Fluorescence of pterin, 6-formylpterin, 6-carboxypterin and folic acid in aqueous solution: pH effects

Enhancement of the Photosensitizing Properties of 6-Carboxypterin through Covalent Binding to the pH-Responsive and Biocompatible Poly(allylamine Hydrochloride)

A polymeric photosensitizer was synthesized through covalent attachment of the natural photosensitizer 6-carboxypterin (Cap) to a poly(allylamine hydrochloride) (PAH) polymer. The optimization of the functionalization steps and purification procedure is described. The overall yield of the functionalization reaction was 67% to generate the modified polymer (PAH-Cap), featuring a Cap substitution degree of approximately 1% and advantageous spectroscopic properties. Photosensitizing properties of PAH-Cap were observed to occur via both photooxidation mechanisms, i.e., type I and type II. This feature was demonstrated using a biologically relevant target molecule, 2'-deoxyguanosine (dG). The spectroscopic, photophysical, and photochemical behaviors in aqueous environments were studied and compared to Cap. To explore possible further relevant biological applications, experiments with PAH-Cap and dG were carried out at physiological pH. PAH-Cap can generate singlet molecular oxygen and initiate an electron transfer process at pH 7 in air-saturated solutions upon UVA irradiation. Moreover, based on its spectroscopic features, visible light can be used to initiate the photooxidation of biological compounds in water, with many interesting advantages compared to free Cap and other related pteridines. These advantages include an enhancement of the photosensitizing effect at physiological pH and the potential of PAH-Cap for its use as a building block in supramolecular assemblies. The functionalization strategy hereby described can be employed for the preparation of robust photoactive polymers with great potential for its application in photodynamic therapy (PDT) and disinfection technologies.

Novel role of folate (vitamin B9) released by fermenting bacteria under Human Intestine like environment

The anaerobic region of the gastrointestinal (GI) tract has been replicated in the anaerobic chamber of a microbial fuel cell (MFC). Electroactive biomolecules released by the facultative anaerobes (Providencia rettgeri) under anoxic conditions have been studied for their potential role for redox balance. MALDI study reveals the presence of vitamin B9 (folate), 6-methylpterin, para-aminobenzoic acid (PABA) and pteroic acid called pterin pool. ATR-FTIR studies further confirm the presence of the aromatic ring and side chains of folate, 6-methylpterin and PABA groups. The photoluminescence spectra of the pool exhibit the maximum emission at 420, 425, 440, and 445 nm when excited by 310, 325, 350, and 365 nm wavelengths (day 20 sample) highlighting the presence of tunable bands. The cyclic voltammetric studies indicate the active participation of pterin pool molecules in the transfer of electrons with redox potentials at - 0.2 V and - 0.4 V for p-aminobenzoate and pterin groups, respectively. In addition, it is observed that under prolonged conditions of continuous oxidative stress (> 20 days), quinonoid tetrahydrofolate is formed, leading to temporary storage of charge. The results of the present study may potentially be useful in designing effective therapeutic strategies for the management of various GI diseases by promoting or blocking folate receptors.

Strongly Emitting Folic Acid-Derived Carbon Nanodots for One- and Two-Photon Imaging of Lyotropic Myelin Figures

Non-invasive imaging of morphological changes in biologically relevant lipidic mesophases is essential for the understanding of membrane-mediated processes. However, its methodological aspects need to be further explored, with particular attention paid to the design of new excellent fluorescent probes. Here, we have demonstrated that bright and biocompatible folic acid-derived carbon nanodots (FA CNDs) may be successfully applied as fluorescent markers in one- and two-photon imaging of bioinspired myelin figures (MFs). Structural and optical properties of these new FA CNDs were first extensively characterized; they revealed remarkable fluorescence performance in linear and non-linear excitation regimes, justifying further applications. Then, confocal fluorescence microscopy and two-photon excited fluorescence microscopy were used to investigate a three-dimensional distribution of FA CNDs within the phospholipid-based MFs. Our results showed that FA CNDs are effective markers for imaging various forms and parts of multilamellar microstructures.

Insights into Molecular Structure of Pterins Suitable for Biomedical Applications

Pterins are an inseparable part of living organisms. Pterins participate in metabolic reactions mostly as tetrahydropterins. Dihydropterins are usually intermediates of these reactions, whereas oxidized pterins can be biomarkers of diseases. In this review, we analyze the available data on the quantum chemistry of unconjugated pterins as well as their photonics. This gives a comprehensive overview about the electronic structure of pterins and offers some benefits for biomedicine applications: (1) one can affect the enzymatic reactions of aromatic amino acid hydroxylases, NO synthases, and alkylglycerol monooxygenase through UV irradiation of H₄pterins since UV provokes electron donor reactions of H₄pterins; (2) the emission properties of H₂pterins and oxidized pterins can be used in fluorescence diagnostics; (3) two-photon absorption (TPA) should be used in such pterin-related infrared therapy because single-photon absorption in the UV range is inefficient and scatters in vivo; (4) one can affect pathogen organisms through TPA excitation of H₄pterin cofactors, such as the molybdenum cofactor, leading to its detachment from proteins and subsequent oxidation; (5) metal nanostructures can be used for the UV-vis, fluorescence, and Raman spectroscopy detection of pterin biomarkers. Therefore, we investigated both the biochemistry and physical chemistry of pterins and suggested some potential prospects for pterin-related biomedicine.

