山東農(nóng)業(yè)大學(xué)學(xué)報(自然科學(xué)版),2011,42(4):483-486Journal of Shandong Agricultural University( Natural Science)乙醇一水分子團(tuán)簇 ETHANOL-( WATER)N(N=1~3)的理論研究韓光占,張超,高吉剛,錢萍山東農(nóng)業(yè)大學(xué)化學(xué)與材料科學(xué)學(xué)院,山東泰安271018)摘要:本文采用密度泛函理論(DFT)的B3LYP方法,在B3LYP6-311++C(2d,2p)//B3LYP/6-311++C(d,p)基組水平上對乙醇-水分子團(tuán)簇 ethanol-( water),(n=1-3)進(jìn)行研究對優(yōu)化計算得到的各種穩(wěn)定構(gòu)型的結(jié)合能及結(jié)構(gòu)參數(shù)進(jìn)行分析。結(jié)果表明對于乙醇-水異二聚體,水分子作為質(zhì)子給體而乙醇分子作為質(zhì)子受體的結(jié)構(gòu)是最穩(wěn)定的;對于乙醇-水異三聚體和異四聚體每個分子即作為質(zhì)子給體又作為質(zhì)子受體的乙醇水環(huán)狀團(tuán)簇構(gòu)型最穩(wěn)定;隨著n值的增大穩(wěn)定性逐漸增強。關(guān)鍵詞:密度泛函理論;團(tuán)簇;氫鍵;結(jié)合能中圖分類號:0641文獻(xiàn)標(biāo)識碼:A文章編號:100-2324(2011)04-0483-04THEORETICAL STUDY OF ETHANOL-(WATERN(N=1-3) CLUSTERSHAN Guang-zhan, ZHANG Chao, GAO Ji-gang, Qian PingChemistry and Material Science Faculty, Shandong Agricultural University, Taian 271018, ChinaAbstract: In this paper, ethanol-water clusters ethanol -(water).(n =1-3)have been calculated at theB3LYP/6-311++G(2d, 2p)//B3LYP/6-311++G(d, p)level. The computed properties characterizingethanol-(water),(n=1-3)clusters include optimal structures, structural parameters, hydrogen bondsbinding energies, and so on. Results show that the most stable structure of ethanol-water heterodimers has theethanol as the proton acceptor and water as the proton donor, and that the cyclic geometric patten, where all themolecules are proton acceptor and proton donor at the same time, are the most stable configurations for ethanolwater heterotrimer and heterotetramer, and that the stability of clusters is gradually reinforcing with the of thenumber of water molecules nKey words Density functional theory; clusters; hydrogen bond; binding energy乙醇-水混合體系在物理化學(xué)生物領(lǐng)域具有非常重要的作用,尤其是乙醇水在可再生能源領(lǐng)域中的重要應(yīng)用邸-n。由生物發(fā)酵獲得的低純度乙醇溶液經(jīng)過純化得到無水乙醇,是一種很好的生物能源時。