Non-aromatic Group Research Articles

Effect of substituents at the C3´, C3´N, C10 and C2-meta-benzoate positions of taxane derivatives on their activity against resistant cancer cells

We tested the effect of substituents at the (1) C3´, C3´N, (2) C10, and (3) C2-meta-benzoate positions of taxane derivatives on their activity against sensitive versus counterpart paclitaxel-resistant breast (MCF-7) and ovarian (SK-OV-3) cancer cells. We found that (1) non-aromatic groups at both C3´ and C3´N positions, when compared with phenyl groups at the same positions of a taxane derivative, significantly reduced the resistance of ABCB1 expressing MCF-7/PacR and SK-OV-3/PacR cancer cells. This is, at least in the case of the SB-T-1216 series, accompanied by an ineffective decrease of intracellular levels in MCF-7/PacR cells. The low binding affinity of SB-T-1216 in the ABCB1 binding cavity can elucidate these effects. (2) Cyclopropanecarbonyl group at the C10 position, when compared with the H atom, seems to increase the potency and capability of the derivative in overcoming paclitaxel resistance in both models. (3) Derivatives with fluorine and methyl substituents at the C2-meta-benzoate position were variously potent against sensitive and resistant cancer cells. All C2 derivatives were less capable of overcoming acquired resistance to paclitaxel in vitro than non-substituted analogs. Notably, fluorine derivatives SB-T-121205 and 121,206 were more potent against sensitive and resistant SK-OV-3 cells, and derivatives SB-T-121405 and 121,406 were more potent against sensitive and resistant MCF-7 cells. (4) The various structure-activity relationships of SB-T derivatives observed in two cell line models known to express ABCB1 favor their complex interaction not based solely on ABCB1.

Synthesis of 5-Benzylamino and 5-Alkylamino-Substituted Pyrimido[4,5-c]quinoline Derivatives as CSNK2A Inhibitors with Antiviral Activity.

A series of 5-benzylamine-substituted pyrimido[4,5-c]quinoline derivatives of the CSNK2A chemical probe SGC-CK2-2 were synthesized with the goal of improving kinase inhibitor cellular potency and antiviral phenotypic activity while maintaining aqueous solubility. Among the range of analogs, those bearing electron-withdrawing (4c and 4g) or donating (4f) substituents on the benzyl ring as well as introduction of non-aromatic groups such as the cyclohexylmethyl (4t) were shown to maintain CSNK2A activity. The CSNK2A activity was also retained with N-methylation of SGC-CK2-2, but α-methyl substitution of the benzyl substituent led to a 10-fold reduction in potency. CSNK2A inhibition potency was restored with indene-based compound 4af, with activity residing in the S-enantiomer (4ag). Analogs with the highest CSNK2A potency showed good activity for inhibition of Mouse Hepatitis Virus (MHV) replication. Conformational analysis indicated that analogs with the best CSNK2A inhibition (4t, 4ac, and 4af) exhibited smaller differences between their ground state conformation and their predicted binding pose. Analogs with reduced activity (4ad, 4ae, and 4ai) required more substantial conformational changes from their ground state within the CSNK2A protein pocket.

Degradation by Design: New Cyclin K Degraders from Old CDK Inhibitors.

Small molecules that induce protein degradation hold the potential to overcome several limitations of the currently available inhibitors. Monovalent or molecular glue degraders, in particular, enable the benefits of protein degradation without the disadvantages of high molecular weight and the resulting challenge in drug development that are associated with bivalent molecules like Proteolysis Targeting Chimeras. One key challenge in designing monovalent degraders is how to build in the degrader activity─how can we convert an inhibitor into a degrader? If degradation activity requires very specific molecular features, it will be difficult to find new degraders and challenging to optimize those degraders toward drugs. Herein, we demonstrate that an unexpectedly wide range of modifications to the degradation-inducing group of the cyclin K degrader CR8 are tolerated, including both aromatic and nonaromatic groups. We used these findings to convert the pan-CDK inhibitors dinaciclib and AT-7519 to Cyclin K degraders, leading to a novel dinaciclib-based compound with improved degradation activity compared to CR8 and confirm the mechanism of degradation. These results suggest that general design principles can be generated for the development and optimization of monovalent degraders.

