Structural, optical, and bioimaging characterization of carbon quantum dots solvothermally synthesized from o-phenylenediamine

Carbon quantum dots as a novel type of carbon nanomaterials have attracted the attention of many researchers because of their unique optical, antibacterial, and anticancer properties as well as their biocompatibility. In this study, for the first time, carbon quantum dots were prepared from o-phenylenediamine dissolved in toluene by a solvothermal route. Subsequently, the prepared carbon quantum dots were encapsulated into polyurethane films by a swelling-encapsulation-shrink method. Analyses of the results obtained by different characterization methods (AFM, TEM, EDS, FTIR, photoluminescence, and EPR) indicate the significant influence of the precursor on structural, chemical, and optical properties. Antibacterial and cytotoxicity tests showed that these dots did not have any antibacterial potential, because of the low extent of reactive oxygen species production, and showed low dark cytotoxicity. By investigating the cellular uptake, it was established that these dots penetrated the HeLa cells and could be used as probes for bioimaging.

Fungal Mobilization of Selenium in the Presence of Hausmannite and Ferric Oxyhydroxides

Bioleaching of mineral phases plays a crucial role in the mobility and availability of various elements, including selenium. Therefore, the leachability of selenium associated with the surfaces of ferric and manganese oxides and oxyhydroxides, the prevailing components of natural geochemical barriers, has been studied in the presence of filamentous fungus. Both geoactive phases were exposed to selenate and subsequently to growing fungus Aspergillus niger for three weeks. This common soil fungus has shown exceptional ability to alter the distribution and mobility of selenium in the presence of both solid phases. The fungus initiated the extensive bioextraction of selenium from the surfaces of amorphous ferric oxyhydroxides, while the hausmannite (Mn₃O₄) was highly susceptible to biodeterioration in the presence of selenium. This resulted in specific outcomes regarding the selenium, iron, and manganese uptake by fungus and residual selenium concentrations in mineral phases as well. The adverse effects of bioleaching on fungal growth are also discussed.

Benzil Photoperoxidations in Polymer Films and Crosslinking by the Resultant Benzoyl Peroxides in Polystyrene and Other Polymers

Benzil (BZ) can be converted almost quantitatively to benzoyl peroxide (BP) in aerated polymer films upon irradiation at >400 nm (i.e., the long-wavelength edge of the n→π* absorption band of BZ, where BP does not absorb). Here, we summarize results for the photoperoxidation of BZ structures with molecular oxygen, principally in glassy polymer matrices. Some of the polymers are doped directly with BZ or its derivatives, and others, contain covalently attached BZ pendant groups from which BP groups are derived. While the decomposition of low-molecular-weight BP doped into polymer films (such as those of polystyrene (PS)) results in a net decrease in polymer molecular weight, thermal decomposition of pendant BP groups is an efficient method for chain crosslinking. Crosslinking of PS films doped with a molecule containing two covalently linked BZ or BP groups proceeds in a similar fashion. Free radicals from the covalently attached BP allow grafting of new monomers, as well. Additionally, the use of radiation filtered through masks has been used to create patterns of polymers on solid surfaces. Crosslinking of photodegradable poly(phenyl vinyl ketone) with BP structures obtained by photoperoxidation of BZ structures for the preparation of photodegradable polymer networks is described as well. In sum, the use of BZ and BP and their derivatives offers simple and convenient routes for modifying polymer chains and, especially, for crosslinking them. Specific applications of each use and process are provided. Although applications with PS are featured here, the methodologies described are amenable to a wide variety of other polymers.

