Innovative Hybrid-Alignment Annotation Method for Bioinformatics Identification and Functional Verification of a Novel Nitric Oxide Synthase in Trichomonas vaginalis.

Both the annotation and identification of genes in pathogenic parasites are still challenging. Although, as a survival factor, nitric oxide (NO) has been proven to be synthesized in Trichomonas vaginalis (TV), nitric oxide synthase (NOS) has not yet been annotated in the TV genome. We developed a witness-to-suspect strategy to identify incorrectly annotated genes in TV via the Smith-Waterman and Needleman-Wunsch algorithms through in-depth and repeated alignment of whole coding sequences of TV against thousands of sequences of known proteins from other organisms. A novel NOS of TV (TV NOS), which was annotated as hydrogenase in the NCBI database, was successfully identified; this TV NOS had a high witness-to-suspect ratio and contained all the NOS cofactor-binding motifs (NADPH, tetrahydrobiopterin (BH4), heme and flavin adenine dinucleotide (FAD) motifs). To confirm this identification, we performed in silico modeling of the protein structure and cofactor docking, cloned the gene, expressed and purified the protein, performed mass spectrometry analysis, and ultimately performed an assay to measure enzymatic activity. Our data showed that although the predicted structure of the TV NOS protein was not similar to the structure of NOSs of other species, all cofactor-binding motifs could interact with their ligands with high affinities. We clearly showed that the purified protein had high enzymatic activity for generating NO in vitro. This study provides an innovative approach to identify incorrectly annotated genes in TV and highlights a novel NOS that might serve as a virulence factor of TV.

A Demand-Centric Repositioning Strategy for Bike-Sharing Systems.

Transport-sharing systems are eco-friendly and the most promising services in smart urban environments, where the booming Internet of things (IoT) technologies play an important role in the smart infrastructure. Due to the imbalanced bike distribution, bikes and stalls in the docking stations could be unavailable when needed, leading to bad customer experiences. We develop a dynamic repositioning strategy for the management of bikes in this paper, which supports dispatchers to keep stations in service. Two open datasets are examined, and the exploratory data analysis presents that there is a significant difference of travel patterns between working and non-working days, where the former has an excess demand at rush hours and the latter is usually at a low demand. To evaluate the effect when the demand outstrips a station's capacity, we propose a non-linear scaling technique to transform demand patterns and perform the clustering analysis for each of five categories obtained from the sophisticated analysis of the dataset. Our repositioning strategy is developed according to the transformed demands. Compared with the previous work, numerical simulations reveal that our strategy has a better performance for high-demand stations, and thus can substantially reduce the repositioning cost, which brings benefit to bike-sharing operators for managing the city bike system.

Propofol-Based Total Intravenous Anesthesia is Associated with Better Survival than Desflurane Anesthesia in Epithelial Ovarian Cancer Surgery: A Retrospective Cohort Study.

Background: Previous studies have shown that anesthetic techniques can affect outcomes of cancer surgery. We investigated the association between anesthetic techniques and patient outcomes after elective epithelial ovarian cancer surgery. Methods: This was a retrospective cohort study of patients who received elective open surgery for epithelial ovarian cancer between January 2009 and December 2014. Patients were grouped according to the administration of propofol or desflurane anesthesia. Kaplan-Meier analysis was performed, and survival curves were constructed from the date of surgery to death. Univariate and multivariate Cox regression models were used to compare hazard ratios for death after propensity matching. Subgroup analyses were performed for age, body mass index, preoperative carbohydrate antigen-125 level, International Federation of Gynecology and Obstetrics staging, and operation and anesthesia time. Results: In total, 165 patients (76 deaths, 46.1%) who received desflurane anesthesia and 119 (30 deaths, 25.2%) who received propofol anesthesia were eligible for analysis. After propensity matching, 104 patients were included in each group. In the matched analysis, patients who received propofol anesthesia had better survival with a hazard ratio of 0.52 (95% confidence interval, 0.33-0.81; p = 0.005). Subgroup analyses also showed significantly better survival with old age, high body mass index, elevated carbohydrate antigen-125 level, advanced International Federation of Gynecology and Obstetrics stage, and prolonged operation and anesthesia time in the matched propofol group. In addition, patients administered with propofol anesthesia had less postoperative recurrence and metastasis than those administered with desflurane anesthesia in the matched analysis. Conclusion: Propofol anesthesia was associated with better survival in patients who underwent elective epithelial ovarian cancer open surgery. Prospective studies are warranted to evaluate the effects of propofol anesthesia on oncological outcomes in patients with epithelial ovarian cancer.