Carbon dots derived from folic acid attenuates osteoarthritis by protecting chondrocytes through NF-κB/MAPK pathway and reprogramming macrophages

Background

Osteoarthritis (OA) is a common joint disorder worldwide which causes great health and economic burden. However, there remains an unmet goal to develop an effective therapeutic method to prevent or delay OA. Chondrocytes, as the major cells involved in OA progression, may serve as a promising therapeutic target.

Results

A kind of carbon dots (CDs) with excellent biocompatibility was fabricated from folic acid via hydrothermal method and could effectively attenuate osteoarthritis. It was demonstrated that CDs treatment could rescue IL1β-induced proinflammatory responses, oxidative stress, cartilage degeneration and extracellular matrix degradation. Moreover, CDs reprogrammed lipopolysaccharide (LPS)-induced macrophage inflammation and polarization. Conditioned medium (CM) from CDs-treated macrophages could attenuate IL1β-induced chondrocyte injury. Also, CM from CDs-treated chondrocytes had immunoregulatory functions on macrophages. Mechanistically, CDs inhibited the activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinases (MAPK) signaling pathways in IL1β-stimulated chondrocytes. In vivo, anterior cruciate ligament transection (ACLT) mice model was adopted and it was indicated that intra-articular injection of CDs effectively delays OA pathogenesis.

Conclusions

Taken together, these findings indicated CDs could mediate OA via promoting cartilage repair and immunomodulating macrophages within local microenvironment, which may provide evidences for utilizing CDs as a novel nanomaterial for OA treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01681-6.

Pterin-lysine photoadduct: a potential candidate for photoallergy

Photoallergy is a photosensitivity disorder associated with a modified ability of the skin to react to the combined effect of drugs and sunlight. It has been attributed to the covalent conjugation of proteins with a photosensitizer, yielding modified macromolecules that can act as antigen provoking the immune system response. The potential role of some endogenous compounds as photoallergens has not been fully established. It has been previously proposed that pterins, which are endogenous photosensitizers present in human skin under pathological conditions, are able to covalently bind to proteins. Here, we evaluated the capability of pterin (Ptr) to form photoadducts with free Lysine (Lys) and poly-L-lysine (poly-Lys). The findings obtained using chromatographic and spectroscopic tools, confirm the formation of photoadducts of Ptr with Lys residues. With poly-Lys the resulting adduct retains the spectroscopic properties of the photosensitizer, suggesting that the aromatic Ptr structure is conserved. On the other hand, the photoproduct formed with free Lys does not behave like Ptr, which suggests that if this product is a photoadduct, a chemical modification may have occurred during the photochemical reaction that alters the pterin moiety.

Synthesis, Redox and Spectroscopic Properties of Pterin of Molybdenum Cofactors

Pterins are bicyclic heterocycles that are found widely across Nature and are involved in a variety of biological functions. Notably, pterins are found at the core of molybdenum cofactor (Moco) containing enzymes in the molybdopterin (MPT) ligand that coordinates molybdenum and facilitates cofactor activity. Pterins are diverse and can be widely functionalized to tune their properties. Herein, the general methods of synthesis, redox and spectroscopic properties of pterin are discussed to provide more insight into pterin chemistry and their importance to biological systems.

A comprehensive review on LED-induced fluorescence in diagnostic pathology

Sensitivity, specificity, mobility, and affordability are important criteria to consider for developing diagnostic instruments in common use. Fluorescence spectroscopy has been demonstrating substantial potential in the clinical diagnosis of diseases and evaluating the underlying causes of pathogenesis. A higher degree of device integration with appropriate sensitivity and reasonable cost would further boost the value of the fluorescence techniques in clinical diagnosis and aid in the reduction of healthcare expenses, which is a key economic concern in emerging markets. Light-emitting diodes (LEDs), which are inexpensive and smaller are attractive alternatives to conventional excitation sources in fluorescence spectroscopy, are gaining a lot of momentum in the development of affordable, compact analytical instruments of clinical relevance. The commercial availability of a broad range of LED wavelengths (255-4600 nm) has opened up new avenues for targeting a wide range of clinically significant molecules (both endogenous and exogenous), thereby diagnosing a range of clinical illnesses. As a result, we have specifically examined the uses of LED-induced fluorescence (LED-IF) in preclinical and clinical evaluations of pathological conditions, considering the present advancements in the field.

UV/Vis absorption spectroelectrochemistry of folic acid

UV/Vis absorption spectroelectrochemistry is a very promising analytical technique due to the complementary information that is simultaneously obtained from electrochemistry and spectroscopy. In this work, this technique is used in a parallel configuration to study the oxidation of folic acid in alkaline medium. Herein, UV/Vis absorption spectroelectrochemistry has been used to detect both the oxidation products and the folic acid consumed at the electrode/solution interface, allowing us to develop an analytical protocol to quantify vitamin B9 in pharmaceutical tablets. Linear ranges of three orders of magnitude have been achieved in basic medium (pH = 12.9), obtaining high repeatability and low detection limits. The spectroelectrochemical determination of folic acid in pharmaceutical tablets at alkaline pH values is particularly interesting because of the changes that occur in the optical signal during the electrochemical oxidation of FA, providing results with very good figures of merit and demonstrating the utility and versatility of this hyphenated technique, UV/Vis absorption spectroelectrochemistry.

