Nanoscale Platelet Formation by Monounsaturated and Saturated Sophorolipids under Basic pH Conditions

The self‐assembly behavior of the yeast‐derived bolaamphiphile sophorolipid (SL) is generally studied under acidic/neutral pH conditions, at which micellar and fibrillar aggregates are commonly found, according to the (un)saturation of the aliphatic chain: the cis form, which corresponds to the oleic acid form of SL, spontaneously forms micelles, whereas the saturated form, which corresponds to the stearic acid form of SL, preferentially forms chiral fibers. By using small‐angle light and X‐ray scattering (SLS, SAXS) combined with high‐sensitivity transmission electron microscopy imaging under cryogenic conditions (cryo‐TEM), the nature of the self‐assembled structures formed by these two compounds above pH 10, which is the pH at which they are negatively charged due to the presence of a carboxylate group, has been explored. Under these conditions, these compounds self‐assemble into nanoscale platelets, despite the different molecular structures. This work shows that the electrostatic repulsion forces generated by COO^? mainly drive the self‐assembly process at basic pH, in contrast with that found at pH below neutrality, at which self‐assembly is driven by van der Waals forces and hydrogen bonding, and thus, is in agreement with previous findings on carbohydrate‐based gemini surfactants.     

Stand up for Electrostatics: The Disiloxane Case

The basicity of the simplest silicone, disiloxane (H₃Si−O−SiH₃), is strongly affected by the Si−O−Si angle (α). We use high-level ab initio MP2/aug′-cc-pVTZ calculations and the molecular electrostatic potential (MEP) to analyze the relationship between the increase in basicity and the reduction of α. Our results clearly point out that this increase can be explained through the MEP, as the interactions between oxygen from disiloxane and the acceptors are mostly electrostatic. Furthermore, the effect of α on the tetrel bond between disiloxane and several Lewis bases can again be rationalized using the MEP. Finally, we explore the cooperativity throughout α for ternary complexes where disiloxane simultaneously interacts with a Lewis acid and a Lewis base. Both non-covalent interactions remain cooperative for all α values, although the largest cooperativity effects are not always those maximizing the binding energy in the binary complexes. Overall, the MEP remains a powerful predictor for noncovalent interactions.     

Enthalpies of Adduct Formation between Boron Trifluoride and Selected Organic Bases in Solution: Toward an Accurate Theoretical Entry to Lewis Basicity

The Lewis basicity of selected organic bases, modeled by the enthalpies of adduct formation between gaseous BF₃ and bases in dichloromethane (DCM) solution, is critically examined. Although experimental enthalpies for a large number of molecules have been reported in the literature, it may be desirable to estimate missing or uncertain data for important Lewis bases. We decided to use high-level ab initio procedures, combined with a polarized continuum solvation model, in which the solvated species were the clusters formed by specific hydrogen bonding of DCM with the Lewis base and the Lewis base/BF₃ adduct. This mode of interaction with DCM corresponds to a specific solvation model (SSM). The results essentially showed that the enthalpy of BF₃ adduct formation in DCM solution was clearly influenced by specific interactions, with DCM acting as hydrogen-bonding donor (HBD) molecule in two ways: base/DCM and adduct/DCM, confirming that specific solvation is an important contribution to experimentally determined Lewis basicity scales. This analysis allowed us to conclude that there are reasons to suspect some gas-phase values to be in error by more than the stated experimental uncertainty. Some experimental values in DCM solution that were uncertain for identified reasons could be complemented by the computed values.     

Mechanism of Conjugated Polymer Organization on SWNT Surfaces

Summary: The interactions between poly{(2,6‐pyridinylenevinylene)‐co‐[(2,5‐dioctyloxy‐p‐phenylene)vinylene]} (PPyPV) and SWNTs have been investigated using UV‐Vis absorption spectroscopy. The SWNTs promoted polymer organization. PPyPV is a Lewis base and can be doped by strong and weak Lewis acids. The basicity strength of the PPyPV depended on the polymer interchain interactions, which were enhanced by the presence of SWNTs. As the SWNT concentration was increased, an increment in the K_b of PPyPV was observed.