Intermolecular Dehydrative Coupling and Intramolecular Cyclization of Ruthenium Vinylidene Complexes Formed from Aromatic Propynes Containing Carbonyl Functionalities.

A remarkable intermolecular dehydrative coupling reaction with the formation of a C-C bond was found for the vinylidene complex 2 a, yielding the dinuclear bisvinylidene complex 4 a. Complex 2 a containing 1-hydroxyindan moiety was first formed from the reaction of o-propynyl benzaldehyde 1 a with [Ru]-Cl ([Ru]=Cp(PPh3 )2 Ru) by a cyclization process. For analogous aldehyde 1 b containing an additional 1,3-dioxolane group on the aryl ring, similar intermolecular coupling yields the dinuclear bisvinylidene complex 4 b. However, the fluoro group on the aryl ring in aldehyde 1 c inhibits the coupling reaction, giving only the vinylidene complex 2 c. For the reactions of [Ru]-Cl in MeOH with compounds 1 f, 1 g and 1 h, each with a ketone functionality, cyclization gives vinylidene complexes 2 f, 2 g and 2 h, respectively. However, no similar intermolecular coupling was observed, instead, the intramolecular dehydration yields 8 f, 8 g and 8 h, respectively. In CDCl3 , catalytic cyclization is observed for the o-propynylphenyl ketone 1 h with [Ru]-Cl at 50 °C giving the isochromene products 14 h. Furthermore, treatment of the o-propynylaryl α,ß-unsaturated ketones 1 k-m and 1 n with [Ru]-Cl in MeOH affords the corresponding vinylidene complexes 10 k-m and 11 n each with 1-benzosuberone moiety in the presence of NH4 PF6 . These intramolecular cyclization products were formed by the addition of Cß onto the terminal carbon of the alkene moiety. All these reaction products were characterized by spectroscopic methods. In addition, structures of complexes 4 a, and 10 l were confirmed by single crystal X-ray diffraction analysis.

Dendrimer- and copolymer-based nanoparticles for magnetic resonance cancer theranostics.

Cancer theranostics is one of the most important approaches for detecting and treating patients at an early stage. To develop such a technique, accurate detection, specific targeting, and controlled delivery are the key components. Various kinds of nanoparticles have been proposed and demonstrated as potential nanovehicles for cancer theranostics. Among them, polymer-like dendrimers and copolymer-based core-shell nanoparticles could potentially be the best possible choices. At present, magnetic resonance imaging (MRI) is widely used for clinical purposes and is generally considered the most convenient and noninvasive imaging modality. Superparamagnetic iron oxide (SPIO) and gadolinium (Gd)-based dendrimers are the major nanostructures that are currently being investigated as nanovehicles for cancer theranostics using MRI. These structures are capable of specific targeting of tumors as well as controlled drug or gene delivery to tumor sites using pH, temperature, or alternating magnetic field (AMF)-controlled mechanisms. Recently, Gd-based pseudo-porous polymer-dendrimer supramolecular nanoparticles have shown 4-fold higher T1 relaxivity along with highly efficient AMF-guided drug release properties. Core-shell copolymer-based nanovehicles are an equally attractive alternative for designing contrast agents and for delivering anti-cancer drugs. Various copolymer materials could be used as core and shell components to provide biostability, modifiable surface properties, and even adjustable imaging contrast enhancement. Recent advances and challenges in MRI cancer theranostics using dendrimer- and copolymer-based nanovehicles have been summarized in this review article, along with new unpublished research results from our laboratories.