Alkaloids as Photosensitisers for the Inactivation of Bacteria

Antimicrobial photodynamic therapy has emerged as a powerful approach to tackle microbial infections. Photodynamic therapy utilises a photosensitiser, light, and oxygen to generate singlet oxygen and/or reactive oxygen species in an irradiated tissue spot, which subsequently react with nearby biomolecules and destroy the cellular environment. Due to the possibility to irradiate in a very precise location, it can be used to eradicate bacteria, fungus, and parasites upon light activation of the photosensitiser. In this regard, natural products are low-cost molecules capable of being obtained in large quantities, and some of them can be used as photosensitisers. Alkaloids are the largest family among natural products and include molecules with a basic nature and aromatic rings. For this study, we collected the naturally occurring alkaloids used to treat microorganism infections using a photodynamic inactivation approach. We gathered their main photophysical properties (excitation/emission wavelengths, quantum yields, and oxygen quantum yield) which characterise the ability to efficiently photosensitise. In addition, we described the antibacterial activity of alkaloids upon irradiation and the mechanisms involved in the microorganism killing. This review will serve as a reference source to obtain the main information on alkaloids used in antimicrobial photodynamic therapy.

Encapsulation of folic acid (vitamin B9) into sporopollenin microcapsules: Physico-chemical characterisation, in vitro controlled release and photoprotection study

Folic acid (FA) is a crucial vitamin for all living creatures. However, it is susceptible to degradation under pH, heat, ultraviolet (UV) and day sunlight conditions, resulting in lowering its bioavailability. Therefore, a versatile protective encapsulation system for FA is highly required to overcome its inherent instability. We report the use of the robust Lycopodium clavatum sporopollenin (LCS) microcapsules, extracted from their natural micrometer-sized raw spores, for FA microencapsulation. The physico-chemical characterisation of the LCS microcapsules are comprehensively investigated before and after the microencapsulation using SEM, elemental, CLSM, FTIR, TGA/DTG and XRD analyses, revealing a successful FA encapsulation within the LCS in an amorphous form. The phenylpropanoid acids, responsible for the UV protection and the autofluorescence of the LCS, were found in the LCS as evidenced by FTIR analysis. TGA/DTG results revealed that the hemi-cellulose and cellulose are the major component of the LCS. A controlled and sustained release of FA from FA-loaded LCS were achieved where the release profile of FA-loaded LCS was found to be pH-dependent. The percentages of cumulative FA released after 10 h at 37 ± 0.5 °C were 45.5% and 76.1% in pH 1.2 and 7.4, respectively, ensuring controlled and slow release in simulated physiological conditions. The FA release kinetic studies indicated the prevalence of the Fickian diffusion mechanism in pH 1.2, while anomalous non-Fickian transport was ascribed for FA release in pH 7.4. The in vitro cytotoxicity assay revealed that the obtained formulations were biocompatible against the human skin fibroblast (HSF) cell line. The versatile LCS microcapsules exhibited intriguing photostability for FA under UV or sunlight irradiation. Concretely, the obtained FA sustained delivery and photoprotection properties of these LCS microcapsules validate their multifunctional characteristics, opening up intriguing applications in oral and topical drug delivery as well as in food industry.

Properties and reactivity of the folic acid and folate photoproduct 6-formylpterin

Folates (vitamin B9) are essential components of our diet and our gut microbiota. They are omnipresent in our cells and blood. Folates are necessary for DNA synthesis, methylation, and other vital bioprocesses. Folic acid (FA), as the synthetic form of folates, is largely found in supplements and fortified foods. FA and folate drugs are also extensively used as therapeutics. Therefore, we are continuously exposed to the pterin derivatives, and their photo-degradation products, such as 6-formylpterin (6-FPT) and pterin-6-carboxylic acid. During ultraviolet radiation, these two photolytic products generate reactive oxygen species (ROS) responsible for the cellular oxidative stress. 6-FPT can exhibit variable pro/anti-oxidative roles depending on the cell type and its environment (acting as a cell protector in normal cells, or as an enhancer of drug-induced cell death in cancer cells). The ROS-modulating capacity of 6-FPT is well-known, whereas its intrinsic reactivity has been much less investigated. Here, we have reviewed the properties of 6-FPT and highlighted its capacity to form covalent adducts with the ROS-scavenging drug edaravone (used to treat stroke and amyotrophic lateral sclerosis) as well as its implication in immune surveillance. 6-FPT and its analogue acetyl-6-FPT function as small molecule antigens, recognized by the major histocompatibility complex-related class I-like molecule, MR1, for presentation to mucosal-associated invariant T (MAIT) cells. As modulators of the MR1/MAIT machinery, 6-FPT derivatives could play a significant immuno-regulatory role in different diseases. This brief review shed light on the multiple properties and cellular activities of 6-FPT, well beyond its primary ROS-generating activity.

