Obaysch: A Hippopotamus in Victorian London tells the remarkable story of Obaysch the hippopotamus, the first ‘star’ animal to be exhibited in the London Zoo. In 1850, a baby hippopotamus arrived in ...England, thought to be the first in Europe since the Roman Empire, and almost certainly the first in Britain since prehistoric times. Captured near an island in the White Nile, Obaysch was donated by the viceroy of Egypt in exchange for greyhounds and deerhounds. His arrival in London was greeted with a wave of ‘hippomania’, doubling the number of visitors to the Zoological Gardens almost overnight. Delving into the circumstances of Obaysch’s capture and exhibition, John Simons investigates the phenomenon of ‘star’ animals in Victorian Britain against the backdrop of an expanding British Empire. He shows how the entangled aims of scientific exploration, commercial ambition, and imperial expansion shaped the treatment of exotic animals throughout the nineteenth and early twentieth centuries. Along the way, he uncovers the strange and moving stories of Obaysch and the other hippos who joined him in Europe as the trade in zoo animals grew.
The anharmonic vibrational spectra of α-d-glucose, β-d-glucose, and sucrose are computed by the vibrational self-consistent field (VSCF) method, using potential energy surfaces from electronic ...structure theory, for the lowest energy conformers that correspond to the gas phase and to the crystalline phase, respectively. The results are compared with ultraviolet−infrared (UV-IR) spectra of phenyl β-d-glucopyranoside in a molecular beam, with literature results for sugars in matrices and with new experimental data for the crystalline state. Car−Parrinello dynamics simulations are also used to study temperature effects on the spectra of α-d-glucose and β-d-glucose and to predict their vibrational spectra at 50, 150, and 300 K. The effects of temperature on the spectral features are analyzed and compared with results of the VSCF calculations conducted at 0 K. The main results include: (i) new potential surfaces, constructed from Hartree−Fock, adjusted to fit harmonic frequencies from Møller−Plesset (MP2) calculations, that give very good agreement with gas phase, matrix, and solid state spectra; (ii) computed infrared spectra of the crystalline solid of α-glucose, which are substantially improved by including mimic groups that represent the effect of the solid environment on the sugar; and (iii) identification of a small number of combination-mode transitions, which are predicted to be strong enough for experimental observation. The results are used to assess the role of anharmonic effects in the spectra of the sugars in isolation and in the solid state and to discuss the spectroscopic accuracy of potentials from different electronic structure methods.
The anomeric effect is a chemical phenomenon that refers to an observed stabilization of six-membered carbohydrate rings when they contain an electronegative substituent at the C1 position of the ...ring. This stereoelectronic effect influences the three-dimensional shapes of many biological molecules. It can be manifested not only in this classical manner involving interaction of the endocyclic oxygen atom (O5) found in such sugars with the C1 substituent (endo-anomeric effect) but also through a corresponding interaction of the electronegative exocyclic substituent with O5 (exo-anomeric effect). However, the underlying physical origin(s) of this phenomenon is still not clear. Here we show, using a combination of laser spectroscopy and computational analysis, that a truncated peptide motif can engage the two anomers of an isolated sugar in the gas phase, an environment lacking extraneous factors which could confound the analysis. (Anomers are isomers that differ in the orientation of the substituent at C1.) Complexes formed between the peptide and the α- or β-anomers of d-galactose are nearly identical structurally; however, the strength of the polarization of their interactions with the peptide differs greatly. Natural bond order calculations support this observation, and together they reveal the dominance of the exo- over the endo-anomeric effect. As interactions between oxygen atoms at positions C1 and C2 (O1 and O2, respectively) on the pyranose ring can alter the exo/endo ratio of a carbohydrate, our results suggest that it will be important to re-evaluate the influence, and biological effects, of substituents at position C2 in sugars.