Properties and Degradation Performances of Biodegradable Poly(lactic acid)/Poly(3-hydroxybutyrate) Blends and Keratin Composites

From environmental aspects, the recovery of keratin waste is one of the important needs and therefore also one of the current topics of many research groups. Here, the keratin hydrolysate after basic hydrolysis was used as a filler in plasticized polylactic acid/poly(3-hydroxybutyrate) blend under loading in the range of 1–20 wt%. The composites were characterized by infrared spectroscopy, and the effect of keratin on changes in molar masses of matrices during processing was investigated using gel permeation chromatography (GPC). Thermal properties of the composites were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of keratin loading on the mechanical properties of composite was investigated by tensile test and dynamic mechanical thermal analysis. Hydrolytic degradation of matrices and composites was investigated by the determination of extractable product amounts, GPC, DSC and NMR. Finally, microbial growth and degradation were investigated. It was found that incorporation of keratin in plasticized PLA/PHB blend provides material with good thermal and mechanical properties and improved degradation under common environmental conditions, indicating its possible application in agriculture and/or packaging.

Photoactive and antioxidant nanochitosan dots/biocellulose hydrogels for wound healing treatment

Bacterial infection and their resistance to known antibiotics delays wound healing. In this study, nanochitosan dots (nChiD) produced by gamma irradiation have been encapsulated in bacterial cellulose (BC) polymer matrix to study the antibacterial potentials of these nanocomposites and their possible usage in wound healing treatment (scratch assay). Detailed analyses show that nChiDs have disc-like shape and average diameter in the range of 40 to 60 nm depending of the applied dose. All nChiDs as well as BC-nChiD nanocomposites emit green photoluminescence independently on the excitation wavelengths. The new designed nanocomposites do not have a cytotoxic effect; antioxidant analysis shows their moderate radical scavenging activity whereas antibacterial properties show significant growth inhibition of strains mostly found in difficult-to-heal wounds. The obtained results confirm that new designed BC-nChiD nanocomposites might be potential agent in wound healing treatment.

Correction: Gamma ray assisted modification of carbon quantum dot/polyurethane nanocomposites: structural, mechanical and photocatalytic study

Correction for ‘Gamma ray assisted modification of carbon quantum dot/polyurethane nanocomposites: structural, mechanical and photocatalytic study’ by Milica Budimir et al., RSC Adv., 2019, 9, 6278–6286.

Functional Polymers and Polymeric Materials From Renewable Alpha-Unsaturated Gamma-Butyrolactones

Sustainable chemistry requires application of green processes and often starting materials originate from renewable resources. Biomass-derived monomers based on five-membered γ-butyrolactone ring represent suitable candidates to replace sources of fossil origin. α-Methylene-γ-butyrolactone, β-hydroxy-α-methylene-γ-butyrolactone, and β- and γ-methyl-α-methylene-γ-butyrolactones bearing exocyclic double bond are available directly by isolation from plants or derived from itaconic or levulinic acids available from biomass feedstock. Exocyclic double bond with structural similarity with methacrylates is highly reactive in chain-growth polymerization. Reaction involves the linking of monomer molecules through vinyl double bonds in the presence of initiators typical for radical, anionic, zwitterionic, group-transfer, organocatalytic, and coordination polymerizations. The formed polymers containing pendant ring are characterized by high glass transition temperature (T g > 195°C) and render decent heat, weathering, scratch, and solvent resistance. The monomers can also be hydrolyzed to open the lactone ring and form water-soluble monomers. Subsequent radical copolymerization in the presence of cross-linker can yield to hydrogels with superior degree of swelling and highly tunable characteristics, depending on the external stimuli. The five-membered lactone ring allows copolymerization of these compounds by ring opening polymerization to provide polyesters with preserved methylene functionality. In addition, both the lactone ring and the methylene double bond can be attacked by amines. Polyaddition with di- or multi-amines leads to functional poly(amidoamines) with properties tunable by structure of the amines. In this mini-review, we summarize the synthetic procedures for preparation of polymeric materials with interesting properties, including thermoplastic elastomers, acrylic latexes, stimuli-sensitive superabsorbent hydrogels, functional biocompatible polyesters, and poly(amidoamines).

