PNA Molecules Research Articles

Synthesis, structure and Hirshfeld surface analysis of diaquadinitratobis(4-nitroaniline)copper(II)

A new metal complex, [Cu(NO3)2(C6H6N2O2)2(H2O)2], was synthesized from water–ethanol solutions of Cu(NO3)2 and 4-nitroaniline (PNA). The complex molecules are located on inversion centers in monoclinic crystals with space group P21/c. The copper(II) ions are monodentately coordinated by two neutral PNA molecules through the nitrogen atom of the amino group, two NO3 − anions and two water molecules. The coordination polyhedron of the central ion is a distorted octahedron as a result of the Jahn–Teller effect. There is a weak intramolecular hydrogen bond between the N—H group and the oxygen atom of one nitrate anion. Six relatively weak intermolecular hydrogen bonds associate the complex molecules into a three-dimensional network. The Hirshfeld surface analysis indicates that 55.8% of the intermolecular interactions are from O...H/H...O contacts, 13.3% are from H...H contacts while other contributions are from C...O/O...C, C...H/H...C, O...O and other contacts.

Application of Single-Stranded DNA and PNA Probes for Electrochemical Detection of miRNA 141

miRNA are known as short RNA molecules that usually consist of 18 – 25 nucleotides and are considered as posttranscriptional regulators of gene expression occurring in plants and animals [1]. Over 60% of all genes which encode proteins are controlled by miRNA [2]. miRNA is engaged in various processes including differentiation, proliferation and apoptosis as well as inflammation. Hence, they might be considered as potential biomarkers of diseases such as cancer, neurodegenerative and cardiovascular [3]. A huge challenge is the actual detection of miRNA because of their short length, low concentration and matrix interferences. The miRNA analysis can be performed with the following techniques such as real-time PCR, northern blotting and microarray [4-6]. However, the above mentioned techniques are rather sophisticated and are costly. An alternative could be the application of electrochemical techniques which are characterized with low detection limits, possibility of miniaturization and high sensitivity. In such a case miRNA could be detected using biosensors containing receptor layers formed of single-stranded DNA or PNA.Herein, we present the studies on the development of ssDNA/PNA – based receptor layers for the electrochemical analysis of miRNA 141, which is a biomarker of pancreatic cancer. Various receptor layers were tested including unlabelled ssDNA, methylene blue-labelled DNA as well as PNA-based. The formation of ssDNA/PNA receptor layer along with its binding to miRNA was confirmed using QCM and SPR techniques. The electrochemical studies revealed that it was not possible to obtain low detection limits for miRNA when MB-labelled ssDNA or PNA molecules were applied. On the contrary, detection limit of 10-4 nM was reached with the application of unlabelled ssDNA molecules. The further analysis showed the possibility of detection of point mutation in ssDNA or miRNA sequence as well as miRNA detection in spiked serum sample.Bibliography:[1] D. P. Bartel, Cell 116 (2004) 281–297[2] A. Krek, D. Grun, M. N. Poy, R. Wolf, L. Rosenberg, E. J. Epstein, P. MacMenamin, I. da Piedade, K. C. Gunsalus, M. Stoffel, N. Rajewsky, N. Nat. Genet. 37 (2005) 495−500.[3] H. Hwang, J. T. Mendell, Br. J. Cancer 94 (2006) 776–780.[4] C. Chen, D. A. Ridzon, A. J. Broomer, Z. Zhou, D. H. Lee, J. T. Nguyen, M. Barbisin, N. L. Xu, V. R. Mahuvakar, M. R. Andersen, K. Q. Lao, K. J. Livak, K. J.Guegler, Nucleic Acids Res. 33 (2005) e179[5] A. Valoczi, C. Hornyik, N. Varga, J. Burgyan, S. Kauppinen, Z. Havelda, Nucleic Acids Res. 32 (2004) e175[6] A. M. Krichevsky, K. S. King, C. P. Donahue, K. Khrapko, K. S.Kosik, RNA 9 (2003) 1274−1281.