Cocoa volatile compounds affect aroma but not taste

Flavor is one of the most essential indicators for determining the quality of cocoa beans, especially fine flavor cocoa. The volatile compound in the beans affect the mechanism the flavor emergence. Therefore, this study aimed to identify the volatile compound in the aromatic and non-aromatic cocoa groups as one of FFCs indicator. It was conducted at the Indonesian Coffee and Cocoa Research Institute, Jember, East Java, Indonesia. Furthermore, the genetic material used consisted of six aromatic cocoa genotypes, such as DR 2, ICCRI 03, ICCRI 07, ICCRI 09, MCC 02, and TSH 858 as well as four non-aromatic genotypes such as Sulawesi1, Sulawesi 2, KW 516, and KEE 2. A completely randomized block design (RCBD) was used with three repetitions. The fermented bean samples of each genotype were analyzed of volatile compound at the Food and Science Laboratory, Jember Polytechnic, East Java and sensory test was conducted by three certified panelists from ICCRI. Data were analyzed by orthogonal contrast analysis with IRRI's STAR 2.0.1 software. While the Microsoft Excel 2019 and R Studio were used for correlation analysis and heatmaps. The results showed aldehydes, acids, esters, pyrroles, and pyrazines of aromatic cocoa bean group higher than the non-aromatic. The alanine and terpenoid compounds was only found in clones DR 2 and ICCRI 03, while the alcohol and phenol compounds dominated in the non-aromatic group. Genotypes were grouped into six groups, based on flavor and volatile compound. ICCRI 09 characterized by strong acidity with a fresh fruit, spicy and sweet aroma as well as containsed aldehydes. Furthermore, ICCRI 03, MCC 02, and TSH 858 bean had weaker acidity and aroma than ICCRI 09 and contain terpenoids. ICCRI 07 had a nutty and woody aroma and was dominated by furan and pyrazine compounds. While Sulawesi 1 had a putrid aroma and alkaloids. The genotype groups of KW 516, KEE2, and Sulawesi 2 had astringent taste, dirty/dusty and moldy aroma as well as contained alcohol and phenol. Keywords: Aromatic; Flavor; Non-aromatic; Theobroma cacao L; Volatile compounds

Differently N-Capped Analogues of Fmoc-FF.

Short and ultra-short peptides have been recently envisioned as excellent building blocks for the formulation of hydrogels with appealing properties. Due to its simplicity and capability to gel under physiological conditions, Fmoc-FF (Nα-fluorenylmethoxycarbonyl-diphenylalanine), remains one of the most studied low molecular-weight hydrogelators. Since its first identification in 2006, a plethora of its analogues were synthetized and investigated for the fabrication of novel supramolecular materials. Here we report a description of the Fmoc-FF analogues in which the aromatic Fmoc group is replaced with other substituents. These analogues are distinguished into five different classes including derivatives: i) customized with solid phase peptide synthesis protecting groups; ii) containing non-aromatic groups, iii) containing aromatic groups, iv) derivatized with metal complexes and v) containing stimuli-responsive groups. The morphological, mechanical, and functional effects caused by this modification on the resulting material are also pointed out.

Protein charge transfer spectra in a monomeric protein with no lysine.

