A meta-analysis of antibiotic residues in the Beibu Gulf.

Antibiotic residue stands as a significant ongoing environmental issue, with aquaculture being a major source of annual antibiotic discharge into the ocean. Nevertheless, there is still an incomplete evaluation of antibiotic residues in the Beibu Gulf, an area encompassed by two prominent aquaculture nations, China and Vietnam. The present systematic review and meta-analysis was conducted to examine the presence antibiotic residues in the Beibu Gulf based on published studies. Data were obtained through eight databases up to December 19th, 2023, and were updated on April 15th, 2024. The pooled concentration of antibiotic residues in seawater was 5.90 (ng/L), ranging from 5.73 to 6.06 (ng/L), and was 8.03 (ng/g), ranging from 7.77 to 8.28 (ng/g) in sediments. Fluoroquinolones, tetracyclines, and macrolides were identified as the main antibiotics found in both seawater and sediment samples. The Beibu Gulf showed higher antibiotic levels in its western and northeastern areas. Additionally, the nearshore mangrove areas displayed the highest prevalence of antibiotic residues. It is strongly advised to conduct regular long-term monitoring of antibiotic residues in the Beibu Gulf. Collaborative surveys covering the entire Beibu Gulf involving China and Vietnam are recommended.

Complete genome of Rossellomorea sp. DA94, an agarolytic and orange-pigmented bacterium isolated from mangrove sediment of the South China Sea.

Rossellomorea sp. DA94, isolated from mangrove sediment in the South China Sea (Beihai, Guangxi province), is an agarolytic and orange-pigmented bacterium. Here, we present the complete genome sequence of strain DA94, which comprises 4.63 Mb sequences with 43.5% GC content. In total, 4589 CDSs, 33 rRNA genes and 110 tRNA genes were obtained. Genomic analysis of strain DA94 revealed that 108 CAZymes were organized in 4578 PULs involved in polysaccharides degradation, transport, and regulation. Further, we performed the diversity of CAZymes and PULs comparison among Rossellomorea strains. Less CAZymes were organized more PULs, indicating highly efficiently polysaccharides utilization in Rossellomorea. Meanwhile, PUL0459, PUL0460 and PUL0316 related to agar degradation, and exolytic beta-agarase GH50, endo-type beta-agarase GH86 and arylsulfatase were identified in the genome of strain DA94. We verified that strain DA94 can degrade agar to form a bright clear zone around the bacterial colonies in the laboratory. Moreover, the carotenoid biosynthetic pathways were proposed, which may be responsible for orange-pigment of Rossellomorea sp. DA94. This study represents a thorough genomic characterization of CAZymes repertoire and carotenoid biosynthetic pathways of Rossellomorea, provides insight into diversity of related enzymes and their potential biotechnological applications.

Bioluminescence Contributes to the Adaptation of Deep-Sea Bacterium Photobacterium phosphoreum ANT-2200 to High Hydrostatic Pressure.

Bioluminescence is a common phenomenon in nature, especially in the deep ocean. The physiological role of bacterial bioluminescence involves protection against oxidative and UV stresses. Yet, it remains unclear if bioluminescence contributes to deep-sea bacterial adaptation to high hydrostatic pressure (HHP). In this study, we constructed a non-luminescent mutant of ΔluxA and its complementary strain c-ΔluxA of Photobacterium phosphoreum ANT-2200, a deep-sea piezophilic bioluminescent bacterium. The wild-type strain, mutant and complementary strain were compared from aspects of pressure tolerance, intracellular reactive oxygen species (ROS) level and expression of ROS-scavenging enzymes. The results showed that, despite similar growth profiles, HHP induced the accumulation of intracellular ROS and up-regulated the expression of ROS-scavenging enzymes such as dyp, katE and katG, specifically in the non-luminescent mutant. Collectively, our results suggested that bioluminescence functions as the primary antioxidant system in strain ANT-2200, in addition to the well-known ROS-scavenging enzymes. Bioluminescence contributes to bacterial adaptation to the deep-sea environment by coping with oxidative stress generated from HHP. These results further expanded our understanding of the physiological significance of bioluminescence as well as a novel strategy for microbial adaptation to a deep-sea environment.

Complete genome sequence of marine Roseobacter lineage member Ruegeria sp. YS9 with five plasmids isolated from red algae.

