5-azido-2-aminopyridine, A New Nitrene/nitrenium Ion Photoaffinity Labeling Agent That Exhibits Reversible Intersystem Crossing Between Singlet And Triplet Nitrenes

The photochemistry of a new photoaffinity labeling (PAL) agent, 5-azido-2-(N,N-diethylamino)pyridine, was studied in aprotic and protic solvents using femtosecond-to-microsecond transient absorption and product analysis, in conjunction with ab initio multiconfigurational and multireference quantum chemical calculations. The excited singlet SI state is spectroscopically dark, whereas photoexcitation to higher-lying singlet excited S-2 and S-3 states drives the photochemical reaction toward a barrierless ultrafast relaxation path via two conical intersections to S-1, where N-2 elimination leads to the formation of the closed-shell singlet nitrene. The singlet nitrene undergoes intersystem crossing (ISC) to the triplet nitrene in aprotic and protic solvents as well as protonation to form the nitrenium ion. The ISC rate constants in aprotic solvents increase with solvent polarity, displaying a direct gap effect, whereas an inverse gap effect is observed in protic solvents. Transient absorption actinometry experiments suggest that a solvent-dependent fraction from 20% to 50% of nitrenium ions is generated on a time scale of a few tens of picoseconds. The closed-shell singlet and triplet nitrene are separated by a small energy gap in protic solvents. As a result, the unreactive triplet state nitrene undergoes delayed, thermally activated reverse ISC to reform the reactive closed-shell singlet nitrene, which subsequently protonates, forming the remaining fraction of nitrenium ions. The product studies demonstrate that the resulting nitrenium ion stabilized by the electron-donating 4-amino group yields the final cross-linked product with high, almost quantitative efficiency. The enhanced PAL function of this new azide with respect to the widely applied 4-amino-3-nitrophenyl azide is discussed

Stabilization of acromioclavicular joint using DogBone dynamic system (Arthrex): a literature review and long-term follow-up

Objectives The purpose of the study was to evaluate long-term follow-ups of stabilized acromioclavicular joint (ACJ) dislocations using button dynamic system applied via arthroscopic technique or mini-open. Material and methods The review included follow-ups of 40 patients (39 males, 1 female) who underwent 40 ACJ stabilization procedures with Arthrex DogBone button between 2014 and 2017 using arthroscopy (n = 28) or mini-open technique (n = 12). The mean age of the patients was 34 years (range, 15 to 59 years). Patient reported outcomes were evaluated with UCLA shoulder rating scale, American Shoulder and Elbow Surgeons (ASES) shoulder score and the Constant Shoulder Score (CSS). Coraco-Clavicular Distance (ССD) was measured on preand postoperative anteroposterior views. Postoperative AP view was used to measure Clavicular Tunnel Distance (CTD). Arthroscopy patients had available preoperative radiographs (n = 21), postoperative radiographs (n = 26) and patient reported outcomes (n = 18). Mini open group had available preoperative radiographs (n = 2), postoperative radiographs (n=8) and patient reported outcomes (n = 8). Results One hundred percent of Arthroscopy/Mini open (26/26) cases were rated as excellent and good on UCLA shoulder rating scale at a long-term follow-up. One hundred percent of Arthroscopy patients (18/18) were rated as excellent and good; 75 % (6/8) of Mini-open cases evaluated as excellent and 25 % (2/8) as good on ASES shoulder score. Sixty seven percent of Arthroscopy (12/18) patients were rated as excellent and 33 % (6/18) as good; 62 % (5/8) of Mini open cases evaluated as excellent and 38 % (3/8) as good. Neither fair nor poor results were observed in both groups. No statistically significant differences were detected in median scores between Arthroscopy and Miniopen groups (p > 0.05). Preoperative radiographs showed Tossy grade IV dislocation (n = 3) and Tossy grade III (n = 20). Distal clavicle fracture was diagnosed in 2 cases. Median preoperative CCD radiologically measured 15.5 mm in both groups (n = 23). Median postoperative CCD and CTD radiologically measured 6.12 mm and 28.9 mm in both groups (n = 35), correspondingly. Decrease in postoperative CCD was significantly different (p = 0.0003). No statistically significant differences in postoperative CCD were detected between Arthroscopy and Miniopen groups (p > 0.05). Statistically significant differences in preoperative CCD were observed in both groups (n = 15) using weight-bearing/no weight-bearing AP views (P = 0.0009). Conclusion Stabilization of dislocated ACJ with dynamic systems is the method of choice providing excellent and good outcomes rated by UCLA rating scale, ASES shoulder score and CSS at long-term follow-up. One-stage surgical treatment is an advantage of dynamic systems with no need of construct removal. Standard and weighted stress radiographs of the involved side indicate to ACJ injury in comparison with contralateral side. Further research is needed for a longer term follow-up with the bone reduction maintained with dynamic system