Single Molecule Investigation of Tandem G-Quadruplex Structures Formed by Human Telomeric Sequence

Human telomeric overhangs consist of 100-300 nucleotide long GGGTTA repeats, which can fold into multiple tandem G-quadruplex (GQ) structures. These structures protect and stabilize the telomeres and have been shown to inhibit telomerase activity, which made them an attractive target for anti-cancer drugs. Using single molecule Forster resonance energy transfer (FRET) spectroscopy, we interrogated the accessibility of 24-144 nucleotide long human telomeric DNA molecules (surface-immobilized and donor labeled) with short PNA molecules (acceptor labeled) that are complementary to a single repetition. These telomeric overhangs contain 4-24 GGGTTA repeats and can form 1-6 GQ structures when fully folded. However, when not fully folded, certain repeats can be accessed by PNA. PNA strands bind to these open sites on the telomeric DNA for a short period of time prior to dissociation, resulting in discrete FRET bursts as observed in the implementations of the FRET-PAINT method. These bursts were analyzed in terms of their dwell times, binding frequencies, and topographic distributions. Both dwell times and binding frequencies were greater for binding to intermediate regions of telomeric DNA compared to 3′-or 5′-ends. Finally, the binding frequency per telomeric repeat decreased monotonically with increasing telomere length, indicating a length-dependent compaction of the structure. These observations provide a potential framework to understand triggering of senescence or apoptosis when telomeric overhangs become shorter than a critical length (∼50 nt) where the necessary compaction may not be possible. The higher stability of the ends is consistent with GQ structures protecting telomeres against exonuclease activity.

Guanine anchoring: a strategy for specific targeting of a G-quadruplex using short PNA, LNA and DNA molecules.

Two separate structural elements of a G-quadruplex (G4), a vacant site and a flanking single-strand, provide an opportunity for specific targeting of a particular G4 structure via dual recognition. Here, we show that a short peptide nucleic acid (PNA) can specifically recognize and bind to a G4 at sub-micromolar affinity based on both G-tetrad vacant site filling and complementary duplex formation. This sequence-guided guanine-anchoring strategy can be further developed for specific targeting of G4 structures using short DNA, LNA and PNA strands.

Nanopore-Assisted, Sequence-Specific Detection, and Single-Molecule Hybridization Analysis of Short, Single-Stranded DNAs.

We report here on the ability of the α-hemolysin (α-HL) nanopore to achieve label-free, selective, and real-time detection of 15 nt long ssDNA fragments in solution, by exploiting their hybridization with freely added, polycationic peptides-functionalized PNAs. At the core of our work lies the paradigm that when PNAs and ssDNA are mixed together, the bulk concentration of free PNA decreases, depending upon the (mis)match degree between complementary strands and their relative concentrations. We demonstrate that the ssDNA sensing principle and throughput of the method are determined by the rate at which nonhybridized, polycationic peptides-functionalized PNA molecules arrive at the α-HL's vestibule entrance and thread into the nanopore. We found that with the application of a 30-fold salt gradient across the nanopore, the method enhances single-molecule detection sensitivity in the nanomolar range of ssDNA concentrations. This study demonstrates that the transmembrane potential-dependent unzip of single PNA-DNA duplexes at the α-HL's β-barrel entry permits discrimination between sequences that differ by one base pair.

Averaged third-order susceptibility of ZnO nanocrystals from Third Harmonic Generation and Third Harmonic Scattering

Both coherent Third Harmonic Generation (THG) at the interfaces of a cuvette filled with a nanocrystal suspension and incoherent Second and Third Harmonic Scattering (THS) from the suspension volume have been studied to quantitatively assess the orientation-averaged third-order susceptibility 〈χNPs(3)〉 of ZnO. These two complementary experimental approaches are based on different calibration routes with a nanocomposite model and fused-silica as a reference material for THG, and pNa molecules for THS. Similar and consistent absolute values of 〈χNPs(3)〉 (above 10−18m2/V2) are derived and discussed according to the particular orientation averaging procedure that holds for each experimental configuration for a 1064 nm excitation wavelength.

Ultrasonic-assisted emulsion synthesis of well-distributed spherical composite CL-20@PNA with enhanced high sensitivity

A novel spherical composite explosive of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane and p-nitroaniline (CL-20@PNA) in a molar ratio of 1:1 has been prepared by ultrasonic-assisted emulsion method. Then, the shape, structure, and thermodynamic behaviours of the spherical composite CL-20@PNA was characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Differential scanning calorimetery (DSC). The SEM results indicate that the composite CL-20@PNA are relatively uniform with an average particle size of micron, and the morphology is spherical. XRD analyses confirm that the spherical composite CL-20@PNA has some peak patterns with large differences from CL-20 and PNA. FT-IR spectra suggest that hydrogen-bonding interactions may exist between CL-20 and PNA molecules. Thermal analysis shows that the spherical composite CL-20@PNA has excellent thermal stability. Moreover, an impact sensitivity test indicates that the sensitivity of the spherical composite CL-20@PNA is sufficiently reduced relative to CL-20 and CL-20/PNA physical mixing, which data is up to 60.1cm.