Cyclization Reactions of Aryl Propargyl Acetates with Tethered Epoxide Induced by Ruthenium Complex.

Reactions of the ruthenium complex [Ru]Cl ([Ru]=Cp(PPh3 )2 Ru; Cp=η5 -C5 H5 ) with several aryl propargyl acetates, each with an ortho-substituted chain of various length containing an epoxide on the aromatic ring and with or without methyl substitutents on the epoxide ring, bring about novel cyclizations. The cyclization reactions of HC≡CCH(OAc)(C6 H4 )CH2 (RC2 H2 O) (R=H, 6 a; R=CH3 , 6 b, where RC2 H2 O is an epoxide ring) in MeOH give the vinylidene complexes 5 a-b, respectively, each with the Cß integrated into a tetrahydro-5H-benzo[7]annulen-6-ol ring. A C-C bond formation takes place between the propargyl acetate and the less substituted carbon of the epoxide ring. Further cyclizations of 5 a-b induced by HBF4 give the corresponding vinylidene complexes 8 a-b each with a new 8-oxabicyclo-[3.2.1]octane ring by removal of a methanol molecule in high yield. For similar aryl propargyl acetates with a shorter epoxide chain, the cyclization gives a mixture of a vinylidene complex with a tetrahydronaphthalen-1-ol ring and a carbene complex with a tricyclic indeno-furan ring. For the cyclization of 18, with a longer epoxide chain, opening of the epoxide is required to afford the vicinal bromohydrin 22, then tandem cyclization occurs in one pot. Products are characterized by spectroscopic methods as well as by XRD analysis.

Effective heating of magnetic nanoparticle aggregates for in vivo nano-theranostic hyperthermia.

Magnetic resonance (MR) nano-theranostic hyperthermia uses magnetic nanoparticles to target and accumulate at the lesions and generate heat to kill lesion cells directly through hyperthermia or indirectly through thermal activation and control releasing of drugs. Preclinical and translational applications of MR nano-theranostic hyperthermia are currently limited by a few major theoretical difficulties and experimental challenges in in vivo conditions. For example, conventional models for estimating the heat generated and the optimal magnetic nanoparticle sizes for hyperthermia do not accurately reproduce reported in vivo experimental results. In this work, a revised cluster-based model was proposed to predict the specific loss power (SLP) by explicitly considering magnetic nanoparticle aggregation in in vivo conditions. By comparing with the reported experimental results of magnetite Fe3O4 and cobalt ferrite CoFe2O4 magnetic nanoparticles, it is shown that the revised cluster-based model provides a more accurate prediction of the experimental values than the conventional models that assume magnetic nanoparticles act as single units. It also provides a clear physical picture: the aggregation of magnetic nanoparticles increases the cluster magnetic anisotropy while reducing both the cluster domain magnetization and the average magnetic moment, which, in turn, shift the predicted SLP toward a smaller magnetic nanoparticle diameter with lower peak values. As a result, the heating efficiency and the SLP values are decreased. The improvement in the prediction accuracy in in vivo conditions is particularly pronounced when the magnetic nanoparticle diameter is in the range of ~10-20 nm. This happens to be an important size range for MR cancer nano-theranostics, as it exhibits the highest efficacy against both primary and metastatic tumors in vivo. Our studies show that a relatively 20%-25% smaller magnetic nanoparticle diameter should be chosen to reach the maximal heating efficiency in comparison with the optimal size predicted by previous models.

The Correlation of Pore Size and Bioactivity of Spray-Pyrolyzed Mesoporous Bioactive Glasses.

