Phototriggered structures: Latest advances in biomedical applications

Non-invasive control of the drug molecules accessibility is a key issue in improving diagnostic and therapeutic procedures. Some studies have explored the spatiotemporal control by light as a peripheral stimulus. Phototriggered drug delivery systems (PTDDSs) have received interest in the past decade among biological researchers due to their capability the control drug release. To this end, a wide range of phototrigger molecular structures participated in the DDSs to serve additional efficiency and a high-conversion release of active fragments under light irradiation. Up to now, several categories of PTDDSs have been extended to upgrade the performance of controlled delivery of therapeutic agents based on well-known phototrigger molecular structures like o-nitrobenzyl, coumarinyl, anthracenyl, quinolinyl, o-hydroxycinnamate and hydroxyphenacyl, where either of one endows an exclusive feature and distinct mechanistic approach. This review conveys the design, photochemical properties and essential mechanism of the most important phototriggered structures for the release of single and dual (similar or different) active molecules that have the ability to quickly reason of the large variety of dynamic biological phenomena for biomedical applications like photo-regulated drug release, synergistic outcomes, real-time monitoring, and biocompatibility potential.

The value of three-dimensional amide proton transfer-weighted imaging and its combination with diffusion weighted imaging in diagnosing breast benign and malignant lesions / 中华放射学杂志

Objective:To investigate the diagnostic value of three-dimensional amide proton transfer-weighted imaging (APTWI) and its combination with diffusion weighted imaging (DWI) for differentiating breast benign from malignant lesions.Methods:This was a prospective study. From July to December 2020, 226 patients with breast lesions confirmed by surgery or puncture pathology in the First Affiliated Hospital of Zhengzhou University were collected. All patients underwent MR T 1-weighted imaging, T 2-weighted imaging, DWI, APTWI, and dynamic contrast-enhanced MRI, and the apparent diffusion coefficient (ADC) value and the magnetization transfer ratio asymmetry at an offset of 3.5 ppm [MTRasym(3.5 ppm)] were obtained from DWI and APTWI respectively. Mann-Whitney U test was used for the comparison of DWI and APTWI parameters between breast benign and malignant lesions. Receiver operating characteristic (ROC) curve was used to evaluate the differences of diagnostic efficacy between DWI, APTWI, and their combination. Results:There were 226 patients with 226 breast lesions, including 124 malignant and 102 benign lesions. The ADC values of patients with malignant breast lesions [1.03 (0.93, 1.13)×10 -3 mm 2/s] and MTRasym (3.5 ppm) [1.95% (1.10%, 2.88%)] were lower than those of benign breast lesions [1.38 (1.11, 1.55)×10 -3 mm 2/s, 3.30% (2.20%, 4.20%), respectively], and the differences were statistically significant ( Z=-8.19, -6.51, P<0.05). The area under the ROC curves (AUC) of DWI, APTWI, and its combination in the differential diagnosis of benign and malignant breast lesions were 0.817, 0.752, and 0.868, respectively. The AUC of the combination of DWI and APTWI was higher than that of DWI and APTWI ( Z=4.00, 2.93, P<0.05), and there was no significant difference in the AUC between DWI and APTWI diagnoses ( Z=1.58, P>0.05). Taking 1.25×10 -3 mm 2/s as the optimal cut-off value for ADC values, the sensitivity, specificity, and accuracy in differentiating benign from malignant breast lesions were 94.4% (117/124), 62.7% (64/102), and 80.1% (181/226), respectively; Taking 2.70% as the optimal cut-off value for MTRasym (3.5 ppm), the sensitivity, specificity, and accuracy in differentiating benign from malignant breast lesions were 73.4% (91/124), 64.7% (66/102), and 69.5% (157/226), respectively, and the sensitivity, specificity, and accuracy of DWI combined with APTWI in differentiating benign from malignant breast lesions were 82.3% (102/124), 79.4% (81/102), and 81.0% (183/226), respectively. Conclusion:APTWI can be used for the differential diagnosis of benign and malignant breast lesions, and the combination of APTWI and DWI can obtain the better diagnostic performance than the single method.