Ruegeria sp. YS9, an aerobic and chemoheterotrophic bacterium belonging to marine Roseobacter lineage, was a putative new species isolated from red algae Eucheuma okamurai in the South China Sea (Beihai, Guangxi province). The complete genome sequence in strain YS9 comprised one circular chromosome with 3,244,635 bp and five circular plasmids ranging from 38,085 to 748,160 bp, with a total length of 4.30 Mb and average GC content of 58.39%. In total, 4129 CDSs, 52 tRNA genes and 9 rRNA genes were obtained. Genomic analysis of strain YS9 revealed that 85 CAZymes were organized in 147 PUL-associated CAZymes involved in polysaccharides metabolism, which were the highest among its two closely related Ruegeria strains. Numerous PULs related to degradation on the cell wall of algae, especially agar, indicated its major player role in the remineralization of algal-derived carbon. Further, the existence of multiple plasmids provided strain YS9 with distinct advantages to facilitate its rapid environmental adaptation, including polysaccharide metabolism, denitrification, resistance to heavy metal stresses such as copper and cobalt, type IV secretion systems and type IV toxin-antitoxin systems, which were obviously different from the two Ruegeria strains. This study provides evidence for polysaccharide metabolic capacity and functions of five plasmids in strain YS9, broadening our understanding of the ecological roles of bacteria in the environment around red algae and the function patterns of plasmids in marine Roseobacter lineage members for environmental adaptation.

Complete genome sequence and Carbohydrate Active Enzymes (CAZymes) repertoire of Gilvimarinus sp. DA14 isolated from the South China Sea.

Gilvimarinus sp. DA14, a putative new species isolated from mangrove sediment in the South China Sea (Beihai, Guangxi province), is an aerobic and heterotrophic agar degrading bacterium. Here, we present the complete genome sequence of strain DA14, which comprises 3.96 Mb sequences with 53.39% GC content. In total, 3391 CDSs, 6 rRNA genes and 44 tRNA genes were obtained. Genomic analysis of strain DA14 revealed that 218 CAZymes classes were identified and they were organized in 371 CAZymes in PULs involved in polysaccharides degradation, transport and regulation. Further, we performed the genome comparison among Gilvimarinus strains and analysis the diversity of CAZymes and PULs. Meanwhile, ability of agar and alginate degradation in strain DA14 were analyzed. This study represents a thorough genomic characterization of CAZymes repertoire of Gilvimarinus, provides insight into diversity of polysaccharide degrading enzymes existing in Gilvimarinus sp. DA14 and their biotechnological applications.

Crassaminicella thermophila sp. nov., a moderately thermophilic bacterium isolated from a deep-sea hydrothermal vent chimney and emended description of the genus Crassaminicella.

A novel moderately thermophilic, anaerobic, heterotrophic bacterium (strain SY095T) was isolated from a hydrothermal vent chimney located on the Southwest Indian Ridge at a depth of 2730 m. Cells were Gram-stain-positive, motile, straight to slightly curved rods forming terminal endospores. SY095T was grown at 45-60 °C (optimum 50-55 °C), pH 6.0-7.5 (optimum 7.0), and in a salinity of 1-4.5 % (w/v) NaCl (optimum 2.5 %). Substrates utilized by SY095T included fructose, glucose, maltose, N-acetyl glucosamine and tryptone. Casamino acid and amino acids (glutamate, glutamine, lysine, methionine, serine and histidine) were also utilized. The main end products from glucose fermentation were acetate, H2 and CO2. Elemental sulphur, sulphate, thiosulphate, sulphite, fumarate, nitrate, nitrite and Fe(III) were not used as terminal electron acceptors. The predominant cellular fatty acids were C14 : 0 (60.5%) and C16 : 0 (7.6 %). The main polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, five unidentified phospholipids and two unidentified aminophospholipids. No respiratory quinones were detected. The chromosomal DNA G+C content was 30.8 mol%. The results of phylogenetic analysis of the 16S rRNA gene sequences indicated that SY095T was closely related to Crassaminicella profunda Ra1766HT (95.8 % 16S rRNA gene sequence identity). SY095T exhibited 78.1 % average nucleotide identity (ANI) to C. profunda Ra1766HT. The in silico DNA-DNA hybridization (DDH) value indicated that SY095T shared 22.7 % DNA relatedness with C. profunda Ra1766HT. On the basis of its phenotypic, genotypic and phylogenetic characteristics, SY095T is suggested to represent a novel species of the genus Crassaminicella, for which the name Crassaminicella thermophila sp. nov. is proposed. The type strain is SY095T (=JCM 34213=MCCC 1K04191). An emended description of the genus Crassaminicella is also proposed.