UV-Visible absorption and luminescence originating from non-aromatic groups in proteins is being intensely investigated today. Earlier work has shown that non-aromatic charge clusters in a folded monomeric protein can collectively act like a chromophore. Incident light in the near UV-Visible wavelength causes photoinduced electron transfer from the Highest Occupied Molecular Orbital (HOMO) of the electron-rich donor (like a carboxylate anion) to the Lowest Unoccupied Molecular Orbital (LUMO) of the electron-deficient acceptor (like a protonated amine or the polypeptide backbone) in the protein giving rise to absorption spectra in the 250-800 nm range referred to as Protein Charge Transfer Spectra (ProCharTS). The transferred electron can relax back from the LUMO to fill up the hole in the HOMO by a charge recombination process, emitting weak ProCharTS luminescence. Previous studies in monomeric proteins displaying ProCharTS absorption/luminescence always involved lysine-containing proteins. The lysine (Lys) sidechain plays a dominant role in ProCharTS; however, experimental evidence for ProCharTS among proteins/peptides devoid of Lys is lacking. Recently, the absorption features of charged amino acids have been examined using time-dependent density functional theory calculations. In this study, we show that amino acids: arginine (Arg), histidine (His) and aspartate (Asp); homo-polypeptides: poly-arginine and poly-aspartate; and a protein: Symfoil PV2 that is rich in Asp, His and Arg, but lacks Lys, profusely display ProCharTS. The folded Symfoil PV2 protein displayed maximum ProCharTS absorptivity in the near UV-Vis region, in comparison to the homo-polypeptides and amino acids. Furthermore, features like overlapping ProCharTS absorption spectra, decreasing ProCharTS luminescence intensity with longer excitation wavelength, large Stokes shift, multiple excitation bands and multiple luminescence lifetime components appeared to be conserved across peptides, proteins and amino acids studied. Our results underscore the utility of ProCharTS as an intrinsic spectral probe to monitor the structure of any protein that is rich in charged amino acids.

Design of competitive inhibitory peptides for HMG-CoA reductase and modeling structural preference for short linear peptides

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is a rate-controlling enzyme in a biosynthesis of cholesterol. In the previous studies, a number of short linear peptides as competitive inhibitors of this enzyme were designed. Short peptides are known as very flexible molecules and a prediction of the structural preferences is an important step in design of such peptides. The effect of the peptide fragmentation in searching of lead peptide candidates was described in the previous design. By using this approach, the present study demonstrates that a relatively stable segment can be selected and it may be used as a basis in investigation of the functionalities of the side chains of the substituted residues during binding. In this connection, a number of heptapeptides were designed by using a substitution in the N-terminus of the designed peptides. The substituted residues were selected to be those that may participate in π-π interaction between non-aromatic groups, and also as the charged residues in some cases. As a result a more active competitive inhibitor for HMGR was designed. The CFGYVAE peptide was found to be more than 25,000-fold active in comparison with the first isolated peptide from soybeans. The obtained spectral and calculation data support to the predicted preference in structures of the designed peptides.

Molecular characterization and genetic diversity analysis of aromatic rice (Oryza sativa L.) landraces using SSR markers

The present investigation was conducted at the Department of Plant Breeding and Genetics, College of Horticulture, Vellanikkara, Thrissur and Regional Agricultural Research Station, Ambalavayal, Wayanad, The study was focused on genetic diversity among popular aromatic rice landraces using Simple Sequence Repeats (SSR) markers. Out of 86 SSR markers used for molecular characterization, 44 markers were polymorphic and remaining 42 were monomorphic. Maximum number of amplicons was exhibited by RM247 with five alleles, followed by RM85, RM251, RM248 and RM493 with four amplicons each. Among 86 SSR markers, 21 markers distinguished Basmati from traditional aromatic landraces of Wayanad viz., Gandhakasala and Jeerakasala. Seven SSR markers distinguished Gandhakasala from Jeerakasala, whereas 23 markers distinguished Basmati from Jeerakasala. Twenty-two markers distinguished Basmati from Gandhakasala and 23 markers distinguished aromatic group from non-aromatic group. Cluster analysis effectively differentiated Basmati, Jeerakasala, Gandhakasala, Uma and Aathira from each other. Among the five clusters formed, cluster III was the largest one comprising all the 12 Gandhakasala morphotypes, followed by cluster IV with all Jeerakasala morphotypes. Cluster I, Cluster II and Cluster V exhibited one genotype each namely Aathira, Uma and Basmati, respectively indicating their genetic distinctness. Key wordsRice, Aromatic landraces, Genetic diversity, Simple sequence repeat, UPGMA.

