Mechanisms of antibiotic removal by nanofiltration membranes: Model development and application

Shah, A.D.,Huang, C.H.,Kim, J.H. Elsevier Scientific Pub. Co 2012 Journal of membrane science Vol.389 No.-

Nanofiltration (NF) membranes have been shown to effectively remove low-molecular-weight compounds, but predicting their rejection has posed challenges due to the fact that multiple mechanisms can be involved (e.g. adsorption, steric-hindrance effects, and electrostatic effects) that concurrently control removal. The objective of this study was to systematically evaluate which factors were responsible for steady-state rejection of selected antibiotics such as sulfamethoxazole (SMX) and carbadox (CDX) for three NF membranes of varying tightness through a unique modeling approach which accounts for the fact that these compounds bear distinctive acid-base speciation properties under varying pH conditions. Both the steric-hindrance/pore-diffusion model for neutral solutes along with the Donnan steric partitioning model for charged solutes were integrated together to predict overall rejection. This is the first known study to evaluate compound rejection of compounds that carry such unique speciation properties as a function of pH by using such a combined approach. Antibiotic rejection was found to vary with both pH and membrane tightness. Rejection controlled by charge repulsion effects was accurately predicted for both negatively charged solutes such as SMX<SUP>-</SUP> and CDX<SUP>-</SUP> and positively charged solutes such as SMX<SUP>+</SUP>. However, rejection controlled by steric-hindrance effects for neutral solutes either overestimated (e.g. SMX) or underestimated (e.g. CDX) rejection by up to 23%. These findings improve the understanding of which transport mechanisms influence rejection of both neutral and charged low-molecular-weight compounds by NF membranes so that removal can be better predicted.

Synthesis of 2-(2¹-Vinyloxyethoxy)-1-naphthylidenemalononitrile and its Polymerization Behaviors

Lee, Ju-Yeon 인제대학교기초과학연구소 1999 자연과학 Vol.3 No.-

2-(2'-비닐옥시에톡시)-1-나프탈데히드(1)를 말로노니트릴롸 축합반응시켜 2-(2'-비닐옥시에톡시)-1-나프릴메틸리덴말로노니트릴(2)를 합성하였다. 이중 기능성 비닐 에테르 단량체 2는 입체방해 효과 때문에 자유 라디칼 개시제에 의해서는 호모중합 또는 전자가 풍부한 에틸 비닐 에테르와 전자가 부족한 벤질리덴말로노니트릴과의 공중합은 진행되지 않았다. 그러나 화합물 2는 양이온 개시체에 의해서는 중합이 잘 진행되어 효과적인 비선형 광학 발색단으로 예상되는 2-옥시-1-나프틸메틸리덴말로노니트릴을 측쇄에 포함하는 중합체 3을 형성하였다. 중합체 3은 아세톤같은 상용 용매에 잘 녹았으며 고유점도는 0.24-0.28 dL/g을 보였다. 아세톤 용액으로부터 얻어진 중합체 필름은 불투명하고 취약성을 보였다. 중합체 3은 300℃까지 열 안정성을 보였으며 DSC로부터 얻어진 유리전이온도는 82℃였다. 2-(2'-Vinyloxyethoxy)-1-naphthylmethylidenemalononitrile (2) was prepared by the condensation of 2-(2'-vinyloxyethoxy)-1-naphthaldehyde(1) with malononitrile. Bifunctional vinylether monomer 2 did not homo-or copolymerize by free radical initiators due to the steric hindrance. However, compound 2 polymerized well by cationic initiators to give poymer 3 having 2-oxy-1-naphthylmethylidenemalononitrile, which is presumably effective NLO-chromophore for second order nonlinear optical applicaions. Polymers 3 was soluble in common solvents such as acetone and DMSO, and the inherent viscosities of the polymers were in the range of 0.24-0.28 dL/g. Films cast from acetone solution were cloudy and brittle. Polymers 3 showed a thermal stability up to 300℃ with a Tg of 82℃ in DSC thermogram.