Chemically Modified Gamma PNAs Targeting microRNA-210 as a Novel Anticancer Therapy With Specificity for Hypoxic Solid Tumors

To test the hypothesis that new generation PNA molecules targeting a key hypoxia induced microRNA, miR-210, will have substantial antineoplastic effects in mouse tumor models. MicroRNAs (miRs) are a class of small non-coding RNAs that regulate the translation and stability of mRNA during post-transcriptional events. miR profiling experiments reveal that certain miRs are widely over-expressed in several cancers, and inhibiting these miRs may offer a promising anticancer therapy. In particular, we have shown that miR-210 exhibits differential expression levels in cancers, especially in hypoxic cancer cells, resulting in a demonstrated capability to mediate cellular transformation and carcinogenesis by acting as an oncomiR and to promote adaptation to hypoxia and radiation resistance. PNAs are a synthetic DNA/RNA mimic in which the phosphodiester backbone is substituted with a neutral N-(2-aminoethyl) glycine backbone. PNA has been shown to bind single-stranded targets sequence-specifically, with high binding affinity, and is not susceptible to protease or nuclease degradation. These salient features make PNAs excellent candidates for targeting miRs. We have used a new class of conformationally pre-organized gamma peptide nucleic acids (γPNAs), which possess superior properties in terms of solubility, binding affinity, biocompatibility, and in vivo delivery in order to target miR-210. For cellular delivery, we used FDA approved poly(lactic-co-glycolic acid) (PLGA) nanoparticles. γPNAs encapsulated in PLGA nanoparticles were evaluated in human cancer cell lines in vitro as well as in xenograft mouse models in vivo. Our results show that nanoparticles containing γPNAs targeting miR-210 cause substantial delay in tumor growth in a xenograft mouse model. Further, histopathological analyses support the potent antimiR-210 and anti-tumor activity of γPNA, with potential impacts on cell death and angiogenesis pathways. Our work provides a framework for an antimiR-210 based therapeutics and a promising clinically translatable system for selectively targeting solid tumors using a PLGA based nanoparticle system.

Abstract 1075: Chemically modified gamma PNAs targeting oncomiR-210 as a potential anticancer therapy

Abstract The specific aims of this study are to test the hypothesis that new generation PNA molecules targeting miR-210 delivered using nanoparticles will have therapeutic effects in xenograft mouse models and in human cancer cell lines. MicroRNAs (miRs) are a class of small non-coding RNAs (22-23nt) that regulate the translation and stability of mRNA during post-transcriptional events. miR profiling experiments reveal that certain miRs are widely over-expressed in several cancers, and inhibiting these miRs may offer a promising anticancer therapy. Little is known about how they work to cause cancer. This warrants further investigation to understand the relationship between miRNAs and cancer, but also to capitalize on fact that oncomiRs may be potent therapeutic targets. In particular, miR-210 exhibit differential expression levels in cancers, especially in hypoxic cancer cells, resulting in a demonstrated capability to affect cellular transformation and carcinogenesis by acting as an oncomiR. Many antisense molecules such as locked nucleic acids (LNA) have been developed that can target specific miRs, but they are few in number and often require further optimization for cellular delivery, off target toxicity, tumor selectivity and enzymatic resistance properties. Unlike most nucleic acids, PNA is a synthetic DNA/RNA mimic in which the phosphodiester backbone is substituted with a neutral N-(2-aminoethyl) glycine backbone. PNA has been shown to bind single-stranded targets sequence-specifically, with high binding affinity, and is not susceptible to protease or nuclease degradation. These salient features make PNAs excellent candidates for targeting miRs. Here, we used a new class of conformationally preorganized gamma peptide nucleic acids (γPNAs), which possess superior properties in terms of solubility, binding affinity, biocompatibility, and in vivo delivery in order to target miR-210. For cellular delivery, we used FDA approved poly(lactic-co-glycolic acid) (PLGA) nanoparticles. γPNA encapsulated in PLGA nanoparticles were evaluated in human cancer cell lines in vitro as well as in xenograft mouse model in vivo. Our results show that nanoparticles containing γPNAs targeting miR-210 cause significant delay in tumor growth in a xenograft mouse model. Further, histopathological analyses also support the enhanced antimiR-210 activity of γPNA. Hence our work will provides a) a framework for a antimiR-210 based therapeutics at the clinical level using γPNA; b) a promising clinically translatable system for selectively targeting cancer using a PLGA based nanoparticle system which can be scaled up easily; c) a step forward for personalized therapy for cancers by inhibiting specific miRs. In addition, use of hydrophilic chains (MP) at the γ position will improve the pharmacokinetic properties of PNA for preclinical and clinical studies for oncomiR-based therapeutics. Citation Format: Anisha Gupta, Yanfeng Liu, Elias E. Quijano, W Mark Saltzman, Peter M. Glazer. Chemically modified gamma PNAs targeting oncomiR-210 as a potential anticancer therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1075.