為了改善或設(shè)計新的提純方法,從分子水平上了解乙醇-水的相互作用機(jī)理很有必要。近年來,關(guān)于甲醇、乙醇以及醇-水團(tuán)簇體系的理論和實驗研究成為熱點方向1, s Mejia.ea.(12),在B3LYP6-31+G(d)算法下優(yōu)化得到36種穩(wěn)定的乙醇-水異三聚體( ethanol)2- water但關(guān)于一乙醇多水ethaodl-( water的文獻(xiàn)報道比較少。在本文工作中擬在密度泛函理論水平下對一乙醇多水團(tuán)簇體系進(jìn)行研究,揭示氫鍵在醇水團(tuán)簇形成過程中的重要作用,期望能為乙醇-水團(tuán)簇的實驗研究提供理論依據(jù)。計算方法根據(jù)文獻(xiàn)報道-1,密度泛函理論在乙醇-水團(tuán)簇研究中有廣泛的應(yīng)用。本文利用 Gaussin03W程收稿日期:2010-10-26基金項目:國家自然科學(xué)基金(No.20903063)和山東農(nóng)業(yè)大學(xué)青年科技創(chuàng)H中國煤化工作者簡介:韓光占(1987-),男,山東濟(jì)寧人,碩士研究生,研究方向為功能通訊作者:Authorforcorrespondence.Emaill:anp@sdau.edu.cnCNMHG·484山東農(nóng)業(yè)大學(xué)學(xué)報(自然科學(xué)版)第42卷序,在BLYP/6-311++G(d,p)方法下進(jìn)行結(jié)構(gòu)的優(yōu)化和頻率計算并保證所得到的優(yōu)化結(jié)構(gòu)是勢能面上的極小值然后采用B3LYP/6-311++G(2d,2p)方法進(jìn)行單點能計算和BSSE校正。乙醇水團(tuán)簇的結(jié)合能(BE)定義為:BE,=E[ethanol-(water)]-ELethanol]-nELwater]其中E[( ethanol-( water)n],E[ ethanol]和E[wter]代表乙醇-水團(tuán)簇、乙醇單體和水單體相應(yīng)的能量。2結(jié)果與討論乙醇存在著順式和反式兩種構(gòu)象由于兩種構(gòu)象與水形成的團(tuán)簇結(jié)構(gòu)相似,因此本文以乙醇的順式為研究對象,考察乙醇-水團(tuán)簇的結(jié)構(gòu)性質(zhì)。因為羥基的雙重性,乙醇和水既可以作為氫鍵中質(zhì)子的給體又可以作為氫鍵中質(zhì)子的受體。為便于分析團(tuán)簇的結(jié)構(gòu)參數(shù)我們將團(tuán)簇中的氫鍵分為三個類別以乙醇水異三聚體e2w-a為例(見圖1),A類氫鍵(HBA)表示水分子作為質(zhì)子給體,乙醇作為受體構(gòu)成的氫鍵;B類氫鍵(HB3)表示乙醇分子作為質(zhì)子的給體,水作為受體構(gòu)成的氫鍵;C類氫鍵(HBc)表示團(tuán)簇中水與水之間形成的氫鍵。etIw-aetlw-betw.bet2w-cet3w.bet3w-det3w-f圖1 Ethanol-( water),(n=1~3)團(tuán)簇的各種低能結(jié)構(gòu)Fig. 1 Optimal structures of ethanol-( water).(n 1-3)clusters表1 Ethanol-( water).(n=1~3)團(tuán)鏃的結(jié)構(gòu)參數(shù)Table 1 Structural parameters of ethanol-( water).(n= 1-3)clustersR(0…H)/(mm)∠(o-H…0)/(°)H-0-C-C(HBBetIw-a173.66178.31etlw-b175.790.19000.1951ehw-a0.18600.19230.1917151.77148.2914747178.02n =2 et2w-b0.19440.21170.2l12152.970.1790.1774167.27166.65166.280.1983290.2074.94150.66141.04179.600.1944380.1918148.03155.14159.28174.26n=3·e3w-d0.18840.190969149.72173.57et3w-e0.17950.20430.2117153.52143.00142.51178.11et3w-f0.18660.18410.1966中國煤化工”1CNMHG第4期韓光占等:乙醇-水分子團(tuán)簇 ETHANOL-( WATER)N(N=1~3)的理論研究表2 Ethanol-( water)n(n=1-3)團(tuán)簇的結(jié)合能(kJ/mol)Table 2 General binding energies(kI/ mol)of ethanol -( water).