Propyl Side Chain Research Articles

Unique Crystal Structure of a Self-Assembled Dinuclear Cu Peptoid Reveals an Unusually Long Cu···Cu Distance.

Studies on a series of molecular dicopper peptoid complexes showed that the Cu···Cu distances measured in X-ray single-crystal diffraction are typically in the range of 4.2-6.9 Å. Herein, we designed a new peptoid, L1, having 2,2'-bipyridine, propyl, and pyridyl side chains and discovered that although it forms a typical dicopper self-assembled structure (complex 1), the Cu···Cu distance is exceedingly long -8.043 Å. By analyzing its structure and surface properties in comparison to a control Cu-peptoid complex (2), in which the pyridyl side chain is modified by an ethanolic side chain, we suggest that the long Cu···Cu distance is contributed by the hydrophilic-hydrophobic interaction influenced by the pyridyl side chain and the steric hindrance of the propyl side chain. This result may motivate the use of dinuclear Cu peptoid complexes for wider applications, such as cooperative catalysis and luminescence.

Catalytic depolymerization of Camellia oleifera shell lignin to phenolic monomers: Insights into the effects of solvent, catalyst and atmosphere

Camellia oleifera shell (COS) is a renewable biomass resource abundant in lignin with significant potential for producing phenolic monomers. However, the dearth of research has led to considerable resource wastage and environmental pollution. Herein, reductive catalytic fractionation (RCF) of COS was performed using noble metal catalysts in different solvents. An 11.1 wt% yield of phenolic monomers was achieved with 91% selectivity toward propylene-substituted monomers in H2O/EtOH (3:7, v/v) cosolvent under N2 atmosphere. Notably, the highest phenolic monomer yield of 17.0 wt% was obtained with impressive selectivity (86.9%) toward propanol-substituted monomers in the presence of H2. The GPC analysis and 2D HSQC NMR spectra indicated the effective depolymerization of lignin oligomers with catalysts. Phenolic monomers with ethyl, propyl, or propanol side chain could be produced from lignin-derived oligomers through hydrogenolysis, hydrogenation, and decarboxylation reactions. Overall, this study has paved the way for the valorization of COS lignin through the RCF strategy.

Structure–Function Relationship within Cu-Peptoid Electrocatalysts for Water Oxidation

Water oxidation (WO) is the first step in the water-splitting process aiming at the production of hydrogen as a green renewable fuel. To successfully perform WO, potent strategies for overcoming the high energetic barrier and slow kinetics of this reaction are urgently required. One such strategy is the use of molecular catalysis. Specifically, Cu-based catalysts have been highlighted over the last decade due to their stability and fast kinetics. Among them, Cu-peptoids, where peptoids are peptidomimetics akin to peptides and are N-substituted glycine oligomers, can act as stable and active catalysts for oxidation transformations including electrocatalytic WO. Previously, we suggested that a benzyl group incorporated as a side chain near the catalytic site within a Cu-peptoid electrocatalyst for WO has a structural role in the activity of the electrocatalyst in phosphate buffer (PBS). Herein, we aimed to test this hypothesis and understand how an incorporated structural element side chain affects WO. To this aim, we prepared a set of peptoid trimers each with a different structural element replacing the benzyl group by either naphthyl, cyclohexyl, benzyl, propyl chloride, or propyl side chains as well as a peptoid lacking a structural element. We studied the structure of their Cu complexes and tested these complexes as electrocatalysts for WO. We discovered that while all the peptoids self-assemble to form dinuclear Cu-peptoid complexes, the duplex that has no structural side chain, Cu2(BE)2, is structurally different from the others in the solid state. Moreover, Cu2(BE)2 remains dinuclear in a PBS at pH 11, while all the other duplexes are mononuclear in the PBS. Finally, though most of the complexes showed low electrocatalytic activity for WO, the dinuclear complex Cu2(BE)2 performed with the highest turnover frequency of 484 s−1. Nevertheless, this dinuclear complex slowly decomposes to the corresponding mononuclear complex as a more stable species during WO, while the other mononuclear complexes retain their structure in solution but display much slower kinetics (ca. 5 to 8 s−1) under the same conditions. Overall, our results demonstrate that bulkier side chains hamper the stability of dinuclear Cu-peptoids in a PBS, and hence, their efficiency as WO electrocatalysts is also hampered.