Kinetic Study on Nucleophilic Displacement Reactions of Phenyl Y-Substituted Phenyl Carbonates with 1,8-Diazabicyclo[5.4.0]undec-7-ene: Effects of Amine Nature on Reaction Mechanism

박경호,Min-Young Kim,엄익환 대한화학회 2016 Bulletin of the Korean Chemical Society Vol.37 No.1

Second-order rate constants (kN) for nucleophilic displacement reactions of phenyl Y-substituted phenyl carbonates (7a–7l) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 oC have been measured spectrophotometrically. The Brønsted-type plot for the reactions of 7a–7l with DBU is linear with βlg = –0.48, indicating that the reactions proceed through a concerted mechanism, which is in contrast to the stepwise mechanism reported previously for the corresponding reactions with ethylamine (a primary amine) and piperidine (a secondary amine). The Hammett plots correlated with σ − and σ o constants exhibit many scattered points. In contrast, the Yukawa–Tsuno plot results in an excellent linear correlation with ρY = 1.27 and r = 0.57, implying that a negative charge develops partially on the O atom of the leaving group in the transition state. The bulky DBU is less reactive than the primary and secondary amines toward substrates possessing a weakly basic leaving group. It has been concluded that steric hindrance exerted by DBU in the plausible intermediate (T±) forces the reactions to proceed through a concerted mechanism because expulsion of the leaving group from T± could reduce the steric hindrance.

Computational simulation on steric hindrance between hydrophobic tails of lamellar matrix composed of acyl glutamate/stearyl alcohol/behenyl alcohol by molecular dynamics

Seo, D.S.,Kim, J.C.,Kim, D.P. Korean Society of Industrial and Engineering Chemi 2008 Journal of industrial and engineering chemistry Vol.14 No.6

Monosodium N-stearoyl-l-glutamate (MSSG), an amino acid surfactant, could associate with higher alcohols such as stearyl alcohol (SA) and behenyl alcohol (BA) and they were self-assembled into a lamella in an aqueous phase. When MSSG, SA and BA were assumed to associate each other in molar ratios of 1:1:1, 1:2:1, 1:1:2, 1:2:2 and 1:1:3, the packing parameter of each associate was calculated using molecular dynamics (MD). Among them, only 1:1:1 associate and 1:1:3 one exhibited packing parameters of around 1. According to the result of colloidal stability, however, the lamella composed of 1:1:3 associate was poorly stable while that of 1:1:1 associate was stable. In order to explain why the colloidal stability is not related to the packing parameter, the concept of steric compressibility was introduced. Steric compressibility is a measure of vertical steric hindrance occurred between hydrophobic tails of lamella. The value of steric compressibility, calculated by MD, of 1:1:1 and 1:1:3 associates were 4.7 and 8.2, respectively. That is, the vertical repulsion in the lamella of 1:1:3 associate might be greater than in the lamella of 1:1:1 associate. This would account for why the lamella of 1:1:3 associate is poorly stable even though the packing parameter is almost 1. Besides the condition that packing parameter is to be around 1, the steric compressibility of lamella should be as low as possible to achieve a stable lamella.

Computational simulation on steric hindrance between hydrophobic tails of lamellar matrix composed of acyl glutamate/stearyl alcohol/behenyl alcohol by molecular dynamics

Dong-Sung Seo,Dong-Pyo Kim,김진철 한국공업화학회 2008 Journal of Industrial and Engineering Chemistry Vol.14 No.6

Monosodium N-stearoyl-L-glutamate (MSSG), an amino acid surfactant, could associate with higher alcohols such as stearyl alcohol (SA) and behenyl alcohol (BA) and they were self-assembled into a lamella in an aqueous phase. When MSSG, SA and BAwere assumed to associate each other in molar ratios of 1:1:1, 1:2:1, 1:1:2, 1:2:2 and 1:1:3, the packing parameter of each associate was calculated using molecular dynamics (MD). Among them, only 1:1:1 associate and 1:1:3 one exhibited packing parameters of around 1. According to the result of colloidal stability, however, the lamella composed of 1:1:3 associate was poorly stable while that of 1:1:1 associate was stable. In order to explain why the colloidal stability is not related to the packing parameter, the concept of steric compressibility was introduced. Steric compressibility is a measure of vertical steric hindrance occurred between hydrophobic tails of lamella. The value of steric compressibility, calculated by MD, of 1:1:1 and 1:1:3 associates were 4.7 and 8.2, respectively. That is, the vertical repulsion in the lamella of 1:1:3 associate might be greater than in the lamella of 1:1:1 associate. This would account for why the lamella of 1:1:3 associate is poorly stable even though the packing parameter is almost 1. Besides the condition that packing parameter is to be around 1, the steric compressibility of lamella should be as low as possible to achieve a stable lamella.