(n=1-3)and the binding energies v:b theZPE and BSSE corrections at the B3LYP/6-311++G(2d, 2p)//B3LYP /6-311++G(d, p) levelCluster22.5114.14etIw-b19.0412.22etlw-a28.87b-61.2140.71-40.7140.4627w-c-40.12111.20et3w-b-87.32et3w-c84.4756.7482.01-56.74et3w-d53-83.76-53.51et3w-f53.35a Binding energy with no zero- point energy and basis set superposition error correctionsergy correctonth the basis Bed bindisy with the zero-point energy and basis get superpositicc Ref [n1f Ref. [191圖1給出了 ethanol-( water),(n=1~3)團(tuán)簇的各種低能結(jié)構(gòu),其氫鍵個數(shù)、結(jié)構(gòu)參數(shù)列于表1中結(jié)合能及經(jīng)過ZPE和BSSE校正之后的能量列于表2。n=1時,乙醇-水二聚體 ethanol- water存在兩種構(gòu)型(圖1),etlw-a的水分子作為質(zhì)子的給體,乙醇分子作為質(zhì)子的受體;etlw-b的乙醇分子作為質(zhì)子的給體,而水分子作為質(zhì)子的受體。由表1可見,etlw-a氫鍵的鍵長R(O…H)比etlw-b短0.0047m,兩者的氫鍵鍵角∠(O-H…0)都在175°左右,它們的乙醇分子的二面角H-0-C一C也非常接近180°,結(jié)合能(見表2)相差3.47kJ/mol左右,與Filet,E.eta.和 Y Katrib.etl.(H的結(jié)果一致。通過以上數(shù)據(jù)可以說明乙醇-水異二聚體中,結(jié)構(gòu)etlw-a比結(jié)構(gòu)etlw-b更加穩(wěn)定。n=2時,乙醇-水異三聚體 ethanol-( water)2有3種穩(wěn)定的低能結(jié)構(gòu)(圖1)。對比其結(jié)構(gòu)參數(shù)我們發(fā)現(xiàn),由一個乙醇分子與兩個水分子構(gòu)成的環(huán)狀構(gòu)型et2w-a,其醇羥基中的氧原子和水分子中的氧原子近似在同一平面上,乙醇分子分別作為質(zhì)子的受體和給體,與兩個水分子形成A、B兩類氫鍵,兩個水分子間形成C類氫鍵。在該團(tuán)簇中,A類型氫鍵的鍵長R(O…H)最短,即0.1860mm,B類型氫鍵的鍵長R(O…H)3是0.1923mm,C類型氫鍵的鍵長R(0…H)c是0.1917m,它的三個氫鍵鍵角∠(0-H…O)在147°~152°之間,且三個氫鍵的鍵角非常接近,主要是由于該構(gòu)型的環(huán)狀結(jié)構(gòu)所決定的;etnw-b構(gòu)型中,兩個水分子對稱分布于乙醇分子的兩側(cè),形成的兩個A類型的氫鍵,鍵長R(O…H)A為0.1944m,鍵角為∠(O-H…O)A為16644°;et2w-c構(gòu)型也是環(huán)狀構(gòu)型,其中乙醇分子只作為質(zhì)子的受體與分布在羥基兩側(cè)的兩個水分子形成兩個A類氫鍵兩個水分子形成C類氫鍵。ew-c構(gòu)型的R(0…H)A為三種構(gòu)型中最長0.2117mm,R(O…H)c為02112m,比e2w-a構(gòu)型R(O…H)c約短0.02m。