Development of a coffee bean certified reference material (KRISS CRM 108-10-023) for elemental analysis.

The development of a novel coffee bean matrix certified reference material (CRM) for elemental analysis is described. The CRM was prepared by processing green coffee beans into a dry homogeneous powder. Mass fractions of elements in the CRM were measured using double isotope dilution inductively coupled plasma mass spectrometry (double ID-ICP-MS), and measurement results for eight elements (Mg, Ca, Fe, Cu, Zn, Cd, Hg, and Pb) of sufficient quality were certified. The mass fraction range was from 0.09476 mg/kg (Cd) to 1908 mg/kg (Mg), with relative expanded uncertainty range of 0.66% (Cd) to 12% (Pb). Measurement results of two elements (Cr and Ni) with insufficient quality were provided for information only. During characterization, an effective approach for the measurement of isotopic abundances and molar masses of elements with high natural isotopic variations for double ID-ICP-MS was developed and applied. The CRM developed in the present study is expected to be a useful measurement standard for assuring the quality of measurement procedures for coffee beans or related materials.

Analgesic effectiveness of continuous versus single-injection adductor canal block in addition to continuous popliteal sciatic nerve block for bimalleolar and trimalleolar ankle fracture surgery: Prospective randomized controlled trial.

BACKGROUND: The adductor canal block is a well-known procedure for controlling postoperative pain after medial malleolus fracture surgery. Continuous nerve block is a viable option for blocking pain for a longer period although the literature on this subject is scarce. Therefore, this study aimed to compare continuous adductor canal block (cACB) group to single-injection adductor canal block (sACB) group in those with bimalleolar or trimalleolar ankle fractures. The procedure was performed in addition to a continuous sciatic nerve block for postoperative pain relief and patient satisfaction. METHODS: The study included 57 patients who had bimalleolar or trimalleolar ankle fractures and underwent open reduction and internal fixation between August 2016 and June 2018. Each patient received a continuous sciatic nerve block and was divided into two groups: those who received cACB and those who received sACB. Each postoperative pain was scored at 4, 8, 12, 24, 48, and 72 h after surgery. Additionally, the consumption of rescue medications and patient satisfaction were evaluated. RESULTS: The two groups displayed no disparity in medial side ankle pain at 4 h and 8 h after surgery, but significantly higher pain in the sACB group at 12, 24, 48, and 72 h after surgery. However, there was no difference in the pain at the lateral side of ankle and consumption of rescue medication. In addition, the cACB group showed more satisfaction than the sACB group did. CONCLUSION: CACB is better than sACB in terms of postoperative pain control and patient satisfaction. cACB can be used for postoperative pain control in ankle fractures involving the medial malleolus. LEVEL OF EVIDENCE: Prospective Randomized Controlled Trial, Level 2.

Suprapatellar intramedullary nail combined with screw fixation has comparable surgical outcomes to minimally invasive locking plate fixation in ipsilateral tibial plateau and shaft fractures.

PURPOSE: To compare union rate, union time, alignment, and complication rate in ipsilateral tibia plateau and shaft fractures treated via suprapatellar intramedullary nailing with screw fixation and minimally invasive locking plate fixation. MATERIALS AND METHODS: A retrospective study was conducted on 48 patients who underwent minimally invasive plate fixation (n = 35) or suprapatellar intramedullary nailing with screw fixation (n = 13), for the treatment of ipsilateral tibial plateau and shaft fractures with at least 1-year follow-up. Union rate, union time, radiologic alignment, and complication rate such as malalignment, nonunion, and fracture-related infection (FRI) were investigated. RESULTS: Demographic data were not different between the two groups. Coronal plane alignment was 0.17 ± 4.23 in the plate group and -0.48 ± 4.17 in the intramedullary nail group (p = 0.637). Sagittal plane alignment was -0.13 ± 5.20 in the plate group and -1.50 ± 4.01 in the suprapatellar intramedullary nail group (p = 0.313). Coronal and sagittal malalignment recorded equal results: (p > 0.99), FRI (p = 0.602), nonunion and union times recorded (p = 0.656) and (p = 0.683, 0.829), respectively, and showed no significant difference between the two groups. CONCLUSION: Suprapatellar intramedullary nailing with screw fixation had similar surgical outcomes with minimally invasive locking plate fixation in ipsilateral tibial plateau and shaft fractures in terms of union rate, union time, alignment, and complication rate. Thus, frequent use of intramedullary nailing combined with screw fixation is anticipated in patients with ipsilateral tibial plateau and shaft fractures when the soft tissue condition is not desirable. LEVEL OF EVIDENCE: Level III.