Thermococcus aciditolerans sp. nov., a piezotolerant, hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent chimney in the Southwest Indian Ridge.

A hyperthermophilic, strictly anaerobic archaeon, designated strain SY113T, was isolated from a deep-sea hydrothermal vent chimney on the Southwest Indian Ridge at a water depth of 2770 m. Enrichment and isolation of strain SY113T were performed at 85 °C at 0.1 MPa. Cells of strain SY113T were irregular motile cocci with peritrichous flagella and generally 0.8-2.4 µm in diameter. Growth was observed at temperatures between 50 and 90 °C (optimum at 85 °C) and under hydrostatic pressures of 0.1-60 MPa (optimum, 27 MPa). Cells of SY113T grew at pH 4.0-9.0 (optimum, pH 5.5) and a NaCl concentration of 0.5-5.5 % (w/v; optimum concentration, 3.0 % NaCl). Strain SY113T was an anaerobic chemoorganoheterotroph and grew on complex proteinaceous substrates such as yeast extract and tryptone, as well as on maltose and starch. Elemental sulphur stimulated growth, but not obligatory for its growth. The G+C content of the genomic DNA was 55.0 mol%. Phylogenetic analysis of the 16S rRNA sequence of strain SY113T showed that the novel isolate belonged to the genus Thermococcus. On the basis of physiological characteristics, average nucleotide identity values and in silico DNA-DNA hybridization results, we propose a novel species, named Thermococcus aciditolerans sp. nov. The type strain is SY113T (=MCCC 1K04190T=JCM 39083T).

The clinical outcomes and biomarker features of severe sepsis/septic shock with severe neutropenia: a retrospective cohort study.

BACKGROUND: Severe sepsis/septic shock with severe neutropenia often leads to poor prognosis. However, it is unknown if severe neutropenia is associated with different clinical outcomes and biomarker features in severe sepsis/septic patients. METHODS: This retrospective cohort study enrolled 141 severe sepsis/septic shock patients admitted to intensive care unit of Shanghai Children's Medical Center between January 2015 and November 2019. Patients were followed up for the development of ventilation support, the use of vasoactive drugs, continuous renal replacement therapy (CRRT) procedure, and mortality. Biomarkers that reflect the level of inflammation in severe sepsis/septic shock patients with neutropenia were compared to that in patients without neutropenia. RESULTS: Of 141 patients enrolled, 54 patients suffered from severe sepsis/septic shock with severe neutropenia. In patients with severe sepsis/septic shock, severe neutropenia as a complication was an independent risk factor for the use of vasoactive drugs (RR 9.796; 95% CI: 3.774, 25.429; P<0.001), but not for ventilation support (RR 0.157; 95% CI: 0.06, 0.414; P<0.001), CRRT procedure (RR 1.032; 95% CI: 0.359, 2.969; P=0.953) or 28-day mortality (RR 1.405; 95% CI: 0.533, 3.708; P=0.492). Severe sepsis/septic patients with severe neutropenia had a higher plasma level of the following biomarkers: c-reaction protein (CRP) (180.5 vs. 121 mg/mL, P<0.001), procalcitonin (PCT) (12.15 vs. 2.7 ng/mL; P=0.005), interleukin (IL)-6 (316.83 vs. 55.77 pg/mL, P<0.001), IL-10 (39.165 vs. 10.09 pg/mL, P<0.001), interferon (IFN)-γ (6.155 vs. 3.71 pg/mL, P=0.016), and the percentage of regulatory T cells (Tregs) (2.7% vs. 2.09%, P=0.003). Based on the receiver operating characteristic curves, IL-10 exhibited high specificity (79.4%) in evaluating the prognosis of septic patients with neutropenia. CONCLUSIONS: In patients with severe sepsis/septic shock, being complicated with severe neutropenia is associated with higher proportion of using vasoactive drugs, and those patients tend to have higher plasma levels of IL-6, IL-10, IFN-γ and percentage of Treg.

Development and application of magnetic solid phase extraction in tandem with liquid-liquid extraction method for determination of four tetracyclines by HPLC with UV detection.