從它的氫鍵鍵角也可以發(fā)現(xiàn)這一特點,A類型的氫鍵鍵角為∠(0-H…0)為152.97°,C類型的氫鍵鍵角為∠(0-H…0)c為145.96°;三種構(gòu)型的乙醇分子的二面角H-0-C-C非常接近,在17581°~179.38°之間。通過對比三聚體各團(tuán)簇的結(jié)合能(見表2),我們可以看到2V凵中國煤化工量結(jié)構(gòu),結(jié)合能是-621kJ/mol,與Y. Katribet al.在B3LYP算法下得到的CNMHGE-61. 51 kJ,486·山東農(nóng)業(yè)大學(xué)學(xué)報(自然科學(xué)版)第42卷mol接近;而e2w-c也是一種環(huán)狀構(gòu)型,結(jié)合能是-40.12k/mol,比et2w-a構(gòu)型高約20.92uJ/mol;e2w-b構(gòu)型只有兩個氫鍵,結(jié)合能是-40.46kJ/mol,稍低于ew-c構(gòu)型。結(jié)合前面對各團(tuán)簇的結(jié)構(gòu)參數(shù)分析,可以看出enw-a構(gòu)型是最穩(wěn)定的構(gòu)型,e2w-b和e2w-c構(gòu)型能量接近,et2w-b構(gòu)型雖只有兩個氫鍵,但是其穩(wěn)定性應(yīng)高于e2w-c構(gòu)型。n=3時,乙醇-水異四聚體 ethanol-( water)3有6種穩(wěn)定的低能結(jié)構(gòu)(圖1)。由圖1可知,乙醇水異四聚體構(gòu)型主要分為兩大類,一類是四元環(huán)狀構(gòu)型(et3w-a),一類是三元環(huán)構(gòu)型(et3w-b、et3w-c、et3w-d、eB3w-e、et3w-f)。e3w-a構(gòu)型有1個A氫鍵,1個B氫鍵和2個C氫鍵,三類氫鍵R(oH)x,R(O…H)3,R(O…H)分別是0.1751m,0.1795mm,0.1774mm,它們的氫鍵鍵角∠(O-H…O都非常接近,在167左右;對于et3w-b,e3w-c,e3w-e和et3w-f低能結(jié)構(gòu),其團(tuán)簇內(nèi)R(O…H)A、R(0…H)g、R(O…H)c鍵的值分別為0.1897mm,0.1869m,0.2019mm,比a構(gòu)型的相應(yīng)鍵更長,氫鍵鍵角在150°左右;et3w-d構(gòu)型是三個水分子構(gòu)成的三元環(huán)和一個醇分子組成的構(gòu)型,它只有A和C兩種氫鍵,其鍵長分別為01884mm,0.1909mm,兩種鍵角差別較大,∠(O-H…0)為176.69°,∠(O-H…O)c為149.72°。e3w-a構(gòu)型的結(jié)合能是-11.20kJ/mol,其余五種構(gòu)型都在-80kJ/mol左右,結(jié)合前面的結(jié)構(gòu)參數(shù)分析,我們可看出,et3w-a構(gòu)型是乙醇-水異四聚體的六種結(jié)構(gòu)中能量最低、最穩(wěn)定的一種構(gòu)型,另外的幾種構(gòu)型結(jié)構(gòu)參數(shù)相近,能量相近。3結(jié)語在密度泛函理論的基礎(chǔ)上,對優(yōu)化得到的乙醇水團(tuán)簇 ethanol-( water),(n=1-3)進(jìn)行了優(yōu)選、分類,并對相對穩(wěn)定的構(gòu)象的結(jié)構(gòu)、能量進(jìn)行分析。對比分析發(fā)現(xiàn),在n=1時,乙醇-水異二聚體構(gòu)型即水分子作為質(zhì)子給體而乙醇分子作為質(zhì)子受體的結(jié)構(gòu)(etlw-a)最穩(wěn)定;在n=2、3的各種尺寸的團(tuán)簇中,單環(huán)環(huán)狀構(gòu)型是最穩(wěn)定的一種構(gòu)型;n=3時,乙醇-水異四聚體中能量略高于其四元環(huán)狀的構(gòu)型是在異三聚體三元環(huán)中加入了一個水分子,并與其中的水和乙醇分子構(gòu)成另外一個三元環(huán)的構(gòu)型(et3wa);在n=1~3時,隨著n值的增大,團(tuán)簇結(jié)合能逐漸降低,穩(wěn)定性增強參考文獻(xiàn)[1] Travers F, Douzou P. 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