Functional Micro-/Nanomaterials for Multiplexed Biodetection

When analyzing biological phenomena and processes, multiplexed biodetection has many advantages over single-factor biodetection and is highly relevant to both human health issues and advancements in the life sciences. However, many key problems with current multiplexed biodetection strategies remain unresolved. Herein, the main issues are analyzed and summarized: 1) generating sufficient signal to label targets, 2) improving the signal-to-noise ratio to ensure total detection sensitivity, and 3) simplifying the detection process to reduce the time and labor costs of multiple target detection. Then, available solutions made possible by designing and controlling the properties of micro- and nanomaterials are introduced. The aim is to emphasize the role that micro-/nanomaterials can play in the improvement of multiplexed biodetection strategies. Through analyzing existing problems, introducing state-of-the-art developments regarding relevant materials, and discussing future directions of the field, it is hopeful to help promote necessary developments in multiplexed biodetection and associated scientific research.

Supramolecular magnetonanohybrids for multimodal targeted therapy of triple-negative breast cancer cells

Despite the undeniable advances in recent decades, cancer remains one of the deadliest diseases of the current millennium, where the triple-negative breast cancer (TNBC) is very aggressive, extremely metastatic, and resistant to conventional chemotherapy. The nanotheranostic approach focusing on targeting membrane receptors often expressed at abnormal levels by cancer cells can be a strategic weapon for fighting malignant tumors. Herein, we introduced a novel "all-in-one nanosoldier" made of colloidal hybrid nanostructures, which were designed for simultaneously targeting, imaging, and killing TNBC cells. These nanohybrids comprised four distinct components: (a) superparamagnetic iron oxide nanoparticles, as bi-functional nanomaterials for inducing ferroptosis via inorganic nanozyme-mediated catalysis and magnetotherapy by hyperthermia treatment; (b) carboxymethyl cellulose biopolymer, as a water-soluble capping macromolecule; (c) folic acid, as the membranotopic vector for targeting folate receptors; (d) and doxorubicin (DOX) drug for chemotherapy. The results demonstrated that this novel strategy was highly effective for targeting and killing TNBC cells in vitro, expressing high levels of folate membrane-receptors. The results evidenced that three integrated mechanisms triggered the deaths of the cancer cells in vitro: (a) ferroptosis, by magnetite nanoparticles inducing a Fenton-like reaction; (b) magneto-hyperthermia effect by generating heat under an alternate magnetic field; and (c) chemotherapy, through the DOX intracellular release causing DNA dysfunction. This "all-in-one nanosoldier" strategy offers a vast realm of prospective alternatives for attacking cancer cells, combining multimodal therapy and the delivery of therapeutic agents to diseased sites and preserving healthy cells, which is one of the most critical clinical challenges faced in fighting drug-resistant breast cancers.

Synthesis of Multi-Functional Carbon Quantum Dots for Targeted Antitumor Therapy

Carbon dots are nano-sized photoluminescence materials which have good biocompatibility and low cytotoxicity, while the previously synthesized carbon dots lack tumor targeting capability and therapy function so that it cannot achieve the purpose of diagnosis and treatment. Herein, a new kind of multi-functional carbon dots (GFCDs) is promising to be applied in tumor cells imaging and clinical targeted therapy. Gallic acid (GA) was used as the carbon resource and antitumor active molecule, folic acid (FA) was used as the nitrogen resource and tumor targeting molecule, and citric acid monohydrate (CA) was used as the auxiliary carbon source. Multi-functional GACDs were synthesized by a simple one-step microwave-assisted procedure and analyzed with UV - vis spectrophotometer, fourier transform infrared spectrometer, transmission electron microscopy and X-ray photoelectron spectrometer. Results show that the diameter of GFCDs is about 3 nm. And GFCDs are pale-yellow under natural light which turn blue under 360 nm UV lamp. Besides ester bond is the connecting mode between functional molecules. In addition, the results of in vitro cell imaging experiments and in vivo antitumor experiments demonstrate the targeting imaging and antitumor abilities towards Hela cells. The synthesis route and properties of GFCDs.

Molecular nature of breakdown of the folic acid under hydrothermal treatment: a combined experimental and DFT study

Using a combination of experimental Raman, FTIR, UV–VIS absorption and emission data, together with the corresponding DFT calculations we propose the mechanism of modification of the folic acid specifically under the hydrothermal treatment at 200 °C. We established that folic acid breaks down into fragments while the pteridine moiety remains intact likely evolving into 6-formylpterin with the latter responsible for the increase in fluorescence emission at 450 nm. The results suggest that hydrothermal approach can be used for production of other purpose-engineered fluorophores.

