We report a detailed study on the IR spectroscopy of HCl-water complexes in superfluid helium nanodroplets in the frequency range from 2660 to 2675 cm(-1). We have recorded spectra of HCl-H2(16)O as well as of HCl-H2(18)O complexes and compared these results with theoretical predictions. In addition, we have carried out mass-selective intensity measurements as a function of partial pressure of HCl as well as of H2(18)O (pick-up curves). The results support a scenario where the IR-absorption in this part of the spectrum contains contributions from undissociated as well as from dissociated clusters with Cl(-)(H2O)3(H3O)(+) being the smallest dissociated complex. These findings are corroborated by additional electric field measurements yielding the orientation of the vibrational transition moment with respect to the permanent dipole moment. As a result we are able to assign a broad absorption band starting at 2675 cm(-1) to dissociated HCl-water clusters (HCl)1(H2O)n with n ≥ 4. The two narrow absorption lines at 2667.9 cm(-1) and 2670 cm(-1) are assigned to an undissociated cluster, in agreement with previous studies.

The chemically stabilized somatostatin-derived cyclic octapeptide octreotate has a number of interesting applications in medicinal chemistry. Here, a number of different organometallic derivatives of octreotate were prepared, and their properties were investigated. Specifically, we report the synthesis and characterization of ruthenocene, ferrocene, and cobaltocenium octreotate derivatives and their fluorophore-labeled conjugates as well as a dicobalt hexacarbonyl alkyne functionalized octreotate. To provide further insights into their characteristics, the log P values and electrochemical properties of the novel metal conjugates were compared. For biological activity, we determined their toxicity in three different cell lines. Cellular uptake and colocalization of selected compounds were studied by fluorescence microscopy with particular focus on efficiency and specificity of their uptake through the somatostatin receptor SSTR to elucidate the value of the metallocene head group for its potential use as a nontoxic and universal peptide label.

The IR-spectrum of the allyl-NO adduct (CH2-CH-CH2-NO) in helium nanodroplets has been recorded in the frequency region 2850-3120 cm(-1). CH2-CH-CH2-NO has been investigated as a prototype of the product of radical-radical reactions at 0.37 K. The product of the reaction, 3-nitroso-1-propene, was formed via the reaction of allyl and NO within the helium droplets. For an assignment we have predicted the conformers of the CH2-CH-CH2-NO using density functional theory (DFT) with a BLYP functional and a TZVPP basis set. By comparison with the experimental spectrum we can show that all three conformers are stabilized in superfluid helium nanodroplets.

Infrared spectra of the allyl radical-HCl complex in superfluid helium nanodroplets have been recorded in the IR frequency range of 2750-3120 cm(-1). Six fundamental bands were observed, five of which have been assigned to the C-H stretch vibrations of the allyl radical. No additional CH bands were observed upon the binding of HCl. The band at 2800.3 cm(-1) can unambiguously be assigned to the bound HCl stretch, which is red-shifted by 106 cm(-1) compared to that of the free HCl. Stark spectra and pickup curves were recorded and support our assignment. In accompanying ab initio calculations, we found four equivalent minima and computed a two-dimensional potential energy surface for the HCl positioning on the allyl radical plane at the CCSD(T)/TZVPP level. Based on our findings, we conclude that the ground-state structure of the complex shows two energetically equivalent T-shaped minimum structures. Because of small barriers between the two minima, a delocalization of the HCl is anticipated.

We have recorded the IR-spectrum of the deuterated allyl radical in the frequency range of the CH stretch vibrations in liquid helium nanodroplets. Comparison to the allyl radical spectrum enabled us to make an unambiguous assignment. Based on these new experimental measurements, a reassignment of the ν2,3 IR bands was deemed necessary.