SiO2-CaO-P2O5-based mesoporous bioactive glasses (MBGs) were synthesized by spray pyrolysis in this study. Three commonly used non-ionic tri-block copolymers (L121, P123, and F127) with various lengths of hydrophilic chains were applied as structural templates to achieve different pore sizes. A mesoporous structure was observed in each as-prepared specimen, and the results showed that the L121-treated MBG had the largest pore size. The results of bioactivity tests indicated that the growth of hydroxyapatite is related to the pore size of the materials.

NEIL1 protects against aflatoxin-induced hepatocellular carcinoma in mice.

Global distribution of hepatocellular carcinomas (HCCs) is dominated by its incidence in developing countries, accounting for >700,000 estimated deaths per year, with dietary exposures to aflatoxin (AFB1) and subsequent DNA adduct formation being a significant driver. Genetic variants that increase individual susceptibility to AFB1-induced HCCs are poorly understood. Herein, it is shown that the DNA base excision repair (BER) enzyme, DNA glycosylase NEIL1, efficiently recognizes and excises the highly mutagenic imidazole ring-opened AFB1-deoxyguanosine adduct (AFB1-Fapy-dG). Consistent with this in vitro result, newborn mice injected with AFB1 show significant increases in the levels of AFB1-Fapy-dG in Neil1-/- vs. wild-type liver DNA. Further, Neil1-/- mice are highly susceptible to AFB1-induced HCCs relative to WT controls, with both the frequency and average size of hepatocellular carcinomas being elevated in Neil1-/- The magnitude of this effect in Neil1-/- mice is greater than that previously measured in Xeroderma pigmentosum complementation group A (XPA) mice that are deficient in nucleotide excision repair (NER). Given that several human polymorphic variants of NEIL1 are catalytically inactive for their DNA glycosylase activity, these deficiencies may increase susceptibility to AFB1-associated HCCs.

Hepatoprotective Effect of Cuscuta campestris Yunck. Whole Plant on Carbon Tetrachloride Induced Chronic Liver Injury in Mice.

Cuscuta seeds and whole plant have been used to nourish the liver and kidney. This study was aimed to investigate the hepatoprotective activity of the ethanol extract of Cuscuta campestris Yunck. whole plant (CCEtOH). The hepatoprotective effect of CCEtOH (20, 100 and 500 mg/kg) was evaluated on carbon tetrachloride (CCl4)-induced chronic liver injury. Serum alanine aminotransferase, aspartate aminotransferase, triglyceride and cholesterol were measured and the fibrosis was histologically examined. CCEtOH exhibited a significant inhibition of the increase of serum alanine aminotransferase, aspartate aminotransferase, triglyceride and cholesterol. Histological analyses showed that fibrosis of liver induced by CCl4 were significantly reduced by CCEtOH. In addition, 20, 100 and 500 mg/kg of the extract decreased the level of malondialdehyde (MDA) and enhanced the activities of anti-oxidative enzymes including superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GRd) in the liver. We demonstrate that the hepatoprotective mechanisms of CCEtOH were likely to be associated to the decrease in MDA level by increasing the activities of antioxidant enzymes such as SOD, GPx and GRd. In addition, our findings provide evidence that C. campestris Yunck. whole plant possesses a hepatoprotective activity to ameliorate chronic liver injury.

DNA polymerase ζ limits chromosomal damage and promotes cell survival following aflatoxin exposure.