Identification of Molecular Fluorophore as a Component of Carbon Dots able to Induce Gelation in a Fluorescent Multivalent-Metal-Ion-Free Alginate Hydrogel

We introduce a simple approach to fabricate fluorescent multivalent metal ion-free alginate hydrogels, which can be produced using carbon dots accessible from natural sources (citric acid and L-cysteine). Molecular fluorophore 5-oxo-2,3-dihydro-5H-[1,3]-thiazolo[3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA), which is formed during the synthesis of carbon dots, is identified as a key segment for the crosslinking of hydrogels. The crosslinking happens through dynamic complexation of carboxylic acid groups of TPDCA and alginate cages along with sodium ions. The TPDCA derived hydrogels are investigated regarding to their thermal, rheological and optical properties, and found to exhibit characteristic fluorescence of this aggregated molecular fluorophore. Moreover, gradient hydrogels with tunable mechanical and optical properties and controlled release are obtained upon immersion of the hydrogel reactors in solutions of divalent metal ions (Ca2+, Cu2+, and Ni2+) with a higher affinity to alginate.

Graphene oxide size and structure pro-oxidant and antioxidant activity and photoinduced cytotoxicity relation on three cancer cell lines

Photoactive materials called photosensitizers can be used for treatment of different types of cancer in combination with light source. In this paper, we have investigated pro-oxidant and antioxidant potentials of four graphene based nanomaterials (graphene oxide-GO, graphene quantum dots-GQDs, carbon quantum dots-CQDs and N-doped carbon quantum dots-N-CQDs) depending on the presence/absence of visible light source. Structural and optical properties of these materials and their potentials for reactive oxygen species generation/quenching are investigated by applying different microscopy and spectroscopy techniques (transmission electron microscopy, FTIR, UV-Vis, photoluminescence, electron paramagnetic resonance). Results show that all types of quantum dots has pro-oxidant and antioxidant potentials whereas GO demonstrated only moderate antioxidant effect. The best free radical scavenger is CQDs sample in the absence of light. CQDs are the best singlet oxygen generator under blue light irradiation as well. To check photo-cytotoxicity of these materials, photo-cytotoxic concentrations of the GO, GQDs, CQDs and N-CQDs were determined for three cellular lines: human rhabdomyosarcoma (RD), cell line derived from human cervix carcinoma Hep2c (HeLa) and fibroblast cell line from murine (L2OB). Cytotoxicity test has indicated that all samples are much less photocytotoxic than cis-diamminedichloroplatinum (cis-DPP). The production method and doping of quantum dots affect the photodynamic activity of tested samples very much.

Antibacterial photodynamic activity of carbon quantum dots/polydimethylsiloxane nanocomposites against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae

Despite great efforts, the design of antibacterial surfaces is still a challenge. In this work, results of structural, mechanical, cytotoxic and antibacterial activities of hydrophobic carbon quantum dots/polydimethylsiloxane surfaces are presented. Antibacterial action of this surface is based on the generation of reactive oxygen species which cause bacteria damage by oxidative stress. At the same time, this surface was not cytotoxic towards the NIH/3T3 cells. Swelling-encapsulation-shrink method is applied for encapsulation of hydrophobic carbon quantum dots in medical grade silicone-polydimethylsiloxane. XPS and photoluminescence spectroscopy analyses confirm that hydrophobic carbon quantum dots have been encapsulated successfully into polydimethylsiloxane polymer matrix. Based on stress-strain test the improvement of mechanical properties of these nanocomposites is established. It is shown by electron paramagnetic resonance spectroscopy and luminescence method that nanocomposite generates singlet oxygen initiated by 470 nm blue light irradiation. Antibacterial testing shows the nanocomposite in the form of foil kills Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae and is very effective after only a 15 min irradiation.

