Guodong Sui

Studies of a novel polymerizable amphiphilic dendrimer

Abstract In the present study, we have synthesized a polymerizable amphiphilic dendrimer by attaching 10,12-pentacosadiynoic acid (PDA) to a third generation poly(amidoamine) (PAMAM) dendrimer core (PDA-PAMAM). This dendrimer was characterized by 1H NMR and MALDI-TOF mass spectroscopy. The amphiphilic property of this dendrimer has been studied. Surface pressure and surface dipole moment–area isotherm measurements have shown that PDA-PAMAM forms a stable monolayer at the air–water interface with a limiting molecular area of 460 A2 per molecule. The compressed monolayer can be readily polymerized upon UV irradiation, as like other PDA derivatives. The topography of the monolayer was observed by Brewster angle microscopy (BAM) as well as by the environmental scanning electron microscopy (ESEM). We found a good correlation between the size and shape of monolayer domains observed with the BAM and ESEM techniques. To our knowledge, this is the first time wet mode ESEM has been used to characterize L–B film. The wet mode ensures that L–B films remain intact without being damaged by the high vacuum system of traditional SEM. As a preliminary study, we have found that this new dendrimer forms colloidal particles in chloroform solution and can be readily polymerized by UV irradiation.

Analysis of matrix metalloproteinase triple-helical peptidase activity with substrates incorporating fluorogenic L- or D-amino acids

The consequences of improper regulation of collagen turnover include diseases such as tumor cell metastasis and arthritis. Several fluorogenic triple-helical peptide (fTHP) substrates have been constructed presently to examine collagenolytic behavior. These substrates incorporate L- or D-2-amino-3-(7-methoxy-4-coumaryl)propionic acid (Amp) or L- or D-2-amino-3-(6,7-dimethoxy-4-coumaryl)propionic acid (Adp) as the fluorophore and N-2,4-dinitrophenyl (Dnp) as the quencher. The desired sequences were C6-(Gly-Pro-Hyp)5-Gly-Pro-[Amp/Adp]-Gly-Pro-Gln-Gly approximately Leu-Arg-Gly-Gln-Lys(Dnp)-Gly-Val-Arg-(Gly-Pro-Hyp)5-NH2. All four fTHPs formed stable triple-helices. Matrix metalloproteinase-2 (MMP-2) rates of hydrolysis for all fTHPs were considerably more rapid than corresponding MMP-1 rates. Evaluation of individual kinetic parameters indicated that MMP-2 bound to the fTHPs more efficiently than MMP-1. Comparison to a triple-helical substrate incorporating the same sequence but with a different fluorophore [Lys((7-methoxycoumarin-4-yl)acetyl); Lys(Mca)] demonstrated that the shorter side chain of Amp or Adp was better tolerated by MMP-1 and MMP-2. Adp may well be the fluorophore of choice for fTHPs, as (a) fTHPs incorporating Adp were obtained in significantly higher yields than the Amp-containing fTHPs, (b) Adp has a larger Stokes shift than either Amp or Lys(Mca) and thus has less chance of self-quenching, (c) Adp has a relatively high quantum yield, (d) the Adp/Dnp pair is compatible with multiwell plate reader formats, and (e) MMPs better tolerate Adp than Lys(Mca).

Metal Complexation with Langmuir Monolayers of Histidyl Peptide Lipids

Langmuir monolayers made from peptide-lipid molecules represent a novel direction in the research areas of biomimetic interfaces and two-dimensional supramolecular chemistry. Peptide structures and molecular recognition activities toward other guest molecules have been the focus of previous study. This study reports the investigation of metal complexation to histidine-containing peptide lipids in the organized Langmuir, Langmuir-Schaefer, or Langmuir-Blodgett films. Three peptide lipids PEP1-PEP3, with a histidine amino acid incorporated in the middle of the peptide, were designed and synthesized. The monolayer structures and metal-binding activities of each peptide lipid and their 1:1:1 molar ratio mixture were studied by thermodynamic and spectroscopic techniques. It was found that hard Lewis acid type metal cations such as K+ and Mg2+, and borderline or soft metal cations such as Zn2+, Cu2+, and Cd2+ exhibit clearly different binding activity toward peptide-lipid monolayers. The conformational changes of peptides upon binding with Cu2+ and Zn2+ were partially revealed by FT-IR spectroscopic studies. Furthermore, by adding a fluorescent-probe lipid to the peptide monolayer, dramatic fluorescence change was observed when Cu2+ or Zn2+ bound to the Langmuir and Langmuir-Schaefer films of peptide-lipid monolayers. Metal-protein complexation plays a crucial role in the function and activity of proteins and enzymes. Investigation of metal complexation to organized peptide Langmuir monolayers may provide an alternative approach for the development of artificial metalloproteins and novel supramolecular systems or materials.

Highly enantioselective synthesis of a fluorescent amino acid

Abstract A high enantiomeric excess (>99.5%) synthesis of l- 2-amino-3-(7-methoxy-4-coumaryl) propionic acid ( l- Amp) is described. The two step synthesis route of this non-proteinogenic amino acid includes an oxazinone derivative as glycine enolate, which is alkylated with the fluorogenic group.

Surface Chemistry Studies of Quantum Dots (QDs) Modified with Surfactants

Since luminescent CdSe quantum dots (QDs) have shown great potential in biological labeling, the surface chemistry behavior of QDs at interfaces is of great research interest. In the present study, CdSe QDs with green luminescence were modified with hydrophobic chains of varying lengths [from C6 to C18]. These modified QDs can be utilized to form stable monolayers at the air/water interface. Surface pressure-area isotherms of modified QDs have been measured and limiting molecular areas have also been extrapolated in order to analyze the size of the QDs. UV absorption spectra of modified QDs at various surface pressures were also determined. Surface chemistry, as well as the topographic properties, of modified QDs in Langmuir and L-B films was discussed.

Synthesis of a coumarin based fluorescent amino acid

L-2-amino-3-(6,7-dimethoxy-4-coumaryl)-propionic acid (L-Adp), as a non-proteinogenic fluorescent amino acid has been synthesized by a highly stereoselective routine (>99.5%). This fluorescent amino acid, as fluorophore-quencher pair, may be used to study peptide assays. For enantiomeric excess determination, the racemic D-Adp (D-2-amino-3-(6,7-dimethoxy-4-coumaryl)-propionic acid) has also been synthesized.

ZL-DHP lignin model compound at the air-water interface

In this paper we present our surface chemistry studies of enzymatically polymerized, poly-coniferyl alcohol lignin model compound (dehydrogenate polymer a.k.a. ZL-DHP) at the air-water interface. Using the CHCl(3)/MeOH (5:1 v/v) spreading solvent, we found an average molecular area of ZL-DHP of approximately 1200 A(2). The monolayer expresses a high compressibility with a collapsed area of 500 A(2) and collapsed surface pressure of 28 mN m(-1). In the range of applied surface pressures, ZL-DHP polymer have no phase changes, as shown by the very high linearity (R=0.994) of absorbance vs. surface pressure cure. There was no symmetry transitions observed as shown by absence of shifts of absorption peak maximums.

Langmuir and Langmuir–Blodgett films of a novel tryptophan peptide lipid

A novel tryptophan peptide lipid, C18H35O (SA)-Gly-Trp-Gly-OH, was synthesized and studied for its surface chemistry and spectroscopic properties.