Closed reduction and internal fixation for tillaux fractures, based on pre-operative three-dimensional computed tomography.

OBJECTIVE: This study aimed to propose treatment protocol and identify patterns of tillaux fractures using three-dimensional (3D) computed tomography (CT) analysis and to describe an effective reduction technique. METHODS: Forty-two juvenile patients with tillaux fractures were evaluated with 3D-CT scan for fracture displacement pattern and received surgical treatment. Tillaux fragment was reduced by pushing the superomedial quadrant part of the fragment slightly downward towards the ankle joint from anterolateral to posteromedial through 5-mm skin incisions with mosquito forceps. A 4.0 cannulated screw was subsequently inserted from the anterolateral to the posteromedial side parallel to the ankle joint. We analysed the distance and direction of fracture displacement with 3D-CT before the surgery. Pre-operative and post-operative plain radiographs were evaluated. RESULTS: Pre-operative 3D-CT analysis revealed a common fracture pattern, varus tilt, and external rotation of fragment. We achieved satisfactory reduction with residual fracture gaps less than 2 mm in 42 cases. Two cases had a 13-mm anterior gap that was reduced by mini-open reduction because of periosteal impingement. No significant clinical complications were found. CONCLUSION: The closed reduction technique developed based on the fracture pattern identified by 3D-CT anatomical analysis is safe and effective in treating tillaux fractures.

Comparison of Contralateral Acceleromyography and Electromyography for Posttetanic Count Measurement.

BACKGROUND: Electromyography has advantages over mechanomyography and acceleromyography. Previously, agreement of the train-of-four counts between acceleromyography and electromyography was found to be fair. The objective of this study was to assess the agreement of posttetanic count including agreement of neuromuscular blockade status (intense block, posttetanic count equal to 0; or deep block, posttetanic count 1 or greater and train-of-four count equal to 0) between acceleromyography and electromyography. METHODS: Thirty-six patients, aged 20 to 65 yr, participated in this study. A dose of 0.6 mg/kg rocuronium, with additional dose of 0.3 mg/kg if required, was administered to the patients. The train-of-four and posttetanic counts were monitored in the contralateral arm using electromyography at the first dorsal interosseus or adductor pollicis, and acceleromyography at the adductor pollicis. Posttetanic count measurements were performed at 6-min intervals; the responses were recorded until the train-of-four count reached 1. The authors evaluated the agreement of degree of neuromuscular blockade (intense or deep block) and that of posttetanic count between acceleromyography and electromyography. RESULTS: The authors analyzed 226 pairs of measurements. The percentage agreement indicating the same neuromuscular blockade status (intense or deep block) between acceleromyography and electromyography was 73%. Cohen's kappa coefficient value was 0.26. After excluding data with acceleromyography-posttetanic counts greater than 15, a total of 184 pairs of posttetanic counts were used to evaluate the agreement between the two monitoring methods. For acceleromyography-posttetanic count, 42 (23%) pairs had the same electromyography-posttetanic count, and 93 (50%) pairs had more than the electromyography-posttetanic count. The mean posttetanic count on electromyography was 38% (95% CI, 20 to 51%) lower than that on acceleromyography (P = 0.0002). CONCLUSIONS: Acceleromyography frequently counted more twitches than electromyography in posttetanic count monitoring. Acceleromyography- and electromyography-posttetanic counts cannot be used interchangeably to assess the degree of neuromuscular blockade.

Hemodynamic responses to 1 MAC desflurane inhalation during anesthesia induction with propofol bolus and remifentanil continuous infusion: a prospective randomized single-blind clinical investigation.

