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Monomeric Units (monomeric + unit)
Selected AbstractsSynthesis of the Monomeric Unit of the Lomaiviticin Aglycon,ANGEWANDTE CHEMIE, Issue 32 2009C. Nicolaou Prof. Zum richtigen Baustein: Das Aglykon der monomeren Einheit von Lomaiviticin (siehe Strukturen) wurde enantioselektiv synthetisiert. Die Route verlief über eine Ullmann-Kupplung, eine Benzoin-Cyclisierung und eine neuartige SmI2 -vermittelte Verschiebung einer Allylalkohol-Funktion. [source] One-Dimensional Coordination Polymers of MnII, CuII, and ZnII Supported by Carboxylate-Appended (2-Pyridyl)alkylamine Ligands , Structure and MagnetismEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2009Himanshu Arora Abstract Four new complexes [MnII(L1OO)(H2O)][ClO4]·2H2O (1), [ZnII(L1OO)][ClO4]·2H2O (2), [CuII(L3OO)][CF3SO3]·H2O (3), and [ZnII(L3OO)][ClO4] (4) (L1OO, = 3-[(2-(pyridine-2-yl)ethyl){2-(pyridine-2-yl)methyl}amino]propionate; L3OO, = 3-[(2-(pyridine-2-yl)ethyl){(dimethylamino)ethyl}amino]propionate) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1, 3, and 4 are one-dimensional chain-like coordination polymers. In 1 distorted octahedral MnN3O3 and in 3 square-pyramidal CuN3O2 coordination is satisfied by three nitrogen atoms and an appended carboxylate oxygen atom of the ligand, and an oxygen atom belonging to the carboxylate group of an adjacent molecule. In 4 trigonal bipyramidal ZnN3O2 coordination environment is provided by two nitrogen atoms and an appended carboxylate oxygen atom of the ligand in the equatorial plane, and the two axial positions are satisfied by a tertiary amine nitrogen and an oxygen atom belonging to the carboxylate group of an adjacent molecule. In 1 the MnII center is coordinated by an additional water molecule. In these complexes each monomeric unit is sequentially connected by syn - anti carboxylate bridges. Temperature-dependent magnetic susceptibilities for 1 and 3 are measured, revealing antiferromagnetic interactions through syn - anti carboxylate bridges between the MII centers. Analysis of the crystal packing diagram reveals that in 1 extensive ,,, stacking involving alternate pyridine rings of adjacent 1D chain exists, which eventually lead to the formation of a 2D network structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Crystal Structure of an EMAP-II-Like Cytokine Released from a Human tRNA SynthetaseHELVETICA CHIMICA ACTA, Issue 4 2003Xiang-Lei Yang Aminoacyl-tRNA synthetases catalyze the first step of protein synthesis by aminoacylation of tRNAs. Remarkably, biological fragments of two human enzymes , tyrosyl-tRNA synthetase (TyrRS) and tryptophanyl-tRNA synthetase , are active cytokines produced by proteolysis or alternative splicing. One is a C-terminal fragment of TyrRS (C-TyrRS) that has potent activity for chemotaxis of leukocytes and monocytes and for stimulating production of other cytokines. Significantly, the cytokine activity of C-TyrRS is absent in the context of the full-length native protein. Unknown is the mechanism by which domain-release from the dimeric native protein activates the cytokine. Here, the crystal structure of C-TyrRS is presented at 2.2,Ĺ resolution. This structure is similar to that of endothelial monocyte-activating protein II (EMAP-II), with critical residues of a heptapeptide element important for chemotaxis activity exposed on the first strand of a , -barrel of the monomeric unit. In contrast, the same residues of C-TyrRS are buried in an operational model for native TyrRS. Importantly, C-TyrRS is shown here to be monomeric when released from dimeric native TyrRS. Further analysis suggests that the critical residues are exposed when tRNA is bound. Thus, tRNA binding to native TyrRS may be an additional or alternative way to activate cytokine signaling. [source] Synthesis and polymerization of fluorinated monomers bearing a reactive lateral group.