Cutaneous Adverse Drug Reactions (CADRs) between Aromatic and Non-Aromatic Antiepileptic Drugs: Clinical Presentation and Severity

Background: Drug hypersensitivity is the most common adverse effect of drug use. Major cutaneous adverse drug reactions (CADRs) represent the higher rates of morbidity and mortality, with up to 5.2% of cases. Current reports revealed the non-aromatic antiepileptic drugs had increasing rates of CADRs from the past. Objective: To study the clinical presentations and the severity of CADRs due to aromatic and non-aromatic antiepileptic drugs. Materials and Methods: A retrospective cohort study was conducted with inpatients and outpatients with CADRs receiving antiepileptic drugs in Phramongkutklao Hospital between January 2009 and December 2018. Results: Among 77 patients with CADRs, 61 patients received aromatic antiepileptic drugs and 16 patients took non-aromatic antiepileptic drugs. Among the patients with aromatic antiepileptic drugs 52.46% developed minor cutaneous drug reactions. The rest, 47.54%, developed major cutaneous drug reactions including Steven-Johnson syndrome or toxic epidermal necrolysis (SJS/TEN) 13.11% and drug rash with eosinophil and systemic symptoms (DRESS) 31.15%. Among the patients with non-aromatic antiepileptic drugs, 62.5% developed minor cutaneous drug reactions. The rest, 37.5%, developed major CADRs including SJS/TEN 12.5% and DRESS 25%. Of the patients receiving aromatic antiepileptic, the major CADRs group showed significant higher level of eosinophil compared with minor CADRs (10.35% and 2.1%, respectively, p<0.001). The study showed significant higher alkaline phosphatase (ALP) levels in 138.5 IU/L among patient with major CADRs who received aromatic antiepileptic drugs compared with minor CADRs in 87 IU/L (p=0.006). No significant difference of laboratory was found among CADRs patients in non-aromatic group. Conclusion: Aromatic antiepileptic drugs tended to cause more severe cutaneous drug reactions than non-aromatic antiepileptic drugs, especially DRESS. The internal organ involvements were significantly identified in the aromatic antiepileptic group regarding to serum eosinophil and ALP level. Keywords: Adverse skin reaction, Aromatic antiepileptic drugs, Non-aromatic antiepileptic drug

Substituents at the C3′ and C3′N positions are critical for taxanes to overcome acquired resistance of cancer cells to paclitaxel

We tested the role of substituents at the C3′ and C3′N positions of the taxane molecule to identify taxane derivatives capable of overcoming acquired resistance to paclitaxel. Paclitaxel-resistant sublines SK-BR-3/PacR and MCF-7/PacR as well as the original paclitaxel-sensitive breast cancer cell lines SK-BR-3 and MCF-7 were used for testing. Increased expression of the ABCB1 transporter was found to be involved in the acquired resistance. We tested three groups of taxane derivatives: (1) phenyl group at both C3′ and C3′N positions, (2) one phenyl at one of the C3′ and C3′N positions and a non-aromatic group at the second position, (3) a non-aromatic group at both C3′ and C3′N positions. We found that the presence of phenyl groups at both C3′ and C3′N positions is associated with low capability of overcoming acquired paclitaxel resistance compared to taxanes containing at least one non-aromatic substituent at the C3′ and C3′N positions. The increase in the ATPase activity of ABCB1 transporter after the application of taxanes from the first group was found to be somewhat higher than after the application of taxanes from the third group. Molecular docking studies demonstrated that the docking score was the lowest, i.e. the highest binding affinity, for taxanes from the first group. It was intermediate for taxanes from the second group, and the highest for taxanes from the third group. We conclude that at least one non-aromatic group at the C3′ and C3′N positions of the taxane structure, resulting in reduced affinity to the ABCB1 transporter, brings about high capability of taxane to overcome acquired resistance of breast cancer cells to paclitaxel, due to less efficient transport of the taxane compound out of the cancer cells.

Pi-Pi contacts are an overlooked protein feature relevant to phase separation.