BACKGROUND: Desflurane is not recommended during anesthesia induction because of its sympathetic stimulation effect, particularly in patients with myocardial ischemic disease. To date, the hemodynamic response to 1 MAC desflurane inhalation in combination with remifentanil infusion during anesthesia induction has rarely been reported. METHODS: This investigation was designed to compare hemodynamic responses to 1 MAC desflurane (group D, n = 200) with sevoflurane (group S, n = 200) during anesthesia induction and endotracheal intubation in adult patients undergoing elective spine surgery. Subgroup analysis of the different age subgroups was also performed. With continuous infusion of remifentanil 0.1 µg/kg/min, anesthesia was induced with propofol bolus, and endotracheal intubation was performed after muscle relaxation. Heart rate (HR) and mean arterial blood pressure (MAP) were measured every minute for 5 min after anesthesia induction (T1-5) and after endotracheal intubation (T6-10). RESULTS: HR was significantly higher in group D (n = 182) than in group S (n = 173) at T3-10 except at T6 (1 min after intubation) (all P < 0.05). In the age-based subgroup analyses, which subdivided the group D and S into four subgroups based on patient's age, the changes in HR from baseline values were significantly different between the coeval subgroups of patients in their 20-29 years and 30-39 years of age (all P < 0.05). MAP was reduced from baseline value, irrespective of group and age. CONCLUSION: Inhalation of 1 MAC desflurane during anesthesia induction with propofol bolus and remifentanil continuous infusion and during endotracheal intubation was more likely to induce elevations in HR more likely than 1 MAC sevoflurane, especially in younger patients. TRIAL REGISTRATION: This study was registered in the Clinical Research Information Service (CRIS, http://cris.nih.go.kr ) of the Republic of Korea on Feb 12, 2016 (Registration No. KCT 0,001,813).

Intraoperative assessment of hindfoot alignment using C-arm fluoroscopy.

BACKGROUND: Hindfoot malalignment can cause various foot and ankle problems. For better surgical performance and correction of hindfoot malalignments, reliable intraoperative determination of hindfoot alignment is essential. However, there is no standard method for the intraoperative assessment of hindfoot alignment. We devised an intraoperative modified Méary posteroanterior (IOPPA) view to assess intraoperative hindfoot alignment. This study aimed to compare this intraoperative method with other radiographic hindfoot alignment measurements. METHODS: Thirty-seven patients (47 feet) with various foot and ankle conditions scheduled to undergo surgery were prospectively recruited. Before surgery, the Saltzman, long axial, and modified Méary views were taken in a controlled and standardized fashion. IOPPA views were obtained under simulated weight bearing conditions using C-arm fluoroscopy in the operating room before surgery. The relationship between the IOPPA view and the three radiographic hindfoot alignments was evaluated using Pearson's correlation. RESULTS: The mean hindfoot alignment angle was varus 3.50° (CI, varus 1.91 to 5.08) on the Saltzman view, varus 2.00° (CI, varus 0.60 to 3.39) on the long axial view, varus 0.13° (CI, valgus 1.41 to varus 1.67) on the modified Méary view, and varus 1.32° (CI, valgus 0.02 to varus 2.65) on IOPPA view. The IOPPA view and the three other hindfoot alignment views were found to be significantly correlated (r = 0.60 for the Saltzman view, r = 0.50 for the long axial view, r = 0.71 for the modified Méary view, P < .05). The intraobserver ICC (Intraclass Correlation Coefficient) value was 0.974 and interobserver ICC (Intraclass Correlation Coefficient) value was 0.988 for the IOPPA view (P < .001). CONCLUSION: There was a statistically significant correlation between the IOPPA view and the other three hindfoot alignment views. We also found that interobserver and intraobserver ICC values were excellent. This study proposes that the IOPPA view can be used as a reliable intraoperative assessment tool for hindfoot alignment. LEVEL OF EVIDENCE: Prospective study.

Reliability of submaximal stimulation for the train-of-four test using acceleromyography and electromyography with individualized stimulation currents.

PURPOSE: The supramaximal stimulation (SMS) of the TOF test causes uncomfortable sensations in patients. We aimed to determine whether the submaximal stimulation would be reliable in TOF tests with reduced painful sensation. METHODS: The accelomyography (AMG) and electromyography (EMG) monitor was applied at each arm and general anesthesia was induced and maintained by total intravenous anesthesia. At extubation, we conducted TOF test three times at each of four different currents: SMS, 70% SMS, 50% SMS, and 30% SMS. The same procedure was performed in the postanesthesia care unit (PACU) only with EMG, and the pain scores on the numerical rating scale (NRS) during the tests were recorded. RESULTS: A total of 36 patients were enrolled. At extubation, TOF ratios with SMS in AMG and EMG were 112.0 ± 13.1% and 93.7 ± 8.9%, respectively. There were no significant differences in TOF ratios between the SMS and lower stimulation intensities. However, 30% and 50% SMS showed significantly higher rates of the unmeasurable results of tests in the PACU. In terms of the stimulation pain, NRS showed a downward pattern as the current decreased and was significantly lower at 50% and 30% SMS than the NRS at SMS. CONCLUSION: The TOF test with submaximal stimulation is still reliable and can reduce stimulation pain. Considering the importance of the TOF results in determining extubation, the authors suggest the minimal current for the TOF test as 70% SMS.