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003Abstract The radical copolymerization in solution of vinylidene fluoride (VDF; or 1,1-difluoroethylene) with methyl 1,1-dihydro-4,7-dioxaperfluoro-5,8-dimethyl non-1-enoate (MDP) initiated by di- tert -butyl peroxide is presented. Six copolymerization reactions were investigated with initial [VDF]0/[MDP]0 molar ratios of 35/65 to 80/20. Both of these comonomers copolymerized in this range of copolymerization. Moreover, these comonomers homopolymerized separately under these conditions. The copolymer compositions of these random copolymers were calculated by means of 19F NMR spectroscopy, which allowed the quantification of the respective amounts of each monomeric unit in the copolymers. The Tidwell,Mortimer method was used for the assessment of the reactivity ratios (ri) of both comonomers, which showed a higher incorporation of MDP in the copolymers (rMDP = 2.41 ± 2.28 and rVDF = 0.38 ± 0.21 at 120 °C). The Alfrey,Price Q and e values of the trifluoroallyl monomer MDP were calculated to be 0.024 (from QVDF = 0.008) or 0.046 (from QVDF = 0.015) and 0.70 (vs eVDF = 0.40) or 0.80 (vs eVDF = 0.50), respectively, indicating that MDP was an electron-accepting monomer. The thermal properties of these fluorinated copolymers were also determined. Except for those containing a high amount of VDF, the copolymers were amorphous. Each showed one glass-transition temperature (Tg) only, and with known laws of Tg's, Tg of the MDP homopolymer was assessed. It was compared to that obtained from the direct radical homopolymerization of MDP and discussed. Indeed, these two values were close (Tg = ,3 °C). Thermogravimetric analyses were performed, and they showed that the copolymers were rather thermostable because the thermal degradation occurred at 280 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3109,3121, 2003 [source] The chiral helical structure of a copper(II) complex with a tridentate Schiff base ligandACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Wen-Juan Shi In the title salt, catena -poly[[[aquacopper(II)]-,-3-(2-pyridylmethyleneamino)propanoato-,4N,N,,O:O,] perchlorate], {[Cu(C9H9N2O2)(H2O)]ClO4}n, the monomeric unit contains a square-based pyramidal CuII centre. The four basal positions are occupied by a tridentate anionic Schiff base ligand which furnishes an NNO-donor set, with the fourth basal position being occupied by an O-donor atom from the carboxylate group of an adjacent Schiff base ligand. The coordination sphere is completed by a water molecule at the apical position. Interestingly, each carboxylate group in the ligand forms a syn,anti -configured bridge between two CuII centres, leading to left-handed chiral helicity. The framework also exhibits O,H...O hydrogen bonds involving the water molecules and an O atom of the perchlorate anion. [source] An Improved Synthesis of Procyanidin Dimers: Regio- and Stereocontrol of the Interflavan BondEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2006Isabelle Tarascou Abstract A direct and general synthesis of procyanidin dimers B1, B2, B3 and B4 (10a,d) is presented. The approach is based on the stoichiometric coupling of two protected monomeric units (the nucleophilic 2a,b and electrophilic 4a,b partners) and deals with the regio- and stereocontrol of the C4,C8 interflavan bond as well as the control of the degree of oligomerization. The synthesis involves a five-step pathway starting from the native catechin (1a) or epicatechin (1b) to the fully deprotected dimers 10a,d. Furthermore, the process appears to be iterative as the coupling intermediates 9a,d themselves can be readily used in further selective syntheses of trimers or higher oligomers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Emulsion polymerization of styrene with amphiphilic random copolymer as surfactant: Predominant droplet nucleationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Li Liu Abstract Amphiphilic random copolymer consisting of monomeric units of poly (butyl acrylate) and poly (maleic acid salt) was synthesized and characterized. The emulsion polymerization kinetics of styrene stabilized by this copolymer was investigated. The influencing factors, including polymeric surfactant concentration, initiator concentration and polymerization temperature, were systematically studied. The kinetic data show that the polymerization rate (RP) increased with the increase of the polymeric surfactant concentration ([S]) and polymerization temperature (T). At the higher [S], droplets nucleation and micelle nucleation coexisted in the polymerization system; at the lower [S], only the droplets nucleation process existed. The polymerization did not follow Smith-Ewart Case II kinetics. Dynamic light scatter and transmission electron microscope were utilized to measure the sizes and shapes of the particles, respectively. It would be speculated that a kind of large heterogeneous particles with multiple-active-sites was formed in the polymerization system. The