Andreas Terfort

Liquid-Phase Epitaxy of Multicomponent Layer-Based Porous Coordination Polymer Thin Films of [M(L)(P)0.5] Type: Importance of Deposition Sequence on the Oriented Growth

The progressive liquid-phase layer-by-layer (LbL) growth of anisotropic multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P)(0.5)] (M: Cu(2+), Zn(2+); L: dicarboxylate linker; P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers (SAMs) on gold substrates as templates. It was found that the deposition of smooth, highly crystalline, and oriented multilayer films of these PCPs depends on the conditions at the early growth cycles. In the case of a two-step process with an equimolar mixture of L and P, growth along the [001] direction is strongly preferred. However, employing a three-step scheme with full separation of all components allows deposition along the [100] direction on carboxyl-terminated SAMs. Interestingly, the growth of additional layers on top of previously grown oriented seeding layers proved to be insensitive to the particular growth scheme and full retention of the initial orientation, either along the [001] or [100] direction, was observed. This homo- and heteroepitaxial LbL growth allows full control over the orientation and the layer sequence, including introduction of functionalized linkers and pillars.

Patterned deposition of metal-organic frameworks onto plastic, paper, and textile substrates by inkjet printing of a precursor solution.

Flexible in many aspects: inkjet printing of metal-organic frameworks permits their larger area, high-resolution deposition in any desired pattern, even in the form of gradients or shades. When flexible substrates are used, many applications can be envisioned, such as sensing and capture of hazardous gases for personal safety measures.

A Universal Scheme to Convert Aromatic Molecular Monolayers into Functional Carbon Nanomembranes

Free-standing nanomembranes with molecular or atomic thickness are currently explored for separation technologies, electronics, and sensing. Their engineering with well-defined structural and functional properties is a challenge for materials research. Here we present a broadly applicable scheme to create mechanically stable carbon nanomembranes (CNMs) with a thickness of ~0.5 to ~3 nm. Monolayers of polyaromatic molecules (oligophenyls, hexaphenylbenzene, and polycyclic aromatic hydrocarbons) were assembled and exposed to electrons that cross-link them into CNMs; subsequent pyrolysis converts the CNMs into graphene sheets. In this transformation the thickness, porosity, and surface functionality of the nanomembranes are determined by the monolayers, and structural and functional features are passed on from the molecules through their monolayers to the CNMs and finally on to the graphene. Our procedure is scalable to large areas and allows the engineering of ultrathin nanomembranes by controlling the composition and structure of precursor molecules and their monolayers.

Self-Assembly of an Operating Electrical Circuit Based on Shape Complementarity and the Hydrophobic Effect

470 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998 0935-9648/98/0604-0470

Making Protein Patterns by Writing in a Protein-Repelling Matrix

17.50+.50/0 Adv. Mater. 1998, 10, No. 6 FTIR (KBr): n = 2245, 2180, 2115, and 1024 cm. 13 C CP MAS NMR (resonance frequence 100.61 MHz, spining rate 12 kHz): d = 80.6, 69.4, 64.6, 56.7, 52.4, 26.3 and 10.9. Elemental analysis: calcd for ZrC12H18O4: Zr 28.75, C 45.39, H 5.67, O 20.19; found: Zr 33.50, C 41.35, H 5.35. Ta(OEt)5 and Ti(O Pr)4: Prepared similarly using 3 (7.54 mmol, 0.83 g) and a mixture of Ta(OEt)5 (3.89 mmol, 1.58 g) and Ti(O Pr)4 (3.37 mmol, 0.96 g), and isolated as a light brown powder (3.23 g). FTIR (KBr): n = 2245, 2180, 2124, and 1028 cm. C CP MAS NMR (resonance frequency 100.61 MHz, spinning rate 12 kHz): d = 78.9, 69.5, 60.7, 50.7, 26.0, and 19.5. Elemental analysis: calcd for TiTaC24H37O9: Ti 6.86, Ta 25.94, C 41.31, H 5.30, O 20.59; found: Ti 6.80, Ta 24.30, C 41.02, H 4.97. Preparation of 5: {Co2(CO)6}2(m2,h:m2,h-HOCH2±C oC±C oC±CH2 OH) 4 was prepared as described in [13]. 4 (0.53 g, 0.78 mmol) was reacted with Ti(OPr)4 (0.23 g, 0.8 mmol) following the procedure described above. 5 was isolated as a deep-brown solid (0.76 g). FTIR (KBr): n = 2102, 2083, 2061, 2027 cm. Elemental analysis: calcd for TiCo4C24H18O18: Ti 5.45, Co 26.85, H 2.07; found: Ti 6.20, Co 29.40, H 2.10.

