Maltose-modified poly(propylene imine) (PPI) dendrimers were synthesized by reductive amination of unmodified second- to fifth-generation PPI dendrimers in the presence of excess maltose. The dendrimers were characterized by using (1)H NMR, (13)C NMR, and IR spectroscopies; laser-induced liquid beam ionization/desorption mass spectrometry; dynamic light scattering analyses; and polyelectrolyte titration. Their scaffolds have enhanced molecular rigidity and their outer spheres, at which two maltose units are bonded to the former primary amino groups on the surface, have hydrogen-bond-forming properties. Furthermore, the structural features reveal the presence of a dense shell. Experiments involving encapsulation (1-anilinonaphthalene-8-sulfonic acid) and biological properties (hemolysis and interactions with human serum albumin (HSA) and prion peptide 185-208) were performed to compare the modified with the unmodified dendrimers. These experiments gave the following results: 1) The modified dendrimers entrapped a low-molecular-weight fluorescent dye by means of a dendritic box effect, in contrast to the interfacial uptake characteristic of the unmodified PPI dendrimers. 2) Both low- and high-generation dendrimers containing maltose units showed markedly reduced toxicity. 3) The desirable features of bio-interactions depended on the generation of the dendrimer; they were retained after maltose substitution, but were now mainly governed by nonspecific hydrogen-bonding interactions involving the maltose units. The modified dendrimers interacted with HSA as strongly as the parent compounds and appeared to have potential use as antiprion agents. These improvements will initiate the development of the next platform of glycodendrimers in which apparently contrary properties can be combined, and this will enable, for example, therapeutic products such as more efficient and less toxic antiamyloid agents to be synthesized.

No abstract

No abstract

Weakly bonded 1:1 complexes between fluorobenzene (Fb)/fluorobenzene-d 5 (Fb-d 5) and fluoroform (Ff) were investigated spectroscopically by infrared ion-depletion spectroscopy (IR/R2PI) and theoretically by correlated ab initio methods. Their predissociation spectra exhibit an absorption comprised of two superimposed bands. These are blue-shifted by 12 and 21 cm-1, respectively, relative to the CH stretch of isolated fluoroform. Each IR band is assigned to a different hydrogen-bonded fluorobenzene·fluoroform isomer. The isomer with the most blue-shifted CH stretching vibration (21 cm-1) is assigned to a sandwich type structure, exhibiting a CH···π hydrogen bond. The cluster structures have been calculated by counterpoise- (CP-) corrected gradient optimization combined with anharmonic vibrational analysis using the CP-corrected Hessians. The predicted blue-shifts are 21 and 20.5 cm-1 for the CH stretching frequencies of fluoroform upon formation of a sandwich and a planar structure, respectively. The theoretical and experimental shifts are thus well comparable. Natural bond orbital (NBO) analysis of the sandwich complex as well as analysis of the type and shape of the occupied molecular orbitals revealed the nature of the blue-shift. It is shown that the nature of the improper, blue-shifting H-bond in this complex differs from that in a common H-bond. While in the common XH···Y hydrogen bond the primary interaction is caused by an electron density transfer (EDT) from the electron donor Y to the antibonding orbitals of XH, leading to the red-shift and bond elongation in XH, the features of the improper, blue-shifting H-bond are due to secondary effects. In the sandwich complex the EDT takes place between the electron donor (π electron clouds of fluorobenzene) and the lone pairs of the fluorine atoms of fluoroform, leading to a structural reorganization of the fluoroform, including the contraction of the CH bond and a corresponding blue-shift of its CH stretching frequency. The NBO analysis as well as the analysis of the type and shape of the HOMO and HOMO-1 orbitals both elucidate the larger blue-shift for the sandwich-type isomer of the fluorobenzene·fluoroform cluster compared to the equivalent chloroform complex.

Recently, Brutschy and co-workers have reported the spectra of (substituted benzene)⋯(H2O)n systems. To investigate the possibility of these systems exhibiting a π–H kind of bonding interaction as observed in benzene⋯(H2O)n systems, we have carried out extensive ab initio calculations on different conformations of the fluorobenzene⋯(H2O) and p-difluorobenzene⋯(H2O) systems using various basis sets. Our results indicate that unlike the π interaction observed in benzene⋯(H2O)n, the O–H of the water molecule is involved in the formation of a six-membered ring system with the F–C–C–H of the aromatic ring. This six-membered ring which results from the formation of two H-bonds (water hydrogen and fluorine, water oxygen and benzene hydrogen), is extensively stabilized by electrostatic interactions. The strength of this σ-bonding interaction of water to fluorobenzene in C6H5F⋯H2O is nearly equal to the corresponding π-bonding interaction of water to benzene in C6H6⋯H2O. However the σ interaction of water to difluorobenzene in p-C6H4F2⋯H2O is somewhat higher than the π interaction in C6H6⋯H2O and slightly higher than the corresponding interaction in C6H5F⋯H2O. The frequency shifts of the predicted OH stretching modes are in reasonable agreement with the experimental vibrational frequency shifts for both C6H5F⋯H2O and p-C6H4F2⋯H2O.

A new version of laser mass-spectrometry is presented, which allows the quantitative analysis of specific biocomplexes in native solution. On-demand micro droplets, injected into vacuum, are irradiated by mid IR-laser pulses. Above a certain intensity threshold they explode due to the transmitted energy, setting free a fraction of the charged biomolecules which are then mass-analyzed. Amounts of analyte in the attomolar range may be detected with the ion intensity being linear over a wide range of molarity. Evidence is given that this method is soft, tolerant against various buffers, reflects properties of the liquid phase, and suitable for studying noncovalently bonded specific complexes. This is highlighted by results from antibiotics specifically binding into the minor groove of duplex DNA.

No abstract

No abstract