The role of β-cyclodextrin and hydroxypropyl β-cyclodextrin in the secondary chemical equilibria associated to the separation of β-carbolines by HPLC

The use of cyclodextrins (CDs) in HPLC as mobile phase additives provides a flexible alternative for the separation of chemically related compounds because these separations can be performed on conventional columns and are economically advantageous over the use of chiral stationary phases. The present paper describes the influence of the presence of β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD) on the separation of the β-carboline alkaloids norharmane, harmane and harmine. The nature of the stationary phase (reverse phases C₁ and C₁₈) affects the chromatographic separations and also the stability of the inclusion complexes that are developed. The changes in the proportion of the organic solvents at constant concentration of CDs (3 mM for β-CD and 15 mM for HPβ-CD) modify the retention factors (k′) for all alkaloids studied. The nature of the organic solvent in the mobile phase also changes the chromatographic parameters. The logarithm of the capacity factor (k′) is linearly increased with the proportion of water in the hydro-organic mobile phase (ethanolic or methanolic) but the slopes obtained vary depending on the CD added to the mobile phase. The role of competitive equilibria, i.e., chromatographic distribution and inclusion complexes formation is discussed. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May, 14–17, 2006     

A Review on Effects of Lubricant Formulations on Tribological Performance and Boundary Lubrication Mechanisms of Non-Doped DLC/DLC Contacts

Tribological efficiency of industrial applications involving boundary lubrication regime can be improved to an appreciable extent by the deposition of hard coatings on interacting surfaces. Among such coatings, diamond-like carbon (DLC) coatings are considered to be one of the most suitable ones for the said role. DLC coatings possess a unique combination of physical, chemical, and material properties due to which they can help in minimizing friction-induced energy and material losses even under starved lubrication conditions. Since commercial lubricants are optimized for steel surfaces, therefore, a lot of experimental investigations were carried out to analyze the tribological compatibility of these lubricants with various DLC coatings. However, there is still a lack of understanding about how DLC coatings interact with conventional lubricant additives. Some researchers reported tribologically beneficial interactions between DLC coatings and formulated lubricants while others observed no such behavior. To address these inconsistencies, there is a need to rearrange the published data in a more apprehensible and organized manner with a special emphasis on the mechanisms responsible for a particular tribological behavior. In this way, it can be determined whether synergistic or antagonistic correlation exists between a particular DLC-lubricant combination and research on DLC coatings can be continued in a logical way. In this article, most widely investigated non-doped DLC coatings (ta-C, a-C:H, a-C, and ta-C:H) are tribologically analyzed. Average values of friction and wear coefficients are calculated for various DLC-lubricant combinations using already published data and compared to quantify the effectiveness of a particular lubricant additive in enhancing tribological characteristics of symmetrical non-doped DLC contacts. Moreover, tribological performance parameters of non-doped DLC coatings are compared with those of doped-DLC coatings to understand differences in their tribological behavior in combination with additives.     

Ethylene/hindered phenol substituted norbornene copolymers: Synthesis and NMR structural determination

A new family of ethylene‐based copolymers with controlled amounts of a norbornene comonomer (N_ArOH) bearing a stabilizing antioxidant functionality (2,6‐di‐tert‐butyl phenol) was prepared. Due to unavoidable exo/endo equilibrium operative in N_ArOH comonomer, a complete and detailed NMR assignment of the structure of the prepared ethylene/N_ArOH copolymers was carried out for the determination of the exo/endo ratio inside the polymer. These novel functionalized comonomers can be considered suitable starting material for preparing ethylene‐based copolymers, with tunable comonomer content, as non‐releasing macromolecular antioxidant additives for specific application in safe food and/or drug packaging © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