Relative stability of thiol and selenol based SAMs on Au(111) — exchange experiments

One of the challenges of modern nanotechnology is the development of reliable, efficient, and flexible methods for the fabrication of ordered and complex patterns of proteins. Such patterns are of importance for biology and medical science: examples are proteomics, panel immunoassays, cell research, pharmaceutical screening for potential drugs, medical diagnostics, and encoding directional biological information. An essential element of almost all the available techniques is a protein-repelling background matrix which surrounds the active protein-adsorbing areas and prevents adsorption of proteins beyond these areas. Such a matrix is usually comprised of oligoor poly(ethylene glycol)based materials, polymers, or self-assembled monolayers (SAMs), and is generally prepared by a backfilling procedure after the fabrication of the protein-attracting patterns. Herein we present an alternative approach, showing that the proteinrepelling films, both SAMand polymer-like, can be used as a primary matrix for direct electron-beam writing of both nonspecific and specific protein patterns of any shape, including gradient ones, on a variable length scale. These factors make the approach quite flexible, which is additionally strengthened by the intrinsic versatility of electron-beam lithography (EBL), a wide range of suitable electron energies, the broad availability of commercial oligoethylene glycol (OEG) compounds, variable substrate material, and the wide choice of the target proteins. The approach is schematically illustrated in Figure 1. We used protein-repelling SAMs of OEG-substituted alkanethiols, HO(CH2CH2O)n(CH2)11SH with n = 3 (EG3) and 7 (EG7), on evaporated Au(111) substrates. Generally, the first step (or steps) to fabricate a protein pattern is to prepare a SAM-based chemical template. Such templates can be made by a combination of direct writing (molecules with specific binding groups to attract or bind proteins or intermediate moieties) and backfilling (OEGbased molecules) as in microcontact printing or dip-pen lithography. 4, 7] In EBL, fabrication of a chemical template suitable for protein adsorption can be performed either by transformation of specific tail groups of an aromatic SAM or by the irradiation-promoted exchange reaction (IPER) between a primary aliphatic SAM and a molecular substituent. The transformation of specific SAM tail groups however, requires an additional exchange-reaction-mediated backfilling of non-irradiated areas by OEG-based molecules, which is a slow process. The possibilities of IPER are limited as well, because of its low efficiency in the case of long-chain OEG-based SAMs. Therefore, only inverse protein patterns (protein-repelling features on a protein-adsorbing background) have been fabricated by the IPER method to date. In view of these problems, patterning aliphatic SAMs directly, similar to the aromatic films, could be considered. However, in contrast to aromatic films, a tail group of an aliphatic SAM usually cannot be specifically modified by electron irradiation without severe damage to the entire film, which deteriorates the overall quality of the template. We found, however, that this behavior does not occur in the case of OEG-terminated SAMs. According to X-ray photoelectron spectroscopy (XPS) data (see Figure 2 a and Figure SI1 in the Supporting Information), the OEG part of such films is extremely sensitive to electron irradiation (similar behavior was previously observed for UV-light exposure). It is modified to a severe extent even at very low doses ( 1 mCcm ), but both the aliphatic part and thiolate anchor of the SAM remain mostly intact, maintaining a thorough coupling of the molecules to the substrate. As a result of the electron-induced decomposition of the OEG chain, the effective thickness of the OEG SAM progressively decreases in the course of irradiation (Figure 2b). Along with the thickness reduction, the cleavage of the C O bonds within the ethylene glycol (EG) units leads to the generation of chemically active sites for subsequent nonspecific binding of different moieties. The amount of adsorbate is governed by the density of these sites, that is, by the primary irradiation dose. As shown in Figure 2b (see also Figure SI2 in the Supporting Information), progressive irradiation of the EG7 and EG3 SAMs results in a progressive increase in protein affinity until saturation (an affinity which is 100 % that of a dodecanthiolate (DDT) SAM) at higher doses. Extensive adsorption of proteins occurs even at small thickness reduction, especially for EG3/Au, thus it is the newly formed chemically active sites that are responsible for the protein attachment and not “holes” in the primary film which occur during the thickness reduction. The selection of an appropriate dose allows a precise tuning of the protein coverage from zero to the values typical for surfaces with high protein affinity (DDT SAMs). By combining this approach with lithography, it is possible to fabricate any desired protein pattern, including gradientlike ones. An example is given in Figure 3a, where an AFM image of a gradient-like fibrinogen pattern surrounded by the [*] Dr. N. Ballav, Prof. Dr. M. Zharnikov Angewandte Physikalische Chemie Universit t Heidelberg, 69120 Heidelberg (Germany) Fax: (+ 49)6221-546-199 E-mail: michael.zharnikov@urz.uni-heidelberg.de