The value of MR amide proton transfer weighted imaging technique in predicting the pathological grade of brainstem glioma / 中华放射学杂志

Objective:To evaluate the clinical application value of MR amide proton transfer weighted imaging (APTWI) in predicting the pathological grade of brainstem glioma (BSG).Methods:The data of 41 BSG patients in Beijing Tiantan Hospital, Capital Medical University from August 2019 to June 2020 who underwent both MRI and APTWI 2 weeks before surgery and had pathological grading results were retrospectively analyzed. According to the pathological results, 41 patients were classified into high-grade BSG (20 patients) and low-grade BSG (21 patients). Combined with conventional MR images, the signal intensity (%) of amide proton transfer (APT) in the parenchymal area of the tumor was obtained on APTWI images. χ 2 test or independent sample t-test was used to analyze the differences in gender distribution, age and APT signal intensity between patients with high and low grade BSG. Receiver operating characteristic (ROC) curve was drawn to predict the efficacy of APT signal intensity in the differential diagnosis of high and low grade BSG, and Youden index was calculated to obtain the optimal diagnostic threshold; the predictive ability of APT signal intensity was analyzed in combination with Hosmer-Lemeshow goodness of fit test. Results:There was no significant difference in age [(23±18) years, (20±17) years, t=0.97, P=0.340] and gender distribution (9/11, 9/12 for males/females, χ 2=0.02, P=0.890) between high-grade and low-grade BSG patients. The APT signal intensity of high-grade BSG [(3.9±0.9)%] was significantly higher than that of low-grade BSG [(2.8±0.9)%], and the difference had statistical significance ( t=4.16, P<0.001). The area under the ROC curve of APT signal intensity to distinguish high-grade and low grade BSG was 0.836, and with 2.85% as the optimal diagnostic threshold of APT signal intensity, its sensitivity for the diagnosis of high-grade BSG was 90.0% and specificity was 71.4%. The Hosmer-Lemeshow test showed that APTWI had a good predictive ability for BSG grade (χ 2=13.33, P=0.101). Conclusion:APTWI can be applied in distinguishing high grade BSG from low grade BSG, and has clinical value in predicting glioma grading.

Application of amide proton transfer-weighted MRI for grading of brainstem glioma in children / 中华全科医师杂志

Objective:To evaluate the application of amide proton transfer weighted (APTw) magnetic resonance imaging(MRI) for grading of brainstem glioma (BSG) in children.Methods:Twenty-five children (16 males and 9 females) aged 0.7-12.4(5.6±3.3)years were diagnosed as BSG by surgery or biopsy in Beijing Children′s Hospital from December 2019 to March 2022, including 13 cases of low-grade BSG and 12 cases of high-grade BSG. APTw imaging and conventional MRI were performed on a 3.0 T MRI scanner. The differences in gender distribution, age, conventional MRI appearance, APTw signal intensity and apparent diffusion coefficient (ADC) between children with high and low grade BSG were analyzed. Receiver operating characteristic (ROC) curve was used to analyze the efficacy of APTw signal intensity in the differential diagnosis of high and low grade BSG, and Youden index was calculated to obtain the optimal diagnostic threshold. Pearson′s correlation coefficient analysis was used to evaluate the correlation between APTw signal intensity and Ki-67 expression.Results:There was no significant difference in age and gender distribution between high-grade and low-grade BSG patients. The maximum diameter of high-grade BSG was significantly larger than that of low-grade BSG [(4.7±0.9) vs. (3.1±1.7)cm; t=-2.94, P=0.007]; the maximum signal intensity of APTw (APTw max) in high-grade BSG was significantly higher than that in low-grade BSG [(4.9±0.6)% vs. (3.0±1.2)%; t=-5.14, P<0.001]; the average signal intensity of APTw (APTw mean) in high-grade BSG was significantly higher than that in low-grade BSG[(3.6±0.4%) vs. (2.7±1.1)%; t=-2.66, P=0.014].The area under the curve(AUC)of APTw max in distinguishing high-and low-grade BSG was 0.897; with 4.07% as the optimal diagnostic threshold of APTw max, the sensitivity for the diagnosis of high-grade BSG was 0.917 and specificity was 0.846. The AUC of APTw mean in distinguishing high-and low-grade BSG was 0.769; with 2.85% as the optimal diagnostic threshold of APTw mean, the sensitivity for the diagnosis of high-grade BSG was 0.917 and specificity was 0.692. There was a positive correlation between the value of APTw max and Ki-67 expression( r=0.453, P=0.023). Conclusion:APTw imaging is helpful to distinguish high-grade and low-grade BSG in children. APTw max value can be used to effectively evaluate the proliferative activity of BSG in children.