用于考察外源添加剂对卷烟常规烟气指标影响的样品制备因子筛选

为筛选用于考察外源添加剂对卷烟常规烟气指标影响的样品制备关键控制因子,采用L_8(2~7)正交试验设计进行香兰素及乙基麦芽酚的添加实验.卷烟常规烟气指标变化数值通过极差分析、方差分析,结果显示:参比卷烟种类是影响卷烟烟气总粒相物、焦油、水分的高度显著因子,就试验采用的1R5F和3R4F参比卷烟而言,添加剂在高焦油3R4F卷烟中对常规烟气指标的影响比其在低焦油1R5F卷烟中的影响大;添加剂种类与浓度的交互作用不仅对卷烟烟气总粒相物有高度显著影响,而且对总粒相物中的水分也有显著影响;因此,规范样品制备,可减少误差、保证后续外源添加剂加入对卷烟常规烟气指标影响评价结果和推断的可靠性及科学性.     

Recent advances of organometallic complexes in emerging photovoltaics

Organometallic complexes (OMCs) consisting of organic and metal active moieties have shown immense potential for application in solar cells. The diverse structure, rich porosity, and unique charge centers of OMCs enable them to be functional in solar cells. In this review, we introduced four types of OMCs, such as crown organometallic complexes, β-diketone metal complexes, cyclometallic complexes, and main chain metal-containing polymers, providing an in-depth analysis of the structure-performance relationship. OMCs could serve as active or interlayer materials in a variety of solar cell systems such as organic solar cells, perovskite solar cells, and dye-sensitized solar cells, especially some metals to improve the photoelectric performance of the device as dopants. In the end, perspectives on the opportunities and challenges of OMCs are given.     

Recent Progress in the Electrolytes of Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) have garnered tremendous attention in the field of next energy storage devices due to their high safety, low cost, abundant resources, and eco-friendliness. As an important component of the zinc-ion battery, the electrolyte plays a vital role in the electrochemical properties, since it will provide a pathway for the migrations of the zinc ions between the cathode and anode, and determine the ionic conductivity, electrochemically stable potential window, and reaction mechanism. In this Minireview, a brief introduction of electrochemical principles of the aqueous ZIBs is discussed and the recent advances of various aqueous electrolytes for ZIBs, including liquid, gel, and multifunctional hydrogel electrolytes are also summarized. Furthermore, the remaining challenges and future directions of electrolytes in aqueous ZIBs are also discussed, which could provide clues for the following development.     

Naturally derived green bio-additives

During the last few years, special attention has been paid by the lubricant industry towards vegetable oil-based lubricants due to their biodegradability, renewability and excellent tribological properties. But to maintain the biodegradability of the final lubricants, the additive in the lubricants must also be biodegradable. Hence, in our present work, multifunctional lubricating oil additive based on castor oil has been investigated as a less toxic, feasible alternative to traditional petroleum based additives. Homopolymer of castor oil and its copolymer with α-pinene were synthesized by a thermal method using azobisisobutyronitrile as a radical initiator. Characterization of the prepared polymers was performed by spectral analysis and gel permeation chromatography (GPC). Additive performances of each of the prepared polymers as viscosity index improvers/viscosity modifiers and pour point depressants were carefully evaluated. Photo micrographic image was used to study the effectiveness of the additives as pour point depressants. Thermogravimetric analysis (TGA) was conducted to investigate the thermal response of the additives at high temperature. Finally, biodegradability of all the polymers was tested against fungal pathogen by the disc diffusion method and soil burial test. The study illuminated excellent additive performances of the polymers and thus their potential for acting as entirely naturally derived green bio-additives for lube oil.     

