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Biomedical subjects

Mark Gray

Publications and source records attributed to Mark Gray.

10 recordsLinked to original sources
PubMed2006

A structural investigation of the N-B interaction in an o-(N,N-dialkylaminomethyl)arylboronate system.

o-(Pyrrolidinylmethyl)phenylboronic acid (4) and its complexes with bifunctional substrates such as catechol, alpha-hydroxyisobutyric acid, and hydrobenzoin have been studied in detail by X-ray crystallography, (11)B NMR, and computational analysis. The N-B interactions in analogous boronic acids and esters have been extensively cited in molecular recognition and chemosensing literature. The focal point of this study was to determine the factors that are pertinent to the formation of an intramolecular N-B dative bond. Our structural study predicts that the formation of an N-B dative bond, and/or solvent insertion to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. Specifically, from (11)B NMR studies, complexation of 4 with electron-withdrawing and/or vicinally bifunctionalized substrates promotes both the formation of N-B dative bonds and the solvation of sp(2) boron to a tetrahedral sp(3) boronate. In the solid state, the presence of an N-B dative bond in the complex of 4 and catechol (7) depends on the solvent from which it crystallizes. From chloroform, an N-B bond was observed, whereas from methanol, a methoxylated boronate was formed, where the methoxy group is hydrogen-bonded with the neighboring tertiary ammonium ion. The structural optimization of compounds 4 and 7 using density functional theory in a simulated water continuum also predicts that complexation of 4 and catechol promotes either the formation of an N-B bond or solvolysis if 1 equiv of water is present. The conclusion from this study will help in the design of future chemosensing technologies based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds that are targeting physiologically important substances such as saccharides, alpha-hydroxycarboxylates, and catecholamines.

Boron↗
PubMed2005

An artificial siderophore for the detection of iron(III).

An artificial siderophore in the form of a squaraine dye (1) has been synthesized. The bidentate ligand chelates to Fe(III) between the deprotonated hydroxyl group on the ortho position of the ring adjacent to the carbonyl group of the cyclobutadiene ring. The optical response is due to a subtle geometry change of 1 on chelation to Fe(III). This artificial siderophore forms a 2 ratio 1 ligand ratio metal complex, as indicated by a sigmoidal isotherm (K(a)= 10(7) M(-1)). The optical response on the addition of Fe(III) is observed at low concentrations in comparison to other metal salts. The X-ray crystal structure and calculated structures of dye (1) are also included, and will be discussed.

Cations↗
PubMed2004

Guanidinium groups act as general-acid catalysts in phosphoryl transfer reactions: a two-proton inventory on a model system.

Cleavage/transesterification of phosphodiesters is catalyzed by various acidic groups in solution and with enzymes. General-acid catalysts can transfer protons to the developing phosphorane intermediate, resulting in a monoprotic-monoanionic intermediate, giving the so-called "triester mechanism". Using a proton inventory on a model compound (1) possessing an intramolecular hydrogen bond between a phosphodiester and a guanidinium group, we find that two protons move in the rate-determining step for cleavage/transesterification. In contrast, HPNP shows a single-proton inventory and is a substrate well accepted to react with the movement of only one proton at the transition state. We therefore propose a mechanism for 1 that involves general-acid catalysis by the guanidinium group. This leads one to conclude that other, more acidic groups, such as ammonium and imidazolium, would also act as general-acid catalysts.

Catalysis↗
PubMed2004

Model systems for flavoenzyme activity: interplay of hydrogen bonding and aromatic stacking in cofactor redox modulation.

[structure: see text] A model system has been developed to study the synergy between aromatic stacking and hydrogen bonding in the binding of a flavin derivative. The results show that the identity of both the hydrogen bonding and pi-stacking units strongly determine the overall receptor affinity for flavin in both the oxidized and radical anion forms.

Flavin Mononucleotide↗
PubMed2003

Model systems for flavoenzyme activity: relationships between cofactor structure, binding and redox properties.

A series of flavins were synthesized bearing electron-withdrawing and -donating substituents. The electrochemical properties of these flavins in a nonpolar solvent were determined. The recognition of these flavins by a diamidopyridine (DAP) receptor and the effect this receptor has on flavin redox potential was also quantified. It was found that the DAP-flavin binding affinity and the reduction potentials (E(1/2)) for both the DAP-bound and unbound flavins correlated well with functions derived from linear free energy relationships (LFERs). These results provide insight and predictive capability for the interplay of electronics and redox state-specific interactions for both abiotic and enzymatic systems.

Electrochemistry↗
PubMed2003

Thermally reversible formation of microspheres through non-covalent polymer cross-linking.

Bis-thymine units were used to noncovalently cross-link a complementary diamidopyridine-functionalized copolymer. Upon combination in noncompetitive solvents, discrete micron-scale spherical aggregates were formed arising from specific three-point polymer-cross-linker hydrogen bonding interactions. The diameter of these microspheres could be controlled through spacer structure. The cross-linking process was fully thermally reversible, with complete dissolution observed at 50 degrees C and reformation of the aggregates upon return to ambient temperature. This process could be repeated multiply, with lower particle dispersity observed arising from the annealing process.

Journal Article↗
PubMed2003

Redox modulation of benzene triimides and diimides via noncovalent interactions.

[reaction: see text] Mellitic triimides undergo three sequential one-electron reduction processes whose potentials are significantly lowered in the presence of alkyl thioureas. The two sequential reductions of benzene diimides are similarly stabilized. Calculation of the relative free energy change between the different electronic states of the imide acceptors and their corresponding alkyl thiourea complexes indicates dramatic increases in hydrogen bond strength with increasing acceptor charge density.

Journal Article↗
PubMed2003

Hydrogen bonding in redox-modulated molecular recognition. An experimental and theoretical investigation.

Two receptors, a diaminotriazine derivative (DAT) and diamidopyridine (DAP), are complementary to the electroactive naphthalimide (N) through three-point hydrogen bonding. The association constants of the two receptors were evaluated for both the fully oxidized and the radical anion forms of N. In the oxidized state, the two receptors displayed identical binding constants. Diamidopyridine, however, lowers the reduction potential of naphthalimide to a far greater extent than does diaminotriazine, indicating a greater affinity for diamidopyridine by naphthalimide in the radical anion form. This behavior was mirrored by EPR experiments that showed small deviations from the hyperfine coupling pattern of N(red) in the presence of DAT, with greater effects seen for the N(red).DAP complex. Computational simulations using the UB3LYP/6-311+G(d,p)//UHF/6-31G(d) hybrid gave theoretical hyperfine constants in good quantitative agreement with the experimental results. Using this correlation, we determined that electrostatics and hydrogen bond polarizability play key roles in controlling redox-modulated molecular recognition.

Hydrogen Bonding↗
PubMed2002

Specific interactions of complementary mono- and multivalent guests with recognition-induced polymersomes.

We have explored the interactions of mono- and multivalent guests with Recognition-Induced Polymersomes (RIPs) formed from complementary random copolymers featuring diamidopyridine and thymine functionality. Addition of monovalent guests featuring imide functionality to these RIPs induced a temporary swelling of the vesicles, followed by dissociation of the vesicles due to competitive binding of the guest. Conversely, multivalent thymine-functionalized nanoparticle guests were rapidly incorporated into the RIPs, inducing a contraction of RIP diameter over time. These mono- and multivalent interactions were extremely specific: highly analogous control systems showed no interaction with the RIP structures. Taken together, these studies demonstrate highly selective molecular "lock and key" control over higher-order assembly and recognition processes.

Binding, Competitive↗