A Comparative Study of Modern Homology Modeling Algorithms for Rhodopsin Structure Prediction

Rhodopsins are seven α-helical membrane proteins that are of great importance in chemistry, biology, and modern biotechnology. Any in silico study on rhodopsin properties and functioning requires a high-quality three-dimensional structure. Due to particular difficulties with obtaining membrane protein structures from the experiment, in silico prediction of the three-dimensional rhodopsin structure based only on its primary sequence is an especially important task. For the last few years, significant progress was made in the field of protein structure prediction, especially for methods based on comparative modeling. However, the majority of this progress was made for soluble proteins and further investigations are needed to achieve similar progress for membrane proteins. In this paper, we evaluate the performance of modern protein structure prediction methodologies (implemented in the Medeller, I-TASSER, and Rosetta packages) for their ability to predict rhodopsin structures. Three widely used methodologies were considered: two general methodologies that are commonly applied to soluble proteins and a methodology that uses constraints that are specific for membrane proteins. The test pool consisted of 36 target-template pairs with different sequence similarities that was constructed on the basis of 24 experimental rhodopsin structures taken from the RCSB database. As a result, we showed that all three considered methodologies allow obtaining rhodopsin structures with the quality that is close to the crystallographic one (root mean square deviation (RMSD) of the predicted structure from the corresponding X-ray structure up to 1.5 Å) if the target-template sequence identity is higher than 40%. Moreover, all considered methodologies provided structures of average quality (RMSD < 4.0 Å) if the target-template sequence identity is higher than 20%. Such structures can be subsequently used for further investigation of molecular mechanisms of protein functioning and for the development of modern protein-based biotechnologies

Influence of Posterior Tibial Slope on the Risk of Recurrence After Anterior Cruciate Ligament Reconstruction

Background. Anterior cruciate ligament (ACL) graft rupture has multifactorial causes, with traumatic factors being the most prevalent. Modern literature presents conflicting data regarding the influence of the posterior tibial slope on the risk of traumatic ACL graft rupture. Aim of the study to determine if there is a correlation between the posterior tibial slope and ACL graft injury in patients who have previously undergone ACL reconstruction. Methods. This was a single-center cohort retrospective study that included patients diagnosed with a complete ACL rupture and who had undergone ACL reconstruction using standard techniques without graft rupture at the last follow-up. Inclusion criteria for the first group included a diagnosis of traumatic ACL rupture followed by reconstruction, a graft composed of semitendinosus and gracilis tendons (St+Gr), femoral fixation with a cortical button, tibial fixation with a sleeve and screw, and the absence of graft rupture at the time of the study. This group included 30 consecutive patients (15 males and 15 females) with a mean age of 36.3 years (min 17, max 59). Inclusion criteria for the second group included an indirect traumatic mechanism of ACL graft rupture and subsequent revision ACL reconstruction. This group consisted of 33 patients (23 males and 10 females) with a mean age of 33.0 years (min 19, max 60). The lateral (LPTS) and medial (MPTS) posterior tibial slopes were measured on lateral knee radiographs. Results. The median time from surgery to the last follow-up in the first group was 65 months (IQR 60; 66), while in the second group, it was 48 months (IQR 9; 84). The median MPTS in the first group was 7.8 (IQR 5.3; 9.4), while in the second group, it was 8.5 (IQR 7.5; 11). The median LPTS in the first group was 9.9 (IQR 8.4; 12.1), whereas in the second group, it was 12.0 (IQR 9; 15.4). There was no statistically significant difference in MPTS and LPTS based on gender in both groups and the entire sample (p0.05). When comparing LPTS values between both groups, a statistically significant difference (p = 0.04) was found, with higher LPTS values in patients in the second group (with ACL graft injury). Conclusion. Increased posterior tibial slope, particularly LPTS, is identified as a potential predictor of ACL graft rupture. The study demonstrates the impact of LPTS on the risk of ACL graft rupture (p0.05) in cases of indirect traumatic injury

Copper&ndash;Ruthenium Composite as Perspective Material for Bioelectrodes: Laser-Assisted Synthesis, Biocompatibility Study, and an Impedance-Based Cellular Biosensor as Proof of Concept