increasing of RP with increasing initiator concentration ([KPS]) was rapid at a medium [KPS], but the slowly increasing was observed at a lower or higher [KPS]. It was attributed to the barrier effect of the polymeric surfactant around the monomer droplets. The polymerization activation energy was 60.29 kJ/mol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Recognition of protonated aliphatic ,,,-diamines by coproporphyrin I tetraanion in waterJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2002Alejandro Flores-Villalobos Abstract Interactions of aliphatic ,,,-diamines [H2N(CH2)nNH2, 2,,,n,,,8] with coproporphyrin I tetraanion (CP) were studied by spectrophotometry, fluorimetry and 1H NMR spectroscopy in the pH range 7,10 and ionic strengths 0.01,0.1,M. Diprotonated diammonium cations induce dimerization of CP by forming 1:1 complexes with CP which undergo much stronger self-aggregation than free CP tetraanions. On increasing the number of methylene units n connecting the ammonium groups, the binding constants for the complex formation with monomeric CP (KL) increase but the dimerization constants of the resulting complexes decrease. A hydrophobic contribution to the binding free energy of ,1.6,±,0.2,kJ,mol,1 per methylene unit was obtained from the linear correlation of logKL values extrapolated to zero ionic strength vs the number of methylene units (n,=,2,6). A model for diammonium-induced porphyrin dimerization is proposed, which involves complexation of diammonium cations with CP monomer via a combination of electrostatic and hydrophobic interactions and subsequent formation of porphyrin face-to-face dimers in which diammonium cations serve as the stabilizing bridges via ion pairing to carboxylate groups of two CP monomeric units. Copyright © 2001 John Wiley & Sons, Ltd. [source] A simple HPLC-MS method for the quantitative determination of the composition of bacterial medium chain-length polyhydroxyalkanoatesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2008Andreas Grubelnik Abstract Bacterial poly(hydroxyalkanoates) (PHAs) vary in the composition of their monomeric units. Besides saturated side-chains, unsaturated ones can also be found. The latter leads to unwanted by-products (THF ester, secondary alcohols) during acidic cleavage of the polymer backbone in the conventional analytical assays. To prevent these problems, we developed a new method for the reductive depolymerization of medium chain-length PHAs, leading to monomeric diols that can be separated and quantified by HPLC/MS. Reduction is performed at room temperature with lithium aluminum hydride within 5,15 min. The new method is faster and simpler than the previous ones and is quantitative. The results are consistent with the ones obtained by quantitative 1H NMR. [source] Molar Mass and Structural Characteristics of Poly[(lactide- co -(aspartic acid)] Block CopolymersMACROMOLECULAR SYMPOSIA, Issue 1 2008Ida Poljan Abstract Summary: We report on various synthetic procedures for the preparation of biodegradable and biocompatible poly(lactide- co -aspartic acid) block copolymers based on natural monomeric units , lactic acid and aspartic acid. Multiblock poly(lactide- co -aspartic acid) copolymers of different comonomer composition were synthesized by heating a mixture of L-aspartic acid and L,L-lactide in melt without the addition of any catalyst or solvent and with further alkaline hydrolysis of the cyclic succinimide rings to aspartic acid units. Diblock poly(lactide- co -aspartic acid) copolymers with different block lengths were prepared by copolymerization of amino terminated poly(, -benzyl-L-aspartate) homopolymer and L,L-lactide with subsequent deprotection of the benzyl protected carboxyl group by hydrogenolysis. The differences in the structure, composition, molar mass characteristics, and water-solubility of the synthesized multiblock and diblock poly(lactide- co -aspartic acid) copolymers are discussed. [source] Studies of Adjacent Re-Entry Folds of Chains of Syndiotactic l,2-Poly(1,3-butadiene) by Molecular Mechanics CalculationsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Roberto Napolitano Abstract The mode of packing and the adjacent re-entry folds of chains of syndiotactic 1,2-poly(1,3-butadiene) have been studied by molecular mechanics calculations with the use of various sets of potential functions. The results of the packing analysis indicate that the crystal grows preferentially along the [100] and [110] directions. Models of fold have been built up on an infinite ab surface completely covered by adjacent re-entry folds in the (100) and (110) planes. The results of energy minimizations show that several almost isoenergetic folds, constituted by four monomeric units, can be realized in the (100) planes, while the fold in the (110) planes has higher energy. The calculated value of the work of fold is in satisfactory agreement with that derived by crystallization kinetics reported in literature. [source] Copolymers of N -methylpyrrole and 3,4-ethylenedioxythiophene: structural, physical and electronic propertiesPOLYMER INTERNATIONAL, Issue 6 2007Cintia Ocampo Abstract The structural, electric and electronic properties of copolymers derived from mixtures of N -methylpyrrole and 3,4-ethylenedioxythiophene (EDOT) with various concentration ratios have been investigated and, additionally, compared with those of the corresponding homopolymers. The electropolymerization kinetics of all the generated copolymers and the homopolymers was examined in terms of current productivity using chronoamperometry. The chemical structure of the linkages between adjacent monomers and the microstructure of the chains were investigated using Fourier transform infrared spectroscopy and quantum mechanical calculations, respectively. The results indicate that the linkages between monomeric units formed during the anodic copolymerization are of the ,,, type, while the microstructure of the copolymers depends on the EDOT content. Theoretical calculations were also used to examine the electronic properties of the systems under study, while the conductivity and the electrical stability were studied using the sheet-resistance method. Interestingly, the electric properties are consistent with the random and block microstructures predicted for the copolymers with low and high EDOT content, respectively. Copyright © 2006 Society of Chemical Industry [source] Codex final definition of dietary fibre: issues of implementationQUALITY ASSURANCE & SAFETY OF CROPS & FOOD, Issue 4 2009Joanne R. Lupton Abstract Introduction At its 30th session in South Africa in November 2008, the Codex Committee on Nutrition and Foods for Special Dietary Uses (CCNFSDU) agreed on a definition of dietary fibre. Although many aspects of what can be called "dietary fibre" were resolved, the application of this definition raises additional issues in need of resolution. Objectives The goal of this paper is to discuss the major areas at issue in implementing the new Codex definition of dietary fibre: (1) the footnote that individual countries can decide whether they accept oligosaccharides with a degree of polymerization (DP) from 3 to 9 (included) as being fibre; and 2) guidance on which physiological effects are beneficial. Less critical but still important is the issue of animal sources of fibre not requiring proof of a beneficial physiological effect; and the effect of processing on fibre. Results and conclusion Unless all countries accept (or do not accept) that carbohydrate polymers with 3,9 monomeric units are dietary fibre, there will be two, rather than one definition. Again, if each country has its own criteria as to the physiological benefits of fibre and how to verify those benefits there will be as many "definitions" of fibre as there are effects accepted by all the member states. Given the importance to consumers, food companies, researchers, and regulatory agencies in having one definition, it is incumbent on all of us in the field to work toward that end. [source] Characterisation via electrospray ionisation multistage mass spectrometry of three related series of nitrido technetium complexes containing phosphinothiolate and dithiocarbamate ligandsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2005Michela Tubaro Nine nitrido technetium compounds comprising bis-substituted Tc(N)(PS)2 (1,4) (PS,=,bidentate phosphinothiolate ligands) and Tc(N)(dtc)2 (5, 6) derivatives (dtc,=,bidentate dithiocarbamate), and mixed-ligand Tc(N)(PS)(dtc) (7,9) species, were subjected to electrospray ionisation mass spectrometry and MSn experiments. Bis-substituted phosphinothiolato complexes 1,4 lead to the straightforward formation of dinuclear species reasonably originating from proton bound dimers. These dinuclear species do not show, under collisionally induced fragmentation processes, the formation of monomeric units but cleavages related to the ligand