Theoretical determination of two-photon absorption in biologically relevant pterin derivatives

Given the prevalence of fluorescence spectroscopy in biological systems, and the prevalence of pterin derivatives throughout biological systems, presented here is an assessment of the two-photon absorption spectroscopy as it applies to a range of the most commonly studied pterin derivatives. QR-CAMB3LYP//ccpVTZ calculations suggest that the use of two-photon spectroscopic methods would enable a more capable differentiation between closely related derivatives in comparison to the one-photon spectra, which show minimal qualitative deviation. Study of short tail derivatives shows that, in most cases, two-photon accessible states solely involve the π* LUMO as the particle orbital, with biopterin, neopterin, and 6-(hydroxymethyl)pterin presenting exceptional potential for targetting. Investigation of derivatives in which the tail contains an aromatic ring resulted in the observation of a series of two-photon accessible states involving charge transfer from the tail to the pterin moiety, the cross sections of which are highly dependent on the adoption of a planar geometry. The observation of these states presents a novel method for tracking the substitution of biologically important molecules such as folic acid and 5-methenyltetrahydrofolylpolyglutamate.

Sulfamethoxazole drug stress upregulates antioxidant immunomodulatory metabolites in Escherichia coli

Escherichia coli is an important model organism in microbiology and a prominent member of the human microbiota¹. Environmental isolates readily colonize the gastrointestinal tract of humans and other animals, and they can serve diverse probiotic, commensal and pathogenic roles in the host^2-4. Although certain strains have been associated with the severity of inflammatory bowel disease (IBD)^2,5, the diverse immunomodulatory phenotypes remain largely unknown at the molecular level. Here, we decode a previously unknown E. coli metabolic pathway that produces a family of hybrid pterin-phenylpyruvate conjugates, which we named the colipterins. The metabolites are upregulated by subinhibitory levels of the antifolate sulfamethoxazole, which is used to treat infections including in patients with IBD^6,7. The genes folX/M and aspC/tyrB involved in monapterin biosynthesis^8-10 and aromatic amino acid transamination,¹¹ respectively, were required to initiate the colipterin pathway. We show that the colipterins are antioxidants, harbour diverse immunological activities in primary human tissues, activate anti-inflammatory interleukin-10 and improve colitis symptoms in a colitis mouse model. Our study defines an antifolate stress response in E. coli and links its associated metabolites to a major immunological marker of IBD.

Cu-In-S/ZnS@carboxymethylcellulose supramolecular structures: Fluorescent nanoarchitectures for targeted-theranostics of cancer cells

Although the field of oncology nanomedicine has shown indisputable progress in recent years, cancer remains one of the most lethal diseases, where the early diagnosis plays a pivotal role in the patient's prognosis and therapy. Herein, we report for the first time, the synthesis of biocompatible nanostructures composed of Cu-In-S and Cu-In-S/ZnS nanoparticles functionalized with carboxymethylcellulose biopolymer produced by a green aqueous process. These inorganic-organic colloidal nanohybrids developed supramolecular architectures stabilized by chemical functional groups of the polysaccharide shell with the fluorescent semiconductor nanocrystal core, which were extensively characterized by several morphological and spectroscopical techniques. Moreover, these nanoconjugates were covalently bonded with folic acid via amide bonds and electrostatically conjugated with the anticancer drug, producing functionalized supramolecular nanostructures. They demonstrated nanotheranostics properties for bioimaging and drug delivery vectorization effective for killing breast cancer cells in vitro. These hybrids offer a new nanoplatform using fluorescent polysaccharide-drug conjugates for cancer theranostics applications.

Mechanism for Inhibition of Folic Acid Photodecomposition by Various Antioxidants

Folic acid, a synthetic form of folate, is a water-soluble vitamin that is essential during periods of rapid cell division and growth. However, it decomposes upon ultraviolet irradiation to form inactive photoproducts. In this study, the protective effect and mechanisms of antioxidants, including cinnamic acids, flavonoids, catechol and its derivatives, stilbenes, p-benzoquinone and its derivatives, isoprenoids, curcumin, oleic acid, and linoleic acid, against folic acid photodecomposition were investigated by using fluorescence and absorbance spectroscopy, high-performance liquid chromatography, and antioxidant assay. It was found that antioxidants could inhibit or delay the folic acid decomposition in varying degrees, among which caffeic acid was the most effective. The increase in its remarkable antioxidant efficiency and absorbance in the UVA region during irradiation contributed to its effective protection. This finding could be useful for the protection of photolabile components in food and other uses.

One step hydrothermal functionalization of gold nanoparticles with folic acid

A new fundamental concept for one-step in-situ functionalization of gold nanoparticles (GNPs) with folic acid using hydrothermal treatment is described. Hydrothermal treatment has been tuned to increase the light emission from the pterin moiety of folic acid molecule, while retain its structure and functionality, thus providing a simple route to multimodal tags for a variety of in vitro and in vivo biomedical applications. Successful functionalization of GNPs with the biological ligand is confirmed by specific binding with anti-folic acid antibody.