Routine dietary consumption of foods that contain aflatoxins is the second leading cause of environmental carcinogenesis worldwide. Aflatoxin-driven mutagenesis is initiated through metabolic activation of aflatoxin B1 (AFB1) to its epoxide form that reacts with N7 guanine in DNA. The resulting AFB1-N7-dG adduct undergoes either spontaneous depurination or imidazole-ring opening yielding formamidopyrimidine AFB1 (AFB1-Fapy-dG). Because this latter adduct is known to persist in human tissues and contributes to the high frequency G-to-T mutation signature associated with many hepatocellular carcinomas, we sought to establish the identity of the polymerase(s) involved in processing this lesion. Although our previous biochemical analyses demonstrated the ability of polymerase ζ (pol ζ) to incorporate an A opposite AFB1-Fapy-dG and extend from this mismatch, biological evidence supporting a unique role for this polymerase in cellular tolerance following aflatoxin exposure has not been established. Following challenge with AFB1, survival of mouse cells deficient in pol ζ (Rev3L-/-) was significantly reduced relative to Rev3L+/- cells or Rev3L-/- cells complemented through expression of the wild-type human REV3L. Furthermore, cell-cycle progression of Rev3L-/- mouse embryo fibroblasts was arrested in late S/G2 following AFB1 exposure. These Rev3L-/- cells showed an increase in replication-dependent formation of γ-H2AX foci, micronuclei, and chromosomal aberrations (chromatid breaks and radials) relative to Rev3L+/- cells. These data suggest that pol ζ is essential for processing AFB1-induced DNA adducts and that, in its absence, cells do not have an efficient backup polymerase or a repair/tolerance mechanism facilitating survival.

Reactions of Ruthenium Complexes Containing Pentatetraenylidene Ligand.

Two ruthenium acetylide complexes [Ru]-C≡C-C≡C-C(OR)(C3 H5 )2 (2, R=H and 2 a, R=CH3 ; [Ru]=Cp(PPh3 )2 Ru) each with two cyclopropyl rings were synthesized from TMS-C≡C-C≡C-C(OH)(C3 H5 )2 (1; TMS=trimethylsilyl). Treatments of 2 and 2 a with allyl halide in the presence of KPF6 afforded the vinylidene complexes 3 and 3 a, respectively. When NH4 PF6 was used, instead of KPF6 , additional ring-opening reaction took place on one of the three-membered ring. Treatment of [Ru]Cl with 1,3-butadiyne (6), bearing an epoxide ring, afforded acetylide complex 7 with a furyl ring. Treatment of 2 a with Ph3 CPF6 presumably afforded pentatetraenylidene complex {[Ru]=C=C=C=C=C(C3 H5 )2 }[PF6 ] (10), which was not isolated. Additions of various alcohols in a solution of 10 generated a number of disubstituted allenylidene complexes {[Ru]=C=C=C(OR)-C=C(C3 H5 )2 }[PF6 ] (11). Treatment of 11 with K2 CO3 afforded the acetylide complex 12 bearing a carbonyl group, characterized by single X-ray diffraction analysis. Addition of a primary amine to 10 caused cleavage of the farthermost C=C bond and several allenylidene complexes {[Ru]=C=C=C(Me)(NHR)}[PF6 ] (18) were isolated.

Ring Expansion and Skeletal Rearrangement of Propargyl Alcohol Substituted Aziridines Induced by Ruthenium Complexes.

The ring expansion and skeletal rearrangement of two types of propargyl alcohol substituted aziridines with or without cycloalkane moieties was induced by a ruthenium cyclopentadienyl phosphine complex. In the simple aziridine system with no cycloalkane, the unique cycloisomerization process altered the absolute connectivity of the two-carbon unit in the three-membered ring to give organometallic products with substituted pyridine or dihydropyridine ligands. For the aziridine on a cyclohexyl ring, the cycloisomerization process was controlled by an interchange process between vinylidene and allenylidene species, thus creating a better relative configuration of the aziridinyl and the alkynyl units. This determines the stereochemistry of the metal carbene products of the octahydroindole derivatives. The structures of five products were determined by X-ray diffraction analysis.

Domino Cyclization of 1,n-Enynes (n = 7, 8, 9) Giving Derivatives of Pyrane, Chromene, Fluorene, Phenanthrene and Dibenzo[7]annulene by Ruthenium Complexes.