Thiol-Michael Coupling and ROMP: Comparison of the Effects of Steric Hindrance with Functional Dendronized Polymer

Tong Wu,Maojie Xuan,Xingyou Wang,Meina Liu 한국고분자학회 2019 폴리머 Vol.43 No.6

Dendronized exo-7-oxanorbornene monomers were synthesized and polymerized via thiol–Michael coupling and ring-opening metathesis polymerization. The polymerization rate was highly dependent on the steric hindrance of the terminal group. The space linker between the polymerizable group and dendron was a crucial factor. Ru-based kinetics was investigated using nuclear magnetic resonance (NMR), which showed that the monomer was completely converted to a generally narrow polydispersity material. The second generation of functional macromonomer was grafted from the first with a different linker length and consumed completely at 50 oC in toluene. Considering the properties of the space linker, we found that a short space linker of dendronized exo-7-oxanorbornene macromonomer leads to narrow molecular weight distributions of obtained dendronized polymers. This work provides a further understanding of the effect of steric hindrance on dendronized polymers, thereby allowing the development of functional materials.

호스트-게스트의 입체선택적 착물형성에 의한 메틸아닐리늄 이온 혼합물의 전기화학적 분석

鄭鍾和,張德眞,李富永,徐戊龍,金載祥,李心星 慶尙大學校 기초과학연구소 1992 基礎科學硏究所報 Vol.8 No.-

메틸기가 한 개 또는 두 개 치환된 10가지 메틸아닐리늄 이온과 18-그라운-6와의 착물형성 및 선택성을 메탄올에서 적하수은 전극에 의해 조사하였다. 메틸아닐리늄 이온과 18-그라운-6와의 착물의 안정도 상수는 메틸기의 위치와 갯수에 따른 입체장애 효과에 의해 큰 차이를 나타내었다. 또한 반파전위의 차가 매우 작아 일반적인 방법으로는 분석이 불가능한 메틸아닐리늄 이성질체 혼합물 등에 보조 착화제로 18-크라운-6를 첨가하여 입체장애에 의한 착물반응의 선택성을 이용하여 분석을 시도하였다. 그 결과 18-크라운-6와 두 게스트 이온의 안정도 상수의 차, Δlog K가 대략 0.4∼1.3인 경우 이성분 혼합물의 확인이 정성적으로 가능하였으며, 1.6 이상인 경우에는 정량적인 개별분석도 가능하였다. 이는 18-크라운-6가 아닐리늄의 메틸치환기의 위치에 따라 입체장애의 정도를 선별적으로 인식하여 큰 착물형성 선택성을 나타낸 결과로 각 환원파의 음전위 이동 정도가 크게 달라지기 때문이다. The complexations and selectivities of the 10 species of mono- and dimethylsubstituted anilinium ions with 18-crown-6 in methanol are examined at dropping mercury electrode. The stability constants of these complexes varies drastically due to the steric hindrance by the positions and numbers of methyl groups. And the analyses of the isomeric mixtures of methylanilinium. which are impossible to detect due to the overlapped peaks in normal conditions, were also accomplished by the additions of 18-crown-6 as the supporting complexing agent using the selective complexations by the steric hindrance effects. As results in case of the difference of stability. Δlog K were about 0.7∼1.3. it was possible to confirm the existance of two species qualitatively. Otherwise when Δlog K were large than 1.6 .the quantitative determinations of each species could be accomplished sucessfully. From these results it is deduced that the selective recognition of the positions and numbers of methyl groups as the steric hindrance in aniliniums by 18-crown-6 cause the large variation of the magnitudes of negative shift of reduction waves for guest ions in mixtures.