Progress in Clinical Research of Amide Proton Transfer Imaging / 中国医疗器械杂志

As a new type of magnetic resonance imaging method, amide proton transfer (APT) imaging can detect the chemical exchange characteristics of free proprotein, peptide amide proton and water proton by water signal changes, reflecting the changes of protein and pH in tissues. In recent years, clinical research on brain tumors, multiple sclerosis, hepatic encephalopathy and cervical cancer have been carried out. It is a radiation-free and non-invasive new magnetic resonance molecular imaging technology. This study briefly reviews the principle of APT technology and its clinical application, and prospects its application prospects in children's abdominal tumors.

Amide proton transfer weighted imaging evaluation on isocitrate dehydrogenase mutation status in patients with high-grade gliomas / 中国医学影像技术

Objective: To observe the value of amide proton transfer weighted (APTw) imaging in predicting isocitrate dehydrogenase (IDH) wild type and IDH mutant of high-grade gliomas. Methods: Twenty-five patients with pathologically confirmed high-grade gliomas were enrolled. All patients underwent preoperative MR scanning, including routine sequences, T1WI enhancement and APTw scanning. According to the pathology, the patients were divided into IDH wild type group and IDH mutant group. ROIs were placed on FLAIR images of all tumor layers to select the solid components of the tumor, and APT values of each layer were obtained to get the mean value. Differences of APT values were analyzed between groups using independent sample t test, and ROC curve analysis was performed to evaluate the diagnostic efficacy of APT values in assessing the gene status of IDH. Results: Among 25 patients of high-grade gliomas, 9 cases were IDH mutant and 16 cases were IDH wild type. APT value of IDH wild type group ([3.21±0.82]%) was significantly higher than that of IDH mutant group ([2.23±0.72]%; t=2.89, P<0.05), and the AUC was 0.84 (P<0.05). The sensitivity and specificity of IDH wild type diagnosis was 93.8% and 66.7%, respectively. Conclusion: APTw imaging can be used to predict gene status of IDH in high-grade gliomas.

Proton Transfer Reaction Time-of-Flight Mass Spectrometry for Detection of Trace Volatile Organic Compounds in Breath / 分析化学

Based on the modification of inlet of a proton transfer reaction time of flight mass spectrometry ( PTR-TOF-MS) instrument developed in our laboratory, a new method for real-time and on-line quantitation of volatile organic compounds ( VOCs) from human exhalation was established. A 28-day real-time and on-line monitoring of exhaled breath from 23 volunteers (11 male healthy subjects, 11 female healthy subjects and 1 stomach-sick patient) was carried out and the experimental results showed that the major potential VOCs markers were identified as formaldehyde, propylene, acetone, acetaldehyde, isopropanol and isoprene, and their concentrations obeyed the Normal Distribution. The concentrations of formaldehyde, propylene and isopropanol were mainly in the range of 40 to 100 ppb, acetaldehyde in the range of 80 to 180 ppb, acetone in the range of 500 to 1500 ppb, and isoprene in the range of 8 to 20 ppb. Meanwhile, the concentrations for some compounds were different for men and women. Men have higher level of acetone, and women have higher levels of acetaldehyde and isopropanol. In addition, the concentrations of formaldehyde and acetone in the exhaled breath of stomach sicknesses were significantly higher than that in healthy people. Ethanol and acetaldehyde were the main potential markers of exhale breath after drinking alcohol. The acetaldehyde was the major metabolite of ethanol, and the concentration of acetaldehyde changed with the concentration variation of ethanol in degradation process.

Research on Peptide Ion Charge Control Method Based on Proton Transfer Ion/Ion Reaction with a Dual-Polarity Ion Trap Mass Spectrometry / 分析化学

Electrospray ionization is most commonly used in mass spectrometry for analysis of biological molecules such as peptides and proteins. However, peptides and proteins ions produced by electrospray ionization usually have multiple charges, and produce multiple spectrum peaks, making the mass spectrum complicated. Gas phase proton transfer ion/ion reaction can effectively regulate the charge states of peptides and proteins ions after electrospray ionization, simplifying the spectrogram, and thus is significant to the analysis of complex proteins and peptides samples. In this study, a dual-polarity linear ion trap ( LIT) mass spectrometer was used to control the charge state of peptide ions by proton transfer ion/ion reaction. The detection effect of the method was verified by using glutathione ( oxidation type) , oxytocin and dynorphin as typical samples. The results showed that this method could remove excess charges in the positive ions. When injecting enough negative ions for eaction, peptide ions with multiple charge valence state could be reduced to the minimum, therefore simplify the spectrogram effectively.