Cyclization of the ether enyne 1 catalyzed by [Ru]NCCH3(+) ([Ru] = Cp(PPh3)2Ru) in CHCl3 generates a diastereomeric mixture of the substituted tetrahydropyran 11. Presumably, formation of an allenylidene complex is followed by a cyclization by nucleophilic addition of the olefinic group to Cγ of the ligand giving a boat-like six-membered ring. The diastereoselectivity is controlled by the 1,3-diaxial interaction. The vinylidene complex 7, a precursor of 11, is obtained from 1 and [Ru]Cl. In a mixture of MeOH/CHCl3, the domino cyclization of 1 further affords 14a, a chromene product catalytically. The second cyclization proceeds via nucleophilic addition of the resulting olefinic unit to Cα of 7. But the ether enyne 3 with a cyclopentyl ring on the olefinic unit undergoes only single cyclization due to steric effect. The propargyl alcohol and the two terminal methyl groups on the olefinic unit shape the cyclization. Thus, similar all-carbon 1,n-enynes (n = 7, 8, 9) 4-6 each with an aromatic linker undergo direct domino cyclization catalyzed by [Ru]NCCH3(+), to give derivatives of tricyclic fluorene, phenanthrene and dibenzo[7]annulene, respectively, with no intermediate observed.

Reactions of a Ruthenium Complex with Substituted N-Propargyl Pyrroles.

In an investigation into the chemical reactions of N-propargyl pyrroles 1 a-c, containing aldehyde, keto, and ester groups on the pyrrole ring, with [Ru]-Cl ([Ru]=Cp(PPh3 )2 Ru; Cp=C5 H5 ), an aldehyde group in the pyrrole ring is found to play a crucial role in stimulating the cyclization reaction. The reaction of 1 a, containing an aldehyde group, with [Ru]-Cl in the presence of NH4 PF6 yields the vinylidene complex 2 a, which further reacts with allyl amine to give the carbene complex 6 a with a pyrrolizine group. However, if 1 a is first reacted with allyl amine to yield the iminenyne 8 a, then the reaction of 8 a with [Ru]-Cl in the presence of NH4 PF6 yields the ruthenium complex 9 a, containing a cationic pyrrolopyrazinium group, which has been fully characterized by XRD analysis. These results can be adequately explained by coordination of the triple bond of the propargyl group to the ruthenium metal center first, followed by two processes, that is, formation of a vinylidene intermediate or direct nucleophilic attack. Additionally, the deprotonation of 2 a by R4 NOH yields the neutral acetylide complex 3 a. In the presence of NH4 PF6 , the attempted alkylation of 3 a resulted in the formation the Fischer-type amino-carbene complex 5 a as a result of the presence of NH3, which served as a nucleophile. With KPF6, the alkylation of 3 a with ethyl and benzyl bromoacetates afforded the disubstituted vinylidene complexes 10 a and 11 a, containing ester groups, which underwent deprotonation reactions to give the furyl complexes 12 a and 13 a, respectively. For 13 a, containing an O-benzyl group, subsequent 1,3-migration of the benzyl group was observed to yield product 14 a with a lactone unit. Similar reactivity was not observed for the corresponding N-propargyl pyrroles 1 b and 1 c, which contained keto and ester groups, respectively, on the pyrrole ring.

Complete mitochondrial DNA genome of Parazacco spilurus (Cypriniformes: Cyprinidae).

In this study, we sequenced the complete mitochondrial genome of Parazacco spilurus (Cypriniformes, Cyprinidae). This mitochondrial genome, consisting of 16,612 base pairs (bp), encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a noncoding control region as those found in other vertebrates, with the gene synteny identical to that of typical vertebrates. Control region (D-Loop), of 926 bp in length, is located between tRNA(Pro) and tRNA(Phe). The overall base composition of the heavy strand shows T 26.91%, C 26.01%, A 30.45% and G 16.63%, with an AT bias of 57.36%.

A New Binning Method for Metagenomics by One-Dimensional Cellular Automata.