Comparison of suprapatellar intramedullary nailing versus minimal invasive locked plating for proximal tibia fractures.

PURPOSE: To compare the radiological alignment, union time, union rate, and complication rate between suprapatellar intramedullary nails and minimally invasive locking plate fixation in the treatment of proximal tibial fractures. MATERIALS AND METHODS: We retrospectively analyzed 103 patients who underwent plate fixation (n = 50) or suprapatellar intramedullary nailing (n = 53) for proximal tibial fractures involving the meta-diaphyseal junction between November 2015 and October 2020 at our institution. The union rate, union time, radiologic alignments, and complications, such as malalignment, nonunion, and deep infection, were investigated. RESULTS: The demographic data did not differ between the plate and suprapatellar intramedullary nail groups. The alignment of the coronal plane was 0.24 ± 3.19 in the plate group and - 0.49 ± 2.22 in the intramedullary nail group (p = 0.196). Sagittal plane alignment was - 0.29 ± 4.97 in the plate group and 0.24 ± 4.12 in the intramedullary nail group (p = 0.571), and coronal malalignment (p = 0.196), sagittal malalignment (p = 0.57), deep infection (p = 0.264), nonunion (p = 0.695), union time (p = 0.329), and final union rate (p = 0.699) were not significantly different between groups. CONCLUSION: Compared with the minimally invasive locking compression plate group, the suprapatellar intramedullary nail group yielded comparable results in terms of radiological alignment and complications. Considering that proximal tibial fractures are associated with high-energy trauma and severe soft tissue damage, we believe that a suprapatellar intramedullary nail may be a good alternative. LEVEL OF EVIDENCE: Level III.

Assessment of Perioperative Atelectasis Using Lung Ultrasonography in Patients Undergoing Pneumoperitoneum Surgery in the Trendelenburg Position: Aspects of Differences according to Ventilatory Mode.

BACKGROUND: During robotic gynecologic pneumoperitoneum surgery in the Trendelenburg position, aeration loss leads to perioperative atelectasis. Recently developed ventilator mode pressure-controlled ventilation volume-guaranteed (PCV-VG) mode could provide adequate ventilation with lower inspiratory pressure compared to volume-controlled ventilation (VCV); we hypothesized that PCV-VG mode may be beneficial in reducing perioperative atelectasis via low tidal volume (VT) of 6 mL/kg ventilation during robotic gynecologic pneumoperitoneum surgery in the Trendelenburg position. We applied lung ultrasound score (LUS) for detecting perioperative atelectasis. We aimed to compare perioperative atelectasis between VCV and PCV-VG with a low VT of 6 mL/kg during pneumoperitoneum surgery in the Trendelenburg position using LUS. METHODS: Patients scheduled for robotic gynecologic surgery were randomly allocated to the VCV (n = 41) or PCV-VG group (n = 41). LUS, ventilatory, and hemodynamic parameters were evaluated at T1 (before induction), T2 (10 minutes after induction in the supine position), T3 (10 minutes after desufflation of CO2 in the supine position), and T4 (30 minutes after emergence from anesthesia in the recovery room). RESULTS: Eighty patients (40 with PCV-VG and 40 with VCV) were included. Demographic data showed no significant differences between the groups. The total LUS has changed from baseline to T4, 0.63 (95% confidence interval [CI], 0.32, 0.94) to 1.77 (95% CI, 1.42, 2.21) in the VCV group and 0.86 (95% CI, 0.56, 1.16) to 1.43 (95% CI, 1.08, 1.78) in the PCV-VG group (P = 0.170). In both groups, total LUS increased significantly compared to the baseline values. CONCLUSION: Using a low VT of 6 mL/kg during pneumoperitoneum surgery in the Trendelenburg position, our study showed no evidence that PCV-VG ventilation was superior to VCV in terms of perioperative atelectasis. TRIAL REGISTRATION: Clinical Research Information Service Identifier: KCT0006404.

Probing drug delivery and mechanisms of action in 3D spheroid cells by quantitative analysis.