Viscosity-Temperature Behavior of Hydroxypropyl Cellulose Solution in Presence of an Electrolyte or a Surfactant: A Convenient Method to Determine the Cloud Point of Polymer Solutions

The viscosity of hydroxypropyl cellulose (HPC) solution with or without an additive has been measured continuously as a function of temperature with the help of a vibro-viscometer. The viscosity of the polymer solution showed a gradual decrease initially with increase in temperature until a particular point beyond which there was a sharp decrease in the viscosity, which coincided with the clouding of the solution. The cloud point temperature (CP) of the polymer solution was determined from the first derivative plot of viscosity vs. temperature. Effect of addition of an electrolyte or a surfactant on the CP of HPC solution has also been studied. While a decrease in CP of HPC solution in presence of fluoride, chloride, or bromide ions was observed, presence of iodide or thiocyanide ions led to an increase in the CP. However, presence of an ionic surfactant initially lowered the CP but beyond a particular surfactant concentration a sharp increase in cloud point was observed due to interaction of the surfactant with the polymer. The results suggest that surfactants with longer hydrophobic tail or more hydrophobic groups have more affinity for HPC.     

Mechanism of Ketone Allylation with Allylboronates as Catalyzed by Zinc Compounds: A DFT Study

The mechanism of the allylation reaction between 4‐chloroacetophenone and pinacol allylboronates catalyzed by ZnEt₂ with alcohols was investigated using density functional theory (DFT) at the M05‐2X/6‐311++G(d,p) level. The calculations reveal that the reaction prefers to proceed through a double γ‐addition stepwise reaction mechanism rather than a Lewis acid‐catalyzed concerted one. The intermediate with a four‐coordinated boron center, which is formed through proton transfer from EtOH to the ethyl group of ZnEt₂ mediated by the boron center, is the active species and an entrance for the catalytic cycle. The latter is composed of three elementary steps: 1) boron to zinc transmetalation leading to the formation of allylzincate species, 2) electrophilic addition of ketone to allylzincate species, and 3) generation of the final product with recovery of the catalyst. The boron to zinc transmetalation step has the largest energy barrier of 61.0 kJ mol^?1 and is predicted to be the rate‐determining step. The calculations indicate that the additive EtOH plays important roles both in lowering the activation free energy for the formation of the four‐coordinated boron active intermediate and in transforming the low catalytic activity ZnEt₂ into high activity zinc alkoxide species. The alcohols with a less sterically encumbering R group might be the effective additives. The substituted groups on the allylboronates might primarily affect the boron to zinc transmetalation, and the allylboronates with substituents on the C_γ atom is poor in reactivity. The comparison of the catalytic effect between the zinc compounds investigated suggest that Zn(OEt)₂, Zn(OH)₂, and ZnF₂ exhibit higher catalytic efficiency for the boron to zinc transmetalation due to the activation of the B? C_α bond through orbital interactions between the p orbitals of the EtO, OH, F groups and the empty p orbital of the boron center.     

Crystal Engineering of Supramolecular 1,4-Benzene Bisamides by Side-Chain Modification – Towards Tuneable Anisotropic Morphologies and Surfaces

Benzene bisamides are promising building blocks for supramolecular nano-objects. Their functionality depends on morphology and surface properties. However, a direct link between surface properties and molecular structure itself is missing for this material class. Here, we investigate this interplay for two series of 1,4-benzene bisamides with symmetric and asymmetric peripheral substitution. We elucidated the crystal structures, determined the nano-object morphologies and derived the wetting behaviour of the preferentially exposed surfaces. The crystal structures were solved by combining single-crystal and powder X-ray diffraction, solid-state NMR spectroscopy and computational modelling. Bulky side groups, here t-butyl groups, serve as a structure-directing motif into a packing pattern, which favours the formation of thin platelets. The use of slim peripheral groups on both sides, in our case linear perfluorinated, alkyl chains, self-assemble the benzene bisamides into a second packing pattern which leads to ribbon-like nano-objects. For both packing types, the preferentially exposed surfaces consist of the ends of the peripheral groups. Asymmetric substitution with bulky and slim groups leads to an ordered alternating arrangement of the groups exposed to the surface. This allows the hydrophobicity of the surfaces to be gradually altered. We thus identified two leitmotifs for molecular packings of benzene bisamides providing the missing link between the molecular structure, the anisotropic morphologies and adjustable surface properties of the supramolecular nano-objects.