More and more developed and inexpensive next-generation sequencing (NGS) technologies allow us to extract vast sequence data from a sample containing multiple species. Characterizing the taxonomic diversity for the planet-size data plays an important role in the metagenomic studies, while a crucial step for doing the study is the binning process to group sequence reads from similar species or taxonomic classes. The metagenomic binning remains a challenge work because of not only the various read noises but also the tremendous data volume. In this work, we propose an unsupervised binning method for NGS reads based on the one-dimensional cellular automaton (1D-CA). Our binning method facilities to reduce the memory usage because 1D-CA costs only linear space. Experiments on synthetic dataset exhibit that our method is helpful to identify species of lower abundance compared to the proposed tool.

Magnetic Resonance Nano-Theranostics for Glioblastoma Multiforme.

Glioblastoma multiforme (GBM) is one of the most challenging diseases to treat in clinical oncology due to its high mortality rates and inefficient conventional treatment methods. Difficulties with early detection, post-surgical recurrences, and resistance to chemotherapy and/or radiotherapy are important reasons for the poor prognosis of those with GBM. Over the past few decades, magnetic resonance (MR) theranostics using magnetic nanoparticles has shown unique advantages and great promises for the diagnosis and treatment of cancers. Magnetic nanoparticles not only serve as "molecular beacons" to enhance tumor contrast in magnetic resonance imaging (MRI), but also serve as "molecular bullets" for targeted drug delivery, controlled release, and induced hyperthermia. Moreover, multiple functions of magnetic nanoparticles can be synergistically engineered into a single nanoplatform, making it possible to simultaneously image, treat, target, and monitor the targeted lesions. The multi-functionality of nanoparticles, also called nano-theranostics, gives rises to effective new approaches for combating GBM. In this work, recent research and progress concerning the applications of MR nano-theranostics on GBM using magnetic nanoparticles will be highlighted, focusing on topics such as diagnosis, therapy, targeting, and hyperthermia, as well as outstanding challenges for MR nanotheranostics in treating GBM. The conclusions are generally applicable to other types of brain tumors.

Light-gated molecular brakes based on pentiptycene-incorporated azobenzenes.

Three azobenzene derivatives (2 R, 2 OR, and 2 NR) that differed in their terminal substituent (alkyl, alkyloxy, and dialkylamino, respectively) have been synthesized and investigated as molecular brakes, in which the rigid H-shaped pentiptycene group functioned as a rotor and the dinitrophenyl group as a "brake pad". The E and Z isomers of these compounds corresponded to the "brake-off" and "brake-on" states, respectively. The rotation rate of the rotor was evaluated by VT NMR spectroscopy for the brake-on state and by DFT calculations for the brake-off state. The difference between the rotation rates for the rotor in the two states was as large as eight orders of magnitude at ambient temperature. Photochemical switching of the azobenzene moieties afforded efficiencies of 55-67%. A combination of photochemical E→Z and thermal Z→E isomerization promoted the switching efficiency up to 78%. The terminal substituent affected both the photochemical and thermal switching efficiencies. Solvent polarity also played an important role in the lifetimes of the Z isomers. These azobenzene systems displayed similar braking powers but superior switching efficiencies to the stilbene analogue (1O R; ca. 60% vs 20%).

A light-gated molecular brake with antilock and fluorescence turn-on alarm functions: application of singlet-state adiabatic cis → trans photoisomerization.

A light-gated molecular brake that displays both high braking power (∼10(7)) and high switching power (∼74%) is reported. The lower rate for brake-on than for brake-off switching of the pentiptycene rotor mimics the function of an antilock braking system (ABS) for vehicles on a loose surface. The brake is also armed with a fluorescence turn-on alarm for accidental deactivation of the ABS function by acids. All of these features are associated with the highly efficient singlet-state adiabatic cis → trans photoisomerization of the phenylstilbene chromophore.