Development of Dipolar Proton Transfer Reaction Mass Spectrometer for Real-time Monitoring of Volatile Organic Compounds in Ambient Air / 分析化学

Volatile organic compounds (VOCs) in ambient air can participate in photochemical reactions, which lead to the generation of secondary pollutants such as ozone and aerosol. So real-time and accurate monitoring of atmospheric VOCs plays an important role in the study of the causes of air pollution. On the basis of proton transfer reaction mass spectrometry (PTR-MS) research, a novel dipolar proton transfer reaction mass spectrometer (DP-PTR-MS) for real-time and on-line monitoring atmospheric VOCs was developed. Compared with the conventional PTR-MS with one kind of reagent ion H3O+, DP-PTR-MS had three kinds of reagent ions H3O+, OH-, (CH)2COH+, which could be switched according to the actual detection need. So DP-PTR-MS can improve the qualitative ability and expand the detection range effectively. The reagent ion H3O+can be used for detecting VOCs whose proton affinities are greater than that of H2O. The reagent ion OH-can be used to identify VOCs cooperating with the reagent ion H3O+,and can also be used for detecting some inorganic substances such as CO2. The reagent ion (CH3)2COH+can be used for accurately detecting NH3under interference elimination circumstances. The limit of detection (LOD) and sensitivity of DP-PTR-MS were measured by using six kinds of standard gases. The results showed that the LOD for detecting toluene was 7×10-12(V/V) and the sensitivity for detecting ammonia has reached 126 cps/10-9 (V/V). The ambient air in Hefei city was on-line and real-time monitored for continuous 78 hours with DP-PTR-MS. The results showed that the newly developed DP-PTR-MS could be used for long-term and real-time monitoring atmospheric VOCs with the concentration of 10-12(V/V) level. DP-PTR-MS is an important tool for the study of the causes of atmospheric pollution and the monitoring of trace VOCs emissions.

Amide proton transfer imaging of neonatal piglet with hypoxic ischemic brain injury / 中国医学影像技术

Objective To investigate the amide proton transfer (APT) values in basal ganglia of neonatal piglet hypoxicischemic brain injury (HIBI) model using MR APT imaging.Methods Totally 35 healthy neonatal piglets were selected.There were 5 piglets underwent sham-operation in control group and 30 piglets used to established HIBI models in HIBI group.According to the time interval between APT imaging and the establishment of HIBI model,the piglets in HIBI group were divided into 0-＜2 h,2-＜6 h,6-＜12 h,12-＜24 h,24-＜48 h and 48-＜72 h subgroups.APT imaging was performed on all piglets.The APT value of basal ganglia between control group and all the subgroups in HIBI group were compared.Results After HIBI occurred,the APT values immediately decreased in 0-2 h,and then increased gradually.In 24 h after HIBI,the APT values were mainly returned to the level of control group,then continuously increased.The APT value in control group and 0-＜2 h,2 ＜6 h,6 ＜12 h,12-＜24 h,24-＜48 h,48-＜72 h subgroups in HIBI group were 0.52 ± 0.09,-0.35 ± 0.08,-0.02 ± 0.14,0.28± 0.04,0.46 ± 0.11,0.80 ± 0.11,1.24 ± 0.18,respectively.The APT values between control group and each subgroups in HIBI group had significant differences (all P＜0.01) except for 12-＜24 h subgroup (P=0.68).Conclusion The APT value decreased firstly and then increased after HIBI in neonatal piglet.APT imaging can provide a non-invasive molecular MR method to evaluate the pathophysiological changes of HIBI.

Depiction of Acute Stroke Using 3-Tesla Clinical Amide Proton Transfer Imaging: Saturation Time Optimization Using an in vivo Rat Stroke Model, and a Preliminary Study in Human