Copper is an inexpensive material that has found wide application in electronics due to its remarkable electric properties. However, the high toxicity of both copper and copper oxide imposes restrictions on the application of this metal as a material for bioelectronics. One way to increase the biocompatibility of pure copper while keeping its remarkable properties is to use copper-based composites. In the present study, we explored a new copper&ndash;ruthenium composite as a potential biocompatible material for bioelectrodes. Sample electrodes were obtained by subsequent laser deposition of copper and ruthenium on glass plates from a solution containing salts of these metals. The fabricated Cu&ndash;Ru electrodes exhibit high effective area and their impedance properties can be described by simple R-CPE equivalent circuits that make them perspective for sensing applications. Finally, we designed a simple impedance cell-based biosensor using this material that allows us to distinguish between dead and alive HeLa cells

A voltage-dependent fluorescent indicator for optogenetic applications, archaerhodopsin-3: Structure and optical properties from in silico modeling [version 2; referees: 1 approved, 2 approved with reservations]

It was demonstrated in recent studies that some rhodopsins can be used in optogenetics as fluorescent indicators of membrane voltage. One of the promising candidates for these applications is archaerhodopsin-3. However, the fluorescent signal for wild-type achaerhodopsin-3 is not strong enough for real applications. Rational design of mutants with an improved signal is an important task, which requires both experimental and theoretical studies. Herein, we used a homology-based computational approach to predict the three-dimensional structure of archaerhodopsin-3, and a Quantum Mechanics/Molecular Mechanics (QM/MM) hybrid approach with high-level multireference ab initio methodology (SORCI+Q/AMBER) to model optical properties of this protein. We demonstrated that this methodology allows for reliable prediction of structure and spectral properties of archaerhodopsin-3. The results of this study can be utilized for computational molecular design of efficient fluorescent indicators of membrane voltage for modern optogenetics on the basis of archaerhodopsin-3

Lanthanide-Ion-Doping Effect on the Morphology and the Structure of NaYF₄:Ln³⁺ Nanoparticles

Two series of β-NaYF4:Ln3+ nanoparticles (Ln = La–Nd, Sm–Lu) containing 20 at. % and 40 at. % of Ln3+ with well-defined morphology and size were synthesized via a facile citric-acid-assisted hydrothermal method using rare-earth chlorides as the precursors. The materials were composed from the particles that have a shape of uniform hexagonal prisms with an approximate size of 80–1100 nm. The mean diameter of NaYF4:Ln3+ crystals non-monotonically depended on the lanthanide atomic number and the minimum size was observed for Gd3+-doped materials. At the same time, the unit cell parameters decreased from La to Lu according to XRD data analysis. The diameter-to-length ratio increased from La to Lu in both studied series. The effect of the doping lanthanide(III) ion nature on particle size and shape was explained in terms of crystal growth dynamics. This study reports the correlation between the nanoparticle morphologies and the type and content of doping lanthanide ions. The obtained results shed light on the understanding of intrinsic factors’ effect on structural features of the nanocrystalline materials

Heterometallic Europium(III)&ndash;Lutetium(III) Terephthalates as Bright Luminescent Antenna MOFs

A new series of luminescent heterometallic europium(III)&ndash;lutetium(III) terephthalate metal&ndash;organic frameworks, namely (EuxLu1&minus;x)2bdc3&middot;nH2O, was synthesized using a direct reaction in a water solution. At the Eu3+ concentration of 1&ndash;40 at %, the MOFs were formed as a binary mixture of the (EuxLu1&minus;x)2bdc3 and (EuxLu1&minus;x)2bdc3&middot;4H2O crystalline phases, where the Ln2bdc3&middot;4H2O crystalline phase was enriched by europium(III) ions. At an Eu3+ concentration of more than 40 at %, only one crystalline phase was formed: (EuxLu1&minus;x)2bdc3&middot;4H2O. All MOFs containing Eu3+ exhibited sensitization of bright Eu3+-centered luminescence upon the 280 nm excitation into a 1&pi;&pi;* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu3+ 5D0-7FJ (J = 0&ndash;4) significantly depended on the Eu3+ concentration. The luminescence quantum yield of Eu3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu3+ due to the absence of Eu-Eu energy migration and the presence of the Ln2bdc3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln2bdc3&middot;4H2O

Fluorescence Imaging of Cell Membrane Potential: From Relative Changes to Absolute Values

Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review