Enabling enelike reactions on Si(111)-7x7 through tuning organic molecular structures.

We previously demonstrated that acetonitrile (N[triple bond]C-CH(3)) binds to the adjacent adatom-rest atom pair of Si(111)-7x7 through a [2+2]-like cycloaddition reaction, forming a (Si)N=C(Si)-CH(3)-like surface species [Tao et al., J. Phys. Chem. B 106, 3890 (2002)]. Current investigation clearly showed that chloroacetonitrile (N[triple bond]C-CH(2)Cl), propargyl chloride (HC[triple bond]C-CH(2)Cl), and 3-chloropropionitrile (N[triple bond]C-CH(2)-CH(2)Cl) react with the surface via enelike reactions, concurrently involving N[triple bond]C/C[triple bond]C as well as the breakage of the C-Cl/C-H bond. Further separation of the unsaturated bond (C[triple bond]C) from the C-Cl bond using CH(2) spacers in 5-chloro-1-pentyne (CH[triple bond]C-CH(2)CH(2)CH(2)Cl) would direct the reaction to a [2+2]-like cycloaddition. These experimental results clearly suggest the possibility of controlling the surface reaction pathways by tuning the organic molecular structures. This strategy can be useful in designing and fabricating functional molecular templates on Si(111)-7x7.

[Impact of epigallocatechin gallate on gene expression profiles of human hepatocellular carcinoma cell lines BEL7404/ADM and BEL7402/5-FU].

BACKGROUND & OBJECTIVE: Epigallocatechin gallate (EGCG) from green tea could reverse multidrug resistance (MDR) in human hepatocellular carcinoma (HCC) in vitro and in vivo. This study was to investigate the mechanism of reversing effect of EGCG on MDR of human hepatocelluar carcinoma cell lines BEL7404/ADM and BEL7402/5-FU. METHODS: Drug sensitivity of BEL7404/ADM and BEL7402/5-FU cells was tested by MTT assay. The different gene expression profiles of BEL7404/ADM and BEL7402/5-FU cells were detected by cDNA microarray before and after treatment of EGCG. The expression of MDR1 and LRP genes was detemined by reverse transcription-polymerase chain reaction (RT-PCR); the expression of Cyclin G1 protein was detected by Western blot to confirm the results of cDNA microarray. RESULTS: The 10% inhibitory concentration (IC10) of EGCG was 24.76 mg/L for BEL7404/ADM cells and 20.60 mg/L for BEL7402/5-FU cells. When treated with 0.05 mg/L adriamycin (ADM) and 100 micromol/L 5-fluorouracil (5-FU) in combination, 20 mg/L EGCG reversed the MDR by 9.66 folds in BEL7404/ADM cells and by 2.36 folds in BEL7402/5-FU cells. After treatment of EGCG, 210 differentially expressed genes were identified in BEL7404/ADM cells: 38 were up-regulated and 172 were down-regulated; the potential MDR-related genes included the up-regulated ABCB10 (MDR/TAP), TOP2A, TOP2B, CCNG1, and down-regulated ABCB1, MVP, ARHD, HDAC5, GSS, GSTPI, HSPA1B, HSPB7, CDKN1A, RAB11B, RAB9P40. After treatment of EGCG, 179 differentially expressed genes were identified in BEL7402/5-FU cells: 31 were up-regulated and 148 were down-regulated; the potential MDR-related genes included the up-regulated ABCG (BCRP), CCNG2, GADD34, RB1, RBBP4, and down-regulated DTYMK, GPX1, USP5, BAX, BAK1, HSPA1L. The down-regulation of MDR1 and LRP expression was confirmed by RT-PCR; the up-regulation of Cyclin G1 expression was confirmed by Western blot. CONCLUSION: EGCG could reverse the MDR of BEL7404/ADM and BEL7402/5-FU cells, but the changes of gene expression profiles of these two HCC cell lines are different.

Binding of glycine and L-cysteine on Si(111)-7 x 7.

The adsorption of glycine and l-cysteine on Si(111)-7 x 7 was investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The observation of the characteristic vibrational modes and electronic structures of NH3+ and COO- groups for physisorbed glycine (l-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of nu(Si-H), nu(Si-O), and nu(C=Omicron) and the absence of nu(O-H) clearly indicate that glycine and l-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7 x 7. XPS results further verified the coexistence of two chemisorption states for each amino acid, corresponding to a Si-NH-CH2-COO-Si [Si-NHCH(CH2SH)COO-Si] species with new sigma-linkages of Si-N and Si-O, and a NH2-CH2-COO-Si [NH2CH(CH2SH)COO-Si] product through the cleavage of the O-H bond, respectively. Glycine/Si(111)-7 x 7 and l-cysteine/Si(111)-7 x 7 can be viewed as model systems for further modification of Si surfaces with biological molecules.

Formation of a tetra-sigma-bonded intermediate in acetylethyne binding on Si(100)-2 x 1.

The covalent binding of acetylethyne on Si(100)-2 x 1 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The HREELS spectra of chemisorbed monolayers show the absence of the C=O, C[triple bond]C, and C(sp)-H stretching modes coupled with the appearance of C=C (at 1580 cm(-1)) and C(sp2)-H (at 3067 cm(-1)) stretching modes. This demonstrates that both of the C=O and CC groups of acetylethyne directly participate in binding with silicon surfaces to form C-O and C=C bonds, respectively, which is further confirmed by the XPS studies. A tetra-sigma-binding configuration through two [2 + 2]-like cycloaddition reactions in acetylethyne binding on Si(100) is proposed to account for the experimental observation. The cycloadduct containing a C=C double bond may be employed as an intermediate for further in situ chemical syntheses of multilayer organic thin films or surface functionalization.

Binding mechanisms of methacrylic acid and methyl methacrylate on si(111)-7 x 7 -- effect of substitution groups.

The interaction of methacrylic acid and methyl methacrylate with Si(111)-7 x 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). While methacrylic acid chemisorbs dissociatively through O-H bond cleavage, methyl methacrylate is covalently attached to the silicon surface via a [4+2] cycloaddition. The different reaction pathways of these two compounds on Si(111)-7 x 7 demonstrate that the substitution groups play an important role in determining the reaction channels for multifunctional molecules, leading to the desired flexibility in the organic modification of silicon surfaces.