Human tumor cells in a 3-dimensional (3D) spheroid can reflect the characteristics of solid tumors by forming cell-cell interactions and microenvironments. This makes 3D cell culture useful for preclinical stability and drug efficacy tests. In this study, the drug delivery and action mechanisms in SK-N-SH neuroblastoma cells cultured in 3D spheroids were quantitatively compared to those cultured in 2D monolayers using confocal microscopy imaging and inductively coupled plasma-mass spectrometry. In the 3D spheroids, cisplatin only accessed the surface, accumulating in the cells on the spheroid exterior. As a result, an increased cellular amount of cisplatin was required to obtain similar cytotoxicity in the 3D spheroid cells to that in 2D monolayers. The mechanisms of reduction of drug efficacy by dimethyl sulfoxide (DMSO) in the 3D spheroid cells compared to those in the 2D monolayer cells were further investigated. DMSO reduced the drug cytotoxicity by forming stable DMSO-substituted compounds that inhibited the cellular uptake of cisplatin and DNA-Pt adduct formation. The quantitative analysis used in this study is promising for understanding drug delivery and drug action mechanisms in cells in various microenvironments.

Structural characterization of small molecular ions by ion mobility mass spectrometry in nitrogen drift gas: improving the accuracy of trajectory method calculations.

The investigation of ion structures based on a combination of ion mobility mass spectrometry (IM-MS) experiments and theoretical collision cross section (CCS) calculations has become important to many fields of research. However, the accuracy of current CCS calculations for ions in nitrogen drift gas limits the information content of many experiments. In particular, few studies have evaluated and attempted to improve the theoretical tools for CCS calculation in nitrogen drift gas. In this study, based on high-quality experimental measurements and theoretical modeling, a comprehensive evaluation of various aspects of CCS calculations in nitrogen drift gas is performed. It is shown that the modification of the ion-nitrogen van der Waals (vdW) interaction potential enables accurate CCS predictions of 29 small ions with ca. 3% maximum relative error. The present method exhibits no apparent systematic bias with respect to ion CCS (size) and dipole moment, suggesting that the method adequately describes the long-range interactions between the ions and the buffer gas. However, the method shows limitations in reproducing experimental CCS at low temperatures (<150 K) and for macromolecular ions, and calculations for these cases should be complemented by CCS calculation methods in helium drift gas. This study presents an accurate and well-characterized CCS calculation method for ions in nitrogen drift gas that is expected to become an important tool for ion structural characterization and molecular identification. The experimental values reported here also provide a foundation for future studies aiming at developing more efficient computational tools.

Effects of Tranexamic Acid Based on its Population Pharmacokinetics in Pediatric Patients Undergoing Distraction Osteogenesis for Craniosynostosis: Rotational Thromboelastometry (ROTEMTM) Analysis.

Background: Distraction osteogenesis for craniosynostosis is associated with significant hemorrhage. Additionally, patients usually require several transfusions. Tranexamic acid (TXA) is effective for reducing blood loss and the need for transfusions during surgeries. However, the significance of TXA infusion has not been thoroughly described yet. Methods: Forty-eight children undergoing distraction osteogenesis for craniosynostosis were administered intraoperative TXA infusion (loading dose of 10 mg/kg for 15 min, followed by continuous infusion at 5 mg/kg/h throughout surgery; n = 23) or normal saline (control, n = 25). Rotational thromboelastometry (ROTEMTM) was conducted to monitor changes in coagulation perioperatively. Results: Blood loss during surgery was significantly lower in the TXA-treated group than it was in the control group (81 vs. 116 mL/kg, P = 0.003). Furthermore, significantly fewer transfusions of red blood cells and fresh frozen plasma were required in the TXA group. In the control group, clotting time during the postoperative period was longer than it was during the preoperative period. Similarly, clot strength was weaker during the postoperative period. D-dimer levels dramatically increased in the control group compared with the TXA group after surgery. The duration of mechanical ventilation and the number of postoperative respiratory-related complications were significantly greater in the control group than they were in the TXA group. Conclusions: TXA infusion based on population pharmacokinetic analysis is effective in reducing blood loss and the need for transfusions during the surgical treatment of craniosynostosis. It can also prevent the increase in D-dimer levels without affecting systemic hemostasis.

Collision cross sections and ion structures: development of a general calculation method via high-quality ion mobility measurements and theoretical modeling.