Folate-Decorated Amphiphilic Cyclodextrins as Cell-Targeted Nanophototherapeutics

Nowadays, active targeting of nanotherapeutics is a challenging issue. Here, we propose a rational design of a ternary nanoassembly (SAP) composed of nonionic amphiphilic β-cyclodextrins (amphiphilic CD) incorporating pheophorbide (Pheo) as a phototherapeutic and an adamantanyl-folic acid conjugate (Ada-FA) to target tumor cells overexpressing α-folate receptor (FR-α(+)). Dynamic light scattering and ζ-potential pointed out the presence of nanoassemblies bearing a negative surface charge (ζ = -51 mV). Morphology of SAP was investigated by atomic force microscopy and microphotoluminescence, indicating the presence of highly emissive near-spherical assemblies of about 280 nm in size. Complementary spectroscopic techniques such as ROESY-NMR, UV/vis and steady-state fluorescence revealed that the folic acid protrudes out of amphiphilic CD rims, prone for recognition with FR-α. Pheo was strongly loaded in the nanoassembly mostly in monomeric form, thus generating singlet oxygen (¹O₂) and consequentely showing phototherapeutic action. SAP remained stable until 2 weeks in aqueous solutions. Stability studies in biologically relevant media pointed out the ability of SAP to interact with serum proteins by means of the oligoethylenglycole fringe, without destabilization. Release experiments demonstrated the sustained release of Pheo from SAP in environments mimiking physiological conditions (∼20% within 1 week), plausibly suggesting low Pheo leaking and high integrity of the assembly within 24 h, time spent on average to reach the target sites. Cellular uptake of SAP was confirmed by confocal microscopy, pointing out that SAP was internalized into the tumoral cells expressing FR-α more efficiently than SP. SAP showed improved phototoxicity in human breast MCF-7 cancer cells FR-α(+) (IC₅₀ = 270 nM) with respect to human prostate carcinoma PC3 cells (IC₅₀ = 700 nM) that express a low level of that receptor (FR-α(-)). Finally, an improved phototoxicity in FR-α(+) MCF-7 cells (IC₅₀ = 270 nM) was assessed after treatment with SAP vs SP (IC₅₀ = 600 nM) which was designed without Ada-FA as a targeting unit.

Microbial (Enzymatic) Degradation of Cyanide to Produce Pterins as Cofactors

Cyanide is one of the most poisonous substances in the environment, which may have originated from natural and anthropogenic sources. There are many enzymes produced by microorganisms which can degrade and utilize cyanide. The major byproducts of cyanide degradation are alanine, glutamic acid, alpha-amino-butyric acid, beta-cyanoalanine, pterin etc. These products have many pharmaceutical and medicinal applications. For the degradation of cyanide, microbes produce necessary cofactors which catalyze the degradation pathways. Pterin is one of the cofactors for cyanide degradation. There are many pathways involved for the degradation of cyanide, cyanate, and thiocyanate. Some of the microorganisms possess resistance to cyanide, since they have developed adaptive alternative pathways for the production of ATP by utilization of cyanide as carbon and nitrogen sources. In this review, we summarized different enzymes, their mechanisms, and corresponding pathways for the degradation of cyanide and production of pterins during cyanide degradation. We aim to enlighten different types of pterin, its classification, and biological significance through this literature review.

Determination of Urinary Pterins by Capillary Electrophoresis Coupled with LED-Induced Fluorescence Detector

Urinary pterins have been found as potential biomarkers in many pathophysiological conditions including inflammation, viral infections, and cancer. However, pterins determination in biological samples is difficult due to their degradation under exposure to air, light, and heat. Besides, they occur at shallow concentration levels, and thus, standard UV detectors cannot be used without additional sample preconcentration. On the other hand, ultra-sensitive laser-induced fluorescence (LIF) detection can be used since pterins exhibit native fluorescence. The main factor that limits an everyday use of LIF detectors is its high price. Here, an alternative detector, i.e., light-emitted diode induced fluorescence (LEDIF) detector, was evaluated for the determination of pterins in urine samples after capillary electrophoresis (CE) separation. An optimized method was validated in terms of linearity range, limit of detection (LOD), limit of quantification (LOQ), intra- and interday precision and accuracy, sample stability in the autosampler, and sample stability during the freezing/thawing cycle. The obtained LOD (0.1 µM) and LOQ (0.3 µM) values were three-order of magnitude lower compared to UV detector, and two orders of magnitude higher compared to previously reported house-built LIF detector. The applicability of the validated method was demonstrated in the analysis of urine samples from healthy individuals and cancer patients.

Controlling the fluorescence and room-temperature phosphorescence behaviour of carbon nanodots with inorganic crystalline nanocomposites

There is a significant drive to identify alternative materials that exhibit room temperature phosphorescence for technologies including bio-imaging, photodynamic therapy and organic light-emitting diodes. Ideally, these materials should be non-toxic and cheap, and it will be possible to control their photoluminescent properties. This was achieved here by embedding carbon nanodots within crystalline particles of alkaline earth carbonates, sulphates and oxalates. The resultant nanocomposites are luminescent and exhibit a bright, sub-second lifetime afterglow. Importantly, the excited state lifetimes, and steady-state and afterglow colours can all be systematically controlled by varying the cations and anions in the host inorganic phase, due to the influence of the cation size and material density on emissive and non-emissive electronic transitions. This simple strategy provides a flexible route for generating materials with specific, phosphorescent properties and is an exciting alternative to approaches relying on the synthesis of custom-made luminescent organic molecules.

Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer

Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins present acid-base and keto-enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (¹ O₂ ) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.

pH-related fluorescence quenching mechanism of pterin derivatives and the effects of 6-site substituents

2-Amino-4-hydroxypteridine (pterin) and its derivatives serve as photooxidants and exhibit strong fluorescence. When they interact with hydrogen acceptors such as acetate and phosphate, their fluorescences are significantly quenched in acidic conditions (pH 4.9–5.5) but are retained in basic conditions (pH 10.0–10.5). This pH-related fluorescence quenching mechanism of pterin and its derivatives are fully investigated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Pterin and its derivatives are demonstrated to show favorable excited-state proton transfer (ESPT) abilities in acidic conditions that induce the experimentally observed fluorescence quenching. In contrast, the ESPT processes are found to be retarded due to the lack of strong hydrogen-bonding interactions in basic environments, which sustain their fluorescence. Interestingly, these ESPT processes are found to show different site specificities depending on the 6-site substituents. The introduction of electron-donating substituent activates the N1 site, making it the preferred ESPT site. By contrast, the introduction of an electron-withdrawing substituent activates the N5 site, making it the favorable ESPT site. The substitutions of different functional groups are found to affect the locations of acidic centers during the excitation and relaxation processes. This further affects the hydrogen-bonding patterns and ultimately brings site specificity to the ESPT process.

A concise treatment of pterins: some recent synthetic and methodology aspects and their applications in molecular sensors

A concise account of pterins in chemistry and biology and their applications in molecular sensors including their optical spectroscopic properties are described. Different natural, synthetic, biological and photophysical aspects are also discussed. Synthetic access to direct functionalised pterins and a recently reported new thiophene annulation technique are described for the synthesis of Form B of molybdenum cofactor. The receptor properties of fluorescent pterin molecules including selenopyrimidines which are rarely reported for their binding of anions and neutral molecules are also of major importance in this review. For such an old and still so young, unexplored pterin system on its power to be sensitive for physical studies especially the interaction with cations, anions and neutral molecules are fascinating and research in this area is relatively new and expected to increase fast. Pterin based receptors are for the first time put into a useful review for the advantage of those who want to explore pterin and modified pterin as chromogenic and fluorogenic sensors.

Multiplexed Isothermal Amplification Based Diagnostic Platform to Detect Zika, Chikungunya, and Dengue 1

Zika, dengue, and chikungunya viruses are transmitted by mosquitoes, causing diseases with similar patient symptoms. However, they have different downstream patient-to-patient transmission potentials, and require very different patient treatments. Thus, recent Zika outbreaks make it urgent to develop tools that rapidly discriminate these viruses in patients and trapped mosquitoes, to select the correct patient treatment, and to understand and manage their epidemiology in real time. Unfortunately, current diagnostic tests, including those receiving 2016 emergency use authorizations and fast-track status, detect viral RNA by reverse transcription polymerase chain reaction (RT-PCR), which requires instrumentation, trained users, and considerable sample preparation. Thus, they must be sent to "approved" reference laboratories, requiring time. Indeed, in August 2016, the Center for Disease Control (CDC) was asking pregnant women who had been bitten by a mosquito and developed a Zika-indicating rash to wait an unacceptable 2 to 4 weeks before learning whether they were infected. We very much need tests that can be done on site, with few resources, and by trained but not necessarily licensed personnel. This video demonstrates an assay that meets these specifications, working with urine or serum (for patients) or crushed mosquito carcasses (for environmental surveillance), all without much sample preparation. Mosquito carcasses are captured on paper carrying quaternary ammonium groups (Q-paper) followed by ammonia treatment to manage biohazards. These are then directly, without RNA isolation, put into assay tubes containing freeze-dried reagents that need no chain of refrigeration. A modified form of reverse transcription loop-mediated isothermal amplification with target-specific fluorescently tagged displaceable probes produces readout, in 30 min, as a three-color fluorescence signal. This is visualized with a handheld, battery-powered device with an orange filter. Forward contamination is prevented with sealed tubes, and the use of thermolabile uracil DNA glycosylase (UDG) in the presence of dUTP in the amplification mixture.

Proteins as Nano-Carriers for Bioactive Compounds. The Case of 7S and 11S Soy Globulins and Folic Acid Complexation

Isolated 7S and 11S globulins obtained from defeated soy flour were complexated with folic acid (FA) in order to generate nano-carriers for this important vitamin in human nutrition. Fluorescence spectroscopy and dynamic light scattering were applied to follow the nano-complexes formation and for their characterization. Fluorescence experimental data were modeled by the Stern-Volmer and a modified double logarithm approach. The results obtained confirmed static quenching. The number of binding sites on the protein molecule was ~1. The values obtained for the binding constants suggest a high affinity between proteins and FA. Particle size distribution allowed to study the protein aggregation phenomenon induced by FA bound to the native proteins. Z-average manifested a clear trend to protein aggregation. 11S-FA nano-complexes resulted in more polydispersity. ζ-potential of FA nano-complexes did not show a remarkable change after FA complexation. The biological activity of nano-complexes loaded with FA was explored in terms of their capacity to enhance the biomass formation of Lactobacillus casei BL23. The results concerning to nano-complexes inclusion in culture media showed higher bacterial growth. Such a result was attributed to the entry of the acid by the specific receptors concomitantly by the peptide receptors. These findings have technological impact for the use of globulins-FA based nano-complexes in nutraceutical, pharmaceutical and food industries.