framework, thereby proving the high stability of the [TcH+Tc] bond. Bis-dithiocarbamate compounds 5 and 6 show, instead, abundant [M+H]+, [M+Na]+ and [2M+Na]+ ions, and their collisionally induced fragmentations are highly favoured with cleavages related to the CN and CS bonds. During these processes, the coordination of a water molecule to [MH,L]+ product ions is observed, as proved by the collisionally induced H2O loss detected for this species. Mixed-ligand compounds 7 and 8 show the protonated molecules and Na+ -cationised ions with fragmentation processes related to the dithiocarbamate moiety. This behaviour indicates that coordination of ether- and ester-substituted dithiocarbamates to the [Tc,,N] group is weaker than that of phosphinothiolates. Conversely, diethyldithiocarbamate inserted in mixed complex 9 enhances both CN and TcS bonds, and fragmentation processes suggest that metal-phosphinothiolate and metal-dithiocarbamate show comparable strength. Copyright © 2005 John Wiley & Sons, Ltd. [source] catena -Poly[[(trifluoromethanesulfonato-,O)silver(I)]-,-di-2-pyridylamine-,2N2:N2,], a chain polymer with short Ag,C contactsACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2006Peter G. Jones The title compound, [Ag(CF3O3S)(C10H9N3)]n, is a chain polymer in which neighbouring monomeric units are related by a glide plane. The silver centre is four-coordinate; the donor atoms are one trifluoromethanesulfonate O atom and one pyridine N atom from each of two symmetry-related dipyridylamines, and an additional and unexpected Ag,C contact [2.6464,(16),Ĺ] is observed to a pyridine C atom. The chains are reinforced by one classical N,H,O and two `weak' C,H,O hydrogen bonds. [source] Poly[trans -diaquamanganese(II)-,-(3-pyridinecarboxylato- N:O)-,-(3-pyridinecarboxylato- O:N)]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2000Xiang Hao The title complex, [MnII(nic)2(H2O)2]n [nic is 3-pyridinecarboxylate (also called nicotinate), C6H4NO2,], has a two-dimensional layer structure with the unique Mn atom on an inversion centre. In each layer, all nicotinate ligands are coordinated to Mn atoms in a bridging/bidentate mode, thus linking the {MnII(nic)2(H2O)2} monomeric units together to form a dative-bond-based layered polymer. The intra-layer hydrogen bonds involving all water molecules and the carboxylate groups may play an auxiliary part in stabilizing the layer. The layers are arranged in an ordered manner along the a axis through van der Waals forces so as to complete the solid-state structure of the crystal. [source] Recombinant human elastin polypeptides self-assemble into biomaterials with elastin-like propertiesBIOPOLYMERS, Issue 4 2003Catherine M. Bellingham Abstract Processes involving self-assembly of monomeric units into organized polymeric arrays are currently the subject of much attention, particularly in the areas of nanotechnology and biomaterials. One biological example of a protein polymer with potential for self-organization is elastin. Elastin is the extracellular matrix protein that imparts the properties of extensibility and elastic recoil to large arteries, lung parenchyma, and other tissues. Tropoelastin, the ,70 kDa soluble monomeric form of elastin, is highly nonpolar in character, consisting essentially of 34 alternating hydrophobic and crosslinking domains. Crosslinking domains contain the lysine residues destined to form the covalent intermolecular crosslinks that stabilize the polymer. We and others have suggested that the hydrophobic domains are sites of interactions that contribute to juxtaposition of lysine residues in preparation for crosslink formation. Here, using recombinant polypeptides based on sequences in human elastin, we demonstrate that as few as three hydrophobic domains flanking two crosslinking domains are sufficient to support a self-assembly process that aligns lysines for zero-length crosslinking, resulting in formation of the crosslinks of native elastin. This process allows fabrication of a polymeric matrix with solubility and mechanical properties similar to those of native elastin. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 445,455, 2003 [source] Dynamic Supramolecular Polymers Based on Benzene-1,3,5-tricarboxamides: The Influence of Amide Connectivity on Aggregate Stability and Amplification of ChiralityCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2010Patrick Abstract N-Centred benzene-1,3,5-tricarboxamides (N-BTAs) composed of chiral and achiral alkyl substituents were synthesised and their solid-state behaviour and self-assembly in dilute alkane solutions were investigated. A combination of differential scanning calorimetry (DSC), polarisation optical microscopy (POM) and X-ray diffraction revealed that the chiral N-BTA derivatives with branched 3,7-dimethyloctanoyl chains were liquid crystalline and the mesophase was assigned as Colho. In contrast, N-BTA derivatives with linear tetradecanoyl or octanoyl chains lacked a mesophase and were obtained as crystalline compounds. Variable-temperature infrared spectroscopy showed the presence of threefold, intermolecular hydrogen bonding between neighbouring molecules in the mesophase of the chiral N-BTAs. In the crystalline state at room temperature a more complicated packing between the molecules was observed. Ultraviolet and circular dichroism spectroscopy on dilute solutions of N-BTAs revealed a cooperative self-assembly behaviour of the N-BTA molecules into supramolecular polymers with preferred helicity when chiral alkyl chains were present. Both the sergeants-and-soldiers as well as the majority-rules principles were operative in stacks of N-BTAs. In fact, the self-assembly of N-BTAs resembles closely that of their carbonyl (CO)-centred counterparts, with the exception that aggregation is weaker and amplification of chirality is less pronounced. The differences in the self-assembly of N- and CO-BTAs were analysed by density functional theory (DFT) calculations. These reveal a substantially lower interaction energy between the monomeric units in the supramolecular polymers of N-BTAs. The lower interaction energy is due to the higher energy penalty for rotation around the PhNH bond compared to the PhCO bond and the diminished magnitude of dipole,dipole interactions. Finally, we observed that mixed stacks are formed in dilute solution when mixing N-BTAs and CO BTAs. [source] Stability and Dynamics of Domain-Swapped Bovine-Seminal RibonucleaseCHEMISTRY & BIODIVERSITY, Issue 5 2004Kalyan The proteins of the ribonuclease-A (RNase-A) family are monomeric, with the exception of bovine-seminal ribonuclease (BS-RNase). BS-RNase is formed by swapping the N-terminal helices across the two monomeric units. A molecular-dynamics (MD) study has been performed on the protein for a simulation time of 5.5,ns to understand the factors responsible for the stability of the dimer. Essential dynamics analysis and motional correlation of the protein atoms yielded the picture of a stabilising, yet flexible, interface. We have investigated the role of intermolecular H-bonding, protein/water interaction, and protein/water networks in stabilising the dimer. The networks of interchain H-bonds involving side-chain/side-chain or side-chain/main-chain (ScHB) interactions between the two chains have also been studied. The ability of protein atoms in retaining particular H2O molecules was investigated as a function of the accessible surface area (ASA), depth, and hydration parameters, as well as their participation in protein/water networks. [source] Rapid Prediction of the Hydrogen Bond Cooperativity in N -methylacetamide ChainsCHEMPHYSCHEM, Issue 18 2009Xiao-Nan Jiang Abstract A method is proposed to rapidly predict the hydrogen bond cooperativity in N -methylacetamide chains. The parameters needed are obtained from the fittings to the hydrogen bonding energies in the formamide chains containing 2 to 8 monomeric units. The scheme is then used to calculate the individual hydrogen bonding energies in N -methylacetamide chains containing 2 to 7 monomeric units. The cooperativity predicted is in good agreement with those obtained from MP2/6-31+G** calculations by including the BSSE correction. Our scheme is further employed to predict the individual hydrogen bonding energies in larger N -methylacetamide chains containing up to 200 monomeric N -methylacetamide units, to which the MP2 method cannot be applied. Based on our scheme, a cooperative effect of over 170,% of the dimer hydrogen bonding energy in long N -methylacetamide chains is predicted. The method is also applied to heterogeneous chains containing formamide, acetamide, N -methylformamide, and N -methylacetamide. The individual hydrogen bonding energies in these heterogeneous chains are also in good agreement with those obtained from MP2 calculations with the BSSE correction, further demonstrating that our method is reasonable. [source] | |||||||||||||