A novel HPLC-UV method was developed for the determination of four tetracyclines based on magnetic solid phase extraction in tandem with liquid-liquid extraction. The water-soluble amino functionalized magnetite nanoparticle (MNP-NH2) was used as an adsorbent for extraction/preconcentration of tetracycline, oxytetracycline, chlortetracycline, and doxycycline from bovine milk samples. Fourier transform infrared spectrometer, transmission electron microscope, X-ray diffraction, and elemental analyze techniques were used to characterize the material. Some key parameters which influence liquid-liquid extraction and magnetic dispersive solid-phase extraction procedure, including volume of extraction solvent, the amount of adsorbent, the pH, extraction and desorption time, the composition of the eluent, and elution frequency were investigated. The proposed method exhibited a linear range of 50.0-2500.0 µg L-1 (r2 = 0.9941) with and good reproducibility (RSD < 2.2%, n = 3). The limit of detection and quantification were 40.0 and 50.0 µg L-1. This method was verified using milk sample spiked with four tetracyclines (100.0-200.0 µg L-1), and accuracies of 87.8-107.5%, which confirmed its applicability in real-sample analysis. The proposed method also shows potential application prospects for other water-soluble adsorbents.

Graphene oxide composites for magnetic solid-phase extraction of twelve quinolones in water samples followed by MALDI-TOF MS.

Antibiotic compounds in natural waters are normally present at low concentrations. In this paper, an easy and highly sensitive screening method using graphene oxide-functionalized magnetic composites (GO@NH2@Fe3O4) combined with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was established for twelve quinolone antibiotics. GO@NH2@Fe3O4 composites were utilized as adsorbents for magnetic solid-phase extraction. This method combines the advantages of magnetic solid-phase extraction and MALDI-TOF MS, which allows for fast detection of quinolones at low concentrations. To improve absorption efficiency, the following parameters were individually optimized: sample acidity, extraction time, amount of adsorbent used, eluent used, and desorption time. Under the optimum conditions, the established method gave a low detection limit of 0.010 mg/L and allowed the high-throughput screening of twelve quinolone antibiotics (enoxacin, norfloxacin, ciprofloxacin, pefloxacin, fleroxacin, gatifloxacin, enrofloxacin, levofloxacin, sparfloxacin, danofloxacin, difloxacin, and lomefloxacin). The proposed method, having an easily prepared sorbent with a high affinity for quinolones and a convenient, high-throughput detection step, has been shown to have merit for the detection of antibiotics in water samples. Graphical abstract Schematic illustration of the (A) preparation of GO@NH2@Fe3O4 and (B) operating procedure for the MSPE and MALDI-TOF MS detection of QNs.

Pressure-Regulated Gene Expression and Enzymatic Activity of the Two Periplasmic Nitrate Reductases in the Deep-Sea Bacterium Shewanella piezotolerans WP3.

Shewanella species are widely distributed in marine environments, from the shallow coasts to the deepest sea bottom. Most Shewanella species possess two isoforms of periplasmic nitrate reductases (NAP-α and NAP-ß) and are able to generate energy through nitrate reduction. However, the contributions of the two NAP systems to bacterial deep-sea adaptation remain unclear. In this study, we found that the deep-sea denitrifier Shewanella piezotolerans WP3 was capable of performing nitrate respiration under high hydrostatic pressure (HHP) conditions. In the wild-type strain, NAP-ß played a dominant role and was induced by both the substrate and an elevated pressure, whereas NAP-α was constitutively expressed at a relatively lower level. Genetic studies showed that each NAP system alone was sufficient to fully sustain nitrate-dependent growth and that both NAP systems exhibited substrate and pressure inducible expression patterns when the other set was absent. Biochemical assays further demonstrated that NAP-α had a higher tolerance to elevated pressure. Collectively, we report for the first time the distinct properties and contributions of the two NAP systems to nitrate reduction under different pressure conditions. The results will shed light on the mechanisms of bacterial HHP adaptation and nitrogen cycling in the deep-sea environment.

Identification and Characterization of a New 7-Aminocephalosporanic Acid Deacetylase from Thermophilic Bacterium Alicyclobacillus tengchongensis.

