The Last Globally Stable Extended Alkane

Lüttschwager, Nils Olaf Bernd; Wassermann, Tobias N.; Mata, Ricardo A.; Suhm, Martin A.

doi:10.1002/anie.201202894

Cited by 118 publications

(156 citation statements)

References 29 publications

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“…These values have been applied previously in weakly interacting systems with good results. [44] A common issue in PAO-based local calculations is the stability of the domain definition. This is particularly important in fragment calculations, in which errors can add up as one builds a total energy out of the sum of many smaller calculations.…”

Section: Computational Detailsmentioning

confidence: 99%

Coupled‐Cluster Interaction Energies for 200‐Atom Host–Guest Systems

Andrejić¹,

Ryde²,

Mata³

et al. 2014

ChemPhysChem

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We have developed a method to calculate interaction energies of large systems (such as host-guest or even protein-ligand systems) at the local coupled-cluster with singles, doubles, and perturbative triples level, and with extrapolation to the limit of a complete basis set. The method is based on the polarizable multipole interactions with supermolecular pairs molecular fractionation approach, which combines a pairwise quantum-mechanical evaluation of the short-range interactions with a polarizable multipole treatment of many-body effects. The method is tested for nine guest molecules binding to an octa-acid host (in total 198-207 atoms), as part of the SAMPL4 blind challenge. From the test calculations, the accuracy of the approach is found to be 10 kJ mol(-1) or better. Comparison with dispersion-corrected density functional theory reveals that the latter underestimates the dispersion contribution for this type of system, which leads to a difference in the ranking of the ligands.

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Section: Computational Detailsmentioning

confidence: 99%

Coupled‐Cluster Interaction Energies for 200‐Atom Host–Guest Systems

Andrejić¹,

Ryde²,

Mata³

et al. 2014

ChemPhysChem

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“…T ) minimizes the number of strained bonds and allows an energetically favorable parallel arrangement of the chain ends, leading it to be the suggested global minimum for longer alkanes. [2][3][4] These three conformational structures are illustrated in Figure 1. It is well known that the computation of relative energies involving weak interactions presents a significant challenge for computational studies.…”

Section: Introductionmentioning

confidence: 99%

At What Chain Length Do Unbranched Alkanes Prefer Folded Conformations?

2014

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Short unbranched alkanes are known to prefer linear conformations, while long unbranched alkanes are folded. It is not known with certainty at what chain length the linear conformation is no longer the global minimum. To clarify this point, we use ab initio and density functional methods to compute the relative energies of the linear and hairpin alkane conformers for increasing chain lengths. Extensive electronic structure calculations are performed to obtain optimized geometries, harmonic frequencies and accurate single point energies for the selected alkane conformers from octane through octadecane. Benchmark CCSD(T)/cc-pVTZ single point calculations are performed for chains through tetradecane, while approximate methods are required for the longer chains up to octadecane. Using frozen natural orbitals to unambiguously truncate the virtual orbital space, we are able to compute composite CCSD FNO(T) single point energies for all the chain lengths. This approximate composite method has significant computational savings compared to full CCSD(T) while retaining ∼ 0.15 kcal/mol accuracy compared to the benchmark results. More approximate dual-basis resolutionof-the-identity double-hybrid DFT calculations are also performed and shown to have reasonable 0.2 − 0.4 kcal/mol errors compared with our benchmark values. After including contributions from temperature dependent internal energy shifts, we find the preference for folded conformations to lie between hexadecane and octadecane, in excellent agreement with recent experiments [Lüttschwager, N. O.; Wassermann, T. N.; Mata, R. A.; Suhm, M. A.

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“…Since the focus of this work is rather on the experiment, an estimate of the critical folding chain length (n c ) based on Raman jet spectra will be discussed first, followed by a comparison to quantum chemical energy predictions [13,14,[93][94][95]. When discussing the experimental estimate, special attention has to be given to the jet-expansion technique, which enables the preparation of low-energy alkane conformers but bears the disadvantage of producing non-equilibrium conformer distributions.…”

Section: Critical Folding Chain Lengthmentioning

confidence: 99%

Unbranched n-Alkanes

Lüttschwager

2014

Raman Spectroscopy of Conformational Rearrangements at Low Temperatures

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In this chapter, the Raman spectroscopic investigation of n-alkane self-solvation will be presented. To support the later analysis, the first section discusses the conformational isomerism of n-alkanes in general and addresses the question to which temperature alkanes must be cooled to work out low-energy conformations. Section 4.2 outlines the vibrational degrees of freedom of unbranched n-alkanes to facilitate the assignment of Raman jet spectra. In Sect. 4.3, the simulation of Raman jet spectra which aid the assignment and provide conformational temperatures is discussed. Raman jet spectra are presented and assigned subsequently in Sect. 4.4. The chapter closes with the determination of the critical folding chain length (n c ) based on the experimental findings and a discussion of computational predictions.

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The Last Globally Stable Extended Alkane

Cited by 118 publications

References 29 publications

Coupled‐Cluster Interaction Energies for 200‐Atom Host–Guest Systems

Coupled‐Cluster Interaction Energies for 200‐Atom Host–Guest Systems

At What Chain Length Do Unbranched Alkanes Prefer Folded Conformations?

Unbranched n-Alkanes

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