Protein phase separation is implicated in formation of membraneless organelles, signaling puncta and the nuclear pore. Multivalent interactions of modular binding domains and their target motifs can drive phase separation. However, forces promoting the more common phase separation of intrinsically disordered regions are less understood, with suggested roles for multivalent cation-pi, pi-pi, and charge interactions and the hydrophobic effect. Known phase-separating proteins are enriched in pi-orbital containing residues and thus we analyzed pi-interactions in folded proteins. We found that pi-pi interactions involving non-aromatic groups are widespread, underestimated by force-fields used in structure calculations and correlated with solvation and lack of regular secondary structure, properties associated with disordered regions. We present a phase separation predictive algorithm based on pi interaction frequency, highlighting proteins involved in biomaterials and RNA processing.

Effect of Lavender Oil Aroma in the Early Hours of Postpartum Period on Maternal Pains, Fatigue, and Mood: A Randomized Clinical Trial.

Background:Busy care providers focus on the serious complications of postpartum period. This issue causes the seemingly trivial complications, such as mother's pains, fatigue, and psychological status, to be less taken into account. The study aimed to determine the effect of lavender oil aroma in the early hours of postpartum period on maternal pains, fatigue, and mood in primiparous mothers.Methods:This randomized clinical trial was conducted on 56 participants; 29 in intervention group and 27 in control group. The intervention group received lavender oil in three doses during the first 24 h after delivery. Sesame oil was used in the control group. Intensity of pain, fatigue, and distress level was measured by visual analog scale before and after the interventions. Besides, mood status was assessed through the positive and negative affect schedule.Results:The mean age of all the participants was 23.88 ± 3.88 years. After the first intervention and also in the tomorrow morning assessment, significant differences were found between the two groups regarding perineal pain (P = 0.004, P < 0.001), physical pain (P < 0.001), fatigue (P = 0.02, P < 0.001), and distress scores (P < 0.001). In addition, significant differences were found concerning the mean scores of positive (P < 0.001) and negative (P = 0.007, P < 0.001) moods between the two groups after the interventions. Repeated measures analyses showed that the two groups were significantly different over time in all the evaluated variables.Conclusions:Lavender oil aromatherapy starting in the first hours of postpartum period resulted in better physical and mood status compared to nonaromatic group.

Application of Group-Based QSAR and Molecular Docking in the Design of Insulin-Like Growth Factor Antagonists

Purpose: To identify the structural requirements for designing a lead key for insulin-like growth factor (IGF-1R) inhibition using group-based quantitative structure activity relationship (GQSAR) and molecular docking.Methods: GQSAR method requires fragmentation of molecules. The molecules in the current dataset were fragmented into three (R1, R2 and R3) by applying common fragmentation pattern, and fragmentbased 2D descriptors were then calculated. GQSAR models were derived by applying various methods including multiple linear regressions and partial least square or k-nearest neighbour.Results: Four generated GQSAR models were selected based on the statistical significance of the model. It was found that the presence of flexible and non-aromatic groups on fragment R1 was conducive for inhibition. Additionally, the existence of amino groups as hydrogen bond donors at fragments R2 and R3 was fruitful for inhibition. Docking studies revealed the binding orientation adopted by the active compounds at several amino acid residues, including Met 1126, Arg, 1128, Met 1052, GLU 1050, Met 1112, Leu 1051, Met 1049, Val 1033, and Val 983 at ATP binding sites of IGF-1R kinase domain.Conclusion: The generated models provide a site-specific insight into the structural requirements for IGF-1R inhibition which can be used to design and develop potent inhibitors.Keywords: Insulin-like growth factor 1 (IGF-1) receptor, Quantitative structure-activity relationship, Adenosine triphosphate, Competitive inhibitors, Electrotopological state index.