Nanoparticles that deliver triplex-forming peptide nucleic acid molecules correct F508del CFTR in airway epithelium.

Cystic fibrosis (CF) is a lethal genetic disorder most commonly caused by the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. It is not readily amenable to gene therapy because of its systemic nature and challenges including in vivo gene delivery and transient gene expression. Here, we use triplex-forming PNA molecules and donor DNA in biodegradable polymer nanoparticles to correct F508del. We confirm modification with sequencing and a functional chloride efflux assay. In vitro correction of chloride efflux occurs in up to 25% of human cells. Deep sequencing reveals negligible off-target effects in partially homologous sites. Intranasal application of nanoparticles in CF mice produces changes in nasal epithelium potential differences consistent with corrected CFTR, with gene correction also detected in lung tissue. This work represents facile genome engineering in vivo with oligonucleotides using a nanoparticle system to achieve clinically relevant levels of gene editing without off-target effects.

Purification and assembly of thermostable Cy5 labeled γ-PNAs into a 3D DNA nanocage.

PNA is hybrid molecule ideally suited for bridging the functional landscape of polypeptides with the structural diversity that can be engineered with DNA nanostructures. However, PNA can be more challenging to work with in aqueous solvents due to its hydrophobic nature. A solution phase method using strain promoted, copper free click chemistry was developed to conjugate the fluorescent dye Cy5 to 2 bifunctional PNA strands as a first step toward building cyclic PNA-polypeptides that can be arranged within 3D DNA nanoscaffolds. A 3D DNA nanocage was designed with binding sites for the 2 fluorescently labeled PNA strands in close proximity to mimic protein active sites. Denaturing polyacrylamide gel electrophoresis (PAGE) is introduced as an efficient method for purifying charged, dye-labeled PNA conjugates from large excesses of unreacted dye and unreacted, neutral PNA. Elution from the gel in water was monitored by fluorescence and found to be more efficient for the more soluble PNA strand. Native PAGE shows that both PNA strands hybridize to their intended binding sites within the DNA nanocage. Förster resonance energy transfer (FRET) with a Cy3 labeled DNA nanocage was used to determine the dissociation temperature of one PNA-Cy5 conjugate to be near 50°C. Steady-state and time resolved fluorescence was used to investigate the dye orientation and interactions within the various complexes. Bifunctional, thermostable PNA molecules are intriguing candidates for controlling the assembly and orientation of peptides within small DNA nanocages for mimicking protein catalytic sites.

Intracellular delivery of peptide nucleic acid and organic molecules using zeolite-L nanocrystals.

The design and synthesis of smart nanomaterials can provide interesting potential applications for biomedical purposes from bioimaging to drug delivery. Manufacturing multifunctional systems in a way to carry bioactive molecules, like peptide nucleic acids able to recognize specific targets in living cells, represents an achievement towards the development of highly selective tools for both diagnosis and therapeutics. This work describes a very first example of the use of zeolite nanocrystals as multifunctional nanocarriers to deliver simultaneously PNA and organic molecules into living cells. Zeolite-L nanocrystals are functionalized by covalently attaching the PNA probes onto the surface, while the channel system is filled with fluorescent guest molecules. The cellular uptake of the PNA/Zeolite-L hybrid material is then significantly increased by coating the whole system with a thin layer of biodegradable poly-L-lysine. The delivery of DAPI as a model drug molecule, inserted into the zeolite pores, is also demonstrated to occur in the cells, proving the multifunctional ability of the system. Using this zeolite nanosystem carrying PNA probes designed to target specific RNA sequences of interest in living cells could open new possibilities for theranostic and gene therapy applications.