UNLABELLED: Deacetylation of 7-aminocephalosporanic acid (7-ACA) at position C-3 provides valuable starting material for producing semisynthetic ß-lactam antibiotics. However, few enzymes have been characterized in this process before now. Comparative analysis of the genome of the thermophilic bacterium Alicyclobacillus tengchongensis revealed a hypothetical protein (EstD1) with typical esterase features. The EstD1 protein was functionally cloned, expressed, and purified from Escherichia coli BL21(DE3). It indeed displayed esterase activity, with optimal activity at around 65°C and pH 8.5, with a preference for esters with short-chain acyl esters (C2 to C4). Sequence alignment revealed that EstD1 is an SGNH hydrolase with the putative catalytic triad Ser15, Asp191, and His194, which belongs to carbohydrate esterase family 12. EstD1 can hydrolyze acetate at the C-3 position of 7-aminocephalosporanic acid (7-ACA) to form deacetyl-7-ACA, which is an important starting material for producing semisynthetic ß-lactam antibiotics. EstD1 retained more than 50% of its initial activity when incubated at pH values ranging from 4 to 11 at 65°C for 1 h. To the best of our knowledge, this enzyme is a new SGNH hydrolase identified from thermophiles that is able to hydrolyze 7-ACA. IMPORTANCE: Deacetyl cephalosporins are highly valuable building blocks for the industrial production of various kinds of semisynthetic ß-lactam antibiotics. These compounds are derived mainly from 7-ACA, which is obtained by chemical or enzymatic processes from cephalosporin C. Enzymatic transformation of 7-ACA is the main method because of the adverse effects chemical deacylation brought to the environment. SGNH hydrolases are widely distributed in plants. However, the tools for identifying and characterizing SGNH hydrolases from bacteria, especially from thermophiles, are rather limited. Here, our work demonstrates that EstD1 belongs to the SGNH family and can hydrolyze acetate at the C-3 position of 7-ACA. Moreover, this study can enrich our understanding of the functions of these enzymes from this family.

Mechanism of the 6-hydroxy-3-succinoyl-pyridine 3-monooxygenase flavoprotein from Pseudomonas putida S16.

6-Hydroxy-3-succinoyl-pyridine (HSP) 3-monooxygenase (HspB), a flavoprotein essential to the pyrrolidine pathway of nicotine degradation, catalyzes pyridine-ring ß-hydroxylation, resulting in carbon-carbon cleavage and production of 2,5-dihydroxypyridine. Here, we generated His6-tagged HspB in Escherichia coli, characterized the properties of the recombinant enzyme, and investigated its mechanism of catalysis. In contrast to conclusions reported previously, the second product of the HspB reaction was shown to be succinate, with isotope labeling experiments providing direct evidence that the newly introduced oxygen atom of succinate is derived from H2O. Phylogenetic analysis reveals that HspB is the most closely related to two p-nitrophenol 4-monooxygenases, and the experimental results exhibit that p-nitrophenol is a substrate of HspB. The reduction of HspB (with maxima at 375 and 460 nm, and a shoulder at 485 nm) by NADH was followed by stopped-flow spectroscopy, and the rate constant for reduction was shown to be stimulated by HSP. Reduced HspB reacts with oxygen to form a C(4a)-(hydro)peroxyflavin intermediate with an absorbance maximum at ∼400 nm within the first few milliseconds before converting to the oxidized flavoenzyme species. The formed C(4a)-hydroperoxyflavin intermediate reacts with HSP to form an intermediate that hydrolyzes to the products 2,5-dihydroxypyridine and succinate. The investigation on the catalytic mechanism of a flavoprotein pyridine-ring ß-position hydroxylase provides useful information for the biosynthesis of pyridine derivatives.

[Review on sustained effect of acupuncture].

The sustained effect of acupuncture refers to the lasting effect after the cease of acupuncture. Through large amount of acupuncture clinical practices and experimental researches, the objective existence of the sustained effect of acupuncture is approved. However, the lasting period of acupuncture effect may be related with category and stage of disease, individualized acupuncture reaction, acupuncture methods, intervals between treatments and therapeutic course. Therefore, it has great scientific significance and practice value to carry out further systematic and in-depth research on effect onset time of different diseases as well as the discipline of the sustained effect, so as to promote and prolong acupuncture effect.

[Acupuncture resources in Cochrane Library].

