Binding of carboxylate and trimethylammonium salts to octa-acid and TEMOA deep-cavity cavitands

In participation of the fifth statistical assessment of modeling of proteins and ligands (SAMPL5), the strength of association of six guests (3–8) to two hosts (1 and 2) were measured by ¹H NMR and ITC. Each host possessed a unique and well-defined binding pocket, whilst the wide array of amphiphilic guests possessed binding moieties that included: a terminal alkyne, nitro-arene, alkyl halide and cyano-arene groups. Solubilizing head groups for the guests included both positively charged trimethylammonium and negatively charged carboxylate functionality. Measured association constants (K _a ) covered five orders of magnitude, ranging from 56 M^?1 for guest 6 binding with host 2 up to 7.43 × 10⁶ M^?1 for guest 6 binding to host 1.     

Controlling photochemistry with distinct hydrophobic nanoenvironments

A combination of hydrophobic forces and guest templation drive the assembly of cavitands into molecular capsules. Encapsulated guests such as dibenzyl ketones reside in an essentially dry environment, and upon irradiation, undergo rearrangement processes that are templated by the shape of the 1 nm x 2 nm cavity.     

A study of the solid solutions (EuO)1−x(LnN)x (where Ln = Nd,Eu, Gd) by europium-151 Mössbauer spectroscopy

The magnitude of the magnetic hyperfine field at Eu^II in the cubic solid solutions (EuO)_1?x(LnN)_x (where Ln = Nd, Eu, Gd) has been determined at 4.2°K by ¹⁵¹Eu Mössbauer spectroscopy. The resultant effective hyperfine field is found to be almost independent of composition because of a number of compensating effects.     

Molecular relaxation processes in very dilute systems: A 13C NMR study of alcohols in alkanes

¹³C T₁ relaxation times have been determined for n-butanol in C₆D₁₂ in the concentration range 0.001 ? _x ? 1 (using ¹³C labelled alcohol) and for t-butanol in the range 0.01 ? _x ? 1. In the former case, this has allowed us to probe molecular mobility down to the region of monomeric alcohols. Comparison with previous results from measurements of ¹H chemical shifts, dielectric relaxation, and the picosecond dynamics of electron solvation allows us to build up a detailed picture of molecular clustering and liquid structure in alkane—alcohol mixtures. For n-butanol, the local liquid structure is established by x = 0.2 while t-butanol does not appear to form aggregates larger than trimers until x = 0.5.     

Ruthenium-99 Mössbauer spectra of some nitrido complexes of Ru(VI)

The quadrupole splittings found in the ⁹⁹Ru Mössbauer spectra of (Bu₄ⁿN)[RuNCl₄ and (Ph₄As)[RuNBr₄] at 4.2 K are the largest yet observed for this isotope. The six component lines are almost resolved, and lead to new estimates for the ratio of the nuclear quadrupole moments of Q_e/Q_g = +2.82 ± 0.09 and for the E2/M1 mixing ratio of δ² = 2.64 ± 0.17. By contrast, the spectrum of Cs₂[RuNCl₅] has a much smaller quadrupole splitting and a more negative isomer shift. These differences can be interpreted empirically in terms of the asymmetric occupation of the 4d orbitals. The new data confirm an earlier deduction that both Q_e and Q_g are positive.     

Ratio of the nuclear quadrupole moments of 99Ru by mössbauer spectroscopy

The ratio of the nuclear quadrupole moments of the first excited and ground states of ⁹⁹Ru has been determined for the first time. The value of Q_e/Q_g = +2.94 ± 0.04 was obtained from the quadrupole splitting observed in the ⁹⁹Ru Mössbauer spectrum of the spinel Co₂RuO₄. Consideration of the ligand-field splitting at the ruthenium site leads to the belief that Q_e and Q_g are both positive, and Q_e > 0.23 × 10^?28 m².     

The impact of Mössbauer spectroscopy on chemistry

The historical development of Mössbauer spectroscopy is briefly described from a chemist's viewpoint, and a critical assessment is made of its role in modern chemistry.     

Patterning small-molecule biocapture surfaces: microcontact insertion printing vs. photolithography

Chemical patterns prepared by self-assembly, combined with soft lithography or photolithography, are directly compared. Pattern fidelity can be controlled in both cases but patterning at the low densities necessary for small-molecule probe capture of large biomolecule targets is better accomplished using microcontact insertion printing (μCIP). Surfaces patterned by μCIP are used to capture biomolecule binding partners for the small molecules dopamine and biotin.     

An improved synthesis of ‘octa-acid’ deep-cavity cavitand

An improved synthesis of a water-soluble deep-cavity cavitand (octa-acid, 1) is presented. Previously (Gibb, C.L.D.; Gibb, B.C. J. Am. Chem. Soc. 2004, 126, 11408–11409), we documented access to host 1 in eight (non-linear) steps starting from resorcinol; a synthesis that required four steps involving chromatographic purification. Here, we reveal a modified synthesis of host 1. Consisting of seven (non-linear) steps, this new synthesis involves only one chromatographic step, and avoids a minor impurity observed in the original approach. This improved synthesis is therefore useful for the laboratories that are investigating the properties of these types of host.