Sulfobetaines Meet Carboxybetaines: Modulation of Thermo- and Ion-Responsivity, Water Structure, Mechanical Properties, and Cell Adhesion

A procedure for the preparation of copolymers bearing sulfobetaine and carboxybetaine methacrylic-based monomers by free-radical polymerization is described and discussed. A combination of monomers affects the upper critical solution temperature (UCST) in water and in the presence of a simple NaCl electrolyte while retaining the zwitterionic character. In addition, hydrogel samples were prepared and showed tunable water structure and mechanical properties. The total nonfreezable water content decreases with the amount of carboxybetaine segment in the hydrogel feed and the compression moduli were in a range of 0.7-1.6 MPa. Responses to external conditions such as temperature and ion strength were investigated and a potential application such as modulated thermal detection is proposed. The presence of the carboxylate group in the carboxybetaine segment enables a small fluorescence probe and peptide bearing RDG motif to be attached to polymer and hydrogel samples, respectively. The hydrogel samples functionalized with the RGD motif exhibit controlled cell adhesion. Such synthetic strategy based on combination of different zwitterionic segments offers a simple pathway for the development of zwitterionic materials with programmable properties.

Gamma ray assisted modification of carbon quantum dot/polyurethane nanocomposites: structural, mechanical and photocatalytic study

In recent years, water pollution and contamination had become a major threat to the ecosystem. However, the use of nanostructured materials has been proven as a very promising approach in the treatment of polluted water. The present study reports the results of the gamma ray-assisted modification of hydrophobic carbon quantum dot (hCQD)/polyurethane nanocomposites for photocatalytic degradation of organic dyes. Different characterization methods were applied to investigate the influence of the different doses of gamma irradiation (1, 10 and 200 kGy) on the physical and chemical properties of nanocomposites (morphology, chemical content, mechanical properties, wettability, and potential for singlet oxygen generation). Surface morphology and mechanical properties analyses showed that gamma rays induced insignificant changes in the structure of nanocomposites, but the potential for singlet oxygen generation increased significantly. Here we also explore, in detail, the photocatalytic properties of gamma-ray modified hCQDs/polyurethane nanocomposites. UV-vis analysis showed that the removal efficiency of the rose bengal dye reached up to 97% for the nanocomposite irradiated with the dose of 200 kGy.

The present study reports the results of the gamma ray-assisted modification of hydrophobic carbon quantum dots (hCQDs)/polyurethane nanocomposites for photocatalytic degradation of organic dyes.

Graphene quantum dots inhibit T cell-mediated neuroinflammation in rats

We investigated the therapeutic capacity of nano-sized graphene sheets, called graphene quantum dots (GQD), in experimental autoimmune encephalomyelitis (EAE), an animal model of immune-mediated central nervous system (CNS) damage. Intraperitoneally administered GQD (10 mg/kg/day) accumulated in the lymph node and CNS cells of Dark Agouti rats in which EAE was induced by immunization with spinal cord homogenate in complete Freund's adjuvant. GQD significantly reduced clinical signs of EAE when applied throughout the course of the disease (day 0-32), while the protection was less pronounced if the treatment was limited to the induction (day 0-7 post-immunization) or effector (from day 8 onwards) phase of the disease. GQD treatment diminished immune infiltration, demyelination, axonal damage, and apoptotic death in the CNS of EAE animals. GQD also reduced the numbers of interferon-γ-expressing T helper (Th)1 cells, as well as the expression of Th1 transcription factor T-bet and proinflammatory cytokines tumor necrosis factor, interleukin-1, and granulocyte-macrophage colony-stimulating factor in the lymph nodes and CNS immune infitrates. The protective effect of GQD in EAE was associated with the activation of p38 and p42/44 mitogen-activated protein kinases (MAPK) and Akt in the lymph nodes and/or CNS. Finally, GQD protected oligodendrocytes and neurons from T cell-mediated damage in the in vitro conditions. Collectively, these data demonstrate the ability of GQD to gain access to both immune and CNS cells during neuroinflammation, and to alleviate immune-mediated CNS damage by modulating MAPK/Akt signaling and encephalitogenic Th1 immune response.