Ion mobility mass spectrometry (IM-MS) has become an important tool for the structural investigation of ions in the gas phase. Accurate theoretical evaluation of ion collision cross sections (CCSs) is essential for the effective application of IM-MS in structural studies. However, current theoretical tools have limitations in accurately describing a broad range of ions from small molecules to macromolecules. Significant difficulties in developing theoretical tools for CCS calculations are associated with obtaining high-quality experimental data and molecular models. In this study, we present a general CCS calculation method by employing two drift-tube IM-MS (DTIM-MS) instruments and thorough molecular modeling procedures. It is demonstrated that an appropriate description of the van der Waals (vdW) interactions is important for accurate CCS calculations in helium drift gas. By utilizing the vdW potentials from molecular mechanics force fields, it is shown that both the appropriate vdW potential-forms and their parameters are necessary for the highly reliable CCS predictions of small molecules. We further show that specific characteristics of the vdW interaction potential become less influential on the calculated CCS with increasing ion size, and that the calculated CCS values for the macromolecules converge to the values at the hard-sphere limit. Based on these results, a general CCS calculation method is presented that can be applied to ions of various sizes and compositions for the gas-phase structural studies.

Probing Distinct Fullerene Formation Processes from Carbon Precursors of Different Sizes and Structures.

Fullerenes, cage-structured carbon allotropes, have been the subject of extensive research as new materials for diverse purposes. Yet, their formation process is still not clearly understood at the molecular level. In this study, we performed laser desorption ionization-ion mobility-mass spectrometry (LDI-IM-MS) of carbon substrates possessing different molecular sizes and structures to understand the formation process of fullerene. Our observations show that the formation process is strongly dependent on the size of the precursor used, with small precursors yielding small fullerenes and large graphitic precursors generally yielding larger fullerenes. These results clearly demonstrate that fullerene formation can proceed via both bottom-up and top-down processes, with the latter being favored for large precursors and more efficient at forming fullerenes. Furthermore, we observed that specific structures of carbon precursors could additionally affect the relative abundance of C60 fullerene. Overall, this study provides an advanced understanding of the mechanistic details underlying the formation processes of fullerene.

Reference Intervals of Thromboelastometric Evaluation of Coagulation in Pediatric Patients with Congenital Heart Diseases: A Retrospective Investigation.

BACKGROUND Rotational thromboelastometry (ROTEM®) is a point-of-care test for coagulation, enabling physicians to make a swift decision. The aim of this investigation was to establish reference intervals of thromboelastometric evaluation for coagulation in pediatric patients with congenital heart diseases (CHD). MATERIAL AND METHODS As baseline data, 3 assays of ROTEM® (INTEM, EXTEM, and FIBTEM) were measured after anesthesia induction. ROTEM® parameters were clotting time (CT), amplitude at 10 min (A10), clot formation time (CFT), a angle, maximal clot firmness (MCF), clot lysis index at 60 min (LI60), and maximal clot elasticity (MCE). As age is a well-known factor for maturation, age groups were determined as follows; 1) <1 month, 2) 1-3 months, 3) 4-12 months, 4) 1-3 years, 5) 4-6 years, 6) 7-12 years, and 7) 13-16 years. Reference limits representing 95% of distribution of ROTEM® parameters and 90% confidence intervals of upper and lower reference limits were calculated. RESULTS The data of 413 patients were analyzed. Although INTEM CT was prolonged, significantly shorter CT and CFT, steeper α, and greater A10, MCF, and MCE were shown in patients age <3 months compared to older children. CONCLUSIONS Reference intervals of thromboelastometric evaluation for coagulation from pediatric patients with CHD were shown to have similar pattern to those obtained from healthy pediatric patients. Pediatric patients with CHD, even with cyanosis, were demonstrated to have functionally intact coagulation profile before surgery.

Manifesting Subtle Differences of Neutral Hydrophilic Guest Isomers in a Molecular Container by Phase Transfer.

Achieving strong host-guest interactions between synthetic hosts and hydrophilic guests in solution is challenging because solvation effects overwhelm other effects. To resolve this issue, we transferred complexes of cucurbit[7]uril (CB[7]) and monosaccharides to the gas phase and report here their intrinsic host-guest chemistry in the absence of solvation effects. It was observed that effective host-guest interactions in the gas phase mediated by ammonium cations allow the differentiation of the monosaccharide isomers in complex with CB[7] upon vibrational excitation. The potential of the unique observation was extended to a quantitative supramolecular analytical method for the monosaccharide guests. The combination of host-guest chemistry and phase transfer presented in this study is an effective approach to overcome current limitations in supramolecular chemistry.