Crystals of Aliphatic Derivatives of [Cu(acac)2 ] have Distinct Atomic-Scale Mechanisms of Bending.

Molecular crystals displaying elastic flexibility have important applications in the fields of optoelectronics and nanophotonic technologies. Understanding the mechanisms by which these materials bend is critical to the design of future materials incorporating these properties. Based on the known elastic properties of bis(acetylacetonato)copper(II), a series of 14 aliphatic derivatives are synthesized and crystallized. All those which grew in a needle morphology display noticeable elasticity, with 1D chains of π-stacked molecules parallel to the long metric length of the crystal a consistent crystallographic feature. Crystallographic mapping is used to measure the mechanism of elasticity at an atomic-scale. Symmetric derivatives with ethyl and propyl side chains are found to have different mechanisms of elasticity, which are further distinguished from the previously reported mechanism of bis(acetylacetonato)copper(II). While crystals of bis(acetylacetonato)copper(II) are known to bend elastically via a molecular rotation mechanism, the elasticity of the compounds presented is facilitated by expansion of their π-stacking interactions.

Lignan (+)-Piperitol-γ,γ-Dimethylallylether from Stem Bark of Zanthoxylum rhetsa (Roxb.) DC (Rutaceae)

Lignans are a group of phenylpropanoid dimers in which the phenylpropane units are linked by their propyl side chains' central carbon (C8). Lignans have various biological activities, including antiviral, anticancer, cancer preventive, and cytotoxic. Zanthoxylum rhetsa (Roxb.) DC is a tree with prickly branchlets belonging to the Zanthoxylum genus, commonly known as panggal buaya in Indonesia. Asian tribes have used this plant as traditional medicine. In this study, (+)-piperitol-γ,γ-dimethylallylether, a furofuran lignan, was successfully isolated. The chemical structure of compound 1 was determined based on spectroscopic data, including 1D- and 2D-NMR, mass spectroscopy, and by comparing with previous spectral data. In addition, compound 1 was tested for its cytotoxic activity against MCF-7 breast cancer cell lines in vitro and showed weak activity with the IC50 value of 261.37 µg/mL.

In Vitro and in Silico Evaluation of Some New 1H-Benzimidazoles Bearing Thiosemicarbazide and Triazole as Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor

A new class of benzimidazole derivatives bearing bis-triazole or bis-thiosemicarbazide structure was designed and synthesized as potential inhibitors of epidermal growth factor receptor (EGFR) tyrosine kinase. In vitro EGFR kinase enzyme inhibition properties were determined in comparison with erlotinib and compound (6b) containing propyl side chain at the 4th position of triazole rings showed 13.8% inhibition. Molecular docking studies were performed and docking score and binding energy were established. The most active compound formed a hydrogen bond between the Asn818 and triazole NH at the 2nd position of the benzimidazole skeleton. Predicted ADME profiles of the compounds were calculated and found to be within the appropriate reference ranges.

Isolation and structural elucidation of bioactive obovatol dimeric neolignans from the bark of Magnolia officinalis var. biloba

(+)/(−)-Diobolignans A–F, six pairs of enantiomeric obovatol dimeric neolignans, were isolated from the bark of Magnolia officinalis var. biloba. (+)/(−)-Diobolignans A to C possessed a dioxane ring between the benzene ring and the propyl side chain, while (+)/(−)-diobolignans D to F possessed a furan ring. Meanwhile, (+)/(−)-diobolignans B and C, as well as (+)/(−)-diobolignans E and F, were two epimeric pairs of enantiomers, respectively. Their structures were determined by extensive analyses of HRESIMS, UV, IR, NMR and electronic circular dichroism (ECD) calculations. The bioassay showed (+)-diobolignan A displayed cytotoxic activities against human cancer cell lines HGC27 and HT29 with the IC50 values of 9.43 and 9.45 μM, respectively. In addition, (−)-diobolignan A and (±)-diobolignan E showed neuroprotective effect on glutamic acid-induced cellular damage in SK-N-SH cell.