Carbon Quantum Dots Modified Polyurethane Nanocomposite as Effective Photocatalytic and Antibacterial Agents

Development of new types of antibacterial coatings or nanocomposites is of great importance due to widespread multidrug-resistant infections including bacterial infections. Herein, we investigated biocompatibility as well as structural, photocatalytic, and antibacterial properties of photoactive hydrophobic carbon quantum dots/polyurethane nanocomposite. The swell-encapsulation-shrink method was applied for production of these nanocomposites. Hydrophobic carbon quantum dots/polyurethane nanocomposites were found to be highly effective generator of singlet oxygen upon irradiation by low-power blue light. Analysis of conducted antibacterial tests on Staphyloccocus aureus and Escherichia coli showed 5-log bactericidal effect of these nanocomposites within 60 min of irradiation. Very powerful degradation of dye (rose bengal) was observed within 180 min of blue light irradiation of the nanocomposites. Biocompatibility studies revealed that nanocomposites were not cytotoxic against mouse embryonic fibroblast cell line, whereas they showed moderate cytotoxicity toward adenocarcinomic human epithelial cell line. Minor hemolytic effect of these nanocomposites toward red blood cells was revealed.

A joint experimental and theoretical study on the electro-optical properties of 1,6- and 1,7-fluorenyl disubstituted perylene diimide isomers

The electronic and optical properties of fluorenyl functionalized perylene diimides are influenced by the substituent position on the perylene core.

Photo-induced antibacterial activity of four graphene based nanomaterials on a wide range of bacteria

Due to controversial reports concerning antibacterial activity of different graphene based materials it is very important to investigate their antibacterial action on a wide range of Gram-positive and Gram-negative bacteria. In this paper we have investigated the structure induced phototoxic antibacterial activity of four types of graphene based materials: graphene oxide (GO), graphene quantum dots (GQDs), carbon quantum dots (CQDs) and nitrogen doped carbon quantum dots (N-CQDs). Antibacterial activity was tested on 19 types of bacteria. It is found that nanometer-size CQDs and N-CQDs are the most potent agents whereas micrometer-size GO has very poor antibacterial activity. Electron paramagnetic resonance measurements confirmed photodynamic production of singlet oxygen for all types of used quantum dots. Detailed analysis has shown that N-CQDs are an excellent photodynamic antibacterial agent for treatment of bacterial infections induced by Enterobacter aerogenes (E. aerogenes), Proteus mirabilis (P. mirabilis), Staphylococcus saprophyticus (S. saprophyticus), Listeria monocytogenes (L. monocytogenes), Salmonella typhimurium (S. typhimurium) and Klebsiella pneumoniae.

Antibacterial potentials of four graphene based nanomaterials are tested on a wide range of bacteria.

Spectral properties of ionic benzotristhiazole based donor-acceptor NLO-phores in polymer matrices and their one- and two-photon cellular imaging ability

A series of ionic benzotristhiazolium (BTT) push-pull chromophores, with different nitrogen donor groups and different lengths of conjugated bridges, was successfully doped in polar polymer matrices (PVC and PSS). The spectral (photophysical) properties of their low concentration thin polymeric films are compared with those in solution and are discussed in terms of matrix polarity/viscosity influence, specific polymer-chromophore interaction, structure-spectral property relationship and Twisted Intramolecular Charge-Transfer (TICT) state formation. The elimination of a non-emissive phantom and TICT state formation by restricted intramolecular rotations in the polymer matrix or viscous solvent results in a relatively high Φ_F of all the investigated NLO-phores; particularly for near-infrared NIR molecular rotors bearing diphenylamino and julolidine donor groups. Because of cationic characteristics, small molecular weight, calculated high second hyperpolarizability and significant emission efficiency dependence on surroundings' viscosity (rigidochromic effect), two dyes were chosen as candidates for potential fluorescent probes for one-photon (1P) and two photon (2P) cellular imaging. The selected BTT NLO-phore with a julolidine donor is promising as a mitochondria-specific fluorescent small molecular probe for live cell super-resolution imaging with low cytotoxicity and good photostability, and is also potentially suitable for super-resolution STED imaging.