     

Localization-consistent electronic energy partitions

Electronic energy partitionings resulting from the classification of occupied molecular orbitals in disjoint subsets are seen to be consistent with localization procedures preserving that classification, regardless of the treatment given to the crossing terms between different subsets. To illustrate the utility of this result, the electronic energies of pyrazole and imidazole are partitioned into σ- and π-localized molecular orbital energy contributions, and the results are related with the aromaticity and basicity differences between both heterocycles. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 121–126, 1997     

氢键碱度的神经网络法计算

氢键在生命科学和化学等领域均起着十分重要的作用.化合物可以通过提供质子和接受质子等两种方式与其它化合物形成分子间氢键,其形成氢键的能力分别称为氢键酸度（hydrogen-bondacidity）和氢键碱度(hydrogen-bondbasicity).可以用正辛醇／水分配系数和环己烷／水分配系数的对数差（ΔlogP）[1]、溶剂化显色参数[2－3]等表示化合物形成氢键的能力,其中应用较多的是Abraham等[4]提出的总氢键酸度（）和总氢键碱度（）.但由于和要通过实验得到,繁琐不便,限制了它们的广泛应用.本文用神经网络法研究了理论计算得到的量子化学参数与之间的相…     

玻璃体系中折射碱度的测定

根据ｌｅｗｉｓ的观点,物质的酸碱性与其内部的电子密度分布有关。一些光学特征(如吸收、折射等)是由介质内部电子云分布所决定的,因而反映这些光学特征的光学参数与ｌｅｗｉｓ碱度之间存在着必然的联系,光学碱度[1]的概念就是由此提出的。摩尔折射Ｒ反映了分子中电子云(主要是价电子云)在外电场中变形能力的大小,它与折射率ｎ的关系可通过其分子量Ｍ和密度ｄ由ＬｏｒｅｎｔｚＬｏｒｅｎｔｚ公式得到:Ｒ=ｎ2-1ｎ2 2·Ｍｄ摩尔折射度与折射率一样具有加和性,因此在氧化物玻璃中可由玻璃的摩尔折射度减去阳离子折射度而得到氧离子的离子折射度…     

吸附量热技术和金属氧化物催化剂的表面酸碱性

 探讨了吸附量热技术及其在测定固体表面酸碱性中的应用．使用NH3和CO2为探针分子,吸附量热技术能够定量地描述固体表面酸碱中心的数目和强度分布．结合原位红外光谱,还能够详细地了解表面酸碱中心的性质：金属氧化物表面的Lewis酸中心和碱中心分别是表面配位不饱和的金属离子和氧负离子,Brnsted酸中心和碱中心则是金属氧化物表面的羟基．通过测量吸附热,金属氧化物的表面酸碱性强度可与Sanderson电负性关联起来,也可以考虑使用Drago参数来描述固体表面的酸碱性．根据酸碱性与电负性的关系以及对表面配位不饱和离子的要求,有可能通过选择合适的复合金属氧化物组成,获得具有一定酸（碱）量和酸（碱）强度的固体酸（碱）．     

1-Alkyl-2-trifluoromethylaziridines: The bacisity and ring-opening reactions under the action of acids

The basicity of 1-alkyl-2-trifluoromethylaziridines is-two orders of magnitude lower than that of non-fluorinated analogs. Aziridines are stable to H₂S and AcOH, but react with AcSH, HCl, HBr, H₂SO₄, TsOH, and picric acid to give products of ring-opening. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1185–1188 June, 1997.     

氧化镧催化剂上甲烷氧化偶联—不同制备方法的比较

本文研究了５种不同制法的Ｌａ＿２Ｏ＿３对甲烷氧化偶联的催化性能，其Ｃ＿２选择性和Ｃ＿２收率的相对顺序为：Ｌａ＿２Ｏ＿３（１）＞Ｌａ＿２Ｏ＿３（２）＞Ｌａ＿２Ｏ＿３（４）＞Ｌａ＿２Ｏ＿３（５）＞Ｌａ＿２Ｏ＿３（３）。并运用ＸＲＵ、ＸＰＳ、ＣＯ＿２－ＴＰＤ、ＮＨ＿３－ＴＰＤ和ＩＰＡ转化反应等技术分别对催化剂的体相结构和表面性质，表面酸碱性进行了测定。结果表明，由于制备方法的不同，导致了Ｌａ＿２Ｏ＿３晶体表面结构的差异，这是影响催化性能的主要原因。同时还发现，催化剂的活性和Ｃ＿２选择性与表面酸碱性存在着相依性，Ｌａ＿２Ｏ＿３表面的总碱位数与总酸位数的比值，与其催化性能有较好的直接对应关系。