Experimental and theoretical studies into the hydroxyl radical mediated transformation of propylparaben to methylparaben in the presence of dissolved organic matter surrogate

Dissolved humic and biogenic substances might be present in the aphotic zone and contribute to the fate of parabens in natural aquatic ecosystem under the fluctuation of water multi-parameters. Through the combination of batch tests with quantum chemical calculation, hydroxyl radical (•OH) mediated degradation of propylparaben (PP) to methylparaben (MP) has been confirmed in the present study. The interaction of dissolved oxygen with environmental relevant concentration of humic acid (HA), algal and bacterial cell lysis leads to a slow production of •OH. Aqueous PP undergoes a mild removal process with the pseudo-first order rate constant (10−7, s−1) higher at 7.43 in HA than at 3.30-4.89 in biogenic cell lysis. PP removal is correlated with the aromaticity of DOM surrogate and the produced •OH concentration, which could be enhanced by the increase of light intensity and DO other than HA. The •OH mediated process on PP removal has been confirmed by the linearly inhibited effect of tert-butanol while totally inhibited effects of higher concentration of sodium azide and co-existent chemical (17β-estradiol). Based on the detection of byproduct MP, two possible reaction pathways, •OH attacking at β-carbon (path-β) and terminal γ-carbon (path-γ) of the propyl side chain of PP, are proposed. Through the analysis of thermal and kinetics parameters, the •OH initiated H-abstraction and the resulting C-C bond cleavage leading to the formation of MP and acetaldehyde in path-β is confirmed to be the dominant reaction mechanism. Considering the universal occurrence of parabens and these DOM surrogates, this mild removal process has special implications for the self-purification of organic pollutants in natural aquatic ecosystems, especially in DOM-rich matrices in the aphotic zone.

Unravelling Main- and Side-Chain Motions in Polymers with NMR Spectroscopy and Relaxometry: The Case of Polyvinyl Butyral.

Polyvinyl butyral (PVB) is an amorphous polymer employed in many technological applications. In order to highlight the relationships between macroscopic properties and dynamics at a microscopic level, motions of the main-chain and of the propyl side-chains were investigated between Tg − 288 °C and Tg + 55 °C, with Tg indicating the glass transition temperature. To this aim, a combination of solid state Nuclear Magnetic Resonance (NMR) methods was applied to two purposely synthesized PVB isotopomers: one fully protonated and the other perdeuterated on the side-chains. 1H time domain NMR and 1H field cycling NMR relaxometry experiments, performed across and above Tg, revealed that the dynamics of the main-chain corresponds to the α-relaxation associated to the glass transition, which was previously characterized by dielectric spectroscopy. A faster secondary relaxation was observed for the first time and ascribed to side-chains. The geometry and rate of motions of the different groups in the side-chains were characterized below Tg by 2H NMR spectroscopy.

Pore Blocking by Phenolates as Deactivation Path during the Cracking of 4-Propylphenol over ZSM-5

Cracking of propyl side chains from 4-propylphenol, a model compound for lignin monomers, is studied for a commercial ZSM-5 zeolite catalyst. The decline of 4-propylphenol conversion with time on stream can be delayed by co-feeding water. FTIR spectroscopy shows the formation of chemisorbed phenolates during reactions and significant amounts of phenolics are detected by GC-MS of the extract from the spent catalysts. Thus, chemisorbed phenolates are identified as the main reason for deactivation in the absence of water. Regardless of the amount of co-fed water, substituted monoaromatics and polyaromatic species are formed. Comprehensive characterization of the spent catalysts including Raman and solid-state 27Al NMR spectroscopy, and thermogravimetric analysis points to a combination of deactivation processes. First, phenolates bind to Lewis acid sites within the zeolite framework and hinder diffusion unless they are hydrolyzed by water. In addition, light olefins created during the cracking process react to form a polyaromatic coke that deactivates the catalyst more permanently.

Chemical constituents from the leaves of Styrax argentifolius H.L. Li and their biological activities