MACVIA-LR (Fighting Chronic Diseases for Active and Healthy Ageing in Languedoc-Roussillon): A Success Story of the European Innovation Partnership on Active and Healthy Ageing

The Région Languedoc Roussillon is the umbrella organisation for an interconnected and integrated project on active and healthy ageing (AHA). It covers the 3 pillars of the European Innovation Partnership on Active and Healthy Ageing (EIP on AHA): (A) Prevention and health promotion, (B) Care and cure, (C) and (D) Active and independent living of elderly people. All sub-activities (poly-pharmacy, falls prevention initiative, prevention of frailty, chronic respiratory diseases, chronic diseases with multimorbidities, chronic infectious diseases, active and independent living and disability) have been included in MACVIA-LR which has a strong political commitment and involves all stakeholders (public, private, patients, policy makers) including CARSAT-LR and the Eurobiomed cluster. It is a Reference Site of the EIP on AHA. The framework of MACVIA-LR has the vision that the prevention and management of chronic diseases is essential for the promotion of AHA and for the reduction of handicap. The main objectives of MACVIA-LR are: (i) to develop innovative solutions for a network of Living labs in order to reduce avoidable hospitalisations and loss of autonomy while improving quality of life, (ii) to disseminate the innovation. The three years of MACVIA-LR activities are reported in this paper.

Parenteral nutrition in childhood and consequences for dentition and gingivae

AIM

Assessment of dentition in children under parenteral nutrition, risk factors for caries, and dental developmental abnormalities.

MATERIALS AND METHODS

The study involved 63 patients (aged 2.25-16.6 years), i.e. 32 subjects receiving parenteral nutrition for a mean period of 5.6±2.94 years, and 31 healthy control subjects. Oral hygiene (OHI-S, PL-I), gingival (GI), and dentition status (caries, DMFT/dmft, enamel defects, shape alterations), frequency of oral meals and frequency of cariogenic snacks consumption were evaluated. Medical records provided information on parenteral meals per week, age parenteral nutrition started, birth body mass, Apgar score, weight deficiency, and antibiotic therapy until aged 1 year. The Mann-Whitney test, chi-squared test, and Spearman rank correlation coefficient were used (p≤0.05).

RESULTS

Dental developmental abnormalities occurred more often in PN subjects (71.87% vs. 25.80%). The prevalence of caries in PN (56.25% vs. 90.32%) and dmft (2.00&#177;3.30 vs. 4.21&#177;3.33) and DMFT (2.47&#177;4.08 vs. 3.33&#177;3.50) were lower. Positive caries Spearman's rank correlation coefficients: frequency of oral meals and frequency of cariogenic snacks consumption, and GI. Negative correlation coefficients: low birth body mass, antibiotic therapy, and low body mass in the first year of life. Positive dental developmental abnormality Spearman's coefficients: low birth body mass, Apgar score < 7, parenteral nutrition duration, low body mass and antibiotic therapy in the first year of life. Beta- lactam, aminoglycoside, glycopeptide and nitroimidazole treatments were related to enamel hypoplasia.

CONCLUSION

Parenteral nutrition in childhood is related to the risk of dental developmental abnormalities, promoted by malnutrition and antibiotic therapy in infancy. Limiting the number of meals and cariogenic snacks, and most probably administration of antibiotics, decreases the risk of caries.

Complex study of the physical properties of a poly(lactic acid)/poly(3-hydroxybutyrate) blend and its carbon black composite during various outdoor and laboratory ageing conditions

Carbon black improved retention of mechanical properties of compostable PLA/PHB – based foil during ageing making it suitable as mulching material.

