(μ-C)(Fe(CO)₄)₂] ( 2 ) and D₃ symmetric [(μ-C)(Fe(CO)₄)₂] ( 3 ) with trigonal bipyramidal coordination at the Fe atoms. Compound 2 features the bridging carbon atom in an equatorial position with respect to the ligands on the TM centre, while 3 features the central carbon atom in an axial position. The bis-pseudoallylic anionic delocalisation proposed in the C2-C1-C3 spine of organic allene is retained in the organometallic allene 2 , and is transformed to a typical three-centre bis-allylic anionic delocalisation in the organometallic allene 3 . The topological analysis of electron density also indicates a bis-allylic anionic type delocalisation in the organometallic allenes. The quantitative bonding analysis using the EDA-NOCV method suggests a transition from classical electron-sharing bonding between the central carbon atom and the terminal groups in 1 to donor-acceptor bonding in 3 . Meanwhile, both electron-sharing and donor-acceptor bonding models are found to be probable heuristic bonding representations in the organometallic allene 2 .