The transition from the native to the acid-state characterized by multi-spectroscopy approach: study for the holo-form of bovine α-lactalbumin.

The transition of the holo-form of bovine α-lactalbumin from the native (N) to the pH-generated acidic-state (A-state) was analyzed by probing its tertiary and secondary structure using a concerted spectroscopic approach combining near- and far-UV circular dichroism (CD), electrospray ionization ion mobility mass spectrometry (ESI-IM-MS), vibrational circular dichroism (VCD), and Fourier transform infrared spectroscopy (FTIR) in the attenuated total reflection (ATR) and transmission (TR) modes. The spectroscopic results, which relied on the interaction of an electromagnetic field with different molecular targets, confirmed the decay of extensive rigid side-chain packing interactions during the pH-induced N→A-state transition and revealed the targets' dependence on secondary structural changes. Independent analyses of the spectral changes using two methods of multivariate analysis, such as principal component analysis and two-dimensional correlation spectroscopy, revealed small but significant differences in the secondary structure as a result of the all-or-none transition. The cooperativity of the transition was quantitatively described using values corresponding to the mid-point (tm) and width of the transition (Δtm). The averages of the two parameters, calculated using the data collected by the different probes, were equal to 3.5±0.2 and 0.6±0.1(SE), respectively. The variable two-state nature of the cooperative N→A-state transition confirmed that the protonation of the side chain carboxyl groups on the Asp and Glu residues and that the release of a Ca(2+) ion induced structural changes on both the secondary and tertiary levels. The changes have been confirmed by results obtained from the concerted spectroscopic approach.

Supramolecular Enhancement of Protein Analysis via the Recognition of Phenylalanine with Cucurbit[7]uril.

Mass spectrometry (MS)-based analysis using enzymatic digestion is widely used for protein sequencing and characterization. The large number of peptides generated from proteolysis, however, suppresses the signal of peptides with low ionization efficiency, thus precluding their observation and analysis. This study describes a technique for improved analysis of peptic peptides by adding the synthetic receptor cucurbit[7]uril (CB[7]), which binds selectively to peptides with N-terminal aromatic residues. Capturing the N-terminal phenylalanine (Phe) of peptides using CB[7] enhances the peptide abundances both in electrospray ionization MS and in matrix-assisted laser desorption ionization MS. Moreover, collision-induced dissociation (CID) of the CB[7]·peptide complex ions generates b- and y-type fragment ions with higher sequence coverage than those generated with uncomplexed peptides. The signal enhancement mediated by CB[7] is attributed to an increase in the peptide proton affinities upon CB[7] complexation. The mechanistic details of the fragmentation process are discussed on the basis of the structures of the complex ions obtained from ion mobility (IM) measurements and molecular modeling. This study demonstrates a novel and powerful approach to the enhancement of protein and peptide analysis using a synthetic receptor, without the need for new instrumentation, chemical modifications, or specialized sample preparation. The simplicity and potential generality of this technique should provide a valuable asset in the toolbox of routine protein and peptide analysis.

Investigating acid-induced structural transitions of lysozyme in an electrospray ionization source.

The effect of acids on the structure of lysozyme (Lyz) during electrospray ionization (ESI) was studied by comparing the solution and gas-phase structures of Lyz. Investigation using circular dichroism spectroscopy and small-angle X-ray scattering demonstrated that the folded conformation of Lyz was maintained in pH 2.2 solutions containing different acids. On the other hand, analysis of the charge state distributions and ion mobility (IM) distributions, combined with molecular dynamics simulations, demonstrated that the gas phase structures of Lyz depend on the pKa of the acid used to acidify the protein solution. Formic acid and acetic acid, which are weak acids (pKa > 3.5), induce unfolding of Lyz during ESI, presumably because the undissociated weak acids provide protons to maintain the acidic groups within Lyz protonated and prevent the formation of salt bridges. However, HCl suppressed the formation of the unfolded conformers because the acid is already dissociated in solution, and chloride anions within the ESI droplet can interact with Lyz to reduce the intramolecular electrostatic repulsion. These trends in the IM distributions are observed for all charge states, demonstrating the significance of the acid effect on the structure of Lyz during ESI.