Point of sampling detection of Zika virus within a multiplexed kit capable of detecting dengue and chikungunya

Background

Zika, dengue, and chikungunya are three mosquito-borne viruses having overlapping transmission vectors. They cause diseases having similar symptoms in human patients, but requiring different immediate management steps. Therefore, rapid (< one hour) discrimination of these three viruses in patient samples and trapped mosquitoes is needed. The need for speed precludes any assay that requires complex up-front sample preparation, such as extraction of nucleic acids from the sample. Also precluded in robust point-of-sampling assays is downstream release of the amplicon mixture, as this risks contamination of future samples that will give false positives.

Methods

Procedures are reported that directly test urine and plasma (for patient diagnostics) or crushed mosquito carcasses (for environmental surveillance). Carcasses are captured on paper samples carrying quaternary ammonium groups (Q-paper), which may be directly introduced into the assay. To avoid the time and instrumentation requirements of PCR, the procedure uses loop-mediated isothermal amplification (LAMP). Downstream detection is done in sealed tubes, with dTTP-dUTP mixtures in the LAMP with a thermolabile uracil DNA glycosylase (UDG); this offers a second mechanism to prevent forward contamination. Reverse transcription LAMP (RT-LAMP) reagents are distributed dry without requiring a continuous chain of refrigeration.

Results

The tests detect viral RNA in unprocessed urine and other biological samples, distinguishing Zika, chikungunya, and dengue in urine and in mosquitoes infected with live Zika and chikungunya viruses. The limits of detection (LODs) are ~0.71 pfu equivalent viral RNAs for Zika, ~1.22 pfu equivalent viral RNAs for dengue, and ~38 copies of chikungunya viral RNA. A handheld, battery-powered device with an orange filter was constructed to visualize the output. Preliminary data showed that this architecture, working with pre-prepared tubes holding lyophilized reagent/enzyme mixtures and shipped without a chain of refrigeration, also worked with human plasma samples to detect chikungunya and dengue in Pune, India.

Conclusions

A kit, complete with a visualization device, is now available for point-of-sampling detection of Zika, chikungunya, and dengue. The assay output is read in ca. 30 min by visualizing (human eye) three-color coded fluorescence signals. Assay in dried format allows it to be run in low-resource environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2382-0) contains supplementary material, which is available to authorized users.

Electronic relaxation pathways of the biologically relevant pterin chromophore

Femtosecond-to-microsecond transient absorption spectroscopy is used to report the ultrafast relaxation mechanism of 2-amino-1H-pteridin-4-one (pterin) for the first time.

Nanoengineering of a Supramolecular Gel by Copolymer Incorporation: Enhancement of Gelation Rate, Mechanical Property, Fluorescence, and Conductivity

In the quest to engineer the nanofibrillar morphology of folic acid (F) gel, poly(4-vinylpyridine-co-styrene) (PVPS) is judiciously integrated as a polymeric additive because of its potential to form H-bonding and π-stacking with F. The hybrid gels are designated as F-PVPSx gels, where x denotes the amount of PVPS (mg) added in 2 mL of F gel (0.3%, w/v). The assistance of PVPS in the gelation of F is manifested from the drop in critical gelation concentration and increased fiber diameter and branching of F-PVPSx gels compared to that of F gel. PVPS induces a magnificent improvement of mechanical properties: a 500 times increase of storage modulus and ∼62 times increase of yield stress in the F-PVPS5 gel compared to the F gel. The complex modulus also increases with increasing PVPS concentration with a maximum in F-PVPS5 gel. Creep recovery experiments suggest PVPS induced elasticity in the otherwise viscous F gel. The fluorescence intensity of F-PVPSx gels at first increases with increasing PVPS concentration showing maxima at F-PVPS5 gel and then slowly decreases. Gelation is monitored by time-dependent fluorescence spectroscopy, and it is observed that F and F-PVPSx gels exhibit perfectly opposite trend; the former shows a sigmoidal decrease in fluorescence intensity during gelation, but the latter shows a sigmoidal increase. The gelation rate constants calculated from Avrami treatment on the time-dependent fluorescence data manifest that PVPS effectively enhances the gelation rate showing a maximum for F-PVPS5 gel. The hybrid gel exhibit 5 orders increase of dc conductivity than that of F-gel showing semiconducting nature in the current-voltage plot. The Nyquist plot in impedance spectra of F-PVPS5 xerogel exhibit a depressed semicircle with a spike at lower frequency region, and the equivalent circuit represents a complex combination of resistance-capacitance circuits attributed to the hybrid morphology of the gel fibers.

Photosensitized reactions initiated by 6-carboxypterin: singlet and triplet reactivity

The photophysical and photochemical properties of 6-carboxypterin, a model compound for the pterin derivatives present at the sea surface microlayer, were studied and its singlet and triplet reactivity toward halides and selected organics demonstrated.

A quantitative structure–property relationship (QSPR) study of singlet oxygen generation by pteridines

Singlet oxygen production quantum yields of pteridine photosensitizers were analyzed with the QSPR method. The ability of pterins and flavins to generate¹O₂in D₂O correlated withE_HOMOand electronegativity, as well as with the dipole moment and some other parameters.