Abstract Searching for bioactive agents from Vietnamese plants, nine compounds, including five nor-lignan-type benzofurans 1–5, two lignans 6 and 7, one sterol 8 and one triterpenoid 9 were separated from Styrax argentifolius for the first time. 5-((E)-2-Carboxyvinyl)-7-methoxy-2-(3′,4′-methylenedioxyphenyl)benzofuran (1) and 5-carboxy-7-methoxy-2-(3′,4′-methylenedioxyphenyl)benzofuran (2) were new benzofurans in nature. Sterol (20R)-24-ethylcholest-5,22-dien-7-one (8) and triterpenoid 2α,3α,24-trihydroxy-urs-12-en-28-oic acid (9) were isolated from the genus Styrax for the first time. Egonol (3) showed potential IC50 values of 18.15–22.11 μg/mL against three cancer cell lines KB, HepG2 and Lu, while the IC50 values of new compound 1, (–)-machicendiol (4), and triterpenoid 9 were comparable with that of the positive control acarbose (IC50 118.43 ± 2.44 μg/mL) in α-glucosidase inhibitory assays. Styrax benzofurans and triterpenoids show cytotoxic and α-glucosidase inhibitory activities. The activities of benzofurans 1 and 3–5 were due to the effect of propyl side chains at carbon C-5.

Antioxidant and antimicrobial activity of two standardized extracts from a new Chinese accession of non-psychotropic Cannabis sativa L.

The purpose of this study was to evaluate the antioxidant and antimicrobial properties of two extracts from a new Chinese accession (G-309) of Cannabis sativa L. (Δ9 -tetrahydrocannabinol <0.2%) with high content of propyl side chain phytocannabinoids. Dried flowering tops, as such and after hydrodistillation of the essential oil, were extracted with acidic hexane to produce the Cannabis Chinese hexane extract 1 (CChHE1) and 2 (CChHE2), respectively. The phytochemical profile of CChHE1 and CChHE2 was investigated by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-diode array detector-electrospray ionization-tandem mass spectrometry (LC-DAD-ESI-MS/MS) analyses. The antioxidant properties were assessed by several in vitro cell-free assays. The antimicrobial activity was evaluated against Gram-positive and Gram-negative bacteria and the yeast Candida albicans. Phytochemical analyses highlighted a high content of cannabidivarinic acid (CBDVA) and tetraydrocannabivarinic acid (THCVA) in CChHE1, and cannabidivarin (CBDV) and tetraydrocannabivarin (THCV) in CChHE2. Both extracts showed remarkable antioxidant activity and strong antimicrobial properties (MIC 39.06 and MBC 39.06-78.13 μg/ml) against both ATCC and methicillin-resistant clinical strains of Staphylococcus aureus. In conclusion, standardized extracts of C. sativa Chinese accession could be promising for their possible use as novel antibacterial agents for the treatment of widespread S. aureus infections.

Bis(3-methyl-1-propyl-1H-imidazol-3-ium) bis-(4,6-disulfanidyl-4,6-disulfanyl-idene-1,2,3,5,4,6-tetra-thia-diphosphinane-κ3 S 2,S 4,S 6)nickel.

The title salt, (PMIM)2[Ni(P2S8)2] (PMIM = 3-methyl-1-propyl-1H-imidazol-3-ium, C7H13N2 +), consists of a nickel-thio-phosphate anion charge-balanced by a pair of crystallographically independent PMIM cations. It crystallizes in the monoclinic space group P21/n. The structure exhibits the known [Ni(P2S8)2]2- anion with two unique imidazolium cations in the asymmetric unit. Whereas one PMIM cation is well ordered, the other is disordered over two orientations with refined occupancies of 0.798 (2) and 0.202 (2). The salt was prepared directly from the elements in the ionic liquid [PMIM]CF3SO3. Whereas one of the PMIM cations is well behaved (it does not exhibit disorder even in the propyl side chain), the other is found in two overlapping positions. The refined occupancies for the two orientations are roughly 80:20. Here, too, there appears to be little disorder in the propyl arm.

The inhibition profiles of 4'‐acylpyrrole–5‐fluoroindolin‐2‐ones with a C‐3' side chain for VEGFR2, PDGFR‐β, and FGFR‐1 protein kinases

AbstractIn this study, we reported the inhibition profiles of 4′‐acylpyrrole–5‐fluoroindolin‐2‐one 3 with a C‐3′ side chain for VEGFR2, PDGFR‐β, and FGFR‐1 protein kinases. The pyrrole‐fused cyclohexanone moiety provided 3 with the best potency to inhibit the three kinases, and the C‐3′ side chains contributed to the different inhibition profiles of 3. Compound 3b with a C‐3′ 2‐carboxylethyl side chain showed good potency for the three kinase (IC50: 25–260 nM), and compound 3g with a N,N‐dialkyl‐2‐carbamoylethyl side chain was more active for VEGFR2 (IC50: 59 nM) and PDGFR‐β (IC50: 16 nM) than FGFR‐1 (IC50: 1.7 μM). The C‐3′ 3‐(dialkylamino)propyl side chain accomplished 3h–j as selective PDGFR‐β inhibitors (IC50: 7.8–13 nM). Compound 3b was further investigated and found potent to inhibit VEGF‐ and FGF‐dependent cell proliferation with moderate in vivo anticancer activity. Results from docking simulations revealed that the interactions of 3b with VEGFR2 and FGFR‐1 which could account for the different inhibition profiles of 3.