A polysulfobetaine hydrogel for immobilization of a glucose-binding protein

A hydrogel based on sulfobetaine methacrylate monomer and crosslinker was investigated as a potential material for fluorescent glucose biosensor applications.

3-(7-Dimethylamino)coumarin N-phenylsemicarbazones in solution and polymer matrices: Tuning their fluorescence via para-phenyl substitution

The photo-physical properties of five new para-phenyl substituted derivatives of 3-(7-dimethylamino)coumarin N-phenylsemicarbazone with various electron-withdrawing substituents R (RF, Br, CF3, CN or NO2) in the para-position on the phenyl ring were investigated in solvents and in polymer matrices. Tuning their fluorescent properties via para-substitution is discussed in terms of Twisted Intra-molecular Charge-Transfer (TICT) state formation, specific solute-solvent interactions (hydrogen bonding), fluorescent H-aggregates formation, and the solvent polarity and polymer matrix effects.

Spectral characteristics of carbonyl substituted 2,2'-bithiophenes in polymer matrices and low polar solvents

The spectral characteristics of monosubstituted derivatives of 2,2'-bithiophene (1-BT) with simple carbonyl substituents, including -COCF3 (trifluoroacetyl, 2-BTCF), -COCH2CN (oxopropanenitrile, 3-BTCN) and -COCH3 (acetyl, 4-BTCE), and the more complex 5'-((9H-fluoren-9-ylidene)methyl)-3-methyl, 5-methyl carboxylate (5-BTFL) were investigated. Absorption and fluorescence spectra and fluorescence lifetimes were measured in solvents with various polarities and compared with those in polymer matrices (polystyrene, PS; polymethyl methacrylate, PMMA; and polyvinyl chloride, PVC). Although the parent, 1-BT, absorbed near 300 nm and exhibited no or weak fluorescence, the substitution of 1-BTwith simple substituents at position 5 resulted in a bathochromic shift of approximately 50 nm or more in absorption and distinct fluorescence above 400 nm. The largest shift in absorption and fluorescence was observed for the complex 5-BTFL with fluorene as a substituent for 1-BT. The most intense fluorescence was observed for the derivative 2-BTCF with trifluoroacetyl as a substituent in the polar PVC matrix. The lifetimes of fluorescence of all substituted 2,2'-bithiophenes were in the range from 0.3 to 3 ns. The polymer matrices increased the intensity of fluorescence to some extent and prolonged the lifetime of the 2,2'-bithiophene derivatives. The reasons for the variation in the fluorescence intensity resulting from the substitution of the parent dimer are discussed.

Can optimal resource allocation models explain why ectotherms grow larger in cold?

Basically all organisms can be classified as determinate growers if their growth stops or almost stops at maturation, or indeterminate growers if growth is still intense after maturation. Adult size for determinate growers is relatively well defined, whereas in indeterminate growers usually two measures are used: size at maturation and asymptotic size. The latter term is in fact not a direct measure but a parameter of a specific growth equation, most often Bertalanffy's growth curve. At a given food level, the growth rate in determinate growers depends under given food level on physiological constraints as well as on investments in repair and other mechanisms that improve future survival. The growth rate in indeterminate growers consists of two phases: juvenile and adult. The mechanisms determining the juvenile growth rate are similar to those in determinate growers, whereas allocation to reproduction (dependent on external mortality rate) seems to be the main factor limiting adult growth. Optimal resource allocation models can explain the temperature-size rule (stating that usually ectotherms grow slower in cold but attain larger size) if the exponents of functions describing the size-dependence of the resource acquisition and metabolic rates change with temperature or mortality increases with temperature. Emerging data support both assumptions. The results obtained with the aid of optimization models represent just a rule and not a law: it is possible to find the ranges of production parameters and mortality rates for which the temperature-size rule does not hold.

Spectral properties of substituted coumarins in solution and polymer matrices

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH₃, OCH₃ and N(CH₃)₂, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH₃)₂ in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH₃)₂ substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5–4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have k_F higher than k_nr in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.