PURPOSE: To optimize the saturation time and maximizing the pH-weighted difference between the normal and ischemic brain regions, on 3-tesla amide proton transfer (APT) imaging using an in vivo rat model. MATERIALS AND METHODS: Three male Wistar rats underwent middle cerebral artery occlusion, and were examined in a 3-tesla magnetic resonance imaging (MRI) scanner. APT imaging acquisition was performed with 3-dimensional turbo spin-echo imaging, using a 32-channel head coil and 2-channel parallel radiofrequency transmission. An off-resonance radiofrequency pulse was applied with a Sinc-Gauss pulse at a B(1,rms) amplitude of 1.2 µT using a 2-channel parallel transmission. Saturation times of 3, 4, or 5 s were tested. The APT effect was quantified using the magnetization-transfer-ratio asymmetry at 3.5 ppm with respect to the water resonance (APT-weighted signal), and compared with the normal and ischemic regions. The result was then applied to an acute stroke patient to evaluate feasibility. RESULTS: Visual detection of ischemic regions was achieved with the 3-, 4-, and 5-s protocols. Among the different saturation times at 1.2 µT power, 4 s showed the maximum difference between the ischemic and normal regions (-0.95%, P = 0.029). The APTw signal difference for 3 and 5 s was -0.9% and -0.7%, respectively. The 4-s saturation time protocol also successfully depicted the pH-weighted differences in an acute stroke patient. CONCLUSION: For 3-tesla turbo spin-echo APT imaging, the maximal pH-weighted difference achieved when using the 1.2 µT power, was with the 4 s saturation time. This protocol will be helpful to depict pH-weighted difference in stroke patients in clinical settings.

Depiction of Acute Stroke Using 3-Tesla Clinical Amide Proton Transfer Imaging: Saturation Time Optimization Using an in vivo Rat Stroke Model, and a Preliminary Study in Human

PURPOSE: To optimize the saturation time and maximizing the pH-weighted difference between the normal and ischemic brain regions, on 3-tesla amide proton transfer (APT) imaging using an in vivo rat model. MATERIALS AND METHODS: Three male Wistar rats underwent middle cerebral artery occlusion, and were examined in a 3-tesla magnetic resonance imaging (MRI) scanner. APT imaging acquisition was performed with 3-dimensional turbo spin-echo imaging, using a 32-channel head coil and 2-channel parallel radiofrequency transmission. An off-resonance radiofrequency pulse was applied with a Sinc-Gauss pulse at a B(1,rms) amplitude of 1.2 µT using a 2-channel parallel transmission. Saturation times of 3, 4, or 5 s were tested. The APT effect was quantified using the magnetization-transfer-ratio asymmetry at 3.5 ppm with respect to the water resonance (APT-weighted signal), and compared with the normal and ischemic regions. The result was then applied to an acute stroke patient to evaluate feasibility. RESULTS: Visual detection of ischemic regions was achieved with the 3-, 4-, and 5-s protocols. Among the different saturation times at 1.2 µT power, 4 s showed the maximum difference between the ischemic and normal regions (-0.95%, P = 0.029). The APTw signal difference for 3 and 5 s was -0.9% and -0.7%, respectively. The 4-s saturation time protocol also successfully depicted the pH-weighted differences in an acute stroke patient. CONCLUSION: For 3-tesla turbo spin-echo APT imaging, the maximal pH-weighted difference achieved when using the 1.2 µT power, was with the 4 s saturation time. This protocol will be helpful to depict pH-weighted difference in stroke patients in clinical settings.

Amide proton transfer MR imaging at 3.0 T of the basal ganglia in Parkinson's disease / 中华神经科杂志

Objective To explore the feasibility of amide proton transfer (APT) MR imaging for the detection of basal ganglia abnormalities in patients with Parkinson' s disease (PD).Methods Twentyseven patients with PD and twenty-three age-matched normal control subjects underwent cerebral APT and structural MR imaging.The magnetic resonance ratio asymmetry (MTRasym) values at 3.5 ppm of bilateral globus pallidus,putamen and caudate were measured on APT images.MTRasym (3.5 ppm) values of cerebral structures between PD patients and control subjects were compared with independent-samples t test.Paired-samples t test was used to compare the difference of MTRasym (3.5 ppm) between the side of onset and contralateral side in patients with PD.The difference of MTRasym (3.5 ppm) among normal controls,early-stage PD,and advanced-stage PD patients was assessed with one-way analysis of variance.Results Compared to normal controls,MTRasym(3.5 ppm) values of globus pallidus,putamen and caudate were significantly increased in PD patients ((0.89 ±0.12)％ vs (0.57 ±0.16)％,(1.05 ± 0.11)％ vs (0.82 ± 0.15)％,(1.15 ±0.13)％ vs (0.78 ±0.19)％; t =3.311,2.562,3.277 respectively,all P values ＜ 0.05).Significant differences in MTRasym (3.5 ppm) values of these cerebral structures were observed among normal controls,early-stage PD and advanced-stage PD patients.And MTRasym (3.5 ppm) values in globus pallidus,putamen and caudate were significantly higher in early-stage PD patients than normal controls.In PD patients,even not statistically significant,MTRasym (3.5 ppm)values of sides of onset were slightly lower than contralateral sides.Conclusions APT MR imaging can sensitively identify the difference of MTRasym (3.5 ppm) in the basal ganglia between PD patients and normal controls.APT might be a useful tool to evaluate abnormal metabolite in basal ganglia of PD patients.