Chemical Dynamics Simulation of Energy Transfer: Propylbenzene Cation and N2 Collisions.

Collisional energy transfer of highly vibrationally excited propylbenzene cation in a N2 bath has been studied with chemical dynamics simulations. In this work, an intermolecular potential of propylbenzene cation interacting with N2 was developed from SCS-MP2/6-311++G** ab initio calculations. Using a particle swarm optimization algorithm, the ab initio results were simultaneously fit to a sum of three two-body potentials, consisting of C a-N, C b-N, and H-N, where C a is carbon on the benzene ring and C b is carbon on the propyl side chain. Using the developed intermolecular potential, classical trajectory calculations were performed with a 100.1 kcal/mol excitation energy at 473 K to compare with experiment. Varying the density of the N2 bath, the single collision limit of propylbenzene cation with the N2 bath was obtained at a density of 20 kg/m3 (28 atm). For the experimental excitation energy and in the single collision limit, the average energy transferred per collision, ⟨Δ Ec⟩, is 1.04 ± 0.04 kcal/mol and in good agreement with the experimental value of 0.82 kcal/mol.

Synthesis of Novel Anti‐inflammatory Psoralen Derivatives ‐ Structures with Distinct Anti‐Inflammatory Activities

As a continuum to our work with coumarins, 12 psoralens were synthesized and evaluated for their anti‐inflammatory activity. Psoralens were prepared in three steps; at first, 7‐hydroxycoumarins were synthesized by von Pechmann condensation and then converted to 7‐(2‐oxopropoxy)coumarins. In the final step, a fused furan ring was introduced in an intramolecular ring‐formation reaction. Based on a SciFinder search, two out of the 12 synthesized psoralen derivatives (compounds 9 and 12) were found to be novel. The derivatives displayed anti‐inflammatory activity by suppressing iNOS and IL‐6 expression, but their mechanism of action seemed to be dependent on the substitution. Compound 6 with propyl side chain inhibited NF‐κB mediated transcription, while compound 10 with a phenyl substituent down‐regulated iNOS expression in a posttranscriptional manner. The results introduce psoralen derivatives as promising anti‐inflammatory compounds with potential for treatment of conditions involving iNOS and/or IL‐6‐mediated adverse responses.

Macromolecular aggregation and electrochemical behavior of pyrrolyl-, anilynyl- and thiophenyl-silicon compounds as precursors for thin hybrid films

Aniline, pyrrole and thiophene substituted with methoxysilyl propyl side chains were investigated by means of spectroscopic and electrochemical techniques. The effect of hydrolysis and ex-situ irradiation of solutions prepared in different solvent mixtures, containing either methanol or methylacetate in excess, was considered also. The development of stable intermediate species in solution is governed by intramolecular polarization of the hydrolyzed monomer rather than by ex-situ photoxidation or electro-oxidation of the monomer head group. Cooperative non-covalent OH-π interactions between the electron deficient silanol (SiOH) and the electron rich aromatic π system leading to mixed- n-p type redox behavior of the hybrid films are confirmed for the case of N-substituted pyrrolyl-silicon derivative. Less efficient interactions of the more basic N-AnSi derivative result from the deprotonation and self-condensation of SiOH, being supported by the prevalent p-type charge transport of the related hybrid film. For the case thiophenyl-silicon derivatives, charge trapping manifesting n-type redox behavior dominates for the case of α-substituted thiophene rather than for the parent β-substituted derivative but with jellification, indicating effective OH-π stabilization of σ-coupled α,α’ dimer structures by a short-range intramolecular mechanism. The establishment and modulation of constructive OH-π interactions determine the macromolecular aggregation and redox behavior of the hybrid films. The diverse properties exhibited by the hybrid precursors support different protection mechanisms against corrosion.