Deposition of Metal-Organic Frameworks by Liquid-Phase Epitaxy: The Influence of Substrate Functional Group Density on Film Orientation

Two fully analogue homologue series of thiol and selenol based aromatic self-assembled monolayers (SAMs) on Au(111) in the form of CH(3)-(C(6)H(4))(2)-(CH(2))(n)-S-Au(111) (BPnS/Au(111), n = 2-6) and CH(3)-(C(6)H(4))(2)-(CH(2))(n)-Se-Au(111) (BPnSe/Au(111), n = 2-6), respectively, have been used to elucidate the relative stability of the S-Au(111) and Se-Au(111) bonding by monitoring their exchange by alkanethiol and alkaneselenol molecules from their respective solutions. The exchange process was monitored using infrared reflection absorption spectroscopy (IRRAS). Two main results obtained by these study are: (1) the selenium-based BPnSe/Au(111) series is significantly more stable than their sulfur analogues; (2) a clear odd-even effect exists for the stability of both BPnS/Au(111) and BPnSe/Au(111) SAMs towards exchange processes with the even-numbered systems being less stable. The results obtained are discussed in view of previously reported microscopic and spectroscopic data of the same SAMs addressing the issue of the relative stability of S-Au(111) and Se-Au(111) bonding, which is an important factor for the rational design of SAMs.

Fabrication of Mixed Self-Assembled Monolayers Designed for Avidin Immobilization by Irradiation Promoted Exchange Reaction

The liquid phase epitaxy (LPE) of the metal-organic framework (MOF) HKUST-1 has been studied for three different COOH-terminated templating organic surfaces prepared by the adsorption of self-assembled monolayers (SAMs) on gold substrates. Three different SAMs were used, mercaptohexadecanoic acid (MHDA), 4’-carboxyterphenyl-4-methanethiol (TPMTA) and 9-carboxy-10-(mercaptomethyl)triptycene (CMMT). The XRD data demonstrate that highly oriented HKUST-1 SURMOFs with an orientation along the (100) direction was obtained on MHDA-SAMs. In the case of the TPMTA-SAM, the quality of the deposited SURMOF films was found to be substantially inferior. Surprisingly, for the CMMT-SAMs, a different growth direction was obtained; XRD data reveal the deposition of highly oriented HKUST-1 SURMOFs grown along the (111) direction.

Switching of Bacterial Adhesion to a Glycosylated Surface by Reversible Reorientation of the Carbohydrate Ligand

An applicability of irradiation-promoted exchange reaction (IPER) to the fabrication of mixed self-assembled monolayers (SAMs) composed of the protein-repelling matrix and the moieties bearing binding sites for specific attachment of a target protein is demonstrated. As test systems, we took mixed films of oligoethylene glycol (OEG)-substituted alkanethiols (OEG-ATs) and biotin-substituted alkanethiols (BATs) on Au{111}. Such SAMs are suitable for the specific immobilization of avidin protein and its variants. The composition of the mixed OEG-AT/BAT SAMs could be precisely controlled by varying the irradiation dose, which is important prerequisite for the fabrication of the respective patterns by electron-beam lithography. While the general trend in the immobilization of avidin onto the mixed OEG-AT/BAT SAMs prepared by IPER was found to be consistent with the earlier reports regarding the analogous films fabricated by the coassembly method, the concentration of the BAT component in the mixed SAMs needed for the maximum surface coverage of the specific protein was found to be somewhat lower, and the maximum avidin coverage somewhat higher in the case of IPER as compared to the coassembly method. We ascribe these differences to the lack of phase segregation and better separation of the individual BAT species in the OEG-AT matrix in the case of IPER.

Postformation Modification of SAMs: Using Click Chemistry to Functionalize Organic Surfaces

The surface recognition in many biological systems is guided by the interaction of carbohydrate-specific proteins (lectins) with carbohydrate epitopes (ligands) located within the unordered glycoconjugate layer (glycocalyx) of cells. Thus, for recognition, the respective ligand has to reorient for a successful matching event. Herein, we present for the first time a model system, in which only the orientation of the ligand is altered in a controlled manner without changing the recognition quality of the ligand itself. The key for this orientational control is the embedding into an interfacial system and the use of a photoswitchable mechanical joint, such as azobenzene.