To identify acupuncture resources in six databases of Cochrane Library (CL) with computer retrieve. Seventy-two literatures were identified in Cochrane Database of Systematic Reviews (CDSR). Among them, 12 Cochrane systematic review (CSR) verified the effectiveness of acupuncture, 29 concerning the indeterminacy of the efficacy of acupuncture with 1 didn't support acupuncture for epilepsy and 31 remained as protocols; 121 literatures were found in Database of Abstracts of Reviews of Effects (DARE) with more types of diseases or symptoms and rich modality comparing to CSR; 4218 randomized controlled trials and clinical controlled trials were identified in Cochrane Central Register of Controlled Trials (CCRCT); 43 literatures in Cochrane Methodology Register Database (CMRD) which focused on blindness study, quality assessment of methodology of research and publication bias and so on; 25 literatures in Health Technology Assessment Database (HTAD) and 18 in NHS Economic Evaluation Database (NHS EED) which were centered on acupuncture analgesia. Consequently, acupuncture literatures in 6 databases of CL do provide good resources for acupuncture researchers due to its abundant content, concrete classification and high quality evidence.

Characterization of environmentally friendly nicotine degradation by Pseudomonas putida biotype A strain S16.

Nicotine and some related alkaloids in tobacco and tobacco wastes are harmful to health and the environment, and a major environmental requirement is to remove them from tobacco and tobacco wastes. In this study, an isolated strain, S16, identified as Pseudomonas putida biotype A, was used to investigate nicotine degradation. Possible intermediates were identified based on the results of NMR, Fourier-transform (FT)-IR and UV spectroscopy, GC-MS and high-resolution MS (HR-MS) analysis. The pathway of nicotine degradation in P. putida was proposed to be from nicotine to 2,5-dihydroxypyridine through the intermediates N-methylmyosmine, 2'-hydroxynicotine, pseudooxynicotine, 3-pyridinebutanal,C-oxo, 3-succinoylpyridine and 6-hydroxy-3-succinoylpyridine. N-Methylmyosmine, 2,5-dihydroxypyridine and succinic acid were detected and satisfactorily verified for the first time as intermediates of nicotine degradation. In addition, an alcohol compound, 1-butanone,4-hydroxy-1-(3-pyridinyl), was found to be a novel product of nicotine degradation. These findings provide new insights into the microbial metabolism of nicotine and the environmentally friendly route of nicotine degradation.

"Green" route to 6-hydroxy-3-succinoyl-pyridine from (S)-nicotine of tobacco waste by whole cells of a Pseudomonas sp.

A new technology for 6-hydroxy-3-succinoyl-pyridine (HSP) production from (S)-nicotine in tobacco waste by whole cells of a Pseudomonas sp. has been developed. When deionized water was used in the transformation reaction as a medium and the initial pH value of reaction mixture was adjusted to 7.0, 1.45 g/L HSP was produced from 3 g/L of nicotine in 5 h with 3.4 g/L of cells in a 5-L flask at 30 degrees C. HSP could be easily purified from the reaction without perplexing separation steps. A quantity of 1.3 g of HSP was recovered without impurity, and the overall yield of HSP was 43.8% (w/w), based on an initial concentration of 3.0 g/L of nicotine in reaction. This biotransformation made it possible to convert nicotine in tobacco wastes with high nicotine content into valuable compounds.

Chiroptical switching polyguanidine synthesized by helix-sense-selective polymerization using [(R)-3,3'-dibromo-2,2'-binaphthoxy](di-tert-butoxy)titanium(IV) catalyst.

A series of chiral binaphthyl titanium alkoxide complexes were synthesized. Among them, chiral titanium complex [(R)-3,3'-dibromo-2,2'-binaphthoxy](di-tert-butoxy)titanium(IV) (R-3) exists as a crystallographic C2 dimer in the solid state but a monomer in solution at room temperature. Application of R-3 in the helix-sense-selective polymerization of achiral carbodiimide, N-(1-anthryl)-N'-octadecylcarbodiimide (1), yielded a well-defined regioregular, stereoregular poly[N-(1-anthryl)-N'-octadecylguanidine] (poly-1b) with a relatively narrow polymer dispersity index of 2.7. Full racemization of poly-1b at +80 degrees C in toluene requires more than 100 h. Interestingly, poly-1b was found to undergo fast reversible chiroptical switching at +38.5 degrees C in toluene. Furthermore, at room temperature, poly-1b shows a positively signed Cotton effect in toluene, but negative ones in THF and chloroform, respectively. The chiroptical switching takes place around the toluene content of 90% (vol) in the mixed toluene/THF solvents. This is the first example of chiroptical switching phenomenon occurring in a helical polymer possessing no chiral moieties in the polymer chains. We believe this reversible chiroptical switching phenomenon occurs by reorientation of anthracene rings relative to the chain director.

Stable helical polyguanidines: poly[N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]guanidines].

Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.