PEROXIDASE ISOZYME IDENTIFICATION OF SOME RICE GENOTYPES IN M1 GENERATION UNDER DROUGHT STRESS LEVEL OF -0.03 MPa

The effort to fulfill the need of rice through the improvement of dryland productivity can be viewed as a more environmentally-friendly way. This research used 36 rice genotypes in M 1 generation that were grown hydrophonically under drought stress level of -0.03 MPa. The identifications were conducted based on peroxidase isozyme marker. The isozyme patterns in zymogram were binary-coded by visual scores for each genotype, based on the thickness and the number in the appearance of bands on certain migration distance. The migration distances were measured based on values of Rf. The similarity coefficients were calculated using Dice’s coefficient that were used to construct dendrogram using the UPGMA employing the SAHN from the NTSYSpc 2.02. The results showed that the most resistant genotype under drought stress was R-4, and the genetic relationships among the genotypes were divided into two main groups, aromatic and non-aromatic group, in which some genotypes experienced the reduced levels of aromatic character (R-8 and R-9) and the drought resistance character (IU-2, IU-3, IU-4, IU-5, IU-6, IU-7, and IU-8), but there were some genotypes to able to improve the resistance under drought stress (R-2, R-3, R-5, R-6, R-7, IT-4, IT-5, and IT-7). Keywords: drought resistance, gamma irradiation, peroxidase isozyme, rice, sodium azide

Polyglycerol‐Derived Amphiphiles for the Solubilization of Single‐Walled Carbon Nanotubes in Water: A Structure–Property Study

A series of nonionic amphiphiles derived from polyglycerol dendrons were studied for their ability to solubilize and isolate single-walled carbon nanotubes. The amphiphiles possessed differently sized polar head groups, hydrophobic tail units, and various aromatic and non-aromatic groups between the head and tail groups. Absorbance analysis revealed that amphiphiles with anchor groups derived from pyrene were far inferior to those that possessed simple linear aliphatic tail groups. Absorbance and near-infrared fluorescence analyses revealed a weak dependence on the dendron size of the head group, but a strong positive trend in suspended nanotube density and fluorescence intensity for amphiphiles with longer tail units. Variations in the moieties linking the head and tail groups led to a range of effects on the suspensions, with linkers imparting flexibility and a bent shape that gave improved performance overall. This was illustrated most dramatically by a pair of benzamide-containing amphiphiles, the para isomer of which showed evidence in the fluorescence data of increased nanotube aggregate formation when compared with the meta isomer. In addition, statistical AFM was used to illustrate more directly the microscopic differences between amphiphiles that were effective at nanotube bundle disruption and those that were not.

Modeling the Binding Affinity of Peptides for Graphitic Surfaces. Influences of Aromatic Content and Interfacial Shape

Interactions between peptide sequences and graphitic surfaces—carbon nanotubes and graphite—are investigated using molecular dynamics simulations with a polarizable force-field. Peptide sequences selected to have a strong affinity for carbon nanotubes [Nat. Mater. 2003, 2, 196.] are rich in tryptophan. We investigate the importance of the tryptophan residue for two of these sequences by mutating each tryptophan with either tyrosine or phenylalanine. We find that, in line with recent experimental observations, the original, tryptophan-containing sequences support relatively stronger binding to both nanotubes and graphite, compared with the mutants. We ascribe this behavior to the additional structural stability conferred by the indole group at the interface. We also explore the effect of interfacial curvature on the binding affinity. Our findings suggest that these nanotube-binding peptides have also been selected for interfacial shape. For the graphite surface our results indicate a compromise exists between maintaining strong ring−surface interactions and allowing nonaromatic groups to also approach the surface.

Nonaromatic hydroxylation of bupivacaine during continuous epidural infusion in man

