Microsolvation of the pyrrole cation (Py+) with nonpolar and polar ligands: infrared spectra ofPy+-L withL=Ar,N ,andH2O(n<=3)
Microsolvation of the pyrrole cation (Py+) with nonpolar and polar ligands: infrared spectra ofPy+-L withL=Ar,N ,andH2O(n<=3)
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吡咯阳离子 (Py ) 与非极性和极性配体的微溶剂化：Py -L 的红外光谱，其中 L=Ar,N 和H2O(n<=3)
DOI：
10.1039/c6cp07251h
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
Murat Ozturka and Otto Dopfer
中科院分区：
文献类型：
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作者：
Markus Schutz;Yoshiteru Matsumoto;Aude Bouchet;Murat Ozturka and Otto Dopfer
芳香族（生物）分子的溶剂化对分子间相互作用和超分子组装体、蛋白质和DNA的功能有很强的影响。本文通过分子束中冷质量选择Py+ -Ln （n≤3）簇的红外光解（IRPD）光谱和B3LYP-D3/ augg -cc- pvtz水平色散校正的密度泛函理论计算，表征了杂环芳香吡啶阳离子（Py+）在2A2基电子态下与非极性、四极性和偶极配体（L = Ar、N2和H2O）的初始微溶剂化过程。NH拉伸频率的大小和同分异构体特异性变化（ΔνNH）揭示了各种配体结合位点之间的竞争、各自分子间键的强度和簇生长。在Py+ -Ar中，Ar与酸性NH基团（NH⋯Ar）的线性H键与芳香环上的π堆叠竞争，并且观察到Py+ -Ar (H)和Py+ -Ar （π）。对于L = N2和H2O，线性NH⋯L氢键比任何其他结合位点和唯一观察到的结合基序都要稳定得多。对于Py+ - ar2和Py+ - (N2)2三聚体，具有一个H键和一个π键配体的H/π异构体与具有两个分叉非线性NH⋯L键的2H异构体强烈竞争。后者对Ar等价，但对N2不等价。Py+ -H2O具有强大的线性NH⋯O氢键，具有电荷偶极子构型和C2v对称性。L = Ar和N2的冷Py+ -H2O-L簇的IRPD光谱显示，Ar比Py+环更倾向于π堆叠，而N2与H2O配体形成OH⋯N2氢键。Py+ -Ln中的ΔνNH频移与NH⋯L氢键强度和L的质子亲和（PA）相关，并且Py+ -L (H)二聚体的ΔνNH与PA之间建立了单调相关关系。与中性的Py-L二聚体比较，揭示了正电荷对NH基团的酸度、NH⋯L氢键的强度和首选配体结合基序的强烈影响。
The solvation of aromatic (bio-)molecular building blocks has a strong impact on the intermolecular interactions and function of supramolecular assemblies, proteins, and DNA. Herein we characterize the initial microsolvation process of the heterocyclic aromatic pyrrole cation (Py+) in its 2A2 ground electronic state with nonpolar, quadrupolar, and dipolar ligands (L = Ar, N2, and H2O) by infrared photodissociation (IRPD) spectroscopy of cold mass-selected Py+–Ln (n ≤ 3) clusters in a molecular beam and dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level. Size- and isomer-specific shifts in the NH stretch frequency (ΔνNH) unravel the competition between various ligand binding sites, the strength of the respective intermolecular bonds, and the cluster growth. In Py+–Ar, linear H-bonding of Ar to the acidic NH group (NH⋯Ar) is competitive with π-stacking to the aromatic ring, and both Py+–Ar(H) and Py+–Ar(π) are observed. For L = N2 and H2O, the linear NH⋯L H-bond is much more stable than any other binding site and the only observed binding motif. For the Py+–Ar2 and Py+–(N2)2 trimers, the H/π isomer with one H-bonded and one π-bonded ligand strongly competes with a 2H isomer with two bifurcated nonlinear NH⋯L bonds. The latter are equivalent for Ar but nonequivalent for N2. Py+–H2O exhibits a strong and linear NH⋯O H-bond with charge-dipole configuration and C2v symmetry. IRPD spectra of cold Py+–H2O–L clusters with L = Ar and N2 reveal that Ar prefers π-stacking to the Py+ ring, while N2 forms an OH⋯N2 H-bond to the H2O ligand. The ΔνNH frequency shifts in Py+–Ln are correlated with the strength of the NH⋯L H-bond and the proton affinity (PA) of L, and a monotonic correlation between ΔνNH of the Py+–L(H) dimers and PA is established. Comparison with neutral Py–L dimers reveals the strong impact of the positive charge on the acidity of the NH group, the strength of the NH⋯L H-bond, and the preferred ligand binding motif.