Steric effects of CO₂ binding to transition metal-benzene complexes: A first-principles study

Bae, Hyeonhu,Huang, Bing,Lee, Hoonkyung ELSEVIER 2016 Current Applied Physics Vol.16 No.9

<P>Using density functional theory (DFT) calculations, we investigated the adsorption of CO2 molecules on 3d transition metal (TM)-benzene complexes. Our calculations show that the maximum number of CO2 molecules adsorbable on Sc or Ti atoms is three, but the 18-electron rule predicts it should be four. The 18-electron rule is generally successful in predicting the maximum H-2 adsorption number for TM atoms including Sc or Ti atoms. We found that the 18-electron rule fails to correctly predict CO2 binding on Sc- or Ti-benzene complexes because CO2 binding, in contrast to H-2 binding, requires additional consideration for steric hindrance due to the large bond length of CO2. We calculated the occupation function for CO2 using the Tolman cone angle, which shows that three CO2 molecules fully occupy the available space around Sc- and Ti-benzene complexes. This estimation is the same maximum CO2 adsorption number predicted by DFT calculations. Therefore, we propose that the occupation function for CO2 using the Tolman cone angle is an efficient model for evaluating steric hindrance of CO2 adsorption on a surface. (C) 2016 Published by Elsevier B.V.</P>

Sorption of Pb(II) and Cu(II) onto multi-amine grafted mesoporous silica embedded with nano-magnetite: Effects of steric factors

Chung, J.,Chun, J.,Lee, J.,Lee, S.H.,Lee, Y.J.,Hong, S.W. Elsevier Scientific Pub. Co 2012 Journal of hazardous materials Vol.239 No.-

Steric factors affecting the mass transfer of Pb(II) and Cu(II) in mesocellular silica foams (MSU-F-S) functionalized with multi- (mono-, di-, tri-) amine groups and nano-magnetite were investigated through batch experiments. We observed that neither the sorption capacities nor the sorption rates were linearly proportional to the number of amine groups introduced to a ligand. Unexpectedly, the tri-amine grafted samples exhibited lower affinity for both metal cations. These results are mainly attributed to two important steric factors, pore blockage and a conformational change of available amine groups. The relatively large pore size (~30nm) of MSU-F-S could enable various functional molecules such as amines and nano-magnetite to be effectively loaded within the pores. However, their excessive densities in the limited pore structure could have adverse effects on the transport of metal ions into the mesopores. An intraparticle diffusion model was applied to elucidate the mechanisms involved in the sorption process. Our results showed that the diffusional mass transfer into the mesopores was significantly inhibited in tri-amine grafted samples. The present findings further the understanding of steric effects on the transport of cationic metals into functionalized mesoporous silica and designing efficient sorbents.

Steric Effect of Neighboring Substituents in the Free Radical Polymerization of Alkyl Vinyl Ethers

Lee, Ju-Yeon 인제대학교기초과학연구소 2001 자연과학 Vol.5 No.-

아릴옥시에틸 비닐 에테르 화합물 4-9를 대응하는 벤즈알데히드 1-3과 말로노니트릴 또는 메틸시아노아세테이트를 각각 반응시켜 합성하였다. 비닐 에테르 화합물 4,6, 및 8은 자유 라디칼 개시제에 의해서 쉽게 중합되어 고도로 가교화된 중합체 10,12 및 14를 생성하였다. 그러나 화합물 5,7 및 9는 이웃하는 치환기에 의한 입체 방해 효과 때문에 라디칼 개시제에 의해서 전혀 중합되지 않았다. 얻어진 중합체 10,12 및 14는 아세톤과 DMF와 같은 상용 유기 용매에 녹지 않았으며 300℃까지 열안정성을 보였다. Compounds 4-9 were synthesized and polymerized by free radical initiators. Vinyl ether compounds 4,6, and 8 polymerized readily with radical initiators to yield highly crosslinked polymers 10,12, and 14. However, compounds 5,7,and 9 were inert to radical initiators due to the steric hindrance of neighboring substituents. The resulting polymers 10,12, and 14 were not soluble in common solvents such as acetone and DMF showing a thermal stability up to 300℃.