Proton transfer from 1,4-pentadiene to superoxide radical anion: a QTAIM analysis / Transferencia de protón desde el 1,4-pentadieno al radical anión superóxido: un análisis QTAIM / Transferência de prótons de 1,4-pentadieno o ânion radical superóxido: uma análise QTAI

We studied the bis-allylic proton transfer reaction from 1,4-pentadiene to superoxide radical anion (O2.-). Minima and transition state geometries, as well as thermochemical parameters were computed at the B3LYP/6-311+G(3df,2p) level of theory. The electronic wave functions of reactants, intermediates, and products were analyzed within the framework of the Quantum Theory of Atoms in Molecules. The results show the formation of strongly hydrogen bonded complexes between the 1,4-pentadien- 3-yl anion and the hydroperoxyl radical as the reaction products. These product complexes (PCs) are more stable than the isolated reactants and much more stable than the isolated products. This reaction occurs via pre-reactive complexes which are more stable than the PCs and the transition states. This is in agreement with the fact that the net proton transfer reaction that leads to free products is an endothermic and nonspontaneous process.

Nosotros estudiamos la reacción de transferencia de protón bis-alílico del 1,4-pentadieno al radical anión superóxido (O2.--). Las geometrías de los mínimos y de los estados de transición, así como también los parámetros termoquímicos se calcularon usando el nivel de teoría B3LYP/6-311+G(3df,2p). Las funciones de onda electrónicas de los reactantes, intermedios y productos se analizaron dentro del marco de la teoría cuántica de átomos en moléculas. Nuestros resultados muestran la formación de complejos estabilizados por enlaces de hidrógeno entre el anión 1,4pentadien-3-ilo y el radical hidroperoxilo como productos de reacción. Estos complejos producto (PCs) son más estables que los reactantes aislados y mucho más estables que los productos aislados. Esta reacción ocurre vía la formación de complejos pre-reactivos, los cuales son más estables que los PCs y los estados de transición. Estos resultados están de acuerdo con el hecho de que la reacción global de transferencia de protón que conduce a la formación de los productos libres es un proceso endotérmico y no espontáneo.

Estudou-se a reação de transferência do próton bis-alílico do 1,4-pentadieno ao radical ânion superóxido (O2.-). As geometrias dos mínimos e dos estados de transição, bem como os parâmetros termoquímicos foram calculadas utilizando o nível de teoria B3LYP/6-311+G(3df, 2p). As funçÃμes de onda eletrònica dos reagentes, intermediários e produtos foram analisadas no âmbito da teoria quântica de átomos em moléculas. Os resultados obtidos demonstram a formação de complexos estabilizados por ligaçÃμes de hidrogênio entre o ânion 1,4-pentadieno- 3-ilo e o radical hidroperoxilo como produtos de reação. Estes complexos formados como produtos (PCs) são mais estáveis do que os reagentes isolados e muito mais estáveis do que os produtos isolados. Esta reação ocorre por meio de complexos pré-reativos mais estáveis do que os PCs e os estados de transição. Estes resultados estão de acordo com o fato da reação global de transferência de próton que conduz à formação dos produtos livres, é um processo endotérmico e não espontâneo.

Absence of kinetic barrier for transfer of protons from aqueous phase to membrane-water interface.

The kinetics of interfacial proton transfer reaction is an important factor in proton transport across membranes. The following experimental system was designed in order to measure this kinetics. Sonicated liposomes having the protonophore SF6847 was suspended in Tris buffer. Application of a temperature jump (in ~ 3 μs) caused a drop in the aqueous phase pH which was subsequently sensed by the membrane-bound SF6847. The kinetics of this interfacial proton transfer reaction was monitored on μs timescales. The estimated bimolecular rate constant of 2×1011 Μ–1 s–1 for this process show that there is no kinetic barrier for the transfer of protons from the aqueous phase to the membrane-water interface.