A combination of vibrational spectroscopy conducted under molecular beam conditions and quantum chemical calculation has established the intrinsic three-dimensional structures of the cellulose ...disaccharide and, focusing on the critical β1,4-linkage at the nonreducing end of the growing cellulose polymer, its C-4′ epimer. Left to their own devices they both adopt a cis (anti-ϕ/syn-ψ) glycosidic configuration, supported in the epimer by strong, cooperative inter-ring hydrogen bonding. In the cellulose disaccharide, however, where the OH-4′(Glc) group is equatorial, the cooperativity is reduced and the corresponding inter-ring hydrogen bonding is relatively weak. The cis conformational preference is still retained in their singly hydrated complexes. In the cellulose disaccharide insertion of the water molecule at the favored binding site between OH-4′ and the neighboring hydroxyl group OH-6′ promotes a structural reorganization to create a configuration that parallels that of its unhydrated epimer and greatly strengthens the inter-ring hydrogen bonding. In the C-4′ epimer, the axial orientation of OH-4′ blocks this binding site and the bound water molecule simply adds on at the end of the (OH-O) n chain, which has a negligible effect on the (already strong) inter-ring bonding. The implications of these results are discussed with respect to the structure and insolubility of native cellulose polymers.
Key interactions: Sugar–arene complexes have been created in molecular‐beam experiments and observed by IR ion‐dip spectroscopy in the gas phase. These complexes are powerful models of the selective ...recognition seen in protein–sugar complexes, for example between the galactose‐specific lectin from Artocarpus hirsute and MeGal (see picture).
The influence of an acetamido group in directing the preferred choice of hydration sites in glucosamine and a consequent extension of the working rules governing regioselective hydration and ...conformational choice, have been revealed through comparisons between the conformations and structures of “free” and multiply hydrated phenyl N‐acetyl‐β‐D‐glucosamine (βpGlcNAc) and phenyl β‐D‐glucopyranoside (βpGlc), isolated in the gas phase at low temperatures. The structures have been assigned through infrared ion depletion spectroscopy conducted in a supersonic jet expansion, coupled with computational methods. The acetamido motif provides a hydration focus that overwhelms the directing role of the hydroxymethyl group; in multiply hydrated βpGlcNAc the water molecules are all located around the acetamido motif, on the “axial” faces of the pyranose ring rather than around its edge, despite the equatorial disposition of all the hydrophilic groups in the ring. The striking and unprecedented role of the C‐2 acetamido group in controlling hydration structures may, in part, explain the differing and widespread roles of GlcNAc, and perhaps GalNAc, in nature.
Selective hydration: The acetamido motif provides a hydration focus that locates bound water molecules on the “axial” faces of the pyranose ring—a striking and unprecedented role that may, in part, explain the differing and widespread role of GlcNAc in nature.
Ab initio vibrational self-consistent field (VSCF) calculations are used to predict the vibrational spectra of an extended series of monosaccharide·D2O complexes, including glucose, galactose, ...mannose, xylose, and fucose in their α and β anomeric forms, and compared with recently published experimental data for their (phenyl-tagged) complexes. Anharmonic VSCF-PT2 frequencies are calculated directly, using ab initio hybrid HF/MP2 potentials, to assess their accuracy in reproducing the vibrational anharmonicities and provide a more rigorous basis for vibrational and structural assignments. The average discrepancies between the calculated and experimental frequencies are ∼1.0–1.5%, and the first-principles spectroscopic calculations, free of any empirical scaling, yield results of high accuracy. They encourage confidence in their future application to the assignment of other carbohydrate systems, both free and complexed, and an improved understanding of their intra- and intermolecular carbohydrate interactions.
The conformation of phenyl-substituted monosaccharides (mannose, galactose, and glucose) and their singly hydrated complexes has been investigated in the gas phase by means of a combination of mass ...selected, conformer specific ultraviolet and infrared double resonance hole burning spectroscopy experiments, and ab initio quantum chemistry calculations. In each case, the water molecule inserts into the carbohydrate at a position where it can replace a weak intramolecular interaction by two stronger intermolecular hydrogen bonds. The insertion can produce significant changes in the conformational preferences of the carbohydrates, and there is a clear preference for structures where cooperative effects enhance the stability of the monosaccharide conformers to which the water molecule chooses to bind. The conclusions drawn from the study of monosaccharide−water complexes are extended to the disaccharide lactose and discussed in the light of the underlying mechanisms that may be involved in the binding of carbohydrate assemblies to proteins and the involvement, or not, of key structural water molecules.