A new peptide nucleotide acid biosensor for electrochemical detection of single nucleotide polymorphism in duplex DNA via triplex structure formation

In this paper, we report a new PNA biosensor for electrochemical detection of point mutation or single nucleotide polymorphism (SNP) in p53 gene corresponding oligonucleotide based on PNA/ds-DNA triplex formation following hybridization of PNA probe with double-stranded DNA (ds-DNA) sample without denaturing the ds-DNA into single-stranded DNA (ss-DNA). As p53 gene is mutated in many human tumors, this research is useful for cancer therapy and genomic study. In this approach, methylene blue (MB) is used for electrochemical signal generation and the interaction between MB and oligonucleotides is studied by differential pulse voltammety (DPV). Probe-modified electrode is prepared by self-assembled monolayer (SAM) formation of thiolated PNA molecules on the surface of Au electrode. A significant increase in the reduction signal of MB following hybridization of the probe with the complementary double-stranded oligonucleotide (ds-oligonucleotide) confirms the function of the biosensor. The selectivity of the PNA sensor is investigated by non-complementary ds-oligonucleotides and the results support the ability of the sensor to detect single-base mismatch directly on ds-oligonucleotide. The influence of probe and ds-DNA concentrations on the effective discrimination against complementary sequence and point mutation is studied and the concentration of 10−6 M is selected as appropriate concentration. Diagnostic performance of the biosensor is described and the detection limit is found to be 4.15 × 10−12 M.

Synthesis and characterization of novel poly(1-naphthylamine)/zinc oxide nanocomposites: Application in catalytic degradation of methylene blue dye

The organic–inorganic poly(1-naphthylamine)/ZnO (PNA/ZnO) nanocomposites were synthesized by in situ chemical oxidative polymerization of 1-naphthylamine monomer and ZnO nanomaterials for the photocatalytic degradation of methylene blue (MB) dye under visible light. The surface properties of PNA molecules were altered by adding the ZnO nanomaterials. The crystalline and the optical properties of PNA/ZnO nanocomposites were improved with the increased contents of ZnO nanomaterials in PNA molecules due to the effective interaction of PNA to the surface of ZnO nanomaterials. The prepared PNA/ZnO nanocomposites presented moderate photocatalytic MB dye degradation of ~22% under visible light. The occurrence of dye degradation under visible light might attribute to high-charge separation of ē-h+ pairs at the interfaces of PNA and ZnO nanomaterials in its excited state under light irradiation.

Electrochemical DNA hybridization detection using peptide nucleic acids and [Ru(NH 3) 6] 3+ on gold electrodes

An electrochemical DNA hybridization detection method based on the electrostatic interactions of [Ru(NH 3) 6] 3+ cations with the anionic phosphate backbone of DNA is proposed. PNA molecules are immobilized as capture probes on the gold substrate. The cationic ruthenium complexes do not interact electrostatically with the PNA probes due to the absence of the anionic phosphate groups on the PNA probes. But after hybridization, [Ru(NH 3) 6] 3+ is adsorbed on the DNA backbone, giving a clear hybridization detection signal in ac voltammetry. The analytical parameters (sensitivity, selectivity and reproducibility) are evaluated. Very good discrimination against the single-base mismatch A2143G, internal to the 23S rRNA gene of Helicobacter pylori, is observed. Moreover the system is successfully applied to the detection of complementary PCR amplicons.

Experimental (SERS) and theoretical (DFT) studies on the adsorption of p-, m-, and o-nitroaniline on gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of p-, m-, and o-nitroaniline (PNA, MNA, and ONA) adsorbed on gold nanoparticles were studied, respectively, in a gold colloidal solution and on dried gold-coated filter paper. Significant changes were found in the SERS spectra of p-, m-, and o-nitroaniline molecules adsorbed on the two substrates, indicating that the behavior of p-, m-, and o-nitroaniline adsorbed on gold nanoparticles coated on filter paper was different from that in gold aqueous colloids. Moreover, on the filter paper it was found that the SERS spectra of the PNA molecules changed with the coverage density of the gold nanoparticles, while the MNA and ONA did not evidently change. The analyses showed that the origins of these changes were the different adsorption behavior of molecules adsorbed on the gold nanoparticles and that the adsorption behavior of molecules was greatly affected by the surface characteristic of the substrate and the surface configuration of the adsorbate. In addition, the vibrational frequencies and Raman scattering intensities of the three nitroanilines were calculated by use of the density functional theory (DFT-B3LYP/6-31G(d)) method. The combination of SERS spectroscopy and DFT calculation is quite useful for studies of adsorption orientation of a molecule on a metal nanoparticle.