Less than 11% of the dose of bupivacaine could be accounted for in urine from 10 patients receiving continuous epidural infusions. HPLC analysis of metabolites confirmed ( S)-bupivacaine was more extensively metabolised than ( R)-bupivacaine, and dealkylation was the predominant metabolic pathway although co-elution of metabolites made quantitation difficult. The percentage of ( S)-2′,6′-pipecoloxylidide and co-eluting metabolites excreted relative to ( R)-2′,6′-pipecoloxylidide from three patients was 0.32±0.05, while for seven patients it was 1.28±0.09. Conversely, the percentage of ( S)-3′-hydroxy bupivacaine and co-eluants excreted relative to ( R)-2′,6′-pipecoloxylidide from the three patients (1.76±0.48) was greater than the seven patients (0.19±0.09). Urinary metabolites were analysed for evidence of aliphatic hydroxylation of bupivacaine. Chiral liquid chromatography–mass spectrometry (LC–MS) on an α 1-glycoprotein column at pH 7 used hydroxylamine acetate as the volatile mobile phase. Compounds tentatively identified as hydroxybupivacaines by MRM were verified by their product ion spectra in a subsequent MS–MS run. Eighteen oxygenated metabolites of bupivacaine were detected, half of which were hydroxylated on nonaromatic groups. Equal numbers of mono- and dihydroxybupivacaines were excreted. There was no evidence to suggest the presence of ( S)-4′-hydroxybupivacaine, 2′-hydroxymethylbupivacaine, 3′-hydroxy-2′,6′-pipecoloxylidide or a piperidone. The metabolite previously identified as ( S)-4′-hydroxybupivacaine was not hydroxylated on the xylyl group.

Interstellar and Circumstellar PAHs

ISO has shown that the mid–IR spectra of almost all sources are dominated by narrow emission features collectively known as the UIR bands. These bands are carried by a family of polycyclic aromatic hydrocarbon molecules containing about 50 C-atoms. Other classes of molecules such as C-chains as well as non-aromatic groups attached to the PAHs are much less abundant. ISO has revealed that the UIR spectrum is incredibly rich with a large number of weaker features, subfeatures, and shoulders; many of which were not known before. Some examples and the new insights they can provide are described. A systematic study of this spectral structure may well allow us to considerably narrow down the composition of the family of PAHs responsible for the observed emission.

Theoretical investigation on the first hyperpolarizability of push–pull polyenes containing non-aromatic cyclic olefines

Abstract Novel push–pull polyenes containing non-aromatic cyclic olefines, such as cyclopentadiene, cyclopropene and cycloheptatriene, have been investigated for application of nonlinear optical (NLO) materials. Their dot products μβ0 of first hyperpolarizability (β0) and dipole moment (μ) are calculated by employing AM1/Finite Field and ZINDO/S approaches. Among them, the largest value is as high as 4.1×10−45 esu. The origin of such high μβ0 was analyzed based on the two-level model. Non-aromatic groups can transform to a stable aromatic anion/cation through gaining/losing an electron in their charge transfer states.

Highly Efficient Charge Transfer in Peptide Cations in the Gas Phase: Threshold Effects and Mechanism

We present new experimental data demonstrating specific, photoactivated positive charge migration in isolated peptide radical cations. The effect exhibits a threshold behavior, which we can directly correlate with energetics of local electronic states. A new very efficient mechanism for charge transfer in cations is proposed that involves an extended coulomb state (EC) of shakeup character. Our investigations are performed on laser-desorbed, cooled, neutral peptides in the gas phase. Charge localization in the peptide is achieved by resonant UV two-photon ionization at an aromatic chromophore. Charge flow in the cations can be activated by absorption of a first visible (VIS) photon. Presence of charge in the aromatic chromophore is probed by resonant absorption of a second VIS photon and monitored by dissociation. While this charge detection is found to work in isolated, positively charged chromophores or amino acids, it is efficiently quenched in some peptides. We explain this by photoactivated charge transfer and charge storage in nonaromatic groups of the peptides. At threshold this process is found to be strongly dependent on amino acid substitution even far away from the site of photoactivation. For analysis we first set up a local molecular orbital model for peptide cations and subsequently obtain a landscape of local electronic cation states formed by local hole and low-lying extended coulomb states. Charge transfer is found to be a through-bond mechanism involving energetically accessible electronic states along the path of charge flow. Charge transfer between hole states is mediated with very high efficiency through saturated carbon bridges by extended coulomb states. This new mechanism seems to be generally applicable to large extended molecular radical cations. Only barriers of the size of a full length of a certain defined amino acid are found to block charge transfer. The model qualitatively accounts for the order of the rates of the processes involved.