Evolution-guided adaptation of an adenylation domain substrate specificity to an unusual amino acid.

Adenylation domains CcbC and LmbC control the specific incorporation of amino acid precursors in the biosynthesis of lincosamide antibiotics celesticetin and lincomycin. Both proteins originate from a common L-proline-specific ancestor, but LmbC was evolutionary adapted to use an unusual substrate, (2S,4R)-4-propyl-proline (PPL). Using site-directed mutagenesis of the LmbC substrate binding pocket and an ATP-[32P]PPi exchange assay, three residues, G308, A207 and L246, were identified as crucial for the PPL activation, presumably forming together a channel of a proper size, shape and hydrophobicity to accommodate the propyl side chain of PPL. Subsequently, we experimentally simulated the molecular evolution leading from L-proline-specific substrate binding pocket to the PPL-specific LmbC. The mere change of three amino acid residues in originally strictly L-proline-specific CcbC switched its substrate specificity to prefer PPL and even synthetic alkyl-L-proline derivatives with prolonged side chain. This is the first time that such a comparative study provided an evidence of the evolutionary relevant adaptation of the adenylation domain substrate binding pocket to a new sterically different substrate by a few point mutations. The herein experimentally simulated rearrangement of the substrate binding pocket seems to be the general principle of the de novo genesis of adenylation domains’ unusual substrate specificities. However, to keep the overall natural catalytic efficiency of the enzyme, a more comprehensive rearrangement of the whole protein would probably be employed within natural evolution process.

An optical method for carbon dioxide isotopes and mole fractions in small gas samples: Tracing microbial respiration from soil, litter, and lignin.

Carbon dioxide isotope (δ13 C value) measurements enable quantification of the sources of soil microbial respiration, thus informing ecosystem C dynamics. Tunable diode lasers (TDLs) can precisely measure CO2 isotopes at low cost and high throughput, but are seldom used for small samples (≤5mL). We developed a TDL method for CO2 mole fraction ([CO2 ]) and δ13 C analysis of soil microcosms. Peaks in infrared absorbance following constant volume sample injection to a carrier were used to independently measure [12 CO2 ] and [13 CO2 ] for subsequent calculation of δ13 C values. Using parallel soil incubations receiving differing C substrates, we partitioned respiration from three sources using mixing models: native soil organic matter (SOM), added litter, and synthetic lignin containing a 13 C label at Cβ of the propyl side chain. Once-daily TDL calibration enabled accurate quantification of δ13 C values and [CO2 ] compared with isotope ratio mass spectrometry (IRMS), with long-term external precision of 0.17 and 0.31‰ for 5 and 1mL samples, respectively, and linear response between 400 and 5000μmol mol-1 CO2 . Production of CO2 from native soil C, added litter, and lignin Cβ varied over four orders of magnitude. Multiple-pool first-order decay models fitted to data (R2 >0.98) indicated substantially slower turnover for lignin Cβ (17years) than for the dominant pool of litter (1.3years) and primed soil C (3.9years). Our TDL method provides a flexible, precise, and high-throughput (60 samples h-1 ) alternative to IRMS for small samples. This enables the use of C isotopes in increasingly sophisticated experiments to test biogeochemical controversies, such as the fate of lignins in soil.

Pyrrolyl-silicon compounds with different alkyl spacer lengths: Synthesis, electrochemical behavior and binding properties

This work reports a joint experimental-theoretical investigation of pyrrolyl-silicon compounds with different alkyl spacers, namely propyl, butyl and hexyl side chains carrying silicon-based end groups. For the electrochemical study, the monomers with methoxysilyl end groups spaced through butyl and hexyl chains were ad-hoc synthesized. Structurally different oligomeric domains are promoted during electropolymerization as a result of irreversible hydrolysis of methoxy end groups by acid intermediate σ-oligomers. The onset of OH-π stabilizing interactions and the charge pinning action of silanol promotes mixed n-p doping behavior of the hybrid films. The more important charge trapping in the case of propyl spacer is attributed to effective (through bond) inductive effects and conformational restrictions. MD simulations of chemisorption of hydrolyzed oligo-pyrroles onto γ-Al2O3 surface confirmed the propyl spacer as the optimum alkyl chain length for stratification and interpenetration of adsorbed hybrid layers.