High-resolution scanning tunneling microscopy and dI/dV map studies of peptidenucleic acid and fluorescein isothiocyanate

Abstract We used scanning tunneling microscopy (STM) to spatially map the local density of states of individual PNA molecules labeled with fluorescein isothiocyanate (FITC) on a Cu(1 1 1) surface. From the observed bias voltage dependences of the topographic height and the dI/dV map of FITC and individual PNA molecules, we confirmed that FITC and PNA have different electrical properties. We clearly differentiated the FITC and PNA molecules by mapping the density of states feature. This study shows that STM with the dI/dV map method is useful in FITC mapping.

Dynamics of p-nitroaniline molecules in FSM-type mesoporous silicas studied by solid-state NMR

Dynamics of p-nitroaniline (pNA) in FSM-type mesoporous silicas was investigated by means of 2H and 13C solid-state NMR. Deuterated pNA (pNA-d) was loaded to FSM-16 (FSM) and modified FSM samples which were prepared by reactions of FSM with trimethylethoxysilane (C1FSM), n-octyltriethoxysilane (C8FSM) and 3-aminopropyltriethoxysilane (NH 2FSM). 13C MAS NMR spectra of the samples at room temperature showed four sharp signals assigned to pNA-d, indicating a fast motion of pNA-d at room temperature. Temperature dependence of 2H NMR spectra exhibited the presence of two modes of motions, the isotropic motion and another motion such as a wobbling one (Motion I). Analysis of spin-lattice relaxation times ( T 1) for 2H spins demonstrated that the apparent activation energies of Motion I were 20 kJ mol −1 for FSM and 31–32 kJ mol −1 for C1FSM and NH 2FSM. On the other hand, temperature dependence of T 1 of Motion I in C8FSM was complicated presumably because of the motion of alkyl chains of the reacted silylating agent. These results indicated that the dynamics of pNA molecules was varied with the surface properties of the mesopores.

Dynamics of p-nitroaniline molecules in siliceous ZSM-5 studied by solid-state NMR

Sites and dynamics of p-nitroaniline (pNA) molecules in the micropores of siliceous ZSM-5 zeolite have been investigated by means of solid-state NMR. The adsorbed amounts of pNA studied were about 1.5, 4 and 6 molecules per unit cell of ZSM-5. 2H NMR and 13C NMR revealed that the motion of pNA was a 180° flip-flop around the C2 axis of the molecule when the adsorbed amount was less than four molecules per unit cell. The rate of the motion was about 50 kHz at 297 K, and the apparent activation energy was 57±17 kJ mol−1. 13C NMR confirmed the presence of different adsorbed states of pNA when the adsorbed amount was more than four molecules. Furthermore, 2H NMR revealed that the flip-flop motion of pNA was largely suppressed. These results indicate that the motion of pNA in the micropores of ZSM-5 depended on the adsorbed amount of pNA, and that the interaction between the guest molecules influenced the dynamics of the guest molecules.

Structure and properties of the composite zeolite silica-ZSM-12/para-nitroaniline

The pure silica form of zeolite ZSM-12 was loaded with hyper-polarizable para-nitroaniline (pNA) molecules to form a composite material pNA/silica-ZSM-12. 7.6 wt.% of pNA is occluded in the straight non-intersecting channels (free diameter ≈6 Å) of the host material. The composite was characterized by optical microscopy, thermal analysis, NMR- and FTIR-spectroscopy, second harmonic generation (SHG) experiments, molecular modelling and X-ray powder diffraction. The pNA molecules are perfectly aligned with their long axis parallel to the channel direction. The molecules have specific docking sites in the channel, and each molecule uses the channel length of two unit cells. However, the overall symmetry of the composite is centrosymmetric. As indicated by FTIR spectroscopy and thermal analysis, the hydrogen bonds between the sorbate molecules inside the host lattice of silica-ZSM-12 (one-dimensional hydrogen bond system) are weaker as compared to pure pNA crystals (three-dimensional hydrogen bond system). The color of the composite material is yellow. The crystals are dichroitic and change their color in polarized light from colorless to bright yellow. pNA/silica-ZSM-12 shows hardly any SHG. This is in contrast to the composite pNA/AlPO 4-5 which contains the highly polarizable pNA molecules in a non-centrosymmetric arrangement yielding, therefore, strong SHG activity.